Function if_vmove_loan

freebsd/net/if.c:1377–1432

* Move an ifnet to or from another child prison/vnet, specified by the jail id. */

 * Move an ifnet to or from another child prison/vnet, specified by the jail id.
 */
static int
if_vmove_loan(struct thread *td, struct ifnet *ifp, char *ifname, int jid)
{
	struct prison *pr;
	struct ifnet *difp;
	int error;
	bool found;
	bool shutdown;

	/* Try to find the prison within our visibility. */
	sx_slock(&allprison_lock);
	pr = prison_find_child(td->td_ucred->cr_prison, jid);
	sx_sunlock(&allprison_lock);
	if (pr == NULL)
		return (ENXIO);
	prison_hold_locked(pr);
	mtx_unlock(&pr->pr_mtx);

	/* Do not try to move the iface from and to the same prison. */
	if (pr->pr_vnet == ifp->if_vnet) {
		prison_free(pr);
		return (EEXIST);
	}

	/* Make sure the named iface does not exists in the dst. prison/vnet. */
	/* XXX Lock interfaces to avoid races. */
	CURVNET_SET_QUIET(pr->pr_vnet);
	difp = ifunit(ifname);
	if (difp != NULL) {
		CURVNET_RESTORE();
		prison_free(pr);
		return (EEXIST);
	}

	/* Make sure the VNET is stable. */
	shutdown = VNET_IS_SHUTTING_DOWN(ifp->if_vnet);
	if (shutdown) {
		CURVNET_RESTORE();
		prison_free(pr);
		return (EBUSY);
	}
	CURVNET_RESTORE();

	found = if_unlink_ifnet(ifp, true);
	MPASS(found);

	/* Move the interface into the child jail/vnet. */
	error = if_vmove(ifp, pr->pr_vnet);

	/* Report the new if_xname back to the userland on success. */
	if (error == 0)
		sprintf(ifname, "%s", ifp->if_xname);

	prison_free(pr);
	return (error);
}

static int