_, err = io.Copy(df, sf)
	df.Close()
	if err != nil {
		mayberemovefile(dst)
		return fmt.Errorf("copying %s to %s: %v", src, dst, err)
	}
	return nil
}

// mayberemovefile removes a file only if it is a regular file
// When running as a user with sufficient privileges, we may delete
// even device files, for example, which is not intended.
func mayberemovefile(s string) {