migration: use switch at the end of migration

It converts the old if clauses into switch, explicitly mentions the
possible migration states.  The old nested "if"s are not clear on what
we do on different states.

Signed-off-by: Peter Xu <[email protected]>
Reviewed-by: Juan Quintela <[email protected]>
Signed-off-by: Juan Quintela <[email protected]>

migration/migration.c

@@ -2341,33 +2341,43 @@ static void *migration_thread(void *opaque)
     cpu_throttle_stop();
 
     qemu_mutex_lock_iothread();
-    if (s->state == MIGRATION_STATUS_COMPLETED) {
+    switch (s->state) {
+    case MIGRATION_STATUS_COMPLETED:
         migration_calculate_complete(s);
         runstate_set(RUN_STATE_POSTMIGRATE);
-    } else {
-        if (s->state == MIGRATION_STATUS_ACTIVE) {
-            /*
-             * We should really assert here, but since it's during
-             * migration, let's try to reduce the usage of assertions.
-             */
-            if (!migrate_colo_enabled()) {
-                error_report("%s: critical error: calling COLO code without "
-                             "COLO enabled", __func__);
-            }
-            migrate_start_colo_process(s);
-            /*
-            * Fixme: we will run VM in COLO no matter its old running state.
-            * After exited COLO, we will keep running.
-            */
-            s->vm_was_running = true;
+        break;
+
+    case MIGRATION_STATUS_ACTIVE:
+        /*
+         * We should really assert here, but since it's during
+         * migration, let's try to reduce the usage of assertions.
+         */
+        if (!migrate_colo_enabled()) {
+            error_report("%s: critical error: calling COLO code without "
+                         "COLO enabled", __func__);
         }
+        migrate_start_colo_process(s);
+        /*
+         * Fixme: we will run VM in COLO no matter its old running state.
+         * After exited COLO, we will keep running.
+         */
+        s->vm_was_running = true;
+        /* Fallthrough */
+    case MIGRATION_STATUS_FAILED:
+    case MIGRATION_STATUS_CANCELLED:
         if (s->vm_was_running) {
             vm_start();
         } else {
             if (runstate_check(RUN_STATE_FINISH_MIGRATE)) {
                 runstate_set(RUN_STATE_POSTMIGRATE);
             }
         }
+        break;
+
+    default:
+        /* Should not reach here, but if so, forgive the VM. */
+        error_report("%s: Unknown ending state %d", __func__, s->state);
+        break;
     }
     qemu_bh_schedule(s->cleanup_bh);
     qemu_mutex_unlock_iothread();