Function tcp_do_segment

freebsd/netinet/tcp_input.c:1498–3343

}

void
tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
    struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos)
{
	int thflags, acked, ourfinisacked, needoutput = 0, sack_changed;
	int rstreason, todrop, win, incforsyn = 0;
	uint32_t tiwin;
	uint16_t nsegs;
	char *s;
	struct in_conninfo *inc;
	struct mbuf *mfree;
	struct tcpopt to;
	int tfo_syn;

#ifdef TCPDEBUG
	/*
	 * The size of tcp_saveipgen must be the size of the max ip header,
	 * now IPv6.
	 */
	u_char tcp_saveipgen[IP6_HDR_LEN];
	struct tcphdr tcp_savetcp;
	short ostate = 0;
#endif
	thflags = th->th_flags;
	inc = &tp->t_inpcb->inp_inc;
	tp->sackhint.last_sack_ack = 0;
	sack_changed = 0;
	nsegs = max(1, m->m_pkthdr.lro_nsegs);

	NET_EPOCH_ASSERT();
	INP_WLOCK_ASSERT(tp->t_inpcb);
	KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
	    __func__));
	KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
	    __func__));

#ifdef TCPPCAP
	/* Save segment, if requested. */
	tcp_pcap_add(th, m, &(tp->t_inpkts));
#endif
	TCP_LOG_EVENT(tp, th, &so->so_rcv, &so->so_snd, TCP_LOG_IN, 0,
	    tlen, NULL, true);

	if ((thflags & TH_SYN) && (thflags & TH_FIN) && V_drop_synfin) {
		if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
			log(LOG_DEBUG, "%s; %s: "
			    "SYN|FIN segment ignored (based on "
			    "sysctl setting)\n", s, __func__);
			free(s, M_TCPLOG);
		}
		goto drop;
	}

	/*
	 * If a segment with the ACK-bit set arrives in the SYN-SENT state
	 * check SEQ.ACK first.
	 */
	if ((tp->t_state == TCPS_SYN_SENT) && (thflags & TH_ACK) &&