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50 files changed, 3159 insertions, 3753 deletions
diff --git a/Documentation/filesystems/btrfs.rst b/Documentation/filesystems/btrfs.rst index d0904f602819..992eddb0e11b 100644 --- a/Documentation/filesystems/btrfs.rst +++ b/Documentation/filesystems/btrfs.rst @@ -19,13 +19,23 @@ The main Btrfs features include: * Subvolumes (separate internal filesystem roots) * Object level mirroring and striping * Checksums on data and metadata (multiple algorithms available) - * Compression + * Compression (multiple algorithms available) + * Reflink, deduplication + * Scrub (on-line checksum verification) + * Hierarchical quota groups (subvolume and snapshot support) * Integrated multiple device support, with several raid algorithms * Offline filesystem check - * Efficient incremental backup and FS mirroring + * Efficient incremental backup and FS mirroring (send/receive) + * Trim/discard * Online filesystem defragmentation + * Swapfile support + * Zoned mode + * Read/write metadata verification + * Online resize (shrink, grow) -For more information please refer to the wiki +For more information please refer to the documentation site or wiki + + https://btrfs.readthedocs.io https://btrfs.wiki.kernel.org diff --git a/Documentation/filesystems/caching/backend-api.rst b/Documentation/filesystems/caching/backend-api.rst index 19fbf6b9aa36..3a199fc50828 100644 --- a/Documentation/filesystems/caching/backend-api.rst +++ b/Documentation/filesystems/caching/backend-api.rst @@ -1,727 +1,479 @@ .. SPDX-License-Identifier: GPL-2.0 -========================== -FS-Cache Cache backend API -========================== +================= +Cache Backend API +================= The FS-Cache system provides an API by which actual caches can be supplied to FS-Cache for it to then serve out to network filesystems and other interested -parties. +parties. This API is used by:: -This API is declared in <linux/fscache-cache.h>. + #include <linux/fscache-cache.h>. -Initialising and Registering a Cache -==================================== - -To start off, a cache definition must be initialised and registered for each -cache the backend wants to make available. For instance, CacheFS does this in -the fill_super() operation on mounting. - -The cache definition (struct fscache_cache) should be initialised by calling:: - - void fscache_init_cache(struct fscache_cache *cache, - struct fscache_cache_ops *ops, - const char *idfmt, - ...); - -Where: - - * "cache" is a pointer to the cache definition; - - * "ops" is a pointer to the table of operations that the backend supports on - this cache; and - - * "idfmt" is a format and printf-style arguments for constructing a label - for the cache. - - -The cache should then be registered with FS-Cache by passing a pointer to the -previously initialised cache definition to:: - - int fscache_add_cache(struct fscache_cache *cache, - struct fscache_object *fsdef, - const char *tagname); - -Two extra arguments should also be supplied: - - * "fsdef" which should point to the object representation for the FS-Cache - master index in this cache. Netfs primary index entries will be created - here. FS-Cache keeps the caller's reference to the index object if - successful and will release it upon withdrawal of the cache. - - * "tagname" which, if given, should be a text string naming this cache. If - this is NULL, the identifier will be used instead. For CacheFS, the - identifier is set to name the underlying block device and the tag can be - supplied by mount. - -This function may return -ENOMEM if it ran out of memory or -EEXIST if the tag -is already in use. 0 will be returned on success. - - -Unregistering a Cache -===================== - -A cache can be withdrawn from the system by calling this function with a -pointer to the cache definition:: - - void fscache_withdraw_cache(struct fscache_cache *cache); - -In CacheFS's case, this is called by put_super(). - - -Security +Overview ======== -The cache methods are executed one of two contexts: - - (1) that of the userspace process that issued the netfs operation that caused - the cache method to be invoked, or - - (2) that of one of the processes in the FS-Cache thread pool. - -In either case, this may not be an appropriate context in which to access the -cache. - -The calling process's fsuid, fsgid and SELinux security identities may need to -be masqueraded for the duration of the cache driver's access to the cache. -This is left to the cache to handle; FS-Cache makes no effort in this regard. - +Interaction with the API is handled on three levels: cache, volume and data +storage, and each level has its own type of cookie object: -Control and Statistics Presentation -=================================== + ======================= ======================= + COOKIE C TYPE + ======================= ======================= + Cache cookie struct fscache_cache + Volume cookie struct fscache_volume + Data storage cookie struct fscache_cookie + ======================= ======================= -The cache may present data to the outside world through FS-Cache's interfaces -in sysfs and procfs - the former for control and the latter for statistics. +Cookies are used to provide some filesystem data to the cache, manage state and +pin the cache during access in addition to acting as reference points for the +API functions. Each cookie has a debugging ID that is included in trace points +to make it easier to correlate traces. Note, though, that debugging IDs are +simply allocated from incrementing counters and will eventually wrap. -A sysfs directory called /sys/fs/fscache/<cachetag>/ is created if CONFIG_SYSFS -is enabled. This is accessible through the kobject struct fscache_cache::kobj -and is for use by the cache as it sees fit. +The cache backend and the network filesystem can both ask for cache cookies - +and if they ask for one of the same name, they'll get the same cookie. Volume +and data cookies, however, are created at the behest of the filesystem only. -Relevant Data Structures -======================== +Cache Cookies +============= - * Index/Data file FS-Cache representation cookie:: +Caches are represented in the API by cache cookies. These are objects of +type:: - struct fscache_cookie { - struct fscache_object_def *def; - struct fscache_netfs *netfs; - void *netfs_data; - ... - }; - - The fields that might be of use to the backend describe the object - definition, the netfs definition and the netfs's data for this cookie. - The object definition contain functions supplied by the netfs for loading - and matching index entries; these are required to provide some of the - cache operations. - - - * In-cache object representation:: - - struct fscache_object { - int debug_id; - enum { - FSCACHE_OBJECT_RECYCLING, - ... - } state; - spinlock_t lock - struct fscache_cache *cache; - struct fscache_cookie *cookie; + struct fscache_cache { + void *cache_priv; + unsigned int debug_id; + char *name; ... }; - Structures of this type should be allocated by the cache backend and - passed to FS-Cache when requested by the appropriate cache operation. In - the case of CacheFS, they're embedded in CacheFS's internal object - structures. +There are a few fields that the cache backend might be interested in. The +``debug_id`` can be used in tracing to match lines referring to the same cache +and ``name`` is the name the cache was registered with. The ``cache_priv`` +member is private data provided by the cache when it is brought online. The +other fields are for internal use. - The debug_id is a simple integer that can be used in debugging messages - that refer to a particular object. In such a case it should be printed - using "OBJ%x" to be consistent with FS-Cache. - Each object contains a pointer to the cookie that represents the object it - is backing. An object should retired when put_object() is called if it is - in state FSCACHE_OBJECT_RECYCLING. The fscache_object struct should be - initialised by calling fscache_object_init(object). +Registering a Cache +=================== +When a cache backend wants to bring a cache online, it should first register +the cache name and that will get it a cache cookie. This is done with:: - * FS-Cache operation record:: + struct fscache_cache *fscache_acquire_cache(const char *name); - struct fscache_operation { - atomic_t usage; - struct fscache_object *object; - unsigned long flags; - #define FSCACHE_OP_EXCLUSIVE - void (*processor)(struct fscache_operation *op); - void (*release)(struct fscache_operation *op); - ... - }; +This will look up and potentially create a cache cookie. The cache cookie may +have already been created by a network filesystem looking for it, in which case +that cache cookie will be used. If the cache cookie is not in use by another +cache, it will be moved into the preparing state, otherwise it will return +busy. - FS-Cache has a pool of threads that it uses to give CPU time to the - various asynchronous operations that need to be done as part of driving - the cache. These are represented by the above structure. The processor - method is called to give the op CPU time, and the release method to get - rid of it when its usage count reaches 0. +If successful, the cache backend can then start setting up the cache. In the +event that the initialisation fails, the cache backend should call:: - An operation can be made exclusive upon an object by setting the - appropriate flag before enqueuing it with fscache_enqueue_operation(). If - an operation needs more processing time, it should be enqueued again. + void fscache_relinquish_cache(struct fscache_cache *cache); +to reset and discard the cookie. - * FS-Cache retrieval operation record:: - struct fscache_retrieval { - struct fscache_operation op; - struct address_space *mapping; - struct list_head *to_do; - ... - }; +Bringing a Cache Online +======================= - A structure of this type is allocated by FS-Cache to record retrieval and - allocation requests made by the netfs. This struct is then passed to the - backend to do the operation. The backend may get extra refs to it by - calling fscache_get_retrieval() and refs may be discarded by calling - fscache_put_retrieval(). +Once the cache is set up, it can be brought online by calling:: - A retrieval operation can be used by the backend to do retrieval work. To - do this, the retrieval->op.processor method pointer should be set - appropriately by the backend and fscache_enqueue_retrieval() called to - submit it to the thread pool. CacheFiles, for example, uses this to queue - page examination when it detects PG_lock being cleared. + int fscache_add_cache(struct fscache_cache *cache, + const struct fscache_cache_ops *ops, + void *cache_priv); - The to_do field is an empty list available for the cache backend to use as - it sees fit. +This stores the cache operations table pointer and cache private data into the +cache cookie and moves the cache to the active state, thereby allowing accesses +to take place. - * FS-Cache storage operation record:: +Withdrawing a Cache From Service +================================ - struct fscache_storage { - struct fscache_operation op; - pgoff_t store_limit; - ... - }; +The cache backend can withdraw a cache from service by calling this function:: - A structure of this type is allocated by FS-Cache to record outstanding - writes to be made. FS-Cache itself enqueues this operation and invokes - the write_page() method on the object at appropriate times to effect - storage. + void fscache_withdraw_cache(struct fscache_cache *cache); +This moves the cache to the withdrawn state to prevent new cache- and +volume-level accesses from starting and then waits for outstanding cache-level +accesses to complete. -Cache Operations -================ +The cache must then go through the data storage objects it has and tell fscache +to withdraw them, calling:: -The cache backend provides FS-Cache with a table of operations that can be -performed on the denizens of the cache. These are held in a structure of type: + void fscache_withdraw_cookie(struct fscache_cookie *cookie); - :: +on the cookie that each object belongs to. This schedules the specified cookie +for withdrawal. This gets offloaded to a workqueue. The cache backend can +wait for completion by calling:: - struct fscache_cache_ops + void fscache_wait_for_objects(struct fscache_cache *cache); - * Name of cache provider [mandatory]:: +Once all the cookies are withdrawn, a cache backend can withdraw all the +volumes, calling:: - const char *name + void fscache_withdraw_volume(struct fscache_volume *volume); - This isn't strictly an operation, but should be pointed at a string naming - the backend. +to tell fscache that a volume has been withdrawn. This waits for all +outstanding accesses on the volume to complete before returning. +When the cache is completely withdrawn, fscache should be notified by +calling:: - * Allocate a new object [mandatory]:: + void fscache_relinquish_cache(struct fscache_cache *cache); - struct fscache_object *(*alloc_object)(struct fscache_cache *cache, - struct fscache_cookie *cookie) +to clear fields in the cookie and discard the caller's ref on it. - This method is used to allocate a cache object representation to back a - cookie in a particular cache. fscache_object_init() should be called on - the object to initialise it prior to returning. - This function may also be used to parse the index key to be used for - multiple lookup calls to turn it into a more convenient form. FS-Cache - will call the lookup_complete() method to allow the cache to release the - form once lookup is complete or aborted. +Volume Cookies +============== +Within a cache, the data storage objects are organised into logical volumes. +These are represented in the API as objects of type:: - * Look up and create object [mandatory]:: + struct fscache_volume { + struct fscache_cache *cache; + void *cache_priv; + unsigned int debug_id; + char *key; + unsigned int key_hash; + ... + u8 coherency_len; + u8 coherency[]; + }; - void (*lookup_object)(struct fscache_object *object) +There are a number of fields here that are of interest to the caching backend: - This method is used to look up an object, given that the object is already - allocated and attached to the cookie. This should instantiate that object - in the cache if it can. + * ``cache`` - The parent cache cookie. - The method should call fscache_object_lookup_negative() as soon as - possible if it determines the object doesn't exist in the cache. If the - object is found to exist and the netfs indicates that it is valid then - fscache_obtained_object() should be called once the object is in a - position to have data stored in it. Similarly, fscache_obtained_object() - should also be called once a non-present object has been created. + * ``cache_priv`` - A place for the cache to stash private data. - If a lookup error occurs, fscache_object_lookup_error() should be called - to abort the lookup of that object. + * ``debug_id`` - A debugging ID for logging in tracepoints. + * ``key`` - A printable string with no '/' characters in it that represents + the index key for the volume. The key is NUL-terminated and padded out to + a multiple of 4 bytes. - * Release lookup data [mandatory]:: + * ``key_hash`` - A hash of the index key. This should work out the same, no + matter the cpu arch and endianness. - void (*lookup_complete)(struct fscache_object *object) + * ``coherency`` - A piece of coherency data that should be checked when the + volume is bound to in the cache. - This method is called to ask the cache to release any resources it was - using to perform a lookup. + * ``coherency_len`` - The amount of data in the coherency buffer. - * Increment object refcount [mandatory]:: +Data Storage Cookies +==================== - struct fscache_object *(*grab_object)(struct fscache_object *object) +A volume is a logical group of data storage objects, each of which is +represented to the network filesystem by a cookie. Cookies are represented in +the API as objects of type:: - This method is called to increment the reference count on an object. It - may fail (for instance if the cache is being withdrawn) by returning NULL. - It should return the object pointer if successful. + struct fscache_cookie { + struct fscache_volume *volume; + void *cache_priv; + unsigned long flags; + unsigned int debug_id; + unsigned int inval_counter; + loff_t object_size; + u8 advice; + u32 key_hash; + u8 key_len; + u8 aux_len; + ... + }; +The fields in the cookie that are of interest to the cache backend are: - * Lock/Unlock object [mandatory]:: + * ``volume`` - The parent volume cookie. - void (*lock_object)(struct fscache_object *object) - void (*unlock_object)(struct fscache_object *object) + * ``cache_priv`` - A place for the cache to stash private data. - These methods are used to exclusively lock an object. It must be possible - to schedule with the lock held, so a spinlock isn't sufficient. + * ``flags`` - A collection of bit flags, including: + * FSCACHE_COOKIE_NO_DATA_TO_READ - There is no data available in the + cache to be read as the cookie has been created or invalidated. - * Pin/Unpin object [optional]:: + * FSCACHE_COOKIE_NEEDS_UPDATE - The coherency data and/or object size has + been changed and needs committing. - int (*pin_object)(struct fscache_object *object) - void (*unpin_object)(struct fscache_object *object) + * FSCACHE_COOKIE_LOCAL_WRITE - The netfs's data has been modified + locally, so the cache object may be in an incoherent state with respect + to the server. - These methods are used to pin an object into the cache. Once pinned an - object cannot be reclaimed to make space. Return -ENOSPC if there's not - enough space in the cache to permit this. + * FSCACHE_COOKIE_HAVE_DATA - The backend should set this if it + successfully stores data into the cache. + * FSCACHE_COOKIE_RETIRED - The cookie was invalidated when it was + relinquished and the cached data should be discarded. - * Check coherency state of an object [mandatory]:: + * ``debug_id`` - A debugging ID for logging in tracepoints. - int (*check_consistency)(struct fscache_object *object) + * ``inval_counter`` - The number of invalidations done on the cookie. - This method is called to have the cache check the saved auxiliary data of - the object against the netfs's idea of the state. 0 should be returned - if they're consistent and -ESTALE otherwise. -ENOMEM and -ERESTARTSYS - may also be returned. + * ``advice`` - Information about how the cookie is to be used. - * Update object [mandatory]:: + * ``key_hash`` - A hash of the index key. This should work out the same, no + matter the cpu arch and endianness. - int (*update_object)(struct fscache_object *object) + * ``key_len`` - The length of the index key. - This is called to update the index entry for the specified object. The - new information should be in object->cookie->netfs_data. This can be - obtained by calling object->cookie->def->get_aux()/get_attr(). + * ``aux_len`` - The length of the coherency data buffer. +Each cookie has an index key, which may be stored inline to the cookie or +elsewhere. A pointer to this can be obtained by calling:: - * Invalidate data object [mandatory]:: + void *fscache_get_key(struct fscache_cookie *cookie); - int (*invalidate_object)(struct fscache_operation *op) +The index key is a binary blob, the storage for which is padded out to a +multiple of 4 bytes. - This is called to invalidate a data object (as pointed to by op->object). - All the data stored for this object should be discarded and an - attr_changed operation should be performed. The caller will follow up - with an object update operation. +Each cookie also has a buffer for coherency data. This may also be inline or +detached from the cookie and a pointer is obtained by calling:: - fscache_op_complete() must be called on op before returning. + void *fscache_get_aux(struct fscache_cookie *cookie); - * Discard object [mandatory]:: - void (*drop_object)(struct fscache_object *object) +Cookie Accounting +================= - This method is called to indicate that an object has been unbound from its - cookie, and that the cache should release the object's resources and - retire it if it's in state FSCACHE_OBJECT_RECYCLING. +Data storage cookies are counted and this is used to block cache withdrawal +completion until all objects have been destroyed. The following functions are +provided to the cache to deal with that:: - This method should not attempt to release any references held by the - caller. The caller will invoke the put_object() method as appropriate. + void fscache_count_object(struct fscache_cache *cache); + void fscache_uncount_object(struct fscache_cache *cache); + void fscache_wait_for_objects(struct fscache_cache *cache); +The count function records the allocation of an object in a cache and the +uncount function records its destruction. Warning: by the time the uncount +function returns, the cache may have been destroyed. - * Release object reference [mandatory]:: +The wait function can be used during the withdrawal procedure to wait for +fscache to finish withdrawing all the objects in the cache. When it completes, +there will be no remaining objects referring to the cache object or any volume +objects. - void (*put_object)(struct fscache_object *object) - This method is used to discard a reference to an object. The object may - be freed when all the references to it are released. +Cache Management API +==================== +The cache backend implements the cache management API by providing a table of +operations that fscache can use to manage various aspects of the cache. These +are held in a structure of type:: - * Synchronise a cache [mandatory]:: + struct fscache_cache_ops { + const char *name; + ... + }; - void (*sync)(struct fscache_cache *cache) +This contains a printable name for the cache backend driver plus a number of +pointers to methods to allow fscache to request management of the cache: - This is called to ask the backend to synchronise a cache with its backing - device. + * Set up a volume cookie [optional]:: + void (*acquire_volume)(struct fscache_volume *volume); - * Dissociate a cache [mandatory]:: + This method is called when a volume cookie is being created. The caller + holds a cache-level access pin to prevent the cache from going away for + the duration. This method should set up the resources to access a volume + in the cache and should not return until it has done so. - void (*dissociate_pages)(struct fscache_cache *cache) + If successful, it can set ``cache_priv`` to its own data. - This is called to ask a cache to perform any page dissociations as part of - cache withdrawal. + * Clean up volume cookie [optional]:: - * Notification that the attributes on a netfs file changed [mandatory]:: + void (*free_volume)(struct fscache_volume *volume); - int (*attr_changed)(struct fscache_object *object); + This method is called when a volume cookie is being released if + ``cache_priv`` is set. - This is called to indicate to the cache that certain attributes on a netfs - file have changed (for example the maximum size a file may reach). The - cache can read these from the netfs by calling the cookie's get_attr() - method. - The cache may use the file size information to reserve space on the cache. - It should also call fscache_set_store_limit() to indicate to FS-Cache the - highest byte it's willing to store for an object. + * Look up a cookie in the cache [mandatory]:: - This method may return -ve if an error occurred or the cache object cannot - be expanded. In such a case, the object will be withdrawn from service. + bool (*lookup_cookie)(struct fscache_cookie *cookie); - This operation is run asynchronously from FS-Cache's thread pool, and - storage and retrieval operations from the netfs are excluded during the - execution of this operation. + This method is called to look up/create the resources needed to access the + data storage for a cookie. It is called from a worker thread with a + volume-level access pin in the cache to prevent it from being withdrawn. + True should be returned if successful and false otherwise. If false is + returned, the withdraw_cookie op (see below) will be called. - * Reserve cache space for an object's data [optional]:: + If lookup fails, but the object could still be created (e.g. it hasn't + been cached before), then:: - int (*reserve_space)(struct fscache_object *object, loff_t size); + void fscache_cookie_lookup_negative( + struct fscache_cookie *cookie); - This is called to request that cache space be reserved to hold the data - for an object and the metadata used to track it. Zero size should be - taken as request to cancel a reservation. + can be called to let the network filesystem proceed and start downloading + stuff whilst the cache backend gets on with the job of creating things. - This should return 0 if successful, -ENOSPC if there isn't enough space - available, or -ENOMEM or -EIO on other errors. + If successful, ``cookie->cache_priv`` can be set. - The reservation may exceed the current size of the object, thus permitting - future expansion. If the amount of space consumed by an object would - exceed the reservation, it's permitted to refuse requests to allocate - pages, but not required. An object may be pruned down to its reservation - size if larger than that already. + * Withdraw an object without any cookie access counts held [mandatory]:: - * Request page be read from cache [mandatory]:: + void (*withdraw_cookie)(struct fscache_cookie *cookie); - int (*read_or_alloc_page)(struct fscache_retrieval *op, - struct page *page, - gfp_t gfp) + This method is called to withdraw a cookie from service. It will be + called when the cookie is relinquished by the netfs, withdrawn or culled + by the cache backend or closed after a period of non-use by fscache. - This is called to attempt to read a netfs page from the cache, or to - reserve a backing block if not. FS-Cache will have done as much checking - as it can before calling, but most of the work belongs to the backend. + The caller doesn't hold any access pins, but it is called from a + non-reentrant work item to manage races between the various ways + withdrawal can occur. - If there's no page in the cache, then -ENODATA should be returned if the - backend managed to reserve a backing block; -ENOBUFS or -ENOMEM if it - didn't. + The cookie will have the ``FSCACHE_COOKIE_RETIRED`` flag set on it if the + associated data is to be removed from the cache. - If there is suitable data in the cache, then a read operation should be - queued and 0 returned. When the read finishes, fscache_end_io() should be - called. - The fscache_mark_pages_cached() should be called for the page if any cache - metadata is retained. This will indicate to the netfs that the page needs - explicit uncaching. This operation takes a pagevec, thus allowing several - pages to be marked at once. + * Change the size of a data storage object [mandatory]:: - The retrieval record pointed to by op should be retained for each page - queued and released when I/O on the page has been formally ended. - fscache_get/put_retrieval() are available for this purpose. + void (*resize_cookie)(struct netfs_cache_resources *cres, + loff_t new_size); - The retrieval record may be used to get CPU time via the FS-Cache thread - pool. If this is desired, the op->op.processor should be set to point to - the appropriate processing routine, and fscache_enqueue_retrieval() should - be called at an appropriate point to request CPU time. For instance, the - retrieval routine could be enqueued upon the completion of a disk read. - The to_do field in the retrieval record is provided to aid in this. + This method is called to inform the cache backend of a change in size of + the netfs file due to local truncation. The cache backend should make all + of the changes it needs to make before returning as this is done under the + netfs inode mutex. - If an I/O error occurs, fscache_io_error() should be called and -ENOBUFS - returned if possible or fscache_end_io() called with a suitable error - code. + The caller holds a cookie-level access pin to prevent a race with + withdrawal and the netfs must have the cookie marked in-use to prevent + garbage collection or culling from removing any resources. - fscache_put_retrieval() should be called after a page or pages are dealt - with. This will complete the operation when all pages are dealt with. + * Invalidate a data storage object [mandatory]:: - * Request pages be read from cache [mandatory]:: + bool (*invalidate_cookie)(struct fscache_cookie *cookie); - int (*read_or_alloc_pages)(struct fscache_retrieval *op, - struct list_head *pages, - unsigned *nr_pages, - gfp_t gfp) + This is called when the network filesystem detects a third-party + modification or when an O_DIRECT write is made locally. This requests + that the cache backend should throw away all the data in the cache for + this object and start afresh. It should return true if successful and + false otherwise. - This is like the read_or_alloc_page() method, except it is handed a list - of pages instead of one page. Any pages on which a read operation is - started must be added to the page cache for the specified mapping and also - to the LRU. Such pages must also be removed from the pages list and - ``*nr_pages`` decremented per page. + On entry, new I O/operations are blocked. Once the cache is in a position + to accept I/O again, the backend should release the block by calling:: - If there was an error such as -ENOMEM, then that should be returned; else - if one or more pages couldn't be read or allocated, then -ENOBUFS should - be returned; else if one or more pages couldn't be read, then -ENODATA - should be returned. If all the pages are dispatched then 0 should be - returned. + void fscache_resume_after_invalidation(struct fscache_cookie *cookie); + If the method returns false, caching will be withdrawn for this cookie. - * Request page be allocated in the cache [mandatory]:: - int (*allocate_page)(struct fscache_retrieval *op, - struct page *page, - gfp_t gfp) + * Prepare to make local modifications to the cache [mandatory]:: - This is like the read_or_alloc_page() method, except that it shouldn't - read from the cache, even if there's data there that could be retrieved. - It should, however, set up any internal metadata required such that - the write_page() method can write to the cache. + void (*prepare_to_write)(struct fscache_cookie *cookie); - If there's no backing block available, then -ENOBUFS should be returned - (or -ENOMEM if there were other problems). If a block is successfully - allocated, then the netfs page should be marked and 0 returned. + This method is called when the network filesystem finds that it is going + to need to modify the contents of the cache due to local writes or + truncations. This gives the cache a chance to note that a cache object + may be incoherent with respect to the server and may need writing back + later. This may also cause the cached data to be scrapped on later + rebinding if not properly committed. - * Request pages be allocated in the cache [mandatory]:: + * Begin an operation for the netfs lib [mandatory]:: - int (*allocate_pages)(struct fscache_retrieval *op, - struct list_head *pages, - unsigned *nr_pages, - gfp_t gfp) + bool (*begin_operation)(struct netfs_cache_resources *cres, + enum fscache_want_state want_state); - This is an multiple page version of the allocate_page() method. pages and - nr_pages should be treated as for the read_or_alloc_pages() method. + This method is called when an I/O operation is being set up (read, write + or resize). The caller holds an access pin on the cookie and must have + marked the cookie as in-use. + If it can, the backend should attach any resources it needs to keep around + to the netfs_cache_resources object and return true. - * Request page be written to cache [mandatory]:: + If it can't complete the setup, it should return false. - int (*write_page)(struct fscache_storage *op, - struct page *page); + The want_state parameter indicates the state the caller needs the cache + object to be in and what it wants to do during the operation: - This is called to write from a page on which there was a previously - successful read_or_alloc_page() call or similar. FS-Cache filters out - pages that don't have mappings. + * ``FSCACHE_WANT_PARAMS`` - The caller just wants to access cache + object parameters; it doesn't need to do data I/O yet. - This method is called asynchronously from the FS-Cache thread pool. It is - not required to actually store anything, provided -ENODATA is then - returned to the next read of this page. + * ``FSCACHE_WANT_READ`` - The caller wants to read data. - If an error occurred, then a negative error code should be returned, - otherwise zero should be returned. FS-Cache will take appropriate action - in response to an error, such as withdrawing this object. + * ``FSCACHE_WANT_WRITE`` - The caller wants to write to or resize the + cache object. - If this method returns success then FS-Cache will inform the netfs - appropriately. + Note that there won't necessarily be anything attached to the cookie's + cache_priv yet if the cookie is still being created. - * Discard retained per-page metadata [mandatory]:: +Data I/O API +============ - void (*uncache_page)(struct fscache_object *object, struct page *page) +A cache backend provides a data I/O API by through the netfs library's ``struct +netfs_cache_ops`` attached to a ``struct netfs_cache_resources`` by the +``begin_operation`` method described above. - This is called when a netfs page is being evicted from the pagecache. The - cache backend should tear down any internal representation or tracking it - maintains for this page. +See the Documentation/filesystems/netfs_library.rst for a description. -FS-Cache Utilities -================== +Miscellaneous Functions +======================= FS-Cache provides some utilities that a cache backend may make use of: * Note occurrence of an I/O error in a cache:: - void fscache_io_error(struct fscache_cache *cache) + void fscache_io_error(struct fscache_cache *cache); - This tells FS-Cache that an I/O error occurred in the cache. After this - has been called, only resource dissociation operations (object and page - release) will be passed from the netfs to the cache backend for the - specified cache. + This tells FS-Cache that an I/O error occurred in the cache. This + prevents any new I/O from being started on the cache. This does not actually withdraw the cache. That must be done separately. + * Note cessation of caching on a cookie due to failure:: - * Invoke the retrieval I/O completion function:: - - void fscache_end_io(struct fscache_retrieval *op, struct page *page, - int error); - - This is called to note the end of an attempt to retrieve a page. The - error value should be 0 if successful and an error otherwise. - - - * Record that one or more pages being retrieved or allocated have been dealt - with:: - - void fscache_retrieval_complete(struct fscache_retrieval *op, - int n_pages); - - This is called to record the fact that one or more pages have been dealt - with and are no longer the concern of this operation. When the number of - pages remaining in the operation reaches 0, the operation will be - completed. - - - * Record operation completion:: - - void fscache_op_complete(struct fscache_operation *op); - - This is called to record the completion of an operation. This deducts - this operation from the parent object's run state, potentially permitting - one or more pending operations to start running. - - - * Set highest store limit:: - - void fscache_set_store_limit(struct fscache_object *object, - loff_t i_size); - - This sets the limit FS-Cache imposes on the highest byte it's willing to - try and store for a netfs. Any page over this limit is automatically - rejected by fscache_read_alloc_page() and co with -ENOBUFS. - - - * Mark pages as being cached:: - - void fscache_mark_pages_cached(struct fscache_retrieval *op, - struct pagevec *pagevec); - - This marks a set of pages as being cached. After this has been called, - the netfs must call fscache_uncache_page() to unmark the pages. - - - * Perform coherency check on an object:: - - enum fscache_checkaux fscache_check_aux(struct fscache_object *object, - const void *data, - uint16_t datalen); - - This asks the netfs to perform a coherency check on an object that has - just been looked up. The cookie attached to the object will determine the - netfs to use. data and datalen should specify where the auxiliary data - retrieved from the cache can be found. - - One of three values will be returned: - - FSCACHE_CHECKAUX_OKAY - The coherency data indicates the object is valid as is. - - FSCACHE_CHECKAUX_NEEDS_UPDATE - The coherency data needs updating, but otherwise the object is - valid. - - FSCACHE_CHECKAUX_OBSOLETE - The coherency data indicates that the object is obsolete and should - be discarded. - - - * Initialise a freshly allocated object:: - - void fscache_object_init(struct fscache_object *object); - - This initialises all the fields in an object representation. - - - * Indicate the destruction of an object:: - - void fscache_object_destroyed(struct fscache_cache *cache); - - This must be called to inform FS-Cache that an object that belonged to a - cache has been destroyed and deallocated. This will allow continuation - of the cache withdrawal process when it is stopped pending destruction of - all the objects. - - - * Indicate negative lookup on an object:: - - void fscache_object_lookup_negative(struct fscache_object *object); - - This is called to indicate to FS-Cache that a lookup process for an object - found a negative result. - - This changes the state of an object to permit reads pending on lookup - completion to go off and start fetching data from the netfs server as it's - known at this point that there can't be any data in the cache. - - This may be called multiple times on an object. Only the first call is - significant - all subsequent calls are ignored. - - - * Indicate an object has been obtained:: - - void fscache_obtained_object(struct fscache_object *object); - - This is called to indicate to FS-Cache that a lookup process for an object - produced a positive result, or that an object was created. This should - only be called once for any particular object. - - This changes the state of an object to indicate: - - (1) if no call to fscache_object_lookup_negative() has been made on - this object, that there may be data available, and that reads can - now go and look for it; and - - (2) that writes may now proceed against this object. - - - * Indicate that object lookup failed:: - - void fscache_object_lookup_error(struct fscache_object *object); - - This marks an object as having encountered a fatal error (usually EIO) - and causes it to move into a state whereby it will be withdrawn as soon - as possible. - - - * Indicate that a stale object was found and discarded:: - - void fscache_object_retrying_stale(struct fscache_object *object); - - This is called to indicate that the lookup procedure found an object in - the cache that the netfs decided was stale. The object has been - discarded from the cache and the lookup will be performed again. - - - * Indicate that the caching backend killed an object:: - - void fscache_object_mark_killed(struct fscache_object *object, - enum fscache_why_object_killed why); - - This is called to indicate that the cache backend preemptively killed an - object. The why parameter should be set to indicate the reason: + void fscache_caching_failed(struct fscache_cookie *cookie); - FSCACHE_OBJECT_IS_STALE - - the object was stale and needs discarding. + This notes that a the caching that was being done on a cookie failed in + some way, for instance the backing storage failed to be created or + invalidation failed and that no further I/O operations should take place + on it until the cache is reset. - FSCACHE_OBJECT_NO_SPACE - - there was insufficient cache space + * Count I/O requests:: - FSCACHE_OBJECT_WAS_RETIRED - - the object was retired when relinquished. + void fscache_count_read(void); + void fscache_count_write(void); - FSCACHE_OBJECT_WAS_CULLED - - the object was culled to make space. + These record reads and writes from/to the cache. The numbers are + displayed in /proc/fs/fscache/stats. + * Count out-of-space errors:: - * Get and release references on a retrieval record:: + void fscache_count_no_write_space(void); + void fscache_count_no_create_space(void); - void fscache_get_retrieval(struct fscache_retrieval *op); - void fscache_put_retrieval(struct fscache_retrieval *op); + These record ENOSPC errors in the cache, divided into failures of data + writes and failures of filesystem object creations (e.g. mkdir). - These two functions are used to retain a retrieval record while doing - asynchronous data retrieval and block allocation. + * Count objects culled:: + void fscache_count_culled(void); - * Enqueue a retrieval record for processing:: + This records the culling of an object. - void fscache_enqueue_retrieval(struct fscache_retrieval *op); + * Get the cookie from a set of cache resources:: - This enqueues a retrieval record for processing by the FS-Cache thread - pool. One of the threads in the pool will invoke the retrieval record's - op->op.processor callback function. This function may be called from - within the callback function. + struct fscache_cookie *fscache_cres_cookie(struct netfs_cache_resources *cres) + Pull a pointer to the cookie from the cache resources. This may return a + NULL cookie if no cookie was set. - * List of object state names:: - const char *fscache_object_states[]; +API Function Reference +====================== - For debugging purposes, this may be used to turn the state that an object - is in into a text string for display purposes. +.. kernel-doc:: include/linux/fscache-cache.h diff --git a/Documentation/filesystems/caching/cachefiles.rst b/Documentation/filesystems/caching/cachefiles.rst index e58bc1fd312a..fc7abf712315 100644 --- a/Documentation/filesystems/caching/cachefiles.rst +++ b/Documentation/filesystems/caching/cachefiles.rst @@ -1,8 +1,8 @@ .. SPDX-License-Identifier: GPL-2.0 -=============================================== -CacheFiles: CACHE ON ALREADY MOUNTED FILESYSTEM -=============================================== +=================================== +Cache on Already Mounted Filesystem +=================================== .. Contents: @@ -28,6 +28,7 @@ CacheFiles: CACHE ON ALREADY MOUNTED FILESYSTEM (*) Debugging. + (*) On-demand Read. Overview @@ -482,3 +483,180 @@ the control file. For example:: echo $((1|4|8)) >/sys/module/cachefiles/parameters/debug will turn on all function entry debugging. + + +On-demand Read +============== + +When working in its original mode, CacheFiles serves as a local cache for a +remote networking fs - while in on-demand read mode, CacheFiles can boost the +scenario where on-demand read semantics are needed, e.g. container image +distribution. + +The essential difference between these two modes is seen when a cache miss +occurs: In the original mode, the netfs will fetch the data from the remote +server and then write it to the cache file; in on-demand read mode, fetching +the data and writing it into the cache is delegated to a user daemon. + +``CONFIG_CACHEFILES_ONDEMAND`` should be enabled to support on-demand read mode. + + +Protocol Communication +---------------------- + +The on-demand read mode uses a simple protocol for communication between kernel +and user daemon. The protocol can be modeled as:: + + kernel --[request]--> user daemon --[reply]--> kernel + +CacheFiles will send requests to the user daemon when needed. The user daemon +should poll the devnode ('/dev/cachefiles') to check if there's a pending +request to be processed. A POLLIN event will be returned when there's a pending +request. + +The user daemon then reads the devnode to fetch a request to process. It should +be noted that each read only gets one request. When it has finished processing +the request, the user daemon should write the reply to the devnode. + +Each request starts with a message header of the form:: + + struct cachefiles_msg { + __u32 msg_id; + __u32 opcode; + __u32 len; + __u32 object_id; + __u8 data[]; + }; + +where: + + * ``msg_id`` is a unique ID identifying this request among all pending + requests. + + * ``opcode`` indicates the type of this request. + + * ``object_id`` is a unique ID identifying the cache file operated on. + + * ``data`` indicates the payload of this request. + + * ``len`` indicates the whole length of this request, including the + header and following type-specific payload. + + +Turning on On-demand Mode +------------------------- + +An optional parameter becomes available to the "bind" command:: + + bind [ondemand] + +When the "bind" command is given no argument, it defaults to the original mode. +When it is given the "ondemand" argument, i.e. "bind ondemand", on-demand read +mode will be enabled. + + +The OPEN Request +---------------- + +When the netfs opens a cache file for the first time, a request with the +CACHEFILES_OP_OPEN opcode, a.k.a an OPEN request will be sent to the user +daemon. The payload format is of the form:: + + struct cachefiles_open { + __u32 volume_key_size; + __u32 cookie_key_size; + __u32 fd; + __u32 flags; + __u8 data[]; + }; + +where: + + * ``data`` contains the volume_key followed directly by the cookie_key. + The volume key is a NUL-terminated string; the cookie key is binary + data. + + * ``volume_key_size`` indicates the size of the volume key in bytes. + + * ``cookie_key_size`` indicates the size of the cookie key in bytes. + + * ``fd`` indicates an anonymous fd referring to the cache file, through + which the user daemon can perform write/llseek file operations on the + cache file. + + +The user daemon can use the given (volume_key, cookie_key) pair to distinguish +the requested cache file. With the given anonymous fd, the user daemon can +fetch the data and write it to the cache file in the background, even when +kernel has not triggered a cache miss yet. + +Be noted that each cache file has a unique object_id, while it may have multiple +anonymous fds. The user daemon may duplicate anonymous fds from the initial +anonymous fd indicated by the @fd field through dup(). Thus each object_id can +be mapped to multiple anonymous fds, while the usr daemon itself needs to +maintain the mapping. + +When implementing a user daemon, please be careful of RLIMIT_NOFILE, +``/proc/sys/fs/nr_open`` and ``/proc/sys/fs/file-max``. Typically these needn't +be huge since they're related to the number of open device blobs rather than +open files of each individual filesystem. + +The user daemon should reply the OPEN request by issuing a "copen" (complete +open) command on the devnode:: + + copen <msg_id>,<cache_size> + +where: + + * ``msg_id`` must match the msg_id field of the OPEN request. + + * When >= 0, ``cache_size`` indicates the size of the cache file; + when < 0, ``cache_size`` indicates any error code encountered by the + user daemon. + + +The CLOSE Request +----------------- + +When a cookie withdrawn, a CLOSE request (opcode CACHEFILES_OP_CLOSE) will be +sent to the user daemon. This tells the user daemon to close all anonymous fds +associated with the given object_id. The CLOSE request has no extra payload, +and shouldn't be replied. + + +The READ Request +---------------- + +When a cache miss is encountered in on-demand read mode, CacheFiles will send a +READ request (opcode CACHEFILES_OP_READ) to the user daemon. This tells the user +daemon to fetch the contents of the requested file range. The payload is of the +form:: + + struct cachefiles_read { + __u64 off; + __u64 len; + }; + +where: + + * ``off`` indicates the starting offset of the requested file range. + + * ``len`` indicates the length of the requested file range. + + +When it receives a READ request, the user daemon should fetch the requested data +and write it to the cache file identified by object_id. + +When it has finished processing the READ request, the user daemon should reply +by using the CACHEFILES_IOC_READ_COMPLETE ioctl on one of the anonymous fds +associated with the object_id given in the READ request. The ioctl is of the +form:: + + ioctl(fd, CACHEFILES_IOC_READ_COMPLETE, msg_id); + +where: + + * ``fd`` is one of the anonymous fds associated with the object_id + given. + + * ``msg_id`` must match the msg_id field of the READ request. diff --git a/Documentation/filesystems/caching/fscache.rst b/Documentation/filesystems/caching/fscache.rst index 70de86922b6a..a74d7b052dc1 100644 --- a/Documentation/filesystems/caching/fscache.rst +++ b/Documentation/filesystems/caching/fscache.rst @@ -10,25 +10,25 @@ Overview This facility is a general purpose cache for network filesystems, though it could be used for caching other things such as ISO9660 filesystems too. -FS-Cache mediates between cache backends (such as CacheFS) and network +FS-Cache mediates between cache backends (such as CacheFiles) and network filesystems:: +---------+ - | | +--------------+ - | NFS |--+ | | - | | | +-->| CacheFS | - +---------+ | +----------+ | | /dev/hda5 | - | | | | +--------------+ - +---------+ +-->| | | - | | | |--+ - | AFS |----->| FS-Cache | - | | | |--+ - +---------+ +-->| | | - | | | | +--------------+ - +---------+ | +----------+ | | | - | | | +-->| CacheFiles | - | ISOFS |--+ | /var/cache | - | | +--------------+ + | | +--------------+ + | NFS |--+ | | + | | | +-->| CacheFS | + +---------+ | +----------+ | | /dev/hda5 | + | | | | +--------------+ + +---------+ +-------------->| | | + | | +-------+ | |--+ + | AFS |----->| | | FS-Cache | + | | | netfs |-->| |--+ + +---------+ +-->| lib | | | | + | | | | | | +--------------+ + +---------+ | +-------+ +----------+ | | | + | | | +-->| CacheFiles | + | 9P |--+ | /var/cache | + | | +--------------+ +---------+ Or to look at it another way, FS-Cache is a module that provides a caching @@ -84,101 +84,62 @@ then serving the pages out of that cache rather than the netfs inode because: one-off access of a small portion of it (such as might be done with the "file" program). -It instead serves the cache out in PAGE_SIZE chunks as and when requested by -the netfs('s) using it. +It instead serves the cache out in chunks as and when requested by the netfs +using it. FS-Cache provides the following facilities: - (1) More than one cache can be used at once. Caches can be selected + * More than one cache can be used at once. Caches can be selected explicitly by use of tags. - (2) Caches can be added / removed at any time. + * Caches can be added / removed at any time, even whilst being accessed. - (3) The netfs is provided with an interface that allows either party to + * The netfs is provided with an interface that allows either party to withdraw caching facilities from a file (required for (2)). - (4) The interface to the netfs returns as few errors as possible, preferring + * The interface to the netfs returns as few errors as possible, preferring rather to let the netfs remain oblivious. - (5) Cookies are used to represent indices, files and other objects to the - netfs. The simplest cookie is just a NULL pointer - indicating nothing - cached there. - - (6) The netfs is allowed to propose - dynamically - any index hierarchy it - desires, though it must be aware that the index search function is - recursive, stack space is limited, and indices can only be children of - indices. - - (7) Data I/O is done direct to and from the netfs's pages. The netfs - indicates that page A is at index B of the data-file represented by cookie - C, and that it should be read or written. The cache backend may or may - not start I/O on that page, but if it does, a netfs callback will be - invoked to indicate completion. The I/O may be either synchronous or - asynchronous. - - (8) Cookies can be "retired" upon release. At this point FS-Cache will mark - them as obsolete and the index hierarchy rooted at that point will get - recycled. - - (9) The netfs provides a "match" function for index searches. In addition to - saying whether a match was made or not, this can also specify that an - entry should be updated or deleted. - -(10) As much as possible is done asynchronously. - - -FS-Cache maintains a virtual indexing tree in which all indices, files, objects -and pages are kept. Bits of this tree may actually reside in one or more -caches:: - - FSDEF - | - +------------------------------------+ - | | - NFS AFS - | | - +--------------------------+ +-----------+ - | | | | - homedir mirror afs.org redhat.com - | | | - +------------+ +---------------+ +----------+ - | | | | | | - 00001 00002 00007 00125 vol00001 vol00002 - | | | | | - +---+---+ +-----+ +---+ +------+------+ +-----+----+ - | | | | | | | | | | | | | - PG0 PG1 PG2 PG0 XATTR PG0 PG1 DIRENT DIRENT DIRENT R/W R/O Bak - | | - PG0 +-------+ - | | - 00001 00003 - | - +---+---+ - | | | - PG0 PG1 PG2 - -In the example above, you can see two netfs's being backed: NFS and AFS. These -have different index hierarchies: - - * The NFS primary index contains per-server indices. Each server index is - indexed by NFS file handles to get data file objects. Each data file - objects can have an array of pages, but may also have further child - objects, such as extended attributes and directory entries. Extended - attribute objects themselves have page-array contents. - - * The AFS primary index contains per-cell indices. Each cell index contains - per-logical-volume indices. Each of volume index contains up to three - indices for the read-write, read-only and backup mirrors of those volumes. - Each of these contains vnode data file objects, each of which contains an - array of pages. - -The very top index is the FS-Cache master index in which individual netfs's -have entries. - -Any index object may reside in more than one cache, provided it only has index -children. Any index with non-index object children will be assumed to only -reside in one cache. + * There are three types of cookie: cache, volume and data file cookies. + Cache cookies represent the cache as a whole and are not normally visible + to the netfs; the netfs gets a volume cookie to represent a collection of + files (typically something that a netfs would get for a superblock); and + data file cookies are used to cache data (something that would be got for + an inode). + + * Volumes are matched using a key. This is a printable string that is used + to encode all the information that might be needed to distinguish one + superblock, say, from another. This would be a compound of things like + cell name or server address, volume name or share path. It must be a + valid pathname. + + * Cookies are matched using a key. This is a binary blob and is used to + represent the object within a volume (so the volume key need not form + part of the blob). This might include things like an inode number and + uniquifier or a file handle. + + * Cookie resources are set up and pinned by marking the cookie in-use. + This prevents the backing resources from being culled. Timed garbage + collection is employed to eliminate cookies that haven't been used for a + short while, thereby reducing resource overload. This is intended to be + used when a file is opened or closed. + + A cookie can be marked in-use multiple times simultaneously; each mark + must be unused. + + * Begin/end access functions are provided to delay cache withdrawal for the + duration of an operation and prevent structs from being freed whilst + we're looking at them. + + * Data I/O is done by asynchronous DIO to/from a buffer described by the + netfs using an iov_iter. + + * An invalidation facility is available to discard data from the cache and + to deal with I/O that's in progress that is accessing old data. + + * Cookies can be "retired" upon release, thereby causing the object to be + removed from the cache. The netfs API to FS-Cache can be found in: @@ -189,11 +150,6 @@ The cache backend API to FS-Cache can be found in: Documentation/filesystems/caching/backend-api.rst -A description of the internal representations and object state machine can be -found in: - - Documentation/filesystems/caching/object.rst - Statistical Information ======================= @@ -201,333 +157,162 @@ Statistical Information If FS-Cache is compiled with the following options enabled:: CONFIG_FSCACHE_STATS=y - CONFIG_FSCACHE_HISTOGRAM=y -then it will gather certain statistics and display them through a number of -proc files. +then it will gather certain statistics and display them through: -/proc/fs/fscache/stats ----------------------- + /proc/fs/fscache/stats - This shows counts of a number of events that can happen in FS-Cache: +This shows counts of a number of events that can happen in FS-Cache: +--------------+-------+-------------------------------------------------------+ |CLASS |EVENT |MEANING | +==============+=======+=======================================================+ -|Cookies |idx=N |Number of index cookies allocated | -+ +-------+-------------------------------------------------------+ -| |dat=N |Number of data storage cookies allocated | +|Cookies |n=N |Number of data storage cookies allocated | + +-------+-------------------------------------------------------+ -| |spc=N |Number of special cookies allocated | -+--------------+-------+-------------------------------------------------------+ -|Objects |alc=N |Number of objects allocated | -+ +-------+-------------------------------------------------------+ -| |nal=N |Number of object allocation failures | +| |v=N |Number of volume index cookies allocated | + +-------+-------------------------------------------------------+ -| |avl=N |Number of objects that reached the available state | -+ +-------+-------------------------------------------------------+ -| |ded=N |Number of objects that reached the dead state | -+--------------+-------+-------------------------------------------------------+ -|ChkAux |non=N |Number of objects that didn't have a coherency check | +| |vcol=N |Number of volume index key collisions | + +-------+-------------------------------------------------------+ -| |ok=N |Number of objects that passed a coherency check | -+ +-------+-------------------------------------------------------+ -| |upd=N |Number of objects that needed a coherency data update | -+ +-------+-------------------------------------------------------+ -| |obs=N |Number of objects that were declared obsolete | -+--------------+-------+-------------------------------------------------------+ -|Pages |mrk=N |Number of pages marked as being cached | -| |unc=N |Number of uncache page requests seen | +| |voom=N |Number of OOM events when allocating volume cookies | +--------------+-------+-------------------------------------------------------+ |Acquire |n=N |Number of acquire cookie requests seen | + +-------+-------------------------------------------------------+ -| |nul=N |Number of acq reqs given a NULL parent | -+ +-------+-------------------------------------------------------+ -| |noc=N |Number of acq reqs rejected due to no cache available | -+ +-------+-------------------------------------------------------+ | |ok=N |Number of acq reqs succeeded | + +-------+-------------------------------------------------------+ -| |nbf=N |Number of acq reqs rejected due to error | -+ +-------+-------------------------------------------------------+ | |oom=N |Number of acq reqs failed on ENOMEM | +--------------+-------+-------------------------------------------------------+ -|Lookups |n=N |Number of lookup calls made on cache backends | +|LRU |n=N |Number of cookies currently on the LRU | + +-------+-------------------------------------------------------+ -| |neg=N |Number of negative lookups made | +| |exp=N |Number of cookies expired off of the LRU | + +-------+-------------------------------------------------------+ -| |pos=N |Number of positive lookups made | +| |rmv=N |Number of cookies removed from the LRU | + +-------+-------------------------------------------------------+ -| |crt=N |Number of objects created by lookup | +| |drp=N |Number of LRU'd cookies relinquished/withdrawn | + +-------+-------------------------------------------------------+ -| |tmo=N |Number of lookups timed out and requeued | +| |at=N |Time till next LRU cull (jiffies) | ++--------------+-------+-------------------------------------------------------+ +|Invals |n=N |Number of invalidations | +--------------+-------+-------------------------------------------------------+ |Updates |n=N |Number of update cookie requests seen | + +-------+-------------------------------------------------------+ -| |nul=N |Number of upd reqs given a NULL parent | +| |rsz=N |Number of resize requests | + +-------+-------------------------------------------------------+ -| |run=N |Number of upd reqs granted CPU time | +| |rsn=N |Number of skipped resize requests | +--------------+-------+-------------------------------------------------------+ |Relinqs |n=N |Number of relinquish cookie requests seen | + +-------+-------------------------------------------------------+ -| |nul=N |Number of rlq reqs given a NULL parent | +| |rtr=N |Number of rlq reqs with retire=true | + +-------+-------------------------------------------------------+ -| |wcr=N |Number of rlq reqs waited on completion of creation | +| |drop=N |Number of cookies no longer blocking re-acquisition | +--------------+-------+-------------------------------------------------------+ -|AttrChg |n=N |Number of attribute changed requests seen | -+ +-------+-------------------------------------------------------+ -| |ok=N |Number of attr changed requests queued | -+ +-------+-------------------------------------------------------+ -| |nbf=N |Number of attr changed rejected -ENOBUFS | +|NoSpace |nwr=N |Number of write requests refused due to lack of space | + +-------+-------------------------------------------------------+ -| |oom=N |Number of attr changed failed -ENOMEM | +| |ncr=N |Number of create requests refused due to lack of space | + +-------+-------------------------------------------------------+ -| |run=N |Number of attr changed ops given CPU time | +| |cull=N |Number of objects culled to make space | +--------------+-------+-------------------------------------------------------+ -|Allocs |n=N |Number of allocation requests seen | +|IO |rd=N |Number of read operations in the cache | + +-------+-------------------------------------------------------+ -| |ok=N |Number of successful alloc reqs | -+ +-------+-------------------------------------------------------+ -| |wt=N |Number of alloc reqs that waited on lookup completion | -+ +-------+-------------------------------------------------------+ -| |nbf=N |Number of alloc reqs rejected -ENOBUFS | -+ +-------+-------------------------------------------------------+ -| |int=N |Number of alloc reqs aborted -ERESTARTSYS | -+ +-------+-------------------------------------------------------+ -| |ops=N |Number of alloc reqs submitted | -+ +-------+-------------------------------------------------------+ -| |owt=N |Number of alloc reqs waited for CPU time | -+ +-------+-------------------------------------------------------+ -| |abt=N |Number of alloc reqs aborted due to object death | -+--------------+-------+-------------------------------------------------------+ -|Retrvls |n=N |Number of retrieval (read) requests seen | -+ +-------+-------------------------------------------------------+ -| |ok=N |Number of successful retr reqs | -+ +-------+-------------------------------------------------------+ -| |wt=N |Number of retr reqs that waited on lookup completion | -+ +-------+-------------------------------------------------------+ -| |nod=N |Number of retr reqs returned -ENODATA | -+ +-------+-------------------------------------------------------+ -| |nbf=N |Number of retr reqs rejected -ENOBUFS | -+ +-------+-------------------------------------------------------+ -| |int=N |Number of retr reqs aborted -ERESTARTSYS | -+ +-------+-------------------------------------------------------+ -| |oom=N |Number of retr reqs failed -ENOMEM | -+ +-------+-------------------------------------------------------+ -| |ops=N |Number of retr reqs submitted | -+ +-------+-------------------------------------------------------+ -| |owt=N |Number of retr reqs waited for CPU time | -+ +-------+-------------------------------------------------------+ -| |abt=N |Number of retr reqs aborted due to object death | -+--------------+-------+-------------------------------------------------------+ -|Stores |n=N |Number of storage (write) requests seen | -+ +-------+-------------------------------------------------------+ -| |ok=N |Number of successful store reqs | -+ +-------+-------------------------------------------------------+ -| |agn=N |Number of store reqs on a page already pending storage | -+ +-------+-------------------------------------------------------+ -| |nbf=N |Number of store reqs rejected -ENOBUFS | -+ +-------+-------------------------------------------------------+ -| |oom=N |Number of store reqs failed -ENOMEM | -+ +-------+-------------------------------------------------------+ -| |ops=N |Number of store reqs submitted | -+ +-------+-------------------------------------------------------+ -| |run=N |Number of store reqs granted CPU time | -+ +-------+-------------------------------------------------------+ -| |pgs=N |Number of pages given store req processing time | -+ +-------+-------------------------------------------------------+ -| |rxd=N |Number of store reqs deleted from tracking tree | -+ +-------+-------------------------------------------------------+ -| |olm=N |Number of store reqs over store limit | -+--------------+-------+-------------------------------------------------------+ -|VmScan |nos=N |Number of release reqs against pages with no | -| | |pending store | -+ +-------+-------------------------------------------------------+ -| |gon=N |Number of release reqs against pages stored by | -| | |time lock granted | -+ +-------+-------------------------------------------------------+ -| |bsy=N |Number of release reqs ignored due to in-progress store| -+ +-------+-------------------------------------------------------+ -| |can=N |Number of page stores cancelled due to release req | -+--------------+-------+-------------------------------------------------------+ -|Ops |pend=N |Number of times async ops added to pending queues | -+ +-------+-------------------------------------------------------+ -| |run=N |Number of times async ops given CPU time | -+ +-------+-------------------------------------------------------+ -| |enq=N |Number of times async ops queued for processing | -+ +-------+-------------------------------------------------------+ -| |can=N |Number of async ops cancelled | -+ +-------+-------------------------------------------------------+ -| |rej=N |Number of async ops rejected due to object | -| | |lookup/create failure | -+ +-------+-------------------------------------------------------+ -| |ini=N |Number of async ops initialised | -+ +-------+-------------------------------------------------------+ -| |dfr=N |Number of async ops queued for deferred release | -+ +-------+-------------------------------------------------------+ -| |rel=N |Number of async ops released | -| | |(should equal ini=N when idle) | -+ +-------+-------------------------------------------------------+ -| |gc=N |Number of deferred-release async ops garbage collected | -+--------------+-------+-------------------------------------------------------+ -|CacheOp |alo=N |Number of in-progress alloc_object() cache ops | -+ +-------+-------------------------------------------------------+ -| |luo=N |Number of in-progress lookup_object() cache ops | -+ +-------+-------------------------------------------------------+ -| |luc=N |Number of in-progress lookup_complete() cache ops | -+ +-------+-------------------------------------------------------+ -| |gro=N |Number of in-progress grab_object() cache ops | -+ +-------+-------------------------------------------------------+ -| |upo=N |Number of in-progress update_object() cache ops | -+ +-------+-------------------------------------------------------+ -| |dro=N |Number of in-progress drop_object() cache ops | -+ +-------+-------------------------------------------------------+ -| |pto=N |Number of in-progress put_object() cache ops | -+ +-------+-------------------------------------------------------+ -| |syn=N |Number of in-progress sync_cache() cache ops | -+ +-------+-------------------------------------------------------+ -| |atc=N |Number of in-progress attr_changed() cache ops | -+ +-------+-------------------------------------------------------+ -| |rap=N |Number of in-progress read_or_alloc_page() cache ops | -+ +-------+-------------------------------------------------------+ -| |ras=N |Number of in-progress read_or_alloc_pages() cache ops | -+ +-------+-------------------------------------------------------+ -| |alp=N |Number of in-progress allocate_page() cache ops | -+ +-------+-------------------------------------------------------+ -| |als=N |Number of in-progress allocate_pages() cache ops | -+ +-------+-------------------------------------------------------+ -| |wrp=N |Number of in-progress write_page() cache ops | -+ +-------+-------------------------------------------------------+ -| |ucp=N |Number of in-progress uncache_page() cache ops | -+ +-------+-------------------------------------------------------+ -| |dsp=N |Number of in-progress dissociate_pages() cache ops | -+--------------+-------+-------------------------------------------------------+ -|CacheEv |nsp=N |Number of object lookups/creations rejected due to | -| | |lack of space | -+ +-------+-------------------------------------------------------+ -| |stl=N |Number of stale objects deleted | -+ +-------+-------------------------------------------------------+ -| |rtr=N |Number of objects retired when relinquished | -+ +-------+-------------------------------------------------------+ -| |cul=N |Number of objects culled | +| |wr=N |Number of write operations in the cache | +--------------+-------+-------------------------------------------------------+ +Netfslib will also add some stats counters of its own. -/proc/fs/fscache/histogram --------------------------- +Cache List +========== - :: +FS-Cache provides a list of cache cookies: - cat /proc/fs/fscache/histogram - JIFS SECS OBJ INST OP RUNS OBJ RUNS RETRV DLY RETRIEVLS - ===== ===== ========= ========= ========= ========= ========= + /proc/fs/fscache/cookies - This shows the breakdown of the number of times each amount of time - between 0 jiffies and HZ-1 jiffies a variety of tasks took to run. The - columns are as follows: +This will look something like:: - ========= ======================================================= - COLUMN TIME MEASUREMENT - ========= ======================================================= - OBJ INST Length of time to instantiate an object - OP RUNS Length of time a call to process an operation took - OBJ RUNS Length of time a call to process an object event took - RETRV DLY Time between an requesting a read and lookup completing - RETRIEVLS Time between beginning and end of a retrieval - ========= ======================================================= + # cat /proc/fs/fscache/caches + CACHE REF VOLS OBJS ACCES S NAME + ======== ===== ===== ===== ===== = =============== + 00000001 2 1 2123 1 A default - Each row shows the number of events that took a particular range of times. - Each step is 1 jiffy in size. The JIFS column indicates the particular - jiffy range covered, and the SECS field the equivalent number of seconds. +where the columns are: + ======= =============================================================== + COLUMN DESCRIPTION + ======= =============================================================== + CACHE Cache cookie debug ID (also appears in traces) + REF Number of references on the cache cookie + VOLS Number of volumes cookies in this cache + OBJS Number of cache objects in use + ACCES Number of accesses pinning the cache + S State + NAME Name of the cache. + ======= =============================================================== + +The state can be (-) Inactive, (P)reparing, (A)ctive, (E)rror or (W)ithdrawing. -Object List +Volume List =========== -If CONFIG_FSCACHE_OBJECT_LIST is enabled, the FS-Cache facility will maintain a -list of all the objects currently allocated and allow them to be viewed -through:: +FS-Cache provides a list of volume cookies: - /proc/fs/fscache/objects + /proc/fs/fscache/volumes This will look something like:: - [root@andromeda ~]# head /proc/fs/fscache/objects - OBJECT PARENT STAT CHLDN OPS OOP IPR EX READS EM EV F S | NETFS_COOKIE_DEF TY FL NETFS_DATA OBJECT_KEY, AUX_DATA - ======== ======== ==== ===== === === === == ===== == == = = | ================ == == ================ ================ - 17e4b 2 ACTV 0 0 0 0 0 0 7b 4 0 0 | NFS.fh DT 0 ffff88001dd82820 010006017edcf8bbc93b43298fdfbe71e50b57b13a172c0117f38472, e567634700000000000000000000000063f2404a000000000000000000000000c9030000000000000000000063f2404a - 1693a 2 ACTV 0 0 0 0 0 0 7b 4 0 0 | NFS.fh DT 0 ffff88002db23380 010006017edcf8bbc93b43298fdfbe71e50b57b1e0162c01a2df0ea6, 420ebc4a000000000000000000000000420ebc4a0000000000000000000000000e1801000000000000000000420ebc4a + VOLUME REF nCOOK ACC FL CACHE KEY + ======== ===== ===== === == =============== ================ + 00000001 55 54 1 00 default afs,example.com,100058 -where the first set of columns before the '|' describe the object: +where the columns are: ======= =============================================================== COLUMN DESCRIPTION ======= =============================================================== - OBJECT Object debugging ID (appears as OBJ%x in some debug messages) - PARENT Debugging ID of parent object - STAT Object state - CHLDN Number of child objects of this object - OPS Number of outstanding operations on this object - OOP Number of outstanding child object management operations - IPR - EX Number of outstanding exclusive operations - READS Number of outstanding read operations - EM Object's event mask - EV Events raised on this object - F Object flags - S Object work item busy state mask (1:pending 2:running) + VOLUME The volume cookie debug ID (also appears in traces) + REF Number of references on the volume cookie + nCOOK Number of cookies in the volume + ACC Number of accesses pinning the cache + FL Flags on the volume cookie + CACHE Name of the cache or "-" + KEY The indexing key for the volume ======= =============================================================== -and the second set of columns describe the object's cookie, if present: - - ================ ====================================================== - COLUMN DESCRIPTION - ================ ====================================================== - NETFS_COOKIE_DEF Name of netfs cookie definition - TY Cookie type (IX - index, DT - data, hex - special) - FL Cookie flags - NETFS_DATA Netfs private data stored in the cookie - OBJECT_KEY Object key } 1 column, with separating comma - AUX_DATA Object aux data } presence may be configured - ================ ====================================================== - -The data shown may be filtered by attaching the a key to an appropriate keyring -before viewing the file. Something like:: - - keyctl add user fscache:objlist <restrictions> @s - -where <restrictions> are a selection of the following letters: - == ========================================================= - K Show hexdump of object key (don't show if not given) - A Show hexdump of object aux data (don't show if not given) - == ========================================================= +Cookie List +=========== -and the following paired letters: +FS-Cache provides a list of cookies: - == ========================================================= - C Show objects that have a cookie - c Show objects that don't have a cookie - B Show objects that are busy - b Show objects that aren't busy - W Show objects that have pending writes - w Show objects that don't have pending writes - R Show objects that have outstanding reads - r Show objects that don't have outstanding reads - S Show objects that have work queued - s Show objects that don't have work queued - == ========================================================= + /proc/fs/fscache/cookies -If neither side of a letter pair is given, then both are implied. For example: +This will look something like:: - keyctl add user fscache:objlist KB @s + # head /proc/fs/fscache/cookies + COOKIE VOLUME REF ACT ACC S FL DEF + ======== ======== === === === = == ================ + 00000435 00000001 1 0 -1 - 08 0000000201d080070000000000000000, 0000000000000000 + 00000436 00000001 1 0 -1 - 00 0000005601d080080000000000000000, 0000000000000051 + 00000437 00000001 1 0 -1 - 08 00023b3001d0823f0000000000000000, 0000000000000000 + 00000438 00000001 1 0 -1 - 08 0000005801d0807b0000000000000000, 0000000000000000 + 00000439 00000001 1 0 -1 - 08 00023b3201d080a10000000000000000, 0000000000000000 + 0000043a 00000001 1 0 -1 - 08 00023b3401d080a30000000000000000, 0000000000000000 + 0000043b 00000001 1 0 -1 - 08 00023b3601d080b30000000000000000, 0000000000000000 + 0000043c 00000001 1 0 -1 - 08 00023b3801d080b40000000000000000, 0000000000000000 -shows objects that are busy, and lists their object keys, but does not dump -their auxiliary data. It also implies "CcWwRrSs", but as 'B' is given, 'b' is -not implied. +where the columns are: -By default all objects and all fields will be shown. + ======= =============================================================== + COLUMN DESCRIPTION + ======= =============================================================== + COOKIE The cookie debug ID (also appears in traces) + VOLUME The parent volume cookie debug ID + REF Number of references on the volume cookie + ACT Number of times the cookie is marked for in use + ACC Number of access pins in the cookie + S State of the cookie + FL Flags on the cookie + DEF Key, auxiliary data + ======= =============================================================== Debugging @@ -549,10 +334,8 @@ This is a bitmask of debugging streams to enable: 3 8 Cookie management Function entry trace 4 16 Function exit trace 5 32 General - 6 64 Page handling Function entry trace - 7 128 Function exit trace - 8 256 General - 9 512 Operation management Function entry trace + 6-8 (Not used) + 9 512 I/O operation management Function entry trace 10 1024 Function exit trace 11 2048 General ======= ======= =============================== ======================= @@ -560,6 +343,6 @@ This is a bitmask of debugging streams to enable: The appropriate set of values should be OR'd together and the result written to the control file. For example:: - echo $((1|8|64)) >/sys/module/fscache/parameters/debug + echo $((1|8|512)) >/sys/module/fscache/parameters/debug will turn on all function entry debugging. diff --git a/Documentation/filesystems/caching/index.rst b/Documentation/filesystems/caching/index.rst index 033da7ac7c6e..df4307124b00 100644 --- a/Documentation/filesystems/caching/index.rst +++ b/Documentation/filesystems/caching/index.rst @@ -7,8 +7,6 @@ Filesystem Caching :maxdepth: 2 fscache - object + netfs-api backend-api cachefiles - netfs-api - operations diff --git a/Documentation/filesystems/caching/netfs-api.rst b/Documentation/filesystems/caching/netfs-api.rst index d9f14b8610ba..1d18e9def183 100644 --- a/Documentation/filesystems/caching/netfs-api.rst +++ b/Documentation/filesystems/caching/netfs-api.rst @@ -1,896 +1,452 @@ .. SPDX-License-Identifier: GPL-2.0 -=============================== -FS-Cache Network Filesystem API -=============================== +============================== +Network Filesystem Caching API +============================== -There's an API by which a network filesystem can make use of the FS-Cache -facilities. This is based around a number of principles: +Fscache provides an API by which a network filesystem can make use of local +caching facilities. The API is arranged around a number of principles: - (1) Caches can store a number of different object types. There are two main - object types: indices and files. The first is a special type used by - FS-Cache to make finding objects faster and to make retiring of groups of - objects easier. + (1) A cache is logically organised into volumes and data storage objects + within those volumes. - (2) Every index, file or other object is represented by a cookie. This cookie - may or may not have anything associated with it, but the netfs doesn't - need to care. + (2) Volumes and data storage objects are represented by various types of + cookie. - (3) Barring the top-level index (one entry per cached netfs), the index - hierarchy for each netfs is structured according the whim of the netfs. + (3) Cookies have keys that distinguish them from their peers. -This API is declared in <linux/fscache.h>. + (4) Cookies have coherency data that allows a cache to determine if the + cached data is still valid. -.. This document contains the following sections: - - (1) Network filesystem definition - (2) Index definition - (3) Object definition - (4) Network filesystem (un)registration - (5) Cache tag lookup - (6) Index registration - (7) Data file registration - (8) Miscellaneous object registration - (9) Setting the data file size - (10) Page alloc/read/write - (11) Page uncaching - (12) Index and data file consistency - (13) Cookie enablement - (14) Miscellaneous cookie operations - (15) Cookie unregistration - (16) Index invalidation - (17) Data file invalidation - (18) FS-Cache specific page flags. - - -Network Filesystem Definition -============================= - -FS-Cache needs a description of the network filesystem. This is specified -using a record of the following structure:: - - struct fscache_netfs { - uint32_t version; - const char *name; - struct fscache_cookie *primary_index; - ... - }; - -This first two fields should be filled in before registration, and the third -will be filled in by the registration function; any other fields should just be -ignored and are for internal use only. - -The fields are: - - (1) The name of the netfs (used as the key in the toplevel index). - - (2) The version of the netfs (if the name matches but the version doesn't, the - entire in-cache hierarchy for this netfs will be scrapped and begun - afresh). - - (3) The cookie representing the primary index will be allocated according to - another parameter passed into the registration function. - -For example, kAFS (linux/fs/afs/) uses the following definitions to describe -itself:: - - struct fscache_netfs afs_cache_netfs = { - .version = 0, - .name = "afs", - }; - - -Index Definition -================ - -Indices are used for two purposes: - - (1) To aid the finding of a file based on a series of keys (such as AFS's - "cell", "volume ID", "vnode ID"). - - (2) To make it easier to discard a subset of all the files cached based around - a particular key - for instance to mirror the removal of an AFS volume. - -However, since it's unlikely that any two netfs's are going to want to define -their index hierarchies in quite the same way, FS-Cache tries to impose as few -restraints as possible on how an index is structured and where it is placed in -the tree. The netfs can even mix indices and data files at the same level, but -it's not recommended. - -Each index entry consists of a key of indeterminate length plus some auxiliary -data, also of indeterminate length. - -There are some limits on indices: - - (1) Any index containing non-index objects should be restricted to a single - cache. Any such objects created within an index will be created in the - first cache only. The cache in which an index is created can be - controlled by cache tags (see below). - - (2) The entry data must be atomically journallable, so it is limited to about - 400 bytes at present. At least 400 bytes will be available. - - (3) The depth of the index tree should be judged with care as the search - function is recursive. Too many layers will run the kernel out of stack. - - -Object Definition -================= - -To define an object, a structure of the following type should be filled out:: - - struct fscache_cookie_def - { - uint8_t name[16]; - uint8_t type; - - struct fscache_cache_tag *(*select_cache)( - const void *parent_netfs_data, - const void *cookie_netfs_data); - - enum fscache_checkaux (*check_aux)(void *cookie_netfs_data, - const void *data, - uint16_t datalen, - loff_t object_size); - - void (*get_context)(void *cookie_netfs_data, void *context); - - void (*put_context)(void *cookie_netfs_data, void *context); - - void (*mark_pages_cached)(void *cookie_netfs_data, - struct address_space *mapping, - struct pagevec *cached_pvec); - }; - -This has the following fields: - - (1) The type of the object [mandatory]. - - This is one of the following values: - - FSCACHE_COOKIE_TYPE_INDEX - This defines an index, which is a special FS-Cache type. - - FSCACHE_COOKIE_TYPE_DATAFILE - This defines an ordinary data file. - - Any other value between 2 and 255 - This defines an extraordinary object such as an XATTR. - - (2) The name of the object type (NUL terminated unless all 16 chars are used) - [optional]. - - (3) A function to select the cache in which to store an index [optional]. - - This function is invoked when an index needs to be instantiated in a cache - during the instantiation of a non-index object. Only the immediate index - parent for the non-index object will be queried. Any indices above that - in the hierarchy may be stored in multiple caches. This function does not - need to be supplied for any non-index object or any index that will only - have index children. - - If this function is not supplied or if it returns NULL then the first - cache in the parent's list will be chosen, or failing that, the first - cache in the master list. - - (4) A function to check the auxiliary data [optional]. - - This function will be called to check that a match found in the cache for - this object is valid. For instance with AFS it could check the auxiliary - data against the data version number returned by the server to determine - whether the index entry in a cache is still valid. - - If this function is absent, it will be assumed that matching objects in a - cache are always valid. - - The function is also passed the cache's idea of the object size and may - use this to manage coherency also. - - If present, the function should return one of the following values: - - FSCACHE_CHECKAUX_OKAY - - the entry is okay as is - - FSCACHE_CHECKAUX_NEEDS_UPDATE - - the entry requires update - - FSCACHE_CHECKAUX_OBSOLETE - - the entry should be deleted + (5) I/O is done asynchronously where possible. - This function can also be used to extract data from the auxiliary data in - the cache and copy it into the netfs's structures. +This API is used by:: - (5) A pair of functions to manage contexts for the completion callback - [optional]. + #include <linux/fscache.h>. - The cache read/write functions are passed a context which is then passed - to the I/O completion callback function. To ensure this context remains - valid until after the I/O completion is called, two functions may be - provided: one to get an extra reference on the context, and one to drop a - reference to it. - - If the context is not used or is a type of object that won't go out of - scope, then these functions are not required. These functions are not - required for indices as indices may not contain data. These functions may - be called in interrupt context and so may not sleep. - - (6) A function to mark a page as retaining cache metadata [optional]. - - This is called by the cache to indicate that it is retaining in-memory - information for this page and that the netfs should uncache the page when - it has finished. This does not indicate whether there's data on the disk - or not. Note that several pages at once may be presented for marking. - - The PG_fscache bit is set on the pages before this function would be - called, so the function need not be provided if this is sufficient. - - This function is not required for indices as they're not permitted data. - - (7) A function to unmark all the pages retaining cache metadata [mandatory]. - - This is called by FS-Cache to indicate that a backing store is being - unbound from a cookie and that all the marks on the pages should be - cleared to prevent confusion. Note that the cache will have torn down all - its tracking information so that the pages don't need to be explicitly - uncached. - - This function is not required for indices as they're not permitted data. - - -Network Filesystem (Un)registration -=================================== - -The first step is to declare the network filesystem to the cache. This also -involves specifying the layout of the primary index (for AFS, this would be the -"cell" level). - -The registration function is:: - - int fscache_register_netfs(struct fscache_netfs *netfs); - -It just takes a pointer to the netfs definition. It returns 0 or an error as -appropriate. - -For kAFS, registration is done as follows:: - - ret = fscache_register_netfs(&afs_cache_netfs); - -The last step is, of course, unregistration:: - - void fscache_unregister_netfs(struct fscache_netfs *netfs); - - -Cache Tag Lookup -================ - -FS-Cache permits the use of more than one cache. To permit particular index -subtrees to be bound to particular caches, the second step is to look up cache -representation tags. This step is optional; it can be left entirely up to -FS-Cache as to which cache should be used. The problem with doing that is that -FS-Cache will always pick the first cache that was registered. - -To get the representation for a named tag:: - - struct fscache_cache_tag *fscache_lookup_cache_tag(const char *name); - -This takes a text string as the name and returns a representation of a tag. It -will never return an error. It may return a dummy tag, however, if it runs out -of memory; this will inhibit caching with this tag. - -Any representation so obtained must be released by passing it to this function:: - - void fscache_release_cache_tag(struct fscache_cache_tag *tag); +.. This document contains the following sections: -The tag will be retrieved by FS-Cache when it calls the object definition -operation select_cache(). + (1) Overview + (2) Volume registration + (3) Data file registration + (4) Declaring a cookie to be in use + (5) Resizing a data file (truncation) + (6) Data I/O API + (7) Data file coherency + (8) Data file invalidation + (9) Write back resource management + (10) Caching of local modifications + (11) Page release and invalidation + + +Overview +======== + +The fscache hierarchy is organised on two levels from a network filesystem's +point of view. The upper level represents "volumes" and the lower level +represents "data storage objects". These are represented by two types of +cookie, hereafter referred to as "volume cookies" and "cookies". + +A network filesystem acquires a volume cookie for a volume using a volume key, +which represents all the information that defines that volume (e.g. cell name +or server address, volume ID or share name). This must be rendered as a +printable string that can be used as a directory name (ie. no '/' characters +and shouldn't begin with a '.'). The maximum name length is one less than the +maximum size of a filename component (allowing the cache backend one char for +its own purposes). + +A filesystem would typically have a volume cookie for each superblock. + +The filesystem then acquires a cookie for each file within that volume using an +object key. Object keys are binary blobs and only need to be unique within +their parent volume. The cache backend is reponsible for rendering the binary +blob into something it can use and may employ hash tables, trees or whatever to +improve its ability to find an object. This is transparent to the network +filesystem. + +A filesystem would typically have a cookie for each inode, and would acquire it +in iget and relinquish it when evicting the cookie. + +Once it has a cookie, the filesystem needs to mark the cookie as being in use. +This causes fscache to send the cache backend off to look up/create resources +for the cookie in the background, to check its coherency and, if necessary, to +mark the object as being under modification. + +A filesystem would typically "use" the cookie in its file open routine and +unuse it in file release and it needs to use the cookie around calls to +truncate the cookie locally. It *also* needs to use the cookie when the +pagecache becomes dirty and unuse it when writeback is complete. This is +slightly tricky, and provision is made for it. + +When performing a read, write or resize on a cookie, the filesystem must first +begin an operation. This copies the resources into a holding struct and puts +extra pins into the cache to stop cache withdrawal from tearing down the +structures being used. The actual operation can then be issued and conflicting +invalidations can be detected upon completion. + +The filesystem is expected to use netfslib to access the cache, but that's not +actually required and it can use the fscache I/O API directly. + + +Volume Registration +=================== + +The first step for a network filsystem is to acquire a volume cookie for the +volume it wants to access:: + + struct fscache_volume * + fscache_acquire_volume(const char *volume_key, + const char *cache_name, + const void *coherency_data, + size_t coherency_len); + +This function creates a volume cookie with the specified volume key as its name +and notes the coherency data. + +The volume key must be a printable string with no '/' characters in it. It +should begin with the name of the filesystem and should be no longer than 254 +characters. It should uniquely represent the volume and will be matched with +what's stored in the cache. + +The caller may also specify the name of the cache to use. If specified, +fscache will look up or create a cache cookie of that name and will use a cache +of that name if it is online or comes online. If no cache name is specified, +it will use the first cache that comes to hand and set the name to that. + +The specified coherency data is stored in the cookie and will be matched +against coherency data stored on disk. The data pointer may be NULL if no data +is provided. If the coherency data doesn't match, the entire cache volume will +be invalidated. + +This function can return errors such as EBUSY if the volume key is already in +use by an acquired volume or ENOMEM if an allocation failure occured. It may +also return a NULL volume cookie if fscache is not enabled. It is safe to +pass a NULL cookie to any function that takes a volume cookie. This will +cause that function to do nothing. + + +When the network filesystem has finished with a volume, it should relinquish it +by calling:: + + void fscache_relinquish_volume(struct fscache_volume *volume, + const void *coherency_data, + bool invalidate); + +This will cause the volume to be committed or removed, and if sealed the +coherency data will be set to the value supplied. The amount of coherency data +must match the length specified when the volume was acquired. Note that all +data cookies obtained in this volume must be relinquished before the volume is +relinquished. -Index Registration -================== +Data File Registration +====================== -The third step is to inform FS-Cache about part of an index hierarchy that can -be used to locate files. This is done by requesting a cookie for each index in -the path to the file:: +Once it has a volume cookie, a network filesystem can use it to acquire a +cookie for data storage:: struct fscache_cookie * - fscache_acquire_cookie(struct fscache_cookie *parent, - const struct fscache_object_def *def, + fscache_acquire_cookie(struct fscache_volume *volume, + u8 advice, const void *index_key, size_t index_key_len, const void *aux_data, size_t aux_data_len, - void *netfs_data, - loff_t object_size, - bool enable); + loff_t object_size) -This function creates an index entry in the index represented by parent, -filling in the index entry by calling the operations pointed to by def. +This creates the cookie in the volume using the specified index key. The index +key is a binary blob of the given length and must be unique for the volume. +This is saved into the cookie. There are no restrictions on the content, but +its length shouldn't exceed about three quarters of the maximum filename length +to allow for encoding. -A unique key that represents the object within the parent must be pointed to by -index_key and is of length index_key_len. +The caller should also pass in a piece of coherency data in aux_data. A buffer +of size aux_data_len will be allocated and the coherency data copied in. It is +assumed that the size is invariant over time. The coherency data is used to +check the validity of data in the cache. Functions are provided by which the +coherency data can be updated. -An optional blob of auxiliary data that is to be stored within the cache can be -pointed to with aux_data and should be of length aux_data_len. This would -typically be used for storing coherency data. +The file size of the object being cached should also be provided. This may be +used to trim the data and will be stored with the coherency data. -The netfs may pass an arbitrary value in netfs_data and this will be presented -to it in the event of any calling back. This may also be used in tracing or -logging of messages. +This function never returns an error, though it may return a NULL cookie on +allocation failure or if fscache is not enabled. It is safe to pass in a NULL +volume cookie and pass the NULL cookie returned to any function that takes it. +This will cause that function to do nothing. -The cache tracks the size of the data attached to an object and this set to be -object_size. For indices, this should be 0. This value will be passed to the -->check_aux() callback. -Note that this function never returns an error - all errors are handled -internally. It may, however, return NULL to indicate no cookie. It is quite -acceptable to pass this token back to this function as the parent to another -acquisition (or even to the relinquish cookie, read page and write page -functions - see below). +When the network filesystem has finished with a cookie, it should relinquish it +by calling:: -Note also that no indices are actually created in a cache until a non-index -object needs to be created somewhere down the hierarchy. Furthermore, an index -may be created in several different caches independently at different times. -This is all handled transparently, and the netfs doesn't see any of it. + void fscache_relinquish_cookie(struct fscache_cookie *cookie, + bool retire); -A cookie will be created in the disabled state if enabled is false. A cookie -must be enabled to do anything with it. A disabled cookie can be enabled by -calling fscache_enable_cookie() (see below). +This will cause fscache to either commit the storage backing the cookie or +delete it. -For example, with AFS, a cell would be added to the primary index. This index -entry would have a dependent inode containing volume mappings within this cell:: - cell->cache = - fscache_acquire_cookie(afs_cache_netfs.primary_index, - &afs_cell_cache_index_def, - cell->name, strlen(cell->name), - NULL, 0, - cell, 0, true); +Marking A Cookie In-Use +======================= -And then a particular volume could be added to that index by ID, creating -another index for vnodes (AFS inode equivalents):: +Once a cookie has been acquired by a network filesystem, the filesystem should +tell fscache when it intends to use the cookie (typically done on file open) +and should say when it has finished with it (typically on file close):: - volume->cache = - fscache_acquire_cookie(volume->cell->cache, - &afs_volume_cache_index_def, - &volume->vid, sizeof(volume->vid), - NULL, 0, - volume, 0, true); + void fscache_use_cookie(struct fscache_cookie *cookie, + bool will_modify); + void fscache_unuse_cookie(struct fscache_cookie *cookie, + const void *aux_data, + const loff_t *object_size); +The *use* function tells fscache that it will use the cookie and, additionally, +indicate if the user is intending to modify the contents locally. If not yet +done, this will trigger the cache backend to go and gather the resources it +needs to access/store data in the cache. This is done in the background, and +so may not be complete by the time the function returns. -Data File Registration -====================== +The *unuse* function indicates that a filesystem has finished using a cookie. +It optionally updates the stored coherency data and object size and then +decreases the in-use counter. When the last user unuses the cookie, it is +scheduled for garbage collection. If not reused within a short time, the +resources will be released to reduce system resource consumption. -The fourth step is to request a data file be created in the cache. This is -identical to index cookie acquisition. The only difference is that the type in -the object definition should be something other than index type:: +A cookie must be marked in-use before it can be accessed for read, write or +resize - and an in-use mark must be kept whilst there is dirty data in the +pagecache in order to avoid an oops due to trying to open a file during process +exit. - vnode->cache = - fscache_acquire_cookie(volume->cache, - &afs_vnode_cache_object_def, - &key, sizeof(key), - &aux, sizeof(aux), - vnode, vnode->status.size, true); +Note that in-use marks are cumulative. For each time a cookie is marked +in-use, it must be unused. -Miscellaneous Object Registration +Resizing A Data File (Truncation) ================================= -An optional step is to request an object of miscellaneous type be created in -the cache. This is almost identical to index cookie acquisition. The only -difference is that the type in the object definition should be something other -than index type. While the parent object could be an index, it's more likely -it would be some other type of object such as a data file:: - - xattr->cache = - fscache_acquire_cookie(vnode->cache, - &afs_xattr_cache_object_def, - &xattr->name, strlen(xattr->name), - NULL, 0, - xattr, strlen(xattr->val), true); - -Miscellaneous objects might be used to store extended attributes or directory -entries for example. - - -Setting the Data File Size -========================== +If a network filesystem file is resized locally by truncation, the following +should be called to notify the cache:: -The fifth step is to set the physical attributes of the file, such as its size. -This doesn't automatically reserve any space in the cache, but permits the -cache to adjust its metadata for data tracking appropriately:: + void fscache_resize_cookie(struct fscache_cookie *cookie, + loff_t new_size); - int fscache_attr_changed(struct fscache_cookie *cookie); +The caller must have first marked the cookie in-use. The cookie and the new +size are passed in and the cache is synchronously resized. This is expected to +be called from ``->setattr()`` inode operation under the inode lock. -The cache will return -ENOBUFS if there is no backing cache or if there is no -space to allocate any extra metadata required in the cache. -Note that attempts to read or write data pages in the cache over this size may -be rebuffed with -ENOBUFS. +Data I/O API +============ -This operation schedules an attribute adjustment to happen asynchronously at -some point in the future, and as such, it may happen after the function returns -to the caller. The attribute adjustment excludes read and write operations. +To do data I/O operations directly through a cookie, the following functions +are available:: + int fscache_begin_read_operation(struct netfs_cache_resources *cres, + struct fscache_cookie *cookie); + int fscache_read(struct netfs_cache_resources *cres, + loff_t start_pos, + struct iov_iter *iter, + enum netfs_read_from_hole read_hole, + netfs_io_terminated_t term_func, + void *term_func_priv); + int fscache_write(struct netfs_cache_resources *cres, + loff_t start_pos, + struct iov_iter *iter, + netfs_io_terminated_t term_func, + void *term_func_priv); -Page alloc/read/write -===================== +The *begin* function sets up an operation, attaching the resources required to +the cache resources block from the cookie. Assuming it doesn't return an error +(for instance, it will return -ENOBUFS if given a NULL cookie, but otherwise do +nothing), then one of the other two functions can be issued. -And the sixth step is to store and retrieve pages in the cache. There are -three functions that are used to do this. +The *read* and *write* functions initiate a direct-IO operation. Both take the +previously set up cache resources block, an indication of the start file +position, and an I/O iterator that describes buffer and indicates the amount of +data. -Note: +The read function also takes a parameter to indicate how it should handle a +partially populated region (a hole) in the disk content. This may be to ignore +it, skip over an initial hole and place zeros in the buffer or give an error. - (1) A page should not be re-read or re-allocated without uncaching it first. - - (2) A read or allocated page must be uncached when the netfs page is released - from the pagecache. - - (3) A page should only be written to the cache if previous read or allocated. - -This permits the cache to maintain its page tracking in proper order. - - -PAGE READ ---------- - -Firstly, the netfs should ask FS-Cache to examine the caches and read the -contents cached for a particular page of a particular file if present, or else -allocate space to store the contents if not:: +The read and write functions can be given an optional termination function that +will be run on completion:: typedef - void (*fscache_rw_complete_t)(struct page *page, - void *context, - int error); - - int fscache_read_or_alloc_page(struct fscache_cookie *cookie, - struct page *page, - fscache_rw_complete_t end_io_func, - void *context, - gfp_t gfp); - -The cookie argument must specify a cookie for an object that isn't an index, -the page specified will have the data loaded into it (and is also used to -specify the page number), and the gfp argument is used to control how any -memory allocations made are satisfied. - -If the cookie indicates the inode is not cached: - - (1) The function will return -ENOBUFS. - -Else if there's a copy of the page resident in the cache: - - (1) The mark_pages_cached() cookie operation will be called on that page. + void (*netfs_io_terminated_t)(void *priv, ssize_t transferred_or_error, + bool was_async); - (2) The function will submit a request to read the data from the cache's - backing device directly into the page specified. +If a termination function is given, the operation will be run asynchronously +and the termination function will be called upon completion. If not given, the +operation will be run synchronously. Note that in the asynchronous case, it is +possible for the operation to complete before the function returns. - (3) The function will return 0. +Both the read and write functions end the operation when they complete, +detaching any pinned resources. - (4) When the read is complete, end_io_func() will be invoked with: +The read operation will fail with ESTALE if invalidation occurred whilst the +operation was ongoing. - * The netfs data supplied when the cookie was created. - * The page descriptor. +Data File Coherency +=================== - * The context argument passed to the above function. This will be - maintained with the get_context/put_context functions mentioned above. - - * An argument that's 0 on success or negative for an error code. - - If an error occurs, it should be assumed that the page contains no usable - data. fscache_readpages_cancel() may need to be called. - - end_io_func() will be called in process context if the read is results in - an error, but it might be called in interrupt context if the read is - successful. - -Otherwise, if there's not a copy available in cache, but the cache may be able -to store the page: - - (1) The mark_pages_cached() cookie operation will be called on that page. - - (2) A block may be reserved in the cache and attached to the object at the - appropriate place. - - (3) The function will return -ENODATA. - -This function may also return -ENOMEM or -EINTR, in which case it won't have -read any data from the cache. - - -Page Allocate -------------- - -Alternatively, if there's not expected to be any data in the cache for a page -because the file has been extended, a block can simply be allocated instead:: - - int fscache_alloc_page(struct fscache_cookie *cookie, - struct page *page, - gfp_t gfp); - -This is similar to the fscache_read_or_alloc_page() function, except that it -never reads from the cache. It will return 0 if a block has been allocated, -rather than -ENODATA as the other would. One or the other must be performed -before writing to the cache. - -The mark_pages_cached() cookie operation will be called on the page if -successful. - - -Page Write ----------- - -Secondly, if the netfs changes the contents of the page (either due to an -initial download or if a user performs a write), then the page should be -written back to the cache:: - - int fscache_write_page(struct fscache_cookie *cookie, - struct page *page, - loff_t object_size, - gfp_t gfp); - -The cookie argument must specify a data file cookie, the page specified should -contain the data to be written (and is also used to specify the page number), -object_size is the revised size of the object and the gfp argument is used to -control how any memory allocations made are satisfied. - -The page must have first been read or allocated successfully and must not have -been uncached before writing is performed. - -If the cookie indicates the inode is not cached then: - - (1) The function will return -ENOBUFS. - -Else if space can be allocated in the cache to hold this page: - - (1) PG_fscache_write will be set on the page. - - (2) The function will submit a request to write the data to cache's backing - device directly from the page specified. - - (3) The function will return 0. - - (4) When the write is complete PG_fscache_write is cleared on the page and - anyone waiting for that bit will be woken up. - -Else if there's no space available in the cache, -ENOBUFS will be returned. It -is also possible for the PG_fscache_write bit to be cleared when no write took -place if unforeseen circumstances arose (such as a disk error). - -Writing takes place asynchronously. - - -Multiple Page Read ------------------- - -A facility is provided to read several pages at once, as requested by the -readpages() address space operation:: - - int fscache_read_or_alloc_pages(struct fscache_cookie *cookie, - struct address_space *mapping, - struct list_head *pages, - int *nr_pages, - fscache_rw_complete_t end_io_func, - void *context, - gfp_t gfp); - -This works in a similar way to fscache_read_or_alloc_page(), except: - - (1) Any page it can retrieve data for is removed from pages and nr_pages and - dispatched for reading to the disk. Reads of adjacent pages on disk may - be merged for greater efficiency. - - (2) The mark_pages_cached() cookie operation will be called on several pages - at once if they're being read or allocated. - - (3) If there was an general error, then that error will be returned. - - Else if some pages couldn't be allocated or read, then -ENOBUFS will be - returned. - - Else if some pages couldn't be read but were allocated, then -ENODATA will - be returned. - - Otherwise, if all pages had reads dispatched, then 0 will be returned, the - list will be empty and ``*nr_pages`` will be 0. - - (4) end_io_func will be called once for each page being read as the reads - complete. It will be called in process context if error != 0, but it may - be called in interrupt context if there is no error. - -Note that a return of -ENODATA, -ENOBUFS or any other error does not preclude -some of the pages being read and some being allocated. Those pages will have -been marked appropriately and will need uncaching. - - -Cancellation of Unread Pages ----------------------------- - -If one or more pages are passed to fscache_read_or_alloc_pages() but not then -read from the cache and also not read from the underlying filesystem then -those pages will need to have any marks and reservations removed. This can be -done by calling:: - - void fscache_readpages_cancel(struct fscache_cookie *cookie, - struct list_head *pages); - -prior to returning to the caller. The cookie argument should be as passed to -fscache_read_or_alloc_pages(). Every page in the pages list will be examined -and any that have PG_fscache set will be uncached. - - -Page Uncaching -============== - -To uncache a page, this function should be called:: - - void fscache_uncache_page(struct fscache_cookie *cookie, - struct page *page); - -This function permits the cache to release any in-memory representation it -might be holding for this netfs page. This function must be called once for -each page on which the read or write page functions above have been called to -make sure the cache's in-memory tracking information gets torn down. - -Note that pages can't be explicitly deleted from the a data file. The whole -data file must be retired (see the relinquish cookie function below). - -Furthermore, note that this does not cancel the asynchronous read or write -operation started by the read/alloc and write functions, so the page -invalidation functions must use:: - - bool fscache_check_page_write(struct fscache_cookie *cookie, - struct page *page); - -to see if a page is being written to the cache, and:: - - void fscache_wait_on_page_write(struct fscache_cookie *cookie, - struct page *page); - -to wait for it to finish if it is. - - -When releasepage() is being implemented, a special FS-Cache function exists to -manage the heuristics of coping with vmscan trying to eject pages, which may -conflict with the cache trying to write pages to the cache (which may itself -need to allocate memory):: - - bool fscache_maybe_release_page(struct fscache_cookie *cookie, - struct page *page, - gfp_t gfp); - -This takes the netfs cookie, and the page and gfp arguments as supplied to -releasepage(). It will return false if the page cannot be released yet for -some reason and if it returns true, the page has been uncached and can now be -released. - -To make a page available for release, this function may wait for an outstanding -storage request to complete, or it may attempt to cancel the storage request - -in which case the page will not be stored in the cache this time. - - -Bulk Image Page Uncache ------------------------ - -A convenience routine is provided to perform an uncache on all the pages -attached to an inode. This assumes that the pages on the inode correspond on a -1:1 basis with the pages in the cache:: - - void fscache_uncache_all_inode_pages(struct fscache_cookie *cookie, - struct inode *inode); - -This takes the netfs cookie that the pages were cached with and the inode that -the pages are attached to. This function will wait for pages to finish being -written to the cache and for the cache to finish with the page generally. No -error is returned. - - -Index and Data File consistency -=============================== - -To find out whether auxiliary data for an object is up to data within the -cache, the following function can be called:: - - int fscache_check_consistency(struct fscache_cookie *cookie, - const void *aux_data); - -This will call back to the netfs to check whether the auxiliary data associated -with a cookie is correct; if aux_data is non-NULL, it will update the auxiliary -data buffer first. It returns 0 if it is and -ESTALE if it isn't; it may also -return -ENOMEM and -ERESTARTSYS. - -To request an update of the index data for an index or other object, the -following function should be called:: +To request an update of the coherency data and file size on a cookie, the +following should be called:: void fscache_update_cookie(struct fscache_cookie *cookie, - const void *aux_data); - -This function will update the cookie's auxiliary data buffer from aux_data if -that is non-NULL and then schedule this to be stored on disk. The update -method in the parent index definition will be called to transfer the data. - -Note that partial updates may happen automatically at other times, such as when -data blocks are added to a data file object. - - -Cookie Enablement -================= - -Cookies exist in one of two states: enabled and disabled. If a cookie is -disabled, it ignores all attempts to acquire child cookies; check, update or -invalidate its state; allocate, read or write backing pages - though it is -still possible to uncache pages and relinquish the cookie. - -The initial enablement state is set by fscache_acquire_cookie(), but the cookie -can be enabled or disabled later. To disable a cookie, call:: - - void fscache_disable_cookie(struct fscache_cookie *cookie, - const void *aux_data, - bool invalidate); - -If the cookie is not already disabled, this locks the cookie against other -enable and disable ops, marks the cookie as being disabled, discards or -invalidates any backing objects and waits for cessation of activity on any -associated object before unlocking the cookie. - -All possible failures are handled internally. The caller should consider -calling fscache_uncache_all_inode_pages() afterwards to make sure all page -markings are cleared up. - -Cookies can be enabled or reenabled with:: - - void fscache_enable_cookie(struct fscache_cookie *cookie, const void *aux_data, - loff_t object_size, - bool (*can_enable)(void *data), - void *data) - -If the cookie is not already enabled, this locks the cookie against other -enable and disable ops, invokes can_enable() and, if the cookie is not an index -cookie, will begin the procedure of acquiring backing objects. - -The optional can_enable() function is passed the data argument and returns a -ruling as to whether or not enablement should actually be permitted to begin. + const loff_t *object_size); -All possible failures are handled internally. The cookie will only be marked -as enabled if provisional backing objects are allocated. +This will update the cookie's coherency data and/or file size. -The object's data size is updated from object_size and is passed to the -->check_aux() function. -In both cases, the cookie's auxiliary data buffer is updated from aux_data if -that is non-NULL inside the enablement lock before proceeding. - - -Miscellaneous Cookie operations -=============================== +Data File Invalidation +====================== -There are a number of operations that can be used to control cookies: +Sometimes it will be necessary to invalidate an object that contains data. +Typically this will be necessary when the server informs the network filesystem +of a remote third-party change - at which point the filesystem has to throw +away the state and cached data that it had for an file and reload from the +server. - * Cookie pinning:: +To indicate that a cache object should be invalidated, the following should be +called:: - int fscache_pin_cookie(struct fscache_cookie *cookie); - void fscache_unpin_cookie(struct fscache_cookie *cookie); + void fscache_invalidate(struct fscache_cookie *cookie, + const void *aux_data, + loff_t size, + unsigned int flags); - These operations permit data cookies to be pinned into the cache and to - have the pinning removed. They are not permitted on index cookies. +This increases the invalidation counter in the cookie to cause outstanding +reads to fail with -ESTALE, sets the coherency data and file size from the +information supplied, blocks new I/O on the cookie and dispatches the cache to +go and get rid of the old data. - The pinning function will return 0 if successful, -ENOBUFS in the cookie - isn't backed by a cache, -EOPNOTSUPP if the cache doesn't support pinning, - -ENOSPC if there isn't enough space to honour the operation, -ENOMEM or - -EIO if there's any other problem. +Invalidation runs asynchronously in a worker thread so that it doesn't block +too much. - * Data space reservation:: - int fscache_reserve_space(struct fscache_cookie *cookie, loff_t size); +Write-Back Resource Management +============================== - This permits a netfs to request cache space be reserved to store up to the - given amount of a file. It is permitted to ask for more than the current - size of the file to allow for future file expansion. +To write data to the cache from network filesystem writeback, the cache +resources required need to be pinned at the point the modification is made (for +instance when the page is marked dirty) as it's not possible to open a file in +a thread that's exiting. - If size is given as zero then the reservation will be cancelled. +The following facilities are provided to manage this: - The function will return 0 if successful, -ENOBUFS in the cookie isn't - backed by a cache, -EOPNOTSUPP if the cache doesn't support reservations, - -ENOSPC if there isn't enough space to honour the operation, -ENOMEM or - -EIO if there's any other problem. + * An inode flag, ``I_PINNING_FSCACHE_WB``, is provided to indicate that an + in-use is held on the cookie for this inode. It can only be changed if the + the inode lock is held. - Note that this doesn't pin an object in a cache; it can still be culled to - make space if it's not in use. + * A flag, ``unpinned_fscache_wb`` is placed in the ``writeback_control`` + struct that gets set if ``__writeback_single_inode()`` clears + ``I_PINNING_FSCACHE_WB`` because all the dirty pages were cleared. +To support this, the following functions are provided:: -Cookie Unregistration -===================== + bool fscache_dirty_folio(struct address_space *mapping, + struct folio *folio, + struct fscache_cookie *cookie); + void fscache_unpin_writeback(struct writeback_control *wbc, + struct fscache_cookie *cookie); + void fscache_clear_inode_writeback(struct fscache_cookie *cookie, + struct inode *inode, + const void *aux); -To get rid of a cookie, this function should be called:: +The *set* function is intended to be called from the filesystem's +``dirty_folio`` address space operation. If ``I_PINNING_FSCACHE_WB`` is not +set, it sets that flag and increments the use count on the cookie (the caller +must already have called ``fscache_use_cookie()``). - void fscache_relinquish_cookie(struct fscache_cookie *cookie, - const void *aux_data, - bool retire); +The *unpin* function is intended to be called from the filesystem's +``write_inode`` superblock operation. It cleans up after writing by unusing +the cookie if unpinned_fscache_wb is set in the writeback_control struct. -If retire is non-zero, then the object will be marked for recycling, and all -copies of it will be removed from all active caches in which it is present. -Not only that but all child objects will also be retired. +The *clear* function is intended to be called from the netfs's ``evict_inode`` +superblock operation. It must be called *after* +``truncate_inode_pages_final()``, but *before* ``clear_inode()``. This cleans +up any hanging ``I_PINNING_FSCACHE_WB``. It also allows the coherency data to +be updated. -If retire is zero, then the object may be available again when next the -acquisition function is called. Retirement here will overrule the pinning on a -cookie. -The cookie's auxiliary data will be updated from aux_data if that is non-NULL -so that the cache can lazily update it on disk. +Caching of Local Modifications +============================== -One very important note - relinquish must NOT be called for a cookie unless all -the cookies for "child" indices, objects and pages have been relinquished -first. +If a network filesystem has locally modified data that it wants to write to the +cache, it needs to mark the pages to indicate that a write is in progress, and +if the mark is already present, it needs to wait for it to be removed first +(presumably due to an already in-progress operation). This prevents multiple +competing DIO writes to the same storage in the cache. +Firstly, the netfs should determine if caching is available by doing something +like:: -Index Invalidation -================== + bool caching = fscache_cookie_enabled(cookie); -There is no direct way to invalidate an index subtree. To do this, the caller -should relinquish and retire the cookie they have, and then acquire a new one. +If caching is to be attempted, pages should be waited for and then marked using +the following functions provided by the netfs helper library:: + void set_page_fscache(struct page *page); + void wait_on_page_fscache(struct page *page); + int wait_on_page_fscache_killable(struct page *page); -Data File Invalidation -====================== +Once all the pages in the span are marked, the netfs can ask fscache to +schedule a write of that region:: -Sometimes it will be necessary to invalidate an object that contains data. -Typically this will be necessary when the server tells the netfs of a foreign -change - at which point the netfs has to throw away all the state it had for an -inode and reload from the server. + void fscache_write_to_cache(struct fscache_cookie *cookie, + struct address_space *mapping, + loff_t start, size_t len, loff_t i_size, + netfs_io_terminated_t term_func, + void *term_func_priv, + bool caching) -To indicate that a cache object should be invalidated, the following function -can be called:: +And if an error occurs before that point is reached, the marks can be removed +by calling:: - void fscache_invalidate(struct fscache_cookie *cookie); + void fscache_clear_page_bits(struct address_space *mapping, + loff_t start, size_t len, + bool caching) -This can be called with spinlocks held as it defers the work to a thread pool. -All extant storage, retrieval and attribute change ops at this point are -cancelled and discarded. Some future operations will be rejected until the -cache has had a chance to insert a barrier in the operations queue. After -that, operations will be queued again behind the invalidation operation. +In these functions, a pointer to the mapping to which the source pages are +attached is passed in and start and len indicate the size of the region that's +going to be written (it doesn't have to align to page boundaries necessarily, +but it does have to align to DIO boundaries on the backing filesystem). The +caching parameter indicates if caching should be skipped, and if false, the +functions do nothing. -The invalidation operation will perform an attribute change operation and an -auxiliary data update operation as it is very likely these will have changed. +The write function takes some additional parameters: the cookie representing +the cache object to be written to, i_size indicates the size of the netfs file +and term_func indicates an optional completion function, to which +term_func_priv will be passed, along with the error or amount written. -Using the following function, the netfs can wait for the invalidation operation -to have reached a point at which it can start submitting ordinary operations -once again:: +Note that the write function will always run asynchronously and will unmark all +the pages upon completion before calling term_func. - void fscache_wait_on_invalidate(struct fscache_cookie *cookie); +Page Release and Invalidation +============================= -FS-cache Specific Page Flag -=========================== +Fscache keeps track of whether we have any data in the cache yet for a cache +object we've just created. It knows it doesn't have to do any reading until it +has done a write and then the page it wrote from has been released by the VM, +after which it *has* to look in the cache. -FS-Cache makes use of a page flag, PG_private_2, for its own purpose. This is -given the alternative name PG_fscache. +To inform fscache that a page might now be in the cache, the following function +should be called from the ``release_folio`` address space op:: -PG_fscache is used to indicate that the page is known by the cache, and that -the cache must be informed if the page is going to go away. It's an indication -to the netfs that the cache has an interest in this page, where an interest may -be a pointer to it, resources allocated or reserved for it, or I/O in progress -upon it. + void fscache_note_page_release(struct fscache_cookie *cookie); -The netfs can use this information in methods such as releasepage() to -determine whether it needs to uncache a page or update it. +if the page has been released (ie. release_folio returned true). -Furthermore, if this bit is set, releasepage() and invalidatepage() operations -will be called on a page to get rid of it, even if PG_private is not set. This -allows caching to attempted on a page before read_cache_pages() to be called -after fscache_read_or_alloc_pages() as the former will try and release pages it -was given under certain circumstances. +Page release and page invalidation should also wait for any mark left on the +page to say that a DIO write is underway from that page:: -This bit does not overlap with such as PG_private. This means that FS-Cache -can be used with a filesystem that uses the block buffering code. + void wait_on_page_fscache(struct page *page); + int wait_on_page_fscache_killable(struct page *page); -There are a number of operations defined on this flag:: - int PageFsCache(struct page *page); - void SetPageFsCache(struct page *page) - void ClearPageFsCache(struct page *page) - int TestSetPageFsCache(struct page *page) - int TestClearPageFsCache(struct page *page) +API Function Reference +====================== -These functions are bit test, bit set, bit clear, bit test and set and bit -test and clear operations on PG_fscache. +.. kernel-doc:: include/linux/fscache.h diff --git a/Documentation/filesystems/caching/object.rst b/Documentation/filesystems/caching/object.rst deleted file mode 100644 index ce0e043ccd33..000000000000 --- a/Documentation/filesystems/caching/object.rst +++ /dev/null @@ -1,313 +0,0 @@ -.. SPDX-License-Identifier: GPL-2.0 - -==================================================== -In-Kernel Cache Object Representation and Management -==================================================== - -By: David Howells <dhowells@redhat.com> - -.. Contents: - - (*) Representation - - (*) Object management state machine. - - - Provision of cpu time. - - Locking simplification. - - (*) The set of states. - - (*) The set of events. - - -Representation -============== - -FS-Cache maintains an in-kernel representation of each object that a netfs is -currently interested in. Such objects are represented by the fscache_cookie -struct and are referred to as cookies. - -FS-Cache also maintains a separate in-kernel representation of the objects that -a cache backend is currently actively caching. Such objects are represented by -the fscache_object struct. The cache backends allocate these upon request, and -are expected to embed them in their own representations. These are referred to -as objects. - -There is a 1:N relationship between cookies and objects. A cookie may be -represented by multiple objects - an index may exist in more than one cache - -or even by no objects (it may not be cached). - -Furthermore, both cookies and objects are hierarchical. The two hierarchies -correspond, but the cookies tree is a superset of the union of the object trees -of multiple caches:: - - NETFS INDEX TREE : CACHE 1 : CACHE 2 - : : - : +-----------+ : - +----------->| IObject | : - +-----------+ | : +-----------+ : - | ICookie |-------+ : | : - +-----------+ | : | : +-----------+ - | +------------------------------>| IObject | - | : | : +-----------+ - | : V : | - | : +-----------+ : | - V +----------->| IObject | : | - +-----------+ | : +-----------+ : | - | ICookie |-------+ : | : V - +-----------+ | : | : +-----------+ - | +------------------------------>| IObject | - +-----+-----+ : | : +-----------+ - | | : | : | - V | : V : | - +-----------+ | : +-----------+ : | - | ICookie |------------------------->| IObject | : | - +-----------+ | : +-----------+ : | - | V : | : V - | +-----------+ : | : +-----------+ - | | ICookie |-------------------------------->| IObject | - | +-----------+ : | : +-----------+ - V | : V : | - +-----------+ | : +-----------+ : | - | DCookie |------------------------->| DObject | : | - +-----------+ | : +-----------+ : | - | : : | - +-------+-------+ : : | - | | : : | - V V : : V - +-----------+ +-----------+ : : +-----------+ - | DCookie | | DCookie |------------------------>| DObject | - +-----------+ +-----------+ : : +-----------+ - : : - -In the above illustration, ICookie and IObject represent indices and DCookie -and DObject represent data storage objects. Indices may have representation in -multiple caches, but currently, non-index objects may not. Objects of any type -may also be entirely unrepresented. - -As far as the netfs API goes, the netfs is only actually permitted to see -pointers to the cookies. The cookies themselves and any objects attached to -those cookies are hidden from it. - - -Object Management State Machine -=============================== - -Within FS-Cache, each active object is managed by its own individual state -machine. The state for an object is kept in the fscache_object struct, in -object->state. A cookie may point to a set of objects that are in different -states. - -Each state has an action associated with it that is invoked when the machine -wakes up in that state. There are four logical sets of states: - - (1) Preparation: states that wait for the parent objects to become ready. The - representations are hierarchical, and it is expected that an object must - be created or accessed with respect to its parent object. - - (2) Initialisation: states that perform lookups in the cache and validate - what's found and that create on disk any missing metadata. - - (3) Normal running: states that allow netfs operations on objects to proceed - and that update the state of objects. - - (4) Termination: states that detach objects from their netfs cookies, that - delete objects from disk, that handle disk and system errors and that free - up in-memory resources. - - -In most cases, transitioning between states is in response to signalled events. -When a state has finished processing, it will usually set the mask of events in -which it is interested (object->event_mask) and relinquish the worker thread. -Then when an event is raised (by calling fscache_raise_event()), if the event -is not masked, the object will be queued for processing (by calling -fscache_enqueue_object()). - - -Provision of CPU Time ---------------------- - -The work to be done by the various states was given CPU time by the threads of -the slow work facility. This was used in preference to the workqueue facility -because: - - (1) Threads may be completely occupied for very long periods of time by a - particular work item. These state actions may be doing sequences of - synchronous, journalled disk accesses (lookup, mkdir, create, setxattr, - getxattr, truncate, unlink, rmdir, rename). - - (2) Threads may do little actual work, but may rather spend a lot of time - sleeping on I/O. This means that single-threaded and 1-per-CPU-threaded - workqueues don't necessarily have the right numbers of threads. - - -Locking Simplification ----------------------- - -Because only one worker thread may be operating on any particular object's -state machine at once, this simplifies the locking, particularly with respect -to disconnecting the netfs's representation of a cache object (fscache_cookie) -from the cache backend's representation (fscache_object) - which may be -requested from either end. - - -The Set of States -================= - -The object state machine has a set of states that it can be in. There are -preparation states in which the object sets itself up and waits for its parent -object to transit to a state that allows access to its children: - - (1) State FSCACHE_OBJECT_INIT. - - Initialise the object and wait for the parent object to become active. In - the cache, it is expected that it will not be possible to look an object - up from the parent object, until that parent object itself has been looked - up. - -There are initialisation states in which the object sets itself up and accesses -disk for the object metadata: - - (2) State FSCACHE_OBJECT_LOOKING_UP. - - Look up the object on disk, using the parent as a starting point. - FS-Cache expects the cache backend to probe the cache to see whether this - object is represented there, and if it is, to see if it's valid (coherency - management). - - The cache should call fscache_object_lookup_negative() to indicate lookup - failure for whatever reason, and should call fscache_obtained_object() to - indicate success. - - At the completion of lookup, FS-Cache will let the netfs go ahead with - read operations, no matter whether the file is yet cached. If not yet - cached, read operations will be immediately rejected with ENODATA until - the first known page is uncached - as to that point there can be no data - to be read out of the cache for that file that isn't currently also held - in the pagecache. - - (3) State FSCACHE_OBJECT_CREATING. - - Create an object on disk, using the parent as a starting point. This - happens if the lookup failed to find the object, or if the object's - coherency data indicated what's on disk is out of date. In this state, - FS-Cache expects the cache to create - - The cache should call fscache_obtained_object() if creation completes - successfully, fscache_object_lookup_negative() otherwise. - - At the completion of creation, FS-Cache will start processing write - operations the netfs has queued for an object. If creation failed, the - write ops will be transparently discarded, and nothing recorded in the - cache. - -There are some normal running states in which the object spends its time -servicing netfs requests: - - (4) State FSCACHE_OBJECT_AVAILABLE. - - A transient state in which pending operations are started, child objects - are permitted to advance from FSCACHE_OBJECT_INIT state, and temporary - lookup data is freed. - - (5) State FSCACHE_OBJECT_ACTIVE. - - The normal running state. In this state, requests the netfs makes will be - passed on to the cache. - - (6) State FSCACHE_OBJECT_INVALIDATING. - - The object is undergoing invalidation. When the state comes here, it - discards all pending read, write and attribute change operations as it is - going to clear out the cache entirely and reinitialise it. It will then - continue to the FSCACHE_OBJECT_UPDATING state. - - (7) State FSCACHE_OBJECT_UPDATING. - - The state machine comes here to update the object in the cache from the - netfs's records. This involves updating the auxiliary data that is used - to maintain coherency. - -And there are terminal states in which an object cleans itself up, deallocates -memory and potentially deletes stuff from disk: - - (8) State FSCACHE_OBJECT_LC_DYING. - - The object comes here if it is dying because of a lookup or creation - error. This would be due to a disk error or system error of some sort. - Temporary data is cleaned up, and the parent is released. - - (9) State FSCACHE_OBJECT_DYING. - - The object comes here if it is dying due to an error, because its parent - cookie has been relinquished by the netfs or because the cache is being - withdrawn. - - Any child objects waiting on this one are given CPU time so that they too - can destroy themselves. This object waits for all its children to go away - before advancing to the next state. - -(10) State FSCACHE_OBJECT_ABORT_INIT. - - The object comes to this state if it was waiting on its parent in - FSCACHE_OBJECT_INIT, but its parent died. The object will destroy itself - so that the parent may proceed from the FSCACHE_OBJECT_DYING state. - -(11) State FSCACHE_OBJECT_RELEASING. -(12) State FSCACHE_OBJECT_RECYCLING. - - The object comes to one of these two states when dying once it is rid of - all its children, if it is dying because the netfs relinquished its - cookie. In the first state, the cached data is expected to persist, and - in the second it will be deleted. - -(13) State FSCACHE_OBJECT_WITHDRAWING. - - The object transits to this state if the cache decides it wants to - withdraw the object from service, perhaps to make space, but also due to - error or just because the whole cache is being withdrawn. - -(14) State FSCACHE_OBJECT_DEAD. - - The object transits to this state when the in-memory object record is - ready to be deleted. The object processor shouldn't ever see an object in - this state. - - -The Set of Events ------------------ - -There are a number of events that can be raised to an object state machine: - - FSCACHE_OBJECT_EV_UPDATE - The netfs requested that an object be updated. The state machine will ask - the cache backend to update the object, and the cache backend will ask the - netfs for details of the change through its cookie definition ops. - - FSCACHE_OBJECT_EV_CLEARED - This is signalled in two circumstances: - - (a) when an object's last child object is dropped and - - (b) when the last operation outstanding on an object is completed. - - This is used to proceed from the dying state. - - FSCACHE_OBJECT_EV_ERROR - This is signalled when an I/O error occurs during the processing of some - object. - - FSCACHE_OBJECT_EV_RELEASE, FSCACHE_OBJECT_EV_RETIRE - These are signalled when the netfs relinquishes a cookie it was using. - The event selected depends on whether the netfs asks for the backing - object to be retired (deleted) or retained. - - FSCACHE_OBJECT_EV_WITHDRAW - This is signalled when the cache backend wants to withdraw an object. - This means that the object will have to be detached from the netfs's - cookie. - -Because the withdrawing releasing/retiring events are all handled by the object -state machine, it doesn't matter if there's a collision with both ends trying -to sever the connection at the same time. The state machine can just pick -which one it wants to honour, and that effects the other. diff --git a/Documentation/filesystems/caching/operations.rst b/Documentation/filesystems/caching/operations.rst deleted file mode 100644 index 9983e1675447..000000000000 --- a/Documentation/filesystems/caching/operations.rst +++ /dev/null @@ -1,210 +0,0 @@ -.. SPDX-License-Identifier: GPL-2.0 - -================================ -Asynchronous Operations Handling -================================ - -By: David Howells <dhowells@redhat.com> - -.. Contents: - - (*) Overview. - - (*) Operation record initialisation. - - (*) Parameters. - - (*) Procedure. - - (*) Asynchronous callback. - - -Overview -======== - -FS-Cache has an asynchronous operations handling facility that it uses for its -data storage and retrieval routines. Its operations are represented by -fscache_operation structs, though these are usually embedded into some other -structure. - -This facility is available to and expected to be used by the cache backends, -and FS-Cache will create operations and pass them off to the appropriate cache -backend for completion. - -To make use of this facility, <linux/fscache-cache.h> should be #included. - - -Operation Record Initialisation -=============================== - -An operation is recorded in an fscache_operation struct:: - - struct fscache_operation { - union { - struct work_struct fast_work; - struct slow_work slow_work; - }; - unsigned long flags; - fscache_operation_processor_t processor; - ... - }; - -Someone wanting to issue an operation should allocate something with this -struct embedded in it. They should initialise it by calling:: - - void fscache_operation_init(struct fscache_operation *op, - fscache_operation_release_t release); - -with the operation to be initialised and the release function to use. - -The op->flags parameter should be set to indicate the CPU time provision and -the exclusivity (see the Parameters section). - -The op->fast_work, op->slow_work and op->processor flags should be set as -appropriate for the CPU time provision (see the Parameters section). - -FSCACHE_OP_WAITING may be set in op->flags prior to each submission of the -operation and waited for afterwards. - - -Parameters -========== - -There are a number of parameters that can be set in the operation record's flag -parameter. There are three options for the provision of CPU time in these -operations: - - (1) The operation may be done synchronously (FSCACHE_OP_MYTHREAD). A thread - may decide it wants to handle an operation itself without deferring it to - another thread. - - This is, for example, used in read operations for calling readpages() on - the backing filesystem in CacheFiles. Although readpages() does an - asynchronous data fetch, the determination of whether pages exist is done - synchronously - and the netfs does not proceed until this has been - determined. - - If this option is to be used, FSCACHE_OP_WAITING must be set in op->flags - before submitting the operation, and the operating thread must wait for it - to be cleared before proceeding:: - - wait_on_bit(&op->flags, FSCACHE_OP_WAITING, - TASK_UNINTERRUPTIBLE); - - - (2) The operation may be fast asynchronous (FSCACHE_OP_FAST), in which case it - will be given to keventd to process. Such an operation is not permitted - to sleep on I/O. - - This is, for example, used by CacheFiles to copy data from a backing fs - page to a netfs page after the backing fs has read the page in. - - If this option is used, op->fast_work and op->processor must be - initialised before submitting the operation:: - - INIT_WORK(&op->fast_work, do_some_work); - - - (3) The operation may be slow asynchronous (FSCACHE_OP_SLOW), in which case it - will be given to the slow work facility to process. Such an operation is - permitted to sleep on I/O. - - This is, for example, used by FS-Cache to handle background writes of - pages that have just been fetched from a remote server. - - If this option is used, op->slow_work and op->processor must be - initialised before submitting the operation:: - - fscache_operation_init_slow(op, processor) - - -Furthermore, operations may be one of two types: - - (1) Exclusive (FSCACHE_OP_EXCLUSIVE). Operations of this type may not run in - conjunction with any other operation on the object being operated upon. - - An example of this is the attribute change operation, in which the file - being written to may need truncation. - - (2) Shareable. Operations of this type may be running simultaneously. It's - up to the operation implementation to prevent interference between other - operations running at the same time. - - -Procedure -========= - -Operations are used through the following procedure: - - (1) The submitting thread must allocate the operation and initialise it - itself. Normally this would be part of a more specific structure with the - generic op embedded within. - - (2) The submitting thread must then submit the operation for processing using - one of the following two functions:: - - int fscache_submit_op(struct fscache_object *object, - struct fscache_operation *op); - - int fscache_submit_exclusive_op(struct fscache_object *object, - struct fscache_operation *op); - - The first function should be used to submit non-exclusive ops and the - second to submit exclusive ones. The caller must still set the - FSCACHE_OP_EXCLUSIVE flag. - - If successful, both functions will assign the operation to the specified - object and return 0. -ENOBUFS will be returned if the object specified is - permanently unavailable. - - The operation manager will defer operations on an object that is still - undergoing lookup or creation. The operation will also be deferred if an - operation of conflicting exclusivity is in progress on the object. - - If the operation is asynchronous, the manager will retain a reference to - it, so the caller should put their reference to it by passing it to:: - - void fscache_put_operation(struct fscache_operation *op); - - (3) If the submitting thread wants to do the work itself, and has marked the - operation with FSCACHE_OP_MYTHREAD, then it should monitor - FSCACHE_OP_WAITING as described above and check the state of the object if - necessary (the object might have died while the thread was waiting). - - When it has finished doing its processing, it should call - fscache_op_complete() and fscache_put_operation() on it. - - (4) The operation holds an effective lock upon the object, preventing other - exclusive ops conflicting until it is released. The operation can be - enqueued for further immediate asynchronous processing by adjusting the - CPU time provisioning option if necessary, eg:: - - op->flags &= ~FSCACHE_OP_TYPE; - op->flags |= ~FSCACHE_OP_FAST; - - and calling:: - - void fscache_enqueue_operation(struct fscache_operation *op) - - This can be used to allow other things to have use of the worker thread - pools. - - -Asynchronous Callback -===================== - -When used in asynchronous mode, the worker thread pool will invoke the -processor method with a pointer to the operation. This should then get at the -container struct by using container_of():: - - static void fscache_write_op(struct fscache_operation *_op) - { - struct fscache_storage *op = - container_of(_op, struct fscache_storage, op); - ... - } - -The caller holds a reference on the operation, and will invoke -fscache_put_operation() when the processor function returns. The processor -function is at liberty to call fscache_enqueue_operation() or to take extra -references. diff --git a/Documentation/filesystems/ceph.rst b/Documentation/filesystems/ceph.rst index 7d2ef4e27273..76ce938e7024 100644 --- a/Documentation/filesystems/ceph.rst +++ b/Documentation/filesystems/ceph.rst @@ -82,7 +82,7 @@ Mount Syntax The basic mount syntax is:: - # mount -t ceph monip[:port][,monip2[:port]...]:/[subdir] mnt + # mount -t ceph user@fsid.fs_name=/[subdir] mnt -o mon_addr=monip1[:port][/monip2[:port]] You only need to specify a single monitor, as the client will get the full list when it connects. (However, if the monitor you specify @@ -90,16 +90,35 @@ happens to be down, the mount won't succeed.) The port can be left off if the monitor is using the default. So if the monitor is at 1.2.3.4:: - # mount -t ceph 1.2.3.4:/ /mnt/ceph + # mount -t ceph cephuser@07fe3187-00d9-42a3-814b-72a4d5e7d5be.cephfs=/ /mnt/ceph -o mon_addr=1.2.3.4 is sufficient. If /sbin/mount.ceph is installed, a hostname can be -used instead of an IP address. +used instead of an IP address and the cluster FSID can be left out +(as the mount helper will fill it in by reading the ceph configuration +file):: + # mount -t ceph cephuser@cephfs=/ /mnt/ceph -o mon_addr=mon-addr +Multiple monitor addresses can be passed by separating each address with a slash (`/`):: + + # mount -t ceph cephuser@cephfs=/ /mnt/ceph -o mon_addr=192.168.1.100/192.168.1.101 + +When using the mount helper, monitor address can be read from ceph +configuration file if available. Note that, the cluster FSID (passed as part +of the device string) is validated by checking it with the FSID reported by +the monitor. Mount Options ============= + mon_addr=ip_address[:port][/ip_address[:port]] + Monitor address to the cluster. This is used to bootstrap the + connection to the cluster. Once connection is established, the + monitor addresses in the monitor map are followed. + + fsid=cluster-id + FSID of the cluster (from `ceph fsid` command). + ip=A.B.C.D[:N] Specify the IP and/or port the client should bind to locally. There is normally not much reason to do this. If the IP is not @@ -184,7 +203,6 @@ For more information on Ceph, see the home page at The Linux kernel client source tree is available at - https://github.com/ceph/ceph-client.git - - git://git.kernel.org/pub/scm/linux/kernel/git/sage/ceph-client.git and the source for the full system is at https://github.com/ceph/ceph.git diff --git a/Documentation/filesystems/cifs/ksmbd.rst b/Documentation/filesystems/cifs/ksmbd.rst index b0d354fd8066..7bed96d794fc 100644 --- a/Documentation/filesystems/cifs/ksmbd.rst +++ b/Documentation/filesystems/cifs/ksmbd.rst @@ -82,10 +82,10 @@ Signing Update Supported. Pre-authentication integrity Supported. SMB3 encryption(CCM, GCM) Supported. (CCM and GCM128 supported, GCM256 in progress) -SMB direct(RDMA) Partially Supported. SMB3 Multi-channel is - required to connect to Windows client. +SMB direct(RDMA) Supported. SMB3 Multi-channel Partially Supported. Planned to implement replay/retry mechanisms for future. +Receive Side Scaling mode Supported. SMB3.1.1 POSIX extension Supported. ACLs Partially Supported. only DACLs available, SACLs (auditing) is planned for the future. For @@ -118,26 +118,44 @@ ksmbd/nfsd interoperability Planned for future. The features that ksmbd How to run ========== -1. Download ksmbd-tools and compile them. - - https://github.com/cifsd-team/ksmbd-tools +1. Download ksmbd-tools(https://github.com/cifsd-team/ksmbd-tools/releases) and + compile them. -2. Create user/password for SMB share. + - Refer README(https://github.com/cifsd-team/ksmbd-tools/blob/master/README.md) + to know how to use ksmbd.mountd/adduser/addshare/control utils - # mkdir /etc/ksmbd/ - # ksmbd.adduser -a <Enter USERNAME for SMB share access> + $ ./autogen.sh + $ ./configure --with-rundir=/run + $ make && sudo make install -3. Create /etc/ksmbd/smb.conf file, add SMB share in smb.conf file - - Refer smb.conf.example and - https://github.com/cifsd-team/ksmbd-tools/blob/master/Documentation/configuration.txt +2. Create /usr/local/etc/ksmbd/ksmbd.conf file, add SMB share in ksmbd.conf file. -4. Insert ksmbd.ko module + - Refer ksmbd.conf.example in ksmbd-utils, See ksmbd.conf manpage + for details to configure shares. - # insmod ksmbd.ko + $ man ksmbd.conf + +3. Create user/password for SMB share. + + - See ksmbd.adduser manpage. + + $ man ksmbd.adduser + $ sudo ksmbd.adduser -a <Enter USERNAME for SMB share access> + +4. Insert ksmbd.ko module after build your kernel. No need to load module + if ksmbd is built into the kernel. + + - Set ksmbd in menuconfig(e.g. $ make menuconfig) + [*] Network File Systems ---> + <M> SMB3 server support (EXPERIMENTAL) + + $ sudo modprobe ksmbd.ko 5. Start ksmbd user space daemon - # ksmbd.mountd -6. Access share from Windows or Linux using CIFS + $ sudo ksmbd.mountd + +6. Access share from Windows or Linux using SMB3 client (cifs.ko or smbclient of samba) Shutdown KSMBD ============== diff --git a/Documentation/filesystems/dax.rst b/Documentation/filesystems/dax.rst index 9a1b8fd9e82b..c04609d8ee24 100644 --- a/Documentation/filesystems/dax.rst +++ b/Documentation/filesystems/dax.rst @@ -23,11 +23,11 @@ on it as usual. The `DAX` code currently only supports files with a block size equal to your kernel's `PAGE_SIZE`, so you may need to specify a block size when creating the filesystem. -Currently 3 filesystems support `DAX`: ext2, ext4 and xfs. Enabling `DAX` on them -is different. +Currently 5 filesystems support `DAX`: ext2, ext4, xfs, virtiofs and erofs. +Enabling `DAX` on them is different. -Enabling DAX on ext2 --------------------- +Enabling DAX on ext2 and erofs +------------------------------ When mounting the filesystem, use the ``-o dax`` option on the command line or add 'dax' to the options in ``/etc/fstab``. This works to enable `DAX` on all files @@ -168,6 +168,22 @@ if the underlying media does not support dax and/or the filesystem is overridden with a mount option. +Enabling DAX on virtiofs +---------------------------- +The semantic of DAX on virtiofs is basically equal to that on ext4 and xfs, +except that when '-o dax=inode' is specified, virtiofs client derives the hint +whether DAX shall be enabled or not from virtiofs server through FUSE protocol, +rather than the persistent `FS_XFLAG_DAX` flag. That is, whether DAX shall be +enabled or not is completely determined by virtiofs server, while virtiofs +server itself may deploy various algorithm making this decision, e.g. depending +on the persistent `FS_XFLAG_DAX` flag on the host. + +It is still supported to set or clear persistent `FS_XFLAG_DAX` flag inside +guest, but it is not guaranteed that DAX will be enabled or disabled for +corresponding file then. Users inside guest still need to call statx(2) and +check the statx flag `STATX_ATTR_DAX` to see if DAX is enabled for this file. + + Implementation Tips for Block Driver Writers -------------------------------------------- diff --git a/Documentation/filesystems/erofs.rst b/Documentation/filesystems/erofs.rst index 01df283c7d04..05e03d54af1a 100644 --- a/Documentation/filesystems/erofs.rst +++ b/Documentation/filesystems/erofs.rst @@ -1,63 +1,82 @@ .. SPDX-License-Identifier: GPL-2.0 ====================================== -Enhanced Read-Only File System - EROFS +EROFS - Enhanced Read-Only File System ====================================== Overview ======== -EROFS file-system stands for Enhanced Read-Only File System. Different -from other read-only file systems, it aims to be designed for flexibility, -scalability, but be kept simple and high performance. +EROFS filesystem stands for Enhanced Read-Only File System. It aims to form a +generic read-only filesystem solution for various read-only use cases instead +of just focusing on storage space saving without considering any side effects +of runtime performance. -It is designed as a better filesystem solution for the following scenarios: +It is designed to meet the needs of flexibility, feature extendability and user +payload friendly, etc. Apart from those, it is still kept as a simple +random-access friendly high-performance filesystem to get rid of unneeded I/O +amplification and memory-resident overhead compared to similar approaches. + +It is implemented to be a better choice for the following scenarios: - read-only storage media or - part of a fully trusted read-only solution, which means it needs to be immutable and bit-for-bit identical to the official golden image for - their releases due to security and other considerations and + their releases due to security or other considerations and - hope to minimize extra storage space with guaranteed end-to-end performance by using compact layout, transparent file compression and direct access, especially for those embedded devices with limited memory and high-density - hosts with numerous containers; + hosts with numerous containers. Here is the main features of EROFS: - Little endian on-disk design; - - Currently 4KB block size (nobh) and therefore maximum 16TB address space; - - - Metadata & data could be mixed by design; + - 4KiB block size and 32-bit block addresses, therefore 16TiB address space + at most for now; - - 2 inode versions for different requirements: + - Two inode layouts for different requirements: - ===================== ============ ===================================== + ===================== ============ ====================================== compact (v1) extended (v2) - ===================== ============ ===================================== + ===================== ============ ====================================== Inode metadata size 32 bytes 64 bytes - Max file size 4 GB 16 EB (also limited by max. vol size) + Max file size 4 GiB 16 EiB (also limited by max. vol size) Max uids/gids 65536 4294967296 - File change time no yes (64 + 32-bit timestamp) + Per-inode timestamp no yes (64 + 32-bit timestamp) Max hardlinks 65536 4294967296 - Metadata reserved 4 bytes 14 bytes - ===================== ============ ===================================== + Metadata reserved 8 bytes 18 bytes + ===================== ============ ====================================== + + - Metadata and data could be mixed as an option; - Support extended attributes (xattrs) as an option; - - Support xattr inline and tail-end data inline for all files; + - Support tailpacking data and xattr inline compared to byte-addressed + unaligned metadata or smaller block size alternatives; - Support POSIX.1e ACLs by using xattrs; - Support transparent data compression as an option: - LZ4 algorithm with the fixed-sized output compression for high performance; + LZ4 and MicroLZMA algorithms can be used on a per-file basis; In addition, + inplace decompression is also supported to avoid bounce compressed buffers + and page cache thrashing. + + - Support direct I/O on uncompressed files to avoid double caching for loop + devices; + + - Support FSDAX on uncompressed images for secure containers and ramdisks in + order to get rid of unnecessary page cache. - - Multiple device support for multi-layer container images. + - Support multiple devices for multi blob container images; + + - Support file-based on-demand loading with the Fscache infrastructure. The following git tree provides the file system user-space tools under -development (ex, formatting tool mkfs.erofs): +development, such as a formatting tool (mkfs.erofs), an on-disk consistency & +compatibility checking tool (fsck.erofs), and a debugging tool (dump.erofs): - git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs-utils.git @@ -91,8 +110,17 @@ dax={always,never} Use direct access (no page cache). See Documentation/filesystems/dax.rst. dax A legacy option which is an alias for ``dax=always``. device=%s Specify a path to an extra device to be used together. +fsid=%s Specify a filesystem image ID for Fscache back-end. =================== ========================================================= +Sysfs Entries +============= + +Information about mounted erofs file systems can be found in /sys/fs/erofs. +Each mounted filesystem will have a directory in /sys/fs/erofs based on its +device name (i.e., /sys/fs/erofs/sda). +(see also Documentation/ABI/testing/sysfs-fs-erofs) + On-disk details =============== @@ -218,8 +246,8 @@ Note that apart from the offset of the first filename, nameoff0 also indicates the total number of directory entries in this block since it is no need to introduce another on-disk field at all. -Chunk-based file ----------------- +Chunk-based files +----------------- In order to support chunk-based data deduplication, a new inode data layout has been supported since Linux v5.15: Files are split in equal-sized data chunks with ``extents`` area of the inode metadata indicating how to get the chunk diff --git a/Documentation/filesystems/ext2.rst b/Documentation/filesystems/ext2.rst index 154101cf0e4f..92aae683e16a 100644 --- a/Documentation/filesystems/ext2.rst +++ b/Documentation/filesystems/ext2.rst @@ -59,8 +59,6 @@ acl Enable POSIX Access Control Lists support (requires CONFIG_EXT2_FS_POSIX_ACL). noacl Don't support POSIX ACLs. -nobh Do not attach buffer_heads to file pagecache. - quota, usrquota Enable user disk quota support (requires CONFIG_QUOTA). diff --git a/Documentation/filesystems/ext4/attributes.rst b/Documentation/filesystems/ext4/attributes.rst index 54386a010a8d..87814696a65b 100644 --- a/Documentation/filesystems/ext4/attributes.rst +++ b/Documentation/filesystems/ext4/attributes.rst @@ -13,8 +13,8 @@ disappeared as of Linux 3.0. There are two places where extended attributes can be found. The first place is between the end of each inode entry and the beginning of the -next inode entry. For example, if inode.i\_extra\_isize = 28 and -sb.inode\_size = 256, then there are 256 - (128 + 28) = 100 bytes +next inode entry. For example, if inode.i_extra_isize = 28 and +sb.inode_size = 256, then there are 256 - (128 + 28) = 100 bytes available for in-inode extended attribute storage. The second place where extended attributes can be found is in the block pointed to by ``inode.i_file_acl``. As of Linux 3.11, it is not possible for this @@ -38,8 +38,8 @@ Extended attributes, when stored after the inode, have a header - Name - Description * - 0x0 - - \_\_le32 - - h\_magic + - __le32 + - h_magic - Magic number for identification, 0xEA020000. This value is set by the Linux driver, though e2fsprogs doesn't seem to check it(?) @@ -55,28 +55,28 @@ The beginning of an extended attribute block is in - Name - Description * - 0x0 - - \_\_le32 - - h\_magic + - __le32 + - h_magic - Magic number for identification, 0xEA020000. * - 0x4 - - \_\_le32 - - h\_refcount + - __le32 + - h_refcount - Reference count. * - 0x8 - - \_\_le32 - - h\_blocks + - __le32 + - h_blocks - Number of disk blocks used. * - 0xC - - \_\_le32 - - h\_hash + - __le32 + - h_hash - Hash value of all attributes. * - 0x10 - - \_\_le32 - - h\_checksum + - __le32 + - h_checksum - Checksum of the extended attribute block. * - 0x14 - - \_\_u32 - - h\_reserved[2] + - __u32 + - h_reserved[3] - Zero. The checksum is calculated against the FS UUID, the 64-bit block number @@ -100,46 +100,46 @@ Attributes stored inside an inode do not need be stored in sorted order. - Name - Description * - 0x0 - - \_\_u8 - - e\_name\_len + - __u8 + - e_name_len - Length of name. * - 0x1 - - \_\_u8 - - e\_name\_index + - __u8 + - e_name_index - Attribute name index. There is a discussion of this below. * - 0x2 - - \_\_le16 - - e\_value\_offs + - __le16 + - e_value_offs - Location of this attribute's value on the disk block where it is stored. Multiple attributes can share the same value. For an inode attribute this value is relative to the start of the first entry; for a block this value is relative to the start of the block (i.e. the header). * - 0x4 - - \_\_le32 - - e\_value\_inum + - __le32 + - e_value_inum - The inode where the value is stored. Zero indicates the value is in the same block as this entry. This field is only used if the - INCOMPAT\_EA\_INODE feature is enabled. + INCOMPAT_EA_INODE feature is enabled. * - 0x8 - - \_\_le32 - - e\_value\_size + - __le32 + - e_value_size - Length of attribute value. * - 0xC - - \_\_le32 - - e\_hash + - __le32 + - e_hash - Hash value of attribute name and attribute value. The kernel doesn't update the hash for in-inode attributes, so for that case this value must be zero, because e2fsck validates any non-zero hash regardless of where the xattr lives. * - 0x10 - char - - e\_name[e\_name\_len] + - e_name[e_name_len] - Attribute name. Does not include trailing NULL. Attribute values can follow the end of the entry table. There appears to be a requirement that they be aligned to 4-byte boundaries. The values are stored starting at the end of the block and grow towards the -xattr\_header/xattr\_entry table. When the two collide, the overflow is +xattr_header/xattr_entry table. When the two collide, the overflow is put into a separate disk block. If the disk block fills up, the filesystem returns -ENOSPC. @@ -167,15 +167,15 @@ the key name. Here is a map of name index values to key prefixes: * - 1 - “user.” * - 2 - - “system.posix\_acl\_access” + - “system.posix_acl_access” * - 3 - - “system.posix\_acl\_default” + - “system.posix_acl_default” * - 4 - “trusted.” * - 6 - “security.” * - 7 - - “system.” (inline\_data only?) + - “system.” (inline_data only?) * - 8 - “system.richacl” (SuSE kernels only?) diff --git a/Documentation/filesystems/ext4/bigalloc.rst b/Documentation/filesystems/ext4/bigalloc.rst index 72075aa608e4..976a180b209c 100644 --- a/Documentation/filesystems/ext4/bigalloc.rst +++ b/Documentation/filesystems/ext4/bigalloc.rst @@ -23,7 +23,7 @@ means that a block group addresses 32 gigabytes instead of 128 megabytes, also shrinking the amount of file system overhead for metadata. The administrator can set a block cluster size at mkfs time (which is -stored in the s\_log\_cluster\_size field in the superblock); from then +stored in the s_log_cluster_size field in the superblock); from then on, the block bitmaps track clusters, not individual blocks. This means that block groups can be several gigabytes in size (instead of just 128MiB); however, the minimum allocation unit becomes a cluster, not a diff --git a/Documentation/filesystems/ext4/bitmaps.rst b/Documentation/filesystems/ext4/bitmaps.rst index c7546dbc197a..91c45d86e9bb 100644 --- a/Documentation/filesystems/ext4/bitmaps.rst +++ b/Documentation/filesystems/ext4/bitmaps.rst @@ -9,15 +9,15 @@ group. The inode bitmap records which entries in the inode table are in use. As with most bitmaps, one bit represents the usage status of one data -block or inode table entry. This implies a block group size of 8 \* -number\_of\_bytes\_in\_a\_logical\_block. +block or inode table entry. This implies a block group size of 8 * +number_of_bytes_in_a_logical_block. NOTE: If ``BLOCK_UNINIT`` is set for a given block group, various parts of the kernel and e2fsprogs code pretends that the block bitmap contains zeros (i.e. all blocks in the group are free). However, it is not necessarily the case that no blocks are in use -- if ``meta_bg`` is set, the bitmaps and group descriptor live inside the group. Unfortunately, -ext2fs\_test\_block\_bitmap2() will return '0' for those locations, +ext2fs_test_block_bitmap2() will return '0' for those locations, which produces confusing debugfs output. Inode Table diff --git a/Documentation/filesystems/ext4/blockgroup.rst b/Documentation/filesystems/ext4/blockgroup.rst index d5d652addce5..46d78f860623 100644 --- a/Documentation/filesystems/ext4/blockgroup.rst +++ b/Documentation/filesystems/ext4/blockgroup.rst @@ -56,39 +56,39 @@ established that the super block and the group descriptor table, if present, will be at the beginning of the block group. The bitmaps and the inode table can be anywhere, and it is quite possible for the bitmaps to come after the inode table, or for both to be in different -groups (flex\_bg). Leftover space is used for file data blocks, indirect +groups (flex_bg). Leftover space is used for file data blocks, indirect block maps, extent tree blocks, and extended attributes. Flexible Block Groups --------------------- Starting in ext4, there is a new feature called flexible block groups -(flex\_bg). In a flex\_bg, several block groups are tied together as one +(flex_bg). In a flex_bg, several block groups are tied together as one logical block group; the bitmap spaces and the inode table space in the -first block group of the flex\_bg are expanded to include the bitmaps -and inode tables of all other block groups in the flex\_bg. For example, -if the flex\_bg size is 4, then group 0 will contain (in order) the +first block group of the flex_bg are expanded to include the bitmaps +and inode tables of all other block groups in the flex_bg. For example, +if the flex_bg size is 4, then group 0 will contain (in order) the superblock, group descriptors, data block bitmaps for groups 0-3, inode bitmaps for groups 0-3, inode tables for groups 0-3, and the remaining space in group 0 is for file data. The effect of this is to group the block group metadata close together for faster loading, and to enable large files to be continuous on disk. Backup copies of the superblock and group descriptors are always at the beginning of block groups, even -if flex\_bg is enabled. The number of block groups that make up a -flex\_bg is given by 2 ^ ``sb.s_log_groups_per_flex``. +if flex_bg is enabled. The number of block groups that make up a +flex_bg is given by 2 ^ ``sb.s_log_groups_per_flex``. Meta Block Groups ----------------- -Without the option META\_BG, for safety concerns, all block group +Without the option META_BG, for safety concerns, all block group descriptors copies are kept in the first block group. Given the default 128MiB(2^27 bytes) block group size and 64-byte group descriptors, ext4 can have at most 2^27/64 = 2^21 block groups. This limits the entire filesystem size to 2^21 * 2^27 = 2^48bytes or 256TiB. The solution to this problem is to use the metablock group feature -(META\_BG), which is already in ext3 for all 2.6 releases. With the -META\_BG feature, ext4 filesystems are partitioned into many metablock +(META_BG), which is already in ext3 for all 2.6 releases. With the +META_BG feature, ext4 filesystems are partitioned into many metablock groups. Each metablock group is a cluster of block groups whose group descriptor structures can be stored in a single disk block. For ext4 filesystems with 4 KB block size, a single metablock group partition @@ -110,7 +110,7 @@ bytes, a meta-block group contains 32 block groups for filesystems with a 1KB block size, and 128 block groups for filesystems with a 4KB blocksize. Filesystems can either be created using this new block group descriptor layout, or existing filesystems can be resized on-line, and -the field s\_first\_meta\_bg in the superblock will indicate the first +the field s_first_meta_bg in the superblock will indicate the first block group using this new layout. Please see an important note about ``BLOCK_UNINIT`` in the section about @@ -121,15 +121,15 @@ Lazy Block Group Initialization A new feature for ext4 are three block group descriptor flags that enable mkfs to skip initializing other parts of the block group -metadata. Specifically, the INODE\_UNINIT and BLOCK\_UNINIT flags mean +metadata. Specifically, the INODE_UNINIT and BLOCK_UNINIT flags mean that the inode and block bitmaps for that group can be calculated and therefore the on-disk bitmap blocks are not initialized. This is generally the case for an empty block group or a block group containing -only fixed-location block group metadata. The INODE\_ZEROED flag means +only fixed-location block group metadata. The INODE_ZEROED flag means that the inode table has been initialized; mkfs will unset this flag and rely on the kernel to initialize the inode tables in the background. By not writing zeroes to the bitmaps and inode table, mkfs time is -reduced considerably. Note the feature flag is RO\_COMPAT\_GDT\_CSUM, -but the dumpe2fs output prints this as “uninit\_bg”. They are the same +reduced considerably. Note the feature flag is RO_COMPAT_GDT_CSUM, +but the dumpe2fs output prints this as “uninit_bg”. They are the same thing. diff --git a/Documentation/filesystems/ext4/blockmap.rst b/Documentation/filesystems/ext4/blockmap.rst index 30e25750d88a..cc596541ce79 100644 --- a/Documentation/filesystems/ext4/blockmap.rst +++ b/Documentation/filesystems/ext4/blockmap.rst @@ -1,7 +1,7 @@ .. SPDX-License-Identifier: GPL-2.0 +---------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ -| i.i\_block Offset | Where It Points | +| i.i_block Offset | Where It Points | +=====================+==============================================================================================================================================================================================================================+ | 0 to 11 | Direct map to file blocks 0 to 11. | +---------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ diff --git a/Documentation/filesystems/ext4/blocks.rst b/Documentation/filesystems/ext4/blocks.rst index bd722ecd92d6..b0f80ea87c90 100644 --- a/Documentation/filesystems/ext4/blocks.rst +++ b/Documentation/filesystems/ext4/blocks.rst @@ -39,7 +39,7 @@ For 32-bit filesystems, limits are as follows: - 4TiB - 8TiB - 16TiB - - 256PiB + - 256TiB * - Blocks Per Block Group - 8,192 - 16,384 diff --git a/Documentation/filesystems/ext4/checksums.rst b/Documentation/filesystems/ext4/checksums.rst index 5519e253810d..e232749daf5f 100644 --- a/Documentation/filesystems/ext4/checksums.rst +++ b/Documentation/filesystems/ext4/checksums.rst @@ -4,7 +4,7 @@ Checksums --------- Starting in early 2012, metadata checksums were added to all major ext4 -and jbd2 data structures. The associated feature flag is metadata\_csum. +and jbd2 data structures. The associated feature flag is metadata_csum. The desired checksum algorithm is indicated in the superblock, though as of October 2012 the only supported algorithm is crc32c. Some data structures did not have space to fit a full 32-bit checksum, so only the @@ -20,7 +20,7 @@ encounters directory blocks that lack sufficient empty space to add a checksum, it will request that you run ``e2fsck -D`` to have the directories rebuilt with checksums. This has the added benefit of removing slack space from the directory files and rebalancing the htree -indexes. If you \_ignore\_ this step, your directories will not be +indexes. If you _ignore_ this step, your directories will not be protected by a checksum! The following table describes the data elements that go into each type @@ -35,39 +35,39 @@ of checksum. The checksum function is whatever the superblock describes - Length - Ingredients * - Superblock - - \_\_le32 + - __le32 - The entire superblock up to the checksum field. The UUID lives inside the superblock. * - MMP - - \_\_le32 + - __le32 - UUID + the entire MMP block up to the checksum field. * - Extended Attributes - - \_\_le32 + - __le32 - UUID + the entire extended attribute block. The checksum field is set to zero. * - Directory Entries - - \_\_le32 + - __le32 - UUID + inode number + inode generation + the directory block up to the fake entry enclosing the checksum field. * - HTREE Nodes - - \_\_le32 + - __le32 - UUID + inode number + inode generation + all valid extents + HTREE tail. The checksum field is set to zero. * - Extents - - \_\_le32 + - __le32 - UUID + inode number + inode generation + the entire extent block up to the checksum field. * - Bitmaps - - \_\_le32 or \_\_le16 + - __le32 or __le16 - UUID + the entire bitmap. Checksums are stored in the group descriptor, and truncated if the group descriptor size is 32 bytes (i.e. ^64bit) * - Inodes - - \_\_le32 + - __le32 - UUID + inode number + inode generation + the entire inode. The checksum field is set to zero. Each inode has its own checksum. * - Group Descriptors - - \_\_le16 - - If metadata\_csum, then UUID + group number + the entire descriptor; - else if gdt\_csum, then crc16(UUID + group number + the entire + - __le16 + - If metadata_csum, then UUID + group number + the entire descriptor; + else if gdt_csum, then crc16(UUID + group number + the entire descriptor). In all cases, only the lower 16 bits are stored. diff --git a/Documentation/filesystems/ext4/directory.rst b/Documentation/filesystems/ext4/directory.rst index 55f618b37144..6eece8e31df8 100644 --- a/Documentation/filesystems/ext4/directory.rst +++ b/Documentation/filesystems/ext4/directory.rst @@ -42,24 +42,24 @@ is at most 263 bytes long, though on disk you'll need to reference - Name - Description * - 0x0 - - \_\_le32 + - __le32 - inode - Number of the inode that this directory entry points to. * - 0x4 - - \_\_le16 - - rec\_len + - __le16 + - rec_len - Length of this directory entry. Must be a multiple of 4. * - 0x6 - - \_\_le16 - - name\_len + - __le16 + - name_len - Length of the file name. * - 0x8 - char - - name[EXT4\_NAME\_LEN] + - name[EXT4_NAME_LEN] - File name. Since file names cannot be longer than 255 bytes, the new directory -entry format shortens the name\_len field and uses the space for a file +entry format shortens the name_len field and uses the space for a file type flag, probably to avoid having to load every inode during directory tree traversal. This format is ``ext4_dir_entry_2``, which is at most 263 bytes long, though on disk you'll need to reference @@ -74,24 +74,24 @@ tree traversal. This format is ``ext4_dir_entry_2``, which is at most - Name - Description * - 0x0 - - \_\_le32 + - __le32 - inode - Number of the inode that this directory entry points to. * - 0x4 - - \_\_le16 - - rec\_len + - __le16 + - rec_len - Length of this directory entry. * - 0x6 - - \_\_u8 - - name\_len + - __u8 + - name_len - Length of the file name. * - 0x7 - - \_\_u8 - - file\_type + - __u8 + - file_type - File type code, see ftype_ table below. * - 0x8 - char - - name[EXT4\_NAME\_LEN] + - name[EXT4_NAME_LEN] - File name. .. _ftype: @@ -137,19 +137,19 @@ entry uses this extension, it may be up to 271 bytes. - Name - Description * - 0x0 - - \_\_le32 + - __le32 - hash - The hash of the directory name * - 0x4 - - \_\_le32 - - minor\_hash + - __le32 + - minor_hash - The minor hash of the directory name In order to add checksums to these classic directory blocks, a phony ``struct ext4_dir_entry`` is placed at the end of each leaf block to hold the checksum. The directory entry is 12 bytes long. The inode -number and name\_len fields are set to zero to fool old software into +number and name_len fields are set to zero to fool old software into ignoring an apparently empty directory entry, and the checksum is stored in the place where the name normally goes. The structure is ``struct ext4_dir_entry_tail``: @@ -163,24 +163,24 @@ in the place where the name normally goes. The structure is - Name - Description * - 0x0 - - \_\_le32 - - det\_reserved\_zero1 + - __le32 + - det_reserved_zero1 - Inode number, which must be zero. * - 0x4 - - \_\_le16 - - det\_rec\_len + - __le16 + - det_rec_len - Length of this directory entry, which must be 12. * - 0x6 - - \_\_u8 - - det\_reserved\_zero2 + - __u8 + - det_reserved_zero2 - Length of the file name, which must be zero. * - 0x7 - - \_\_u8 - - det\_reserved\_ft + - __u8 + - det_reserved_ft - File type, which must be 0xDE. * - 0x8 - - \_\_le32 - - det\_checksum + - __le32 + - det_checksum - Directory leaf block checksum. The leaf directory block checksum is calculated against the FS UUID, the @@ -194,7 +194,7 @@ Hash Tree Directories A linear array of directory entries isn't great for performance, so a new feature was added to ext3 to provide a faster (but peculiar) balanced tree keyed off a hash of the directory entry name. If the -EXT4\_INDEX\_FL (0x1000) flag is set in the inode, this directory uses a +EXT4_INDEX_FL (0x1000) flag is set in the inode, this directory uses a hashed btree (htree) to organize and find directory entries. For backwards read-only compatibility with ext2, this tree is actually hidden inside the directory file, masquerading as “empty” directory data @@ -206,14 +206,14 @@ rest of the directory block is empty so that it moves on. The root of the tree always lives in the first data block of the directory. By ext2 custom, the '.' and '..' entries must appear at the beginning of this first block, so they are put here as two -``struct ext4_dir_entry_2``\ s and not stored in the tree. The rest of +``struct ext4_dir_entry_2`` s and not stored in the tree. The rest of the root node contains metadata about the tree and finally a hash->block map to find nodes that are lower in the htree. If ``dx_root.info.indirect_levels`` is non-zero then the htree has two levels; the data block pointed to by the root node's map is an interior node, which is indexed by a minor hash. Interior nodes in this tree contains a zeroed out ``struct ext4_dir_entry_2`` followed by a -minor\_hash->block map to find leafe nodes. Leaf nodes contain a linear +minor_hash->block map to find leafe nodes. Leaf nodes contain a linear array of all ``struct ext4_dir_entry_2``; all of these entries (presumably) hash to the same value. If there is an overflow, the entries simply overflow into the next leaf node, and the @@ -245,83 +245,83 @@ of a data block: - Name - Description * - 0x0 - - \_\_le32 + - __le32 - dot.inode - inode number of this directory. * - 0x4 - - \_\_le16 - - dot.rec\_len + - __le16 + - dot.rec_len - Length of this record, 12. * - 0x6 - u8 - - dot.name\_len + - dot.name_len - Length of the name, 1. * - 0x7 - u8 - - dot.file\_type + - dot.file_type - File type of this entry, 0x2 (directory) (if the feature flag is set). * - 0x8 - char - dot.name[4] - - “.\\0\\0\\0” + - “.\0\0\0” * - 0xC - - \_\_le32 + - __le32 - dotdot.inode - inode number of parent directory. * - 0x10 - - \_\_le16 - - dotdot.rec\_len - - block\_size - 12. The record length is long enough to cover all htree + - __le16 + - dotdot.rec_len + - block_size - 12. The record length is long enough to cover all htree data. * - 0x12 - u8 - - dotdot.name\_len + - dotdot.name_len - Length of the name, 2. * - 0x13 - u8 - - dotdot.file\_type + - dotdot.file_type - File type of this entry, 0x2 (directory) (if the feature flag is set). * - 0x14 - char - - dotdot\_name[4] - - “..\\0\\0” + - dotdot_name[4] + - “..\0\0” * - 0x18 - - \_\_le32 - - struct dx\_root\_info.reserved\_zero + - __le32 + - struct dx_root_info.reserved_zero - Zero. * - 0x1C - u8 - - struct dx\_root\_info.hash\_version + - struct dx_root_info.hash_version - Hash type, see dirhash_ table below. * - 0x1D - u8 - - struct dx\_root\_info.info\_length + - struct dx_root_info.info_length - Length of the tree information, 0x8. * - 0x1E - u8 - - struct dx\_root\_info.indirect\_levels - - Depth of the htree. Cannot be larger than 3 if the INCOMPAT\_LARGEDIR + - struct dx_root_info.indirect_levels + - Depth of the htree. Cannot be larger than 3 if the INCOMPAT_LARGEDIR feature is set; cannot be larger than 2 otherwise. * - 0x1F - u8 - - struct dx\_root\_info.unused\_flags + - struct dx_root_info.unused_flags - * - 0x20 - - \_\_le16 + - __le16 - limit - - Maximum number of dx\_entries that can follow this header, plus 1 for + - Maximum number of dx_entries that can follow this header, plus 1 for the header itself. * - 0x22 - - \_\_le16 + - __le16 - count - - Actual number of dx\_entries that follow this header, plus 1 for the + - Actual number of dx_entries that follow this header, plus 1 for the header itself. * - 0x24 - - \_\_le32 + - __le32 - block - The block number (within the directory file) that goes with hash=0. * - 0x28 - - struct dx\_entry + - struct dx_entry - entries[0] - As many 8-byte ``struct dx_entry`` as fits in the rest of the data block. @@ -362,38 +362,38 @@ also the full length of a data block: - Name - Description * - 0x0 - - \_\_le32 + - __le32 - fake.inode - Zero, to make it look like this entry is not in use. * - 0x4 - - \_\_le16 - - fake.rec\_len - - The size of the block, in order to hide all of the dx\_node data. + - __le16 + - fake.rec_len + - The size of the block, in order to hide all of the dx_node data. * - 0x6 - u8 - - name\_len + - name_len - Zero. There is no name for this “unused” directory entry. * - 0x7 - u8 - - file\_type + - file_type - Zero. There is no file type for this “unused” directory entry. * - 0x8 - - \_\_le16 + - __le16 - limit - - Maximum number of dx\_entries that can follow this header, plus 1 for + - Maximum number of dx_entries that can follow this header, plus 1 for the header itself. * - 0xA - - \_\_le16 + - __le16 - count - - Actual number of dx\_entries that follow this header, plus 1 for the + - Actual number of dx_entries that follow this header, plus 1 for the header itself. * - 0xE - - \_\_le32 + - __le32 - block - The block number (within the directory file) that goes with the lowest hash value of this block. This value is stored in the parent block. * - 0x12 - - struct dx\_entry + - struct dx_entry - entries[0] - As many 8-byte ``struct dx_entry`` as fits in the rest of the data block. @@ -410,11 +410,11 @@ long: - Name - Description * - 0x0 - - \_\_le32 + - __le32 - hash - Hash code. * - 0x4 - - \_\_le32 + - __le32 - block - Block number (within the directory file, not filesystem blocks) of the next node in the htree. @@ -423,13 +423,13 @@ long: author.) If metadata checksums are enabled, the last 8 bytes of the directory -block (precisely the length of one dx\_entry) are used to store a +block (precisely the length of one dx_entry) are used to store a ``struct dx_tail``, which contains the checksum. The ``limit`` and -``count`` entries in the dx\_root/dx\_node structures are adjusted as -necessary to fit the dx\_tail into the block. If there is no space for -the dx\_tail, the user is notified to run e2fsck -D to rebuild the +``count`` entries in the dx_root/dx_node structures are adjusted as +necessary to fit the dx_tail into the block. If there is no space for +the dx_tail, the user is notified to run e2fsck -D to rebuild the directory index (which will ensure that there's space for the checksum. -The dx\_tail structure is 8 bytes long and looks like this: +The dx_tail structure is 8 bytes long and looks like this: .. list-table:: :widths: 8 8 24 40 @@ -441,13 +441,13 @@ The dx\_tail structure is 8 bytes long and looks like this: - Description * - 0x0 - u32 - - dt\_reserved + - dt_reserved - Zero. * - 0x4 - - \_\_le32 - - dt\_checksum + - __le32 + - dt_checksum - Checksum of the htree directory block. The checksum is calculated against the FS UUID, the htree index header -(dx\_root or dx\_node), all of the htree indices (dx\_entry) that are in -use, and the tail block (dx\_tail). +(dx_root or dx_node), all of the htree indices (dx_entry) that are in +use, and the tail block (dx_tail). diff --git a/Documentation/filesystems/ext4/eainode.rst b/Documentation/filesystems/ext4/eainode.rst index ecc0d01a0a72..7a2ef26b064a 100644 --- a/Documentation/filesystems/ext4/eainode.rst +++ b/Documentation/filesystems/ext4/eainode.rst @@ -5,14 +5,14 @@ Large Extended Attribute Values To enable ext4 to store extended attribute values that do not fit in the inode or in the single extended attribute block attached to an inode, -the EA\_INODE feature allows us to store the value in the data blocks of +the EA_INODE feature allows us to store the value in the data blocks of a regular file inode. This “EA inode” is linked only from the extended attribute name index and must not appear in a directory entry. The -inode's i\_atime field is used to store a checksum of the xattr value; -and i\_ctime/i\_version store a 64-bit reference count, which enables +inode's i_atime field is used to store a checksum of the xattr value; +and i_ctime/i_version store a 64-bit reference count, which enables sharing of large xattr values between multiple owning inodes. For backward compatibility with older versions of this feature, the -i\_mtime/i\_generation *may* store a back-reference to the inode number -and i\_generation of the **one** owning inode (in cases where the EA +i_mtime/i_generation *may* store a back-reference to the inode number +and i_generation of the **one** owning inode (in cases where the EA inode is not referenced by multiple inodes) to verify that the EA inode is the correct one being accessed. diff --git a/Documentation/filesystems/ext4/group_descr.rst b/Documentation/filesystems/ext4/group_descr.rst index 7ba6114e7f5c..392ec44f8fb0 100644 --- a/Documentation/filesystems/ext4/group_descr.rst +++ b/Documentation/filesystems/ext4/group_descr.rst @@ -7,34 +7,34 @@ Each block group on the filesystem has one of these descriptors associated with it. As noted in the Layout section above, the group descriptors (if present) are the second item in the block group. The standard configuration is for each block group to contain a full copy of -the block group descriptor table unless the sparse\_super feature flag +the block group descriptor table unless the sparse_super feature flag is set. Notice how the group descriptor records the location of both bitmaps and the inode table (i.e. they can float). This means that within a block group, the only data structures with fixed locations are the superblock -and the group descriptor table. The flex\_bg mechanism uses this +and the group descriptor table. The flex_bg mechanism uses this property to group several block groups into a flex group and lay out all of the groups' bitmaps and inode tables into one long run in the first group of the flex group. -If the meta\_bg feature flag is set, then several block groups are -grouped together into a meta group. Note that in the meta\_bg case, +If the meta_bg feature flag is set, then several block groups are +grouped together into a meta group. Note that in the meta_bg case, however, the first and last two block groups within the larger meta group contain only group descriptors for the groups inside the meta group. -flex\_bg and meta\_bg do not appear to be mutually exclusive features. +flex_bg and meta_bg do not appear to be mutually exclusive features. In ext2, ext3, and ext4 (when the 64bit feature is not enabled), the block group descriptor was only 32 bytes long and therefore ends at -bg\_checksum. On an ext4 filesystem with the 64bit feature enabled, the +bg_checksum. On an ext4 filesystem with the 64bit feature enabled, the block group descriptor expands to at least the 64 bytes described below; the size is stored in the superblock. -If gdt\_csum is set and metadata\_csum is not set, the block group +If gdt_csum is set and metadata_csum is not set, the block group checksum is the crc16 of the FS UUID, the group number, and the group -descriptor structure. If metadata\_csum is set, then the block group +descriptor structure. If metadata_csum is set, then the block group checksum is the lower 16 bits of the checksum of the FS UUID, the group number, and the group descriptor structure. Both block and inode bitmap checksums are calculated against the FS UUID, the group number, and the @@ -51,59 +51,59 @@ The block group descriptor is laid out in ``struct ext4_group_desc``. - Name - Description * - 0x0 - - \_\_le32 - - bg\_block\_bitmap\_lo + - __le32 + - bg_block_bitmap_lo - Lower 32-bits of location of block bitmap. * - 0x4 - - \_\_le32 - - bg\_inode\_bitmap\_lo + - __le32 + - bg_inode_bitmap_lo - Lower 32-bits of location of inode bitmap. * - 0x8 - - \_\_le32 - - bg\_inode\_table\_lo + - __le32 + - bg_inode_table_lo - Lower 32-bits of location of inode table. * - 0xC - - \_\_le16 - - bg\_free\_blocks\_count\_lo + - __le16 + - bg_free_blocks_count_lo - Lower 16-bits of free block count. * - 0xE - - \_\_le16 - - bg\_free\_inodes\_count\_lo + - __le16 + - bg_free_inodes_count_lo - Lower 16-bits of free inode count. * - 0x10 - - \_\_le16 - - bg\_used\_dirs\_count\_lo + - __le16 + - bg_used_dirs_count_lo - Lower 16-bits of directory count. * - 0x12 - - \_\_le16 - - bg\_flags + - __le16 + - bg_flags - Block group flags. See the bgflags_ table below. * - 0x14 - - \_\_le32 - - bg\_exclude\_bitmap\_lo + - __le32 + - bg_exclude_bitmap_lo - Lower 32-bits of location of snapshot exclusion bitmap. * - 0x18 - - \_\_le16 - - bg\_block\_bitmap\_csum\_lo + - __le16 + - bg_block_bitmap_csum_lo - Lower 16-bits of the block bitmap checksum. * - 0x1A - - \_\_le16 - - bg\_inode\_bitmap\_csum\_lo + - __le16 + - bg_inode_bitmap_csum_lo - Lower 16-bits of the inode bitmap checksum. * - 0x1C - - \_\_le16 - - bg\_itable\_unused\_lo + - __le16 + - bg_itable_unused_lo - Lower 16-bits of unused inode count. If set, we needn't scan past the - ``(sb.s_inodes_per_group - gdt.bg_itable_unused)``\ th entry in the + ``(sb.s_inodes_per_group - gdt.bg_itable_unused)`` th entry in the inode table for this group. * - 0x1E - - \_\_le16 - - bg\_checksum - - Group descriptor checksum; crc16(sb\_uuid+group\_num+bg\_desc) if the - RO\_COMPAT\_GDT\_CSUM feature is set, or - crc32c(sb\_uuid+group\_num+bg\_desc) & 0xFFFF if the - RO\_COMPAT\_METADATA\_CSUM feature is set. The bg\_checksum - field in bg\_desc is skipped when calculating crc16 checksum, + - __le16 + - bg_checksum + - Group descriptor checksum; crc16(sb_uuid+group_num+bg_desc) if the + RO_COMPAT_GDT_CSUM feature is set, or + crc32c(sb_uuid+group_num+bg_desc) & 0xFFFF if the + RO_COMPAT_METADATA_CSUM feature is set. The bg_checksum + field in bg_desc is skipped when calculating crc16 checksum, and set to zero if crc32c checksum is used. * - - @@ -111,48 +111,48 @@ The block group descriptor is laid out in ``struct ext4_group_desc``. - These fields only exist if the 64bit feature is enabled and s_desc_size > 32. * - 0x20 - - \_\_le32 - - bg\_block\_bitmap\_hi + - __le32 + - bg_block_bitmap_hi - Upper 32-bits of location of block bitmap. * - 0x24 - - \_\_le32 - - bg\_inode\_bitmap\_hi + - __le32 + - bg_inode_bitmap_hi - Upper 32-bits of location of inodes bitmap. * - 0x28 - - \_\_le32 - - bg\_inode\_table\_hi + - __le32 + - bg_inode_table_hi - Upper 32-bits of location of inodes table. * - 0x2C - - \_\_le16 - - bg\_free\_blocks\_count\_hi + - __le16 + - bg_free_blocks_count_hi - Upper 16-bits of free block count. * - 0x2E - - \_\_le16 - - bg\_free\_inodes\_count\_hi + - __le16 + - bg_free_inodes_count_hi - Upper 16-bits of free inode count. * - 0x30 - - \_\_le16 - - bg\_used\_dirs\_count\_hi + - __le16 + - bg_used_dirs_count_hi - Upper 16-bits of directory count. * - 0x32 - - \_\_le16 - - bg\_itable\_unused\_hi + - __le16 + - bg_itable_unused_hi - Upper 16-bits of unused inode count. * - 0x34 - - \_\_le32 - - bg\_exclude\_bitmap\_hi + - __le32 + - bg_exclude_bitmap_hi - Upper 32-bits of location of snapshot exclusion bitmap. * - 0x38 - - \_\_le16 - - bg\_block\_bitmap\_csum\_hi + - __le16 + - bg_block_bitmap_csum_hi - Upper 16-bits of the block bitmap checksum. * - 0x3A - - \_\_le16 - - bg\_inode\_bitmap\_csum\_hi + - __le16 + - bg_inode_bitmap_csum_hi - Upper 16-bits of the inode bitmap checksum. * - 0x3C - - \_\_u32 - - bg\_reserved + - __u32 + - bg_reserved - Padding to 64 bytes. .. _bgflags: @@ -166,8 +166,8 @@ Block group flags can be any combination of the following: * - Value - Description * - 0x1 - - inode table and bitmap are not initialized (EXT4\_BG\_INODE\_UNINIT). + - inode table and bitmap are not initialized (EXT4_BG_INODE_UNINIT). * - 0x2 - - block bitmap is not initialized (EXT4\_BG\_BLOCK\_UNINIT). + - block bitmap is not initialized (EXT4_BG_BLOCK_UNINIT). * - 0x4 - - inode table is zeroed (EXT4\_BG\_INODE\_ZEROED). + - inode table is zeroed (EXT4_BG_INODE_ZEROED). diff --git a/Documentation/filesystems/ext4/ifork.rst b/Documentation/filesystems/ext4/ifork.rst index b9816d5a896b..dc31f505e6c8 100644 --- a/Documentation/filesystems/ext4/ifork.rst +++ b/Documentation/filesystems/ext4/ifork.rst @@ -1,6 +1,6 @@ .. SPDX-License-Identifier: GPL-2.0 -The Contents of inode.i\_block +The Contents of inode.i_block ------------------------------ Depending on the type of file an inode describes, the 60 bytes of @@ -47,7 +47,7 @@ In ext4, the file to logical block map has been replaced with an extent tree. Under the old scheme, allocating a contiguous run of 1,000 blocks requires an indirect block to map all 1,000 entries; with extents, the mapping is reduced to a single ``struct ext4_extent`` with -``ee_len = 1000``. If flex\_bg is enabled, it is possible to allocate +``ee_len = 1000``. If flex_bg is enabled, it is possible to allocate very large files with a single extent, at a considerable reduction in metadata block use, and some improvement in disk efficiency. The inode must have the extents flag (0x80000) flag set for this feature to be in @@ -76,28 +76,28 @@ which is 12 bytes long: - Name - Description * - 0x0 - - \_\_le16 - - eh\_magic + - __le16 + - eh_magic - Magic number, 0xF30A. * - 0x2 - - \_\_le16 - - eh\_entries + - __le16 + - eh_entries - Number of valid entries following the header. * - 0x4 - - \_\_le16 - - eh\_max + - __le16 + - eh_max - Maximum number of entries that could follow the header. * - 0x6 - - \_\_le16 - - eh\_depth + - __le16 + - eh_depth - Depth of this extent node in the extent tree. 0 = this extent node points to data blocks; otherwise, this extent node points to other extent nodes. The extent tree can be at most 5 levels deep: a logical block number can be at most ``2^32``, and the smallest ``n`` that satisfies ``4*(((blocksize - 12)/12)^n) >= 2^32`` is 5. * - 0x8 - - \_\_le32 - - eh\_generation + - __le32 + - eh_generation - Generation of the tree. (Used by Lustre, but not standard ext4). Internal nodes of the extent tree, also known as index nodes, are @@ -112,22 +112,22 @@ recorded as ``struct ext4_extent_idx``, and are 12 bytes long: - Name - Description * - 0x0 - - \_\_le32 - - ei\_block + - __le32 + - ei_block - This index node covers file blocks from 'block' onward. * - 0x4 - - \_\_le32 - - ei\_leaf\_lo + - __le32 + - ei_leaf_lo - Lower 32-bits of the block number of the extent node that is the next level lower in the tree. The tree node pointed to can be either another internal node or a leaf node, described below. * - 0x8 - - \_\_le16 - - ei\_leaf\_hi + - __le16 + - ei_leaf_hi - Upper 16-bits of the previous field. * - 0xA - - \_\_u16 - - ei\_unused + - __u16 + - ei_unused - Leaf nodes of the extent tree are recorded as ``struct ext4_extent``, @@ -142,24 +142,24 @@ and are also 12 bytes long: - Name - Description * - 0x0 - - \_\_le32 - - ee\_block + - __le32 + - ee_block - First file block number that this extent covers. * - 0x4 - - \_\_le16 - - ee\_len + - __le16 + - ee_len - Number of blocks covered by extent. If the value of this field is <= 32768, the extent is initialized. If the value of the field is > 32768, the extent is uninitialized and the actual extent length is ``ee_len`` - 32768. Therefore, the maximum length of a initialized extent is 32768 blocks, and the maximum length of an uninitialized extent is 32767. * - 0x6 - - \_\_le16 - - ee\_start\_hi + - __le16 + - ee_start_hi - Upper 16-bits of the block number to which this extent points. * - 0x8 - - \_\_le32 - - ee\_start\_lo + - __le32 + - ee_start_lo - Lower 32-bits of the block number to which this extent points. Prior to the introduction of metadata checksums, the extent header + @@ -182,8 +182,8 @@ including) the checksum itself. - Name - Description * - 0x0 - - \_\_le32 - - eb\_checksum + - __le32 + - eb_checksum - Checksum of the extent block, crc32c(uuid+inum+igeneration+extentblock) Inline Data diff --git a/Documentation/filesystems/ext4/inlinedata.rst b/Documentation/filesystems/ext4/inlinedata.rst index d1075178ce0b..a728af0d2fd0 100644 --- a/Documentation/filesystems/ext4/inlinedata.rst +++ b/Documentation/filesystems/ext4/inlinedata.rst @@ -11,12 +11,12 @@ file is smaller than 60 bytes, then the data are stored inline in attribute space, then it might be found as an extended attribute “system.data” within the inode body (“ibody EA”). This of course constrains the amount of extended attributes one can attach to an inode. -If the data size increases beyond i\_block + ibody EA, a regular block +If the data size increases beyond i_block + ibody EA, a regular block is allocated and the contents moved to that block. Pending a change to compact the extended attribute key used to store inline data, one ought to be able to store 160 bytes of data in a -256-byte inode (as of June 2015, when i\_extra\_isize is 28). Prior to +256-byte inode (as of June 2015, when i_extra_isize is 28). Prior to that, the limit was 156 bytes due to inefficient use of inode space. The inline data feature requires the presence of an extended attribute @@ -25,12 +25,12 @@ for “system.data”, even if the attribute value is zero length. Inline Directories ~~~~~~~~~~~~~~~~~~ -The first four bytes of i\_block are the inode number of the parent +The first four bytes of i_block are the inode number of the parent directory. Following that is a 56-byte space for an array of directory entries; see ``struct ext4_dir_entry``. If there is a “system.data” attribute in the inode body, the EA value is an array of ``struct ext4_dir_entry`` as well. Note that for inline directories, the -i\_block and EA space are treated as separate dirent blocks; directory +i_block and EA space are treated as separate dirent blocks; directory entries cannot span the two. Inline directory entries are not checksummed, as the inode checksum diff --git a/Documentation/filesystems/ext4/inodes.rst b/Documentation/filesystems/ext4/inodes.rst index 6c5ce666e63f..cfc6c1659931 100644 --- a/Documentation/filesystems/ext4/inodes.rst +++ b/Documentation/filesystems/ext4/inodes.rst @@ -38,138 +38,138 @@ The inode table entry is laid out in ``struct ext4_inode``. - Name - Description * - 0x0 - - \_\_le16 - - i\_mode + - __le16 + - i_mode - File mode. See the table i_mode_ below. * - 0x2 - - \_\_le16 - - i\_uid + - __le16 + - i_uid - Lower 16-bits of Owner UID. * - 0x4 - - \_\_le32 - - i\_size\_lo + - __le32 + - i_size_lo - Lower 32-bits of size in bytes. * - 0x8 - - \_\_le32 - - i\_atime - - Last access time, in seconds since the epoch. However, if the EA\_INODE + - __le32 + - i_atime + - Last access time, in seconds since the epoch. However, if the EA_INODE inode flag is set, this inode stores an extended attribute value and this field contains the checksum of the value. * - 0xC - - \_\_le32 - - i\_ctime + - __le32 + - i_ctime - Last inode change time, in seconds since the epoch. However, if the - EA\_INODE inode flag is set, this inode stores an extended attribute + EA_INODE inode flag is set, this inode stores an extended attribute value and this field contains the lower 32 bits of the attribute value's reference count. * - 0x10 - - \_\_le32 - - i\_mtime + - __le32 + - i_mtime - Last data modification time, in seconds since the epoch. However, if the - EA\_INODE inode flag is set, this inode stores an extended attribute + EA_INODE inode flag is set, this inode stores an extended attribute value and this field contains the number of the inode that owns the extended attribute. * - 0x14 - - \_\_le32 - - i\_dtime + - __le32 + - i_dtime - Deletion Time, in seconds since the epoch. * - 0x18 - - \_\_le16 - - i\_gid + - __le16 + - i_gid - Lower 16-bits of GID. * - 0x1A - - \_\_le16 - - i\_links\_count + - __le16 + - i_links_count - Hard link count. Normally, ext4 does not permit an inode to have more than 65,000 hard links. This applies to files as well as directories, which means that there cannot be more than 64,998 subdirectories in a directory (each subdirectory's '..' entry counts as a hard link, as does - the '.' entry in the directory itself). With the DIR\_NLINK feature + the '.' entry in the directory itself). With the DIR_NLINK feature enabled, ext4 supports more than 64,998 subdirectories by setting this field to 1 to indicate that the number of hard links is not known. * - 0x1C - - \_\_le32 - - i\_blocks\_lo - - Lower 32-bits of “block” count. If the huge\_file feature flag is not + - __le32 + - i_blocks_lo + - Lower 32-bits of “block” count. If the huge_file feature flag is not set on the filesystem, the file consumes ``i_blocks_lo`` 512-byte blocks - on disk. If huge\_file is set and EXT4\_HUGE\_FILE\_FL is NOT set in + on disk. If huge_file is set and EXT4_HUGE_FILE_FL is NOT set in ``inode.i_flags``, then the file consumes ``i_blocks_lo + (i_blocks_hi - << 32)`` 512-byte blocks on disk. If huge\_file is set and - EXT4\_HUGE\_FILE\_FL IS set in ``inode.i_flags``, then this file + << 32)`` 512-byte blocks on disk. If huge_file is set and + EXT4_HUGE_FILE_FL IS set in ``inode.i_flags``, then this file consumes (``i_blocks_lo + i_blocks_hi`` << 32) filesystem blocks on disk. * - 0x20 - - \_\_le32 - - i\_flags + - __le32 + - i_flags - Inode flags. See the table i_flags_ below. * - 0x24 - 4 bytes - - i\_osd1 + - i_osd1 - See the table i_osd1_ for more details. * - 0x28 - 60 bytes - - i\_block[EXT4\_N\_BLOCKS=15] - - Block map or extent tree. See the section “The Contents of inode.i\_block”. + - i_block[EXT4_N_BLOCKS=15] + - Block map or extent tree. See the section “The Contents of inode.i_block”. * - 0x64 - - \_\_le32 - - i\_generation + - __le32 + - i_generation - File version (for NFS). * - 0x68 - - \_\_le32 - - i\_file\_acl\_lo + - __le32 + - i_file_acl_lo - Lower 32-bits of extended attribute block. ACLs are of course one of many possible extended attributes; I think the name of this field is a result of the first use of extended attributes being for ACLs. * - 0x6C - - \_\_le32 - - i\_size\_high / i\_dir\_acl + - __le32 + - i_size_high / i_dir_acl - Upper 32-bits of file/directory size. In ext2/3 this field was named - i\_dir\_acl, though it was usually set to zero and never used. + i_dir_acl, though it was usually set to zero and never used. * - 0x70 - - \_\_le32 - - i\_obso\_faddr + - __le32 + - i_obso_faddr - (Obsolete) fragment address. * - 0x74 - 12 bytes - - i\_osd2 + - i_osd2 - See the table i_osd2_ for more details. * - 0x80 - - \_\_le16 - - i\_extra\_isize + - __le16 + - i_extra_isize - Size of this inode - 128. Alternately, the size of the extended inode fields beyond the original ext2 inode, including this field. * - 0x82 - - \_\_le16 - - i\_checksum\_hi + - __le16 + - i_checksum_hi - Upper 16-bits of the inode checksum. * - 0x84 - - \_\_le32 - - i\_ctime\_extra + - __le32 + - i_ctime_extra - Extra change time bits. This provides sub-second precision. See Inode Timestamps section. * - 0x88 - - \_\_le32 - - i\_mtime\_extra + - __le32 + - i_mtime_extra - Extra modification time bits. This provides sub-second precision. * - 0x8C - - \_\_le32 - - i\_atime\_extra + - __le32 + - i_atime_extra - Extra access time bits. This provides sub-second precision. * - 0x90 - - \_\_le32 - - i\_crtime + - __le32 + - i_crtime - File creation time, in seconds since the epoch. * - 0x94 - - \_\_le32 - - i\_crtime\_extra + - __le32 + - i_crtime_extra - Extra file creation time bits. This provides sub-second precision. * - 0x98 - - \_\_le32 - - i\_version\_hi + - __le32 + - i_version_hi - Upper 32-bits for version number. * - 0x9C - - \_\_le32 - - i\_projid + - __le32 + - i_projid - Project ID. .. _i_mode: @@ -183,45 +183,45 @@ The ``i_mode`` value is a combination of the following flags: * - Value - Description * - 0x1 - - S\_IXOTH (Others may execute) + - S_IXOTH (Others may execute) * - 0x2 - - S\_IWOTH (Others may write) + - S_IWOTH (Others may write) * - 0x4 - - S\_IROTH (Others may read) + - S_IROTH (Others may read) * - 0x8 - - S\_IXGRP (Group members may execute) + - S_IXGRP (Group members may execute) * - 0x10 - - S\_IWGRP (Group members may write) + - S_IWGRP (Group members may write) * - 0x20 - - S\_IRGRP (Group members may read) + - S_IRGRP (Group members may read) * - 0x40 - - S\_IXUSR (Owner may execute) + - S_IXUSR (Owner may execute) * - 0x80 - - S\_IWUSR (Owner may write) + - S_IWUSR (Owner may write) * - 0x100 - - S\_IRUSR (Owner may read) + - S_IRUSR (Owner may read) * - 0x200 - - S\_ISVTX (Sticky bit) + - S_ISVTX (Sticky bit) * - 0x400 - - S\_ISGID (Set GID) + - S_ISGID (Set GID) * - 0x800 - - S\_ISUID (Set UID) + - S_ISUID (Set UID) * - - These are mutually-exclusive file types: * - 0x1000 - - S\_IFIFO (FIFO) + - S_IFIFO (FIFO) * - 0x2000 - - S\_IFCHR (Character device) + - S_IFCHR (Character device) * - 0x4000 - - S\_IFDIR (Directory) + - S_IFDIR (Directory) * - 0x6000 - - S\_IFBLK (Block device) + - S_IFBLK (Block device) * - 0x8000 - - S\_IFREG (Regular file) + - S_IFREG (Regular file) * - 0xA000 - - S\_IFLNK (Symbolic link) + - S_IFLNK (Symbolic link) * - 0xC000 - - S\_IFSOCK (Socket) + - S_IFSOCK (Socket) .. _i_flags: @@ -234,56 +234,56 @@ The ``i_flags`` field is a combination of these values: * - Value - Description * - 0x1 - - This file requires secure deletion (EXT4\_SECRM\_FL). (not implemented) + - This file requires secure deletion (EXT4_SECRM_FL). (not implemented) * - 0x2 - This file should be preserved, should undeletion be desired - (EXT4\_UNRM\_FL). (not implemented) + (EXT4_UNRM_FL). (not implemented) * - 0x4 - - File is compressed (EXT4\_COMPR\_FL). (not really implemented) + - File is compressed (EXT4_COMPR_FL). (not really implemented) * - 0x8 - - All writes to the file must be synchronous (EXT4\_SYNC\_FL). + - All writes to the file must be synchronous (EXT4_SYNC_FL). * - 0x10 - - File is immutable (EXT4\_IMMUTABLE\_FL). + - File is immutable (EXT4_IMMUTABLE_FL). * - 0x20 - - File can only be appended (EXT4\_APPEND\_FL). + - File can only be appended (EXT4_APPEND_FL). * - 0x40 - - The dump(1) utility should not dump this file (EXT4\_NODUMP\_FL). + - The dump(1) utility should not dump this file (EXT4_NODUMP_FL). * - 0x80 - - Do not update access time (EXT4\_NOATIME\_FL). + - Do not update access time (EXT4_NOATIME_FL). * - 0x100 - - Dirty compressed file (EXT4\_DIRTY\_FL). (not used) + - Dirty compressed file (EXT4_DIRTY_FL). (not used) * - 0x200 - - File has one or more compressed clusters (EXT4\_COMPRBLK\_FL). (not used) + - File has one or more compressed clusters (EXT4_COMPRBLK_FL). (not used) * - 0x400 - - Do not compress file (EXT4\_NOCOMPR\_FL). (not used) + - Do not compress file (EXT4_NOCOMPR_FL). (not used) * - 0x800 - - Encrypted inode (EXT4\_ENCRYPT\_FL). This bit value previously was - EXT4\_ECOMPR\_FL (compression error), which was never used. + - Encrypted inode (EXT4_ENCRYPT_FL). This bit value previously was + EXT4_ECOMPR_FL (compression error), which was never used. * - 0x1000 - - Directory has hashed indexes (EXT4\_INDEX\_FL). + - Directory has hashed indexes (EXT4_INDEX_FL). * - 0x2000 - - AFS magic directory (EXT4\_IMAGIC\_FL). + - AFS magic directory (EXT4_IMAGIC_FL). * - 0x4000 - File data must always be written through the journal - (EXT4\_JOURNAL\_DATA\_FL). + (EXT4_JOURNAL_DATA_FL). * - 0x8000 - - File tail should not be merged (EXT4\_NOTAIL\_FL). (not used by ext4) + - File tail should not be merged (EXT4_NOTAIL_FL). (not used by ext4) * - 0x10000 - All directory entry data should be written synchronously (see - ``dirsync``) (EXT4\_DIRSYNC\_FL). + ``dirsync``) (EXT4_DIRSYNC_FL). * - 0x20000 - - Top of directory hierarchy (EXT4\_TOPDIR\_FL). + - Top of directory hierarchy (EXT4_TOPDIR_FL). * - 0x40000 - - This is a huge file (EXT4\_HUGE\_FILE\_FL). + - This is a huge file (EXT4_HUGE_FILE_FL). * - 0x80000 - - Inode uses extents (EXT4\_EXTENTS\_FL). + - Inode uses extents (EXT4_EXTENTS_FL). * - 0x100000 - - Verity protected file (EXT4\_VERITY\_FL). + - Verity protected file (EXT4_VERITY_FL). * - 0x200000 - Inode stores a large extended attribute value in its data blocks - (EXT4\_EA\_INODE\_FL). + (EXT4_EA_INODE_FL). * - 0x400000 - - This file has blocks allocated past EOF (EXT4\_EOFBLOCKS\_FL). + - This file has blocks allocated past EOF (EXT4_EOFBLOCKS_FL). (deprecated) * - 0x01000000 - Inode is a snapshot (``EXT4_SNAPFILE_FL``). (not in mainline) @@ -294,21 +294,21 @@ The ``i_flags`` field is a combination of these values: - Snapshot shrink has completed (``EXT4_SNAPFILE_SHRUNK_FL``). (not in mainline) * - 0x10000000 - - Inode has inline data (EXT4\_INLINE\_DATA\_FL). + - Inode has inline data (EXT4_INLINE_DATA_FL). * - 0x20000000 - - Create children with the same project ID (EXT4\_PROJINHERIT\_FL). + - Create children with the same project ID (EXT4_PROJINHERIT_FL). * - 0x80000000 - - Reserved for ext4 library (EXT4\_RESERVED\_FL). + - Reserved for ext4 library (EXT4_RESERVED_FL). * - - Aggregate flags: * - 0x705BDFFF - User-visible flags. * - 0x604BC0FF - - User-modifiable flags. Note that while EXT4\_JOURNAL\_DATA\_FL and - EXT4\_EXTENTS\_FL can be set with setattr, they are not in the kernel's - EXT4\_FL\_USER\_MODIFIABLE mask, since it needs to handle the setting of + - User-modifiable flags. Note that while EXT4_JOURNAL_DATA_FL and + EXT4_EXTENTS_FL can be set with setattr, they are not in the kernel's + EXT4_FL_USER_MODIFIABLE mask, since it needs to handle the setting of these flags in a special manner and they are masked out of the set of - flags that are saved directly to i\_flags. + flags that are saved directly to i_flags. .. _i_osd1: @@ -325,9 +325,9 @@ Linux: - Name - Description * - 0x0 - - \_\_le32 - - l\_i\_version - - Inode version. However, if the EA\_INODE inode flag is set, this inode + - __le32 + - l_i_version + - Inode version. However, if the EA_INODE inode flag is set, this inode stores an extended attribute value and this field contains the upper 32 bits of the attribute value's reference count. @@ -342,8 +342,8 @@ Hurd: - Name - Description * - 0x0 - - \_\_le32 - - h\_i\_translator + - __le32 + - h_i_translator - ?? Masix: @@ -357,8 +357,8 @@ Masix: - Name - Description * - 0x0 - - \_\_le32 - - m\_i\_reserved + - __le32 + - m_i_reserved - ?? .. _i_osd2: @@ -376,30 +376,30 @@ Linux: - Name - Description * - 0x0 - - \_\_le16 - - l\_i\_blocks\_high + - __le16 + - l_i_blocks_high - Upper 16-bits of the block count. Please see the note attached to - i\_blocks\_lo. + i_blocks_lo. * - 0x2 - - \_\_le16 - - l\_i\_file\_acl\_high + - __le16 + - l_i_file_acl_high - Upper 16-bits of the extended attribute block (historically, the file ACL location). See the Extended Attributes section below. * - 0x4 - - \_\_le16 - - l\_i\_uid\_high + - __le16 + - l_i_uid_high - Upper 16-bits of the Owner UID. * - 0x6 - - \_\_le16 - - l\_i\_gid\_high + - __le16 + - l_i_gid_high - Upper 16-bits of the GID. * - 0x8 - - \_\_le16 - - l\_i\_checksum\_lo + - __le16 + - l_i_checksum_lo - Lower 16-bits of the inode checksum. * - 0xA - - \_\_le16 - - l\_i\_reserved + - __le16 + - l_i_reserved - Unused. Hurd: @@ -413,24 +413,24 @@ Hurd: - Name - Description * - 0x0 - - \_\_le16 - - h\_i\_reserved1 + - __le16 + - h_i_reserved1 - ?? * - 0x2 - - \_\_u16 - - h\_i\_mode\_high + - __u16 + - h_i_mode_high - Upper 16-bits of the file mode. * - 0x4 - - \_\_le16 - - h\_i\_uid\_high + - __le16 + - h_i_uid_high - Upper 16-bits of the Owner UID. * - 0x6 - - \_\_le16 - - h\_i\_gid\_high + - __le16 + - h_i_gid_high - Upper 16-bits of the GID. * - 0x8 - - \_\_u32 - - h\_i\_author + - __u32 + - h_i_author - Author code? Masix: @@ -444,17 +444,17 @@ Masix: - Name - Description * - 0x0 - - \_\_le16 - - h\_i\_reserved1 + - __le16 + - h_i_reserved1 - ?? * - 0x2 - - \_\_u16 - - m\_i\_file\_acl\_high + - __u16 + - m_i_file_acl_high - Upper 16-bits of the extended attribute block (historically, the file ACL location). * - 0x4 - - \_\_u32 - - m\_i\_reserved2[2] + - __u32 + - m_i_reserved2[2] - ?? Inode Size @@ -466,11 +466,11 @@ In ext2 and ext3, the inode structure size was fixed at 128 bytes on-disk inode at format time for all inodes in the filesystem to provide space beyond the end of the original ext2 inode. The on-disk inode record size is recorded in the superblock as ``s_inode_size``. The -number of bytes actually used by struct ext4\_inode beyond the original +number of bytes actually used by struct ext4_inode beyond the original 128-byte ext2 inode is recorded in the ``i_extra_isize`` field for each -inode, which allows struct ext4\_inode to grow for a new kernel without +inode, which allows struct ext4_inode to grow for a new kernel without having to upgrade all of the on-disk inodes. Access to fields beyond -EXT2\_GOOD\_OLD\_INODE\_SIZE should be verified to be within +EXT2_GOOD_OLD_INODE_SIZE should be verified to be within ``i_extra_isize``. By default, ext4 inode records are 256 bytes, and (as of August 2019) the inode structure is 160 bytes (``i_extra_isize = 32``). The extra space between the end of the inode @@ -516,7 +516,7 @@ creation time (crtime); this field is 64-bits wide and decoded in the same manner as 64-bit [cma]time. Neither crtime nor dtime are accessible through the regular stat() interface, though debugfs will report them. -We use the 32-bit signed time value plus (2^32 \* (extra epoch bits)). +We use the 32-bit signed time value plus (2^32 * (extra epoch bits)). In other words: .. list-table:: @@ -525,8 +525,8 @@ In other words: * - Extra epoch bits - MSB of 32-bit time - - Adjustment for signed 32-bit to 64-bit tv\_sec - - Decoded 64-bit tv\_sec + - Adjustment for signed 32-bit to 64-bit tv_sec + - Decoded 64-bit tv_sec - valid time range * - 0 0 - 1 diff --git a/Documentation/filesystems/ext4/journal.rst b/Documentation/filesystems/ext4/journal.rst index 5fad38860f17..a6bef5293a60 100644 --- a/Documentation/filesystems/ext4/journal.rst +++ b/Documentation/filesystems/ext4/journal.rst @@ -63,8 +63,8 @@ Generally speaking, the journal has this format: :header-rows: 1 * - Superblock - - descriptor\_block (data\_blocks or revocation\_block) [more data or - revocations] commmit\_block + - descriptor_block (data_blocks or revocation_block) [more data or + revocations] commmit_block - [more transactions...] * - - One transaction @@ -93,8 +93,8 @@ superblock. * - 1024 bytes of padding - ext4 Superblock - Journal Superblock - - descriptor\_block (data\_blocks or revocation\_block) [more data or - revocations] commmit\_block + - descriptor_block (data_blocks or revocation_block) [more data or + revocations] commmit_block - [more transactions...] * - - @@ -117,17 +117,17 @@ Every block in the journal starts with a common 12-byte header - Name - Description * - 0x0 - - \_\_be32 - - h\_magic + - __be32 + - h_magic - jbd2 magic number, 0xC03B3998. * - 0x4 - - \_\_be32 - - h\_blocktype + - __be32 + - h_blocktype - Description of what this block contains. See the jbd2_blocktype_ table below. * - 0x8 - - \_\_be32 - - h\_sequence + - __be32 + - h_sequence - The transaction ID that goes with this block. .. _jbd2_blocktype: @@ -177,99 +177,99 @@ which is 1024 bytes long: - - Static information describing the journal. * - 0x0 - - journal\_header\_t (12 bytes) - - s\_header + - journal_header_t (12 bytes) + - s_header - Common header identifying this as a superblock. * - 0xC - - \_\_be32 - - s\_blocksize + - __be32 + - s_blocksize - Journal device block size. * - 0x10 - - \_\_be32 - - s\_maxlen + - __be32 + - s_maxlen - Total number of blocks in this journal. * - 0x14 - - \_\_be32 - - s\_first + - __be32 + - s_first - First block of log information. * - - - - Dynamic information describing the current state of the log. * - 0x18 - - \_\_be32 - - s\_sequence + - __be32 + - s_sequence - First commit ID expected in log. * - 0x1C - - \_\_be32 - - s\_start + - __be32 + - s_start - Block number of the start of log. Contrary to the comments, this field being zero does not imply that the journal is clean! * - 0x20 - - \_\_be32 - - s\_errno - - Error value, as set by jbd2\_journal\_abort(). + - __be32 + - s_errno + - Error value, as set by jbd2_journal_abort(). * - - - - The remaining fields are only valid in a v2 superblock. * - 0x24 - - \_\_be32 - - s\_feature\_compat; + - __be32 + - s_feature_compat; - Compatible feature set. See the table jbd2_compat_ below. * - 0x28 - - \_\_be32 - - s\_feature\_incompat + - __be32 + - s_feature_incompat - Incompatible feature set. See the table jbd2_incompat_ below. * - 0x2C - - \_\_be32 - - s\_feature\_ro\_compat + - __be32 + - s_feature_ro_compat - Read-only compatible feature set. There aren't any of these currently. * - 0x30 - - \_\_u8 - - s\_uuid[16] + - __u8 + - s_uuid[16] - 128-bit uuid for journal. This is compared against the copy in the ext4 super block at mount time. * - 0x40 - - \_\_be32 - - s\_nr\_users + - __be32 + - s_nr_users - Number of file systems sharing this journal. * - 0x44 - - \_\_be32 - - s\_dynsuper + - __be32 + - s_dynsuper - Location of dynamic super block copy. (Not used?) * - 0x48 - - \_\_be32 - - s\_max\_transaction + - __be32 + - s_max_transaction - Limit of journal blocks per transaction. (Not used?) * - 0x4C - - \_\_be32 - - s\_max\_trans\_data + - __be32 + - s_max_trans_data - Limit of data blocks per transaction. (Not used?) * - 0x50 - - \_\_u8 - - s\_checksum\_type + - __u8 + - s_checksum_type - Checksum algorithm used for the journal. See jbd2_checksum_type_ for more info. * - 0x51 - - \_\_u8[3] - - s\_padding2 + - __u8[3] + - s_padding2 - * - 0x54 - - \_\_be32 - - s\_num\_fc\_blocks + - __be32 + - s_num_fc_blocks - Number of fast commit blocks in the journal. * - 0x58 - - \_\_u32 - - s\_padding[42] + - __u32 + - s_padding[42] - * - 0xFC - - \_\_be32 - - s\_checksum + - __be32 + - s_checksum - Checksum of the entire superblock, with this field set to zero. * - 0x100 - - \_\_u8 - - s\_users[16\*48] + - __u8 + - s_users[16*48] - ids of all file systems sharing the log. e2fsprogs/Linux don't allow shared external journals, but I imagine Lustre (or ocfs2?), which use the jbd2 code, might. @@ -286,7 +286,7 @@ The journal compat features are any combination of the following: - Description * - 0x1 - Journal maintains checksums on the data blocks. - (JBD2\_FEATURE\_COMPAT\_CHECKSUM) + (JBD2_FEATURE_COMPAT_CHECKSUM) .. _jbd2_incompat: @@ -299,23 +299,23 @@ The journal incompat features are any combination of the following: * - Value - Description * - 0x1 - - Journal has block revocation records. (JBD2\_FEATURE\_INCOMPAT\_REVOKE) + - Journal has block revocation records. (JBD2_FEATURE_INCOMPAT_REVOKE) * - 0x2 - Journal can deal with 64-bit block numbers. - (JBD2\_FEATURE\_INCOMPAT\_64BIT) + (JBD2_FEATURE_INCOMPAT_64BIT) * - 0x4 - - Journal commits asynchronously. (JBD2\_FEATURE\_INCOMPAT\_ASYNC\_COMMIT) + - Journal commits asynchronously. (JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT) * - 0x8 - This journal uses v2 of the checksum on-disk format. Each journal metadata block gets its own checksum, and the block tags in the descriptor table contain checksums for each of the data blocks in the - journal. (JBD2\_FEATURE\_INCOMPAT\_CSUM\_V2) + journal. (JBD2_FEATURE_INCOMPAT_CSUM_V2) * - 0x10 - This journal uses v3 of the checksum on-disk format. This is the same as v2, but the journal block tag size is fixed regardless of the size of - block numbers. (JBD2\_FEATURE\_INCOMPAT\_CSUM\_V3) + block numbers. (JBD2_FEATURE_INCOMPAT_CSUM_V3) * - 0x20 - - Journal has fast commit blocks. (JBD2\_FEATURE\_INCOMPAT\_FAST\_COMMIT) + - Journal has fast commit blocks. (JBD2_FEATURE_INCOMPAT_FAST_COMMIT) .. _jbd2_checksum_type: @@ -355,11 +355,11 @@ Descriptor blocks consume at least 36 bytes, but use a full block: - Name - Descriptor * - 0x0 - - journal\_header\_t + - journal_header_t - (open coded) - Common block header. * - 0xC - - struct journal\_block\_tag\_s + - struct journal_block_tag_s - open coded array[] - Enough tags either to fill up the block or to describe all the data blocks that follow this descriptor block. @@ -367,7 +367,7 @@ Descriptor blocks consume at least 36 bytes, but use a full block: Journal block tags have any of the following formats, depending on which journal feature and block tag flags are set. -If JBD2\_FEATURE\_INCOMPAT\_CSUM\_V3 is set, the journal block tag is +If JBD2_FEATURE_INCOMPAT_CSUM_V3 is set, the journal block tag is defined as ``struct journal_block_tag3_s``, which looks like the following. The size is 16 or 32 bytes. @@ -380,24 +380,24 @@ following. The size is 16 or 32 bytes. - Name - Descriptor * - 0x0 - - \_\_be32 - - t\_blocknr + - __be32 + - t_blocknr - Lower 32-bits of the location of where the corresponding data block should end up on disk. * - 0x4 - - \_\_be32 - - t\_flags + - __be32 + - t_flags - Flags that go with the descriptor. See the table jbd2_tag_flags_ for more info. * - 0x8 - - \_\_be32 - - t\_blocknr\_high + - __be32 + - t_blocknr_high - Upper 32-bits of the location of where the corresponding data block - should end up on disk. This is zero if JBD2\_FEATURE\_INCOMPAT\_64BIT is + should end up on disk. This is zero if JBD2_FEATURE_INCOMPAT_64BIT is not enabled. * - 0xC - - \_\_be32 - - t\_checksum + - __be32 + - t_checksum - Checksum of the journal UUID, the sequence number, and the data block. * - - @@ -433,7 +433,7 @@ The journal tag flags are any combination of the following: * - 0x8 - This is the last tag in this descriptor block. -If JBD2\_FEATURE\_INCOMPAT\_CSUM\_V3 is NOT set, the journal block tag +If JBD2_FEATURE_INCOMPAT_CSUM_V3 is NOT set, the journal block tag is defined as ``struct journal_block_tag_s``, which looks like the following. The size is 8, 12, 24, or 28 bytes: @@ -446,18 +446,18 @@ following. The size is 8, 12, 24, or 28 bytes: - Name - Descriptor * - 0x0 - - \_\_be32 - - t\_blocknr + - __be32 + - t_blocknr - Lower 32-bits of the location of where the corresponding data block should end up on disk. * - 0x4 - - \_\_be16 - - t\_checksum + - __be16 + - t_checksum - Checksum of the journal UUID, the sequence number, and the data block. Note that only the lower 16 bits are stored. * - 0x6 - - \_\_be16 - - t\_flags + - __be16 + - t_flags - Flags that go with the descriptor. See the table jbd2_tag_flags_ for more info. * - @@ -466,8 +466,8 @@ following. The size is 8, 12, 24, or 28 bytes: - This next field is only present if the super block indicates support for 64-bit block numbers. * - 0x8 - - \_\_be32 - - t\_blocknr\_high + - __be32 + - t_blocknr_high - Upper 32-bits of the location of where the corresponding data block should end up on disk. * - @@ -483,8 +483,8 @@ following. The size is 8, 12, 24, or 28 bytes: ``j_uuid`` field in ``struct journal_s``, but only tune2fs touches that field. -If JBD2\_FEATURE\_INCOMPAT\_CSUM\_V2 or -JBD2\_FEATURE\_INCOMPAT\_CSUM\_V3 are set, the end of the block is a +If JBD2_FEATURE_INCOMPAT_CSUM_V2 or +JBD2_FEATURE_INCOMPAT_CSUM_V3 are set, the end of the block is a ``struct jbd2_journal_block_tail``, which looks like this: .. list-table:: @@ -496,8 +496,8 @@ JBD2\_FEATURE\_INCOMPAT\_CSUM\_V3 are set, the end of the block is a - Name - Descriptor * - 0x0 - - \_\_be32 - - t\_checksum + - __be32 + - t_checksum - Checksum of the journal UUID + the descriptor block, with this field set to zero. @@ -538,25 +538,25 @@ length, but use a full block: - Name - Description * - 0x0 - - journal\_header\_t - - r\_header + - journal_header_t + - r_header - Common block header. * - 0xC - - \_\_be32 - - r\_count + - __be32 + - r_count - Number of bytes used in this block. * - 0x10 - - \_\_be32 or \_\_be64 + - __be32 or __be64 - blocks[0] - Blocks to revoke. -After r\_count is a linear array of block numbers that are effectively +After r_count is a linear array of block numbers that are effectively revoked by this transaction. The size of each block number is 8 bytes if the superblock advertises 64-bit block number support, or 4 bytes otherwise. -If JBD2\_FEATURE\_INCOMPAT\_CSUM\_V2 or -JBD2\_FEATURE\_INCOMPAT\_CSUM\_V3 are set, the end of the revocation +If JBD2_FEATURE_INCOMPAT_CSUM_V2 or +JBD2_FEATURE_INCOMPAT_CSUM_V3 are set, the end of the revocation block is a ``struct jbd2_journal_revoke_tail``, which has this format: .. list-table:: @@ -568,8 +568,8 @@ block is a ``struct jbd2_journal_revoke_tail``, which has this format: - Name - Description * - 0x0 - - \_\_be32 - - r\_checksum + - __be32 + - r_checksum - Checksum of the journal UUID + revocation block Commit Block @@ -592,38 +592,38 @@ bytes long (but uses a full block): - Name - Descriptor * - 0x0 - - journal\_header\_s + - journal_header_s - (open coded) - Common block header. * - 0xC - unsigned char - - h\_chksum\_type + - h_chksum_type - The type of checksum to use to verify the integrity of the data blocks in the transaction. See jbd2_checksum_type_ for more info. * - 0xD - unsigned char - - h\_chksum\_size + - h_chksum_size - The number of bytes used by the checksum. Most likely 4. * - 0xE - unsigned char - - h\_padding[2] + - h_padding[2] - * - 0x10 - - \_\_be32 - - h\_chksum[JBD2\_CHECKSUM\_BYTES] + - __be32 + - h_chksum[JBD2_CHECKSUM_BYTES] - 32 bytes of space to store checksums. If - JBD2\_FEATURE\_INCOMPAT\_CSUM\_V2 or JBD2\_FEATURE\_INCOMPAT\_CSUM\_V3 + JBD2_FEATURE_INCOMPAT_CSUM_V2 or JBD2_FEATURE_INCOMPAT_CSUM_V3 are set, the first ``__be32`` is the checksum of the journal UUID and the entire commit block, with this field zeroed. If - JBD2\_FEATURE\_COMPAT\_CHECKSUM is set, the first ``__be32`` is the + JBD2_FEATURE_COMPAT_CHECKSUM is set, the first ``__be32`` is the crc32 of all the blocks already written to the transaction. * - 0x30 - - \_\_be64 - - h\_commit\_sec + - __be64 + - h_commit_sec - The time that the transaction was committed, in seconds since the epoch. * - 0x38 - - \_\_be32 - - h\_commit\_nsec + - __be32 + - h_commit_nsec - Nanoseconds component of the above timestamp. Fast commits diff --git a/Documentation/filesystems/ext4/mmp.rst b/Documentation/filesystems/ext4/mmp.rst index 25660981d93c..174dd6538737 100644 --- a/Documentation/filesystems/ext4/mmp.rst +++ b/Documentation/filesystems/ext4/mmp.rst @@ -7,8 +7,8 @@ Multiple mount protection (MMP) is a feature that protects the filesystem against multiple hosts trying to use the filesystem simultaneously. When a filesystem is opened (for mounting, or fsck, etc.), the MMP code running on the node (call it node A) checks a -sequence number. If the sequence number is EXT4\_MMP\_SEQ\_CLEAN, the -open continues. If the sequence number is EXT4\_MMP\_SEQ\_FSCK, then +sequence number. If the sequence number is EXT4_MMP_SEQ_CLEAN, the +open continues. If the sequence number is EXT4_MMP_SEQ_FSCK, then fsck is (hopefully) running, and open fails immediately. Otherwise, the open code will wait for twice the specified MMP check interval and check the sequence number again. If the sequence number has changed, then the @@ -40,38 +40,38 @@ The MMP structure (``struct mmp_struct``) is as follows: - Name - Description * - 0x0 - - \_\_le32 - - mmp\_magic + - __le32 + - mmp_magic - Magic number for MMP, 0x004D4D50 (“MMP”). * - 0x4 - - \_\_le32 - - mmp\_seq + - __le32 + - mmp_seq - Sequence number, updated periodically. * - 0x8 - - \_\_le64 - - mmp\_time + - __le64 + - mmp_time - Time that the MMP block was last updated. * - 0x10 - char[64] - - mmp\_nodename + - mmp_nodename - Hostname of the node that opened the filesystem. * - 0x50 - char[32] - - mmp\_bdevname + - mmp_bdevname - Block device name of the filesystem. * - 0x70 - - \_\_le16 - - mmp\_check\_interval + - __le16 + - mmp_check_interval - The MMP re-check interval, in seconds. * - 0x72 - - \_\_le16 - - mmp\_pad1 + - __le16 + - mmp_pad1 - Zero. * - 0x74 - - \_\_le32[226] - - mmp\_pad2 + - __le32[226] + - mmp_pad2 - Zero. * - 0x3FC - - \_\_le32 - - mmp\_checksum + - __le32 + - mmp_checksum - Checksum of the MMP block. diff --git a/Documentation/filesystems/ext4/overview.rst b/Documentation/filesystems/ext4/overview.rst index 123ebfde47ee..0fad6eda6e15 100644 --- a/Documentation/filesystems/ext4/overview.rst +++ b/Documentation/filesystems/ext4/overview.rst @@ -7,7 +7,7 @@ An ext4 file system is split into a series of block groups. To reduce performance difficulties due to fragmentation, the block allocator tries very hard to keep each file's blocks within the same group, thereby reducing seek times. The size of a block group is specified in -``sb.s_blocks_per_group`` blocks, though it can also calculated as 8 \* +``sb.s_blocks_per_group`` blocks, though it can also calculated as 8 * ``block_size_in_bytes``. With the default block size of 4KiB, each group will contain 32,768 blocks, for a length of 128MiB. The number of block groups is the size of the device divided by the size of a block group. diff --git a/Documentation/filesystems/ext4/special_inodes.rst b/Documentation/filesystems/ext4/special_inodes.rst index 94f304e3a0a7..fc0636901fa0 100644 --- a/Documentation/filesystems/ext4/special_inodes.rst +++ b/Documentation/filesystems/ext4/special_inodes.rst @@ -34,7 +34,7 @@ ext4 reserves some inode for special features, as follows: * - 10 - Replica inode, used for some non-upstream feature? * - 11 - - Traditional first non-reserved inode. Usually this is the lost+found directory. See s\_first\_ino in the superblock. + - Traditional first non-reserved inode. Usually this is the lost+found directory. See s_first_ino in the superblock. Note that there are also some inodes allocated from non-reserved inode numbers for other filesystem features which are not referenced from standard directory @@ -47,9 +47,9 @@ hierarchy. These are generally reference from the superblock. They are: * - Superblock field - Description - * - s\_lpf\_ino + * - s_lpf_ino - Inode number of lost+found directory. - * - s\_prj\_quota\_inum + * - s_prj_quota_inum - Inode number of quota file tracking project quotas - * - s\_orphan\_file\_inum + * - s_orphan_file_inum - Inode number of file tracking orphan inodes. diff --git a/Documentation/filesystems/ext4/super.rst b/Documentation/filesystems/ext4/super.rst index f6a548e957bb..0152888cac29 100644 --- a/Documentation/filesystems/ext4/super.rst +++ b/Documentation/filesystems/ext4/super.rst @@ -7,7 +7,7 @@ The superblock records various information about the enclosing filesystem, such as block counts, inode counts, supported features, maintenance information, and more. -If the sparse\_super feature flag is set, redundant copies of the +If the sparse_super feature flag is set, redundant copies of the superblock and group descriptors are kept only in the groups whose group number is either 0 or a power of 3, 5, or 7. If the flag is not set, redundant copies are kept in all groups. @@ -27,107 +27,107 @@ The ext4 superblock is laid out as follows in - Name - Description * - 0x0 - - \_\_le32 - - s\_inodes\_count + - __le32 + - s_inodes_count - Total inode count. * - 0x4 - - \_\_le32 - - s\_blocks\_count\_lo + - __le32 + - s_blocks_count_lo - Total block count. * - 0x8 - - \_\_le32 - - s\_r\_blocks\_count\_lo + - __le32 + - s_r_blocks_count_lo - This number of blocks can only be allocated by the super-user. * - 0xC - - \_\_le32 - - s\_free\_blocks\_count\_lo + - __le32 + - s_free_blocks_count_lo - Free block count. * - 0x10 - - \_\_le32 - - s\_free\_inodes\_count + - __le32 + - s_free_inodes_count - Free inode count. * - 0x14 - - \_\_le32 - - s\_first\_data\_block + - __le32 + - s_first_data_block - First data block. This must be at least 1 for 1k-block filesystems and is typically 0 for all other block sizes. * - 0x18 - - \_\_le32 - - s\_log\_block\_size - - Block size is 2 ^ (10 + s\_log\_block\_size). + - __le32 + - s_log_block_size + - Block size is 2 ^ (10 + s_log_block_size). * - 0x1C - - \_\_le32 - - s\_log\_cluster\_size - - Cluster size is 2 ^ (10 + s\_log\_cluster\_size) blocks if bigalloc is - enabled. Otherwise s\_log\_cluster\_size must equal s\_log\_block\_size. + - __le32 + - s_log_cluster_size + - Cluster size is 2 ^ (10 + s_log_cluster_size) blocks if bigalloc is + enabled. Otherwise s_log_cluster_size must equal s_log_block_size. * - 0x20 - - \_\_le32 - - s\_blocks\_per\_group + - __le32 + - s_blocks_per_group - Blocks per group. * - 0x24 - - \_\_le32 - - s\_clusters\_per\_group + - __le32 + - s_clusters_per_group - Clusters per group, if bigalloc is enabled. Otherwise - s\_clusters\_per\_group must equal s\_blocks\_per\_group. + s_clusters_per_group must equal s_blocks_per_group. * - 0x28 - - \_\_le32 - - s\_inodes\_per\_group + - __le32 + - s_inodes_per_group - Inodes per group. * - 0x2C - - \_\_le32 - - s\_mtime + - __le32 + - s_mtime - Mount time, in seconds since the epoch. * - 0x30 - - \_\_le32 - - s\_wtime + - __le32 + - s_wtime - Write time, in seconds since the epoch. * - 0x34 - - \_\_le16 - - s\_mnt\_count + - __le16 + - s_mnt_count - Number of mounts since the last fsck. * - 0x36 - - \_\_le16 - - s\_max\_mnt\_count + - __le16 + - s_max_mnt_count - Number of mounts beyond which a fsck is needed. * - 0x38 - - \_\_le16 - - s\_magic + - __le16 + - s_magic - Magic signature, 0xEF53 * - 0x3A - - \_\_le16 - - s\_state + - __le16 + - s_state - File system state. See super_state_ for more info. * - 0x3C - - \_\_le16 - - s\_errors + - __le16 + - s_errors - Behaviour when detecting errors. See super_errors_ for more info. * - 0x3E - - \_\_le16 - - s\_minor\_rev\_level + - __le16 + - s_minor_rev_level - Minor revision level. * - 0x40 - - \_\_le32 - - s\_lastcheck + - __le32 + - s_lastcheck - Time of last check, in seconds since the epoch. * - 0x44 - - \_\_le32 - - s\_checkinterval + - __le32 + - s_checkinterval - Maximum time between checks, in seconds. * - 0x48 - - \_\_le32 - - s\_creator\_os + - __le32 + - s_creator_os - Creator OS. See the table super_creator_ for more info. * - 0x4C - - \_\_le32 - - s\_rev\_level + - __le32 + - s_rev_level - Revision level. See the table super_revision_ for more info. * - 0x50 - - \_\_le16 - - s\_def\_resuid + - __le16 + - s_def_resuid - Default uid for reserved blocks. * - 0x52 - - \_\_le16 - - s\_def\_resgid + - __le16 + - s_def_resgid - Default gid for reserved blocks. * - - @@ -143,50 +143,50 @@ The ext4 superblock is laid out as follows in about a feature in either the compatible or incompatible feature set, it must abort and not try to meddle with things it doesn't understand... * - 0x54 - - \_\_le32 - - s\_first\_ino + - __le32 + - s_first_ino - First non-reserved inode. * - 0x58 - - \_\_le16 - - s\_inode\_size + - __le16 + - s_inode_size - Size of inode structure, in bytes. * - 0x5A - - \_\_le16 - - s\_block\_group\_nr + - __le16 + - s_block_group_nr - Block group # of this superblock. * - 0x5C - - \_\_le32 - - s\_feature\_compat + - __le32 + - s_feature_compat - Compatible feature set flags. Kernel can still read/write this fs even if it doesn't understand a flag; fsck should not do that. See the super_compat_ table for more info. * - 0x60 - - \_\_le32 - - s\_feature\_incompat + - __le32 + - s_feature_incompat - Incompatible feature set. If the kernel or fsck doesn't understand one of these bits, it should stop. See the super_incompat_ table for more info. * - 0x64 - - \_\_le32 - - s\_feature\_ro\_compat + - __le32 + - s_feature_ro_compat - Readonly-compatible feature set. If the kernel doesn't understand one of these bits, it can still mount read-only. See the super_rocompat_ table for more info. * - 0x68 - - \_\_u8 - - s\_uuid[16] + - __u8 + - s_uuid[16] - 128-bit UUID for volume. * - 0x78 - char - - s\_volume\_name[16] + - s_volume_name[16] - Volume label. * - 0x88 - char - - s\_last\_mounted[64] + - s_last_mounted[64] - Directory where filesystem was last mounted. * - 0xC8 - - \_\_le32 - - s\_algorithm\_usage\_bitmap + - __le32 + - s_algorithm_usage_bitmap - For compression (Not used in e2fsprogs/Linux) * - - @@ -194,18 +194,18 @@ The ext4 superblock is laid out as follows in - Performance hints. Directory preallocation should only happen if the EXT4_FEATURE_COMPAT_DIR_PREALLOC flag is on. * - 0xCC - - \_\_u8 - - s\_prealloc\_blocks + - __u8 + - s_prealloc_blocks - #. of blocks to try to preallocate for ... files? (Not used in e2fsprogs/Linux) * - 0xCD - - \_\_u8 - - s\_prealloc\_dir\_blocks + - __u8 + - s_prealloc_dir_blocks - #. of blocks to preallocate for directories. (Not used in e2fsprogs/Linux) * - 0xCE - - \_\_le16 - - s\_reserved\_gdt\_blocks + - __le16 + - s_reserved_gdt_blocks - Number of reserved GDT entries for future filesystem expansion. * - - @@ -213,281 +213,281 @@ The ext4 superblock is laid out as follows in - Journalling support is valid only if EXT4_FEATURE_COMPAT_HAS_JOURNAL is set. * - 0xD0 - - \_\_u8 - - s\_journal\_uuid[16] + - __u8 + - s_journal_uuid[16] - UUID of journal superblock * - 0xE0 - - \_\_le32 - - s\_journal\_inum + - __le32 + - s_journal_inum - inode number of journal file. * - 0xE4 - - \_\_le32 - - s\_journal\_dev + - __le32 + - s_journal_dev - Device number of journal file, if the external journal feature flag is set. * - 0xE8 - - \_\_le32 - - s\_last\_orphan + - __le32 + - s_last_orphan - Start of list of orphaned inodes to delete. * - 0xEC - - \_\_le32 - - s\_hash\_seed[4] + - __le32 + - s_hash_seed[4] - HTREE hash seed. * - 0xFC - - \_\_u8 - - s\_def\_hash\_version + - __u8 + - s_def_hash_version - Default hash algorithm to use for directory hashes. See super_def_hash_ for more info. * - 0xFD - - \_\_u8 - - s\_jnl\_backup\_type - - If this value is 0 or EXT3\_JNL\_BACKUP\_BLOCKS (1), then the + - __u8 + - s_jnl_backup_type + - If this value is 0 or EXT3_JNL_BACKUP_BLOCKS (1), then the ``s_jnl_blocks`` field contains a duplicate copy of the inode's ``i_block[]`` array and ``i_size``. * - 0xFE - - \_\_le16 - - s\_desc\_size + - __le16 + - s_desc_size - Size of group descriptors, in bytes, if the 64bit incompat feature flag is set. * - 0x100 - - \_\_le32 - - s\_default\_mount\_opts + - __le32 + - s_default_mount_opts - Default mount options. See the super_mountopts_ table for more info. * - 0x104 - - \_\_le32 - - s\_first\_meta\_bg - - First metablock block group, if the meta\_bg feature is enabled. + - __le32 + - s_first_meta_bg + - First metablock block group, if the meta_bg feature is enabled. * - 0x108 - - \_\_le32 - - s\_mkfs\_time + - __le32 + - s_mkfs_time - When the filesystem was created, in seconds since the epoch. * - 0x10C - - \_\_le32 - - s\_jnl\_blocks[17] + - __le32 + - s_jnl_blocks[17] - Backup copy of the journal inode's ``i_block[]`` array in the first 15 - elements and i\_size\_high and i\_size in the 16th and 17th elements, + elements and i_size_high and i_size in the 16th and 17th elements, respectively. * - - - - 64bit support is valid only if EXT4_FEATURE_COMPAT_64BIT is set. * - 0x150 - - \_\_le32 - - s\_blocks\_count\_hi + - __le32 + - s_blocks_count_hi - High 32-bits of the block count. * - 0x154 - - \_\_le32 - - s\_r\_blocks\_count\_hi + - __le32 + - s_r_blocks_count_hi - High 32-bits of the reserved block count. * - 0x158 - - \_\_le32 - - s\_free\_blocks\_count\_hi + - __le32 + - s_free_blocks_count_hi - High 32-bits of the free block count. * - 0x15C - - \_\_le16 - - s\_min\_extra\_isize + - __le16 + - s_min_extra_isize - All inodes have at least # bytes. * - 0x15E - - \_\_le16 - - s\_want\_extra\_isize + - __le16 + - s_want_extra_isize - New inodes should reserve # bytes. * - 0x160 - - \_\_le32 - - s\_flags + - __le32 + - s_flags - Miscellaneous flags. See the super_flags_ table for more info. * - 0x164 - - \_\_le16 - - s\_raid\_stride + - __le16 + - s_raid_stride - RAID stride. This is the number of logical blocks read from or written to the disk before moving to the next disk. This affects the placement of filesystem metadata, which will hopefully make RAID storage faster. * - 0x166 - - \_\_le16 - - s\_mmp\_interval + - __le16 + - s_mmp_interval - #. seconds to wait in multi-mount prevention (MMP) checking. In theory, MMP is a mechanism to record in the superblock which host and device have mounted the filesystem, in order to prevent multiple mounts. This feature does not seem to be implemented... * - 0x168 - - \_\_le64 - - s\_mmp\_block + - __le64 + - s_mmp_block - Block # for multi-mount protection data. * - 0x170 - - \_\_le32 - - s\_raid\_stripe\_width + - __le32 + - s_raid_stripe_width - RAID stripe width. This is the number of logical blocks read from or written to the disk before coming back to the current disk. This is used by the block allocator to try to reduce the number of read-modify-write operations in a RAID5/6. * - 0x174 - - \_\_u8 - - s\_log\_groups\_per\_flex + - __u8 + - s_log_groups_per_flex - Size of a flexible block group is 2 ^ ``s_log_groups_per_flex``. * - 0x175 - - \_\_u8 - - s\_checksum\_type + - __u8 + - s_checksum_type - Metadata checksum algorithm type. The only valid value is 1 (crc32c). * - 0x176 - - \_\_le16 - - s\_reserved\_pad + - __le16 + - s_reserved_pad - * - 0x178 - - \_\_le64 - - s\_kbytes\_written + - __le64 + - s_kbytes_written - Number of KiB written to this filesystem over its lifetime. * - 0x180 - - \_\_le32 - - s\_snapshot\_inum + - __le32 + - s_snapshot_inum - inode number of active snapshot. (Not used in e2fsprogs/Linux.) * - 0x184 - - \_\_le32 - - s\_snapshot\_id + - __le32 + - s_snapshot_id - Sequential ID of active snapshot. (Not used in e2fsprogs/Linux.) * - 0x188 - - \_\_le64 - - s\_snapshot\_r\_blocks\_count + - __le64 + - s_snapshot_r_blocks_count - Number of blocks reserved for active snapshot's future use. (Not used in e2fsprogs/Linux.) * - 0x190 - - \_\_le32 - - s\_snapshot\_list + - __le32 + - s_snapshot_list - inode number of the head of the on-disk snapshot list. (Not used in e2fsprogs/Linux.) * - 0x194 - - \_\_le32 - - s\_error\_count + - __le32 + - s_error_count - Number of errors seen. * - 0x198 - - \_\_le32 - - s\_first\_error\_time + - __le32 + - s_first_error_time - First time an error happened, in seconds since the epoch. * - 0x19C - - \_\_le32 - - s\_first\_error\_ino + - __le32 + - s_first_error_ino - inode involved in first error. * - 0x1A0 - - \_\_le64 - - s\_first\_error\_block + - __le64 + - s_first_error_block - Number of block involved of first error. * - 0x1A8 - - \_\_u8 - - s\_first\_error\_func[32] + - __u8 + - s_first_error_func[32] - Name of function where the error happened. * - 0x1C8 - - \_\_le32 - - s\_first\_error\_line + - __le32 + - s_first_error_line - Line number where error happened. * - 0x1CC - - \_\_le32 - - s\_last\_error\_time + - __le32 + - s_last_error_time - Time of most recent error, in seconds since the epoch. * - 0x1D0 - - \_\_le32 - - s\_last\_error\_ino + - __le32 + - s_last_error_ino - inode involved in most recent error. * - 0x1D4 - - \_\_le32 - - s\_last\_error\_line + - __le32 + - s_last_error_line - Line number where most recent error happened. * - 0x1D8 - - \_\_le64 - - s\_last\_error\_block + - __le64 + - s_last_error_block - Number of block involved in most recent error. * - 0x1E0 - - \_\_u8 - - s\_last\_error\_func[32] + - __u8 + - s_last_error_func[32] - Name of function where the most recent error happened. * - 0x200 - - \_\_u8 - - s\_mount\_opts[64] + - __u8 + - s_mount_opts[64] - ASCIIZ string of mount options. * - 0x240 - - \_\_le32 - - s\_usr\_quota\_inum + - __le32 + - s_usr_quota_inum - Inode number of user `quota <quota>`__ file. * - 0x244 - - \_\_le32 - - s\_grp\_quota\_inum + - __le32 + - s_grp_quota_inum - Inode number of group `quota <quota>`__ file. * - 0x248 - - \_\_le32 - - s\_overhead\_blocks + - __le32 + - s_overhead_blocks - Overhead blocks/clusters in fs. (Huh? This field is always zero, which means that the kernel calculates it dynamically.) * - 0x24C - - \_\_le32 - - s\_backup\_bgs[2] - - Block groups containing superblock backups (if sparse\_super2) + - __le32 + - s_backup_bgs[2] + - Block groups containing superblock backups (if sparse_super2) * - 0x254 - - \_\_u8 - - s\_encrypt\_algos[4] + - __u8 + - s_encrypt_algos[4] - Encryption algorithms in use. There can be up to four algorithms in use at any time; valid algorithm codes are given in the super_encrypt_ table below. * - 0x258 - - \_\_u8 - - s\_encrypt\_pw\_salt[16] + - __u8 + - s_encrypt_pw_salt[16] - Salt for the string2key algorithm for encryption. * - 0x268 - - \_\_le32 - - s\_lpf\_ino + - __le32 + - s_lpf_ino - Inode number of lost+found * - 0x26C - - \_\_le32 - - s\_prj\_quota\_inum + - __le32 + - s_prj_quota_inum - Inode that tracks project quotas. * - 0x270 - - \_\_le32 - - s\_checksum\_seed - - Checksum seed used for metadata\_csum calculations. This value is - crc32c(~0, $orig\_fs\_uuid). + - __le32 + - s_checksum_seed + - Checksum seed used for metadata_csum calculations. This value is + crc32c(~0, $orig_fs_uuid). * - 0x274 - - \_\_u8 - - s\_wtime_hi + - __u8 + - s_wtime_hi - Upper 8 bits of the s_wtime field. * - 0x275 - - \_\_u8 - - s\_mtime_hi + - __u8 + - s_mtime_hi - Upper 8 bits of the s_mtime field. * - 0x276 - - \_\_u8 - - s\_mkfs_time_hi + - __u8 + - s_mkfs_time_hi - Upper 8 bits of the s_mkfs_time field. * - 0x277 - - \_\_u8 - - s\_lastcheck_hi - - Upper 8 bits of the s_lastcheck_hi field. + - __u8 + - s_lastcheck_hi + - Upper 8 bits of the s_lastcheck field. * - 0x278 - - \_\_u8 - - s\_first_error_time_hi - - Upper 8 bits of the s_first_error_time_hi field. + - __u8 + - s_first_error_time_hi + - Upper 8 bits of the s_first_error_time field. * - 0x279 - - \_\_u8 - - s\_last_error_time_hi - - Upper 8 bits of the s_last_error_time_hi field. + - __u8 + - s_last_error_time_hi + - Upper 8 bits of the s_last_error_time field. * - 0x27A - - \_\_u8 - - s\_pad[2] + - __u8 + - s_pad[2] - Zero padding. * - 0x27C - - \_\_le16 - - s\_encoding + - __le16 + - s_encoding - Filename charset encoding. * - 0x27E - - \_\_le16 - - s\_encoding_flags + - __le16 + - s_encoding_flags - Filename charset encoding flags. * - 0x280 - - \_\_le32 - - s\_orphan\_file\_inum + - __le32 + - s_orphan_file_inum - Orphan file inode number. * - 0x284 - - \_\_le32 - - s\_reserved[94] + - __le32 + - s_reserved[94] - Padding to the end of the block. * - 0x3FC - - \_\_le32 - - s\_checksum + - __le32 + - s_checksum - Superblock checksum. .. _super_state: @@ -574,44 +574,44 @@ following: * - Value - Description * - 0x1 - - Directory preallocation (COMPAT\_DIR\_PREALLOC). + - Directory preallocation (COMPAT_DIR_PREALLOC). * - 0x2 - “imagic inodes”. Not clear from the code what this does - (COMPAT\_IMAGIC\_INODES). + (COMPAT_IMAGIC_INODES). * - 0x4 - - Has a journal (COMPAT\_HAS\_JOURNAL). + - Has a journal (COMPAT_HAS_JOURNAL). * - 0x8 - - Supports extended attributes (COMPAT\_EXT\_ATTR). + - Supports extended attributes (COMPAT_EXT_ATTR). * - 0x10 - Has reserved GDT blocks for filesystem expansion - (COMPAT\_RESIZE\_INODE). Requires RO\_COMPAT\_SPARSE\_SUPER. + (COMPAT_RESIZE_INODE). Requires RO_COMPAT_SPARSE_SUPER. * - 0x20 - - Has directory indices (COMPAT\_DIR\_INDEX). + - Has directory indices (COMPAT_DIR_INDEX). * - 0x40 - “Lazy BG”. Not in Linux kernel, seems to have been for uninitialized - block groups? (COMPAT\_LAZY\_BG) + block groups? (COMPAT_LAZY_BG) * - 0x80 - - “Exclude inode”. Not used. (COMPAT\_EXCLUDE\_INODE). + - “Exclude inode”. Not used. (COMPAT_EXCLUDE_INODE). * - 0x100 - “Exclude bitmap”. Seems to be used to indicate the presence of snapshot-related exclude bitmaps? Not defined in kernel or used in - e2fsprogs (COMPAT\_EXCLUDE\_BITMAP). + e2fsprogs (COMPAT_EXCLUDE_BITMAP). * - 0x200 - - Sparse Super Block, v2. If this flag is set, the SB field s\_backup\_bgs + - Sparse Super Block, v2. If this flag is set, the SB field s_backup_bgs points to the two block groups that contain backup superblocks - (COMPAT\_SPARSE\_SUPER2). + (COMPAT_SPARSE_SUPER2). * - 0x400 - Fast commits supported. Although fast commits blocks are backward incompatible, fast commit blocks are not always present in the journal. If fast commit blocks are present in the journal, JBD2 incompat feature - (JBD2\_FEATURE\_INCOMPAT\_FAST\_COMMIT) gets - set (COMPAT\_FAST\_COMMIT). + (JBD2_FEATURE_INCOMPAT_FAST_COMMIT) gets + set (COMPAT_FAST_COMMIT). * - 0x1000 - Orphan file allocated. This is the special file for more efficient tracking of unlinked but still open inodes. When there may be any entries in the file, we additionally set proper rocompat feature - (RO\_COMPAT\_ORPHAN\_PRESENT). + (RO_COMPAT_ORPHAN_PRESENT). .. _super_incompat: @@ -625,45 +625,45 @@ following: * - Value - Description * - 0x1 - - Compression (INCOMPAT\_COMPRESSION). + - Compression (INCOMPAT_COMPRESSION). * - 0x2 - - Directory entries record the file type. See ext4\_dir\_entry\_2 below - (INCOMPAT\_FILETYPE). + - Directory entries record the file type. See ext4_dir_entry_2 below + (INCOMPAT_FILETYPE). * - 0x4 - - Filesystem needs recovery (INCOMPAT\_RECOVER). + - Filesystem needs recovery (INCOMPAT_RECOVER). * - 0x8 - - Filesystem has a separate journal device (INCOMPAT\_JOURNAL\_DEV). + - Filesystem has a separate journal device (INCOMPAT_JOURNAL_DEV). * - 0x10 - Meta block groups. See the earlier discussion of this feature - (INCOMPAT\_META\_BG). + (INCOMPAT_META_BG). * - 0x40 - - Files in this filesystem use extents (INCOMPAT\_EXTENTS). + - Files in this filesystem use extents (INCOMPAT_EXTENTS). * - 0x80 - - Enable a filesystem size of 2^64 blocks (INCOMPAT\_64BIT). + - Enable a filesystem size of 2^64 blocks (INCOMPAT_64BIT). * - 0x100 - - Multiple mount protection (INCOMPAT\_MMP). + - Multiple mount protection (INCOMPAT_MMP). * - 0x200 - Flexible block groups. See the earlier discussion of this feature - (INCOMPAT\_FLEX\_BG). + (INCOMPAT_FLEX_BG). * - 0x400 - Inodes can be used to store large extended attribute values - (INCOMPAT\_EA\_INODE). + (INCOMPAT_EA_INODE). * - 0x1000 - - Data in directory entry (INCOMPAT\_DIRDATA). (Not implemented?) + - Data in directory entry (INCOMPAT_DIRDATA). (Not implemented?) * - 0x2000 - Metadata checksum seed is stored in the superblock. This feature enables - the administrator to change the UUID of a metadata\_csum filesystem + the administrator to change the UUID of a metadata_csum filesystem while the filesystem is mounted; without it, the checksum definition - requires all metadata blocks to be rewritten (INCOMPAT\_CSUM\_SEED). + requires all metadata blocks to be rewritten (INCOMPAT_CSUM_SEED). * - 0x4000 - - Large directory >2GB or 3-level htree (INCOMPAT\_LARGEDIR). Prior to + - Large directory >2GB or 3-level htree (INCOMPAT_LARGEDIR). Prior to this feature, directories could not be larger than 4GiB and could not have an htree more than 2 levels deep. If this feature is enabled, directories can be larger than 4GiB and have a maximum htree depth of 3. * - 0x8000 - - Data in inode (INCOMPAT\_INLINE\_DATA). + - Data in inode (INCOMPAT_INLINE_DATA). * - 0x10000 - - Encrypted inodes are present on the filesystem. (INCOMPAT\_ENCRYPT). + - Encrypted inodes are present on the filesystem. (INCOMPAT_ENCRYPT). .. _super_rocompat: @@ -678,54 +678,54 @@ the following: - Description * - 0x1 - Sparse superblocks. See the earlier discussion of this feature - (RO\_COMPAT\_SPARSE\_SUPER). + (RO_COMPAT_SPARSE_SUPER). * - 0x2 - This filesystem has been used to store a file greater than 2GiB - (RO\_COMPAT\_LARGE\_FILE). + (RO_COMPAT_LARGE_FILE). * - 0x4 - - Not used in kernel or e2fsprogs (RO\_COMPAT\_BTREE\_DIR). + - Not used in kernel or e2fsprogs (RO_COMPAT_BTREE_DIR). * - 0x8 - This filesystem has files whose sizes are represented in units of logical blocks, not 512-byte sectors. This implies a very large file - indeed! (RO\_COMPAT\_HUGE\_FILE) + indeed! (RO_COMPAT_HUGE_FILE) * - 0x10 - Group descriptors have checksums. In addition to detecting corruption, this is useful for lazy formatting with uninitialized groups - (RO\_COMPAT\_GDT\_CSUM). + (RO_COMPAT_GDT_CSUM). * - 0x20 - Indicates that the old ext3 32,000 subdirectory limit no longer applies - (RO\_COMPAT\_DIR\_NLINK). A directory's i\_links\_count will be set to 1 + (RO_COMPAT_DIR_NLINK). A directory's i_links_count will be set to 1 if it is incremented past 64,999. * - 0x40 - Indicates that large inodes exist on this filesystem - (RO\_COMPAT\_EXTRA\_ISIZE). + (RO_COMPAT_EXTRA_ISIZE). * - 0x80 - - This filesystem has a snapshot (RO\_COMPAT\_HAS\_SNAPSHOT). + - This filesystem has a snapshot (RO_COMPAT_HAS_SNAPSHOT). * - 0x100 - - `Quota <Quota>`__ (RO\_COMPAT\_QUOTA). + - `Quota <Quota>`__ (RO_COMPAT_QUOTA). * - 0x200 - This filesystem supports “bigalloc”, which means that file extents are tracked in units of clusters (of blocks) instead of blocks - (RO\_COMPAT\_BIGALLOC). + (RO_COMPAT_BIGALLOC). * - 0x400 - This filesystem supports metadata checksumming. - (RO\_COMPAT\_METADATA\_CSUM; implies RO\_COMPAT\_GDT\_CSUM, though - GDT\_CSUM must not be set) + (RO_COMPAT_METADATA_CSUM; implies RO_COMPAT_GDT_CSUM, though + GDT_CSUM must not be set) * - 0x800 - Filesystem supports replicas. This feature is neither in the kernel nor - e2fsprogs. (RO\_COMPAT\_REPLICA) + e2fsprogs. (RO_COMPAT_REPLICA) * - 0x1000 - Read-only filesystem image; the kernel will not mount this image read-write and most tools will refuse to write to the image. - (RO\_COMPAT\_READONLY) + (RO_COMPAT_READONLY) * - 0x2000 - - Filesystem tracks project quotas. (RO\_COMPAT\_PROJECT) + - Filesystem tracks project quotas. (RO_COMPAT_PROJECT) * - 0x8000 - - Verity inodes may be present on the filesystem. (RO\_COMPAT\_VERITY) + - Verity inodes may be present on the filesystem. (RO_COMPAT_VERITY) * - 0x10000 - Indicates orphan file may have valid orphan entries and thus we need to clean them up when mounting the filesystem - (RO\_COMPAT\_ORPHAN\_PRESENT). + (RO_COMPAT_ORPHAN_PRESENT). .. _super_def_hash: @@ -761,36 +761,36 @@ The ``s_default_mount_opts`` field is any combination of the following: * - Value - Description * - 0x0001 - - Print debugging info upon (re)mount. (EXT4\_DEFM\_DEBUG) + - Print debugging info upon (re)mount. (EXT4_DEFM_DEBUG) * - 0x0002 - New files take the gid of the containing directory (instead of the fsgid - of the current process). (EXT4\_DEFM\_BSDGROUPS) + of the current process). (EXT4_DEFM_BSDGROUPS) * - 0x0004 - - Support userspace-provided extended attributes. (EXT4\_DEFM\_XATTR\_USER) + - Support userspace-provided extended attributes. (EXT4_DEFM_XATTR_USER) * - 0x0008 - - Support POSIX access control lists (ACLs). (EXT4\_DEFM\_ACL) + - Support POSIX access control lists (ACLs). (EXT4_DEFM_ACL) * - 0x0010 - - Do not support 32-bit UIDs. (EXT4\_DEFM\_UID16) + - Do not support 32-bit UIDs. (EXT4_DEFM_UID16) * - 0x0020 - All data and metadata are commited to the journal. - (EXT4\_DEFM\_JMODE\_DATA) + (EXT4_DEFM_JMODE_DATA) * - 0x0040 - All data are flushed to the disk before metadata are committed to the - journal. (EXT4\_DEFM\_JMODE\_ORDERED) + journal. (EXT4_DEFM_JMODE_ORDERED) * - 0x0060 - Data ordering is not preserved; data may be written after the metadata - has been written. (EXT4\_DEFM\_JMODE\_WBACK) + has been written. (EXT4_DEFM_JMODE_WBACK) * - 0x0100 - - Disable write flushes. (EXT4\_DEFM\_NOBARRIER) + - Disable write flushes. (EXT4_DEFM_NOBARRIER) * - 0x0200 - Track which blocks in a filesystem are metadata and therefore should not be used as data blocks. This option will be enabled by default on 3.18, - hopefully. (EXT4\_DEFM\_BLOCK\_VALIDITY) + hopefully. (EXT4_DEFM_BLOCK_VALIDITY) * - 0x0400 - Enable DISCARD support, where the storage device is told about blocks - becoming unused. (EXT4\_DEFM\_DISCARD) + becoming unused. (EXT4_DEFM_DISCARD) * - 0x0800 - - Disable delayed allocation. (EXT4\_DEFM\_NODELALLOC) + - Disable delayed allocation. (EXT4_DEFM_NODELALLOC) .. _super_flags: @@ -820,12 +820,12 @@ The ``s_encrypt_algos`` list can contain any of the following: * - Value - Description * - 0 - - Invalid algorithm (ENCRYPTION\_MODE\_INVALID). + - Invalid algorithm (ENCRYPTION_MODE_INVALID). * - 1 - - 256-bit AES in XTS mode (ENCRYPTION\_MODE\_AES\_256\_XTS). + - 256-bit AES in XTS mode (ENCRYPTION_MODE_AES_256_XTS). * - 2 - - 256-bit AES in GCM mode (ENCRYPTION\_MODE\_AES\_256\_GCM). + - 256-bit AES in GCM mode (ENCRYPTION_MODE_AES_256_GCM). * - 3 - - 256-bit AES in CBC mode (ENCRYPTION\_MODE\_AES\_256\_CBC). + - 256-bit AES in CBC mode (ENCRYPTION_MODE_AES_256_CBC). Total size of the superblock is 1024 bytes. diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst index d7b84695f56a..17df9a02ccff 100644 --- a/Documentation/filesystems/f2fs.rst +++ b/Documentation/filesystems/f2fs.rst @@ -198,6 +198,7 @@ fault_type=%d Support configuring fault injection type, should be FAULT_WRITE_IO 0x000004000 FAULT_SLAB_ALLOC 0x000008000 FAULT_DQUOT_INIT 0x000010000 + FAULT_LOCK_OP 0x000020000 =================== =========== mode=%s Control block allocation mode which supports "adaptive" and "lfs". In "lfs" mode, there should be no random @@ -234,12 +235,6 @@ offgrpjquota Turn off group journalled quota. offprjjquota Turn off project journalled quota. quota Enable plain user disk quota accounting. noquota Disable all plain disk quota option. -whint_mode=%s Control which write hints are passed down to block - layer. This supports "off", "user-based", and - "fs-based". In "off" mode (default), f2fs does not pass - down hints. In "user-based" mode, f2fs tries to pass - down hints given by users. And in "fs-based" mode, f2fs - passes down hints with its policy. alloc_mode=%s Adjust block allocation policy, which supports "reuse" and "default". fsync_mode=%s Control the policy of fsync. Currently supports "posix", @@ -291,9 +286,8 @@ compress_algorithm=%s:%d Control compress algorithm and its compress level, now, algorithm level range lz4 3 - 16 zstd 1 - 22 -compress_log_size=%u Support configuring compress cluster size, the size will - be 4KB * (1 << %u), 16KB is minimum size, also it's - default size. +compress_log_size=%u Support configuring compress cluster size. The size will + be 4KB * (1 << %u). The default and minimum sizes are 16KB. compress_extension=%s Support adding specified extension, so that f2fs can enable compression on those corresponding files, e.g. if all files with '.ext' has high compression rate, we can set the '.ext' @@ -341,6 +335,11 @@ discard_unit=%s Control discard unit, the argument can be "block", "segment" default, it is helpful for large sized SMR or ZNS devices to reduce memory cost by getting rid of fs metadata supports small discard. +memory=%s Control memory mode. This supports "normal" and "low" modes. + "low" mode is introduced to support low memory devices. + Because of the nature of low memory devices, in this mode, f2fs + will try to save memory sometimes by sacrificing performance. + "normal" mode is the default mode and same as before. ======================== ============================================================ Debugfs Entries @@ -750,70 +749,6 @@ In order to identify whether the data in the victim segment are valid or not, F2FS manages a bitmap. Each bit represents the validity of a block, and the bitmap is composed of a bit stream covering whole blocks in main area. -Write-hint Policy ------------------ - -1) whint_mode=off. F2FS only passes down WRITE_LIFE_NOT_SET. - -2) whint_mode=user-based. F2FS tries to pass down hints given by -users. - -===================== ======================== =================== -User F2FS Block -===================== ======================== =================== -N/A META WRITE_LIFE_NOT_SET -N/A HOT_NODE " -N/A WARM_NODE " -N/A COLD_NODE " -ioctl(COLD) COLD_DATA WRITE_LIFE_EXTREME -extension list " " - --- buffered io -WRITE_LIFE_EXTREME COLD_DATA WRITE_LIFE_EXTREME -WRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT -WRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_NOT_SET -WRITE_LIFE_NONE " " -WRITE_LIFE_MEDIUM " " -WRITE_LIFE_LONG " " - --- direct io -WRITE_LIFE_EXTREME COLD_DATA WRITE_LIFE_EXTREME -WRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT -WRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_NOT_SET -WRITE_LIFE_NONE " WRITE_LIFE_NONE -WRITE_LIFE_MEDIUM " WRITE_LIFE_MEDIUM -WRITE_LIFE_LONG " WRITE_LIFE_LONG -===================== ======================== =================== - -3) whint_mode=fs-based. F2FS passes down hints with its policy. - -===================== ======================== =================== -User F2FS Block -===================== ======================== =================== -N/A META WRITE_LIFE_MEDIUM; -N/A HOT_NODE WRITE_LIFE_NOT_SET -N/A WARM_NODE " -N/A COLD_NODE WRITE_LIFE_NONE -ioctl(COLD) COLD_DATA WRITE_LIFE_EXTREME -extension list " " - --- buffered io -WRITE_LIFE_EXTREME COLD_DATA WRITE_LIFE_EXTREME -WRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT -WRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_LONG -WRITE_LIFE_NONE " " -WRITE_LIFE_MEDIUM " " -WRITE_LIFE_LONG " " - --- direct io -WRITE_LIFE_EXTREME COLD_DATA WRITE_LIFE_EXTREME -WRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT -WRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_NOT_SET -WRITE_LIFE_NONE " WRITE_LIFE_NONE -WRITE_LIFE_MEDIUM " WRITE_LIFE_MEDIUM -WRITE_LIFE_LONG " WRITE_LIFE_LONG -===================== ======================== =================== - Fallocate(2) Policy ------------------- @@ -887,10 +822,11 @@ Compression implementation Instead, the main goal is to reduce data writes to flash disk as much as possible, resulting in extending disk life time as well as relaxing IO congestion. Alternatively, we've added ioctl(F2FS_IOC_RELEASE_COMPRESS_BLOCKS) - interface to reclaim compressed space and show it to user after putting the - immutable bit. Immutable bit, after release, it doesn't allow writing/mmaping - on the file, until reserving compressed space via - ioctl(F2FS_IOC_RESERVE_COMPRESS_BLOCKS) or truncating filesize to zero. + interface to reclaim compressed space and show it to user after setting a + special flag to the inode. Once the compressed space is released, the flag + will block writing data to the file until either the compressed space is + reserved via ioctl(F2FS_IOC_RESERVE_COMPRESS_BLOCKS) or the file size is + truncated to zero. Compress metadata layout:: @@ -899,12 +835,12 @@ Compress metadata layout:: | cluster 1 | cluster 2 | ......... | cluster N | +-----------------------------------------------+ . . . . - . . . . + . . . . . Compressed Cluster . . Normal Cluster . +----------+---------+---------+---------+ +---------+---------+---------+---------+ |compr flag| block 1 | block 2 | block 3 | | block 1 | block 2 | block 3 | block 4 | +----------+---------+---------+---------+ +---------+---------+---------+---------+ - . . + . . . . . . +-------------+-------------+----------+----------------------------+ diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst index 4d5d50dca65c..5ba5817c17c2 100644 --- a/Documentation/filesystems/fscrypt.rst +++ b/Documentation/filesystems/fscrypt.rst @@ -337,6 +337,7 @@ Currently, the following pairs of encryption modes are supported: - AES-256-XTS for contents and AES-256-CTS-CBC for filenames - AES-128-CBC for contents and AES-128-CTS-CBC for filenames - Adiantum for both contents and filenames +- AES-256-XTS for contents and AES-256-HCTR2 for filenames (v2 policies only) If unsure, you should use the (AES-256-XTS, AES-256-CTS-CBC) pair. @@ -357,6 +358,17 @@ To use Adiantum, CONFIG_CRYPTO_ADIANTUM must be enabled. Also, fast implementations of ChaCha and NHPoly1305 should be enabled, e.g. CONFIG_CRYPTO_CHACHA20_NEON and CONFIG_CRYPTO_NHPOLY1305_NEON for ARM. +AES-256-HCTR2 is another true wide-block encryption mode that is intended for +use on CPUs with dedicated crypto instructions. AES-256-HCTR2 has the property +that a bitflip in the plaintext changes the entire ciphertext. This property +makes it desirable for filename encryption since initialization vectors are +reused within a directory. For more details on AES-256-HCTR2, see the paper +"Length-preserving encryption with HCTR2" +(https://eprint.iacr.org/2021/1441.pdf). To use AES-256-HCTR2, +CONFIG_CRYPTO_HCTR2 must be enabled. Also, fast implementations of XCTR and +POLYVAL should be enabled, e.g. CRYPTO_POLYVAL_ARM64_CE and +CRYPTO_AES_ARM64_CE_BLK for ARM64. + New encryption modes can be added relatively easily, without changes to individual filesystems. However, authenticated encryption (AE) modes are not currently supported because of the difficulty of dealing @@ -404,11 +416,11 @@ alternatively has the file's nonce (for `DIRECT_KEY policies`_) or inode number (for `IV_INO_LBLK_64 policies`_) included in the IVs. Thus, IV reuse is limited to within a single directory. -With CTS-CBC, the IV reuse means that when the plaintext filenames -share a common prefix at least as long as the cipher block size (16 -bytes for AES), the corresponding encrypted filenames will also share -a common prefix. This is undesirable. Adiantum does not have this -weakness, as it is a wide-block encryption mode. +With CTS-CBC, the IV reuse means that when the plaintext filenames share a +common prefix at least as long as the cipher block size (16 bytes for AES), the +corresponding encrypted filenames will also share a common prefix. This is +undesirable. Adiantum and HCTR2 do not have this weakness, as they are +wide-block encryption modes. All supported filenames encryption modes accept any plaintext length >= 16 bytes; cipher block alignment is not required. However, @@ -1047,8 +1059,8 @@ astute users may notice some differences in behavior: may be used to overwrite the source files but isn't guaranteed to be effective on all filesystems and storage devices. -- Direct I/O is not supported on encrypted files. Attempts to use - direct I/O on such files will fall back to buffered I/O. +- Direct I/O is supported on encrypted files only under some + circumstances. For details, see `Direct I/O support`_. - The fallocate operations FALLOC_FL_COLLAPSE_RANGE and FALLOC_FL_INSERT_RANGE are not supported on encrypted files and will @@ -1179,6 +1191,27 @@ Inline encryption doesn't affect the ciphertext or other aspects of the on-disk format, so users may freely switch back and forth between using "inlinecrypt" and not using "inlinecrypt". +Direct I/O support +================== + +For direct I/O on an encrypted file to work, the following conditions +must be met (in addition to the conditions for direct I/O on an +unencrypted file): + +* The file must be using inline encryption. Usually this means that + the filesystem must be mounted with ``-o inlinecrypt`` and inline + encryption hardware must be present. However, a software fallback + is also available. For details, see `Inline encryption support`_. + +* The I/O request must be fully aligned to the filesystem block size. + This means that the file position the I/O is targeting, the lengths + of all I/O segments, and the memory addresses of all I/O buffers + must be multiples of this value. Note that the filesystem block + size may be greater than the logical block size of the block device. + +If either of the above conditions is not met, then direct I/O on the +encrypted file will fall back to buffered I/O. + Implementation details ====================== @@ -1235,7 +1268,7 @@ inline encryption hardware will encrypt/decrypt the file contents. When inline encryption isn't used, filesystems must encrypt/decrypt the file contents themselves, as described below: -For the read path (->readpage()) of regular files, filesystems can +For the read path (->read_folio()) of regular files, filesystems can read the ciphertext into the page cache and decrypt it in-place. The page lock must be held until decryption has finished, to prevent the page from becoming visible to userspace prematurely. diff --git a/Documentation/filesystems/fsverity.rst b/Documentation/filesystems/fsverity.rst index 1d831e3cbcb3..cb8e7573882a 100644 --- a/Documentation/filesystems/fsverity.rst +++ b/Documentation/filesystems/fsverity.rst @@ -11,9 +11,9 @@ Introduction fs-verity (``fs/verity/``) is a support layer that filesystems can hook into to support transparent integrity and authenticity protection -of read-only files. Currently, it is supported by the ext4 and f2fs -filesystems. Like fscrypt, not too much filesystem-specific code is -needed to support fs-verity. +of read-only files. Currently, it is supported by the ext4, f2fs, and +btrfs filesystems. Like fscrypt, not too much filesystem-specific +code is needed to support fs-verity. fs-verity is similar to `dm-verity <https://www.kernel.org/doc/Documentation/device-mapper/verity.txt>`_ @@ -70,12 +70,23 @@ must live on a read-write filesystem because they are independently updated and potentially user-installed, so dm-verity cannot be used. The base fs-verity feature is a hashing mechanism only; actually -authenticating the files is up to userspace. However, to meet some -users' needs, fs-verity optionally supports a simple signature -verification mechanism where users can configure the kernel to require -that all fs-verity files be signed by a key loaded into a keyring; see -`Built-in signature verification`_. Support for fs-verity file hashes -in IMA (Integrity Measurement Architecture) policies is also planned. +authenticating the files may be done by: + +* Userspace-only + +* Builtin signature verification + userspace policy + + fs-verity optionally supports a simple signature verification + mechanism where users can configure the kernel to require that + all fs-verity files be signed by a key loaded into a keyring; + see `Built-in signature verification`_. + +* Integrity Measurement Architecture (IMA) + + IMA supports including fs-verity file digests and signatures in the + IMA measurement list and verifying fs-verity based file signatures + stored as security.ima xattrs, based on policy. + User API ======== @@ -462,9 +473,9 @@ files being swapped around. Filesystem support ================== -fs-verity is currently supported by the ext4 and f2fs filesystems. -The CONFIG_FS_VERITY kconfig option must be enabled to use fs-verity -on either filesystem. +fs-verity is supported by several filesystems, described below. The +CONFIG_FS_VERITY kconfig option must be enabled to use fs-verity on +any of these filesystems. ``include/linux/fsverity.h`` declares the interface between the ``fs/verity/`` support layer and filesystems. Briefly, filesystems @@ -533,6 +544,13 @@ Currently, f2fs verity only supports a Merkle tree block size of 4096. Also, f2fs doesn't support enabling verity on files that currently have atomic or volatile writes pending. +btrfs +----- + +btrfs supports fs-verity since Linux v5.15. Verity-enabled inodes are +marked with a RO_COMPAT inode flag, and the verity metadata is stored +in separate btree items. + Implementation details ====================== @@ -548,8 +566,8 @@ already verified). Below, we describe how filesystems implement this. Pagecache ~~~~~~~~~ -For filesystems using Linux's pagecache, the ``->readpage()`` and -``->readpages()`` methods must be modified to verify pages before they +For filesystems using Linux's pagecache, the ``->read_folio()`` and +``->readahead()`` methods must be modified to verify pages before they are marked Uptodate. Merely hooking ``->read_iter()`` would be insufficient, since ``->read_iter()`` is not used for memory maps. @@ -611,14 +629,14 @@ workqueue, and then the workqueue work does the decryption or verification. Finally, pages where no decryption or verity error occurred are marked Uptodate, and the pages are unlocked. -Files on ext4 and f2fs may contain holes. Normally, ``->readpages()`` -simply zeroes holes and sets the corresponding pages Uptodate; no bios -are issued. To prevent this case from bypassing fs-verity, these -filesystems use fsverity_verify_page() to verify hole pages. +On many filesystems, files can contain holes. Normally, +``->readahead()`` simply zeroes holes and sets the corresponding pages +Uptodate; no bios are issued. To prevent this case from bypassing +fs-verity, these filesystems use fsverity_verify_page() to verify hole +pages. -ext4 and f2fs disable direct I/O on verity files, since otherwise -direct I/O would bypass fs-verity. (They also do the same for -encrypted files.) +Filesystems also disable direct I/O on verity files, since otherwise +direct I/O would bypass fs-verity. Userspace utility ================= @@ -637,7 +655,7 @@ Tests To test fs-verity, use xfstests. For example, using `kvm-xfstests <https://github.com/tytso/xfstests-bld/blob/master/Documentation/kvm-quickstart.md>`_:: - kvm-xfstests -c ext4,f2fs -g verity + kvm-xfstests -c ext4,f2fs,btrfs -g verity FAQ === @@ -653,12 +671,12 @@ weren't already directly answered in other parts of this document. hashed and what to do with those hashes, such as log them, authenticate them, or add them to a measurement list. - IMA is planned to support the fs-verity hashing mechanism as an - alternative to doing full file hashes, for people who want the - performance and security benefits of the Merkle tree based hash. - But it doesn't make sense to force all uses of fs-verity to be - through IMA. As a standalone filesystem feature, fs-verity - already meets many users' needs, and it's testable like other + IMA supports the fs-verity hashing mechanism as an alternative + to full file hashes, for those who want the performance and + security benefits of the Merkle tree based hash. However, it + doesn't make sense to force all uses of fs-verity to be through + IMA. fs-verity already meets many users' needs even as a + standalone filesystem feature, and it's testable like other filesystem features e.g. with xfstests. :Q: Isn't fs-verity useless because the attacker can just modify the @@ -760,15 +778,15 @@ weren't already directly answered in other parts of this document. e.g. magically trigger construction of a Merkle tree. :Q: Does fs-verity support remote filesystems? -:A: Only ext4 and f2fs support is implemented currently, but in - principle any filesystem that can store per-file verity metadata - can support fs-verity, regardless of whether it's local or remote. - Some filesystems may have fewer options of where to store the - verity metadata; one possibility is to store it past the end of - the file and "hide" it from userspace by manipulating i_size. The - data verification functions provided by ``fs/verity/`` also assume - that the filesystem uses the Linux pagecache, but both local and - remote filesystems normally do so. +:A: So far all filesystems that have implemented fs-verity support are + local filesystems, but in principle any filesystem that can store + per-file verity metadata can support fs-verity, regardless of + whether it's local or remote. Some filesystems may have fewer + options of where to store the verity metadata; one possibility is + to store it past the end of the file and "hide" it from userspace + by manipulating i_size. The data verification functions provided + by ``fs/verity/`` also assume that the filesystem uses the Linux + pagecache, but both local and remote filesystems normally do so. :Q: Why is anything filesystem-specific at all? Shouldn't fs-verity be implemented entirely at the VFS level? @@ -778,7 +796,7 @@ weren't already directly answered in other parts of this document. - To prevent bypassing verification, pages must not be marked Uptodate until they've been verified. Currently, each filesystem is responsible for marking pages Uptodate via - ``->readpages()``. Therefore, currently it's not possible for + ``->readahead()``. Therefore, currently it's not possible for the VFS to do the verification on its own. Changing this would require significant changes to the VFS and all filesystems. diff --git a/Documentation/filesystems/fuse.rst b/Documentation/filesystems/fuse.rst index 8120c3c0cb4e..1e31e87aee68 100644 --- a/Documentation/filesystems/fuse.rst +++ b/Documentation/filesystems/fuse.rst @@ -279,7 +279,7 @@ How are requirements fulfilled? the filesystem or not. Note that the *ptrace* check is not strictly necessary to - prevent B/2/i, it is enough to check if mount owner has enough + prevent C/2/i, it is enough to check if mount owner has enough privilege to send signal to the process accessing the filesystem, since *SIGSTOP* can be used to get a similar effect. @@ -288,10 +288,29 @@ I think these limitations are unacceptable? If a sysadmin trusts the users enough, or can ensure through other measures, that system processes will never enter non-privileged -mounts, it can relax the last limitation with a 'user_allow_other' -config option. If this config option is set, the mounting user can -add the 'allow_other' mount option which disables the check for other -users' processes. +mounts, it can relax the last limitation in several ways: + + - With the 'user_allow_other' config option. If this config option is + set, the mounting user can add the 'allow_other' mount option which + disables the check for other users' processes. + + User namespaces have an unintuitive interaction with 'allow_other': + an unprivileged user - normally restricted from mounting with + 'allow_other' - could do so in a user namespace where they're + privileged. If any process could access such an 'allow_other' mount + this would give the mounting user the ability to manipulate + processes in user namespaces where they're unprivileged. For this + reason 'allow_other' restricts access to users in the same userns + or a descendant. + + - With the 'allow_sys_admin_access' module option. If this option is + set, super user's processes have unrestricted access to mounts + irrespective of allow_other setting or user namespace of the + mounting user. + +Note that both of these relaxations expose the system to potential +information leak or *DoS* as described in points B and C/2/i-ii in the +preceding section. Kernel - userspace interface ============================ diff --git a/Documentation/filesystems/idmappings.rst b/Documentation/filesystems/idmappings.rst index 1229a75ec75d..b9b31066aef2 100644 --- a/Documentation/filesystems/idmappings.rst +++ b/Documentation/filesystems/idmappings.rst @@ -369,6 +369,11 @@ kernel maps the caller's userspace id down into a kernel id according to the caller's idmapping and then maps that kernel id up according to the filesystem's idmapping. +Let's see some examples with caller/filesystem idmapping but without mount +idmappings. This will exhibit some problems we can hit. After that we will +revisit/reconsider these examples, this time using mount idmappings, to see how +they can solve the problems we observed before. + Example 1 ~~~~~~~~~ @@ -656,7 +661,7 @@ idmappings:: mount idmapping: u0:k10000:r10000 Assume a file owned by ``u1000`` is read from disk. The filesystem maps this id -to ``k21000`` according to it's idmapping. This is what is stored in the +to ``k21000`` according to its idmapping. This is what is stored in the inode's ``i_uid`` and ``i_gid`` fields. When the caller queries the ownership of this file via ``stat()`` the kernel @@ -952,75 +957,3 @@ The raw userspace id that is put on disk is ``u1000`` so when the user takes their home directory back to their home computer where they are assigned ``u1000`` using the initial idmapping and mount the filesystem with the initial idmapping they will see all those files owned by ``u1000``. - -Shortcircuting --------------- - -Currently, the implementation of idmapped mounts enforces that the filesystem -is mounted with the initial idmapping. The reason is simply that none of the -filesystems that we targeted were mountable with a non-initial idmapping. But -that might change soon enough. As we've seen above, thanks to the properties of -idmappings the translation works for both filesystems mounted with the initial -idmapping and filesystem with non-initial idmappings. - -Based on this current restriction to filesystem mounted with the initial -idmapping two noticeable shortcuts have been taken: - -1. We always stash a reference to the initial user namespace in ``struct - vfsmount``. Idmapped mounts are thus mounts that have a non-initial user - namespace attached to them. - - In order to support idmapped mounts this needs to be changed. Instead of - stashing the initial user namespace the user namespace the filesystem was - mounted with must be stashed. An idmapped mount is then any mount that has - a different user namespace attached then the filesystem was mounted with. - This has no user-visible consequences. - -2. The translation algorithms in ``mapped_fs*id()`` and ``i_*id_into_mnt()`` - are simplified. - - Let's consider ``mapped_fs*id()`` first. This function translates the - caller's kernel id into a kernel id in the filesystem's idmapping via - a mount's idmapping. The full algorithm is:: - - mapped_fsuid(kid): - /* Map the kernel id up into a userspace id in the mount's idmapping. */ - from_kuid(mount-idmapping, kid) = uid - - /* Map the userspace id down into a kernel id in the filesystem's idmapping. */ - make_kuid(filesystem-idmapping, uid) = kuid - - We know that the filesystem is always mounted with the initial idmapping as - we enforce this in ``mount_setattr()``. So this can be shortened to:: - - mapped_fsuid(kid): - /* Map the kernel id up into a userspace id in the mount's idmapping. */ - from_kuid(mount-idmapping, kid) = uid - - /* Map the userspace id down into a kernel id in the filesystem's idmapping. */ - KUIDT_INIT(uid) = kuid - - Similarly, for ``i_*id_into_mnt()`` which translated the filesystem's kernel - id into a mount's kernel id:: - - i_uid_into_mnt(kid): - /* Map the kernel id up into a userspace id in the filesystem's idmapping. */ - from_kuid(filesystem-idmapping, kid) = uid - - /* Map the userspace id down into a kernel id in the mounts's idmapping. */ - make_kuid(mount-idmapping, uid) = kuid - - Again, we know that the filesystem is always mounted with the initial - idmapping as we enforce this in ``mount_setattr()``. So this can be - shortened to:: - - i_uid_into_mnt(kid): - /* Map the kernel id up into a userspace id in the filesystem's idmapping. */ - __kuid_val(kid) = uid - - /* Map the userspace id down into a kernel id in the mounts's idmapping. */ - make_kuid(mount-idmapping, uid) = kuid - -Handling filesystems mounted with non-initial idmappings requires that the -translation functions be converted to their full form. They can still be -shortcircuited on non-idmapped mounts. This has no user-visible consequences. diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst index d36fe79167b3..8f737e76935c 100644 --- a/Documentation/filesystems/locking.rst +++ b/Documentation/filesystems/locking.rst @@ -79,7 +79,8 @@ prototypes:: int (*atomic_open)(struct inode *, struct dentry *, struct file *, unsigned open_flag, umode_t create_mode); - int (*tmpfile) (struct inode *, struct dentry *, umode_t); + int (*tmpfile) (struct user_namespace *, struct inode *, + struct file *, umode_t); int (*fileattr_set)(struct user_namespace *mnt_userns, struct dentry *dentry, struct fileattr *fa); int (*fileattr_get)(struct dentry *dentry, struct fileattr *fa); @@ -169,7 +170,6 @@ prototypes:: int (*show_options)(struct seq_file *, struct dentry *); ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t); ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t); - int (*bdev_try_to_free_page)(struct super_block*, struct page*, gfp_t); locking rules: All may block [not true, see below] @@ -194,7 +194,6 @@ umount_begin: no show_options: no (namespace_sem) quota_read: no (see below) quota_write: no (see below) -bdev_try_to_free_page: no (see below) ====================== ============ ======================== ->statfs() has s_umount (shared) when called by ustat(2) (native or @@ -210,9 +209,6 @@ dqio_sem) (unless an admin really wants to screw up something and writes to quota files with quotas on). For other details about locking see also dquot_operations section. -->bdev_try_to_free_page is called from the ->releasepage handler of -the block device inode. See there for more details. - file_system_type ================ @@ -242,71 +238,64 @@ address_space_operations prototypes:: int (*writepage)(struct page *page, struct writeback_control *wbc); - int (*readpage)(struct file *, struct page *); + int (*read_folio)(struct file *, struct folio *); int (*writepages)(struct address_space *, struct writeback_control *); - int (*set_page_dirty)(struct page *page); + bool (*dirty_folio)(struct address_space *, struct folio *folio); void (*readahead)(struct readahead_control *); - int (*readpages)(struct file *filp, struct address_space *mapping, - struct list_head *pages, unsigned nr_pages); int (*write_begin)(struct file *, struct address_space *mapping, - loff_t pos, unsigned len, unsigned flags, + loff_t pos, unsigned len, struct page **pagep, void **fsdata); int (*write_end)(struct file *, struct address_space *mapping, loff_t pos, unsigned len, unsigned copied, struct page *page, void *fsdata); sector_t (*bmap)(struct address_space *, sector_t); - void (*invalidatepage) (struct page *, unsigned int, unsigned int); - int (*releasepage) (struct page *, int); - void (*freepage)(struct page *); + void (*invalidate_folio) (struct folio *, size_t start, size_t len); + bool (*release_folio)(struct folio *, gfp_t); + void (*free_folio)(struct folio *); int (*direct_IO)(struct kiocb *, struct iov_iter *iter); - bool (*isolate_page) (struct page *, isolate_mode_t); - int (*migratepage)(struct address_space *, struct page *, struct page *); - void (*putback_page) (struct page *); - int (*launder_page)(struct page *); - int (*is_partially_uptodate)(struct page *, unsigned long, unsigned long); + int (*migrate_folio)(struct address_space *, struct folio *dst, + struct folio *src, enum migrate_mode); + int (*launder_folio)(struct folio *); + bool (*is_partially_uptodate)(struct folio *, size_t from, size_t count); int (*error_remove_page)(struct address_space *, struct page *); - int (*swap_activate)(struct file *); + int (*swap_activate)(struct swap_info_struct *sis, struct file *f, sector_t *span) int (*swap_deactivate)(struct file *); + int (*swap_rw)(struct kiocb *iocb, struct iov_iter *iter); locking rules: - All except set_page_dirty and freepage may block + All except dirty_folio and free_folio may block ====================== ======================== ========= =============== -ops PageLocked(page) i_rwsem invalidate_lock +ops folio locked i_rwsem invalidate_lock ====================== ======================== ========= =============== writepage: yes, unlocks (see below) -readpage: yes, unlocks shared +read_folio: yes, unlocks shared writepages: -set_page_dirty no +dirty_folio: maybe readahead: yes, unlocks shared -readpages: no shared write_begin: locks the page exclusive write_end: yes, unlocks exclusive bmap: -invalidatepage: yes exclusive -releasepage: yes -freepage: yes +invalidate_folio: yes exclusive +release_folio: yes +free_folio: yes direct_IO: -isolate_page: yes -migratepage: yes (both) -putback_page: yes -launder_page: yes +migrate_folio: yes (both) +launder_folio: yes is_partially_uptodate: yes error_remove_page: yes swap_activate: no swap_deactivate: no +swap_rw: yes, unlocks ====================== ======================== ========= =============== -->write_begin(), ->write_end() and ->readpage() may be called from +->write_begin(), ->write_end() and ->read_folio() may be called from the request handler (/dev/loop). -->readpage() unlocks the page, either synchronously or via I/O +->read_folio() unlocks the folio, either synchronously or via I/O completion. -->readahead() unlocks the pages that I/O is attempted on like ->readpage(). - -->readpages() populates the pagecache with the passed pages and starts -I/O against them. They come unlocked upon I/O completion. +->readahead() unlocks the folios that I/O is attempted on like ->read_folio(). ->writepage() is used for two purposes: for "memory cleansing" and for "sync". These are quite different operations and the behaviour may differ @@ -366,46 +355,50 @@ If nr_to_write is NULL, all dirty pages must be written. writepages should _only_ write pages which are present on mapping->io_pages. -->set_page_dirty() is called from various places in the kernel -when the target page is marked as needing writeback. It may be called -under spinlock (it cannot block) and is sometimes called with the page -not locked. +->dirty_folio() is called from various places in the kernel when +the target folio is marked as needing writeback. The folio cannot be +truncated because either the caller holds the folio lock, or the caller +has found the folio while holding the page table lock which will block +truncation. ->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some filesystems and by the swapper. The latter will eventually go away. Please, keep it that way and don't breed new callers. -->invalidatepage() is called when the filesystem must attempt to drop +->invalidate_folio() is called when the filesystem must attempt to drop some or all of the buffers from the page when it is being truncated. It -returns zero on success. If ->invalidatepage is zero, the kernel uses -block_invalidatepage() instead. The filesystem must exclusively acquire -invalidate_lock before invalidating page cache in truncate / hole punch path -(and thus calling into ->invalidatepage) to block races between page cache -invalidation and page cache filling functions (fault, read, ...). - -->releasepage() is called when the kernel is about to try to drop the -buffers from the page in preparation for freeing it. It returns zero to -indicate that the buffers are (or may be) freeable. If ->releasepage is zero, -the kernel assumes that the fs has no private interest in the buffers. - -->freepage() is called when the kernel is done dropping the page +returns zero on success. The filesystem must exclusively acquire +invalidate_lock before invalidating page cache in truncate / hole punch +path (and thus calling into ->invalidate_folio) to block races between page +cache invalidation and page cache filling functions (fault, read, ...). + +->release_folio() is called when the kernel is about to try to drop the +buffers from the folio in preparation for freeing it. It returns false to +indicate that the buffers are (or may be) freeable. If ->release_folio is +NULL, the kernel assumes that the fs has no private interest in the buffers. + +->free_folio() is called when the kernel has dropped the folio from the page cache. -->launder_page() may be called prior to releasing a page if -it is still found to be dirty. It returns zero if the page was successfully -cleaned, or an error value if not. Note that in order to prevent the page +->launder_folio() may be called prior to releasing a folio if +it is still found to be dirty. It returns zero if the folio was successfully +cleaned, or an error value if not. Note that in order to prevent the folio getting mapped back in and redirtied, it needs to be kept locked across the entire operation. -->swap_activate will be called with a non-zero argument on -files backing (non block device backed) swapfiles. A return value -of zero indicates success, in which case this file can be used for -backing swapspace. The swapspace operations will be proxied to the -address space operations. +->swap_activate() will be called to prepare the given file for swap. It +should perform any validation and preparation necessary to ensure that +writes can be performed with minimal memory allocation. It should call +add_swap_extent(), or the helper iomap_swapfile_activate(), and return +the number of extents added. If IO should be submitted through +->swap_rw(), it should set SWP_FS_OPS, otherwise IO will be submitted +directly to the block device ``sis->bdev``. ->swap_deactivate() will be called in the sys_swapoff() path after ->swap_activate() returned success. +->swap_rw will be called for swap IO if SWP_FS_OPS was set by ->swap_activate(). + file_lock_operations ==================== @@ -439,17 +432,21 @@ prototypes:: void (*lm_break)(struct file_lock *); /* break_lease callback */ int (*lm_change)(struct file_lock **, int); bool (*lm_breaker_owns_lease)(struct file_lock *); + bool (*lm_lock_expirable)(struct file_lock *); + void (*lm_expire_lock)(void); locking rules: ====================== ============= ================= ========= -ops inode->i_lock blocked_lock_lock may block +ops flc_lock blocked_lock_lock may block ====================== ============= ================= ========= -lm_notify: yes yes no +lm_notify: no yes no lm_grant: no no no lm_break: yes no no lm_change yes no no -lm_breaker_owns_lease: no no no +lm_breaker_owns_lease: yes no no +lm_lock_expirable yes no no +lm_expire_lock no no yes ====================== ============= ================= ========= buffer_head diff --git a/Documentation/filesystems/netfs_library.rst b/Documentation/filesystems/netfs_library.rst index 375baca7edcd..73a4176144b3 100644 --- a/Documentation/filesystems/netfs_library.rst +++ b/Documentation/filesystems/netfs_library.rst @@ -7,6 +7,8 @@ Network Filesystem Helper Library .. Contents: - Overview. + - Per-inode context. + - Inode context helper functions. - Buffered read helpers. - Read helper functions. - Read helper structures. @@ -28,10 +30,72 @@ Note that the library module doesn't link against local caching directly, so access must be provided by the netfs. +Per-Inode Context +================= + +The network filesystem helper library needs a place to store a bit of state for +its use on each netfs inode it is helping to manage. To this end, a context +structure is defined:: + + struct netfs_inode { + struct inode inode; + const struct netfs_request_ops *ops; + struct fscache_cookie *cache; + }; + +A network filesystem that wants to use netfs lib must place one of these in its +inode wrapper struct instead of the VFS ``struct inode``. This can be done in +a way similar to the following:: + + struct my_inode { + struct netfs_inode netfs; /* Netfslib context and vfs inode */ + ... + }; + +This allows netfslib to find its state by using ``container_of()`` from the +inode pointer, thereby allowing the netfslib helper functions to be pointed to +directly by the VFS/VM operation tables. + +The structure contains the following fields: + + * ``inode`` + + The VFS inode structure. + + * ``ops`` + + The set of operations provided by the network filesystem to netfslib. + + * ``cache`` + + Local caching cookie, or NULL if no caching is enabled. This field does not + exist if fscache is disabled. + + +Inode Context Helper Functions +------------------------------ + +To help deal with the per-inode context, a number helper functions are +provided. Firstly, a function to perform basic initialisation on a context and +set the operations table pointer:: + + void netfs_inode_init(struct netfs_inode *ctx, + const struct netfs_request_ops *ops); + +then a function to cast from the VFS inode structure to the netfs context:: + + struct netfs_inode *netfs_node(struct inode *inode); + +and finally, a function to get the cache cookie pointer from the context +attached to an inode (or NULL if fscache is disabled):: + + struct fscache_cookie *netfs_i_cookie(struct netfs_inode *ctx); + + Buffered Read Helpers ===================== -The library provides a set of read helpers that handle the ->readpage(), +The library provides a set of read helpers that handle the ->read_folio(), ->readahead() and much of the ->write_begin() VM operations and translate them into a common call framework. @@ -70,38 +134,22 @@ Read Helper Functions Three read helpers are provided:: - void netfs_readahead(struct readahead_control *ractl, - const struct netfs_read_request_ops *ops, - void *netfs_priv); - int netfs_readpage(struct file *file, - struct folio *folio, - const struct netfs_read_request_ops *ops, - void *netfs_priv); - int netfs_write_begin(struct file *file, + void netfs_readahead(struct readahead_control *ractl); + int netfs_read_folio(struct file *file, + struct folio *folio); + int netfs_write_begin(struct netfs_inode *ctx, + struct file *file, struct address_space *mapping, loff_t pos, unsigned int len, - unsigned int flags, struct folio **_folio, - void **_fsdata, - const struct netfs_read_request_ops *ops, - void *netfs_priv); + void **_fsdata); -Each corresponds to a VM operation, with the addition of a couple of parameters -for the use of the read helpers: - - * ``ops`` - - A table of operations through which the helpers can talk to the filesystem. - - * ``netfs_priv`` +Each corresponds to a VM address space operation. These operations use the +state in the per-inode context. - Filesystem private data (can be NULL). - -Both of these values will be stored into the read request structure. - -For ->readahead() and ->readpage(), the network filesystem should just jump -into the corresponding read helper; whereas for ->write_begin(), it may be a +For ->readahead() and ->read_folio(), the network filesystem just point directly +at the corresponding read helper; whereas for ->write_begin(), it may be a little more complicated as the network filesystem might want to flush conflicting writes or track dirty data and needs to put the acquired folio if an error occurs after calling the helper. @@ -110,13 +158,14 @@ The helpers manage the read request, calling back into the network filesystem through the suppplied table of operations. Waits will be performed as necessary before returning for helpers that are meant to be synchronous. -If an error occurs and netfs_priv is non-NULL, ops->cleanup() will be called to -deal with it. If some parts of the request are in progress when an error -occurs, the request will get partially completed if sufficient data is read. +If an error occurs, the ->free_request() will be called to clean up the +netfs_io_request struct allocated. If some parts of the request are in +progress when an error occurs, the request will get partially completed if +sufficient data is read. Additionally, there is:: - * void netfs_subreq_terminated(struct netfs_read_subrequest *subreq, + * void netfs_subreq_terminated(struct netfs_io_subrequest *subreq, ssize_t transferred_or_error, bool was_async); @@ -132,7 +181,7 @@ Read Helper Structures The read helpers make use of a couple of structures to maintain the state of the read. The first is a structure that manages a read request as a whole:: - struct netfs_read_request { + struct netfs_io_request { struct inode *inode; struct address_space *mapping; struct netfs_cache_resources cache_resources; @@ -140,7 +189,7 @@ the read. The first is a structure that manages a read request as a whole:: loff_t start; size_t len; loff_t i_size; - const struct netfs_read_request_ops *netfs_ops; + const struct netfs_request_ops *netfs_ops; unsigned int debug_id; ... }; @@ -160,8 +209,7 @@ The above fields are the ones the netfs can use. They are: * ``netfs_priv`` The network filesystem's private data. The value for this can be passed in - to the helper functions or set during the request. The ->cleanup() op will - be called if this is non-NULL at the end. + to the helper functions or set during the request. * ``start`` * ``len`` @@ -187,8 +235,8 @@ The above fields are the ones the netfs can use. They are: The second structure is used to manage individual slices of the overall read request:: - struct netfs_read_subrequest { - struct netfs_read_request *rreq; + struct netfs_io_subrequest { + struct netfs_io_request *rreq; loff_t start; size_t len; size_t transferred; @@ -244,31 +292,30 @@ Read Helper Operations The network filesystem must provide the read helpers with a table of operations through which it can issue requests and negotiate:: - struct netfs_read_request_ops { - void (*init_rreq)(struct netfs_read_request *rreq, struct file *file); - bool (*is_cache_enabled)(struct inode *inode); - int (*begin_cache_operation)(struct netfs_read_request *rreq); - void (*expand_readahead)(struct netfs_read_request *rreq); - bool (*clamp_length)(struct netfs_read_subrequest *subreq); - void (*issue_op)(struct netfs_read_subrequest *subreq); - bool (*is_still_valid)(struct netfs_read_request *rreq); + struct netfs_request_ops { + void (*init_request)(struct netfs_io_request *rreq, struct file *file); + void (*free_request)(struct netfs_io_request *rreq); + int (*begin_cache_operation)(struct netfs_io_request *rreq); + void (*expand_readahead)(struct netfs_io_request *rreq); + bool (*clamp_length)(struct netfs_io_subrequest *subreq); + void (*issue_read)(struct netfs_io_subrequest *subreq); + bool (*is_still_valid)(struct netfs_io_request *rreq); int (*check_write_begin)(struct file *file, loff_t pos, unsigned len, - struct folio *folio, void **_fsdata); - void (*done)(struct netfs_read_request *rreq); - void (*cleanup)(struct address_space *mapping, void *netfs_priv); + struct folio **foliop, void **_fsdata); + void (*done)(struct netfs_io_request *rreq); }; The operations are as follows: - * ``init_rreq()`` + * ``init_request()`` [Optional] This is called to initialise the request structure. It is given - the file for reference and can modify the ->netfs_priv value. + the file for reference. - * ``is_cache_enabled()`` + * ``free_request()`` - [Required] This is called by netfs_write_begin() to ask if the file is being - cached. It should return true if it is being cached and false otherwise. + [Optional] This is called as the request is being deallocated so that the + filesystem can clean up any state it has attached there. * ``begin_cache_operation()`` @@ -305,7 +352,7 @@ The operations are as follows: This should return 0 on success and an error code on error. - * ``issue_op()`` + * ``issue_read()`` [Required] The helpers use this to dispatch a subrequest to the server for reading. In the subrequest, ->start, ->len and ->transferred indicate what @@ -334,19 +381,16 @@ The operations are as follows: allocated/grabbed the folio to be modified to allow the filesystem to flush conflicting state before allowing it to be modified. - It should return 0 if everything is now fine, -EAGAIN if the folio should be - regrabbed and any other error code to abort the operation. + It may unlock and discard the folio it was given and set the caller's folio + pointer to NULL. It should return 0 if everything is now fine (``*foliop`` + left set) or the op should be retried (``*foliop`` cleared) and any other + error code to abort the operation. * ``done`` [Optional] This is called after the folios in the request have all been unlocked (and marked uptodate if applicable). - * ``cleanup`` - - [Optional] This is called as the request is being deallocated so that the - filesystem can clean up ->netfs_priv. - Read Helper Procedure @@ -420,12 +464,12 @@ The network filesystem's ->begin_cache_operation() method is called to set up a cache and this must call into the cache to do the work. If using fscache, for example, the cache would call:: - int fscache_begin_read_operation(struct netfs_read_request *rreq, + int fscache_begin_read_operation(struct netfs_io_request *rreq, struct fscache_cookie *cookie); passing in the request pointer and the cookie corresponding to the file. -The netfs_read_request object contains a place for the cache to hang its +The netfs_io_request object contains a place for the cache to hang its state:: struct netfs_cache_resources { @@ -443,7 +487,7 @@ operation table looks like the following:: void (*expand_readahead)(struct netfs_cache_resources *cres, loff_t *_start, size_t *_len, loff_t i_size); - enum netfs_read_source (*prepare_read)(struct netfs_read_subrequest *subreq, + enum netfs_io_source (*prepare_read)(struct netfs_io_subrequest *subreq, loff_t i_size); int (*read)(struct netfs_cache_resources *cres, @@ -454,13 +498,18 @@ operation table looks like the following:: void *term_func_priv); int (*prepare_write)(struct netfs_cache_resources *cres, - loff_t *_start, size_t *_len, loff_t i_size); + loff_t *_start, size_t *_len, loff_t i_size, + bool no_space_allocated_yet); int (*write)(struct netfs_cache_resources *cres, loff_t start_pos, struct iov_iter *iter, netfs_io_terminated_t term_func, void *term_func_priv); + + int (*query_occupancy)(struct netfs_cache_resources *cres, + loff_t start, size_t len, size_t granularity, + loff_t *_data_start, size_t *_data_len); }; With a termination handler function pointer:: @@ -515,11 +564,14 @@ The methods defined in the table are: * ``prepare_write()`` - [Required] Called to adjust a write to the cache and check that there is - sufficient space in the cache. The start and length values indicate the - size of the write that netfslib is proposing, and this can be adjusted by - the cache to respect DIO boundaries. The file size is passed for - information. + [Required] Called to prepare a write to the cache to take place. This + involves checking to see whether the cache has sufficient space to honour + the write. ``*_start`` and ``*_len`` indicate the region to be written; the + region can be shrunk or it can be expanded to a page boundary either way as + necessary to align for direct I/O. i_size holds the size of the object and + is provided for reference. no_space_allocated_yet is set to true if the + caller is certain that no data has been written to that region - for example + if it tried to do a read from there already. * ``write()`` @@ -532,6 +584,18 @@ The methods defined in the table are: indicating whether the termination is definitely happening in the caller's context. + * ``query_occupancy()`` + + [Required] Called to find out where the next piece of data is within a + particular region of the cache. The start and length of the region to be + queried are passed in, along with the granularity to which the answer needs + to be aligned. The function passes back the start and length of the data, + if any, available within that region. Note that there may be a hole at the + front. + + It returns 0 if some data was found, -ENODATA if there was no usable data + within the region or -ENOBUFS if there is no caching on this file. + Note that these methods are passed a pointer to the cache resource structure, not the read request structure as they could be used in other situations where there isn't a read request structure as well, such as writing dirty data to the @@ -542,4 +606,5 @@ API Function Reference ====================== .. kernel-doc:: include/linux/netfs.h -.. kernel-doc:: fs/netfs/read_helper.c +.. kernel-doc:: fs/netfs/buffered_read.c +.. kernel-doc:: fs/netfs/io.c diff --git a/Documentation/filesystems/nfs/client-identifier.rst b/Documentation/filesystems/nfs/client-identifier.rst new file mode 100644 index 000000000000..5147e15815a1 --- /dev/null +++ b/Documentation/filesystems/nfs/client-identifier.rst @@ -0,0 +1,216 @@ +.. SPDX-License-Identifier: GPL-2.0 + +======================= +NFSv4 client identifier +======================= + +This document explains how the NFSv4 protocol identifies client +instances in order to maintain file open and lock state during +system restarts. A special identifier and principal are maintained +on each client. These can be set by administrators, scripts +provided by site administrators, or tools provided by Linux +distributors. + +There are risks if a client's NFSv4 identifier and its principal +are not chosen carefully. + + +Introduction +------------ + +The NFSv4 protocol uses "lease-based file locking". Leases help +NFSv4 servers provide file lock guarantees and manage their +resources. + +Simply put, an NFSv4 server creates a lease for each NFSv4 client. +The server collects each client's file open and lock state under +the lease for that client. + +The client is responsible for periodically renewing its leases. +While a lease remains valid, the server holding that lease +guarantees the file locks the client has created remain in place. + +If a client stops renewing its lease (for example, if it crashes), +the NFSv4 protocol allows the server to remove the client's open +and lock state after a certain period of time. When a client +restarts, it indicates to servers that open and lock state +associated with its previous leases is no longer valid and can be +destroyed immediately. + +In addition, each NFSv4 server manages a persistent list of client +leases. When the server restarts and clients attempt to recover +their state, the server uses this list to distinguish amongst +clients that held state before the server restarted and clients +sending fresh OPEN and LOCK requests. This enables file locks to +persist safely across server restarts. + +NFSv4 client identifiers +------------------------ + +Each NFSv4 client presents an identifier to NFSv4 servers so that +they can associate the client with its lease. Each client's +identifier consists of two elements: + + - co_ownerid: An arbitrary but fixed string. + + - boot verifier: A 64-bit incarnation verifier that enables a + server to distinguish successive boot epochs of the same client. + +The NFSv4.0 specification refers to these two items as an +"nfs_client_id4". The NFSv4.1 specification refers to these two +items as a "client_owner4". + +NFSv4 servers tie this identifier to the principal and security +flavor that the client used when presenting it. Servers use this +principal to authorize subsequent lease modification operations +sent by the client. Effectively this principal is a third element of +the identifier. + +As part of the identity presented to servers, a good +"co_ownerid" string has several important properties: + + - The "co_ownerid" string identifies the client during reboot + recovery, therefore the string is persistent across client + reboots. + - The "co_ownerid" string helps servers distinguish the client + from others, therefore the string is globally unique. Note + that there is no central authority that assigns "co_ownerid" + strings. + - Because it often appears on the network in the clear, the + "co_ownerid" string does not reveal private information about + the client itself. + - The content of the "co_ownerid" string is set and unchanging + before the client attempts NFSv4 mounts after a restart. + - The NFSv4 protocol places a 1024-byte limit on the size of the + "co_ownerid" string. + +Protecting NFSv4 lease state +---------------------------- + +NFSv4 servers utilize the "client_owner4" as described above to +assign a unique lease to each client. Under this scheme, there are +circumstances where clients can interfere with each other. This is +referred to as "lease stealing". + +If distinct clients present the same "co_ownerid" string and use +the same principal (for example, AUTH_SYS and UID 0), a server is +unable to tell that the clients are not the same. Each distinct +client presents a different boot verifier, so it appears to the +server as if there is one client that is rebooting frequently. +Neither client can maintain open or lock state in this scenario. + +If distinct clients present the same "co_ownerid" string and use +distinct principals, the server is likely to allow the first client +to operate normally but reject subsequent clients with the same +"co_ownerid" string. + +If a client's "co_ownerid" string or principal are not stable, +state recovery after a server or client reboot is not guaranteed. +If a client unexpectedly restarts but presents a different +"co_ownerid" string or principal to the server, the server orphans +the client's previous open and lock state. This blocks access to +locked files until the server removes the orphaned state. + +If the server restarts and a client presents a changed "co_ownerid" +string or principal to the server, the server will not allow the +client to reclaim its open and lock state, and may give those locks +to other clients in the meantime. This is referred to as "lock +stealing". + +Lease stealing and lock stealing increase the potential for denial +of service and in rare cases even data corruption. + +Selecting an appropriate client identifier +------------------------------------------ + +By default, the Linux NFSv4 client implementation constructs its +"co_ownerid" string starting with the words "Linux NFS" followed by +the client's UTS node name (the same node name, incidentally, that +is used as the "machine name" in an AUTH_SYS credential). In small +deployments, this construction is usually adequate. Often, however, +the node name by itself is not adequately unique, and can change +unexpectedly. Problematic situations include: + + - NFS-root (diskless) clients, where the local DCHP server (or + equivalent) does not provide a unique host name. + + - "Containers" within a single Linux host. If each container has + a separate network namespace, but does not use the UTS namespace + to provide a unique host name, then there can be multiple NFS + client instances with the same host name. + + - Clients across multiple administrative domains that access a + common NFS server. If hostnames are not assigned centrally + then uniqueness cannot be guaranteed unless a domain name is + included in the hostname. + +Linux provides two mechanisms to add uniqueness to its "co_ownerid" +string: + + nfs.nfs4_unique_id + This module parameter can set an arbitrary uniquifier string + via the kernel command line, or when the "nfs" module is + loaded. + + /sys/fs/nfs/client/net/identifier + This virtual file, available since Linux 5.3, is local to the + network namespace in which it is accessed and so can provide + distinction between network namespaces (containers) when the + hostname remains uniform. + +Note that this file is empty on name-space creation. If the +container system has access to some sort of per-container identity +then that uniquifier can be used. For example, a uniquifier might +be formed at boot using the container's internal identifier: + + sha256sum /etc/machine-id | awk '{print $1}' \\ + > /sys/fs/nfs/client/net/identifier + +Security considerations +----------------------- + +The use of cryptographic security for lease management operations +is strongly encouraged. + +If NFS with Kerberos is not configured, a Linux NFSv4 client uses +AUTH_SYS and UID 0 as the principal part of its client identity. +This configuration is not only insecure, it increases the risk of +lease and lock stealing. However, it might be the only choice for +client configurations that have no local persistent storage. +"co_ownerid" string uniqueness and persistence is critical in this +case. + +When a Kerberos keytab is present on a Linux NFS client, the client +attempts to use one of the principals in that keytab when +identifying itself to servers. The "sec=" mount option does not +control this behavior. Alternately, a single-user client with a +Kerberos principal can use that principal in place of the client's +host principal. + +Using Kerberos for this purpose enables the client and server to +use the same lease for operations covered by all "sec=" settings. +Additionally, the Linux NFS client uses the RPCSEC_GSS security +flavor with Kerberos and the integrity QOS to prevent in-transit +modification of lease modification requests. + +Additional notes +---------------- +The Linux NFSv4 client establishes a single lease on each NFSv4 +server it accesses. NFSv4 mounts from a Linux NFSv4 client of a +particular server then share that lease. + +Once a client establishes open and lock state, the NFSv4 protocol +enables lease state to transition to other servers, following data +that has been migrated. This hides data migration completely from +running applications. The Linux NFSv4 client facilitates state +migration by presenting the same "client_owner4" to all servers it +encounters. + +======== +See Also +======== + + - nfs(5) + - kerberos(7) + - RFC 7530 for the NFSv4.0 specification + - RFC 8881 for the NFSv4.1 specification. diff --git a/Documentation/filesystems/nfs/index.rst b/Documentation/filesystems/nfs/index.rst index 288d8ddb2bc6..8536134f31fd 100644 --- a/Documentation/filesystems/nfs/index.rst +++ b/Documentation/filesystems/nfs/index.rst @@ -6,6 +6,8 @@ NFS .. toctree:: :maxdepth: 1 + client-identifier + exporting pnfs rpc-cache rpc-server-gss diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst index 7da6c30ed596..4c76fda07645 100644 --- a/Documentation/filesystems/overlayfs.rst +++ b/Documentation/filesystems/overlayfs.rst @@ -607,7 +607,7 @@ can be removed. User xattr ---------- -The the "-o userxattr" mount option forces overlayfs to use the +The "-o userxattr" mount option forces overlayfs to use the "user.overlay." xattr namespace instead of "trusted.overlay.". This is useful for unprivileged mounting of overlayfs. diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst index bf19fd6b86e7..df0dc37e6f58 100644 --- a/Documentation/filesystems/porting.rst +++ b/Documentation/filesystems/porting.rst @@ -45,6 +45,12 @@ typically between calling iget_locked() and unlocking the inode. At some point that will become mandatory. +**mandatory** + +The foo_inode_info should always be allocated through alloc_inode_sb() rather +than kmem_cache_alloc() or kmalloc() related to set up the inode reclaim context +correctly. + --- **mandatory** @@ -618,7 +624,7 @@ any symlink that might use page_follow_link_light/page_put_link() must have inode_nohighmem(inode) called before anything might start playing with its pagecache. No highmem pages should end up in the pagecache of such symlinks. That includes any preseeding that might be done during symlink -creation. __page_symlink() will honour the mapping gfp flags, so once +creation. page_symlink() will honour the mapping gfp flags, so once you've done inode_nohighmem() it's safe to use, but if you allocate and insert the page manually, make sure to use the right gfp flags. @@ -908,3 +914,32 @@ Calling conventions for file_open_root() changed; now it takes struct path * instead of passing mount and dentry separately. For callers that used to pass <mnt, mnt->mnt_root> pair (i.e. the root of given mount), a new helper is provided - file_open_root_mnt(). In-tree users adjusted. + +--- + +**mandatory** + +no_llseek is gone; don't set .llseek to that - just leave it NULL instead. +Checks for "does that file have llseek(2), or should it fail with ESPIPE" +should be done by looking at FMODE_LSEEK in file->f_mode. + +--- + +*mandatory* + +filldir_t (readdir callbacks) calling conventions have changed. Instead of +returning 0 or -E... it returns bool now. false means "no more" (as -E... used +to) and true - "keep going" (as 0 in old calling conventions). Rationale: +callers never looked at specific -E... values anyway. ->iterate() and +->iterate_shared() instance require no changes at all, all filldir_t ones in +the tree converted. + +--- + +**mandatory** + +Calling conventions for ->tmpfile() have changed. It now takes a struct +file pointer instead of struct dentry pointer. d_tmpfile() is similarly +changed to simplify callers. The passed file is in a non-open state and on +success must be opened before returning (e.g. by calling +finish_open_simple()). diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst index 8d7f141c6fc7..898c99eae8e4 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst @@ -426,12 +426,14 @@ with the memory region, as the case would be with BSS (uninitialized data). The "pathname" shows the name associated file for this mapping. If the mapping is not associated with a file: - ======= ==================================== + ============= ==================================== [heap] the heap of the program [stack] the stack of the main process [vdso] the "virtual dynamic shared object", the kernel system call handler - ======= ==================================== + [anon:<name>] an anonymous mapping that has been + named by userspace + ============= ==================================== or if empty, the mapping is anonymous. @@ -446,6 +448,7 @@ Memory Area, or VMA) there is a series of lines such as the following:: MMUPageSize: 4 kB Rss: 892 kB Pss: 374 kB + Pss_Dirty: 0 kB Shared_Clean: 892 kB Shared_Dirty: 0 kB Private_Clean: 0 kB @@ -477,7 +480,9 @@ dirty shared and private pages in the mapping. The "proportional set size" (PSS) of a process is the count of pages it has in memory, where each page is divided by the number of processes sharing it. So if a process has 1000 pages all to itself, and 1000 shared with one other -process, its PSS will be 1500. +process, its PSS will be 1500. "Pss_Dirty" is the portion of PSS which +consists of dirty pages. ("Pss_Clean" is not included, but it can be +calculated by subtracting "Pss_Dirty" from "Pss".) Note that even a page which is part of a MAP_SHARED mapping, but has only a single pte mapped, i.e. is currently used by only one process, is accounted @@ -512,8 +517,10 @@ replaced by copy-on-write) part of the underlying shmem object out on swap. "SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this does not take into account swapped out page of underlying shmem objects. "Locked" indicates whether the mapping is locked in memory or not. + "THPeligible" indicates whether the mapping is eligible for allocating THP -pages - 1 if true, 0 otherwise. It just shows the current status. +pages as well as the THP is PMD mappable or not - 1 if true, 0 otherwise. +It just shows the current status. "VmFlags" field deserves a separate description. This member represents the kernel flags associated with the particular virtual memory area in two letter @@ -940,56 +947,74 @@ can be substantial. In many cases there are other means to find out additional memory using subsystem specific interfaces, for instance /proc/net/sockstat for TCP memory allocations. -The following is from a 16GB PIII, which has highmem enabled. -You may not have all of these fields. +Example output. You may not have all of these fields. :: > cat /proc/meminfo - MemTotal: 16344972 kB - MemFree: 13634064 kB - MemAvailable: 14836172 kB - Buffers: 3656 kB - Cached: 1195708 kB - SwapCached: 0 kB - Active: 891636 kB - Inactive: 1077224 kB - HighTotal: 15597528 kB - HighFree: 13629632 kB - LowTotal: 747444 kB - LowFree: 4432 kB - SwapTotal: 0 kB - SwapFree: 0 kB - Dirty: 968 kB - Writeback: 0 kB - AnonPages: 861800 kB - Mapped: 280372 kB - Shmem: 644 kB - KReclaimable: 168048 kB - Slab: 284364 kB - SReclaimable: 159856 kB - SUnreclaim: 124508 kB - PageTables: 24448 kB - NFS_Unstable: 0 kB - Bounce: 0 kB - WritebackTmp: 0 kB - CommitLimit: 7669796 kB - Committed_AS: 100056 kB - VmallocTotal: 112216 kB - VmallocUsed: 428 kB - VmallocChunk: 111088 kB - Percpu: 62080 kB - HardwareCorrupted: 0 kB - AnonHugePages: 49152 kB - ShmemHugePages: 0 kB - ShmemPmdMapped: 0 kB + MemTotal: 32858820 kB + MemFree: 21001236 kB + MemAvailable: 27214312 kB + Buffers: 581092 kB + Cached: 5587612 kB + SwapCached: 0 kB + Active: 3237152 kB + Inactive: 7586256 kB + Active(anon): 94064 kB + Inactive(anon): 4570616 kB + Active(file): 3143088 kB + Inactive(file): 3015640 kB + Unevictable: 0 kB + Mlocked: 0 kB + SwapTotal: 0 kB + SwapFree: 0 kB + Zswap: 1904 kB + Zswapped: 7792 kB + Dirty: 12 kB + Writeback: 0 kB + AnonPages: 4654780 kB + Mapped: 266244 kB + Shmem: 9976 kB + KReclaimable: 517708 kB + Slab: 660044 kB + SReclaimable: 517708 kB + SUnreclaim: 142336 kB + KernelStack: 11168 kB + PageTables: 20540 kB + SecPageTables: 0 kB + NFS_Unstable: 0 kB + Bounce: 0 kB + WritebackTmp: 0 kB + CommitLimit: 16429408 kB + Committed_AS: 7715148 kB + VmallocTotal: 34359738367 kB + VmallocUsed: 40444 kB + VmallocChunk: 0 kB + Percpu: 29312 kB + HardwareCorrupted: 0 kB + AnonHugePages: 4149248 kB + ShmemHugePages: 0 kB + ShmemPmdMapped: 0 kB + FileHugePages: 0 kB + FilePmdMapped: 0 kB + CmaTotal: 0 kB + CmaFree: 0 kB + HugePages_Total: 0 + HugePages_Free: 0 + HugePages_Rsvd: 0 + HugePages_Surp: 0 + Hugepagesize: 2048 kB + Hugetlb: 0 kB + DirectMap4k: 401152 kB + DirectMap2M: 10008576 kB + DirectMap1G: 24117248 kB MemTotal Total usable RAM (i.e. physical RAM minus a few reserved bits and the kernel binary code) MemFree - The sum of LowFree+HighFree + Total free RAM. On highmem systems, the sum of LowFree+HighFree MemAvailable An estimate of how much memory is available for starting new applications, without swapping. Calculated from MemFree, @@ -1003,8 +1028,9 @@ Buffers Relatively temporary storage for raw disk blocks shouldn't get tremendously large (20MB or so) Cached - in-memory cache for files read from the disk (the - pagecache). Doesn't include SwapCached + In-memory cache for files read from the disk (the + pagecache) as well as tmpfs & shmem. + Doesn't include SwapCached. SwapCached Memory that once was swapped out, is swapped back in but still also is in the swapfile (if memory is needed it @@ -1016,6 +1042,11 @@ Active Inactive Memory which has been less recently used. It is more eligible to be reclaimed for other purposes +Unevictable + Memory allocated for userspace which cannot be reclaimed, such + as mlocked pages, ramfs backing pages, secret memfd pages etc. +Mlocked + Memory locked with mlock(). HighTotal, HighFree Highmem is all memory above ~860MB of physical memory. Highmem areas are for use by userspace programs, or @@ -1032,26 +1063,20 @@ SwapTotal SwapFree Memory which has been evicted from RAM, and is temporarily on the disk +Zswap + Memory consumed by the zswap backend (compressed size) +Zswapped + Amount of anonymous memory stored in zswap (original size) Dirty Memory which is waiting to get written back to the disk Writeback Memory which is actively being written back to the disk AnonPages Non-file backed pages mapped into userspace page tables -HardwareCorrupted - The amount of RAM/memory in KB, the kernel identifies as - corrupted. -AnonHugePages - Non-file backed huge pages mapped into userspace page tables Mapped files which have been mmaped, such as libraries Shmem Total memory used by shared memory (shmem) and tmpfs -ShmemHugePages - Memory used by shared memory (shmem) and tmpfs allocated - with huge pages -ShmemPmdMapped - Shared memory mapped into userspace with huge pages KReclaimable Kernel allocations that the kernel will attempt to reclaim under memory pressure. Includes SReclaimable (below), and other @@ -1062,9 +1087,13 @@ SReclaimable Part of Slab, that might be reclaimed, such as caches SUnreclaim Part of Slab, that cannot be reclaimed on memory pressure +KernelStack + Memory consumed by the kernel stacks of all tasks PageTables - amount of memory dedicated to the lowest level of page - tables. + Memory consumed by userspace page tables +SecPageTables + Memory consumed by secondary page tables, this currently + currently includes KVM mmu allocations on x86 and arm64. NFS_Unstable Always zero. Previous counted pages which had been written to the server, but has not been committed to stable storage. @@ -1089,14 +1118,14 @@ CommitLimit yield a CommitLimit of 7.3G. For more details, see the memory overcommit documentation - in vm/overcommit-accounting. + in mm/overcommit-accounting. Committed_AS The amount of memory presently allocated on the system. The committed memory is a sum of all of the memory which has been allocated by processes, even if it has not been "used" by them as of yet. A process which malloc()'s 1G of memory, but only touches 300M of it will show up as - using 1G. This 1G is memory which has been "committed" to + using 1G. This 1G is memory which has been "committed" to by the VM and can be used at any time by the allocating application. With strict overcommit enabled on the system (mode 2 in 'vm.overcommit_memory'), allocations which would @@ -1105,7 +1134,7 @@ Committed_AS not fail due to lack of memory once that memory has been successfully allocated. VmallocTotal - total size of vmalloc memory area + total size of vmalloc virtual address space VmallocUsed amount of vmalloc area which is used VmallocChunk @@ -1113,6 +1142,30 @@ VmallocChunk Percpu Memory allocated to the percpu allocator used to back percpu allocations. This stat excludes the cost of metadata. +HardwareCorrupted + The amount of RAM/memory in KB, the kernel identifies as + corrupted. +AnonHugePages + Non-file backed huge pages mapped into userspace page tables +ShmemHugePages + Memory used by shared memory (shmem) and tmpfs allocated + with huge pages +ShmemPmdMapped + Shared memory mapped into userspace with huge pages +FileHugePages + Memory used for filesystem data (page cache) allocated + with huge pages +FilePmdMapped + Page cache mapped into userspace with huge pages +CmaTotal + Memory reserved for the Contiguous Memory Allocator (CMA) +CmaFree + Free remaining memory in the CMA reserves +HugePages_Total, HugePages_Free, HugePages_Rsvd, HugePages_Surp, Hugepagesize, Hugetlb + See Documentation/admin-guide/mm/hugetlbpage.rst. +DirectMap4k, DirectMap2M, DirectMap1G + Breakdown of page table sizes used in the kernel's + identity mapping of RAM vmallocinfo ~~~~~~~~~~~ @@ -1181,85 +1234,7 @@ Provides counts of softirq handlers serviced since boot time, for each CPU. HRTIMER: 0 0 0 0 RCU: 1678 1769 2178 2250 - -1.3 IDE devices in /proc/ide ----------------------------- - -The subdirectory /proc/ide contains information about all IDE devices of which -the kernel is aware. There is one subdirectory for each IDE controller, the -file drivers and a link for each IDE device, pointing to the device directory -in the controller specific subtree. - -The file 'drivers' contains general information about the drivers used for the -IDE devices:: - - > cat /proc/ide/drivers - ide-cdrom version 4.53 - ide-disk version 1.08 - -More detailed information can be found in the controller specific -subdirectories. These are named ide0, ide1 and so on. Each of these -directories contains the files shown in table 1-6. - - -.. table:: Table 1-6: IDE controller info in /proc/ide/ide? - - ======= ======================================= - File Content - ======= ======================================= - channel IDE channel (0 or 1) - config Configuration (only for PCI/IDE bridge) - mate Mate name - model Type/Chipset of IDE controller - ======= ======================================= - -Each device connected to a controller has a separate subdirectory in the -controllers directory. The files listed in table 1-7 are contained in these -directories. - - -.. table:: Table 1-7: IDE device information - - ================ ========================================== - File Content - ================ ========================================== - cache The cache - capacity Capacity of the medium (in 512Byte blocks) - driver driver and version - geometry physical and logical geometry - identify device identify block - media media type - model device identifier - settings device setup - smart_thresholds IDE disk management thresholds - smart_values IDE disk management values - ================ ========================================== - -The most interesting file is ``settings``. This file contains a nice -overview of the drive parameters:: - - # cat /proc/ide/ide0/hda/settings - name value min max mode - ---- ----- --- --- ---- - bios_cyl 526 0 65535 rw - bios_head 255 0 255 rw - bios_sect 63 0 63 rw - breada_readahead 4 0 127 rw - bswap 0 0 1 r - file_readahead 72 0 2097151 rw - io_32bit 0 0 3 rw - keepsettings 0 0 1 rw - max_kb_per_request 122 1 127 rw - multcount 0 0 8 rw - nice1 1 0 1 rw - nowerr 0 0 1 rw - pio_mode write-only 0 255 w - slow 0 0 1 rw - unmaskirq 0 0 1 rw - using_dma 0 0 1 rw - - -1.4 Networking info in /proc/net +1.3 Networking info in /proc/net -------------------------------- The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the @@ -1338,7 +1313,7 @@ It will contain information that is specific to that bond, such as the current slaves of the bond, the link status of the slaves, and how many times the slaves link has failed. -1.5 SCSI info +1.4 SCSI info ------------- If you have a SCSI host adapter in your system, you'll find a subdirectory @@ -1401,7 +1376,7 @@ AHA-2940 SCSI adapter:: Total transfers 0 (0 reads and 0 writes) -1.6 Parallel port info in /proc/parport +1.5 Parallel port info in /proc/parport --------------------------------------- The directory /proc/parport contains information about the parallel ports of @@ -1426,7 +1401,7 @@ These directories contain the four files shown in Table 1-10. number or none). ========= ==================================================================== -1.7 TTY info in /proc/tty +1.6 TTY info in /proc/tty ------------------------- Information about the available and actually used tty's can be found in the @@ -1461,7 +1436,7 @@ To see which tty's are currently in use, you can simply look into the file unknown /dev/tty 4 1-63 console -1.8 Miscellaneous kernel statistics in /proc/stat +1.7 Miscellaneous kernel statistics in /proc/stat ------------------------------------------------- Various pieces of information about kernel activity are available in the @@ -1534,7 +1509,7 @@ softirqs serviced; each subsequent column is the total for that particular softirq. -1.9 Ext4 file system parameters +1.8 Ext4 file system parameters ------------------------------- Information about mounted ext4 file systems can be found in @@ -1550,7 +1525,7 @@ in Table 1-12, below. mb_groups details of multiblock allocator buddy cache of free blocks ============== ========================================================== -1.10 /proc/consoles +1.9 /proc/consoles ------------------- Shows registered system console lines. diff --git a/Documentation/filesystems/qnx6.rst b/Documentation/filesystems/qnx6.rst index fd13433d362c..523b798f04e7 100644 --- a/Documentation/filesystems/qnx6.rst +++ b/Documentation/filesystems/qnx6.rst @@ -176,7 +176,7 @@ Then userspace. The requirement for a static, fixed preallocated system area comes from how qnx6fs deals with writes. -Each superblock got it's own half of the system area. So superblock #1 +Each superblock got its own half of the system area. So superblock #1 always uses blocks from the lower half while superblock #2 just writes to blocks represented by the upper half bitmap system area bits. diff --git a/Documentation/filesystems/spufs/spufs.rst b/Documentation/filesystems/spufs/spufs.rst index 8a42859bb100..ca0441cbe37e 100644 --- a/Documentation/filesystems/spufs/spufs.rst +++ b/Documentation/filesystems/spufs/spufs.rst @@ -227,7 +227,7 @@ Files from the data buffer, updating the value of the specified signal notification register. The signal notification register will either be replaced with the input data or will be updated to the - bitwise OR or the old value and the input data, depending on the + bitwise OR of the old value and the input data, depending on the contents of the signal1_type, or signal2_type respectively, file. diff --git a/Documentation/filesystems/sysfs.rst b/Documentation/filesystems/sysfs.rst index 004d490179f3..8bba676b1365 100644 --- a/Documentation/filesystems/sysfs.rst +++ b/Documentation/filesystems/sysfs.rst @@ -263,7 +263,7 @@ A very simple (and naive) implementation of a device attribute is:: static ssize_t show_name(struct device *dev, struct device_attribute *attr, char *buf) { - return scnprintf(buf, PAGE_SIZE, "%s\n", dev->name); + return sysfs_emit(buf, "%s\n", dev->name); } static ssize_t store_name(struct device *dev, struct device_attribute *attr, diff --git a/Documentation/filesystems/ubifs.rst b/Documentation/filesystems/ubifs.rst index e6ee99762534..ced2f7679ddb 100644 --- a/Documentation/filesystems/ubifs.rst +++ b/Documentation/filesystems/ubifs.rst @@ -59,7 +59,7 @@ differences. * JFFS2 is a write-through file-system, while UBIFS supports write-back, which makes UBIFS much faster on writes. -Similarly to JFFS2, UBIFS supports on-the-flight compression which makes +Similarly to JFFS2, UBIFS supports on-the-fly compression which makes it possible to fit quite a lot of data to the flash. Similarly to JFFS2, UBIFS is tolerant of unclean reboots and power-cuts. diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst index bf5c48066fac..2b55f71e2ae1 100644 --- a/Documentation/filesystems/vfs.rst +++ b/Documentation/filesystems/vfs.rst @@ -274,6 +274,9 @@ or bottom half). This is specifically for the inode itself being marked dirty, not its data. If the update needs to be persisted by fdatasync(), then I_DIRTY_DATASYNC will be set in the flags argument. + I_DIRTY_TIME will be set in the flags in case lazytime is enabled + and struct inode has times updated since the last ->dirty_inode + call. ``write_inode`` this method is called when the VFS needs to write an inode to @@ -439,7 +442,7 @@ As of kernel 2.6.22, the following members are defined: void (*update_time)(struct inode *, struct timespec *, int); int (*atomic_open)(struct inode *, struct dentry *, struct file *, unsigned open_flag, umode_t create_mode); - int (*tmpfile) (struct user_namespace *, struct inode *, struct dentry *, umode_t); + int (*tmpfile) (struct user_namespace *, struct inode *, struct file *, umode_t); int (*set_acl)(struct user_namespace *, struct inode *, struct posix_acl *, int); int (*fileattr_set)(struct user_namespace *mnt_userns, struct dentry *dentry, struct fileattr *fa); @@ -589,7 +592,9 @@ otherwise noted. ``tmpfile`` called in the end of O_TMPFILE open(). Optional, equivalent to atomically creating, opening and unlinking a file in given - directory. + directory. On success needs to return with the file already + open; this can be done by calling finish_open_simple() right at + the end. ``fileattr_get`` called on ioctl(FS_IOC_GETFLAGS) and ioctl(FS_IOC_FSGETXATTR) to @@ -620,9 +625,9 @@ Writeback. The first can be used independently to the others. The VM can try to either write dirty pages in order to clean them, or release clean pages in order to reuse them. To do this it can call the ->writepage method -on dirty pages, and ->releasepage on clean pages with PagePrivate set. -Clean pages without PagePrivate and with no external references will be -released without notice being given to the address_space. +on dirty pages, and ->release_folio on clean folios with the private +flag set. Clean pages without PagePrivate and with no external references +will be released without notice being given to the address_space. To achieve this functionality, pages need to be placed on an LRU with lru_cache_add and mark_page_active needs to be called whenever the page @@ -656,9 +661,9 @@ by memory-mapping the page. Data is written into the address space by the application, and then written-back to storage typically in whole pages, however the address_space has finer control of write sizes. -The read process essentially only requires 'readpage'. The write +The read process essentially only requires 'read_folio'. The write process is more complicated and uses write_begin/write_end or -set_page_dirty to write data into the address_space, and writepage and +dirty_folio to write data into the address_space, and writepage and writepages to writeback data to storage. Adding and removing pages to/from an address_space is protected by the @@ -722,37 +727,32 @@ cache in your filesystem. The following members are defined: struct address_space_operations { int (*writepage)(struct page *page, struct writeback_control *wbc); - int (*readpage)(struct file *, struct page *); + int (*read_folio)(struct file *, struct folio *); int (*writepages)(struct address_space *, struct writeback_control *); - int (*set_page_dirty)(struct page *page); + bool (*dirty_folio)(struct address_space *, struct folio *); void (*readahead)(struct readahead_control *); - int (*readpages)(struct file *filp, struct address_space *mapping, - struct list_head *pages, unsigned nr_pages); int (*write_begin)(struct file *, struct address_space *mapping, - loff_t pos, unsigned len, unsigned flags, + loff_t pos, unsigned len, struct page **pagep, void **fsdata); int (*write_end)(struct file *, struct address_space *mapping, loff_t pos, unsigned len, unsigned copied, struct page *page, void *fsdata); sector_t (*bmap)(struct address_space *, sector_t); - void (*invalidatepage) (struct page *, unsigned int, unsigned int); - int (*releasepage) (struct page *, int); - void (*freepage)(struct page *); + void (*invalidate_folio) (struct folio *, size_t start, size_t len); + bool (*release_folio)(struct folio *, gfp_t); + void (*free_folio)(struct folio *); ssize_t (*direct_IO)(struct kiocb *, struct iov_iter *iter); - /* isolate a page for migration */ - bool (*isolate_page) (struct page *, isolate_mode_t); - /* migrate the contents of a page to the specified target */ - int (*migratepage) (struct page *, struct page *); - /* put migration-failed page back to right list */ - void (*putback_page) (struct page *); - int (*launder_page) (struct page *); - - int (*is_partially_uptodate) (struct page *, unsigned long, - unsigned long); - void (*is_dirty_writeback) (struct page *, bool *, bool *); + int (*migrate_folio)(struct mapping *, struct folio *dst, + struct folio *src, enum migrate_mode); + int (*launder_folio) (struct folio *); + + bool (*is_partially_uptodate) (struct folio *, size_t from, + size_t count); + void (*is_dirty_writeback)(struct folio *, bool *, bool *); int (*error_remove_page) (struct mapping *mapping, struct page *page); - int (*swap_activate)(struct file *); + int (*swap_activate)(struct swap_info_struct *sis, struct file *f, sector_t *span) int (*swap_deactivate)(struct file *); + int (*swap_rw)(struct kiocb *iocb, struct iov_iter *iter); }; ``writepage`` @@ -774,14 +774,39 @@ cache in your filesystem. The following members are defined: See the file "Locking" for more details. -``readpage`` - called by the VM to read a page from backing store. The page - will be Locked when readpage is called, and should be unlocked - and marked uptodate once the read completes. If ->readpage - discovers that it needs to unlock the page for some reason, it - can do so, and then return AOP_TRUNCATED_PAGE. In this case, - the page will be relocated, relocked and if that all succeeds, - ->readpage will be called again. +``read_folio`` + Called by the page cache to read a folio from the backing store. + The 'file' argument supplies authentication information to network + filesystems, and is generally not used by block based filesystems. + It may be NULL if the caller does not have an open file (eg if + the kernel is performing a read for itself rather than on behalf + of a userspace process with an open file). + + If the mapping does not support large folios, the folio will + contain a single page. The folio will be locked when read_folio + is called. If the read completes successfully, the folio should + be marked uptodate. The filesystem should unlock the folio + once the read has completed, whether it was successful or not. + The filesystem does not need to modify the refcount on the folio; + the page cache holds a reference count and that will not be + released until the folio is unlocked. + + Filesystems may implement ->read_folio() synchronously. + In normal operation, folios are read through the ->readahead() + method. Only if this fails, or if the caller needs to wait for + the read to complete will the page cache call ->read_folio(). + Filesystems should not attempt to perform their own readahead + in the ->read_folio() operation. + + If the filesystem cannot perform the read at this time, it can + unlock the folio, do whatever action it needs to ensure that the + read will succeed in the future and return AOP_TRUNCATED_PAGE. + In this case, the caller should look up the folio, lock it, + and call ->read_folio again. + + Callers may invoke the ->read_folio() method directly, but using + read_mapping_folio() will take care of locking, waiting for the + read to complete and handle cases such as AOP_TRUNCATED_PAGE. ``writepages`` called by the VM to write out pages associated with the @@ -793,34 +818,29 @@ cache in your filesystem. The following members are defined: This will choose pages from the address space that are tagged as DIRTY and will pass them to ->writepage. -``set_page_dirty`` - called by the VM to set a page dirty. This is particularly - needed if an address space attaches private data to a page, and - that data needs to be updated when a page is dirtied. This is +``dirty_folio`` + called by the VM to mark a folio as dirty. This is particularly + needed if an address space attaches private data to a folio, and + that data needs to be updated when a folio is dirtied. This is called, for example, when a memory mapped page gets modified. - If defined, it should set the PageDirty flag, and the - PAGECACHE_TAG_DIRTY tag in the radix tree. + If defined, it should set the folio dirty flag, and the + PAGECACHE_TAG_DIRTY search mark in i_pages. ``readahead`` Called by the VM to read pages associated with the address_space object. The pages are consecutive in the page cache and are locked. The implementation should decrement the page refcount after starting I/O on each page. Usually the page will be - unlocked by the I/O completion handler. If the filesystem decides - to stop attempting I/O before reaching the end of the readahead - window, it can simply return. The caller will decrement the page - refcount and unlock the remaining pages for you. Set PageUptodate - if the I/O completes successfully. Setting PageError on any page - will be ignored; simply unlock the page if an I/O error occurs. - -``readpages`` - called by the VM to read pages associated with the address_space - object. This is essentially just a vector version of readpage. - Instead of just one page, several pages are requested. - readpages is only used for read-ahead, so read errors are - ignored. If anything goes wrong, feel free to give up. - This interface is deprecated and will be removed by the end of - 2020; implement readahead instead. + unlocked by the I/O completion handler. The set of pages are + divided into some sync pages followed by some async pages, + rac->ra->async_size gives the number of async pages. The + filesystem should attempt to read all sync pages but may decide + to stop once it reaches the async pages. If it does decide to + stop attempting I/O, it can simply return. The caller will + remove the remaining pages from the address space, unlock them + and decrement the page refcount. Set PageUptodate if the I/O + completes successfully. Setting PageError on any page will be + ignored; simply unlock the page if an I/O error occurs. ``write_begin`` Called by the generic buffered write code to ask the filesystem @@ -839,9 +859,6 @@ cache in your filesystem. The following members are defined: passed to write_begin is greater than the number of bytes copied into the page). - flags is a field for AOP_FLAG_xxx flags, described in - include/linux/fs.h. - A void * may be returned in fsdata, which then gets passed into write_end. @@ -868,42 +885,41 @@ cache in your filesystem. The following members are defined: to find out where the blocks in the file are and uses those addresses directly. -``invalidatepage`` - If a page has PagePrivate set, then invalidatepage will be - called when part or all of the page is to be removed from the +``invalidate_folio`` + If a folio has private data, then invalidate_folio will be + called when part or all of the folio is to be removed from the address space. This generally corresponds to either a truncation, punch hole or a complete invalidation of the address space (in the latter case 'offset' will always be 0 and 'length' - will be PAGE_SIZE). Any private data associated with the page + will be folio_size()). Any private data associated with the folio should be updated to reflect this truncation. If offset is 0 - and length is PAGE_SIZE, then the private data should be - released, because the page must be able to be completely - discarded. This may be done by calling the ->releasepage + and length is folio_size(), then the private data should be + released, because the folio must be able to be completely + discarded. This may be done by calling the ->release_folio function, but in this case the release MUST succeed. -``releasepage`` - releasepage is called on PagePrivate pages to indicate that the - page should be freed if possible. ->releasepage should remove - any private data from the page and clear the PagePrivate flag. - If releasepage() fails for some reason, it must indicate failure - with a 0 return value. releasepage() is used in two distinct - though related cases. The first is when the VM finds a clean - page with no active users and wants to make it a free page. If - ->releasepage succeeds, the page will be removed from the - address_space and become free. +``release_folio`` + release_folio is called on folios with private data to tell the + filesystem that the folio is about to be freed. ->release_folio + should remove any private data from the folio and clear the + private flag. If release_folio() fails, it should return false. + release_folio() is used in two distinct though related cases. + The first is when the VM wants to free a clean folio with no + active users. If ->release_folio succeeds, the folio will be + removed from the address_space and be freed. The second case is when a request has been made to invalidate - some or all pages in an address_space. This can happen through - the fadvise(POSIX_FADV_DONTNEED) system call or by the - filesystem explicitly requesting it as nfs and 9fs do (when they + some or all folios in an address_space. This can happen + through the fadvise(POSIX_FADV_DONTNEED) system call or by the + filesystem explicitly requesting it as nfs and 9p do (when they believe the cache may be out of date with storage) by calling invalidate_inode_pages2(). If the filesystem makes such a call, - and needs to be certain that all pages are invalidated, then its - releasepage will need to ensure this. Possibly it can clear the - PageUptodate bit if it cannot free private data yet. + and needs to be certain that all folios are invalidated, then + its release_folio will need to ensure this. Possibly it can + clear the uptodate flag if it cannot free private data yet. -``freepage`` - freepage is called once the page is no longer visible in the +``free_folio`` + free_folio is called once the folio is no longer visible in the page cache in order to allow the cleanup of any private data. Since it may be called by the memory reclaimer, it should not assume that the original address_space mapping still exists, and @@ -915,41 +931,33 @@ cache in your filesystem. The following members are defined: data directly between the storage and the application's address space. -``isolate_page`` - Called by the VM when isolating a movable non-lru page. If page - is successfully isolated, VM marks the page as PG_isolated via - __SetPageIsolated. - -``migrate_page`` +``migrate_folio`` This is used to compact the physical memory usage. If the VM - wants to relocate a page (maybe off a memory card that is - signalling imminent failure) it will pass a new page and an old - page to this function. migrate_page should transfer any private - data across and update any references that it has to the page. - -``putback_page`` - Called by the VM when isolated page's migration fails. - -``launder_page`` - Called before freeing a page - it writes back the dirty page. - To prevent redirtying the page, it is kept locked during the + wants to relocate a folio (maybe from a memory device that is + signalling imminent failure) it will pass a new folio and an old + folio to this function. migrate_folio should transfer any private + data across and update any references that it has to the folio. + +``launder_folio`` + Called before freeing a folio - it writes back the dirty folio. + To prevent redirtying the folio, it is kept locked during the whole operation. ``is_partially_uptodate`` Called by the VM when reading a file through the pagecache when - the underlying blocksize != pagesize. If the required block is - up to date then the read can complete without needing the IO to - bring the whole page up to date. + the underlying blocksize is smaller than the size of the folio. + If the required block is up to date then the read can complete + without needing I/O to bring the whole page up to date. ``is_dirty_writeback`` - Called by the VM when attempting to reclaim a page. The VM uses + Called by the VM when attempting to reclaim a folio. The VM uses dirty and writeback information to determine if it needs to stall to allow flushers a chance to complete some IO. - Ordinarily it can use PageDirty and PageWriteback but some - filesystems have more complex state (unstable pages in NFS + Ordinarily it can use folio_test_dirty and folio_test_writeback but + some filesystems have more complex state (unstable folios in NFS prevent reclaim) or do not set those flags due to locking problems. This callback allows a filesystem to indicate to the - VM if a page should be treated as dirty or writeback for the + VM if a folio should be treated as dirty or writeback for the purposes of stalling. ``error_remove_page`` @@ -959,15 +967,21 @@ cache in your filesystem. The following members are defined: unless you have them locked or reference counts increased. ``swap_activate`` - Called when swapon is used on a file to allocate space if - necessary and pin the block lookup information in memory. A - return value of zero indicates success, in which case this file - can be used to back swapspace. + + Called to prepare the given file for swap. It should perform + any validation and preparation necessary to ensure that writes + can be performed with minimal memory allocation. It should call + add_swap_extent(), or the helper iomap_swapfile_activate(), and + return the number of extents added. If IO should be submitted + through ->swap_rw(), it should set SWP_FS_OPS, otherwise IO will + be submitted directly to the block device ``sis->bdev``. ``swap_deactivate`` Called during swapoff on files where swap_activate was successful. +``swap_rw`` + Called to read or write swap pages when SWP_FS_OPS is set. The File Object =============== diff --git a/Documentation/filesystems/xfs-delayed-logging-design.rst b/Documentation/filesystems/xfs-delayed-logging-design.rst index 464405d2801e..6402ab8e370c 100644 --- a/Documentation/filesystems/xfs-delayed-logging-design.rst +++ b/Documentation/filesystems/xfs-delayed-logging-design.rst @@ -1,29 +1,314 @@ .. SPDX-License-Identifier: GPL-2.0 -========================== -XFS Delayed Logging Design -========================== - -Introduction to Re-logging in XFS -================================= - -XFS logging is a combination of logical and physical logging. Some objects, -such as inodes and dquots, are logged in logical format where the details -logged are made up of the changes to in-core structures rather than on-disk -structures. Other objects - typically buffers - have their physical changes -logged. The reason for these differences is to reduce the amount of log space -required for objects that are frequently logged. Some parts of inodes are more -frequently logged than others, and inodes are typically more frequently logged -than any other object (except maybe the superblock buffer) so keeping the -amount of metadata logged low is of prime importance. - -The reason that this is such a concern is that XFS allows multiple separate -modifications to a single object to be carried in the log at any given time. -This allows the log to avoid needing to flush each change to disk before -recording a new change to the object. XFS does this via a method called -"re-logging". Conceptually, this is quite simple - all it requires is that any -new change to the object is recorded with a *new copy* of all the existing -changes in the new transaction that is written to the log. +================== +XFS Logging Design +================== + +Preamble +======== + +This document describes the design and algorithms that the XFS journalling +subsystem is based on. This document describes the design and algorithms that +the XFS journalling subsystem is based on so that readers may familiarize +themselves with the general concepts of how transaction processing in XFS works. + +We begin with an overview of transactions in XFS, followed by describing how +transaction reservations are structured and accounted, and then move into how we +guarantee forwards progress for long running transactions with finite initial +reservations bounds. At this point we need to explain how relogging works. With +the basic concepts covered, the design of the delayed logging mechanism is +documented. + + +Introduction +============ + +XFS uses Write Ahead Logging for ensuring changes to the filesystem metadata +are atomic and recoverable. For reasons of space and time efficiency, the +logging mechanisms are varied and complex, combining intents, logical and +physical logging mechanisms to provide the necessary recovery guarantees the +filesystem requires. + +Some objects, such as inodes and dquots, are logged in logical format where the +details logged are made up of the changes to in-core structures rather than +on-disk structures. Other objects - typically buffers - have their physical +changes logged. Long running atomic modifications have individual changes +chained together by intents, ensuring that journal recovery can restart and +finish an operation that was only partially done when the system stopped +functioning. + +The reason for these differences is to keep the amount of log space and CPU time +required to process objects being modified as small as possible and hence the +logging overhead as low as possible. Some items are very frequently modified, +and some parts of objects are more frequently modified than others, so keeping +the overhead of metadata logging low is of prime importance. + +The method used to log an item or chain modifications together isn't +particularly important in the scope of this document. It suffices to know that +the method used for logging a particular object or chaining modifications +together are different and are dependent on the object and/or modification being +performed. The logging subsystem only cares that certain specific rules are +followed to guarantee forwards progress and prevent deadlocks. + + +Transactions in XFS +=================== + +XFS has two types of high level transactions, defined by the type of log space +reservation they take. These are known as "one shot" and "permanent" +transactions. Permanent transaction reservations can take reservations that span +commit boundaries, whilst "one shot" transactions are for a single atomic +modification. + +The type and size of reservation must be matched to the modification taking +place. This means that permanent transactions can be used for one-shot +modifications, but one-shot reservations cannot be used for permanent +transactions. + +In the code, a one-shot transaction pattern looks somewhat like this:: + + tp = xfs_trans_alloc(<reservation>) + <lock items> + <join item to transaction> + <do modification> + xfs_trans_commit(tp); + +As items are modified in the transaction, the dirty regions in those items are +tracked via the transaction handle. Once the transaction is committed, all +resources joined to it are released, along with the remaining unused reservation +space that was taken at the transaction allocation time. + +In contrast, a permanent transaction is made up of multiple linked individual +transactions, and the pattern looks like this:: + + tp = xfs_trans_alloc(<reservation>) + xfs_ilock(ip, XFS_ILOCK_EXCL) + + loop { + xfs_trans_ijoin(tp, 0); + <do modification> + xfs_trans_log_inode(tp, ip); + xfs_trans_roll(&tp); + } + + xfs_trans_commit(tp); + xfs_iunlock(ip, XFS_ILOCK_EXCL); + +While this might look similar to a one-shot transaction, there is an important +difference: xfs_trans_roll() performs a specific operation that links two +transactions together:: + + ntp = xfs_trans_dup(tp); + xfs_trans_commit(tp); + xfs_trans_reserve(ntp); + +This results in a series of "rolling transactions" where the inode is locked +across the entire chain of transactions. Hence while this series of rolling +transactions is running, nothing else can read from or write to the inode and +this provides a mechanism for complex changes to appear atomic from an external +observer's point of view. + +It is important to note that a series of rolling transactions in a permanent +transaction does not form an atomic change in the journal. While each +individual modification is atomic, the chain is *not atomic*. If we crash half +way through, then recovery will only replay up to the last transactional +modification the loop made that was committed to the journal. + +This affects long running permanent transactions in that it is not possible to +predict how much of a long running operation will actually be recovered because +there is no guarantee of how much of the operation reached stale storage. Hence +if a long running operation requires multiple transactions to fully complete, +the high level operation must use intents and deferred operations to guarantee +recovery can complete the operation once the first transactions is persisted in +the on-disk journal. + + +Transactions are Asynchronous +============================= + +In XFS, all high level transactions are asynchronous by default. This means that +xfs_trans_commit() does not guarantee that the modification has been committed +to stable storage when it returns. Hence when a system crashes, not all the +completed transactions will be replayed during recovery. + +However, the logging subsystem does provide global ordering guarantees, such +that if a specific change is seen after recovery, all metadata modifications +that were committed prior to that change will also be seen. + +For single shot operations that need to reach stable storage immediately, or +ensuring that a long running permanent transaction is fully committed once it is +complete, we can explicitly tag a transaction as synchronous. This will trigger +a "log force" to flush the outstanding committed transactions to stable storage +in the journal and wait for that to complete. + +Synchronous transactions are rarely used, however, because they limit logging +throughput to the IO latency limitations of the underlying storage. Instead, we +tend to use log forces to ensure modifications are on stable storage only when +a user operation requires a synchronisation point to occur (e.g. fsync). + + +Transaction Reservations +======================== + +It has been mentioned a number of times now that the logging subsystem needs to +provide a forwards progress guarantee so that no modification ever stalls +because it can't be written to the journal due to a lack of space in the +journal. This is achieved by the transaction reservations that are made when +a transaction is first allocated. For permanent transactions, these reservations +are maintained as part of the transaction rolling mechanism. + +A transaction reservation provides a guarantee that there is physical log space +available to write the modification into the journal before we start making +modifications to objects and items. As such, the reservation needs to be large +enough to take into account the amount of metadata that the change might need to +log in the worst case. This means that if we are modifying a btree in the +transaction, we have to reserve enough space to record a full leaf-to-root split +of the btree. As such, the reservations are quite complex because we have to +take into account all the hidden changes that might occur. + +For example, a user data extent allocation involves allocating an extent from +free space, which modifies the free space trees. That's two btrees. Inserting +the extent into the inode's extent map might require a split of the extent map +btree, which requires another allocation that can modify the free space trees +again. Then we might have to update reverse mappings, which modifies yet +another btree which might require more space. And so on. Hence the amount of +metadata that a "simple" operation can modify can be quite large. + +This "worst case" calculation provides us with the static "unit reservation" +for the transaction that is calculated at mount time. We must guarantee that the +log has this much space available before the transaction is allowed to proceed +so that when we come to write the dirty metadata into the log we don't run out +of log space half way through the write. + +For one-shot transactions, a single unit space reservation is all that is +required for the transaction to proceed. For permanent transactions, however, we +also have a "log count" that affects the size of the reservation that is to be +made. + +While a permanent transaction can get by with a single unit of space +reservation, it is somewhat inefficient to do this as it requires the +transaction rolling mechanism to re-reserve space on every transaction roll. We +know from the implementation of the permanent transactions how many transaction +rolls are likely for the common modifications that need to be made. + +For example, an inode allocation is typically two transactions - one to +physically allocate a free inode chunk on disk, and another to allocate an inode +from an inode chunk that has free inodes in it. Hence for an inode allocation +transaction, we might set the reservation log count to a value of 2 to indicate +that the common/fast path transaction will commit two linked transactions in a +chain. Each time a permanent transaction rolls, it consumes an entire unit +reservation. + +Hence when the permanent transaction is first allocated, the log space +reservation is increased from a single unit reservation to multiple unit +reservations. That multiple is defined by the reservation log count, and this +means we can roll the transaction multiple times before we have to re-reserve +log space when we roll the transaction. This ensures that the common +modifications we make only need to reserve log space once. + +If the log count for a permanent transaction reaches zero, then it needs to +re-reserve physical space in the log. This is somewhat complex, and requires +an understanding of how the log accounts for space that has been reserved. + + +Log Space Accounting +==================== + +The position in the log is typically referred to as a Log Sequence Number (LSN). +The log is circular, so the positions in the log are defined by the combination +of a cycle number - the number of times the log has been overwritten - and the +offset into the log. A LSN carries the cycle in the upper 32 bits and the +offset in the lower 32 bits. The offset is in units of "basic blocks" (512 +bytes). Hence we can do realtively simple LSN based math to keep track of +available space in the log. + +Log space accounting is done via a pair of constructs called "grant heads". The +position of the grant heads is an absolute value, so the amount of space +available in the log is defined by the distance between the position of the +grant head and the current log tail. That is, how much space can be +reserved/consumed before the grant heads would fully wrap the log and overtake +the tail position. + +The first grant head is the "reserve" head. This tracks the byte count of the +reservations currently held by active transactions. It is a purely in-memory +accounting of the space reservation and, as such, actually tracks byte offsets +into the log rather than basic blocks. Hence it technically isn't using LSNs to +represent the log position, but it is still treated like a split {cycle,offset} +tuple for the purposes of tracking reservation space. + +The reserve grant head is used to accurately account for exact transaction +reservations amounts and the exact byte count that modifications actually make +and need to write into the log. The reserve head is used to prevent new +transactions from taking new reservations when the head reaches the current +tail. It will block new reservations in a FIFO queue and as the log tail moves +forward it will wake them in order once sufficient space is available. This FIFO +mechanism ensures no transaction is starved of resources when log space +shortages occur. + +The other grant head is the "write" head. Unlike the reserve head, this grant +head contains an LSN and it tracks the physical space usage in the log. While +this might sound like it is accounting the same state as the reserve grant head +- and it mostly does track exactly the same location as the reserve grant head - +there are critical differences in behaviour between them that provides the +forwards progress guarantees that rolling permanent transactions require. + +These differences when a permanent transaction is rolled and the internal "log +count" reaches zero and the initial set of unit reservations have been +exhausted. At this point, we still require a log space reservation to continue +the next transaction in the sequeunce, but we have none remaining. We cannot +sleep during the transaction commit process waiting for new log space to become +available, as we may end up on the end of the FIFO queue and the items we have +locked while we sleep could end up pinning the tail of the log before there is +enough free space in the log to fulfill all of the pending reservations and +then wake up transaction commit in progress. + +To take a new reservation without sleeping requires us to be able to take a +reservation even if there is no reservation space currently available. That is, +we need to be able to *overcommit* the log reservation space. As has already +been detailed, we cannot overcommit physical log space. However, the reserve +grant head does not track physical space - it only accounts for the amount of +reservations we currently have outstanding. Hence if the reserve head passes +over the tail of the log all it means is that new reservations will be throttled +immediately and remain throttled until the log tail is moved forward far enough +to remove the overcommit and start taking new reservations. In other words, we +can overcommit the reserve head without violating the physical log head and tail +rules. + +As a result, permanent transactions only "regrant" reservation space during +xfs_trans_commit() calls, while the physical log space reservation - tracked by +the write head - is then reserved separately by a call to xfs_log_reserve() +after the commit completes. Once the commit completes, we can sleep waiting for +physical log space to be reserved from the write grant head, but only if one +critical rule has been observed:: + + Code using permanent reservations must always log the items they hold + locked across each transaction they roll in the chain. + +"Re-logging" the locked items on every transaction roll ensures that the items +attached to the transaction chain being rolled are always relocated to the +physical head of the log and so do not pin the tail of the log. If a locked item +pins the tail of the log when we sleep on the write reservation, then we will +deadlock the log as we cannot take the locks needed to write back that item and +move the tail of the log forwards to free up write grant space. Re-logging the +locked items avoids this deadlock and guarantees that the log reservation we are +making cannot self-deadlock. + +If all rolling transactions obey this rule, then they can all make forwards +progress independently because nothing will block the progress of the log +tail moving forwards and hence ensuring that write grant space is always +(eventually) made available to permanent transactions no matter how many times +they roll. + + +Re-logging Explained +==================== + +XFS allows multiple separate modifications to a single object to be carried in +the log at any given time. This allows the log to avoid needing to flush each +change to disk before recording a new change to the object. XFS does this via a +method called "re-logging". Conceptually, this is quite simple - all it requires +is that any new change to the object is recorded with a *new copy* of all the +existing changes in the new transaction that is written to the log. That is, if we have a sequence of changes A through to F, and the object was written to disk after change D, we would see in the log the following series @@ -42,16 +327,13 @@ transaction:: In other words, each time an object is relogged, the new transaction contains the aggregation of all the previous changes currently held only in the log. -This relogging technique also allows objects to be moved forward in the log so -that an object being relogged does not prevent the tail of the log from ever -moving forward. This can be seen in the table above by the changing -(increasing) LSN of each subsequent transaction - the LSN is effectively a -direct encoding of the location in the log of the transaction. +This relogging technique allows objects to be moved forward in the log so that +an object being relogged does not prevent the tail of the log from ever moving +forward. This can be seen in the table above by the changing (increasing) LSN +of each subsequent transaction, and it's the technique that allows us to +implement long-running, multiple-commit permanent transactions. -This relogging is also used to implement long-running, multiple-commit -transactions. These transaction are known as rolling transactions, and require -a special log reservation known as a permanent transaction reservation. A -typical example of a rolling transaction is the removal of extents from an +A typical example of a rolling transaction is the removal of extents from an inode which can only be done at a rate of two extents per transaction because of reservation size limitations. Hence a rolling extent removal transaction keeps relogging the inode and btree buffers as they get modified in each @@ -67,12 +349,13 @@ the log over and over again. Worse is the fact that objects tend to get dirtier as they get relogged, so each subsequent transaction is writing more metadata into the log. -Another feature of the XFS transaction subsystem is that most transactions are -asynchronous. That is, they don't commit to disk until either a log buffer is -filled (a log buffer can hold multiple transactions) or a synchronous operation -forces the log buffers holding the transactions to disk. This means that XFS is -doing aggregation of transactions in memory - batching them, if you like - to -minimise the impact of the log IO on transaction throughput. +It should now also be obvious how relogging and asynchronous transactions go +hand in hand. That is, transactions don't get written to the physical journal +until either a log buffer is filled (a log buffer can hold multiple +transactions) or a synchronous operation forces the log buffers holding the +transactions to disk. This means that XFS is doing aggregation of transactions +in memory - batching them, if you like - to minimise the impact of the log IO on +transaction throughput. The limitation on asynchronous transaction throughput is the number and size of log buffers made available by the log manager. By default there are 8 log @@ -268,14 +551,14 @@ Essentially, this shows that an item that is in the AIL can still be modified and relogged, so any tracking must be separate to the AIL infrastructure. As such, we cannot reuse the AIL list pointers for tracking committed items, nor can we store state in any field that is protected by the AIL lock. Hence the -committed item tracking needs it's own locks, lists and state fields in the log +committed item tracking needs its own locks, lists and state fields in the log item. Similar to the AIL, tracking of committed items is done through a new list called the Committed Item List (CIL). The list tracks log items that have been committed and have formatted memory buffers attached to them. It tracks objects in transaction commit order, so when an object is relogged it is removed from -it's place in the list and re-inserted at the tail. This is entirely arbitrary +its place in the list and re-inserted at the tail. This is entirely arbitrary and done to make it easy for debugging - the last items in the list are the ones that are most recently modified. Ordering of the CIL is not necessary for transactional integrity (as discussed in the next section) so the ordering is @@ -332,7 +615,7 @@ those changes into the current checkpoint context. We then initialise a new context and attach that to the CIL for aggregation of new transactions. This allows us to unlock the CIL immediately after transfer of all the -committed items and effectively allow new transactions to be issued while we +committed items and effectively allows new transactions to be issued while we are formatting the checkpoint into the log. It also allows concurrent checkpoints to be written into the log buffers in the case of log force heavy workloads, just like the existing transaction commit code does. This, however, @@ -601,9 +884,9 @@ pin the object the first time it is inserted into the CIL - if it is already in the CIL during a transaction commit, then we do not pin it again. Because there can be multiple outstanding checkpoint contexts, we can still see elevated pin counts, but as each checkpoint completes the pin count will retain the correct -value according to it's context. +value according to its context. -Just to make matters more slightly more complex, this checkpoint level context +Just to make matters slightly more complex, this checkpoint level context for the pin count means that the pinning of an item must take place under the CIL commit/flush lock. If we pin the object outside this lock, we cannot guarantee which context the pin count is associated with. This is because of diff --git a/Documentation/filesystems/zonefs.rst b/Documentation/filesystems/zonefs.rst index 6b213fe9a33e..394b9f15dce0 100644 --- a/Documentation/filesystems/zonefs.rst +++ b/Documentation/filesystems/zonefs.rst @@ -306,8 +306,15 @@ Further notes: Mount options ------------- -zonefs define the "errors=<behavior>" mount option to allow the user to specify -zonefs behavior in response to I/O errors, inode size inconsistencies or zone +zonefs defines several mount options: +* errors=<behavior> +* explicit-open + +"errors=<behavior>" option +~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The "errors=<behavior>" option mount option allows the user to specify zonefs +behavior in response to I/O errors, inode size inconsistencies or zone condition changes. The defined behaviors are as follow: * remount-ro (default) @@ -326,6 +333,9 @@ discover the amount of data that has been written to the zone. In the case of a read-only zone discovered at run-time, as indicated in the previous section. The size of the zone file is left unchanged from its last updated value. +"explicit-open" option +~~~~~~~~~~~~~~~~~~~~~~ + A zoned block device (e.g. an NVMe Zoned Namespace device) may have limits on the number of zones that can be active, that is, zones that are in the implicit open, explicit open or closed conditions. This potential limitation @@ -341,6 +351,44 @@ guaranteed that write requests can be processed. Conversely, the to the device on the last close() of a zone file if the zone is not full nor empty. +Runtime sysfs attributes +------------------------ + +zonefs defines several sysfs attributes for mounted devices. All attributes +are user readable and can be found in the directory /sys/fs/zonefs/<dev>/, +where <dev> is the name of the mounted zoned block device. + +The attributes defined are as follows. + +* **max_wro_seq_files**: This attribute reports the maximum number of + sequential zone files that can be open for writing. This number corresponds + to the maximum number of explicitly or implicitly open zones that the device + supports. A value of 0 means that the device has no limit and that any zone + (any file) can be open for writing and written at any time, regardless of the + state of other zones. When the *explicit-open* mount option is used, zonefs + will fail any open() system call requesting to open a sequential zone file for + writing when the number of sequential zone files already open for writing has + reached the *max_wro_seq_files* limit. +* **nr_wro_seq_files**: This attribute reports the current number of sequential + zone files open for writing. When the "explicit-open" mount option is used, + this number can never exceed *max_wro_seq_files*. If the *explicit-open* + mount option is not used, the reported number can be greater than + *max_wro_seq_files*. In such case, it is the responsibility of the + application to not write simultaneously more than *max_wro_seq_files* + sequential zone files. Failure to do so can result in write errors. +* **max_active_seq_files**: This attribute reports the maximum number of + sequential zone files that are in an active state, that is, sequential zone + files that are partially writen (not empty nor full) or that have a zone that + is explicitly open (which happens only if the *explicit-open* mount option is + used). This number is always equal to the maximum number of active zones that + the device supports. A value of 0 means that the mounted device has no limit + on the number of sequential zone files that can be active. +* **nr_active_seq_files**: This attributes reports the current number of + sequential zone files that are active. If *max_active_seq_files* is not 0, + then the value of *nr_active_seq_files* can never exceed the value of + *nr_active_seq_files*, regardless of the use of the *explicit-open* mount + option. + Zonefs User Space Tools ======================= |