Configuration element for describing video drivers.

The configuration is needed to allow the users to select
a non default video driver.

Partially implements blueprint libvirt-video-driver-selection
Change-Id: Ic6b3e44cfb7e22e0a215f7b159963df35ee1ebac

nova/tests/virt/libvirt/test_libvirt_config.py

@@ -1542,3 +1542,28 @@ class LibvirtConfigNodeDevicePciSubFunctionCap(LibvirtConfigBaseTest):
         self.assertEqual([("0000", "0x0a", "0x1", "0x1"),
                           ("0001", "0x0a", "0x02", "0x03"), ],
                          fun_capability.device_addrs)
+
+
+class LibvirtConfigGuestVideoTest(LibvirtConfigBaseTest):
+
+    def test_config_video_driver(self):
+        obj = config.LibvirtConfigGuestVideo()
+        obj.type = 'qxl'
+
+        xml = obj.to_xml()
+        self.assertXmlEqual(xml, """
+                <video>
+                    <model type='qxl'/>
+                </video>""")
+
+    def test_config_video_driver_vram_heads(self):
+        obj = config.LibvirtConfigGuestVideo()
+        obj.type = 'qxl'
+        obj.vram = '9216'
+        obj.heads = '1'
+
+        xml = obj.to_xml()
+        self.assertXmlEqual(xml, """
+                <video>
+                    <model type='qxl' vram='9216' heads='1'/>
+                </video>""")

nova/virt/libvirt/config.py

@@ -906,6 +906,33 @@ class LibvirtConfigGuestGraphics(LibvirtConfigGuestDevice):
         return dev
 
 
+class LibvirtConfigGuestVideo(LibvirtConfigGuestDevice):
+
+    def __init__(self, **kwargs):
+        super(LibvirtConfigGuestVideo, self).__init__(root_name="video",
+                                                      **kwargs)
+
+        self.type = 'cirrus'
+        self.vram = None
+        self.heads = None
+
+    def format_dom(self):
+        dev = super(LibvirtConfigGuestVideo, self).format_dom()
+
+        model = etree.Element("model")
+        model.set("type", self.type)
+
+        if self.vram:
+            model.set("vram", str(self.vram))
+
+        if self.heads:
+            model.set("heads", str(self.heads))
+
+        dev.append(model)
+
+        return dev
+
+
 class LibvirtConfigGuestHostdev(LibvirtConfigGuestDevice):
     def __init__(self, **kwargs):
         super(LibvirtConfigGuestHostdev, self).\