| 1 | /* $Id: tcp_timer.c 98103 2023-01-17 14:15:46Z vboxsync $ */
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| 2 | /** @file
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| 3 | * NAT - TCP timers.
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| 4 | */
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| 5 |
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| 6 | /*
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| 7 | * Copyright (C) 2006-2023 Oracle and/or its affiliates.
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| 8 | *
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| 9 | * This file is part of VirtualBox base platform packages, as
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| 10 | * available from https://www.virtualbox.org.
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| 11 | *
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| 12 | * This program is free software; you can redistribute it and/or
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| 13 | * modify it under the terms of the GNU General Public License
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| 14 | * as published by the Free Software Foundation, in version 3 of the
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| 15 | * License.
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| 16 | *
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| 17 | * This program is distributed in the hope that it will be useful, but
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| 18 | * WITHOUT ANY WARRANTY; without even the implied warranty of
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| 19 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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| 20 | * General Public License for more details.
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| 21 | *
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| 22 | * You should have received a copy of the GNU General Public License
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| 23 | * along with this program; if not, see <https://www.gnu.org/licenses>.
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| 24 | *
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| 25 | * SPDX-License-Identifier: GPL-3.0-only
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| 26 | */
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| 27 |
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| 28 | /*
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| 29 | * This code is based on:
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| 30 | *
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| 31 | * Copyright (c) 1982, 1986, 1988, 1990, 1993
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| 32 | * The Regents of the University of California. All rights reserved.
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| 33 | *
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| 34 | * Redistribution and use in source and binary forms, with or without
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| 35 | * modification, are permitted provided that the following conditions
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| 36 | * are met:
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| 37 | * 1. Redistributions of source code must retain the above copyright
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| 38 | * notice, this list of conditions and the following disclaimer.
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| 39 | * 2. Redistributions in binary form must reproduce the above copyright
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| 40 | * notice, this list of conditions and the following disclaimer in the
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| 41 | * documentation and/or other materials provided with the distribution.
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| 42 | * 3. Neither the name of the University nor the names of its contributors
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| 43 | * may be used to endorse or promote products derived from this software
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| 44 | * without specific prior written permission.
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| 45 | *
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| 46 | * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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| 47 | * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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| 48 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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| 49 | * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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| 50 | * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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| 51 | * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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| 52 | * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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| 53 | * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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| 54 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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| 55 | * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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| 56 | * SUCH DAMAGE.
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| 57 | *
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| 58 | * @(#)tcp_timer.c 8.1 (Berkeley) 6/10/93
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| 59 | * tcp_timer.c,v 1.2 1994/08/02 07:49:10 davidg Exp
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| 60 | */
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| 61 |
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| 62 | #include <slirp.h>
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| 63 |
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| 64 |
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| 65 | static struct tcpcb *tcp_timers(PNATState pData, register struct tcpcb *tp, int timer);
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| 66 | /*
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| 67 | * Fast timeout routine for processing delayed acks
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| 68 | */
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| 69 | void
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| 70 | tcp_fasttimo(PNATState pData)
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| 71 | {
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| 72 | register struct socket *so, *so_next;
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| 73 | register struct tcpcb *tp;
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| 74 |
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| 75 | LogFlowFuncEnter();
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| 76 |
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| 77 | so = tcb.so_next;
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| 78 | if (so)
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| 79 | QSOCKET_FOREACH (so, so_next, tcp)
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| 80 | /* { */
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| 81 | if ( (tp = (struct tcpcb *)so->so_tcpcb)
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| 82 | && (tp->t_flags & TF_DELACK))
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| 83 | {
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| 84 | tp->t_flags &= ~TF_DELACK;
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| 85 | tp->t_flags |= TF_ACKNOW;
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| 86 | tcpstat.tcps_delack++;
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| 87 | TCP_OUTPUT(pData, tp);
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| 88 | }
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| 89 | LOOP_LABEL(tcp, so, so_next);
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| 90 | }
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| 91 | }
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| 92 |
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| 93 | /*
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| 94 | * Tcp protocol timeout routine called every 500 ms.
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| 95 | * Updates the timers in all active tcb's and
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| 96 | * causes finite state machine actions if timers expire.
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| 97 | */
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| 98 | void
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| 99 | tcp_slowtimo(PNATState pData)
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| 100 | {
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| 101 | register struct socket *ip, *ipnxt;
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| 102 | register struct tcpcb *tp;
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| 103 | register int i;
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| 104 |
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| 105 | LogFlowFuncEnter();
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| 106 |
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| 107 | /*
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| 108 | * Search through tcb's and update active timers.
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| 109 | */
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| 110 | ip = tcb.so_next;
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| 111 | if (ip == 0)
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| 112 | return;
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| 113 | QSOCKET_FOREACH(ip, ipnxt, tcp)
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| 114 | /* { */
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| 115 | ipnxt = ip->so_next;
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| 116 | tp = sototcpcb(ip);
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| 117 | if (tp == 0)
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| 118 | CONTINUE(tcp);
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| 119 | for (i = 0; i < TCPT_NTIMERS; i++)
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| 120 | {
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| 121 | if (tp->t_timer[i] && --tp->t_timer[i] == 0)
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| 122 | {
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| 123 | tcp_timers(pData, tp, i);
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| 124 | if (ipnxt->so_prev != ip)
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| 125 | goto tpgone;
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| 126 | }
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| 127 | }
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| 128 | tp->t_idle++;
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| 129 | if (tp->t_rtt)
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| 130 | tp->t_rtt++;
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| 131 | tpgone:
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| 132 | ;
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| 133 | LOOP_LABEL(tcp, ip, ipnxt);
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| 134 | }
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| 135 | tcp_iss += TCP_ISSINCR / PR_SLOWHZ; /* increment iss */
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| 136 | #ifdef TCP_COMPAT_42
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| 137 | if ((int)tcp_iss < 0)
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| 138 | tcp_iss = 0; /* XXX */
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| 139 | #endif
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| 140 | tcp_now++; /* for timestamps */
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| 141 | }
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| 142 |
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| 143 | /*
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| 144 | * Cancel all timers for TCP tp.
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| 145 | */
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| 146 | void
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| 147 | tcp_canceltimers(struct tcpcb *tp)
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| 148 | {
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| 149 | register int i;
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| 150 |
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| 151 | for (i = 0; i < TCPT_NTIMERS; i++)
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| 152 | tp->t_timer[i] = 0;
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| 153 | }
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| 154 |
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| 155 | const int tcp_backoff[TCP_MAXRXTSHIFT + 1] =
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| 156 | {
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| 157 | 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64
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| 158 | };
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| 159 |
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| 160 | /*
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| 161 | * TCP timer processing.
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| 162 | */
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| 163 | static struct tcpcb *
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| 164 | tcp_timers(PNATState pData, register struct tcpcb *tp, int timer)
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| 165 | {
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| 166 | register int rexmt;
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| 167 | int fUninitializedTemplate = 0;
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| 168 |
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| 169 | LogFlowFunc(("ENTER: tp:%R[tcpcb793], timer:%d\n", tp, timer));
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| 170 | fUninitializedTemplate = RT_BOOL(( tp->t_template.ti_src.s_addr == INADDR_ANY
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| 171 | || tp->t_template.ti_dst.s_addr == INADDR_ANY));
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| 172 | if (fUninitializedTemplate)
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| 173 | {
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| 174 | tp = tcp_drop(pData, tp, 0);
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| 175 | return tp;
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| 176 | }
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| 177 |
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| 178 | switch (timer)
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| 179 | {
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| 180 | /*
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| 181 | * 2 MSL timeout in shutdown went off. If we're closed but
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| 182 | * still waiting for peer to close and connection has been idle
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| 183 | * too long, or if 2MSL time is up from TIME_WAIT, delete connection
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| 184 | * control block. Otherwise, check again in a bit.
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| 185 | */
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| 186 | case TCPT_2MSL:
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| 187 | if (tp->t_state != TCPS_TIME_WAIT &&
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| 188 | tp->t_idle <= tcp_maxidle)
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| 189 | tp->t_timer[TCPT_2MSL] = tcp_keepintvl;
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| 190 | else
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| 191 | tp = tcp_close(pData, tp);
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| 192 | break;
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| 193 |
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| 194 | /*
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| 195 | * Retransmission timer went off. Message has not
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| 196 | * been acked within retransmit interval. Back off
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| 197 | * to a longer retransmit interval and retransmit one segment.
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| 198 | */
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| 199 | case TCPT_REXMT:
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| 200 | STAM_COUNTER_INC(&pData->StatTCP_retransmit);
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| 201 | /*
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| 202 | * XXX If a packet has timed out, then remove all the queued
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| 203 | * packets for that session.
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| 204 | */
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| 205 | if (++tp->t_rxtshift > TCP_MAXRXTSHIFT)
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| 206 | {
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| 207 | /*
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| 208 | * This is a hack to suit our terminal server here at the uni of canberra
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| 209 | * since they have trouble with zeroes... It usually lets them through
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| 210 | * unharmed, but under some conditions, it'll eat the zeros. If we
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| 211 | * keep retransmitting it, it'll keep eating the zeroes, so we keep
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| 212 | * retransmitting, and eventually the connection dies...
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| 213 | * (this only happens on incoming data)
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| 214 | *
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| 215 | * So, if we were gonna drop the connection from too many retransmits,
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| 216 | * don't... instead halve the t_maxseg, which might break up the NULLs and
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| 217 | * let them through
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| 218 | *
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| 219 | * *sigh*
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| 220 | */
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| 221 | tp->t_maxseg >>= 1;
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| 222 | if (tp->t_maxseg < 32)
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| 223 | {
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| 224 | /*
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| 225 | * We tried our best, now the connection must die!
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| 226 | */
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| 227 | tp->t_rxtshift = TCP_MAXRXTSHIFT;
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| 228 | tcpstat.tcps_timeoutdrop++;
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| 229 | tp = tcp_drop(pData, tp, tp->t_softerror);
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| 230 | /* tp->t_softerror : ETIMEDOUT); */ /* XXX */
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| 231 | return (tp); /* XXX */
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| 232 | }
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| 233 |
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| 234 | /*
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| 235 | * Set rxtshift to 6, which is still at the maximum
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| 236 | * backoff time
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| 237 | */
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| 238 | tp->t_rxtshift = 6;
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| 239 | }
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| 240 | tcpstat.tcps_rexmttimeo++;
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| 241 | rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
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| 242 | TCPT_RANGESET(tp->t_rxtcur, rexmt,
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| 243 | (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */
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| 244 | tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
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| 245 | /*
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| 246 | * If losing, let the lower level know and try for
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| 247 | * a better route. Also, if we backed off this far,
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| 248 | * our srtt estimate is probably bogus. Clobber it
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| 249 | * so we'll take the next rtt measurement as our srtt;
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| 250 | * move the current srtt into rttvar to keep the current
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| 251 | * retransmit times until then.
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| 252 | */
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| 253 | if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4)
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| 254 | {
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| 255 | /* in_losing(tp->t_inpcb); */
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| 256 | tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
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| 257 | tp->t_srtt = 0;
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| 258 | }
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| 259 | tp->snd_nxt = tp->snd_una;
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| 260 | /*
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| 261 | * If timing a segment in this window, stop the timer.
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| 262 | */
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| 263 | tp->t_rtt = 0;
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| 264 | /*
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| 265 | * Close the congestion window down to one segment
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| 266 | * (we'll open it by one segment for each ack we get).
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| 267 | * Since we probably have a window's worth of unacked
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| 268 | * data accumulated, this "slow start" keeps us from
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| 269 | * dumping all that data as back-to-back packets (which
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| 270 | * might overwhelm an intermediate gateway).
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| 271 | *
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| 272 | * There are two phases to the opening: Initially we
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| 273 | * open by one mss on each ack. This makes the window
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| 274 | * size increase exponentially with time. If the
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| 275 | * window is larger than the path can handle, this
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| 276 | * exponential growth results in dropped packet(s)
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| 277 | * almost immediately. To get more time between
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| 278 | * drops but still "push" the network to take advantage
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| 279 | * of improving conditions, we switch from exponential
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| 280 | * to linear window opening at some threshold size.
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| 281 | * For a threshold, we use half the current window
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| 282 | * size, truncated to a multiple of the mss.
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| 283 | *
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| 284 | * (the minimum cwnd that will give us exponential
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| 285 | * growth is 2 mss. We don't allow the threshold
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| 286 | * to go below this.)
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| 287 | */
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| 288 | {
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| 289 | u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
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| 290 | if (win < 2)
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| 291 | win = 2;
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| 292 | tp->snd_cwnd = tp->t_maxseg;
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| 293 | tp->snd_ssthresh = win * tp->t_maxseg;
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| 294 | tp->t_dupacks = 0;
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| 295 | }
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| 296 | (void) tcp_output(pData, tp);
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| 297 | break;
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| 298 |
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| 299 | /*
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| 300 | * Persistence timer into zero window.
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| 301 | * Force a byte to be output, if possible.
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| 302 | */
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| 303 | case TCPT_PERSIST:
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| 304 | tcpstat.tcps_persisttimeo++;
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| 305 | tcp_setpersist(tp);
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| 306 | tp->t_force = 1;
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| 307 | (void) tcp_output(pData, tp);
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| 308 | tp->t_force = 0;
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| 309 | break;
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| 310 |
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| 311 | /*
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| 312 | * Keep-alive timer went off; send something
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| 313 | * or drop connection if idle for too long.
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| 314 | */
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| 315 | case TCPT_KEEP:
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| 316 | tcpstat.tcps_keeptimeo++;
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| 317 | if (tp->t_state < TCPS_ESTABLISHED)
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| 318 | goto dropit;
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| 319 | /* if (tp->t_socket->so_options & SO_KEEPALIVE && */
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| 320 | if ((so_options) && tp->t_state <= TCPS_CLOSE_WAIT)
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| 321 | {
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| 322 | if (tp->t_idle >= tcp_keepidle + tcp_maxidle)
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| 323 | goto dropit;
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| 324 | /*
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| 325 | * Send a packet designed to force a response
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| 326 | * if the peer is up and reachable:
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| 327 | * either an ACK if the connection is still alive,
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| 328 | * or an RST if the peer has closed the connection
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| 329 | * due to timeout or reboot.
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| 330 | * Using sequence number tp->snd_una-1
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| 331 | * causes the transmitted zero-length segment
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| 332 | * to lie outside the receive window;
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| 333 | * by the protocol spec, this requires the
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| 334 | * correspondent TCP to respond.
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| 335 | */
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| 336 | tcpstat.tcps_keepprobe++;
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| 337 | #ifdef TCP_COMPAT_42
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| 338 | /*
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| 339 | * The keepalive packet must have nonzero length
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| 340 | * to get a 4.2 host to respond.
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| 341 | */
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| 342 | tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
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| 343 | tp->rcv_nxt - 1, tp->snd_una - 1, 0);
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| 344 | #else
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| 345 | tcp_respond(pData, tp, &tp->t_template, (struct mbuf *)NULL,
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| 346 | tp->rcv_nxt, tp->snd_una - 1, 0);
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| 347 | #endif
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| 348 | tp->t_timer[TCPT_KEEP] = tcp_keepintvl;
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| 349 | }
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| 350 | else
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| 351 | tp->t_timer[TCPT_KEEP] = tcp_keepidle;
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| 352 | break;
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| 353 |
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| 354 | dropit:
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| 355 | tcpstat.tcps_keepdrops++;
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| 356 | tp = tcp_drop(pData, tp, 0); /* ETIMEDOUT); */
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| 357 | break;
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| 358 | }
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| 359 |
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| 360 | return tp;
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| 361 | }
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