Function tcp_mssopt

freebsd/netinet/tcp_input.c:3882–3919

* Determine the MSS option to send on an outgoing SYN. */

 * Determine the MSS option to send on an outgoing SYN.
 */
int
tcp_mssopt(struct in_conninfo *inc)
{
	int mss = 0;
	uint32_t thcmtu = 0;
	uint32_t maxmtu = 0;
	size_t min_protoh;

	KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));

#ifdef INET6
	if (inc->inc_flags & INC_ISIPV6) {
		mss = V_tcp_v6mssdflt;
		maxmtu = tcp_maxmtu6(inc, NULL);
		min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
	}
#endif
#if defined(INET) && defined(INET6)
	else
#endif
#ifdef INET
	{
		mss = V_tcp_mssdflt;
		maxmtu = tcp_maxmtu(inc, NULL);
		min_protoh = sizeof(struct tcpiphdr);
	}
#endif
#if defined(INET6) || defined(INET)
	thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
#endif

	if (maxmtu && thcmtu)
		mss = min(maxmtu, thcmtu) - min_protoh;
	else if (maxmtu || thcmtu)
		mss = max(maxmtu, thcmtu) - min_protoh;

	return (mss);
}

void
tcp_prr_partialack(struct tcpcb *tp, struct tcphdr *th)