code: def add_udev_trigger(self, trigger_action, subsystem):
          
          if self._py3_wrapper.udev_monitor.subscribe(self, trigger_action, subsystem):
              if trigger_action == "refresh_and_freeze":
                  # FIXME: we may want to disable refresh instead of using cache_timeout
                  self.module_class.cache_timeout = PY3_CACHE_FOREVER
docs: Subscribe to the requested udev subsystem and apply the given action.