#define _GNU_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/syscall.h>
#include <signal.h>
#include <linux/sched.h>

int pipefd[2];

int init(void *arg)
{
	int nr, i, err;
	sighandler_t sigret;
	char c;

	close(pipefd[0]);

	err = setsid();
	if (err < 0) {
		perror("setsid");
		abort();
	}

	sigret = signal(SIGCHLD, SIG_IGN);
	if (sigret == SIG_ERR) {
		fprintf(stderr, "signal\n");
		abort();
	}
	
	nr = atoi(arg);
	for (i = 0; i < nr; i++) {
		err = fork();
		if (err < 0) {
			perror("fork");
			abort();
		} else if (err == 0) {
			printf("%d before\n", getpid());
			fflush(stdout);
			pause();
			printf("%d after\n", getpid());
			fflush(stdout);
			return 0;
		}
	}

	err = write(pipefd[1], &c, 1);
	if (err != 1) {
		perror("write");
		abort();
	}

	pause();

	return 0;
}

int main(int argc, char *argv[])
{
	long stack_size = sysconf(_SC_PAGESIZE);
	void *stack = alloca(stack_size) + stack_size;
	pid_t pid;
	char c;
	int ret;

	ret = pipe(pipefd);
	if (ret) {
		perror("pipe");
		abort();
	}

	ret = clone(init, stack, CLONE_NEWPID | SIGCHLD, argv[1]);
	if (ret < 0) {
		perror("clone");
		abort();
	}
	pid = ret;
	printf("%d\n", pid);
	fflush(stdout);

	close(pipefd[1]);
	ret = read(pipefd[0], &c, 1);
	if (ret != 1) {
		if (ret) {
			perror("read");
			abort();
		} else {
			sleep(5);
		}
	}

	printf("killing %d\n", pid);
	fflush(stdout);
	ret = kill(-pid, SIGKILL);
	if (ret) {
		perror("kill");
		abort();
	}

	return 0;
}