/*
 * A program that randomly runs between user and kernel space.
 * It writes to /dev/delay to do a busy loop in kernel.
 *
 * Copyright (C) 2001 MontaVista Software Inc.
 * Author: Jun Sun, jsun@mvista.com or jsun@junsun.net
 *
 * This program is free software; you can redistribute  it and/or modify it
 * under  the terms of  the GNU General  Public License as published by the
 * Free Software Foundation;  either version 2 of the  License, or (at your
 * option) any later version.
 *
 */

#include <stdio.h>
#include <stdlib.h>

#include <fcntl.h>
#include <unistd.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>


/*
 * CONFIGURE
 */
#define		PER_KERNEL		100	/* 20% in kernel */
#define		MAX_SYSCALL		1024	/* max syscall duration */

main()
{
	unsigned long period;
	int fd = open("/dev/delay", O_WRONLY);

	if (fd < 0) {
		printf("failed to open /dev/delay\n");
		printf("Did you mknod /dev/delay and inmod delay.o?\n");
		exit(-1);
	}

	{
		/* set random seed */
		struct timeval curr;
		gettimeofday(&curr, 0);
		srand(curr.tv_usec);
	}

	printf("do_delay setup : %d%% in userland, %d%% in kernel\n",
			100 - PER_KERNEL, PER_KERNEL);
	printf("\tsyscall duration is randomly distributed between 0 to %d usecs.\n",
			MAX_SYSCALL);
	printf("Now loop forever ...\n");

	for(;;) {
		int delay;
		int ret;
		delay= rand() % MAX_SYSCALL;
		ret = write(fd, &delay, sizeof(delay));
		if (ret != sizeof(delay)) printf("write failed. %d\n", ret);
		delay= (rand() % MAX_SYSCALL) * (100 - PER_KERNEL) / PER_KERNEL;
		if (delay) {
			usleep(delay);
		}
	}
}