Set sensible defaults for cpu match and feature policy

To enable the CPU XML from the capabilities to be pasted directly
into the guest XML with no editing, pick a sensible default for
match and feature policy. The CPU match will be exact and the
feature policy will be require. This should ensure safety for
migration and give DWIM semantics for users

* src/conf/cpu_conf.c: Default to exact match and require policy
* docs/formatdomain.html.in: Document new defaults

docs/formatdomain.html.in

@@ -276,6 +276,9 @@
           <dd>The guest will not be created unless the host CPU does exactly
             match the specification.</dd>
         </dl>
+
+	<span class="since">Since 0.8.5</span> the <code>match</code>
+	attribute can be omitted and will default to <code>exact</code>.
       </dd>
 
       <dt><code>model</code></dt>
@@ -322,6 +325,9 @@
           <dd>Guest creation will fail if the feature is supported by host
             CPU.</dd>
         </dl>
+
+	<span class="since">Since 0.8.5</span> the <code>policy</code>
+	attribute can be omitted and will default to <code>require</code>.
       </dd>
     </dl>
 

src/conf/cpu_conf.c

@@ -147,12 +147,10 @@ virCPUDefParseXML(const xmlNodePtr node,
         char *match = virXMLPropString(node, "match");
 
         if (!match) {
-            if (virXPathBoolean("boolean(./model)", ctxt)) {
-                virCPUReportError(VIR_ERR_INTERNAL_ERROR,
-                        "%s", _("Missing match attribute for CPU specification"));
-                goto error;
-            }
-            def->match = -1;
+            if (virXPathBoolean("boolean(./model)", ctxt))
+                def->match = VIR_CPU_MATCH_EXACT;
+            else
+                def->match = -1;
         } else {
             def->match = virCPUMatchTypeFromString(match);
             VIR_FREE(match);
@@ -251,7 +249,10 @@ virCPUDefParseXML(const xmlNodePtr node,
             char *strpolicy;
 
             strpolicy = virXMLPropString(nodes[i], "policy");
-            policy = virCPUFeaturePolicyTypeFromString(strpolicy);
+            if (strpolicy == NULL)
+                policy = VIR_CPU_FEATURE_REQUIRE;
+            else
+                policy = virCPUFeaturePolicyTypeFromString(strpolicy);
             VIR_FREE(strpolicy);
 
             if (policy < 0) {