Requesting help on using g_threads with clone()

[Venkateswararao Jujjuri <jvrao linux vnet ibm com>]

Resending after subscribing to the list:


First time writing to this list. Appreciate any help/pointers.

We are considering glib threads for developing a secure user space
file-server.
In this effort, we would like to use clone(2) system call which performs
a chroot(/exported/path)
followed by g_thread_pool_new(). The threads created will inherit the
chroot'ed name
space and hence we are are creating a secure zone of exported region for
the fileserver to operate.

Questions.

-What is the best way to demonize the threads created by
g_thread_pool_new()? In the experimentation, all the threads are exiting if the
process which called g_thread_pool_new()  exits.
The clone'd process doesn't need to hang around after
calling g_thread_pool_new()...if there is a way to keep the new
threads around.

- Is there any simple way to add/remove threads to the exclusive pool on
the fly?


Attaching my simple program to illustrate what I am trying to achieve.

$ export C_INCLUDE_PATH=$C_INCLUDE_PATH:/usr/include/glib-2.0/
$ cc jv_cloneth_demo.c -o jv_cloneth_demo -lglib-2.0 -lgthread-2.0

$ sudo ./jv_cloneth_demo
This should fail: /etc/passwd stat err:-1 errno:2
This should pass: /passwd stat err:0 errno:0

Thanks in advance,
Venkateswararao Jujjuri (JV)
VirtFS-KVM Project
IBM.



#include <malloc.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <signal.h>
#include <sched.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <sys/syscall.h>   
#include <sys/stat.h>
#include <stdlib.h>
#include <glib-2.0/glib.h>


int gdata;
GThreadPool *pool;

void jv_thread_routine(gpointer data, gpointer user_data)
{
	int *ldata = data;
	struct stat buf;
	int err;
	*ldata = *ldata + 1;
	errno = 0;
	err = stat("/etc/passwd", &buf);
	printf("This should fail: /etc/passwd stat err:%d errno:%d\n",
			err, errno);
	errno = 0;
	err = stat("/passwd", &buf);
	printf("This should pass: /passwd stat err:%d errno:%d\n", err, errno);
}


// The child thread will execute this function
int threadFunction( void* argument )
{
	GError *err;
	if (chroot("/etc") < 0) {
		perror("chroot. Are you super user?");
		exit(3);
	}
	if (!g_thread_supported()) {
		g_thread_init(NULL);
	}
	pool = g_thread_pool_new(jv_thread_routine, &gdata, 2,
			TRUE, &err);
	if (pool == NULL) {
		exit(4);
	}
	sleep(5); /*Q: If I remove this sleep, jv_thread_routine won't execute. How can I quit this function while keeping thread pool active? */
	return 0;
}

int main()
{
	void* stack;
	pid_t pid;

	stack = malloc(8096);
	if (stack == 0) {
		perror("malloc: stack alloc failed");
		exit(1);
	}

	// Call the clone system call to create the child thread
	pid = clone(&threadFunction, (char*) stack + 8096,
			SIGCHLD | CLONE_FILES | CLONE_SIGHAND |
			CLONE_VM |CLONE_THREAD, 0 );
	if (pid == -1) {
		perror("clone");
		exit(2);
	}

	// Wait for the clone to do g_thread_pool_new
	while (pool == NULL) {
		sleep(1);
	}

	g_thread_pool_push(pool, &gdata, NULL);
	sleep(6);
	free(stack);
	return 0;
}