diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/filesystems/ext4.txt | 20 | ||||
| -rw-r--r-- | Documentation/filesystems/proc.txt | 39 | ||||
| -rw-r--r-- | Documentation/kbuild/kconfig-language.txt | 111 |
3 files changed, 163 insertions, 7 deletions
diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt index 6a4adcae9f9a..560f88dc7090 100644 --- a/Documentation/filesystems/ext4.txt +++ b/Documentation/filesystems/ext4.txt @@ -86,9 +86,21 @@ Alex is working on a new set of patches right now. When mounting an ext4 filesystem, the following option are accepted: (*) == default -extents ext4 will use extents to address file data. The +extents (*) ext4 will use extents to address file data. The file system will no longer be mountable by ext3. +noextents ext4 will not use extents for newly created files + +journal_checksum Enable checksumming of the journal transactions. + This will allow the recovery code in e2fsck and the + kernel to detect corruption in the kernel. It is a + compatible change and will be ignored by older kernels. + +journal_async_commit Commit block can be written to disk without waiting + for descriptor blocks. If enabled older kernels cannot + mount the device. This will enable 'journal_checksum' + internally. + journal=update Update the ext4 file system's journal to the current format. @@ -196,6 +208,12 @@ nobh (a) cache disk block mapping information "nobh" option tries to avoid associating buffer heads (supported only for "writeback" mode). +mballoc (*) Use the multiple block allocator for block allocation +nomballoc disabled multiple block allocator for block allocation. +stripe=n Number of filesystem blocks that mballoc will try + to use for allocation size and alignment. For RAID5/6 + systems this should be the number of data + disks * RAID chunk size in file system blocks. Data Mode --------- diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index dec99455321f..4413a2d4646f 100644 --- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -857,6 +857,45 @@ CPUs. The "procs_blocked" line gives the number of processes currently blocked, waiting for I/O to complete. +1.9 Ext4 file system parameters +------------------------------ +Ext4 file system have one directory per partition under /proc/fs/ext4/ +# ls /proc/fs/ext4/hdc/ +group_prealloc max_to_scan mb_groups mb_history min_to_scan order2_req +stats stream_req + +mb_groups: +This file gives the details of mutiblock allocator buddy cache of free blocks + +mb_history: +Multiblock allocation history. + +stats: +This file indicate whether the multiblock allocator should start collecting +statistics. The statistics are shown during unmount + +group_prealloc: +The multiblock allocator normalize the block allocation request to +group_prealloc filesystem blocks if we don't have strip value set. +The stripe value can be specified at mount time or during mke2fs. + +max_to_scan: +How long multiblock allocator can look for a best extent (in found extents) + +min_to_scan: +How long multiblock allocator must look for a best extent + +order2_req: +Multiblock allocator use 2^N search using buddies only for requests greater +than or equal to order2_req. The request size is specfied in file system +blocks. A value of 2 indicate only if the requests are greater than or equal +to 4 blocks. + +stream_req: +Files smaller than stream_req are served by the stream allocator, whose +purpose is to pack requests as close each to other as possible to +produce smooth I/O traffic. Avalue of 16 indicate that file smaller than 16 +filesystem block size will use group based preallocation. ------------------------------------------------------------------------------ Summary diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.txt index 616043a6da99..649cb8799890 100644 --- a/Documentation/kbuild/kconfig-language.txt +++ b/Documentation/kbuild/kconfig-language.txt @@ -24,7 +24,7 @@ visible if its parent entry is also visible. Menu entries ------------ -Most entries define a config option, all other entries help to organize +Most entries define a config option; all other entries help to organize them. A single configuration option is defined like this: config MODVERSIONS @@ -50,7 +50,7 @@ applicable everywhere (see syntax). - type definition: "bool"/"tristate"/"string"/"hex"/"int" Every config option must have a type. There are only two basic types: - tristate and string, the other types are based on these two. The type + tristate and string; the other types are based on these two. The type definition optionally accepts an input prompt, so these two examples are equivalent: @@ -108,7 +108,7 @@ applicable everywhere (see syntax). equal to 'y' without visiting the dependencies. So abusing select you are able to select a symbol FOO even if FOO depends on BAR that is not set. In general use select only for - non-visible symbols (no promts anywhere) and for symbols with + non-visible symbols (no prompts anywhere) and for symbols with no dependencies. That will limit the usefulness but on the other hand avoid the illegal configurations all over. kconfig should one day warn about such things. @@ -127,6 +127,27 @@ applicable everywhere (see syntax). used to help visually separate configuration logic from help within the file as an aid to developers. +- misc options: "option" <symbol>[=<value>] + Various less common options can be defined via this option syntax, + which can modify the behaviour of the menu entry and its config + symbol. These options are currently possible: + + - "defconfig_list" + This declares a list of default entries which can be used when + looking for the default configuration (which is used when the main + .config doesn't exists yet.) + + - "modules" + This declares the symbol to be used as the MODULES symbol, which + enables the third modular state for all config symbols. + + - "env"=<value> + This imports the environment variable into Kconfig. It behaves like + a default, except that the value comes from the environment, this + also means that the behaviour when mixing it with normal defaults is + undefined at this point. The symbol is currently not exported back + to the build environment (if this is desired, it can be done via + another symbol). Menu dependencies ----------------- @@ -162,9 +183,9 @@ An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2 respectively for calculations). A menu entry becomes visible when it's expression evaluates to 'm' or 'y'. -There are two types of symbols: constant and nonconstant symbols. -Nonconstant symbols are the most common ones and are defined with the -'config' statement. Nonconstant symbols consist entirely of alphanumeric +There are two types of symbols: constant and non-constant symbols. +Non-constant symbols are the most common ones and are defined with the +'config' statement. Non-constant symbols consist entirely of alphanumeric characters or underscores. Constant symbols are only part of expressions. Constant symbols are always surrounded by single or double quotes. Within the quote, any @@ -301,3 +322,81 @@ mainmenu: This sets the config program's title bar if the config program chooses to use it. + + +Kconfig hints +------------- +This is a collection of Kconfig tips, most of which aren't obvious at +first glance and most of which have become idioms in several Kconfig +files. + +Adding common features and make the usage configurable +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +It is a common idiom to implement a feature/functionality that are +relevant for some architectures but not all. +The recommended way to do so is to use a config variable named HAVE_* +that is defined in a common Kconfig file and selected by the relevant +architectures. +An example is the generic IOMAP functionality. + +We would in lib/Kconfig see: + +# Generic IOMAP is used to ... +config HAVE_GENERIC_IOMAP + +config GENERIC_IOMAP + depends on HAVE_GENERIC_IOMAP && FOO + +And in lib/Makefile we would see: +obj-$(CONFIG_GENERIC_IOMAP) += iomap.o + +For each architecture using the generic IOMAP functionality we would see: + +config X86 + select ... + select HAVE_GENERIC_IOMAP + select ... + +Note: we use the existing config option and avoid creating a new +config variable to select HAVE_GENERIC_IOMAP. + +Note: the use of the internal config variable HAVE_GENERIC_IOMAP, it is +introduced to overcome the limitation of select which will force a +config option to 'y' no matter the dependencies. +The dependencies are moved to the symbol GENERIC_IOMAP and we avoid the +situation where select forces a symbol equals to 'y'. + +Build as module only +~~~~~~~~~~~~~~~~~~~~ +To restrict a component build to module-only, qualify its config symbol +with "depends on m". E.g.: + +config FOO + depends on BAR && m + +limits FOO to module (=m) or disabled (=n). + + +Build limited by a third config symbol which may be =y or =m +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +A common idiom that we see (and sometimes have problems with) is this: + +When option C in B (module or subsystem) uses interfaces from A (module +or subsystem), and both A and B are tristate (could be =y or =m if they +were independent of each other, but they aren't), then we need to limit +C such that it cannot be built statically if A is built as a loadable +module. (C already depends on B, so there is no dependency issue to +take care of here.) + +If A is linked statically into the kernel image, C can be built +statically or as loadable module(s). However, if A is built as loadable +module(s), then C must be restricted to loadable module(s) also. This +can be expressed in kconfig language as: + +config C + depends on A = y || A = B + +or for real examples, use this command in a kernel tree: + +$ find . -name Kconfig\* | xargs grep -ns "depends on.*=.*||.*=" | grep -v orig + |