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docs: filesystems: f2fs: fix description about compress ioctl

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Since commit c61404153e ("f2fs: introduce FI_COMPRESS_RELEASED
instead of using IMMUTABLE bit"), we no longer use the IMMUTABLE
bit to prevent writing data for compression. Let's correct the
corresponding documentation.

BTW, this patch fixes some alignment issues in the compress
metadata layout.

Signed-off-by: Chao Liu <liuchao@coolpad.com>
Link: https://lore.kernel.org/r/20220613020800.3379482-1-chaoliu719@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Chao Liu 2022-06-13 10:08:00 +08:00 committed by Jonathan Corbet
parent 910cb3137c
commit d218bee86a
1 changed files with 7 additions and 6 deletions
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13
Documentation/filesystems/f2fs.rst
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@ -818,10 +818,11 @@ 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::
@ -830,12 +831,12 @@ 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 |
+----------+---------+---------+---------+ +---------+---------+---------+---------+
. .
. .
. .
. .
+-------------+-------------+----------+----------------------------+