Handle NotImplementedError for image cache cloning

The base driver throws NotImplementedError, so if a driver does
not override create_cloned_volume the image caching needs to handle
this and treat it like a general cloning failure to failback to
the default handling.

Change-Id: I06ad0e71e6c502945975629141ec573110482954
Closes-bug: #1642394

cinder/tests/unit/volume/flows/test_create_volume_flow.py

@@ -781,6 +781,7 @@ class CreateVolumeFlowManagerGlanceCinderBackendCase(test.TestCase):
         self.test_create_from_image_volume(location=False)
 
 
+@ddt.ddt
 @mock.patch('cinder.image.image_utils.TemporaryImages.fetch')
 @mock.patch('cinder.volume.flows.manager.create_volume.'
             'CreateVolumeFromSpecTask.'
@@ -907,6 +908,36 @@ class CreateVolumeFlowManagerImageCacheTestCase(test.TestCase):
             image_meta=image_meta
         )
 
+    @ddt.data(
+        NotImplementedError('Driver does not support clone'),
+        exception.CinderException('Error during cloning'))
+    def test_create_from_image_clone_failure(
+            self, effect, mock_get_internal_context,
+            mock_create_from_img_dl, mock_create_from_src,
+            mock_handle_bootable, mock_fetch_img):
+        mock_get_internal_context.return_value = None
+        volume = fake_volume.fake_volume_obj(self.ctxt)
+        mock_create_from_src.side_effect = effect
+
+        image_id = fakes.IMAGE_ID
+        image_meta = {'virtual_size': '1073741824'}
+
+        manager = create_volume_manager.CreateVolumeFromSpecTask(
+            self.mock_volume_manager,
+            self.mock_db,
+            self.mock_driver,
+            image_volume_cache=self.mock_cache
+        )
+
+        model, result = manager._create_from_image_cache(self.ctxt,
+                                                         None,
+                                                         volume,
+                                                         image_id,
+                                                         image_meta)
+
+        self.assertIsNone(model)
+        self.assertFalse(result)
+
     def test_create_from_image_bigger_size(
             self, mock_get_internal_context,
             mock_create_from_img_dl, mock_create_from_src,

cinder/volume/flows/manager/create_volume.py

@@ -685,9 +685,12 @@ class CreateVolumeFromSpecTask(flow_utils.CinderTask):
                     cache_entry['volume_id']
                 )
                 return model_update, True
+        except NotImplementedError:
+            LOG.warning(_LW('Backend does not support creating image-volume '
+                            'clone. Image will be downloaded from Glance.'))
         except exception.CinderException as e:
             LOG.warning(_LW('Failed to create volume from image-volume cache, '
-                            'will fall back to default behavior. Error: '
+                            'image will be downloaded from Glance. Error: '
                             '%(exception)s'), {'exception': e})
         return None, False