code: func (l *LogFile) searchFirstAvPath() error {
  	for {
  		if fsutil.Exists(l.Path()) {
  			stats, err := os.Stat(l.Path())
  			if err != nil {
  				return err
  			}
  			if stats.Size() >= l.size {
  				l.idx++
  			} else {
  				return nil
  			}
  		} else {
  			return nil
  		}
  	}
  }
docs: // helper function to retrieve the first available file for writing