#define _GNU_SOURCE

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <fcntl.h>
#include <libgen.h>
#include <errno.h>

void
recursive_fork(size_t size)
{
	pid_t pid;

	while ((pid = fork() == 0))
	{
		if (size) {
			void *buf;
			buf = malloc(size);
			if (!buf) {
				perror("malloc error");
				exit(-errno);
			}
			memset(buf, 0, size);
			free(buf);
		}
	}
	if (pid < 0) {
		perror("fork error(child)");
		exit(-errno);
	}
	exit(0);
}

void usage(const char *cmd)
{
	fprintf(stderr, "Usage: %s [-c <num child>] [-s <size in bytes>] [-p <cgroup path>]\n", cmd);
	exit(-1);
}

int
main(int argc, char *argv[])
{
	pid_t pid;
	int opt;
	unsigned int numchild = 1;
	size_t alloc_size = 0;
	char path[64];
	int fd;

	while ((opt = getopt(argc, argv, "c:s:p:")) != -1) {
		switch (opt) {
		case 'c':
			numchild = atoi(optarg);
			break;
		case 's':
			alloc_size = atoi(optarg);
			break;
		case 'p':
			snprintf(path, sizeof(path), "%s/tasks", optarg);
			fd = open(path, O_WRONLY);
			if (fd < 0) {
				perror("open error");
				exit(-errno);
			}
			write(fd, "\0", 1);
			close(fd);
			break;
		default:
			usage(basename(argv[0]));
		}
	}

	while (numchild--) {
		pid = fork();
		if (pid < 0) {
			perror("fork error(parent)");
			exit(-errno);
		}
		if (pid == 0)	/* child */
			recursive_fork(alloc_size);
	}

	return 0;
}