2 * Copyright (c) 1982, 1986, 1988, 1990, 1993
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6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
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14 * may be used to endorse or promote products derived from this software
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19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * @(#)tcp_output.c 8.3 (Berkeley) 12/30/93
30 * tcp_output.c,v 1.3 1994/09/15 10:36:55 davidg Exp
34 * Changes and additions relating to SLiRP
35 * Copyright (c) 1995 Danny Gasparovski.
37 * Please read the file COPYRIGHT for the
38 * terms and conditions of the copyright.
43 static const u_char tcp_outflags
[TCP_NSTATES
] = {
44 TH_RST
|TH_ACK
, 0, TH_SYN
, TH_SYN
|TH_ACK
,
45 TH_ACK
, TH_ACK
, TH_FIN
|TH_ACK
, TH_FIN
|TH_ACK
,
46 TH_FIN
|TH_ACK
, TH_ACK
, TH_ACK
,
50 #define MAX_TCPOPTLEN 32 /* max # bytes that go in options */
53 * Tcp output routine: figure out what should be sent and send it.
56 tcp_output(struct tcpcb
*tp
)
58 register struct socket
*so
= tp
->t_socket
;
59 register long len
, win
;
60 int off
, flags
, error
;
61 register struct mbuf
*m
;
62 register struct tcpiphdr
*ti
;
63 u_char opt
[MAX_TCPOPTLEN
];
64 unsigned optlen
, hdrlen
;
67 DEBUG_CALL("tcp_output");
68 DEBUG_ARG("tp = %lx", (long )tp
);
71 * Determine length of data that should be transmitted,
72 * and flags that will be used.
73 * If there is some data or critical controls (SYN, RST)
74 * to send, then transmit; otherwise, investigate further.
76 idle
= (tp
->snd_max
== tp
->snd_una
);
77 if (idle
&& tp
->t_idle
>= tp
->t_rxtcur
)
79 * We have been idle for "a while" and no acks are
80 * expected to clock out any data we send --
81 * slow start to get ack "clock" running again.
83 tp
->snd_cwnd
= tp
->t_maxseg
;
86 off
= tp
->snd_nxt
- tp
->snd_una
;
87 win
= min(tp
->snd_wnd
, tp
->snd_cwnd
);
89 flags
= tcp_outflags
[tp
->t_state
];
91 DEBUG_MISC((dfd
, " --- tcp_output flags = 0x%x\n",flags
));
94 * If in persist timeout with window of 0, send 1 byte.
95 * Otherwise, if window is small but nonzero
96 * and timer expired, we will send what we can
97 * and go to transmit state.
102 * If we still have some data to send, then
103 * clear the FIN bit. Usually this would
104 * happen below when it realizes that we
105 * aren't sending all the data. However,
106 * if we have exactly 1 byte of unset data,
107 * then it won't clear the FIN bit below,
108 * and if we are in persist state, we wind
109 * up sending the packet without recording
110 * that we sent the FIN bit.
112 * We can't just blindly clear the FIN bit,
113 * because if we don't have any more data
114 * to send then the probe will be the FIN
117 if (off
< so
->so_snd
.sb_cc
)
121 tp
->t_timer
[TCPT_PERSIST
] = 0;
126 len
= min(so
->so_snd
.sb_cc
, win
) - off
;
130 * If FIN has been sent but not acked,
131 * but we haven't been called to retransmit,
132 * len will be -1. Otherwise, window shrank
133 * after we sent into it. If window shrank to 0,
134 * cancel pending retransmit and pull snd_nxt
135 * back to (closed) window. We will enter persist
136 * state below. If the window didn't close completely,
137 * just wait for an ACK.
141 tp
->t_timer
[TCPT_REXMT
] = 0;
142 tp
->snd_nxt
= tp
->snd_una
;
146 if (len
> tp
->t_maxseg
) {
150 if (SEQ_LT(tp
->snd_nxt
+ len
, tp
->snd_una
+ so
->so_snd
.sb_cc
))
153 win
= sbspace(&so
->so_rcv
);
156 * Sender silly window avoidance. If connection is idle
157 * and can send all data, a maximum segment,
158 * at least a maximum default-size segment do it,
159 * or are forced, do it; otherwise don't bother.
160 * If peer's buffer is tiny, then send
161 * when window is at least half open.
162 * If retransmitting (possibly after persist timer forced us
163 * to send into a small window), then must resend.
166 if (len
== tp
->t_maxseg
)
168 if ((1 || idle
|| tp
->t_flags
& TF_NODELAY
) &&
169 len
+ off
>= so
->so_snd
.sb_cc
)
173 if (len
>= tp
->max_sndwnd
/ 2 && tp
->max_sndwnd
> 0)
175 if (SEQ_LT(tp
->snd_nxt
, tp
->snd_max
))
180 * Compare available window to amount of window
181 * known to peer (as advertised window less
182 * next expected input). If the difference is at least two
183 * max size segments, or at least 50% of the maximum possible
184 * window, then want to send a window update to peer.
188 * "adv" is the amount we can increase the window,
189 * taking into account that we are limited by
190 * TCP_MAXWIN << tp->rcv_scale.
192 long adv
= min(win
, (long)TCP_MAXWIN
<< tp
->rcv_scale
) -
193 (tp
->rcv_adv
- tp
->rcv_nxt
);
195 if (adv
>= (long) (2 * tp
->t_maxseg
))
197 if (2 * adv
>= (long) so
->so_rcv
.sb_datalen
)
202 * Send if we owe peer an ACK.
204 if (tp
->t_flags
& TF_ACKNOW
)
206 if (flags
& (TH_SYN
|TH_RST
))
208 if (SEQ_GT(tp
->snd_up
, tp
->snd_una
))
211 * If our state indicates that FIN should be sent
212 * and we have not yet done so, or we're retransmitting the FIN,
213 * then we need to send.
215 if (flags
& TH_FIN
&&
216 ((tp
->t_flags
& TF_SENTFIN
) == 0 || tp
->snd_nxt
== tp
->snd_una
))
220 * TCP window updates are not reliable, rather a polling protocol
221 * using ``persist'' packets is used to insure receipt of window
222 * updates. The three ``states'' for the output side are:
223 * idle not doing retransmits or persists
224 * persisting to move a small or zero window
225 * (re)transmitting and thereby not persisting
227 * tp->t_timer[TCPT_PERSIST]
228 * is set when we are in persist state.
230 * is set when we are called to send a persist packet.
231 * tp->t_timer[TCPT_REXMT]
232 * is set when we are retransmitting
233 * The output side is idle when both timers are zero.
235 * If send window is too small, there is data to transmit, and no
236 * retransmit or persist is pending, then go to persist state.
237 * If nothing happens soon, send when timer expires:
238 * if window is nonzero, transmit what we can,
239 * otherwise force out a byte.
241 if (so
->so_snd
.sb_cc
&& tp
->t_timer
[TCPT_REXMT
] == 0 &&
242 tp
->t_timer
[TCPT_PERSIST
] == 0) {
248 * No reason to send a segment, just return.
250 STAT(tcpstat
.tcps_didnuttin
++);
256 * Before ESTABLISHED, force sending of initial options
257 * unless TCP set not to do any options.
258 * NOTE: we assume that the IP/TCP header plus TCP options
259 * always fit in a single mbuf, leaving room for a maximum
261 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MHLEN
264 hdrlen
= sizeof (struct tcpiphdr
);
265 if (flags
& TH_SYN
) {
266 tp
->snd_nxt
= tp
->iss
;
267 if ((tp
->t_flags
& TF_NOOPT
) == 0) {
270 opt
[0] = TCPOPT_MAXSEG
;
272 mss
= htons((u_int16_t
) tcp_mss(tp
, 0));
273 memcpy((caddr_t
)(opt
+ 2), (caddr_t
)&mss
, sizeof(mss
));
276 /* if ((tp->t_flags & TF_REQ_SCALE) &&
277 * ((flags & TH_ACK) == 0 ||
278 * (tp->t_flags & TF_RCVD_SCALE))) {
279 * *((u_int32_t *) (opt + optlen)) = htonl(
281 * TCPOPT_WINDOW << 16 |
282 * TCPOLEN_WINDOW << 8 |
283 * tp->request_r_scale);
291 * Send a timestamp and echo-reply if this is a SYN and our side
292 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side
293 * and our peer have sent timestamps in our SYN's.
295 /* if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
296 * (flags & TH_RST) == 0 &&
297 * ((flags & (TH_SYN|TH_ACK)) == TH_SYN ||
298 * (tp->t_flags & TF_RCVD_TSTMP))) {
299 * u_int32_t *lp = (u_int32_t *)(opt + optlen);
301 * / * Form timestamp option as shown in appendix A of RFC 1323. * /
302 * *lp++ = htonl(TCPOPT_TSTAMP_HDR);
303 * *lp++ = htonl(tcp_now);
304 * *lp = htonl(tp->ts_recent);
305 * optlen += TCPOLEN_TSTAMP_APPA;
311 * Adjust data length if insertion of options will
312 * bump the packet length beyond the t_maxseg length.
314 if (len
> tp
->t_maxseg
- optlen
) {
315 len
= tp
->t_maxseg
- optlen
;
320 * Grab a header mbuf, attaching a copy of data to
321 * be transmitted, and initialize the header from
322 * the template for sends on this connection.
325 if (tp
->t_force
&& len
== 1)
326 STAT(tcpstat
.tcps_sndprobe
++);
327 else if (SEQ_LT(tp
->snd_nxt
, tp
->snd_max
)) {
328 STAT(tcpstat
.tcps_sndrexmitpack
++);
329 STAT(tcpstat
.tcps_sndrexmitbyte
+= len
);
331 STAT(tcpstat
.tcps_sndpack
++);
332 STAT(tcpstat
.tcps_sndbyte
+= len
);
337 /* error = ENOBUFS; */
341 m
->m_data
+= IF_MAXLINKHDR
;
345 * This will always succeed, since we make sure our mbufs
346 * are big enough to hold one MSS packet + header + ... etc.
348 /* if (len <= MHLEN - hdrlen - max_linkhdr) { */
350 sbcopy(&so
->so_snd
, off
, (int) len
, mtod(m
, caddr_t
) + hdrlen
);
354 * m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len);
355 * if (m->m_next == 0)
360 * If we're sending everything we've got, set PUSH.
361 * (This will keep happy those implementations which only
362 * give data to the user when a buffer fills or
365 if (off
+ len
== so
->so_snd
.sb_cc
)
368 if (tp
->t_flags
& TF_ACKNOW
)
369 STAT(tcpstat
.tcps_sndacks
++);
370 else if (flags
& (TH_SYN
|TH_FIN
|TH_RST
))
371 STAT(tcpstat
.tcps_sndctrl
++);
372 else if (SEQ_GT(tp
->snd_up
, tp
->snd_una
))
373 STAT(tcpstat
.tcps_sndurg
++);
375 STAT(tcpstat
.tcps_sndwinup
++);
379 /* error = ENOBUFS; */
383 m
->m_data
+= IF_MAXLINKHDR
;
387 ti
= mtod(m
, struct tcpiphdr
*);
389 memcpy((caddr_t
)ti
, &tp
->t_template
, sizeof (struct tcpiphdr
));
392 * Fill in fields, remembering maximum advertised
393 * window for use in delaying messages about window sizes.
394 * If resending a FIN, be sure not to use a new sequence number.
396 if (flags
& TH_FIN
&& tp
->t_flags
& TF_SENTFIN
&&
397 tp
->snd_nxt
== tp
->snd_max
)
400 * If we are doing retransmissions, then snd_nxt will
401 * not reflect the first unsent octet. For ACK only
402 * packets, we do not want the sequence number of the
403 * retransmitted packet, we want the sequence number
404 * of the next unsent octet. So, if there is no data
405 * (and no SYN or FIN), use snd_max instead of snd_nxt
406 * when filling in ti_seq. But if we are in persist
407 * state, snd_max might reflect one byte beyond the
408 * right edge of the window, so use snd_nxt in that
409 * case, since we know we aren't doing a retransmission.
410 * (retransmit and persist are mutually exclusive...)
412 if (len
|| (flags
& (TH_SYN
|TH_FIN
)) || tp
->t_timer
[TCPT_PERSIST
])
413 ti
->ti_seq
= htonl(tp
->snd_nxt
);
415 ti
->ti_seq
= htonl(tp
->snd_max
);
416 ti
->ti_ack
= htonl(tp
->rcv_nxt
);
418 memcpy((caddr_t
)(ti
+ 1), (caddr_t
)opt
, optlen
);
419 ti
->ti_off
= (sizeof (struct tcphdr
) + optlen
) >> 2;
421 ti
->ti_flags
= flags
;
423 * Calculate receive window. Don't shrink window,
424 * but avoid silly window syndrome.
426 if (win
< (long)(so
->so_rcv
.sb_datalen
/ 4) && win
< (long)tp
->t_maxseg
)
428 if (win
> (long)TCP_MAXWIN
<< tp
->rcv_scale
)
429 win
= (long)TCP_MAXWIN
<< tp
->rcv_scale
;
430 if (win
< (long)(tp
->rcv_adv
- tp
->rcv_nxt
))
431 win
= (long)(tp
->rcv_adv
- tp
->rcv_nxt
);
432 ti
->ti_win
= htons((u_int16_t
) (win
>>tp
->rcv_scale
));
434 if (SEQ_GT(tp
->snd_up
, tp
->snd_una
)) {
435 ti
->ti_urp
= htons((u_int16_t
)(tp
->snd_up
- ntohl(ti
->ti_seq
)));
437 if (SEQ_GT(tp
->snd_up
, tp
->snd_nxt
)) {
438 ti
->ti_urp
= htons((u_int16_t
)(tp
->snd_up
- tp
->snd_nxt
));
440 ti
->ti_flags
|= TH_URG
;
443 * If no urgent pointer to send, then we pull
444 * the urgent pointer to the left edge of the send window
445 * so that it doesn't drift into the send window on sequence
448 tp
->snd_up
= tp
->snd_una
; /* drag it along */
451 * Put TCP length in extended header, and then
452 * checksum extended header and data.
455 ti
->ti_len
= htons((u_int16_t
)(sizeof (struct tcphdr
) +
457 ti
->ti_sum
= cksum(m
, (int)(hdrlen
+ len
));
460 * In transmit state, time the transmission and arrange for
461 * the retransmit. In persist state, just set snd_max.
463 if (tp
->t_force
== 0 || tp
->t_timer
[TCPT_PERSIST
] == 0) {
464 tcp_seq startseq
= tp
->snd_nxt
;
467 * Advance snd_nxt over sequence space of this segment.
469 if (flags
& (TH_SYN
|TH_FIN
)) {
472 if (flags
& TH_FIN
) {
474 tp
->t_flags
|= TF_SENTFIN
;
478 if (SEQ_GT(tp
->snd_nxt
, tp
->snd_max
)) {
479 tp
->snd_max
= tp
->snd_nxt
;
481 * Time this transmission if not a retransmission and
482 * not currently timing anything.
484 if (tp
->t_rtt
== 0) {
486 tp
->t_rtseq
= startseq
;
487 STAT(tcpstat
.tcps_segstimed
++);
492 * Set retransmit timer if not currently set,
493 * and not doing an ack or a keep-alive probe.
494 * Initial value for retransmit timer is smoothed
495 * round-trip time + 2 * round-trip time variance.
496 * Initialize shift counter which is used for backoff
497 * of retransmit time.
499 if (tp
->t_timer
[TCPT_REXMT
] == 0 &&
500 tp
->snd_nxt
!= tp
->snd_una
) {
501 tp
->t_timer
[TCPT_REXMT
] = tp
->t_rxtcur
;
502 if (tp
->t_timer
[TCPT_PERSIST
]) {
503 tp
->t_timer
[TCPT_PERSIST
] = 0;
508 if (SEQ_GT(tp
->snd_nxt
+ len
, tp
->snd_max
))
509 tp
->snd_max
= tp
->snd_nxt
+ len
;
512 * Fill in IP length and desired time to live and
513 * send to IP level. There should be a better way
514 * to handle ttl and tos; we could keep them in
515 * the template, but need a way to checksum without them.
517 m
->m_len
= hdrlen
+ len
; /* XXX Needed? m_len should be correct */
521 ((struct ip
*)ti
)->ip_len
= m
->m_len
;
523 ((struct ip
*)ti
)->ip_ttl
= IPDEFTTL
;
524 ((struct ip
*)ti
)->ip_tos
= so
->so_iptos
;
527 /* Don't do IP options... */
528 /* error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
529 * so->so_options & SO_DONTROUTE, 0);
531 error
= ip_output(so
, m
);
534 * error = ip_output(m, (struct mbuf *)0, &tp->t_inpcb->inp_route,
535 * so->so_options & SO_DONTROUTE);
541 /* if (error == ENOBUFS) {
542 * tcp_quench(tp->t_inpcb, 0);
546 /* if ((error == EHOSTUNREACH || error == ENETDOWN)
547 * && TCPS_HAVERCVDSYN(tp->t_state)) {
548 * tp->t_softerror = error;
554 STAT(tcpstat
.tcps_sndtotal
++);
557 * Data sent (as far as we can tell).
558 * If this advertises a larger window than any other segment,
559 * then remember the size of the advertised window.
560 * Any pending ACK has now been sent.
562 if (win
> 0 && SEQ_GT(tp
->rcv_nxt
+win
, tp
->rcv_adv
))
563 tp
->rcv_adv
= tp
->rcv_nxt
+ win
;
564 tp
->last_ack_sent
= tp
->rcv_nxt
;
565 tp
->t_flags
&= ~(TF_ACKNOW
|TF_DELACK
);
573 tcp_setpersist(struct tcpcb
*tp
)
575 int t
= ((tp
->t_srtt
>> 2) + tp
->t_rttvar
) >> 1;
577 /* if (tp->t_timer[TCPT_REXMT])
578 * panic("tcp_output REXMT");
581 * Start/restart persistence timer.
583 TCPT_RANGESET(tp
->t_timer
[TCPT_PERSIST
],
584 t
* tcp_backoff
[tp
->t_rxtshift
],
585 TCPTV_PERSMIN
, TCPTV_PERSMAX
);
586 if (tp
->t_rxtshift
< TCP_MAXRXTSHIFT
)