code: func WriteRootfsDir(tarWriter *tar.Writer) error {
  	hdr := getGenericTarHeader()
  	hdr.Name = "rootfs"
  	hdr.Mode = 0755
  	hdr.Size = int64(0)
  	hdr.Typeflag = tar.TypeDir
  
  	return tarWriter.WriteHeader(hdr)
  }
docs: // WriteRootfsDir writes a "rootfs" dir entry on a tar.Writer.