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

[Yuto Ohnuki <ytohnuki@amazon.com>]

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




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