#define _GNU_SOURCE
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <signal.h>
#include <sched.h>
#include <assert.h>
#include <sys/wait.h>

int childfn(void *p)
{
    int fd = open("/", O_RDONLY | O_DIRECTORY);
    assert(fd == 3);
    return 0;
}

int main()
{
    char buf[10000];
    pid_t pid;
    int res;

    pid = clone(childfn, buf+5000, CLONE_NEWNS | CLONE_FILES |  SIGCHLD, NULL);
    if (pid == -1) {
        perror("clone");
        return 1;
    }
    wait(&res);
    if (res != 0) {
        fprintf(stderr, "child exited with error %i\n", res);
        return 1;
    }
    res = fchdir(3);
    if (res == -1) {
        perror("fchdir");
        return 1;
    }
    mkdir("/tmp/mnt", 0755);
    return system("mount --bind . /tmp/mnt");
}