code: func indexByPVCKey(obj interface{}) ([]string, error) {
  	pod, ok := obj.(*v1.Pod)
  	if !ok {
  		return []string{}, nil
  	}
  	if len(pod.Spec.NodeName) == 0 || volumeutil.IsPodTerminated(pod, pod.Status) {
  		return []string{}, nil
  	}
  	keys := []string{}
  	for _, podVolume := range pod.Spec.Volumes {
  		if pvcSource := podVolume.VolumeSource.PersistentVolumeClaim; pvcSource != nil {
  			keys = append(keys, fmt.Sprintf("%s/%s", pod.Namespace, pvcSource.ClaimName))
  		}
  	}
  	return keys, nil
  }
docs: // indexByPVCKey returns PVC keys for given pod. Note that the index is only
  // used for attaching, so we are only interested in active pods with nodeName
  // set.