2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994
3 * The Regents of the University of California. All rights reserved.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
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. Neither the name of the University nor the names of its contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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_input.c 8.5 (Berkeley) 4/10/94
30 * tcp_input.c,v 1.10 1994/10/13 18:36:32 wollman 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.
41 #include "qemu/osdep.h"
45 #define TCPREXMTTHRESH 3
47 #define TCP_PAWS_IDLE (24 * 24 * 60 * 60 * PR_SLOWHZ)
49 /* for modulo comparisons of timestamps */
50 #define TSTMP_LT(a,b) ((int)((a)-(b)) < 0)
51 #define TSTMP_GEQ(a,b) ((int)((a)-(b)) >= 0)
54 * Insert segment ti into reassembly queue of tcp with
55 * control block tp. Return TH_FIN if reassembly now includes
56 * a segment with FIN. The macro form does the common case inline
57 * (segment is the next to be received on an established connection,
58 * and the queue is empty), avoiding linkage into and removal
59 * from the queue and repetition of various conversions.
60 * Set DELACK for segments received in order, but ack immediately
61 * when segments are out of order (so fast retransmit can work).
64 #define TCP_REASS(tp, ti, m, so, flags) {\
65 if ((ti)->ti_seq == (tp)->rcv_nxt && \
66 tcpfrag_list_empty(tp) && \
67 (tp)->t_state == TCPS_ESTABLISHED) {\
68 if (ti->ti_flags & TH_PUSH) \
69 tp->t_flags |= TF_ACKNOW; \
71 tp->t_flags |= TF_DELACK; \
72 (tp)->rcv_nxt += (ti)->ti_len; \
73 flags = (ti)->ti_flags & TH_FIN; \
75 if (tcp_emu((so),(m))) sbappend((so), (m)); \
77 sbappend((so), (m)); \
79 (flags) = tcp_reass((tp), (ti), (m)); \
80 tp->t_flags |= TF_ACKNOW; \
84 #define TCP_REASS(tp, ti, m, so, flags) { \
85 if ((ti)->ti_seq == (tp)->rcv_nxt && \
86 tcpfrag_list_empty(tp) && \
87 (tp)->t_state == TCPS_ESTABLISHED) { \
88 tp->t_flags |= TF_DELACK; \
89 (tp)->rcv_nxt += (ti)->ti_len; \
90 flags = (ti)->ti_flags & TH_FIN; \
92 if (tcp_emu((so),(m))) sbappend(so, (m)); \
94 sbappend((so), (m)); \
96 (flags) = tcp_reass((tp), (ti), (m)); \
97 tp->t_flags |= TF_ACKNOW; \
101 static void tcp_dooptions(struct tcpcb
*tp
, u_char
*cp
, int cnt
,
102 struct tcpiphdr
*ti
);
103 static void tcp_xmit_timer(register struct tcpcb
*tp
, int rtt
);
106 tcp_reass(register struct tcpcb
*tp
, register struct tcpiphdr
*ti
,
109 register struct tcpiphdr
*q
;
110 struct socket
*so
= tp
->t_socket
;
114 * Call with ti==NULL after become established to
115 * force pre-ESTABLISHED data up to user socket.
121 * Find a segment which begins after this one does.
123 for (q
= tcpfrag_list_first(tp
); !tcpfrag_list_end(q
, tp
);
124 q
= tcpiphdr_next(q
))
125 if (SEQ_GT(q
->ti_seq
, ti
->ti_seq
))
129 * If there is a preceding segment, it may provide some of
130 * our data already. If so, drop the data from the incoming
131 * segment. If it provides all of our data, drop us.
133 if (!tcpfrag_list_end(tcpiphdr_prev(q
), tp
)) {
135 q
= tcpiphdr_prev(q
);
136 /* conversion to int (in i) handles seq wraparound */
137 i
= q
->ti_seq
+ q
->ti_len
- ti
->ti_seq
;
139 if (i
>= ti
->ti_len
) {
142 * Try to present any queued data
143 * at the left window edge to the user.
144 * This is needed after the 3-WHS
147 goto present
; /* ??? */
153 q
= tcpiphdr_next(q
);
158 * While we overlap succeeding segments trim them or,
159 * if they are completely covered, dequeue them.
161 while (!tcpfrag_list_end(q
, tp
)) {
162 register int i
= (ti
->ti_seq
+ ti
->ti_len
) - q
->ti_seq
;
168 m_adj(q
->ti_mbuf
, i
);
171 q
= tcpiphdr_next(q
);
172 m
= tcpiphdr_prev(q
)->ti_mbuf
;
173 remque(tcpiphdr2qlink(tcpiphdr_prev(q
)));
178 * Stick new segment in its place.
180 insque(tcpiphdr2qlink(ti
), tcpiphdr2qlink(tcpiphdr_prev(q
)));
184 * Present data to user, advancing rcv_nxt through
185 * completed sequence space.
187 if (!TCPS_HAVEESTABLISHED(tp
->t_state
))
189 ti
= tcpfrag_list_first(tp
);
190 if (tcpfrag_list_end(ti
, tp
) || ti
->ti_seq
!= tp
->rcv_nxt
)
192 if (tp
->t_state
== TCPS_SYN_RECEIVED
&& ti
->ti_len
)
195 tp
->rcv_nxt
+= ti
->ti_len
;
196 flags
= ti
->ti_flags
& TH_FIN
;
197 remque(tcpiphdr2qlink(ti
));
199 ti
= tcpiphdr_next(ti
);
200 if (so
->so_state
& SS_FCANTSENDMORE
)
204 if (tcp_emu(so
,m
)) sbappend(so
, m
);
208 } while (ti
!= (struct tcpiphdr
*)tp
&& ti
->ti_seq
== tp
->rcv_nxt
);
213 * TCP input routine, follows pages 65-76 of the
214 * protocol specification dated September, 1981 very closely.
217 tcp_input(struct mbuf
*m
, int iphlen
, struct socket
*inso
, unsigned short af
)
219 struct ip save_ip
, *ip
;
220 struct ip6 save_ip6
, *ip6
;
221 register struct tcpiphdr
*ti
;
225 register struct tcpcb
*tp
= NULL
;
226 register int tiflags
;
227 struct socket
*so
= NULL
;
228 int todrop
, acked
, ourfinisacked
, needoutput
= 0;
232 struct sockaddr_storage lhost
, fhost
;
233 struct sockaddr_in
*lhost4
, *fhost4
;
234 struct sockaddr_in6
*lhost6
, *fhost6
;
235 struct ex_list
*ex_ptr
;
238 DEBUG_CALL("tcp_input");
239 DEBUG_ARGS((dfd
, " m = %p iphlen = %2d inso = %p\n",
243 * If called with m == 0, then we're continuing the connect
249 /* Re-set a few variables */
255 tiflags
= ti
->ti_flags
;
261 ip
= mtod(m
, struct ip
*);
262 ip6
= mtod(m
, struct ip6
*);
266 if (iphlen
> sizeof(struct ip
)) {
267 ip_stripoptions(m
, (struct mbuf
*)0);
268 iphlen
= sizeof(struct ip
);
270 /* XXX Check if too short */
274 * Save a copy of the IP header in case we want restore it
275 * for sending an ICMP error message in response.
278 save_ip
.ip_len
+= iphlen
;
281 * Get IP and TCP header together in first mbuf.
282 * Note: IP leaves IP header in first mbuf.
284 m
->m_data
-= sizeof(struct tcpiphdr
) - sizeof(struct ip
)
285 - sizeof(struct tcphdr
);
286 m
->m_len
+= sizeof(struct tcpiphdr
) - sizeof(struct ip
)
287 - sizeof(struct tcphdr
);
288 ti
= mtod(m
, struct tcpiphdr
*);
291 * Checksum extended TCP header and data.
294 tcpiphdr2qlink(ti
)->next
= tcpiphdr2qlink(ti
)->prev
= NULL
;
295 memset(&ti
->ih_mbuf
, 0 , sizeof(struct mbuf_ptr
));
296 memset(&ti
->ti
, 0, sizeof(ti
->ti
));
298 ti
->ti_src
= save_ip
.ip_src
;
299 ti
->ti_dst
= save_ip
.ip_dst
;
300 ti
->ti_pr
= save_ip
.ip_p
;
301 ti
->ti_len
= htons((uint16_t)tlen
);
306 * Save a copy of the IP header in case we want restore it
307 * for sending an ICMP error message in response.
311 * Get IP and TCP header together in first mbuf.
312 * Note: IP leaves IP header in first mbuf.
314 m
->m_data
-= sizeof(struct tcpiphdr
) - (sizeof(struct ip6
)
315 + sizeof(struct tcphdr
));
316 m
->m_len
+= sizeof(struct tcpiphdr
) - (sizeof(struct ip6
)
317 + sizeof(struct tcphdr
));
318 ti
= mtod(m
, struct tcpiphdr
*);
321 tcpiphdr2qlink(ti
)->next
= tcpiphdr2qlink(ti
)->prev
= NULL
;
322 memset(&ti
->ih_mbuf
, 0 , sizeof(struct mbuf_ptr
));
323 memset(&ti
->ti
, 0, sizeof(ti
->ti
));
325 ti
->ti_src6
= save_ip6
.ip_src
;
326 ti
->ti_dst6
= save_ip6
.ip_dst
;
327 ti
->ti_nh6
= save_ip6
.ip_nh
;
328 ti
->ti_len
= htons((uint16_t)tlen
);
332 g_assert_not_reached();
335 len
= ((sizeof(struct tcpiphdr
) - sizeof(struct tcphdr
)) + tlen
);
341 * Check that TCP offset makes sense,
342 * pull out TCP options and adjust length. XXX
344 off
= ti
->ti_off
<< 2;
345 if (off
< sizeof (struct tcphdr
) || off
> tlen
) {
350 if (off
> sizeof (struct tcphdr
)) {
351 optlen
= off
- sizeof (struct tcphdr
);
352 optp
= mtod(m
, caddr_t
) + sizeof (struct tcpiphdr
);
354 tiflags
= ti
->ti_flags
;
357 * Convert TCP protocol specific fields to host format.
365 * Drop TCP, IP headers and TCP options.
367 m
->m_data
+= sizeof(struct tcpiphdr
)+off
-sizeof(struct tcphdr
);
368 m
->m_len
-= sizeof(struct tcpiphdr
)+off
-sizeof(struct tcphdr
);
371 * Locate pcb for segment.
374 lhost
.ss_family
= af
;
375 fhost
.ss_family
= af
;
378 lhost4
= (struct sockaddr_in
*) &lhost
;
379 lhost4
->sin_addr
= ti
->ti_src
;
380 lhost4
->sin_port
= ti
->ti_sport
;
381 fhost4
= (struct sockaddr_in
*) &fhost
;
382 fhost4
->sin_addr
= ti
->ti_dst
;
383 fhost4
->sin_port
= ti
->ti_dport
;
386 lhost6
= (struct sockaddr_in6
*) &lhost
;
387 lhost6
->sin6_addr
= ti
->ti_src6
;
388 lhost6
->sin6_port
= ti
->ti_sport
;
389 fhost6
= (struct sockaddr_in6
*) &fhost
;
390 fhost6
->sin6_addr
= ti
->ti_dst6
;
391 fhost6
->sin6_port
= ti
->ti_dport
;
394 g_assert_not_reached();
397 so
= solookup(&slirp
->tcp_last_so
, &slirp
->tcb
, &lhost
, &fhost
);
400 * If the state is CLOSED (i.e., TCB does not exist) then
401 * all data in the incoming segment is discarded.
402 * If the TCB exists but is in CLOSED state, it is embryonic,
403 * but should either do a listen or a connect soon.
405 * state == CLOSED means we've done socreate() but haven't
406 * attached it to a protocol yet...
408 * XXX If a TCB does not exist, and the TH_SYN flag is
409 * the only flag set, then create a session, mark it
410 * as if it was LISTENING, and continue...
413 if (slirp
->restricted
) {
414 /* Any hostfwds will have an existing socket, so we only get here
415 * for non-hostfwd connections. These should be dropped, unless it
416 * happens to be a guestfwd.
418 for (ex_ptr
= slirp
->exec_list
; ex_ptr
; ex_ptr
= ex_ptr
->ex_next
) {
419 if (ex_ptr
->ex_fport
== ti
->ti_dport
&&
420 ti
->ti_dst
.s_addr
== ex_ptr
->ex_addr
.s_addr
) {
429 if ((tiflags
& (TH_SYN
|TH_FIN
|TH_RST
|TH_URG
|TH_ACK
)) != TH_SYN
)
432 if ((so
= socreate(slirp
)) == NULL
)
434 if (tcp_attach(so
) < 0) {
435 free(so
); /* Not sofree (if it failed, it's not insqued) */
439 sbreserve(&so
->so_snd
, TCP_SNDSPACE
);
440 sbreserve(&so
->so_rcv
, TCP_RCVSPACE
);
442 so
->lhost
.ss
= lhost
;
443 so
->fhost
.ss
= fhost
;
445 so
->so_iptos
= tcp_tos(so
);
446 if (so
->so_iptos
== 0) {
449 so
->so_iptos
= ((struct ip
*)ti
)->ip_tos
;
454 g_assert_not_reached();
459 tp
->t_state
= TCPS_LISTEN
;
463 * If this is a still-connecting socket, this probably
464 * a retransmit of the SYN. Whether it's a retransmit SYN
465 * or something else, we nuke it.
467 if (so
->so_state
& SS_ISFCONNECTING
)
472 /* XXX Should never fail */
475 if (tp
->t_state
== TCPS_CLOSED
)
481 * Segment received on connection.
482 * Reset idle time and keep-alive timer.
486 tp
->t_timer
[TCPT_KEEP
] = TCPTV_KEEPINTVL
;
488 tp
->t_timer
[TCPT_KEEP
] = TCPTV_KEEP_IDLE
;
491 * Process options if not in LISTEN state,
492 * else do it below (after getting remote address).
494 if (optp
&& tp
->t_state
!= TCPS_LISTEN
)
495 tcp_dooptions(tp
, (u_char
*)optp
, optlen
, ti
);
498 * Header prediction: check for the two common cases
499 * of a uni-directional data xfer. If the packet has
500 * no control flags, is in-sequence, the window didn't
501 * change and we're not retransmitting, it's a
502 * candidate. If the length is zero and the ack moved
503 * forward, we're the sender side of the xfer. Just
504 * free the data acked & wake any higher level process
505 * that was blocked waiting for space. If the length
506 * is non-zero and the ack didn't move, we're the
507 * receiver side. If we're getting packets in-order
508 * (the reassembly queue is empty), add the data to
509 * the socket buffer and note that we need a delayed ack.
511 * XXX Some of these tests are not needed
512 * eg: the tiwin == tp->snd_wnd prevents many more
513 * predictions.. with no *real* advantage..
515 if (tp
->t_state
== TCPS_ESTABLISHED
&&
516 (tiflags
& (TH_SYN
|TH_FIN
|TH_RST
|TH_URG
|TH_ACK
)) == TH_ACK
&&
517 ti
->ti_seq
== tp
->rcv_nxt
&&
518 tiwin
&& tiwin
== tp
->snd_wnd
&&
519 tp
->snd_nxt
== tp
->snd_max
) {
520 if (ti
->ti_len
== 0) {
521 if (SEQ_GT(ti
->ti_ack
, tp
->snd_una
) &&
522 SEQ_LEQ(ti
->ti_ack
, tp
->snd_max
) &&
523 tp
->snd_cwnd
>= tp
->snd_wnd
) {
525 * this is a pure ack for outstanding data.
528 SEQ_GT(ti
->ti_ack
, tp
->t_rtseq
))
529 tcp_xmit_timer(tp
, tp
->t_rtt
);
530 acked
= ti
->ti_ack
- tp
->snd_una
;
531 sbdrop(&so
->so_snd
, acked
);
532 tp
->snd_una
= ti
->ti_ack
;
536 * If all outstanding data are acked, stop
537 * retransmit timer, otherwise restart timer
538 * using current (possibly backed-off) value.
539 * If process is waiting for space,
540 * wakeup/selwakeup/signal. If data
541 * are ready to send, let tcp_output
542 * decide between more output or persist.
544 if (tp
->snd_una
== tp
->snd_max
)
545 tp
->t_timer
[TCPT_REXMT
] = 0;
546 else if (tp
->t_timer
[TCPT_PERSIST
] == 0)
547 tp
->t_timer
[TCPT_REXMT
] = tp
->t_rxtcur
;
550 * This is called because sowwakeup might have
551 * put data into so_snd. Since we don't so sowwakeup,
552 * we don't need this.. XXX???
554 if (so
->so_snd
.sb_cc
)
555 (void) tcp_output(tp
);
559 } else if (ti
->ti_ack
== tp
->snd_una
&&
560 tcpfrag_list_empty(tp
) &&
561 ti
->ti_len
<= sbspace(&so
->so_rcv
)) {
563 * this is a pure, in-sequence data packet
564 * with nothing on the reassembly queue and
565 * we have enough buffer space to take it.
567 tp
->rcv_nxt
+= ti
->ti_len
;
569 * Add data to socket buffer.
572 if (tcp_emu(so
,m
)) sbappend(so
, m
);
577 * If this is a short packet, then ACK now - with Nagel
578 * congestion avoidance sender won't send more until
581 * It is better to not delay acks at all to maximize
582 * TCP throughput. See RFC 2581.
584 tp
->t_flags
|= TF_ACKNOW
;
588 } /* header prediction */
590 * Calculate amount of space in receive window,
591 * and then do TCP input processing.
592 * Receive window is amount of space in rcv queue,
593 * but not less than advertised window.
596 win
= sbspace(&so
->so_rcv
);
599 tp
->rcv_wnd
= max(win
, (int)(tp
->rcv_adv
- tp
->rcv_nxt
));
602 switch (tp
->t_state
) {
605 * If the state is LISTEN then ignore segment if it contains an RST.
606 * If the segment contains an ACK then it is bad and send a RST.
607 * If it does not contain a SYN then it is not interesting; drop it.
608 * Don't bother responding if the destination was a broadcast.
609 * Otherwise initialize tp->rcv_nxt, and tp->irs, select an initial
610 * tp->iss, and send a segment:
611 * <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
612 * Also initialize tp->snd_nxt to tp->iss+1 and tp->snd_una to tp->iss.
613 * Fill in remote peer address fields if not previously specified.
614 * Enter SYN_RECEIVED state, and process any other fields of this
615 * segment in this state.
619 if (tiflags
& TH_RST
)
621 if (tiflags
& TH_ACK
)
623 if ((tiflags
& TH_SYN
) == 0)
627 * This has way too many gotos...
628 * But a bit of spaghetti code never hurt anybody :)
632 * If this is destined for the control address, then flag to
633 * tcp_ctl once connected, otherwise connect
636 (so
->so_faddr
.s_addr
& slirp
->vnetwork_mask
.s_addr
) ==
637 slirp
->vnetwork_addr
.s_addr
) {
638 if (so
->so_faddr
.s_addr
!= slirp
->vhost_addr
.s_addr
&&
639 so
->so_faddr
.s_addr
!= slirp
->vnameserver_addr
.s_addr
) {
640 /* May be an add exec */
641 for (ex_ptr
= slirp
->exec_list
; ex_ptr
;
642 ex_ptr
= ex_ptr
->ex_next
) {
643 if(ex_ptr
->ex_fport
== so
->so_fport
&&
644 so
->so_faddr
.s_addr
== ex_ptr
->ex_addr
.s_addr
) {
645 so
->so_state
|= SS_CTL
;
649 if (so
->so_state
& SS_CTL
) {
653 /* CTL_ALIAS: Do nothing, tcp_fconnect will be called on it */
656 if (so
->so_emu
& EMU_NOCONNECT
) {
657 so
->so_emu
&= ~EMU_NOCONNECT
;
661 if ((tcp_fconnect(so
, so
->so_ffamily
) == -1) &&
663 (errno
!= EINPROGRESS
) && (errno
!= EWOULDBLOCK
)
666 DEBUG_MISC((dfd
, " tcp fconnect errno = %d-%s\n",
667 errno
,strerror(errno
)));
668 if(errno
== ECONNREFUSED
) {
669 /* ACK the SYN, send RST to refuse the connection */
670 tcp_respond(tp
, ti
, m
, ti
->ti_seq
+ 1, (tcp_seq
) 0,
671 TH_RST
| TH_ACK
, af
);
675 code
= ICMP_UNREACH_NET
;
676 if (errno
== EHOSTUNREACH
) {
677 code
= ICMP_UNREACH_HOST
;
681 code
= ICMP6_UNREACH_NO_ROUTE
;
682 if (errno
== EHOSTUNREACH
) {
683 code
= ICMP6_UNREACH_ADDRESS
;
687 g_assert_not_reached();
689 HTONL(ti
->ti_seq
); /* restore tcp header */
693 m
->m_data
-= sizeof(struct tcpiphdr
)+off
-sizeof(struct tcphdr
);
694 m
->m_len
+= sizeof(struct tcpiphdr
)+off
-sizeof(struct tcphdr
);
697 m
->m_data
+= sizeof(struct tcpiphdr
) - sizeof(struct ip
)
698 - sizeof(struct tcphdr
);
699 m
->m_len
-= sizeof(struct tcpiphdr
) - sizeof(struct ip
)
700 - sizeof(struct tcphdr
);
702 icmp_send_error(m
, ICMP_UNREACH
, code
, 0, strerror(errno
));
705 m
->m_data
+= sizeof(struct tcpiphdr
) - (sizeof(struct ip6
)
706 + sizeof(struct tcphdr
));
707 m
->m_len
-= sizeof(struct tcpiphdr
) - (sizeof(struct ip6
)
708 + sizeof(struct tcphdr
));
710 icmp6_send_error(m
, ICMP6_UNREACH
, code
);
713 g_assert_not_reached();
720 * Haven't connected yet, save the current mbuf
722 * XXX Some OS's don't tell us whether the connect()
723 * succeeded or not. So we must time it out.
727 tp
->t_timer
[TCPT_KEEP
] = TCPTV_KEEP_INIT
;
728 tp
->t_state
= TCPS_SYN_RECEIVED
;
730 * Initialize receive sequence numbers now so that we can send a
731 * valid RST if the remote end rejects our connection.
733 tp
->irs
= ti
->ti_seq
;
741 * Check if the connect succeeded
743 if (so
->so_state
& SS_NOFDREF
) {
751 tcp_dooptions(tp
, (u_char
*)optp
, optlen
, ti
);
756 tp
->iss
= slirp
->tcp_iss
;
757 slirp
->tcp_iss
+= TCP_ISSINCR
/2;
758 tp
->irs
= ti
->ti_seq
;
761 tp
->t_flags
|= TF_ACKNOW
;
762 tp
->t_state
= TCPS_SYN_RECEIVED
;
763 tp
->t_timer
[TCPT_KEEP
] = TCPTV_KEEP_INIT
;
765 } /* case TCPS_LISTEN */
768 * If the state is SYN_SENT:
769 * if seg contains an ACK, but not for our SYN, drop the input.
770 * if seg contains a RST, then drop the connection.
771 * if seg does not contain SYN, then drop it.
772 * Otherwise this is an acceptable SYN segment
773 * initialize tp->rcv_nxt and tp->irs
774 * if seg contains ack then advance tp->snd_una
775 * if SYN has been acked change to ESTABLISHED else SYN_RCVD state
776 * arrange for segment to be acked (eventually)
777 * continue processing rest of data/controls, beginning with URG
780 if ((tiflags
& TH_ACK
) &&
781 (SEQ_LEQ(ti
->ti_ack
, tp
->iss
) ||
782 SEQ_GT(ti
->ti_ack
, tp
->snd_max
)))
785 if (tiflags
& TH_RST
) {
786 if (tiflags
& TH_ACK
) {
787 tcp_drop(tp
, 0); /* XXX Check t_softerror! */
792 if ((tiflags
& TH_SYN
) == 0)
794 if (tiflags
& TH_ACK
) {
795 tp
->snd_una
= ti
->ti_ack
;
796 if (SEQ_LT(tp
->snd_nxt
, tp
->snd_una
))
797 tp
->snd_nxt
= tp
->snd_una
;
800 tp
->t_timer
[TCPT_REXMT
] = 0;
801 tp
->irs
= ti
->ti_seq
;
803 tp
->t_flags
|= TF_ACKNOW
;
804 if (tiflags
& TH_ACK
&& SEQ_GT(tp
->snd_una
, tp
->iss
)) {
806 tp
->t_state
= TCPS_ESTABLISHED
;
808 (void) tcp_reass(tp
, (struct tcpiphdr
*)0,
811 * if we didn't have to retransmit the SYN,
812 * use its rtt as our initial srtt & rtt var.
815 tcp_xmit_timer(tp
, tp
->t_rtt
);
817 tp
->t_state
= TCPS_SYN_RECEIVED
;
821 * Advance ti->ti_seq to correspond to first data byte.
822 * If data, trim to stay within window,
823 * dropping FIN if necessary.
826 if (ti
->ti_len
> tp
->rcv_wnd
) {
827 todrop
= ti
->ti_len
- tp
->rcv_wnd
;
829 ti
->ti_len
= tp
->rcv_wnd
;
832 tp
->snd_wl1
= ti
->ti_seq
- 1;
833 tp
->rcv_up
= ti
->ti_seq
;
835 } /* switch tp->t_state */
837 * States other than LISTEN or SYN_SENT.
838 * Check that at least some bytes of segment are within
839 * receive window. If segment begins before rcv_nxt,
840 * drop leading data (and SYN); if nothing left, just ack.
842 todrop
= tp
->rcv_nxt
- ti
->ti_seq
;
844 if (tiflags
& TH_SYN
) {
854 * Following if statement from Stevens, vol. 2, p. 960.
856 if (todrop
> ti
->ti_len
857 || (todrop
== ti
->ti_len
&& (tiflags
& TH_FIN
) == 0)) {
859 * Any valid FIN must be to the left of the window.
860 * At this point the FIN must be a duplicate or out
861 * of sequence; drop it.
866 * Send an ACK to resynchronize and drop any data.
867 * But keep on processing for RST or ACK.
869 tp
->t_flags
|= TF_ACKNOW
;
873 ti
->ti_seq
+= todrop
;
874 ti
->ti_len
-= todrop
;
875 if (ti
->ti_urp
> todrop
)
876 ti
->ti_urp
-= todrop
;
883 * If new data are received on a connection after the
884 * user processes are gone, then RST the other end.
886 if ((so
->so_state
& SS_NOFDREF
) &&
887 tp
->t_state
> TCPS_CLOSE_WAIT
&& ti
->ti_len
) {
893 * If segment ends after window, drop trailing data
894 * (and PUSH and FIN); if nothing left, just ACK.
896 todrop
= (ti
->ti_seq
+ti
->ti_len
) - (tp
->rcv_nxt
+tp
->rcv_wnd
);
898 if (todrop
>= ti
->ti_len
) {
900 * If a new connection request is received
901 * while in TIME_WAIT, drop the old connection
902 * and start over if the sequence numbers
903 * are above the previous ones.
905 if (tiflags
& TH_SYN
&&
906 tp
->t_state
== TCPS_TIME_WAIT
&&
907 SEQ_GT(ti
->ti_seq
, tp
->rcv_nxt
)) {
908 iss
= tp
->rcv_nxt
+ TCP_ISSINCR
;
913 * If window is closed can only take segments at
914 * window edge, and have to drop data and PUSH from
915 * incoming segments. Continue processing, but
916 * remember to ack. Otherwise, drop segment
919 if (tp
->rcv_wnd
== 0 && ti
->ti_seq
== tp
->rcv_nxt
) {
920 tp
->t_flags
|= TF_ACKNOW
;
926 ti
->ti_len
-= todrop
;
927 tiflags
&= ~(TH_PUSH
|TH_FIN
);
931 * If the RST bit is set examine the state:
932 * SYN_RECEIVED STATE:
933 * If passive open, return to LISTEN state.
934 * If active open, inform user that connection was refused.
935 * ESTABLISHED, FIN_WAIT_1, FIN_WAIT2, CLOSE_WAIT STATES:
936 * Inform user that connection was reset, and close tcb.
937 * CLOSING, LAST_ACK, TIME_WAIT STATES
940 if (tiflags
&TH_RST
) switch (tp
->t_state
) {
942 case TCPS_SYN_RECEIVED
:
943 case TCPS_ESTABLISHED
:
944 case TCPS_FIN_WAIT_1
:
945 case TCPS_FIN_WAIT_2
:
946 case TCPS_CLOSE_WAIT
:
947 tp
->t_state
= TCPS_CLOSED
;
959 * If a SYN is in the window, then this is an
960 * error and we send an RST and drop the connection.
962 if (tiflags
& TH_SYN
) {
968 * If the ACK bit is off we drop the segment and return.
970 if ((tiflags
& TH_ACK
) == 0) goto drop
;
975 switch (tp
->t_state
) {
977 * In SYN_RECEIVED state if the ack ACKs our SYN then enter
978 * ESTABLISHED state and continue processing, otherwise
979 * send an RST. una<=ack<=max
981 case TCPS_SYN_RECEIVED
:
983 if (SEQ_GT(tp
->snd_una
, ti
->ti_ack
) ||
984 SEQ_GT(ti
->ti_ack
, tp
->snd_max
))
986 tp
->t_state
= TCPS_ESTABLISHED
;
988 * The sent SYN is ack'ed with our sequence number +1
989 * The first data byte already in the buffer will get
990 * lost if no correction is made. This is only needed for
991 * SS_CTL since the buffer is empty otherwise.
994 tp
->snd_una
=ti
->ti_ack
;
995 if (so
->so_state
& SS_CTL
) {
996 /* So tcp_ctl reports the right state */
1000 so
->so_state
&= ~SS_CTL
; /* success XXX */
1001 } else if (ret
== 2) {
1002 so
->so_state
&= SS_PERSISTENT_MASK
;
1003 so
->so_state
|= SS_NOFDREF
; /* CTL_CMD */
1006 tp
->t_state
= TCPS_FIN_WAIT_1
;
1012 (void) tcp_reass(tp
, (struct tcpiphdr
*)0, (struct mbuf
*)0);
1013 tp
->snd_wl1
= ti
->ti_seq
- 1;
1014 /* Avoid ack processing; snd_una==ti_ack => dup ack */
1019 * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
1020 * ACKs. If the ack is in the range
1021 * tp->snd_una < ti->ti_ack <= tp->snd_max
1022 * then advance tp->snd_una to ti->ti_ack and drop
1023 * data from the retransmission queue. If this ACK reflects
1024 * more up to date window information we update our window information.
1026 case TCPS_ESTABLISHED
:
1027 case TCPS_FIN_WAIT_1
:
1028 case TCPS_FIN_WAIT_2
:
1029 case TCPS_CLOSE_WAIT
:
1032 case TCPS_TIME_WAIT
:
1034 if (SEQ_LEQ(ti
->ti_ack
, tp
->snd_una
)) {
1035 if (ti
->ti_len
== 0 && tiwin
== tp
->snd_wnd
) {
1036 DEBUG_MISC((dfd
, " dup ack m = %p so = %p\n",
1039 * If we have outstanding data (other than
1040 * a window probe), this is a completely
1041 * duplicate ack (ie, window info didn't
1042 * change), the ack is the biggest we've
1043 * seen and we've seen exactly our rexmt
1044 * threshold of them, assume a packet
1045 * has been dropped and retransmit it.
1046 * Kludge snd_nxt & the congestion
1047 * window so we send only this one
1050 * We know we're losing at the current
1051 * window size so do congestion avoidance
1052 * (set ssthresh to half the current window
1053 * and pull our congestion window back to
1054 * the new ssthresh).
1056 * Dup acks mean that packets have left the
1057 * network (they're now cached at the receiver)
1058 * so bump cwnd by the amount in the receiver
1059 * to keep a constant cwnd packets in the
1062 if (tp
->t_timer
[TCPT_REXMT
] == 0 ||
1063 ti
->ti_ack
!= tp
->snd_una
)
1065 else if (++tp
->t_dupacks
== TCPREXMTTHRESH
) {
1066 tcp_seq onxt
= tp
->snd_nxt
;
1068 min(tp
->snd_wnd
, tp
->snd_cwnd
) / 2 /
1073 tp
->snd_ssthresh
= win
* tp
->t_maxseg
;
1074 tp
->t_timer
[TCPT_REXMT
] = 0;
1076 tp
->snd_nxt
= ti
->ti_ack
;
1077 tp
->snd_cwnd
= tp
->t_maxseg
;
1078 (void) tcp_output(tp
);
1079 tp
->snd_cwnd
= tp
->snd_ssthresh
+
1080 tp
->t_maxseg
* tp
->t_dupacks
;
1081 if (SEQ_GT(onxt
, tp
->snd_nxt
))
1084 } else if (tp
->t_dupacks
> TCPREXMTTHRESH
) {
1085 tp
->snd_cwnd
+= tp
->t_maxseg
;
1086 (void) tcp_output(tp
);
1095 * If the congestion window was inflated to account
1096 * for the other side's cached packets, retract it.
1098 if (tp
->t_dupacks
> TCPREXMTTHRESH
&&
1099 tp
->snd_cwnd
> tp
->snd_ssthresh
)
1100 tp
->snd_cwnd
= tp
->snd_ssthresh
;
1102 if (SEQ_GT(ti
->ti_ack
, tp
->snd_max
)) {
1105 acked
= ti
->ti_ack
- tp
->snd_una
;
1108 * If transmit timer is running and timed sequence
1109 * number was acked, update smoothed round trip time.
1110 * Since we now have an rtt measurement, cancel the
1111 * timer backoff (cf., Phil Karn's retransmit alg.).
1112 * Recompute the initial retransmit timer.
1114 if (tp
->t_rtt
&& SEQ_GT(ti
->ti_ack
, tp
->t_rtseq
))
1115 tcp_xmit_timer(tp
,tp
->t_rtt
);
1118 * If all outstanding data is acked, stop retransmit
1119 * timer and remember to restart (more output or persist).
1120 * If there is more data to be acked, restart retransmit
1121 * timer, using current (possibly backed-off) value.
1123 if (ti
->ti_ack
== tp
->snd_max
) {
1124 tp
->t_timer
[TCPT_REXMT
] = 0;
1126 } else if (tp
->t_timer
[TCPT_PERSIST
] == 0)
1127 tp
->t_timer
[TCPT_REXMT
] = tp
->t_rxtcur
;
1129 * When new data is acked, open the congestion window.
1130 * If the window gives us less than ssthresh packets
1131 * in flight, open exponentially (maxseg per packet).
1132 * Otherwise open linearly: maxseg per window
1133 * (maxseg^2 / cwnd per packet).
1136 register u_int cw
= tp
->snd_cwnd
;
1137 register u_int incr
= tp
->t_maxseg
;
1139 if (cw
> tp
->snd_ssthresh
)
1140 incr
= incr
* incr
/ cw
;
1141 tp
->snd_cwnd
= min(cw
+ incr
, TCP_MAXWIN
<<tp
->snd_scale
);
1143 if (acked
> so
->so_snd
.sb_cc
) {
1144 tp
->snd_wnd
-= so
->so_snd
.sb_cc
;
1145 sbdrop(&so
->so_snd
, (int )so
->so_snd
.sb_cc
);
1148 sbdrop(&so
->so_snd
, acked
);
1149 tp
->snd_wnd
-= acked
;
1152 tp
->snd_una
= ti
->ti_ack
;
1153 if (SEQ_LT(tp
->snd_nxt
, tp
->snd_una
))
1154 tp
->snd_nxt
= tp
->snd_una
;
1156 switch (tp
->t_state
) {
1159 * In FIN_WAIT_1 STATE in addition to the processing
1160 * for the ESTABLISHED state if our FIN is now acknowledged
1161 * then enter FIN_WAIT_2.
1163 case TCPS_FIN_WAIT_1
:
1164 if (ourfinisacked
) {
1166 * If we can't receive any more
1167 * data, then closing user can proceed.
1168 * Starting the timer is contrary to the
1169 * specification, but if we don't get a FIN
1170 * we'll hang forever.
1172 if (so
->so_state
& SS_FCANTRCVMORE
) {
1173 tp
->t_timer
[TCPT_2MSL
] = TCP_MAXIDLE
;
1175 tp
->t_state
= TCPS_FIN_WAIT_2
;
1180 * In CLOSING STATE in addition to the processing for
1181 * the ESTABLISHED state if the ACK acknowledges our FIN
1182 * then enter the TIME-WAIT state, otherwise ignore
1186 if (ourfinisacked
) {
1187 tp
->t_state
= TCPS_TIME_WAIT
;
1188 tcp_canceltimers(tp
);
1189 tp
->t_timer
[TCPT_2MSL
] = 2 * TCPTV_MSL
;
1194 * In LAST_ACK, we may still be waiting for data to drain
1195 * and/or to be acked, as well as for the ack of our FIN.
1196 * If our FIN is now acknowledged, delete the TCB,
1197 * enter the closed state and return.
1200 if (ourfinisacked
) {
1207 * In TIME_WAIT state the only thing that should arrive
1208 * is a retransmission of the remote FIN. Acknowledge
1209 * it and restart the finack timer.
1211 case TCPS_TIME_WAIT
:
1212 tp
->t_timer
[TCPT_2MSL
] = 2 * TCPTV_MSL
;
1215 } /* switch(tp->t_state) */
1219 * Update window information.
1220 * Don't look at window if no ACK: TAC's send garbage on first SYN.
1222 if ((tiflags
& TH_ACK
) &&
1223 (SEQ_LT(tp
->snd_wl1
, ti
->ti_seq
) ||
1224 (tp
->snd_wl1
== ti
->ti_seq
&& (SEQ_LT(tp
->snd_wl2
, ti
->ti_ack
) ||
1225 (tp
->snd_wl2
== ti
->ti_ack
&& tiwin
> tp
->snd_wnd
))))) {
1226 tp
->snd_wnd
= tiwin
;
1227 tp
->snd_wl1
= ti
->ti_seq
;
1228 tp
->snd_wl2
= ti
->ti_ack
;
1229 if (tp
->snd_wnd
> tp
->max_sndwnd
)
1230 tp
->max_sndwnd
= tp
->snd_wnd
;
1235 * Process segments with URG.
1237 if ((tiflags
& TH_URG
) && ti
->ti_urp
&&
1238 TCPS_HAVERCVDFIN(tp
->t_state
) == 0) {
1240 * This is a kludge, but if we receive and accept
1241 * random urgent pointers, we'll crash in
1242 * soreceive. It's hard to imagine someone
1243 * actually wanting to send this much urgent data.
1245 if (ti
->ti_urp
+ so
->so_rcv
.sb_cc
> so
->so_rcv
.sb_datalen
) {
1251 * If this segment advances the known urgent pointer,
1252 * then mark the data stream. This should not happen
1253 * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
1254 * a FIN has been received from the remote side.
1255 * In these states we ignore the URG.
1257 * According to RFC961 (Assigned Protocols),
1258 * the urgent pointer points to the last octet
1259 * of urgent data. We continue, however,
1260 * to consider it to indicate the first octet
1261 * of data past the urgent section as the original
1262 * spec states (in one of two places).
1264 if (SEQ_GT(ti
->ti_seq
+ti
->ti_urp
, tp
->rcv_up
)) {
1265 tp
->rcv_up
= ti
->ti_seq
+ ti
->ti_urp
;
1266 so
->so_urgc
= so
->so_rcv
.sb_cc
+
1267 (tp
->rcv_up
- tp
->rcv_nxt
); /* -1; */
1268 tp
->rcv_up
= ti
->ti_seq
+ ti
->ti_urp
;
1273 * If no out of band data is expected,
1274 * pull receive urgent pointer along
1275 * with the receive window.
1277 if (SEQ_GT(tp
->rcv_nxt
, tp
->rcv_up
))
1278 tp
->rcv_up
= tp
->rcv_nxt
;
1282 * If this is a small packet, then ACK now - with Nagel
1283 * congestion avoidance sender won't send more until
1286 if (ti
->ti_len
&& (unsigned)ti
->ti_len
<= 5 &&
1287 ((struct tcpiphdr_2
*)ti
)->first_char
== (char)27) {
1288 tp
->t_flags
|= TF_ACKNOW
;
1292 * Process the segment text, merging it into the TCP sequencing queue,
1293 * and arranging for acknowledgment of receipt if necessary.
1294 * This process logically involves adjusting tp->rcv_wnd as data
1295 * is presented to the user (this happens in tcp_usrreq.c,
1296 * case PRU_RCVD). If a FIN has already been received on this
1297 * connection then we just ignore the text.
1299 if ((ti
->ti_len
|| (tiflags
&TH_FIN
)) &&
1300 TCPS_HAVERCVDFIN(tp
->t_state
) == 0) {
1301 TCP_REASS(tp
, ti
, m
, so
, tiflags
);
1308 * If FIN is received ACK the FIN and let the user know
1309 * that the connection is closing.
1311 if (tiflags
& TH_FIN
) {
1312 if (TCPS_HAVERCVDFIN(tp
->t_state
) == 0) {
1314 * If we receive a FIN we can't send more data,
1316 * Shutdown the socket if there is no rx data in the
1318 * soread() is called on completion of shutdown() and
1319 * will got to TCPS_LAST_ACK, and use tcp_output()
1324 tp
->t_flags
|= TF_ACKNOW
;
1327 switch (tp
->t_state
) {
1330 * In SYN_RECEIVED and ESTABLISHED STATES
1331 * enter the CLOSE_WAIT state.
1333 case TCPS_SYN_RECEIVED
:
1334 case TCPS_ESTABLISHED
:
1335 if(so
->so_emu
== EMU_CTL
) /* no shutdown on socket */
1336 tp
->t_state
= TCPS_LAST_ACK
;
1338 tp
->t_state
= TCPS_CLOSE_WAIT
;
1342 * If still in FIN_WAIT_1 STATE FIN has not been acked so
1343 * enter the CLOSING state.
1345 case TCPS_FIN_WAIT_1
:
1346 tp
->t_state
= TCPS_CLOSING
;
1350 * In FIN_WAIT_2 state enter the TIME_WAIT state,
1351 * starting the time-wait timer, turning off the other
1354 case TCPS_FIN_WAIT_2
:
1355 tp
->t_state
= TCPS_TIME_WAIT
;
1356 tcp_canceltimers(tp
);
1357 tp
->t_timer
[TCPT_2MSL
] = 2 * TCPTV_MSL
;
1361 * In TIME_WAIT state restart the 2 MSL time_wait timer.
1363 case TCPS_TIME_WAIT
:
1364 tp
->t_timer
[TCPT_2MSL
] = 2 * TCPTV_MSL
;
1370 * Return any desired output.
1372 if (needoutput
|| (tp
->t_flags
& TF_ACKNOW
)) {
1373 (void) tcp_output(tp
);
1379 * Generate an ACK dropping incoming segment if it occupies
1380 * sequence space, where the ACK reflects our state.
1382 if (tiflags
& TH_RST
)
1385 tp
->t_flags
|= TF_ACKNOW
;
1386 (void) tcp_output(tp
);
1390 /* reuses m if m!=NULL, m_free() unnecessary */
1391 if (tiflags
& TH_ACK
)
1392 tcp_respond(tp
, ti
, m
, (tcp_seq
)0, ti
->ti_ack
, TH_RST
, af
);
1394 if (tiflags
& TH_SYN
) ti
->ti_len
++;
1395 tcp_respond(tp
, ti
, m
, ti
->ti_seq
+ ti
->ti_len
, (tcp_seq
) 0,
1396 TH_RST
| TH_ACK
, af
);
1403 * Drop space held by incoming segment and return.
1409 tcp_dooptions(struct tcpcb
*tp
, u_char
*cp
, int cnt
, struct tcpiphdr
*ti
)
1414 DEBUG_CALL("tcp_dooptions");
1415 DEBUG_ARGS((dfd
, " tp = %p cnt=%i\n", tp
, cnt
));
1417 for (; cnt
> 0; cnt
-= optlen
, cp
+= optlen
) {
1419 if (opt
== TCPOPT_EOL
)
1421 if (opt
== TCPOPT_NOP
)
1434 if (optlen
!= TCPOLEN_MAXSEG
)
1436 if (!(ti
->ti_flags
& TH_SYN
))
1438 memcpy((char *) &mss
, (char *) cp
+ 2, sizeof(mss
));
1440 (void) tcp_mss(tp
, mss
); /* sets t_maxseg */
1448 * Pull out of band byte out of a segment so
1449 * it doesn't appear in the user's data queue.
1450 * It is still reflected in the segment length for
1451 * sequencing purposes.
1457 tcp_pulloutofband(so
, ti
, m
)
1459 struct tcpiphdr
*ti
;
1460 register struct mbuf
*m
;
1462 int cnt
= ti
->ti_urp
- 1;
1465 if (m
->m_len
> cnt
) {
1466 char *cp
= mtod(m
, caddr_t
) + cnt
;
1467 struct tcpcb
*tp
= sototcpcb(so
);
1470 tp
->t_oobflags
|= TCPOOB_HAVEDATA
;
1471 memcpy(sp
, cp
+1, (unsigned)(m
->m_len
- cnt
- 1));
1476 m
= m
->m_next
; /* XXX WRONG! Fix it! */
1480 panic("tcp_pulloutofband");
1486 * Collect new round-trip time estimate
1487 * and update averages and current timeout.
1491 tcp_xmit_timer(register struct tcpcb
*tp
, int rtt
)
1493 register short delta
;
1495 DEBUG_CALL("tcp_xmit_timer");
1496 DEBUG_ARG("tp = %p", tp
);
1497 DEBUG_ARG("rtt = %d", rtt
);
1499 if (tp
->t_srtt
!= 0) {
1501 * srtt is stored as fixed point with 3 bits after the
1502 * binary point (i.e., scaled by 8). The following magic
1503 * is equivalent to the smoothing algorithm in rfc793 with
1504 * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
1505 * point). Adjust rtt to origin 0.
1507 delta
= rtt
- 1 - (tp
->t_srtt
>> TCP_RTT_SHIFT
);
1508 if ((tp
->t_srtt
+= delta
) <= 0)
1511 * We accumulate a smoothed rtt variance (actually, a
1512 * smoothed mean difference), then set the retransmit
1513 * timer to smoothed rtt + 4 times the smoothed variance.
1514 * rttvar is stored as fixed point with 2 bits after the
1515 * binary point (scaled by 4). The following is
1516 * equivalent to rfc793 smoothing with an alpha of .75
1517 * (rttvar = rttvar*3/4 + |delta| / 4). This replaces
1518 * rfc793's wired-in beta.
1522 delta
-= (tp
->t_rttvar
>> TCP_RTTVAR_SHIFT
);
1523 if ((tp
->t_rttvar
+= delta
) <= 0)
1527 * No rtt measurement yet - use the unsmoothed rtt.
1528 * Set the variance to half the rtt (so our first
1529 * retransmit happens at 3*rtt).
1531 tp
->t_srtt
= rtt
<< TCP_RTT_SHIFT
;
1532 tp
->t_rttvar
= rtt
<< (TCP_RTTVAR_SHIFT
- 1);
1538 * the retransmit should happen at rtt + 4 * rttvar.
1539 * Because of the way we do the smoothing, srtt and rttvar
1540 * will each average +1/2 tick of bias. When we compute
1541 * the retransmit timer, we want 1/2 tick of rounding and
1542 * 1 extra tick because of +-1/2 tick uncertainty in the
1543 * firing of the timer. The bias will give us exactly the
1544 * 1.5 tick we need. But, because the bias is
1545 * statistical, we have to test that we don't drop below
1546 * the minimum feasible timer (which is 2 ticks).
1548 TCPT_RANGESET(tp
->t_rxtcur
, TCP_REXMTVAL(tp
),
1549 (short)tp
->t_rttmin
, TCPTV_REXMTMAX
); /* XXX */
1552 * We received an ack for a packet that wasn't retransmitted;
1553 * it is probably safe to discard any error indications we've
1554 * received recently. This isn't quite right, but close enough
1555 * for now (a route might have failed after we sent a segment,
1556 * and the return path might not be symmetrical).
1558 tp
->t_softerror
= 0;
1562 * Determine a reasonable value for maxseg size.
1563 * If the route is known, check route for mtu.
1564 * If none, use an mss that can be handled on the outgoing
1565 * interface without forcing IP to fragment; if bigger than
1566 * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
1567 * to utilize large mbufs. If no route is found, route has no mtu,
1568 * or the destination isn't local, use a default, hopefully conservative
1569 * size (usually 512 or the default IP max size, but no more than the mtu
1570 * of the interface), as we can't discover anything about intervening
1571 * gateways or networks. We also initialize the congestion/slow start
1572 * window to be a single segment if the destination isn't local.
1573 * While looking at the routing entry, we also initialize other path-dependent
1574 * parameters from pre-set or cached values in the routing entry.
1578 tcp_mss(struct tcpcb
*tp
, u_int offer
)
1580 struct socket
*so
= tp
->t_socket
;
1583 DEBUG_CALL("tcp_mss");
1584 DEBUG_ARG("tp = %p", tp
);
1585 DEBUG_ARG("offer = %d", offer
);
1587 switch (so
->so_ffamily
) {
1589 mss
= min(IF_MTU
, IF_MRU
) - sizeof(struct tcphdr
)
1590 + sizeof(struct ip
);
1593 mss
= min(IF_MTU
, IF_MRU
) - sizeof(struct tcphdr
)
1594 + sizeof(struct ip6
);
1597 g_assert_not_reached();
1601 mss
= min(mss
, offer
);
1603 if (mss
< tp
->t_maxseg
|| offer
!= 0)
1608 sbreserve(&so
->so_snd
, TCP_SNDSPACE
+ ((TCP_SNDSPACE
% mss
) ?
1609 (mss
- (TCP_SNDSPACE
% mss
)) :
1611 sbreserve(&so
->so_rcv
, TCP_RCVSPACE
+ ((TCP_RCVSPACE
% mss
) ?
1612 (mss
- (TCP_RCVSPACE
% mss
)) :
1615 DEBUG_MISC((dfd
, " returning mss = %d\n", mss
));