code: func ValidateLogOpt(cfg map[string]string) error {
  	for key := range cfg {
  		switch key {
  		case "env":
  		case "env-regex":
  		case "labels":
  		case "labels-regex":
  		case "tag":
  		case addressKey:
  		case bufferLimitKey:
  		case retryWaitKey:
  		case maxRetriesKey:
  		case asyncConnectKey:
  		case subSecondPrecisionKey:
  			// Accepted
  		default:
  			return fmt.Errorf("unknown log opt '%s' for fluentd log driver", key)
  		}
  	}
  
  	_, err := parseAddress(cfg[addressKey])
  	return err
  }
docs: // ValidateLogOpt looks for fluentd specific log option fluentd-address.