>> 	if I were you I would put
>> 		#ifdef DIAGNOSTIC
>> 			if (MHLEN > 20 + 64)
>> 				panic("foo");
>> 		#endif
>Why is that 20 + 64 ?  Isn't an IPv6 header 40 bytes long, not 64 ?
>4 + 2 + 1 + 1 + 2 * 16 = 40

	you right, i made a typo.  assuming that there's no tcp option,
	"40 + 20" or "sizeof(struct ip6_hdr) + sizeof(struct tcphdr)".

	also, the check is backwards... "MHLEN < foo".

>Should I also include:
>  		#ifdef DIAGNOSTIC
>  			if (MHLEN > 20 + 20)
>  				panic("foo");
>  		#endif
>For the plain IPv4 case ?
>I mean if we can't get a basic TCP + IPv* header into a single MBUF we're
>in a seriously screwed position and we'll be up the creek in so many ways.

	for plain 4.4BSD systems MHLEN >= 20 + 64 must be true, so i don't
	think we really need the above check.
	NetBSD has no such limitation any more in tcp/udp input path,
	we just need MHLEN > 64.

itojun