int getentropy(void *buf, size_t len)
{
	int ret, pre_errno = errno;

	if (len > 256) {
		errno = EIO;
		return -1;
	}
	while ((ret = __syscall(SYS_getrandom, buf, len, 0)) == -EINTR);
	if (ret != len)
		return -1;
	errno = pre_errno;
	return 0;
}