code: func (fo *FileWriterOutput) Output(ll LogLevel, message []byte) {
  	if fo.WriterOutput == nil {
  		fh, err := fo.openFile()
  		if err != nil {
  			fo.fallbackLog("Could not open %#v: %s", fo.path, err)
  			return
  		}
  		fo.WriterOutput = NewWriterOutput(fh)
  	}
  	fo.WriterOutput.Output(ll, message)
  }
docs: // Output a log line by writing it to the file. If the file has been
  // released, try to open it again. If that fails, cry for a little
  // while, then throw away the message and carry on.