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

#define NEWROOT "/newroot"
#define OLDROOT "/newroot/oldroot"
#define DEV "/dev"
#define PROC "/proc"
#define SYS "/sys"
#define RUN "/run"

static void die(const char *msg) {
    perror(msg);
    _exit(1);
}

int main(void) {
    mount("proc", PROC, "proc", 0, NULL);
    mount("sysfs", SYS, "sysfs", 0, NULL);
    mount("devtmpfs", DEV, "devtmpfs", 0, NULL);
    mount("tmpfs", RUN, "tmpfs", 0, "mode=0755");

    if (mount("/dev/mmcblk1p1", NEWROOT, "ext4", 0, NULL) != 0) die("mount newroot");
    mkdir(OLDROOT, 0755);

    if (syscall(SYS_pivot_root, NEWROOT, OLDROOT) != 0) die("pivot_root");
    if (chdir("/") != 0) die("chdir /");

    mount("/dev", DEV, NULL, MS_MOVE, NULL);
    mount("/proc", PROC, NULL, MS_MOVE, NULL);
    mount("/sys", SYS, NULL, MS_MOVE, NULL);
    mount("/run", RUN, NULL, MS_MOVE, NULL);

    umount2("/oldroot", MNT_DETACH);
    rmdir("/oldroot");

    execl("/sbin/init.real", "init", NULL);
    die("exec init failed");

    return 0;
}