RBD: Skip update_features when features = 0

librbd errors when update_features is called w/
features = 0 -- when this situation would occur,
skip calling update_features.

Closes-Bug: #1997980
Change-Id: Iab6a990ce7dee2c13deb4f46aeec0f46ffb7cd62

cinder/tests/unit/volume/drivers/test_rbd.py

@@ -3316,6 +3316,17 @@ class RBDTestCase(test.TestCase):
             {'provider_location':
              "{\"saved_features\":%s}" % image_features}, ret)
 
+    @common_mocks
+    def test_enable_multiattach_no_features(self):
+        image = self.mock_proxy.return_value.__enter__.return_value
+        image.features.return_value = 0
+
+        ret = self.driver._enable_multiattach(self.volume_a)
+
+        image.update_features.assert_not_called()
+
+        self.assertEqual({'provider_location': '{"saved_features":0}'}, ret)
+
     @ddt.data(MULTIATTACH_FULL_FEATURES, MULTIATTACH_REDUCED_FEATURES)
     @common_mocks
     def test_disable_multiattach(self, features):
@@ -3329,6 +3340,18 @@ class RBDTestCase(test.TestCase):
 
         self.assertEqual({'provider_location': None}, ret)
 
+    @common_mocks
+    def test_disable_multiattach_no_features(self):
+        image = self.mock_proxy.return_value.__enter__.return_value
+        self.volume_a.provider_location = '{"saved_features": 0}'
+        image.features.return_value = 0
+
+        ret = self.driver._disable_multiattach(self.volume_a)
+
+        image.update_features.assert_not_called()
+
+        self.assertEqual({'provider_location': None}, ret)
+
 
 class ManagedRBDTestCase(test_driver.BaseDriverTestCase):
     driver_name = "cinder.volume.drivers.rbd.RBDDriver"

cinder/volume/drivers/rbd.py

@@ -965,7 +965,8 @@ class RBDDriver(driver.CloneableImageVD, driver.MigrateVD,
         with RBDVolumeProxy(self, vol_name) as image:
             image_features = image.features()
             change_features = self.MULTIATTACH_EXCLUSIONS & image_features
-            image.update_features(change_features, False)
+            if change_features != 0:
+                image.update_features(change_features, False)
 
         return {'provider_location':
                 self._dumps({'saved_features': image_features})}
@@ -977,7 +978,8 @@ class RBDDriver(driver.CloneableImageVD, driver.MigrateVD,
                 provider_location = json.loads(volume.provider_location)
                 image_features = provider_location['saved_features']
                 change_features = self.MULTIATTACH_EXCLUSIONS & image_features
-                image.update_features(change_features, True)
+                if change_features != 0:
+                    image.update_features(change_features, True)
             except IndexError:
                 msg = "Could not find saved image features."
                 raise RBDDriverException(reason=msg)

releasenotes/notes/rbd-update-features-bugfix-df97b50864ce9712.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    `Bug #1997980 <https://bugs.launchpad.net/cinder/+bug/1997980>`_: RBD:
+    Fixed failure to update rbd image features for multi-attach when
+    features = 0.