dm: change max_io_len() to use blk_max_size_offset()

Using blk_max_size_offset() enables DM core's splitting to impose
ti->max_io_len (via q->limits.chunk_sectors) and also fallback to
respecting q->limits.max_sectors if chunk_sectors isn't set.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm.c

@@ -1051,22 +1051,18 @@ static sector_t max_io_len_target_boundary(sector_t sector, struct dm_target *ti
 static sector_t max_io_len(sector_t sector, struct dm_target *ti)
 {
 	sector_t len = max_io_len_target_boundary(sector, ti);
-	sector_t offset, max_len;
+	sector_t max_len;
 
 	/*
 	 * Does the target need to split even further?
+	 * - q->limits.chunk_sectors reflects ti->max_io_len so
+	 *   blk_max_size_offset() provides required splitting.
+	 * - blk_max_size_offset() also respects q->limits.max_sectors
 	 */
-	if (ti->max_io_len) {
-		offset = dm_target_offset(ti, sector);
-		if (unlikely(ti->max_io_len & (ti->max_io_len - 1)))
-			max_len = sector_div(offset, ti->max_io_len);
-		else
-			max_len = offset & (ti->max_io_len - 1);
-		max_len = ti->max_io_len - max_len;
-
-		if (len > max_len)
-			len = max_len;
-	}
+	max_len = blk_max_size_offset(dm_table_get_md(ti->table)->queue,
+				      dm_target_offset(ti, sector));
+	if (len > max_len)
+		len = max_len;
 
 	return len;
 }