code: func (l *Log) flushAll() {
  	// Flush from fatal down, in case there's trouble flushing.
  	for s := FatalLog; s >= InfoLog; s-- {
  		file := l.file[s]
  		if file != nil {
  			file.Flush() // ignore error
  			file.Sync()  // ignore error
  		}
  	}
  }
docs: // flushAll flushes all the logs and attempts to "sync" their data to disk.
  // l.mu is held.