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
  42 #include <sys/param.h>
  43 #include <sys/systm.h>
  44 #include <sys/arb.h>
  45 #include <sys/domain.h>
  46 #ifdef TCP_HHOOK
  47 #include <sys/hhook.h>
  48 #endif
  49 #include <sys/kernel.h>
  50 #ifdef KERN_TLS
  51 #include <sys/ktls.h>
  52 #endif
  53 #include <sys/lock.h>
  54 #include <sys/mbuf.h>
  55 #include <sys/mutex.h>
  56 #include <sys/protosw.h>
  57 #include <sys/qmath.h>
  58 #include <sys/sdt.h>
  59 #include <sys/socket.h>
  60 #include <sys/socketvar.h>
  61 #include <sys/sysctl.h>
  62 #include <sys/stats.h>
  63
  64 #include <net/if.h>
  65 #include <net/route.h>
  66 #include <net/route/nhop.h>
  67 #include <net/vnet.h>
  68
  69 #include <netinet/in.h>
  70 #include <netinet/in_kdtrace.h>
  71 #include <netinet/in_systm.h>
  72 #include <netinet/ip.h>
  73 #include <netinet/in_pcb.h>
  74 #include <netinet/ip_var.h>
  75 #include <netinet/ip_options.h>
  76 #ifdef INET6
  77 #include <netinet6/in6_pcb.h>
  78 #include <netinet/ip6.h>
  79 #include <netinet6/ip6_var.h>
  80 #endif
  81 #include <netinet/tcp.h>
  82 #define TCPOUTFLAGS
  83 #include <netinet/tcp_fsm.h>
  84 #include <netinet/tcp_log_buf.h>
  85 #include <netinet/tcp_seq.h>
  86 #include <netinet/tcp_var.h>
  87 #include <netinet/tcp_syncache.h>
  88 #include <netinet/tcp_timer.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 TCP_OFFLOAD
  96 #include <netinet/tcp_offload.h>
  97 #endif
  98 #include <netinet/tcp_ecn.h>
  99
 100 #include <netipsec/ipsec_support.h>
 101
 102 #include <netinet/udp.h>
 103 #include <netinet/udp_var.h>
 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 #ifdef TCP_HHOOK
 155 /*
 156  * Wrapper for the TCP established output helper hook.
 157  */
 158 void
 159 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
 160     struct tcpopt *to, uint32_t len, int tso)
 161 {
 162         struct tcp_hhook_data hhook_data;
 163
 164         if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
 165                 hhook_data.tp = tp;
 166                 hhook_data.th = th;
 167                 hhook_data.to = to;
 168                 hhook_data.len = len;
 169                 hhook_data.tso = tso;
 170
 171                 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
 172                     &tp->t_osd);
 173         }
 174 }
 175 #endif
 176
 177 /*
 178  * CC wrapper hook functions
 179  */
 180 void
 181 cc_after_idle(struct tcpcb *tp)
 182 {
 183         INP_WLOCK_ASSERT(tptoinpcb(tp));
 184
 185         if (CC_ALGO(tp)->after_idle != NULL)
 186                 CC_ALGO(tp)->after_idle(&tp->t_ccv);
 187 }
 188
 189 /*
 190  * Tcp output routine: figure out what should be sent and send it.
 191  */
 192 int
 193 tcp_default_output(struct tcpcb *tp)
 194 {
 195         struct socket *so = tptosocket(tp);
 196         struct inpcb *inp = tptoinpcb(tp);
 197         int32_t len;
 198         uint32_t recwin, sendwin;
 199         uint16_t flags;
 200         int off, 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         struct tcphdr *th;
 206         u_char opt[TCP_MAXOLEN];
 207         unsigned ipoptlen, optlen, hdrlen, ulen;
 208 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 209         unsigned ipsec_optlen = 0;
 210 #endif
 211         int idle, sendalot, curticks;
 212         int sack_rxmit, sack_bytes_rxmt;
 213         struct sackhole *p;
 214         int tso, mtu;
 215         struct tcpopt to;
 216         struct udphdr *udp = NULL;
 217         struct tcp_log_buffer *lgb;
 218         unsigned int wanted_cookie = 0;
 219         unsigned int dont_sendalot = 0;
 220 #if 0
 221         int maxburst = TCP_MAXBURST;
 222 #endif
 223 #ifdef INET6
 224         struct ip6_hdr *ip6 = NULL;
 225         int isipv6;
 226
 227         isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
 228 #endif
 229 #ifdef KERN_TLS
 230         const bool hw_tls = (so->so_snd.sb_flags & SB_TLS_IFNET) != 0;
 231 #else
 232         const bool hw_tls = false;
 233 #endif
 234
 235         NET_EPOCH_ASSERT();
 236         INP_WLOCK_ASSERT(inp);
 237
 238 #ifdef TCP_OFFLOAD
 239         if (tp->t_flags & TF_TOE)
 240                 return (tcp_offload_output(tp));
 241 #endif
 242
 243         /*
 244          * For TFO connections in SYN_SENT or SYN_RECEIVED,
 245          * only allow the initial SYN or SYN|ACK and those sent
 246          * by the retransmit timer.
 247          */
 248         if (IS_FASTOPEN(tp->t_flags) &&
 249             ((tp->t_state == TCPS_SYN_SENT) ||
 250              (tp->t_state == TCPS_SYN_RECEIVED)) &&
 251             SEQ_GT(tp->snd_max, tp->snd_una) && /* initial SYN or SYN|ACK sent */
 252             (tp->snd_nxt != tp->snd_una))       /* not a retransmit */
 253                 return (0);
 254
 255         /*
 256          * Determine length of data that should be transmitted,
 257          * and flags that will be used.
 258          * If there is some data or critical controls (SYN, RST)
 259          * to send, then transmit; otherwise, investigate further.
 260          */
 261         idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
 262         if (idle && (((ticks - tp->t_rcvtime) >= tp->t_rxtcur) ||
 263             (tp->t_sndtime && ((ticks - tp->t_sndtime) >= tp->t_rxtcur))))
 264                 cc_after_idle(tp);
 265         tp->t_flags &= ~TF_LASTIDLE;
 266         if (idle) {
 267                 if (tp->t_flags & TF_MORETOCOME) {
 268                         tp->t_flags |= TF_LASTIDLE;
 269                         idle = 0;
 270                 }
 271         }
 272 again:
 273         /*
 274          * If we've recently taken a timeout, snd_max will be greater than
 275          * snd_nxt.  There may be SACK information that allows us to avoid
 276          * resending already delivered data.  Adjust snd_nxt accordingly.
 277          */
 278         if ((tp->t_flags & TF_SACK_PERMIT) &&
 279             SEQ_LT(tp->snd_nxt, tp->snd_max))
 280                 tcp_sack_adjust(tp);
 281         sendalot = 0;
 282         tso = 0;
 283         mtu = 0;
 284         off = tp->snd_nxt - tp->snd_una;
 285         sendwin = min(tp->snd_wnd, tp->snd_cwnd);
 286
 287         flags = tcp_outflags[tp->t_state];
 288         /*
 289          * Send any SACK-generated retransmissions.  If we're explicitly trying
 290          * to send out new data (when sendalot is 1), bypass this function.
 291          * If we retransmit in fast recovery mode, decrement snd_cwnd, since
 292          * we're replacing a (future) new transmission with a retransmission
 293          * now, and we previously incremented snd_cwnd in tcp_input().
 294          */
 295         /*
 296          * Still in sack recovery , reset rxmit flag to zero.
 297          */
 298         sack_rxmit = 0;
 299         sack_bytes_rxmt = 0;
 300         len = 0;
 301         p = NULL;
 302         if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
 303             (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
 304                 uint32_t cwin;
 305
 306                 cwin =
 307                     imax(min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt, 0);
 308                 /* Do not retransmit SACK segments beyond snd_recover */
 309                 if (SEQ_GT(p->end, tp->snd_recover)) {
 310                         /*
 311                          * (At least) part of sack hole extends beyond
 312                          * snd_recover. Check to see if we can rexmit data
 313                          * for this hole.
 314                          */
 315                         if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
 316                                 /*
 317                                  * Can't rexmit any more data for this hole.
 318                                  * That data will be rexmitted in the next
 319                                  * sack recovery episode, when snd_recover
 320                                  * moves past p->rxmit.
 321                                  */
 322                                 p = NULL;
 323                                 goto after_sack_rexmit;
 324                         } else {
 325                                 /* Can rexmit part of the current hole */
 326                                 len = ((int32_t)ulmin(cwin,
 327                                     SEQ_SUB(tp->snd_recover, p->rxmit)));
 328                         }
 329                 } else {
 330                         len = ((int32_t)ulmin(cwin,
 331                             SEQ_SUB(p->end, p->rxmit)));
 332                 }
 333                 if (len > 0) {
 334                         off = SEQ_SUB(p->rxmit, tp->snd_una);
 335                         KASSERT(off >= 0,("%s: sack block to the left of una : %d",
 336                             __func__, off));
 337                         sack_rxmit = 1;
 338                         sendalot = 1;
 339                         TCPSTAT_INC(tcps_sack_rexmits);
 340                         TCPSTAT_ADD(tcps_sack_rexmit_bytes,
 341                             min(len, tcp_maxseg(tp)));
 342                 }
 343         }
 344 after_sack_rexmit:
 345         /*
 346          * Get standard flags, and add SYN or FIN if requested by 'hidden'
 347          * state flags.
 348          */
 349         if (tp->t_flags & TF_NEEDFIN)
 350                 flags |= TH_FIN;
 351         if (tp->t_flags & TF_NEEDSYN)
 352                 flags |= TH_SYN;
 353
 354         SOCKBUF_LOCK(&so->so_snd);
 355         /*
 356          * If in persist timeout with window of 0, send 1 byte.
 357          * Otherwise, if window is small but nonzero
 358          * and timer expired, we will send what we can
 359          * and go to transmit state.
 360          */
 361         if (tp->t_flags & TF_FORCEDATA) {
 362                 if (sendwin == 0) {
 363                         /*
 364                          * If we still have some data to send, then
 365                          * clear the FIN bit.  Usually this would
 366                          * happen below when it realizes that we
 367                          * aren't sending all the data.  However,
 368                          * if we have exactly 1 byte of unsent data,
 369                          * then it won't clear the FIN bit below,
 370                          * and if we are in persist state, we wind
 371                          * up sending the packet without recording
 372                          * that we sent the FIN bit.
 373                          *
 374                          * We can't just blindly clear the FIN bit,
 375                          * because if we don't have any more data
 376                          * to send then the probe will be the FIN
 377                          * itself.
 378                          */
 379                         if (off < sbused(&so->so_snd))
 380                                 flags &= ~TH_FIN;
 381                         sendwin = 1;
 382                 } else {
 383                         tcp_timer_activate(tp, TT_PERSIST, 0);
 384                         tp->t_rxtshift = 0;
 385                 }
 386         }
 387
 388         /*
 389          * If snd_nxt == snd_max and we have transmitted a FIN, the
 390          * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
 391          * a negative length.  This can also occur when TCP opens up
 392          * its congestion window while receiving additional duplicate
 393          * acks after fast-retransmit because TCP will reset snd_nxt
 394          * to snd_max after the fast-retransmit.
 395          *
 396          * In the normal retransmit-FIN-only case, however, snd_nxt will
 397          * be set to snd_una, the offset will be 0, and the length may
 398          * wind up 0.
 399          *
 400          * If sack_rxmit is true we are retransmitting from the scoreboard
 401          * in which case len is already set.
 402          */
 403         if (sack_rxmit == 0) {
 404                 if (sack_bytes_rxmt == 0)
 405                         len = ((int32_t)min(sbavail(&so->so_snd), sendwin) -
 406                             off);
 407                 else {
 408                         int32_t cwin;
 409
 410                         /*
 411                          * We are inside of a SACK recovery episode and are
 412                          * sending new data, having retransmitted all the
 413                          * data possible in the scoreboard.
 414                          */
 415                         len = ((int32_t)min(sbavail(&so->so_snd), tp->snd_wnd) -
 416                             off);
 417                         /*
 418                          * Don't remove this (len > 0) check !
 419                          * We explicitly check for len > 0 here (although it
 420                          * isn't really necessary), to work around a gcc
 421                          * optimization issue - to force gcc to compute
 422                          * len above. Without this check, the computation
 423                          * of len is bungled by the optimizer.
 424                          */
 425                         if (len > 0) {
 426                                 cwin = tp->snd_cwnd - imax(0, (int32_t)
 427                                         (tp->snd_nxt - tp->snd_recover)) -
 428                                         sack_bytes_rxmt;
 429                                 if (cwin < 0)
 430                                         cwin = 0;
 431                                 len = imin(len, cwin);
 432                         }
 433                 }
 434         }
 435
 436         /*
 437          * Lop off SYN bit if it has already been sent.  However, if this
 438          * is SYN-SENT state and if segment contains data and if we don't
 439          * know that foreign host supports TAO, suppress sending segment.
 440          */
 441         if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
 442                 if (tp->t_state != TCPS_SYN_RECEIVED)
 443                         flags &= ~TH_SYN;
 444                 /*
 445                  * When sending additional segments following a TFO SYN|ACK,
 446                  * do not include the SYN bit.
 447                  */
 448                 if (IS_FASTOPEN(tp->t_flags) &&
 449                     (tp->t_state == TCPS_SYN_RECEIVED))
 450                         flags &= ~TH_SYN;
 451                 off--, len++;
 452         }
 453
 454         /*
 455          * Be careful not to send data and/or FIN on SYN segments.
 456          * This measure is needed to prevent interoperability problems
 457          * with not fully conformant TCP implementations.
 458          */
 459         if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
 460                 len = 0;
 461                 flags &= ~TH_FIN;
 462         }
 463
 464         /*
 465          * On TFO sockets, ensure no data is sent in the following cases:
 466          *
 467          *  - When retransmitting SYN|ACK on a passively-created socket
 468          *
 469          *  - When retransmitting SYN on an actively created socket
 470          *
 471          *  - When sending a zero-length cookie (cookie request) on an
 472          *    actively created socket
 473          *
 474          *  - When the socket is in the CLOSED state (RST is being sent)
 475          */
 476         if (IS_FASTOPEN(tp->t_flags) &&
 477             (((flags & TH_SYN) && (tp->t_rxtshift > 0)) ||
 478              ((tp->t_state == TCPS_SYN_SENT) &&
 479               (tp->t_tfo_client_cookie_len == 0)) ||
 480              (flags & TH_RST)))
 481                 len = 0;
 482         if (len <= 0) {
 483                 /*
 484                  * If FIN has been sent but not acked,
 485                  * but we haven't been called to retransmit,
 486                  * len will be < 0.  Otherwise, window shrank
 487                  * after we sent into it.  If window shrank to 0,
 488                  * cancel pending retransmit, pull snd_nxt back
 489                  * to (closed) window, and set the persist timer
 490                  * if it isn't already going.  If the window didn't
 491                  * close completely, just wait for an ACK.
 492                  *
 493                  * We also do a general check here to ensure that
 494                  * we will set the persist timer when we have data
 495                  * to send, but a 0-byte window. This makes sure
 496                  * the persist timer is set even if the packet
 497                  * hits one of the "goto send" lines below.
 498                  */
 499                 len = 0;
 500                 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
 501                     (off < (int) sbavail(&so->so_snd)) &&
 502                     !tcp_timer_active(tp, TT_PERSIST)) {
 503                         tcp_timer_activate(tp, TT_REXMT, 0);
 504                         tp->t_rxtshift = 0;
 505                         tp->snd_nxt = tp->snd_una;
 506                         if (!tcp_timer_active(tp, TT_PERSIST))
 507                                 tcp_setpersist(tp);
 508                 }
 509         }
 510
 511         /* len will be >= 0 after this point. */
 512         KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
 513
 514         tcp_sndbuf_autoscale(tp, so, sendwin);
 515
 516         /*
 517          * Decide if we can use TCP Segmentation Offloading (if supported by
 518          * hardware).
 519          *
 520          * TSO may only be used if we are in a pure bulk sending state.  The
 521          * presence of TCP-MD5, SACK retransmits, SACK advertizements and
 522          * IP options prevent using TSO.  With TSO the TCP header is the same
 523          * (except for the sequence number) for all generated packets.  This
 524          * makes it impossible to transmit any options which vary per generated
 525          * segment or packet.
 526          *
 527          * IPv4 handling has a clear separation of ip options and ip header
 528          * flags while IPv6 combines both in in6p_outputopts. ip6_optlen() does
 529          * the right thing below to provide length of just ip options and thus
 530          * checking for ipoptlen is enough to decide if ip options are present.
 531          */
 532 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 533         /*
 534          * Pre-calculate here as we save another lookup into the darknesses
 535          * of IPsec that way and can actually decide if TSO is ok.
 536          */
 537 #ifdef INET6
 538         if (isipv6 && IPSEC_ENABLED(ipv6))
 539                 ipsec_optlen = IPSEC_HDRSIZE(ipv6, inp);
 540 #ifdef INET
 541         else
 542 #endif
 543 #endif /* INET6 */
 544 #ifdef INET
 545         if (IPSEC_ENABLED(ipv4))
 546                 ipsec_optlen = IPSEC_HDRSIZE(ipv4, inp);
 547 #endif /* INET */
 548 #endif /* IPSEC */
 549 #ifdef INET6
 550         if (isipv6)
 551                 ipoptlen = ip6_optlen(inp);
 552         else
 553 #endif
 554         if (inp->inp_options)
 555                 ipoptlen = inp->inp_options->m_len -
 556                                 offsetof(struct ipoption, ipopt_list);
 557         else
 558                 ipoptlen = 0;
 559 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 560         ipoptlen += ipsec_optlen;
 561 #endif
 562
 563         if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
 564             (tp->t_port == 0) &&
 565             ((tp->t_flags & TF_SIGNATURE) == 0) &&
 566             tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
 567             ipoptlen == 0 && !(flags & TH_SYN))
 568                 tso = 1;
 569
 570         if (sack_rxmit) {
 571                 if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
 572                         flags &= ~TH_FIN;
 573         } else {
 574                 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
 575                     sbused(&so->so_snd)))
 576                         flags &= ~TH_FIN;
 577         }
 578
 579         recwin = lmin(lmax(sbspace(&so->so_rcv), 0),
 580             (long)TCP_MAXWIN << tp->rcv_scale);
 581
 582         /*
 583          * Sender silly window avoidance.   We transmit under the following
 584          * conditions when len is non-zero:
 585          *
 586          *      - We have a full segment (or more with TSO)
 587          *      - This is the last buffer in a write()/send() and we are
 588          *        either idle or running NODELAY
 589          *      - we've timed out (e.g. persist timer)
 590          *      - we have more then 1/2 the maximum send window's worth of
 591          *        data (receiver may be limited the window size)
 592          *      - we need to retransmit
 593          */
 594         if (len) {
 595                 if (len >= tp->t_maxseg)
 596                         goto send;
 597                 /*
 598                  * As the TCP header options are now
 599                  * considered when setting up the initial
 600                  * window, we would not send the last segment
 601                  * if we skip considering the option length here.
 602                  * Note: this may not work when tcp headers change
 603                  * very dynamically in the future.
 604                  */
 605                 if ((((tp->t_flags & TF_SIGNATURE) ?
 606                         PADTCPOLEN(TCPOLEN_SIGNATURE) : 0) +
 607                     ((tp->t_flags & TF_RCVD_TSTMP) ?
 608                         PADTCPOLEN(TCPOLEN_TIMESTAMP) : 0) +
 609                     len) >= tp->t_maxseg)
 610                         goto send;
 611                 /*
 612                  * NOTE! on localhost connections an 'ack' from the remote
 613                  * end may occur synchronously with the output and cause
 614                  * us to flush a buffer queued with moretocome.  XXX
 615                  *
 616                  * note: the len + off check is almost certainly unnecessary.
 617                  */
 618                 if (!(tp->t_flags & TF_MORETOCOME) &&   /* normal case */
 619                     (idle || (tp->t_flags & TF_NODELAY)) &&
 620                     (uint32_t)len + (uint32_t)off >= sbavail(&so->so_snd) &&
 621                     (tp->t_flags & TF_NOPUSH) == 0) {
 622                         goto send;
 623                 }
 624                 if (tp->t_flags & TF_FORCEDATA)         /* typ. timeout case */
 625                         goto send;
 626                 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
 627                         goto send;
 628                 if (SEQ_LT(tp->snd_nxt, tp->snd_max))   /* retransmit case */
 629                         goto send;
 630                 if (sack_rxmit)
 631                         goto send;
 632         }
 633
 634         /*
 635          * Sending of standalone window updates.
 636          *
 637          * Window updates are important when we close our window due to a
 638          * full socket buffer and are opening it again after the application
 639          * reads data from it.  Once the window has opened again and the
 640          * remote end starts to send again the ACK clock takes over and
 641          * provides the most current window information.
 642          *
 643          * We must avoid the silly window syndrome whereas every read
 644          * from the receive buffer, no matter how small, causes a window
 645          * update to be sent.  We also should avoid sending a flurry of
 646          * window updates when the socket buffer had queued a lot of data
 647          * and the application is doing small reads.
 648          *
 649          * Prevent a flurry of pointless window updates by only sending
 650          * an update when we can increase the advertized window by more
 651          * than 1/4th of the socket buffer capacity.  When the buffer is
 652          * getting full or is very small be more aggressive and send an
 653          * update whenever we can increase by two mss sized segments.
 654          * In all other situations the ACK's to new incoming data will
 655          * carry further window increases.
 656          *
 657          * Don't send an independent window update if a delayed
 658          * ACK is pending (it will get piggy-backed on it) or the
 659          * remote side already has done a half-close and won't send
 660          * more data.  Skip this if the connection is in T/TCP
 661          * half-open state.
 662          */
 663         if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
 664             !(tp->t_flags & TF_DELACK) &&
 665             !TCPS_HAVERCVDFIN(tp->t_state)) {
 666                 /*
 667                  * "adv" is the amount we could increase the window,
 668                  * taking into account that we are limited by
 669                  * TCP_MAXWIN << tp->rcv_scale.
 670                  */
 671                 int32_t adv;
 672                 int oldwin;
 673
 674                 adv = recwin;
 675                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
 676                         oldwin = (tp->rcv_adv - tp->rcv_nxt);
 677                         if (adv > oldwin)
 678                                 adv -= oldwin;
 679                         else
 680                                 adv = 0;
 681                 } else
 682                         oldwin = 0;
 683
 684                 /*
 685                  * If the new window size ends up being the same as or less
 686                  * than the old size when it is scaled, then don't force
 687                  * a window update.
 688                  */
 689                 if (oldwin >> tp->rcv_scale >= (adv + oldwin) >> tp->rcv_scale)
 690                         goto dontupdate;
 691
 692                 if (adv >= (int32_t)(2 * tp->t_maxseg) &&
 693                     (adv >= (int32_t)(so->so_rcv.sb_hiwat / 4) ||
 694                      recwin <= (so->so_rcv.sb_hiwat / 8) ||
 695                      so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg ||
 696                      adv >= TCP_MAXWIN << tp->rcv_scale))
 697                         goto send;
 698                 if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat)
 699                         goto send;
 700         }
 701 dontupdate:
 702
 703         /*
 704          * Send if we owe the peer an ACK, RST, SYN, or urgent data.  ACKNOW
 705          * is also a catch-all for the retransmit timer timeout case.
 706          */
 707         if (tp->t_flags & TF_ACKNOW)
 708                 goto send;
 709         if ((flags & TH_RST) ||
 710             ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
 711                 goto send;
 712         if (SEQ_GT(tp->snd_up, tp->snd_una))
 713                 goto send;
 714         /*
 715          * If our state indicates that FIN should be sent
 716          * and we have not yet done so, then we need to send.
 717          */
 718         if (flags & TH_FIN &&
 719             ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
 720                 goto send;
 721         /*
 722          * In SACK, it is possible for tcp_output to fail to send a segment
 723          * after the retransmission timer has been turned off.  Make sure
 724          * that the retransmission timer is set.
 725          */
 726         if ((tp->t_flags & TF_SACK_PERMIT) &&
 727             SEQ_GT(tp->snd_max, tp->snd_una) &&
 728             !tcp_timer_active(tp, TT_REXMT) &&
 729             !tcp_timer_active(tp, TT_PERSIST)) {
 730                 tcp_timer_activate(tp, TT_REXMT, TP_RXTCUR(tp));
 731                 goto just_return;
 732         }
 733         /*
 734          * TCP window updates are not reliable, rather a polling protocol
 735          * using ``persist'' packets is used to insure receipt of window
 736          * updates.  The three ``states'' for the output side are:
 737          *      idle                    not doing retransmits or persists
 738          *      persisting              to move a small or zero window
 739          *      (re)transmitting        and thereby not persisting
 740          *
 741          * tcp_timer_active(tp, TT_PERSIST)
 742          *      is true when we are in persist state.
 743          * (tp->t_flags & TF_FORCEDATA)
 744          *      is set when we are called to send a persist packet.
 745          * tcp_timer_active(tp, TT_REXMT)
 746          *      is set when we are retransmitting
 747          * The output side is idle when both timers are zero.
 748          *
 749          * If send window is too small, there is data to transmit, and no
 750          * retransmit or persist is pending, then go to persist state.
 751          * If nothing happens soon, send when timer expires:
 752          * if window is nonzero, transmit what we can,
 753          * otherwise force out a byte.
 754          */
 755         if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) &&
 756             !tcp_timer_active(tp, TT_PERSIST)) {
 757                 tp->t_rxtshift = 0;
 758                 tcp_setpersist(tp);
 759         }
 760
 761         /*
 762          * No reason to send a segment, just return.
 763          */
 764 just_return:
 765         SOCKBUF_UNLOCK(&so->so_snd);
 766         return (0);
 767
 768 send:
 769         SOCKBUF_LOCK_ASSERT(&so->so_snd);
 770         if (len > 0) {
 771                 if (len >= tp->t_maxseg)
 772                         tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
 773                 else
 774                         tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
 775         }
 776         /*
 777          * Before ESTABLISHED, force sending of initial options
 778          * unless TCP set not to do any options.
 779          * NOTE: we assume that the IP/TCP header plus TCP options
 780          * always fit in a single mbuf, leaving room for a maximum
 781          * link header, i.e.
 782          *      max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
 783          */
 784         optlen = 0;
 785 #ifdef INET6
 786         if (isipv6)
 787                 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
 788         else
 789 #endif
 790                 hdrlen = sizeof (struct tcpiphdr);
 791
 792         if (flags & TH_SYN) {
 793                 tp->snd_nxt = tp->iss;
 794         }
 795
 796         /*
 797          * Compute options for segment.
 798          * We only have to care about SYN and established connection
 799          * segments.  Options for SYN-ACK segments are handled in TCP
 800          * syncache.
 801          */
 802         to.to_flags = 0;
 803         if ((tp->t_flags & TF_NOOPT) == 0) {
 804                 /* Maximum segment size. */
 805                 if (flags & TH_SYN) {
 806                         to.to_mss = tcp_mssopt(&inp->inp_inc);
 807                         if (tp->t_port)
 808                                 to.to_mss -= V_tcp_udp_tunneling_overhead;
 809                         to.to_flags |= TOF_MSS;
 810
 811                         /*
 812                          * On SYN or SYN|ACK transmits on TFO connections,
 813                          * only include the TFO option if it is not a
 814                          * retransmit, as the presence of the TFO option may
 815                          * have caused the original SYN or SYN|ACK to have
 816                          * been dropped by a middlebox.
 817                          */
 818                         if (IS_FASTOPEN(tp->t_flags) &&
 819                             (tp->t_rxtshift == 0)) {
 820                                 if (tp->t_state == TCPS_SYN_RECEIVED) {
 821                                         to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
 822                                         to.to_tfo_cookie =
 823                                             (u_int8_t *)&tp->t_tfo_cookie.server;
 824                                         to.to_flags |= TOF_FASTOPEN;
 825                                         wanted_cookie = 1;
 826                                 } else if (tp->t_state == TCPS_SYN_SENT) {
 827                                         to.to_tfo_len =
 828                                             tp->t_tfo_client_cookie_len;
 829                                         to.to_tfo_cookie =
 830                                             tp->t_tfo_cookie.client;
 831                                         to.to_flags |= TOF_FASTOPEN;
 832                                         wanted_cookie = 1;
 833                                         /*
 834                                          * If we wind up having more data to
 835                                          * send with the SYN than can fit in
 836                                          * one segment, don't send any more
 837                                          * until the SYN|ACK comes back from
 838                                          * the other end.
 839                                          */
 840                                         dont_sendalot = 1;
 841                                 }
 842                         }
 843                 }
 844                 /* Window scaling. */
 845                 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
 846                         to.to_wscale = tp->request_r_scale;
 847                         to.to_flags |= TOF_SCALE;
 848                 }
 849                 /* Timestamps. */
 850                 if ((tp->t_flags & TF_RCVD_TSTMP) ||
 851                     ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
 852                         curticks = tcp_ts_getticks();
 853                         to.to_tsval = curticks + tp->ts_offset;
 854                         to.to_tsecr = tp->ts_recent;
 855                         to.to_flags |= TOF_TS;
 856                         if (tp->t_rxtshift == 1)
 857                                 tp->t_badrxtwin = curticks;
 858                 }
 859
 860                 /* Set receive buffer autosizing timestamp. */
 861                 if (tp->rfbuf_ts == 0 &&
 862                     (so->so_rcv.sb_flags & SB_AUTOSIZE))
 863                         tp->rfbuf_ts = tcp_ts_getticks();
 864
 865                 /* Selective ACK's. */
 866                 if (tp->t_flags & TF_SACK_PERMIT) {
 867                         if (flags & TH_SYN)
 868                                 to.to_flags |= TOF_SACKPERM;
 869                         else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
 870                             tp->rcv_numsacks > 0) {
 871                                 to.to_flags |= TOF_SACK;
 872                                 to.to_nsacks = tp->rcv_numsacks;
 873                                 to.to_sacks = (u_char *)tp->sackblks;
 874                         }
 875                 }
 876 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 877                 /* TCP-MD5 (RFC2385). */
 878                 /*
 879                  * Check that TCP_MD5SIG is enabled in tcpcb to
 880                  * account the size needed to set this TCP option.
 881                  */
 882                 if (tp->t_flags & TF_SIGNATURE)
 883                         to.to_flags |= TOF_SIGNATURE;
 884 #endif /* TCP_SIGNATURE */
 885
 886                 /* Processing the options. */
 887                 hdrlen += optlen = tcp_addoptions(&to, opt);
 888                 /*
 889                  * If we wanted a TFO option to be added, but it was unable
 890                  * to fit, ensure no data is sent.
 891                  */
 892                 if (IS_FASTOPEN(tp->t_flags) && wanted_cookie &&
 893                     !(to.to_flags & TOF_FASTOPEN))
 894                         len = 0;
 895         }
 896         if (tp->t_port) {
 897                 if (V_tcp_udp_tunneling_port == 0) {
 898                         /* The port was removed?? */
 899                         SOCKBUF_UNLOCK(&so->so_snd);
 900                         return (EHOSTUNREACH);
 901                 }
 902                 hdrlen += sizeof(struct udphdr);
 903         }
 904         /*
 905          * Adjust data length if insertion of options will
 906          * bump the packet length beyond the t_maxseg length.
 907          * Clear the FIN bit because we cut off the tail of
 908          * the segment.
 909          */
 910         if (len + optlen + ipoptlen > tp->t_maxseg) {
 911                 flags &= ~TH_FIN;
 912
 913                 if (tso) {
 914                         u_int if_hw_tsomax;
 915                         u_int moff;
 916                         int max_len;
 917
 918                         /* extract TSO information */
 919                         if_hw_tsomax = tp->t_tsomax;
 920                         if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
 921                         if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
 922
 923                         /*
 924                          * Limit a TSO burst to prevent it from
 925                          * overflowing or exceeding the maximum length
 926                          * allowed by the network interface:
 927                          */
 928                         KASSERT(ipoptlen == 0,
 929                             ("%s: TSO can't do IP options", __func__));
 930
 931                         /*
 932                          * Check if we should limit by maximum payload
 933                          * length:
 934                          */
 935                         if (if_hw_tsomax != 0) {
 936                                 /* compute maximum TSO length */
 937                                 max_len = (if_hw_tsomax - hdrlen -
 938                                     max_linkhdr);
 939                                 if (max_len <= 0) {
 940                                         len = 0;
 941                                 } else if (len > max_len) {
 942                                         sendalot = 1;
 943                                         len = max_len;
 944                                 }
 945                         }
 946
 947                         /*
 948                          * Prevent the last segment from being
 949                          * fractional unless the send sockbuf can be
 950                          * emptied:
 951                          */
 952                         max_len = (tp->t_maxseg - optlen);
 953                         if (((uint32_t)off + (uint32_t)len) <
 954                             sbavail(&so->so_snd)) {
 955                                 moff = len % max_len;
 956                                 if (moff != 0) {
 957                                         len -= moff;
 958                                         sendalot = 1;
 959                                 }
 960                         }
 961
 962                         /*
 963                          * In case there are too many small fragments
 964                          * don't use TSO:
 965                          */
 966                         if (len <= max_len) {
 967                                 len = max_len;
 968                                 sendalot = 1;
 969                                 tso = 0;
 970                         }
 971
 972                         /*
 973                          * Send the FIN in a separate segment
 974                          * after the bulk sending is done.
 975                          * We don't trust the TSO implementations
 976                          * to clear the FIN flag on all but the
 977                          * last segment.
 978                          */
 979                         if (tp->t_flags & TF_NEEDFIN)
 980                                 sendalot = 1;
 981                 } else {
 982                         if (optlen + ipoptlen >= tp->t_maxseg) {
 983                                 /*
 984                                  * Since we don't have enough space to put
 985                                  * the IP header chain and the TCP header in
 986                                  * one packet as required by RFC 7112, don't
 987                                  * send it. Also ensure that at least one
 988                                  * byte of the payload can be put into the
 989                                  * TCP segment.
 990                                  */
 991                                 SOCKBUF_UNLOCK(&so->so_snd);
 992                                 error = EMSGSIZE;
 993                                 sack_rxmit = 0;
 994                                 goto out;
 995                         }
 996                         len = tp->t_maxseg - optlen - ipoptlen;
 997                         sendalot = 1;
 998                         if (dont_sendalot)
 999                                 sendalot = 0;
1000                 }
1001         } else
1002                 tso = 0;
1003
1004         KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
1005             ("%s: len > IP_MAXPACKET", __func__));
1006
1007 /*#ifdef DIAGNOSTIC*/
1008 #ifdef INET6
1009         if (max_linkhdr + hdrlen > MCLBYTES)
1010 #else
1011         if (max_linkhdr + hdrlen > MHLEN)
1012 #endif
1013                 panic("tcphdr too big");
1014 /*#endif*/
1015
1016         /*
1017          * This KASSERT is here to catch edge cases at a well defined place.
1018          * Before, those had triggered (random) panic conditions further down.
1019          */
1020         KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
1021
1022         /*
1023          * Grab a header mbuf, attaching a copy of data to
1024          * be transmitted, and initialize the header from
1025          * the template for sends on this connection.
1026          */
1027         if (len) {
1028                 struct mbuf *mb;
1029                 struct sockbuf *msb;
1030                 u_int moff;
1031
1032                 if ((tp->t_flags & TF_FORCEDATA) && len == 1) {
1033                         TCPSTAT_INC(tcps_sndprobe);
1034 #ifdef STATS
1035                         if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1036                                 stats_voi_update_abs_u32(tp->t_stats,
1037                                 VOI_TCP_RETXPB, len);
1038                         else
1039                                 stats_voi_update_abs_u64(tp->t_stats,
1040                                     VOI_TCP_TXPB, len);
1041 #endif /* STATS */
1042                 } else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
1043                         tp->t_sndrexmitpack++;
1044                         TCPSTAT_INC(tcps_sndrexmitpack);
1045                         TCPSTAT_ADD(tcps_sndrexmitbyte, len);
1046 #ifdef STATS
1047                         stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_RETXPB,
1048                             len);
1049 #endif /* STATS */
1050                 } else {
1051                         TCPSTAT_INC(tcps_sndpack);
1052                         TCPSTAT_ADD(tcps_sndbyte, len);
1053 #ifdef STATS
1054                         stats_voi_update_abs_u64(tp->t_stats, VOI_TCP_TXPB,
1055                             len);
1056 #endif /* STATS */
1057                 }
1058 #ifdef INET6
1059                 if (MHLEN < hdrlen + max_linkhdr)
1060                         m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
1061                 else
1062 #endif
1063                         m = m_gethdr(M_NOWAIT, MT_DATA);
1064
1065                 if (m == NULL) {
1066                         SOCKBUF_UNLOCK(&so->so_snd);
1067                         error = ENOBUFS;
1068                         sack_rxmit = 0;
1069                         goto out;
1070                 }
1071
1072                 m->m_data += max_linkhdr;
1073                 m->m_len = hdrlen;
1074
1075                 /*
1076                  * Start the m_copy functions from the closest mbuf
1077                  * to the offset in the socket buffer chain.
1078                  */
1079                 mb = sbsndptr_noadv(&so->so_snd, off, &moff);
1080                 if (len <= MHLEN - hdrlen - max_linkhdr && !hw_tls) {
1081                         m_copydata(mb, moff, len,
1082                             mtod(m, caddr_t) + hdrlen);
1083                         if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1084                                 sbsndptr_adv(&so->so_snd, mb, len);
1085                         m->m_len += len;
1086                 } else {
1087                         if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1088                                 msb = NULL;
1089                         else
1090                                 msb = &so->so_snd;
1091                         m->m_next = tcp_m_copym(mb, moff,
1092                             &len, if_hw_tsomaxsegcount,
1093                             if_hw_tsomaxsegsize, msb, hw_tls);
1094                         if (len <= (tp->t_maxseg - optlen)) {
1095                                 /*
1096                                  * Must have ran out of mbufs for the copy
1097                                  * shorten it to no longer need tso. Lets
1098                                  * not put on sendalot since we are low on
1099                                  * mbufs.
1100                                  */
1101                                 tso = 0;
1102                         }
1103                         if (m->m_next == NULL) {
1104                                 SOCKBUF_UNLOCK(&so->so_snd);
1105                                 (void) m_free(m);
1106                                 error = ENOBUFS;
1107                                 sack_rxmit = 0;
1108                                 goto out;
1109                         }
1110                 }
1111
1112                 /*
1113                  * If we're sending everything we've got, set PUSH.
1114                  * (This will keep happy those implementations which only
1115                  * give data to the user when a buffer fills or
1116                  * a PUSH comes in.)
1117                  */
1118                 if (((uint32_t)off + (uint32_t)len == sbused(&so->so_snd)) &&
1119                     !(flags & TH_SYN))
1120                         flags |= TH_PUSH;
1121                 SOCKBUF_UNLOCK(&so->so_snd);
1122         } else {
1123                 SOCKBUF_UNLOCK(&so->so_snd);
1124                 if (tp->t_flags & TF_ACKNOW)
1125                         TCPSTAT_INC(tcps_sndacks);
1126                 else if (flags & (TH_SYN|TH_FIN|TH_RST))
1127                         TCPSTAT_INC(tcps_sndctrl);
1128                 else if (SEQ_GT(tp->snd_up, tp->snd_una))
1129                         TCPSTAT_INC(tcps_sndurg);
1130                 else
1131                         TCPSTAT_INC(tcps_sndwinup);
1132
1133                 m = m_gethdr(M_NOWAIT, MT_DATA);
1134                 if (m == NULL) {
1135                         error = ENOBUFS;
1136                         sack_rxmit = 0;
1137                         goto out;
1138                 }
1139 #ifdef INET6
1140                 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
1141                     MHLEN >= hdrlen) {
1142                         M_ALIGN(m, hdrlen);
1143                 } else
1144 #endif
1145                 m->m_data += max_linkhdr;
1146                 m->m_len = hdrlen;
1147         }
1148         SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
1149         m->m_pkthdr.rcvif = (struct ifnet *)0;
1150 #ifdef MAC
1151         mac_inpcb_create_mbuf(inp, m);
1152 #endif
1153 #ifdef INET6
1154         if (isipv6) {
1155                 ip6 = mtod(m, struct ip6_hdr *);
1156                 if (tp->t_port) {
1157                         udp = (struct udphdr *)((caddr_t)ip6 + sizeof(struct ip6_hdr));
1158                         udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1159                         udp->uh_dport = tp->t_port;
1160                         ulen = hdrlen + len - sizeof(struct ip6_hdr);
1161                         udp->uh_ulen = htons(ulen);
1162                         th = (struct tcphdr *)(udp + 1);
1163                 } else {
1164                         th = (struct tcphdr *)(ip6 + 1);
1165                 }
1166                 tcpip_fillheaders(inp, tp->t_port, ip6, th);
1167         } else
1168 #endif /* INET6 */
1169         {
1170                 ip = mtod(m, struct ip *);
1171                 if (tp->t_port) {
1172                         udp = (struct udphdr *)((caddr_t)ip + sizeof(struct ip));
1173                         udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1174                         udp->uh_dport = tp->t_port;
1175                         ulen = hdrlen + len - sizeof(struct ip);
1176                         udp->uh_ulen = htons(ulen);
1177                         th = (struct tcphdr *)(udp + 1);
1178                 } else
1179                         th = (struct tcphdr *)(ip + 1);
1180                 tcpip_fillheaders(inp, tp->t_port, ip, th);
1181         }
1182
1183         /*
1184          * Fill in fields, remembering maximum advertised
1185          * window for use in delaying messages about window sizes.
1186          * If resending a FIN, be sure not to use a new sequence number.
1187          */
1188         if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1189             tp->snd_nxt == tp->snd_max)
1190                 tp->snd_nxt--;
1191         /*
1192          * If we are starting a connection, send ECN setup
1193          * SYN packet. If we are on a retransmit, we may
1194          * resend those bits a number of times as per
1195          * RFC 3168.
1196          */
1197         if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn) {
1198                 flags |= tcp_ecn_output_syn_sent(tp);
1199         }
1200         /* Also handle parallel SYN for ECN */
1201         if ((TCPS_HAVERCVDSYN(tp->t_state)) &&
1202             (tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT))) {
1203                 int ect = tcp_ecn_output_established(tp, &flags, len, sack_rxmit);
1204                 if ((tp->t_state == TCPS_SYN_RECEIVED) &&
1205                     (tp->t_flags2 & TF2_ECN_SND_ECE))
1206                         tp->t_flags2 &= ~TF2_ECN_SND_ECE;
1207 #ifdef INET6
1208                 if (isipv6) {
1209                         ip6->ip6_flow &= ~htonl(IPTOS_ECN_MASK << 20);
1210                         ip6->ip6_flow |= htonl(ect << 20);
1211                 }
1212                 else
1213 #endif
1214                 {
1215                         ip->ip_tos &= ~IPTOS_ECN_MASK;
1216                         ip->ip_tos |= ect;
1217                 }
1218         }
1219
1220         /*
1221          * If we are doing retransmissions, then snd_nxt will
1222          * not reflect the first unsent octet.  For ACK only
1223          * packets, we do not want the sequence number of the
1224          * retransmitted packet, we want the sequence number
1225          * of the next unsent octet.  So, if there is no data
1226          * (and no SYN or FIN), use snd_max instead of snd_nxt
1227          * when filling in ti_seq.  But if we are in persist
1228          * state, snd_max might reflect one byte beyond the
1229          * right edge of the window, so use snd_nxt in that
1230          * case, since we know we aren't doing a retransmission.
1231          * (retransmit and persist are mutually exclusive...)
1232          */
1233         if (sack_rxmit == 0) {
1234                 if (len || (flags & (TH_SYN|TH_FIN)) ||
1235                     tcp_timer_active(tp, TT_PERSIST))
1236                         th->th_seq = htonl(tp->snd_nxt);
1237                 else
1238                         th->th_seq = htonl(tp->snd_max);
1239         } else {
1240                 th->th_seq = htonl(p->rxmit);
1241                 p->rxmit += len;
1242                 /*
1243                  * Lost Retransmission Detection
1244                  * trigger resending of a (then
1245                  * still existing) hole, when
1246                  * fack acks recoverypoint.
1247                  */
1248                 if ((tp->t_flags & TF_LRD) && SEQ_GEQ(p->rxmit, p->end))
1249                         p->rxmit = tp->snd_recover;
1250                 tp->sackhint.sack_bytes_rexmit += len;
1251         }
1252         if (IN_RECOVERY(tp->t_flags)) {
1253                 /*
1254                  * Account all bytes transmitted while
1255                  * IN_RECOVERY, simplifying PRR and
1256                  * Lost Retransmit Detection
1257                  */
1258                 tp->sackhint.prr_out += len;
1259         }
1260         th->th_ack = htonl(tp->rcv_nxt);
1261         if (optlen) {
1262                 bcopy(opt, th + 1, optlen);
1263                 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
1264         }
1265         tcp_set_flags(th, flags);
1266         /*
1267          * Calculate receive window.  Don't shrink window,
1268          * but avoid silly window syndrome.
1269          * If a RST segment is sent, advertise a window of zero.
1270          */
1271         if (flags & TH_RST) {
1272                 recwin = 0;
1273         } else {
1274                 if (recwin < (so->so_rcv.sb_hiwat / 4) &&
1275                     recwin < tp->t_maxseg)
1276                         recwin = 0;
1277                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
1278                     recwin < (tp->rcv_adv - tp->rcv_nxt))
1279                         recwin = (tp->rcv_adv - tp->rcv_nxt);
1280         }
1281         /*
1282          * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1283          * or <SYN,ACK>) segment itself is never scaled.  The <SYN,ACK>
1284          * case is handled in syncache.
1285          */
1286         if (flags & TH_SYN)
1287                 th->th_win = htons((u_short)
1288                                 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1289         else {
1290                 /* Avoid shrinking window with window scaling. */
1291                 recwin = roundup2(recwin, 1 << tp->rcv_scale);
1292                 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
1293         }
1294
1295         /*
1296          * Adjust the RXWIN0SENT flag - indicate that we have advertised
1297          * a 0 window.  This may cause the remote transmitter to stall.  This
1298          * flag tells soreceive() to disable delayed acknowledgements when
1299          * draining the buffer.  This can occur if the receiver is attempting
1300          * to read more data than can be buffered prior to transmitting on
1301          * the connection.
1302          */
1303         if (th->th_win == 0) {
1304                 tp->t_sndzerowin++;
1305                 tp->t_flags |= TF_RXWIN0SENT;
1306         } else
1307                 tp->t_flags &= ~TF_RXWIN0SENT;
1308         if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1309                 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1310                 th->th_flags |= TH_URG;
1311         } else
1312                 /*
1313                  * If no urgent pointer to send, then we pull
1314                  * the urgent pointer to the left edge of the send window
1315                  * so that it doesn't drift into the send window on sequence
1316                  * number wraparound.
1317                  */
1318                 tp->snd_up = tp->snd_una;               /* drag it along */
1319
1320         /*
1321          * Put TCP length in extended header, and then
1322          * checksum extended header and data.
1323          */
1324         m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1325
1326 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1327         if (to.to_flags & TOF_SIGNATURE) {
1328                 /*
1329                  * Calculate MD5 signature and put it into the place
1330                  * determined before.
1331                  * NOTE: since TCP options buffer doesn't point into
1332                  * mbuf's data, calculate offset and use it.
1333                  */
1334                 if (!TCPMD5_ENABLED() || (error = TCPMD5_OUTPUT(m, th,
1335                     (u_char *)(th + 1) + (to.to_signature - opt))) != 0) {
1336                         /*
1337                          * Do not send segment if the calculation of MD5
1338                          * digest has failed.
1339                          */
1340                         m_freem(m);
1341                         goto out;
1342                 }
1343         }
1344 #endif
1345 #ifdef INET6
1346         if (isipv6) {
1347                 /*
1348                  * There is no need to fill in ip6_plen right now.
1349                  * It will be filled later by ip6_output.
1350                  */
1351                 if (tp->t_port) {
1352                         m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
1353                         m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
1354                         udp->uh_sum = in6_cksum_pseudo(ip6, ulen, IPPROTO_UDP, 0);
1355                         th->th_sum = htons(0);
1356                         UDPSTAT_INC(udps_opackets);
1357                 } else {
1358                         m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1359                         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1360                         th->th_sum = in6_cksum_pseudo(ip6,
1361                             sizeof(struct tcphdr) + optlen + len, IPPROTO_TCP,
1362                             0);
1363                 }
1364         }
1365 #endif
1366 #if defined(INET6) && defined(INET)
1367         else
1368 #endif
1369 #ifdef INET
1370         {
1371                 if (tp->t_port) {
1372                         m->m_pkthdr.csum_flags = CSUM_UDP;
1373                         m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
1374                         udp->uh_sum = in_pseudo(ip->ip_src.s_addr,
1375                            ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP));
1376                         th->th_sum = htons(0);
1377                         UDPSTAT_INC(udps_opackets);
1378                 } else {
1379                         m->m_pkthdr.csum_flags = CSUM_TCP;
1380                         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1381                         th->th_sum = in_pseudo(ip->ip_src.s_addr,
1382                             ip->ip_dst.s_addr, htons(sizeof(struct tcphdr) +
1383                             IPPROTO_TCP + len + optlen));
1384                 }
1385
1386                 /* IP version must be set here for ipv4/ipv6 checking later */
1387                 KASSERT(ip->ip_v == IPVERSION,
1388                     ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1389         }
1390 #endif
1391
1392         /*
1393          * Enable TSO and specify the size of the segments.
1394          * The TCP pseudo header checksum is always provided.
1395          */
1396         if (tso) {
1397                 KASSERT(len > tp->t_maxseg - optlen,
1398                     ("%s: len <= tso_segsz", __func__));
1399                 m->m_pkthdr.csum_flags |= CSUM_TSO;
1400                 m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen;
1401         }
1402
1403         KASSERT(len + hdrlen == m_length(m, NULL),
1404             ("%s: mbuf chain shorter than expected: %d + %u != %u",
1405             __func__, len, hdrlen, m_length(m, NULL)));
1406
1407 #ifdef TCP_HHOOK
1408         /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1409         hhook_run_tcp_est_out(tp, th, &to, len, tso);
1410 #endif
1411
1412         TCP_PROBE3(debug__output, tp, th, m);
1413
1414         /* We're getting ready to send; log now. */
1415         /* XXXMT: We are not honoring verbose logging. */
1416         if (tp->t_logstate != TCP_LOG_STATE_OFF)
1417                 lgb = tcp_log_event_(tp, th, &so->so_rcv, &so->so_snd,
1418                     TCP_LOG_OUT, ERRNO_UNK, len, NULL, false, NULL, NULL, 0,
1419                     NULL);
1420         else
1421                 lgb = NULL;
1422
1423         /*
1424          * Fill in IP length and desired time to live and
1425          * send to IP level.  There should be a better way
1426          * to handle ttl and tos; we could keep them in
1427          * the template, but need a way to checksum without them.
1428          */
1429         /*
1430          * m->m_pkthdr.len should have been set before checksum calculation,
1431          * because in6_cksum() need it.
1432          */
1433 #ifdef INET6
1434         if (isipv6) {
1435                 /*
1436                  * we separately set hoplimit for every segment, since the
1437                  * user might want to change the value via setsockopt.
1438                  * Also, desired default hop limit might be changed via
1439                  * Neighbor Discovery.
1440                  */
1441                 ip6->ip6_hlim = in6_selecthlim(inp, NULL);
1442
1443                 /*
1444                  * Set the packet size here for the benefit of DTrace probes.
1445                  * ip6_output() will set it properly; it's supposed to include
1446                  * the option header lengths as well.
1447                  */
1448                 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
1449
1450                 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss)
1451                         tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1452                 else
1453                         tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1454
1455                 if (tp->t_state == TCPS_SYN_SENT)
1456                         TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
1457
1458                 TCP_PROBE5(send, NULL, tp, ip6, tp, th);
1459
1460 #ifdef TCPPCAP
1461                 /* Save packet, if requested. */
1462                 tcp_pcap_add(th, m, &(tp->t_outpkts));
1463 #endif
1464
1465                 /* TODO: IPv6 IP6TOS_ECT bit on */
1466                 error = ip6_output(m, inp->in6p_outputopts, &inp->inp_route6,
1467                     ((so->so_options & SO_DONTROUTE) ?  IP_ROUTETOIF : 0),
1468                     NULL, NULL, inp);
1469
1470                 if (error == EMSGSIZE && inp->inp_route6.ro_nh != NULL)
1471                         mtu = inp->inp_route6.ro_nh->nh_mtu;
1472         }
1473 #endif /* INET6 */
1474 #if defined(INET) && defined(INET6)
1475         else
1476 #endif
1477 #ifdef INET
1478     {
1479         ip->ip_len = htons(m->m_pkthdr.len);
1480 #ifdef INET6
1481         if (inp->inp_vflag & INP_IPV6PROTO)
1482                 ip->ip_ttl = in6_selecthlim(inp, NULL);
1483 #endif /* INET6 */
1484         /*
1485          * If we do path MTU discovery, then we set DF on every packet.
1486          * This might not be the best thing to do according to RFC3390
1487          * Section 2. However the tcp hostcache migitates the problem
1488          * so it affects only the first tcp connection with a host.
1489          *
1490          * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1491          */
1492         if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) {
1493                 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1494                 if (tp->t_port == 0 || len < V_tcp_minmss) {
1495                         ip->ip_off |= htons(IP_DF);
1496                 }
1497         } else {
1498                 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1499         }
1500
1501         if (tp->t_state == TCPS_SYN_SENT)
1502                 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
1503
1504         TCP_PROBE5(send, NULL, tp, ip, tp, th);
1505
1506 #ifdef TCPPCAP
1507         /* Save packet, if requested. */
1508         tcp_pcap_add(th, m, &(tp->t_outpkts));
1509 #endif
1510
1511         error = ip_output(m, inp->inp_options, &inp->inp_route,
1512             ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0, inp);
1513
1514         if (error == EMSGSIZE && inp->inp_route.ro_nh != NULL)
1515                 mtu = inp->inp_route.ro_nh->nh_mtu;
1516     }
1517 #endif /* INET */
1518
1519         if (lgb != NULL) {
1520                 lgb->tlb_errno = error;
1521                 lgb = NULL;
1522         }
1523 out:
1524         if (error == 0)
1525                 tcp_account_for_send(tp, len, (tp->snd_nxt != tp->snd_max), 0, hw_tls);
1526         /*
1527          * In transmit state, time the transmission and arrange for
1528          * the retransmit.  In persist state, just set snd_max.
1529          */
1530         if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1531             !tcp_timer_active(tp, TT_PERSIST)) {
1532                 tcp_seq startseq = tp->snd_nxt;
1533
1534                 /*
1535                  * Advance snd_nxt over sequence space of this segment.
1536                  */
1537                 if (flags & (TH_SYN|TH_FIN)) {
1538                         if (flags & TH_SYN)
1539                                 tp->snd_nxt++;
1540                         if (flags & TH_FIN) {
1541                                 tp->snd_nxt++;
1542                                 tp->t_flags |= TF_SENTFIN;
1543                         }
1544                 }
1545                 if (sack_rxmit)
1546                         goto timer;
1547                 tp->snd_nxt += len;
1548                 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1549                         /*
1550                          * Update "made progress" indication if we just
1551                          * added new data to an empty socket buffer.
1552                          */
1553                         if (tp->snd_una == tp->snd_max)
1554                                 tp->t_acktime = ticks;
1555                         tp->snd_max = tp->snd_nxt;
1556                         /*
1557                          * Time this transmission if not a retransmission and
1558                          * not currently timing anything.
1559                          */
1560                         tp->t_sndtime = ticks;
1561                         if (tp->t_rtttime == 0) {
1562                                 tp->t_rtttime = ticks;
1563                                 tp->t_rtseq = startseq;
1564                                 TCPSTAT_INC(tcps_segstimed);
1565                         }
1566 #ifdef STATS
1567                         if (!(tp->t_flags & TF_GPUTINPROG) && len) {
1568                                 tp->t_flags |= TF_GPUTINPROG;
1569                                 tp->gput_seq = startseq;
1570                                 tp->gput_ack = startseq +
1571                                     ulmin(sbavail(&so->so_snd) - off, sendwin);
1572                                 tp->gput_ts = tcp_ts_getticks();
1573                         }
1574 #endif /* STATS */
1575                 }
1576
1577                 /*
1578                  * Set retransmit timer if not currently set,
1579                  * and not doing a pure ack or a keep-alive probe.
1580                  * Initial value for retransmit timer is smoothed
1581                  * round-trip time + 2 * round-trip time variance.
1582                  * Initialize shift counter which is used for backoff
1583                  * of retransmit time.
1584                  */
1585 timer:
1586                 if (!tcp_timer_active(tp, TT_REXMT) &&
1587                     ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1588                      (tp->snd_nxt != tp->snd_una))) {
1589                         if (tcp_timer_active(tp, TT_PERSIST)) {
1590                                 tcp_timer_activate(tp, TT_PERSIST, 0);
1591                                 tp->t_rxtshift = 0;
1592                         }
1593                         tcp_timer_activate(tp, TT_REXMT, TP_RXTCUR(tp));
1594                 } else if (len == 0 && sbavail(&so->so_snd) &&
1595                     !tcp_timer_active(tp, TT_REXMT) &&
1596                     !tcp_timer_active(tp, TT_PERSIST)) {
1597                         /*
1598                          * Avoid a situation where we do not set persist timer
1599                          * after a zero window condition. For example:
1600                          * 1) A -> B: packet with enough data to fill the window
1601                          * 2) B -> A: ACK for #1 + new data (0 window
1602                          *    advertisement)
1603                          * 3) A -> B: ACK for #2, 0 len packet
1604                          *
1605                          * In this case, A will not activate the persist timer,
1606                          * because it chose to send a packet. Unless tcp_output
1607                          * is called for some other reason (delayed ack timer,
1608                          * another input packet from B, socket syscall), A will
1609                          * not send zero window probes.
1610                          *
1611                          * So, if you send a 0-length packet, but there is data
1612                          * in the socket buffer, and neither the rexmt or
1613                          * persist timer is already set, then activate the
1614                          * persist timer.
1615                          */
1616                         tp->t_rxtshift = 0;
1617                         tcp_setpersist(tp);
1618                 }
1619         } else {
1620                 /*
1621                  * Persist case, update snd_max but since we are in
1622                  * persist mode (no window) we do not update snd_nxt.
1623                  */
1624                 int xlen = len;
1625                 if (flags & TH_SYN)
1626                         ++xlen;
1627                 if (flags & TH_FIN) {
1628                         ++xlen;
1629                         tp->t_flags |= TF_SENTFIN;
1630                 }
1631                 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1632                         tp->snd_max = tp->snd_nxt + xlen;
1633         }
1634         if ((error == 0) &&
1635             (TCPS_HAVEESTABLISHED(tp->t_state) &&
1636              (tp->t_flags & TF_SACK_PERMIT) &&
1637              tp->rcv_numsacks > 0)) {
1638                     /* Clean up any DSACK's sent */
1639                     tcp_clean_dsack_blocks(tp);
1640         }
1641         if (error) {
1642                 /*
1643                  * We know that the packet was lost, so back out the
1644                  * sequence number advance, if any.
1645                  *
1646                  * If the error is EPERM the packet got blocked by the
1647                  * local firewall.  Normally we should terminate the
1648                  * connection but the blocking may have been spurious
1649                  * due to a firewall reconfiguration cycle.  So we treat
1650                  * it like a packet loss and let the retransmit timer and
1651                  * timeouts do their work over time.
1652                  * XXX: It is a POLA question whether calling tcp_drop right
1653                  * away would be the really correct behavior instead.
1654                  */
1655                 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1656                     !tcp_timer_active(tp, TT_PERSIST)) &&
1657                     ((flags & TH_SYN) == 0) &&
1658                     (error != EPERM)) {
1659                         if (sack_rxmit) {
1660                                 p->rxmit -= len;
1661                                 tp->sackhint.sack_bytes_rexmit -= len;
1662                                 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1663                                     ("sackhint bytes rtx >= 0"));
1664                                 KASSERT((flags & TH_FIN) == 0,
1665                                     ("error while FIN with SACK rxmit"));
1666                         } else {
1667                                 tp->snd_nxt -= len;
1668                                 if (flags & TH_FIN)
1669                                         tp->snd_nxt--;
1670                         }
1671                 }
1672                 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);     /* Check gotos. */
1673                 switch (error) {
1674                 case EACCES:
1675                 case EPERM:
1676                         tp->t_softerror = error;
1677                         return (error);
1678                 case ENOBUFS:
1679                         TCP_XMIT_TIMER_ASSERT(tp, len, flags);
1680                         tp->snd_cwnd = tp->t_maxseg;
1681                         return (0);
1682                 case EMSGSIZE:
1683                         /*
1684                          * For some reason the interface we used initially
1685                          * to send segments changed to another or lowered
1686                          * its MTU.
1687                          * If TSO was active we either got an interface
1688                          * without TSO capabilits or TSO was turned off.
1689                          * If we obtained mtu from ip_output() then update
1690                          * it and try again.
1691                          */
1692                         if (tso)
1693                                 tp->t_flags &= ~TF_TSO;
1694                         if (mtu != 0) {
1695                                 tcp_mss_update(tp, -1, mtu, NULL, NULL);
1696                                 goto again;
1697                         }
1698                         return (error);
1699                 case EHOSTDOWN:
1700                 case EHOSTUNREACH:
1701                 case ENETDOWN:
1702                 case ENETUNREACH:
1703                         if (TCPS_HAVERCVDSYN(tp->t_state)) {
1704                                 tp->t_softerror = error;
1705                                 return (0);
1706                         }
1707                         /* FALLTHROUGH */
1708                 default:
1709                         return (error);
1710                 }
1711         }
1712         TCPSTAT_INC(tcps_sndtotal);
1713
1714         /*
1715          * Data sent (as far as we can tell).
1716          * If this advertises a larger window than any other segment,
1717          * then remember the size of the advertised window.
1718          * Any pending ACK has now been sent.
1719          */
1720         if (SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1721                 tp->rcv_adv = tp->rcv_nxt + recwin;
1722         tp->last_ack_sent = tp->rcv_nxt;
1723         tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1724         if (tcp_timer_active(tp, TT_DELACK))
1725                 tcp_timer_activate(tp, TT_DELACK, 0);
1726 #if 0
1727         /*
1728          * This completely breaks TCP if newreno is turned on.  What happens
1729          * is that if delayed-acks are turned on on the receiver, this code
1730          * on the transmitter effectively destroys the TCP window, forcing
1731          * it to four packets (1.5Kx4 = 6K window).
1732          */
1733         if (sendalot && --maxburst)
1734                 goto again;
1735 #endif
1736         if (sendalot)
1737                 goto again;
1738         return (0);
1739 }
1740
1741 void
1742 tcp_setpersist(struct tcpcb *tp)
1743 {
1744         int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1745         int tt;
1746         int maxunacktime;
1747
1748         tp->t_flags &= ~TF_PREVVALID;
1749         if (tcp_timer_active(tp, TT_REXMT))
1750                 panic("tcp_setpersist: retransmit pending");
1751         /*
1752          * If the state is already closed, don't bother.
1753          */
1754         if (tp->t_state == TCPS_CLOSED)
1755                 return;
1756
1757         /*
1758          * Start/restart persistence timer.
1759          */
1760         TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1761                       tcp_persmin, tcp_persmax);
1762         if (TP_MAXUNACKTIME(tp) && tp->t_acktime) {
1763                 maxunacktime = tp->t_acktime + TP_MAXUNACKTIME(tp) - ticks;
1764                 if (maxunacktime < 1)
1765                         maxunacktime = 1;
1766                 if (maxunacktime < tt)
1767                         tt = maxunacktime;
1768         }
1769         tcp_timer_activate(tp, TT_PERSIST, tt);
1770         if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1771                 tp->t_rxtshift++;
1772 }
1773
1774 /*
1775  * Insert TCP options according to the supplied parameters to the place
1776  * optp in a consistent way.  Can handle unaligned destinations.
1777  *
1778  * The order of the option processing is crucial for optimal packing and
1779  * alignment for the scarce option space.
1780  *
1781  * The optimal order for a SYN/SYN-ACK segment is:
1782  *   MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1783  *   Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1784  *
1785  * The SACK options should be last.  SACK blocks consume 8*n+2 bytes.
1786  * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1787  * At minimum we need 10 bytes (to generate 1 SACK block).  If both
1788  * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1789  * we only have 10 bytes for SACK options (40 - (12 + 18)).
1790  */
1791 int
1792 tcp_addoptions(struct tcpopt *to, u_char *optp)
1793 {
1794         u_int32_t mask, optlen = 0;
1795
1796         for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1797                 if ((to->to_flags & mask) != mask)
1798                         continue;
1799                 if (optlen == TCP_MAXOLEN)
1800                         break;
1801                 switch (to->to_flags & mask) {
1802                 case TOF_MSS:
1803                         while (optlen % 4) {
1804                                 optlen += TCPOLEN_NOP;
1805                                 *optp++ = TCPOPT_NOP;
1806                         }
1807                         if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1808                                 continue;
1809                         optlen += TCPOLEN_MAXSEG;
1810                         *optp++ = TCPOPT_MAXSEG;
1811                         *optp++ = TCPOLEN_MAXSEG;
1812                         to->to_mss = htons(to->to_mss);
1813                         bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1814                         optp += sizeof(to->to_mss);
1815                         break;
1816                 case TOF_SCALE:
1817                         while (!optlen || optlen % 2 != 1) {
1818                                 optlen += TCPOLEN_NOP;
1819                                 *optp++ = TCPOPT_NOP;
1820                         }
1821                         if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1822                                 continue;
1823                         optlen += TCPOLEN_WINDOW;
1824                         *optp++ = TCPOPT_WINDOW;
1825                         *optp++ = TCPOLEN_WINDOW;
1826                         *optp++ = to->to_wscale;
1827                         break;
1828                 case TOF_SACKPERM:
1829                         while (optlen % 2) {
1830                                 optlen += TCPOLEN_NOP;
1831                                 *optp++ = TCPOPT_NOP;
1832                         }
1833                         if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1834                                 continue;
1835                         optlen += TCPOLEN_SACK_PERMITTED;
1836                         *optp++ = TCPOPT_SACK_PERMITTED;
1837                         *optp++ = TCPOLEN_SACK_PERMITTED;
1838                         break;
1839                 case TOF_TS:
1840                         while (!optlen || optlen % 4 != 2) {
1841                                 optlen += TCPOLEN_NOP;
1842                                 *optp++ = TCPOPT_NOP;
1843                         }
1844                         if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1845                                 continue;
1846                         optlen += TCPOLEN_TIMESTAMP;
1847                         *optp++ = TCPOPT_TIMESTAMP;
1848                         *optp++ = TCPOLEN_TIMESTAMP;
1849                         to->to_tsval = htonl(to->to_tsval);
1850                         to->to_tsecr = htonl(to->to_tsecr);
1851                         bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1852                         optp += sizeof(to->to_tsval);
1853                         bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1854                         optp += sizeof(to->to_tsecr);
1855                         break;
1856                 case TOF_SIGNATURE:
1857                         {
1858                         int siglen = TCPOLEN_SIGNATURE - 2;
1859
1860                         while (!optlen || optlen % 4 != 2) {
1861                                 optlen += TCPOLEN_NOP;
1862                                 *optp++ = TCPOPT_NOP;
1863                         }
1864                         if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) {
1865                                 to->to_flags &= ~TOF_SIGNATURE;
1866                                 continue;
1867                         }
1868                         optlen += TCPOLEN_SIGNATURE;
1869                         *optp++ = TCPOPT_SIGNATURE;
1870                         *optp++ = TCPOLEN_SIGNATURE;
1871                         to->to_signature = optp;
1872                         while (siglen--)
1873                                  *optp++ = 0;
1874                         break;
1875                         }
1876                 case TOF_SACK:
1877                         {
1878                         int sackblks = 0;
1879                         struct sackblk *sack = (struct sackblk *)to->to_sacks;
1880                         tcp_seq sack_seq;
1881
1882                         while (!optlen || optlen % 4 != 2) {
1883                                 optlen += TCPOLEN_NOP;
1884                                 *optp++ = TCPOPT_NOP;
1885                         }
1886                         if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1887                                 continue;
1888                         optlen += TCPOLEN_SACKHDR;
1889                         *optp++ = TCPOPT_SACK;
1890                         sackblks = min(to->to_nsacks,
1891                                         (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1892                         *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1893                         while (sackblks--) {
1894                                 sack_seq = htonl(sack->start);
1895                                 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1896                                 optp += sizeof(sack_seq);
1897                                 sack_seq = htonl(sack->end);
1898                                 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1899                                 optp += sizeof(sack_seq);
1900                                 optlen += TCPOLEN_SACK;
1901                                 sack++;
1902                         }
1903                         TCPSTAT_INC(tcps_sack_send_blocks);
1904                         break;
1905                         }
1906                 case TOF_FASTOPEN:
1907                         {
1908                         int total_len;
1909
1910                         /* XXX is there any point to aligning this option? */
1911                         total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len;
1912                         if (TCP_MAXOLEN - optlen < total_len) {
1913                                 to->to_flags &= ~TOF_FASTOPEN;
1914                                 continue;
1915                         }
1916                         *optp++ = TCPOPT_FAST_OPEN;
1917                         *optp++ = total_len;
1918                         if (to->to_tfo_len > 0) {
1919                                 bcopy(to->to_tfo_cookie, optp, to->to_tfo_len);
1920                                 optp += to->to_tfo_len;
1921                         }
1922                         optlen += total_len;
1923                         break;
1924                         }
1925                 default:
1926                         panic("%s: unknown TCP option type", __func__);
1927                         break;
1928                 }
1929         }
1930
1931         /* Terminate and pad TCP options to a 4 byte boundary. */
1932         if (optlen % 4) {
1933                 optlen += TCPOLEN_EOL;
1934                 *optp++ = TCPOPT_EOL;
1935         }
1936         /*
1937          * According to RFC 793 (STD0007):
1938          *   "The content of the header beyond the End-of-Option option
1939          *    must be header padding (i.e., zero)."
1940          *   and later: "The padding is composed of zeros."
1941          */
1942         while (optlen % 4) {
1943                 optlen += TCPOLEN_PAD;
1944                 *optp++ = TCPOPT_PAD;
1945         }
1946
1947         KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));
1948         return (optlen);
1949 }
1950
1951 /*
1952  * This is a copy of m_copym(), taking the TSO segment size/limit
1953  * constraints into account, and advancing the sndptr as it goes.
1954  */
1955 struct mbuf *
1956 tcp_m_copym(struct mbuf *m, int32_t off0, int32_t *plen,
1957     int32_t seglimit, int32_t segsize, struct sockbuf *sb, bool hw_tls)
1958 {
1959 #ifdef KERN_TLS
1960         struct ktls_session *tls, *ntls;
1961         struct mbuf *start __diagused;
1962 #endif
1963         struct mbuf *n, **np;
1964         struct mbuf *top;
1965         int32_t off = off0;
1966         int32_t len = *plen;
1967         int32_t fragsize;
1968         int32_t len_cp = 0;
1969         int32_t *pkthdrlen;
1970         uint32_t mlen, frags;
1971         bool copyhdr;
1972
1973         KASSERT(off >= 0, ("tcp_m_copym, negative off %d", off));
1974         KASSERT(len >= 0, ("tcp_m_copym, negative len %d", len));
1975         if (off == 0 && m->m_flags & M_PKTHDR)
1976                 copyhdr = true;
1977         else
1978                 copyhdr = false;
1979         while (off > 0) {
1980                 KASSERT(m != NULL, ("tcp_m_copym, offset > size of mbuf chain"));
1981                 if (off < m->m_len)
1982                         break;
1983                 off -= m->m_len;
1984                 if ((sb) && (m == sb->sb_sndptr)) {
1985                         sb->sb_sndptroff += m->m_len;
1986                         sb->sb_sndptr = m->m_next;
1987                 }
1988                 m = m->m_next;
1989         }
1990         np = &top;
1991         top = NULL;
1992         pkthdrlen = NULL;
1993 #ifdef KERN_TLS
1994         if (hw_tls && (m->m_flags & M_EXTPG))
1995                 tls = m->m_epg_tls;
1996         else
1997                 tls = NULL;
1998         start = m;
1999 #endif
2000         while (len > 0) {
2001                 if (m == NULL) {
2002                         KASSERT(len == M_COPYALL,
2003                             ("tcp_m_copym, length > size of mbuf chain"));
2004                         *plen = len_cp;
2005                         if (pkthdrlen != NULL)
2006                                 *pkthdrlen = len_cp;
2007                         break;
2008                 }
2009 #ifdef KERN_TLS
2010                 if (hw_tls) {
2011                         if (m->m_flags & M_EXTPG)
2012                                 ntls = m->m_epg_tls;
2013                         else
2014                                 ntls = NULL;
2015
2016                         /*
2017                          * Avoid mixing TLS records with handshake
2018                          * data or TLS records from different
2019                          * sessions.
2020                          */
2021                         if (tls != ntls) {
2022                                 MPASS(m != start);
2023                                 *plen = len_cp;
2024                                 if (pkthdrlen != NULL)
2025                                         *pkthdrlen = len_cp;
2026                                 break;
2027                         }
2028                 }
2029 #endif
2030                 mlen = min(len, m->m_len - off);
2031                 if (seglimit) {
2032                         /*
2033                          * For M_EXTPG mbufs, add 3 segments
2034                          * + 1 in case we are crossing page boundaries
2035                          * + 2 in case the TLS hdr/trailer are used
2036                          * It is cheaper to just add the segments
2037                          * than it is to take the cache miss to look
2038                          * at the mbuf ext_pgs state in detail.
2039                          */
2040                         if (m->m_flags & M_EXTPG) {
2041                                 fragsize = min(segsize, PAGE_SIZE);
2042                                 frags = 3;
2043                         } else {
2044                                 fragsize = segsize;
2045                                 frags = 0;
2046                         }
2047
2048                         /* Break if we really can't fit anymore. */
2049                         if ((frags + 1) >= seglimit) {
2050                                 *plen = len_cp;
2051                                 if (pkthdrlen != NULL)
2052                                         *pkthdrlen = len_cp;
2053                                 break;
2054                         }
2055
2056                         /*
2057                          * Reduce size if you can't copy the whole
2058                          * mbuf. If we can't copy the whole mbuf, also
2059                          * adjust len so the loop will end after this
2060                          * mbuf.
2061                          */
2062                         if ((frags + howmany(mlen, fragsize)) >= seglimit) {
2063                                 mlen = (seglimit - frags - 1) * fragsize;
2064                                 len = mlen;
2065                                 *plen = len_cp + len;
2066                                 if (pkthdrlen != NULL)
2067                                         *pkthdrlen = *plen;
2068                         }
2069                         frags += howmany(mlen, fragsize);
2070                         if (frags == 0)
2071                                 frags++;
2072                         seglimit -= frags;
2073                         KASSERT(seglimit > 0,
2074                             ("%s: seglimit went too low", __func__));
2075                 }
2076                 if (copyhdr)
2077                         n = m_gethdr(M_NOWAIT, m->m_type);
2078                 else
2079                         n = m_get(M_NOWAIT, m->m_type);
2080                 *np = n;
2081                 if (n == NULL)
2082                         goto nospace;
2083                 if (copyhdr) {
2084                         if (!m_dup_pkthdr(n, m, M_NOWAIT))
2085                                 goto nospace;
2086                         if (len == M_COPYALL)
2087                                 n->m_pkthdr.len -= off0;
2088                         else
2089                                 n->m_pkthdr.len = len;
2090                         pkthdrlen = &n->m_pkthdr.len;
2091                         copyhdr = false;
2092                 }
2093                 n->m_len = mlen;
2094                 len_cp += n->m_len;
2095                 if (m->m_flags & (M_EXT|M_EXTPG)) {
2096                         n->m_data = m->m_data + off;
2097                         mb_dupcl(n, m);
2098                 } else
2099                         bcopy(mtod(m, caddr_t)+off, mtod(n, caddr_t),
2100                             (u_int)n->m_len);
2101
2102                 if (sb && (sb->sb_sndptr == m) &&
2103                     ((n->m_len + off) >= m->m_len) && m->m_next) {
2104                         sb->sb_sndptroff += m->m_len;
2105                         sb->sb_sndptr = m->m_next;
2106                 }
2107                 off = 0;
2108                 if (len != M_COPYALL) {
2109                         len -= n->m_len;
2110                 }
2111                 m = m->m_next;
2112                 np = &n->m_next;
2113         }
2114         return (top);
2115 nospace:
2116         m_freem(top);
2117         return (NULL);
2118 }
2119
2120 void
2121 tcp_sndbuf_autoscale(struct tcpcb *tp, struct socket *so, uint32_t sendwin)
2122 {
2123
2124         /*
2125          * Automatic sizing of send socket buffer.  Often the send buffer
2126          * size is not optimally adjusted to the actual network conditions
2127          * at hand (delay bandwidth product).  Setting the buffer size too
2128          * small limits throughput on links with high bandwidth and high
2129          * delay (eg. trans-continental/oceanic links).  Setting the
2130          * buffer size too big consumes too much real kernel memory,
2131          * especially with many connections on busy servers.
2132          *
2133          * The criteria to step up the send buffer one notch are:
2134          *  1. receive window of remote host is larger than send buffer
2135          *     (with a fudge factor of 5/4th);
2136          *  2. send buffer is filled to 7/8th with data (so we actually
2137          *     have data to make use of it);
2138          *  3. send buffer fill has not hit maximal automatic size;
2139          *  4. our send window (slow start and cogestion controlled) is
2140          *     larger than sent but unacknowledged data in send buffer.
2141          *
2142          * The remote host receive window scaling factor may limit the
2143          * growing of the send buffer before it reaches its allowed
2144          * maximum.
2145          *
2146          * It scales directly with slow start or congestion window
2147          * and does at most one step per received ACK.  This fast
2148          * scaling has the drawback of growing the send buffer beyond
2149          * what is strictly necessary to make full use of a given
2150          * delay*bandwidth product.  However testing has shown this not
2151          * to be much of an problem.  At worst we are trading wasting
2152          * of available bandwidth (the non-use of it) for wasting some
2153          * socket buffer memory.
2154          *
2155          * TODO: Shrink send buffer during idle periods together
2156          * with congestion window.  Requires another timer.  Has to
2157          * wait for upcoming tcp timer rewrite.
2158          *
2159          * XXXGL: should there be used sbused() or sbavail()?
2160          */
2161         if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
2162                 int lowat;
2163
2164                 lowat = V_tcp_sendbuf_auto_lowat ? so->so_snd.sb_lowat : 0;
2165                 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat - lowat &&
2166                     sbused(&so->so_snd) >=
2167                     (so->so_snd.sb_hiwat / 8 * 7) - lowat &&
2168                     sbused(&so->so_snd) < V_tcp_autosndbuf_max &&
2169                     sendwin >= (sbused(&so->so_snd) -
2170                     (tp->snd_nxt - tp->snd_una))) {
2171                         if (!sbreserve_locked(so, SO_SND,
2172                             min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
2173                              V_tcp_autosndbuf_max), curthread))
2174                                 so->so_snd.sb_flags &= ~SB_AUTOSIZE;
2175                 }
2176         }
2177 }