devices: video: Use virtio default more often

This is from Gerd's suggestions here:
https://www.kraxel.org/blog/2019/09/display-devices-in-qemu/

When the guest supports it, we should use virtio. qxl is on the way
out, and the benefits are marginal and add a security and maintenance
burden.

While here, check domcaps that qxl or virtio are actually available.
Modern qemu has device modules, so device support may not be installed.

Signed-off-by: Cole Robinson <crobinso@redhat.com>

tests/data/cli/compare/virt-install-graphics-usb-disable.xml

@@ -54,7 +54,7 @@
     </graphics>
     <sound model="ich9"/>
     <video>
-      <model type="qxl"/>
+      <model type="virtio"/>
     </video>
     <memballoon model="virtio"/>
     <rng model="virtio">

tests/data/cli/compare/virt-install-kvm-fedoralatest-url.xml

@@ -49,7 +49,7 @@
       <image compression="off"/>
     </graphics>
     <video>
-      <model type="qxl"/>
+      <model type="virtio"/>
     </video>
     <memballoon model="virtio"/>
     <rng model="virtio">
@@ -106,7 +106,7 @@
       <image compression="off"/>
     </graphics>
     <video>
-      <model type="qxl"/>
+      <model type="virtio"/>
     </video>
     <memballoon model="virtio"/>
     <rng model="virtio">

tests/data/cli/compare/virt-install-singleton-config-2.xml

@@ -217,7 +217,7 @@
     </tpm>
     <graphics type="vnc" port="-1"/>
     <video>
-      <model type="bochs"/>
+      <model type="virtio"/>
     </video>
     <watchdog model="ib700" action="pause"/>
     <memballoon model="virtio" autodeflate="on" freePageReporting="on">
@@ -505,7 +505,7 @@
     </tpm>
     <graphics type="vnc" port="-1"/>
     <video>
-      <model type="bochs"/>
+      <model type="virtio"/>
     </video>
     <watchdog model="ib700" action="pause"/>
     <memballoon model="virtio" autodeflate="on" freePageReporting="on">

tests/data/cli/compare/virt-install-x86_64-graphics.xml

@@ -48,7 +48,7 @@
     <input type="tablet" bus="usb"/>
     <graphics type="vnc" port="-1"/>
     <video>
-      <model type="vga"/>
+      <model type="virtio"/>
     </video>
     <memballoon model="virtio"/>
     <rng model="virtio">

virtinst/devices/video.py

@@ -44,8 +44,13 @@ class DeviceVideo(Device):
             # virtio is implied in this case
             return "virtio"
 
+        if (guest.lookup_domcaps().supports_video_virtio() and
+            guest.osinfo.supports_virtiogpu()):
+            # When the guest supports it, this is the top preference
+            return "virtio"
         if (guest.os.is_x86() and
-            guest.has_spice()):
+            guest.has_spice() and
+            guest.lookup_domcaps().supports_video_qxl()):
             # qxl is only beneficial over regular vga when paired with spice.
             # The device still may not be available though
             return "qxl"

virtinst/domcapabilities.py

@@ -44,6 +44,9 @@ class _CapsBlock(_HasValues):
     def enum_names(self):
         return [e.name for e in self.enums]
 
+    def has_enum(self, name):
+        return name in self.enum_names()
+
     def get_enum(self, name):
         for enum in self.enums:
             if enum.name == name:
@@ -359,6 +362,16 @@ class DomainCapabilities(XMLBuilder):
         models = self.devices.video.get_enum("modelType").get_values()
         return bool("bochs" in models)
 
+    def supports_video_qxl(self):
+        if not self.devices.video.has_enum("modelType"):
+            # qxl long predates modelType in domcaps, so if it is missing,
+            # use spice support as a rough value
+            return self.supports_graphics_spice()
+        return "qxl" in self.devices.video.get_enum("modelType").get_values()
+
+    def supports_video_virtio(self):
+        return "virtio" in self.devices.video.get_enum("modelType").get_values()
+
     def supports_tpm_emulator(self):
         """
         Returns False if either libvirt or qemu do not have support for
@@ -393,7 +406,6 @@ class DomainCapabilities(XMLBuilder):
         sourceTypes = self.memorybacking.get_enum("sourceType").get_values()
         return bool("memfd" in sourceTypes)
 
-
     XML_NAME = "domainCapabilities"
     os = XMLChildProperty(_OS, is_single=True)
     cpu = XMLChildProperty(_CPU, is_single=True)

virtinst/osdict.py

@@ -469,6 +469,11 @@ class _OsVariant(object):
                   "http://pcisig.com/pci/1af4/1044"]
         return bool(self._device_filter(devids=devids, extra_devs=extra_devs))
 
+    def supports_virtiogpu(self, extra_devs=None):
+        # virtio1.0-gpu and virtio1.0
+        devids = ["http://pcisig.com/pci/1af4/1050"]
+        return bool(self._device_filter(devids=devids, extra_devs=extra_devs))
+
     def supports_virtioballoon(self, extra_devs=None):
         # virtio-balloon and virtio1.0-balloon
         devids = ["http://pcisig.com/pci/1af4/1002",