CLONE_FS Example

This post we will write a code, which will give us an observation what changes when CLONE_FS is added and when it is removed.

Code:

	#define _GNU_SOURCE
	#include <stdio.h>
	#include <sched.h>
	#include <stdlib.h>
	#include <string.h>
	#include <unistd.h>
	#include <sys/wait.h>
	#define STACK_SIZE 65536
	static int child_func(void *arg)
	{
	printf("Child:Current Working Directory:%s\n",
	get_current_dir_name());
	chdir("/opt");
	printf("Child:Current Working Directory:%s\n",
	get_current_dir_name());
	return 0;
	}
	int main(int argc, char *argv[])
	{
	//Allocate stack for child task
	char *stack = malloc(STACK_SIZE);
	unsigned long flags = 0;
	char buf[256];
	int status;
	printf("Parent:Current Working Directory:%s\n",
	get_current_dir_name());
	if (!stack) {
	perror("Failed to allocate memory\n");
	exit(1);
	}
	if (argc == 2 && !strcmp(argv[1], "fs"))
	flags |= CLONE_FS;
	if (clone(child_func, stack + STACK_SIZE, flags | SIGCHLD, NULL) == -1) {
	perror("clone");
	exit(1);
	}
	if (wait(&status) == -1) {
	perror("Wait");
	exit(1);
	}
	printf("Child exited with status:%d\t cwd:%s\n",
	status, get_current_dir_name());
	return 0;
	}

view raw clone_fs.c hosted with ❤ by GitHub

Output:

Notes:

1. You can see when CLONE_FS is set, changing the working directory in the child process has changed in the parent process.
2. Similarly other attributes like root directory will also change if CLONE_FS is set.