private static void Download_VM(Session session, List <ObjectChange> changes)
        {
            Dictionary <XenRef <VM>, VM> records = VM.get_all_records(session);

            foreach (KeyValuePair <XenRef <VM>, VM> entry in records)
            {
                changes.Add(new ObjectChange(typeof(VM), entry.Key.opaque_ref, entry.Value));
            }
        }