static void extract_cpu(ProcessHandle sandbox) {
	int fd = process_rootfs_open(sandbox, RUN_CPU_CFG);
	if (fd < 0)
		return; // not configured

	FILE *fp = fdopen(fd, "r");
	if (!fp)
		errExit("fdopen");

	unsigned tmp;
	if (fscanf(fp, "%x", &tmp) == 1)
		cfg.cpus = (uint32_t) tmp;
	fclose(fp);
}
static void extract_cpu(ProcessHandle sandbox) {
	int fd = process_rootfs_open(sandbox, RUN_CPU_CFG);
	if (fd < 0)
		return;  

	FILE *fp = fdopen(fd, "r");
	if (!fp)
		errExit("fdopen");

	unsigned tmp;
	if (fscanf(fp, "%x", &tmp) == 1)
		cfg.cpus = (uint32_t) tmp;
	fclose(fp);
}