494 lines
14 KiB
C
494 lines
14 KiB
C
/*
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* Copyright (c) 1982, 1986, 1988, 1990, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)tcp_output.c 8.3 (Berkeley) 12/30/93
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* tcp_output.c,v 1.3 1994/09/15 10:36:55 davidg Exp
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*/
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/*
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* Changes and additions relating to SLiRP
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* Copyright (c) 1995 Danny Gasparovski.
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*
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* Please read the file COPYRIGHT for the
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* terms and conditions of the copyright.
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*/
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#include <slirp.h>
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static const u_char tcp_outflags[TCP_NSTATES] = {
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TH_RST|TH_ACK, 0, TH_SYN, TH_SYN|TH_ACK,
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TH_ACK, TH_ACK, TH_FIN|TH_ACK, TH_FIN|TH_ACK,
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TH_FIN|TH_ACK, TH_ACK, TH_ACK,
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};
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#undef MAX_TCPOPTLEN
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#define MAX_TCPOPTLEN 32 /* max # bytes that go in options */
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/*
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* Tcp output routine: figure out what should be sent and send it.
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*/
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int
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tcp_output(struct tcpcb *tp)
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{
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register struct socket *so = tp->t_socket;
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register long len, win;
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int off, flags, error;
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register struct mbuf *m;
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register struct tcpiphdr *ti;
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u_char opt[MAX_TCPOPTLEN];
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unsigned optlen, hdrlen;
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int idle, sendalot;
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DEBUG_CALL("tcp_output");
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DEBUG_ARG("tp = %lx", (long )tp);
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/*
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* Determine length of data that should be transmitted,
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* and flags that will be used.
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* If there is some data or critical controls (SYN, RST)
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* to send, then transmit; otherwise, investigate further.
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*/
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idle = (tp->snd_max == tp->snd_una);
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if (idle && tp->t_idle >= tp->t_rxtcur)
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/*
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* We have been idle for "a while" and no acks are
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* expected to clock out any data we send --
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* slow start to get ack "clock" running again.
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*/
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tp->snd_cwnd = tp->t_maxseg;
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again:
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sendalot = 0;
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off = tp->snd_nxt - tp->snd_una;
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win = min(tp->snd_wnd, tp->snd_cwnd);
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flags = tcp_outflags[tp->t_state];
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DEBUG_MISC((dfd, " --- tcp_output flags = 0x%x\n",flags));
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/*
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* If in persist timeout with window of 0, send 1 byte.
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* Otherwise, if window is small but nonzero
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* and timer expired, we will send what we can
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* and go to transmit state.
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*/
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if (tp->t_force) {
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if (win == 0) {
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/*
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* If we still have some data to send, then
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* clear the FIN bit. Usually this would
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* happen below when it realizes that we
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* aren't sending all the data. However,
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* if we have exactly 1 byte of unset data,
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* then it won't clear the FIN bit below,
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* and if we are in persist state, we wind
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* up sending the packet without recording
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* that we sent the FIN bit.
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*
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* We can't just blindly clear the FIN bit,
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* because if we don't have any more data
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* to send then the probe will be the FIN
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* itself.
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*/
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if (off < so->so_snd.sb_cc)
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flags &= ~TH_FIN;
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win = 1;
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} else {
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tp->t_timer[TCPT_PERSIST] = 0;
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tp->t_rxtshift = 0;
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}
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}
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len = min(so->so_snd.sb_cc, win) - off;
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if (len < 0) {
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/*
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* If FIN has been sent but not acked,
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* but we haven't been called to retransmit,
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* len will be -1. Otherwise, window shrank
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* after we sent into it. If window shrank to 0,
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* cancel pending retransmit and pull snd_nxt
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* back to (closed) window. We will enter persist
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* state below. If the window didn't close completely,
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* just wait for an ACK.
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*/
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len = 0;
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if (win == 0) {
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tp->t_timer[TCPT_REXMT] = 0;
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tp->snd_nxt = tp->snd_una;
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}
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}
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if (len > tp->t_maxseg) {
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len = tp->t_maxseg;
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sendalot = 1;
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}
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if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
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flags &= ~TH_FIN;
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win = sbspace(&so->so_rcv);
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/*
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* Sender silly window avoidance. If connection is idle
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* and can send all data, a maximum segment,
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* at least a maximum default-size segment do it,
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* or are forced, do it; otherwise don't bother.
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* If peer's buffer is tiny, then send
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* when window is at least half open.
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* If retransmitting (possibly after persist timer forced us
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* to send into a small window), then must resend.
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*/
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if (len) {
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if (len == tp->t_maxseg)
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goto send;
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if ((1 || idle || tp->t_flags & TF_NODELAY) &&
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len + off >= so->so_snd.sb_cc)
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goto send;
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if (tp->t_force)
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goto send;
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if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
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goto send;
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if (SEQ_LT(tp->snd_nxt, tp->snd_max))
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goto send;
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}
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/*
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* Compare available window to amount of window
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* known to peer (as advertised window less
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* next expected input). If the difference is at least two
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* max size segments, or at least 50% of the maximum possible
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* window, then want to send a window update to peer.
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*/
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if (win > 0) {
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/*
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* "adv" is the amount we can increase the window,
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* taking into account that we are limited by
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* TCP_MAXWIN << tp->rcv_scale.
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*/
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long adv = min(win, (long)TCP_MAXWIN << tp->rcv_scale) -
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(tp->rcv_adv - tp->rcv_nxt);
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if (adv >= (long) (2 * tp->t_maxseg))
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goto send;
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if (2 * adv >= (long) so->so_rcv.sb_datalen)
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goto send;
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}
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/*
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* Send if we owe peer an ACK.
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*/
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if (tp->t_flags & TF_ACKNOW)
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goto send;
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if (flags & (TH_SYN|TH_RST))
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goto send;
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if (SEQ_GT(tp->snd_up, tp->snd_una))
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goto send;
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/*
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* If our state indicates that FIN should be sent
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* and we have not yet done so, or we're retransmitting the FIN,
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* then we need to send.
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*/
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if (flags & TH_FIN &&
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((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
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goto send;
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/*
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* TCP window updates are not reliable, rather a polling protocol
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* using ``persist'' packets is used to insure receipt of window
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* updates. The three ``states'' for the output side are:
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* idle not doing retransmits or persists
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* persisting to move a small or zero window
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* (re)transmitting and thereby not persisting
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*
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* tp->t_timer[TCPT_PERSIST]
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* is set when we are in persist state.
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* tp->t_force
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* is set when we are called to send a persist packet.
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* tp->t_timer[TCPT_REXMT]
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* is set when we are retransmitting
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* The output side is idle when both timers are zero.
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*
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* If send window is too small, there is data to transmit, and no
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* retransmit or persist is pending, then go to persist state.
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* If nothing happens soon, send when timer expires:
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* if window is nonzero, transmit what we can,
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* otherwise force out a byte.
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*/
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if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 &&
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tp->t_timer[TCPT_PERSIST] == 0) {
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tp->t_rxtshift = 0;
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tcp_setpersist(tp);
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}
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/*
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* No reason to send a segment, just return.
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*/
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return (0);
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send:
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/*
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* Before ESTABLISHED, force sending of initial options
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* unless TCP set not to do any options.
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* NOTE: we assume that the IP/TCP header plus TCP options
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* always fit in a single mbuf, leaving room for a maximum
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* link header, i.e.
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* max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MHLEN
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*/
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optlen = 0;
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hdrlen = sizeof (struct tcpiphdr);
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if (flags & TH_SYN) {
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tp->snd_nxt = tp->iss;
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if ((tp->t_flags & TF_NOOPT) == 0) {
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uint16_t mss;
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opt[0] = TCPOPT_MAXSEG;
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opt[1] = 4;
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mss = htons((uint16_t) tcp_mss(tp, 0));
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memcpy((caddr_t)(opt + 2), (caddr_t)&mss, sizeof(mss));
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optlen = 4;
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}
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}
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hdrlen += optlen;
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/*
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* Adjust data length if insertion of options will
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* bump the packet length beyond the t_maxseg length.
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*/
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if (len > tp->t_maxseg - optlen) {
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len = tp->t_maxseg - optlen;
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sendalot = 1;
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}
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/*
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* Grab a header mbuf, attaching a copy of data to
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* be transmitted, and initialize the header from
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* the template for sends on this connection.
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*/
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if (len) {
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m = m_get(so->slirp);
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if (m == NULL) {
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error = 1;
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goto out;
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}
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m->m_data += IF_MAXLINKHDR;
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m->m_len = hdrlen;
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sbcopy(&so->so_snd, off, (int) len, mtod(m, caddr_t) + hdrlen);
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m->m_len += len;
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/*
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* If we're sending everything we've got, set PUSH.
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* (This will keep happy those implementations which only
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* give data to the user when a buffer fills or
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* a PUSH comes in.)
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*/
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if (off + len == so->so_snd.sb_cc)
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flags |= TH_PUSH;
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} else {
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m = m_get(so->slirp);
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if (m == NULL) {
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error = 1;
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goto out;
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}
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m->m_data += IF_MAXLINKHDR;
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m->m_len = hdrlen;
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}
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ti = mtod(m, struct tcpiphdr *);
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memcpy((caddr_t)ti, &tp->t_template, sizeof (struct tcpiphdr));
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/*
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* Fill in fields, remembering maximum advertised
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* window for use in delaying messages about window sizes.
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* If resending a FIN, be sure not to use a new sequence number.
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*/
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if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
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tp->snd_nxt == tp->snd_max)
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tp->snd_nxt--;
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/*
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* If we are doing retransmissions, then snd_nxt will
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* not reflect the first unsent octet. For ACK only
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* packets, we do not want the sequence number of the
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* retransmitted packet, we want the sequence number
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* of the next unsent octet. So, if there is no data
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* (and no SYN or FIN), use snd_max instead of snd_nxt
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* when filling in ti_seq. But if we are in persist
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* state, snd_max might reflect one byte beyond the
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* right edge of the window, so use snd_nxt in that
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* case, since we know we aren't doing a retransmission.
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* (retransmit and persist are mutually exclusive...)
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*/
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if (len || (flags & (TH_SYN|TH_FIN)) || tp->t_timer[TCPT_PERSIST])
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ti->ti_seq = htonl(tp->snd_nxt);
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else
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ti->ti_seq = htonl(tp->snd_max);
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ti->ti_ack = htonl(tp->rcv_nxt);
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if (optlen) {
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memcpy((caddr_t)(ti + 1), (caddr_t)opt, optlen);
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ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;
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}
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ti->ti_flags = flags;
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/*
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* Calculate receive window. Don't shrink window,
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* but avoid silly window syndrome.
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*/
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if (win < (long)(so->so_rcv.sb_datalen / 4) && win < (long)tp->t_maxseg)
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win = 0;
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if (win > (long)TCP_MAXWIN << tp->rcv_scale)
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win = (long)TCP_MAXWIN << tp->rcv_scale;
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if (win < (long)(tp->rcv_adv - tp->rcv_nxt))
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win = (long)(tp->rcv_adv - tp->rcv_nxt);
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ti->ti_win = htons((uint16_t) (win>>tp->rcv_scale));
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if (SEQ_GT(tp->snd_up, tp->snd_una)) {
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ti->ti_urp = htons((uint16_t)(tp->snd_up - ntohl(ti->ti_seq)));
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ti->ti_flags |= TH_URG;
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} else
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/*
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* If no urgent pointer to send, then we pull
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* the urgent pointer to the left edge of the send window
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* so that it doesn't drift into the send window on sequence
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* number wraparound.
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*/
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tp->snd_up = tp->snd_una; /* drag it along */
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/*
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* Put TCP length in extended header, and then
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* checksum extended header and data.
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*/
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if (len + optlen)
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ti->ti_len = htons((uint16_t)(sizeof (struct tcphdr) +
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optlen + len));
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ti->ti_sum = cksum(m, (int)(hdrlen + len));
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/*
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* In transmit state, time the transmission and arrange for
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* the retransmit. In persist state, just set snd_max.
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*/
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if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) {
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tcp_seq startseq = tp->snd_nxt;
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/*
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* Advance snd_nxt over sequence space of this segment.
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*/
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if (flags & (TH_SYN|TH_FIN)) {
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if (flags & TH_SYN)
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tp->snd_nxt++;
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if (flags & TH_FIN) {
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tp->snd_nxt++;
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tp->t_flags |= TF_SENTFIN;
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}
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}
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tp->snd_nxt += len;
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if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
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tp->snd_max = tp->snd_nxt;
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/*
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* Time this transmission if not a retransmission and
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* not currently timing anything.
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*/
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if (tp->t_rtt == 0) {
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tp->t_rtt = 1;
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tp->t_rtseq = startseq;
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}
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}
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/*
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* Set retransmit timer if not currently set,
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* and not doing an ack or a keep-alive probe.
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* Initial value for retransmit timer is smoothed
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* round-trip time + 2 * round-trip time variance.
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* Initialize shift counter which is used for backoff
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* of retransmit time.
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*/
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if (tp->t_timer[TCPT_REXMT] == 0 &&
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tp->snd_nxt != tp->snd_una) {
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tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
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if (tp->t_timer[TCPT_PERSIST]) {
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tp->t_timer[TCPT_PERSIST] = 0;
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tp->t_rxtshift = 0;
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}
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}
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} else
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if (SEQ_GT(tp->snd_nxt + len, tp->snd_max))
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tp->snd_max = tp->snd_nxt + len;
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/*
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* Fill in IP length and desired time to live and
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* send to IP level. There should be a better way
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* to handle ttl and tos; we could keep them in
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* the template, but need a way to checksum without them.
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*/
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m->m_len = hdrlen + len; /* XXX Needed? m_len should be correct */
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{
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((struct ip *)ti)->ip_len = m->m_len;
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((struct ip *)ti)->ip_ttl = IPDEFTTL;
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((struct ip *)ti)->ip_tos = so->so_iptos;
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error = ip_output(so, m);
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}
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if (error) {
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out:
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return (error);
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}
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/*
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* Data sent (as far as we can tell).
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* If this advertises a larger window than any other segment,
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* then remember the size of the advertised window.
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* Any pending ACK has now been sent.
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*/
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if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))
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tp->rcv_adv = tp->rcv_nxt + win;
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tp->last_ack_sent = tp->rcv_nxt;
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tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);
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if (sendalot)
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goto again;
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return (0);
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}
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void
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tcp_setpersist(struct tcpcb *tp)
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{
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int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
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/*
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* Start/restart persistence timer.
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*/
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TCPT_RANGESET(tp->t_timer[TCPT_PERSIST],
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t * tcp_backoff[tp->t_rxtshift],
|
|
TCPTV_PERSMIN, TCPTV_PERSMAX);
|
|
if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
|
|
tp->t_rxtshift++;
|
|
}
|