code: func pwlToMap(pwl []string) map[string]struct{} {
  	if len(pwl) == 0 {
  		return nil
  	}
  	m := make(map[string]struct{}, len(pwl))
  	for _, name := range pwl {
  		relpath := filepath.Join("rootfs", name)
  		m[relpath] = struct{}{}
  	}
  	return m
  }
docs: // pwlToMap converts a pathWhiteList slice to a map for faster search
  // It will also prepend "rootfs/" to the provided paths and they will be
  // relative to "/" so they can be easily compared with the tar.Header.Name
  // If pwl length is 0, a nil map is returned