int idle, sendalot;
int idle, sendalot = 0;
tcp_output(tp)	register struct tcpcb *tp;{	register struct socket *so = tp->t_inpcb->inp_socket;	register long len, win;	int off, flags, error;	register struct mbuf *m;	register struct tcphdr *th;	u_char opt[MAX_TCPOPTLEN];	unsigned int optlen, hdrlen;	int idle, sendalot;#ifdef TCP_SACK	int i, sack_rxmit = 0;	struct sackhole *p;#endif#if defined(TCP_SACK)	int maxburst = TCP_MAXBURST;#endif#ifdef TCP_SIGNATURE	unsigned int sigoff;#endif /* TCP_SIGNATURE */#if defined(TCP_SACK) && defined(TCP_SIGNATURE) && defined(DIAGNOSTIC)	if (!tp->sack_disable && (tp->t_flags & TF_SIGNATURE))		return (EINVAL);#endif /* defined(TCP_SACK) && defined(TCP_SIGNATURE) && defined(DIAGNOSTIC) */	/*	 * Determine length of data that should be transmitted,	 * and flags that will be used.	 * If there is some data or critical controls (SYN, RST)	 * to send, then transmit; otherwise, investigate further.	 */	idle = (tp->snd_max == tp->snd_una);	if (idle && tp->t_idle >= tp->t_rxtcur)		/*		 * We have been idle for "a while" and no acks are		 * expected to clock out any data we send --		 * slow start to get ack "clock" running again.		 */		tp->snd_cwnd = tp->t_maxseg;again:	sendalot = 0;#ifdef TCP_SACK	/*	 * If we've recently taken a timeout, snd_max will be greater than	 * snd_nxt.  There may be SACK information that allows us to avoid	 * resending already delivered data.  Adjust snd_nxt accordingly.	 */	if (!tp->sack_disable && SEQ_LT(tp->snd_nxt, tp->snd_max))		tcp_sack_adjust(tp);#endif	off = tp->snd_nxt - tp->snd_una;	win = ulmin(tp->snd_wnd, tp->snd_cwnd);	flags = tcp_outflags[tp->t_state];	/*	 * If in persist timeout with window of 0, send 1 byte.	 * Otherwise, if window is small but nonzero	 * and timer expired, we will send what we can	 * and go to transmit state.	 */#ifdef TCP_SACK	/* 	 * Send any SACK-generated retransmissions.  If we're explicitly trying	 * to send out new data (when sendalot is 1), bypass this function.	 * If we retransmit in fast recovery mode, decrement snd_cwnd, since	 * we're replacing a (future) new transmission with a retransmission 	 * now, and we previously incremented snd_cwnd in tcp_input().	 */	if (!tp->sack_disable && !sendalot) {		if ((p = tcp_sack_output(tp))) {			off = p->rxmit - tp->snd_una;			sack_rxmit = 1;#if 0			/* Coalesce holes into a single retransmission */#endif			len = min(tp->t_maxseg, p->end - p->rxmit);#ifndef TCP_FACK			/* in FACK, hold snd_cwnd constant during recovery */			if (SEQ_LT(tp->snd_una, tp->snd_last))				tp->snd_cwnd -= tp->t_maxseg;#endif    		}	}#endif /* TCP_SACK */	if (tp->t_force) {		if (win == 0) {			/*			 * If we still have some data to send, then			 * clear the FIN bit.  Usually this would			 * happen below when it realizes that we			 * aren't sending all the data.  However,			 * if we have exactly 1 byte of unset data,			 * then it won't clear the FIN bit below,			 * and if we are in persist state, we wind			 * up sending the packet without recording			 * that we sent the FIN bit.			 *			 * We can't just blindly clear the FIN bit,			 * because if we don't have any more data			 * to send then the probe will be the FIN			 * itself.			 */			if (off < so->so_snd.sb_cc)				flags &= ~TH_FIN;			win = 1;		} else {			tp->t_timer[TCPT_PERSIST] = 0;			tp->t_rxtshift = 0;		}	}#ifdef TCP_SACK	if (!sack_rxmit) {#endif	len = ulmin(so->so_snd.sb_cc, win) - off;#if defined(TCP_SACK) && defined(TCP_FACK)	/* 	 * If we're in fast recovery (SEQ_GT(tp->snd_last, tp->snd_una)), and 	 * amount of outstanding data (snd_awnd) is >= snd_cwnd, then	 * do not send data (like zero window conditions)	 */	if (!tp->sack_disable && len && SEQ_GT(tp->snd_last, tp->snd_una) && 	    (tp->snd_awnd >= tp->snd_cwnd)) 		len = 0;#endif /* TCP_FACK */#ifdef TCP_SACK	}#endif	if (len < 0) {		/*		 * If FIN has been sent but not acked,		 * but we haven't been called to retransmit,		 * len will be -1.  Otherwise, window shrank		 * after we sent into it.  If window shrank to 0,		 * cancel pending retransmit and pull snd_nxt		 * back to (closed) window.  We will enter persist		 * state below.  If the window didn't close completely,		 * just wait for an ACK.		 */		len = 0;		if (win == 0) {			tp->t_timer[TCPT_REXMT] = 0;			tp->snd_nxt = tp->snd_una;		}	}	if (len > tp->t_maxseg) {		len = tp->t_maxseg;		sendalot = 1;	}	if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))		flags &= ~TH_FIN;	win = sbspace(&so->so_rcv);	/*	 * Sender silly window avoidance.  If connection is idle	 * and can send all data, a maximum segment,	 * at least a maximum default-size segment do it,	 * or are forced, do it; otherwise don't bother.	 * If peer's buffer is tiny, then send	 * when window is at least half open.	 * If retransmitting (possibly after persist timer forced us	 * to send into a small window), then must resend.	 */	if (len) {		if (len == tp->t_maxseg)			goto send;		if ((idle || tp->t_flags & TF_NODELAY) &&		    len + off >= so->so_snd.sb_cc)			goto send;		if (tp->t_force)			goto send;		if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)			goto send;		if (SEQ_LT(tp->snd_nxt, tp->snd_max))			goto send;#ifdef TCP_SACK		if (sack_rxmit)			goto send;#endif	}	/*	 * Compare available window to amount of window	 * known to peer (as advertised window less	 * next expected input).  If the difference is at least two	 * max size segments, or at least 50% of the maximum possible	 * window, then want to send a window update to peer.	 */	if (win > 0) {		/* 		 * "adv" is the amount we can increase the window,		 * taking into account that we are limited by		 * TCP_MAXWIN << tp->rcv_scale.		 */		long adv = lmin(win, (long)TCP_MAXWIN << tp->rcv_scale) -			(tp->rcv_adv - tp->rcv_nxt);		if (adv >= (long) (2 * tp->t_maxseg))			goto send;		if (2 * adv >= (long) so->so_rcv.sb_hiwat)			goto send;	}	/*	 * Send if we owe peer an ACK.	 */	if (tp->t_flags & TF_ACKNOW)		goto send;	if (flags & (TH_SYN|TH_RST))		goto send;	if (SEQ_GT(tp->snd_up, tp->snd_una))		goto send;	/*	 * If our state indicates that FIN should be sent	 * and we have not yet done so, or we're retransmitting the FIN,	 * then we need to send.	 */	if (flags & TH_FIN &&	    ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))		goto send;#ifdef TCP_SACK	/*	 * In SACK, it is possible for tcp_output to fail to send a segment 	 * after the retransmission timer has been turned off.  Make sure	 * that the retransmission timer is set.	 */	if (SEQ_GT(tp->snd_max, tp->snd_una) &&	    tp->t_timer[TCPT_REXMT] == 0 &&	    tp->t_timer[TCPT_PERSIST] == 0) {		tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;		return (0);	}#endif /* TCP_SACK */	/*	 * TCP window updates are not reliable, rather a polling protocol	 * using ``persist'' packets is used to insure receipt of window	 * updates.  The three ``states'' for the output side are:	 *	idle			not doing retransmits or persists	 *	persisting		to move a small or zero window	 *	(re)transmitting	and thereby not persisting	 *	 * tp->t_timer[TCPT_PERSIST]	 *	is set when we are in persist state.	 * tp->t_force	 *	is set when we are called to send a persist packet.	 * tp->t_timer[TCPT_REXMT]	 *	is set when we are retransmitting	 * The output side is idle when both timers are zero.	 *	 * If send window is too small, there is data to transmit, and no	 * retransmit or persist is pending, then go to persist state.	 * If nothing happens soon, send when timer expires:	 * if window is nonzero, transmit what we can,	 * otherwise force out a byte.	 */	if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 &&	    tp->t_timer[TCPT_PERSIST] == 0) {		tp->t_rxtshift = 0;		tcp_setpersist(tp);	}	/*	 * No reason to send a segment, just return.	 */	return (0);send:	/*	 * Before ESTABLISHED, force sending of initial options	 * unless TCP set not to do any options.	 * NOTE: we assume that the IP/TCP header plus TCP options	 * always fit in a single mbuf, leaving room for a maximum	 * link header, i.e.	 *	max_linkhdr + sizeof(network header) + sizeof(struct tcphdr +	 * 		optlen <= MHLEN	 */	optlen = 0;	switch (tp->pf) {	case 0:	/*default to PF_INET*/#ifdef INET	case PF_INET:		hdrlen = sizeof(struct ip) + sizeof(struct tcphdr);		break;#endif /* INET */#ifdef INET6	case PF_INET6:		hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);		break;#endif /* INET6 */	default:		return (EPFNOSUPPORT);	}	if (flags & TH_SYN) {		tp->snd_nxt = tp->iss;		if ((tp->t_flags & TF_NOOPT) == 0) {			u_int16_t mss;			opt[0] = TCPOPT_MAXSEG;			opt[1] = 4;			mss = htons((u_int16_t) tcp_mss(tp, 0));			bcopy((caddr_t)&mss, (caddr_t)(opt + 2), sizeof(mss));			optlen = 4;#ifdef TCP_SACK			/* 			 * If this is the first SYN of connection (not a SYN 			 * ACK), include SACK_PERMIT_HDR option.  If this is a 			 * SYN ACK, include SACK_PERMIT_HDR option if peer has 			 * already done so.			 */			if (!tp->sack_disable && ((flags & TH_ACK) == 0 ||			    (tp->t_flags & TF_SACK_PERMIT))) {				*((u_int32_t *) (opt + optlen)) =				    htonl(TCPOPT_SACK_PERMIT_HDR);				optlen += 4;			}#endif	 			if ((tp->t_flags & TF_REQ_SCALE) &&			    ((flags & TH_ACK) == 0 ||			    (tp->t_flags & TF_RCVD_SCALE))) {				*((u_int32_t *) (opt + optlen)) = htonl(					TCPOPT_NOP << 24 |					TCPOPT_WINDOW << 16 |					TCPOLEN_WINDOW << 8 |					tp->request_r_scale);				optlen += 4;			}		}	} 	/*	 * Send a timestamp and echo-reply if this is a SYN and our side 	 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side	 * and our peer have sent timestamps in our SYN's.	 */	if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&	     (flags & TH_RST) == 0 &&	    ((flags & (TH_SYN|TH_ACK)) == TH_SYN ||	     (tp->t_flags & TF_RCVD_TSTMP))) {		u_int32_t *lp = (u_int32_t *)(opt + optlen); 		/* Form timestamp option as shown in appendix A of RFC 1323. */		*lp++ = htonl(TCPOPT_TSTAMP_HDR);		*lp++ = htonl(tcp_now);		*lp   = htonl(tp->ts_recent);		optlen += TCPOLEN_TSTAMP_APPA;	}#ifdef TCP_SIGNATURE	if (tp->t_flags & TF_SIGNATURE) {		u_int8_t *bp = (u_int8_t *)(opt + optlen);		/* Send signature option */		*(bp++) = TCPOPT_SIGNATURE;		*(bp++) = TCPOLEN_SIGNATURE;		sigoff = optlen + 2;		{			unsigned int i;			for (i = 0; i < 16; i++)				*(bp++) = 0;		}		optlen += TCPOLEN_SIGNATURE;		/* Pad options list to the next 32 bit boundary and 		 * terminate it.		 */		*bp++ = TCPOPT_NOP;		*bp++ = TCPOPT_EOL;		optlen += 2;	}#endif /* TCP_SIGNATURE */#ifdef TCP_SACK	/*	 * Send SACKs if necessary.  This should be the last option processed.	 * Only as many SACKs are sent as are permitted by the maximum options	 * size.  No more than three SACKs are sent.	 */	if (!tp->sack_disable && tp->t_state == TCPS_ESTABLISHED &&	    (tp->t_flags & (TF_SACK_PERMIT|TF_NOOPT)) == TF_SACK_PERMIT &&	    tp->rcv_numsacks) {		u_int32_t *lp = (u_int32_t *)(opt + optlen);		u_int32_t *olp = lp++;		int count = 0;  /* actual number of SACKs inserted */		int maxsack = (MAX_TCPOPTLEN - (optlen + 4))/TCPOLEN_SACK;		maxsack = min(maxsack, TCP_MAX_SACK);		for (i = 0; (i < tp->rcv_numsacks && count < maxsack); i++) {			struct sackblk sack = tp->sackblks[i];			if (sack.start == 0 && sack.end == 0)				continue;			*lp++ = htonl(sack.start);			*lp++ = htonl(sack.end);			count++;		}		*olp = htonl(TCPOPT_SACK_HDR|(TCPOLEN_SACK*count+2));		optlen += TCPOLEN_SACK*count + 4; /* including leading NOPs */	}#endif /* TCP_SACK */#ifdef DIAGNOSTIC	if (optlen > MAX_TCPOPTLEN)		panic("tcp_output: options too long");#endif /* DIAGNOSTIC */	hdrlen += optlen; 	/*	 * Adjust data length if insertion of options will	 * bump the packet length beyond the t_maxopd length.	 */	if (len > tp->t_maxopd - optlen) {		len = tp->t_maxopd - optlen;		sendalot = 1;		flags &= ~TH_FIN;	 }#ifdef DIAGNOSTIC	if (max_linkhdr + hdrlen > MCLBYTES)		panic("tcphdr too big");#endif	/*	 * Grab a header mbuf, attaching a copy of data to	 * be transmitted, and initialize the header from	 * the template for sends on this connection.	 */	if (len) {		if (tp->t_force && len == 1)			tcpstat.tcps_sndprobe++;		else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {			tcpstat.tcps_sndrexmitpack++;			tcpstat.tcps_sndrexmitbyte += len;		} else {			tcpstat.tcps_sndpack++;			tcpstat.tcps_sndbyte += len;		}#ifdef notyet		if ((m = m_copypack(so->so_snd.sb_mb, off,		    (int)len, max_linkhdr + hdrlen)) == 0) {			error = ENOBUFS;			goto out;		}		/*		 * m_copypack left space for our hdr; use it.		 */		m->m_len += hdrlen;		m->m_data -= hdrlen;#else		MGETHDR(m, M_DONTWAIT, MT_HEADER);		if (m != NULL) {			MCLGET(m, M_DONTWAIT);			if ((m->m_flags & M_EXT) == 0) {				m_freem(m);				m = NULL;			}		}		if (m == NULL) {			error = ENOBUFS;			goto out;		}		m->m_data += max_linkhdr;		m->m_len = hdrlen;		if (len <= MCLBYTES - hdrlen - max_linkhdr) {			m_copydata(so->so_snd.sb_mb, off, (int) len,			    mtod(m, caddr_t) + hdrlen);			m->m_len += len;		} else {			m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len);			if (m->m_next == 0) {				(void) m_free(m);				error = ENOBUFS;				goto out;			}		}#endif		/*		 * If we're sending everything we've got, set PUSH.		 * (This will keep happy those implementations which only		 * give data to the user when a buffer fills or		 * a PUSH comes in.)		 */		if (off + len == so->so_snd.sb_cc)			flags |= TH_PUSH;	} else {		if (tp->t_flags & TF_ACKNOW)			tcpstat.tcps_sndacks++;		else if (flags & (TH_SYN|TH_FIN|TH_RST))			tcpstat.tcps_sndctrl++;		else if (SEQ_GT(tp->snd_up, tp->snd_una))			tcpstat.tcps_sndurg++;		else			tcpstat.tcps_sndwinup++;		MGETHDR(m, M_DONTWAIT, MT_HEADER);		if (m != NULL) {			MCLGET(m, M_DONTWAIT);			if ((m->m_flags & M_EXT) == 0) {				m_freem(m);				m = NULL;			}		}		if (m == NULL) {			error = ENOBUFS;			goto out;		}		m->m_data += max_linkhdr;		m->m_len = hdrlen;	}	m->m_pkthdr.rcvif = (struct ifnet *)0;	if (!tp->t_template)		panic("tcp_output");#ifdef DIAGNOSTIC	if (tp->t_template->m_len != hdrlen - optlen)		panic("tcp_output: template len != hdrlen - optlen");#endif /* DIAGNOSTIC */	bcopy(mtod(tp->t_template, caddr_t), mtod(m, caddr_t),		tp->t_template->m_len);	th = (struct tcphdr *)(mtod(m, caddr_t) + tp->t_template->m_len -		sizeof(struct tcphdr));	/*	 * Fill in fields, remembering maximum advertised	 * window for use in delaying messages about window sizes.	 * If resending a FIN, be sure not to use a new sequence number.	 */	if ((flags & TH_FIN) && (tp->t_flags & TF_SENTFIN) && 	    (tp->snd_nxt == tp->snd_max))		tp->snd_nxt--;	/*	 * If we are doing retransmissions, then snd_nxt will	 * not reflect the first unsent octet.  For ACK only	 * packets, we do not want the sequence number of the	 * retransmitted packet, we want the sequence number	 * of the next unsent octet.  So, if there is no data	 * (and no SYN or FIN), use snd_max instead of snd_nxt	 * when filling in ti_seq.  But if we are in persist	 * state, snd_max might reflect one byte beyond the	 * right edge of the window, so use snd_nxt in that	 * case, since we know we aren't doing a retransmission.	 * (retransmit and persist are mutually exclusive...)	 */	if (len || (flags & (TH_SYN|TH_FIN)) || tp->t_timer[TCPT_PERSIST])		th->th_seq = htonl(tp->snd_nxt);	else		th->th_seq = htonl(tp->snd_max);#ifdef TCP_SACK	if (sack_rxmit) {		/* 		 * If sendalot was turned on (due to option stuffing), turn it 		 * off. Properly set th_seq field.  Advance the ret'x pointer 		 * by len.  		 */		if (sendalot)			sendalot = 0;		th->th_seq = htonl(p->rxmit);		p->rxmit += len;#if defined(TCP_SACK) && defined(TCP_FACK)		tp->retran_data += len;#endif /* TCP_FACK */	}#endif /* TCP_SACK */	th->th_ack = htonl(tp->rcv_nxt);	if (optlen) {		bcopy((caddr_t)opt, (caddr_t)(th + 1), optlen);		th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;	}	th->th_flags = flags;	/*	 * Calculate receive window.  Don't shrink window,	 * but avoid silly window syndrome.	 */	if (win < (long)(so->so_rcv.sb_hiwat / 4) && win < (long)tp->t_maxseg)		win = 0;	if (win > (long)TCP_MAXWIN << tp->rcv_scale)		win = (long)TCP_MAXWIN << tp->rcv_scale;	if (win < (long)(tp->rcv_adv - tp->rcv_nxt))		win = (long)(tp->rcv_adv - tp->rcv_nxt);	if (flags & TH_RST)		win = 0;	th->th_win = htons((u_int16_t) (win>>tp->rcv_scale));	if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {		u_int32_t urp = tp->snd_up - tp->snd_nxt;		if (urp > IP_MAXPACKET)			urp = IP_MAXPACKET;		th->th_urp = htons((u_int16_t)urp);		th->th_flags |= TH_URG;	} else		/*		 * If no urgent pointer to send, then we pull		 * the urgent pointer to the left edge of the send window		 * so that it doesn't drift into the send window on sequence		 * number wraparound.		 */		tp->snd_up = tp->snd_una;		/* drag it along */	/* Put TCP length in pseudo-header */	switch (tp->pf) {	case 0:	/*default to PF_INET*/#ifdef INET	case AF_INET:		if (len + optlen)			mtod(m, struct ipovly *)->ih_len = htons((u_int16_t)(				sizeof (struct tcphdr) + optlen + len));		break;#endif /* INET */#ifdef INET6	case AF_INET6:		break;#endif /* INET6 */	}#ifdef TCP_SIGNATURE	if (tp->t_flags & TF_SIGNATURE) {		MD5_CTX ctx;		union sockaddr_union sa;		struct tdb *tdb;		bzero(&sa, sizeof(union sockaddr_union));		switch (tp->pf) {		case 0:	/*default to PF_INET*/#ifdef INET		case AF_INET:			sa.sa.sa_len = sizeof(struct sockaddr_in);			sa.sa.sa_family = AF_INET;			sa.sin.sin_addr = mtod(m, struct ip *)->ip_dst;			break;#endif /* INET */#ifdef INET6		case AF_INET6:			sa.sa.sa_len = sizeof(struct sockaddr_in6);			sa.sa.sa_family = AF_INET6;			sa.sin6.sin6_addr = mtod(m, struct ip6_hdr *)->ip6_dst;			break;#endif /* INET6 */		}		/* XXX gettdb() should really be called at spltdb().      */		/* XXX this is splsoftnet(), currently they are the same. */		tdb = gettdb(0, &sa, IPPROTO_TCP);		if (tdb == NULL)			return (EPERM);		MD5Init(&ctx);		switch (tp->pf) {		case 0:	/*default to PF_INET*/#ifdef INET		case AF_INET:			{				struct ippseudo ippseudo;				struct ipovly *ipovly;				ipovly = mtod(m, struct ipovly *);				ippseudo.ippseudo_src = ipovly->ih_src;				ippseudo.ippseudo_dst = ipovly->ih_dst;				ippseudo.ippseudo_pad = 0;				ippseudo.ippseudo_p   = IPPROTO_TCP;				ippseudo.ippseudo_len = ipovly->ih_len;				MD5Update(&ctx, (char *)&ippseudo,					sizeof(struct ippseudo));				MD5Update(&ctx, mtod(m, caddr_t) +					sizeof(struct ip),					sizeof(struct tcphdr));			}			break;#endif /* INET */#ifdef INET6		case AF_INET6:			{				static int printed = 0;				if (!printed) {					printf("error: TCP MD5 support for "						"IPv6 not yet implemented.\n");					printed = 1;				}			}			break;#endif /* INET6 */		}		if (len && m_apply(m, hdrlen, len, tcp_signature_apply,				(caddr_t)&ctx))			return (EINVAL);		MD5Update(&ctx, tdb->tdb_amxkey, tdb->tdb_amxkeylen);		MD5Final(mtod(m, caddr_t) + hdrlen - optlen + sigoff, &ctx);	}#endif /* TCP_SIGNATURE */	/*	 * Put TCP length in extended header, and then	 * checksum extended header and data.	 */	switch (tp->pf) {	case 0:	/*default to PF_INET*/#ifdef INET	case AF_INET:		th->th_sum = in_cksum(m, (int)(hdrlen + len));		break;#endif /* INET */#ifdef INET6	case AF_INET6:		m->m_pkthdr.len = hdrlen + len;  		th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr),			hdrlen - sizeof(struct ip6_hdr) + len);		break;#endif /* INET6 */	}	/*	 * In transmit state, time the transmission and arrange for	 * the retransmit.  In persist state, just set snd_max.	 */	if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) {		tcp_seq startseq = tp->snd_nxt;		/*		 * Advance snd_nxt over sequence space of this segment.		 */		if (flags & (TH_SYN|TH_FIN)) {			if (flags & TH_SYN)				tp->snd_nxt++;			if (flags & TH_FIN) {				tp->snd_nxt++;				tp->t_flags |= TF_SENTFIN;			}		}#ifdef TCP_SACK		if (!tp->sack_disable) {			if (sack_rxmit && (p->rxmit != tp->snd_nxt)) {				goto timer;			}		}#endif		tp->snd_nxt += len;		if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {			tp->snd_max = tp->snd_nxt;			/*			 * Time this transmission if not a retransmission and			 * not currently timing anything.			 */			if (tp->t_rtt == 0) {				tp->t_rtt = 1;				tp->t_rtseq = startseq;				tcpstat.tcps_segstimed++;			}		}		/*		 * Set retransmit timer if not currently set,		 * and not doing an ack or a keep-alive probe.		 * Initial value for retransmit timer is smoothed		 * round-trip time + 2 * round-trip time variance.		 * Initialize shift counter which is used for backoff		 * of retransmit time.		 */#ifdef TCP_SACK timer:		if (!tp->sack_disable && sack_rxmit &&		    tp->t_timer[TCPT_REXMT] == 0 &&		    tp->snd_nxt != tp->snd_max) {			tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;			if (tp->t_timer[TCPT_PERSIST]) {				tp->t_timer[TCPT_PERSIST] = 0;				tp->t_rxtshift = 0;			}		}#endif		if (tp->t_timer[TCPT_REXMT] == 0 &&		    tp->snd_nxt != tp->snd_una) {			tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;			if (tp->t_timer[TCPT_PERSIST]) {				tp->t_timer[TCPT_PERSIST] = 0;				tp->t_rxtshift = 0;			}		}	} else		if (SEQ_GT(tp->snd_nxt + len, tp->snd_max))			tp->snd_max = tp->snd_nxt + len;	/*	 * Trace.	 */	if (so->so_options & SO_DEBUG)		tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, caddr_t), 0,			len);	/*	 * Fill in IP length and desired time to live and	 * send to IP level.  There should be a better way	 * to handle ttl and tos; we could keep them in	 * the template, but need a way to checksum without them.	 */	m->m_pkthdr.len = hdrlen + len;	switch (tp->pf) {	case 0:	/*default to PF_INET*/#ifdef INET	case AF_INET:		{			struct ip *ip;			ip = mtod(m, struct ip *);			ip->ip_len = m->m_pkthdr.len;			ip->ip_ttl = tp->t_inpcb->inp_ip.ip_ttl;			ip->ip_tos = tp->t_inpcb->inp_ip.ip_tos;		}		error = ip_output(m, tp->t_inpcb->inp_options,			&tp->t_inpcb->inp_route, so->so_options & SO_DONTROUTE,			0, tp->t_inpcb);		break;#endif /* INET */#ifdef INET6	case AF_INET6:		{			struct ip6_hdr *ipv6;						ipv6 = mtod(m, struct ip6_hdr *);			ipv6->ip6_plen = m->m_pkthdr.len -				sizeof(struct ip6_hdr);			ipv6->ip6_nxt = IPPROTO_TCP;			ipv6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);		}		error = ip6_output(m, tp->t_inpcb->inp_outputopts6,			  &tp->t_inpcb->inp_route6,			  (so->so_options & SO_DONTROUTE), NULL, NULL);		break;#endif /* INET6 */#ifdef TUBA	case AF_ISO:		if (tp->t_tuba_pcb)			error = tuba_output(m, tp);		break;#endif /* TUBA */	}#if defined(TCP_SACK) && defined(TCP_FACK)	/* Update snd_awnd to reflect the new data that was sent.  */	tp->snd_awnd = tcp_seq_subtract(tp->snd_max, tp->snd_fack) +		tp->retran_data;                #endif /* defined(TCP_SACK) && defined(TCP_FACK) */	if (error) {out:		if (error == ENOBUFS) {			tcp_quench(tp->t_inpcb, 0);			return (0);		}		if ((error == EHOSTUNREACH || error == ENETDOWN)		    && TCPS_HAVERCVDSYN(tp->t_state)) {			tp->t_softerror = error;			return (0);		}		return (error);	}	tcpstat.tcps_sndtotal++;	/*	 * Data sent (as far as we can tell).	 * If this advertises a larger window than any other segment,	 * then remember the size of the advertised window.	 * Any pending ACK has now been sent.	 */	if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))		tp->rcv_adv = tp->rcv_nxt + win;	tp->last_ack_sent = tp->rcv_nxt;	tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);#if defined(TCP_SACK)	if (sendalot && --maxburst)#else	if (sendalot)#endif		goto again;	return (0);}