Remove unnecessary retrieval of Migration object

This has already been retrieved with an elevated context. There's no
need to retrieve it again.

Change-Id: I5fa7786523bc1b6001247c6daaee7e984e9a3b65
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

nova/compute/manager.py

@@ -4171,29 +4171,19 @@ class ComputeManager(manager.Manager):
         source host.
         """
         @utils.synchronized(instance.uuid)
-        def do_confirm_resize(context, instance, migration_id):
-            # NOTE(wangpan): Get the migration status from db, if it has been
-            #                confirmed, we do nothing and return here
-            LOG.debug("Going to confirm migration %s", migration_id,
+        def do_confirm_resize(context, instance, migration):
+            LOG.debug("Going to confirm migration %s", migration.id,
                       instance=instance)
-            try:
-                # TODO(russellb) Why are we sending the migration object just
-                # to turn around and look it up from the db again?
-                migration = objects.Migration.get_by_id(
-                                    context.elevated(), migration_id)
-            except exception.MigrationNotFound:
-                LOG.error("Migration %s is not found during confirmation",
-                          migration_id, instance=instance)
-                return
 
             if migration.status == 'confirmed':
                 LOG.info("Migration %s is already confirmed",
-                         migration_id, instance=instance)
+                         migration.id, instance=instance)
                 return
-            elif migration.status not in ('finished', 'confirming'):
+
+            if migration.status not in ('finished', 'confirming'):
                 LOG.warning("Unexpected confirmation status '%(status)s' "
                             "of migration %(id)s, exit confirmation process",
-                            {"status": migration.status, "id": migration_id},
+                            {"status": migration.status, "id": migration.id},
                             instance=instance)
                 return
 
@@ -4237,7 +4227,7 @@ class ComputeManager(manager.Manager):
                     self._delete_scheduler_instance_info(
                         context, instance.uuid)
 
-        do_confirm_resize(context, instance, migration.id)
+        do_confirm_resize(context, instance, migration)
 
     def _get_updated_nw_info_with_pci_mapping(self, nw_info, pci_mapping):
         # NOTE(adrianc): This method returns a copy of nw_info if modifications

nova/tests/unit/compute/test_compute.py

@@ -8110,21 +8110,6 @@ class ComputeTestCase(BaseTestCase,
                 event.EVENT_LIFECYCLE_STOPPED)
         self.compute.handle_events(event_instance)
 
-    @mock.patch.object(objects.Migration, 'get_by_id')
-    def test_confirm_resize_roll_back_quota_migration_not_found(self,
-            mock_get_by_id):
-        instance = self._create_fake_instance_obj()
-
-        migration = objects.Migration()
-        migration.instance_uuid = instance.uuid
-        migration.status = 'finished'
-        migration.id = 0
-
-        mock_get_by_id.side_effect = exception.MigrationNotFound(
-                migration_id=0)
-        self.compute.confirm_resize(self.context, instance=instance,
-                                    migration=migration)
-
     @mock.patch.object(instance_obj.Instance, 'get_by_uuid')
     def test_confirm_resize_roll_back_quota_instance_not_found(self,
             mock_get_by_id):

nova/tests/unit/compute/test_compute_mgr.py

@@ -8615,20 +8615,18 @@ class ComputeManagerMigrationTestCase(test.NoDBTestCase,
 
     @mock.patch('nova.objects.MigrationContext.get_pci_mapping_for_migration')
     @mock.patch('nova.compute.utils.add_instance_fault_from_exc')
-    @mock.patch('nova.objects.Migration.get_by_id')
     @mock.patch('nova.objects.Instance.get_by_uuid')
     @mock.patch('nova.compute.utils.notify_about_instance_usage')
     @mock.patch('nova.compute.utils.notify_about_instance_action')
     @mock.patch('nova.objects.Instance.save')
     def test_confirm_resize_driver_confirm_migration_fails(
             self, instance_save, notify_action, notify_usage,
-            instance_get_by_uuid, migration_get_by_id, add_fault, get_mapping):
+            instance_get_by_uuid, add_fault, get_mapping):
         """Tests the scenario that driver.confirm_migration raises some error
         to make sure the error is properly handled, like the instance and
         migration status is set to 'error'.
         """
         self.migration.status = 'confirming'
-        migration_get_by_id.return_value = self.migration
         instance_get_by_uuid.return_value = self.instance
         self.instance.migration_context = objects.MigrationContext()
 
@@ -8667,7 +8665,6 @@ class ComputeManagerMigrationTestCase(test.NoDBTestCase,
         confirm_migration.assert_called_once()
         network_api.setup_networks_on_host.assert_called_once()
         instance_get_by_uuid.assert_called_once()
-        migration_get_by_id.assert_called_once()
 
     def test_confirm_resize_calls_virt_driver_with_old_pci(self):
         @mock.patch.object(self.migration, 'save')