// an error.
func readDirFn(dirPath string, filter func(name string, typ os.FileMode) error) error {
	// Ensure we don't pick up files as directories.
	globAll := filepath.Clean(dirPath) + `\*`
	globAllP, err := syscall.UTF16PtrFromString(globAll)
	if err != nil {
		return errInvalidArgument
	}
	data := &syscall.Win32finddata{}
	handle, err := syscall.FindFirstFile(globAllP, data)
	if err != nil {