#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <fcntl.h>

int main(int argc, char *argv[])
{
	char buf[1];
	int max, loop, fd, tmp, rw;

	fd = open("/proc/rwsem",O_RDWR);
	if (fd<0) {
		perror("open");
		return 1;
	}

	max = (argc>1) ? atoi(argv[1]) : 50;
	rw = max<0;
	max = abs(max);

	for (loop=max; loop>0; loop--) {
		switch (fork()) {
		case -1:
			perror("fork");
			return 1;
		case 0:
			rw ? write(fd," ",1) : read(fd,buf,1);
			exit(1);
		default:
			break;
		}
	}

	for (loop=max; loop>0; loop--) {
		if (wait(&tmp)<0) {
			perror("wait");
			return 1;
		}
	}

	return 0;
}