xfs: change bmap scrubber to store the previous mapping

Convert the inode data/attr/cow fork scrubber to remember the entire
previous mapping, not just the next expected offset.  No behavior
changes here, but this will enable some better checking in subsequent
patches.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

fs/xfs/scrub/bmap.c

@@ -96,11 +96,23 @@ xchk_setup_inode_bmap(
 
 struct xchk_bmap_info {
 	struct xfs_scrub	*sc;
+
+	/* Incore extent tree cursor */
 	struct xfs_iext_cursor	icur;
-	xfs_fileoff_t		lastoff;
+
+	/* Previous fork mapping that we examined */
+	struct xfs_bmbt_irec	prev_rec;
+
+	/* Is this a realtime fork? */
 	bool			is_rt;
+
+	/* May mappings point to shared space? */
 	bool			is_shared;
+
+	/* Was the incore extent tree loaded? */
 	bool			was_loaded;
+
+	/* Which inode fork are we checking? */
 	int			whichfork;
 };
 
@@ -405,7 +417,8 @@ xchk_bmap_iextent(
 	 * Check for out-of-order extents.  This record could have come
 	 * from the incore list, for which there is no ordering check.
 	 */
-	if (irec->br_startoff < info->lastoff)
+	if (irec->br_startoff < info->prev_rec.br_startoff +
+				info->prev_rec.br_blockcount)
 		xchk_fblock_set_corrupt(info->sc, info->whichfork,
 				irec->br_startoff);
 
@@ -712,7 +725,8 @@ xchk_bmap_iextent_delalloc(
 	 * Check for out-of-order extents.  This record could have come
 	 * from the incore list, for which there is no ordering check.
 	 */
-	if (irec->br_startoff < info->lastoff)
+	if (irec->br_startoff < info->prev_rec.br_startoff +
+				info->prev_rec.br_blockcount)
 		xchk_fblock_set_corrupt(info->sc, info->whichfork,
 				irec->br_startoff);
 
@@ -806,7 +820,6 @@ xchk_bmap(
 		goto out;
 
 	/* Scrub extent records. */
-	info.lastoff = 0;
 	ifp = xfs_ifork_ptr(ip, whichfork);
 	for_each_xfs_iext(ifp, &info.icur, &irec) {
 		if (xchk_should_terminate(sc, &error) ||
@@ -823,7 +836,7 @@ xchk_bmap(
 			xchk_bmap_iextent_delalloc(ip, &info, &irec);
 		else
 			xchk_bmap_iextent(ip, &info, &irec);
-		info.lastoff = irec.br_startoff + irec.br_blockcount;
+		memcpy(&info.prev_rec, &irec, sizeof(struct xfs_bmbt_irec));
 	}
 
 	error = xchk_bmap_check_rmaps(sc, whichfork);