[PATCH v3 1/3] xfs: zero entire directory data block header region at init

[Yuto Ohnuki <ytohnuki@amazon.com>]

xfs_dir3_data_init currently zeroes only the xfs_dir3_blk_hdr portion of
the directory data block header, then manually initializes the bestfree
entries in a loop. This leaves the pad field in xfs_dir3_data_hdr
uninitialized and requires explicit zeroing of each bestfree slot.

Zero the entire header region (geo->data_entry_offset bytes)
unconditionally before setting individual fields. This covers all
current and future header fields, all padding (implicit and explicit),
and the bestfree array, so the manual zeroing loop for bestfree can be
removed.

Suggested-by: Dave Chinner <dgc@kernel.org>
Signed-off-by: Yuto Ohnuki <ytohnuki@amazon.com>
---
 fs/xfs/libxfs/xfs_dir2_data.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_dir2_data.c b/fs/xfs/libxfs/xfs_dir2_data.c
index 80ba94f51e5c..35ff119aa84b 100644
--- a/fs/xfs/libxfs/xfs_dir2_data.c
+++ b/fs/xfs/libxfs/xfs_dir2_data.c
@@ -728,7 +728,6 @@ xfs_dir3_data_init(
 	struct xfs_dir2_data_unused	*dup;
 	struct xfs_dir2_data_free 	*bf;
 	int				error;
-	int				i;
 
 	/*
 	 * Get the buffer set up for the block.
@@ -741,13 +740,16 @@ xfs_dir3_data_init(
 	xfs_trans_buf_set_type(tp, bp, XFS_BLFT_DIR_DATA_BUF);
 
 	/*
-	 * Initialize the header.
+	 * Initialize the whole directory header region to zero
+	 * so that all padding, bestfree entries, and any
+	 * future header fields are clean.
 	 */
 	hdr = bp->b_addr;
+	memset(hdr, 0, geo->data_entry_offset);
+
 	if (xfs_has_crc(mp)) {
 		struct xfs_dir3_blk_hdr *hdr3 = bp->b_addr;
 
-		memset(hdr3, 0, sizeof(*hdr3));
 		hdr3->magic = cpu_to_be32(XFS_DIR3_DATA_MAGIC);
 		hdr3->blkno = cpu_to_be64(xfs_buf_daddr(bp));
 		hdr3->owner = cpu_to_be64(args->owner);
@@ -759,10 +761,6 @@ xfs_dir3_data_init(
 	bf = xfs_dir2_data_bestfree_p(mp, hdr);
 	bf[0].offset = cpu_to_be16(geo->data_entry_offset);
 	bf[0].length = cpu_to_be16(geo->blksize - geo->data_entry_offset);
-	for (i = 1; i < XFS_DIR2_DATA_FD_COUNT; i++) {
-		bf[i].length = 0;
-		bf[i].offset = 0;
-	}
 
 	/*
 	 * Set up an unused entry for the block's body.
-- 
2.50.1




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