xfs: alert the user about data/attr fork mappings that could be merged

If the data or attr forks have mappings that could be merged, let the
user know that the structure could be optimized.  This isn't a
filesystem corruption since the regular filesystem does not try to be
smart about merging bmbt records.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

fs/xfs/scrub/bmap.c

@@ -764,6 +764,7 @@ xchk_bmap_iext_iter(
 {
 	struct xfs_bmbt_irec	got;
 	struct xfs_ifork	*ifp;
+	xfs_filblks_t		prev_len;
 
 	ifp = xfs_ifork_ptr(info->sc->ip, info->whichfork);
 
@@ -782,6 +783,7 @@ xchk_bmap_iext_iter(
 	 * Iterate subsequent iextent records and merge them with the one
 	 * that we just read, if possible.
 	 */
+	prev_len = irec->br_blockcount;
 	while (xfs_iext_peek_next_extent(ifp, &info->icur, &got)) {
 		if (!xchk_are_bmaps_contiguous(irec, &got))
 			break;
@@ -792,7 +794,16 @@ xchk_bmap_iext_iter(
 			return false;
 		}
 
+		/*
+		 * Notify the user of mergeable records in the data or attr
+		 * forks.  CoW forks only exist in memory so we ignore them.
+		 */
+		if (info->whichfork != XFS_COW_FORK &&
+		    prev_len + got.br_blockcount > BMBT_BLOCKCOUNT_MASK)
+			xchk_ino_set_preen(info->sc, info->sc->ip->i_ino);
+
 		irec->br_blockcount += got.br_blockcount;
+		prev_len = got.br_blockcount;
 		xfs_iext_next(ifp, &info->icur);
 	}