code: func (md *metricsDu) runDiskUsage(metrics *Metrics) error {
  	used, err := fs.DiskUsage(md.path)
  	if err != nil {
  		return err
  	}
  	metrics.Used = used
  	return nil
  }
docs: // runDiskUsage gets disk usage of md.path and writes the results to metrics.Used