diff options
Diffstat (limited to 'Documentation/filesystems')
| -rw-r--r-- | Documentation/filesystems/Locking | 2 | ||||
| -rw-r--r-- | Documentation/filesystems/devpts.txt | 132 | ||||
| -rw-r--r-- | Documentation/filesystems/files.txt | 6 | ||||
| -rw-r--r-- | Documentation/filesystems/ocfs2.txt | 3 | ||||
| -rw-r--r-- | Documentation/filesystems/ubifs.txt | 3 | ||||
| -rw-r--r-- | Documentation/filesystems/vfs.txt | 5 |
6 files changed, 141 insertions, 10 deletions
diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking index 23d2f4460deb..ccec55394380 100644 --- a/Documentation/filesystems/Locking +++ b/Documentation/filesystems/Locking @@ -394,7 +394,6 @@ prototypes: unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long); int (*check_flags)(int); - int (*dir_notify)(struct file *, unsigned long); }; locking rules: @@ -424,7 +423,6 @@ sendfile: no sendpage: no get_unmapped_area: no check_flags: no -dir_notify: no ->llseek() locking has moved from llseek to the individual llseek implementations. If your fs is not using generic_file_llseek, you diff --git a/Documentation/filesystems/devpts.txt b/Documentation/filesystems/devpts.txt new file mode 100644 index 000000000000..68dffd87f9b7 --- /dev/null +++ b/Documentation/filesystems/devpts.txt @@ -0,0 +1,132 @@ + +To support containers, we now allow multiple instances of devpts filesystem, +such that indices of ptys allocated in one instance are independent of indices +allocated in other instances of devpts. + +To preserve backward compatibility, this support for multiple instances is +enabled only if: + + - CONFIG_DEVPTS_MULTIPLE_INSTANCES=y, and + - '-o newinstance' mount option is specified while mounting devpts + +IOW, devpts now supports both single-instance and multi-instance semantics. + +If CONFIG_DEVPTS_MULTIPLE_INSTANCES=n, there is no change in behavior and +this referred to as the "legacy" mode. In this mode, the new mount options +(-o newinstance and -o ptmxmode) will be ignored with a 'bogus option' message +on console. + +If CONFIG_DEVPTS_MULTIPLE_INSTANCES=y and devpts is mounted without the +'newinstance' option (as in current start-up scripts) the new mount binds +to the initial kernel mount of devpts. This mode is referred to as the +'single-instance' mode and the current, single-instance semantics are +preserved, i.e PTYs are common across the system. + +The only difference between this single-instance mode and the legacy mode +is the presence of new, '/dev/pts/ptmx' node with permissions 0000, which +can safely be ignored. + +If CONFIG_DEVPTS_MULTIPLE_INSTANCES=y and 'newinstance' option is specified, +the mount is considered to be in the multi-instance mode and a new instance +of the devpts fs is created. Any ptys created in this instance are independent +of ptys in other instances of devpts. Like in the single-instance mode, the +/dev/pts/ptmx node is present. To effectively use the multi-instance mode, +open of /dev/ptmx must be a redirected to '/dev/pts/ptmx' using a symlink or +bind-mount. + +Eg: A container startup script could do the following: + + $ chmod 0666 /dev/pts/ptmx + $ rm /dev/ptmx + $ ln -s pts/ptmx /dev/ptmx + $ ns_exec -cm /bin/bash + + # We are now in new container + + $ umount /dev/pts + $ mount -t devpts -o newinstance lxcpts /dev/pts + $ sshd -p 1234 + +where 'ns_exec -cm /bin/bash' calls clone() with CLONE_NEWNS flag and execs +/bin/bash in the child process. A pty created by the sshd is not visible in +the original mount of /dev/pts. + +User-space changes +------------------ + +In multi-instance mode (i.e '-o newinstance' mount option is specified at least +once), following user-space issues should be noted. + +1. If -o newinstance mount option is never used, /dev/pts/ptmx can be ignored + and no change is needed to system-startup scripts. + +2. To effectively use multi-instance mode (i.e -o newinstance is specified) + administrators or startup scripts should "redirect" open of /dev/ptmx to + /dev/pts/ptmx using either a bind mount or symlink. + + $ mount -t devpts -o newinstance devpts /dev/pts + + followed by either + + $ rm /dev/ptmx + $ ln -s pts/ptmx /dev/ptmx + $ chmod 666 /dev/pts/ptmx + or + $ mount -o bind /dev/pts/ptmx /dev/ptmx + +3. The '/dev/ptmx -> pts/ptmx' symlink is the preferred method since it + enables better error-reporting and treats both single-instance and + multi-instance mounts similarly. + + But this method requires that system-startup scripts set the mode of + /dev/pts/ptmx correctly (default mode is 0000). The scripts can set the + mode by, either + + - adding ptmxmode mount option to devpts entry in /etc/fstab, or + - using 'chmod 0666 /dev/pts/ptmx' + +4. If multi-instance mode mount is needed for containers, but the system + startup scripts have not yet been updated, container-startup scripts + should bind mount /dev/ptmx to /dev/pts/ptmx to avoid breaking single- + instance mounts. + + Or, in general, container-startup scripts should use: + + mount -t devpts -o newinstance -o ptmxmode=0666 devpts /dev/pts + if [ ! -L /dev/ptmx ]; then + mount -o bind /dev/pts/ptmx /dev/ptmx + fi + + When all devpts mounts are multi-instance, /dev/ptmx can permanently be + a symlink to pts/ptmx and the bind mount can be ignored. + +5. A multi-instance mount that is not accompanied by the /dev/ptmx to + /dev/pts/ptmx redirection would result in an unusable/unreachable pty. + + mount -t devpts -o newinstance lxcpts /dev/pts + + immediately followed by: + + open("/dev/ptmx") + + would create a pty, say /dev/pts/7, in the initial kernel mount. + But /dev/pts/7 would be invisible in the new mount. + +6. The permissions for /dev/pts/ptmx node should be specified when mounting + /dev/pts, using the '-o ptmxmode=%o' mount option (default is 0000). + + mount -t devpts -o newinstance -o ptmxmode=0644 devpts /dev/pts + + The permissions can be later be changed as usual with 'chmod'. + + chmod 666 /dev/pts/ptmx + +7. A mount of devpts without the 'newinstance' option results in binding to + initial kernel mount. This behavior while preserving legacy semantics, + does not provide strict isolation in a container environment. i.e by + mounting devpts without the 'newinstance' option, a container could + get visibility into the 'host' or root container's devpts. + + To workaround this and have strict isolation, all mounts of devpts, + including the mount in the root container, should use the newinstance + option. diff --git a/Documentation/filesystems/files.txt b/Documentation/filesystems/files.txt index bb0142f61084..ac2facc50d2a 100644 --- a/Documentation/filesystems/files.txt +++ b/Documentation/filesystems/files.txt @@ -76,13 +76,13 @@ the fdtable structure - 5. Handling of the file structures is special. Since the look-up of the fd (fget()/fget_light()) are lock-free, it is possible that look-up may race with the last put() operation on the - file structure. This is avoided using atomic_inc_not_zero() + file structure. This is avoided using atomic_long_inc_not_zero() on ->f_count : rcu_read_lock(); file = fcheck_files(files, fd); if (file) { - if (atomic_inc_not_zero(&file->f_count)) + if (atomic_long_inc_not_zero(&file->f_count)) *fput_needed = 1; else /* Didn't get the reference, someone's freed */ @@ -92,7 +92,7 @@ the fdtable structure - .... return file; - atomic_inc_not_zero() detects if refcounts is already zero or + atomic_long_inc_not_zero() detects if refcounts is already zero or goes to zero during increment. If it does, we fail fget()/fget_light(). diff --git a/Documentation/filesystems/ocfs2.txt b/Documentation/filesystems/ocfs2.txt index 67310fbbb7df..c2a0871280a0 100644 --- a/Documentation/filesystems/ocfs2.txt +++ b/Documentation/filesystems/ocfs2.txt @@ -31,7 +31,6 @@ Features which OCFS2 does not support yet: - quotas - Directory change notification (F_NOTIFY) - Distributed Caching (F_SETLEASE/F_GETLEASE/break_lease) - - POSIX ACLs Mount options ============= @@ -79,3 +78,5 @@ inode64 Indicates that Ocfs2 is allowed to create inodes at bits of significance. user_xattr (*) Enables Extended User Attributes. nouser_xattr Disables Extended User Attributes. +acl Enables POSIX Access Control Lists support. +noacl (*) Disables POSIX Access Control Lists support. diff --git a/Documentation/filesystems/ubifs.txt b/Documentation/filesystems/ubifs.txt index dd84ea3c10da..84da2a4ba25a 100644 --- a/Documentation/filesystems/ubifs.txt +++ b/Documentation/filesystems/ubifs.txt @@ -95,6 +95,9 @@ no_chk_data_crc skip checking of CRCs on data nodes in order to of this option is that corruption of the contents of a file can go unnoticed. chk_data_crc (*) do not skip checking CRCs on data nodes +compr=none override default compressor and set it to "none" +compr=lzo override default compressor and set it to "lzo" +compr=zlib override default compressor and set it to "zlib" Quick usage instructions diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt index 5579bda58a6d..ef19afa186a9 100644 --- a/Documentation/filesystems/vfs.txt +++ b/Documentation/filesystems/vfs.txt @@ -733,7 +733,6 @@ struct file_operations { ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int); unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long); int (*check_flags)(int); - int (*dir_notify)(struct file *filp, unsigned long arg); int (*flock) (struct file *, int, struct file_lock *); ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, size_t, unsigned int); ssize_t (*splice_read)(struct file *, struct pipe_inode_info *, size_t, unsigned int); @@ -800,8 +799,6 @@ otherwise noted. check_flags: called by the fcntl(2) system call for F_SETFL command - dir_notify: called by the fcntl(2) system call for F_NOTIFY command - flock: called by the flock(2) system call splice_write: called by the VFS to splice data from a pipe to a file. This @@ -931,7 +928,7 @@ manipulate dentries: d_lookup: look up a dentry given its parent and path name component It looks up the child of that given name from the dcache hash table. If it is found, the reference count is incremented - and the dentry is returned. The caller must use d_put() + and the dentry is returned. The caller must use dput() to free the dentry when it finishes using it. For further information on dentry locking, please refer to the document |