The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_output.c

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    1 /*
    2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
    3  *      The Regents of the University of California.  All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  * 4. Neither the name of the University nor the names of its contributors
   14  *    may be used to endorse or promote products derived from this software
   15  *    without specific prior written permission.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   27  * SUCH DAMAGE.
   28  *
   29  *      @(#)tcp_output.c        8.4 (Berkeley) 5/24/95
   30  * $FreeBSD: releng/5.3/sys/netinet/tcp_output.c 137082 2004-10-30 20:50:06Z rwatson $
   31  */
   32 
   33 #include "opt_inet.h"
   34 #include "opt_inet6.h"
   35 #include "opt_ipsec.h"
   36 #include "opt_mac.h"
   37 #include "opt_tcpdebug.h"
   38 #include "opt_tcp_sack.h"
   39 
   40 #include <sys/param.h>
   41 #include <sys/systm.h>
   42 #include <sys/domain.h>
   43 #include <sys/kernel.h>
   44 #include <sys/lock.h>
   45 #include <sys/mac.h>
   46 #include <sys/mbuf.h>
   47 #include <sys/mutex.h>
   48 #include <sys/protosw.h>
   49 #include <sys/socket.h>
   50 #include <sys/socketvar.h>
   51 #include <sys/sysctl.h>
   52 
   53 #include <net/route.h>
   54 
   55 #include <netinet/in.h>
   56 #include <netinet/in_systm.h>
   57 #include <netinet/ip.h>
   58 #include <netinet/in_pcb.h>
   59 #include <netinet/ip_var.h>
   60 #ifdef INET6
   61 #include <netinet6/in6_pcb.h>
   62 #include <netinet/ip6.h>
   63 #include <netinet6/ip6_var.h>
   64 #endif
   65 #include <netinet/tcp.h>
   66 #define TCPOUTFLAGS
   67 #include <netinet/tcp_fsm.h>
   68 #include <netinet/tcp_seq.h>
   69 #include <netinet/tcp_timer.h>
   70 #include <netinet/tcp_var.h>
   71 #include <netinet/tcpip.h>
   72 #ifdef TCPDEBUG
   73 #include <netinet/tcp_debug.h>
   74 #endif
   75 
   76 #ifdef IPSEC
   77 #include <netinet6/ipsec.h>
   78 #endif /*IPSEC*/
   79 
   80 #ifdef FAST_IPSEC
   81 #include <netipsec/ipsec.h>
   82 #define IPSEC
   83 #endif /*FAST_IPSEC*/
   84 
   85 #include <machine/in_cksum.h>
   86 
   87 #ifdef notyet
   88 extern struct mbuf *m_copypack();
   89 #endif
   90 
   91 int path_mtu_discovery = 1;
   92 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW,
   93         &path_mtu_discovery, 1, "Enable Path MTU Discovery");
   94 
   95 int ss_fltsz = 1;
   96 SYSCTL_INT(_net_inet_tcp, OID_AUTO, slowstart_flightsize, CTLFLAG_RW,
   97         &ss_fltsz, 1, "Slow start flight size");
   98 
   99 int ss_fltsz_local = 4;
  100 SYSCTL_INT(_net_inet_tcp, OID_AUTO, local_slowstart_flightsize, CTLFLAG_RW,
  101         &ss_fltsz_local, 1, "Slow start flight size for local networks");
  102 
  103 int     tcp_do_newreno = 1;
  104 SYSCTL_INT(_net_inet_tcp, OID_AUTO, newreno, CTLFLAG_RW, &tcp_do_newreno,
  105         0, "Enable NewReno Algorithms");
  106 
  107 /*
  108  * Tcp output routine: figure out what should be sent and send it.
  109  */
  110 int
  111 tcp_output(struct tcpcb *tp)
  112 {
  113         struct socket *so = tp->t_inpcb->inp_socket;
  114         long len, recwin, sendwin;
  115         int off, flags, error;
  116 #ifdef TCP_SIGNATURE
  117         int sigoff = 0;
  118 #endif
  119         struct mbuf *m;
  120         struct ip *ip = NULL;
  121         struct ipovly *ipov = NULL;
  122         struct tcphdr *th;
  123         u_char opt[TCP_MAXOLEN];
  124         unsigned ipoptlen, optlen, hdrlen;
  125         int idle, sendalot;
  126         int i, sack_rxmit;
  127         struct sackhole *p;
  128 #if 0
  129         int maxburst = TCP_MAXBURST;
  130 #endif
  131         struct rmxp_tao tao;
  132 #ifdef INET6
  133         struct ip6_hdr *ip6 = NULL;
  134         int isipv6;
  135 
  136         bzero(&tao, sizeof(tao));
  137         isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
  138 #endif
  139 
  140         INP_LOCK_ASSERT(tp->t_inpcb);
  141 
  142         /*
  143          * Determine length of data that should be transmitted,
  144          * and flags that will be used.
  145          * If there is some data or critical controls (SYN, RST)
  146          * to send, then transmit; otherwise, investigate further.
  147          */
  148         idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
  149         if (idle && (ticks - tp->t_rcvtime) >= tp->t_rxtcur) {
  150                 /*
  151                  * We have been idle for "a while" and no acks are
  152                  * expected to clock out any data we send --
  153                  * slow start to get ack "clock" running again.
  154                  *
  155                  * Set the slow-start flight size depending on whether
  156                  * this is a local network or not.
  157                  */
  158                 int ss = ss_fltsz;
  159 #ifdef INET6
  160                 if (isipv6) {
  161                         if (in6_localaddr(&tp->t_inpcb->in6p_faddr))
  162                                 ss = ss_fltsz_local;
  163                 } else
  164 #endif /* INET6 */
  165                 if (in_localaddr(tp->t_inpcb->inp_faddr))
  166                         ss = ss_fltsz_local;
  167                 tp->snd_cwnd = tp->t_maxseg * ss;
  168         }
  169         tp->t_flags &= ~TF_LASTIDLE;
  170         if (idle) {
  171                 if (tp->t_flags & TF_MORETOCOME) {
  172                         tp->t_flags |= TF_LASTIDLE;
  173                         idle = 0;
  174                 }
  175         }
  176 again:
  177         /*
  178          * If we've recently taken a timeout, snd_max will be greater than
  179          * snd_nxt.  There may be SACK information that allows us to avoid
  180          * resending already delivered data.  Adjust snd_nxt accordingly.
  181          */
  182         if (tp->sack_enable && SEQ_LT(tp->snd_nxt, tp->snd_max))
  183                 tcp_sack_adjust(tp);
  184         sendalot = 0;
  185         off = tp->snd_nxt - tp->snd_una;
  186         sendwin = min(tp->snd_wnd, tp->snd_cwnd);
  187         sendwin = min(sendwin, tp->snd_bwnd);
  188 
  189         flags = tcp_outflags[tp->t_state];
  190         /*
  191          * Send any SACK-generated retransmissions.  If we're explicitly trying
  192          * to send out new data (when sendalot is 1), bypass this function.
  193          * If we retransmit in fast recovery mode, decrement snd_cwnd, since
  194          * we're replacing a (future) new transmission with a retransmission
  195          * now, and we previously incremented snd_cwnd in tcp_input().
  196          */
  197         /*
  198          * Still in sack recovery , reset rxmit flag to zero.
  199          */
  200         sack_rxmit = 0;
  201         len = 0;
  202         p = NULL;
  203         if (tp->sack_enable && IN_FASTRECOVERY(tp) &&
  204             (p = tcp_sack_output(tp))) {
  205                 KASSERT(tp->snd_cwnd >= 0,
  206                         ("%s: CWIN is negative : %ld", __func__, tp->snd_cwnd));
  207                 /* Do not retransmit SACK segments beyond snd_recover */
  208                 if (SEQ_GT(p->end, tp->snd_recover)) {
  209                         /*
  210                          * (At least) part of sack hole extends beyond
  211                          * snd_recover. Check to see if we can rexmit data
  212                          * for this hole.
  213                          */
  214                         if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
  215                                 /*
  216                                  * Can't rexmit any more data for this hole.
  217                                  * That data will be rexmitted in the next
  218                                  * sack recovery episode, when snd_recover
  219                                  * moves past p->rxmit.
  220                                  */
  221                                 p = NULL;
  222                                 goto after_sack_rexmit;
  223                         } else
  224                                 /* Can rexmit part of the current hole */
  225                                 len = ((long)ulmin(tp->snd_cwnd,
  226                                           tp->snd_recover - p->rxmit));
  227                 } else
  228                         len = ((long)ulmin(tp->snd_cwnd, p->end - p->rxmit));
  229                 off = p->rxmit - tp->snd_una;
  230                 KASSERT(off >= 0,("%s: sack block to the left of una : %d",
  231                     __func__, off));
  232                 if (len > 0) {
  233                         sack_rxmit = 1;
  234                         sendalot = 1;
  235                         tcpstat.tcps_sack_rexmits++;
  236                         tcpstat.tcps_sack_rexmit_bytes +=
  237                             min(len, tp->t_maxseg);
  238                 }
  239         }
  240 after_sack_rexmit:
  241         /*
  242          * Get standard flags, and add SYN or FIN if requested by 'hidden'
  243          * state flags.
  244          */
  245         if (tp->t_flags & TF_NEEDFIN)
  246                 flags |= TH_FIN;
  247         if (tp->t_flags & TF_NEEDSYN)
  248                 flags |= TH_SYN;
  249 
  250         SOCKBUF_LOCK(&so->so_snd);
  251         /*
  252          * If in persist timeout with window of 0, send 1 byte.
  253          * Otherwise, if window is small but nonzero
  254          * and timer expired, we will send what we can
  255          * and go to transmit state.
  256          */
  257         if (tp->t_force) {
  258                 if (sendwin == 0) {
  259                         /*
  260                          * If we still have some data to send, then
  261                          * clear the FIN bit.  Usually this would
  262                          * happen below when it realizes that we
  263                          * aren't sending all the data.  However,
  264                          * if we have exactly 1 byte of unsent data,
  265                          * then it won't clear the FIN bit below,
  266                          * and if we are in persist state, we wind
  267                          * up sending the packet without recording
  268                          * that we sent the FIN bit.
  269                          *
  270                          * We can't just blindly clear the FIN bit,
  271                          * because if we don't have any more data
  272                          * to send then the probe will be the FIN
  273                          * itself.
  274                          */
  275                         if (off < so->so_snd.sb_cc)
  276                                 flags &= ~TH_FIN;
  277                         sendwin = 1;
  278                 } else {
  279                         callout_stop(tp->tt_persist);
  280                         tp->t_rxtshift = 0;
  281                 }
  282         }
  283 
  284         /*
  285          * If snd_nxt == snd_max and we have transmitted a FIN, the
  286          * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
  287          * a negative length.  This can also occur when TCP opens up
  288          * its congestion window while receiving additional duplicate
  289          * acks after fast-retransmit because TCP will reset snd_nxt
  290          * to snd_max after the fast-retransmit.
  291          *
  292          * In the normal retransmit-FIN-only case, however, snd_nxt will
  293          * be set to snd_una, the offset will be 0, and the length may
  294          * wind up 0.
  295          *
  296          * If sack_rxmit is true we are retransmitting from the scoreboard
  297          * in which case len is already set.
  298          */
  299         if (!sack_rxmit)
  300                 len = ((long)ulmin(so->so_snd.sb_cc, sendwin) - off);
  301 
  302         /*
  303          * Lop off SYN bit if it has already been sent.  However, if this
  304          * is SYN-SENT state and if segment contains data and if we don't
  305          * know that foreign host supports TAO, suppress sending segment.
  306          */
  307         if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
  308                 flags &= ~TH_SYN;
  309                 off--, len++;
  310                 if (tcp_do_rfc1644)
  311                         tcp_hc_gettao(&tp->t_inpcb->inp_inc, &tao);
  312                 if (len > 0 && tp->t_state == TCPS_SYN_SENT &&
  313                      tao.tao_ccsent == 0)
  314                         goto just_return;
  315         }
  316 
  317         /*
  318          * Be careful not to send data and/or FIN on SYN segments
  319          * in cases when no CC option will be sent.
  320          * This measure is needed to prevent interoperability problems
  321          * with not fully conformant TCP implementations.
  322          */
  323         if ((flags & TH_SYN) &&
  324             ((tp->t_flags & TF_NOOPT) || !(tp->t_flags & TF_REQ_CC) ||
  325              ((flags & TH_ACK) && !(tp->t_flags & TF_RCVD_CC)))) {
  326                 len = 0;
  327                 flags &= ~TH_FIN;
  328         }
  329 
  330         if (len < 0) {
  331                 /*
  332                  * If FIN has been sent but not acked,
  333                  * but we haven't been called to retransmit,
  334                  * len will be < 0.  Otherwise, window shrank
  335                  * after we sent into it.  If window shrank to 0,
  336                  * cancel pending retransmit, pull snd_nxt back
  337                  * to (closed) window, and set the persist timer
  338                  * if it isn't already going.  If the window didn't
  339                  * close completely, just wait for an ACK.
  340                  */
  341                 len = 0;
  342                 if (sendwin == 0) {
  343                         callout_stop(tp->tt_rexmt);
  344                         tp->t_rxtshift = 0;
  345                         tp->snd_nxt = tp->snd_una;
  346                         if (!callout_active(tp->tt_persist))
  347                                 tcp_setpersist(tp);
  348                 }
  349         }
  350 
  351         /*
  352          * len will be >= 0 after this point.  Truncate to the maximum
  353          * segment length and ensure that FIN is removed if the length
  354          * no longer contains the last data byte.
  355          */
  356         if (len > tp->t_maxseg) {
  357                 len = tp->t_maxseg;
  358                 sendalot = 1;
  359         }
  360         if (sack_rxmit) {
  361                 if (SEQ_LT(p->rxmit + len, tp->snd_una + so->so_snd.sb_cc))
  362                         flags &= ~TH_FIN;
  363         } else {
  364                 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
  365                         flags &= ~TH_FIN;
  366         }
  367 
  368         recwin = sbspace(&so->so_rcv);
  369 
  370         /*
  371          * Sender silly window avoidance.   We transmit under the following
  372          * conditions when len is non-zero:
  373          *
  374          *      - We have a full segment
  375          *      - This is the last buffer in a write()/send() and we are
  376          *        either idle or running NODELAY
  377          *      - we've timed out (e.g. persist timer)
  378          *      - we have more then 1/2 the maximum send window's worth of
  379          *        data (receiver may be limited the window size)
  380          *      - we need to retransmit
  381          */
  382         if (len) {
  383                 if (len == tp->t_maxseg)
  384                         goto send;
  385                 /*
  386                  * NOTE! on localhost connections an 'ack' from the remote
  387                  * end may occur synchronously with the output and cause
  388                  * us to flush a buffer queued with moretocome.  XXX
  389                  *
  390                  * note: the len + off check is almost certainly unnecessary.
  391                  */
  392                 if (!(tp->t_flags & TF_MORETOCOME) &&   /* normal case */
  393                     (idle || (tp->t_flags & TF_NODELAY)) &&
  394                     len + off >= so->so_snd.sb_cc &&
  395                     (tp->t_flags & TF_NOPUSH) == 0) {
  396                         goto send;
  397                 }
  398                 if (tp->t_force)                        /* typ. timeout case */
  399                         goto send;
  400                 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
  401                         goto send;
  402                 if (SEQ_LT(tp->snd_nxt, tp->snd_max))   /* retransmit case */
  403                         goto send;
  404                 if (sack_rxmit)
  405                         goto send;
  406         }
  407 
  408         /*
  409          * Compare available window to amount of window
  410          * known to peer (as advertised window less
  411          * next expected input).  If the difference is at least two
  412          * max size segments, or at least 50% of the maximum possible
  413          * window, then want to send a window update to peer.
  414          * Skip this if the connection is in T/TCP half-open state.
  415          */
  416         if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN)) {
  417                 /*
  418                  * "adv" is the amount we can increase the window,
  419                  * taking into account that we are limited by
  420                  * TCP_MAXWIN << tp->rcv_scale.
  421                  */
  422                 long adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale) -
  423                         (tp->rcv_adv - tp->rcv_nxt);
  424 
  425                 if (adv >= (long) (2 * tp->t_maxseg))
  426                         goto send;
  427                 if (2 * adv >= (long) so->so_rcv.sb_hiwat)
  428                         goto send;
  429         }
  430 
  431         /*
  432          * Send if we owe the peer an ACK, RST, SYN, or urgent data.  ACKNOW
  433          * is also a catch-all for the retransmit timer timeout case.
  434          */
  435         if (tp->t_flags & TF_ACKNOW)
  436                 goto send;
  437         if ((flags & TH_RST) ||
  438             ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
  439                 goto send;
  440         if (SEQ_GT(tp->snd_up, tp->snd_una))
  441                 goto send;
  442         /*
  443          * If our state indicates that FIN should be sent
  444          * and we have not yet done so, then we need to send.
  445          */
  446         if (flags & TH_FIN &&
  447             ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
  448                 goto send;
  449         /*
  450          * In SACK, it is possible for tcp_output to fail to send a segment
  451          * after the retransmission timer has been turned off.  Make sure
  452          * that the retransmission timer is set.
  453          */
  454         if (tp->sack_enable && SEQ_GT(tp->snd_max, tp->snd_una) &&
  455             !callout_active(tp->tt_rexmt) &&
  456             !callout_active(tp->tt_persist)) {
  457                 callout_reset(tp->tt_rexmt, tp->t_rxtcur,
  458                               tcp_timer_rexmt, tp);
  459                 goto just_return;
  460         } 
  461         /*
  462          * TCP window updates are not reliable, rather a polling protocol
  463          * using ``persist'' packets is used to insure receipt of window
  464          * updates.  The three ``states'' for the output side are:
  465          *      idle                    not doing retransmits or persists
  466          *      persisting              to move a small or zero window
  467          *      (re)transmitting        and thereby not persisting
  468          *
  469          * callout_active(tp->tt_persist)
  470          *      is true when we are in persist state.
  471          * tp->t_force
  472          *      is set when we are called to send a persist packet.
  473          * callout_active(tp->tt_rexmt)
  474          *      is set when we are retransmitting
  475          * The output side is idle when both timers are zero.
  476          *
  477          * If send window is too small, there is data to transmit, and no
  478          * retransmit or persist is pending, then go to persist state.
  479          * If nothing happens soon, send when timer expires:
  480          * if window is nonzero, transmit what we can,
  481          * otherwise force out a byte.
  482          */
  483         if (so->so_snd.sb_cc && !callout_active(tp->tt_rexmt) &&
  484             !callout_active(tp->tt_persist)) {
  485                 tp->t_rxtshift = 0;
  486                 tcp_setpersist(tp);
  487         }
  488 
  489         /*
  490          * No reason to send a segment, just return.
  491          */
  492 just_return:
  493         SOCKBUF_UNLOCK(&so->so_snd);
  494         return (0);
  495 
  496 send:
  497         SOCKBUF_LOCK_ASSERT(&so->so_snd);
  498         /*
  499          * Before ESTABLISHED, force sending of initial options
  500          * unless TCP set not to do any options.
  501          * NOTE: we assume that the IP/TCP header plus TCP options
  502          * always fit in a single mbuf, leaving room for a maximum
  503          * link header, i.e.
  504          *      max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
  505          */
  506         optlen = 0;
  507 #ifdef INET6
  508         if (isipv6)
  509                 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
  510         else
  511 #endif
  512         hdrlen = sizeof (struct tcpiphdr);
  513         if (flags & TH_SYN) {
  514                 tp->snd_nxt = tp->iss;
  515                 if ((tp->t_flags & TF_NOOPT) == 0) {
  516                         u_short mss;
  517 
  518                         opt[0] = TCPOPT_MAXSEG;
  519                         opt[1] = TCPOLEN_MAXSEG;
  520                         mss = htons((u_short) tcp_mssopt(&tp->t_inpcb->inp_inc));
  521                         (void)memcpy(opt + 2, &mss, sizeof(mss));
  522                         optlen = TCPOLEN_MAXSEG;
  523 
  524                         /*
  525                          * If this is the first SYN of connection (not a SYN
  526                          * ACK), include SACK_PERMIT_HDR option.  If this is a
  527                          * SYN ACK, include SACK_PERMIT_HDR option if peer has
  528                          * already done so. This is only for active connect,
  529                          * since the syncache takes care of the passive connect.
  530                          */
  531                         if (tp->sack_enable && ((flags & TH_ACK) == 0 ||
  532                             (tp->t_flags & TF_SACK_PERMIT))) {
  533                                 *((u_int32_t *) (opt + optlen)) =
  534                                         htonl(TCPOPT_SACK_PERMIT_HDR);
  535                                 optlen += 4;
  536                         }
  537                         if ((tp->t_flags & TF_REQ_SCALE) &&
  538                             ((flags & TH_ACK) == 0 ||
  539                             (tp->t_flags & TF_RCVD_SCALE))) {
  540                                 *((u_int32_t *)(opt + optlen)) = htonl(
  541                                         TCPOPT_NOP << 24 |
  542                                         TCPOPT_WINDOW << 16 |
  543                                         TCPOLEN_WINDOW << 8 |
  544                                         tp->request_r_scale);
  545                                 optlen += 4;
  546                         }
  547                 }
  548         }
  549 
  550         /*
  551          * Send a timestamp and echo-reply if this is a SYN and our side
  552          * wants to use timestamps (TF_REQ_TSTMP is set) or both our side
  553          * and our peer have sent timestamps in our SYN's.
  554          */
  555         if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
  556             (flags & TH_RST) == 0 &&
  557             ((flags & TH_ACK) == 0 ||
  558              (tp->t_flags & TF_RCVD_TSTMP))) {
  559                 u_int32_t *lp = (u_int32_t *)(opt + optlen);
  560 
  561                 /* Form timestamp option as shown in appendix A of RFC 1323. */
  562                 *lp++ = htonl(TCPOPT_TSTAMP_HDR);
  563                 *lp++ = htonl(ticks);
  564                 *lp   = htonl(tp->ts_recent);
  565                 optlen += TCPOLEN_TSTAMP_APPA;
  566         }
  567 
  568         /*
  569          * Send SACKs if necessary.  This should be the last option processed.
  570          * Only as many SACKs are sent as are permitted by the maximum options
  571          * size.  No more than three SACKs are sent.
  572          */
  573         if (tp->sack_enable && tp->t_state == TCPS_ESTABLISHED &&
  574             (tp->t_flags & (TF_SACK_PERMIT|TF_NOOPT)) == TF_SACK_PERMIT &&
  575             tp->rcv_numsacks) {
  576                 u_int32_t *lp = (u_int32_t *)(opt + optlen);
  577                 u_int32_t *olp = lp++;
  578                 int count = 0;  /* actual number of SACKs inserted */
  579                 int maxsack = (MAX_TCPOPTLEN - (optlen + 4))/TCPOLEN_SACK;
  580 
  581                 tcpstat.tcps_sack_send_blocks++;
  582                 maxsack = min(maxsack, TCP_MAX_SACK);
  583                 for (i = 0; (i < tp->rcv_numsacks && count < maxsack); i++) {
  584                         struct sackblk sack = tp->sackblks[i];
  585                         if (sack.start == 0 && sack.end == 0)
  586                                 continue;
  587                         *lp++ = htonl(sack.start);
  588                         *lp++ = htonl(sack.end);
  589                         count++;
  590                 }
  591                 *olp = htonl(TCPOPT_SACK_HDR|(TCPOLEN_SACK*count+2));
  592                 optlen += TCPOLEN_SACK*count + 4; /* including leading NOPs */
  593         }
  594         /*
  595          * Send `CC-family' options if our side wants to use them (TF_REQ_CC),
  596          * options are allowed (!TF_NOOPT) and it's not a RST.
  597          */
  598         if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
  599              (flags & TH_RST) == 0) {
  600                 switch (flags & (TH_SYN|TH_ACK)) {
  601                 /*
  602                  * This is a normal ACK, send CC if we received CC before
  603                  * from our peer.
  604                  */
  605                 case TH_ACK:
  606                         if (!(tp->t_flags & TF_RCVD_CC))
  607                                 break;
  608                         /*FALLTHROUGH*/
  609 
  610                 /*
  611                  * We can only get here in T/TCP's SYN_SENT* state, when
  612                  * we're a sending a non-SYN segment without waiting for
  613                  * the ACK of our SYN.  A check above assures that we only
  614                  * do this if our peer understands T/TCP.
  615                  */
  616                 case 0:
  617                         opt[optlen++] = TCPOPT_NOP;
  618                         opt[optlen++] = TCPOPT_NOP;
  619                         opt[optlen++] = TCPOPT_CC;
  620                         opt[optlen++] = TCPOLEN_CC;
  621                         *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send);
  622 
  623                         optlen += 4;
  624                         break;
  625 
  626                 /*
  627                  * This is our initial SYN, check whether we have to use
  628                  * CC or CC.new.
  629                  */
  630                 case TH_SYN:
  631                         opt[optlen++] = TCPOPT_NOP;
  632                         opt[optlen++] = TCPOPT_NOP;
  633                         opt[optlen++] = tp->t_flags & TF_SENDCCNEW ?
  634                                                 TCPOPT_CCNEW : TCPOPT_CC;
  635                         opt[optlen++] = TCPOLEN_CC;
  636                         *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send);
  637                         optlen += 4;
  638                         break;
  639 
  640                 /*
  641                  * This is a SYN,ACK; send CC and CC.echo if we received
  642                  * CC from our peer.
  643                  */
  644                 case (TH_SYN|TH_ACK):
  645                         if (tp->t_flags & TF_RCVD_CC) {
  646                                 opt[optlen++] = TCPOPT_NOP;
  647                                 opt[optlen++] = TCPOPT_NOP;
  648                                 opt[optlen++] = TCPOPT_CC;
  649                                 opt[optlen++] = TCPOLEN_CC;
  650                                 *(u_int32_t *)&opt[optlen] =
  651                                         htonl(tp->cc_send);
  652                                 optlen += 4;
  653                                 opt[optlen++] = TCPOPT_NOP;
  654                                 opt[optlen++] = TCPOPT_NOP;
  655                                 opt[optlen++] = TCPOPT_CCECHO;
  656                                 opt[optlen++] = TCPOLEN_CC;
  657                                 *(u_int32_t *)&opt[optlen] =
  658                                         htonl(tp->cc_recv);
  659                                 optlen += 4;
  660                         }
  661                         break;
  662                 }
  663         }
  664 
  665 #ifdef TCP_SIGNATURE
  666 #ifdef INET6
  667         if (!isipv6)
  668 #endif
  669         if (tp->t_flags & TF_SIGNATURE) {
  670                 int i;
  671                 u_char *bp;
  672 
  673                 /* Initialize TCP-MD5 option (RFC2385) */
  674                 bp = (u_char *)opt + optlen;
  675                 *bp++ = TCPOPT_SIGNATURE;
  676                 *bp++ = TCPOLEN_SIGNATURE;
  677                 sigoff = optlen + 2;
  678                 for (i = 0; i < TCP_SIGLEN; i++)
  679                         *bp++ = 0;
  680                 optlen += TCPOLEN_SIGNATURE;
  681 
  682                 /* Terminate options list and maintain 32-bit alignment. */
  683                 *bp++ = TCPOPT_NOP;
  684                 *bp++ = TCPOPT_EOL;
  685                 optlen += 2;
  686         }
  687 #endif /* TCP_SIGNATURE */
  688 
  689         hdrlen += optlen;
  690 
  691 #ifdef INET6
  692         if (isipv6)
  693                 ipoptlen = ip6_optlen(tp->t_inpcb);
  694         else
  695 #endif
  696         if (tp->t_inpcb->inp_options)
  697                 ipoptlen = tp->t_inpcb->inp_options->m_len -
  698                                 offsetof(struct ipoption, ipopt_list);
  699         else
  700                 ipoptlen = 0;
  701 #ifdef IPSEC
  702         ipoptlen += ipsec_hdrsiz_tcp(tp);
  703 #endif
  704 
  705         /*
  706          * Adjust data length if insertion of options will
  707          * bump the packet length beyond the t_maxopd length.
  708          * Clear the FIN bit because we cut off the tail of
  709          * the segment.
  710          */
  711         if (len + optlen + ipoptlen > tp->t_maxopd) {
  712                 /*
  713                  * If there is still more to send, don't close the connection.
  714                  */
  715                 flags &= ~TH_FIN;
  716                 len = tp->t_maxopd - optlen - ipoptlen;
  717                 sendalot = 1;
  718         }
  719 
  720 /*#ifdef DIAGNOSTIC*/
  721 #ifdef INET6
  722         if (max_linkhdr + hdrlen > MCLBYTES)
  723 #else
  724         if (max_linkhdr + hdrlen > MHLEN)
  725 #endif
  726                 panic("tcphdr too big");
  727 /*#endif*/
  728 
  729         /*
  730          * Grab a header mbuf, attaching a copy of data to
  731          * be transmitted, and initialize the header from
  732          * the template for sends on this connection.
  733          */
  734         if (len) {
  735                 if (tp->t_force && len == 1)
  736                         tcpstat.tcps_sndprobe++;
  737                 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
  738                         tcpstat.tcps_sndrexmitpack++;
  739                         tcpstat.tcps_sndrexmitbyte += len;
  740                 } else {
  741                         tcpstat.tcps_sndpack++;
  742                         tcpstat.tcps_sndbyte += len;
  743                 }
  744 #ifdef notyet
  745                 if ((m = m_copypack(so->so_snd.sb_mb, off,
  746                     (int)len, max_linkhdr + hdrlen)) == 0) {
  747                         SOCKBUF_UNLOCK(&so->so_snd);
  748                         error = ENOBUFS;
  749                         goto out;
  750                 }
  751                 /*
  752                  * m_copypack left space for our hdr; use it.
  753                  */
  754                 m->m_len += hdrlen;
  755                 m->m_data -= hdrlen;
  756 #else
  757                 MGETHDR(m, M_DONTWAIT, MT_HEADER);
  758                 if (m == NULL) {
  759                         SOCKBUF_UNLOCK(&so->so_snd);
  760                         error = ENOBUFS;
  761                         goto out;
  762                 }
  763 #ifdef INET6
  764                 if (MHLEN < hdrlen + max_linkhdr) {
  765                         MCLGET(m, M_DONTWAIT);
  766                         if ((m->m_flags & M_EXT) == 0) {
  767                                 SOCKBUF_UNLOCK(&so->so_snd);
  768                                 m_freem(m);
  769                                 error = ENOBUFS;
  770                                 goto out;
  771                         }
  772                 }
  773 #endif
  774                 m->m_data += max_linkhdr;
  775                 m->m_len = hdrlen;
  776                 if (len <= MHLEN - hdrlen - max_linkhdr) {
  777                         m_copydata(so->so_snd.sb_mb, off, (int) len,
  778                             mtod(m, caddr_t) + hdrlen);
  779                         m->m_len += len;
  780                 } else {
  781                         m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len);
  782                         if (m->m_next == 0) {
  783                                 SOCKBUF_UNLOCK(&so->so_snd);
  784                                 (void) m_free(m);
  785                                 error = ENOBUFS;
  786                                 goto out;
  787                         }
  788                 }
  789 #endif
  790                 /*
  791                  * If we're sending everything we've got, set PUSH.
  792                  * (This will keep happy those implementations which only
  793                  * give data to the user when a buffer fills or
  794                  * a PUSH comes in.)
  795                  */
  796                 if (off + len == so->so_snd.sb_cc)
  797                         flags |= TH_PUSH;
  798                 SOCKBUF_UNLOCK(&so->so_snd);
  799         } else {
  800                 SOCKBUF_UNLOCK(&so->so_snd);
  801                 if (tp->t_flags & TF_ACKNOW)
  802                         tcpstat.tcps_sndacks++;
  803                 else if (flags & (TH_SYN|TH_FIN|TH_RST))
  804                         tcpstat.tcps_sndctrl++;
  805                 else if (SEQ_GT(tp->snd_up, tp->snd_una))
  806                         tcpstat.tcps_sndurg++;
  807                 else
  808                         tcpstat.tcps_sndwinup++;
  809 
  810                 MGETHDR(m, M_DONTWAIT, MT_HEADER);
  811                 if (m == NULL) {
  812                         error = ENOBUFS;
  813                         goto out;
  814                 }
  815 #ifdef INET6
  816                 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
  817                     MHLEN >= hdrlen) {
  818                         MH_ALIGN(m, hdrlen);
  819                 } else
  820 #endif
  821                 m->m_data += max_linkhdr;
  822                 m->m_len = hdrlen;
  823         }
  824         SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
  825         m->m_pkthdr.rcvif = (struct ifnet *)0;
  826 #ifdef MAC
  827         mac_create_mbuf_from_inpcb(tp->t_inpcb, m);
  828 #endif
  829 #ifdef INET6
  830         if (isipv6) {
  831                 ip6 = mtod(m, struct ip6_hdr *);
  832                 th = (struct tcphdr *)(ip6 + 1);
  833                 tcpip_fillheaders(tp->t_inpcb, ip6, th);
  834         } else
  835 #endif /* INET6 */
  836         {
  837                 ip = mtod(m, struct ip *);
  838                 ipov = (struct ipovly *)ip;
  839                 th = (struct tcphdr *)(ip + 1);
  840                 tcpip_fillheaders(tp->t_inpcb, ip, th);
  841         }
  842 
  843         /*
  844          * Fill in fields, remembering maximum advertised
  845          * window for use in delaying messages about window sizes.
  846          * If resending a FIN, be sure not to use a new sequence number.
  847          */
  848         if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
  849             tp->snd_nxt == tp->snd_max)
  850                 tp->snd_nxt--;
  851         /*
  852          * If we are doing retransmissions, then snd_nxt will
  853          * not reflect the first unsent octet.  For ACK only
  854          * packets, we do not want the sequence number of the
  855          * retransmitted packet, we want the sequence number
  856          * of the next unsent octet.  So, if there is no data
  857          * (and no SYN or FIN), use snd_max instead of snd_nxt
  858          * when filling in ti_seq.  But if we are in persist
  859          * state, snd_max might reflect one byte beyond the
  860          * right edge of the window, so use snd_nxt in that
  861          * case, since we know we aren't doing a retransmission.
  862          * (retransmit and persist are mutually exclusive...)
  863          */
  864         if (len || (flags & (TH_SYN|TH_FIN))
  865             || callout_active(tp->tt_persist))
  866                 th->th_seq = htonl(tp->snd_nxt);
  867         else
  868                 th->th_seq = htonl(tp->snd_max);
  869         if (sack_rxmit) {
  870                 th->th_seq = htonl(p->rxmit);
  871                 p->rxmit += len;
  872         }
  873         th->th_ack = htonl(tp->rcv_nxt);
  874         if (optlen) {
  875                 bcopy(opt, th + 1, optlen);
  876                 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
  877         }
  878         th->th_flags = flags;
  879         /*
  880          * Calculate receive window.  Don't shrink window,
  881          * but avoid silly window syndrome.
  882          */
  883         if (recwin < (long)(so->so_rcv.sb_hiwat / 4) &&
  884             recwin < (long)tp->t_maxseg)
  885                 recwin = 0;
  886         if (recwin < (long)(tp->rcv_adv - tp->rcv_nxt))
  887                 recwin = (long)(tp->rcv_adv - tp->rcv_nxt);
  888         if (recwin > (long)TCP_MAXWIN << tp->rcv_scale)
  889                 recwin = (long)TCP_MAXWIN << tp->rcv_scale;
  890         th->th_win = htons((u_short) (recwin >> tp->rcv_scale));
  891 
  892 
  893         /*
  894          * Adjust the RXWIN0SENT flag - indicate that we have advertised
  895          * a 0 window.  This may cause the remote transmitter to stall.  This
  896          * flag tells soreceive() to disable delayed acknowledgements when
  897          * draining the buffer.  This can occur if the receiver is attempting
  898          * to read more data then can be buffered prior to transmitting on
  899          * the connection.
  900          */
  901         if (recwin == 0)
  902                 tp->t_flags |= TF_RXWIN0SENT;
  903         else
  904                 tp->t_flags &= ~TF_RXWIN0SENT;
  905         if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
  906                 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
  907                 th->th_flags |= TH_URG;
  908         } else
  909                 /*
  910                  * If no urgent pointer to send, then we pull
  911                  * the urgent pointer to the left edge of the send window
  912                  * so that it doesn't drift into the send window on sequence
  913                  * number wraparound.
  914                  */
  915                 tp->snd_up = tp->snd_una;               /* drag it along */
  916 
  917 #ifdef TCP_SIGNATURE
  918 #ifdef INET6
  919         if (!isipv6)
  920 #endif
  921         if (tp->t_flags & TF_SIGNATURE)
  922                 tcp_signature_compute(m, sizeof(struct ip), len, optlen,
  923                     (u_char *)(th + 1) + sigoff, IPSEC_DIR_OUTBOUND);
  924 #endif
  925 
  926         /*
  927          * Put TCP length in extended header, and then
  928          * checksum extended header and data.
  929          */
  930         m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
  931 #ifdef INET6
  932         if (isipv6)
  933                 /*
  934                  * ip6_plen is not need to be filled now, and will be filled
  935                  * in ip6_output.
  936                  */
  937                 th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr),
  938                                        sizeof(struct tcphdr) + optlen + len);
  939         else
  940 #endif /* INET6 */
  941         {
  942                 m->m_pkthdr.csum_flags = CSUM_TCP;
  943                 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
  944                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
  945                     htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen));
  946 
  947                 /* IP version must be set here for ipv4/ipv6 checking later */
  948                 KASSERT(ip->ip_v == IPVERSION,
  949                     ("%s: IP version incorrect: %d", __func__, ip->ip_v));
  950         }
  951 
  952         /*
  953          * In transmit state, time the transmission and arrange for
  954          * the retransmit.  In persist state, just set snd_max.
  955          */
  956         if (tp->t_force == 0 || !callout_active(tp->tt_persist)) {
  957                 tcp_seq startseq = tp->snd_nxt;
  958 
  959                 /*
  960                  * Advance snd_nxt over sequence space of this segment.
  961                  */
  962                 if (flags & (TH_SYN|TH_FIN)) {
  963                         if (flags & TH_SYN)
  964                                 tp->snd_nxt++;
  965                         if (flags & TH_FIN) {
  966                                 tp->snd_nxt++;
  967                                 tp->t_flags |= TF_SENTFIN;
  968                         }
  969                 }
  970                 if (tp->sack_enable && sack_rxmit)
  971                         goto timer;
  972                 tp->snd_nxt += len;
  973                 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
  974                         tp->snd_max = tp->snd_nxt;
  975                         /*
  976                          * Time this transmission if not a retransmission and
  977                          * not currently timing anything.
  978                          */
  979                         if (tp->t_rtttime == 0) {
  980                                 tp->t_rtttime = ticks;
  981                                 tp->t_rtseq = startseq;
  982                                 tcpstat.tcps_segstimed++;
  983                         }
  984                 }
  985 
  986                 /*
  987                  * Set retransmit timer if not currently set,
  988                  * and not doing a pure ack or a keep-alive probe.
  989                  * Initial value for retransmit timer is smoothed
  990                  * round-trip time + 2 * round-trip time variance.
  991                  * Initialize shift counter which is used for backoff
  992                  * of retransmit time.
  993                  */
  994 timer:
  995                 if (tp->sack_enable && sack_rxmit &&
  996                     !callout_active(tp->tt_rexmt) &&
  997                     tp->snd_nxt != tp->snd_max) {
  998                         callout_reset(tp->tt_rexmt, tp->t_rxtcur,
  999                                       tcp_timer_rexmt, tp);
 1000                         if (callout_active(tp->tt_persist)) {
 1001                                 callout_stop(tp->tt_persist);
 1002                                 tp->t_rxtshift = 0;
 1003                         }
 1004                 }
 1005                 if (!callout_active(tp->tt_rexmt) &&
 1006                     tp->snd_nxt != tp->snd_una) {
 1007                         if (callout_active(tp->tt_persist)) {
 1008                                 callout_stop(tp->tt_persist);
 1009                                 tp->t_rxtshift = 0;
 1010                         }
 1011                         callout_reset(tp->tt_rexmt, tp->t_rxtcur,
 1012                                       tcp_timer_rexmt, tp);
 1013                 }
 1014         } else {
 1015                 /*
 1016                  * Persist case, update snd_max but since we are in
 1017                  * persist mode (no window) we do not update snd_nxt.
 1018                  */
 1019                 int xlen = len;
 1020                 if (flags & TH_SYN)
 1021                         ++xlen;
 1022                 if (flags & TH_FIN) {
 1023                         ++xlen;
 1024                         tp->t_flags |= TF_SENTFIN;
 1025                 }
 1026                 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
 1027                         tp->snd_max = tp->snd_nxt + len;
 1028         }
 1029 
 1030 #ifdef TCPDEBUG
 1031         /*
 1032          * Trace.
 1033          */
 1034         if (so->so_options & SO_DEBUG) {
 1035                 u_short save = 0;
 1036 #ifdef INET6
 1037                 if (!isipv6)
 1038 #endif
 1039                 {
 1040                         save = ipov->ih_len;
 1041                         ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
 1042                 }
 1043                 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
 1044 #ifdef INET6
 1045                 if (!isipv6)
 1046 #endif
 1047                 ipov->ih_len = save;
 1048         }
 1049 #endif
 1050 
 1051         /*
 1052          * Fill in IP length and desired time to live and
 1053          * send to IP level.  There should be a better way
 1054          * to handle ttl and tos; we could keep them in
 1055          * the template, but need a way to checksum without them.
 1056          */
 1057         /*
 1058          * m->m_pkthdr.len should have been set before cksum calcuration,
 1059          * because in6_cksum() need it.
 1060          */
 1061 #ifdef INET6
 1062         if (isipv6) {
 1063                 /*
 1064                  * we separately set hoplimit for every segment, since the
 1065                  * user might want to change the value via setsockopt.
 1066                  * Also, desired default hop limit might be changed via
 1067                  * Neighbor Discovery.
 1068                  */
 1069                 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
 1070 
 1071                 /* TODO: IPv6 IP6TOS_ECT bit on */
 1072                 error = ip6_output(m,
 1073                             tp->t_inpcb->in6p_outputopts, NULL,
 1074                             (so->so_options & SO_DONTROUTE), NULL, NULL,
 1075                             tp->t_inpcb);
 1076         } else
 1077 #endif /* INET6 */
 1078     {
 1079         ip->ip_len = m->m_pkthdr.len;
 1080 #ifdef INET6
 1081         if (INP_CHECK_SOCKAF(so, AF_INET6))
 1082                 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
 1083 #endif /* INET6 */
 1084         /*
 1085          * If we do path MTU discovery, then we set DF on every packet.
 1086          * This might not be the best thing to do according to RFC3390
 1087          * Section 2. However the tcp hostcache migitates the problem
 1088          * so it affects only the first tcp connection with a host.
 1089          */
 1090         if (path_mtu_discovery)
 1091                 ip->ip_off |= IP_DF;
 1092 
 1093         error = ip_output(m, tp->t_inpcb->inp_options, NULL,
 1094             (so->so_options & SO_DONTROUTE), 0, tp->t_inpcb);
 1095     }
 1096         if (error) {
 1097 
 1098                 /*
 1099                  * We know that the packet was lost, so back out the
 1100                  * sequence number advance, if any.
 1101                  */
 1102                 if (tp->t_force == 0 || !callout_active(tp->tt_persist)) {
 1103                         /*
 1104                          * No need to check for TH_FIN here because
 1105                          * the TF_SENTFIN flag handles that case.
 1106                          */
 1107                         if ((flags & TH_SYN) == 0) {
 1108                                 if (sack_rxmit)
 1109                                         p->rxmit -= len;
 1110                                 else
 1111                                         tp->snd_nxt -= len;
 1112                         }
 1113                 }
 1114 
 1115 out:
 1116                 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);     /* Check gotos. */
 1117                 if (error == ENOBUFS) {
 1118                         if (!callout_active(tp->tt_rexmt) &&
 1119                             !callout_active(tp->tt_persist))
 1120                                 callout_reset(tp->tt_rexmt, tp->t_rxtcur,
 1121                                     tcp_timer_rexmt, tp);
 1122                         tcp_quench(tp->t_inpcb, 0);
 1123                         return (0);
 1124                 }
 1125                 if (error == EMSGSIZE) {
 1126                         /*
 1127                          * ip_output() will have already fixed the route
 1128                          * for us.  tcp_mtudisc() will, as its last action,
 1129                          * initiate retransmission, so it is important to
 1130                          * not do so here.
 1131                          */
 1132                         tcp_mtudisc(tp->t_inpcb, 0);
 1133                         return 0;
 1134                 }
 1135                 if ((error == EHOSTUNREACH || error == ENETDOWN)
 1136                     && TCPS_HAVERCVDSYN(tp->t_state)) {
 1137                         tp->t_softerror = error;
 1138                         return (0);
 1139                 }
 1140                 return (error);
 1141         }
 1142         tcpstat.tcps_sndtotal++;
 1143 
 1144         /*
 1145          * Data sent (as far as we can tell).
 1146          * If this advertises a larger window than any other segment,
 1147          * then remember the size of the advertised window.
 1148          * Any pending ACK has now been sent.
 1149          */
 1150         if (recwin > 0 && SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
 1151                 tp->rcv_adv = tp->rcv_nxt + recwin;
 1152         tp->last_ack_sent = tp->rcv_nxt;
 1153         tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
 1154         if (callout_active(tp->tt_delack))
 1155                 callout_stop(tp->tt_delack);
 1156 #if 0
 1157         /*
 1158          * This completely breaks TCP if newreno is turned on.  What happens
 1159          * is that if delayed-acks are turned on on the receiver, this code
 1160          * on the transmitter effectively destroys the TCP window, forcing
 1161          * it to four packets (1.5Kx4 = 6K window).
 1162          */
 1163         if (sendalot && (!tcp_do_newreno || --maxburst))
 1164                 goto again;
 1165 #endif
 1166         if (sendalot)
 1167                 goto again;
 1168         return (0);
 1169 }
 1170 
 1171 void
 1172 tcp_setpersist(tp)
 1173         register struct tcpcb *tp;
 1174 {
 1175         int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
 1176         int tt;
 1177 
 1178         if (callout_active(tp->tt_rexmt))
 1179                 panic("tcp_setpersist: retransmit pending");
 1180         /*
 1181          * Start/restart persistance timer.
 1182          */
 1183         TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
 1184                       TCPTV_PERSMIN, TCPTV_PERSMAX);
 1185         callout_reset(tp->tt_persist, tt, tcp_timer_persist, tp);
 1186         if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
 1187                 tp->t_rxtshift++;
 1188 }

Cache object: c85f37a35ab0c6de99ca62938b3b61c8


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