code: func (mc CommunicatingPlugin) Prebind(pc *framework.PluginContext, pod *v1.Pod, nodeName string) *framework.Status {
  	if pod == nil {
  		return framework.NewStatus(framework.Error, "pod cannot be nil")
  	}
  	pc.RLock()
  	defer pc.RUnlock()
  	if v, e := pc.Read(framework.ContextKey(pod.Name)); e == nil && v == "never bind" {
  		return framework.NewStatus(framework.Unschedulable, "pod is not permitted")
  	}
  	return nil
  }
docs: // Prebind is the functions invoked by the framework at "prebind" extension point.