Function tcp_twstart

freebsd/netinet/tcp_timewait.c:228–372

* Move a TCP connection into TIME_WAIT state. * tcbinfo is locked. * inp is locked, and is unlocked before returning. */

 *    inp is locked, and is unlocked before returning.
 */
void
tcp_twstart(struct tcpcb *tp)
{
	struct tcptw twlocal, *tw;
	struct inpcb *inp = tp->t_inpcb;
	struct socket *so;
	uint32_t recwin;
	bool acknow, local;
#ifdef INET6
	bool isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
#endif

	NET_EPOCH_ASSERT();
	INP_WLOCK_ASSERT(inp);

	/* A dropped inp should never transition to TIME_WAIT state. */
	KASSERT((inp->inp_flags & INP_DROPPED) == 0, ("tcp_twstart: "
	    "(inp->inp_flags & INP_DROPPED) != 0"));

	if (V_nolocaltimewait) {
#ifdef INET6
		if (isipv6)
			local = in6_localaddr(&inp->in6p_faddr);
		else
#endif
#ifdef INET
			local = in_localip(inp->inp_faddr);
#else
			local = false;
#endif
	} else
		local = false;

	/*
	 * For use only by DTrace.  We do not reference the state
	 * after this point so modifying it in place is not a problem.
	 */
	tcp_state_change(tp, TCPS_TIME_WAIT);

	if (local)
		tw = &twlocal;
	else
		tw = uma_zalloc(V_tcptw_zone, M_NOWAIT);
	if (tw == NULL) {
		/*
		 * Reached limit on total number of TIMEWAIT connections
		 * allowed. Remove a connection from TIMEWAIT queue in LRU
		 * fashion to make room for this connection.
		 *
		 * XXX:  Check if it possible to always have enough room
		 * in advance based on guarantees provided by uma_zalloc().
		 */
		tw = tcp_tw_2msl_scan(1);
		if (tw == NULL) {
			tp = tcp_close(tp);
			if (tp != NULL)
				INP_WUNLOCK(inp);
			return;