tests/qtest: switch to using event callbacks for STOP event

Change the migration test to use the new qtest event callback to watch
for the stop event. This ensures that we only watch for the STOP event
on the source QEMU. The previous code would set the single 'got_stop'
flag when either source or dest QEMU got the STOP event.

Reviewed-by: Juan Quintela <quintela@redhat.com>
Acked-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20230601161347.1803440-6-berrange@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

tests/qtest/migration-helpers.c

@@ -23,15 +23,17 @@
  */
 #define MIGRATION_STATUS_WAIT_TIMEOUT 120
 
-bool got_stop;
-
-static void check_stop_event(QTestState *who)
+bool migrate_watch_for_stop(QTestState *who, const char *name,
+                            QDict *event, void *opaque)
 {
-    QDict *event = qtest_qmp_event_ref(who, "STOP");
-    if (event) {
-        got_stop = true;
-        qobject_unref(event);
+    bool *seen = opaque;
+
+    if (g_str_equal(name, "STOP")) {
+        *seen = true;
+        return true;
     }
+
+    return false;
 }
 
 #ifndef _WIN32
@@ -48,7 +50,6 @@ QDict *wait_command_fd(QTestState *who, int fd, const char *command, ...)
     va_end(ap);
 
     resp = qtest_qmp_receive(who);
-    check_stop_event(who);
 
     g_assert(!qdict_haskey(resp, "error"));
     g_assert(qdict_haskey(resp, "return"));
@@ -73,8 +74,6 @@ QDict *wait_command(QTestState *who, const char *command, ...)
     resp = qtest_vqmp(who, command, ap);
     va_end(ap);
 
-    check_stop_event(who);
-
     g_assert(!qdict_haskey(resp, "error"));
     g_assert(qdict_haskey(resp, "return"));
 

tests/qtest/migration-helpers.h

@@ -15,7 +15,8 @@
 
 #include "libqtest.h"
 
-extern bool got_stop;
+bool migrate_watch_for_stop(QTestState *who, const char *name,
+                            QDict *event, void *opaque);
 
 #ifndef _WIN32
 G_GNUC_PRINTF(3, 4)

tests/qtest/migration-test.c

@@ -43,6 +43,7 @@
 unsigned start_address;
 unsigned end_address;
 static bool uffd_feature_thread_id;
+static bool got_stop;
 
 /*
  * Dirtylimit stop working if dirty page rate error
@@ -703,6 +704,9 @@ static int test_migrate_start(QTestState **from, QTestState **to,
                                  ignore_stderr);
     if (!args->only_target) {
         *from = qtest_init(cmd_source);
+        qtest_qmp_set_event_callback(*from,
+                                     migrate_watch_for_stop,
+                                     &got_stop);
     }
 
     cmd_target = g_strdup_printf("-accel kvm%s -accel tcg%s%s "