442 lines
12 KiB
C
442 lines
12 KiB
C
/*
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* Copyright (c) 1982, 1986 Regents of the University of California.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms are permitted
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* provided that this notice is preserved and that due credit is given
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* to the University of California at Berkeley. The name of the University
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* may not be used to endorse or promote products derived from this
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* software without specific prior written permission. This software
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* is provided ``as is'' without express or implied warranty.
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*
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* @(#)tcp_output.c 1.1 94/10/31 SMI; from UCB 7.13.1.3 3/24/88
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*/
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/mbuf.h>
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#include <sys/protosw.h>
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#include <sys/socket.h>
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#include <sys/socketvar.h>
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#include <sys/errno.h>
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#include <net/route.h>
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#include <netinet/in.h>
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#include <netinet/in_pcb.h>
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#include <netinet/in_systm.h>
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#include <netinet/ip.h>
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#include <netinet/ip_var.h>
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#include <netinet/tcp.h>
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#define TCPOUTFLAGS
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#include <netinet/tcp_fsm.h>
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#include <netinet/tcp_seq.h>
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#include <netinet/tcp_timer.h>
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#include <netinet/tcp_var.h>
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#include <netinet/tcpip.h>
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#include <netinet/tcp_debug.h>
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/*
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* Enough bytes so that the lower-level drivers normally do not need to
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* allocate another mbuf near the front of the chain.
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*/
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#define TCP_PRE_PAD 48
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/*
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* Initial options.
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*/
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u_char tcp_initopt[4] = { TCPOPT_MAXSEG, 4, 0x0, 0x0, };
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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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tcp_output(tp)
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register struct tcpcb *tp;
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{
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register struct socket *so = tp->t_inpcb->inp_socket;
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register int len, win;
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struct mbuf *m0;
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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;
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unsigned optlen = 0;
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int idle, sendalot;
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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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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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/*
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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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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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flags = tcp_outflags[tp->t_state];
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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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* 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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* 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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* 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 ((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)
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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 35% 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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int adv = win - (tp->rcv_adv - tp->rcv_nxt);
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if (so->so_rcv.sb_cc == 0 && adv >= 2 * tp->t_maxseg)
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goto send;
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if (100 * adv / so->so_rcv.sb_hiwat >= 35)
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goto send;
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}
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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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* 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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* Ideally we would just decrement m_off in the normal case here,
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* but for now, we just leave some space before and after the header
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* to reduce the number of extra mbuf allocations at the lower levels.
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*/
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MGET(m, M_DONTWAIT, MT_HEADER);
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if (m == NULL)
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return (ENOBUFS);
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m->m_off = MMAXOFF - sizeof (struct tcpiphdr) - TCP_PRE_PAD;
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m->m_len = sizeof (struct tcpiphdr);
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if (len) {
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if (tp->t_force && len == 1)
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tcpstat.tcps_sndprobe++;
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else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
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tcpstat.tcps_sndrexmitpack++;
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tcpstat.tcps_sndrexmitbyte += len;
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} else {
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tcpstat.tcps_sndpack++;
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tcpstat.tcps_sndbyte += len;
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}
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m->m_next = m_copy(so->so_snd.sb_mb, off, len);
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if (m->m_next == 0)
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len = 0;
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} else if (tp->t_flags & TF_ACKNOW)
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tcpstat.tcps_sndacks++;
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else if (flags & (TH_SYN|TH_FIN|TH_RST))
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tcpstat.tcps_sndctrl++;
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else if (SEQ_GT(tp->snd_up, tp->snd_una))
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tcpstat.tcps_sndurg++;
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else
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tcpstat.tcps_sndwinup++;
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ti = mtod(m, struct tcpiphdr *);
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if (tp->t_template == 0)
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panic("tcp_output");
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bcopy((caddr_t)tp->t_template, (caddr_t)ti, 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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ti->ti_seq = htonl(tp->snd_nxt);
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ti->ti_ack = htonl(tp->rcv_nxt);
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/*
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* Before ESTABLISHED, force sending of initial options
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* unless TCP set to not do any options.
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*/
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opt = NULL;
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if (flags & TH_SYN && (tp->t_flags & TF_NOOPT) == 0) {
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u_short mss;
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mss = tcp_mss(tp);
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if (mss > IP_MSS - sizeof(struct tcpiphdr)) {
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opt = tcp_initopt;
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optlen = sizeof (tcp_initopt);
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*(u_short *)(opt + 2) = htons(mss);
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}
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}
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if (opt) {
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m0 = m->m_next;
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m->m_next = m_get(M_DONTWAIT, MT_DATA);
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if (m->m_next == 0) {
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(void) m_free(m);
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m_freem(m0);
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return (ENOBUFS);
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}
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m->m_next->m_next = m0;
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m0 = m->m_next;
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m0->m_len = optlen;
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bcopy((caddr_t)opt, mtod(m0, caddr_t), optlen);
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opt = (u_char *)(mtod(m0, caddr_t) + optlen);
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while (m0->m_len & 0x3) {
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*opt++ = TCPOPT_EOL;
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m0->m_len++;
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}
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optlen = m0->m_len;
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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_hiwat / 4 && win < (long)tp->t_maxseg)
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win = 0;
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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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if (win > IP_MAXPACKET)
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win = IP_MAXPACKET;
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ti->ti_win = htons((u_short)win);
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if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
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ti->ti_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
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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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* If anything to send and we can send it all, 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 a PUSH comes in.)
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*/
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if (len && off+len == so->so_snd.sb_cc)
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ti->ti_flags |= TH_PUSH;
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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((u_short)(sizeof(struct tcphdr) +
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optlen + len));
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ti->ti_sum = in_cksum(m, sizeof (struct tcpiphdr) + (int)optlen + 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)
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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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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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tcpstat.tcps_segstimed++;
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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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* Trace.
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*/
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if (so->so_options & SO_DEBUG)
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tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0);
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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.
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*/
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((struct ip *)ti)->ip_len = sizeof (struct tcpiphdr) + optlen + len;
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((struct ip *)ti)->ip_ttl = tcp_ttl;
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error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
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so->so_options & SO_DONTROUTE);
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if (error) {
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if (error == ENOBUFS) {
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tcp_quench(tp->t_inpcb);
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return (0);
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}
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return (error);
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}
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tcpstat.tcps_sndtotal++;
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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->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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tcp_setpersist(tp)
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register struct tcpcb *tp;
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{
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register t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
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if (tp->t_timer[TCPT_REXMT])
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panic("tcp_output REXMT");
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/*
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* Start/restart persistance 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],
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TCPTV_PERSMIN, TCPTV_PERSMAX);
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if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
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tp->t_rxtshift++;
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}
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