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233e8c18e8
freebsd-skq/sys/netinet/tcp_input.c
Garrett Wollman 233e8c18e8 A number of performance-reducing flaws fixed based on comments 
from Larry Peterson &co. at Arizona:

- Header prediction for ACKs did not exclude Fast Retransmit/Recovery.
- srtt calculation tended to get ``stuck'' and could never decrease
  when below 8.  It still can't, but the scaling factors are adjusted
  so that this artifact does not cause as bad an effect on the RTO
  value as it used to.

The paper also points out the incr/8 error that has been long since fixed,
and the problems with ACKing frequency resulting from the use of options
which I suspect to be fixed already as well (as part of the T/TCP work).

Obtained from:	Brakmo & Peterson, ``Performance Problems in BSD4.4 TCP''
1996-03-22 18:09:21 +00:00

2145 lines
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/*
* Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
* $Id: tcp_input.c,v 1.38 1996/03/11 15:13:29 davidg Exp $
*/
#ifndef TUBA_INCLUDE
#include <sys/param.h>
#include <sys/queue.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/errno.h>
#include <machine/cpu.h> /* before tcp_seq.h, for tcp_random18() */
#include <net/if.h>
#include <net/route.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/in_pcb.h>
#include <netinet/ip_var.h>
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet/tcpip.h>
#ifdef TCPDEBUG
#include <netinet/tcp_debug.h>
static struct tcpiphdr tcp_saveti;
#endif
static int tcprexmtthresh = 3;
tcp_seq tcp_iss;
tcp_cc tcp_ccgen;
struct tcpstat tcpstat;
SYSCTL_STRUCT(_net_inet_tcp, TCPCTL_STATS, stats,
CTLFLAG_RD, &tcpstat , tcpstat, "");
u_long tcp_now;
struct inpcbhead tcb;
struct inpcbinfo tcbinfo;
static void tcp_dooptions __P((struct tcpcb *,
u_char *, int, struct tcpiphdr *, struct tcpopt *));
static void tcp_pulloutofband __P((struct socket *,
struct tcpiphdr *, struct mbuf *));
static int tcp_reass __P((struct tcpcb *, struct tcpiphdr *, struct mbuf *));
static void tcp_xmit_timer __P((struct tcpcb *, int));
#endif /* TUBA_INCLUDE */
/*
* Insert segment ti into reassembly queue of tcp with
* control block tp. Return TH_FIN if reassembly now includes
* a segment with FIN. The macro form does the common case inline
* (segment is the next to be received on an established connection,
* and the queue is empty), avoiding linkage into and removal
* from the queue and repetition of various conversions.
* Set DELACK for segments received in order, but ack immediately
* when segments are out of order (so fast retransmit can work).
*/
#ifdef TCP_ACK_HACK
#define TCP_REASS(tp, ti, m, so, flags) { \
if ((ti)->ti_seq == (tp)->rcv_nxt && \
(tp)->seg_next == (struct tcpiphdr *)(tp) && \
(tp)->t_state == TCPS_ESTABLISHED) { \
if (ti->ti_flags & TH_PUSH) \
tp->t_flags |= TF_ACKNOW; \
else \
tp->t_flags |= TF_DELACK; \
(tp)->rcv_nxt += (ti)->ti_len; \
flags = (ti)->ti_flags & TH_FIN; \
tcpstat.tcps_rcvpack++;\
tcpstat.tcps_rcvbyte += (ti)->ti_len;\
sbappend(&(so)->so_rcv, (m)); \
sorwakeup(so); \
} else { \
(flags) = tcp_reass((tp), (ti), (m)); \
tp->t_flags |= TF_ACKNOW; \
} \
}
#else
#define TCP_REASS(tp, ti, m, so, flags) { \
if ((ti)->ti_seq == (tp)->rcv_nxt && \
(tp)->seg_next == (struct tcpiphdr *)(tp) && \
(tp)->t_state == TCPS_ESTABLISHED) { \
tp->t_flags |= TF_DELACK; \
(tp)->rcv_nxt += (ti)->ti_len; \
flags = (ti)->ti_flags & TH_FIN; \
tcpstat.tcps_rcvpack++;\
tcpstat.tcps_rcvbyte += (ti)->ti_len;\
sbappend(&(so)->so_rcv, (m)); \
sorwakeup(so); \
} else { \
(flags) = tcp_reass((tp), (ti), (m)); \
tp->t_flags |= TF_ACKNOW; \
} \
}
#endif
#ifndef TUBA_INCLUDE
static int
tcp_reass(tp, ti, m)
register struct tcpcb *tp;
register struct tcpiphdr *ti;
struct mbuf *m;
{
register struct tcpiphdr *q;
struct socket *so = tp->t_inpcb->inp_socket;
int flags;
/*
* Call with ti==0 after become established to
* force pre-ESTABLISHED data up to user socket.
*/
if (ti == 0)
goto present;
/*
* Find a segment which begins after this one does.
*/
for (q = tp->seg_next; q != (struct tcpiphdr *)tp;
q = (struct tcpiphdr *)q->ti_next)
if (SEQ_GT(q->ti_seq, ti->ti_seq))
break;
/*
* If there is a preceding segment, it may provide some of
* our data already. If so, drop the data from the incoming
* segment. If it provides all of our data, drop us.
*/
if ((struct tcpiphdr *)q->ti_prev != (struct tcpiphdr *)tp) {
register int i;
q = (struct tcpiphdr *)q->ti_prev;
/* conversion to int (in i) handles seq wraparound */
i = q->ti_seq + q->ti_len - ti->ti_seq;
if (i > 0) {
if (i >= ti->ti_len) {
tcpstat.tcps_rcvduppack++;
tcpstat.tcps_rcvdupbyte += ti->ti_len;
m_freem(m);
/*
* Try to present any queued data
* at the left window edge to the user.
* This is needed after the 3-WHS
* completes.
*/
goto present; /* ??? */
}
m_adj(m, i);
ti->ti_len -= i;
ti->ti_seq += i;
}
q = (struct tcpiphdr *)(q->ti_next);
}
tcpstat.tcps_rcvoopack++;
tcpstat.tcps_rcvoobyte += ti->ti_len;
REASS_MBUF(ti) = m; /* XXX */
/*
* While we overlap succeeding segments trim them or,
* if they are completely covered, dequeue them.
*/
while (q != (struct tcpiphdr *)tp) {
register int i = (ti->ti_seq + ti->ti_len) - q->ti_seq;
if (i <= 0)
break;
if (i < q->ti_len) {
q->ti_seq += i;
q->ti_len -= i;
m_adj(REASS_MBUF(q), i);
break;
}
q = (struct tcpiphdr *)q->ti_next;
m = REASS_MBUF((struct tcpiphdr *)q->ti_prev);
remque(q->ti_prev);
m_freem(m);
}
/*
* Stick new segment in its place.
*/
insque(ti, q->ti_prev);
present:
/*
* Present data to user, advancing rcv_nxt through
* completed sequence space.
*/
if (!TCPS_HAVEESTABLISHED(tp->t_state))
return (0);
ti = tp->seg_next;
if (ti == (struct tcpiphdr *)tp || ti->ti_seq != tp->rcv_nxt)
return (0);
do {
tp->rcv_nxt += ti->ti_len;
flags = ti->ti_flags & TH_FIN;
remque(ti);
m = REASS_MBUF(ti);
ti = (struct tcpiphdr *)ti->ti_next;
if (so->so_state & SS_CANTRCVMORE)
m_freem(m);
else
sbappend(&so->so_rcv, m);
} while (ti != (struct tcpiphdr *)tp && ti->ti_seq == tp->rcv_nxt);
sorwakeup(so);
return (flags);
}
/*
* TCP input routine, follows pages 65-76 of the
* protocol specification dated September, 1981 very closely.
*/
void
tcp_input(m, iphlen)
register struct mbuf *m;
int iphlen;
{
register struct tcpiphdr *ti;
register struct inpcb *inp;
u_char *optp = NULL;
int optlen = 0;
int len, tlen, off;
register struct tcpcb *tp = 0;
register int tiflags;
struct socket *so = 0;
int todrop, acked, ourfinisacked, needoutput = 0;
struct in_addr laddr;
int dropsocket = 0;
int iss = 0;
u_long tiwin;
struct tcpopt to; /* options in this segment */
struct rmxp_tao *taop; /* pointer to our TAO cache entry */
struct rmxp_tao tao_noncached; /* in case there's no cached entry */
#ifdef TCPDEBUG
short ostate = 0;
#endif
bzero((char *)&to, sizeof(to));
tcpstat.tcps_rcvtotal++;
/*
* Get IP and TCP header together in first mbuf.
* Note: IP leaves IP header in first mbuf.
*/
ti = mtod(m, struct tcpiphdr *);
if (iphlen > sizeof (struct ip))
ip_stripoptions(m, (struct mbuf *)0);
if (m->m_len < sizeof (struct tcpiphdr)) {
if ((m = m_pullup(m, sizeof (struct tcpiphdr))) == 0) {
tcpstat.tcps_rcvshort++;
return;
}
ti = mtod(m, struct tcpiphdr *);
}
/*
* Checksum extended TCP header and data.
*/
tlen = ((struct ip *)ti)->ip_len;
len = sizeof (struct ip) + tlen;
ti->ti_next = ti->ti_prev = 0;
ti->ti_x1 = 0;
ti->ti_len = (u_short)tlen;
HTONS(ti->ti_len);
ti->ti_sum = in_cksum(m, len);
if (ti->ti_sum) {
tcpstat.tcps_rcvbadsum++;
goto drop;
}
#endif /* TUBA_INCLUDE */
/*
* Check that TCP offset makes sense,
* pull out TCP options and adjust length. XXX
*/
off = ti->ti_off << 2;
if (off < sizeof (struct tcphdr) || off > tlen) {
tcpstat.tcps_rcvbadoff++;
goto drop;
}
tlen -= off;
ti->ti_len = tlen;
if (off > sizeof (struct tcphdr)) {
if (m->m_len < sizeof(struct ip) + off) {
if ((m = m_pullup(m, sizeof (struct ip) + off)) == 0) {
tcpstat.tcps_rcvshort++;
return;
}
ti = mtod(m, struct tcpiphdr *);
}
optlen = off - sizeof (struct tcphdr);
optp = mtod(m, u_char *) + sizeof (struct tcpiphdr);
}
tiflags = ti->ti_flags;
/*
* Convert TCP protocol specific fields to host format.
*/
NTOHL(ti->ti_seq);
NTOHL(ti->ti_ack);
NTOHS(ti->ti_win);
NTOHS(ti->ti_urp);
/*
* Drop TCP, IP headers and TCP options.
*/
m->m_data += sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
m->m_len -= sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
/*
* Locate pcb for segment.
*/
findpcb:
/*
* First look for an exact match.
*/
inp = in_pcblookuphash(&tcbinfo, ti->ti_src, ti->ti_sport,
ti->ti_dst, ti->ti_dport);
/*
* ...and if that fails, do a wildcard search.
*/
if (inp == NULL) {
inp = in_pcblookup(&tcb, ti->ti_src, ti->ti_sport,
ti->ti_dst, ti->ti_dport, INPLOOKUP_WILDCARD);
}
/*
* If the state is CLOSED (i.e., TCB does not exist) then
* all data in the incoming segment is discarded.
* If the TCB exists but is in CLOSED state, it is embryonic,
* but should either do a listen or a connect soon.
*/
if (inp == NULL)
goto dropwithreset;
tp = intotcpcb(inp);
if (tp == 0)
goto dropwithreset;
if (tp->t_state == TCPS_CLOSED)
goto drop;
/* Unscale the window into a 32-bit value. */
if ((tiflags & TH_SYN) == 0)
tiwin = ti->ti_win << tp->snd_scale;
else
tiwin = ti->ti_win;
so = inp->inp_socket;
if (so->so_options & (SO_DEBUG|SO_ACCEPTCONN)) {
#ifdef TCPDEBUG
if (so->so_options & SO_DEBUG) {
ostate = tp->t_state;
tcp_saveti = *ti;
}
#endif
if (so->so_options & SO_ACCEPTCONN) {
register struct tcpcb *tp0 = tp;
so = sonewconn(so, 0);
if (so == 0) {
tcpstat.tcps_listendrop++;
goto drop;
}
/*
* This is ugly, but ....
*
* Mark socket as temporary until we're
* committed to keeping it. The code at
* ``drop'' and ``dropwithreset'' check the
* flag dropsocket to see if the temporary
* socket created here should be discarded.
* We mark the socket as discardable until
* we're committed to it below in TCPS_LISTEN.
*/
dropsocket++;
inp = (struct inpcb *)so->so_pcb;
inp->inp_laddr = ti->ti_dst;
inp->inp_lport = ti->ti_dport;
in_pcbrehash(inp);
#if BSD>=43
inp->inp_options = ip_srcroute();
#endif
tp = intotcpcb(inp);
tp->t_state = TCPS_LISTEN;
tp->t_flags |= tp0->t_flags & (TF_NOPUSH|TF_NOOPT);
/* Compute proper scaling value from buffer space */
while (tp->request_r_scale < TCP_MAX_WINSHIFT &&
TCP_MAXWIN << tp->request_r_scale < so->so_rcv.sb_hiwat)
tp->request_r_scale++;
}
}
/*
* Segment received on connection.
* Reset idle time and keep-alive timer.
*/
tp->t_idle = 0;
tp->t_timer[TCPT_KEEP] = tcp_keepidle;
/*
* Process options if not in LISTEN state,
* else do it below (after getting remote address).
*/
if (tp->t_state != TCPS_LISTEN)
tcp_dooptions(tp, optp, optlen, ti, &to);
/*
* Header prediction: check for the two common cases
* of a uni-directional data xfer. If the packet has
* no control flags, is in-sequence, the window didn't
* change and we're not retransmitting, it's a
* candidate. If the length is zero and the ack moved
* forward, we're the sender side of the xfer. Just
* free the data acked & wake any higher level process
* that was blocked waiting for space. If the length
* is non-zero and the ack didn't move, we're the
* receiver side. If we're getting packets in-order
* (the reassembly queue is empty), add the data to
* the socket buffer and note that we need a delayed ack.
* Make sure that the hidden state-flags are also off.
* Since we check for TCPS_ESTABLISHED above, it can only
* be TH_NEEDSYN.
*/
if (tp->t_state == TCPS_ESTABLISHED &&
(tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
((to.to_flag & TOF_TS) == 0 ||
TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
/*
* Using the CC option is compulsory if once started:
* the segment is OK if no T/TCP was negotiated or
* if the segment has a CC option equal to CCrecv
*/
((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) != (TF_REQ_CC|TF_RCVD_CC) ||
(to.to_flag & TOF_CC) != 0 && to.to_cc == tp->cc_recv) &&
ti->ti_seq == tp->rcv_nxt &&
tiwin && tiwin == tp->snd_wnd &&
tp->snd_nxt == tp->snd_max) {
/*
* If last ACK falls within this segment's sequence numbers,
* record the timestamp.
* NOTE that the test is modified according to the latest
* proposal of the tcplw@cray.com list (Braden 1993/04/26).
*/
if ((to.to_flag & TOF_TS) != 0 &&
SEQ_LEQ(ti->ti_seq, tp->last_ack_sent)) {
tp->ts_recent_age = tcp_now;
tp->ts_recent = to.to_tsval;
}
if (ti->ti_len == 0) {
if (SEQ_GT(ti->ti_ack, tp->snd_una) &&
SEQ_LEQ(ti->ti_ack, tp->snd_max) &&
tp->snd_cwnd >= tp->snd_wnd &&
tp->t_dupacks < tcprexmtthresh) {
/*
* this is a pure ack for outstanding data.
*/
++tcpstat.tcps_predack;
if ((to.to_flag & TOF_TS) != 0)
tcp_xmit_timer(tp,
tcp_now - to.to_tsecr + 1);
else if (tp->t_rtt &&
SEQ_GT(ti->ti_ack, tp->t_rtseq))
tcp_xmit_timer(tp, tp->t_rtt);
acked = ti->ti_ack - tp->snd_una;
tcpstat.tcps_rcvackpack++;
tcpstat.tcps_rcvackbyte += acked;
sbdrop(&so->so_snd, acked);
tp->snd_una = ti->ti_ack;
m_freem(m);
/*
* If all outstanding data are acked, stop
* retransmit timer, otherwise restart timer
* using current (possibly backed-off) value.
* If process is waiting for space,
* wakeup/selwakeup/signal. If data
* are ready to send, let tcp_output
* decide between more output or persist.
*/
if (tp->snd_una == tp->snd_max)
tp->t_timer[TCPT_REXMT] = 0;
else if (tp->t_timer[TCPT_PERSIST] == 0)
tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
if (so->so_snd.sb_flags & SB_NOTIFY)
sowwakeup(so);
if (so->so_snd.sb_cc)
(void) tcp_output(tp);
return;
}
} else if (ti->ti_ack == tp->snd_una &&
tp->seg_next == (struct tcpiphdr *)tp &&
ti->ti_len <= sbspace(&so->so_rcv)) {
/*
* this is a pure, in-sequence data packet
* with nothing on the reassembly queue and
* we have enough buffer space to take it.
*/
++tcpstat.tcps_preddat;
tp->rcv_nxt += ti->ti_len;
tcpstat.tcps_rcvpack++;
tcpstat.tcps_rcvbyte += ti->ti_len;
/*
* Add data to socket buffer.
*/
sbappend(&so->so_rcv, m);
sorwakeup(so);
#ifdef TCP_ACK_HACK
/*
* If this is a short packet, then ACK now - with Nagel
* congestion avoidance sender won't send more until
* he gets an ACK.
*/
if (tiflags & TH_PUSH) {
tp->t_flags |= TF_ACKNOW;
tcp_output(tp);
} else {
tp->t_flags |= TF_DELACK;
}
#else
tp->t_flags |= TF_DELACK;
#endif
return;
}
}
/*
* Calculate amount of space in receive window,
* and then do TCP input processing.
* Receive window is amount of space in rcv queue,
* but not less than advertised window.
*/
{ int win;
win = sbspace(&so->so_rcv);
if (win < 0)
win = 0;
tp->rcv_wnd = max(win, (int)(tp->rcv_adv - tp->rcv_nxt));
}
switch (tp->t_state) {
/*
* If the state is LISTEN then ignore segment if it contains an RST.
* If the segment contains an ACK then it is bad and send a RST.
* If it does not contain a SYN then it is not interesting; drop it.
* Don't bother responding if the destination was a broadcast.
* Otherwise initialize tp->rcv_nxt, and tp->irs, select an initial
* tp->iss, and send a segment:
* <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
* Also initialize tp->snd_nxt to tp->iss+1 and tp->snd_una to tp->iss.
* Fill in remote peer address fields if not previously specified.
* Enter SYN_RECEIVED state, and process any other fields of this
* segment in this state.
*/
case TCPS_LISTEN: {
struct mbuf *am;
register struct sockaddr_in *sin;
if (tiflags & TH_RST)
goto drop;
if (tiflags & TH_ACK)
goto dropwithreset;
if ((tiflags & TH_SYN) == 0)
goto drop;
/*
* RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
* in_broadcast() should never return true on a received
* packet with M_BCAST not set.
*/
if (m->m_flags & (M_BCAST|M_MCAST) ||
IN_MULTICAST(ntohl(ti->ti_dst.s_addr)))
goto drop;
am = m_get(M_DONTWAIT, MT_SONAME); /* XXX */
if (am == NULL)
goto drop;
am->m_len = sizeof (struct sockaddr_in);
sin = mtod(am, struct sockaddr_in *);
sin->sin_family = AF_INET;
sin->sin_len = sizeof(*sin);
sin->sin_addr = ti->ti_src;
sin->sin_port = ti->ti_sport;
bzero((caddr_t)sin->sin_zero, sizeof(sin->sin_zero));
laddr = inp->inp_laddr;
if (inp->inp_laddr.s_addr == INADDR_ANY)
inp->inp_laddr = ti->ti_dst;
if (in_pcbconnect(inp, am)) {
inp->inp_laddr = laddr;
(void) m_free(am);
goto drop;
}
(void) m_free(am);
tp->t_template = tcp_template(tp);
if (tp->t_template == 0) {
tp = tcp_drop(tp, ENOBUFS);
dropsocket = 0; /* socket is already gone */
goto drop;
}
if ((taop = tcp_gettaocache(inp)) == NULL) {
taop = &tao_noncached;
bzero(taop, sizeof(*taop));
}
tcp_dooptions(tp, optp, optlen, ti, &to);
if (iss)
tp->iss = iss;
else
tp->iss = tcp_iss;
tcp_iss += TCP_ISSINCR/4;
tp->irs = ti->ti_seq;
tcp_sendseqinit(tp);
tcp_rcvseqinit(tp);
/*
* Initialization of the tcpcb for transaction;
* set SND.WND = SEG.WND,
* initialize CCsend and CCrecv.
*/
tp->snd_wnd = tiwin; /* initial send-window */
tp->cc_send = CC_INC(tcp_ccgen);
tp->cc_recv = to.to_cc;
/*
* Perform TAO test on incoming CC (SEG.CC) option, if any.
* - compare SEG.CC against cached CC from the same host,
* if any.
* - if SEG.CC > chached value, SYN must be new and is accepted
* immediately: save new CC in the cache, mark the socket
* connected, enter ESTABLISHED state, turn on flag to
* send a SYN in the next segment.
* A virtual advertised window is set in rcv_adv to
* initialize SWS prevention. Then enter normal segment
* processing: drop SYN, process data and FIN.
* - otherwise do a normal 3-way handshake.
*/
if ((to.to_flag & TOF_CC) != 0) {
if (taop->tao_cc != 0 && CC_GT(to.to_cc, taop->tao_cc)) {
taop->tao_cc = to.to_cc;
tp->t_state = TCPS_ESTABLISHED;
/*
* If there is a FIN, or if there is data and the
* connection is local, then delay SYN,ACK(SYN) in
* the hope of piggy-backing it on a response
* segment. Otherwise must send ACK now in case
* the other side is slow starting.
*/
if ((tiflags & TH_FIN) || (ti->ti_len != 0 &&
in_localaddr(inp->inp_faddr)))
tp->t_flags |= (TF_DELACK | TF_NEEDSYN);
else
tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
/*
* Limit the `virtual advertised window' to TCP_MAXWIN
* here. Even if we requested window scaling, it will
* become effective only later when our SYN is acked.
*/
tp->rcv_adv += min(tp->rcv_wnd, TCP_MAXWIN);
tcpstat.tcps_connects++;
soisconnected(so);
tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT;
dropsocket = 0; /* committed to socket */
tcpstat.tcps_accepts++;
goto trimthenstep6;
}
/* else do standard 3-way handshake */
} else {
/*
* No CC option, but maybe CC.NEW:
* invalidate cached value.
*/
taop->tao_cc = 0;
}
/*
* TAO test failed or there was no CC option,
* do a standard 3-way handshake.
*/
tp->t_flags |= TF_ACKNOW;
tp->t_state = TCPS_SYN_RECEIVED;
tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT;
dropsocket = 0; /* committed to socket */
tcpstat.tcps_accepts++;
goto trimthenstep6;
}
/*
* If the state is SYN_SENT:
* if seg contains an ACK, but not for our SYN, drop the input.
* if seg contains a RST, then drop the connection.
* if seg does not contain SYN, then drop it.
* Otherwise this is an acceptable SYN segment
* initialize tp->rcv_nxt and tp->irs
* if seg contains ack then advance tp->snd_una
* if SYN has been acked change to ESTABLISHED else SYN_RCVD state
* arrange for segment to be acked (eventually)
* continue processing rest of data/controls, beginning with URG
*/
case TCPS_SYN_SENT:
if ((taop = tcp_gettaocache(inp)) == NULL) {
taop = &tao_noncached;
bzero(taop, sizeof(*taop));
}
if ((tiflags & TH_ACK) &&
(SEQ_LEQ(ti->ti_ack, tp->iss) ||
SEQ_GT(ti->ti_ack, tp->snd_max))) {
/*
* If we have a cached CCsent for the remote host,
* hence we haven't just crashed and restarted,
* do not send a RST. This may be a retransmission
* from the other side after our earlier ACK was lost.
* Our new SYN, when it arrives, will serve as the
* needed ACK.
*/
if (taop->tao_ccsent != 0)
goto drop;
else
goto dropwithreset;
}
if (tiflags & TH_RST) {
if (tiflags & TH_ACK)
tp = tcp_drop(tp, ECONNREFUSED);
goto drop;
}
if ((tiflags & TH_SYN) == 0)
goto drop;
tp->snd_wnd = ti->ti_win; /* initial send window */
tp->cc_recv = to.to_cc; /* foreign CC */
tp->irs = ti->ti_seq;
tcp_rcvseqinit(tp);
if (tiflags & TH_ACK) {
/*
* Our SYN was acked. If segment contains CC.ECHO
* option, check it to make sure this segment really
* matches our SYN. If not, just drop it as old
* duplicate, but send an RST if we're still playing
* by the old rules.
*/
if ((to.to_flag & TOF_CCECHO) &&
tp->cc_send != to.to_ccecho) {
if (taop->tao_ccsent != 0)
goto drop;
else
goto dropwithreset;
}
tcpstat.tcps_connects++;
soisconnected(so);
/* Do window scaling on this connection? */
if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
(TF_RCVD_SCALE|TF_REQ_SCALE)) {
tp->snd_scale = tp->requested_s_scale;
tp->rcv_scale = tp->request_r_scale;
}
/* Segment is acceptable, update cache if undefined. */
if (taop->tao_ccsent == 0)
taop->tao_ccsent = to.to_ccecho;
tp->rcv_adv += tp->rcv_wnd;
tp->snd_una++; /* SYN is acked */
/*
* If there's data, delay ACK; if there's also a FIN
* ACKNOW will be turned on later.
*/
if (ti->ti_len != 0)
tp->t_flags |= TF_DELACK;
else
tp->t_flags |= TF_ACKNOW;
/*
* Received <SYN,ACK> in SYN_SENT[*] state.
* Transitions:
* SYN_SENT --> ESTABLISHED
* SYN_SENT* --> FIN_WAIT_1
*/
if (tp->t_flags & TF_NEEDFIN) {
tp->t_state = TCPS_FIN_WAIT_1;
tp->t_flags &= ~TF_NEEDFIN;
tiflags &= ~TH_SYN;
} else
tp->t_state = TCPS_ESTABLISHED;
} else {
/*
* Received initial SYN in SYN-SENT[*] state => simul-
* taneous open. If segment contains CC option and there is
* a cached CC, apply TAO test; if it succeeds, connection is
* half-synchronized. Otherwise, do 3-way handshake:
* SYN-SENT -> SYN-RECEIVED
* SYN-SENT* -> SYN-RECEIVED*
* If there was no CC option, clear cached CC value.
*/
tp->t_flags |= TF_ACKNOW;
tp->t_timer[TCPT_REXMT] = 0;
if (to.to_flag & TOF_CC) {
if (taop->tao_cc != 0 &&
CC_GT(to.to_cc, taop->tao_cc)) {
/*
* update cache and make transition:
* SYN-SENT -> ESTABLISHED*
* SYN-SENT* -> FIN-WAIT-1*
*/
taop->tao_cc = to.to_cc;
if (tp->t_flags & TF_NEEDFIN) {
tp->t_state = TCPS_FIN_WAIT_1;
tp->t_flags &= ~TF_NEEDFIN;
} else
tp->t_state = TCPS_ESTABLISHED;
tp->t_flags |= TF_NEEDSYN;
} else
tp->t_state = TCPS_SYN_RECEIVED;
} else {
/* CC.NEW or no option => invalidate cache */
taop->tao_cc = 0;
tp->t_state = TCPS_SYN_RECEIVED;
}
}
trimthenstep6:
/*
* Advance ti->ti_seq to correspond to first data byte.
* If data, trim to stay within window,
* dropping FIN if necessary.
*/
ti->ti_seq++;
if (ti->ti_len > tp->rcv_wnd) {
todrop = ti->ti_len - tp->rcv_wnd;
m_adj(m, -todrop);
ti->ti_len = tp->rcv_wnd;
tiflags &= ~TH_FIN;
tcpstat.tcps_rcvpackafterwin++;
tcpstat.tcps_rcvbyteafterwin += todrop;
}
tp->snd_wl1 = ti->ti_seq - 1;
tp->rcv_up = ti->ti_seq;
/*
* Client side of transaction: already sent SYN and data.
* If the remote host used T/TCP to validate the SYN,
* our data will be ACK'd; if so, enter normal data segment
* processing in the middle of step 5, ack processing.
* Otherwise, goto step 6.
*/
if (tiflags & TH_ACK)
goto process_ACK;
goto step6;
/*
* If the state is LAST_ACK or CLOSING or TIME_WAIT:
* if segment contains a SYN and CC [not CC.NEW] option:
* if state == TIME_WAIT and connection duration > MSL,
* drop packet and send RST;
*
* if SEG.CC > CCrecv then is new SYN, and can implicitly
* ack the FIN (and data) in retransmission queue.
* Complete close and delete TCPCB. Then reprocess
* segment, hoping to find new TCPCB in LISTEN state;
*
* else must be old SYN; drop it.
* else do normal processing.
*/
case TCPS_LAST_ACK:
case TCPS_CLOSING:
case TCPS_TIME_WAIT:
if ((tiflags & TH_SYN) &&
(to.to_flag & TOF_CC) && tp->cc_recv != 0) {
if (tp->t_state == TCPS_TIME_WAIT &&
tp->t_duration > TCPTV_MSL)
goto dropwithreset;
if (CC_GT(to.to_cc, tp->cc_recv)) {
tp = tcp_close(tp);
goto findpcb;
}
else
goto drop;
}
break; /* continue normal processing */
}
/*
* States other than LISTEN or SYN_SENT.
* First check timestamp, if present.
* Then check the connection count, if present.
* Then check that at least some bytes of segment are within
* receive window. If segment begins before rcv_nxt,
* drop leading data (and SYN); if nothing left, just ack.
*
* RFC 1323 PAWS: If we have a timestamp reply on this segment
* and it's less than ts_recent, drop it.
*/
if ((to.to_flag & TOF_TS) != 0 && (tiflags & TH_RST) == 0 &&
tp->ts_recent && TSTMP_LT(to.to_tsval, tp->ts_recent)) {
/* Check to see if ts_recent is over 24 days old. */
if ((int)(tcp_now - tp->ts_recent_age) > TCP_PAWS_IDLE) {
/*
* Invalidate ts_recent. If this segment updates
* ts_recent, the age will be reset later and ts_recent
* will get a valid value. If it does not, setting
* ts_recent to zero will at least satisfy the
* requirement that zero be placed in the timestamp
* echo reply when ts_recent isn't valid. The
* age isn't reset until we get a valid ts_recent
* because we don't want out-of-order segments to be
* dropped when ts_recent is old.
*/
tp->ts_recent = 0;
} else {
tcpstat.tcps_rcvduppack++;
tcpstat.tcps_rcvdupbyte += ti->ti_len;
tcpstat.tcps_pawsdrop++;
goto dropafterack;
}
}
/*
* T/TCP mechanism
* If T/TCP was negotiated and the segment doesn't have CC,
* or if it's CC is wrong then drop the segment.
* RST segments do not have to comply with this.
*/
if ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) == (TF_REQ_CC|TF_RCVD_CC) &&
((to.to_flag & TOF_CC) == 0 || tp->cc_recv != to.to_cc) &&
(tiflags & TH_RST) == 0)
goto dropafterack;
todrop = tp->rcv_nxt - ti->ti_seq;
if (todrop > 0) {
if (tiflags & TH_SYN) {
tiflags &= ~TH_SYN;
ti->ti_seq++;
if (ti->ti_urp > 1)
ti->ti_urp--;
else
tiflags &= ~TH_URG;
todrop--;
}
/*
* Following if statement from Stevens, vol. 2, p. 960.
*/
if (todrop > ti->ti_len
|| (todrop == ti->ti_len && (tiflags & TH_FIN) == 0)) {
/*
* Any valid FIN must be to the left of the window.
* At this point the FIN must be a duplicate or out
* of sequence; drop it.
*/
tiflags &= ~TH_FIN;
/*
* Send an ACK to resynchronize and drop any data.
* But keep on processing for RST or ACK.
*/
tp->t_flags |= TF_ACKNOW;
todrop = ti->ti_len;
tcpstat.tcps_rcvduppack++;
tcpstat.tcps_rcvdupbyte += todrop;
} else {
tcpstat.tcps_rcvpartduppack++;
tcpstat.tcps_rcvpartdupbyte += todrop;
}
m_adj(m, todrop);
ti->ti_seq += todrop;
ti->ti_len -= todrop;
if (ti->ti_urp > todrop)
ti->ti_urp -= todrop;
else {
tiflags &= ~TH_URG;
ti->ti_urp = 0;
}
}
/*
* If new data are received on a connection after the
* user processes are gone, then RST the other end.
*/
if ((so->so_state & SS_NOFDREF) &&
tp->t_state > TCPS_CLOSE_WAIT && ti->ti_len) {
tp = tcp_close(tp);
tcpstat.tcps_rcvafterclose++;
goto dropwithreset;
}
/*
* If segment ends after window, drop trailing data
* (and PUSH and FIN); if nothing left, just ACK.
*/
todrop = (ti->ti_seq+ti->ti_len) - (tp->rcv_nxt+tp->rcv_wnd);
if (todrop > 0) {
tcpstat.tcps_rcvpackafterwin++;
if (todrop >= ti->ti_len) {
tcpstat.tcps_rcvbyteafterwin += ti->ti_len;
/*
* If a new connection request is received
* while in TIME_WAIT, drop the old connection
* and start over if the sequence numbers
* are above the previous ones.
*/
if (tiflags & TH_SYN &&
tp->t_state == TCPS_TIME_WAIT &&
SEQ_GT(ti->ti_seq, tp->rcv_nxt)) {
iss = tp->rcv_nxt + TCP_ISSINCR;
tp = tcp_close(tp);
goto findpcb;
}
/*
* If window is closed can only take segments at
* window edge, and have to drop data and PUSH from
* incoming segments. Continue processing, but
* remember to ack. Otherwise, drop segment
* and ack.
*/
if (tp->rcv_wnd == 0 && ti->ti_seq == tp->rcv_nxt) {
tp->t_flags |= TF_ACKNOW;
tcpstat.tcps_rcvwinprobe++;
} else
goto dropafterack;
} else
tcpstat.tcps_rcvbyteafterwin += todrop;
m_adj(m, -todrop);
ti->ti_len -= todrop;
tiflags &= ~(TH_PUSH|TH_FIN);
}
/*
* If last ACK falls within this segment's sequence numbers,
* record its timestamp.
* NOTE that the test is modified according to the latest
* proposal of the tcplw@cray.com list (Braden 1993/04/26).
*/
if ((to.to_flag & TOF_TS) != 0 &&
SEQ_LEQ(ti->ti_seq, tp->last_ack_sent)) {
tp->ts_recent_age = tcp_now;
tp->ts_recent = to.to_tsval;
}
/*
* If the RST bit is set examine the state:
* SYN_RECEIVED STATE:
* If passive open, return to LISTEN state.
* If active open, inform user that connection was refused.
* ESTABLISHED, FIN_WAIT_1, FIN_WAIT2, CLOSE_WAIT STATES:
* Inform user that connection was reset, and close tcb.
* CLOSING, LAST_ACK, TIME_WAIT STATES
* Close the tcb.
*/
if (tiflags&TH_RST) switch (tp->t_state) {
case TCPS_SYN_RECEIVED:
so->so_error = ECONNREFUSED;
goto close;
case TCPS_ESTABLISHED:
case TCPS_FIN_WAIT_1:
case TCPS_FIN_WAIT_2:
case TCPS_CLOSE_WAIT:
so->so_error = ECONNRESET;
close:
tp->t_state = TCPS_CLOSED;
tcpstat.tcps_drops++;
tp = tcp_close(tp);
goto drop;
case TCPS_CLOSING:
case TCPS_LAST_ACK:
case TCPS_TIME_WAIT:
tp = tcp_close(tp);
goto drop;
}
/*
* If a SYN is in the window, then this is an
* error and we send an RST and drop the connection.
*/
if (tiflags & TH_SYN) {
tp = tcp_drop(tp, ECONNRESET);
goto dropwithreset;
}
/*
* If the ACK bit is off: if in SYN-RECEIVED state or SENDSYN
* flag is on (half-synchronized state), then queue data for
* later processing; else drop segment and return.
*/
if ((tiflags & TH_ACK) == 0) {
if (tp->t_state == TCPS_SYN_RECEIVED ||
(tp->t_flags & TF_NEEDSYN))
goto step6;
else
goto drop;
}
/*
* Ack processing.
*/
switch (tp->t_state) {
/*
* In SYN_RECEIVED state if the ack ACKs our SYN then enter
* ESTABLISHED state and continue processing, otherwise
* send an RST.
*/
case TCPS_SYN_RECEIVED:
if (SEQ_GT(tp->snd_una, ti->ti_ack) ||
SEQ_GT(ti->ti_ack, tp->snd_max))
goto dropwithreset;
tcpstat.tcps_connects++;
soisconnected(so);
/* Do window scaling? */
if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
(TF_RCVD_SCALE|TF_REQ_SCALE)) {
tp->snd_scale = tp->requested_s_scale;
tp->rcv_scale = tp->request_r_scale;
}
/*
* Upon successful completion of 3-way handshake,
* update cache.CC if it was undefined, pass any queued
* data to the user, and advance state appropriately.
*/
if ((taop = tcp_gettaocache(inp)) != NULL &&
taop->tao_cc == 0)
taop->tao_cc = tp->cc_recv;
/*
* Make transitions:
* SYN-RECEIVED -> ESTABLISHED
* SYN-RECEIVED* -> FIN-WAIT-1
*/
if (tp->t_flags & TF_NEEDFIN) {
tp->t_state = TCPS_FIN_WAIT_1;
tp->t_flags &= ~TF_NEEDFIN;
} else
tp->t_state = TCPS_ESTABLISHED;
/*
* If segment contains data or ACK, will call tcp_reass()
* later; if not, do so now to pass queued data to user.
*/
if (ti->ti_len == 0 && (tiflags & TH_FIN) == 0)
(void) tcp_reass(tp, (struct tcpiphdr *)0,
(struct mbuf *)0);
tp->snd_wl1 = ti->ti_seq - 1;
/* fall into ... */
/*
* In ESTABLISHED state: drop duplicate ACKs; ACK out of range
* ACKs. If the ack is in the range
* tp->snd_una < ti->ti_ack <= tp->snd_max
* then advance tp->snd_una to ti->ti_ack and drop
* data from the retransmission queue. If this ACK reflects
* more up to date window information we update our window information.
*/
case TCPS_ESTABLISHED:
case TCPS_FIN_WAIT_1:
case TCPS_FIN_WAIT_2:
case TCPS_CLOSE_WAIT:
case TCPS_CLOSING:
case TCPS_LAST_ACK:
case TCPS_TIME_WAIT:
if (SEQ_LEQ(ti->ti_ack, tp->snd_una)) {
if (ti->ti_len == 0 && tiwin == tp->snd_wnd) {
tcpstat.tcps_rcvdupack++;
/*
* If we have outstanding data (other than
* a window probe), this is a completely
* duplicate ack (ie, window info didn't
* change), the ack is the biggest we've
* seen and we've seen exactly our rexmt
* threshhold of them, assume a packet
* has been dropped and retransmit it.
* Kludge snd_nxt & the congestion
* window so we send only this one
* packet.
*
* We know we're losing at the current
* window size so do congestion avoidance
* (set ssthresh to half the current window
* and pull our congestion window back to
* the new ssthresh).
*
* Dup acks mean that packets have left the
* network (they're now cached at the receiver)
* so bump cwnd by the amount in the receiver
* to keep a constant cwnd packets in the
* network.
*/
if (tp->t_timer[TCPT_REXMT] == 0 ||
ti->ti_ack != tp->snd_una)
tp->t_dupacks = 0;
else if (++tp->t_dupacks == tcprexmtthresh) {
tcp_seq onxt = tp->snd_nxt;
u_int win =
min(tp->snd_wnd, tp->snd_cwnd) / 2 /
tp->t_maxseg;
if (win < 2)
win = 2;
tp->snd_ssthresh = win * tp->t_maxseg;
tp->t_timer[TCPT_REXMT] = 0;
tp->t_rtt = 0;
tp->snd_nxt = ti->ti_ack;
tp->snd_cwnd = tp->t_maxseg;
(void) tcp_output(tp);
tp->snd_cwnd = tp->snd_ssthresh +
tp->t_maxseg * tp->t_dupacks;
if (SEQ_GT(onxt, tp->snd_nxt))
tp->snd_nxt = onxt;
goto drop;
} else if (tp->t_dupacks > tcprexmtthresh) {
tp->snd_cwnd += tp->t_maxseg;
(void) tcp_output(tp);
goto drop;
}
} else
tp->t_dupacks = 0;
break;
}
/*
* If the congestion window was inflated to account
* for the other side's cached packets, retract it.
*/
if (tp->t_dupacks >= tcprexmtthresh &&
tp->snd_cwnd > tp->snd_ssthresh)
tp->snd_cwnd = tp->snd_ssthresh;
tp->t_dupacks = 0;
if (SEQ_GT(ti->ti_ack, tp->snd_max)) {
tcpstat.tcps_rcvacktoomuch++;
goto dropafterack;
}
/*
* If we reach this point, ACK is not a duplicate,
* i.e., it ACKs something we sent.
*/
if (tp->t_flags & TF_NEEDSYN) {
/*
* T/TCP: Connection was half-synchronized, and our
* SYN has been ACK'd (so connection is now fully
* synchronized). Go to non-starred state,
* increment snd_una for ACK of SYN, and check if
* we can do window scaling.
*/
tp->t_flags &= ~TF_NEEDSYN;
tp->snd_una++;
/* Do window scaling? */
if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
(TF_RCVD_SCALE|TF_REQ_SCALE)) {
tp->snd_scale = tp->requested_s_scale;
tp->rcv_scale = tp->request_r_scale;
}
}
process_ACK:
acked = ti->ti_ack - tp->snd_una;
tcpstat.tcps_rcvackpack++;
tcpstat.tcps_rcvackbyte += acked;
/*
* If we have a timestamp reply, update smoothed
* round trip time. If no timestamp is present but
* transmit timer is running and timed sequence
* number was acked, update smoothed round trip time.
* Since we now have an rtt measurement, cancel the
* timer backoff (cf., Phil Karn's retransmit alg.).
* Recompute the initial retransmit timer.
*/
if (to.to_flag & TOF_TS)
tcp_xmit_timer(tp, tcp_now - to.to_tsecr + 1);
else if (tp->t_rtt && SEQ_GT(ti->ti_ack, tp->t_rtseq))
tcp_xmit_timer(tp,tp->t_rtt);
/*
* If all outstanding data is acked, stop retransmit
* timer and remember to restart (more output or persist).
* If there is more data to be acked, restart retransmit
* timer, using current (possibly backed-off) value.
*/
if (ti->ti_ack == tp->snd_max) {
tp->t_timer[TCPT_REXMT] = 0;
needoutput = 1;
} else if (tp->t_timer[TCPT_PERSIST] == 0)
tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
/*
* If no data (only SYN) was ACK'd,
* skip rest of ACK processing.
*/
if (acked == 0)
goto step6;
/*
* When new data is acked, open the congestion window.
* If the window gives us less than ssthresh packets
* in flight, open exponentially (maxseg per packet).
* Otherwise open linearly: maxseg per window
* (maxseg^2 / cwnd per packet).
*/
{
register u_int cw = tp->snd_cwnd;
register u_int incr = tp->t_maxseg;
if (cw > tp->snd_ssthresh)
incr = incr * incr / cw;
tp->snd_cwnd = min(cw + incr, TCP_MAXWIN<<tp->snd_scale);
}
if (acked > so->so_snd.sb_cc) {
tp->snd_wnd -= so->so_snd.sb_cc;
sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
ourfinisacked = 1;
} else {
sbdrop(&so->so_snd, acked);
tp->snd_wnd -= acked;
ourfinisacked = 0;
}
if (so->so_snd.sb_flags & SB_NOTIFY)
sowwakeup(so);
tp->snd_una = ti->ti_ack;
if (SEQ_LT(tp->snd_nxt, tp->snd_una))
tp->snd_nxt = tp->snd_una;
switch (tp->t_state) {
/*
* In FIN_WAIT_1 STATE in addition to the processing
* for the ESTABLISHED state if our FIN is now acknowledged
* then enter FIN_WAIT_2.
*/
case TCPS_FIN_WAIT_1:
if (ourfinisacked) {
/*
* If we can't receive any more
* data, then closing user can proceed.
* Starting the timer is contrary to the
* specification, but if we don't get a FIN
* we'll hang forever.
*/
if (so->so_state & SS_CANTRCVMORE) {
soisdisconnected(so);
tp->t_timer[TCPT_2MSL] = tcp_maxidle;
}
tp->t_state = TCPS_FIN_WAIT_2;
}
break;
/*
* In CLOSING STATE in addition to the processing for
* the ESTABLISHED state if the ACK acknowledges our FIN
* then enter the TIME-WAIT state, otherwise ignore
* the segment.
*/
case TCPS_CLOSING:
if (ourfinisacked) {
tp->t_state = TCPS_TIME_WAIT;
tcp_canceltimers(tp);
/* Shorten TIME_WAIT [RFC-1644, p.28] */
if (tp->cc_recv != 0 &&
tp->t_duration < TCPTV_MSL)
tp->t_timer[TCPT_2MSL] =
tp->t_rxtcur * TCPTV_TWTRUNC;
else
tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
soisdisconnected(so);
}
break;
/*
* In LAST_ACK, we may still be waiting for data to drain
* and/or to be acked, as well as for the ack of our FIN.
* If our FIN is now acknowledged, delete the TCB,
* enter the closed state and return.
*/
case TCPS_LAST_ACK:
if (ourfinisacked) {
tp = tcp_close(tp);
goto drop;
}
break;
/*
* In TIME_WAIT state the only thing that should arrive
* is a retransmission of the remote FIN. Acknowledge
* it and restart the finack timer.
*/
case TCPS_TIME_WAIT:
tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
goto dropafterack;
}
}
step6:
/*
* Update window information.
* Don't look at window if no ACK: TAC's send garbage on first SYN.
*/
if ((tiflags & TH_ACK) &&
(SEQ_LT(tp->snd_wl1, ti->ti_seq) ||
(tp->snd_wl1 == ti->ti_seq && (SEQ_LT(tp->snd_wl2, ti->ti_ack) ||
(tp->snd_wl2 == ti->ti_ack && tiwin > tp->snd_wnd))))) {
/* keep track of pure window updates */
if (ti->ti_len == 0 &&
tp->snd_wl2 == ti->ti_ack && tiwin > tp->snd_wnd)
tcpstat.tcps_rcvwinupd++;
tp->snd_wnd = tiwin;
tp->snd_wl1 = ti->ti_seq;
tp->snd_wl2 = ti->ti_ack;
if (tp->snd_wnd > tp->max_sndwnd)
tp->max_sndwnd = tp->snd_wnd;
needoutput = 1;
}
/*
* Process segments with URG.
*/
if ((tiflags & TH_URG) && ti->ti_urp &&
TCPS_HAVERCVDFIN(tp->t_state) == 0) {
/*
* This is a kludge, but if we receive and accept
* random urgent pointers, we'll crash in
* soreceive. It's hard to imagine someone
* actually wanting to send this much urgent data.
*/
if (ti->ti_urp + so->so_rcv.sb_cc > sb_max) {
ti->ti_urp = 0; /* XXX */
tiflags &= ~TH_URG; /* XXX */
goto dodata; /* XXX */
}
/*
* If this segment advances the known urgent pointer,
* then mark the data stream. This should not happen
* in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
* a FIN has been received from the remote side.
* In these states we ignore the URG.
*
* According to RFC961 (Assigned Protocols),
* the urgent pointer points to the last octet
* of urgent data. We continue, however,
* to consider it to indicate the first octet
* of data past the urgent section as the original
* spec states (in one of two places).
*/
if (SEQ_GT(ti->ti_seq+ti->ti_urp, tp->rcv_up)) {
tp->rcv_up = ti->ti_seq + ti->ti_urp;
so->so_oobmark = so->so_rcv.sb_cc +
(tp->rcv_up - tp->rcv_nxt) - 1;
if (so->so_oobmark == 0)
so->so_state |= SS_RCVATMARK;
sohasoutofband(so);
tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
}
/*
* Remove out of band data so doesn't get presented to user.
* This can happen independent of advancing the URG pointer,
* but if two URG's are pending at once, some out-of-band
* data may creep in... ick.
*/
if (ti->ti_urp <= (u_long)ti->ti_len
#ifdef SO_OOBINLINE
&& (so->so_options & SO_OOBINLINE) == 0
#endif
)
tcp_pulloutofband(so, ti, m);
} else
/*
* If no out of band data is expected,
* pull receive urgent pointer along
* with the receive window.
*/
if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
tp->rcv_up = tp->rcv_nxt;
dodata: /* XXX */
/*
* Process the segment text, merging it into the TCP sequencing queue,
* and arranging for acknowledgment of receipt if necessary.
* This process logically involves adjusting tp->rcv_wnd as data
* is presented to the user (this happens in tcp_usrreq.c,
* case PRU_RCVD). If a FIN has already been received on this
* connection then we just ignore the text.
*/
if ((ti->ti_len || (tiflags&TH_FIN)) &&
TCPS_HAVERCVDFIN(tp->t_state) == 0) {
TCP_REASS(tp, ti, m, so, tiflags);
/*
* Note the amount of data that peer has sent into
* our window, in order to estimate the sender's
* buffer size.
*/
len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
} else {
m_freem(m);
tiflags &= ~TH_FIN;
}
/*
* If FIN is received ACK the FIN and let the user know
* that the connection is closing.
*/
if (tiflags & TH_FIN) {
if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
socantrcvmore(so);
/*
* If connection is half-synchronized
* (ie NEEDSYN flag on) then delay ACK,
* so it may be piggybacked when SYN is sent.
* Otherwise, since we received a FIN then no
* more input can be expected, send ACK now.
*/
if (tp->t_flags & TF_NEEDSYN)
tp->t_flags |= TF_DELACK;
else
tp->t_flags |= TF_ACKNOW;
tp->rcv_nxt++;
}
switch (tp->t_state) {
/*
* In SYN_RECEIVED and ESTABLISHED STATES
* enter the CLOSE_WAIT state.
*/
case TCPS_SYN_RECEIVED:
case TCPS_ESTABLISHED:
tp->t_state = TCPS_CLOSE_WAIT;
break;
/*
* If still in FIN_WAIT_1 STATE FIN has not been acked so
* enter the CLOSING state.
*/
case TCPS_FIN_WAIT_1:
tp->t_state = TCPS_CLOSING;
break;
/*
* In FIN_WAIT_2 state enter the TIME_WAIT state,
* starting the time-wait timer, turning off the other
* standard timers.
*/
case TCPS_FIN_WAIT_2:
tp->t_state = TCPS_TIME_WAIT;
tcp_canceltimers(tp);
/* Shorten TIME_WAIT [RFC-1644, p.28] */
if (tp->cc_recv != 0 &&
tp->t_duration < TCPTV_MSL) {
tp->t_timer[TCPT_2MSL] =
tp->t_rxtcur * TCPTV_TWTRUNC;
/* For transaction client, force ACK now. */
tp->t_flags |= TF_ACKNOW;
}
else
tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
soisdisconnected(so);
break;
/*
* In TIME_WAIT state restart the 2 MSL time_wait timer.
*/
case TCPS_TIME_WAIT:
tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
break;
}
}
#ifdef TCPDEBUG
if (so->so_options & SO_DEBUG)
tcp_trace(TA_INPUT, ostate, tp, &tcp_saveti, 0);
#endif
/*
* Return any desired output.
*/
if (needoutput || (tp->t_flags & TF_ACKNOW))
(void) tcp_output(tp);
return;
dropafterack:
/*
* Generate an ACK dropping incoming segment if it occupies
* sequence space, where the ACK reflects our state.
*/
if (tiflags & TH_RST)
goto drop;
#ifdef TCPDEBUG
if (so->so_options & SO_DEBUG)
tcp_trace(TA_DROP, ostate, tp, &tcp_saveti, 0);
#endif
m_freem(m);
tp->t_flags |= TF_ACKNOW;
(void) tcp_output(tp);
return;
dropwithreset:
/*
* Generate a RST, dropping incoming segment.
* Make ACK acceptable to originator of segment.
* Don't bother to respond if destination was broadcast/multicast.
*/
if ((tiflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST) ||
IN_MULTICAST(ntohl(ti->ti_dst.s_addr)))
goto drop;
#ifdef TCPDEBUG
if (tp == 0 || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
tcp_trace(TA_DROP, ostate, tp, &tcp_saveti, 0);
#endif
if (tiflags & TH_ACK)
tcp_respond(tp, ti, m, (tcp_seq)0, ti->ti_ack, TH_RST);
else {
if (tiflags & TH_SYN)
ti->ti_len++;
tcp_respond(tp, ti, m, ti->ti_seq+ti->ti_len, (tcp_seq)0,
TH_RST|TH_ACK);
}
/* destroy temporarily created socket */
if (dropsocket)
(void) soabort(so);
return;
drop:
/*
* Drop space held by incoming segment and return.
*/
#ifdef TCPDEBUG
if (tp == 0 || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
tcp_trace(TA_DROP, ostate, tp, &tcp_saveti, 0);
#endif
m_freem(m);
/* destroy temporarily created socket */
if (dropsocket)
(void) soabort(so);
return;
#ifndef TUBA_INCLUDE
}
static void
tcp_dooptions(tp, cp, cnt, ti, to)
struct tcpcb *tp;
u_char *cp;
int cnt;
struct tcpiphdr *ti;
struct tcpopt *to;
{
u_short mss = 0;
int opt, optlen;
for (; cnt > 0; cnt -= optlen, cp += optlen) {
opt = cp[0];
if (opt == TCPOPT_EOL)
break;
if (opt == TCPOPT_NOP)
optlen = 1;
else {
optlen = cp[1];
if (optlen <= 0)
break;
}
switch (opt) {
default:
continue;
case TCPOPT_MAXSEG:
if (optlen != TCPOLEN_MAXSEG)
continue;
if (!(ti->ti_flags & TH_SYN))
continue;
bcopy((char *) cp + 2, (char *) &mss, sizeof(mss));
NTOHS(mss);
break;
case TCPOPT_WINDOW:
if (optlen != TCPOLEN_WINDOW)
continue;
if (!(ti->ti_flags & TH_SYN))
continue;
tp->t_flags |= TF_RCVD_SCALE;
tp->requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
break;
case TCPOPT_TIMESTAMP:
if (optlen != TCPOLEN_TIMESTAMP)
continue;
to->to_flag |= TOF_TS;
bcopy((char *)cp + 2,
(char *)&to->to_tsval, sizeof(to->to_tsval));
NTOHL(to->to_tsval);
bcopy((char *)cp + 6,
(char *)&to->to_tsecr, sizeof(to->to_tsecr));
NTOHL(to->to_tsecr);
/*
* A timestamp received in a SYN makes
* it ok to send timestamp requests and replies.
*/
if (ti->ti_flags & TH_SYN) {
tp->t_flags |= TF_RCVD_TSTMP;
tp->ts_recent = to->to_tsval;
tp->ts_recent_age = tcp_now;
}
break;
case TCPOPT_CC:
if (optlen != TCPOLEN_CC)
continue;
to->to_flag |= TOF_CC;
bcopy((char *)cp + 2,
(char *)&to->to_cc, sizeof(to->to_cc));
NTOHL(to->to_cc);
/*
* A CC or CC.new option received in a SYN makes
* it ok to send CC in subsequent segments.
*/
if (ti->ti_flags & TH_SYN)
tp->t_flags |= TF_RCVD_CC;
break;
case TCPOPT_CCNEW:
if (optlen != TCPOLEN_CC)
continue;
if (!(ti->ti_flags & TH_SYN))
continue;
to->to_flag |= TOF_CCNEW;
bcopy((char *)cp + 2,
(char *)&to->to_cc, sizeof(to->to_cc));
NTOHL(to->to_cc);
/*
* A CC or CC.new option received in a SYN makes
* it ok to send CC in subsequent segments.
*/
tp->t_flags |= TF_RCVD_CC;
break;
case TCPOPT_CCECHO:
if (optlen != TCPOLEN_CC)
continue;
if (!(ti->ti_flags & TH_SYN))
continue;
to->to_flag |= TOF_CCECHO;
bcopy((char *)cp + 2,
(char *)&to->to_ccecho, sizeof(to->to_ccecho));
NTOHL(to->to_ccecho);
break;
}
}
if (ti->ti_flags & TH_SYN)
tcp_mss(tp, mss); /* sets t_maxseg */
}
/*
* Pull out of band byte out of a segment so
* it doesn't appear in the user's data queue.
* It is still reflected in the segment length for
* sequencing purposes.
*/
static void
tcp_pulloutofband(so, ti, m)
struct socket *so;
struct tcpiphdr *ti;
register struct mbuf *m;
{
int cnt = ti->ti_urp - 1;
while (cnt >= 0) {
if (m->m_len > cnt) {
char *cp = mtod(m, caddr_t) + cnt;
struct tcpcb *tp = sototcpcb(so);
tp->t_iobc = *cp;
tp->t_oobflags |= TCPOOB_HAVEDATA;
bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
m->m_len--;
return;
}
cnt -= m->m_len;
m = m->m_next;
if (m == 0)
break;
}
panic("tcp_pulloutofband");
}
/*
* Collect new round-trip time estimate
* and update averages and current timeout.
*/
static void
tcp_xmit_timer(tp, rtt)
register struct tcpcb *tp;
short rtt;
{
#ifdef notdef
register short delta;
tcpstat.tcps_rttupdated++;
tp->t_rttupdated++;
if (tp->t_srtt != 0) {
/*
* srtt is stored as fixed point with 3 bits after the
* binary point (i.e., scaled by 8). The following magic
* is equivalent to the smoothing algorithm in rfc793 with
* an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
* point). Adjust rtt to origin 0.
*/
delta = rtt - 1 - (tp->t_srtt >> TCP_RTT_SHIFT);
if ((tp->t_srtt += delta) <= 0)
tp->t_srtt = 1;
/*
* We accumulate a smoothed rtt variance (actually, a
* smoothed mean difference), then set the retransmit
* timer to smoothed rtt + 4 times the smoothed variance.
* rttvar is stored as fixed point with 2 bits after the
* binary point (scaled by 4). The following is
* equivalent to rfc793 smoothing with an alpha of .75
* (rttvar = rttvar*3/4 + |delta| / 4). This replaces
* rfc793's wired-in beta.
*/
if (delta < 0)
delta = -delta;
delta -= (tp->t_rttvar >> TCP_RTTVAR_SHIFT);
if ((tp->t_rttvar += delta) <= 0)
tp->t_rttvar = 1;
} else {
/*
* No rtt measurement yet - use the unsmoothed rtt.
* Set the variance to half the rtt (so our first
* retransmit happens at 3*rtt).
*/
tp->t_srtt = rtt << TCP_RTT_SHIFT;
tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
}
#else /* Peterson paper */
register int delta;
tcpstat.tcps_rttupdated++;
tp->t_rttupdated++;
if (tp->t_srtt != 0) {
/*
* srtt is stored as fixed point with 5 bits after the
* binary point (i.e., scaled by 8). The following magic
* is equivalent to the smoothing algorithm in rfc793 with
* an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
* point). Adjust rtt to origin 0.
*/
delta = ((rtt - 1) << TCP_DELTA_SHIFT)
- (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
if ((tp->t_srtt += delta) <= 0)
tp->t_srtt = 1;
/*
* We accumulate a smoothed rtt variance (actually, a
* smoothed mean difference), then set the retransmit
* timer to smoothed rtt + 4 times the smoothed variance.
* rttvar is stored as fixed point with 4 bits after the
* binary point (scaled by 16). The following is
* equivalent to rfc793 smoothing with an alpha of .75
* (rttvar = rttvar*3/4 + |delta| / 4). This replaces
* rfc793's wired-in beta.
*/
if (delta < 0)
delta = -delta;
delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
if ((tp->t_rttvar += delta) <= 0)
tp->t_rttvar = 1;
} else {
/*
* No rtt measurement yet - use the unsmoothed rtt.
* Set the variance to half the rtt (so our first
* retransmit happens at 3*rtt).
*/
tp->t_srtt = rtt << TCP_RTT_SHIFT;
tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
}
#endif
tp->t_rtt = 0;
tp->t_rxtshift = 0;
/*
* the retransmit should happen at rtt + 4 * rttvar.
* Because of the way we do the smoothing, srtt and rttvar
* will each average +1/2 tick of bias. When we compute
* the retransmit timer, we want 1/2 tick of rounding and
* 1 extra tick because of +-1/2 tick uncertainty in the
* firing of the timer. The bias will give us exactly the
* 1.5 tick we need. But, because the bias is
* statistical, we have to test that we don't drop below
* the minimum feasible timer (which is 2 ticks).
*/
#ifdef notdef
TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
tp->t_rttmin, TCPTV_REXMTMAX);
#else /* Peterson */
TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
max(tp->t_rttmin, TCPTV_MIN + rtt - 1), TCPTV_REXMTMAX);
#endif
/*
* We received an ack for a packet that wasn't retransmitted;
* it is probably safe to discard any error indications we've
* received recently. This isn't quite right, but close enough
* for now (a route might have failed after we sent a segment,
* and the return path might not be symmetrical).
*/
tp->t_softerror = 0;
}
/*
* Determine a reasonable value for maxseg size.
* If the route is known, check route for mtu.
* If none, use an mss that can be handled on the outgoing
* interface without forcing IP to fragment; if bigger than
* an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
* to utilize large mbufs. If no route is found, route has no mtu,
* or the destination isn't local, use a default, hopefully conservative
* size (usually 512 or the default IP max size, but no more than the mtu
* of the interface), as we can't discover anything about intervening
* gateways or networks. We also initialize the congestion/slow start
* window to be a single segment if the destination isn't local.
* While looking at the routing entry, we also initialize other path-dependent
* parameters from pre-set or cached values in the routing entry.
*
* Also take into account the space needed for options that we
* send regularly. Make maxseg shorter by that amount to assure
* that we can send maxseg amount of data even when the options
* are present. Store the upper limit of the length of options plus
* data in maxopd.
*
* NOTE that this routine is only called when we process an incoming
* segment, for outgoing segments only tcp_mssopt is called.
*
* In case of T/TCP, we call this routine during implicit connection
* setup as well (offer = -1), to initialize maxseg from the cached
* MSS of our peer.
*/
void
tcp_mss(tp, offer)
struct tcpcb *tp;
int offer;
{
register struct rtentry *rt;
struct ifnet *ifp;
register int rtt, mss;
u_long bufsize;
struct inpcb *inp;
struct socket *so;
struct rmxp_tao *taop;
int origoffer = offer;
inp = tp->t_inpcb;
if ((rt = tcp_rtlookup(inp)) == NULL) {
tp->t_maxopd = tp->t_maxseg = tcp_mssdflt;
return;
}
ifp = rt->rt_ifp;
so = inp->inp_socket;
taop = rmx_taop(rt->rt_rmx);
/*
* Offer == -1 means that we didn't receive SYN yet,
* use cached value in that case;
*/
if (offer == -1)
offer = taop->tao_mssopt;
/*
* Offer == 0 means that there was no MSS on the SYN segment,
* in this case we use tcp_mssdflt.
*/
if (offer == 0)
offer = tcp_mssdflt;
else
/*
* Sanity check: make sure that maxopd will be large
* enough to allow some data on segments even is the
* all the option space is used (40bytes). Otherwise
* funny things may happen in tcp_output.
*/
offer = max(offer, 64);
taop->tao_mssopt = offer;
/*
* While we're here, check if there's an initial rtt
* or rttvar. Convert from the route-table units
* to scaled multiples of the slow timeout timer.
*/
if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
/*
* XXX the lock bit for RTT indicates that the value
* is also a minimum value; this is subject to time.
*/
if (rt->rt_rmx.rmx_locks & RTV_RTT)
tp->t_rttmin = rtt / (RTM_RTTUNIT / PR_SLOWHZ);
tp->t_srtt = rtt / (RTM_RTTUNIT / (PR_SLOWHZ * TCP_RTT_SCALE));
tcpstat.tcps_usedrtt++;
if (rt->rt_rmx.rmx_rttvar) {
tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
(RTM_RTTUNIT / (PR_SLOWHZ * TCP_RTTVAR_SCALE));
tcpstat.tcps_usedrttvar++;
} else {
/* default variation is +- 1 rtt */
tp->t_rttvar =
tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
}
TCPT_RANGESET(tp->t_rxtcur,
((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
tp->t_rttmin, TCPTV_REXMTMAX);
}
/*
* if there's an mtu associated with the route, use it
*/
if (rt->rt_rmx.rmx_mtu)
mss = rt->rt_rmx.rmx_mtu - sizeof(struct tcpiphdr);
else
{
mss = ifp->if_mtu - sizeof(struct tcpiphdr);
if (!in_localaddr(inp->inp_faddr))
mss = min(mss, tcp_mssdflt);
}
mss = min(mss, offer);
/*
* maxopd stores the maximum length of data AND options
* in a segment; maxseg is the amount of data in a normal
* segment. We need to store this value (maxopd) apart
* from maxseg, because now every segment carries options
* and thus we normally have somewhat less data in segments.
*/
tp->t_maxopd = mss;
/*
* In case of T/TCP, origoffer==-1 indicates, that no segments
* were received yet. In this case we just guess, otherwise
* we do the same as before T/TCP.
*/
if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
(origoffer == -1 ||
(tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
mss -= TCPOLEN_TSTAMP_APPA;
if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
(origoffer == -1 ||
(tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC))
mss -= TCPOLEN_CC_APPA;
#if (MCLBYTES & (MCLBYTES - 1)) == 0
if (mss > MCLBYTES)
mss &= ~(MCLBYTES-1);
#else
if (mss > MCLBYTES)
mss = mss / MCLBYTES * MCLBYTES;
#endif
/*
* If there's a pipesize, change the socket buffer
* to that size. Make the socket buffers an integral
* number of mss units; if the mss is larger than
* the socket buffer, decrease the mss.
*/
#ifdef RTV_SPIPE
if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
#endif
bufsize = so->so_snd.sb_hiwat;
if (bufsize < mss)
mss = bufsize;
else {
bufsize = roundup(bufsize, mss);
if (bufsize > sb_max)
bufsize = sb_max;
(void)sbreserve(&so->so_snd, bufsize);
}
tp->t_maxseg = mss;
#ifdef RTV_RPIPE
if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
#endif
bufsize = so->so_rcv.sb_hiwat;
if (bufsize > mss) {
bufsize = roundup(bufsize, mss);
if (bufsize > sb_max)
bufsize = sb_max;
(void)sbreserve(&so->so_rcv, bufsize);
}
/*
* Don't force slow-start on local network.
*/
if (!in_localaddr(inp->inp_faddr))
tp->snd_cwnd = mss;
if (rt->rt_rmx.rmx_ssthresh) {
/*
* There's some sort of gateway or interface
* buffer limit on the path. Use this to set
* the slow start threshhold, but set the
* threshold to no less than 2*mss.
*/
tp->snd_ssthresh = max(2 * mss, rt->rt_rmx.rmx_ssthresh);
tcpstat.tcps_usedssthresh++;
}
}
/*
* Determine the MSS option to send on an outgoing SYN.
*/
int
tcp_mssopt(tp)
struct tcpcb *tp;
{
struct rtentry *rt;
rt = tcp_rtlookup(tp->t_inpcb);
if (rt == NULL)
return tcp_mssdflt;
return rt->rt_ifp->if_mtu - sizeof(struct tcpiphdr);
}
#endif /* TUBA_INCLUDE */
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