Function bbr_fastack

freebsd/netinet/tcp_stacks/bbr.c:8641–8829

* This subfunction is used to try to highly optimize the * fast path. We again allow window updates that are * in sequence to remain in the fast-path. We also add * in the __predict's to attempt to help the compiler. * Note that if we return a 0, then we can *not* process * it and the caller should push the packet into the * slow-path. If we return 1, then all is well and * the packet is fu

 * the packet is fully processed.
 */
static int
bbr_fastack(struct mbuf *m, struct tcphdr *th, struct socket *so,
    struct tcpcb *tp, struct tcpopt *to, int32_t drop_hdrlen, int32_t tlen,
    uint32_t tiwin, int32_t nxt_pkt, uint8_t iptos)
{
	int32_t acked;
	uint16_t nsegs;
	uint32_t sack_changed;
#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
	uint32_t prev_acked = 0;
	struct tcp_bbr *bbr;

	if (__predict_false(SEQ_LEQ(th->th_ack, tp->snd_una))) {
		/* Old ack, behind (or duplicate to) the last one rcv'd */
		return (0);
	}
	if (__predict_false(SEQ_GT(th->th_ack, tp->snd_max))) {
		/* Above what we have sent? */
		return (0);
	}
	if (__predict_false(tiwin == 0)) {
		/* zero window */
		return (0);
	}
	if (__predict_false(tp->t_flags & (TF_NEEDSYN | TF_NEEDFIN))) {
		/* We need a SYN or a FIN, unlikely.. */
		return (0);
	}
	if ((to->to_flags & TOF_TS) && __predict_false(TSTMP_LT(to->to_tsval, tp->ts_recent))) {
		/* Timestamp is behind .. old ack with seq wrap? */
		return (0);
	}
	if (__predict_false(IN_RECOVERY(tp->t_flags))) {
		/* Still recovering */
		return (0);
	}
	bbr = (struct tcp_bbr *)tp->t_fb_ptr;
	if (__predict_false(bbr->r_ctl.rc_resend != NULL)) {
		/* We are retransmitting */
		return (0);
	}
	if (__predict_false(bbr->rc_in_persist != 0)) {
		/* In persist mode */
		return (0);
	}
	if (bbr->r_ctl.rc_sacked) {
		/* We have sack holes on our scoreboard */
		return (0);
	}