[PATCH v2 2/6] xfs_repair: don't error out on dirs with a single leafn block

["Darrick J. Wong" <darrick.wong@oracle.com>]

From: Darrick J. Wong <darrick.wong@oracle.com>

In process_node_dir2, we need to distinguish between a directory with a
single leafn block (yes, they exist) having no interior da nodes, and a
directory with a da tree that incorrectly points to dablk 0.  If we
happened to fill out any part of the da cursor then we have a da btree
with garbage in it; otherwise, we have a single leafn block.

This was found by repair repeatedly rebuilding a directory containing a
single leafn block (xfs/495).

Fixes: 67a79e2cc932 ("xfs_repair: treat zero da btree pointers as corruption")
Reported-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
v2: now that the regression test has landed, mention that in the
changelog
---
 repair/dir2.c |   15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/repair/dir2.c b/repair/dir2.c
index ba5763ed..e67ec590 100644
--- a/repair/dir2.c
+++ b/repair/dir2.c
@@ -1243,10 +1243,21 @@ process_node_dir2(
 
 	/*
 	 * Skip directories with a root marked XFS_DIR2_LEAFN_MAGIC
+	 *
+	 * Be careful here: If any level of the da cursor was filled out then
+	 * the directory has a da btree containing an invalid before pointer to
+	 * dblock 0, and we should move on to rebuilding the directory.  If no
+	 * levels in the da cursor got filled out, then we just have a single
+	 * leafn block and we're done.
 	 */
 	if (bno == 0) {
-		release_da_cursor(mp, &da_cursor, 0);
-		return 0;
+		if (da_cursor.active > 0) {
+			err_release_da_cursor(mp, &da_cursor, 0);
+			return 1;
+		} else {
+			release_da_cursor(mp, &da_cursor, 0);
+			return 0;
+		}
 	} else {
 		/*
 		 * Now pass cursor and bno into leaf-block processing routine.