Function iflib_if_ioctl

freebsd/net/iflib.c:4234–4411

		     IFCAP_VLAN_HWTSO | IFCAP_VLAN_HWCSUM | IFCAP_NOMAP)

static int
iflib_if_ioctl(if_t ifp, u_long command, caddr_t data)
{
	if_ctx_t ctx = if_getsoftc(ifp);
	struct ifreq	*ifr = (struct ifreq *)data;
#if defined(INET) || defined(INET6)
	struct ifaddr	*ifa = (struct ifaddr *)data;
#endif
	bool		avoid_reset = false;
	int		err = 0, reinit = 0, bits;

	switch (command) {
	case SIOCSIFADDR:
#ifdef INET
		if (ifa->ifa_addr->sa_family == AF_INET)
			avoid_reset = true;
#endif
#ifdef INET6
		if (ifa->ifa_addr->sa_family == AF_INET6)
			avoid_reset = true;
#endif
		/*
		** Calling init results in link renegotiation,
		** so we avoid doing it when possible.
		*/
		if (avoid_reset) {
			if_setflagbits(ifp, IFF_UP,0);
			if (!(if_getdrvflags(ifp) & IFF_DRV_RUNNING))
				reinit = 1;
#ifdef INET
			if (!(if_getflags(ifp) & IFF_NOARP))
				arp_ifinit(ifp, ifa);
#endif
		} else
			err = ether_ioctl(ifp, command, data);
		break;
	case SIOCSIFMTU:
		CTX_LOCK(ctx);
		if (ifr->ifr_mtu == if_getmtu(ifp)) {
			CTX_UNLOCK(ctx);
			break;
		}
		bits = if_getdrvflags(ifp);
		/* stop the driver and free any clusters before proceeding */
		iflib_stop(ctx);

		if ((err = IFDI_MTU_SET(ctx, ifr->ifr_mtu)) == 0) {
			STATE_LOCK(ctx);
			if (ifr->ifr_mtu > ctx->ifc_max_fl_buf_size)
				ctx->ifc_flags |= IFC_MULTISEG;
			else
				ctx->ifc_flags &= ~IFC_MULTISEG;
			STATE_UNLOCK(ctx);
			err = if_setmtu(ifp, ifr->ifr_mtu);
		}
		iflib_init_locked(ctx);
		STATE_LOCK(ctx);
		if_setdrvflags(ifp, bits);