Fix possibility of duplicate MAC assignment

plugins/modules/virt.py

@@ -620,24 +620,36 @@ def handle_define(module, v):
                 # if fuzzy_match is False, we only match on aliases
                 fuzzy_match = flag == 'ADD_MAC_ADDRESSES_FUZZY'
 
+                # this set of nodes gets manipulated (elements removed), so be
+                # careful if using using `existing_xml` later
                 existing_devices = existing_xml.find('./devices')
-                for interface in incoming_xml.findall('./devices/interface'):
-                    mac = interface.find('mac')
-                    if mac is None:
-                        # incoming interface is missing MAC address, so we will add it
-                        # from the existing domain if it has a matching interface
-                        matched_interface = _match_interface(interface,
-                                                             existing_devices.findall('./interface'),
-                                                             fuzzy_match)
-
-                        if matched_interface is not None:
-                            # Remove matched_interface from possible candidates to prevent duplicate
-                            # MAC address assignments (which is possible when fuzzy_match = True)
-                            existing_devices.remove(matched_interface)
-
-                            etree.SubElement(interface, 'mac', {
-                                'address': matched_interface.find('./mac').get('address'),
-                            })
+
+                # iterate user-defined <mac> elements
+                for mac in incoming_xml.findall('./devices/interface/mac'):
+                    # remove from existing_devices any interfaces containing a
+                    # MAC contained in incoming_xml, so we don't later match
+                    # against one of these interfaces if a user provides MAC
+                    # addresses for some but not all interfaces
+                    for existing_interface in \
+                            existing_devices.xpath('./interface[mac[@address="%s"]]' % mac.get('address')):
+                        existing_devices.remove(existing_interface)
+
+                # iterate user-defined interfaces _without_ a mac element
+                for interface in incoming_xml.xpath('./devices/interface[not(mac)]'):
+                    # incoming interface is missing MAC address, so we will add it
+                    # from the existing domain if it has a matching interface
+                    matched_interface = _match_interface(interface,
+                                                         existing_devices.findall('./interface'),
+                                                         fuzzy_match)
+
+                    if matched_interface is not None:
+                        # Remove matched_interface from possible candidates to prevent duplicate
+                        # MAC address assignments (which is possible when fuzzy_match = True)
+                        existing_devices.remove(matched_interface)
+
+                        etree.SubElement(interface, 'mac', {
+                            'address': matched_interface.find('./mac').get('address'),
+                        })
 
     try:
         domain_xml = etree.tostring(incoming_xml).decode()