1 /*

     2  * Copyright (c) 1982, 1986, 1988, 1990, 1993

     3  *	The Regents of the University of California.  All rights reserved.

     4  *

     5  * Redistribution and use in source and binary forms, with or without

     6  * modification, are permitted provided that the following conditions

     7  * are met:

     8  * 1. Redistributions of source code must retain the above copyright

     9  *    notice, this list of conditions and the following disclaimer.

    10  * 2. Redistributions in binary form must reproduce the above copyright

    11  *    notice, this list of conditions and the following disclaimer in the

    12  *    documentation and/or other materials provided with the distribution.

    13  * 3. All advertising materials mentioning features or use of this software

    14  *    must display the following acknowledgement:

    15  *	This product includes software developed by the University of

    16  *	California, Berkeley and its contributors.

    17  * 4. Neither the name of the University nor the names of its contributors

    18  *    may be used to endorse or promote products derived from this software

    19  *    without specific prior written permission.

    20  *

    21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND

    22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

    23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

    24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE

    25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

    26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

    27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

    28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

    29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

    30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

    31  * SUCH DAMAGE.

    32  *

    33  *	@(#)tcp_output.c	8.3 (Berkeley) 12/30/93

    34  * tcp_output.c,v 1.3 1994/09/15 10:36:55 davidg Exp

    35  */

    36 

    37 /*

    38  * Changes and additions relating to SLiRP

    39  * Copyright (c) 1995 Danny Gasparovski.

    40  *

    41  * Please read the file COPYRIGHT for the

    42  * terms and conditions of the copyright.

    43  */

    44 

    45 #include <slirp.h>

    46 

    47 /*

    48  * Since this is only used in "stats socket", we give meaning

    49  * names instead of the REAL names

    50  */

    51 const char * const tcpstates[] = {

    52 /*	"CLOSED",       "LISTEN",       "SYN_SENT",     "SYN_RCVD", */

    53 	"REDIRECT",	"LISTEN",	"SYN_SENT",     "SYN_RCVD",

    54 	"ESTABLISHED",  "CLOSE_WAIT",   "FIN_WAIT_1",   "CLOSING",

    55 	"LAST_ACK",     "FIN_WAIT_2",   "TIME_WAIT",

    56 };

    57 

    58 static const u_char  tcp_outflags[TCP_NSTATES] = {

    59 	TH_RST|TH_ACK, 0,      TH_SYN,        TH_SYN|TH_ACK,

    60 	TH_ACK,        TH_ACK, TH_FIN|TH_ACK, TH_FIN|TH_ACK,

    61 	TH_FIN|TH_ACK, TH_ACK, TH_ACK,

    62 };

    63 

    64 

    65 #define MAX_TCPOPTLEN	32	/* max # bytes that go in options */

    66 

    67 /*

    68  * Tcp output routine: figure out what should be sent and send it.

    69  */

    70 int

    71 tcp_output(tp)

    72 	register struct tcpcb *tp;

    73 {

    74 	register struct socket *so = tp->t_socket;

    75 	register long len, win;

    76 	int off, flags, error;

    77 	register struct mbuf *m;

    78 	register struct tcpiphdr *ti;

    79 	u_char opt[MAX_TCPOPTLEN];

    80 	unsigned optlen, hdrlen;

    81 	int idle, sendalot;

    82 

    83 	DEBUG_CALL("tcp_output");

    84 	DEBUG_ARG("tp = %lx", (long )tp);

    85 

    86 	/*

    87 	 * Determine length of data that should be transmitted,

    88 	 * and flags that will be used.

    89 	 * If there is some data or critical controls (SYN, RST)

    90 	 * to send, then transmit; otherwise, investigate further.

    91 	 */

    92 	idle = (tp->snd_max == tp->snd_una);

    93 	if (idle && tp->t_idle >= tp->t_rxtcur)

    94 		/*

    95 		 * We have been idle for "a while" and no acks are

    96 		 * expected to clock out any data we send --

    97 		 * slow start to get ack "clock" running again.

    98 		 */

    99 		tp->snd_cwnd = tp->t_maxseg;

   100 again:

   101 	sendalot = 0;

   102 	off = tp->snd_nxt - tp->snd_una;

   103 	win = min(tp->snd_wnd, tp->snd_cwnd);

   104 

   105 	flags = tcp_outflags[tp->t_state];

   106 

   107 	DEBUG_MISC((dfd, " --- tcp_output flags = 0x%x\n",flags));

   108 

   109 	/*

   110 	 * If in persist timeout with window of 0, send 1 byte.

   111 	 * Otherwise, if window is small but nonzero

   112 	 * and timer expired, we will send what we can

   113 	 * and go to transmit state.

   114 	 */

   115 	if (tp->t_force) {

   116 		if (win == 0) {

   117 			/*

   118 			 * If we still have some data to send, then

   119 			 * clear the FIN bit.  Usually this would

   120 			 * happen below when it realizes that we

   121 			 * aren't sending all the data.  However,

   122 			 * if we have exactly 1 byte of unset data,

   123 			 * then it won't clear the FIN bit below,

   124 			 * and if we are in persist state, we wind

   125 			 * up sending the packet without recording

   126 			 * that we sent the FIN bit.

   127 			 *

   128 			 * We can't just blindly clear the FIN bit,

   129 			 * because if we don't have any more data

   130 			 * to send then the probe will be the FIN

   131 			 * itself.

   132 			 */

   133 			if (off < so->so_snd.sb_cc)

   134 				flags &= ~TH_FIN;

   135 			win = 1;

   136 		} else {

   137 			tp->t_timer[TCPT_PERSIST] = 0;

   138 			tp->t_rxtshift = 0;

   139 		}

   140 	}

   141 

   142 	len = min(so->so_snd.sb_cc, win) - off;

   143 

   144 	if (len < 0) {

   145 		/*

   146 		 * If FIN has been sent but not acked,

   147 		 * but we haven't been called to retransmit,

   148 		 * len will be -1.  Otherwise, window shrank

   149 		 * after we sent into it.  If window shrank to 0,

   150 		 * cancel pending retransmit and pull snd_nxt

   151 		 * back to (closed) window.  We will enter persist

   152 		 * state below.  If the window didn't close completely,

   153 		 * just wait for an ACK.

   154 		 */

   155 		len = 0;

   156 		if (win == 0) {

   157 			tp->t_timer[TCPT_REXMT] = 0;

   158 			tp->snd_nxt = tp->snd_una;

   159 		}

   160 	}

   161 

   162 	if (len > tp->t_maxseg) {

   163 		len = tp->t_maxseg;

   164 		sendalot = 1;

   165 	}

   166 	if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))

   167 		flags &= ~TH_FIN;

   168 

   169 	win = sbspace(&so->so_rcv);

   170 

   171 	/*

   172 	 * Sender silly window avoidance.  If connection is idle

   173 	 * and can send all data, a maximum segment,

   174 	 * at least a maximum default-size segment do it,

   175 	 * or are forced, do it; otherwise don't bother.

   176 	 * If peer's buffer is tiny, then send

   177 	 * when window is at least half open.

   178 	 * If retransmitting (possibly after persist timer forced us

   179 	 * to send into a small window), then must resend.

   180 	 */

   181 	if (len) {

   182 		if (len == tp->t_maxseg)

   183 			goto send;

   184 		if ((1 || idle || tp->t_flags & TF_NODELAY) &&

   185 		    len + off >= so->so_snd.sb_cc)

   186 			goto send;

   187 		if (tp->t_force)

   188 			goto send;

   189 		if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)

   190 			goto send;

   191 		if (SEQ_LT(tp->snd_nxt, tp->snd_max))

   192 			goto send;

   193 	}

   194 

   195 	/*

   196 	 * Compare available window to amount of window

   197 	 * known to peer (as advertised window less

   198 	 * next expected input).  If the difference is at least two

   199 	 * max size segments, or at least 50% of the maximum possible

   200 	 * window, then want to send a window update to peer.

   201 	 */

   202 	if (win > 0) {

   203 		/*

   204 		 * "adv" is the amount we can increase the window,

   205 		 * taking into account that we are limited by

   206 		 * TCP_MAXWIN << tp->rcv_scale.

   207 		 */

   208 		long adv = min(win, (long)TCP_MAXWIN << tp->rcv_scale) -

   209 			(tp->rcv_adv - tp->rcv_nxt);

   210 

   211 		if (adv >= (long) (2 * tp->t_maxseg))

   212 			goto send;

   213 		if (2 * adv >= (long) so->so_rcv.sb_datalen)

   214 			goto send;

   215 	}

   216 

   217 	/*

   218 	 * Send if we owe peer an ACK.

   219 	 */

   220 	if (tp->t_flags & TF_ACKNOW)

   221 		goto send;

   222 	if (flags & (TH_SYN|TH_RST))

   223 		goto send;

   224 	if (SEQ_GT(tp->snd_up, tp->snd_una))

   225 		goto send;

   226 	/*

   227 	 * If our state indicates that FIN should be sent

   228 	 * and we have not yet done so, or we're retransmitting the FIN,

   229 	 * then we need to send.

   230 	 */

   231 	if (flags & TH_FIN &&

   232 	    ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))

   233 		goto send;

   234 

   235 	/*

   236 	 * TCP window updates are not reliable, rather a polling protocol

   237 	 * using ``persist'' packets is used to insure receipt of window

   238 	 * updates.  The three ``states'' for the output side are:

   239 	 *	idle			not doing retransmits or persists

   240 	 *	persisting		to move a small or zero window

   241 	 *	(re)transmitting	and thereby not persisting

   242 	 *

   243 	 * tp->t_timer[TCPT_PERSIST]

   244 	 *	is set when we are in persist state.

   245 	 * tp->t_force

   246 	 *	is set when we are called to send a persist packet.

   247 	 * tp->t_timer[TCPT_REXMT]

   248 	 *	is set when we are retransmitting

   249 	 * The output side is idle when both timers are zero.

   250 	 *

   251 	 * If send window is too small, there is data to transmit, and no

   252 	 * retransmit or persist is pending, then go to persist state.

   253 	 * If nothing happens soon, send when timer expires:

   254 	 * if window is nonzero, transmit what we can,

   255 	 * otherwise force out a byte.

   256 	 */

   257 	if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 &&

   258 	    tp->t_timer[TCPT_PERSIST] == 0) {

   259 		tp->t_rxtshift = 0;

   260 		tcp_setpersist(tp);

   261 	}

   262 

   263 	/*

   264 	 * No reason to send a segment, just return.

   265 	 */

   266 	STAT(tcpstat.tcps_didnuttin++);

   267 

   268 	return (0);

   269 

   270 send:

   271 	/*

   272 	 * Before ESTABLISHED, force sending of initial options

   273 	 * unless TCP set not to do any options.

   274 	 * NOTE: we assume that the IP/TCP header plus TCP options

   275 	 * always fit in a single mbuf, leaving room for a maximum

   276 	 * link header, i.e.

   277 	 *	max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MHLEN

   278 	 */

   279 	optlen = 0;

   280 	hdrlen = sizeof (struct tcpiphdr);

   281 	if (flags & TH_SYN) {

   282 		tp->snd_nxt = tp->iss;

   283 		if ((tp->t_flags & TF_NOOPT) == 0) {

   284 			u_int16_t mss;

   285 

   286 			opt[0] = TCPOPT_MAXSEG;

   287 			opt[1] = 4;

   288 			mss = htons((u_int16_t) tcp_mss(tp, 0));

   289 			memcpy((caddr_t)(opt + 2), (caddr_t)&mss, sizeof(mss));

   290 			optlen = 4;

   291 

   292 /*			if ((tp->t_flags & TF_REQ_SCALE) &&

   293  *			    ((flags & TH_ACK) == 0 ||

   294  *			    (tp->t_flags & TF_RCVD_SCALE))) {

   295  *				*((u_int32_t *) (opt + optlen)) = htonl(

   296  *					TCPOPT_NOP << 24 |

   297  *					TCPOPT_WINDOW << 16 |

   298  *					TCPOLEN_WINDOW << 8 |

   299  *					tp->request_r_scale);

   300  *				optlen += 4;

   301  *			}

   302  */

   303 		}

   304  	}

   305 

   306  	/*

   307 	 * Send a timestamp and echo-reply if this is a SYN and our side

   308 	 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side

   309 	 * and our peer have sent timestamps in our SYN's.

   310  	 */

   311 /* 	if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&

   312  *	     (flags & TH_RST) == 0 &&

   313  *	    ((flags & (TH_SYN|TH_ACK)) == TH_SYN ||

   314  *	     (tp->t_flags & TF_RCVD_TSTMP))) {

   315  *		u_int32_t *lp = (u_int32_t *)(opt + optlen);

   316  *

   317  *		/ * Form timestamp option as shown in appendix A of RFC 1323. *  /

   318  *		*lp++ = htonl(TCPOPT_TSTAMP_HDR);

   319  *		*lp++ = htonl(tcp_now);

   320  *		*lp   = htonl(tp->ts_recent);

   321  *		optlen += TCPOLEN_TSTAMP_APPA;

   322  *	}

   323  */

   324  	hdrlen += optlen;

   325 

   326 	/*

   327 	 * Adjust data length if insertion of options will

   328 	 * bump the packet length beyond the t_maxseg length.

   329 	 */

   330 	 if (len > tp->t_maxseg - optlen) {

   331 		len = tp->t_maxseg - optlen;

   332 		sendalot = 1;

   333 	 }

   334 

   335 	/*

   336 	 * Grab a header mbuf, attaching a copy of data to

   337 	 * be transmitted, and initialize the header from

   338 	 * the template for sends on this connection.

   339 	 */

   340 	if (len) {

   341 		if (tp->t_force && len == 1)

   342 			STAT(tcpstat.tcps_sndprobe++);

   343 		else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {

   344 			STAT(tcpstat.tcps_sndrexmitpack++);

   345 			STAT(tcpstat.tcps_sndrexmitbyte += len);

   346 		} else {

   347 			STAT(tcpstat.tcps_sndpack++);

   348 			STAT(tcpstat.tcps_sndbyte += len);

   349 		}

   350 

   351 		m = m_get();

   352 		if (m == NULL) {

   353 /*			error = ENOBUFS; */

   354 			error = 1;

   355 			goto out;

   356 		}

   357 		m->m_data += IF_MAXLINKHDR;

   358 		m->m_len = hdrlen;

   359 

   360 		/*

   361 		 * This will always succeed, since we make sure our mbufs

   362 		 * are big enough to hold one MSS packet + header + ... etc.

   363 		 */

   364 /*		if (len <= MHLEN - hdrlen - max_linkhdr) { */

   365 

   366 			sbcopy(&so->so_snd, off, (int) len, mtod(m, caddr_t) + hdrlen);

   367 			m->m_len += len;

   368 

   369 /*		} else {

   370  *			m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len);

   371  *			if (m->m_next == 0)

   372  *				len = 0;

   373  *		}

   374  */

   375 		/*

   376 		 * If we're sending everything we've got, set PUSH.

   377 		 * (This will keep happy those implementations which only

   378 		 * give data to the user when a buffer fills or

   379 		 * a PUSH comes in.)

   380 		 */

   381 		if (off + len == so->so_snd.sb_cc)

   382 			flags |= TH_PUSH;

   383 	} else {

   384 		if (tp->t_flags & TF_ACKNOW)

   385 			STAT(tcpstat.tcps_sndacks++);

   386 		else if (flags & (TH_SYN|TH_FIN|TH_RST))

   387 			STAT(tcpstat.tcps_sndctrl++);

   388 		else if (SEQ_GT(tp->snd_up, tp->snd_una))

   389 			STAT(tcpstat.tcps_sndurg++);

   390 		else

   391 			STAT(tcpstat.tcps_sndwinup++);

   392 

   393 		m = m_get();

   394 		if (m == NULL) {

   395 /*			error = ENOBUFS; */

   396 			error = 1;

   397 			goto out;

   398 		}

   399 		m->m_data += IF_MAXLINKHDR;

   400 		m->m_len = hdrlen;

   401 	}

   402 

   403 	ti = mtod(m, struct tcpiphdr *);

   404 

   405 	memcpy((caddr_t)ti, &tp->t_template, sizeof (struct tcpiphdr));

   406 

   407 	/*

   408 	 * Fill in fields, remembering maximum advertised

   409 	 * window for use in delaying messages about window sizes.

   410 	 * If resending a FIN, be sure not to use a new sequence number.

   411 	 */

   412 	if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&

   413 	    tp->snd_nxt == tp->snd_max)

   414 		tp->snd_nxt--;

   415 	/*

   416 	 * If we are doing retransmissions, then snd_nxt will

   417 	 * not reflect the first unsent octet.  For ACK only

   418 	 * packets, we do not want the sequence number of the

   419 	 * retransmitted packet, we want the sequence number

   420 	 * of the next unsent octet.  So, if there is no data

   421 	 * (and no SYN or FIN), use snd_max instead of snd_nxt

   422 	 * when filling in ti_seq.  But if we are in persist

   423 	 * state, snd_max might reflect one byte beyond the

   424 	 * right edge of the window, so use snd_nxt in that

   425 	 * case, since we know we aren't doing a retransmission.

   426 	 * (retransmit and persist are mutually exclusive...)

   427 	 */

   428 	if (len || (flags & (TH_SYN|TH_FIN)) || tp->t_timer[TCPT_PERSIST])

   429 		ti->ti_seq = htonl(tp->snd_nxt);

   430 	else

   431 		ti->ti_seq = htonl(tp->snd_max);

   432 	ti->ti_ack = htonl(tp->rcv_nxt);

   433 	if (optlen) {

   434 		memcpy((caddr_t)(ti + 1), (caddr_t)opt, optlen);

   435 		ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;

   436 	}

   437 	ti->ti_flags = flags;

   438 	/*

   439 	 * Calculate receive window.  Don't shrink window,

   440 	 * but avoid silly window syndrome.

   441 	 */

   442 	if (win < (long)(so->so_rcv.sb_datalen / 4) && win < (long)tp->t_maxseg)

   443 		win = 0;

   444 	if (win > (long)TCP_MAXWIN << tp->rcv_scale)

   445 		win = (long)TCP_MAXWIN << tp->rcv_scale;

   446 	if (win < (long)(tp->rcv_adv - tp->rcv_nxt))

   447 		win = (long)(tp->rcv_adv - tp->rcv_nxt);

   448 	ti->ti_win = htons((u_int16_t) (win>>tp->rcv_scale));

   449 

   450 	if (SEQ_GT(tp->snd_up, tp->snd_una)) {

   451 		ti->ti_urp = htons((u_int16_t)(tp->snd_up - ntohl(ti->ti_seq)));

   452 #ifdef notdef

   453 	if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {

   454 		ti->ti_urp = htons((u_int16_t)(tp->snd_up - tp->snd_nxt));

   455 #endif

   456 		ti->ti_flags |= TH_URG;

   457 	} else

   458 		/*

   459 		 * If no urgent pointer to send, then we pull

   460 		 * the urgent pointer to the left edge of the send window

   461 		 * so that it doesn't drift into the send window on sequence

   462 		 * number wraparound.

   463 		 */

   464 		tp->snd_up = tp->snd_una;		/* drag it along */

   465 

   466 	/*

   467 	 * Put TCP length in extended header, and then

   468 	 * checksum extended header and data.

   469 	 */

   470 	if (len + optlen)

   471 		ti->ti_len = htons((u_int16_t)(sizeof (struct tcphdr) +

   472 		    optlen + len));

   473 	ti->ti_sum = cksum(m, (int)(hdrlen + len));

   474 

   475 	/*

   476 	 * In transmit state, time the transmission and arrange for

   477 	 * the retransmit.  In persist state, just set snd_max.

   478 	 */

   479 	if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) {

   480 		tcp_seq startseq = tp->snd_nxt;

   481 

   482 		/*

   483 		 * Advance snd_nxt over sequence space of this segment.

   484 		 */

   485 		if (flags & (TH_SYN|TH_FIN)) {

   486 			if (flags & TH_SYN)

   487 				tp->snd_nxt++;

   488 			if (flags & TH_FIN) {

   489 				tp->snd_nxt++;

   490 				tp->t_flags |= TF_SENTFIN;

   491 			}

   492 		}

   493 		tp->snd_nxt += len;

   494 		if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {

   495 			tp->snd_max = tp->snd_nxt;

   496 			/*

   497 			 * Time this transmission if not a retransmission and

   498 			 * not currently timing anything.

   499 			 */

   500 			if (tp->t_rtt == 0) {

   501 				tp->t_rtt = 1;

   502 				tp->t_rtseq = startseq;

   503 				STAT(tcpstat.tcps_segstimed++);

   504 			}

   505 		}

   506 

   507 		/*

   508 		 * Set retransmit timer if not currently set,

   509 		 * and not doing an ack or a keep-alive probe.

   510 		 * Initial value for retransmit timer is smoothed

   511 		 * round-trip time + 2 * round-trip time variance.

   512 		 * Initialize shift counter which is used for backoff

   513 		 * of retransmit time.

   514 		 */

   515 		if (tp->t_timer[TCPT_REXMT] == 0 &&

   516 		    tp->snd_nxt != tp->snd_una) {

   517 			tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;

   518 			if (tp->t_timer[TCPT_PERSIST]) {

   519 				tp->t_timer[TCPT_PERSIST] = 0;

   520 				tp->t_rxtshift = 0;

   521 			}

   522 		}

   523 	} else

   524 		if (SEQ_GT(tp->snd_nxt + len, tp->snd_max))

   525 			tp->snd_max = tp->snd_nxt + len;

   526 

   527 	/*

   528 	 * Fill in IP length and desired time to live and

   529 	 * send to IP level.  There should be a better way

   530 	 * to handle ttl and tos; we could keep them in

   531 	 * the template, but need a way to checksum without them.

   532 	 */

   533 	m->m_len = hdrlen + len; /* XXX Needed? m_len should be correct */

   534 

   535     {

   536 

   537 	((struct ip *)ti)->ip_len = m->m_len;

   538 

   539 	((struct ip *)ti)->ip_ttl = IPDEFTTL;

   540 	((struct ip *)ti)->ip_tos = so->so_iptos;

   541 

   542 /* #if BSD >= 43 */

   543 	/* Don't do IP options... */

   544 /*	error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,

   545  *	    so->so_options & SO_DONTROUTE, 0);

   546  */

   547 	error = ip_output(so, m);

   548 

   549 /* #else

   550  *	error = ip_output(m, (struct mbuf *)0, &tp->t_inpcb->inp_route,

   551  *	    so->so_options & SO_DONTROUTE);

   552  * #endif

   553  */

   554     }

   555 	if (error) {

   556 out:

   557 /*		if (error == ENOBUFS) {

   558  *			tcp_quench(tp->t_inpcb, 0);

   559  *			return (0);

   560  *		}

   561  */

   562 /*		if ((error == EHOSTUNREACH || error == ENETDOWN)

   563  *		    && TCPS_HAVERCVDSYN(tp->t_state)) {

   564  *			tp->t_softerror = error;

   565  *			return (0);

   566  *		}

   567  */

   568 		return (error);

   569 	}

   570 	STAT(tcpstat.tcps_sndtotal++);

   571 

   572 	/*

   573 	 * Data sent (as far as we can tell).

   574 	 * If this advertises a larger window than any other segment,

   575 	 * then remember the size of the advertised window.

   576 	 * Any pending ACK has now been sent.

   577 	 */

   578 	if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))

   579 		tp->rcv_adv = tp->rcv_nxt + win;

   580 	tp->last_ack_sent = tp->rcv_nxt;

   581 	tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);

   582 	if (sendalot)

   583 		goto again;

   584 

   585 	return (0);

   586 }

   587 

   588 void

   589 tcp_setpersist(tp)

   590 	register struct tcpcb *tp;

   591 {

   592     int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;

   593 

   594 /*	if (tp->t_timer[TCPT_REXMT])

   595  *		panic("tcp_output REXMT");

   596  */

   597 	/*

   598 	 * Start/restart persistence timer.

   599 	 */

   600 	TCPT_RANGESET(tp->t_timer[TCPT_PERSIST],

   601 	    t * tcp_backoff[tp->t_rxtshift],

   602 	    TCPTV_PERSMIN, TCPTV_PERSMAX);

   603 	if (tp->t_rxtshift < TCP_MAXRXTSHIFT)

   604 		tp->t_rxtshift++;

   605 }