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btrfs-progs: docs: add sysfs doc
This patch will add a dedicated section for btrfs sysfs interfaces. It will include: - Directory layout explanation Including: * Description * Introduced in which kernel version - Files explanation Including: * RW/RO type * Description * Introduced in which kernel version Signed-off-by: Qu Wenruo <wqu@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Qu Wenruo
David Sterba
parent
3e023b19f8
commit
0d901db20a
@ -11,6 +11,7 @@ tools. Currently covers:
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#. filesystem features
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#. checksum algorithms
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#. compression
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#. sysfs interface
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#. filesystem exclusive operations
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#. filesystem limits
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#. bootloader support
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@ -191,6 +192,11 @@ COMPRESSION
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.. include:: ch-compression.rst
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SYSFS INTERFACE
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---------------
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.. include:: ch-sysfs.rst
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FILESYSTEM EXCLUSIVE OPERATIONS
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-------------------------------
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234
Documentation/ch-sysfs.rst
Normal file
234
Documentation/ch-sysfs.rst
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@ -0,0 +1,234 @@
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Btrfs has a sysfs interface to provide extra knobs.
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The top level path is `/sys/fs/btrfs/`, and the main directory layout is the following:
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============================= =================================== ========
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Relative Path Description Version
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============================= =================================== ========
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features/ All supported features 3.14+
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<UUID>/ Mounted fs UUID 3.14+
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<UUID>/allocation/ Space allocation info 3.14+
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<UUID>/features/ Features of the filesystem 3.14+
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<UUID>/devices/<DEVID>/ Symlink to each block device sysfs 5.6+
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<UUID>/devinfo/<DEVID>/ Btrfs specific info for each device 5.6+
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<UUID>/qgroups/ Global qgroup info 5.9+
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<UUID>/qgroups/<LEVEL>_<ID>/ Info for each qgroup 5.9+
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============================= =================================== ========
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For `/sys/fs/btrfs/features/` directory, each file means a supported feature
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for the current kernel.
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For `/sys/fs/btrfs/<UUID>/features/` directory, each file means an enabled
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feature for the mounted filesystem.
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The features shares the same name in section *FILESYSTEM FEATURES*.
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Files in `/sys/fs/btrfs/<UUID>/` directory are:
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bg_reclaim_threshold
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(RW, since: 5.19)
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Used space percentage to start auto block group claim.
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Mostly for zoned devices.
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checksum
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(RO, since: 5.5)
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The checksum used for the mounted filesystem.
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This includes both the checksum type (see section *CHECKSUM ALGORITHMS*)
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and the implemented driver (mostly shows if it's hardware accelerated).
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clone_alignment
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(RO, since: 3.16)
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The bytes alignment for *clone* and *dedupe* ioctls.
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commit_stats
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(RW, since: 6.0)
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The performance statistics for btrfs transaction commit.
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Mostly for debug purposes.
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Writing into this file will reset the maximum commit duration to
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the input value.
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exclusive_operation
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(RO, since: 5.10)
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Shows the running exclusive operation.
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Check section *FILESYSTEM EXCLUSIVE OPERATIONS* for details.
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generation
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(RO, since: 5.11)
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Show the generation of the mounted filesystem.
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label
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(RW, since: 3.14)
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Show the current label of the mounted filesystem.
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metadata_uuid
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(RO, since: 5.0)
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Shows the metadata uuid of the mounted filesystem.
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Check `metadata_uuid` feature for more details.
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nodeisze
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(RO, since: 3.14)
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Show the nodesize of the mounted filesystem.
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quota_override
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(RW, since: 4.13)
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Shows the current quota override status.
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0 means no quota override.
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1 means quota override, quota can ignore the existing limit settings.
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read_policy
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(RW, since: 5.11)
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Shows the current balance policy for reads.
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Currently only "pid" (balance using pid value) is supported.
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sectorsize
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(RO, since: 3.14)
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Shows the sectorsize of the mounted filesystem.
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Files and directories in `/sys/fs/btrfs/<UUID>/allocations` directory are:
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global_rsv_reserved
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(RO, since: 3.14)
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The used bytes of the global reservation.
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global_rsv_size
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(RO, since: 3.14)
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The total size of the global reservation.
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`data/`, `metadata/` and `system/` directories
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(RO, since: 5.14)
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Space info accounting for the 3 chunk types.
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Mostly for debug purposes.
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Files in `/sys/fs/btrfs/<UUID>/devinfo/<DEVID>` directory are:
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error_stats:
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(RO, since: 5.14)
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Shows all the history error numbers of the device.
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fsid:
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(RO, since: 5.17)
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Shows the fsid which the device belongs to.
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It can be different than the `<UUID>` if it's a seed device.
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in_fs_metadata
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(RO, since: 5.6)
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Shows whether we have found the device.
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Should always be 1, as if this turns to 0, the `<DEVID>` directory
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would get removed automatically.
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missing
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(RO, since: 5.6)
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Shows whether the device is missing.
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replace_target
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(RO, since: 5.6)
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Shows whether the device is the replace target.
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If no dev-replace is running, this value should be 0.
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scrub_speed_max
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(RW, since: 5.14)
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Shows the scrub speed limit for this device. The unit is Bytes/s.
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0 means no limit.
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writeable
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(RO, since: 5.6)
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Show if the device is writeable.
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Files in `/sys/fs/btrfs/<UUID>/qgroups/` directory are:
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enabled
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(RO, since: 6.1)
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Shows if qgroup is enabled.
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Also, if qgroup is disabled, the `qgroups` directory would
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be removed automatically.
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inconsistent
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(RO, since: 6.1)
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Shows if the qgroup numbers are inconsistent.
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If 1, it's recommended to do a qgroup rescan.
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drop_subtree_threshold
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(RW, since: 6.1)
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Shows the subtree drop threshold to automatically mark qgroup inconsistent.
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When dropping large subvolumes with qgroup enabled, there would be a huge
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load for qgroup accounting.
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If we have a subtree whose level is larger than or equal to this value,
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we will not trigger qgroup account at all, but mark qgroup inconsistent to
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avoid the huge workload.
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Default value is 8, where no subtree drop can trigger qgroup.
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Lower value can reduce qgroup workload, at the cost of extra qgroup rescan
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to re-calculate the numbers.
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Files in `/sys/fs/btrfs/<UUID>/<LEVEL>_<ID>/` directory are:
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exclusive
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(RO, since: 5.9)
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Shows the exclusively owned bytes of the qgroup.
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limit_flags
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(RO, since: 5.9)
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Shows the numeric value of the limit flags.
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If 0, means no limit implied.
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max_exclusive
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(RO, since: 5.9)
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Shows the limits on exclusively owned bytes.
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max_referenced
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(RO, since: 5.9)
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Shows the limits on referenced bytes.
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referenced
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(RO, since: 5.9)
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Shows the referenced bytes of the qgroup.
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rsv_data
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(RO, since: 5.9)
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Shows the reserved bytes for data.
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rsv_meta_pertrans
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(RO, since: 5.9)
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Shows the reserved bytes for per transaction metadata.
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rsv_meta_prealloc
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(RO, since: 5.9)
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Shows the reserved bytes for preallocated metadata.
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