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/11.0/sys/netinet/tcp_output.c 300981 2016-05-30 03:31:37Z sephe $");
   34 
   35 #include "opt_inet.h"
   36 #include "opt_inet6.h"
   37 #include "opt_ipsec.h"
   38 #include "opt_tcpdebug.h"
   39 
   40 #include <sys/param.h>
   41 #include <sys/systm.h>
   42 #include <sys/domain.h>
   43 #include <sys/hhook.h>
   44 #include <sys/kernel.h>
   45 #include <sys/lock.h>
   46 #include <sys/mbuf.h>
   47 #include <sys/mutex.h>
   48 #include <sys/protosw.h>
   49 #include <sys/sdt.h>
   50 #include <sys/socket.h>
   51 #include <sys/socketvar.h>
   52 #include <sys/sysctl.h>
   53 
   54 #include <net/if.h>
   55 #include <net/route.h>
   56 #include <net/vnet.h>
   57 
   58 #include <netinet/in.h>
   59 #include <netinet/in_kdtrace.h>
   60 #include <netinet/in_systm.h>
   61 #include <netinet/ip.h>
   62 #include <netinet/in_pcb.h>
   63 #include <netinet/ip_var.h>
   64 #include <netinet/ip_options.h>
   65 #ifdef INET6
   66 #include <netinet6/in6_pcb.h>
   67 #include <netinet/ip6.h>
   68 #include <netinet6/ip6_var.h>
   69 #endif
   70 #ifdef TCP_RFC7413
   71 #include <netinet/tcp_fastopen.h>
   72 #endif
   73 #include <netinet/tcp.h>
   74 #define TCPOUTFLAGS
   75 #include <netinet/tcp_fsm.h>
   76 #include <netinet/tcp_seq.h>
   77 #include <netinet/tcp_timer.h>
   78 #include <netinet/tcp_var.h>
   79 #include <netinet/tcpip.h>
   80 #include <netinet/cc/cc.h>
   81 #ifdef TCPPCAP
   82 #include <netinet/tcp_pcap.h>
   83 #endif
   84 #ifdef TCPDEBUG
   85 #include <netinet/tcp_debug.h>
   86 #endif
   87 #ifdef TCP_OFFLOAD
   88 #include <netinet/tcp_offload.h>
   89 #endif
   90 
   91 #ifdef IPSEC
   92 #include <netipsec/ipsec.h>
   93 #endif /*IPSEC*/
   94 
   95 #include <machine/in_cksum.h>
   96 
   97 #include <security/mac/mac_framework.h>
   98 
   99 VNET_DEFINE(int, path_mtu_discovery) = 1;
  100 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_VNET | CTLFLAG_RW,
  101         &VNET_NAME(path_mtu_discovery), 1,
  102         "Enable Path MTU Discovery");
  103 
  104 VNET_DEFINE(int, tcp_do_tso) = 1;
  105 #define V_tcp_do_tso            VNET(tcp_do_tso)
  106 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_VNET | CTLFLAG_RW,
  107         &VNET_NAME(tcp_do_tso), 0,
  108         "Enable TCP Segmentation Offload");
  109 
  110 VNET_DEFINE(int, tcp_sendspace) = 1024*32;
  111 #define V_tcp_sendspace VNET(tcp_sendspace)
  112 SYSCTL_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_VNET | CTLFLAG_RW,
  113         &VNET_NAME(tcp_sendspace), 0, "Initial send socket buffer size");
  114 
  115 VNET_DEFINE(int, tcp_do_autosndbuf) = 1;
  116 #define V_tcp_do_autosndbuf     VNET(tcp_do_autosndbuf)
  117 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
  118         &VNET_NAME(tcp_do_autosndbuf), 0,
  119         "Enable automatic send buffer sizing");
  120 
  121 VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024;
  122 #define V_tcp_autosndbuf_inc    VNET(tcp_autosndbuf_inc)
  123 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_VNET | CTLFLAG_RW,
  124         &VNET_NAME(tcp_autosndbuf_inc), 0,
  125         "Incrementor step size of automatic send buffer");
  126 
  127 VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024;
  128 #define V_tcp_autosndbuf_max    VNET(tcp_autosndbuf_max)
  129 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
  130         &VNET_NAME(tcp_autosndbuf_max), 0,
  131         "Max size of automatic send buffer");
  132 
  133 /*
  134  * Make sure that either retransmit or persist timer is set for SYN, FIN and
  135  * non-ACK.
  136  */
  137 #define TCP_XMIT_TIMER_ASSERT(tp, len, th_flags)                        \
  138         KASSERT(((len) == 0 && ((th_flags) & (TH_SYN | TH_FIN)) == 0) ||\
  139             tcp_timer_active((tp), TT_REXMT) ||                         \
  140             tcp_timer_active((tp), TT_PERSIST),                         \
  141             ("neither rexmt nor persist timer is set"))
  142 
  143 static void inline      hhook_run_tcp_est_out(struct tcpcb *tp,
  144                             struct tcphdr *th, struct tcpopt *to,
  145                             long len, int tso);
  146 static void inline      cc_after_idle(struct tcpcb *tp);
  147 
  148 /*
  149  * Wrapper for the TCP established output helper hook.
  150  */
  151 static void inline
  152 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
  153     struct tcpopt *to, long len, int tso)
  154 {
  155         struct tcp_hhook_data hhook_data;
  156 
  157         if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
  158                 hhook_data.tp = tp;
  159                 hhook_data.th = th;
  160                 hhook_data.to = to;
  161                 hhook_data.len = len;
  162                 hhook_data.tso = tso;
  163 
  164                 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
  165                     tp->osd);
  166         }
  167 }
  168 
  169 /*
  170  * CC wrapper hook functions
  171  */
  172 static void inline
  173 cc_after_idle(struct tcpcb *tp)
  174 {
  175         INP_WLOCK_ASSERT(tp->t_inpcb);
  176 
  177         if (CC_ALGO(tp)->after_idle != NULL)
  178                 CC_ALGO(tp)->after_idle(tp->ccv);
  179 }
  180 
  181 /*
  182  * Tcp output routine: figure out what should be sent and send it.
  183  */
  184 int
  185 tcp_output(struct tcpcb *tp)
  186 {
  187         struct socket *so = tp->t_inpcb->inp_socket;
  188         long len, recwin, sendwin;
  189         int off, flags, error = 0;      /* Keep compiler happy */
  190         struct mbuf *m;
  191         struct ip *ip = NULL;
  192         struct ipovly *ipov = NULL;
  193         struct tcphdr *th;
  194         u_char opt[TCP_MAXOLEN];
  195         unsigned ipoptlen, optlen, hdrlen;
  196 #ifdef IPSEC
  197         unsigned ipsec_optlen = 0;
  198 #endif
  199         int idle, sendalot;
  200         int sack_rxmit, sack_bytes_rxmt;
  201         struct sackhole *p;
  202         int tso, mtu;
  203         struct tcpopt to;
  204 #if 0
  205         int maxburst = TCP_MAXBURST;
  206 #endif
  207 #ifdef INET6
  208         struct ip6_hdr *ip6 = NULL;
  209         int isipv6;
  210 
  211         isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
  212 #endif
  213 
  214         INP_WLOCK_ASSERT(tp->t_inpcb);
  215 
  216 #ifdef TCP_OFFLOAD
  217         if (tp->t_flags & TF_TOE)
  218                 return (tcp_offload_output(tp));
  219 #endif
  220 
  221 #ifdef TCP_RFC7413
  222         /*
  223          * For TFO connections in SYN_RECEIVED, only allow the initial
  224          * SYN|ACK and those sent by the retransmit timer.
  225          */
  226         if ((tp->t_flags & TF_FASTOPEN) &&
  227             (tp->t_state == TCPS_SYN_RECEIVED) &&
  228             SEQ_GT(tp->snd_max, tp->snd_una) &&    /* initial SYN|ACK sent */
  229             (tp->snd_nxt != tp->snd_una))          /* not a retransmit */
  230                 return (0);
  231 #endif
  232         /*
  233          * Determine length of data that should be transmitted,
  234          * and flags that will be used.
  235          * If there is some data or critical controls (SYN, RST)
  236          * to send, then transmit; otherwise, investigate further.
  237          */
  238         idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
  239         if (idle && ticks - tp->t_rcvtime >= tp->t_rxtcur)
  240                 cc_after_idle(tp);
  241         tp->t_flags &= ~TF_LASTIDLE;
  242         if (idle) {
  243                 if (tp->t_flags & TF_MORETOCOME) {
  244                         tp->t_flags |= TF_LASTIDLE;
  245                         idle = 0;
  246                 }
  247         }
  248 again:
  249         /*
  250          * If we've recently taken a timeout, snd_max will be greater than
  251          * snd_nxt.  There may be SACK information that allows us to avoid
  252          * resending already delivered data.  Adjust snd_nxt accordingly.
  253          */
  254         if ((tp->t_flags & TF_SACK_PERMIT) &&
  255             SEQ_LT(tp->snd_nxt, tp->snd_max))
  256                 tcp_sack_adjust(tp);
  257         sendalot = 0;
  258         tso = 0;
  259         mtu = 0;
  260         off = tp->snd_nxt - tp->snd_una;
  261         sendwin = min(tp->snd_wnd, tp->snd_cwnd);
  262 
  263         flags = tcp_outflags[tp->t_state];
  264         /*
  265          * Send any SACK-generated retransmissions.  If we're explicitly trying
  266          * to send out new data (when sendalot is 1), bypass this function.
  267          * If we retransmit in fast recovery mode, decrement snd_cwnd, since
  268          * we're replacing a (future) new transmission with a retransmission
  269          * now, and we previously incremented snd_cwnd in tcp_input().
  270          */
  271         /*
  272          * Still in sack recovery , reset rxmit flag to zero.
  273          */
  274         sack_rxmit = 0;
  275         sack_bytes_rxmt = 0;
  276         len = 0;
  277         p = NULL;
  278         if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
  279             (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
  280                 long cwin;
  281                 
  282                 cwin = min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt;
  283                 if (cwin < 0)
  284                         cwin = 0;
  285                 /* Do not retransmit SACK segments beyond snd_recover */
  286                 if (SEQ_GT(p->end, tp->snd_recover)) {
  287                         /*
  288                          * (At least) part of sack hole extends beyond
  289                          * snd_recover. Check to see if we can rexmit data
  290                          * for this hole.
  291                          */
  292                         if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
  293                                 /*
  294                                  * Can't rexmit any more data for this hole.
  295                                  * That data will be rexmitted in the next
  296                                  * sack recovery episode, when snd_recover
  297                                  * moves past p->rxmit.
  298                                  */
  299                                 p = NULL;
  300                                 goto after_sack_rexmit;
  301                         } else
  302                                 /* Can rexmit part of the current hole */
  303                                 len = ((long)ulmin(cwin,
  304                                                    tp->snd_recover - p->rxmit));
  305                 } else
  306                         len = ((long)ulmin(cwin, p->end - p->rxmit));
  307                 off = p->rxmit - tp->snd_una;
  308                 KASSERT(off >= 0,("%s: sack block to the left of una : %d",
  309                     __func__, off));
  310                 if (len > 0) {
  311                         sack_rxmit = 1;
  312                         sendalot = 1;
  313                         TCPSTAT_INC(tcps_sack_rexmits);
  314                         TCPSTAT_ADD(tcps_sack_rexmit_bytes,
  315                             min(len, tp->t_maxseg));
  316                 }
  317         }
  318 after_sack_rexmit:
  319         /*
  320          * Get standard flags, and add SYN or FIN if requested by 'hidden'
  321          * state flags.
  322          */
  323         if (tp->t_flags & TF_NEEDFIN)
  324                 flags |= TH_FIN;
  325         if (tp->t_flags & TF_NEEDSYN)
  326                 flags |= TH_SYN;
  327 
  328         SOCKBUF_LOCK(&so->so_snd);
  329         /*
  330          * If in persist timeout with window of 0, send 1 byte.
  331          * Otherwise, if window is small but nonzero
  332          * and timer expired, we will send what we can
  333          * and go to transmit state.
  334          */
  335         if (tp->t_flags & TF_FORCEDATA) {
  336                 if (sendwin == 0) {
  337                         /*
  338                          * If we still have some data to send, then
  339                          * clear the FIN bit.  Usually this would
  340                          * happen below when it realizes that we
  341                          * aren't sending all the data.  However,
  342                          * if we have exactly 1 byte of unsent data,
  343                          * then it won't clear the FIN bit below,
  344                          * and if we are in persist state, we wind
  345                          * up sending the packet without recording
  346                          * that we sent the FIN bit.
  347                          *
  348                          * We can't just blindly clear the FIN bit,
  349                          * because if we don't have any more data
  350                          * to send then the probe will be the FIN
  351                          * itself.
  352                          */
  353                         if (off < sbused(&so->so_snd))
  354                                 flags &= ~TH_FIN;
  355                         sendwin = 1;
  356                 } else {
  357                         tcp_timer_activate(tp, TT_PERSIST, 0);
  358                         tp->t_rxtshift = 0;
  359                 }
  360         }
  361 
  362         /*
  363          * If snd_nxt == snd_max and we have transmitted a FIN, the
  364          * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
  365          * a negative length.  This can also occur when TCP opens up
  366          * its congestion window while receiving additional duplicate
  367          * acks after fast-retransmit because TCP will reset snd_nxt
  368          * to snd_max after the fast-retransmit.
  369          *
  370          * In the normal retransmit-FIN-only case, however, snd_nxt will
  371          * be set to snd_una, the offset will be 0, and the length may
  372          * wind up 0.
  373          *
  374          * If sack_rxmit is true we are retransmitting from the scoreboard
  375          * in which case len is already set.
  376          */
  377         if (sack_rxmit == 0) {
  378                 if (sack_bytes_rxmt == 0)
  379                         len = ((long)ulmin(sbavail(&so->so_snd), sendwin) -
  380                             off);
  381                 else {
  382                         long cwin;
  383 
  384                         /*
  385                          * We are inside of a SACK recovery episode and are
  386                          * sending new data, having retransmitted all the
  387                          * data possible in the scoreboard.
  388                          */
  389                         len = ((long)ulmin(sbavail(&so->so_snd), tp->snd_wnd) -
  390                             off);
  391                         /*
  392                          * Don't remove this (len > 0) check !
  393                          * We explicitly check for len > 0 here (although it 
  394                          * isn't really necessary), to work around a gcc 
  395                          * optimization issue - to force gcc to compute
  396                          * len above. Without this check, the computation
  397                          * of len is bungled by the optimizer.
  398                          */
  399                         if (len > 0) {
  400                                 cwin = tp->snd_cwnd - 
  401                                         (tp->snd_nxt - tp->sack_newdata) -
  402                                         sack_bytes_rxmt;
  403                                 if (cwin < 0)
  404                                         cwin = 0;
  405                                 len = lmin(len, cwin);
  406                         }
  407                 }
  408         }
  409 
  410         /*
  411          * Lop off SYN bit if it has already been sent.  However, if this
  412          * is SYN-SENT state and if segment contains data and if we don't
  413          * know that foreign host supports TAO, suppress sending segment.
  414          */
  415         if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
  416                 if (tp->t_state != TCPS_SYN_RECEIVED)
  417                         flags &= ~TH_SYN;
  418 #ifdef TCP_RFC7413
  419                 /*
  420                  * When sending additional segments following a TFO SYN|ACK,
  421                  * do not include the SYN bit.
  422                  */
  423                 if ((tp->t_flags & TF_FASTOPEN) &&
  424                     (tp->t_state == TCPS_SYN_RECEIVED))
  425                         flags &= ~TH_SYN;
  426 #endif
  427                 off--, len++;
  428         }
  429 
  430         /*
  431          * Be careful not to send data and/or FIN on SYN segments.
  432          * This measure is needed to prevent interoperability problems
  433          * with not fully conformant TCP implementations.
  434          */
  435         if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
  436                 len = 0;
  437                 flags &= ~TH_FIN;
  438         }
  439 
  440 #ifdef TCP_RFC7413
  441         /*
  442          * When retransmitting SYN|ACK on a passively-created TFO socket,
  443          * don't include data, as the presence of data may have caused the
  444          * original SYN|ACK to have been dropped by a middlebox.
  445          */
  446         if ((tp->t_flags & TF_FASTOPEN) &&
  447             (((tp->t_state == TCPS_SYN_RECEIVED) && (tp->t_rxtshift > 0)) ||
  448              (flags & TH_RST)))
  449                 len = 0;
  450 #endif
  451         if (len <= 0) {
  452                 /*
  453                  * If FIN has been sent but not acked,
  454                  * but we haven't been called to retransmit,
  455                  * len will be < 0.  Otherwise, window shrank
  456                  * after we sent into it.  If window shrank to 0,
  457                  * cancel pending retransmit, pull snd_nxt back
  458                  * to (closed) window, and set the persist timer
  459                  * if it isn't already going.  If the window didn't
  460                  * close completely, just wait for an ACK.
  461                  *
  462                  * We also do a general check here to ensure that
  463                  * we will set the persist timer when we have data
  464                  * to send, but a 0-byte window. This makes sure
  465                  * the persist timer is set even if the packet
  466                  * hits one of the "goto send" lines below.
  467                  */
  468                 len = 0;
  469                 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
  470                         (off < (int) sbavail(&so->so_snd))) {
  471                         tcp_timer_activate(tp, TT_REXMT, 0);
  472                         tp->t_rxtshift = 0;
  473                         tp->snd_nxt = tp->snd_una;
  474                         if (!tcp_timer_active(tp, TT_PERSIST))
  475                                 tcp_setpersist(tp);
  476                 }
  477         }
  478 
  479         /* len will be >= 0 after this point. */
  480         KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
  481 
  482         /*
  483          * Automatic sizing of send socket buffer.  Often the send buffer
  484          * size is not optimally adjusted to the actual network conditions
  485          * at hand (delay bandwidth product).  Setting the buffer size too
  486          * small limits throughput on links with high bandwidth and high
  487          * delay (eg. trans-continental/oceanic links).  Setting the
  488          * buffer size too big consumes too much real kernel memory,
  489          * especially with many connections on busy servers.
  490          *
  491          * The criteria to step up the send buffer one notch are:
  492          *  1. receive window of remote host is larger than send buffer
  493          *     (with a fudge factor of 5/4th);
  494          *  2. send buffer is filled to 7/8th with data (so we actually
  495          *     have data to make use of it);
  496          *  3. send buffer fill has not hit maximal automatic size;
  497          *  4. our send window (slow start and cogestion controlled) is
  498          *     larger than sent but unacknowledged data in send buffer.
  499          *
  500          * The remote host receive window scaling factor may limit the
  501          * growing of the send buffer before it reaches its allowed
  502          * maximum.
  503          *
  504          * It scales directly with slow start or congestion window
  505          * and does at most one step per received ACK.  This fast
  506          * scaling has the drawback of growing the send buffer beyond
  507          * what is strictly necessary to make full use of a given
  508          * delay*bandwidth product.  However testing has shown this not
  509          * to be much of an problem.  At worst we are trading wasting
  510          * of available bandwidth (the non-use of it) for wasting some
  511          * socket buffer memory.
  512          *
  513          * TODO: Shrink send buffer during idle periods together
  514          * with congestion window.  Requires another timer.  Has to
  515          * wait for upcoming tcp timer rewrite.
  516          *
  517          * XXXGL: should there be used sbused() or sbavail()?
  518          */
  519         if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
  520                 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat &&
  521                     sbused(&so->so_snd) >= (so->so_snd.sb_hiwat / 8 * 7) &&
  522                     sbused(&so->so_snd) < V_tcp_autosndbuf_max &&
  523                     sendwin >= (sbused(&so->so_snd) -
  524                     (tp->snd_nxt - tp->snd_una))) {
  525                         if (!sbreserve_locked(&so->so_snd,
  526                             min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
  527                              V_tcp_autosndbuf_max), so, curthread))
  528                                 so->so_snd.sb_flags &= ~SB_AUTOSIZE;
  529                 }
  530         }
  531 
  532         /*
  533          * Decide if we can use TCP Segmentation Offloading (if supported by
  534          * hardware).
  535          *
  536          * TSO may only be used if we are in a pure bulk sending state.  The
  537          * presence of TCP-MD5, SACK retransmits, SACK advertizements and
  538          * IP options prevent using TSO.  With TSO the TCP header is the same
  539          * (except for the sequence number) for all generated packets.  This
  540          * makes it impossible to transmit any options which vary per generated
  541          * segment or packet.
  542          */
  543 #ifdef IPSEC
  544         /*
  545          * Pre-calculate here as we save another lookup into the darknesses
  546          * of IPsec that way and can actually decide if TSO is ok.
  547          */
  548         ipsec_optlen = ipsec_hdrsiz_tcp(tp);
  549 #endif
  550         if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
  551             ((tp->t_flags & TF_SIGNATURE) == 0) &&
  552             tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
  553 #ifdef IPSEC
  554             ipsec_optlen == 0 &&
  555 #endif
  556             tp->t_inpcb->inp_options == NULL &&
  557             tp->t_inpcb->in6p_options == NULL)
  558                 tso = 1;
  559 
  560         if (sack_rxmit) {
  561                 if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
  562                         flags &= ~TH_FIN;
  563         } else {
  564                 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
  565                     sbused(&so->so_snd)))
  566                         flags &= ~TH_FIN;
  567         }
  568 
  569         recwin = sbspace(&so->so_rcv);
  570 
  571         /*
  572          * Sender silly window avoidance.   We transmit under the following
  573          * conditions when len is non-zero:
  574          *
  575          *      - We have a full segment (or more with TSO)
  576          *      - This is the last buffer in a write()/send() and we are
  577          *        either idle or running NODELAY
  578          *      - we've timed out (e.g. persist timer)
  579          *      - we have more then 1/2 the maximum send window's worth of
  580          *        data (receiver may be limited the window size)
  581          *      - we need to retransmit
  582          */
  583         if (len) {
  584                 if (len >= tp->t_maxseg)
  585                         goto send;
  586                 /*
  587                  * NOTE! on localhost connections an 'ack' from the remote
  588                  * end may occur synchronously with the output and cause
  589                  * us to flush a buffer queued with moretocome.  XXX
  590                  *
  591                  * note: the len + off check is almost certainly unnecessary.
  592                  */
  593                 if (!(tp->t_flags & TF_MORETOCOME) &&   /* normal case */
  594                     (idle || (tp->t_flags & TF_NODELAY)) &&
  595                     len + off >= sbavail(&so->so_snd) &&
  596                     (tp->t_flags & TF_NOPUSH) == 0) {
  597                         goto send;
  598                 }
  599                 if (tp->t_flags & TF_FORCEDATA)         /* typ. timeout case */
  600                         goto send;
  601                 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
  602                         goto send;
  603                 if (SEQ_LT(tp->snd_nxt, tp->snd_max))   /* retransmit case */
  604                         goto send;
  605                 if (sack_rxmit)
  606                         goto send;
  607         }
  608 
  609         /*
  610          * Sending of standalone window updates.
  611          *
  612          * Window updates are important when we close our window due to a
  613          * full socket buffer and are opening it again after the application
  614          * reads data from it.  Once the window has opened again and the
  615          * remote end starts to send again the ACK clock takes over and
  616          * provides the most current window information.
  617          *
  618          * We must avoid the silly window syndrome whereas every read
  619          * from the receive buffer, no matter how small, causes a window
  620          * update to be sent.  We also should avoid sending a flurry of
  621          * window updates when the socket buffer had queued a lot of data
  622          * and the application is doing small reads.
  623          *
  624          * Prevent a flurry of pointless window updates by only sending
  625          * an update when we can increase the advertized window by more
  626          * than 1/4th of the socket buffer capacity.  When the buffer is
  627          * getting full or is very small be more aggressive and send an
  628          * update whenever we can increase by two mss sized segments.
  629          * In all other situations the ACK's to new incoming data will
  630          * carry further window increases.
  631          *
  632          * Don't send an independent window update if a delayed
  633          * ACK is pending (it will get piggy-backed on it) or the
  634          * remote side already has done a half-close and won't send
  635          * more data.  Skip this if the connection is in T/TCP
  636          * half-open state.
  637          */
  638         if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
  639             !(tp->t_flags & TF_DELACK) &&
  640             !TCPS_HAVERCVDFIN(tp->t_state)) {
  641                 /*
  642                  * "adv" is the amount we could increase the window,
  643                  * taking into account that we are limited by
  644                  * TCP_MAXWIN << tp->rcv_scale.
  645                  */
  646                 long adv;
  647                 int oldwin;
  648 
  649                 adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale);
  650                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
  651                         oldwin = (tp->rcv_adv - tp->rcv_nxt);
  652                         adv -= oldwin;
  653                 } else
  654                         oldwin = 0;
  655 
  656                 /* 
  657                  * If the new window size ends up being the same as the old
  658                  * size when it is scaled, then don't force a window update.
  659                  */
  660                 if (oldwin >> tp->rcv_scale == (adv + oldwin) >> tp->rcv_scale)
  661                         goto dontupdate;
  662 
  663                 if (adv >= (long)(2 * tp->t_maxseg) &&
  664                     (adv >= (long)(so->so_rcv.sb_hiwat / 4) ||
  665                      recwin <= (long)(so->so_rcv.sb_hiwat / 8) ||
  666                      so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg))
  667                         goto send;
  668         }
  669 dontupdate:
  670 
  671         /*
  672          * Send if we owe the peer an ACK, RST, SYN, or urgent data.  ACKNOW
  673          * is also a catch-all for the retransmit timer timeout case.
  674          */
  675         if (tp->t_flags & TF_ACKNOW)
  676                 goto send;
  677         if ((flags & TH_RST) ||
  678             ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
  679                 goto send;
  680         if (SEQ_GT(tp->snd_up, tp->snd_una))
  681                 goto send;
  682         /*
  683          * If our state indicates that FIN should be sent
  684          * and we have not yet done so, then we need to send.
  685          */
  686         if (flags & TH_FIN &&
  687             ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
  688                 goto send;
  689         /*
  690          * In SACK, it is possible for tcp_output to fail to send a segment
  691          * after the retransmission timer has been turned off.  Make sure
  692          * that the retransmission timer is set.
  693          */
  694         if ((tp->t_flags & TF_SACK_PERMIT) &&
  695             SEQ_GT(tp->snd_max, tp->snd_una) &&
  696             !tcp_timer_active(tp, TT_REXMT) &&
  697             !tcp_timer_active(tp, TT_PERSIST)) {
  698                 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
  699                 goto just_return;
  700         } 
  701         /*
  702          * TCP window updates are not reliable, rather a polling protocol
  703          * using ``persist'' packets is used to insure receipt of window
  704          * updates.  The three ``states'' for the output side are:
  705          *      idle                    not doing retransmits or persists
  706          *      persisting              to move a small or zero window
  707          *      (re)transmitting        and thereby not persisting
  708          *
  709          * tcp_timer_active(tp, TT_PERSIST)
  710          *      is true when we are in persist state.
  711          * (tp->t_flags & TF_FORCEDATA)
  712          *      is set when we are called to send a persist packet.
  713          * tcp_timer_active(tp, TT_REXMT)
  714          *      is set when we are retransmitting
  715          * The output side is idle when both timers are zero.
  716          *
  717          * If send window is too small, there is data to transmit, and no
  718          * retransmit or persist is pending, then go to persist state.
  719          * If nothing happens soon, send when timer expires:
  720          * if window is nonzero, transmit what we can,
  721          * otherwise force out a byte.
  722          */
  723         if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) &&
  724             !tcp_timer_active(tp, TT_PERSIST)) {
  725                 tp->t_rxtshift = 0;
  726                 tcp_setpersist(tp);
  727         }
  728 
  729         /*
  730          * No reason to send a segment, just return.
  731          */
  732 just_return:
  733         SOCKBUF_UNLOCK(&so->so_snd);
  734         return (0);
  735 
  736 send:
  737         SOCKBUF_LOCK_ASSERT(&so->so_snd);
  738         if (len > 0) {
  739                 if (len >= tp->t_maxseg)
  740                         tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
  741                 else
  742                         tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
  743         }
  744         /*
  745          * Before ESTABLISHED, force sending of initial options
  746          * unless TCP set not to do any options.
  747          * NOTE: we assume that the IP/TCP header plus TCP options
  748          * always fit in a single mbuf, leaving room for a maximum
  749          * link header, i.e.
  750          *      max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
  751          */
  752         optlen = 0;
  753 #ifdef INET6
  754         if (isipv6)
  755                 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
  756         else
  757 #endif
  758                 hdrlen = sizeof (struct tcpiphdr);
  759 
  760         /*
  761          * Compute options for segment.
  762          * We only have to care about SYN and established connection
  763          * segments.  Options for SYN-ACK segments are handled in TCP
  764          * syncache.
  765          */
  766         to.to_flags = 0;
  767         if ((tp->t_flags & TF_NOOPT) == 0) {
  768                 /* Maximum segment size. */
  769                 if (flags & TH_SYN) {
  770                         tp->snd_nxt = tp->iss;
  771                         to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc);
  772                         to.to_flags |= TOF_MSS;
  773 #ifdef TCP_RFC7413
  774                         /*
  775                          * Only include the TFO option on the first
  776                          * transmission of the SYN|ACK on a
  777                          * passively-created TFO socket, as the presence of
  778                          * the TFO option may have caused the original
  779                          * SYN|ACK to have been dropped by a middlebox.
  780                          */
  781                         if ((tp->t_flags & TF_FASTOPEN) &&
  782                             (tp->t_state == TCPS_SYN_RECEIVED) &&
  783                             (tp->t_rxtshift == 0)) {
  784                                 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
  785                                 to.to_tfo_cookie = (u_char *)&tp->t_tfo_cookie;
  786                                 to.to_flags |= TOF_FASTOPEN;
  787                         }
  788 #endif
  789                 }
  790                 /* Window scaling. */
  791                 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
  792                         to.to_wscale = tp->request_r_scale;
  793                         to.to_flags |= TOF_SCALE;
  794                 }
  795                 /* Timestamps. */
  796                 if ((tp->t_flags & TF_RCVD_TSTMP) ||
  797                     ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
  798                         to.to_tsval = tcp_ts_getticks() + tp->ts_offset;
  799                         to.to_tsecr = tp->ts_recent;
  800                         to.to_flags |= TOF_TS;
  801                         /* Set receive buffer autosizing timestamp. */
  802                         if (tp->rfbuf_ts == 0 &&
  803                             (so->so_rcv.sb_flags & SB_AUTOSIZE))
  804                                 tp->rfbuf_ts = tcp_ts_getticks();
  805                 }
  806                 /* Selective ACK's. */
  807                 if (tp->t_flags & TF_SACK_PERMIT) {
  808                         if (flags & TH_SYN)
  809                                 to.to_flags |= TOF_SACKPERM;
  810                         else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
  811                             (tp->t_flags & TF_SACK_PERMIT) &&
  812                             tp->rcv_numsacks > 0) {
  813                                 to.to_flags |= TOF_SACK;
  814                                 to.to_nsacks = tp->rcv_numsacks;
  815                                 to.to_sacks = (u_char *)tp->sackblks;
  816                         }
  817                 }
  818 #ifdef TCP_SIGNATURE
  819                 /* TCP-MD5 (RFC2385). */
  820                 if (tp->t_flags & TF_SIGNATURE)
  821                         to.to_flags |= TOF_SIGNATURE;
  822 #endif /* TCP_SIGNATURE */
  823 
  824                 /* Processing the options. */
  825                 hdrlen += optlen = tcp_addoptions(&to, opt);
  826         }
  827 
  828 #ifdef INET6
  829         if (isipv6)
  830                 ipoptlen = ip6_optlen(tp->t_inpcb);
  831         else
  832 #endif
  833         if (tp->t_inpcb->inp_options)
  834                 ipoptlen = tp->t_inpcb->inp_options->m_len -
  835                                 offsetof(struct ipoption, ipopt_list);
  836         else
  837                 ipoptlen = 0;
  838 #ifdef IPSEC
  839         ipoptlen += ipsec_optlen;
  840 #endif
  841 
  842         /*
  843          * Adjust data length if insertion of options will
  844          * bump the packet length beyond the t_maxseg length.
  845          * Clear the FIN bit because we cut off the tail of
  846          * the segment.
  847          */
  848         if (len + optlen + ipoptlen > tp->t_maxseg) {
  849                 flags &= ~TH_FIN;
  850 
  851                 if (tso) {
  852                         u_int if_hw_tsomax;
  853                         u_int if_hw_tsomaxsegcount;
  854                         u_int if_hw_tsomaxsegsize;
  855                         struct mbuf *mb;
  856                         u_int moff;
  857                         int max_len;
  858 
  859                         /* extract TSO information */
  860                         if_hw_tsomax = tp->t_tsomax;
  861                         if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
  862                         if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
  863 
  864                         /*
  865                          * Limit a TSO burst to prevent it from
  866                          * overflowing or exceeding the maximum length
  867                          * allowed by the network interface:
  868                          */
  869                         KASSERT(ipoptlen == 0,
  870                             ("%s: TSO can't do IP options", __func__));
  871 
  872                         /*
  873                          * Check if we should limit by maximum payload
  874                          * length:
  875                          */
  876                         if (if_hw_tsomax != 0) {
  877                                 /* compute maximum TSO length */
  878                                 max_len = (if_hw_tsomax - hdrlen -
  879                                     max_linkhdr);
  880                                 if (max_len <= 0) {
  881                                         len = 0;
  882                                 } else if (len > max_len) {
  883                                         sendalot = 1;
  884                                         len = max_len;
  885                                 }
  886                         }
  887 
  888                         /*
  889                          * Check if we should limit by maximum segment
  890                          * size and count:
  891                          */
  892                         if (if_hw_tsomaxsegcount != 0 &&
  893                             if_hw_tsomaxsegsize != 0) {
  894                                 /*
  895                                  * Subtract one segment for the LINK
  896                                  * and TCP/IP headers mbuf that will
  897                                  * be prepended to this mbuf chain
  898                                  * after the code in this section
  899                                  * limits the number of mbufs in the
  900                                  * chain to if_hw_tsomaxsegcount.
  901                                  */
  902                                 if_hw_tsomaxsegcount -= 1;
  903                                 max_len = 0;
  904                                 mb = sbsndmbuf(&so->so_snd, off, &moff);
  905 
  906                                 while (mb != NULL && max_len < len) {
  907                                         u_int mlen;
  908                                         u_int frags;
  909 
  910                                         /*
  911                                          * Get length of mbuf fragment
  912                                          * and how many hardware frags,
  913                                          * rounded up, it would use:
  914                                          */
  915                                         mlen = (mb->m_len - moff);
  916                                         frags = howmany(mlen,
  917                                             if_hw_tsomaxsegsize);
  918 
  919                                         /* Handle special case: Zero Length Mbuf */
  920                                         if (frags == 0)
  921                                                 frags = 1;
  922 
  923                                         /*
  924                                          * Check if the fragment limit
  925                                          * will be reached or exceeded:
  926                                          */
  927                                         if (frags >= if_hw_tsomaxsegcount) {
  928                                                 max_len += min(mlen,
  929                                                     if_hw_tsomaxsegcount *
  930                                                     if_hw_tsomaxsegsize);
  931                                                 break;
  932                                         }
  933                                         max_len += mlen;
  934                                         if_hw_tsomaxsegcount -= frags;
  935                                         moff = 0;
  936                                         mb = mb->m_next;
  937                                 }
  938                                 if (max_len <= 0) {
  939                                         len = 0;
  940                                 } else if (len > max_len) {
  941                                         sendalot = 1;
  942                                         len = max_len;
  943                                 }
  944                         }
  945 
  946                         /*
  947                          * Prevent the last segment from being
  948                          * fractional unless the send sockbuf can be
  949                          * emptied:
  950                          */
  951                         max_len = (tp->t_maxseg - optlen);
  952                         if ((off + len) < sbavail(&so->so_snd)) {
  953                                 moff = len % max_len;
  954                                 if (moff != 0) {
  955                                         len -= moff;
  956                                         sendalot = 1;
  957                                 }
  958                         }
  959 
  960                         /*
  961                          * In case there are too many small fragments
  962                          * don't use TSO:
  963                          */
  964                         if (len <= max_len) {
  965                                 len = max_len;
  966                                 sendalot = 1;
  967                                 tso = 0;
  968                         }
  969 
  970                         /*
  971                          * Send the FIN in a separate segment
  972                          * after the bulk sending is done.
  973                          * We don't trust the TSO implementations
  974                          * to clear the FIN flag on all but the
  975                          * last segment.
  976                          */
  977                         if (tp->t_flags & TF_NEEDFIN)
  978                                 sendalot = 1;
  979 
  980                 } else {
  981                         len = tp->t_maxseg - optlen - ipoptlen;
  982                         sendalot = 1;
  983                 }
  984         } else
  985                 tso = 0;
  986 
  987         KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
  988             ("%s: len > IP_MAXPACKET", __func__));
  989 
  990 /*#ifdef DIAGNOSTIC*/
  991 #ifdef INET6
  992         if (max_linkhdr + hdrlen > MCLBYTES)
  993 #else
  994         if (max_linkhdr + hdrlen > MHLEN)
  995 #endif
  996                 panic("tcphdr too big");
  997 /*#endif*/
  998 
  999         /*
 1000          * This KASSERT is here to catch edge cases at a well defined place.
 1001          * Before, those had triggered (random) panic conditions further down.
 1002          */
 1003         KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
 1004 
 1005         /*
 1006          * Grab a header mbuf, attaching a copy of data to
 1007          * be transmitted, and initialize the header from
 1008          * the template for sends on this connection.
 1009          */
 1010         if (len) {
 1011                 struct mbuf *mb;
 1012                 u_int moff;
 1013 
 1014                 if ((tp->t_flags & TF_FORCEDATA) && len == 1)
 1015                         TCPSTAT_INC(tcps_sndprobe);
 1016                 else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
 1017                         tp->t_sndrexmitpack++;
 1018                         TCPSTAT_INC(tcps_sndrexmitpack);
 1019                         TCPSTAT_ADD(tcps_sndrexmitbyte, len);
 1020                 } else {
 1021                         TCPSTAT_INC(tcps_sndpack);
 1022                         TCPSTAT_ADD(tcps_sndbyte, len);
 1023                 }
 1024 #ifdef INET6
 1025                 if (MHLEN < hdrlen + max_linkhdr)
 1026                         m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
 1027                 else
 1028 #endif
 1029                         m = m_gethdr(M_NOWAIT, MT_DATA);
 1030 
 1031                 if (m == NULL) {
 1032                         SOCKBUF_UNLOCK(&so->so_snd);
 1033                         error = ENOBUFS;
 1034                         sack_rxmit = 0;
 1035                         goto out;
 1036                 }
 1037 
 1038                 m->m_data += max_linkhdr;
 1039                 m->m_len = hdrlen;
 1040 
 1041                 /*
 1042                  * Start the m_copy functions from the closest mbuf
 1043                  * to the offset in the socket buffer chain.
 1044                  */
 1045                 mb = sbsndptr(&so->so_snd, off, len, &moff);
 1046 
 1047                 if (len <= MHLEN - hdrlen - max_linkhdr) {
 1048                         m_copydata(mb, moff, (int)len,
 1049                             mtod(m, caddr_t) + hdrlen);
 1050                         m->m_len += len;
 1051                 } else {
 1052                         m->m_next = m_copy(mb, moff, (int)len);
 1053                         if (m->m_next == NULL) {
 1054                                 SOCKBUF_UNLOCK(&so->so_snd);
 1055                                 (void) m_free(m);
 1056                                 error = ENOBUFS;
 1057                                 sack_rxmit = 0;
 1058                                 goto out;
 1059                         }
 1060                 }
 1061 
 1062                 /*
 1063                  * If we're sending everything we've got, set PUSH.
 1064                  * (This will keep happy those implementations which only
 1065                  * give data to the user when a buffer fills or
 1066                  * a PUSH comes in.)
 1067                  */
 1068                 if ((off + len == sbused(&so->so_snd)) && !(flags & TH_SYN))
 1069                         flags |= TH_PUSH;
 1070                 SOCKBUF_UNLOCK(&so->so_snd);
 1071         } else {
 1072                 SOCKBUF_UNLOCK(&so->so_snd);
 1073                 if (tp->t_flags & TF_ACKNOW)
 1074                         TCPSTAT_INC(tcps_sndacks);
 1075                 else if (flags & (TH_SYN|TH_FIN|TH_RST))
 1076                         TCPSTAT_INC(tcps_sndctrl);
 1077                 else if (SEQ_GT(tp->snd_up, tp->snd_una))
 1078                         TCPSTAT_INC(tcps_sndurg);
 1079                 else
 1080                         TCPSTAT_INC(tcps_sndwinup);
 1081 
 1082                 m = m_gethdr(M_NOWAIT, MT_DATA);
 1083                 if (m == NULL) {
 1084                         error = ENOBUFS;
 1085                         sack_rxmit = 0;
 1086                         goto out;
 1087                 }
 1088 #ifdef INET6
 1089                 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
 1090                     MHLEN >= hdrlen) {
 1091                         M_ALIGN(m, hdrlen);
 1092                 } else
 1093 #endif
 1094                 m->m_data += max_linkhdr;
 1095                 m->m_len = hdrlen;
 1096         }
 1097         SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
 1098         m->m_pkthdr.rcvif = (struct ifnet *)0;
 1099 #ifdef MAC
 1100         mac_inpcb_create_mbuf(tp->t_inpcb, m);
 1101 #endif
 1102 #ifdef INET6
 1103         if (isipv6) {
 1104                 ip6 = mtod(m, struct ip6_hdr *);
 1105                 th = (struct tcphdr *)(ip6 + 1);
 1106                 tcpip_fillheaders(tp->t_inpcb, ip6, th);
 1107         } else
 1108 #endif /* INET6 */
 1109         {
 1110                 ip = mtod(m, struct ip *);
 1111                 ipov = (struct ipovly *)ip;
 1112                 th = (struct tcphdr *)(ip + 1);
 1113                 tcpip_fillheaders(tp->t_inpcb, ip, th);
 1114         }
 1115 
 1116         /*
 1117          * Fill in fields, remembering maximum advertised
 1118          * window for use in delaying messages about window sizes.
 1119          * If resending a FIN, be sure not to use a new sequence number.
 1120          */
 1121         if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
 1122             tp->snd_nxt == tp->snd_max)
 1123                 tp->snd_nxt--;
 1124         /*
 1125          * If we are starting a connection, send ECN setup
 1126          * SYN packet. If we are on a retransmit, we may
 1127          * resend those bits a number of times as per
 1128          * RFC 3168.
 1129          */
 1130         if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn == 1) {
 1131                 if (tp->t_rxtshift >= 1) {
 1132                         if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
 1133                                 flags |= TH_ECE|TH_CWR;
 1134                 } else
 1135                         flags |= TH_ECE|TH_CWR;
 1136         }
 1137         
 1138         if (tp->t_state == TCPS_ESTABLISHED &&
 1139             (tp->t_flags & TF_ECN_PERMIT)) {
 1140                 /*
 1141                  * If the peer has ECN, mark data packets with
 1142                  * ECN capable transmission (ECT).
 1143                  * Ignore pure ack packets, retransmissions and window probes.
 1144                  */
 1145                 if (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
 1146                     !((tp->t_flags & TF_FORCEDATA) && len == 1)) {
 1147 #ifdef INET6
 1148                         if (isipv6)
 1149                                 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20);
 1150                         else
 1151 #endif
 1152                                 ip->ip_tos |= IPTOS_ECN_ECT0;
 1153                         TCPSTAT_INC(tcps_ecn_ect0);
 1154                 }
 1155                 
 1156                 /*
 1157                  * Reply with proper ECN notifications.
 1158                  */
 1159                 if (tp->t_flags & TF_ECN_SND_CWR) {
 1160                         flags |= TH_CWR;
 1161                         tp->t_flags &= ~TF_ECN_SND_CWR;
 1162                 } 
 1163                 if (tp->t_flags & TF_ECN_SND_ECE)
 1164                         flags |= TH_ECE;
 1165         }
 1166         
 1167         /*
 1168          * If we are doing retransmissions, then snd_nxt will
 1169          * not reflect the first unsent octet.  For ACK only
 1170          * packets, we do not want the sequence number of the
 1171          * retransmitted packet, we want the sequence number
 1172          * of the next unsent octet.  So, if there is no data
 1173          * (and no SYN or FIN), use snd_max instead of snd_nxt
 1174          * when filling in ti_seq.  But if we are in persist
 1175          * state, snd_max might reflect one byte beyond the
 1176          * right edge of the window, so use snd_nxt in that
 1177          * case, since we know we aren't doing a retransmission.
 1178          * (retransmit and persist are mutually exclusive...)
 1179          */
 1180         if (sack_rxmit == 0) {
 1181                 if (len || (flags & (TH_SYN|TH_FIN)) ||
 1182                     tcp_timer_active(tp, TT_PERSIST))
 1183                         th->th_seq = htonl(tp->snd_nxt);
 1184                 else
 1185                         th->th_seq = htonl(tp->snd_max);
 1186         } else {
 1187                 th->th_seq = htonl(p->rxmit);
 1188                 p->rxmit += len;
 1189                 tp->sackhint.sack_bytes_rexmit += len;
 1190         }
 1191         th->th_ack = htonl(tp->rcv_nxt);
 1192         if (optlen) {
 1193                 bcopy(opt, th + 1, optlen);
 1194                 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
 1195         }
 1196         th->th_flags = flags;
 1197         /*
 1198          * Calculate receive window.  Don't shrink window,
 1199          * but avoid silly window syndrome.
 1200          */
 1201         if (recwin < (long)(so->so_rcv.sb_hiwat / 4) &&
 1202             recwin < (long)tp->t_maxseg)
 1203                 recwin = 0;
 1204         if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
 1205             recwin < (long)(tp->rcv_adv - tp->rcv_nxt))
 1206                 recwin = (long)(tp->rcv_adv - tp->rcv_nxt);
 1207         if (recwin > (long)TCP_MAXWIN << tp->rcv_scale)
 1208                 recwin = (long)TCP_MAXWIN << tp->rcv_scale;
 1209 
 1210         /*
 1211          * According to RFC1323 the window field in a SYN (i.e., a <SYN>
 1212          * or <SYN,ACK>) segment itself is never scaled.  The <SYN,ACK>
 1213          * case is handled in syncache.
 1214          */
 1215         if (flags & TH_SYN)
 1216                 th->th_win = htons((u_short)
 1217                                 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
 1218         else
 1219                 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
 1220 
 1221         /*
 1222          * Adjust the RXWIN0SENT flag - indicate that we have advertised
 1223          * a 0 window.  This may cause the remote transmitter to stall.  This
 1224          * flag tells soreceive() to disable delayed acknowledgements when
 1225          * draining the buffer.  This can occur if the receiver is attempting
 1226          * to read more data than can be buffered prior to transmitting on
 1227          * the connection.
 1228          */
 1229         if (th->th_win == 0) {
 1230                 tp->t_sndzerowin++;
 1231                 tp->t_flags |= TF_RXWIN0SENT;
 1232         } else
 1233                 tp->t_flags &= ~TF_RXWIN0SENT;
 1234         if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
 1235                 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
 1236                 th->th_flags |= TH_URG;
 1237         } else
 1238                 /*
 1239                  * If no urgent pointer to send, then we pull
 1240                  * the urgent pointer to the left edge of the send window
 1241                  * so that it doesn't drift into the send window on sequence
 1242                  * number wraparound.
 1243                  */
 1244                 tp->snd_up = tp->snd_una;               /* drag it along */
 1245 
 1246 #ifdef TCP_SIGNATURE
 1247         if (to.to_flags & TOF_SIGNATURE) {
 1248                 int sigoff = to.to_signature - opt;
 1249                 tcp_signature_compute(m, 0, len, optlen,
 1250                     (u_char *)(th + 1) + sigoff, IPSEC_DIR_OUTBOUND);
 1251         }
 1252 #endif
 1253 
 1254         /*
 1255          * Put TCP length in extended header, and then
 1256          * checksum extended header and data.
 1257          */
 1258         m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
 1259         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 1260 #ifdef INET6
 1261         if (isipv6) {
 1262                 /*
 1263                  * ip6_plen is not need to be filled now, and will be filled
 1264                  * in ip6_output.
 1265                  */
 1266                 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
 1267                 th->th_sum = in6_cksum_pseudo(ip6, sizeof(struct tcphdr) +
 1268                     optlen + len, IPPROTO_TCP, 0);
 1269         }
 1270 #endif
 1271 #if defined(INET6) && defined(INET)
 1272         else
 1273 #endif
 1274 #ifdef INET
 1275         {
 1276                 m->m_pkthdr.csum_flags = CSUM_TCP;
 1277                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 1278                     htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen));
 1279 
 1280                 /* IP version must be set here for ipv4/ipv6 checking later */
 1281                 KASSERT(ip->ip_v == IPVERSION,
 1282                     ("%s: IP version incorrect: %d", __func__, ip->ip_v));
 1283         }
 1284 #endif
 1285 
 1286         /*
 1287          * Enable TSO and specify the size of the segments.
 1288          * The TCP pseudo header checksum is always provided.
 1289          */
 1290         if (tso) {
 1291                 KASSERT(len > tp->t_maxseg - optlen,
 1292                     ("%s: len <= tso_segsz", __func__));
 1293                 m->m_pkthdr.csum_flags |= CSUM_TSO;
 1294                 m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen;
 1295         }
 1296 
 1297 #ifdef IPSEC
 1298         KASSERT(len + hdrlen + ipoptlen - ipsec_optlen == m_length(m, NULL),
 1299             ("%s: mbuf chain shorter than expected: %ld + %u + %u - %u != %u",
 1300             __func__, len, hdrlen, ipoptlen, ipsec_optlen, m_length(m, NULL)));
 1301 #else
 1302         KASSERT(len + hdrlen + ipoptlen == m_length(m, NULL),
 1303             ("%s: mbuf chain shorter than expected: %ld + %u + %u != %u",
 1304             __func__, len, hdrlen, ipoptlen, m_length(m, NULL)));
 1305 #endif
 1306 
 1307         /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
 1308         hhook_run_tcp_est_out(tp, th, &to, len, tso);
 1309 
 1310 #ifdef TCPDEBUG
 1311         /*
 1312          * Trace.
 1313          */
 1314         if (so->so_options & SO_DEBUG) {
 1315                 u_short save = 0;
 1316 #ifdef INET6
 1317                 if (!isipv6)
 1318 #endif
 1319                 {
 1320                         save = ipov->ih_len;
 1321                         ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
 1322                 }
 1323                 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
 1324 #ifdef INET6
 1325                 if (!isipv6)
 1326 #endif
 1327                 ipov->ih_len = save;
 1328         }
 1329 #endif /* TCPDEBUG */
 1330         TCP_PROBE3(debug__output, tp, th, mtod(m, const char *));
 1331 
 1332         /*
 1333          * Fill in IP length and desired time to live and
 1334          * send to IP level.  There should be a better way
 1335          * to handle ttl and tos; we could keep them in
 1336          * the template, but need a way to checksum without them.
 1337          */
 1338         /*
 1339          * m->m_pkthdr.len should have been set before checksum calculation,
 1340          * because in6_cksum() need it.
 1341          */
 1342 #ifdef INET6
 1343         if (isipv6) {
 1344                 struct route_in6 ro;
 1345 
 1346                 bzero(&ro, sizeof(ro));
 1347                 /*
 1348                  * we separately set hoplimit for every segment, since the
 1349                  * user might want to change the value via setsockopt.
 1350                  * Also, desired default hop limit might be changed via
 1351                  * Neighbor Discovery.
 1352                  */
 1353                 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
 1354 
 1355                 /*
 1356                  * Set the packet size here for the benefit of DTrace probes.
 1357                  * ip6_output() will set it properly; it's supposed to include
 1358                  * the option header lengths as well.
 1359                  */
 1360                 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
 1361 
 1362                 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss)
 1363                         tp->t_flags2 |= TF2_PLPMTU_PMTUD;
 1364                 else
 1365                         tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
 1366 
 1367                 if (tp->t_state == TCPS_SYN_SENT)
 1368                         TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
 1369 
 1370                 TCP_PROBE5(send, NULL, tp, ip6, tp, th);
 1371 
 1372 #ifdef TCPPCAP
 1373                 /* Save packet, if requested. */
 1374                 tcp_pcap_add(th, m, &(tp->t_outpkts));
 1375 #endif
 1376 
 1377                 /* TODO: IPv6 IP6TOS_ECT bit on */
 1378                 error = ip6_output(m, tp->t_inpcb->in6p_outputopts, &ro,
 1379                     ((so->so_options & SO_DONTROUTE) ?  IP_ROUTETOIF : 0),
 1380                     NULL, NULL, tp->t_inpcb);
 1381 
 1382                 if (error == EMSGSIZE && ro.ro_rt != NULL)
 1383                         mtu = ro.ro_rt->rt_mtu;
 1384                 RO_RTFREE(&ro);
 1385         }
 1386 #endif /* INET6 */
 1387 #if defined(INET) && defined(INET6)
 1388         else
 1389 #endif
 1390 #ifdef INET
 1391     {
 1392         ip->ip_len = htons(m->m_pkthdr.len);
 1393 #ifdef INET6
 1394         if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO)
 1395                 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
 1396 #endif /* INET6 */
 1397         /*
 1398          * If we do path MTU discovery, then we set DF on every packet.
 1399          * This might not be the best thing to do according to RFC3390
 1400          * Section 2. However the tcp hostcache migitates the problem
 1401          * so it affects only the first tcp connection with a host.
 1402          *
 1403          * NB: Don't set DF on small MTU/MSS to have a safe fallback.
 1404          */
 1405         if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) {
 1406                 ip->ip_off |= htons(IP_DF);
 1407                 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
 1408         } else {
 1409                 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
 1410         }
 1411 
 1412         if (tp->t_state == TCPS_SYN_SENT)
 1413                 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
 1414 
 1415         TCP_PROBE5(send, NULL, tp, ip, tp, th);
 1416 
 1417 #ifdef TCPPCAP
 1418         /* Save packet, if requested. */
 1419         tcp_pcap_add(th, m, &(tp->t_outpkts));
 1420 #endif
 1421 
 1422         error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
 1423             ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
 1424             tp->t_inpcb);
 1425 
 1426         if (error == EMSGSIZE && tp->t_inpcb->inp_route.ro_rt != NULL)
 1427                 mtu = tp->t_inpcb->inp_route.ro_rt->rt_mtu;
 1428     }
 1429 #endif /* INET */
 1430 
 1431 out:
 1432         /*
 1433          * In transmit state, time the transmission and arrange for
 1434          * the retransmit.  In persist state, just set snd_max.
 1435          */
 1436         if ((tp->t_flags & TF_FORCEDATA) == 0 || 
 1437             !tcp_timer_active(tp, TT_PERSIST)) {
 1438                 tcp_seq startseq = tp->snd_nxt;
 1439 
 1440                 /*
 1441                  * Advance snd_nxt over sequence space of this segment.
 1442                  */
 1443                 if (flags & (TH_SYN|TH_FIN)) {
 1444                         if (flags & TH_SYN)
 1445                                 tp->snd_nxt++;
 1446                         if (flags & TH_FIN) {
 1447                                 tp->snd_nxt++;
 1448                                 tp->t_flags |= TF_SENTFIN;
 1449                         }
 1450                 }
 1451                 if (sack_rxmit)
 1452                         goto timer;
 1453                 tp->snd_nxt += len;
 1454                 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
 1455                         tp->snd_max = tp->snd_nxt;
 1456                         /*
 1457                          * Time this transmission if not a retransmission and
 1458                          * not currently timing anything.
 1459                          */
 1460                         if (tp->t_rtttime == 0) {
 1461                                 tp->t_rtttime = ticks;
 1462                                 tp->t_rtseq = startseq;
 1463                                 TCPSTAT_INC(tcps_segstimed);
 1464                         }
 1465                 }
 1466 
 1467                 /*
 1468                  * Set retransmit timer if not currently set,
 1469                  * and not doing a pure ack or a keep-alive probe.
 1470                  * Initial value for retransmit timer is smoothed
 1471                  * round-trip time + 2 * round-trip time variance.
 1472                  * Initialize shift counter which is used for backoff
 1473                  * of retransmit time.
 1474                  */
 1475 timer:
 1476                 if (!tcp_timer_active(tp, TT_REXMT) &&
 1477                     ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
 1478                      (tp->snd_nxt != tp->snd_una))) {
 1479                         if (tcp_timer_active(tp, TT_PERSIST)) {
 1480                                 tcp_timer_activate(tp, TT_PERSIST, 0);
 1481                                 tp->t_rxtshift = 0;
 1482                         }
 1483                         tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
 1484                 } else if (len == 0 && sbavail(&so->so_snd) &&
 1485                     !tcp_timer_active(tp, TT_REXMT) &&
 1486                     !tcp_timer_active(tp, TT_PERSIST)) {
 1487                         /*
 1488                          * Avoid a situation where we do not set persist timer
 1489                          * after a zero window condition. For example:
 1490                          * 1) A -> B: packet with enough data to fill the window
 1491                          * 2) B -> A: ACK for #1 + new data (0 window
 1492                          *    advertisement)
 1493                          * 3) A -> B: ACK for #2, 0 len packet
 1494                          *
 1495                          * In this case, A will not activate the persist timer,
 1496                          * because it chose to send a packet. Unless tcp_output
 1497                          * is called for some other reason (delayed ack timer,
 1498                          * another input packet from B, socket syscall), A will
 1499                          * not send zero window probes.
 1500                          *
 1501                          * So, if you send a 0-length packet, but there is data
 1502                          * in the socket buffer, and neither the rexmt or
 1503                          * persist timer is already set, then activate the
 1504                          * persist timer.
 1505                          */
 1506                         tp->t_rxtshift = 0;
 1507                         tcp_setpersist(tp);
 1508                 }
 1509         } else {
 1510                 /*
 1511                  * Persist case, update snd_max but since we are in
 1512                  * persist mode (no window) we do not update snd_nxt.
 1513                  */
 1514                 int xlen = len;
 1515                 if (flags & TH_SYN)
 1516                         ++xlen;
 1517                 if (flags & TH_FIN) {
 1518                         ++xlen;
 1519                         tp->t_flags |= TF_SENTFIN;
 1520                 }
 1521                 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
 1522                         tp->snd_max = tp->snd_nxt + len;
 1523         }
 1524 
 1525         if (error) {
 1526 
 1527                 /*
 1528                  * We know that the packet was lost, so back out the
 1529                  * sequence number advance, if any.
 1530                  *
 1531                  * If the error is EPERM the packet got blocked by the
 1532                  * local firewall.  Normally we should terminate the
 1533                  * connection but the blocking may have been spurious
 1534                  * due to a firewall reconfiguration cycle.  So we treat
 1535                  * it like a packet loss and let the retransmit timer and
 1536                  * timeouts do their work over time.
 1537                  * XXX: It is a POLA question whether calling tcp_drop right
 1538                  * away would be the really correct behavior instead.
 1539                  */
 1540                 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
 1541                     !tcp_timer_active(tp, TT_PERSIST)) &&
 1542                     ((flags & TH_SYN) == 0) &&
 1543                     (error != EPERM)) {
 1544                         if (sack_rxmit) {
 1545                                 p->rxmit -= len;
 1546                                 tp->sackhint.sack_bytes_rexmit -= len;
 1547                                 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
 1548                                     ("sackhint bytes rtx >= 0"));
 1549                         } else
 1550                                 tp->snd_nxt -= len;
 1551                 }
 1552                 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);     /* Check gotos. */
 1553                 switch (error) {
 1554                 case EPERM:
 1555                         tp->t_softerror = error;
 1556                         return (error);
 1557                 case ENOBUFS:
 1558                         TCP_XMIT_TIMER_ASSERT(tp, len, flags);
 1559                         tp->snd_cwnd = tp->t_maxseg;
 1560                         return (0);
 1561                 case EMSGSIZE:
 1562                         /*
 1563                          * For some reason the interface we used initially
 1564                          * to send segments changed to another or lowered
 1565                          * its MTU.
 1566                          * If TSO was active we either got an interface
 1567                          * without TSO capabilits or TSO was turned off.
 1568                          * If we obtained mtu from ip_output() then update
 1569                          * it and try again.
 1570                          */
 1571                         if (tso)
 1572                                 tp->t_flags &= ~TF_TSO;
 1573                         if (mtu != 0) {
 1574                                 tcp_mss_update(tp, -1, mtu, NULL, NULL);
 1575                                 goto again;
 1576                         }
 1577                         return (error);
 1578                 case EHOSTDOWN:
 1579                 case EHOSTUNREACH:
 1580                 case ENETDOWN:
 1581                 case ENETUNREACH:
 1582                         if (TCPS_HAVERCVDSYN(tp->t_state)) {
 1583                                 tp->t_softerror = error;
 1584                                 return (0);
 1585                         }
 1586                         /* FALLTHROUGH */
 1587                 default:
 1588                         return (error);
 1589                 }
 1590         }
 1591         TCPSTAT_INC(tcps_sndtotal);
 1592 
 1593         /*
 1594          * Data sent (as far as we can tell).
 1595          * If this advertises a larger window than any other segment,
 1596          * then remember the size of the advertised window.
 1597          * Any pending ACK has now been sent.
 1598          */
 1599         if (recwin >= 0 && SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
 1600                 tp->rcv_adv = tp->rcv_nxt + recwin;
 1601         tp->last_ack_sent = tp->rcv_nxt;
 1602         tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
 1603         if (tcp_timer_active(tp, TT_DELACK))
 1604                 tcp_timer_activate(tp, TT_DELACK, 0);
 1605 #if 0
 1606         /*
 1607          * This completely breaks TCP if newreno is turned on.  What happens
 1608          * is that if delayed-acks are turned on on the receiver, this code
 1609          * on the transmitter effectively destroys the TCP window, forcing
 1610          * it to four packets (1.5Kx4 = 6K window).
 1611          */
 1612         if (sendalot && --maxburst)
 1613                 goto again;
 1614 #endif
 1615         if (sendalot)
 1616                 goto again;
 1617         return (0);
 1618 }
 1619 
 1620 void
 1621 tcp_setpersist(struct tcpcb *tp)
 1622 {
 1623         int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
 1624         int tt;
 1625 
 1626         tp->t_flags &= ~TF_PREVVALID;
 1627         if (tcp_timer_active(tp, TT_REXMT))
 1628                 panic("tcp_setpersist: retransmit pending");
 1629         /*
 1630          * Start/restart persistence timer.
 1631          */
 1632         TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
 1633                       tcp_persmin, tcp_persmax);
 1634         tcp_timer_activate(tp, TT_PERSIST, tt);
 1635         if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
 1636                 tp->t_rxtshift++;
 1637 }
 1638 
 1639 /*
 1640  * Insert TCP options according to the supplied parameters to the place
 1641  * optp in a consistent way.  Can handle unaligned destinations.
 1642  *
 1643  * The order of the option processing is crucial for optimal packing and
 1644  * alignment for the scarce option space.
 1645  *
 1646  * The optimal order for a SYN/SYN-ACK segment is:
 1647  *   MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
 1648  *   Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
 1649  *
 1650  * The SACK options should be last.  SACK blocks consume 8*n+2 bytes.
 1651  * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
 1652  * At minimum we need 10 bytes (to generate 1 SACK block).  If both
 1653  * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
 1654  * we only have 10 bytes for SACK options (40 - (12 + 18)).
 1655  */
 1656 int
 1657 tcp_addoptions(struct tcpopt *to, u_char *optp)
 1658 {
 1659         u_int32_t mask, optlen = 0;
 1660 
 1661         for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
 1662                 if ((to->to_flags & mask) != mask)
 1663                         continue;
 1664                 if (optlen == TCP_MAXOLEN)
 1665                         break;
 1666                 switch (to->to_flags & mask) {
 1667                 case TOF_MSS:
 1668                         while (optlen % 4) {
 1669                                 optlen += TCPOLEN_NOP;
 1670                                 *optp++ = TCPOPT_NOP;
 1671                         }
 1672                         if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
 1673                                 continue;
 1674                         optlen += TCPOLEN_MAXSEG;
 1675                         *optp++ = TCPOPT_MAXSEG;
 1676                         *optp++ = TCPOLEN_MAXSEG;
 1677                         to->to_mss = htons(to->to_mss);
 1678                         bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
 1679                         optp += sizeof(to->to_mss);
 1680                         break;
 1681                 case TOF_SCALE:
 1682                         while (!optlen || optlen % 2 != 1) {
 1683                                 optlen += TCPOLEN_NOP;
 1684                                 *optp++ = TCPOPT_NOP;
 1685                         }
 1686                         if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
 1687                                 continue;
 1688                         optlen += TCPOLEN_WINDOW;
 1689                         *optp++ = TCPOPT_WINDOW;
 1690                         *optp++ = TCPOLEN_WINDOW;
 1691                         *optp++ = to->to_wscale;
 1692                         break;
 1693                 case TOF_SACKPERM:
 1694                         while (optlen % 2) {
 1695                                 optlen += TCPOLEN_NOP;
 1696                                 *optp++ = TCPOPT_NOP;
 1697                         }
 1698                         if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
 1699                                 continue;
 1700                         optlen += TCPOLEN_SACK_PERMITTED;
 1701                         *optp++ = TCPOPT_SACK_PERMITTED;
 1702                         *optp++ = TCPOLEN_SACK_PERMITTED;
 1703                         break;
 1704                 case TOF_TS:
 1705                         while (!optlen || optlen % 4 != 2) {
 1706                                 optlen += TCPOLEN_NOP;
 1707                                 *optp++ = TCPOPT_NOP;
 1708                         }
 1709                         if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
 1710                                 continue;
 1711                         optlen += TCPOLEN_TIMESTAMP;
 1712                         *optp++ = TCPOPT_TIMESTAMP;
 1713                         *optp++ = TCPOLEN_TIMESTAMP;
 1714                         to->to_tsval = htonl(to->to_tsval);
 1715                         to->to_tsecr = htonl(to->to_tsecr);
 1716                         bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
 1717                         optp += sizeof(to->to_tsval);
 1718                         bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
 1719                         optp += sizeof(to->to_tsecr);
 1720                         break;
 1721 #ifdef TCP_SIGNATURE
 1722                 case TOF_SIGNATURE:
 1723                         {
 1724                         int siglen = TCPOLEN_SIGNATURE - 2;
 1725 
 1726                         while (!optlen || optlen % 4 != 2) {
 1727                                 optlen += TCPOLEN_NOP;
 1728                                 *optp++ = TCPOPT_NOP;
 1729                         }
 1730                         if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE)
 1731                                 continue;
 1732                         optlen += TCPOLEN_SIGNATURE;
 1733                         *optp++ = TCPOPT_SIGNATURE;
 1734                         *optp++ = TCPOLEN_SIGNATURE;
 1735                         to->to_signature = optp;
 1736                         while (siglen--)
 1737                                  *optp++ = 0;
 1738                         break;
 1739                         }
 1740 #endif
 1741                 case TOF_SACK:
 1742                         {
 1743                         int sackblks = 0;
 1744                         struct sackblk *sack = (struct sackblk *)to->to_sacks;
 1745                         tcp_seq sack_seq;
 1746 
 1747                         while (!optlen || optlen % 4 != 2) {
 1748                                 optlen += TCPOLEN_NOP;
 1749                                 *optp++ = TCPOPT_NOP;
 1750                         }
 1751                         if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
 1752                                 continue;
 1753                         optlen += TCPOLEN_SACKHDR;
 1754                         *optp++ = TCPOPT_SACK;
 1755                         sackblks = min(to->to_nsacks,
 1756                                         (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
 1757                         *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
 1758                         while (sackblks--) {
 1759                                 sack_seq = htonl(sack->start);
 1760                                 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
 1761                                 optp += sizeof(sack_seq);
 1762                                 sack_seq = htonl(sack->end);
 1763                                 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
 1764                                 optp += sizeof(sack_seq);
 1765                                 optlen += TCPOLEN_SACK;
 1766                                 sack++;
 1767                         }
 1768                         TCPSTAT_INC(tcps_sack_send_blocks);
 1769                         break;
 1770                         }
 1771 #ifdef TCP_RFC7413
 1772                 case TOF_FASTOPEN:
 1773                         {
 1774                         int total_len;
 1775 
 1776                         /* XXX is there any point to aligning this option? */
 1777                         total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len;
 1778                         if (TCP_MAXOLEN - optlen < total_len)
 1779                                 continue;
 1780                         *optp++ = TCPOPT_FAST_OPEN;
 1781                         *optp++ = total_len;
 1782                         if (to->to_tfo_len > 0) {
 1783                                 bcopy(to->to_tfo_cookie, optp, to->to_tfo_len);
 1784                                 optp += to->to_tfo_len;
 1785                         }
 1786                         optlen += total_len;
 1787                         break;
 1788                         }
 1789 #endif
 1790                 default:
 1791                         panic("%s: unknown TCP option type", __func__);
 1792                         break;
 1793                 }
 1794         }
 1795 
 1796         /* Terminate and pad TCP options to a 4 byte boundary. */
 1797         if (optlen % 4) {
 1798                 optlen += TCPOLEN_EOL;
 1799                 *optp++ = TCPOPT_EOL;
 1800         }
 1801         /*
 1802          * According to RFC 793 (STD0007):
 1803          *   "The content of the header beyond the End-of-Option option
 1804          *    must be header padding (i.e., zero)."
 1805          *   and later: "The padding is composed of zeros."
 1806          */
 1807         while (optlen % 4) {
 1808                 optlen += TCPOLEN_PAD;
 1809                 *optp++ = TCPOPT_PAD;
 1810         }
 1811 
 1812         KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));
 1813         return (optlen);
 1814 }
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FreeBSD/Linux Kernel Cross Reference sys/netinet/tcp_output.c

FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_output.c
