Function tcp_timer_persist

freebsd/netinet/tcp_timer.c:520–607

}

void
tcp_timer_persist(void *xtp)
{
	struct tcpcb *tp = xtp;
	struct inpcb *inp;
	struct epoch_tracker et;
	CURVNET_SET(tp->t_vnet);
#ifdef TCPDEBUG
	int ostate;

	ostate = tp->t_state;
#endif
	inp = tp->t_inpcb;
	KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
	INP_WLOCK(inp);
	if (callout_pending(&tp->t_timers->tt_persist) ||
	    !callout_active(&tp->t_timers->tt_persist)) {
		INP_WUNLOCK(inp);
		CURVNET_RESTORE();
		return;
	}
	callout_deactivate(&tp->t_timers->tt_persist);
	if ((inp->inp_flags & INP_DROPPED) != 0) {
		INP_WUNLOCK(inp);
		CURVNET_RESTORE();
		return;
	}
	KASSERT((tp->t_timers->tt_flags & TT_STOPPED) == 0,
		("%s: tp %p tcpcb can't be stopped here", __func__, tp));
	/*
	 * Persistence timer into zero window.
	 * Force a byte to be output, if possible.
	 */
	TCPSTAT_INC(tcps_persisttimeo);
	/*
	 * Hack: if the peer is dead/unreachable, we do not
	 * time out if the window is closed.  After a full
	 * backoff, drop the connection if the idle time
	 * (no responses to probes) reaches the maximum
	 * backoff that we would use if retransmitting.
	 */
	if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
	    (ticks - tp->t_rcvtime >= tcp_maxpersistidle ||
	     ticks - tp->t_rcvtime >= TCP_REXMTVAL(tp) * tcp_totbackoff)) {
		TCPSTAT_INC(tcps_persistdrop);
		if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
			tcp_inpinfo_lock_del(inp, tp);
			goto out;
		}
		NET_EPOCH_ENTER(et);
		tp = tcp_drop(tp, ETIMEDOUT);
		NET_EPOCH_EXIT(et);
		tcp_inpinfo_lock_del(inp, tp);
		goto out;
	}
	/*
	 * If the user has closed the socket then drop a persisting
	 * connection after a much reduced timeout.