domcaps: Add CPU usable flag

In case a hypervisor is able to tell us a list of supported CPU models
and whether each CPU models can be used on the current host, we can
propagate this to domain capabilities. This is a better alternative
to calling virConnectCompareCPU for each supported CPU model.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>

docs/formatdomaincaps.html.in

@@ -156,9 +156,9 @@
     <mode name='host-passthrough' supported='yes'/>
     <mode name='host-model' supported='yes'/>
     <mode name='custom' supported='yes'>
-      <model>Broadwell</model>
-      <model>Broadwell-noTSX</model>
-      <model>Haswell</model>
+      <model usable='no'>Broadwell</model>
+      <model usable='yes'>Broadwell-noTSX</model>
+      <model usable='no'>Haswell</model>
       ...
     </mode>
   </cpu>
@@ -183,6 +183,10 @@
       <dd>
         The <code>mode</code> element contains a list of supported CPU
         models, each described by a dedicated <code>model</code> element.
+        The <code>usable</code> attribute specifies whether the model can
+        be used on the host. A special value <code>unknown</code> indicates
+        libvirt does not have enough information to provide the usability
+        data.
       </dd>
     </dl>
 

docs/schemas/domaincaps.rng

@@ -105,6 +105,13 @@
       <ref name='supported'/>
       <zeroOrMore>
         <element name='model'>
+          <attribute name='usable'>
+            <choice>
+              <value>yes</value>
+              <value>no</value>
+              <value>unknown</value>
+            </choice>
+          </attribute>
           <text/>
         </element>
       </zeroOrMore>