Re: [PATCH v2] xfs: check v5 superblock features early

On Wed, Jul 29, 2026 at 03:00:58PM +0200, Christoph Hellwig wrote:
> When working on a new features that reuses the existing pad in the
> superblock, I noticed that mounting such a file system on an old kernel
> logs a rather confusing warning:
> 
>     XFS (vdc): Metadir superblock padding fields must be zero.
> 
> This is because we only validate the various feature fields in v5
> superblocks after the common superblock validation helper is called.
> 
> Fix this by calling the feature validation first.
> 
> Fixes: eca383fcd63b ("xfs: refactor superblock verifiers")
> Signed-off-by: Christoph Hellwig <[email protected]>

Makes sense, and should probably get backported for the improved error
message.  Not sure if we care about pre-6.18 kernels though, since none
of them really support metadir.

Cc: <[email protected]> # v4.19
Reviewed-by: "Darrick J. Wong" <[email protected]>

--D

> ---
> 
> Changes since v1:
>  - minimize the fix, and implement all the good ideas later
> 
>  fs/xfs/libxfs/xfs_sb.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
> index 47322adb7690..75f2a021ee6d 100644
> --- a/fs/xfs/libxfs/xfs_sb.c
> +++ b/fs/xfs/libxfs/xfs_sb.c
> @@ -1118,10 +1118,10 @@ xfs_sb_read_verify(
>  	 * because _verify_common checks the on-disk values.
>  	 */
>  	__xfs_sb_from_disk(&sb, dsb, false);
> -	error = xfs_validate_sb_common(mp, bp, &sb);
> +	error = xfs_validate_sb_read(mp, &sb);
>  	if (error)
>  		goto out_error;
> -	error = xfs_validate_sb_read(mp, &sb);
> +	error = xfs_validate_sb_common(mp, bp, &sb);
>  
>  out_error:
>  	if (error == -EFSCORRUPTED || error == -EFSBADCRC)
> -- 
> 2.53.0
> 
>