dotcloud/docker

#define _GNU_SOURCE
#include <errno.h>
#include <sched.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <unistd.h>

#define STACK_SIZE (1024 * 1024)    /* Stack size for cloned child */

struct clone_args {
    char **argv;
};

// child_exec is the func that will be executed as the result of clone
static int child_exec(void *stuff)
{
    struct clone_args *args = (struct clone_args *)stuff;
    if (execvp(args->argv[0], args->argv) != 0) {
        fprintf(stderr, "failed to execvp arguments %s\n",
            strerror(errno));
        exit(-1);
    }
    // we should never reach here!
    exit(EXIT_FAILURE);
}

int main(int argc, char **argv)
{
    struct clone_args args;
    args.argv = &argv[1];

    int clone_flags = CLONE_NEWNS | CLONE_NEWPID | SIGCHLD;

    // allocate stack for child
    char *stack;        /* Start of stack buffer */
    char *child_stack;    /* End of stack buffer */
    stack =
        mmap(NULL, STACK_SIZE, PROT_READ | PROT_WRITE,
         MAP_SHARED | MAP_ANON | MAP_STACK, -1, 0);
    if (stack == MAP_FAILED) {
        fprintf(stderr, "mmap failed: %s\n", strerror(errno));
        exit(EXIT_FAILURE);
    }
    child_stack = stack + STACK_SIZE;    /* Assume stack grows downward */

    // the result of this call is that our child_exec will be run in another
    // process returning its pid
    pid_t pid = clone(child_exec, child_stack, clone_flags, &args);
    if (pid < 0) {
        fprintf(stderr, "clone failed: %s\n", strerror(errno));
        exit(EXIT_FAILURE);
    }
    // lets wait on our child process here before we, the parent, exits
    if (waitpid(pid, NULL, 0) == -1) {
        fprintf(stderr, "failed to wait pid %d\n", pid);
        exit(EXIT_FAILURE);
    }
    exit(EXIT_SUCCESS);
}