Re: [PATCH 4/6] xfs: fix zero byte checking in the superblock scrubber

[Christoph Hellwig <hch@infradead.org>]

On Tue, Dec 03, 2024 at 07:03:16PM -0800, Darrick J. Wong wrote:
> +/* Calculate the ondisk superblock size in bytes */
> +STATIC size_t
> +xchk_superblock_ondisk_size(
> +	struct xfs_mount	*mp)
> +{
> +	if (xfs_has_metadir(mp))
> +		return offsetofend(struct xfs_dsb, sb_pad);
> +	if (xfs_has_metauuid(mp))
> +		return offsetofend(struct xfs_dsb, sb_meta_uuid);
> +	if (xfs_has_crc(mp))
> +		return offsetofend(struct xfs_dsb, sb_lsn);
> +	if (xfs_sb_version_hasmorebits(&mp->m_sb))
> +		return offsetofend(struct xfs_dsb, sb_bad_features2);
> +	if (xfs_has_logv2(mp))
> +		return offsetofend(struct xfs_dsb, sb_logsunit);
> +	if (xfs_has_sector(mp))
> +		return offsetofend(struct xfs_dsb, sb_logsectsize);
> +	/* only support dirv2 or more recent */
> +	return offsetofend(struct xfs_dsb, sb_dirblklog);

This really should be libxfs so tht it can be shared with
secondary_sb_whack in xfsrepair.  The comment at the end of
the xfs_dsb definition should also be changed to point to this
libxfs version.

> +}
>  	/* Everything else must be zero. */
> -	if (memchr_inv(sb + 1, 0,
> -			BBTOB(bp->b_length) - sizeof(struct xfs_dsb)))
> +	sblen = xchk_superblock_ondisk_size(mp);
> +	if (memchr_inv((char *)sb + sblen, 0, BBTOB(bp->b_length) - sblen))

This could be simplified to

	if (memchr_inv(bp->b_addr + sblen, 0, BBTOB(bp->b_length) - sblen))

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>