Track in-progress writes on the merging snapshot device and delay merging
the chunk until all writes to that chunk finish.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 drivers/md/dm-snap.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

Index: linux-2.6.26-devel/drivers/md/dm-snap.c
===================================================================
--- linux-2.6.26-devel.orig/drivers/md/dm-snap.c	2008-07-14 20:23:54.000000000 +0200
+++ linux-2.6.26-devel/drivers/md/dm-snap.c	2008-07-14 20:23:58.000000000 +0200
@@ -610,7 +610,8 @@ static void snapshot_merge_process(struc
 	s->merge_write_interlock_n = 1;
 	up_write(&s->lock);
 
-	/* !!! FIXME: wait until writes to this chunk drain */
+	while (__chunk_is_tracked(s, old_chunk))
+		yield();
 
 	dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, merge_callback, s);
 	return;
@@ -1299,7 +1300,11 @@ static int snapshot_merge_map(struct dm_
 			r = DM_MAPIO_SUBMITTED;
 			goto out_unlock;
 		}
+
 		remap_exception(s, e, bio, chunk);
+
+		if (bio_rw(bio) == WRITE)
+			map_context->ptr = track_chunk(s, chunk);
 		goto out_unlock;
 	}