Fix deepcopy usage for BlockDeviceMapping in get_root_info

The method get_root_info sometimes receives a BlockDeviceMapping object,
which lacks a copy method. The previous code assumed root_bdm was always
an instance of DriverBlockDevice, a subclass of dict that supports the copy()
method. However, during testing, it was discovered that root_bdm could also
be a BlockDeviceMapping object, which does not have a copy method.

To address this, the change replaces the copy() call with copy.deepcopy()
according to the suggestion in the comment [1], which works for both
BlockDeviceMapping and DriverBlockDevice instances. The deepcopy method is
supported because oslo.versionedobjects implements the __deepcopy__ method.

This change ensures the function handles both object types correctly,
preventing the AttributeError observed during testing.

[1] https://review.opendev.org/c/openstack/nova/+/909611/4/nova/virt/libvirt/blockinfo.py

Change-Id: I9432718586855ff57e8e6a5cae064e0685dd01e8
(cherry picked from commit 065bf99fc7)
Signed-off-by: Zhang Hua <joshua.zhang@canonical.com>
(cherry picked from commit 9ff4953954)
(cherry picked from commit 608a73ee68)

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

@@ -1289,6 +1289,7 @@ class LibvirtBlockInfoTest(test.NoDBTestCase):
 
     @mock.patch('nova.virt.libvirt.blockinfo.get_info_from_bdm')
     def test_get_root_info_bdm(self, mock_get_info):
+        # call get_root_info() with DriverBlockDevice
         instance = objects.Instance(**self.test_instance)
         image_meta = objects.ImageMeta.from_dict(self.test_image_meta)
         root_bdm = {'mount_device': '/dev/vda',
@@ -1318,6 +1319,49 @@ class LibvirtBlockInfoTest(test.NoDBTestCase):
                                               {}, 'virtio')
         mock_get_info.reset_mock()
 
+    @mock.patch('nova.virt.libvirt.blockinfo.get_info_from_bdm')
+    def test_get_root_info_bdm_with_deepcopy(self, mock_get_info):
+        # call get_root_info() with BlockDeviceMapping
+        instance = objects.Instance(**self.test_instance)
+        image_meta = objects.ImageMeta.from_dict(self.test_image_meta)
+        root_bdm = objects.BlockDeviceMapping(self.context,
+            **fake_block_device.FakeDbBlockDeviceDict(
+                {'id': 3, 'instance_uuid': uuids.instance,
+                 'device_name': '/dev/sda',
+                 'source_type': 'blank',
+                 'destination_type': 'local',
+                 'device_type': 'cdrom',
+                 'disk_bus': 'virtio',
+                 'volume_id': 'fake-volume-id-1',
+                 'boot_index': 0}))
+        # No root_device_name
+        blockinfo.get_root_info(
+            instance, 'kvm', image_meta, root_bdm, 'virtio', 'ide')
+        mock_get_info.assert_called_once_with(
+            instance, 'kvm', image_meta, root_bdm, {}, 'virtio')
+        mock_get_info.reset_mock()
+        # Both device names
+        blockinfo.get_root_info(
+            instance, 'kvm', image_meta, root_bdm, 'virtio', 'scsi',
+            root_device_name='/dev/sda')
+        mock_get_info.assert_called_once_with(
+            instance, 'kvm', image_meta, root_bdm, {}, 'virtio')
+        mock_get_info.reset_mock()
+        # Missing device names
+        original_bdm = copy.deepcopy(root_bdm)
+        root_bdm.device_name = ''
+        blockinfo.get_root_info(
+            instance, 'kvm', image_meta, root_bdm, 'virtio', 'scsi',
+            root_device_name='/dev/sda')
+        mock_get_info.assert_called_with(
+            instance, 'kvm', image_meta, mock.ANY, {}, 'virtio')
+        actual_call = mock_get_info.call_args
+        _, _, _, actual_bdm, _, _ = actual_call[0]
+        self.assertEqual(
+            original_bdm.obj_to_primitive(),
+            actual_bdm.obj_to_primitive()
+        )
+
     def test_get_boot_order_simple(self):
         disk_info = {
             'disk_bus': 'virtio',

nova/virt/libvirt/blockinfo.py

@@ -69,6 +69,7 @@ variables / types used
 
 """
 
+import copy
 import itertools
 import operator
 
@@ -444,12 +445,13 @@ def get_root_info(instance, virt_type, image_meta, root_bdm,
                 'dev': block_device.strip_dev(root_device_name),
                 'boot_index': '1'}
 
+    root_bdm_copy = root_bdm
     if not get_device_name(root_bdm) and root_device_name:
-        root_bdm = root_bdm.copy()
-        root_bdm['device_name'] = root_device_name
+        root_bdm_copy = copy.deepcopy(root_bdm)
+        root_bdm_copy['device_name'] = root_device_name
 
     return get_info_from_bdm(
-        instance, virt_type, image_meta, root_bdm, {}, disk_bus,
+        instance, virt_type, image_meta, root_bdm_copy, {}, disk_bus,
     )