Re: [PATCH v3 2/3] xfs: zero directory data block padding on write verification

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

On Sat, Apr 11, 2026 at 03:24:14PM +0100, Yuto Ohnuki wrote:
> Old kernels did not zero the pad field in xfs_dir3_data_hdr when
> initializing directory data blocks, so existing filesystems may have
> non-zero padding on disk.
> 
> Zero the pad field in xfs_dir3_data_write_verify alongside the existing
> LSN and checksum updates. The pad field is pure alignment padding with
> no runtime meaning, so zeroing it during write verification is safe and
> has no additional I/O cost. This lets filesystems gradually self-heal
> stale non-zero padding as directories are modified, without requiring an
> explicit repair pass.
> 
> Suggested-by: Dave Chinner <dgc@kernel.org>
> Signed-off-by: Yuto Ohnuki <ytohnuki@amazon.com>
> ---
>  fs/xfs/libxfs/xfs_dir2_data.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/fs/xfs/libxfs/xfs_dir2_data.c b/fs/xfs/libxfs/xfs_dir2_data.c
> index 35ff119aa84b..aecbab61014c 100644
> --- a/fs/xfs/libxfs/xfs_dir2_data.c
> +++ b/fs/xfs/libxfs/xfs_dir2_data.c
> @@ -382,6 +382,7 @@ xfs_dir3_data_write_verify(
>  	struct xfs_mount	*mp = bp->b_mount;
>  	struct xfs_buf_log_item	*bip = bp->b_log_item;
>  	struct xfs_dir3_blk_hdr	*hdr3 = bp->b_addr;
> +	struct xfs_dir3_data_hdr *datahdr3 = bp->b_addr;
>  	xfs_failaddr_t		fa;
>  
>  	fa = xfs_dir3_data_verify(bp);
> @@ -396,6 +397,11 @@ xfs_dir3_data_write_verify(
>  	if (bip)
>  		hdr3->lsn = cpu_to_be64(bip->bli_item.li_lsn);
>  
> +	/*
> +	 * Zero padding that may be stale from old kernels.
> +	 */
> +	datahdr3->pad = 0;

This needs to be gated on the directory block actually having a dir3
data header (aka xfs_has_crc()).

--D

> +
>  	xfs_buf_update_cksum(bp, XFS_DIR3_DATA_CRC_OFF);
>  }
>  
> -- 
> 2.50.1
> 
> 
> 
> 
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