Function sys_jail_attach

freebsd/kern/kern_jail.c:2421–2453

* struct jail_attach_args { * int jid; * }; */

 * };
 */
int
sys_jail_attach(struct thread *td, struct jail_attach_args *uap)
{
	struct prison *pr;
	int error;

	error = priv_check(td, PRIV_JAIL_ATTACH);
	if (error)
		return (error);

	/*
	 * Start with exclusive hold on allprison_lock to ensure that a possible
	 * PR_METHOD_REMOVE call isn't concurrent with jail_set or jail_remove.
	 * But then immediately downgrade it since we don't need to stop
	 * readers.
	 */
	sx_xlock(&allprison_lock);
	sx_downgrade(&allprison_lock);
	pr = prison_find_child(td->td_ucred->cr_prison, uap->jid);
	if (pr == NULL) {
		sx_sunlock(&allprison_lock);
		return (EINVAL);
	}

	/* Do not allow a process to attach to a prison that is not alive. */
	if (!prison_isalive(pr)) {
		mtx_unlock(&pr->pr_mtx);
		sx_sunlock(&allprison_lock);
		return (EINVAL);
	}

	return (do_jail_attach(td, pr));
}

static int
do_jail_attach(struct thread *td, struct prison *pr)