Change __find_pending_exception to return error code instead of a null pointer.

It will be needed for the next patch that fixes a race condition in
__find_pending_exception.

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

---
 drivers/md/dm-snap.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

Index: linux-2.6.28-devel/drivers/md/dm-snap.c
===================================================================
--- linux-2.6.28-devel.orig/drivers/md/dm-snap.c	2009-02-20 15:54:51.000000000 +0100
+++ linux-2.6.28-devel/drivers/md/dm-snap.c	2009-02-20 15:54:55.000000000 +0100
@@ -978,7 +978,7 @@ __find_pending_exception(struct dm_snaps
 
 	if (!s->valid) {
 		free_pending_exception(pe);
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 	}
 
 	e = lookup_exception(&s->pending, chunk);
@@ -997,7 +997,7 @@ __find_pending_exception(struct dm_snaps
 
 	if (s->store.prepare_exception(&s->store, &pe->e)) {
 		free_pending_exception(pe);
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 	}
 
 	get_pending_exception(pe);
@@ -1055,8 +1055,8 @@ static int snapshot_map(struct dm_target
 	 */
 	if (bio_rw(bio) == WRITE) {
 		pe = __find_pending_exception(s, bio);
-		if (!pe) {
-			__invalidate_snapshot(s, -ENOMEM);
+		if (IS_ERR(pe)) {
+			__invalidate_snapshot(s, PTR_ERR(pe));
 			r = -EIO;
 			goto out_unlock;
 		}
@@ -1189,8 +1189,8 @@ static int __origin_write(struct list_he
 			goto next_snapshot;
 
 		pe = __find_pending_exception(snap, bio);
-		if (!pe) {
-			__invalidate_snapshot(snap, -ENOMEM);
+		if (IS_ERR(pe)) {
+			__invalidate_snapshot(snap, PTR_ERR(pe));
 			goto next_snapshot;
 		}