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_kern_tls.h"
  41 #include "opt_tcpdebug.h"
  42
  43 #include <sys/param.h>
  44 #include <sys/systm.h>
  45 #include <sys/arb.h>
  46 #include <sys/domain.h>
  47 #ifdef TCP_HHOOK
  48 #include <sys/hhook.h>
  49 #endif
  50 #include <sys/kernel.h>
  51 #ifdef KERN_TLS
  52 #include <sys/ktls.h>
  53 #endif
  54 #include <sys/lock.h>
  55 #include <sys/mbuf.h>
  56 #include <sys/mutex.h>
  57 #include <sys/protosw.h>
  58 #include <sys/qmath.h>
  59 #include <sys/sdt.h>
  60 #include <sys/socket.h>
  61 #include <sys/socketvar.h>
  62 #include <sys/sysctl.h>
  63 #include <sys/stats.h>
  64
  65 #include <net/if.h>
  66 #include <net/route.h>
  67 #include <net/route/nhop.h>
  68 #include <net/vnet.h>
  69
  70 #include <netinet/in.h>
  71 #include <netinet/in_kdtrace.h>
  72 #include <netinet/in_systm.h>
  73 #include <netinet/ip.h>
  74 #include <netinet/in_pcb.h>
  75 #include <netinet/ip_var.h>
  76 #include <netinet/ip_options.h>
  77 #ifdef INET6
  78 #include <netinet6/in6_pcb.h>
  79 #include <netinet/ip6.h>
  80 #include <netinet6/ip6_var.h>
  81 #endif
  82 #include <netinet/tcp.h>
  83 #define TCPOUTFLAGS
  84 #include <netinet/tcp_fsm.h>
  85 #include <netinet/tcp_log_buf.h>
  86 #include <netinet/tcp_seq.h>
  87 #include <netinet/tcp_timer.h>
  88 #include <netinet/tcp_var.h>
  89 #include <netinet/tcpip.h>
  90 #include <netinet/cc/cc.h>
  91 #include <netinet/tcp_fastopen.h>
  92 #ifdef TCPPCAP
  93 #include <netinet/tcp_pcap.h>
  94 #endif
  95 #ifdef TCPDEBUG
  96 #include <netinet/tcp_debug.h>
  97 #endif
  98 #ifdef TCP_OFFLOAD
  99 #include <netinet/tcp_offload.h>
 100 #endif
 101
 102 #include <netipsec/ipsec_support.h>
 103
 104 #include <machine/in_cksum.h>
 105
 106 #include <security/mac/mac_framework.h>
 107
 108 VNET_DEFINE(int, path_mtu_discovery) = 1;
 109 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_VNET | CTLFLAG_RW,
 110         &VNET_NAME(path_mtu_discovery), 1,
 111         "Enable Path MTU Discovery");
 112
 113 VNET_DEFINE(int, tcp_do_tso) = 1;
 114 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_VNET | CTLFLAG_RW,
 115         &VNET_NAME(tcp_do_tso), 0,
 116         "Enable TCP Segmentation Offload");
 117
 118 VNET_DEFINE(int, tcp_sendspace) = 1024*32;
 119 #define V_tcp_sendspace VNET(tcp_sendspace)
 120 SYSCTL_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_VNET | CTLFLAG_RW,
 121         &VNET_NAME(tcp_sendspace), 0, "Initial send socket buffer size");
 122
 123 VNET_DEFINE(int, tcp_do_autosndbuf) = 1;
 124 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
 125         &VNET_NAME(tcp_do_autosndbuf), 0,
 126         "Enable automatic send buffer sizing");
 127
 128 VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024;
 129 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_VNET | CTLFLAG_RW,
 130         &VNET_NAME(tcp_autosndbuf_inc), 0,
 131         "Incrementor step size of automatic send buffer");
 132
 133 VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024;
 134 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
 135         &VNET_NAME(tcp_autosndbuf_max), 0,
 136         "Max size of automatic send buffer");
 137
 138 VNET_DEFINE(int, tcp_sendbuf_auto_lowat) = 0;
 139 #define V_tcp_sendbuf_auto_lowat        VNET(tcp_sendbuf_auto_lowat)
 140 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto_lowat, CTLFLAG_VNET | CTLFLAG_RW,
 141         &VNET_NAME(tcp_sendbuf_auto_lowat), 0,
 142         "Modify threshold for auto send buffer growth to account for SO_SNDLOWAT");
 143
 144 /*
 145  * Make sure that either retransmit or persist timer is set for SYN, FIN and
 146  * non-ACK.
 147  */
 148 #define TCP_XMIT_TIMER_ASSERT(tp, len, th_flags)                        \
 149         KASSERT(((len) == 0 && ((th_flags) & (TH_SYN | TH_FIN)) == 0) ||\
 150             tcp_timer_active((tp), TT_REXMT) ||                         \
 151             tcp_timer_active((tp), TT_PERSIST),                         \
 152             ("neither rexmt nor persist timer is set"))
 153
 154 static void inline      cc_after_idle(struct tcpcb *tp);
 155
 156 #ifdef TCP_HHOOK
 157 /*
 158  * Wrapper for the TCP established output helper hook.
 159  */
 160 void
 161 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
 162     struct tcpopt *to, uint32_t len, int tso)
 163 {
 164         struct tcp_hhook_data hhook_data;
 165
 166         if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
 167                 hhook_data.tp = tp;
 168                 hhook_data.th = th;
 169                 hhook_data.to = to;
 170                 hhook_data.len = len;
 171                 hhook_data.tso = tso;
 172
 173                 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
 174                     tp->osd);
 175         }
 176 }
 177 #endif
 178
 179 /*
 180  * CC wrapper hook functions
 181  */
 182 static void inline
 183 cc_after_idle(struct tcpcb *tp)
 184 {
 185         INP_WLOCK_ASSERT(tp->t_inpcb);
 186
 187         if (CC_ALGO(tp)->after_idle != NULL)
 188                 CC_ALGO(tp)->after_idle(tp->ccv);
 189 }
 190
 191 /*
 192  * Tcp output routine: figure out what should be sent and send it.
 193  */
 194 int
 195 tcp_output(struct tcpcb *tp)
 196 {
 197         struct socket *so = tp->t_inpcb->inp_socket;
 198         int32_t len;
 199         uint32_t recwin, sendwin;
 200         int off, flags, error = 0;      /* Keep compiler happy */
 201         u_int if_hw_tsomaxsegcount = 0;
 202         u_int if_hw_tsomaxsegsize = 0;
 203         struct mbuf *m;
 204         struct ip *ip = NULL;
 205 #ifdef TCPDEBUG
 206         struct ipovly *ipov = NULL;
 207 #endif
 208         struct tcphdr *th;
 209         u_char opt[TCP_MAXOLEN];
 210         unsigned ipoptlen, optlen, hdrlen;
 211 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 212         unsigned ipsec_optlen = 0;
 213 #endif
 214         int idle, sendalot, curticks;
 215         int sack_rxmit, sack_bytes_rxmt;
 216         struct sackhole *p;
 217         int tso, mtu;
 218         struct tcpopt to;
 219         unsigned int wanted_cookie = 0;
 220         unsigned int dont_sendalot = 0;
 221 #if 0
 222         int maxburst = TCP_MAXBURST;
 223 #endif
 224 #ifdef INET6
 225         struct ip6_hdr *ip6 = NULL;
 226         int isipv6;
 227
 228         isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
 229 #endif
 230 #ifdef KERN_TLS
 231         const bool hw_tls = (so->so_snd.sb_flags & SB_TLS_IFNET) != 0;
 232 #else
 233         const bool hw_tls = false;
 234 #endif
 235
 236         NET_EPOCH_ASSERT();
 237         INP_WLOCK_ASSERT(tp->t_inpcb);
 238
 239 #ifdef TCP_OFFLOAD
 240         if (tp->t_flags & TF_TOE)
 241                 return (tcp_offload_output(tp));
 242 #endif
 243
 244         /*
 245          * For TFO connections in SYN_SENT or SYN_RECEIVED,
 246          * only allow the initial SYN or SYN|ACK and those sent
 247          * by the retransmit timer.
 248          */
 249         if (IS_FASTOPEN(tp->t_flags) &&
 250             ((tp->t_state == TCPS_SYN_SENT) ||
 251              (tp->t_state == TCPS_SYN_RECEIVED)) &&
 252             SEQ_GT(tp->snd_max, tp->snd_una) && /* initial SYN or SYN|ACK sent */
 253             (tp->snd_nxt != tp->snd_una))       /* not a retransmit */
 254                 return (0);
 255
 256         /*
 257          * Determine length of data that should be transmitted,
 258          * and flags that will be used.
 259          * If there is some data or critical controls (SYN, RST)
 260          * to send, then transmit; otherwise, investigate further.
 261          */
 262         idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
 263         if (idle && (((ticks - tp->t_rcvtime) >= tp->t_rxtcur) ||
 264             (tp->t_sndtime && ((ticks - tp->t_sndtime) >= tp->t_rxtcur))))
 265                 cc_after_idle(tp);
 266         tp->t_flags &= ~TF_LASTIDLE;
 267         if (idle) {
 268                 if (tp->t_flags & TF_MORETOCOME) {
 269                         tp->t_flags |= TF_LASTIDLE;
 270                         idle = 0;
 271                 }
 272         }
 273 again:
 274         /*
 275          * If we've recently taken a timeout, snd_max will be greater than
 276          * snd_nxt.  There may be SACK information that allows us to avoid
 277          * resending already delivered data.  Adjust snd_nxt accordingly.
 278          */
 279         if ((tp->t_flags & TF_SACK_PERMIT) &&
 280             SEQ_LT(tp->snd_nxt, tp->snd_max))
 281                 tcp_sack_adjust(tp);
 282         sendalot = 0;
 283         tso = 0;
 284         mtu = 0;
 285         off = tp->snd_nxt - tp->snd_una;
 286         sendwin = min(tp->snd_wnd, tp->snd_cwnd);
 287
 288         flags = tcp_outflags[tp->t_state];
 289         /*
 290          * Send any SACK-generated retransmissions.  If we're explicitly trying
 291          * to send out new data (when sendalot is 1), bypass this function.
 292          * If we retransmit in fast recovery mode, decrement snd_cwnd, since
 293          * we're replacing a (future) new transmission with a retransmission
 294          * now, and we previously incremented snd_cwnd in tcp_input().
 295          */
 296         /*
 297          * Still in sack recovery , reset rxmit flag to zero.
 298          */
 299         sack_rxmit = 0;
 300         sack_bytes_rxmt = 0;
 301         len = 0;
 302         p = NULL;
 303         if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
 304             (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
 305                 uint32_t cwin;
 306
 307                 cwin =
 308                     imax(min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt, 0);
 309                 /* Do not retransmit SACK segments beyond snd_recover */
 310                 if (SEQ_GT(p->end, tp->snd_recover)) {
 311                         /*
 312                          * (At least) part of sack hole extends beyond
 313                          * snd_recover. Check to see if we can rexmit data
 314                          * for this hole.
 315                          */
 316                         if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
 317                                 /*
 318                                  * Can't rexmit any more data for this hole.
 319                                  * That data will be rexmitted in the next
 320                                  * sack recovery episode, when snd_recover
 321                                  * moves past p->rxmit.
 322                                  */
 323                                 p = NULL;
 324                                 goto after_sack_rexmit;
 325                         } else
 326                                 /* Can rexmit part of the current hole */
 327                                 len = ((int32_t)ulmin(cwin,
 328                                                    tp->snd_recover - p->rxmit));
 329                 } else
 330                         len = ((int32_t)ulmin(cwin, p->end - p->rxmit));
 331                 off = p->rxmit - tp->snd_una;
 332                 KASSERT(off >= 0,("%s: sack block to the left of una : %d",
 333                     __func__, off));
 334                 if (len > 0) {
 335                         sack_rxmit = 1;
 336                         sendalot = 1;
 337                         TCPSTAT_INC(tcps_sack_rexmits);
 338                         TCPSTAT_ADD(tcps_sack_rexmit_bytes,
 339                             min(len, tcp_maxseg(tp)));
 340                 }
 341         }
 342 after_sack_rexmit:
 343         /*
 344          * Get standard flags, and add SYN or FIN if requested by 'hidden'
 345          * state flags.
 346          */
 347         if (tp->t_flags & TF_NEEDFIN)
 348                 flags |= TH_FIN;
 349         if (tp->t_flags & TF_NEEDSYN)
 350                 flags |= TH_SYN;
 351
 352         SOCKBUF_LOCK(&so->so_snd);
 353         /*
 354          * If in persist timeout with window of 0, send 1 byte.
 355          * Otherwise, if window is small but nonzero
 356          * and timer expired, we will send what we can
 357          * and go to transmit state.
 358          */
 359         if (tp->t_flags & TF_FORCEDATA) {
 360                 if (sendwin == 0) {
 361                         /*
 362                          * If we still have some data to send, then
 363                          * clear the FIN bit.  Usually this would
 364                          * happen below when it realizes that we
 365                          * aren't sending all the data.  However,
 366                          * if we have exactly 1 byte of unsent data,
 367                          * then it won't clear the FIN bit below,
 368                          * and if we are in persist state, we wind
 369                          * up sending the packet without recording
 370                          * that we sent the FIN bit.
 371                          *
 372                          * We can't just blindly clear the FIN bit,
 373                          * because if we don't have any more data
 374                          * to send then the probe will be the FIN
 375                          * itself.
 376                          */
 377                         if (off < sbused(&so->so_snd))
 378                                 flags &= ~TH_FIN;
 379                         sendwin = 1;
 380                 } else {
 381                         tcp_timer_activate(tp, TT_PERSIST, 0);
 382                         tp->t_rxtshift = 0;
 383                 }
 384         }
 385
 386         /*
 387          * If snd_nxt == snd_max and we have transmitted a FIN, the
 388          * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
 389          * a negative length.  This can also occur when TCP opens up
 390          * its congestion window while receiving additional duplicate
 391          * acks after fast-retransmit because TCP will reset snd_nxt
 392          * to snd_max after the fast-retransmit.
 393          *
 394          * In the normal retransmit-FIN-only case, however, snd_nxt will
 395          * be set to snd_una, the offset will be 0, and the length may
 396          * wind up 0.
 397          *
 398          * If sack_rxmit is true we are retransmitting from the scoreboard
 399          * in which case len is already set.
 400          */
 401         if (sack_rxmit == 0) {
 402                 if (sack_bytes_rxmt == 0)
 403                         len = ((int32_t)min(sbavail(&so->so_snd), sendwin) -
 404                             off);
 405                 else {
 406                         int32_t cwin;
 407
 408                         /*
 409                          * We are inside of a SACK recovery episode and are
 410                          * sending new data, having retransmitted all the
 411                          * data possible in the scoreboard.
 412                          */
 413                         len = ((int32_t)min(sbavail(&so->so_snd), tp->snd_wnd) -
 414                             off);
 415                         /*
 416                          * Don't remove this (len > 0) check !
 417                          * We explicitly check for len > 0 here (although it
 418                          * isn't really necessary), to work around a gcc
 419                          * optimization issue - to force gcc to compute
 420                          * len above. Without this check, the computation
 421                          * of len is bungled by the optimizer.
 422                          */
 423                         if (len > 0) {
 424                                 cwin = tp->snd_cwnd -
 425                                         (tp->snd_nxt - tp->snd_recover) -
 426                                         sack_bytes_rxmt;
 427                                 if (cwin < 0)
 428                                         cwin = 0;
 429                                 len = imin(len, cwin);
 430                         }
 431                 }
 432         }
 433
 434         /*
 435          * Lop off SYN bit if it has already been sent.  However, if this
 436          * is SYN-SENT state and if segment contains data and if we don't
 437          * know that foreign host supports TAO, suppress sending segment.
 438          */
 439         if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
 440                 if (tp->t_state != TCPS_SYN_RECEIVED)
 441                         flags &= ~TH_SYN;
 442                 /*
 443                  * When sending additional segments following a TFO SYN|ACK,
 444                  * do not include the SYN bit.
 445                  */
 446                 if (IS_FASTOPEN(tp->t_flags) &&
 447                     (tp->t_state == TCPS_SYN_RECEIVED))
 448                         flags &= ~TH_SYN;
 449                 off--, len++;
 450         }
 451
 452         /*
 453          * Be careful not to send data and/or FIN on SYN segments.
 454          * This measure is needed to prevent interoperability problems
 455          * with not fully conformant TCP implementations.
 456          */
 457         if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
 458                 len = 0;
 459                 flags &= ~TH_FIN;
 460         }
 461
 462         /*
 463          * On TFO sockets, ensure no data is sent in the following cases:
 464          *
 465          *  - When retransmitting SYN|ACK on a passively-created socket
 466          *
 467          *  - When retransmitting SYN on an actively created socket
 468          *
 469          *  - When sending a zero-length cookie (cookie request) on an
 470          *    actively created socket
 471          *
 472          *  - When the socket is in the CLOSED state (RST is being sent)
 473          */
 474         if (IS_FASTOPEN(tp->t_flags) &&
 475             (((flags & TH_SYN) && (tp->t_rxtshift > 0)) ||
 476              ((tp->t_state == TCPS_SYN_SENT) &&
 477               (tp->t_tfo_client_cookie_len == 0)) ||
 478              (flags & TH_RST)))
 479                 len = 0;
 480         if (len <= 0) {
 481                 /*
 482                  * If FIN has been sent but not acked,
 483                  * but we haven't been called to retransmit,
 484                  * len will be < 0.  Otherwise, window shrank
 485                  * after we sent into it.  If window shrank to 0,
 486                  * cancel pending retransmit, pull snd_nxt back
 487                  * to (closed) window, and set the persist timer
 488                  * if it isn't already going.  If the window didn't
 489                  * close completely, just wait for an ACK.
 490                  *
 491                  * We also do a general check here to ensure that
 492                  * we will set the persist timer when we have data
 493                  * to send, but a 0-byte window. This makes sure
 494                  * the persist timer is set even if the packet
 495                  * hits one of the "goto send" lines below.
 496                  */
 497                 len = 0;
 498                 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
 499                         (off < (int) sbavail(&so->so_snd))) {
 500                         tcp_timer_activate(tp, TT_REXMT, 0);
 501                         tp->t_rxtshift = 0;
 502                         tp->snd_nxt = tp->snd_una;
 503                         if (!tcp_timer_active(tp, TT_PERSIST))
 504                                 tcp_setpersist(tp);
 505                 }
 506         }
 507
 508         /* len will be >= 0 after this point. */
 509         KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
 510
 511         tcp_sndbuf_autoscale(tp, so, sendwin);
 512
 513         /*
 514          * Decide if we can use TCP Segmentation Offloading (if supported by
 515          * hardware).
 516          *
 517          * TSO may only be used if we are in a pure bulk sending state.  The
 518          * presence of TCP-MD5, SACK retransmits, SACK advertizements and
 519          * IP options prevent using TSO.  With TSO the TCP header is the same
 520          * (except for the sequence number) for all generated packets.  This
 521          * makes it impossible to transmit any options which vary per generated
 522          * segment or packet.
 523          *
 524          * IPv4 handling has a clear separation of ip options and ip header
 525          * flags while IPv6 combines both in in6p_outputopts. ip6_optlen() does
 526          * the right thing below to provide length of just ip options and thus
 527          * checking for ipoptlen is enough to decide if ip options are present.
 528          */
 529 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 530         /*
 531          * Pre-calculate here as we save another lookup into the darknesses
 532          * of IPsec that way and can actually decide if TSO is ok.
 533          */
 534 #ifdef INET6
 535         if (isipv6 && IPSEC_ENABLED(ipv6))
 536                 ipsec_optlen = IPSEC_HDRSIZE(ipv6, tp->t_inpcb);
 537 #ifdef INET
 538         else
 539 #endif
 540 #endif /* INET6 */
 541 #ifdef INET
 542         if (IPSEC_ENABLED(ipv4))
 543                 ipsec_optlen = IPSEC_HDRSIZE(ipv4, tp->t_inpcb);
 544 #endif /* INET */
 545 #endif /* IPSEC */
 546 #ifdef INET6
 547         if (isipv6)
 548                 ipoptlen = ip6_optlen(tp->t_inpcb);
 549         else
 550 #endif
 551         if (tp->t_inpcb->inp_options)
 552                 ipoptlen = tp->t_inpcb->inp_options->m_len -
 553                                 offsetof(struct ipoption, ipopt_list);
 554         else
 555                 ipoptlen = 0;
 556 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 557         ipoptlen += ipsec_optlen;
 558 #endif
 559
 560         if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
 561             ((tp->t_flags & TF_SIGNATURE) == 0) &&
 562             tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
 563             ipoptlen == 0 && !(flags & TH_SYN))
 564                 tso = 1;
 565
 566         if (sack_rxmit) {
 567                 if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
 568                         flags &= ~TH_FIN;
 569         } else {
 570                 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
 571                     sbused(&so->so_snd)))
 572                         flags &= ~TH_FIN;
 573         }
 574
 575         recwin = lmin(lmax(sbspace(&so->so_rcv), 0),
 576             (long)TCP_MAXWIN << tp->rcv_scale);
 577
 578         /*
 579          * Sender silly window avoidance.   We transmit under the following
 580          * conditions when len is non-zero:
 581          *
 582          *      - We have a full segment (or more with TSO)
 583          *      - This is the last buffer in a write()/send() and we are
 584          *        either idle or running NODELAY
 585          *      - we've timed out (e.g. persist timer)
 586          *      - we have more then 1/2 the maximum send window's worth of
 587          *        data (receiver may be limited the window size)
 588          *      - we need to retransmit
 589          */
 590         if (len) {
 591                 if (len >= tp->t_maxseg)
 592                         goto send;
 593                 /*
 594                  * As the TCP header options are now
 595                  * considered when setting up the initial
 596                  * window, we would not send the last segment
 597                  * if we skip considering the option length here.
 598                  * Note: this may not work when tcp headers change
 599                  * very dynamically in the future.
 600                  */
 601                 if ((((tp->t_flags & TF_SIGNATURE) ?
 602                         PADTCPOLEN(TCPOLEN_SIGNATURE) : 0) +
 603                     ((tp->t_flags & TF_RCVD_TSTMP) ?
 604                         PADTCPOLEN(TCPOLEN_TIMESTAMP) : 0) +
 605                     len) >= tp->t_maxseg)
 606                         goto send;
 607                 /*
 608                  * NOTE! on localhost connections an 'ack' from the remote
 609                  * end may occur synchronously with the output and cause
 610                  * us to flush a buffer queued with moretocome.  XXX
 611                  *
 612                  * note: the len + off check is almost certainly unnecessary.
 613                  */
 614                 if (!(tp->t_flags & TF_MORETOCOME) &&   /* normal case */
 615                     (idle || (tp->t_flags & TF_NODELAY)) &&
 616                     (uint32_t)len + (uint32_t)off >= sbavail(&so->so_snd) &&
 617                     (tp->t_flags & TF_NOPUSH) == 0) {
 618                         goto send;
 619                 }
 620                 if (tp->t_flags & TF_FORCEDATA)         /* typ. timeout case */
 621                         goto send;
 622                 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
 623                         goto send;
 624                 if (SEQ_LT(tp->snd_nxt, tp->snd_max))   /* retransmit case */
 625                         goto send;
 626                 if (sack_rxmit)
 627                         goto send;
 628         }
 629
 630         /*
 631          * Sending of standalone window updates.
 632          *
 633          * Window updates are important when we close our window due to a
 634          * full socket buffer and are opening it again after the application
 635          * reads data from it.  Once the window has opened again and the
 636          * remote end starts to send again the ACK clock takes over and
 637          * provides the most current window information.
 638          *
 639          * We must avoid the silly window syndrome whereas every read
 640          * from the receive buffer, no matter how small, causes a window
 641          * update to be sent.  We also should avoid sending a flurry of
 642          * window updates when the socket buffer had queued a lot of data
 643          * and the application is doing small reads.
 644          *
 645          * Prevent a flurry of pointless window updates by only sending
 646          * an update when we can increase the advertized window by more
 647          * than 1/4th of the socket buffer capacity.  When the buffer is
 648          * getting full or is very small be more aggressive and send an
 649          * update whenever we can increase by two mss sized segments.
 650          * In all other situations the ACK's to new incoming data will
 651          * carry further window increases.
 652          *
 653          * Don't send an independent window update if a delayed
 654          * ACK is pending (it will get piggy-backed on it) or the
 655          * remote side already has done a half-close and won't send
 656          * more data.  Skip this if the connection is in T/TCP
 657          * half-open state.
 658          */
 659         if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
 660             !(tp->t_flags & TF_DELACK) &&
 661             !TCPS_HAVERCVDFIN(tp->t_state)) {
 662                 /*
 663                  * "adv" is the amount we could increase the window,
 664                  * taking into account that we are limited by
 665                  * TCP_MAXWIN << tp->rcv_scale.
 666                  */
 667                 int32_t adv;
 668                 int oldwin;
 669
 670                 adv = recwin;
 671                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
 672                         oldwin = (tp->rcv_adv - tp->rcv_nxt);
 673                         if (adv > oldwin)
 674                                 adv -= oldwin;
 675                         else
 676                                 adv = 0;
 677                 } else
 678                         oldwin = 0;
 679
 680                 /*
 681                  * If the new window size ends up being the same as or less
 682                  * than the old size when it is scaled, then don't force
 683                  * a window update.
 684                  */
 685                 if (oldwin >> tp->rcv_scale >= (adv + oldwin) >> tp->rcv_scale)
 686                         goto dontupdate;
 687
 688                 if (adv >= (int32_t)(2 * tp->t_maxseg) &&
 689                     (adv >= (int32_t)(so->so_rcv.sb_hiwat / 4) ||
 690                      recwin <= (so->so_rcv.sb_hiwat / 8) ||
 691                      so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg ||
 692                      adv >= TCP_MAXWIN << tp->rcv_scale))
 693                         goto send;
 694                 if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat)
 695                         goto send;
 696         }
 697 dontupdate:
 698
 699         /*
 700          * Send if we owe the peer an ACK, RST, SYN, or urgent data.  ACKNOW
 701          * is also a catch-all for the retransmit timer timeout case.
 702          */
 703         if (tp->t_flags & TF_ACKNOW)
 704                 goto send;
 705         if ((flags & TH_RST) ||
 706             ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
 707                 goto send;
 708         if (SEQ_GT(tp->snd_up, tp->snd_una))
 709                 goto send;
 710         /*
 711          * If our state indicates that FIN should be sent
 712          * and we have not yet done so, then we need to send.
 713          */
 714         if (flags & TH_FIN &&
 715             ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
 716                 goto send;
 717         /*
 718          * In SACK, it is possible for tcp_output to fail to send a segment
 719          * after the retransmission timer has been turned off.  Make sure
 720          * that the retransmission timer is set.
 721          */
 722         if ((tp->t_flags & TF_SACK_PERMIT) &&
 723             SEQ_GT(tp->snd_max, tp->snd_una) &&
 724             !tcp_timer_active(tp, TT_REXMT) &&
 725             !tcp_timer_active(tp, TT_PERSIST)) {
 726                 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
 727                 goto just_return;
 728         }
 729         /*
 730          * TCP window updates are not reliable, rather a polling protocol
 731          * using ``persist'' packets is used to insure receipt of window
 732          * updates.  The three ``states'' for the output side are:
 733          *      idle                    not doing retransmits or persists
 734          *      persisting              to move a small or zero window
 735          *      (re)transmitting        and thereby not persisting
 736          *
 737          * tcp_timer_active(tp, TT_PERSIST)
 738          *      is true when we are in persist state.
 739          * (tp->t_flags & TF_FORCEDATA)
 740          *      is set when we are called to send a persist packet.
 741          * tcp_timer_active(tp, TT_REXMT)
 742          *      is set when we are retransmitting
 743          * The output side is idle when both timers are zero.
 744          *
 745          * If send window is too small, there is data to transmit, and no
 746          * retransmit or persist is pending, then go to persist state.
 747          * If nothing happens soon, send when timer expires:
 748          * if window is nonzero, transmit what we can,
 749          * otherwise force out a byte.
 750          */
 751         if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) &&
 752             !tcp_timer_active(tp, TT_PERSIST)) {
 753                 tp->t_rxtshift = 0;
 754                 tcp_setpersist(tp);
 755         }
 756
 757         /*
 758          * No reason to send a segment, just return.
 759          */
 760 just_return:
 761         SOCKBUF_UNLOCK(&so->so_snd);
 762         return (0);
 763
 764 send:
 765         SOCKBUF_LOCK_ASSERT(&so->so_snd);
 766         if (len > 0) {
 767                 if (len >= tp->t_maxseg)
 768                         tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
 769                 else
 770                         tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
 771         }
 772         /*
 773          * Before ESTABLISHED, force sending of initial options
 774          * unless TCP set not to do any options.
 775          * NOTE: we assume that the IP/TCP header plus TCP options
 776          * always fit in a single mbuf, leaving room for a maximum
 777          * link header, i.e.
 778          *      max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
 779          */
 780         optlen = 0;
 781 #ifdef INET6
 782         if (isipv6)
 783                 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
 784         else
 785 #endif
 786                 hdrlen = sizeof (struct tcpiphdr);
 787
 788         if (flags & TH_SYN) {
 789                 tp->snd_nxt = tp->iss;
 790         }
 791
 792         /*
 793          * Compute options for segment.
 794          * We only have to care about SYN and established connection
 795          * segments.  Options for SYN-ACK segments are handled in TCP
 796          * syncache.
 797          */
 798         to.to_flags = 0;
 799         if ((tp->t_flags & TF_NOOPT) == 0) {
 800                 /* Maximum segment size. */
 801                 if (flags & TH_SYN) {
 802                         to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc);
 803                         to.to_flags |= TOF_MSS;
 804
 805                         /*
 806                          * On SYN or SYN|ACK transmits on TFO connections,
 807                          * only include the TFO option if it is not a
 808                          * retransmit, as the presence of the TFO option may
 809                          * have caused the original SYN or SYN|ACK to have
 810                          * been dropped by a middlebox.
 811                          */
 812                         if (IS_FASTOPEN(tp->t_flags) &&
 813                             (tp->t_rxtshift == 0)) {
 814                                 if (tp->t_state == TCPS_SYN_RECEIVED) {
 815                                         to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
 816                                         to.to_tfo_cookie =
 817                                             (u_int8_t *)&tp->t_tfo_cookie.server;
 818                                         to.to_flags |= TOF_FASTOPEN;
 819                                         wanted_cookie = 1;
 820                                 } else if (tp->t_state == TCPS_SYN_SENT) {
 821                                         to.to_tfo_len =
 822                                             tp->t_tfo_client_cookie_len;
 823                                         to.to_tfo_cookie =
 824                                             tp->t_tfo_cookie.client;
 825                                         to.to_flags |= TOF_FASTOPEN;
 826                                         wanted_cookie = 1;
 827                                         /*
 828                                          * If we wind up having more data to
 829                                          * send with the SYN than can fit in
 830                                          * one segment, don't send any more
 831                                          * until the SYN|ACK comes back from
 832                                          * the other end.
 833                                          */
 834                                         dont_sendalot = 1;
 835                                 }
 836                         }
 837                 }
 838                 /* Window scaling. */
 839                 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
 840                         to.to_wscale = tp->request_r_scale;
 841                         to.to_flags |= TOF_SCALE;
 842                 }
 843                 /* Timestamps. */
 844                 if ((tp->t_flags & TF_RCVD_TSTMP) ||
 845                     ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
 846                         curticks = tcp_ts_getticks();
 847                         to.to_tsval = curticks + tp->ts_offset;
 848                         to.to_tsecr = tp->ts_recent;
 849                         to.to_flags |= TOF_TS;
 850                         if (tp->t_rxtshift == 1)
 851                                 tp->t_badrxtwin = curticks;
 852                 }
 853
 854                 /* Set receive buffer autosizing timestamp. */
 855                 if (tp->rfbuf_ts == 0 &&
 856                     (so->so_rcv.sb_flags & SB_AUTOSIZE))
 857                         tp->rfbuf_ts = tcp_ts_getticks();
 858
 859                 /* Selective ACK's. */
 860                 if (tp->t_flags & TF_SACK_PERMIT) {
 861                         if (flags & TH_SYN)
 862                                 to.to_flags |= TOF_SACKPERM;
 863                         else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
 864                             tp->rcv_numsacks > 0) {
 865                                 to.to_flags |= TOF_SACK;
 866                                 to.to_nsacks = tp->rcv_numsacks;
 867                                 to.to_sacks = (u_char *)tp->sackblks;
 868                         }
 869                 }
 870 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 871                 /* TCP-MD5 (RFC2385). */
 872                 /*
 873                  * Check that TCP_MD5SIG is enabled in tcpcb to
 874                  * account the size needed to set this TCP option.
 875                  */
 876                 if (tp->t_flags & TF_SIGNATURE)
 877                         to.to_flags |= TOF_SIGNATURE;
 878 #endif /* TCP_SIGNATURE */
 879
 880                 /* Processing the options. */
 881                 hdrlen += optlen = tcp_addoptions(&to, opt);
 882                 /*
 883                  * If we wanted a TFO option to be added, but it was unable
 884                  * to fit, ensure no data is sent.
 885                  */
 886                 if (IS_FASTOPEN(tp->t_flags) && wanted_cookie &&
 887                     !(to.to_flags & TOF_FASTOPEN))
 888                         len = 0;
 889         }
 890
 891         /*
 892          * Adjust data length if insertion of options will
 893          * bump the packet length beyond the t_maxseg length.
 894          * Clear the FIN bit because we cut off the tail of
 895          * the segment.
 896          */
 897         if (len + optlen + ipoptlen > tp->t_maxseg) {
 898                 flags &= ~TH_FIN;
 899
 900                 if (tso) {
 901                         u_int if_hw_tsomax;
 902                         u_int moff;
 903                         int max_len;
 904
 905                         /* extract TSO information */
 906                         if_hw_tsomax = tp->t_tsomax;
 907                         if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
 908                         if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
 909
 910                         /*
 911                          * Limit a TSO burst to prevent it from
 912                          * overflowing or exceeding the maximum length
 913                          * allowed by the network interface:
 914                          */
 915                         KASSERT(ipoptlen == 0,
 916                             ("%s: TSO can't do IP options", __func__));
 917
 918                         /*
 919                          * Check if we should limit by maximum payload
 920                          * length:
 921                          */
 922                         if (if_hw_tsomax != 0) {
 923                                 /* compute maximum TSO length */
 924                                 max_len = (if_hw_tsomax - hdrlen -
 925                                     max_linkhdr);
 926                                 if (max_len <= 0) {
 927                                         len = 0;
 928                                 } else if (len > max_len) {
 929                                         sendalot = 1;
 930                                         len = max_len;
 931                                 }
 932                         }
 933
 934                         /*
 935                          * Prevent the last segment from being
 936                          * fractional unless the send sockbuf can be
 937                          * emptied:
 938                          */
 939                         max_len = (tp->t_maxseg - optlen);
 940                         if (((uint32_t)off + (uint32_t)len) <
 941                             sbavail(&so->so_snd)) {
 942                                 moff = len % max_len;
 943                                 if (moff != 0) {
 944                                         len -= moff;
 945                                         sendalot = 1;
 946                                 }
 947                         }
 948
 949                         /*
 950                          * In case there are too many small fragments
 951                          * don't use TSO:
 952                          */
 953                         if (len <= max_len) {
 954                                 len = max_len;
 955                                 sendalot = 1;
 956                                 tso = 0;
 957                         }
 958
 959                         /*
 960                          * Send the FIN in a separate segment
 961                          * after the bulk sending is done.
 962                          * We don't trust the TSO implementations
 963                          * to clear the FIN flag on all but the
 964                          * last segment.
 965                          */
 966                         if (tp->t_flags & TF_NEEDFIN)
 967                                 sendalot = 1;
 968                 } else {
 969                         if (optlen + ipoptlen >= tp->t_maxseg) {
 970                                 /*
 971                                  * Since we don't have enough space to put
 972                                  * the IP header chain and the TCP header in
 973                                  * one packet as required by RFC 7112, don't
 974                                  * send it. Also ensure that at least one
 975                                  * byte of the payload can be put into the
 976                                  * TCP segment.
 977                                  */
 978                                 SOCKBUF_UNLOCK(&so->so_snd);
 979                                 error = EMSGSIZE;
 980                                 sack_rxmit = 0;
 981                                 goto out;
 982                         }
 983                         len = tp->t_maxseg - optlen - ipoptlen;
 984                         sendalot = 1;
 985                         if (dont_sendalot)
 986                                 sendalot = 0;
 987                 }
 988         } else
 989                 tso = 0;
 990
 991         KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
 992             ("%s: len > IP_MAXPACKET", __func__));
 993
 994 /*#ifdef DIAGNOSTIC*/
 995 #ifdef INET6
 996         if (max_linkhdr + hdrlen > MCLBYTES)
 997 #else
 998         if (max_linkhdr + hdrlen > MHLEN)
 999 #endif
1000                 panic("tcphdr too big");
1001 /*#endif*/
1002
1003         /*
1004          * This KASSERT is here to catch edge cases at a well defined place.
1005          * Before, those had triggered (random) panic conditions further down.
1006          */
1007         KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
1008
1009         /*
1010          * Grab a header mbuf, attaching a copy of data to
1011          * be transmitted, and initialize the header from
1012          * the template for sends on this connection.
1013          */
1014         if (len) {
1015                 struct mbuf *mb;
1016                 struct sockbuf *msb;
1017                 u_int moff;
1018
1019                 if ((tp->t_flags & TF_FORCEDATA) && len == 1) {
1020                         TCPSTAT_INC(tcps_sndprobe);
1021 #ifdef STATS
1022                         if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1023                                 stats_voi_update_abs_u32(tp->t_stats,
1024                                 VOI_TCP_RETXPB, len);
1025                         else
1026                                 stats_voi_update_abs_u64(tp->t_stats,
1027                                     VOI_TCP_TXPB, len);
1028 #endif /* STATS */
1029                 } else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
1030                         tp->t_sndrexmitpack++;
1031                         TCPSTAT_INC(tcps_sndrexmitpack);
1032                         TCPSTAT_ADD(tcps_sndrexmitbyte, len);
1033 #ifdef STATS
1034                         stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_RETXPB,
1035                             len);
1036 #endif /* STATS */
1037                 } else {
1038                         TCPSTAT_INC(tcps_sndpack);
1039                         TCPSTAT_ADD(tcps_sndbyte, len);
1040 #ifdef STATS
1041                         stats_voi_update_abs_u64(tp->t_stats, VOI_TCP_TXPB,
1042                             len);
1043 #endif /* STATS */
1044                 }
1045 #ifdef INET6
1046                 if (MHLEN < hdrlen + max_linkhdr)
1047                         m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
1048                 else
1049 #endif
1050                         m = m_gethdr(M_NOWAIT, MT_DATA);
1051
1052                 if (m == NULL) {
1053                         SOCKBUF_UNLOCK(&so->so_snd);
1054                         error = ENOBUFS;
1055                         sack_rxmit = 0;
1056                         goto out;
1057                 }
1058
1059                 m->m_data += max_linkhdr;
1060                 m->m_len = hdrlen;
1061
1062                 /*
1063                  * Start the m_copy functions from the closest mbuf
1064                  * to the offset in the socket buffer chain.
1065                  */
1066                 mb = sbsndptr_noadv(&so->so_snd, off, &moff);
1067                 if (len <= MHLEN - hdrlen - max_linkhdr && !hw_tls) {
1068                         m_copydata(mb, moff, len,
1069                             mtod(m, caddr_t) + hdrlen);
1070                         if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1071                                 sbsndptr_adv(&so->so_snd, mb, len);
1072                         m->m_len += len;
1073                 } else {
1074                         if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1075                                 msb = NULL;
1076                         else
1077                                 msb = &so->so_snd;
1078                         m->m_next = tcp_m_copym(mb, moff,
1079                             &len, if_hw_tsomaxsegcount,
1080                             if_hw_tsomaxsegsize, msb, hw_tls);
1081                         if (len <= (tp->t_maxseg - optlen)) {
1082                                 /*
1083                                  * Must have ran out of mbufs for the copy
1084                                  * shorten it to no longer need tso. Lets
1085                                  * not put on sendalot since we are low on
1086                                  * mbufs.
1087                                  */
1088                                 tso = 0;
1089                         }
1090                         if (m->m_next == NULL) {
1091                                 SOCKBUF_UNLOCK(&so->so_snd);
1092                                 (void) m_free(m);
1093                                 error = ENOBUFS;
1094                                 sack_rxmit = 0;
1095                                 goto out;
1096                         }
1097                 }
1098
1099                 /*
1100                  * If we're sending everything we've got, set PUSH.
1101                  * (This will keep happy those implementations which only
1102                  * give data to the user when a buffer fills or
1103                  * a PUSH comes in.)
1104                  */
1105                 if (((uint32_t)off + (uint32_t)len == sbused(&so->so_snd)) &&
1106                     !(flags & TH_SYN))
1107                         flags |= TH_PUSH;
1108                 SOCKBUF_UNLOCK(&so->so_snd);
1109         } else {
1110                 SOCKBUF_UNLOCK(&so->so_snd);
1111                 if (tp->t_flags & TF_ACKNOW)
1112                         TCPSTAT_INC(tcps_sndacks);
1113                 else if (flags & (TH_SYN|TH_FIN|TH_RST))
1114                         TCPSTAT_INC(tcps_sndctrl);
1115                 else if (SEQ_GT(tp->snd_up, tp->snd_una))
1116                         TCPSTAT_INC(tcps_sndurg);
1117                 else
1118                         TCPSTAT_INC(tcps_sndwinup);
1119
1120                 m = m_gethdr(M_NOWAIT, MT_DATA);
1121                 if (m == NULL) {
1122                         error = ENOBUFS;
1123                         sack_rxmit = 0;
1124                         goto out;
1125                 }
1126 #ifdef INET6
1127                 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
1128                     MHLEN >= hdrlen) {
1129                         M_ALIGN(m, hdrlen);
1130                 } else
1131 #endif
1132                 m->m_data += max_linkhdr;
1133                 m->m_len = hdrlen;
1134         }
1135         SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
1136         m->m_pkthdr.rcvif = (struct ifnet *)0;
1137 #ifdef MAC
1138         mac_inpcb_create_mbuf(tp->t_inpcb, m);
1139 #endif
1140 #ifdef INET6
1141         if (isipv6) {
1142                 ip6 = mtod(m, struct ip6_hdr *);
1143                 th = (struct tcphdr *)(ip6 + 1);
1144                 tcpip_fillheaders(tp->t_inpcb, ip6, th);
1145         } else
1146 #endif /* INET6 */
1147         {
1148                 ip = mtod(m, struct ip *);
1149 #ifdef TCPDEBUG
1150                 ipov = (struct ipovly *)ip;
1151 #endif
1152                 th = (struct tcphdr *)(ip + 1);
1153                 tcpip_fillheaders(tp->t_inpcb, ip, th);
1154         }
1155
1156         /*
1157          * Fill in fields, remembering maximum advertised
1158          * window for use in delaying messages about window sizes.
1159          * If resending a FIN, be sure not to use a new sequence number.
1160          */
1161         if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1162             tp->snd_nxt == tp->snd_max)
1163                 tp->snd_nxt--;
1164         /*
1165          * If we are starting a connection, send ECN setup
1166          * SYN packet. If we are on a retransmit, we may
1167          * resend those bits a number of times as per
1168          * RFC 3168.
1169          */
1170         if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn == 1) {
1171                 if (tp->t_rxtshift >= 1) {
1172                         if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
1173                                 flags |= TH_ECE|TH_CWR;
1174                 } else
1175                         flags |= TH_ECE|TH_CWR;
1176         }
1177         /* Handle parallel SYN for ECN */
1178         if ((tp->t_state == TCPS_SYN_RECEIVED) &&
1179             (tp->t_flags2 & TF2_ECN_SND_ECE)) {
1180                         flags |= TH_ECE;
1181                         tp->t_flags2 &= ~TF2_ECN_SND_ECE;
1182         }
1183
1184         if (tp->t_state == TCPS_ESTABLISHED &&
1185             (tp->t_flags2 & TF2_ECN_PERMIT)) {
1186                 /*
1187                  * If the peer has ECN, mark data packets with
1188                  * ECN capable transmission (ECT).
1189                  * Ignore pure ack packets, retransmissions and window probes.
1190                  */
1191                 if (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
1192                     (sack_rxmit == 0) &&
1193                     !((tp->t_flags & TF_FORCEDATA) && len == 1 &&
1194                     SEQ_LT(tp->snd_una, tp->snd_max))) {
1195 #ifdef INET6
1196                         if (isipv6)
1197                                 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20);
1198                         else
1199 #endif
1200                                 ip->ip_tos |= IPTOS_ECN_ECT0;
1201                         TCPSTAT_INC(tcps_ecn_ect0);
1202                         /*
1203                          * Reply with proper ECN notifications.
1204                          * Only set CWR on new data segments.
1205                          */
1206                         if (tp->t_flags2 & TF2_ECN_SND_CWR) {
1207                                 flags |= TH_CWR;
1208                                 tp->t_flags2 &= ~TF2_ECN_SND_CWR;
1209                         }
1210                 }
1211                 if (tp->t_flags2 & TF2_ECN_SND_ECE)
1212                         flags |= TH_ECE;
1213         }
1214
1215         /*
1216          * If we are doing retransmissions, then snd_nxt will
1217          * not reflect the first unsent octet.  For ACK only
1218          * packets, we do not want the sequence number of the
1219          * retransmitted packet, we want the sequence number
1220          * of the next unsent octet.  So, if there is no data
1221          * (and no SYN or FIN), use snd_max instead of snd_nxt
1222          * when filling in ti_seq.  But if we are in persist
1223          * state, snd_max might reflect one byte beyond the
1224          * right edge of the window, so use snd_nxt in that
1225          * case, since we know we aren't doing a retransmission.
1226          * (retransmit and persist are mutually exclusive...)
1227          */
1228         if (sack_rxmit == 0) {
1229                 if (len || (flags & (TH_SYN|TH_FIN)) ||
1230                     tcp_timer_active(tp, TT_PERSIST))
1231                         th->th_seq = htonl(tp->snd_nxt);
1232                 else
1233                         th->th_seq = htonl(tp->snd_max);
1234         } else {
1235                 th->th_seq = htonl(p->rxmit);
1236                 p->rxmit += len;
1237                 tp->sackhint.sack_bytes_rexmit += len;
1238         }
1239         th->th_ack = htonl(tp->rcv_nxt);
1240         if (optlen) {
1241                 bcopy(opt, th + 1, optlen);
1242                 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
1243         }
1244         th->th_flags = flags;
1245         /*
1246          * Calculate receive window.  Don't shrink window,
1247          * but avoid silly window syndrome.
1248          * If a RST segment is sent, advertise a window of zero.
1249          */
1250         if (flags & TH_RST) {
1251                 recwin = 0;
1252         } else {
1253                 if (recwin < (so->so_rcv.sb_hiwat / 4) &&
1254                     recwin < tp->t_maxseg)
1255                         recwin = 0;
1256                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
1257                     recwin < (tp->rcv_adv - tp->rcv_nxt))
1258                         recwin = (tp->rcv_adv - tp->rcv_nxt);
1259         }
1260         /*
1261          * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1262          * or <SYN,ACK>) segment itself is never scaled.  The <SYN,ACK>
1263          * case is handled in syncache.
1264          */
1265         if (flags & TH_SYN)
1266                 th->th_win = htons((u_short)
1267                                 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1268         else {
1269                 /* Avoid shrinking window with window scaling. */
1270                 recwin = roundup2(recwin, 1 << tp->rcv_scale);
1271                 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
1272         }
1273
1274         /*
1275          * Adjust the RXWIN0SENT flag - indicate that we have advertised
1276          * a 0 window.  This may cause the remote transmitter to stall.  This
1277          * flag tells soreceive() to disable delayed acknowledgements when
1278          * draining the buffer.  This can occur if the receiver is attempting
1279          * to read more data than can be buffered prior to transmitting on
1280          * the connection.
1281          */
1282         if (th->th_win == 0) {
1283                 tp->t_sndzerowin++;
1284                 tp->t_flags |= TF_RXWIN0SENT;
1285         } else
1286                 tp->t_flags &= ~TF_RXWIN0SENT;
1287         if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1288                 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1289                 th->th_flags |= TH_URG;
1290         } else
1291                 /*
1292                  * If no urgent pointer to send, then we pull
1293                  * the urgent pointer to the left edge of the send window
1294                  * so that it doesn't drift into the send window on sequence
1295                  * number wraparound.
1296                  */
1297                 tp->snd_up = tp->snd_una;               /* drag it along */
1298
1299         /*
1300          * Put TCP length in extended header, and then
1301          * checksum extended header and data.
1302          */
1303         m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1304         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1305
1306 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1307         if (to.to_flags & TOF_SIGNATURE) {
1308                 /*
1309                  * Calculate MD5 signature and put it into the place
1310                  * determined before.
1311                  * NOTE: since TCP options buffer doesn't point into
1312                  * mbuf's data, calculate offset and use it.
1313                  */
1314                 if (!TCPMD5_ENABLED() || (error = TCPMD5_OUTPUT(m, th,
1315                     (u_char *)(th + 1) + (to.to_signature - opt))) != 0) {
1316                         /*
1317                          * Do not send segment if the calculation of MD5
1318                          * digest has failed.
1319                          */
1320                         m_freem(m);
1321                         goto out;
1322                 }
1323         }
1324 #endif
1325 #ifdef INET6
1326         if (isipv6) {
1327                 /*
1328                  * There is no need to fill in ip6_plen right now.
1329                  * It will be filled later by ip6_output.
1330                  */
1331                 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1332                 th->th_sum = in6_cksum_pseudo(ip6, sizeof(struct tcphdr) +
1333                     optlen + len, IPPROTO_TCP, 0);
1334         }
1335 #endif
1336 #if defined(INET6) && defined(INET)
1337         else
1338 #endif
1339 #ifdef INET
1340         {
1341                 m->m_pkthdr.csum_flags = CSUM_TCP;
1342                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1343                     htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen));
1344
1345                 /* IP version must be set here for ipv4/ipv6 checking later */
1346                 KASSERT(ip->ip_v == IPVERSION,
1347                     ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1348         }
1349 #endif
1350
1351         /*
1352          * Enable TSO and specify the size of the segments.
1353          * The TCP pseudo header checksum is always provided.
1354          */
1355         if (tso) {
1356                 KASSERT(len > tp->t_maxseg - optlen,
1357                     ("%s: len <= tso_segsz", __func__));
1358                 m->m_pkthdr.csum_flags |= CSUM_TSO;
1359                 m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen;
1360         }
1361
1362         KASSERT(len + hdrlen == m_length(m, NULL),
1363             ("%s: mbuf chain shorter than expected: %d + %u != %u",
1364             __func__, len, hdrlen, m_length(m, NULL)));
1365
1366 #ifdef TCP_HHOOK
1367         /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1368         hhook_run_tcp_est_out(tp, th, &to, len, tso);
1369 #endif
1370
1371 #ifdef TCPDEBUG
1372         /*
1373          * Trace.
1374          */
1375         if (so->so_options & SO_DEBUG) {
1376                 u_short save = 0;
1377 #ifdef INET6
1378                 if (!isipv6)
1379 #endif
1380                 {
1381                         save = ipov->ih_len;
1382                         ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
1383                 }
1384                 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
1385 #ifdef INET6
1386                 if (!isipv6)
1387 #endif
1388                 ipov->ih_len = save;
1389         }
1390 #endif /* TCPDEBUG */
1391         TCP_PROBE3(debug__output, tp, th, m);
1392
1393         /* We're getting ready to send; log now. */
1394         TCP_LOG_EVENT(tp, th, &so->so_rcv, &so->so_snd, TCP_LOG_OUT, ERRNO_UNK,
1395             len, NULL, false);
1396
1397         /*
1398          * Fill in IP length and desired time to live and
1399          * send to IP level.  There should be a better way
1400          * to handle ttl and tos; we could keep them in
1401          * the template, but need a way to checksum without them.
1402          */
1403         /*
1404          * m->m_pkthdr.len should have been set before checksum calculation,
1405          * because in6_cksum() need it.
1406          */
1407 #ifdef INET6
1408         if (isipv6) {
1409                 /*
1410                  * we separately set hoplimit for every segment, since the
1411                  * user might want to change the value via setsockopt.
1412                  * Also, desired default hop limit might be changed via
1413                  * Neighbor Discovery.
1414                  */
1415                 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
1416
1417                 /*
1418                  * Set the packet size here for the benefit of DTrace probes.
1419                  * ip6_output() will set it properly; it's supposed to include
1420                  * the option header lengths as well.
1421                  */
1422                 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
1423
1424                 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss)
1425                         tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1426                 else
1427                         tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1428
1429                 if (tp->t_state == TCPS_SYN_SENT)
1430                         TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
1431
1432                 TCP_PROBE5(send, NULL, tp, ip6, tp, th);
1433
1434 #ifdef TCPPCAP
1435                 /* Save packet, if requested. */
1436                 tcp_pcap_add(th, m, &(tp->t_outpkts));
1437 #endif
1438
1439                 /* TODO: IPv6 IP6TOS_ECT bit on */
1440                 error = ip6_output(m, tp->t_inpcb->in6p_outputopts,
1441                     &tp->t_inpcb->inp_route6,
1442                     ((so->so_options & SO_DONTROUTE) ?  IP_ROUTETOIF : 0),
1443                     NULL, NULL, tp->t_inpcb);
1444
1445                 if (error == EMSGSIZE && tp->t_inpcb->inp_route6.ro_nh != NULL)
1446                         mtu = tp->t_inpcb->inp_route6.ro_nh->nh_mtu;
1447         }
1448 #endif /* INET6 */
1449 #if defined(INET) && defined(INET6)
1450         else
1451 #endif
1452 #ifdef INET
1453     {
1454         ip->ip_len = htons(m->m_pkthdr.len);
1455 #ifdef INET6
1456         if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO)
1457                 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
1458 #endif /* INET6 */
1459         /*
1460          * If we do path MTU discovery, then we set DF on every packet.
1461          * This might not be the best thing to do according to RFC3390
1462          * Section 2. However the tcp hostcache migitates the problem
1463          * so it affects only the first tcp connection with a host.
1464          *
1465          * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1466          */
1467         if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) {
1468                 ip->ip_off |= htons(IP_DF);
1469                 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1470         } else {
1471                 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1472         }
1473
1474         if (tp->t_state == TCPS_SYN_SENT)
1475                 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
1476
1477         TCP_PROBE5(send, NULL, tp, ip, tp, th);
1478
1479 #ifdef TCPPCAP
1480         /* Save packet, if requested. */
1481         tcp_pcap_add(th, m, &(tp->t_outpkts));
1482 #endif
1483
1484         error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
1485             ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
1486             tp->t_inpcb);
1487
1488         if (error == EMSGSIZE && tp->t_inpcb->inp_route.ro_nh != NULL)
1489                 mtu = tp->t_inpcb->inp_route.ro_nh->nh_mtu;
1490     }
1491 #endif /* INET */
1492
1493 out:
1494         /*
1495          * In transmit state, time the transmission and arrange for
1496          * the retransmit.  In persist state, just set snd_max.
1497          */
1498         if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1499             !tcp_timer_active(tp, TT_PERSIST)) {
1500                 tcp_seq startseq = tp->snd_nxt;
1501
1502                 /*
1503                  * Advance snd_nxt over sequence space of this segment.
1504                  */
1505                 if (flags & (TH_SYN|TH_FIN)) {
1506                         if (flags & TH_SYN)
1507                                 tp->snd_nxt++;
1508                         if (flags & TH_FIN) {
1509                                 tp->snd_nxt++;
1510                                 tp->t_flags |= TF_SENTFIN;
1511                         }
1512                 }
1513                 if (sack_rxmit)
1514                         goto timer;
1515                 tp->snd_nxt += len;
1516                 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1517                         tp->snd_max = tp->snd_nxt;
1518                         /*
1519                          * Time this transmission if not a retransmission and
1520                          * not currently timing anything.
1521                          */
1522                         tp->t_sndtime = ticks;
1523                         if (tp->t_rtttime == 0) {
1524                                 tp->t_rtttime = ticks;
1525                                 tp->t_rtseq = startseq;
1526                                 TCPSTAT_INC(tcps_segstimed);
1527                         }
1528 #ifdef STATS
1529                         if (!(tp->t_flags & TF_GPUTINPROG) && len) {
1530                                 tp->t_flags |= TF_GPUTINPROG;
1531                                 tp->gput_seq = startseq;
1532                                 tp->gput_ack = startseq +
1533                                     ulmin(sbavail(&so->so_snd) - off, sendwin);
1534                                 tp->gput_ts = tcp_ts_getticks();
1535                         }
1536 #endif /* STATS */
1537                 }
1538
1539                 /*
1540                  * Set retransmit timer if not currently set,
1541                  * and not doing a pure ack or a keep-alive probe.
1542                  * Initial value for retransmit timer is smoothed
1543                  * round-trip time + 2 * round-trip time variance.
1544                  * Initialize shift counter which is used for backoff
1545                  * of retransmit time.
1546                  */
1547 timer:
1548                 if (!tcp_timer_active(tp, TT_REXMT) &&
1549                     ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1550                      (tp->snd_nxt != tp->snd_una))) {
1551                         if (tcp_timer_active(tp, TT_PERSIST)) {
1552                                 tcp_timer_activate(tp, TT_PERSIST, 0);
1553                                 tp->t_rxtshift = 0;
1554                         }
1555                         tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1556                 } else if (len == 0 && sbavail(&so->so_snd) &&
1557                     !tcp_timer_active(tp, TT_REXMT) &&
1558                     !tcp_timer_active(tp, TT_PERSIST)) {
1559                         /*
1560                          * Avoid a situation where we do not set persist timer
1561                          * after a zero window condition. For example:
1562                          * 1) A -> B: packet with enough data to fill the window
1563                          * 2) B -> A: ACK for #1 + new data (0 window
1564                          *    advertisement)
1565                          * 3) A -> B: ACK for #2, 0 len packet
1566                          *
1567                          * In this case, A will not activate the persist timer,
1568                          * because it chose to send a packet. Unless tcp_output
1569                          * is called for some other reason (delayed ack timer,
1570                          * another input packet from B, socket syscall), A will
1571                          * not send zero window probes.
1572                          *
1573                          * So, if you send a 0-length packet, but there is data
1574                          * in the socket buffer, and neither the rexmt or
1575                          * persist timer is already set, then activate the
1576                          * persist timer.
1577                          */
1578                         tp->t_rxtshift = 0;
1579                         tcp_setpersist(tp);
1580                 }
1581         } else {
1582                 /*
1583                  * Persist case, update snd_max but since we are in
1584                  * persist mode (no window) we do not update snd_nxt.
1585                  */
1586                 int xlen = len;
1587                 if (flags & TH_SYN)
1588                         ++xlen;
1589                 if (flags & TH_FIN) {
1590                         ++xlen;
1591                         tp->t_flags |= TF_SENTFIN;
1592                 }
1593                 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1594                         tp->snd_max = tp->snd_nxt + xlen;
1595         }
1596         if ((error == 0) &&
1597             (TCPS_HAVEESTABLISHED(tp->t_state) &&
1598              (tp->t_flags & TF_SACK_PERMIT) &&
1599              tp->rcv_numsacks > 0)) {
1600                     /* Clean up any DSACK's sent */
1601                     tcp_clean_dsack_blocks(tp);
1602         }
1603         if (error) {
1604                 /* Record the error. */
1605                 TCP_LOG_EVENT(tp, NULL, &so->so_rcv, &so->so_snd, TCP_LOG_OUT,
1606                     error, 0, NULL, false);
1607
1608                 /*
1609                  * We know that the packet was lost, so back out the
1610                  * sequence number advance, if any.
1611                  *
1612                  * If the error is EPERM the packet got blocked by the
1613                  * local firewall.  Normally we should terminate the
1614                  * connection but the blocking may have been spurious
1615                  * due to a firewall reconfiguration cycle.  So we treat
1616                  * it like a packet loss and let the retransmit timer and
1617                  * timeouts do their work over time.
1618                  * XXX: It is a POLA question whether calling tcp_drop right
1619                  * away would be the really correct behavior instead.
1620                  */
1621                 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1622                     !tcp_timer_active(tp, TT_PERSIST)) &&
1623                     ((flags & TH_SYN) == 0) &&
1624                     (error != EPERM)) {
1625                         if (sack_rxmit) {
1626                                 p->rxmit -= len;
1627                                 tp->sackhint.sack_bytes_rexmit -= len;
1628                                 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1629                                     ("sackhint bytes rtx >= 0"));
1630                         } else
1631                                 tp->snd_nxt -= len;
1632                 }
1633                 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);     /* Check gotos. */
1634                 switch (error) {
1635                 case EACCES:
1636                 case EPERM:
1637                         tp->t_softerror = error;
1638                         return (error);
1639                 case ENOBUFS:
1640                         TCP_XMIT_TIMER_ASSERT(tp, len, flags);
1641                         tp->snd_cwnd = tp->t_maxseg;
1642                         return (0);
1643                 case EMSGSIZE:
1644                         /*
1645                          * For some reason the interface we used initially
1646                          * to send segments changed to another or lowered
1647                          * its MTU.
1648                          * If TSO was active we either got an interface
1649                          * without TSO capabilits or TSO was turned off.
1650                          * If we obtained mtu from ip_output() then update
1651                          * it and try again.
1652                          */
1653                         if (tso)
1654                                 tp->t_flags &= ~TF_TSO;
1655                         if (mtu != 0) {
1656                                 tcp_mss_update(tp, -1, mtu, NULL, NULL);
1657                                 goto again;
1658                         }
1659                         return (error);
1660                 case EHOSTDOWN:
1661                 case EHOSTUNREACH:
1662                 case ENETDOWN:
1663                 case ENETUNREACH:
1664                         if (TCPS_HAVERCVDSYN(tp->t_state)) {
1665                                 tp->t_softerror = error;
1666                                 return (0);
1667                         }
1668                         /* FALLTHROUGH */
1669                 default:
1670                         return (error);
1671                 }
1672         }
1673         TCPSTAT_INC(tcps_sndtotal);
1674
1675         /*
1676          * Data sent (as far as we can tell).
1677          * If this advertises a larger window than any other segment,
1678          * then remember the size of the advertised window.
1679          * Any pending ACK has now been sent.
1680          */
1681         if (SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1682                 tp->rcv_adv = tp->rcv_nxt + recwin;
1683         tp->last_ack_sent = tp->rcv_nxt;
1684         tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1685         if (tcp_timer_active(tp, TT_DELACK))
1686                 tcp_timer_activate(tp, TT_DELACK, 0);
1687 #if 0
1688         /*
1689          * This completely breaks TCP if newreno is turned on.  What happens
1690          * is that if delayed-acks are turned on on the receiver, this code
1691          * on the transmitter effectively destroys the TCP window, forcing
1692          * it to four packets (1.5Kx4 = 6K window).
1693          */
1694         if (sendalot && --maxburst)
1695                 goto again;
1696 #endif
1697         if (sendalot)
1698                 goto again;
1699         return (0);
1700 }
1701
1702 void
1703 tcp_setpersist(struct tcpcb *tp)
1704 {
1705         int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1706         int tt;
1707
1708         tp->t_flags &= ~TF_PREVVALID;
1709         if (tcp_timer_active(tp, TT_REXMT))
1710                 panic("tcp_setpersist: retransmit pending");
1711         /*
1712          * Start/restart persistence timer.
1713          */
1714         TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1715                       tcp_persmin, tcp_persmax);
1716         tcp_timer_activate(tp, TT_PERSIST, tt);
1717         if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1718                 tp->t_rxtshift++;
1719 }
1720
1721 /*
1722  * Insert TCP options according to the supplied parameters to the place
1723  * optp in a consistent way.  Can handle unaligned destinations.
1724  *
1725  * The order of the option processing is crucial for optimal packing and
1726  * alignment for the scarce option space.
1727  *
1728  * The optimal order for a SYN/SYN-ACK segment is:
1729  *   MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1730  *   Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1731  *
1732  * The SACK options should be last.  SACK blocks consume 8*n+2 bytes.
1733  * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1734  * At minimum we need 10 bytes (to generate 1 SACK block).  If both
1735  * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1736  * we only have 10 bytes for SACK options (40 - (12 + 18)).
1737  */
1738 int
1739 tcp_addoptions(struct tcpopt *to, u_char *optp)
1740 {
1741         u_int32_t mask, optlen = 0;
1742
1743         for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1744                 if ((to->to_flags & mask) != mask)
1745                         continue;
1746                 if (optlen == TCP_MAXOLEN)
1747                         break;
1748                 switch (to->to_flags & mask) {
1749                 case TOF_MSS:
1750                         while (optlen % 4) {
1751                                 optlen += TCPOLEN_NOP;
1752                                 *optp++ = TCPOPT_NOP;
1753                         }
1754                         if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1755                                 continue;
1756                         optlen += TCPOLEN_MAXSEG;
1757                         *optp++ = TCPOPT_MAXSEG;
1758                         *optp++ = TCPOLEN_MAXSEG;
1759                         to->to_mss = htons(to->to_mss);
1760                         bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1761                         optp += sizeof(to->to_mss);
1762                         break;
1763                 case TOF_SCALE:
1764                         while (!optlen || optlen % 2 != 1) {
1765                                 optlen += TCPOLEN_NOP;
1766                                 *optp++ = TCPOPT_NOP;
1767                         }
1768                         if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1769                                 continue;
1770                         optlen += TCPOLEN_WINDOW;
1771                         *optp++ = TCPOPT_WINDOW;
1772                         *optp++ = TCPOLEN_WINDOW;
1773                         *optp++ = to->to_wscale;
1774                         break;
1775                 case TOF_SACKPERM:
1776                         while (optlen % 2) {
1777                                 optlen += TCPOLEN_NOP;
1778                                 *optp++ = TCPOPT_NOP;
1779                         }
1780                         if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1781                                 continue;
1782                         optlen += TCPOLEN_SACK_PERMITTED;
1783                         *optp++ = TCPOPT_SACK_PERMITTED;
1784                         *optp++ = TCPOLEN_SACK_PERMITTED;
1785                         break;
1786                 case TOF_TS:
1787                         while (!optlen || optlen % 4 != 2) {
1788                                 optlen += TCPOLEN_NOP;
1789                                 *optp++ = TCPOPT_NOP;
1790                         }
1791                         if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1792                                 continue;
1793                         optlen += TCPOLEN_TIMESTAMP;
1794                         *optp++ = TCPOPT_TIMESTAMP;
1795                         *optp++ = TCPOLEN_TIMESTAMP;
1796                         to->to_tsval = htonl(to->to_tsval);
1797                         to->to_tsecr = htonl(to->to_tsecr);
1798                         bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1799                         optp += sizeof(to->to_tsval);
1800                         bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1801                         optp += sizeof(to->to_tsecr);
1802                         break;
1803                 case TOF_SIGNATURE:
1804                         {
1805                         int siglen = TCPOLEN_SIGNATURE - 2;
1806
1807                         while (!optlen || optlen % 4 != 2) {
1808                                 optlen += TCPOLEN_NOP;
1809                                 *optp++ = TCPOPT_NOP;
1810                         }
1811                         if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) {
1812                                 to->to_flags &= ~TOF_SIGNATURE;
1813                                 continue;
1814                         }
1815                         optlen += TCPOLEN_SIGNATURE;
1816                         *optp++ = TCPOPT_SIGNATURE;
1817                         *optp++ = TCPOLEN_SIGNATURE;
1818                         to->to_signature = optp;
1819                         while (siglen--)
1820                                  *optp++ = 0;
1821                         break;
1822                         }
1823                 case TOF_SACK:
1824                         {
1825                         int sackblks = 0;
1826                         struct sackblk *sack = (struct sackblk *)to->to_sacks;
1827                         tcp_seq sack_seq;
1828
1829                         while (!optlen || optlen % 4 != 2) {
1830                                 optlen += TCPOLEN_NOP;
1831                                 *optp++ = TCPOPT_NOP;
1832                         }
1833                         if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1834                                 continue;
1835                         optlen += TCPOLEN_SACKHDR;
1836                         *optp++ = TCPOPT_SACK;
1837                         sackblks = min(to->to_nsacks,
1838                                         (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1839                         *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1840                         while (sackblks--) {
1841                                 sack_seq = htonl(sack->start);
1842                                 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1843                                 optp += sizeof(sack_seq);
1844                                 sack_seq = htonl(sack->end);
1845                                 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1846                                 optp += sizeof(sack_seq);
1847                                 optlen += TCPOLEN_SACK;
1848                                 sack++;
1849                         }
1850                         TCPSTAT_INC(tcps_sack_send_blocks);
1851                         break;
1852                         }
1853                 case TOF_FASTOPEN:
1854                         {
1855                         int total_len;
1856
1857                         /* XXX is there any point to aligning this option? */
1858                         total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len;
1859                         if (TCP_MAXOLEN - optlen < total_len) {
1860                                 to->to_flags &= ~TOF_FASTOPEN;
1861                                 continue;
1862                         }
1863                         *optp++ = TCPOPT_FAST_OPEN;
1864                         *optp++ = total_len;
1865                         if (to->to_tfo_len > 0) {
1866                                 bcopy(to->to_tfo_cookie, optp, to->to_tfo_len);
1867                                 optp += to->to_tfo_len;
1868                         }
1869                         optlen += total_len;
1870                         break;
1871                         }
1872                 default:
1873                         panic("%s: unknown TCP option type", __func__);
1874                         break;
1875                 }
1876         }
1877
1878         /* Terminate and pad TCP options to a 4 byte boundary. */
1879         if (optlen % 4) {
1880                 optlen += TCPOLEN_EOL;
1881                 *optp++ = TCPOPT_EOL;
1882         }
1883         /*
1884          * According to RFC 793 (STD0007):
1885          *   "The content of the header beyond the End-of-Option option
1886          *    must be header padding (i.e., zero)."
1887          *   and later: "The padding is composed of zeros."
1888          */
1889         while (optlen % 4) {
1890                 optlen += TCPOLEN_PAD;
1891                 *optp++ = TCPOPT_PAD;
1892         }
1893
1894         KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));
1895         return (optlen);
1896 }
1897
1898 /*
1899  * This is a copy of m_copym(), taking the TSO segment size/limit
1900  * constraints into account, and advancing the sndptr as it goes.
1901  */
1902 struct mbuf *
1903 tcp_m_copym(struct mbuf *m, int32_t off0, int32_t *plen,
1904     int32_t seglimit, int32_t segsize, struct sockbuf *sb, bool hw_tls)
1905 {
1906 #ifdef KERN_TLS
1907         struct ktls_session *tls, *ntls;
1908         struct mbuf *start;
1909 #endif
1910         struct mbuf *n, **np;
1911         struct mbuf *top;
1912         int32_t off = off0;
1913         int32_t len = *plen;
1914         int32_t fragsize;
1915         int32_t len_cp = 0;
1916         int32_t *pkthdrlen;
1917         uint32_t mlen, frags;
1918         bool copyhdr;
1919
1920         KASSERT(off >= 0, ("tcp_m_copym, negative off %d", off));
1921         KASSERT(len >= 0, ("tcp_m_copym, negative len %d", len));
1922         if (off == 0 && m->m_flags & M_PKTHDR)
1923                 copyhdr = true;
1924         else
1925                 copyhdr = false;
1926         while (off > 0) {
1927                 KASSERT(m != NULL, ("tcp_m_copym, offset > size of mbuf chain"));
1928                 if (off < m->m_len)
1929                         break;
1930                 off -= m->m_len;
1931                 if ((sb) && (m == sb->sb_sndptr)) {
1932                         sb->sb_sndptroff += m->m_len;
1933                         sb->sb_sndptr = m->m_next;
1934                 }
1935                 m = m->m_next;
1936         }
1937         np = &top;
1938         top = NULL;
1939         pkthdrlen = NULL;
1940 #ifdef KERN_TLS
1941         if (hw_tls && (m->m_flags & M_EXTPG))
1942                 tls = m->m_epg_tls;
1943         else
1944                 tls = NULL;
1945         start = m;
1946 #endif
1947         while (len > 0) {
1948                 if (m == NULL) {
1949                         KASSERT(len == M_COPYALL,
1950                             ("tcp_m_copym, length > size of mbuf chain"));
1951                         *plen = len_cp;
1952                         if (pkthdrlen != NULL)
1953                                 *pkthdrlen = len_cp;
1954                         break;
1955                 }
1956 #ifdef KERN_TLS
1957                 if (hw_tls) {
1958                         if (m->m_flags & M_EXTPG)
1959                                 ntls = m->m_epg_tls;
1960                         else
1961                                 ntls = NULL;
1962
1963                         /*
1964                          * Avoid mixing TLS records with handshake
1965                          * data or TLS records from different
1966                          * sessions.
1967                          */
1968                         if (tls != ntls) {
1969                                 MPASS(m != start);
1970                                 *plen = len_cp;
1971                                 if (pkthdrlen != NULL)
1972                                         *pkthdrlen = len_cp;
1973                                 break;
1974                         }
1975                 }
1976 #endif
1977                 mlen = min(len, m->m_len - off);
1978                 if (seglimit) {
1979                         /*
1980                          * For M_EXTPG mbufs, add 3 segments
1981                          * + 1 in case we are crossing page boundaries
1982                          * + 2 in case the TLS hdr/trailer are used
1983                          * It is cheaper to just add the segments
1984                          * than it is to take the cache miss to look
1985                          * at the mbuf ext_pgs state in detail.
1986                          */
1987                         if (m->m_flags & M_EXTPG) {
1988                                 fragsize = min(segsize, PAGE_SIZE);
1989                                 frags = 3;
1990                         } else {
1991                                 fragsize = segsize;
1992                                 frags = 0;
1993                         }
1994
1995                         /* Break if we really can't fit anymore. */
1996                         if ((frags + 1) >= seglimit) {
1997                                 *plen = len_cp;
1998                                 if (pkthdrlen != NULL)
1999                                         *pkthdrlen = len_cp;
2000                                 break;
2001                         }
2002
2003                         /*
2004                          * Reduce size if you can't copy the whole
2005                          * mbuf. If we can't copy the whole mbuf, also
2006                          * adjust len so the loop will end after this
2007                          * mbuf.
2008                          */
2009                         if ((frags + howmany(mlen, fragsize)) >= seglimit) {
2010                                 mlen = (seglimit - frags - 1) * fragsize;
2011                                 len = mlen;
2012                                 *plen = len_cp + len;
2013                                 if (pkthdrlen != NULL)
2014                                         *pkthdrlen = *plen;
2015                         }
2016                         frags += howmany(mlen, fragsize);
2017                         if (frags == 0)
2018                                 frags++;
2019                         seglimit -= frags;
2020                         KASSERT(seglimit > 0,
2021                             ("%s: seglimit went too low", __func__));
2022                 }
2023                 if (copyhdr)
2024                         n = m_gethdr(M_NOWAIT, m->m_type);
2025                 else
2026                         n = m_get(M_NOWAIT, m->m_type);
2027                 *np = n;
2028                 if (n == NULL)
2029                         goto nospace;
2030                 if (copyhdr) {
2031                         if (!m_dup_pkthdr(n, m, M_NOWAIT))
2032                                 goto nospace;
2033                         if (len == M_COPYALL)
2034                                 n->m_pkthdr.len -= off0;
2035                         else
2036                                 n->m_pkthdr.len = len;
2037                         pkthdrlen = &n->m_pkthdr.len;
2038                         copyhdr = false;
2039                 }
2040                 n->m_len = mlen;
2041                 len_cp += n->m_len;
2042                 if (m->m_flags & (M_EXT|M_EXTPG)) {
2043                         n->m_data = m->m_data + off;
2044                         mb_dupcl(n, m);
2045                 } else
2046                         bcopy(mtod(m, caddr_t)+off, mtod(n, caddr_t),
2047                             (u_int)n->m_len);
2048
2049                 if (sb && (sb->sb_sndptr == m) &&
2050                     ((n->m_len + off) >= m->m_len) && m->m_next) {
2051                         sb->sb_sndptroff += m->m_len;
2052                         sb->sb_sndptr = m->m_next;
2053                 }
2054                 off = 0;
2055                 if (len != M_COPYALL) {
2056                         len -= n->m_len;
2057                 }
2058                 m = m->m_next;
2059                 np = &n->m_next;
2060         }
2061         return (top);
2062 nospace:
2063         m_freem(top);
2064         return (NULL);
2065 }
2066
2067 void
2068 tcp_sndbuf_autoscale(struct tcpcb *tp, struct socket *so, uint32_t sendwin)
2069 {
2070
2071         /*
2072          * Automatic sizing of send socket buffer.  Often the send buffer
2073          * size is not optimally adjusted to the actual network conditions
2074          * at hand (delay bandwidth product).  Setting the buffer size too
2075          * small limits throughput on links with high bandwidth and high
2076          * delay (eg. trans-continental/oceanic links).  Setting the
2077          * buffer size too big consumes too much real kernel memory,
2078          * especially with many connections on busy servers.
2079          *
2080          * The criteria to step up the send buffer one notch are:
2081          *  1. receive window of remote host is larger than send buffer
2082          *     (with a fudge factor of 5/4th);
2083          *  2. send buffer is filled to 7/8th with data (so we actually
2084          *     have data to make use of it);
2085          *  3. send buffer fill has not hit maximal automatic size;
2086          *  4. our send window (slow start and cogestion controlled) is
2087          *     larger than sent but unacknowledged data in send buffer.
2088          *
2089          * The remote host receive window scaling factor may limit the
2090          * growing of the send buffer before it reaches its allowed
2091          * maximum.
2092          *
2093          * It scales directly with slow start or congestion window
2094          * and does at most one step per received ACK.  This fast
2095          * scaling has the drawback of growing the send buffer beyond
2096          * what is strictly necessary to make full use of a given
2097          * delay*bandwidth product.  However testing has shown this not
2098          * to be much of an problem.  At worst we are trading wasting
2099          * of available bandwidth (the non-use of it) for wasting some
2100          * socket buffer memory.
2101          *
2102          * TODO: Shrink send buffer during idle periods together
2103          * with congestion window.  Requires another timer.  Has to
2104          * wait for upcoming tcp timer rewrite.
2105          *
2106          * XXXGL: should there be used sbused() or sbavail()?
2107          */
2108         if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
2109                 int lowat;
2110
2111                 lowat = V_tcp_sendbuf_auto_lowat ? so->so_snd.sb_lowat : 0;
2112                 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat - lowat &&
2113                     sbused(&so->so_snd) >=
2114                     (so->so_snd.sb_hiwat / 8 * 7) - lowat &&
2115                     sbused(&so->so_snd) < V_tcp_autosndbuf_max &&
2116                     sendwin >= (sbused(&so->so_snd) -
2117                     (tp->snd_nxt - tp->snd_una))) {
2118                         if (!sbreserve_locked(&so->so_snd,
2119                             min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
2120                              V_tcp_autosndbuf_max), so, curthread))
2121                                 so->so_snd.sb_flags &= ~SB_AUTOSIZE;
2122                 }
2123         }
2124 }