Allow 'bochs' as a display device option

The 'bochs' display device is a recommended[1] safe option for UEFI
guests.  This is supported in libvirt from version 5.6.0; Nova's current
MIN_LIBVIRT_VERSION (6.0.0) satisfies this requirement.

Partially quoting the "bochs display device" section from a post written
by a QEMU graphics maintainer[1]:

    [...] Main advantage over standard VGA is that this device is alot
    simpler.  The code size and complexity needed to emulate this device
    is an order of magnitude smaller, resulting in a reduced attack
    surface. Another nice feature is that you can place this device in a
    PCI Express slot.

    For UEFI guests it is safe to use the bochs display device instead
    of the standard VGA device. The firmware will setup a linear
    framebuffer as GOP anyway and never use any legacy VGA features.

    For BIOS guests this device might be useable as well, depending on
    whenever they depend on direct VGA hardware access or not. There is
    a vgabios which supports text rendering on a linear framebuffer, so
    software which uses the vgabios services for text output will
    continue to work. Linux bootloaders typically fall into this
    category. The linux text mode console (vgacon) uses direct hardware
    access and does not work. The framebuffer console (fbcon running on
    vesafb or bochs-drm) works.

[1] https://www.kraxel.org/blog/2019/09/display-devices-in-qemu/

Implements: blueprint add-bochs-display-device

Change-Id: Id194028f5d2cbaac1c5e699b71fd9751f87f5da5
Signed-off-by: Kashyap Chamarthy <[email protected]>

Author: kashyapc

doc/notification_samples/common_payloads/ImageMetaPropsPayload.json

@@ -4,5 +4,5 @@
         "hw_architecture": "x86_64"
     },
     "nova_object.name": "ImageMetaPropsPayload",
-    "nova_object.version": "1.7"
+    "nova_object.version": "1.8"
 }

nova/notifications/objects/image.py

@@ -124,7 +124,8 @@ class ImageMetaPropsPayload(base.NotificationPayloadBase):
     # Version 1.5: Added 'hw_tpm_model' and 'hw_tpm_version' fields
     # Version 1.6: Added 'socket' to hw_pci_numa_affinity_policy
     # Version 1.7: Added 'hw_input_bus' field
-    VERSION = '1.7'
+    # Version 1.8: Added 'bochs' as an option to 'hw_video_model'
+    VERSION = '1.8'
 
     SCHEMA = {
         k: ('image_meta_props', k) for k in image_meta.ImageMetaProps.fields}

nova/objects/fields.py

@@ -577,8 +577,9 @@ class VideoModel(BaseNovaEnum):
     VIRTIO = 'virtio'
     GOP = 'gop'
     NONE = 'none'
+    BOCHS = 'bochs'
 
-    ALL = (CIRRUS, QXL, VGA, VMVGA, XEN, VIRTIO, GOP, NONE)
+    ALL = (CIRRUS, QXL, VGA, VMVGA, XEN, VIRTIO, GOP, NONE, BOCHS)
 
 
 class VIFModel(BaseNovaEnum):

nova/objects/image_meta.py

@@ -178,14 +178,22 @@ class ImageMetaProps(base.NovaObject):
     # Version 1.27: Added 'hw_tpm_model' and 'hw_tpm_version' fields
     # Version 1.28: Added 'socket' to 'hw_pci_numa_affinity_policy'
     # Version 1.29: Added 'hw_input_bus' field
+    # Version 1.30: Added 'bochs' as an option to 'hw_video_model'
     # NOTE(efried): When bumping this version, the version of
     # ImageMetaPropsPayload must also be bumped. See its docstring for details.
-    VERSION = '1.29'
+    VERSION = '1.30'
 
     def obj_make_compatible(self, primitive, target_version):
         super(ImageMetaProps, self).obj_make_compatible(primitive,
                                                         target_version)
         target_version = versionutils.convert_version_to_tuple(target_version)
+        if target_version < (1, 30):
+            video = primitive.get('hw_video_model', None)
+            if video == fields.VideoModel.BOCHS:
+                raise exception.ObjectActionError(
+                    action='obj_make_compatible',
+                    reason='hw_video_model=%s not supported in version %s' %
+                           (video, target_version))
         if target_version < (1, 29):
             primitive.pop('hw_input_bus', None)
         if target_version < (1, 28):

nova/tests/functional/notification_sample_tests/test_instance.py

@@ -1236,7 +1236,7 @@ def test_rebuild_server(self):
                     'nova_object.data': {},
                     'nova_object.name': 'ImageMetaPropsPayload',
                     'nova_object.namespace': 'nova',
-                    'nova_object.version': '1.7',
+                    'nova_object.version': '1.8',
                 },
                 'image.size': 58145823,
                 'image.tags': [],
@@ -1332,7 +1332,7 @@ def test_rebuild_server_with_trusted_cert(self):
                     'nova_object.data': {},
                     'nova_object.name': 'ImageMetaPropsPayload',
                     'nova_object.namespace': 'nova',
-                    'nova_object.version': '1.7',
+                    'nova_object.version': '1.8',
                 },
                 'image.size': 58145823,
                 'image.tags': [],

nova/tests/unit/notifications/objects/test_notification.py

@@ -387,7 +387,7 @@ def test_payload_is_not_generated_if_notification_format_is_unversioned(
     # ImageMetaProps, so when you see a fail here for that reason, you must
     # *also* bump the version of ImageMetaPropsPayload. See its docstring for
     # more information.
-    'ImageMetaPropsPayload': '1.7-652a6048036c0d0cb8740ea62521c459',
+    'ImageMetaPropsPayload': '1.8-080bdcba9b96122eab57bf39d47348f7',
     'InstanceActionNotification': '1.0-a73147b93b520ff0061865849d3dfa56',
     'InstanceActionPayload': '1.8-4fa3da9cbf0761f1f700ae578f36dc2f',
     'InstanceActionRebuildNotification':

nova/tests/unit/objects/test_image_meta.py

@@ -390,6 +390,28 @@ def test_obj_make_compatible_video_model(self):
                                    obj.obj_to_primitive, '1.21')
             self.assertIn('hw_video_model', str(ex))
 
+    def test_obj_bochs_model_positive(self):
+        """Test "bochs" support from Nova object version 1.30 onwards
+        """
+        obj = objects.ImageMetaProps(
+            hw_video_model=objects.fields.VideoModel.BOCHS,
+        )
+        primitive = obj.obj_to_primitive('1.30')
+        self.assertEqual(
+            objects.fields.VideoModel.BOCHS,
+            primitive['nova_object.data']['hw_video_model'])
+
+    def test_obj_bochs_model_negative(self):
+        """Make sure an exception is raised for Nova object version <
+        1.30
+        """
+        obj = objects.ImageMetaProps(
+            hw_video_model=objects.fields.VideoModel.BOCHS,
+        )
+        ex = self.assertRaises(exception.ObjectActionError,
+                               obj.obj_to_primitive, '1.29')
+        self.assertIn('hw_video_model=bochs not supported', str(ex))
+
     def test_obj_make_compatible_watchdog_action_not_disabled(self):
         """Tests that we don't pop the hw_watchdog_action if the value is not
         'disabled'.

nova/tests/unit/objects/test_objects.py

@@ -1074,7 +1074,7 @@ def obj_name(cls):
     'HyperVLiveMigrateData': '1.4-e265780e6acfa631476c8170e8d6fce0',
     'IDEDeviceBus': '1.0-29d4c9f27ac44197f01b6ac1b7e16502',
     'ImageMeta': '1.8-642d1b2eb3e880a367f37d72dd76162d',
-    'ImageMetaProps': '1.29-5c02bd7b1e050ef39513d3fca728e543',
+    'ImageMetaProps': '1.30-5bfc3dd01bbfdbb28cb3a096c0b2f383',
     'Instance': '2.7-d187aec68cad2e4d8b8a03a68e4739ce',
     'InstanceAction': '1.2-9a5abc87fdd3af46f45731960651efb5',
     'InstanceActionEvent': '1.4-5b1f361bd81989f8bb2c20bb7e8a4cb4',

releasenotes/notes/releasenotes/notes/bochs-ffaa289da97d08c8.yaml

@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    Add support for the ``bochs`` libvirt video model.  This is a
+    legacy-free video model that is best suited for UEFI guests.  In
+    limited cases (e.g. if the guest does not depend on direct VGA
+    hardware access), it can be useable for BIOS guests as well.