xfs: btree scrub should check minrecs

Strengthen the btree block header checks to detect the number of records
being less than the btree type's minimum record count.  Certain blocks
are allowed to violate this constraint -- specifically any btree block
at the top of the tree can have fewer than minrecs records.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

fs/xfs/scrub/btree.c

@@ -454,6 +454,44 @@ xfs_scrub_btree_check_owner(
 	return xfs_scrub_btree_check_block_owner(bs, level, XFS_BUF_ADDR(bp));
 }
 
+/*
+ * Check that this btree block has at least minrecs records or is one of the
+ * special blocks that don't require that.
+ */
+STATIC void
+xfs_scrub_btree_check_minrecs(
+	struct xfs_scrub_btree	*bs,
+	int			level,
+	struct xfs_btree_block	*block)
+{
+	unsigned int		numrecs;
+	int			ok_level;
+
+	numrecs = be16_to_cpu(block->bb_numrecs);
+
+	/* More records than minrecs means the block is ok. */
+	if (numrecs >= bs->cur->bc_ops->get_minrecs(bs->cur, level))
+		return;
+
+	/*
+	 * Certain btree blocks /can/ have fewer than minrecs records.  Any
+	 * level greater than or equal to the level of the highest dedicated
+	 * btree block are allowed to violate this constraint.
+	 *
+	 * For a btree rooted in a block, the btree root can have fewer than
+	 * minrecs records.  If the btree is rooted in an inode and does not
+	 * store records in the root, the direct children of the root and the
+	 * root itself can have fewer than minrecs records.
+	 */
+	ok_level = bs->cur->bc_nlevels - 1;
+	if (bs->cur->bc_flags & XFS_BTREE_ROOT_IN_INODE)
+		ok_level--;
+	if (level >= ok_level)
+		return;
+
+	xfs_scrub_btree_set_corrupt(bs->sc, bs->cur, level);
+}
+
 /*
  * Grab and scrub a btree block given a btree pointer.  Returns block
  * and buffer pointers (if applicable) if they're ok to use.
@@ -491,6 +529,8 @@ xfs_scrub_btree_get_block(
 	if (*pbp)
 		xfs_scrub_buffer_recheck(bs->sc, *pbp);
 
+	xfs_scrub_btree_check_minrecs(bs, level, *pblock);
+
 	/*
 	 * Check the block's owner; this function absorbs error codes
 	 * for us.