code: func (d *Daemon) CheckServiceUpdateState(service string) func(*check.C) (interface{}, check.CommentInterface) {
  	return func(c *check.C) (interface{}, check.CommentInterface) {
  		service := d.GetService(c, service)
  		if service.UpdateStatus == nil {
  			return "", nil
  		}
  		return service.UpdateStatus.State, nil
  	}
  }
docs: // CheckServiceUpdateState returns the current update state for the specified service