migration: check magic value for deciding the mapping of channels

Current logic assumes that channel connections on the destination side are
always established in the same order as the source and the first one will
always be the main channel followed by the multifid or post-copy
preemption channel. This may not be always true, as even if a channel has a
connection established on the source side it can be in the pending state on
the destination side and a newer connection can be established first.
Basically causing out of order mapping of channels on the destination side.
Currently, all channels except post-copy preempt send a magic number, this
patch uses that magic number to decide the type of channel. This logic is
applicable only for precopy(multifd) live migration, as mentioned, the
post-copy preempt channel does not send any magic number. Also, tls live
migrations already does tls handshake before creating other channels, so
this issue is not possible with tls, hence this logic is avoided for tls
live migrations. This patch uses read peek to check the magic number of
channels so that current data/control stream management remains
un-effected.

Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Suggested-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: manish.mishra <manish.mishra@nutanix.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

1 files changed, 10 insertions, 9 deletions

diff --git a/migration/multifd.c b/migration/multifd.c
index 000ca4d..eeb4fb8 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -1164,9 +1164,14 @@ int multifd_load_setup(Error **errp)
     uint32_t page_count = MULTIFD_PACKET_SIZE / qemu_target_page_size();
     uint8_t i;
 
-    if (!migrate_use_multifd()) {
+    /*
+     * Return successfully if multiFD recv state is already initialised
+     * or multiFD is not enabled.
+     */
+    if (multifd_recv_state || !migrate_use_multifd()) {
         return 0;
     }
+
     if (!migrate_multi_channels_is_allowed()) {
         error_setg(errp, "multifd is not supported by current protocol");
         return -1;
@@ -1227,11 +1232,9 @@ bool multifd_recv_all_channels_created(void)
 
 /*
  * Try to receive all multifd channels to get ready for the migration.
- * - Return true and do not set @errp when correctly receiving all channels;
- * - Return false and do not set @errp when correctly receiving the current one;
- * - Return false and set @errp when failing to receive the current channel.
+ * Sets @errp when failing to receive the current channel.
  */
-bool multifd_recv_new_channel(QIOChannel *ioc, Error **errp)
+void multifd_recv_new_channel(QIOChannel *ioc, Error **errp)
 {
     MultiFDRecvParams *p;
     Error *local_err = NULL;
@@ -1244,7 +1247,7 @@ bool multifd_recv_new_channel(QIOChannel *ioc, Error **errp)
                                 "failed to receive packet"
                                 " via multifd channel %d: ",
                                 qatomic_read(&multifd_recv_state->count));
-        return false;
+        return;
     }
     trace_multifd_recv_new_channel(id);
 
@@ -1254,7 +1257,7 @@ bool multifd_recv_new_channel(QIOChannel *ioc, Error **errp)
                    id);
         multifd_recv_terminate_threads(local_err);
         error_propagate(errp, local_err);
-        return false;
+        return;
     }
     p->c = ioc;
     object_ref(OBJECT(ioc));
@@ -1265,6 +1268,4 @@ bool multifd_recv_new_channel(QIOChannel *ioc, Error **errp)
     qemu_thread_create(&p->thread, p->name, multifd_recv_thread, p,
                        QEMU_THREAD_JOINABLE);
     qatomic_inc(&multifd_recv_state->count);
-    return qatomic_read(&multifd_recv_state->count) ==
-           migrate_multifd_channels();
 }