nodedev: make iommuGroup optional for mdevs

When parsing a nodedev xml file, the iommuGroup element should be
optional. This element should be read-only and is determined by the
device driver. While this is a change to existing behavior, it doesn't
break backwards-compatibility because it makes the parser less strict.
Signed-off-by: NJonathon Jongsma <jjongsma@redhat.com>
Reviewed-by: NErik Skultety <eskultet@redhat.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>

docs/formatnode.html.in

@@ -390,8 +390,9 @@
               <dt><code>iommuGroup</code></dt>
               <dd>
                 This element supports a single attribute <code>number</code>
-                which holds the IOMMU group number the mediated device belongs
-                  to.
+                which holds the IOMMU group number to which the mediated device
+                belongs. This is a read-only field that is reported by the
+                device driver.
               </dd>
             </dl>
           </dd>

docs/schemas/nodedev.rng

@@ -629,11 +629,13 @@
         <data type='string'/>
       </attribute>
     </element>
-    <element name='iommuGroup'>
-      <attribute name='number'>
-        <ref name='unsignedInt'/>
-      </attribute>
-    </element>
+    <optional>
+      <element name='iommuGroup'>
+        <attribute name='number'>
+          <ref name='unsignedInt'/>
+        </attribute>
+      </element>
+    </optional>
   </define>
 
   <define name='capccwdev'>

src/conf/node_device_conf.c

@@ -1775,13 +1775,15 @@ virNodeDevCapMdevParseXML(xmlXPathContextPtr ctxt,
         goto out;
     }
 
-    if (virNodeDevCapsDefParseULong("number(./iommuGroup[1]/@number)", ctxt,
-                                    &mdev->iommuGroupNumber, def,
-                                    _("missing iommuGroup number attribute for "
-                                      "'%s'"),
-                                    _("invalid iommuGroup number attribute for "
-                                      "'%s'")) < 0)
+    /* 'iommuGroup' is optional, only report an error if the supplied value is
+     * invalid (-2), not if it's missing (-1) */
+    if (virXPathUInt("number(./iommuGroup[1]/@number)",
+                     ctxt, &mdev->iommuGroupNumber) < -1) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("invalid iommuGroup number attribute for '%s'"),
+                       def->name);
         goto out;
+    }
 
     ret = 0;
  out: