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  */
   31 
   32 #include <sys/cdefs.h>
   33 __FBSDID("$FreeBSD: releng/10.1/sys/netinet/tcp_output.c 293894 2016-01-14 09:11:16Z glebius $");
   34 
   35 #include "opt_inet.h"
   36 #include "opt_inet6.h"
   37 #include "opt_ipsec.h"
   38 #include "opt_kdtrace.h"
   39 #include "opt_tcpdebug.h"
   40 
   41 #include <sys/param.h>
   42 #include <sys/systm.h>
   43 #include <sys/domain.h>
   44 #include <sys/hhook.h>
   45 #include <sys/kernel.h>
   46 #include <sys/lock.h>
   47 #include <sys/mbuf.h>
   48 #include <sys/mutex.h>
   49 #include <sys/protosw.h>
   50 #include <sys/sdt.h>
   51 #include <sys/socket.h>
   52 #include <sys/socketvar.h>
   53 #include <sys/sysctl.h>
   54 
   55 #include <net/if.h>
   56 #include <net/route.h>
   57 #include <net/vnet.h>
   58 
   59 #include <netinet/cc.h>
   60 #include <netinet/in.h>
   61 #include <netinet/in_kdtrace.h>
   62 #include <netinet/in_systm.h>
   63 #include <netinet/ip.h>
   64 #include <netinet/in_pcb.h>
   65 #include <netinet/ip_var.h>
   66 #include <netinet/ip_options.h>
   67 #ifdef INET6
   68 #include <netinet6/in6_pcb.h>
   69 #include <netinet/ip6.h>
   70 #include <netinet6/ip6_var.h>
   71 #endif
   72 #define TCPOUTFLAGS
   73 #include <netinet/tcp_fsm.h>
   74 #include <netinet/tcp_seq.h>
   75 #include <netinet/tcp_timer.h>
   76 #include <netinet/tcp_var.h>
   77 #include <netinet/tcpip.h>
   78 #ifdef TCPDEBUG
   79 #include <netinet/tcp_debug.h>
   80 #endif
   81 #ifdef TCP_OFFLOAD
   82 #include <netinet/tcp_offload.h>
   83 #endif
   84 
   85 #ifdef IPSEC
   86 #include <netipsec/ipsec.h>
   87 #endif /*IPSEC*/
   88 
   89 #include <machine/in_cksum.h>
   90 
   91 #include <security/mac/mac_framework.h>
   92 
   93 VNET_DEFINE(int, path_mtu_discovery) = 1;
   94 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW,
   95         &VNET_NAME(path_mtu_discovery), 1,
   96         "Enable Path MTU Discovery");
   97 
   98 VNET_DEFINE(int, tcp_do_tso) = 1;
   99 #define V_tcp_do_tso            VNET(tcp_do_tso)
  100 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_RW,
  101         &VNET_NAME(tcp_do_tso), 0,
  102         "Enable TCP Segmentation Offload");
  103 
  104 VNET_DEFINE(int, tcp_sendspace) = 1024*32;
  105 #define V_tcp_sendspace VNET(tcp_sendspace)
  106 SYSCTL_VNET_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_RW,
  107         &VNET_NAME(tcp_sendspace), 0, "Initial send socket buffer size");
  108 
  109 VNET_DEFINE(int, tcp_do_autosndbuf) = 1;
  110 #define V_tcp_do_autosndbuf     VNET(tcp_do_autosndbuf)
  111 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_RW,
  112         &VNET_NAME(tcp_do_autosndbuf), 0,
  113         "Enable automatic send buffer sizing");
  114 
  115 VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024;
  116 #define V_tcp_autosndbuf_inc    VNET(tcp_autosndbuf_inc)
  117 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_RW,
  118         &VNET_NAME(tcp_autosndbuf_inc), 0,
  119         "Incrementor step size of automatic send buffer");
  120 
  121 VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024;
  122 #define V_tcp_autosndbuf_max    VNET(tcp_autosndbuf_max)
  123 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_RW,
  124         &VNET_NAME(tcp_autosndbuf_max), 0,
  125         "Max size of automatic send buffer");
  126 
  127 static void inline      hhook_run_tcp_est_out(struct tcpcb *tp,
  128                             struct tcphdr *th, struct tcpopt *to,
  129                             long len, int tso);
  130 static void inline      cc_after_idle(struct tcpcb *tp);
  131 
  132 /*
  133  * Wrapper for the TCP established output helper hook.
  134  */
  135 static void inline
  136 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
  137     struct tcpopt *to, long len, int tso)
  138 {
  139         struct tcp_hhook_data hhook_data;
  140 
  141         if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
  142                 hhook_data.tp = tp;
  143                 hhook_data.th = th;
  144                 hhook_data.to = to;
  145                 hhook_data.len = len;
  146                 hhook_data.tso = tso;
  147 
  148                 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
  149                     tp->osd);
  150         }
  151 }
  152 
  153 /*
  154  * CC wrapper hook functions
  155  */
  156 static void inline
  157 cc_after_idle(struct tcpcb *tp)
  158 {
  159         INP_WLOCK_ASSERT(tp->t_inpcb);
  160 
  161         if (CC_ALGO(tp)->after_idle != NULL)
  162                 CC_ALGO(tp)->after_idle(tp->ccv);
  163 }
  164 
  165 /*
  166  * Tcp output routine: figure out what should be sent and send it.
  167  */
  168 int
  169 tcp_output(struct tcpcb *tp)
  170 {
  171         struct socket *so = tp->t_inpcb->inp_socket;
  172         long len, recwin, sendwin;
  173         int off, flags, error = 0;      /* Keep compiler happy */
  174         struct mbuf *m;
  175         struct ip *ip = NULL;
  176         struct ipovly *ipov = NULL;
  177         struct tcphdr *th;
  178         u_char opt[TCP_MAXOLEN];
  179         unsigned ipoptlen, optlen, hdrlen;
  180 #ifdef IPSEC
  181         unsigned ipsec_optlen = 0;
  182 #endif
  183         int idle, sendalot;
  184         int sack_rxmit, sack_bytes_rxmt;
  185         struct sackhole *p;
  186         int tso, mtu;
  187         struct tcpopt to;
  188 #if 0
  189         int maxburst = TCP_MAXBURST;
  190 #endif
  191 #ifdef INET6
  192         struct ip6_hdr *ip6 = NULL;
  193         int isipv6;
  194 
  195         isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
  196 #endif
  197 
  198         INP_WLOCK_ASSERT(tp->t_inpcb);
  199 
  200 #ifdef TCP_OFFLOAD
  201         if (tp->t_flags & TF_TOE)
  202                 return (tcp_offload_output(tp));
  203 #endif
  204 
  205         /*
  206          * Determine length of data that should be transmitted,
  207          * and flags that will be used.
  208          * If there is some data or critical controls (SYN, RST)
  209          * to send, then transmit; otherwise, investigate further.
  210          */
  211         idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
  212         if (idle && ticks - tp->t_rcvtime >= tp->t_rxtcur)
  213                 cc_after_idle(tp);
  214         tp->t_flags &= ~TF_LASTIDLE;
  215         if (idle) {
  216                 if (tp->t_flags & TF_MORETOCOME) {
  217                         tp->t_flags |= TF_LASTIDLE;
  218                         idle = 0;
  219                 }
  220         }
  221 again:
  222         /*
  223          * If we've recently taken a timeout, snd_max will be greater than
  224          * snd_nxt.  There may be SACK information that allows us to avoid
  225          * resending already delivered data.  Adjust snd_nxt accordingly.
  226          */
  227         if ((tp->t_flags & TF_SACK_PERMIT) &&
  228             SEQ_LT(tp->snd_nxt, tp->snd_max))
  229                 tcp_sack_adjust(tp);
  230         sendalot = 0;
  231         tso = 0;
  232         mtu = 0;
  233         off = tp->snd_nxt - tp->snd_una;
  234         sendwin = min(tp->snd_wnd, tp->snd_cwnd);
  235 
  236         flags = tcp_outflags[tp->t_state];
  237         /*
  238          * Send any SACK-generated retransmissions.  If we're explicitly trying
  239          * to send out new data (when sendalot is 1), bypass this function.
  240          * If we retransmit in fast recovery mode, decrement snd_cwnd, since
  241          * we're replacing a (future) new transmission with a retransmission
  242          * now, and we previously incremented snd_cwnd in tcp_input().
  243          */
  244         /*
  245          * Still in sack recovery , reset rxmit flag to zero.
  246          */
  247         sack_rxmit = 0;
  248         sack_bytes_rxmt = 0;
  249         len = 0;
  250         p = NULL;
  251         if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
  252             (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
  253                 long cwin;
  254                 
  255                 cwin = min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt;
  256                 if (cwin < 0)
  257                         cwin = 0;
  258                 /* Do not retransmit SACK segments beyond snd_recover */
  259                 if (SEQ_GT(p->end, tp->snd_recover)) {
  260                         /*
  261                          * (At least) part of sack hole extends beyond
  262                          * snd_recover. Check to see if we can rexmit data
  263                          * for this hole.
  264                          */
  265                         if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
  266                                 /*
  267                                  * Can't rexmit any more data for this hole.
  268                                  * That data will be rexmitted in the next
  269                                  * sack recovery episode, when snd_recover
  270                                  * moves past p->rxmit.
  271                                  */
  272                                 p = NULL;
  273                                 goto after_sack_rexmit;
  274                         } else
  275                                 /* Can rexmit part of the current hole */
  276                                 len = ((long)ulmin(cwin,
  277                                                    tp->snd_recover - p->rxmit));
  278                 } else
  279                         len = ((long)ulmin(cwin, p->end - p->rxmit));
  280                 off = p->rxmit - tp->snd_una;
  281                 KASSERT(off >= 0,("%s: sack block to the left of una : %d",
  282                     __func__, off));
  283                 if (len > 0) {
  284                         sack_rxmit = 1;
  285                         sendalot = 1;
  286                         TCPSTAT_INC(tcps_sack_rexmits);
  287                         TCPSTAT_ADD(tcps_sack_rexmit_bytes,
  288                             min(len, tp->t_maxseg));
  289                 }
  290         }
  291 after_sack_rexmit:
  292         /*
  293          * Get standard flags, and add SYN or FIN if requested by 'hidden'
  294          * state flags.
  295          */
  296         if (tp->t_flags & TF_NEEDFIN)
  297                 flags |= TH_FIN;
  298         if (tp->t_flags & TF_NEEDSYN)
  299                 flags |= TH_SYN;
  300 
  301         SOCKBUF_LOCK(&so->so_snd);
  302         /*
  303          * If in persist timeout with window of 0, send 1 byte.
  304          * Otherwise, if window is small but nonzero
  305          * and timer expired, we will send what we can
  306          * and go to transmit state.
  307          */
  308         if (tp->t_flags & TF_FORCEDATA) {
  309                 if (sendwin == 0) {
  310                         /*
  311                          * If we still have some data to send, then
  312                          * clear the FIN bit.  Usually this would
  313                          * happen below when it realizes that we
  314                          * aren't sending all the data.  However,
  315                          * if we have exactly 1 byte of unsent data,
  316                          * then it won't clear the FIN bit below,
  317                          * and if we are in persist state, we wind
  318                          * up sending the packet without recording
  319                          * that we sent the FIN bit.
  320                          *
  321                          * We can't just blindly clear the FIN bit,
  322                          * because if we don't have any more data
  323                          * to send then the probe will be the FIN
  324                          * itself.
  325                          */
  326                         if (off < so->so_snd.sb_cc)
  327                                 flags &= ~TH_FIN;
  328                         sendwin = 1;
  329                 } else {
  330                         tcp_timer_activate(tp, TT_PERSIST, 0);
  331                         tp->t_rxtshift = 0;
  332                 }
  333         }
  334 
  335         /*
  336          * If snd_nxt == snd_max and we have transmitted a FIN, the
  337          * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
  338          * a negative length.  This can also occur when TCP opens up
  339          * its congestion window while receiving additional duplicate
  340          * acks after fast-retransmit because TCP will reset snd_nxt
  341          * to snd_max after the fast-retransmit.
  342          *
  343          * In the normal retransmit-FIN-only case, however, snd_nxt will
  344          * be set to snd_una, the offset will be 0, and the length may
  345          * wind up 0.
  346          *
  347          * If sack_rxmit is true we are retransmitting from the scoreboard
  348          * in which case len is already set.
  349          */
  350         if (sack_rxmit == 0) {
  351                 if (sack_bytes_rxmt == 0)
  352                         len = ((long)ulmin(so->so_snd.sb_cc, sendwin) - off);
  353                 else {
  354                         long cwin;
  355 
  356                         /*
  357                          * We are inside of a SACK recovery episode and are
  358                          * sending new data, having retransmitted all the
  359                          * data possible in the scoreboard.
  360                          */
  361                         len = ((long)ulmin(so->so_snd.sb_cc, tp->snd_wnd) 
  362                                - off);
  363                         /*
  364                          * Don't remove this (len > 0) check !
  365                          * We explicitly check for len > 0 here (although it 
  366                          * isn't really necessary), to work around a gcc 
  367                          * optimization issue - to force gcc to compute
  368                          * len above. Without this check, the computation
  369                          * of len is bungled by the optimizer.
  370                          */
  371                         if (len > 0) {
  372                                 cwin = tp->snd_cwnd - 
  373                                         (tp->snd_nxt - tp->sack_newdata) -
  374                                         sack_bytes_rxmt;
  375                                 if (cwin < 0)
  376                                         cwin = 0;
  377                                 len = lmin(len, cwin);
  378                         }
  379                 }
  380         }
  381 
  382         /*
  383          * Lop off SYN bit if it has already been sent.  However, if this
  384          * is SYN-SENT state and if segment contains data and if we don't
  385          * know that foreign host supports TAO, suppress sending segment.
  386          */
  387         if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
  388                 if (tp->t_state != TCPS_SYN_RECEIVED)
  389                         flags &= ~TH_SYN;
  390                 off--, len++;
  391         }
  392 
  393         /*
  394          * Be careful not to send data and/or FIN on SYN segments.
  395          * This measure is needed to prevent interoperability problems
  396          * with not fully conformant TCP implementations.
  397          */
  398         if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
  399                 len = 0;
  400                 flags &= ~TH_FIN;
  401         }
  402 
  403         if (len <= 0) {
  404                 /*
  405                  * If FIN has been sent but not acked,
  406                  * but we haven't been called to retransmit,
  407                  * len will be < 0.  Otherwise, window shrank
  408                  * after we sent into it.  If window shrank to 0,
  409                  * cancel pending retransmit, pull snd_nxt back
  410                  * to (closed) window, and set the persist timer
  411                  * if it isn't already going.  If the window didn't
  412                  * close completely, just wait for an ACK.
  413                  *
  414                  * We also do a general check here to ensure that
  415                  * we will set the persist timer when we have data
  416                  * to send, but a 0-byte window. This makes sure
  417                  * the persist timer is set even if the packet
  418                  * hits one of the "goto send" lines below.
  419                  */
  420                 len = 0;
  421                 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
  422                         (off < (int) so->so_snd.sb_cc)) {
  423                         tcp_timer_activate(tp, TT_REXMT, 0);
  424                         tp->t_rxtshift = 0;
  425                         tp->snd_nxt = tp->snd_una;
  426                         if (!tcp_timer_active(tp, TT_PERSIST))
  427                                 tcp_setpersist(tp);
  428                 }
  429         }
  430 
  431         /* len will be >= 0 after this point. */
  432         KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
  433 
  434         /*
  435          * Automatic sizing of send socket buffer.  Often the send buffer
  436          * size is not optimally adjusted to the actual network conditions
  437          * at hand (delay bandwidth product).  Setting the buffer size too
  438          * small limits throughput on links with high bandwidth and high
  439          * delay (eg. trans-continental/oceanic links).  Setting the
  440          * buffer size too big consumes too much real kernel memory,
  441          * especially with many connections on busy servers.
  442          *
  443          * The criteria to step up the send buffer one notch are:
  444          *  1. receive window of remote host is larger than send buffer
  445          *     (with a fudge factor of 5/4th);
  446          *  2. send buffer is filled to 7/8th with data (so we actually
  447          *     have data to make use of it);
  448          *  3. send buffer fill has not hit maximal automatic size;
  449          *  4. our send window (slow start and cogestion controlled) is
  450          *     larger than sent but unacknowledged data in send buffer.
  451          *
  452          * The remote host receive window scaling factor may limit the
  453          * growing of the send buffer before it reaches its allowed
  454          * maximum.
  455          *
  456          * It scales directly with slow start or congestion window
  457          * and does at most one step per received ACK.  This fast
  458          * scaling has the drawback of growing the send buffer beyond
  459          * what is strictly necessary to make full use of a given
  460          * delay*bandwith product.  However testing has shown this not
  461          * to be much of an problem.  At worst we are trading wasting
  462          * of available bandwith (the non-use of it) for wasting some
  463          * socket buffer memory.
  464          *
  465          * TODO: Shrink send buffer during idle periods together
  466          * with congestion window.  Requires another timer.  Has to
  467          * wait for upcoming tcp timer rewrite.
  468          */
  469         if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
  470                 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat &&
  471                     so->so_snd.sb_cc >= (so->so_snd.sb_hiwat / 8 * 7) &&
  472                     so->so_snd.sb_cc < V_tcp_autosndbuf_max &&
  473                     sendwin >= (so->so_snd.sb_cc - (tp->snd_nxt - tp->snd_una))) {
  474                         if (!sbreserve_locked(&so->so_snd,
  475                             min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
  476                              V_tcp_autosndbuf_max), so, curthread))
  477                                 so->so_snd.sb_flags &= ~SB_AUTOSIZE;
  478                 }
  479         }
  480 
  481         /*
  482          * Decide if we can use TCP Segmentation Offloading (if supported by
  483          * hardware).
  484          *
  485          * TSO may only be used if we are in a pure bulk sending state.  The
  486          * presence of TCP-MD5, SACK retransmits, SACK advertizements and
  487          * IP options prevent using TSO.  With TSO the TCP header is the same
  488          * (except for the sequence number) for all generated packets.  This
  489          * makes it impossible to transmit any options which vary per generated
  490          * segment or packet.
  491          */
  492 #ifdef IPSEC
  493         /*
  494          * Pre-calculate here as we save another lookup into the darknesses
  495          * of IPsec that way and can actually decide if TSO is ok.
  496          */
  497         ipsec_optlen = ipsec_hdrsiz_tcp(tp);
  498 #endif
  499         if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
  500             ((tp->t_flags & TF_SIGNATURE) == 0) &&
  501             tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
  502 #ifdef IPSEC
  503             ipsec_optlen == 0 &&
  504 #endif
  505             tp->t_inpcb->inp_options == NULL &&
  506             tp->t_inpcb->in6p_options == NULL)
  507                 tso = 1;
  508 
  509         if (sack_rxmit) {
  510                 if (SEQ_LT(p->rxmit + len, tp->snd_una + so->so_snd.sb_cc))
  511                         flags &= ~TH_FIN;
  512         } else {
  513                 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
  514                         flags &= ~TH_FIN;
  515         }
  516 
  517         recwin = sbspace(&so->so_rcv);
  518 
  519         /*
  520          * Sender silly window avoidance.   We transmit under the following
  521          * conditions when len is non-zero:
  522          *
  523          *      - We have a full segment (or more with TSO)
  524          *      - This is the last buffer in a write()/send() and we are
  525          *        either idle or running NODELAY
  526          *      - we've timed out (e.g. persist timer)
  527          *      - we have more then 1/2 the maximum send window's worth of
  528          *        data (receiver may be limited the window size)
  529          *      - we need to retransmit
  530          */
  531         if (len) {
  532                 if (len >= tp->t_maxseg)
  533                         goto send;
  534                 /*
  535                  * NOTE! on localhost connections an 'ack' from the remote
  536                  * end may occur synchronously with the output and cause
  537                  * us to flush a buffer queued with moretocome.  XXX
  538                  *
  539                  * note: the len + off check is almost certainly unnecessary.
  540                  */
  541                 if (!(tp->t_flags & TF_MORETOCOME) &&   /* normal case */
  542                     (idle || (tp->t_flags & TF_NODELAY)) &&
  543                     len + off >= so->so_snd.sb_cc &&
  544                     (tp->t_flags & TF_NOPUSH) == 0) {
  545                         goto send;
  546                 }
  547                 if (tp->t_flags & TF_FORCEDATA)         /* typ. timeout case */
  548                         goto send;
  549                 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
  550                         goto send;
  551                 if (SEQ_LT(tp->snd_nxt, tp->snd_max))   /* retransmit case */
  552                         goto send;
  553                 if (sack_rxmit)
  554                         goto send;
  555         }
  556 
  557         /*
  558          * Sending of standalone window updates.
  559          *
  560          * Window updates are important when we close our window due to a
  561          * full socket buffer and are opening it again after the application
  562          * reads data from it.  Once the window has opened again and the
  563          * remote end starts to send again the ACK clock takes over and
  564          * provides the most current window information.
  565          *
  566          * We must avoid the silly window syndrome whereas every read
  567          * from the receive buffer, no matter how small, causes a window
  568          * update to be sent.  We also should avoid sending a flurry of
  569          * window updates when the socket buffer had queued a lot of data
  570          * and the application is doing small reads.
  571          *
  572          * Prevent a flurry of pointless window updates by only sending
  573          * an update when we can increase the advertized window by more
  574          * than 1/4th of the socket buffer capacity.  When the buffer is
  575          * getting full or is very small be more aggressive and send an
  576          * update whenever we can increase by two mss sized segments.
  577          * In all other situations the ACK's to new incoming data will
  578          * carry further window increases.
  579          *
  580          * Don't send an independent window update if a delayed
  581          * ACK is pending (it will get piggy-backed on it) or the
  582          * remote side already has done a half-close and won't send
  583          * more data.  Skip this if the connection is in T/TCP
  584          * half-open state.
  585          */
  586         if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
  587             !(tp->t_flags & TF_DELACK) &&
  588             !TCPS_HAVERCVDFIN(tp->t_state)) {
  589                 /*
  590                  * "adv" is the amount we could increase the window,
  591                  * taking into account that we are limited by
  592                  * TCP_MAXWIN << tp->rcv_scale.
  593                  */
  594                 long adv;
  595                 int oldwin;
  596 
  597                 adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale);
  598                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
  599                         oldwin = (tp->rcv_adv - tp->rcv_nxt);
  600                         adv -= oldwin;
  601                 } else
  602                         oldwin = 0;
  603 
  604                 /* 
  605                  * If the new window size ends up being the same as the old
  606                  * size when it is scaled, then don't force a window update.
  607                  */
  608                 if (oldwin >> tp->rcv_scale == (adv + oldwin) >> tp->rcv_scale)
  609                         goto dontupdate;
  610 
  611                 if (adv >= (long)(2 * tp->t_maxseg) &&
  612                     (adv >= (long)(so->so_rcv.sb_hiwat / 4) ||
  613                      recwin <= (long)(so->so_rcv.sb_hiwat / 8) ||
  614                      so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg))
  615                         goto send;
  616         }
  617 dontupdate:
  618 
  619         /*
  620          * Send if we owe the peer an ACK, RST, SYN, or urgent data.  ACKNOW
  621          * is also a catch-all for the retransmit timer timeout case.
  622          */
  623         if (tp->t_flags & TF_ACKNOW)
  624                 goto send;
  625         if ((flags & TH_RST) ||
  626             ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
  627                 goto send;
  628         if (SEQ_GT(tp->snd_up, tp->snd_una))
  629                 goto send;
  630         /*
  631          * If our state indicates that FIN should be sent
  632          * and we have not yet done so, then we need to send.
  633          */
  634         if (flags & TH_FIN &&
  635             ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
  636                 goto send;
  637         /*
  638          * In SACK, it is possible for tcp_output to fail to send a segment
  639          * after the retransmission timer has been turned off.  Make sure
  640          * that the retransmission timer is set.
  641          */
  642         if ((tp->t_flags & TF_SACK_PERMIT) &&
  643             SEQ_GT(tp->snd_max, tp->snd_una) &&
  644             !tcp_timer_active(tp, TT_REXMT) &&
  645             !tcp_timer_active(tp, TT_PERSIST)) {
  646                 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
  647                 goto just_return;
  648         } 
  649         /*
  650          * TCP window updates are not reliable, rather a polling protocol
  651          * using ``persist'' packets is used to insure receipt of window
  652          * updates.  The three ``states'' for the output side are:
  653          *      idle                    not doing retransmits or persists
  654          *      persisting              to move a small or zero window
  655          *      (re)transmitting        and thereby not persisting
  656          *
  657          * tcp_timer_active(tp, TT_PERSIST)
  658          *      is true when we are in persist state.
  659          * (tp->t_flags & TF_FORCEDATA)
  660          *      is set when we are called to send a persist packet.
  661          * tcp_timer_active(tp, TT_REXMT)
  662          *      is set when we are retransmitting
  663          * The output side is idle when both timers are zero.
  664          *
  665          * If send window is too small, there is data to transmit, and no
  666          * retransmit or persist is pending, then go to persist state.
  667          * If nothing happens soon, send when timer expires:
  668          * if window is nonzero, transmit what we can,
  669          * otherwise force out a byte.
  670          */
  671         if (so->so_snd.sb_cc && !tcp_timer_active(tp, TT_REXMT) &&
  672             !tcp_timer_active(tp, TT_PERSIST)) {
  673                 tp->t_rxtshift = 0;
  674                 tcp_setpersist(tp);
  675         }
  676 
  677         /*
  678          * No reason to send a segment, just return.
  679          */
  680 just_return:
  681         SOCKBUF_UNLOCK(&so->so_snd);
  682         return (0);
  683 
  684 send:
  685         SOCKBUF_LOCK_ASSERT(&so->so_snd);
  686         /*
  687          * Before ESTABLISHED, force sending of initial options
  688          * unless TCP set not to do any options.
  689          * NOTE: we assume that the IP/TCP header plus TCP options
  690          * always fit in a single mbuf, leaving room for a maximum
  691          * link header, i.e.
  692          *      max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
  693          */
  694         optlen = 0;
  695 #ifdef INET6
  696         if (isipv6)
  697                 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
  698         else
  699 #endif
  700                 hdrlen = sizeof (struct tcpiphdr);
  701 
  702         /*
  703          * Compute options for segment.
  704          * We only have to care about SYN and established connection
  705          * segments.  Options for SYN-ACK segments are handled in TCP
  706          * syncache.
  707          */
  708         to.to_flags = 0;
  709         if ((tp->t_flags & TF_NOOPT) == 0) {
  710                 /* Maximum segment size. */
  711                 if (flags & TH_SYN) {
  712                         tp->snd_nxt = tp->iss;
  713                         to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc);
  714                         to.to_flags |= TOF_MSS;
  715                 }
  716                 /* Window scaling. */
  717                 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
  718                         to.to_wscale = tp->request_r_scale;
  719                         to.to_flags |= TOF_SCALE;
  720                 }
  721                 /* Timestamps. */
  722                 if ((tp->t_flags & TF_RCVD_TSTMP) ||
  723                     ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
  724                         to.to_tsval = tcp_ts_getticks() + tp->ts_offset;
  725                         to.to_tsecr = tp->ts_recent;
  726                         to.to_flags |= TOF_TS;
  727                         /* Set receive buffer autosizing timestamp. */
  728                         if (tp->rfbuf_ts == 0 &&
  729                             (so->so_rcv.sb_flags & SB_AUTOSIZE))
  730                                 tp->rfbuf_ts = tcp_ts_getticks();
  731                 }
  732                 /* Selective ACK's. */
  733                 if (tp->t_flags & TF_SACK_PERMIT) {
  734                         if (flags & TH_SYN)
  735                                 to.to_flags |= TOF_SACKPERM;
  736                         else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
  737                             (tp->t_flags & TF_SACK_PERMIT) &&
  738                             tp->rcv_numsacks > 0) {
  739                                 to.to_flags |= TOF_SACK;
  740                                 to.to_nsacks = tp->rcv_numsacks;
  741                                 to.to_sacks = (u_char *)tp->sackblks;
  742                         }
  743                 }
  744 #ifdef TCP_SIGNATURE
  745                 /* TCP-MD5 (RFC2385). */
  746                 if (tp->t_flags & TF_SIGNATURE)
  747                         to.to_flags |= TOF_SIGNATURE;
  748 #endif /* TCP_SIGNATURE */
  749 
  750                 /* Processing the options. */
  751                 hdrlen += optlen = tcp_addoptions(&to, opt);
  752         }
  753 
  754 #ifdef INET6
  755         if (isipv6)
  756                 ipoptlen = ip6_optlen(tp->t_inpcb);
  757         else
  758 #endif
  759         if (tp->t_inpcb->inp_options)
  760                 ipoptlen = tp->t_inpcb->inp_options->m_len -
  761                                 offsetof(struct ipoption, ipopt_list);
  762         else
  763                 ipoptlen = 0;
  764 #ifdef IPSEC
  765         ipoptlen += ipsec_optlen;
  766 #endif
  767 
  768         /*
  769          * Adjust data length if insertion of options will
  770          * bump the packet length beyond the t_maxopd length.
  771          * Clear the FIN bit because we cut off the tail of
  772          * the segment.
  773          */
  774         if (len + optlen + ipoptlen > tp->t_maxopd) {
  775                 flags &= ~TH_FIN;
  776 
  777                 if (tso) {
  778                         KASSERT(ipoptlen == 0,
  779                             ("%s: TSO can't do IP options", __func__));
  780 
  781                         /*
  782                          * Limit a burst to t_tsomax minus IP,
  783                          * TCP and options length to keep ip->ip_len
  784                          * from overflowing or exceeding the maximum
  785                          * length allowed by the network interface.
  786                          */
  787                         if (len > tp->t_tsomax - hdrlen) {
  788                                 len = tp->t_tsomax - hdrlen;
  789                                 sendalot = 1;
  790                         }
  791 
  792                         /*
  793                          * Prevent the last segment from being
  794                          * fractional unless the send sockbuf can
  795                          * be emptied.
  796                          */
  797                         if (sendalot && off + len < so->so_snd.sb_cc) {
  798                                 len -= len % (tp->t_maxopd - optlen);
  799                                 sendalot = 1;
  800                         }
  801 
  802                         /*
  803                          * Send the FIN in a separate segment
  804                          * after the bulk sending is done.
  805                          * We don't trust the TSO implementations
  806                          * to clear the FIN flag on all but the
  807                          * last segment.
  808                          */
  809                         if (tp->t_flags & TF_NEEDFIN)
  810                                 sendalot = 1;
  811 
  812                 } else {
  813                         len = tp->t_maxopd - optlen - ipoptlen;
  814                         sendalot = 1;
  815                 }
  816         } else
  817                 tso = 0;
  818 
  819         KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
  820             ("%s: len > IP_MAXPACKET", __func__));
  821 
  822 /*#ifdef DIAGNOSTIC*/
  823 #ifdef INET6
  824         if (max_linkhdr + hdrlen > MCLBYTES)
  825 #else
  826         if (max_linkhdr + hdrlen > MHLEN)
  827 #endif
  828                 panic("tcphdr too big");
  829 /*#endif*/
  830 
  831         /*
  832          * This KASSERT is here to catch edge cases at a well defined place.
  833          * Before, those had triggered (random) panic conditions further down.
  834          */
  835         KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
  836 
  837         /*
  838          * Grab a header mbuf, attaching a copy of data to
  839          * be transmitted, and initialize the header from
  840          * the template for sends on this connection.
  841          */
  842         if (len) {
  843                 struct mbuf *mb;
  844                 u_int moff;
  845 
  846                 if ((tp->t_flags & TF_FORCEDATA) && len == 1)
  847                         TCPSTAT_INC(tcps_sndprobe);
  848                 else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
  849                         tp->t_sndrexmitpack++;
  850                         TCPSTAT_INC(tcps_sndrexmitpack);
  851                         TCPSTAT_ADD(tcps_sndrexmitbyte, len);
  852                 } else {
  853                         TCPSTAT_INC(tcps_sndpack);
  854                         TCPSTAT_ADD(tcps_sndbyte, len);
  855                 }
  856 #ifdef INET6
  857                 if (MHLEN < hdrlen + max_linkhdr)
  858                         m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
  859                 else
  860 #endif
  861                         m = m_gethdr(M_NOWAIT, MT_DATA);
  862 
  863                 if (m == NULL) {
  864                         SOCKBUF_UNLOCK(&so->so_snd);
  865                         error = ENOBUFS;
  866                         sack_rxmit = 0;
  867                         goto out;
  868                 }
  869 
  870                 m->m_data += max_linkhdr;
  871                 m->m_len = hdrlen;
  872 
  873                 /*
  874                  * Start the m_copy functions from the closest mbuf
  875                  * to the offset in the socket buffer chain.
  876                  */
  877                 mb = sbsndptr(&so->so_snd, off, len, &moff);
  878 
  879                 if (len <= MHLEN - hdrlen - max_linkhdr) {
  880                         m_copydata(mb, moff, (int)len,
  881                             mtod(m, caddr_t) + hdrlen);
  882                         m->m_len += len;
  883                 } else {
  884                         m->m_next = m_copy(mb, moff, (int)len);
  885                         if (m->m_next == NULL) {
  886                                 SOCKBUF_UNLOCK(&so->so_snd);
  887                                 (void) m_free(m);
  888                                 error = ENOBUFS;
  889                                 sack_rxmit = 0;
  890                                 goto out;
  891                         }
  892                 }
  893 
  894                 /*
  895                  * If we're sending everything we've got, set PUSH.
  896                  * (This will keep happy those implementations which only
  897                  * give data to the user when a buffer fills or
  898                  * a PUSH comes in.)
  899                  */
  900                 if (off + len == so->so_snd.sb_cc)
  901                         flags |= TH_PUSH;
  902                 SOCKBUF_UNLOCK(&so->so_snd);
  903         } else {
  904                 SOCKBUF_UNLOCK(&so->so_snd);
  905                 if (tp->t_flags & TF_ACKNOW)
  906                         TCPSTAT_INC(tcps_sndacks);
  907                 else if (flags & (TH_SYN|TH_FIN|TH_RST))
  908                         TCPSTAT_INC(tcps_sndctrl);
  909                 else if (SEQ_GT(tp->snd_up, tp->snd_una))
  910                         TCPSTAT_INC(tcps_sndurg);
  911                 else
  912                         TCPSTAT_INC(tcps_sndwinup);
  913 
  914                 m = m_gethdr(M_NOWAIT, MT_DATA);
  915                 if (m == NULL) {
  916                         error = ENOBUFS;
  917                         sack_rxmit = 0;
  918                         goto out;
  919                 }
  920 #ifdef INET6
  921                 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
  922                     MHLEN >= hdrlen) {
  923                         MH_ALIGN(m, hdrlen);
  924                 } else
  925 #endif
  926                 m->m_data += max_linkhdr;
  927                 m->m_len = hdrlen;
  928         }
  929         SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
  930         m->m_pkthdr.rcvif = (struct ifnet *)0;
  931 #ifdef MAC
  932         mac_inpcb_create_mbuf(tp->t_inpcb, m);
  933 #endif
  934 #ifdef INET6
  935         if (isipv6) {
  936                 ip6 = mtod(m, struct ip6_hdr *);
  937                 th = (struct tcphdr *)(ip6 + 1);
  938                 tcpip_fillheaders(tp->t_inpcb, ip6, th);
  939         } else
  940 #endif /* INET6 */
  941         {
  942                 ip = mtod(m, struct ip *);
  943                 ipov = (struct ipovly *)ip;
  944                 th = (struct tcphdr *)(ip + 1);
  945                 tcpip_fillheaders(tp->t_inpcb, ip, th);
  946         }
  947 
  948         /*
  949          * Fill in fields, remembering maximum advertised
  950          * window for use in delaying messages about window sizes.
  951          * If resending a FIN, be sure not to use a new sequence number.
  952          */
  953         if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
  954             tp->snd_nxt == tp->snd_max)
  955                 tp->snd_nxt--;
  956         /*
  957          * If we are starting a connection, send ECN setup
  958          * SYN packet. If we are on a retransmit, we may
  959          * resend those bits a number of times as per
  960          * RFC 3168.
  961          */
  962         if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn) {
  963                 if (tp->t_rxtshift >= 1) {
  964                         if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
  965                                 flags |= TH_ECE|TH_CWR;
  966                 } else
  967                         flags |= TH_ECE|TH_CWR;
  968         }
  969         
  970         if (tp->t_state == TCPS_ESTABLISHED &&
  971             (tp->t_flags & TF_ECN_PERMIT)) {
  972                 /*
  973                  * If the peer has ECN, mark data packets with
  974                  * ECN capable transmission (ECT).
  975                  * Ignore pure ack packets, retransmissions and window probes.
  976                  */
  977                 if (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
  978                     !((tp->t_flags & TF_FORCEDATA) && len == 1)) {
  979 #ifdef INET6
  980                         if (isipv6)
  981                                 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20);
  982                         else
  983 #endif
  984                                 ip->ip_tos |= IPTOS_ECN_ECT0;
  985                         TCPSTAT_INC(tcps_ecn_ect0);
  986                 }
  987                 
  988                 /*
  989                  * Reply with proper ECN notifications.
  990                  */
  991                 if (tp->t_flags & TF_ECN_SND_CWR) {
  992                         flags |= TH_CWR;
  993                         tp->t_flags &= ~TF_ECN_SND_CWR;
  994                 } 
  995                 if (tp->t_flags & TF_ECN_SND_ECE)
  996                         flags |= TH_ECE;
  997         }
  998         
  999         /*
 1000          * If we are doing retransmissions, then snd_nxt will
 1001          * not reflect the first unsent octet.  For ACK only
 1002          * packets, we do not want the sequence number of the
 1003          * retransmitted packet, we want the sequence number
 1004          * of the next unsent octet.  So, if there is no data
 1005          * (and no SYN or FIN), use snd_max instead of snd_nxt
 1006          * when filling in ti_seq.  But if we are in persist
 1007          * state, snd_max might reflect one byte beyond the
 1008          * right edge of the window, so use snd_nxt in that
 1009          * case, since we know we aren't doing a retransmission.
 1010          * (retransmit and persist are mutually exclusive...)
 1011          */
 1012         if (sack_rxmit == 0) {
 1013                 if (len || (flags & (TH_SYN|TH_FIN)) ||
 1014                     tcp_timer_active(tp, TT_PERSIST))
 1015                         th->th_seq = htonl(tp->snd_nxt);
 1016                 else
 1017                         th->th_seq = htonl(tp->snd_max);
 1018         } else {
 1019                 th->th_seq = htonl(p->rxmit);
 1020                 p->rxmit += len;
 1021                 tp->sackhint.sack_bytes_rexmit += len;
 1022         }
 1023         th->th_ack = htonl(tp->rcv_nxt);
 1024         if (optlen) {
 1025                 bcopy(opt, th + 1, optlen);
 1026                 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
 1027         }
 1028         th->th_flags = flags;
 1029         /*
 1030          * Calculate receive window.  Don't shrink window,
 1031          * but avoid silly window syndrome.
 1032          */
 1033         if (recwin < (long)(so->so_rcv.sb_hiwat / 4) &&
 1034             recwin < (long)tp->t_maxseg)
 1035                 recwin = 0;
 1036         if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
 1037             recwin < (long)(tp->rcv_adv - tp->rcv_nxt))
 1038                 recwin = (long)(tp->rcv_adv - tp->rcv_nxt);
 1039         if (recwin > (long)TCP_MAXWIN << tp->rcv_scale)
 1040                 recwin = (long)TCP_MAXWIN << tp->rcv_scale;
 1041 
 1042         /*
 1043          * According to RFC1323 the window field in a SYN (i.e., a <SYN>
 1044          * or <SYN,ACK>) segment itself is never scaled.  The <SYN,ACK>
 1045          * case is handled in syncache.
 1046          */
 1047         if (flags & TH_SYN)
 1048                 th->th_win = htons((u_short)
 1049                                 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
 1050         else
 1051                 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
 1052 
 1053         /*
 1054          * Adjust the RXWIN0SENT flag - indicate that we have advertised
 1055          * a 0 window.  This may cause the remote transmitter to stall.  This
 1056          * flag tells soreceive() to disable delayed acknowledgements when
 1057          * draining the buffer.  This can occur if the receiver is attempting
 1058          * to read more data than can be buffered prior to transmitting on
 1059          * the connection.
 1060          */
 1061         if (th->th_win == 0) {
 1062                 tp->t_sndzerowin++;
 1063                 tp->t_flags |= TF_RXWIN0SENT;
 1064         } else
 1065                 tp->t_flags &= ~TF_RXWIN0SENT;
 1066         if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
 1067                 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
 1068                 th->th_flags |= TH_URG;
 1069         } else
 1070                 /*
 1071                  * If no urgent pointer to send, then we pull
 1072                  * the urgent pointer to the left edge of the send window
 1073                  * so that it doesn't drift into the send window on sequence
 1074                  * number wraparound.
 1075                  */
 1076                 tp->snd_up = tp->snd_una;               /* drag it along */
 1077 
 1078 #ifdef TCP_SIGNATURE
 1079         if (to.to_flags & TOF_SIGNATURE) {
 1080                 int sigoff = to.to_signature - opt;
 1081                 tcp_signature_compute(m, 0, len, optlen,
 1082                     (u_char *)(th + 1) + sigoff, IPSEC_DIR_OUTBOUND);
 1083         }
 1084 #endif
 1085 
 1086         /*
 1087          * Put TCP length in extended header, and then
 1088          * checksum extended header and data.
 1089          */
 1090         m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
 1091         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1092 #ifdef INET6
 1093         if (isipv6) {
 1094                 /*
 1095                  * ip6_plen is not need to be filled now, and will be filled
 1096                  * in ip6_output.
 1097                  */
 1098                 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
 1099                 th->th_sum = in6_cksum_pseudo(ip6, sizeof(struct tcphdr) +
 1100                     optlen + len, IPPROTO_TCP, 0);
 1101         }
 1102 #endif
 1103 #if defined(INET6) && defined(INET)
 1104         else
 1105 #endif
 1106 #ifdef INET
 1107         {
 1108                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1109                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1110                     htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen));
 1111 
 1112                 /* IP version must be set here for ipv4/ipv6 checking later */
 1113                 KASSERT(ip->ip_v == IPVERSION,
 1114                     ("%s: IP version incorrect: %d", __func__, ip->ip_v));
 1115         }
 1116 #endif
 1117 
 1118         /*
 1119          * Enable TSO and specify the size of the segments.
 1120          * The TCP pseudo header checksum is always provided.
 1121          * XXX: Fixme: This is currently not the case for IPv6.
 1122          */
 1123         if (tso) {
 1124                 KASSERT(len > tp->t_maxopd - optlen,
 1125                     ("%s: len <= tso_segsz", __func__));
 1126                 m->m_pkthdr.csum_flags |= CSUM_TSO;
 1127                 m->m_pkthdr.tso_segsz = tp->t_maxopd - optlen;
 1128         }
 1129 
 1130 #ifdef IPSEC
 1131         KASSERT(len + hdrlen + ipoptlen - ipsec_optlen == m_length(m, NULL),
 1132             ("%s: mbuf chain shorter than expected: %ld + %u + %u - %u != %u",
 1133             __func__, len, hdrlen, ipoptlen, ipsec_optlen, m_length(m, NULL)));
 1134 #else
 1135         KASSERT(len + hdrlen + ipoptlen == m_length(m, NULL),
 1136             ("%s: mbuf chain shorter than expected: %ld + %u + %u != %u",
 1137             __func__, len, hdrlen, ipoptlen, m_length(m, NULL)));
 1138 #endif
 1139 
 1140         /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
 1141         hhook_run_tcp_est_out(tp, th, &to, len, tso);
 1142 
 1143 #ifdef TCPDEBUG
 1144         /*
 1145          * Trace.
 1146          */
 1147         if (so->so_options & SO_DEBUG) {
 1148                 u_short save = 0;
 1149 #ifdef INET6
 1150                 if (!isipv6)
 1151 #endif
 1152                 {
 1153                         save = ipov->ih_len;
 1154                         ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
 1155                 }
 1156                 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
 1157 #ifdef INET6
 1158                 if (!isipv6)
 1159 #endif
 1160                 ipov->ih_len = save;
 1161         }
 1162 #endif /* TCPDEBUG */
 1163 
 1164         /*
 1165          * Fill in IP length and desired time to live and
 1166          * send to IP level.  There should be a better way
 1167          * to handle ttl and tos; we could keep them in
 1168          * the template, but need a way to checksum without them.
 1169          */
 1170         /*
 1171          * m->m_pkthdr.len should have been set before cksum calcuration,
 1172          * because in6_cksum() need it.
 1173          */
 1174 #ifdef INET6
 1175         if (isipv6) {
 1176                 struct route_in6 ro;
 1177 
 1178                 bzero(&ro, sizeof(ro));
 1179                 /*
 1180                  * we separately set hoplimit for every segment, since the
 1181                  * user might want to change the value via setsockopt.
 1182                  * Also, desired default hop limit might be changed via
 1183                  * Neighbor Discovery.
 1184                  */
 1185                 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
 1186 
 1187                 /*
 1188                  * Set the packet size here for the benefit of DTrace probes.
 1189                  * ip6_output() will set it properly; it's supposed to include
 1190                  * the option header lengths as well.
 1191                  */
 1192                 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
 1193 
 1194                 if (tp->t_state == TCPS_SYN_SENT)
 1195                         TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
 1196 
 1197                 TCP_PROBE5(send, NULL, tp, ip6, tp, th);
 1198 
 1199                 /* TODO: IPv6 IP6TOS_ECT bit on */
 1200                 error = ip6_output(m, tp->t_inpcb->in6p_outputopts, &ro,
 1201                     ((so->so_options & SO_DONTROUTE) ?  IP_ROUTETOIF : 0),
 1202                     NULL, NULL, tp->t_inpcb);
 1203 
 1204                 if (error == EMSGSIZE && ro.ro_rt != NULL)
 1205                         mtu = ro.ro_rt->rt_mtu;
 1206                 RO_RTFREE(&ro);
 1207         }
 1208 #endif /* INET6 */
 1209 #if defined(INET) && defined(INET6)
 1210         else
 1211 #endif
 1212 #ifdef INET
 1213     {
 1214         struct route ro;
 1215 
 1216         bzero(&ro, sizeof(ro));
 1217         ip->ip_len = htons(m->m_pkthdr.len);
 1218 #ifdef INET6
 1219         if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO)
 1220                 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
 1221 #endif /* INET6 */
 1222         /*
 1223          * If we do path MTU discovery, then we set DF on every packet.
 1224          * This might not be the best thing to do according to RFC3390
 1225          * Section 2. However the tcp hostcache migitates the problem
 1226          * so it affects only the first tcp connection with a host.
 1227          *
 1228          * NB: Don't set DF on small MTU/MSS to have a safe fallback.
 1229          */
 1230         if (V_path_mtu_discovery && tp->t_maxopd > V_tcp_minmss)
 1231                 ip->ip_off |= htons(IP_DF);
 1232 
 1233         if (tp->t_state == TCPS_SYN_SENT)
 1234                 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
 1235 
 1236         TCP_PROBE5(send, NULL, tp, ip, tp, th);
 1237 
 1238         error = ip_output(m, tp->t_inpcb->inp_options, &ro,
 1239             ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
 1240             tp->t_inpcb);
 1241 
 1242         if (error == EMSGSIZE && ro.ro_rt != NULL)
 1243                 mtu = ro.ro_rt->rt_mtu;
 1244         RO_RTFREE(&ro);
 1245     }
 1246 #endif /* INET */
 1247 
 1248 out:
 1249         /*
 1250          * In transmit state, time the transmission and arrange for
 1251          * the retransmit.  In persist state, just set snd_max.
 1252          */
 1253         if ((tp->t_flags & TF_FORCEDATA) == 0 || 
 1254             !tcp_timer_active(tp, TT_PERSIST)) {
 1255                 tcp_seq startseq = tp->snd_nxt;
 1256 
 1257                 /*
 1258                  * Advance snd_nxt over sequence space of this segment.
 1259                  */
 1260                 if (flags & (TH_SYN|TH_FIN)) {
 1261                         if (flags & TH_SYN)
 1262                                 tp->snd_nxt++;
 1263                         if (flags & TH_FIN) {
 1264                                 tp->snd_nxt++;
 1265                                 tp->t_flags |= TF_SENTFIN;
 1266                         }
 1267                 }
 1268                 if (sack_rxmit)
 1269                         goto timer;
 1270                 tp->snd_nxt += len;
 1271                 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
 1272                         tp->snd_max = tp->snd_nxt;
 1273                         /*
 1274                          * Time this transmission if not a retransmission and
 1275                          * not currently timing anything.
 1276                          */
 1277                         if (tp->t_rtttime == 0) {
 1278                                 tp->t_rtttime = ticks;
 1279                                 tp->t_rtseq = startseq;
 1280                                 TCPSTAT_INC(tcps_segstimed);
 1281                         }
 1282                 }
 1283 
 1284                 /*
 1285                  * Set retransmit timer if not currently set,
 1286                  * and not doing a pure ack or a keep-alive probe.
 1287                  * Initial value for retransmit timer is smoothed
 1288                  * round-trip time + 2 * round-trip time variance.
 1289                  * Initialize shift counter which is used for backoff
 1290                  * of retransmit time.
 1291                  */
 1292 timer:
 1293                 if (!tcp_timer_active(tp, TT_REXMT) &&
 1294                     ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
 1295                      (tp->snd_nxt != tp->snd_una))) {
 1296                         if (tcp_timer_active(tp, TT_PERSIST)) {
 1297                                 tcp_timer_activate(tp, TT_PERSIST, 0);
 1298                                 tp->t_rxtshift = 0;
 1299                         }
 1300                         tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
 1301                 }
 1302         } else {
 1303                 /*
 1304                  * Persist case, update snd_max but since we are in
 1305                  * persist mode (no window) we do not update snd_nxt.
 1306                  */
 1307                 int xlen = len;
 1308                 if (flags & TH_SYN)
 1309                         ++xlen;
 1310                 if (flags & TH_FIN) {
 1311                         ++xlen;
 1312                         tp->t_flags |= TF_SENTFIN;
 1313                 }
 1314                 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
 1315                         tp->snd_max = tp->snd_nxt + len;
 1316         }
 1317 
 1318         if (error) {
 1319 
 1320                 /*
 1321                  * We know that the packet was lost, so back out the
 1322                  * sequence number advance, if any.
 1323                  *
 1324                  * If the error is EPERM the packet got blocked by the
 1325                  * local firewall.  Normally we should terminate the
 1326                  * connection but the blocking may have been spurious
 1327                  * due to a firewall reconfiguration cycle.  So we treat
 1328                  * it like a packet loss and let the retransmit timer and
 1329                  * timeouts do their work over time.
 1330                  * XXX: It is a POLA question whether calling tcp_drop right
 1331                  * away would be the really correct behavior instead.
 1332                  */
 1333                 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
 1334                     !tcp_timer_active(tp, TT_PERSIST)) &&
 1335                     ((flags & TH_SYN) == 0) &&
 1336                     (error != EPERM)) {
 1337                         if (sack_rxmit) {
 1338                                 p->rxmit -= len;
 1339                                 tp->sackhint.sack_bytes_rexmit -= len;
 1340                                 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
 1341                                     ("sackhint bytes rtx >= 0"));
 1342                         } else
 1343                                 tp->snd_nxt -= len;
 1344                 }
 1345                 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);     /* Check gotos. */
 1346                 switch (error) {
 1347                 case EPERM:
 1348                         tp->t_softerror = error;
 1349                         return (error);
 1350                 case ENOBUFS:
 1351                         if (!tcp_timer_active(tp, TT_REXMT) &&
 1352                             !tcp_timer_active(tp, TT_PERSIST))
 1353                                 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
 1354                         tp->snd_cwnd = tp->t_maxseg;
 1355                         return (0);
 1356                 case EMSGSIZE:
 1357                         /*
 1358                          * For some reason the interface we used initially
 1359                          * to send segments changed to another or lowered
 1360                          * its MTU.
 1361                          * If TSO was active we either got an interface
 1362                          * without TSO capabilits or TSO was turned off.
 1363                          * If we obtained mtu from ip_output() then update
 1364                          * it and try again.
 1365                          */
 1366                         if (tso)
 1367                                 tp->t_flags &= ~TF_TSO;
 1368                         if (mtu != 0) {
 1369                                 tcp_mss_update(tp, -1, mtu, NULL, NULL);
 1370                                 goto again;
 1371                         }
 1372                         return (error);
 1373                 case EHOSTDOWN:
 1374                 case EHOSTUNREACH:
 1375                 case ENETDOWN:
 1376                 case ENETUNREACH:
 1377                         if (TCPS_HAVERCVDSYN(tp->t_state)) {
 1378                                 tp->t_softerror = error;
 1379                                 return (0);
 1380                         }
 1381                         /* FALLTHROUGH */
 1382                 default:
 1383                         return (error);
 1384                 }
 1385         }
 1386         TCPSTAT_INC(tcps_sndtotal);
 1387 
 1388         /*
 1389          * Data sent (as far as we can tell).
 1390          * If this advertises a larger window than any other segment,
 1391          * then remember the size of the advertised window.
 1392          * Any pending ACK has now been sent.
 1393          */
 1394         if (recwin >= 0 && SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
 1395                 tp->rcv_adv = tp->rcv_nxt + recwin;
 1396         tp->last_ack_sent = tp->rcv_nxt;
 1397         tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
 1398         if (tcp_timer_active(tp, TT_DELACK))
 1399                 tcp_timer_activate(tp, TT_DELACK, 0);
 1400 #if 0
 1401         /*
 1402          * This completely breaks TCP if newreno is turned on.  What happens
 1403          * is that if delayed-acks are turned on on the receiver, this code
 1404          * on the transmitter effectively destroys the TCP window, forcing
 1405          * it to four packets (1.5Kx4 = 6K window).
 1406          */
 1407         if (sendalot && --maxburst)
 1408                 goto again;
 1409 #endif
 1410         if (sendalot)
 1411                 goto again;
 1412         return (0);
 1413 }
 1414 
 1415 void
 1416 tcp_setpersist(struct tcpcb *tp)
 1417 {
 1418         int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
 1419         int tt;
 1420 
 1421         tp->t_flags &= ~TF_PREVVALID;
 1422         if (tcp_timer_active(tp, TT_REXMT))
 1423                 panic("tcp_setpersist: retransmit pending");
 1424         /*
 1425          * Start/restart persistance timer.
 1426          */
 1427         TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
 1428                       TCPTV_PERSMIN, TCPTV_PERSMAX);
 1429         tcp_timer_activate(tp, TT_PERSIST, tt);
 1430         if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
 1431                 tp->t_rxtshift++;
 1432 }
 1433 
 1434 /*
 1435  * Insert TCP options according to the supplied parameters to the place
 1436  * optp in a consistent way.  Can handle unaligned destinations.
 1437  *
 1438  * The order of the option processing is crucial for optimal packing and
 1439  * alignment for the scarce option space.
 1440  *
 1441  * The optimal order for a SYN/SYN-ACK segment is:
 1442  *   MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
 1443  *   Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
 1444  *
 1445  * The SACK options should be last.  SACK blocks consume 8*n+2 bytes.
 1446  * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
 1447  * At minimum we need 10 bytes (to generate 1 SACK block).  If both
 1448  * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
 1449  * we only have 10 bytes for SACK options (40 - (12 + 18)).
 1450  */
 1451 int
 1452 tcp_addoptions(struct tcpopt *to, u_char *optp)
 1453 {
 1454         u_int mask, optlen = 0;
 1455 
 1456         for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
 1457                 if ((to->to_flags & mask) != mask)
 1458                         continue;
 1459                 if (optlen == TCP_MAXOLEN)
 1460                         break;
 1461                 switch (to->to_flags & mask) {
 1462                 case TOF_MSS:
 1463                         while (optlen % 4) {
 1464                                 optlen += TCPOLEN_NOP;
 1465                                 *optp++ = TCPOPT_NOP;
 1466                         }
 1467                         if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
 1468                                 continue;
 1469                         optlen += TCPOLEN_MAXSEG;
 1470                         *optp++ = TCPOPT_MAXSEG;
 1471                         *optp++ = TCPOLEN_MAXSEG;
 1472                         to->to_mss = htons(to->to_mss);
 1473                         bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
 1474                         optp += sizeof(to->to_mss);
 1475                         break;
 1476                 case TOF_SCALE:
 1477                         while (!optlen || optlen % 2 != 1) {
 1478                                 optlen += TCPOLEN_NOP;
 1479                                 *optp++ = TCPOPT_NOP;
 1480                         }
 1481                         if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
 1482                                 continue;
 1483                         optlen += TCPOLEN_WINDOW;
 1484                         *optp++ = TCPOPT_WINDOW;
 1485                         *optp++ = TCPOLEN_WINDOW;
 1486                         *optp++ = to->to_wscale;
 1487                         break;
 1488                 case TOF_SACKPERM:
 1489                         while (optlen % 2) {
 1490                                 optlen += TCPOLEN_NOP;
 1491                                 *optp++ = TCPOPT_NOP;
 1492                         }
 1493                         if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
 1494                                 continue;
 1495                         optlen += TCPOLEN_SACK_PERMITTED;
 1496                         *optp++ = TCPOPT_SACK_PERMITTED;
 1497                         *optp++ = TCPOLEN_SACK_PERMITTED;
 1498                         break;
 1499                 case TOF_TS:
 1500                         while (!optlen || optlen % 4 != 2) {
 1501                                 optlen += TCPOLEN_NOP;
 1502                                 *optp++ = TCPOPT_NOP;
 1503                         }
 1504                         if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
 1505                                 continue;
 1506                         optlen += TCPOLEN_TIMESTAMP;
 1507                         *optp++ = TCPOPT_TIMESTAMP;
 1508                         *optp++ = TCPOLEN_TIMESTAMP;
 1509                         to->to_tsval = htonl(to->to_tsval);
 1510                         to->to_tsecr = htonl(to->to_tsecr);
 1511                         bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
 1512                         optp += sizeof(to->to_tsval);
 1513                         bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
 1514                         optp += sizeof(to->to_tsecr);
 1515                         break;
 1516 #ifdef TCP_SIGNATURE
 1517                 case TOF_SIGNATURE:
 1518                         {
 1519                         int siglen = TCPOLEN_SIGNATURE - 2;
 1520 
 1521                         while (!optlen || optlen % 4 != 2) {
 1522                                 optlen += TCPOLEN_NOP;
 1523                                 *optp++ = TCPOPT_NOP;
 1524                         }
 1525                         if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE)
 1526                                 continue;
 1527                         optlen += TCPOLEN_SIGNATURE;
 1528                         *optp++ = TCPOPT_SIGNATURE;
 1529                         *optp++ = TCPOLEN_SIGNATURE;
 1530                         to->to_signature = optp;
 1531                         while (siglen--)
 1532                                  *optp++ = 0;
 1533                         break;
 1534                         }
 1535 #endif
 1536                 case TOF_SACK:
 1537                         {
 1538                         int sackblks = 0;
 1539                         struct sackblk *sack = (struct sackblk *)to->to_sacks;
 1540                         tcp_seq sack_seq;
 1541 
 1542                         while (!optlen || optlen % 4 != 2) {
 1543                                 optlen += TCPOLEN_NOP;
 1544                                 *optp++ = TCPOPT_NOP;
 1545                         }
 1546                         if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
 1547                                 continue;
 1548                         optlen += TCPOLEN_SACKHDR;
 1549                         *optp++ = TCPOPT_SACK;
 1550                         sackblks = min(to->to_nsacks,
 1551                                         (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
 1552                         *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
 1553                         while (sackblks--) {
 1554                                 sack_seq = htonl(sack->start);
 1555                                 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
 1556                                 optp += sizeof(sack_seq);
 1557                                 sack_seq = htonl(sack->end);
 1558                                 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
 1559                                 optp += sizeof(sack_seq);
 1560                                 optlen += TCPOLEN_SACK;
 1561                                 sack++;
 1562                         }
 1563                         TCPSTAT_INC(tcps_sack_send_blocks);
 1564                         break;
 1565                         }
 1566                 default:
 1567                         panic("%s: unknown TCP option type", __func__);
 1568                         break;
 1569                 }
 1570         }
 1571 
 1572         /* Terminate and pad TCP options to a 4 byte boundary. */
 1573         if (optlen % 4) {
 1574                 optlen += TCPOLEN_EOL;
 1575                 *optp++ = TCPOPT_EOL;
 1576         }
 1577         /*
 1578          * According to RFC 793 (STD0007):
 1579          *   "The content of the header beyond the End-of-Option option
 1580          *    must be header padding (i.e., zero)."
 1581          *   and later: "The padding is composed of zeros."
 1582          */
 1583         while (optlen % 4) {
 1584                 optlen += TCPOLEN_PAD;
 1585                 *optp++ = TCPOPT_PAD;
 1586         }
 1587 
 1588         KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));
 1589         return (optlen);
 1590 }

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