code: func (dsc *DaemonSetsController) getDaemonSetsForHistory(history *apps.ControllerRevision) []*apps.DaemonSet {
  	daemonSets, err := dsc.dsLister.GetHistoryDaemonSets(history)
  	if err != nil || len(daemonSets) == 0 {
  		return nil
  	}
  	if len(daemonSets) > 1 {
  		// ControllerRef will ensure we don't do anything crazy, but more than one
  		// item in this list nevertheless constitutes user error.
  		klog.V(4).Infof("User error! more than one DaemonSets is selecting ControllerRevision %s/%s with labels: %#v",
  			history.Namespace, history.Name, history.Labels)
  	}
  	return daemonSets
  }
docs: // getDaemonSetsForHistory returns a list of DaemonSets that potentially
  // match a ControllerRevision.