Store pointer to the snapshot device to tracked chunk.
This is needed for the following patch that reroutes origin to the merging
snapshot --- requests directed to the origin are tracked at the snapshot and
it is not possible to identify the snapshot in origin's end_io (finding the
snapshot needs to take a semaphore).

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

---
 drivers/md/dm-snap.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

Index: linux-2.6.26-rc5-devel/drivers/md/dm-snap.c
===================================================================
--- linux-2.6.26-rc5-devel.orig/drivers/md/dm-snap.c	2008-06-17 01:20:04.000000000 +0200
+++ linux-2.6.26-rc5-devel/drivers/md/dm-snap.c	2008-06-17 01:20:09.000000000 +0200
@@ -81,6 +81,7 @@
 struct dm_snap_tracked_chunk {
 	struct hlist_node node;
 	chunk_t chunk;
+	struct dm_snapshot *snap;
 };
 
 static struct kmem_cache *tracked_chunk_cache;
@@ -93,6 +94,7 @@
 	unsigned long flags;
 
 	c->chunk = chunk;
+	c->snap = s;
 
 	spin_lock_irqsave(&s->tracked_chunk_lock, flags);
 	hlist_add_head(&c->node,
@@ -102,9 +104,10 @@
 	return c;
 }
 
-static void stop_tracking_chunk(struct dm_snapshot *s, struct dm_snap_tracked_chunk *c)
+static void stop_tracking_chunk(struct dm_snap_tracked_chunk *c)
 {
 	unsigned long flags;
+	struct dm_snapshot *s = c->snap;
 
 	spin_lock_irqsave(&s->tracked_chunk_lock, flags);
 	hlist_del(&c->node);
@@ -1381,11 +1384,10 @@
 static int snapshot_end_io(struct dm_target *ti, struct bio *bio,
 			   int error, union map_info *map_context)
 {
-	struct dm_snapshot *s = ti->private;
 	struct dm_snap_tracked_chunk *c = map_context->ptr;
 
 	if (c)
-		stop_tracking_chunk(s, c);
+		stop_tracking_chunk(c);
 
 	return 0;
 }