Re: [PATCH v3 1/5] btrfs: fix -o compress= level getting inherited by compression xattr property

[Zygo Blaxell <ce3g8jdj@umail.furryterror.org>]

On Sun, Aug 09, 2026 at 08:52:59PM +0200, koraynilay wrote:
> When setting the btrfs.compression xattr, btrfs uses the mount option level
> (since levels in the xattr aren't supported yet) to compress the data, even
> if the compression algorithm between the property and the compress= option
> are different (!!).
> For example, when mounting with compress=zstd:15 and setting
> btrfs.compression=zlib, the data would get compressed at zlib:9, because
> btrfs would take "zlib" from the xattr but "15" from the mount option,
> which would then get correctly clamped at 9.
> 
> To fix, just hard-code the compress level at 0, forcing the property's
> algorithm default.
> 
> Reported-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
> Signed-off-by: koraynilay <koray.fra@gmail.com>
> ---
>  fs/btrfs/inode.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 2534cd9284d5..6d7f2aa2555c 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -938,6 +938,7 @@ static void compress_file_range(struct btrfs_work *work)
>  		compress_level = inode->defrag_compress_level;
>  	} else if (inode->prop_compress) {
>  		compress_type = inode->prop_compress;
> +		compress_level = 0;

This set to zero should be conditional on inode->prop_compress !=
fs_info->compress_type; otherwise, it prevents the compress-level mount
option from working in the common case where 'btrfs.compression=zstd'
or 'chattr +c' has been set.

>  	}
>  
>  	/* Compression level is applied here. */
> @@ -2326,6 +2327,7 @@ static int run_delalloc_inline(struct btrfs_inode *inode, struct folio *locked_f
>  			compress_level = inode->defrag_compress_level;
>  		} else if (inode->prop_compress) {
>  			compress_type = inode->prop_compress;
> +			compress_level = 0;
>  		}
>  		cb = btrfs_compress_bio(inode, 0, blocksize, compress_type, compress_level, 0);
>  		if (IS_ERR(cb)) {
> -- 
> 2.55.0
> 
>