Libvirt: disallow live-mig for volume-backed with local disk

This patch makes libvirt raise an error if a live migration was
requested without shared storage for a volume-backed instance, if that
instance has any local disks.

The reason is that without shared storage, local disks will be
re-created on the destination node which can result in loss of data.

Change-Id: Ic96dabf6020e957309280862b325792faf44b1f5
Closes-bug: 1236356

nova/tests/virt/libvirt/test_libvirt.py

@@ -2861,6 +2861,8 @@ def test_check_can_live_migrate_source_works_correctly(self):
 
         self.mox.StubOutWithMock(conn, "_check_shared_storage_test_file")
         conn._check_shared_storage_test_file("file").AndReturn(False)
+        self.mox.StubOutWithMock(conn, "get_instance_disk_info")
+        conn.get_instance_disk_info(instance_ref['name']).AndReturn('[]')
 
         self.mox.StubOutWithMock(conn, "_assert_dest_node_has_enough_disk")
         conn._assert_dest_node_has_enough_disk(
@@ -2881,12 +2883,32 @@ def test_check_can_live_migrate_source_vol_backed_works_correctly(self):
         conn = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
         self.mox.StubOutWithMock(conn, "_check_shared_storage_test_file")
         conn._check_shared_storage_test_file("file").AndReturn(False)
+        self.mox.StubOutWithMock(conn, "get_instance_disk_info")
+        conn.get_instance_disk_info(instance_ref['name']).AndReturn('[]')
         self.mox.ReplayAll()
         ret = conn.check_can_live_migrate_source(self.context, instance_ref,
                                                  dest_check_data)
         self.assertTrue(type(ret) == dict)
         self.assertTrue('is_shared_storage' in ret)
 
+    def test_check_can_live_migrate_source_vol_backed_w_disk_raises(self):
+        instance_ref = db.instance_create(self.context, self.test_instance)
+        dest_check_data = {"filename": "file",
+                           "block_migration": False,
+                           "disk_over_commit": False,
+                           "disk_available_mb": 1024,
+                           "is_volume_backed": True}
+        conn = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
+        self.mox.StubOutWithMock(conn, "_check_shared_storage_test_file")
+        conn._check_shared_storage_test_file("file").AndReturn(False)
+        self.mox.StubOutWithMock(conn, "get_instance_disk_info")
+        conn.get_instance_disk_info(instance_ref['name']).AndReturn(
+                '[{"fake_disk_attr": "fake_disk_val"}]')
+        self.mox.ReplayAll()
+        self.assertRaises(exception.InvalidSharedStorage,
+                          conn.check_can_live_migrate_source, self.context,
+                          instance_ref, dest_check_data)
+
     def test_check_can_live_migrate_source_vol_backed_fails(self):
         instance_ref = db.instance_create(self.context, self.test_instance)
         dest_check_data = {"filename": "file",
@@ -2897,6 +2919,9 @@ def test_check_can_live_migrate_source_vol_backed_fails(self):
         conn = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
         self.mox.StubOutWithMock(conn, "_check_shared_storage_test_file")
         conn._check_shared_storage_test_file("file").AndReturn(False)
+        self.mox.StubOutWithMock(conn, "get_instance_disk_info")
+        conn.get_instance_disk_info(instance_ref['name']).AndReturn(
+                '[{"fake_disk_attr": "fake_disk_val"}]')
         self.mox.ReplayAll()
         self.assertRaises(exception.InvalidSharedStorage,
                           conn.check_can_live_migrate_source, self.context,
@@ -2912,6 +2937,8 @@ def test_check_can_live_migrate_dest_fail_shared_storage_with_blockm(self):
 
         self.mox.StubOutWithMock(conn, "_check_shared_storage_test_file")
         conn._check_shared_storage_test_file("file").AndReturn(True)
+        self.mox.StubOutWithMock(conn, "get_instance_disk_info")
+        conn.get_instance_disk_info(instance_ref['name']).AndReturn('[]')
 
         self.mox.ReplayAll()
         self.assertRaises(exception.InvalidLocalStorage,
@@ -2928,6 +2955,8 @@ def test_check_can_live_migrate_no_shared_storage_no_blck_mig_raises(self):
 
         self.mox.StubOutWithMock(conn, "_check_shared_storage_test_file")
         conn._check_shared_storage_test_file("file").AndReturn(False)
+        self.mox.StubOutWithMock(conn, "get_instance_disk_info")
+        conn.get_instance_disk_info(instance_ref['name']).AndReturn('[]')
 
         self.mox.ReplayAll()
         self.assertRaises(exception.InvalidSharedStorage,
@@ -2944,6 +2973,8 @@ def test_check_can_live_migrate_source_with_dest_not_enough_disk(self):
         self.mox.StubOutWithMock(conn, "get_instance_disk_info")
         conn.get_instance_disk_info(instance_ref["name"]).AndReturn(
                                             '[{"virt_disk_size":2}]')
+        conn.get_instance_disk_info(instance_ref["name"]).AndReturn(
+                                            '[{"virt_disk_size":2}]')
 
         dest_check_data = {"filename": "file",
                            "disk_available_mb": 0,

nova/virt/libvirt/driver.py

@@ -3812,6 +3812,8 @@ def check_can_live_migrate_source(self, context, instance,
         filename = dest_check_data["filename"]
         block_migration = dest_check_data["block_migration"]
         is_volume_backed = dest_check_data.get('is_volume_backed', False)
+        has_local_disks = bool(
+                jsonutils.loads(self.get_instance_disk_info(instance['name'])))
 
         shared = self._check_shared_storage_test_file(filename)
 
@@ -3824,7 +3826,7 @@ def check_can_live_migrate_source(self, context, instance,
                                     dest_check_data['disk_available_mb'],
                                     dest_check_data['disk_over_commit'])
 
-        elif not shared and not is_volume_backed:
+        elif not shared and (not is_volume_backed or has_local_disks):
             reason = _("Live migration can not be used "
                        "without shared storage.")
             raise exception.InvalidSharedStorage(reason=reason, path=source)