[PATCH v2] xfs: check da node block pad field during scrub

[Yuto Ohnuki <ytohnuki@amazon.com>]

The da node block header (xfs_da3_node_hdr) contains a __pad32 field
that should always be zero. Add a check for this during directory and
attribute btree scrubbing.

Since old kernels may have written non-zero padding without issues, flag
this as an optimization opportunity (preen) rather than corruption.

Signed-off-by: Yuto Ohnuki <ytohnuki@amazon.com>
---
Changes in v2:
- Use xchk_da_set_preen instead of xchk_da_set_corrupt since
  old kernels may have written non-zero padding without issues.
- Link to v1: https://lore.kernel.org/all/20260404143043.65268-2-ytohnuki@amazon.com/
---
 fs/xfs/scrub/dabtree.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/scrub/dabtree.c b/fs/xfs/scrub/dabtree.c
index 1a71d36898b1..b55922d3e988 100644
--- a/fs/xfs/scrub/dabtree.c
+++ b/fs/xfs/scrub/dabtree.c
@@ -454,7 +454,12 @@ xchk_da_btree_block(
 			}
 		}
 
-		/* XXX: Check hdr3.pad32 once we know how to fix it. */
+		if (xfs_has_crc(ip->i_mount)) {
+			struct xfs_da3_node_hdr *nodehdr3 = blk->bp->b_addr;
+
+			if (be32_to_cpu(nodehdr3->__pad32) != 0)
+				xchk_da_set_preen(ds, level);
+		}
 		break;
 	default:
 		xchk_da_set_corrupt(ds, level);
-- 
2.50.1




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