Function tcp_default_fb_init

freebsd/netinet/tcp_subr.c:699–753

* tfb_tcp_fb_init() function for the default stack. * * This handles making sure we have appropriate timers set if you are * transitioning a socket that has some amount of setup done. * * The init() fuction from the default can *never* return non-zero i.e. * it is required to always succeed since it is the stack of last resort! */

 * it is required to always succeed since it is the stack of last resort!
 */
static int
tcp_default_fb_init(struct tcpcb *tp)
{

	struct socket *so;

	INP_WLOCK_ASSERT(tp->t_inpcb);

	KASSERT(tp->t_state >= 0 && tp->t_state < TCPS_TIME_WAIT,
	    ("%s: connection %p in unexpected state %d", __func__, tp,
	    tp->t_state));

	/*
	 * Nothing to do for ESTABLISHED or LISTEN states. And, we don't
	 * know what to do for unexpected states (which includes TIME_WAIT).
	 */
	if (tp->t_state <= TCPS_LISTEN || tp->t_state >= TCPS_TIME_WAIT)
		return (0);

	/*
	 * Make sure some kind of transmission timer is set if there is
	 * outstanding data.
	 */
	so = tp->t_inpcb->inp_socket;
	if ((!TCPS_HAVEESTABLISHED(tp->t_state) || sbavail(&so->so_snd) ||
	    tp->snd_una != tp->snd_max) && !(tcp_timer_active(tp, TT_REXMT) ||
	    tcp_timer_active(tp, TT_PERSIST))) {
		/*
		 * If the session has established and it looks like it should
		 * be in the persist state, set the persist timer. Otherwise,
		 * set the retransmit timer.
		 */
		if (TCPS_HAVEESTABLISHED(tp->t_state) && tp->snd_wnd == 0 &&
		    (int32_t)(tp->snd_nxt - tp->snd_una) <
		    (int32_t)sbavail(&so->so_snd))
			tcp_setpersist(tp);
		else
			tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
	}

	/* All non-embryonic sessions get a keepalive timer. */
	if (!tcp_timer_active(tp, TT_KEEP))
		tcp_timer_activate(tp, TT_KEEP,
		    TCPS_HAVEESTABLISHED(tp->t_state) ? TP_KEEPIDLE(tp) :
		    TP_KEEPINIT(tp));

	/*
	 * Make sure critical variables are initialized
	 * if transitioning while in Recovery.
	 */
	if IN_FASTRECOVERY(tp->t_flags) {
		if (tp->sackhint.recover_fs == 0)
			tp->sackhint.recover_fs = max(1,
			    tp->snd_nxt - tp->snd_una);
	}

	return (0);
}