xfs: create helpers to scrub a metadata btree

Create helper functions and tracepoints to deal with errors while
scrubbing a metadata btree.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
diff --git a/fs/xfs/scrub/trace.c b/fs/xfs/scrub/trace.c
index 88b5ccb..472080e 100644
--- a/fs/xfs/scrub/trace.c
+++ b/fs/xfs/scrub/trace.c
@@ -30,10 +30,27 @@
 #include "xfs_inode.h"
 #include "xfs_btree.h"
 #include "xfs_trans.h"
+#include "xfs_bit.h"
 #include "scrub/xfs_scrub.h"
 #include "scrub/scrub.h"
 #include "scrub/common.h"
 
+/* Figure out which block the btree cursor was pointing to. */
+static inline xfs_fsblock_t
+xfs_scrub_btree_cur_fsbno(
+	struct xfs_btree_cur		*cur,
+	int				level)
+{
+	if (level < cur->bc_nlevels && cur->bc_bufs[level])
+		return XFS_DADDR_TO_FSB(cur->bc_mp, cur->bc_bufs[level]->b_bn);
+	else if (level == cur->bc_nlevels - 1 &&
+		 cur->bc_flags & XFS_BTREE_LONG_PTRS)
+		return XFS_INO_TO_FSB(cur->bc_mp, cur->bc_private.b.ip->i_ino);
+	else if (!(cur->bc_flags & XFS_BTREE_LONG_PTRS))
+		return XFS_AGB_TO_FSB(cur->bc_mp, cur->bc_private.a.agno, 0);
+	return NULLFSBLOCK;
+}
+
 /*
  * We include this last to have the helpers above available for the trace
  * event implementations.