libvirt: Allow use of live snapshots with RBD snapshot/clone

The recently merged functionality for making use of RBD snapshot/clone
when available is very valuable for the Ceph/RBD users out there.
The new method also makes it possible to do live instance snapshots
with Ceph/RBD.  However, the current code explicitly forbids it.

This patch allows the use of live instance snapshots when a RBD
snapshot/clone is performed directly, and reverts back to cold
instance snapshot when the old method is used.

Co-Authored-By: Nicolas Simonds <nic@metacloud.com>
Change-Id: Ic3a3c73898aa868d6c510639ab12d2401dcb5001
Closes-Bug: #1539179
(cherry picked from commit 2318323549)

nova/tests/unit/virt/libvirt/test_driver.py

@@ -16932,6 +16932,62 @@ class LibvirtSnapshotTests(_BaseSnapshotTests):
         rbd.remove_snap.assert_called_with('c', 'd', ignore_errors=True,
                                            pool='b', force=True)
 
+    @mock.patch.object(imagebackend.Image, 'direct_snapshot')
+    @mock.patch.object(imagebackend.Image, 'resolve_driver_format')
+    @mock.patch.object(host.Host, 'has_min_version', return_value=True)
+    @mock.patch.object(host.Host, 'get_guest')
+    def test_raw_with_rbd_clone_is_live_snapshot(self,
+                                                 mock_get_guest,
+                                                 mock_version,
+                                                 mock_resolve,
+                                                 mock_snapshot):
+        self.flags(disable_libvirt_livesnapshot=False, group='workarounds')
+        self.flags(images_type='rbd', group='libvirt')
+        mock_guest = mock.Mock(spec=libvirt_guest.Guest)
+        mock_guest._domain = mock.Mock()
+        mock_get_guest.return_value = mock_guest
+        driver = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
+        recv_meta = self._create_image()
+        with mock.patch.object(driver, "suspend") as mock_suspend:
+            driver.snapshot(self.context, self.instance_ref, recv_meta['id'],
+                            self.mock_update_task_state)
+            self.assertFalse(mock_suspend.called)
+
+    @mock.patch.object(libvirt_driver.imagebackend.images, 'convert_image',
+                       side_effect=_fake_convert_image)
+    @mock.patch.object(fake_libvirt_utils, 'find_disk')
+    @mock.patch.object(imagebackend.Image, 'resolve_driver_format')
+    @mock.patch.object(host.Host, 'has_min_version', return_value=True)
+    @mock.patch.object(host.Host, 'get_guest')
+    @mock.patch.object(rbd_utils, 'RBDDriver')
+    @mock.patch.object(rbd_utils, 'rbd')
+    def test_raw_with_rbd_clone_failure_does_cold_snapshot(self,
+                                                           mock_rbd,
+                                                           mock_driver,
+                                                           mock_get_guest,
+                                                           mock_version,
+                                                           mock_resolve,
+                                                           mock_find_disk,
+                                                           mock_convert):
+        self.flags(disable_libvirt_livesnapshot=False, group='workarounds')
+        self.flags(images_type='rbd', group='libvirt')
+        rbd = mock_driver.return_value
+        rbd.parent_info = mock.Mock(side_effect=exception.ImageUnacceptable(
+            image_id='fake_id', reason='rbd testing'))
+        mock_find_disk.return_value = ('rbd://some/fake/rbd/image', 'raw')
+        mock_guest = mock.Mock(spec=libvirt_guest.Guest)
+        mock_guest.get_power_state.return_value = power_state.RUNNING
+        mock_guest._domain = mock.Mock()
+        mock_get_guest.return_value = mock_guest
+        driver = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
+        recv_meta = self._create_image()
+
+        with mock.patch.object(fake_libvirt_utils, 'disk_type', new='rbd'):
+            with mock.patch.object(driver, "suspend") as mock_suspend:
+                driver.snapshot(self.context, self.instance_ref,
+                                recv_meta['id'], self.mock_update_task_state)
+                self.assertTrue(mock_suspend.called)
+
 
 class LXCSnapshotTests(LibvirtSnapshotTests):
     """Repeat all of the Libvirt snapshot tests, but with LXC enabled"""
@@ -16939,6 +16995,9 @@ class LXCSnapshotTests(LibvirtSnapshotTests):
         super(LXCSnapshotTests, self).setUp()
         self.flags(virt_type='lxc', group='libvirt')
 
+    def test_raw_with_rbd_clone_failure_does_cold_snapshot(self):
+        self.skipTest("managedSave is not supported with LXC")
+
 
 class LVMSnapshotTests(_BaseSnapshotTests):
     @mock.patch.object(fake_libvirt_utils, 'disk_type', new='lvm')

nova/virt/libvirt/driver.py

@@ -1638,7 +1638,7 @@ class LibvirtDriver(driver.ComputeDriver):
         if (self._host.has_min_version(MIN_LIBVIRT_LIVESNAPSHOT_VERSION,
                                        MIN_QEMU_LIVESNAPSHOT_VERSION,
                                        host.HV_DRIVER_QEMU)
-             and source_type not in ('lvm', 'rbd')
+             and source_type not in ('lvm')
              and not CONF.ephemeral_storage_encryption.enabled
              and not CONF.workarounds.disable_libvirt_livesnapshot):
             live_snapshot = True
@@ -1703,6 +1703,15 @@ class LibvirtDriver(driver.ComputeDriver):
             update_task_state(task_state=task_states.IMAGE_PENDING_UPLOAD,
                               expected_state=task_states.IMAGE_UPLOADING)
 
+            # TODO(nic): possibly abstract this out to the snapshot_backend
+            if source_type == 'rbd' and live_snapshot:
+                # Standard snapshot uses qemu-img convert from RBD which is
+                # not safe to run with live_snapshot.
+                live_snapshot = False
+                # Suspend the guest, so this is no longer a live snapshot
+                self._prepare_domain_for_snapshot(context, live_snapshot,
+                                                  state, instance)
+
             snapshot_directory = CONF.libvirt.snapshots_directory
             fileutils.ensure_tree(snapshot_directory)
             with utils.tempdir(dir=snapshot_directory) as tmpdir: