[libvirt] Live migration fails when config_drive_format=iso9660

This patch enables block live migration with read-only config drive.
Basically it copies config drive to destination host prior to migration
start, so that QEMU will not try to write to read-only device and
therefore it will not raise an exception.

Co-Authored-By: Bartosz Fic <bartosz.fic@intel.com>
Co-Authored-By: Michael Still <mikal@stillhq.com>

Change-Id: I9ddaef658e3d9a77e4982275d7df9e56b0a5459f
Closes-Bug: #1246201
(cherry picked from commit bc4b9980fa74e15e98aed5633c61480c751767b5)

2 files changed, 47 insertions, 30 deletions

diff --git a/nova/tests/unit/virt/libvirt/test_driver.py b/nova/tests/unit/virt/libvirt/test_driver.py
index 28950c67f4..421e99e62b 100644
--- a/nova/tests/unit/virt/libvirt/test_driver.py
+++ b/nova/tests/unit/virt/libvirt/test_driver.py
@@ -81,7 +81,6 @@ from nova.tests.unit.virt.libvirt import fakelibvirt
 from nova import utils
 from nova import version
 from nova.virt import block_device as driver_block_device
-from nova.virt import configdrive
 from nova.virt.disk import api as disk
 from nova.virt import driver
 from nova.virt import fake
@@ -8357,27 +8356,48 @@ class LibvirtConnTestCase(test.NoDBTestCase):
                 pre_migration_result=True)['pre_live_migration_result'],
             target_ret)
 
-    def test_pre_live_migration_block_with_config_drive_mocked(self):
-        # Creating testdata
+    @mock.patch.object(os, 'mkdir')
+    @mock.patch('nova.virt.libvirt.utils.get_instance_path_at_destination')
+    @mock.patch('nova.virt.libvirt.driver.remotefs.'
+                'RemoteFilesystem.copy_file')
+    @mock.patch('nova.virt.driver.block_device_info_get_mapping')
+    @mock.patch('nova.virt.configdrive.required_by', return_value=True)
+    def test_pre_live_migration_block_with_config_drive_success(
+            self, mock_required_by, block_device_info_get_mapping,
+            mock_copy_file, mock_get_instance_path, mock_mkdir):
+        self.flags(config_drive_format='iso9660')
         vol = {'block_device_mapping': [
                   {'connection_info': 'dummy', 'mount_device': '/dev/sda'},
                   {'connection_info': 'dummy', 'mount_device': '/dev/sdb'}]}
+        fake_instance_path = os.path.join(cfg.CONF.instances_path,
+                                          '/fake_instance_uuid')
+        mock_get_instance_path.return_value = fake_instance_path
+
         drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
 
-        def fake_true(*args, **kwargs):
-            return True
+        instance = objects.Instance(**self.test_instance)
+        migrate_data = objects.LibvirtLiveMigrateData()
+        migrate_data.is_shared_instance_path = False
+        migrate_data.is_shared_block_storage = False
+        migrate_data.block_migration = True
+        migrate_data.instance_relative_path = 'foo'
+        src = "%s:%s/disk.config" % (instance.host, fake_instance_path)
 
-        self.stubs.Set(configdrive, 'required_by', fake_true)
+        result = drvr.pre_live_migration(
+            self.context, instance, vol, [], None, migrate_data)
 
-        instance = objects.Instance(**self.test_instance)
-        c = context.get_admin_context()
+        block_device_info_get_mapping.assert_called_once_with(
+            {'block_device_mapping': [
+                {'connection_info': 'dummy', 'mount_device': '/dev/sda'},
+                {'connection_info': 'dummy', 'mount_device': '/dev/sdb'}
+            ]}
+        )
+        mock_copy_file.assert_called_once_with(src, fake_instance_path)
 
-        self.assertRaises(exception.NoLiveMigrationForConfigDriveInLibVirt,
-                          drvr.pre_live_migration, c, instance, vol, None,
-                          None, {'is_shared_instance_path': False,
-                                 'is_shared_block_storage': False,
-                                 'block_migration': False,
-                                 'instance_relative_path': 'foo'})
+        migrate_data.graphics_listen_addrs_vnc = '127.0.0.1'
+        migrate_data.graphics_listen_addrs_spice = '127.0.0.1'
+        migrate_data.serial_listen_addr = '127.0.0.1'
+        self.assertEqual(migrate_data, result)
 
     @mock.patch('nova.virt.driver.block_device_info_get_mapping',
                 return_value=())
diff --git a/nova/virt/libvirt/driver.py b/nova/virt/libvirt/driver.py
index bac17cfbec..8e2ea91673 100644
--- a/nova/virt/libvirt/driver.py
+++ b/nova/virt/libvirt/driver.py
@@ -6614,22 +6614,6 @@ class LibvirtDriver(driver.ComputeDriver):
             is_shared_instance_path = migrate_data.is_shared_instance_path
             is_block_migration = migrate_data.block_migration
 
-        if configdrive.required_by(instance):
-                # NOTE(sileht): configdrive is stored into the block storage
-                # kvm is a block device, live migration will work
-                # NOTE(sileht): the configdrive is stored into a shared path
-                # kvm don't need to migrate it, live migration will work
-                # NOTE(dims): Using config drive with iso format does not work
-                # because of a bug in libvirt with read only devices. However
-                # one can use vfat as config_drive_format which works fine.
-                # Please see bug/1246201 for details on the libvirt bug.
-            if (is_shared_block_storage or
-                is_shared_instance_path or
-                CONF.config_drive_format == 'vfat'):
-                pass
-            else:
-                raise exception.NoLiveMigrationForConfigDriveInLibVirt()
-
         if not is_shared_instance_path:
             instance_dir = libvirt_utils.get_instance_path_at_destination(
                             instance, migrate_data)
@@ -6666,6 +6650,19 @@ class LibvirtDriver(driver.ComputeDriver):
                 self._create_images_and_backing(
                     context, instance, instance_dir, disk_info,
                     fallback_from_host=instance.host)
+                if (configdrive.required_by(instance) and
+                        CONF.config_drive_format == 'iso9660'):
+                    # NOTE(pkoniszewski): Due to a bug in libvirt iso config
+                    # drive needs to be copied to destination prior to
+                    # migration when instance path is not shared and block
+                    # storage is not shared. Files that are already present
+                    # on destination are excluded from a list of files that
+                    # need to be copied to destination. If we don't do that
+                    # live migration will fail on copying iso config drive to
+                    # destination and writing to read-only device.
+                    # Please see bug/1246201 for more details.
+                    src = "%s:%s/disk.config" % (instance.host, instance_dir)
+                    self._remotefs.copy_file(src, instance_dir)
 
             if not is_block_migration:
                 # NOTE(angdraug): when block storage is shared between source