sys/netinet/tcp_output.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-3-Clause
   3  *
   4  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  * 3. Neither the name of the University nor the names of its contributors
  16  *    may be used to endorse or promote products derived from this software
  17  *    without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  29  * SUCH DAMAGE.
  30  *
  31  *      @(#)tcp_output.c        8.4 (Berkeley) 5/24/95
  32  */
  33
  34 #include <sys/cdefs.h>
  35 __FBSDID("$FreeBSD$");
  36
  37 #include "opt_inet.h"
  38 #include "opt_inet6.h"
  39 #include "opt_ipsec.h"
  40 #include "opt_tcpdebug.h"
  41
  42 #include <sys/param.h>
  43 #include <sys/systm.h>
  44 #include <sys/domain.h>
  45 #ifdef TCP_HHOOK
  46 #include <sys/hhook.h>
  47 #endif
  48 #include <sys/kernel.h>
  49 #include <sys/lock.h>
  50 #include <sys/mbuf.h>
  51 #include <sys/mutex.h>
  52 #include <sys/protosw.h>
  53 #include <sys/sdt.h>
  54 #include <sys/socket.h>
  55 #include <sys/socketvar.h>
  56 #include <sys/sysctl.h>
  57
  58 #include <net/if.h>
  59 #include <net/route.h>
  60 #include <net/vnet.h>
  61
  62 #include <netinet/in.h>
  63 #include <netinet/in_kdtrace.h>
  64 #include <netinet/in_systm.h>
  65 #include <netinet/ip.h>
  66 #include <netinet/in_pcb.h>
  67 #include <netinet/ip_var.h>
  68 #include <netinet/ip_options.h>
  69 #ifdef INET6
  70 #include <netinet6/in6_pcb.h>
  71 #include <netinet/ip6.h>
  72 #include <netinet6/ip6_var.h>
  73 #endif
  74 #include <netinet/tcp.h>
  75 #define TCPOUTFLAGS
  76 #include <netinet/tcp_fsm.h>
  77 #include <netinet/tcp_log_buf.h>
  78 #include <netinet/tcp_seq.h>
  79 #include <netinet/tcp_timer.h>
  80 #include <netinet/tcp_var.h>
  81 #include <netinet/tcpip.h>
  82 #include <netinet/cc/cc.h>
  83 #include <netinet/tcp_fastopen.h>
  84 #ifdef TCPPCAP
  85 #include <netinet/tcp_pcap.h>
  86 #endif
  87 #ifdef TCPDEBUG
  88 #include <netinet/tcp_debug.h>
  89 #endif
  90 #ifdef TCP_OFFLOAD
  91 #include <netinet/tcp_offload.h>
  92 #endif
  93
  94 #include <netipsec/ipsec_support.h>
  95
  96 #include <machine/in_cksum.h>
  97
  98 #include <security/mac/mac_framework.h>
  99
 100 VNET_DEFINE(int, path_mtu_discovery) = 1;
 101 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_VNET | CTLFLAG_RW,
 102         &VNET_NAME(path_mtu_discovery), 1,
 103         "Enable Path MTU Discovery");
 104
 105 VNET_DEFINE(int, tcp_do_tso) = 1;
 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 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
 117         &VNET_NAME(tcp_do_autosndbuf), 0,
 118         "Enable automatic send buffer sizing");
 119
 120 VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024;
 121 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_VNET | CTLFLAG_RW,
 122         &VNET_NAME(tcp_autosndbuf_inc), 0,
 123         "Incrementor step size of automatic send buffer");
 124
 125 VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024;
 126 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
 127         &VNET_NAME(tcp_autosndbuf_max), 0,
 128         "Max size of automatic send buffer");
 129
 130 VNET_DEFINE(int, tcp_sendbuf_auto_lowat) = 0;
 131 #define V_tcp_sendbuf_auto_lowat        VNET(tcp_sendbuf_auto_lowat)
 132 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto_lowat, CTLFLAG_VNET | CTLFLAG_RW,
 133         &VNET_NAME(tcp_sendbuf_auto_lowat), 0,
 134         "Modify threshold for auto send buffer growth to account for SO_SNDLOWAT");
 135
 136 /*
 137  * Make sure that either retransmit or persist timer is set for SYN, FIN and
 138  * non-ACK.
 139  */
 140 #define TCP_XMIT_TIMER_ASSERT(tp, len, th_flags)                        \
 141         KASSERT(((len) == 0 && ((th_flags) & (TH_SYN | TH_FIN)) == 0) ||\
 142             tcp_timer_active((tp), TT_REXMT) ||                         \
 143             tcp_timer_active((tp), TT_PERSIST),                         \
 144             ("neither rexmt nor persist timer is set"))
 145
 146 static void inline      cc_after_idle(struct tcpcb *tp);
 147
 148 #ifdef TCP_HHOOK
 149 /*
 150  * Wrapper for the TCP established output helper hook.
 151  */
 152 void
 153 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
 154     struct tcpopt *to, uint32_t len, int tso)
 155 {
 156         struct tcp_hhook_data hhook_data;
 157
 158         if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
 159                 hhook_data.tp = tp;
 160                 hhook_data.th = th;
 161                 hhook_data.to = to;
 162                 hhook_data.len = len;
 163                 hhook_data.tso = tso;
 164
 165                 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
 166                     tp->osd);
 167         }
 168 }
 169 #endif
 170
 171 /*
 172  * Flags used when sending segments in tcp_output.  Basic flags (TH_RST,
 173  * TH_ACK,TH_SYN,TH_FIN) are totally determined by state, with the proviso
 174  * that TH_FIN is sent only if all data queued for output is included in the
 175  * segment.
 176  */
 177 u_char  tcp_outflags[TCP_NSTATES] = {
 178         TH_RST|TH_ACK,          /* 0, CLOSED */
 179         0,                      /* 1, LISTEN */
 180         TH_SYN,                 /* 2, SYN_SENT */
 181         TH_SYN|TH_ACK,          /* 3, SYN_RECEIVED */
 182         TH_ACK,                 /* 4, ESTABLISHED */
 183         TH_ACK,                 /* 5, CLOSE_WAIT */
 184         TH_FIN|TH_ACK,          /* 6, FIN_WAIT_1 */
 185         TH_FIN|TH_ACK,          /* 7, CLOSING */
 186         TH_FIN|TH_ACK,          /* 8, LAST_ACK */
 187         TH_ACK,                 /* 9, FIN_WAIT_2 */
 188         TH_ACK,                 /* 10, TIME_WAIT */
 189 };
 190
 191 /*
 192  * CC wrapper hook functions
 193  */
 194 static void inline
 195 cc_after_idle(struct tcpcb *tp)
 196 {
 197         INP_WLOCK_ASSERT(tp->t_inpcb);
 198
 199         if (CC_ALGO(tp)->after_idle != NULL)
 200                 CC_ALGO(tp)->after_idle(tp->ccv);
 201 }
 202
 203 /*
 204  * Tcp output routine: figure out what should be sent and send it.
 205  */
 206 int
 207 tcp_output(struct tcpcb *tp)
 208 {
 209         struct socket *so = tp->t_inpcb->inp_socket;
 210         int32_t len;
 211         uint32_t recwin, sendwin;
 212         int off, flags, error = 0;      /* Keep compiler happy */
 213         struct mbuf *m;
 214         struct ip *ip = NULL;
 215 #ifdef TCPDEBUG
 216         struct ipovly *ipov = NULL;
 217 #endif
 218         struct tcphdr *th;
 219         u_char opt[TCP_MAXOLEN];
 220         unsigned ipoptlen, optlen, hdrlen;
 221 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 222         unsigned ipsec_optlen = 0;
 223 #endif
 224         int idle, sendalot, curticks;
 225         int sack_rxmit, sack_bytes_rxmt;
 226         struct sackhole *p;
 227         int tso, mtu;
 228         struct tcpopt to;
 229         unsigned int wanted_cookie = 0;
 230         unsigned int dont_sendalot = 0;
 231 #if 0
 232         int maxburst = TCP_MAXBURST;
 233 #endif
 234 #ifdef INET6
 235         struct ip6_hdr *ip6 = NULL;
 236         int isipv6;
 237
 238         isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
 239 #endif
 240
 241         INP_WLOCK_ASSERT(tp->t_inpcb);
 242
 243 #ifdef TCP_OFFLOAD
 244         if (tp->t_flags & TF_TOE)
 245                 return (tcp_offload_output(tp));
 246 #endif
 247
 248         /*
 249          * For TFO connections in SYN_RECEIVED, only allow the initial
 250          * SYN|ACK and those sent by the retransmit timer.
 251          */
 252         if (IS_FASTOPEN(tp->t_flags) &&
 253             (tp->t_state == TCPS_SYN_RECEIVED) &&
 254             SEQ_GT(tp->snd_max, tp->snd_una) &&    /* initial SYN|ACK sent */
 255             (tp->snd_nxt != tp->snd_una))         /* not a retransmit */
 256                 return (0);
 257
 258         /*
 259          * Determine length of data that should be transmitted,
 260          * and flags that will be used.
 261          * If there is some data or critical controls (SYN, RST)
 262          * to send, then transmit; otherwise, investigate further.
 263          */
 264         idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
 265         if (idle && ticks - tp->t_rcvtime >= tp->t_rxtcur)
 266                 cc_after_idle(tp);
 267         tp->t_flags &= ~TF_LASTIDLE;
 268         if (idle) {
 269                 if (tp->t_flags & TF_MORETOCOME) {
 270                         tp->t_flags |= TF_LASTIDLE;
 271                         idle = 0;
 272                 }
 273         }
 274 again:
 275         /*
 276          * If we've recently taken a timeout, snd_max will be greater than
 277          * snd_nxt.  There may be SACK information that allows us to avoid
 278          * resending already delivered data.  Adjust snd_nxt accordingly.
 279          */
 280         if ((tp->t_flags & TF_SACK_PERMIT) &&
 281             SEQ_LT(tp->snd_nxt, tp->snd_max))
 282                 tcp_sack_adjust(tp);
 283         sendalot = 0;
 284         tso = 0;
 285         mtu = 0;
 286         off = tp->snd_nxt - tp->snd_una;
 287         sendwin = min(tp->snd_wnd, tp->snd_cwnd);
 288
 289         flags = tcp_outflags[tp->t_state];
 290         /*
 291          * Send any SACK-generated retransmissions.  If we're explicitly trying
 292          * to send out new data (when sendalot is 1), bypass this function.
 293          * If we retransmit in fast recovery mode, decrement snd_cwnd, since
 294          * we're replacing a (future) new transmission with a retransmission
 295          * now, and we previously incremented snd_cwnd in tcp_input().
 296          */
 297         /*
 298          * Still in sack recovery , reset rxmit flag to zero.
 299          */
 300         sack_rxmit = 0;
 301         sack_bytes_rxmt = 0;
 302         len = 0;
 303         p = NULL;
 304         if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
 305             (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
 306                 uint32_t cwin;
 307
 308                 cwin =
 309                     imax(min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt, 0);
 310                 /* Do not retransmit SACK segments beyond snd_recover */
 311                 if (SEQ_GT(p->end, tp->snd_recover)) {
 312                         /*
 313                          * (At least) part of sack hole extends beyond
 314                          * snd_recover. Check to see if we can rexmit data
 315                          * for this hole.
 316                          */
 317                         if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
 318                                 /*
 319                                  * Can't rexmit any more data for this hole.
 320                                  * That data will be rexmitted in the next
 321                                  * sack recovery episode, when snd_recover
 322                                  * moves past p->rxmit.
 323                                  */
 324                                 p = NULL;
 325                                 goto after_sack_rexmit;
 326                         } else
 327                                 /* Can rexmit part of the current hole */
 328                                 len = ((int32_t)ulmin(cwin,
 329                                                    tp->snd_recover - p->rxmit));
 330                 } else
 331                         len = ((int32_t)ulmin(cwin, p->end - p->rxmit));
 332                 off = p->rxmit - tp->snd_una;
 333                 KASSERT(off >= 0,("%s: sack block to the left of una : %d",
 334                     __func__, off));
 335                 if (len > 0) {
 336                         sack_rxmit = 1;
 337                         sendalot = 1;
 338                         TCPSTAT_INC(tcps_sack_rexmits);
 339                         TCPSTAT_ADD(tcps_sack_rexmit_bytes,
 340                             min(len, tp->t_maxseg));
 341                 }
 342         }
 343 after_sack_rexmit:
 344         /*
 345          * Get standard flags, and add SYN or FIN if requested by 'hidden'
 346          * state flags.
 347          */
 348         if (tp->t_flags & TF_NEEDFIN)
 349                 flags |= TH_FIN;
 350         if (tp->t_flags & TF_NEEDSYN)
 351                 flags |= TH_SYN;
 352
 353         SOCKBUF_LOCK(&so->so_snd);
 354         /*
 355          * If in persist timeout with window of 0, send 1 byte.
 356          * Otherwise, if window is small but nonzero
 357          * and timer expired, we will send what we can
 358          * and go to transmit state.
 359          */
 360         if (tp->t_flags & TF_FORCEDATA) {
 361                 if (sendwin == 0) {
 362                         /*
 363                          * If we still have some data to send, then
 364                          * clear the FIN bit.  Usually this would
 365                          * happen below when it realizes that we
 366                          * aren't sending all the data.  However,
 367                          * if we have exactly 1 byte of unsent data,
 368                          * then it won't clear the FIN bit below,
 369                          * and if we are in persist state, we wind
 370                          * up sending the packet without recording
 371                          * that we sent the FIN bit.
 372                          *
 373                          * We can't just blindly clear the FIN bit,
 374                          * because if we don't have any more data
 375                          * to send then the probe will be the FIN
 376                          * itself.
 377                          */
 378                         if (off < sbused(&so->so_snd))
 379                                 flags &= ~TH_FIN;
 380                         sendwin = 1;
 381                 } else {
 382                         tcp_timer_activate(tp, TT_PERSIST, 0);
 383                         tp->t_rxtshift = 0;
 384                 }
 385         }
 386
 387         /*
 388          * If snd_nxt == snd_max and we have transmitted a FIN, the
 389          * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
 390          * a negative length.  This can also occur when TCP opens up
 391          * its congestion window while receiving additional duplicate
 392          * acks after fast-retransmit because TCP will reset snd_nxt
 393          * to snd_max after the fast-retransmit.
 394          *
 395          * In the normal retransmit-FIN-only case, however, snd_nxt will
 396          * be set to snd_una, the offset will be 0, and the length may
 397          * wind up 0.
 398          *
 399          * If sack_rxmit is true we are retransmitting from the scoreboard
 400          * in which case len is already set.
 401          */
 402         if (sack_rxmit == 0) {
 403                 if (sack_bytes_rxmt == 0)
 404                         len = ((int32_t)min(sbavail(&so->so_snd), sendwin) -
 405                             off);
 406                 else {
 407                         int32_t cwin;
 408
 409                         /*
 410                          * We are inside of a SACK recovery episode and are
 411                          * sending new data, having retransmitted all the
 412                          * data possible in the scoreboard.
 413                          */
 414                         len = ((int32_t)min(sbavail(&so->so_snd), tp->snd_wnd) -
 415                             off);
 416                         /*
 417                          * Don't remove this (len > 0) check !
 418                          * We explicitly check for len > 0 here (although it
 419                          * isn't really necessary), to work around a gcc
 420                          * optimization issue - to force gcc to compute
 421                          * len above. Without this check, the computation
 422                          * of len is bungled by the optimizer.
 423                          */
 424                         if (len > 0) {
 425                                 cwin = tp->snd_cwnd -
 426                                         (tp->snd_nxt - tp->sack_newdata) -
 427                                         sack_bytes_rxmt;
 428                                 if (cwin < 0)
 429                                         cwin = 0;
 430                                 len = imin(len, cwin);
 431                         }
 432                 }
 433         }
 434
 435         /*
 436          * Lop off SYN bit if it has already been sent.  However, if this
 437          * is SYN-SENT state and if segment contains data and if we don't
 438          * know that foreign host supports TAO, suppress sending segment.
 439          */
 440         if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
 441                 if (tp->t_state != TCPS_SYN_RECEIVED)
 442                         flags &= ~TH_SYN;
 443                 /*
 444                  * When sending additional segments following a TFO SYN|ACK,
 445                  * do not include the SYN bit.
 446                  */
 447                 if (IS_FASTOPEN(tp->t_flags) &&
 448                     (tp->t_state == TCPS_SYN_RECEIVED))
 449                         flags &= ~TH_SYN;
 450                 off--, len++;
 451         }
 452
 453         /*
 454          * Be careful not to send data and/or FIN on SYN segments.
 455          * This measure is needed to prevent interoperability problems
 456          * with not fully conformant TCP implementations.
 457          */
 458         if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
 459                 len = 0;
 460                 flags &= ~TH_FIN;
 461         }
 462
 463         /*
 464          * On TFO sockets, ensure no data is sent in the following cases:
 465          *
 466          *  - When retransmitting SYN|ACK on a passively-created socket
 467          *
 468          *  - When retransmitting SYN on an actively created socket
 469          *
 470          *  - When sending a zero-length cookie (cookie request) on an
 471          *    actively created socket
 472          *
 473          *  - When the socket is in the CLOSED state (RST is being sent)
 474          */
 475         if (IS_FASTOPEN(tp->t_flags) &&
 476             (((flags & TH_SYN) && (tp->t_rxtshift > 0)) ||
 477              ((tp->t_state == TCPS_SYN_SENT) &&
 478               (tp->t_tfo_client_cookie_len == 0)) ||
 479              (flags & TH_RST)))
 480                 len = 0;
 481         if (len <= 0) {
 482                 /*
 483                  * If FIN has been sent but not acked,
 484                  * but we haven't been called to retransmit,
 485                  * len will be < 0.  Otherwise, window shrank
 486                  * after we sent into it.  If window shrank to 0,
 487                  * cancel pending retransmit, pull snd_nxt back
 488                  * to (closed) window, and set the persist timer
 489                  * if it isn't already going.  If the window didn't
 490                  * close completely, just wait for an ACK.
 491                  *
 492                  * We also do a general check here to ensure that
 493                  * we will set the persist timer when we have data
 494                  * to send, but a 0-byte window. This makes sure
 495                  * the persist timer is set even if the packet
 496                  * hits one of the "goto send" lines below.
 497                  */
 498                 len = 0;
 499                 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
 500                         (off < (int) sbavail(&so->so_snd))) {
 501                         tcp_timer_activate(tp, TT_REXMT, 0);
 502                         tp->t_rxtshift = 0;
 503                         tp->snd_nxt = tp->snd_una;
 504                         if (!tcp_timer_active(tp, TT_PERSIST))
 505                                 tcp_setpersist(tp);
 506                 }
 507         }
 508
 509         /* len will be >= 0 after this point. */
 510         KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
 511
 512         tcp_sndbuf_autoscale(tp, so, sendwin);
 513
 514         /*
 515          * Decide if we can use TCP Segmentation Offloading (if supported by
 516          * hardware).
 517          *
 518          * TSO may only be used if we are in a pure bulk sending state.  The
 519          * presence of TCP-MD5, SACK retransmits, SACK advertizements and
 520          * IP options prevent using TSO.  With TSO the TCP header is the same
 521          * (except for the sequence number) for all generated packets.  This
 522          * makes it impossible to transmit any options which vary per generated
 523          * segment or packet.
 524          *
 525          * IPv4 handling has a clear separation of ip options and ip header
 526          * flags while IPv6 combines both in in6p_outputopts. ip6_optlen() does
 527          * the right thing below to provide length of just ip options and thus
 528          * checking for ipoptlen is enough to decide if ip options are present.
 529          */
 530 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 531         /*
 532          * Pre-calculate here as we save another lookup into the darknesses
 533          * of IPsec that way and can actually decide if TSO is ok.
 534          */
 535 #ifdef INET6
 536         if (isipv6 && IPSEC_ENABLED(ipv6))
 537                 ipsec_optlen = IPSEC_HDRSIZE(ipv6, tp->t_inpcb);
 538 #ifdef INET
 539         else
 540 #endif
 541 #endif /* INET6 */
 542 #ifdef INET
 543         if (IPSEC_ENABLED(ipv4))
 544                 ipsec_optlen = IPSEC_HDRSIZE(ipv4, tp->t_inpcb);
 545 #endif /* INET */
 546 #endif /* IPSEC */
 547 #ifdef INET6
 548         if (isipv6)
 549                 ipoptlen = ip6_optlen(tp->t_inpcb);
 550         else
 551 #endif
 552         if (tp->t_inpcb->inp_options)
 553                 ipoptlen = tp->t_inpcb->inp_options->m_len -
 554                                 offsetof(struct ipoption, ipopt_list);
 555         else
 556                 ipoptlen = 0;
 557 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 558         ipoptlen += ipsec_optlen;
 559 #endif
 560
 561         if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
 562             ((tp->t_flags & TF_SIGNATURE) == 0) &&
 563             tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
 564             ipoptlen == 0 && !(flags & TH_SYN))
 565                 tso = 1;
 566
 567         if (sack_rxmit) {
 568                 if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
 569                         flags &= ~TH_FIN;
 570         } else {
 571                 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
 572                     sbused(&so->so_snd)))
 573                         flags &= ~TH_FIN;
 574         }
 575
 576         recwin = lmin(lmax(sbspace(&so->so_rcv), 0),
 577             (long)TCP_MAXWIN << tp->rcv_scale);
 578
 579         /*
 580          * Sender silly window avoidance.   We transmit under the following
 581          * conditions when len is non-zero:
 582          *
 583          *      - We have a full segment (or more with TSO)
 584          *      - This is the last buffer in a write()/send() and we are
 585          *        either idle or running NODELAY
 586          *      - we've timed out (e.g. persist timer)
 587          *      - we have more then 1/2 the maximum send window's worth of
 588          *        data (receiver may be limited the window size)
 589          *      - we need to retransmit
 590          */
 591         if (len) {
 592                 if (len >= tp->t_maxseg)
 593                         goto send;
 594                 /*
 595                  * NOTE! on localhost connections an 'ack' from the remote
 596                  * end may occur synchronously with the output and cause
 597                  * us to flush a buffer queued with moretocome.  XXX
 598                  *
 599                  * note: the len + off check is almost certainly unnecessary.
 600                  */
 601                 if (!(tp->t_flags & TF_MORETOCOME) &&   /* normal case */
 602                     (idle || (tp->t_flags & TF_NODELAY)) &&
 603                     (uint32_t)len + (uint32_t)off >= sbavail(&so->so_snd) &&
 604                     (tp->t_flags & TF_NOPUSH) == 0) {
 605                         goto send;
 606                 }
 607                 if (tp->t_flags & TF_FORCEDATA)         /* typ. timeout case */
 608                         goto send;
 609                 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
 610                         goto send;
 611                 if (SEQ_LT(tp->snd_nxt, tp->snd_max))   /* retransmit case */
 612                         goto send;
 613                 if (sack_rxmit)
 614                         goto send;
 615         }
 616
 617         /*
 618          * Sending of standalone window updates.
 619          *
 620          * Window updates are important when we close our window due to a
 621          * full socket buffer and are opening it again after the application
 622          * reads data from it.  Once the window has opened again and the
 623          * remote end starts to send again the ACK clock takes over and
 624          * provides the most current window information.
 625          *
 626          * We must avoid the silly window syndrome whereas every read
 627          * from the receive buffer, no matter how small, causes a window
 628          * update to be sent.  We also should avoid sending a flurry of
 629          * window updates when the socket buffer had queued a lot of data
 630          * and the application is doing small reads.
 631          *
 632          * Prevent a flurry of pointless window updates by only sending
 633          * an update when we can increase the advertized window by more
 634          * than 1/4th of the socket buffer capacity.  When the buffer is
 635          * getting full or is very small be more aggressive and send an
 636          * update whenever we can increase by two mss sized segments.
 637          * In all other situations the ACK's to new incoming data will
 638          * carry further window increases.
 639          *
 640          * Don't send an independent window update if a delayed
 641          * ACK is pending (it will get piggy-backed on it) or the
 642          * remote side already has done a half-close and won't send
 643          * more data.  Skip this if the connection is in T/TCP
 644          * half-open state.
 645          */
 646         if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
 647             !(tp->t_flags & TF_DELACK) &&
 648             !TCPS_HAVERCVDFIN(tp->t_state)) {
 649                 /*
 650                  * "adv" is the amount we could increase the window,
 651                  * taking into account that we are limited by
 652                  * TCP_MAXWIN << tp->rcv_scale.
 653                  */
 654                 int32_t adv;
 655                 int oldwin;
 656
 657                 adv = recwin;
 658                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
 659                         oldwin = (tp->rcv_adv - tp->rcv_nxt);
 660                         adv -= oldwin;
 661                 } else
 662                         oldwin = 0;
 663
 664                 /*
 665                  * If the new window size ends up being the same as or less
 666                  * than the old size when it is scaled, then don't force
 667                  * a window update.
 668                  */
 669                 if (oldwin >> tp->rcv_scale >= (adv + oldwin) >> tp->rcv_scale)
 670                         goto dontupdate;
 671
 672                 if (adv >= (int32_t)(2 * tp->t_maxseg) &&
 673                     (adv >= (int32_t)(so->so_rcv.sb_hiwat / 4) ||
 674                      recwin <= (so->so_rcv.sb_hiwat / 8) ||
 675                      so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg))
 676                         goto send;
 677                 if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat)
 678                         goto send;
 679         }
 680 dontupdate:
 681
 682         /*
 683          * Send if we owe the peer an ACK, RST, SYN, or urgent data.  ACKNOW
 684          * is also a catch-all for the retransmit timer timeout case.
 685          */
 686         if (tp->t_flags & TF_ACKNOW)
 687                 goto send;
 688         if ((flags & TH_RST) ||
 689             ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
 690                 goto send;
 691         if (SEQ_GT(tp->snd_up, tp->snd_una))
 692                 goto send;
 693         /*
 694          * If our state indicates that FIN should be sent
 695          * and we have not yet done so, then we need to send.
 696          */
 697         if (flags & TH_FIN &&
 698             ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
 699                 goto send;
 700         /*
 701          * In SACK, it is possible for tcp_output to fail to send a segment
 702          * after the retransmission timer has been turned off.  Make sure
 703          * that the retransmission timer is set.
 704          */
 705         if ((tp->t_flags & TF_SACK_PERMIT) &&
 706             SEQ_GT(tp->snd_max, tp->snd_una) &&
 707             !tcp_timer_active(tp, TT_REXMT) &&
 708             !tcp_timer_active(tp, TT_PERSIST)) {
 709                 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
 710                 goto just_return;
 711         }
 712         /*
 713          * TCP window updates are not reliable, rather a polling protocol
 714          * using ``persist'' packets is used to insure receipt of window
 715          * updates.  The three ``states'' for the output side are:
 716          *      idle                    not doing retransmits or persists
 717          *      persisting              to move a small or zero window
 718          *      (re)transmitting        and thereby not persisting
 719          *
 720          * tcp_timer_active(tp, TT_PERSIST)
 721          *      is true when we are in persist state.
 722          * (tp->t_flags & TF_FORCEDATA)
 723          *      is set when we are called to send a persist packet.
 724          * tcp_timer_active(tp, TT_REXMT)
 725          *      is set when we are retransmitting
 726          * The output side is idle when both timers are zero.
 727          *
 728          * If send window is too small, there is data to transmit, and no
 729          * retransmit or persist is pending, then go to persist state.
 730          * If nothing happens soon, send when timer expires:
 731          * if window is nonzero, transmit what we can,
 732          * otherwise force out a byte.
 733          */
 734         if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) &&
 735             !tcp_timer_active(tp, TT_PERSIST)) {
 736                 tp->t_rxtshift = 0;
 737                 tcp_setpersist(tp);
 738         }
 739
 740         /*
 741          * No reason to send a segment, just return.
 742          */
 743 just_return:
 744         SOCKBUF_UNLOCK(&so->so_snd);
 745         return (0);
 746
 747 send:
 748         SOCKBUF_LOCK_ASSERT(&so->so_snd);
 749         if (len > 0) {
 750                 if (len >= tp->t_maxseg)
 751                         tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
 752                 else
 753                         tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
 754         }
 755         /*
 756          * Before ESTABLISHED, force sending of initial options
 757          * unless TCP set not to do any options.
 758          * NOTE: we assume that the IP/TCP header plus TCP options
 759          * always fit in a single mbuf, leaving room for a maximum
 760          * link header, i.e.
 761          *      max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
 762          */
 763         optlen = 0;
 764 #ifdef INET6
 765         if (isipv6)
 766                 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
 767         else
 768 #endif
 769                 hdrlen = sizeof (struct tcpiphdr);
 770
 771         /*
 772          * Compute options for segment.
 773          * We only have to care about SYN and established connection
 774          * segments.  Options for SYN-ACK segments are handled in TCP
 775          * syncache.
 776          */
 777         to.to_flags = 0;
 778         if ((tp->t_flags & TF_NOOPT) == 0) {
 779                 /* Maximum segment size. */
 780                 if (flags & TH_SYN) {
 781                         tp->snd_nxt = tp->iss;
 782                         to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc);
 783                         to.to_flags |= TOF_MSS;
 784
 785                         /*
 786                          * On SYN or SYN|ACK transmits on TFO connections,
 787                          * only include the TFO option if it is not a
 788                          * retransmit, as the presence of the TFO option may
 789                          * have caused the original SYN or SYN|ACK to have
 790                          * been dropped by a middlebox.
 791                          */
 792                         if (IS_FASTOPEN(tp->t_flags) &&
 793                             (tp->t_rxtshift == 0)) {
 794                                 if (tp->t_state == TCPS_SYN_RECEIVED) {
 795                                         to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
 796                                         to.to_tfo_cookie =
 797                                             (u_int8_t *)&tp->t_tfo_cookie.server;
 798                                         to.to_flags |= TOF_FASTOPEN;
 799                                         wanted_cookie = 1;
 800                                 } else if (tp->t_state == TCPS_SYN_SENT) {
 801                                         to.to_tfo_len =
 802                                             tp->t_tfo_client_cookie_len;
 803                                         to.to_tfo_cookie =
 804                                             tp->t_tfo_cookie.client;
 805                                         to.to_flags |= TOF_FASTOPEN;
 806                                         wanted_cookie = 1;
 807                                         /*
 808                                          * If we wind up having more data to
 809                                          * send with the SYN than can fit in
 810                                          * one segment, don't send any more
 811                                          * until the SYN|ACK comes back from
 812                                          * the other end.
 813                                          */
 814                                         dont_sendalot = 1;
 815                                 }
 816                         }
 817                 }
 818                 /* Window scaling. */
 819                 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
 820                         to.to_wscale = tp->request_r_scale;
 821                         to.to_flags |= TOF_SCALE;
 822                 }
 823                 /* Timestamps. */
 824                 if ((tp->t_flags & TF_RCVD_TSTMP) ||
 825                     ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
 826                         curticks = tcp_ts_getticks();
 827                         to.to_tsval = curticks + tp->ts_offset;
 828                         to.to_tsecr = tp->ts_recent;
 829                         to.to_flags |= TOF_TS;
 830                         if (tp->t_rxtshift == 1)
 831                                 tp->t_badrxtwin = curticks;
 832                 }
 833
 834                 /* Set receive buffer autosizing timestamp. */
 835                 if (tp->rfbuf_ts == 0 &&
 836                     (so->so_rcv.sb_flags & SB_AUTOSIZE))
 837                         tp->rfbuf_ts = tcp_ts_getticks();
 838
 839                 /* Selective ACK's. */
 840                 if (tp->t_flags & TF_SACK_PERMIT) {
 841                         if (flags & TH_SYN)
 842                                 to.to_flags |= TOF_SACKPERM;
 843                         else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
 844                             (tp->t_flags & TF_SACK_PERMIT) &&
 845                             tp->rcv_numsacks > 0) {
 846                                 to.to_flags |= TOF_SACK;
 847                                 to.to_nsacks = tp->rcv_numsacks;
 848                                 to.to_sacks = (u_char *)tp->sackblks;
 849                         }
 850                 }
 851 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 852                 /* TCP-MD5 (RFC2385). */
 853                 /*
 854                  * Check that TCP_MD5SIG is enabled in tcpcb to
 855                  * account the size needed to set this TCP option.
 856                  */
 857                 if (tp->t_flags & TF_SIGNATURE)
 858                         to.to_flags |= TOF_SIGNATURE;
 859 #endif /* TCP_SIGNATURE */
 860
 861                 /* Processing the options. */
 862                 hdrlen += optlen = tcp_addoptions(&to, opt);
 863                 /*
 864                  * If we wanted a TFO option to be added, but it was unable
 865                  * to fit, ensure no data is sent.
 866                  */
 867                 if (IS_FASTOPEN(tp->t_flags) && wanted_cookie &&
 868                     !(to.to_flags & TOF_FASTOPEN))
 869                         len = 0;
 870         }
 871
 872         /*
 873          * Adjust data length if insertion of options will
 874          * bump the packet length beyond the t_maxseg length.
 875          * Clear the FIN bit because we cut off the tail of
 876          * the segment.
 877          */
 878         if (len + optlen + ipoptlen > tp->t_maxseg) {
 879                 flags &= ~TH_FIN;
 880
 881                 if (tso) {
 882                         u_int if_hw_tsomax;
 883                         u_int if_hw_tsomaxsegcount;
 884                         u_int if_hw_tsomaxsegsize;
 885                         struct mbuf *mb;
 886                         u_int moff;
 887                         int max_len;
 888
 889                         /* extract TSO information */
 890                         if_hw_tsomax = tp->t_tsomax;
 891                         if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
 892                         if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
 893
 894                         /*
 895                          * Limit a TSO burst to prevent it from
 896                          * overflowing or exceeding the maximum length
 897                          * allowed by the network interface:
 898                          */
 899                         KASSERT(ipoptlen == 0,
 900                             ("%s: TSO can't do IP options", __func__));
 901
 902                         /*
 903                          * Check if we should limit by maximum payload
 904                          * length:
 905                          */
 906                         if (if_hw_tsomax != 0) {
 907                                 /* compute maximum TSO length */
 908                                 max_len = (if_hw_tsomax - hdrlen -
 909                                     max_linkhdr);
 910                                 if (max_len <= 0) {
 911                                         len = 0;
 912                                 } else if (len > max_len) {
 913                                         sendalot = 1;
 914                                         len = max_len;
 915                                 }
 916                         }
 917
 918                         /*
 919                          * Check if we should limit by maximum segment
 920                          * size and count:
 921                          */
 922                         if (if_hw_tsomaxsegcount != 0 &&
 923                             if_hw_tsomaxsegsize != 0) {
 924                                 /*
 925                                  * Subtract one segment for the LINK
 926                                  * and TCP/IP headers mbuf that will
 927                                  * be prepended to this mbuf chain
 928                                  * after the code in this section
 929                                  * limits the number of mbufs in the
 930                                  * chain to if_hw_tsomaxsegcount.
 931                                  */
 932                                 if_hw_tsomaxsegcount -= 1;
 933                                 max_len = 0;
 934                                 mb = sbsndmbuf(&so->so_snd, off, &moff);
 935
 936                                 while (mb != NULL && max_len < len) {
 937                                         u_int mlen;
 938                                         u_int frags;
 939
 940                                         /*
 941                                          * Get length of mbuf fragment
 942                                          * and how many hardware frags,
 943                                          * rounded up, it would use:
 944                                          */
 945                                         mlen = (mb->m_len - moff);
 946                                         frags = howmany(mlen,
 947                                             if_hw_tsomaxsegsize);
 948
 949                                         /* Handle special case: Zero Length Mbuf */
 950                                         if (frags == 0)
 951                                                 frags = 1;
 952
 953                                         /*
 954                                          * Check if the fragment limit
 955                                          * will be reached or exceeded:
 956                                          */
 957                                         if (frags >= if_hw_tsomaxsegcount) {
 958                                                 max_len += min(mlen,
 959                                                     if_hw_tsomaxsegcount *
 960                                                     if_hw_tsomaxsegsize);
 961                                                 break;
 962                                         }
 963                                         max_len += mlen;
 964                                         if_hw_tsomaxsegcount -= frags;
 965                                         moff = 0;
 966                                         mb = mb->m_next;
 967                                 }
 968                                 if (max_len <= 0) {
 969                                         len = 0;
 970                                 } else if (len > max_len) {
 971                                         sendalot = 1;
 972                                         len = max_len;
 973                                 }
 974                         }
 975
 976                         /*
 977                          * Prevent the last segment from being
 978                          * fractional unless the send sockbuf can be
 979                          * emptied:
 980                          */
 981                         max_len = (tp->t_maxseg - optlen);
 982                         if (((uint32_t)off + (uint32_t)len) <
 983                             sbavail(&so->so_snd)) {
 984                                 moff = len % max_len;
 985                                 if (moff != 0) {
 986                                         len -= moff;
 987                                         sendalot = 1;
 988                                 }
 989                         }
 990
 991                         /*
 992                          * In case there are too many small fragments
 993                          * don't use TSO:
 994                          */
 995                         if (len <= max_len) {
 996                                 len = max_len;
 997                                 sendalot = 1;
 998                                 tso = 0;
 999                         }
1000
1001                         /*
1002                          * Send the FIN in a separate segment
1003                          * after the bulk sending is done.
1004                          * We don't trust the TSO implementations
1005                          * to clear the FIN flag on all but the
1006                          * last segment.
1007                          */
1008                         if (tp->t_flags & TF_NEEDFIN)
1009                                 sendalot = 1;
1010
1011                 } else {
1012                         len = tp->t_maxseg - optlen - ipoptlen;
1013                         sendalot = 1;
1014                         if (dont_sendalot)
1015                                 sendalot = 0;
1016                 }
1017         } else
1018                 tso = 0;
1019
1020         KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
1021             ("%s: len > IP_MAXPACKET", __func__));
1022
1023 /*#ifdef DIAGNOSTIC*/
1024 #ifdef INET6
1025         if (max_linkhdr + hdrlen > MCLBYTES)
1026 #else
1027         if (max_linkhdr + hdrlen > MHLEN)
1028 #endif
1029                 panic("tcphdr too big");
1030 /*#endif*/
1031
1032         /*
1033          * This KASSERT is here to catch edge cases at a well defined place.
1034          * Before, those had triggered (random) panic conditions further down.
1035          */
1036         KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
1037
1038         /*
1039          * Grab a header mbuf, attaching a copy of data to
1040          * be transmitted, and initialize the header from
1041          * the template for sends on this connection.
1042          */
1043         if (len) {
1044                 struct mbuf *mb;
1045                 u_int moff;
1046
1047                 if ((tp->t_flags & TF_FORCEDATA) && len == 1)
1048                         TCPSTAT_INC(tcps_sndprobe);
1049                 else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
1050                         tp->t_sndrexmitpack++;
1051                         TCPSTAT_INC(tcps_sndrexmitpack);
1052                         TCPSTAT_ADD(tcps_sndrexmitbyte, len);
1053                 } else {
1054                         TCPSTAT_INC(tcps_sndpack);
1055                         TCPSTAT_ADD(tcps_sndbyte, len);
1056                 }
1057 #ifdef INET6
1058                 if (MHLEN < hdrlen + max_linkhdr)
1059                         m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
1060                 else
1061 #endif
1062                         m = m_gethdr(M_NOWAIT, MT_DATA);
1063
1064                 if (m == NULL) {
1065                         SOCKBUF_UNLOCK(&so->so_snd);
1066                         error = ENOBUFS;
1067                         sack_rxmit = 0;
1068                         goto out;
1069                 }
1070
1071                 m->m_data += max_linkhdr;
1072                 m->m_len = hdrlen;
1073
1074                 /*
1075                  * Start the m_copy functions from the closest mbuf
1076                  * to the offset in the socket buffer chain.
1077                  */
1078                 mb = sbsndptr(&so->so_snd, off, len, &moff);
1079
1080                 if (len <= MHLEN - hdrlen - max_linkhdr) {
1081                         m_copydata(mb, moff, len,
1082                             mtod(m, caddr_t) + hdrlen);
1083                         m->m_len += len;
1084                 } else {
1085                         m->m_next = m_copym(mb, moff, len, M_NOWAIT);
1086                         if (m->m_next == NULL) {
1087                                 SOCKBUF_UNLOCK(&so->so_snd);
1088                                 (void) m_free(m);
1089                                 error = ENOBUFS;
1090                                 sack_rxmit = 0;
1091                                 goto out;
1092                         }
1093                 }
1094
1095                 /*
1096                  * If we're sending everything we've got, set PUSH.
1097                  * (This will keep happy those implementations which only
1098                  * give data to the user when a buffer fills or
1099                  * a PUSH comes in.)
1100                  */
1101                 if (((uint32_t)off + (uint32_t)len == sbused(&so->so_snd)) &&
1102                     !(flags & TH_SYN))
1103                         flags |= TH_PUSH;
1104                 SOCKBUF_UNLOCK(&so->so_snd);
1105         } else {
1106                 SOCKBUF_UNLOCK(&so->so_snd);
1107                 if (tp->t_flags & TF_ACKNOW)
1108                         TCPSTAT_INC(tcps_sndacks);
1109                 else if (flags & (TH_SYN|TH_FIN|TH_RST))
1110                         TCPSTAT_INC(tcps_sndctrl);
1111                 else if (SEQ_GT(tp->snd_up, tp->snd_una))
1112                         TCPSTAT_INC(tcps_sndurg);
1113                 else
1114                         TCPSTAT_INC(tcps_sndwinup);
1115
1116                 m = m_gethdr(M_NOWAIT, MT_DATA);
1117                 if (m == NULL) {
1118                         error = ENOBUFS;
1119                         sack_rxmit = 0;
1120                         goto out;
1121                 }
1122 #ifdef INET6
1123                 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
1124                     MHLEN >= hdrlen) {
1125                         M_ALIGN(m, hdrlen);
1126                 } else
1127 #endif
1128                 m->m_data += max_linkhdr;
1129                 m->m_len = hdrlen;
1130         }
1131         SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
1132         m->m_pkthdr.rcvif = (struct ifnet *)0;
1133 #ifdef MAC
1134         mac_inpcb_create_mbuf(tp->t_inpcb, m);
1135 #endif
1136 #ifdef INET6
1137         if (isipv6) {
1138                 ip6 = mtod(m, struct ip6_hdr *);
1139                 th = (struct tcphdr *)(ip6 + 1);
1140                 tcpip_fillheaders(tp->t_inpcb, ip6, th);
1141         } else
1142 #endif /* INET6 */
1143         {
1144                 ip = mtod(m, struct ip *);
1145 #ifdef TCPDEBUG
1146                 ipov = (struct ipovly *)ip;
1147 #endif
1148                 th = (struct tcphdr *)(ip + 1);
1149                 tcpip_fillheaders(tp->t_inpcb, ip, th);
1150         }
1151
1152         /*
1153          * Fill in fields, remembering maximum advertised
1154          * window for use in delaying messages about window sizes.
1155          * If resending a FIN, be sure not to use a new sequence number.
1156          */
1157         if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1158             tp->snd_nxt == tp->snd_max)
1159                 tp->snd_nxt--;
1160         /*
1161          * If we are starting a connection, send ECN setup
1162          * SYN packet. If we are on a retransmit, we may
1163          * resend those bits a number of times as per
1164          * RFC 3168.
1165          */
1166         if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn == 1) {
1167                 if (tp->t_rxtshift >= 1) {
1168                         if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
1169                                 flags |= TH_ECE|TH_CWR;
1170                 } else
1171                         flags |= TH_ECE|TH_CWR;
1172         }
1173
1174         if (tp->t_state == TCPS_ESTABLISHED &&
1175             (tp->t_flags & TF_ECN_PERMIT)) {
1176                 /*
1177                  * If the peer has ECN, mark data packets with
1178                  * ECN capable transmission (ECT).
1179                  * Ignore pure ack packets, retransmissions and window probes.
1180                  */
1181                 if (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
1182                     !((tp->t_flags & TF_FORCEDATA) && len == 1)) {
1183 #ifdef INET6
1184                         if (isipv6)
1185                                 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20);
1186                         else
1187 #endif
1188                                 ip->ip_tos |= IPTOS_ECN_ECT0;
1189                         TCPSTAT_INC(tcps_ecn_ect0);
1190                 }
1191
1192                 /*
1193                  * Reply with proper ECN notifications.
1194                  */
1195                 if (tp->t_flags & TF_ECN_SND_CWR) {
1196                         flags |= TH_CWR;
1197                         tp->t_flags &= ~TF_ECN_SND_CWR;
1198                 }
1199                 if (tp->t_flags & TF_ECN_SND_ECE)
1200                         flags |= TH_ECE;
1201         }
1202
1203         /*
1204          * If we are doing retransmissions, then snd_nxt will
1205          * not reflect the first unsent octet.  For ACK only
1206          * packets, we do not want the sequence number of the
1207          * retransmitted packet, we want the sequence number
1208          * of the next unsent octet.  So, if there is no data
1209          * (and no SYN or FIN), use snd_max instead of snd_nxt
1210          * when filling in ti_seq.  But if we are in persist
1211          * state, snd_max might reflect one byte beyond the
1212          * right edge of the window, so use snd_nxt in that
1213          * case, since we know we aren't doing a retransmission.
1214          * (retransmit and persist are mutually exclusive...)
1215          */
1216         if (sack_rxmit == 0) {
1217                 if (len || (flags & (TH_SYN|TH_FIN)) ||
1218                     tcp_timer_active(tp, TT_PERSIST))
1219                         th->th_seq = htonl(tp->snd_nxt);
1220                 else
1221                         th->th_seq = htonl(tp->snd_max);
1222         } else {
1223                 th->th_seq = htonl(p->rxmit);
1224                 p->rxmit += len;
1225                 tp->sackhint.sack_bytes_rexmit += len;
1226         }
1227         th->th_ack = htonl(tp->rcv_nxt);
1228         if (optlen) {
1229                 bcopy(opt, th + 1, optlen);
1230                 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
1231         }
1232         th->th_flags = flags;
1233         /*
1234          * Calculate receive window.  Don't shrink window,
1235          * but avoid silly window syndrome.
1236          */
1237         if (recwin < (so->so_rcv.sb_hiwat / 4) &&
1238             recwin < tp->t_maxseg)
1239                 recwin = 0;
1240         if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
1241             recwin < (tp->rcv_adv - tp->rcv_nxt))
1242                 recwin = (tp->rcv_adv - tp->rcv_nxt);
1243
1244         /*
1245          * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1246          * or <SYN,ACK>) segment itself is never scaled.  The <SYN,ACK>
1247          * case is handled in syncache.
1248          */
1249         if (flags & TH_SYN)
1250                 th->th_win = htons((u_short)
1251                                 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1252         else
1253                 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
1254
1255         /*
1256          * Adjust the RXWIN0SENT flag - indicate that we have advertised
1257          * a 0 window.  This may cause the remote transmitter to stall.  This
1258          * flag tells soreceive() to disable delayed acknowledgements when
1259          * draining the buffer.  This can occur if the receiver is attempting
1260          * to read more data than can be buffered prior to transmitting on
1261          * the connection.
1262          */
1263         if (th->th_win == 0) {
1264                 tp->t_sndzerowin++;
1265                 tp->t_flags |= TF_RXWIN0SENT;
1266         } else
1267                 tp->t_flags &= ~TF_RXWIN0SENT;
1268         if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1269                 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1270                 th->th_flags |= TH_URG;
1271         } else
1272                 /*
1273                  * If no urgent pointer to send, then we pull
1274                  * the urgent pointer to the left edge of the send window
1275                  * so that it doesn't drift into the send window on sequence
1276                  * number wraparound.
1277                  */
1278                 tp->snd_up = tp->snd_una;               /* drag it along */
1279
1280         /*
1281          * Put TCP length in extended header, and then
1282          * checksum extended header and data.
1283          */
1284         m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1285         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1286
1287 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1288         if (to.to_flags & TOF_SIGNATURE) {
1289                 /*
1290                  * Calculate MD5 signature and put it into the place
1291                  * determined before.
1292                  * NOTE: since TCP options buffer doesn't point into
1293                  * mbuf's data, calculate offset and use it.
1294                  */
1295                 if (!TCPMD5_ENABLED() || (error = TCPMD5_OUTPUT(m, th,
1296                     (u_char *)(th + 1) + (to.to_signature - opt))) != 0) {
1297                         /*
1298                          * Do not send segment if the calculation of MD5
1299                          * digest has failed.
1300                          */
1301                         m_freem(m);
1302                         goto out;
1303                 }
1304         }
1305 #endif
1306 #ifdef INET6
1307         if (isipv6) {
1308                 /*
1309                  * There is no need to fill in ip6_plen right now.
1310                  * It will be filled later by ip6_output.
1311                  */
1312                 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1313                 th->th_sum = in6_cksum_pseudo(ip6, sizeof(struct tcphdr) +
1314                     optlen + len, IPPROTO_TCP, 0);
1315         }
1316 #endif
1317 #if defined(INET6) && defined(INET)
1318         else
1319 #endif
1320 #ifdef INET
1321         {
1322                 m->m_pkthdr.csum_flags = CSUM_TCP;
1323                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1324                     htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen));
1325
1326                 /* IP version must be set here for ipv4/ipv6 checking later */
1327                 KASSERT(ip->ip_v == IPVERSION,
1328                     ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1329         }
1330 #endif
1331
1332         /*
1333          * Enable TSO and specify the size of the segments.
1334          * The TCP pseudo header checksum is always provided.
1335          */
1336         if (tso) {
1337                 KASSERT(len > tp->t_maxseg - optlen,
1338                     ("%s: len <= tso_segsz", __func__));
1339                 m->m_pkthdr.csum_flags |= CSUM_TSO;
1340                 m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen;
1341         }
1342
1343 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
1344         KASSERT(len + hdrlen + ipoptlen - ipsec_optlen == m_length(m, NULL),
1345             ("%s: mbuf chain shorter than expected: %d + %u + %u - %u != %u",
1346             __func__, len, hdrlen, ipoptlen, ipsec_optlen, m_length(m, NULL)));
1347 #else
1348         KASSERT(len + hdrlen + ipoptlen == m_length(m, NULL),
1349             ("%s: mbuf chain shorter than expected: %d + %u + %u != %u",
1350             __func__, len, hdrlen, ipoptlen, m_length(m, NULL)));
1351 #endif
1352
1353 #ifdef TCP_HHOOK
1354         /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1355         hhook_run_tcp_est_out(tp, th, &to, len, tso);
1356 #endif
1357
1358 #ifdef TCPDEBUG
1359         /*
1360          * Trace.
1361          */
1362         if (so->so_options & SO_DEBUG) {
1363                 u_short save = 0;
1364 #ifdef INET6
1365                 if (!isipv6)
1366 #endif
1367                 {
1368                         save = ipov->ih_len;
1369                         ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
1370                 }
1371                 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
1372 #ifdef INET6
1373                 if (!isipv6)
1374 #endif
1375                 ipov->ih_len = save;
1376         }
1377 #endif /* TCPDEBUG */
1378         TCP_PROBE3(debug__output, tp, th, m);
1379
1380         /* We're getting ready to send; log now. */
1381         TCP_LOG_EVENT(tp, th, &so->so_rcv, &so->so_snd, TCP_LOG_OUT, ERRNO_UNK,
1382             len, NULL, false);
1383
1384         /*
1385          * Fill in IP length and desired time to live and
1386          * send to IP level.  There should be a better way
1387          * to handle ttl and tos; we could keep them in
1388          * the template, but need a way to checksum without them.
1389          */
1390         /*
1391          * m->m_pkthdr.len should have been set before checksum calculation,
1392          * because in6_cksum() need it.
1393          */
1394 #ifdef INET6
1395         if (isipv6) {
1396                 /*
1397                  * we separately set hoplimit for every segment, since the
1398                  * user might want to change the value via setsockopt.
1399                  * Also, desired default hop limit might be changed via
1400                  * Neighbor Discovery.
1401                  */
1402                 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
1403
1404                 /*
1405                  * Set the packet size here for the benefit of DTrace probes.
1406                  * ip6_output() will set it properly; it's supposed to include
1407                  * the option header lengths as well.
1408                  */
1409                 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
1410
1411                 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss)
1412                         tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1413                 else
1414                         tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1415
1416                 if (tp->t_state == TCPS_SYN_SENT)
1417                         TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
1418
1419                 TCP_PROBE5(send, NULL, tp, ip6, tp, th);
1420
1421 #ifdef TCPPCAP
1422                 /* Save packet, if requested. */
1423                 tcp_pcap_add(th, m, &(tp->t_outpkts));
1424 #endif
1425
1426                 /* TODO: IPv6 IP6TOS_ECT bit on */
1427                 error = ip6_output(m, tp->t_inpcb->in6p_outputopts,
1428                     &tp->t_inpcb->inp_route6,
1429                     ((so->so_options & SO_DONTROUTE) ?  IP_ROUTETOIF : 0),
1430                     NULL, NULL, tp->t_inpcb);
1431
1432                 if (error == EMSGSIZE && tp->t_inpcb->inp_route6.ro_rt != NULL)
1433                         mtu = tp->t_inpcb->inp_route6.ro_rt->rt_mtu;
1434         }
1435 #endif /* INET6 */
1436 #if defined(INET) && defined(INET6)
1437         else
1438 #endif
1439 #ifdef INET
1440     {
1441         ip->ip_len = htons(m->m_pkthdr.len);
1442 #ifdef INET6
1443         if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO)
1444                 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
1445 #endif /* INET6 */
1446         /*
1447          * If we do path MTU discovery, then we set DF on every packet.
1448          * This might not be the best thing to do according to RFC3390
1449          * Section 2. However the tcp hostcache migitates the problem
1450          * so it affects only the first tcp connection with a host.
1451          *
1452          * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1453          */
1454         if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) {
1455                 ip->ip_off |= htons(IP_DF);
1456                 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1457         } else {
1458                 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1459         }
1460
1461         if (tp->t_state == TCPS_SYN_SENT)
1462                 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
1463
1464         TCP_PROBE5(send, NULL, tp, ip, tp, th);
1465
1466 #ifdef TCPPCAP
1467         /* Save packet, if requested. */
1468         tcp_pcap_add(th, m, &(tp->t_outpkts));
1469 #endif
1470
1471         error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
1472             ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
1473             tp->t_inpcb);
1474
1475         if (error == EMSGSIZE && tp->t_inpcb->inp_route.ro_rt != NULL)
1476                 mtu = tp->t_inpcb->inp_route.ro_rt->rt_mtu;
1477     }
1478 #endif /* INET */
1479
1480 out:
1481         /*
1482          * In transmit state, time the transmission and arrange for
1483          * the retransmit.  In persist state, just set snd_max.
1484          */
1485         if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1486             !tcp_timer_active(tp, TT_PERSIST)) {
1487                 tcp_seq startseq = tp->snd_nxt;
1488
1489                 /*
1490                  * Advance snd_nxt over sequence space of this segment.
1491                  */
1492                 if (flags & (TH_SYN|TH_FIN)) {
1493                         if (flags & TH_SYN)
1494                                 tp->snd_nxt++;
1495                         if (flags & TH_FIN) {
1496                                 tp->snd_nxt++;
1497                                 tp->t_flags |= TF_SENTFIN;
1498                         }
1499                 }
1500                 if (sack_rxmit)
1501                         goto timer;
1502                 tp->snd_nxt += len;
1503                 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1504                         tp->snd_max = tp->snd_nxt;
1505                         /*
1506                          * Time this transmission if not a retransmission and
1507                          * not currently timing anything.
1508                          */
1509                         if (tp->t_rtttime == 0) {
1510                                 tp->t_rtttime = ticks;
1511                                 tp->t_rtseq = startseq;
1512                                 TCPSTAT_INC(tcps_segstimed);
1513                         }
1514                 }
1515
1516                 /*
1517                  * Set retransmit timer if not currently set,
1518                  * and not doing a pure ack or a keep-alive probe.
1519                  * Initial value for retransmit timer is smoothed
1520                  * round-trip time + 2 * round-trip time variance.
1521                  * Initialize shift counter which is used for backoff
1522                  * of retransmit time.
1523                  */
1524 timer:
1525                 if (!tcp_timer_active(tp, TT_REXMT) &&
1526                     ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1527                      (tp->snd_nxt != tp->snd_una))) {
1528                         if (tcp_timer_active(tp, TT_PERSIST)) {
1529                                 tcp_timer_activate(tp, TT_PERSIST, 0);
1530                                 tp->t_rxtshift = 0;
1531                         }
1532                         tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1533                 } else if (len == 0 && sbavail(&so->so_snd) &&
1534                     !tcp_timer_active(tp, TT_REXMT) &&
1535                     !tcp_timer_active(tp, TT_PERSIST)) {
1536                         /*
1537                          * Avoid a situation where we do not set persist timer
1538                          * after a zero window condition. For example:
1539                          * 1) A -> B: packet with enough data to fill the window
1540                          * 2) B -> A: ACK for #1 + new data (0 window
1541                          *    advertisement)
1542                          * 3) A -> B: ACK for #2, 0 len packet
1543                          *
1544                          * In this case, A will not activate the persist timer,
1545                          * because it chose to send a packet. Unless tcp_output
1546                          * is called for some other reason (delayed ack timer,
1547                          * another input packet from B, socket syscall), A will
1548                          * not send zero window probes.
1549                          *
1550                          * So, if you send a 0-length packet, but there is data
1551                          * in the socket buffer, and neither the rexmt or
1552                          * persist timer is already set, then activate the
1553                          * persist timer.
1554                          */
1555                         tp->t_rxtshift = 0;
1556                         tcp_setpersist(tp);
1557                 }
1558         } else {
1559                 /*
1560                  * Persist case, update snd_max but since we are in
1561                  * persist mode (no window) we do not update snd_nxt.
1562                  */
1563                 int xlen = len;
1564                 if (flags & TH_SYN)
1565                         ++xlen;
1566                 if (flags & TH_FIN) {
1567                         ++xlen;
1568                         tp->t_flags |= TF_SENTFIN;
1569                 }
1570                 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1571                         tp->snd_max = tp->snd_nxt + xlen;
1572         }
1573
1574         if (error) {
1575                 /* Record the error. */
1576                 TCP_LOG_EVENT(tp, NULL, &so->so_rcv, &so->so_snd, TCP_LOG_OUT,
1577                     error, 0, NULL, false);
1578
1579                 /*
1580                  * We know that the packet was lost, so back out the
1581                  * sequence number advance, if any.
1582                  *
1583                  * If the error is EPERM the packet got blocked by the
1584                  * local firewall.  Normally we should terminate the
1585                  * connection but the blocking may have been spurious
1586                  * due to a firewall reconfiguration cycle.  So we treat
1587                  * it like a packet loss and let the retransmit timer and
1588                  * timeouts do their work over time.
1589                  * XXX: It is a POLA question whether calling tcp_drop right
1590                  * away would be the really correct behavior instead.
1591                  */
1592                 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1593                     !tcp_timer_active(tp, TT_PERSIST)) &&
1594                     ((flags & TH_SYN) == 0) &&
1595                     (error != EPERM)) {
1596                         if (sack_rxmit) {
1597                                 p->rxmit -= len;
1598                                 tp->sackhint.sack_bytes_rexmit -= len;
1599                                 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1600                                     ("sackhint bytes rtx >= 0"));
1601                         } else
1602                                 tp->snd_nxt -= len;
1603                 }
1604                 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);     /* Check gotos. */
1605                 switch (error) {
1606                 case EACCES:
1607                 case EPERM:
1608                         tp->t_softerror = error;
1609                         return (error);
1610                 case ENOBUFS:
1611                         TCP_XMIT_TIMER_ASSERT(tp, len, flags);
1612                         tp->snd_cwnd = tp->t_maxseg;
1613                         return (0);
1614                 case EMSGSIZE:
1615                         /*
1616                          * For some reason the interface we used initially
1617                          * to send segments changed to another or lowered
1618                          * its MTU.
1619                          * If TSO was active we either got an interface
1620                          * without TSO capabilits or TSO was turned off.
1621                          * If we obtained mtu from ip_output() then update
1622                          * it and try again.
1623                          */
1624                         if (tso)
1625                                 tp->t_flags &= ~TF_TSO;
1626                         if (mtu != 0) {
1627                                 tcp_mss_update(tp, -1, mtu, NULL, NULL);
1628                                 goto again;
1629                         }
1630                         return (error);
1631                 case EHOSTDOWN:
1632                 case EHOSTUNREACH:
1633                 case ENETDOWN:
1634                 case ENETUNREACH:
1635                         if (TCPS_HAVERCVDSYN(tp->t_state)) {
1636                                 tp->t_softerror = error;
1637                                 return (0);
1638                         }
1639                         /* FALLTHROUGH */
1640                 default:
1641                         return (error);
1642                 }
1643         }
1644         TCPSTAT_INC(tcps_sndtotal);
1645
1646         /*
1647          * Data sent (as far as we can tell).
1648          * If this advertises a larger window than any other segment,
1649          * then remember the size of the advertised window.
1650          * Any pending ACK has now been sent.
1651          */
1652         if (SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1653                 tp->rcv_adv = tp->rcv_nxt + recwin;
1654         tp->last_ack_sent = tp->rcv_nxt;
1655         tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1656         if (tcp_timer_active(tp, TT_DELACK))
1657                 tcp_timer_activate(tp, TT_DELACK, 0);
1658 #if 0
1659         /*
1660          * This completely breaks TCP if newreno is turned on.  What happens
1661          * is that if delayed-acks are turned on on the receiver, this code
1662          * on the transmitter effectively destroys the TCP window, forcing
1663          * it to four packets (1.5Kx4 = 6K window).
1664          */
1665         if (sendalot && --maxburst)
1666                 goto again;
1667 #endif
1668         if (sendalot)
1669                 goto again;
1670         return (0);
1671 }
1672
1673 void
1674 tcp_setpersist(struct tcpcb *tp)
1675 {
1676         int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1677         int tt;
1678
1679         tp->t_flags &= ~TF_PREVVALID;
1680         if (tcp_timer_active(tp, TT_REXMT))
1681                 panic("tcp_setpersist: retransmit pending");
1682         /*
1683          * Start/restart persistence timer.
1684          */
1685         TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1686                       tcp_persmin, tcp_persmax);
1687         tcp_timer_activate(tp, TT_PERSIST, tt);
1688         if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1689                 tp->t_rxtshift++;
1690 }
1691
1692 /*
1693  * Insert TCP options according to the supplied parameters to the place
1694  * optp in a consistent way.  Can handle unaligned destinations.
1695  *
1696  * The order of the option processing is crucial for optimal packing and
1697  * alignment for the scarce option space.
1698  *
1699  * The optimal order for a SYN/SYN-ACK segment is:
1700  *   MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1701  *   Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1702  *
1703  * The SACK options should be last.  SACK blocks consume 8*n+2 bytes.
1704  * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1705  * At minimum we need 10 bytes (to generate 1 SACK block).  If both
1706  * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1707  * we only have 10 bytes for SACK options (40 - (12 + 18)).
1708  */
1709 int
1710 tcp_addoptions(struct tcpopt *to, u_char *optp)
1711 {
1712         u_int32_t mask, optlen = 0;
1713
1714         for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1715                 if ((to->to_flags & mask) != mask)
1716                         continue;
1717                 if (optlen == TCP_MAXOLEN)
1718                         break;
1719                 switch (to->to_flags & mask) {
1720                 case TOF_MSS:
1721                         while (optlen % 4) {
1722                                 optlen += TCPOLEN_NOP;
1723                                 *optp++ = TCPOPT_NOP;
1724                         }
1725                         if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1726                                 continue;
1727                         optlen += TCPOLEN_MAXSEG;
1728                         *optp++ = TCPOPT_MAXSEG;
1729                         *optp++ = TCPOLEN_MAXSEG;
1730                         to->to_mss = htons(to->to_mss);
1731                         bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1732                         optp += sizeof(to->to_mss);
1733                         break;
1734                 case TOF_SCALE:
1735                         while (!optlen || optlen % 2 != 1) {
1736                                 optlen += TCPOLEN_NOP;
1737                                 *optp++ = TCPOPT_NOP;
1738                         }
1739                         if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1740                                 continue;
1741                         optlen += TCPOLEN_WINDOW;
1742                         *optp++ = TCPOPT_WINDOW;
1743                         *optp++ = TCPOLEN_WINDOW;
1744                         *optp++ = to->to_wscale;
1745                         break;
1746                 case TOF_SACKPERM:
1747                         while (optlen % 2) {
1748                                 optlen += TCPOLEN_NOP;
1749                                 *optp++ = TCPOPT_NOP;
1750                         }
1751                         if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1752                                 continue;
1753                         optlen += TCPOLEN_SACK_PERMITTED;
1754                         *optp++ = TCPOPT_SACK_PERMITTED;
1755                         *optp++ = TCPOLEN_SACK_PERMITTED;
1756                         break;
1757                 case TOF_TS:
1758                         while (!optlen || optlen % 4 != 2) {
1759                                 optlen += TCPOLEN_NOP;
1760                                 *optp++ = TCPOPT_NOP;
1761                         }
1762                         if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1763                                 continue;
1764                         optlen += TCPOLEN_TIMESTAMP;
1765                         *optp++ = TCPOPT_TIMESTAMP;
1766                         *optp++ = TCPOLEN_TIMESTAMP;
1767                         to->to_tsval = htonl(to->to_tsval);
1768                         to->to_tsecr = htonl(to->to_tsecr);
1769                         bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1770                         optp += sizeof(to->to_tsval);
1771                         bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1772                         optp += sizeof(to->to_tsecr);
1773                         break;
1774                 case TOF_SIGNATURE:
1775                         {
1776                         int siglen = TCPOLEN_SIGNATURE - 2;
1777
1778                         while (!optlen || optlen % 4 != 2) {
1779                                 optlen += TCPOLEN_NOP;
1780                                 *optp++ = TCPOPT_NOP;
1781                         }
1782                         if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) {
1783                                 to->to_flags &= ~TOF_SIGNATURE;
1784                                 continue;
1785                         }
1786                         optlen += TCPOLEN_SIGNATURE;
1787                         *optp++ = TCPOPT_SIGNATURE;
1788                         *optp++ = TCPOLEN_SIGNATURE;
1789                         to->to_signature = optp;
1790                         while (siglen--)
1791                                  *optp++ = 0;
1792                         break;
1793                         }
1794                 case TOF_SACK:
1795                         {
1796                         int sackblks = 0;
1797                         struct sackblk *sack = (struct sackblk *)to->to_sacks;
1798                         tcp_seq sack_seq;
1799
1800                         while (!optlen || optlen % 4 != 2) {
1801                                 optlen += TCPOLEN_NOP;
1802                                 *optp++ = TCPOPT_NOP;
1803                         }
1804                         if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1805                                 continue;
1806                         optlen += TCPOLEN_SACKHDR;
1807                         *optp++ = TCPOPT_SACK;
1808                         sackblks = min(to->to_nsacks,
1809                                         (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1810                         *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1811                         while (sackblks--) {
1812                                 sack_seq = htonl(sack->start);
1813                                 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1814                                 optp += sizeof(sack_seq);
1815                                 sack_seq = htonl(sack->end);
1816                                 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1817                                 optp += sizeof(sack_seq);
1818                                 optlen += TCPOLEN_SACK;
1819                                 sack++;
1820                         }
1821                         TCPSTAT_INC(tcps_sack_send_blocks);
1822                         break;
1823                         }
1824                 case TOF_FASTOPEN:
1825                         {
1826                         int total_len;
1827
1828                         /* XXX is there any point to aligning this option? */
1829                         total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len;
1830                         if (TCP_MAXOLEN - optlen < total_len) {
1831                                 to->to_flags &= ~TOF_FASTOPEN;
1832                                 continue;
1833                         }
1834                         *optp++ = TCPOPT_FAST_OPEN;
1835                         *optp++ = total_len;
1836                         if (to->to_tfo_len > 0) {
1837                                 bcopy(to->to_tfo_cookie, optp, to->to_tfo_len);
1838                                 optp += to->to_tfo_len;
1839                         }
1840                         optlen += total_len;
1841                         break;
1842                         }
1843                 default:
1844                         panic("%s: unknown TCP option type", __func__);
1845                         break;
1846                 }
1847         }
1848
1849         /* Terminate and pad TCP options to a 4 byte boundary. */
1850         if (optlen % 4) {
1851                 optlen += TCPOLEN_EOL;
1852                 *optp++ = TCPOPT_EOL;
1853         }
1854         /*
1855          * According to RFC 793 (STD0007):
1856          *   "The content of the header beyond the End-of-Option option
1857          *    must be header padding (i.e., zero)."
1858          *   and later: "The padding is composed of zeros."
1859          */
1860         while (optlen % 4) {
1861                 optlen += TCPOLEN_PAD;
1862                 *optp++ = TCPOPT_PAD;
1863         }
1864
1865         KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));
1866         return (optlen);
1867 }
1868
1869 /*
1870  * This is a copy of m_copym(), taking the TSO segment size/limit
1871  * constraints into account, and advancing the sndptr as it goes.
1872  */
1873 struct mbuf *
1874 tcp_m_copym(struct mbuf *m, int32_t off0, int32_t *plen,
1875     int32_t seglimit, int32_t segsize, struct sockbuf *sb)
1876 {
1877         struct mbuf *n, **np;
1878         struct mbuf *top;
1879         int32_t off = off0;
1880         int32_t len = *plen;
1881         int32_t fragsize;
1882         int32_t len_cp = 0;
1883         int32_t *pkthdrlen;
1884         uint32_t mlen, frags;
1885         bool copyhdr;
1886
1887
1888         KASSERT(off >= 0, ("tcp_m_copym, negative off %d", off));
1889         KASSERT(len >= 0, ("tcp_m_copym, negative len %d", len));
1890         if (off == 0 && m->m_flags & M_PKTHDR)
1891                 copyhdr = true;
1892         else
1893                 copyhdr = false;
1894         while (off > 0) {
1895                 KASSERT(m != NULL, ("tcp_m_copym, offset > size of mbuf chain"));
1896                 if (off < m->m_len)
1897                         break;
1898                 off -= m->m_len;
1899                 if ((sb) && (m == sb->sb_sndptr)) {
1900                         sb->sb_sndptroff += m->m_len;
1901                         sb->sb_sndptr = m->m_next;
1902                 }
1903                 m = m->m_next;
1904         }
1905         np = &top;
1906         top = NULL;
1907         pkthdrlen = NULL;
1908         while (len > 0) {
1909                 if (m == NULL) {
1910                         KASSERT(len == M_COPYALL,
1911                             ("tcp_m_copym, length > size of mbuf chain"));
1912                         *plen = len_cp;
1913                         if (pkthdrlen != NULL)
1914                                 *pkthdrlen = len_cp;
1915                         break;
1916                 }
1917                 mlen = min(len, m->m_len - off);
1918                 if (seglimit) {
1919                         /*
1920                          * For M_NOMAP mbufs, add 3 segments
1921                          * + 1 in case we are crossing page boundaries
1922                          * + 2 in case the TLS hdr/trailer are used
1923                          * It is cheaper to just add the segments
1924                          * than it is to take the cache miss to look
1925                          * at the mbuf ext_pgs state in detail.
1926                          */
1927                         if (m->m_flags & M_NOMAP) {
1928                                 fragsize = min(segsize, PAGE_SIZE);
1929                                 frags = 3;
1930                         } else {
1931                                 fragsize = segsize;
1932                                 frags = 0;
1933                         }
1934
1935                         /* Break if we really can't fit anymore. */
1936                         if ((frags + 1) >= seglimit) {
1937                                 *plen = len_cp;
1938                                 if (pkthdrlen != NULL)
1939                                         *pkthdrlen = len_cp;
1940                                 break;
1941                         }
1942
1943                         /*
1944                          * Reduce size if you can't copy the whole
1945                          * mbuf. If we can't copy the whole mbuf, also
1946                          * adjust len so the loop will end after this
1947                          * mbuf.
1948                          */
1949                         if ((frags + howmany(mlen, fragsize)) >= seglimit) {
1950                                 mlen = (seglimit - frags - 1) * fragsize;
1951                                 len = mlen;
1952                                 *plen = len_cp + len;
1953                                 if (pkthdrlen != NULL)
1954                                         *pkthdrlen = *plen;
1955                         }
1956                         frags += howmany(mlen, fragsize);
1957                         if (frags == 0)
1958                                 frags++;
1959                         seglimit -= frags;
1960                         KASSERT(seglimit > 0,
1961                             ("%s: seglimit went too low", __func__));
1962                 }
1963                 if (copyhdr)
1964                         n = m_gethdr(M_NOWAIT, m->m_type);
1965                 else
1966                         n = m_get(M_NOWAIT, m->m_type);
1967                 *np = n;
1968                 if (n == NULL)
1969                         goto nospace;
1970                 if (copyhdr) {
1971                         if (!m_dup_pkthdr(n, m, M_NOWAIT))
1972                                 goto nospace;
1973                         if (len == M_COPYALL)
1974                                 n->m_pkthdr.len -= off0;
1975                         else
1976                                 n->m_pkthdr.len = len;
1977                         pkthdrlen = &n->m_pkthdr.len;
1978                         copyhdr = false;
1979                 }
1980                 n->m_len = mlen;
1981                 len_cp += n->m_len;
1982                 if (m->m_flags & M_EXT) {
1983                         n->m_data = m->m_data + off;
1984                         mb_dupcl(n, m);
1985                 } else
1986                         bcopy(mtod(m, caddr_t)+off, mtod(n, caddr_t),
1987                             (u_int)n->m_len);
1988
1989                 if (sb && (sb->sb_sndptr == m) &&
1990                     ((n->m_len + off) >= m->m_len) && m->m_next) {
1991                         sb->sb_sndptroff += m->m_len;
1992                         sb->sb_sndptr = m->m_next;
1993                 }
1994                 off = 0;
1995                 if (len != M_COPYALL) {
1996                         len -= n->m_len;
1997                 }
1998                 m = m->m_next;
1999                 np = &n->m_next;
2000         }
2001         return (top);
2002 nospace:
2003         m_freem(top);
2004         return (NULL);
2005 }
2006
2007 void
2008 tcp_sndbuf_autoscale(struct tcpcb *tp, struct socket *so, uint32_t sendwin)
2009 {
2010
2011         /*
2012          * Automatic sizing of send socket buffer.  Often the send buffer
2013          * size is not optimally adjusted to the actual network conditions
2014          * at hand (delay bandwidth product).  Setting the buffer size too
2015          * small limits throughput on links with high bandwidth and high
2016          * delay (eg. trans-continental/oceanic links).  Setting the
2017          * buffer size too big consumes too much real kernel memory,
2018          * especially with many connections on busy servers.
2019          *
2020          * The criteria to step up the send buffer one notch are:
2021          *  1. receive window of remote host is larger than send buffer
2022          *     (with a fudge factor of 5/4th);
2023          *  2. send buffer is filled to 7/8th with data (so we actually
2024          *     have data to make use of it);
2025          *  3. send buffer fill has not hit maximal automatic size;
2026          *  4. our send window (slow start and cogestion controlled) is
2027          *     larger than sent but unacknowledged data in send buffer.
2028          *
2029          * The remote host receive window scaling factor may limit the
2030          * growing of the send buffer before it reaches its allowed
2031          * maximum.
2032          *
2033          * It scales directly with slow start or congestion window
2034          * and does at most one step per received ACK.  This fast
2035          * scaling has the drawback of growing the send buffer beyond
2036          * what is strictly necessary to make full use of a given
2037          * delay*bandwidth product.  However testing has shown this not
2038          * to be much of an problem.  At worst we are trading wasting
2039          * of available bandwidth (the non-use of it) for wasting some
2040          * socket buffer memory.
2041          *
2042          * TODO: Shrink send buffer during idle periods together
2043          * with congestion window.  Requires another timer.  Has to
2044          * wait for upcoming tcp timer rewrite.
2045          *
2046          * XXXGL: should there be used sbused() or sbavail()?
2047          */
2048         if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
2049                 int lowat;
2050
2051                 lowat = V_tcp_sendbuf_auto_lowat ? so->so_snd.sb_lowat : 0;
2052                 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat - lowat &&
2053                     sbused(&so->so_snd) >=
2054                     (so->so_snd.sb_hiwat / 8 * 7) - lowat &&
2055                     sbused(&so->so_snd) < V_tcp_autosndbuf_max &&
2056                     sendwin >= (sbused(&so->so_snd) -
2057                     (tp->snd_nxt - tp->snd_una))) {
2058                         if (!sbreserve_locked(&so->so_snd,
2059                             min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
2060                              V_tcp_autosndbuf_max), so, curthread))
2061                                 so->so_snd.sb_flags &= ~SB_AUTOSIZE;
2062                 }
2063         }
2064 }