code: func (c *Cluster) UpdateAttachment(target, containerID string, config *network.NetworkingConfig) error {
  	c.mu.Lock()
  	attacher, ok := c.attachers[attacherKey(target, containerID)]
  	if !ok || attacher == nil {
  		c.mu.Unlock()
  		return fmt.Errorf("could not find attacher for container %s to network %s", containerID, target)
  	}
  	if attacher.inProgress {
  		logrus.Debugf("Discarding redundant notice of resource allocation on network %s for task id %s", target, attacher.taskID)
  		c.mu.Unlock()
  		return nil
  	}
  	attacher.inProgress = true
  	c.mu.Unlock()
  
  	attacher.attachWaitCh <- config
  
  	return nil
  }
docs: // UpdateAttachment signals the attachment config to the attachment
  // waiter who is trying to start or attach the container to the
  // network.