dm: record old_sector in dm_target_io before calling map function

Prep for being able to defer trace_block_bio_remap() until when the
bio is remapped and submitted by the DM target.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-core.h

@@ -216,6 +216,7 @@ struct dm_target_io {
 	unsigned int target_bio_nr;
 	unsigned int *len_ptr;
 	bool inside_dm_io;
+	sector_t old_sector;
 	struct bio clone;
 };
 

drivers/md/dm.c

@@ -584,6 +584,7 @@ static struct bio *alloc_tio(struct clone_info *ci, struct dm_target *ti,
 	tio->ti = ti;
 	tio->target_bio_nr = target_bio_nr;
 	tio->len_ptr = len;
+	tio->old_sector = 0;
 
 	return &tio->clone;
 }
@@ -1139,7 +1140,6 @@ static void __map_bio(struct bio *clone)
 {
 	struct dm_target_io *tio = clone_to_tio(clone);
 	int r;
-	sector_t sector;
 	struct dm_io *io = tio->io;
 	struct dm_target *ti = tio->ti;
 
@@ -1151,7 +1151,7 @@ static void __map_bio(struct bio *clone)
 	 * this io.
 	 */
 	dm_io_inc_pending(io);
-	sector = clone->bi_iter.bi_sector;
+	tio->old_sector = clone->bi_iter.bi_sector;
 
 	if (unlikely(swap_bios_limit(ti, clone))) {
 		struct mapped_device *md = io->md;
@@ -1176,7 +1176,8 @@ static void __map_bio(struct bio *clone)
 		break;
 	case DM_MAPIO_REMAPPED:
 		/* the bio has been remapped so dispatch it */
-		trace_block_bio_remap(clone, bio_dev(io->orig_bio), sector);
+		trace_block_bio_remap(clone, bio_dev(io->orig_bio),
+				      tio->old_sector);
 		submit_bio_noacct(clone);
 		break;
 	case DM_MAPIO_KILL: