code: func filterSandbox(p *pb.PodSandbox, filter *pb.PodSandboxFilter) bool {
  	if filter != nil {
  		if filter.State != nil {
  			if p.State != filter.State.State {
  				return false
  			}
  		}
  		if filter.LabelSelector != nil {
  			sel := fields.SelectorFromSet(filter.LabelSelector)
  			if !sel.Matches(fields.Set(p.Labels)) {
  				return false
  			}
  		}
  	}
  	return true
  }
docs: // filterSandbox returns whether passed container matches filtering criteria