tests: introduce ability to provide hooks for migration precopy test

There are alot of different scenarios to test with migration due to the
wide number of parameters and capabilities available. To enable sharing
of the basic precopy test scenario, we need to be able to set arbitrary
parameters and capabilities before the migration is initiated, but don't
want to have all this logic in the common helper function. Solve this
by defining two hooks that can be provided by the test case, one before
migration starts and one after migration finishes.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20220310171821.3724080-10-berrange@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

tests/qtest/migration-test.c

@@ -778,6 +778,30 @@ static void test_baddest(void)
     test_migrate_end(from, to, false);
 }
 
+/*
+ * A hook that runs after the src and dst QEMUs have been
+ * created, but before the migration is started. This can
+ * be used to set migration parameters and capabilities.
+ *
+ * Returns: NULL, or a pointer to opaque state to be
+ *          later passed to the TestMigrateFinishHook
+ */
+typedef void * (*TestMigrateStartHook)(QTestState *from,
+                                       QTestState *to);
+
+/*
+ * A hook that runs after the migration has finished,
+ * regardless of whether it succeeded or failed, but
+ * before QEMU has terminated (unless it self-terminated
+ * due to migration error)
+ *
+ * @opaque is a pointer to state previously returned
+ * by the TestMigrateStartHook if any, or NULL.
+ */
+typedef void (*TestMigrateFinishHook)(QTestState *from,
+                                      QTestState *to,
+                                      void *opaque);
+
 typedef struct {
     /* Optional: fine tune start parameters */
     MigrateStart start;
@@ -792,11 +816,17 @@ typedef struct {
      * This allows for dynamically picking a free TCP port.
      */
     const char *connect_uri;
+
+    /* Optional: callback to run at start to set migration parameters */
+    TestMigrateStartHook start_hook;
+    /* Optional: callback to run at finish to cleanup */
+    TestMigrateFinishHook finish_hook;
 } MigrateCommon;
 
 static void test_precopy_common(MigrateCommon *args)
 {
     QTestState *from, *to;
+    void *data_hook = NULL;
 
     if (test_migrate_start(&from, &to, args->listen_uri, &args->start)) {
         return;
@@ -812,6 +842,10 @@ static void test_precopy_common(MigrateCommon *args)
     /* 1GB/s */
     migrate_set_parameter_int(from, "max-bandwidth", 1000000000);
 
+    if (args->start_hook) {
+        data_hook = args->start_hook(from, to);
+    }
+
     /* Wait for the first serial output from the source */
     wait_for_serial("src_serial");
 
@@ -837,6 +871,10 @@ static void test_precopy_common(MigrateCommon *args)
     wait_for_serial("dest_serial");
     wait_for_migration_complete(from);
 
+    if (args->finish_hook) {
+        args->finish_hook(from, to, data_hook);
+    }
+
     test_migrate_end(from, to, true);
 }