Return path: Send responses from destination to source

Add migrate_send_rp_message to send a message from destination to source along the return path.
  (It uses a mutex to let it be called from multiple threads)
Add migrate_send_rp_shut to send a 'shut' message to indicate
  the destination is finished with the RP.
Add migrate_send_rp_ack to send a 'PONG' message in response to a PING
  Use it in the MSG_RP_PING handler

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

2 files changed, 46 insertions, 1 deletions

diff --git a/migration/migration.c b/migration/migration.c
index bb7dcb9b06..8380e2f2d1 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -97,6 +97,7 @@ MigrationIncomingState *migration_incoming_state_new(QEMUFile* f)
     mis_current = g_new0(MigrationIncomingState, 1);
     mis_current->from_src_file = f;
     QLIST_INIT(&mis_current->loadvm_handlers);
+    qemu_mutex_init(&mis_current->rp_mutex);
 
     return mis_current;
 }
@@ -344,6 +345,50 @@ void process_incoming_migration(QEMUFile *f)
     qemu_coroutine_enter(co, f);
 }
 
+/*
+ * Send a message on the return channel back to the source
+ * of the migration.
+ */
+void migrate_send_rp_message(MigrationIncomingState *mis,
+                             enum mig_rp_message_type message_type,
+                             uint16_t len, void *data)
+{
+    trace_migrate_send_rp_message((int)message_type, len);
+    qemu_mutex_lock(&mis->rp_mutex);
+    qemu_put_be16(mis->to_src_file, (unsigned int)message_type);
+    qemu_put_be16(mis->to_src_file, len);
+    qemu_put_buffer(mis->to_src_file, data, len);
+    qemu_fflush(mis->to_src_file);
+    qemu_mutex_unlock(&mis->rp_mutex);
+}
+
+/*
+ * Send a 'SHUT' message on the return channel with the given value
+ * to indicate that we've finished with the RP.  Non-0 value indicates
+ * error.
+ */
+void migrate_send_rp_shut(MigrationIncomingState *mis,
+                          uint32_t value)
+{
+    uint32_t buf;
+
+    buf = cpu_to_be32(value);
+    migrate_send_rp_message(mis, MIG_RP_MSG_SHUT, sizeof(buf), &buf);
+}
+
+/*
+ * Send a 'PONG' message on the return channel with the given value
+ * (normally in response to a 'PING')
+ */
+void migrate_send_rp_pong(MigrationIncomingState *mis,
+                          uint32_t value)
+{
+    uint32_t buf;
+
+    buf = cpu_to_be32(value);
+    migrate_send_rp_message(mis, MIG_RP_MSG_PONG, sizeof(buf), &buf);
+}
+
 /* amount of nanoseconds we are willing to wait for migration to be down.
  * the choice of nanoseconds is because it is the maximum resolution that
  * get_clock() can achieve. It is an internal measure. All user-visible
diff --git a/migration/savevm.c b/migration/savevm.c
index d47c55b61c..1ffe7b0a57 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1103,7 +1103,7 @@ static int loadvm_process_command(QEMUFile *f)
                          tmp32);
             return -1;
         }
-        /* migrate_send_rp_pong(mis, tmp32); TODO: gets added later */
+        migrate_send_rp_pong(mis, tmp32);
         break;
     }