Function rack_process_ack

freebsd/netinet/tcp_stacks/rack.c:8202–8411

* Return value of 1, we do not need to call rack_process_data(). * return value of 0, rack_process_data can be called. * For ret_val if its 0 the TCP is locked, if its non-zero * its unlocked and probably unsafe to touch the TCB. */

 * its unlocked and probably unsafe to touch the TCB.
 */
static int
rack_process_ack(struct mbuf *m, struct tcphdr *th, struct socket *so,
    struct tcpcb *tp, struct tcpopt *to,
    uint32_t tiwin, int32_t tlen,
    int32_t * ofia, int32_t thflags, int32_t * ret_val)
{
	int32_t ourfinisacked = 0;
	int32_t nsegs, acked_amount;
	int32_t acked;
	struct mbuf *mfree;
	struct tcp_rack *rack;
	int32_t under_pacing = 0;
	int32_t recovery = 0;

	rack = (struct tcp_rack *)tp->t_fb_ptr;
	if (SEQ_GT(th->th_ack, tp->snd_max)) {
		ctf_do_dropafterack(m, tp, th, thflags, tlen, ret_val);
		rack->r_wanted_output = 1;
		return (1);
	}
	if (rack->rc_gp_filled &&
	    (rack->r_ctl.rc_hpts_flags & PACE_PKT_OUTPUT)) {
		under_pacing = 1;
	}
	if (SEQ_GEQ(th->th_ack, tp->snd_una) || to->to_nsacks) {
		if (rack->rc_in_persist)
			tp->t_rxtshift = 0;
		if ((th->th_ack == tp->snd_una) && (tiwin == tp->snd_wnd))
			rack_strike_dupack(rack);
		rack_log_ack(tp, to, th);
	}
	if (__predict_false(SEQ_LEQ(th->th_ack, tp->snd_una))) {
		/*
		 * Old ack, behind (or duplicate to) the last one rcv'd
		 * Note: Should mark reordering is occuring! We should also
		 * look for sack blocks arriving e.g. ack 1, 4-4 then ack 1,
		 * 3-3, 4-4 would be reording. As well as ack 1, 3-3 <no
		 * retran and> ack 3
		 */
		return (0);
	}
	/*
	 * If we reach this point, ACK is not a duplicate, i.e., it ACKs
	 * something we sent.
	 */
	if (tp->t_flags & TF_NEEDSYN) {
		/*
		 * T/TCP: Connection was half-synchronized, and our SYN has
		 * been ACK'd (so connection is now fully synchronized).  Go
		 * to non-starred state, increment snd_una for ACK of SYN,
		 * and check if we can do window scaling.
		 */
		tp->t_flags &= ~TF_NEEDSYN;
		tp->snd_una++;
		/* Do window scaling? */
		if ((tp->t_flags & (TF_RCVD_SCALE | TF_REQ_SCALE)) ==
		    (TF_RCVD_SCALE | TF_REQ_SCALE)) {
			tp->rcv_scale = tp->request_r_scale;