Page request: Add MIG_RP_MSG_REQ_PAGES reverse command

Add MIG_RP_MSG_REQ_PAGES command on Return path for the postcopy
destination to request a page from the source.

Two versions exist:
   MIG_RP_MSG_REQ_PAGES_ID that includes a RAMBlock name and start/len
   MIG_RP_MSG_REQ_PAGES that just has start/len for use with the same
                        RAMBlock as a previous MIG_RP_MSG_REQ_PAGES_ID

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
diff --git a/trace-events b/trace-events
index 401d4c3..2bafa12 100644
--- a/trace-events
+++ b/trace-events
@@ -1451,6 +1451,7 @@
 migrate_fd_cleanup(void) ""
 migrate_fd_error(void) ""
 migrate_fd_cancel(void) ""
+migrate_handle_rp_req_pages(const char *rbname, size_t start, size_t len) "in %s at %zx len %zx"
 migrate_pending(uint64_t size, uint64_t max, uint64_t post, uint64_t nonpost) "pending size %" PRIu64 " max %" PRIu64 " (post=%" PRIu64 " nonpost=%" PRIu64 ")"
 migrate_send_rp_message(int msg_type, uint16_t len) "%d: len %d"
 migration_completion_file_err(void) ""