dm snapshot: support barriers

Flush support for dm-snapshot target.

This patch just forwards the flush request to either the origin or the snapshot
device.  (It doesn't flush exception store metadata.)

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index d73f17fc7778..d573165cd2b7 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -678,6 +678,7 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 
         ti->private = s;
         ti->split_io = s->store->chunk_size;
+        ti->num_flush_requests = 1;
 
         return 0;
 
@@ -1030,6 +1031,11 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio,
         chunk_t chunk;
         struct dm_snap_pending_exception *pe = NULL;
 
+        if (unlikely(bio_empty_barrier(bio))) {
+                bio->bi_bdev = s->store->cow->bdev;
+                return DM_MAPIO_REMAPPED;
+        }
+
         chunk = sector_to_chunk(s->store, bio->bi_sector);
 
         /* Full snapshots are not usable */
@@ -1338,6 +1344,8 @@ static int origin_ctr(struct dm_target *ti, unsigned int argc, char **argv)
         }
 
         ti->private = dev;
+        ti->num_flush_requests = 1;
+
         return 0;
 }
 
@@ -1353,6 +1361,9 @@ static int origin_map(struct dm_target *ti, struct bio *bio,
         struct dm_dev *dev = ti->private;
         bio->bi_bdev = dev->bdev;
 
+        if (unlikely(bio_empty_barrier(bio)))
+                return DM_MAPIO_REMAPPED;
+
         /* Only tell snapshots if this is a write */
         return (bio_rw(bio) == WRITE) ? do_origin(dev, bio) : DM_MAPIO_REMAPPED;
 }