code: func getSourceMount(source string) (string, string, error) {
  	// Ensure any symlinks are resolved.
  	sourcePath, err := filepath.EvalSymlinks(source)
  	if err != nil {
  		return "", "", err
  	}
  
  	mi, err := mount.GetMounts(mount.ParentsFilter(sourcePath))
  	if err != nil {
  		return "", "", err
  	}
  	if len(mi) < 1 {
  		return "", "", fmt.Errorf("Can't find mount point of %s", source)
  	}
  
  	// find the longest mount point
  	var idx, maxlen int
  	for i := range mi {
  		if len(mi[i].Mountpoint) > maxlen {
  			maxlen = len(mi[i].Mountpoint)
  			idx = i
  		}
  	}
  	return mi[idx].Mountpoint, mi[idx].Optional, nil
  }
docs: // Get the source mount point of directory passed in as argument. Also return
  // optional fields.