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1.1 root 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.
1.1.1.2 ! root 40: *
! 41: * Please read the file COPYRIGHT for the
1.1 root 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: */
1.1.1.2 ! root 51: const char * const tcpstates[] = {
1.1 root 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:
1.1.1.2 ! root 58: static const u_char tcp_outflags[TCP_NSTATES] = {
1.1 root 59: TH_RST|TH_ACK, 0, TH_SYN, TH_SYN|TH_ACK,
1.1.1.2 ! root 60: TH_ACK, TH_ACK, TH_FIN|TH_ACK, TH_FIN|TH_ACK,
1.1 root 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;
1.1.1.2 ! root 82:
1.1 root 83: DEBUG_CALL("tcp_output");
84: DEBUG_ARG("tp = %lx", (long )tp);
1.1.1.2 ! root 85:
1.1 root 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];
1.1.1.2 ! root 106:
1.1 root 107: DEBUG_MISC((dfd, " --- tcp_output flags = 0x%x\n",flags));
1.1.1.2 ! root 108:
1.1 root 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: }
1.1.1.2 ! root 161:
1.1 root 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) {
1.1.1.2 ! root 203: /*
1.1 root 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: */
1.1.1.2 ! root 266: STAT(tcpstat.tcps_didnuttin++);
! 267:
1.1 root 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: }
1.1.1.2 ! root 305:
1.1 root 306: /*
1.1.1.2 ! root 307: * Send a timestamp and echo-reply if this is a SYN and our side
1.1 root 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;
1.1.1.2 ! root 325:
1.1 root 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)
1.1.1.2 ! root 342: STAT(tcpstat.tcps_sndprobe++);
1.1 root 343: else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
1.1.1.2 ! root 344: STAT(tcpstat.tcps_sndrexmitpack++);
! 345: STAT(tcpstat.tcps_sndrexmitbyte += len);
1.1 root 346: } else {
1.1.1.2 ! root 347: STAT(tcpstat.tcps_sndpack++);
! 348: STAT(tcpstat.tcps_sndbyte += len);
1.1 root 349: }
350:
351: m = m_get();
352: if (m == NULL) {
353: /* error = ENOBUFS; */
354: error = 1;
355: goto out;
356: }
1.1.1.2 ! root 357: m->m_data += IF_MAXLINKHDR;
1.1 root 358: m->m_len = hdrlen;
1.1.1.2 ! root 359:
! 360: /*
1.1 root 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)
1.1.1.2 ! root 385: STAT(tcpstat.tcps_sndacks++);
1.1 root 386: else if (flags & (TH_SYN|TH_FIN|TH_RST))
1.1.1.2 ! root 387: STAT(tcpstat.tcps_sndctrl++);
1.1 root 388: else if (SEQ_GT(tp->snd_up, tp->snd_una))
1.1.1.2 ! root 389: STAT(tcpstat.tcps_sndurg++);
1.1 root 390: else
1.1.1.2 ! root 391: STAT(tcpstat.tcps_sndwinup++);
1.1 root 392:
393: m = m_get();
394: if (m == NULL) {
395: /* error = ENOBUFS; */
396: error = 1;
397: goto out;
398: }
1.1.1.2 ! root 399: m->m_data += IF_MAXLINKHDR;
1.1 root 400: m->m_len = hdrlen;
401: }
402:
403: ti = mtod(m, struct tcpiphdr *);
1.1.1.2 ! root 404:
1.1 root 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: */
1.1.1.2 ! root 412: if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1.1 root 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));
1.1.1.2 ! root 449:
1.1 root 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)));
1.1.1.2 ! root 452: #ifdef notdef
1.1 root 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;
1.1.1.2 ! root 503: STAT(tcpstat.tcps_segstimed++);
1.1 root 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 */
1.1.1.2 ! root 534:
1.1 root 535: {
1.1.1.2 ! root 536:
1.1 root 537: ((struct ip *)ti)->ip_len = m->m_len;
538:
1.1.1.2 ! root 539: ((struct ip *)ti)->ip_ttl = IPDEFTTL;
1.1 root 540: ((struct ip *)ti)->ip_tos = so->so_iptos;
1.1.1.2 ! root 541:
1.1 root 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
1.1.1.2 ! root 550: * error = ip_output(m, (struct mbuf *)0, &tp->t_inpcb->inp_route,
1.1 root 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: }
1.1.1.2 ! root 570: STAT(tcpstat.tcps_sndtotal++);
1.1 root 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: }
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