396  * Type of "mtu": rt_mtu is u_long, ifnet.ifr_mtu is int, and nd_ifinfo.linkmtu
419 	u_long mtu;  in ip6_output()  local
660 	mtu = 0;  in ip6_output()
709 			mtu = ifp->if_mtu;  in ip6_output()
782 	 * mtu can be 0 and will be refined later.  in ip6_output()
794 		if ((error = IPSEC_OUTPUT(ipv6, ifp, m, inp, mtu == 0 ?  in ip6_output()
795 		    ifp->if_mtu : mtu)) != 0) {  in ip6_output()
940 	/* Determine path MTU. */  in ip6_output()
941 	ip6_getpmtu(ro_pmtu, ro != ro_pmtu, ifp, &ip6->ip6_dst, &mtu, fibnum,  in ip6_output()
943 	KASSERT(mtu > 0, ("%s:%d: mtu %ld, ro_pmtu %p ro %p ifp %p fibnum %u",  in ip6_output()
944 	    __func__, __LINE__, mtu, ro_pmtu, ro, ifp, fibnum));  in ip6_output()
947 	 * The caller of this function may specify to use the minimum MTU  in ip6_output()
949 	 * An advanced API option (IPV6_USE_MIN_MTU) can also override MTU  in ip6_output()
951 	 * packets will follow path MTU while multicast packets will be sent at  in ip6_output()
952 	 * the minimum MTU.  If IP6PO_MINMTU_ALL is specified, all packets  in ip6_output()
953 	 * including unicast ones will be sent at the minimum MTU.  Multicast  in ip6_output()
954 	 * packets will always be sent at the minimum MTU unless  in ip6_output()
958 	if (mtu > IPV6_MMTU) {  in ip6_output()
960 			mtu = IPV6_MMTU;  in ip6_output()
962 			mtu = IPV6_MMTU;  in ip6_output()
966 			mtu = IPV6_MMTU;  in ip6_output()
1122 	 * 1-a:	send as is if tlen <= path mtu  in ip6_output()
1123 	 * 1-b:	fragment if tlen > path mtu  in ip6_output()
1126 	 * 2-a:	send as is if tlen <= interface mtu  in ip6_output()
1127 	 * 2-b:	error if tlen > interface mtu  in ip6_output()
1153 		 * packet when the data length is larger than the MTU of the  in ip6_output()
1156 		 * application wanted to know the MTU value. Also return an  in ip6_output()
1160 			ip6_notify_pmtu(inp, &dst_sa, (u_int32_t)mtu);  in ip6_output()
1166 	if (dontfrag || tlen <= mtu) {	/* Cases 1-a and 2-a. */  in ip6_output()
1183 	if (mtu < IPV6_MMTU) {  in ip6_output()
1184 		/* Path MTU cannot be less than IPV6_MMTU. */  in ip6_output()
1201 		if (mtu > IPV6_MAXPACKET)  in ip6_output()
1202 			mtu = IPV6_MAXPACKET;  in ip6_output()
1204 		len = (mtu - unfragpartlen - sizeof(struct ip6_frag)) & ~7;  in ip6_output()
1448  * Calculates IPv6 path mtu for destination @dst.
1449  * Resulting MTU is stored in @mtup.
1477  * Calculates IPv6 path MTU for @dst based on transmit @ifp,
1479  * MTU from (successful) route lookup is saved (along with dst)
1483  * Stores mtu into @mtup.
1494 	u_long mtu;  in ip6_getpmtu()  local
1498 	mtu = 0;  in ip6_getpmtu()
1503 		 * Use ro_pmtu destination since mtu might differ.  in ip6_getpmtu()
1521 				mtu = nh->nh_mtu;  in ip6_getpmtu()
1523 					ro_pmtu->ro_mtu = mtu;  in ip6_getpmtu()
1526 			mtu = ro_pmtu->ro_mtu;  in ip6_getpmtu()
1530 		mtu = ro_pmtu->ro_nh->nh_mtu;  in ip6_getpmtu()
1532 	ip6_calcmtu(ifp, dst, mtu, mtup, proto);  in ip6_getpmtu()
1536  * Calculate MTU based on transmit @ifp, route mtu @rt_mtu and
1538  * Stores mtu into @mtup.
1544 	u_long mtu = 0;  in ip6_calcmtu()  local
1554 			mtu = tcp_hc_getmtu(&inc);  in ip6_calcmtu()
1557 		if (mtu)  in ip6_calcmtu()
1558 			mtu = min(mtu, rt_mtu);  in ip6_calcmtu()
1560 			mtu = rt_mtu;  in ip6_calcmtu()
1563 	if (mtu == 0)  in ip6_calcmtu()
1564 		mtu = IN6_LINKMTU(ifp);  in ip6_calcmtu()
1566 	*mtup = mtu;  in ip6_calcmtu()