snapshot: create bdrv_all_create_snapshot helper

to create snapshot for all loaded block drivers.

The patch also ensures proper locking.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
Tested-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
diff --git a/migration/savevm.c b/migration/savevm.c
index 63c07e1..80107e3 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1996,19 +1996,10 @@
         goto the_end;
     }
 
-    /* create the snapshots */
-
-    bs1 = NULL;
-    while ((bs1 = bdrv_next(bs1))) {
-        if (bdrv_can_snapshot(bs1)) {
-            /* Write VM state size only to the image that contains the state */
-            sn->vm_state_size = (bs == bs1 ? vm_state_size : 0);
-            ret = bdrv_snapshot_create(bs1, sn);
-            if (ret < 0) {
-                monitor_printf(mon, "Error while creating snapshot on '%s'\n",
-                               bdrv_get_device_name(bs1));
-            }
-        }
+    ret = bdrv_all_create_snapshot(sn, bs, vm_state_size, &bs);
+    if (ret < 0) {
+        monitor_printf(mon, "Error while creating snapshot on '%s'\n",
+                       bdrv_get_device_name(bs));
     }
 
  the_end: