code: func FindOldReplicaSets(deployment *apps.Deployment, rsList []*apps.ReplicaSet) ([]*apps.ReplicaSet, []*apps.ReplicaSet) {
  	var requiredRSs []*apps.ReplicaSet
  	var allRSs []*apps.ReplicaSet
  	newRS := FindNewReplicaSet(deployment, rsList)
  	for _, rs := range rsList {
  		// Filter out new replica set
  		if newRS != nil && rs.UID == newRS.UID {
  			continue
  		}
  		allRSs = append(allRSs, rs)
  		if *(rs.Spec.Replicas) != 0 {
  			requiredRSs = append(requiredRSs, rs)
  		}
  	}
  	return requiredRSs, allRSs
  }
docs: // FindOldReplicaSets returns the old replica sets targeted by the given Deployment, with the given slice of RSes.
  // Note that the first set of old replica sets doesn't include the ones with no pods, and the second set of old replica sets include all old replica sets.