namespaces_clone_unshare_demo.c

#define _GNU_SOURCE
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <unistd.h>
#define STACK_SIZE (1024 * 1024)

static char child_stack[STACK_SIZE];

static int metrics_fn() {
  printf("child PID: %ld\n", (long)getpid());
  printf("parent PID: %ld\n", (long)getppid());
  printf("New `net` Namespace:\n");
  system("ip link");
  printf("\n\n");
  return 0;
}

void* unshare_fn(int flags, void* fn) {
	unshare(flags);
	return fn;
}

int run_child(char* msg, void* fn, int flags){
  printf(msg);
  pid_t child_pid = clone(fn, child_stack+STACK_SIZE, flags, NULL);
  printf("clone() = %ld\n", (long)child_pid);
  waitpid(child_pid, NULL, 0);	
}

int main() {
  printf("=== PARENT ===\n");
  metrics_fn();

  run_child("=== JUST CLONE ===\n", metrics_fn, SIGCHLD);
  run_child("=== NEW PID ===\n", metrics_fn, CLONE_NEWPID | SIGCHLD);
  run_child("=== NETWORK ===\n", metrics_fn, CLONE_NEWNET | SIGCHLD);
  run_child("=== UNSHARE ===\n", unshare_fn(CLONE_NEWNET | CLONE_NEWCGROUP | CLONE_NEWPID, metrics_fn), SIGCHLD);
  return 0;
}