#define _GNU_SOURCE
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <errno.h>
#include <sys/mount.h>
#include <sys/syscall.h>
#include <sched.h>

int main()
{
	const char *child  = "/tmp/child";
	int ret;

	printf("main pid = %d\n", getpid());	

	/* make our own private playground ... */
	ret = unshare(CLONE_NEWNS);
	if (ret) {
		perror("unshare");
		exit(1);
	}

	ret = mount("none", "/", NULL, MS_REC|MS_PRIVATE, NULL);
	if (ret) {
		perror("mount");
		exit(1);
	}

	ret = mount("none", "/", NULL, MS_REC|MS_SHARED, NULL);
	if (ret) {
		perror("mount2");
		exit(1);
	}

	/* fork monitor ... */
	ret = fork();
	if (ret < 0) {
		perror("fork");
		exit(1);
	} else if (!ret) {
		printf("monitor pid = %d\n", getpid());

		ret = unshare(CLONE_NEWNS);
		if (ret) {
			perror("unshare in monitor");
			exit(1);
		}

		ret = mount("none", "/", NULL, MS_REC|MS_SHARED, NULL);
		if (ret) {
			perror("mount in monitor");
			exit(1);
		}

		ret = mount("none", "/", NULL, MS_REC|MS_SLAVE, NULL);
		if (ret) {
			perror("mount2 in monitor");
			exit(1);
		}

		sleep(-1);
	}

	/* wait monitor to setup */
	sleep(1);


	/* fork child ... */	
	ret = fork();
	if (ret < 0) {
		perror("fork");
		exit(1);
	} else if (!ret) {
		printf("child pid = %d\n", getpid());

		ret = unshare(CLONE_NEWNS);
		if (ret) {
			perror("unshare in child");
			exit(1);
		}

		ret = mount("none", "/", NULL, MS_REC|MS_SLAVE, NULL);
		if (ret) {
			perror("mount in child");
			exit(1);
		}
		ret = mount(NULL, "/", NULL, MS_REC|MS_SHARED, NULL);
		if (ret) {
			perror("mount2 in child");
			exit(1);
		}

		if (!fork()) { /* grand-child */
			printf("grand-child pid = %d\n", getpid());
			ret = unshare(CLONE_NEWNS);
			if (ret) {
				perror("unshare in grand-child");
				exit(1);
			}

			ret = mount("none", "/", NULL, MS_REC|MS_SHARED, NULL);
			if (ret) {
				perror("mount in grand-child");
				exit(1);
			}

			ret = mount("none", "/", NULL, MS_REC|MS_SLAVE, NULL);
			if (ret) {
				perror("mount2 in grand-child");
				exit(1);
			}

			sleep(-1);
		}

		sleep(-1);
	}

	/* wait child and grand-child to setup */
	sleep(1);
	
	ret = mkdir(child, 0755);
	if (ret &&  errno != EEXIST) {
		perror("mkdir");
		exit(1);
	}

	/* let "child" mount slip to everyone' namespaces ... */
	ret = mount(child, child, NULL, MS_BIND, NULL);
	if (ret) {
		perror("bind mount");
		exit(1);
	}

	sleep(-1);
}