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btrfs-progs: docs: add feature by version table from wiki

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Copy contents from https://btrfs.wiki.kernel.org/index.php/Changelog#By_feature

The formatting is done by a definition and list, instead of a table.
Unfortunatelly RST does not wrap long text in table cells so the width
exceeds visible area.

Signed-off-by: David Sterba <dsterba@suse.com>
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David Sterba 2022-06-14 20:39:42 +02:00
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Changes (feature/version)
=========================
Major features or significant feature enhancements by kernel version. For more
information look below.
The version states at which version a feature has been merged into the mainline
kernel. It does not tell anything about at which kernel version it is
considered mature enough for production use. For an estimation on stability of
features see [[Status]] page.
3.x
---
3.0 - scrub
Read all data and verify checksums, repair if possible.
3.2 - auto raid repair
Automatic repair of broken data from a good copy
3.2 - root backups
Save a few previous versions of the most imporant tree roots at commit time, used by *-o recovery*
3.3 - integrity checker
Optional infrastructure to verify integrity of written metadata blocks
3.3 - backref walking
Groundwork to allow tracking owner of blocks, used via *inspect-internal*
3.3 - restriper
RAID profiles can be changed on-line, balance filters
3.4 - big metadata blocks
Support for metadata blocks larger than page size
.. note::
Default nodesize is 16k since btrfs-progs 3.12
3.4 - error handling
Generic infrastructure for graceful error handling (EIO)
3.5 - device statistics
Persistent statistics about device errors
3.5 - fsync speedup
Noticeable improvements in fsync() implementation
3.6 - qgroups
Subvolume-aware quotas
3.6 - send/receive
Ability to transfer one filesystem via a data stream (full or
incremental) and apply the changes on a remote filesystem.
3.7 - extrefs
Hardlink count limit is lifted to 64k
.. note::
Default since btrfs-progs 3.12
3.7 - hole puching
Implement the FALLOC_FL_PUNCH_HOLE mode of *fallocate*
3.8 - device replace
Efficient replacement of existing device (add/remove in one go)
3.9 - raid 5/6 *(incomplete)*
Basic support for RAD5/6 profiles, no crash resiliency, replace and scrub support
3.9 - snapshot-aware defrag
Defrag does not break links between shared extents (snapshots, reflinked files)
.. note::
Disabled since 3.14 (and backported to some stable kernel versions)
due to problems. Will be enabled in the future.
3.9 - lightweight send
A mode of *send* that does not add the actual file data to the stream
3.9 - on-line label set/get
Label editable on mounted filesystems
3.10 - skinny metadata
Reduced metadata size (format change) of extents
.. note::
Default since btrfs-progs 3.18
3.10 - qgroup rescan
Sync qgroups with existing filesystem data
3.12 - uuid tree
A map of subvolume/UUID that vastly speeds up send/receive
3.12 - out-of-bound dedup
Support for deduplicating extents on a given set of files.
3.14 - no-holes
No extent representation for file holes (format change), may reduce overall metadata consumption
3.14 - feature bits in sysfs
/sys/fs/btrfs exports various bits about filesystem capabilities and feature support
3.16 - O_TMPFILE
Mode of open() to safely create a temporary file
3.16 - search ioctl v2
The extended SEARCH_TREE ioctl able to get more than a 4k data
3.18 - auto blockgroup reclaim
Automatically remove blockgroups (aka. chunks) that become completely empty.
3.19 - raid56: scrub, replace
Scrub and device replace works on RAID56 filesystems.
4.x
---
4.0 - store otime
Save creation time (otime) for all new files and directories. For
future use, current tool cannot read it directly.
4.2 - rootid ioctl accessible
The INO_LOOKUP will return root id (id of the containing subvolume),
unrestricted and to all users if the *treeid* is 0.
4.2 - dedupe possible on the same inode
The EXTENT_SAME ioctl will accept the same inode as source and
destination (ranges must not overlap).
4.3 - trim all free space
Trim will be performed also on the space that's not allocated by the
chunks, not only free space within the allocated chunks.
4.4 - balance filter updates
Enhanced syntax and new balance filters:
* limit=min..max
* usage=min..max
* stripes=min..max
4.5 - free space tree
Improved implementation of free space cache (aka v2), using b-trees.
.. note::
Default since btrfs-progs 5.15, Kernel 4.9 fixes endianity bugs on
big-endian machines, x86* is ok
4.5 - balance filter updates
Conversion to data/DUP profile possible through balance filters -- on single-device filesytem.
.. note::
mkfs.btrfs allows creating DUP on single device in the non-mixed mode since 4.4
4.6 - max_inline default
The default value of max_inline changed to 2048.
4.6 - read features from control device
The existing ioctl GET_SUPPORTED_FEATURES can be now used on the
control device (/dev/btrfs-control) and returns the supported features
without any mounted filesystem.
4.7 - delete device by id
Add new ioctl RM_DEV_V2, pass device to be deleted by its ID.
4.7 - more renameat2 modes
Add support for RENAME_EXCHANGE and RENAME_WHITEOUT to *renameat2*
syscall. This also means that *overlayfs* is now supported on top of
btrfs.
4.7 - balance filter updates
Conversion to data/DUP profile possible through balance filters -- on multiple-device filesystems.
.. note::
mkfs.btrfs allows creating DUP on multiple devices since 4.5.1
4.12 - raid56: auto repair
Scrub will attempt auto-repair (similar to raid1/raid10)
4.13 - statx
Support for the enhanced statx syscall; file creation timestamp
4.13 - sysfs qgroups override
qgroups: new sysfs control file to allow temporary quota override with CAP_SYS_RESOURCE
4.13 - *deprecated mount option alloc_start*
That was a debugging helper, not used and not supposed to be used nowadays.
4.14 - ZSTD compression
New compression algorithm ZSTD, supposedly better ratio/speed performance.
4.14 - improved degraded mount
Allow degraded mount based on the chunk constraints, not device number
constraints. Eg. when one device is missing but the remaining one holds
all *single* chunks.
4.14 - *deprecated user transaction ioctl*
BTRFS_IOC_TRANS_START and BTRFS_IOC_TRANS_END, no known users, tricky
to use; scheduled to be removed in 4.17
4.14 - refine SSD optimizations
The mount option *ssd* does not make any assumptions about block layout
or management by the device anymore, leaving only the speedups based on
low seek cost active. This could avoid some corner cases leading to
excessive fragmentation.
https://git.kernel.org/linus/583b723151794e2ff1691f1510b4e43710293875
The story so far.
4.15 - overlayfs
Overlayfs can now use btrfs as the lower filesystem.
4.15 - *ref-verify*
Debugging functionality to verify extent references. New mount option
<i>ref-verify</i>, must be built with CONFIG_BTRFS_FS_REF_VERIFY.
4.15 - zlib level
Allow to set the zlib compression level via mount option, eg. like
*compress=zlib:9*. The levels match the default zlib compression
levels. The default is 3.
4.15 - v2 of LOGICAL_INO ioctl
An enhanced version of ioctl that can translate logical extent offset
to inode numbers, "who owns this block". For certain usecases the V1
performs bad and this is addressed by V2.
[https://git.kernel.org/linus/d24a67b2d997c860a42516076f3315c2ad2d2884
Read more.]
4.15 - compression heuristics
Apply a few heuristics to the data before they're compressed to decide
if it's likely to gain any space savings. The methods: frequency
sampling, repeated pattern detection, Shannon entropy calculation.
4.16 - fallocate: zero range
Mode of the [http://man7.org/linux/man-pages/man2/fallocate.2.html
*fallocate*] syscall to zero file range.
4.17 - *removed user transaction ioctl*
deprecated in 4.14, see above
4.17 - *rmdir* on subvolumes
Allow rmdir to delete an empty subvolume.
4.18 - XFLAGS ioctl
Add support for ioctl FS_IOC_FSSETXATTR/FS_IOC_FSGETXATTR, successor of
FS_IOC_SETFLAGS/FS_IOC_GETFLAGS ioctl. Currently supports: APPEND,
IMMUTABLE, NOATIME, NODUMP, SYNC. Note that the naming is very
confusing, though it's named *xattr*, it does not mean the extended
attributes. It should be referenced as extended inode flags or
*xflags*.
4.18 - EXTENT_SAME ioctl / 16MiB chunks
The range for out-of-band deduplication implemented by the EXTENT_SAME
ioctl will split the range into 16MiB chunks. Up to now this was the
overall limit and effectively only the first 16MiB was deduplicated.
4.18 - GET_SUBVOL_INFO ioctl
New ioctl to read subvolume information (id, directory name,
generation, flags, UUIDs, time). This does not require root
permissions, only the regular access to to the subvolume.
4.18 - GET_SUBVOL_ROOTREF ioctl
New ioctl to enumerate subvolume references of a given subvolume. This
does not require root permissions, only the regular access to to the
subvolume.
4.18 - INO_LOOKUP_USER ioctl
New ioctl to lookup path by inode number. This does not require root
permissions, only the regular access to to the subvolume, unlike the
INO_LOOKUP ioctl.
4.19 - defrag ro/rw
Allow to run defrag on files that are normally accesible for
read-write, but are currently opened in read-only mode.
5.x
---
5.0 - swapfile
With some limitations where COW design does not work well with the swap
implementation (nodatacow file, no compression, cannot be snapshotted,
not possible on multiple devices, ...), as this is the most restricted
but working setup, we'll try to improve that in the future
5.0 - metadata uuid
An optional incompat feature to assign a new filesystem UUID without
overwriting all metadata blocks, stored only in superblock, unlike what
``btrfstune -u``
5.1 - FORGET_DEV ioctl
Unregister devices previously added by the scan ioctl, same effect as
if the kernel module is reloaded.
5.1 - zstd level
Allow to set the zstd compression level via mount option, eg. like
*compress=zstd:9*. The levels match the default zstd compression
levels. The default is 3, maximum is 15.
5.2 - pre-write checks
Verify metadata blocks before submitting them to the devices. This can
catch consistency problems or bitflips.
5.5 - more checksums
New checksum algorithms: xxhash (64b), SHA256 (256b), BLAKE2b (256b).
5.5 - RAID1C34
RAID1 with 3- and 4- copies (over all devices).
5.6 - async discard
Mode of discard (*mount -o discard=async*) that merges freed extents to
larger chunks and submits them for discard in a less intrusive way
5.6 - device info in sysfs
More information about device state can be found in per-filesystem sysfs directory.
5.7 - reflink/clone works on inline files
Inline files can be reflinked to the tail extent of other files
5.7 - faster balance cancel
More cancellation points in balance that will shorten the time to stop
processing once <tt>btrfs balance cancel</tt> is called.
5.7 - *removed flag BTRFS_SUBVOL_CREATE_ASYNC*
Remove support of flag BTRFS_SUBVOL_CREATE_ASYNC from subvolume creation ioctl.
5.7 - v2 of snapshot deletion ioctl
New ioctl BTRFS_IOC_SNAP_DESTROY_V2, deletion by subvolume id is now possible.
5.9 - mount option *rescue*
Unified mount option for actions that may help to access a damaged
filesystem. Now supports: nologreplay, usebackuproot
5.9 - qgroups in sysfs
The information about qgroup status and relations is exported in */sys/fs/UUID/qgroups*
5.9 - FS_INFO ioctl
Export more information: checksum type, checksum size, generation, metadata_uuid
5.10 - exclusive ops in sysfs
Export which filesystem exclusive operation is running (balance,
resize, device add/delete/relpace, ...)
5.11 - remove *inode_cache*
Remove inode number caching feature (mount -o inode_cache)
5.11 - more rescue=
Additional modes for mount option *rescue=*: ignorebadroots/ibadroots,
ignoredatacsums/idatacsums. All are exported in sysfs.
5.12 - zoned mode
Support for zoned devices with special allocation/write mode to
fixed-size zones. See [[Zoned]].
5.13 - supported_sectorsizes in sysfs
List supported sector sizes in sysfs file /sys/fs/btrfs/features/supported_sectorsizes
5.14 - sysfs scrub bw limit
Tunable bandwidth limit
(/sys/fs/btrfs/FSID/devinfo/DEVID/scrub_speed_max) for scrub (and
device replace) for a given device.
5.14 - sysfs device stats
The device stats can be also found in /sys/fs/btrfs/FSID/devinfo/DEVID/error_stats.
5.14 - cancellable resize, device delete
The filesystem resize and device delete operations can be cancelled by
specifying *cancel* as the device name.
5.14 - property value reset
Change how empty value is interpreted. New behaviour will delete the
value and reset it to default. This affects *btrfs.compression* where
value *no* sets NOCOMPRESS bit while empty value resets all compression
settings (either compression or NOCOMPRESS bit).
5.15 - fsverity
The fs-verity is a support layer that filesystems can hook into to
support transparent integrity and authenticity protection of read-only
files. https://www.kernel.org/doc/html/latest/filesystems/fsverity.html
5.15 - idmapped mount
Support mount with uid/gid mapped according to another namespace.
https://lwn.net/Articles/837566/
5.16 - ZNS in zoned
Zoned namespaces. https://zonedstorage.io/docs/introduction/zns ,
https://lwn.net/Articles/865988/
5.17 - send and relocation
Send and relocation (balance, device remove, shrink, block group
reclaim) can now work in parallel
5.17 - device add vs balance
It is possible to add a device with paused balance
.. note::
Since kernel 5.17.7 and btrfs-progs 5.17.1
5.17 - *no warning with flushoncommit*
Mounting with *-o flushoncommit* does not triggher the (harmless)
warning at each transaction commit
.. note::
Also backported to 5.15.27 and 5.16.13
5.18 - zoned and DUP metadata
DUP metadata works with zoned mode
5.18 - encoded data ioctl
New ioctls to read and write pre-encoded data (ie. no transformation
and directly written as extents), now works for compressed data
5.18 - *removed balance ioctl v1*
The support for ioctl BTRFS_IOC_BALANCE has been removed, superseded by
BTRFS_IOC_BALANCE_V2m long time ago

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Documentation/index.rst
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@ -12,6 +12,7 @@ Welcome to BTRFS documentation!
Administration
Hardware
CHANGES
Feature-by-version
Glossary
INSTALL