code: func (d *Driver) Diff(id, parent string) (io.ReadCloser, error) {
  	if useNaiveDiff(d.home) || !d.isParent(id, parent) {
  		return d.naiveDiff.Diff(id, parent)
  	}
  
  	diffPath := d.getDiffPath(id)
  	logger.Debugf("Tar with options on %s", diffPath)
  	return archive.TarWithOptions(diffPath, &archive.TarOptions{
  		Compression:    archive.Uncompressed,
  		UIDMaps:        d.uidMaps,
  		GIDMaps:        d.gidMaps,
  		WhiteoutFormat: archive.OverlayWhiteoutFormat,
  	})
  }
docs: // Diff produces an archive of the changes between the specified
  // layer and its parent layer which may be "".