conf: Add fields for recording actually-selected virtio video device

QEMU's commandline generator picks for virtio video between various
actual device models not only based on the XML definition but also
capabilities present. Since none of the devices is actually ABI
compatible we need to record the actually selected device in the XML.

Introduce 'device' attribute:

      <video>
        <model type='virtio' heads='1' primary='yes' device='virtio-gpu'/>

which will record the actually selected model so that we can preserve
ABI across restarts on deployment changes but more importantly across
migrations where the deployment differs.

The code specifically avoids an ABI stability check for the new field
because there are already possibly broken configurations that the users
may want to fix by picking the proper model which could be forbidden.

Users are instructed to not set the field in the XML.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

docs/formatdomain.rst

@@ -7365,6 +7365,14 @@ A video device.
    guest. The ``edid`` attribute is only valid for model types ``vga``, ``bochs``,
    and ``virtio``.
 
+   :since:`Since 12.5.0` the ``virtio`` video model has an additional attribute
+   ``device``, which records the specific virtio device model which was picked
+   for the configuration, to preserve guest ABI and migration compatibility.
+   Users do not need to set this attribute as aprropriate value is picked and
+   filled in automatically. Accepted values are ``virtio-vga``, ``virtio-gpu``,
+   ``virtio-vga-gl``, and ``virtio-gpu-gl``, but not all combinations of config
+   and this field make sense.
+
 ``acceleration``
    Configure if video acceleration should be enabled.
 

src/conf/domain_conf.c

@@ -910,6 +910,17 @@ VIR_ENUM_IMPL(virDomainVideoVGAConf,
               "off",
 );
 
+VIR_ENUM_IMPL(virDomainVideoVirtioDevice,
+              VIR_DOMAIN_VIDEO_VIRTIO_DEVICE_LAST,
+              "",
+              "virtio-vga",
+              "virtio-gpu",
+              "virtio-vga-gl",
+              "virtio-gpu-gl",
+              "vhost-user-vga",
+              "vhost-user-gpu",
+);
+
 VIR_ENUM_IMPL(virDomainInput,
               VIR_DOMAIN_INPUT_TYPE_LAST,
               "mouse",
@@ -13816,6 +13827,14 @@ virDomainVideoModelDefParseXML(virDomainVideoDef *def,
                               VIR_DOMAIN_VIDEO_TYPE_DEFAULT) < 0)
         return -1;
 
+    if (def->type == VIR_DOMAIN_VIDEO_TYPE_VIRTIO) {
+        if (virXMLPropEnumDefault(node, "device",
+                                  virDomainVideoVirtioDeviceTypeFromString,
+                                  VIR_XML_PROP_NONZERO, &def->virtiodevice,
+                                  VIR_DOMAIN_VIDEO_VIRTIO_DEVICE_DEFAULT) < 0)
+            return -1;
+    }
+
     if (virXMLPropUInt(node, "ram", 10, VIR_XML_PROP_NONE, &def->ram) < 0)
         return -1;
 
@@ -21694,6 +21713,18 @@ virDomainVideoDefCheckABIStability(virDomainVideoDef *src,
         return false;
     }
 
+    /* While 'src->virtiodevice' vs 'dst->virtiodevice' match is considered
+     * guest ABI (both the device looks different to the guest OS and qemu
+     * refuses to migrate into wrong device) we deliberately omit the check
+     * here due to historical reasons.
+     *
+     * The actual values were not recorded in the XML after picking a device
+     * based on capabilities and thus, if the host configuration changes
+     * different defaults can be picked. Users might want to fix their
+     * saveimage or migration by specifying the proper model which will differ
+     * from the one that will be auto-picked via post-parse callback when the
+     * XML is loaded for the first time */
+
     if (!virDomainVirtioOptionsCheckABIStability(src->virtio, dst->virtio))
         return false;
 
@@ -27395,6 +27426,10 @@ virDomainVideoDefFormat(virBuffer *buf,
     if (def->edid != VIR_TRISTATE_SWITCH_ABSENT)
         virBufferAsprintf(&modelAttrBuf, " edid='%s'", virTristateSwitchTypeToString(def->edid));
 
+    if (def->virtiodevice != VIR_DOMAIN_VIDEO_VIRTIO_DEVICE_DEFAULT)
+        virBufferAsprintf(&modelAttrBuf, " device='%s'",
+                          virDomainVideoVirtioDeviceTypeToString(def->virtiodevice));
+
     virDomainVideoAccelDefFormat(&modelChildBuf, def->accel);
     virDomainVideoResolutionDefFormat(&modelChildBuf, def->res);
 

src/conf/domain_conf.h

@@ -1885,6 +1885,20 @@ typedef enum {
 
 VIR_ENUM_DECL(virDomainVideoVGAConf);
 
+typedef enum {
+    VIR_DOMAIN_VIDEO_VIRTIO_DEVICE_DEFAULT = 0,
+    VIR_DOMAIN_VIDEO_VIRTIO_DEVICE_VGA,
+    VIR_DOMAIN_VIDEO_VIRTIO_DEVICE_GPU,
+    VIR_DOMAIN_VIDEO_VIRTIO_DEVICE_VGA_GL,
+    VIR_DOMAIN_VIDEO_VIRTIO_DEVICE_GPU_GL,
+    VIR_DOMAIN_VIDEO_VIRTIO_DEVICE_VHOST_USER_VGA,
+    VIR_DOMAIN_VIDEO_VIRTIO_DEVICE_VHOST_USER_GPU,
+
+    VIR_DOMAIN_VIDEO_VIRTIO_DEVICE_LAST
+} virDomainVideoVirtioDevice;
+
+VIR_ENUM_DECL(virDomainVideoVirtioDevice);
+
 struct _virDomainVideoAccelDef {
     virTristateBool accel2d;
     virTristateBool accel3d;
@@ -1915,6 +1929,7 @@ struct _virDomainVideoDef {
     virDomainVideoResolutionDef *res;
     virTristateSwitch blob;
     virDomainVideoDriverDef *driver;
+    virDomainVideoVirtioDevice virtiodevice; /* virtio device frontend */
     virDomainDeviceInfo info;
     virDomainVirtioOptions *virtio;
     virDomainVideoBackendType backend;

src/conf/schemas/domaincommon.rng

@@ -4874,7 +4874,6 @@
                   <value>vmvga</value>
                   <value>xen</value>
                   <value>vbox</value>
-                  <value>virtio</value>
                   <value>gop</value>
                   <value>none</value>
                   <value>bochs</value>
@@ -4901,6 +4900,23 @@
                   </attribute>
                 </optional>
               </group>
+              <group>
+                <attribute name="type">
+                  <value>virtio</value>
+                </attribute>
+                <optional>
+                  <attribute name="device">
+                    <choice>
+                      <value>virtio-vga</value>
+                      <value>virtio-vga-gl</value>
+                      <value>virtio-gpu</value>
+                      <value>virtio-gpu-gl</value>
+                      <value>vhost-user-vga</value>
+                      <value>vhost-user-gpu</value>
+                    </choice>
+                  </attribute>
+                </optional>
+              </group>
             </choice>
             <optional>
               <attribute name="vram">

src/libvirt_private.syms

@@ -731,6 +731,7 @@ virDomainVideoTypeFromString;
 virDomainVideoTypeToString;
 virDomainVideoVGAConfTypeFromString;
 virDomainVideoVGAConfTypeToString;
+virDomainVideoVirtioDeviceTypeToString;
 virDomainVirtTypeFromString;
 virDomainVirtTypeToString;
 virDomainVsockDefEquals;