Re: [PATCH] xfs: improve RT geometry validation

["Darrick J. Wong" <djwong@kernel.org>]

On Thu, May 07, 2026 at 07:25:35AM +0200, Christoph Hellwig wrote:
> Make sure the rtgcount is plausible for the given RT group size.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/libxfs/xfs_sb.c | 22 +++++++++++++++-------
>  1 file changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
> index 47322adb7690..c0354f43704f 100644
> --- a/fs/xfs/libxfs/xfs_sb.c
> +++ b/fs/xfs/libxfs/xfs_sb.c
> @@ -302,17 +302,25 @@ xfs_validate_rt_geometry(
>  		return false;
>  
>  	if (xfs_sb_is_v5(sbp) &&
> -	    (sbp->sb_features_incompat & XFS_SB_FEAT_INCOMPAT_ZONED)) {
> +	    (sbp->sb_features_incompat & XFS_SB_FEAT_INCOMPAT_METADIR)) {
> +		uint64_t		nr_rgs;
>  		uint32_t		mod;
>  
>  		/*
> -		 * Zoned RT devices must be aligned to the RT group size,
> -		 * because garbage collection assumes that all zones have the
> -		 * same size to avoid insane complexity if that weren't the
> -		 * case.
> +		 * Check that the number of rgcounts is plausible for the RG
> +		 * size.
> +		 */
> +		nr_rgs = div_u64_rem(sbp->sb_rextents, sbp->sb_rgextents, &mod);
> +		if (nr_rgs != sbp->sb_rgcount + !!mod)
> +			return false;

Isn't this already covered by xfs_validate_sb_rtgroups?


	groups = howmany_64(sbp->sb_rextents, sbp->sb_rgextents);
	if (groups != sbp->sb_rgcount) {
		xfs_warn(mp,
"Realtime groups (%u) do not cover the entire rt section; need (%llu) groups.",
				sbp->sb_rgcount, groups);
		return -EINVAL;
	}

> +
> +		/*
> +		 * Zoned RT devices must be aligned to the RT group size because
> +		 * garbage collection assumes that all zones have the same size
> +		 * to avoid insane complexity if that weren't the case.
>  		 */
> -		div_u64_rem(sbp->sb_rextents, sbp->sb_rgextents, &mod);
> -		if (mod)
> +		if ((sbp->sb_features_incompat & XFS_SB_FEAT_INCOMPAT_ZONED) &&
> +		    mod > 0)
>  			return false;

And shouldn't this be in xfs_validate_sb_zoned?

Or do you want this in xfs_validate_rt_geometry because that's what
xfs_repair calls to check the superblock?

--D