// and when remapping, should be the previous mappedFile.
func openMapped(name string, meta string, existing *mappedFile) (_ *mappedFile, err error) {
	hdr, err := mappedHeader(meta)
	if err != nil {
		return nil, err
	}

	f, err := os.OpenFile(name, os.O_RDWR|os.O_CREATE, 0666)
	if err != nil {
		return nil, err
	}
	// Note: using local variable m here, not return value,