func (r *Reader) openLookup(name string) *fileListEntry {
	if name == "." {
		return dotFile
	}

	dir, elem, _ := split(name)
	files := r.fileList
	i := sort.Search(len(files), func(i int) bool {
		idir, ielem, _ := split(files[i].name)
		return idir > dir || idir == dir && ielem >= elem
	})
	if i < len(files) {
		fname := files[i].name