vgpu: add enabled white list

Some pGPUs (e.g. NVIDIA GRID K1) support different vGPU types. User can
use `enabled_vgpu_types` to specify the enabled vGPU types that a guest
could consume from the host.

NOTE(sbauza) :
Since that configuration is shared between all virt drivers, we need to
provide a single change that will just add that conf opt and then use
it in separate series as a common base. That implies that configuration
option is useless until we merge the code that reads it, but that's a
necessary compromise for making sure we can move both Xen and libvirt
efforts in parallel.

Partially Implements: blueprint add-support-for-vgpu
Co-Authored-By: Sylvain Bauza <sbauza@redhat.com>

Change-Id: I56f9597e968eac041832cdb90fe52cf0d3b4a4ef

nova/conf/__init__.py

@@ -32,6 +32,7 @@ from nova.conf import console
 from nova.conf import consoleauth
 from nova.conf import crypto
 from nova.conf import database
+from nova.conf import devices
 from nova.conf import ephemeral_storage
 from nova.conf import flavors
 from nova.conf import glance
@@ -84,6 +85,7 @@ console.register_opts(CONF)
 consoleauth.register_opts(CONF)
 crypto.register_opts(CONF)
 database.register_opts(CONF)
+devices.register_opts(CONF)
 ephemeral_storage.register_opts(CONF)
 flavors.register_opts(CONF)
 glance.register_opts(CONF)

nova/conf/devices.py

@@ -0,0 +1,40 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from oslo_config import cfg
+
+devices_group = cfg.OptGroup(
+    name='devices',
+    title='physical or virtual device options')
+
+vgpu_opts = [
+    cfg.ListOpt('enabled_vgpu_types',
+        default=[],
+        help="""
+A list of the vGPU types enabled in the compute node.
+
+Some pGPUs (e.g. NVIDIA GRID K1) support different vGPU types. User can use
+this option to specify a list of enabled vGPU types that may be assigned to a
+guest instance. An example is as the following:
+    [devices]
+    enabled_vgpu_types = ['GRID K100', 'Intel GVT-g', 'MxGPU.2', 'nvidia-11']
+""")
+]
+
+
+def register_opts(conf):
+    conf.register_group(devices_group)
+    conf.register_opts(vgpu_opts, group=devices_group)
+
+
+def list_opts():
+    return {devices_group: vgpu_opts}