nodedev_xml: extend MdevXML with attr elements

Add support for attribute elements of the mediated device
capability xml, e.g.:

```
 <attr name='assign_adapter' value='3'/>
 <attr name='assign_domain' value='43'/>
```

Signed-off-by: Sebastian Mitterle <[email protected]>

virttest/libvirt_xml/nodedev_xml.py

@@ -152,16 +152,66 @@ class MdevXML(CAPXML):
     """
     class for capability whose type is mdev
     """
-    __slots__ = ('type_id', 'uuid')
+    __slots__ = ('type_id', 'uuid', 'attrs')
 
     def __init__(self, virsh_instance=base.virsh):
         accessors.XMLAttribute('type_id', self, parent_xpath='/',
                                tag_name='type', attribute='id')
         accessors.XMLElementText('uuid', self, parent_xpath='/',
                                  tag_name='uuid')
+        accessors.XMLElementList(property_name='attrs',
+                                 libvirtxml=self,
+                                 parent_xpath='/',
+                                 marshal_from=self.marshal_from_attrs,
+                                 marshal_to=self.marshal_to_attrs,
+                                 has_subclass=True)
         super(MdevXML, self).__init__(virsh_instance=virsh_instance)
         self.xml = (' <capability type=\'mdev\'></capability>')
 
+    @staticmethod
+    def marshal_from_attrs(item, index, libvirtxml):
+        """
+        Convert an AttrXML object to attr tag and xml element.
+        """
+        if isinstance(item, AttrXML):
+            return 'attr', item
+        elif isinstance(item, dict):
+            attr = AttrXML()
+            attr.setup_attrs(**item)
+        else:
+            raise xcepts.LibvirtXMLError("Expected a list of capability attr "
+                                         " not a %s" % item)
+
+    @staticmethod
+    def marshal_to_attrs(tag, new_treefile, index, libvirtxml):
+        """
+        Convert an attr tag xml element to an object of AttrXML.
+        """
+        if tag != 'attr':
+            return None    # Don't convert this item
+        newone = AttrXML(virsh_instance=libvirtxml.virsh)
+        newone.xmltreefile = new_treefile
+        return newone
+
+
+class AttrXML(base.LibvirtXMLBase):
+    """
+    Attribute elements of MdevXML
+    """
+    __slots__ = ('attr', 'name', 'value')
+
+    def __init__(self, virsh_instance=base.virsh):
+        accessors.XMLElementDict(property_name='attr',
+                             libvirtxml=self,
+                             parent_xpath='/',
+                             tag_name='attr')
+        accessors.XMLAttribute('name', self, parent_xpath='/',
+                               tag_name='attr', attribute='name')
+        accessors.XMLAttribute('value', self, parent_xpath='/',
+                               tag_name='attr', attribute='value')
+        super(AttrXML, self).__init__(virsh_instance=virsh_instance)
+        self.xml = '<attr/>'
+
 
 class StorageXML(CAPXML):