diff options
| author | Daeho Jeong <daehojeong@google.com> | 2024-10-17 10:31:53 -0700 |
|---|---|---|
| committer | Jaegeuk Kim <jaegeuk@kernel.org> | 2024-11-01 01:19:00 +0000 |
| commit | 128d333f0dff2fbe41c546581c6f151e9d68cd4c (patch) | |
| tree | 701a9e56664e7121726a72d1c48c2eb6cd4a6348 /Documentation/filesystems | |
| parent | fa08972bcb7baaf5f1f4fdf251dc08bdd3ab1cf0 (diff) | |
f2fs: introduce device aliasing file
F2FS should understand how the device aliasing file works and support
deleting the file after use. A device aliasing file can be created by
mkfs.f2fs tool and it can map the whole device with an extent, not
using node blocks. The file space should be pinned and normally used for
read-only usages.
Signed-off-by: Daeho Jeong <daehojeong@google.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Diffstat (limited to 'Documentation/filesystems')
| -rw-r--r-- | Documentation/filesystems/f2fs.rst | 44 |
1 files changed, 44 insertions, 0 deletions
diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst index 68a0885fb5e6..fb7d2ee022bc 100644 --- a/Documentation/filesystems/f2fs.rst +++ b/Documentation/filesystems/f2fs.rst @@ -943,3 +943,47 @@ NVMe Zoned Namespace devices can start before the zone-capacity and span across zone-capacity boundary. Such spanning segments are also considered as usable segments. All blocks past the zone-capacity are considered unusable in these segments. + +Device aliasing feature +----------------------- + +f2fs can utilize a special file called a "device aliasing file." This file allows +the entire storage device to be mapped with a single, large extent, not using +the usual f2fs node structures. This mapped area is pinned and primarily intended +for holding the space. + +Essentially, this mechanism allows a portion of the f2fs area to be temporarily +reserved and used by another filesystem or for different purposes. Once that +external usage is complete, the device aliasing file can be deleted, releasing +the reserved space back to F2FS for its own use. + +<use-case> + +# ls /dev/vd* +/dev/vdb (32GB) /dev/vdc (32GB) +# mkfs.ext4 /dev/vdc +# mkfs.f2fs -c /dev/vdc@vdc.file /dev/vdb +# mount /dev/vdb /mnt/f2fs +# ls -l /mnt/f2fs +vdc.file +# df -h +/dev/vdb 64G 33G 32G 52% /mnt/f2fs + +# mount -o loop /dev/vdc /mnt/ext4 +# df -h +/dev/vdb 64G 33G 32G 52% /mnt/f2fs +/dev/loop7 32G 24K 30G 1% /mnt/ext4 +# umount /mnt/ext4 + +# f2fs_io getflags /mnt/f2fs/vdc.file +get a flag on /mnt/f2fs/vdc.file ret=0, flags=nocow(pinned),immutable +# f2fs_io setflags noimmutable /mnt/f2fs/vdc.file +get a flag on noimmutable ret=0, flags=800010 +set a flag on /mnt/f2fs/vdc.file ret=0, flags=noimmutable +# rm /mnt/f2fs/vdc.file +# df -h +/dev/vdb 64G 753M 64G 2% /mnt/f2fs + +So, the key idea is, user can do any file operations on /dev/vdc, and +reclaim the space after the use, while the space is counted as /data. +That doesn't require modifying partition size and filesystem format. |