Re: [PATCH v2] btrfs: test defrag --nocomp converts compressed extents to uncompressed

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

在 2026/9/20 21:41, Dhruva G 写道:
> "btrfs filesystem defragment --nocomp" rewrites already compressed file
> data as uncompressed data. The kernel flag was added by commit
> 009b2056cb25 ("btrfs: defrag: add flag to force no-compression") in
> v6.17, and the userspace option shipped in btrfs-progs v6.16. There is
> no test for it.
> 
> Add a test that writes compressible data in 128K blocks on a filesystem
> mounted with compress=zlib, runs defragment with --nocomp, and uses the
> FIEMAP encoded flag to verify that no extent remains compressed. Also
> verify that the file contents are unchanged after a remount. Keeping
> compression enabled throughout the test confirms that the defrag ioctl
> takes precedence over the mount option.
> 
> Regular defrag deliberately leaves maximum-sized compressed extents
> alone, as asserted by btrfs/259. Creating maximum-sized compressed
> extents therefore ensures that an implementation which silently treats
> --nocomp as regular defrag fails the test.
> 
> Check support in two stages: first require btrfs-progs to advertise
> --nocomp, then invoke it on a 10-byte file to verify that the kernel
> accepts the flag. Kernels with the unknown-flag validation from commit
> 173431b274a9 return EOPNOTSUPP when NOCOMPRESS is unavailable. Kernels
> predating that validation may silently ignore the flag and fail the
> semantic checks instead of skipping.
> 
> Signed-off-by: Dhruva Gole <goledhruva@gmail.com>

Looks good to me overall.

Reviewed-by: Qu Wenruo <wqu@suse.com>

Thanks,
Qu