Function if_vmove

freebsd/net/if.c:1301–1372

* if_vmove() performs a limited version of if_detach() in current * vnet and if_attach()es the ifnet to the vnet specified as 2nd arg. * An attempt is made to shrink if_index in current vnet, find an * unused if_index in target vnet and calls if_grow() if necessary, * and finally find an unused if_xname for the target vnet. */

 * and finally find an unused if_xname for the target vnet.
 */
static int
if_vmove(struct ifnet *ifp, struct vnet *new_vnet)
{
	struct if_clone *ifc;
#ifdef DEV_BPF
	u_int bif_dlt, bif_hdrlen;
#endif
	void *old;
	int rc;

#ifdef DEV_BPF
 	/*
	 * if_detach_internal() will call the eventhandler to notify
	 * interface departure.  That will detach if_bpf.  We need to
	 * safe the dlt and hdrlen so we can re-attach it later.
	 */
	bpf_get_bp_params(ifp->if_bpf, &bif_dlt, &bif_hdrlen);
#endif

	/*
	 * Detach from current vnet, but preserve LLADDR info, do not
	 * mark as dead etc. so that the ifnet can be reattached later.
	 * If we cannot find it, we lost the race to someone else.
	 */
	rc = if_detach_internal(ifp, 1, &ifc);
	if (rc != 0)
		return (rc);

	/*
	 * Unlink the ifnet from ifindex_table[] in current vnet, and shrink
	 * the if_index for that vnet if possible.
	 *
	 * NOTE: IFNET_WLOCK/IFNET_WUNLOCK() are assumed to be unvirtualized,
	 * or we'd lock on one vnet and unlock on another.
	 */
	IFNET_WLOCK();
	ifindex_free_locked(ifp->if_index);
	IFNET_WUNLOCK();

	/*
	 * Perform interface-specific reassignment tasks, if provided by
	 * the driver.
	 */
	if (ifp->if_reassign != NULL)
		ifp->if_reassign(ifp, new_vnet, NULL);

	/*
	 * Switch to the context of the target vnet.
	 */
	CURVNET_SET_QUIET(new_vnet);
 restart:
	IFNET_WLOCK();
	ifp->if_index = ifindex_alloc(&old);
	if (__predict_false(ifp->if_index == USHRT_MAX)) {
		IFNET_WUNLOCK();
		epoch_wait_preempt(net_epoch_preempt);
		free(old, M_IFNET);
		goto restart;