A method to hand over an exception store to another snapshot.

You copy the exception store structure to another place, change "snap" pointer
and call handover to fix internal pointers.

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

---
 drivers/md/dm-exception-store.c |   13 +++++++++++++
 drivers/md/dm-snap.h            |    5 +++++
 2 files changed, 18 insertions(+)

Index: linux-2.6.28-rc3-devel/drivers/md/dm-exception-store.c
===================================================================
--- linux-2.6.28-rc3-devel.orig/drivers/md/dm-exception-store.c	2008-11-05 09:01:10.000000000 +0100
+++ linux-2.6.28-rc3-devel/drivers/md/dm-exception-store.c	2008-11-05 09:01:16.000000000 +0100
@@ -655,6 +655,13 @@ static void persistent_drop(struct excep
 		DMWARN("write header failed");
 }
 
+static void persistent_handover(struct exception_store *store)
+{
+	struct pstore *ps = get_info(store);
+
+	ps->snap = store->snap;
+}
+
 int dm_create_persistent(struct exception_store *store)
 {
 	struct pstore *ps;
@@ -688,6 +695,7 @@ int dm_create_persistent(struct exceptio
 	store->commit_exception = persistent_commit;
 	store->drop_snapshot = persistent_drop;
 	store->fraction_full = persistent_fraction_full;
+	store->handover = persistent_handover;
 	store->context = ps;
 
 	return 0;
@@ -741,6 +749,10 @@ static void transient_fraction_full(stru
 	*denominator = get_dev_size(store->snap->cow->bdev);
 }
 
+static void transient_handover(struct exception_store *store)
+{
+}
+
 int dm_create_transient(struct exception_store *store)
 {
 	struct transient_c *tc;
@@ -751,6 +763,7 @@ int dm_create_transient(struct exception
 	store->commit_exception = transient_commit;
 	store->drop_snapshot = NULL;
 	store->fraction_full = transient_fraction_full;
+	store->handover = transient_handover;
 
 	tc = kmalloc(sizeof(struct transient_c), GFP_KERNEL);
 	if (!tc)
Index: linux-2.6.28-rc3-devel/drivers/md/dm-snap.h
===================================================================
--- linux-2.6.28-rc3-devel.orig/drivers/md/dm-snap.h	2008-11-05 09:01:15.000000000 +0100
+++ linux-2.6.28-rc3-devel/drivers/md/dm-snap.h	2008-11-05 09:01:16.000000000 +0100
@@ -137,6 +137,11 @@ struct exception_store {
 			       sector_t *numerator,
 			       sector_t *denominator);
 
+	/*
+	 * Must be called when you move store to different snapshot.
+	 */
+	void (*handover) (struct exception_store *store);
+
 	struct dm_snapshot *snap;
 	void *context;
 };