Move file system freeze after end of mirroring

The file system before the start of mirroring generates kernel task
blocked for more than 120 seconds. The file system freeze after the
start of mirroring and just before stopping the mirror between the
original disk and copy of disk reduce the time of the freeze.

Related-Bug: #1939116
Change-Id: I067382ec676b65f8698772a262c5e4cea7a1216d

Author: plibeau

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

@@ -19715,9 +19715,10 @@ def _test_live_snapshot(
                 mock.patch('nova.virt.libvirt.utils.get_disk_backing_file'),
                 mock.patch('nova.virt.libvirt.utils.create_cow_image'),
                 mock.patch('nova.virt.libvirt.utils.extract_snapshot'),
-                mock.patch.object(drvr, '_set_quiesced')
+                mock.patch.object(drvr, '_set_quiesced'),
+                mock.patch.object(drvr, '_can_quiesce')
         ) as (mock_define, mock_size, mock_backing, mock_create_cow,
-              mock_snapshot, mock_quiesce):
+              mock_snapshot, mock_quiesce, mock_can_quiesce):
 
             xmldoc = "<domain/>"
             srcfile = "/first/path"
@@ -19732,7 +19733,7 @@ def _test_live_snapshot(
             guest = libvirt_guest.Guest(mock_dom)
 
             if not can_quiesce:
-                mock_quiesce.side_effect = (
+                mock_can_quiesce.side_effect = (
                     exception.InstanceQuiesceNotSupported(
                         instance_id=self.test_instance['id'], reason='test'))
 
@@ -19763,6 +19764,7 @@ def _test_live_snapshot(
             mock_define.assert_called_once_with(xmldoc)
             mock_quiesce.assert_any_call(mock.ANY, self.test_instance,
                                          mock.ANY, True)
+
             if can_quiesce:
                 mock_quiesce.assert_any_call(mock.ANY, self.test_instance,
                                              mock.ANY, False)

nova/virt/libvirt/driver.py

@@ -3164,14 +3164,15 @@ def _live_snapshot(self, context, instance, guest, disk_path, out_path,
         libvirt_utils.create_cow_image(src_back_path, disk_delta,
                                        src_disk_size)
 
-        quiesced = False
         try:
-            self._set_quiesced(context, instance, image_meta, True)
-            quiesced = True
+            self._can_quiesce(instance, image_meta)
         except exception.NovaException as err:
-            if self._requires_quiesce(image_meta):
+            if image_meta.properties.get('os_require_quiesce', False):
+                LOG.error('Quiescing instance failed but image property '
+                          '"os_require_quiesce" is set: %(reason)s.',
+                          {'reason': err}, instance=instance)
                 raise
-            LOG.info('Skipping quiescing instance: %(reason)s.',
+            LOG.info('Quiescing instance not available: %(reason)s.',
                      {'reason': err}, instance=instance)
 
         try:
@@ -3192,12 +3193,24 @@ def _live_snapshot(self, context, instance, guest, disk_path, out_path,
             while not dev.is_job_complete():
                 time.sleep(0.5)
 
+        finally:
+            quiesced = False
+            try:
+                # NOTE: The freeze FS is applied after the end of
+                # the mirroring of the disk to minimize the time of
+                # the freeze. The mirror between both disks is finished,
+                # sync continuously, and stopped after abort_job().
+                self.quiesce(context, instance, image_meta)
+                quiesced = True
+            except exception.NovaException as err:
+                LOG.info('Skipping quiescing instance: %(reason)s.',
+                         {'reason': err}, instance=instance)
+
             dev.abort_job()
             nova.privsep.path.chown(disk_delta, uid=os.getuid())
-        finally:
             self._host.write_instance_config(xml)
             if quiesced:
-                self._set_quiesced(context, instance, image_meta, False)
+                self.unquiesce(context, instance, image_meta)
 
         # Convert the delta (CoW) image with a backing file to a flat
         # image with no backing file.