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
  32 #include <sys/cdefs.h>
  33 #include "opt_inet.h"
  34 #include "opt_inet6.h"
  35 #include "opt_ipsec.h"
  36 #include "opt_kern_tls.h"
  37
  38 #include <sys/param.h>
  39 #include <sys/systm.h>
  40 #include <sys/arb.h>
  41 #include <sys/domain.h>
  42 #ifdef TCP_HHOOK
  43 #include <sys/hhook.h>
  44 #endif
  45 #include <sys/kernel.h>
  46 #ifdef KERN_TLS
  47 #include <sys/ktls.h>
  48 #endif
  49 #include <sys/lock.h>
  50 #include <sys/mbuf.h>
  51 #include <sys/mutex.h>
  52 #include <sys/protosw.h>
  53 #include <sys/qmath.h>
  54 #include <sys/sdt.h>
  55 #include <sys/socket.h>
  56 #include <sys/socketvar.h>
  57 #include <sys/sysctl.h>
  58 #include <sys/stats.h>
  59
  60 #include <net/if.h>
  61 #include <net/route.h>
  62 #include <net/route/nhop.h>
  63 #include <net/vnet.h>
  64
  65 #include <netinet/in.h>
  66 #include <netinet/in_kdtrace.h>
  67 #include <netinet/in_systm.h>
  68 #include <netinet/ip.h>
  69 #include <netinet/in_pcb.h>
  70 #include <netinet/ip_var.h>
  71 #include <netinet/ip_options.h>
  72 #ifdef INET6
  73 #include <netinet6/in6_pcb.h>
  74 #include <netinet/ip6.h>
  75 #include <netinet6/ip6_var.h>
  76 #endif
  77 #include <netinet/tcp.h>
  78 #define TCPOUTFLAGS
  79 #include <netinet/tcp_fsm.h>
  80 #include <netinet/tcp_seq.h>
  81 #include <netinet/tcp_var.h>
  82 #include <netinet/tcp_log_buf.h>
  83 #include <netinet/tcp_syncache.h>
  84 #include <netinet/tcp_timer.h>
  85 #include <netinet/tcpip.h>
  86 #include <netinet/cc/cc.h>
  87 #include <netinet/tcp_fastopen.h>
  88 #ifdef TCPPCAP
  89 #include <netinet/tcp_pcap.h>
  90 #endif
  91 #ifdef TCP_OFFLOAD
  92 #include <netinet/tcp_offload.h>
  93 #endif
  94 #include <netinet/tcp_ecn.h>
  95
  96 #include <netipsec/ipsec_support.h>
  97
  98 #include <netinet/udp.h>
  99 #include <netinet/udp_var.h>
 100 #include <machine/in_cksum.h>
 101
 102 #include <security/mac/mac_framework.h>
 103
 104 VNET_DEFINE(int, path_mtu_discovery) = 1;
 105 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_VNET | CTLFLAG_RW,
 106         &VNET_NAME(path_mtu_discovery), 1,
 107         "Enable Path MTU Discovery");
 108
 109 VNET_DEFINE(int, tcp_do_tso) = 1;
 110 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_VNET | CTLFLAG_RW,
 111         &VNET_NAME(tcp_do_tso), 0,
 112         "Enable TCP Segmentation Offload");
 113
 114 VNET_DEFINE(int, tcp_sendspace) = 1024*32;
 115 #define V_tcp_sendspace VNET(tcp_sendspace)
 116 SYSCTL_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_VNET | CTLFLAG_RW,
 117         &VNET_NAME(tcp_sendspace), 0, "Initial send socket buffer size");
 118
 119 VNET_DEFINE(int, tcp_do_autosndbuf) = 1;
 120 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
 121         &VNET_NAME(tcp_do_autosndbuf), 0,
 122         "Enable automatic send buffer sizing");
 123
 124 VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024;
 125 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_VNET | CTLFLAG_RW,
 126         &VNET_NAME(tcp_autosndbuf_inc), 0,
 127         "Incrementor step size of automatic send buffer");
 128
 129 VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024;
 130 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
 131         &VNET_NAME(tcp_autosndbuf_max), 0,
 132         "Max size of automatic send buffer");
 133
 134 VNET_DEFINE(int, tcp_sendbuf_auto_lowat) = 0;
 135 #define V_tcp_sendbuf_auto_lowat        VNET(tcp_sendbuf_auto_lowat)
 136 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto_lowat, CTLFLAG_VNET | CTLFLAG_RW,
 137         &VNET_NAME(tcp_sendbuf_auto_lowat), 0,
 138         "Modify threshold for auto send buffer growth to account for SO_SNDLOWAT");
 139
 140 /*
 141  * Make sure that either retransmit or persist timer is set for SYN, FIN and
 142  * non-ACK.
 143  */
 144 #define TCP_XMIT_TIMER_ASSERT(tp, len, th_flags)                        \
 145         KASSERT(((len) == 0 && ((th_flags) & (TH_SYN | TH_FIN)) == 0) ||\
 146             tcp_timer_active((tp), TT_REXMT) ||                         \
 147             tcp_timer_active((tp), TT_PERSIST),                         \
 148             ("neither rexmt nor persist timer is set"))
 149
 150 #ifdef TCP_HHOOK
 151 /*
 152  * Wrapper for the TCP established output helper hook.
 153  */
 154 void
 155 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
 156     struct tcpopt *to, uint32_t len, int tso)
 157 {
 158         struct tcp_hhook_data hhook_data;
 159
 160         if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
 161                 hhook_data.tp = tp;
 162                 hhook_data.th = th;
 163                 hhook_data.to = to;
 164                 hhook_data.len = len;
 165                 hhook_data.tso = tso;
 166
 167                 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
 168                     &tp->t_osd);
 169         }
 170 }
 171 #endif
 172
 173 /*
 174  * CC wrapper hook functions
 175  */
 176 void
 177 cc_after_idle(struct tcpcb *tp)
 178 {
 179         INP_WLOCK_ASSERT(tptoinpcb(tp));
 180
 181         if (CC_ALGO(tp)->after_idle != NULL)
 182                 CC_ALGO(tp)->after_idle(&tp->t_ccv);
 183 }
 184
 185 /*
 186  * Tcp output routine: figure out what should be sent and send it.
 187  */
 188 int
 189 tcp_default_output(struct tcpcb *tp)
 190 {
 191         struct socket *so = tptosocket(tp);
 192         struct inpcb *inp = tptoinpcb(tp);
 193         int32_t len;
 194         uint32_t recwin, sendwin;
 195         uint16_t flags;
 196         int off, error = 0;     /* Keep compiler happy */
 197         u_int if_hw_tsomaxsegcount = 0;
 198         u_int if_hw_tsomaxsegsize = 0;
 199         struct mbuf *m;
 200         struct ip *ip = NULL;
 201         struct tcphdr *th;
 202         u_char opt[TCP_MAXOLEN];
 203         unsigned ipoptlen, optlen, hdrlen, ulen;
 204 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 205         unsigned ipsec_optlen = 0;
 206 #endif
 207         int idle, sendalot, curticks;
 208         int sack_rxmit, sack_bytes_rxmt;
 209         struct sackhole *p;
 210         int tso, mtu;
 211         struct tcpopt to;
 212         struct udphdr *udp = NULL;
 213         struct tcp_log_buffer *lgb;
 214         unsigned int wanted_cookie = 0;
 215         unsigned int dont_sendalot = 0;
 216 #if 0
 217         int maxburst = TCP_MAXBURST;
 218 #endif
 219 #ifdef INET6
 220         struct ip6_hdr *ip6 = NULL;
 221         const bool isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
 222 #endif
 223 #ifdef KERN_TLS
 224         const bool hw_tls = tp->t_nic_ktls_xmit != 0;
 225 #else
 226         const bool hw_tls = false;
 227 #endif
 228
 229         NET_EPOCH_ASSERT();
 230         INP_WLOCK_ASSERT(inp);
 231
 232 #ifdef TCP_OFFLOAD
 233         if (tp->t_flags & TF_TOE)
 234                 return (tcp_offload_output(tp));
 235 #endif
 236
 237         /*
 238          * For TFO connections in SYN_SENT or SYN_RECEIVED,
 239          * only allow the initial SYN or SYN|ACK and those sent
 240          * by the retransmit timer.
 241          */
 242         if (IS_FASTOPEN(tp->t_flags) &&
 243             ((tp->t_state == TCPS_SYN_SENT) ||
 244              (tp->t_state == TCPS_SYN_RECEIVED)) &&
 245             SEQ_GT(tp->snd_max, tp->snd_una) && /* initial SYN or SYN|ACK sent */
 246             (tp->snd_nxt != tp->snd_una))       /* not a retransmit */
 247                 return (0);
 248
 249         /*
 250          * Determine length of data that should be transmitted,
 251          * and flags that will be used.
 252          * If there is some data or critical controls (SYN, RST)
 253          * to send, then transmit; otherwise, investigate further.
 254          */
 255         idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
 256         if (idle && (((ticks - tp->t_rcvtime) >= tp->t_rxtcur) ||
 257             (tp->t_sndtime && ((ticks - tp->t_sndtime) >= tp->t_rxtcur))))
 258                 cc_after_idle(tp);
 259         tp->t_flags &= ~TF_LASTIDLE;
 260         if (idle) {
 261                 if (tp->t_flags & TF_MORETOCOME) {
 262                         tp->t_flags |= TF_LASTIDLE;
 263                         idle = 0;
 264                 }
 265         }
 266 again:
 267         /*
 268          * If we've recently taken a timeout, snd_max will be greater than
 269          * snd_nxt.  There may be SACK information that allows us to avoid
 270          * resending already delivered data.  Adjust snd_nxt accordingly.
 271          */
 272         if ((tp->t_flags & TF_SACK_PERMIT) &&
 273             SEQ_LT(tp->snd_nxt, tp->snd_max))
 274                 tcp_sack_adjust(tp);
 275         sendalot = 0;
 276         tso = 0;
 277         mtu = 0;
 278         off = tp->snd_nxt - tp->snd_una;
 279         sendwin = min(tp->snd_wnd, tp->snd_cwnd);
 280
 281         flags = tcp_outflags[tp->t_state];
 282         /*
 283          * Send any SACK-generated retransmissions.  If we're explicitly trying
 284          * to send out new data (when sendalot is 1), bypass this function.
 285          * If we retransmit in fast recovery mode, decrement snd_cwnd, since
 286          * we're replacing a (future) new transmission with a retransmission
 287          * now, and we previously incremented snd_cwnd in tcp_input().
 288          */
 289         /*
 290          * Still in sack recovery , reset rxmit flag to zero.
 291          */
 292         sack_rxmit = 0;
 293         sack_bytes_rxmt = 0;
 294         len = 0;
 295         p = NULL;
 296         if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
 297             (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
 298                 uint32_t cwin;
 299
 300                 cwin =
 301                     imax(min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt, 0);
 302                 /* Do not retransmit SACK segments beyond snd_recover */
 303                 if (SEQ_GT(p->end, tp->snd_recover)) {
 304                         /*
 305                          * (At least) part of sack hole extends beyond
 306                          * snd_recover. Check to see if we can rexmit data
 307                          * for this hole.
 308                          */
 309                         if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
 310                                 /*
 311                                  * Can't rexmit any more data for this hole.
 312                                  * That data will be rexmitted in the next
 313                                  * sack recovery episode, when snd_recover
 314                                  * moves past p->rxmit.
 315                                  */
 316                                 p = NULL;
 317                                 goto after_sack_rexmit;
 318                         } else {
 319                                 /* Can rexmit part of the current hole */
 320                                 len = ((int32_t)ulmin(cwin,
 321                                     SEQ_SUB(tp->snd_recover, p->rxmit)));
 322                         }
 323                 } else {
 324                         len = ((int32_t)ulmin(cwin,
 325                             SEQ_SUB(p->end, p->rxmit)));
 326                 }
 327                 if (len > 0) {
 328                         off = SEQ_SUB(p->rxmit, tp->snd_una);
 329                         KASSERT(off >= 0,("%s: sack block to the left of una : %d",
 330                             __func__, off));
 331                         sack_rxmit = 1;
 332                         sendalot = 1;
 333                         TCPSTAT_INC(tcps_sack_rexmits);
 334                         TCPSTAT_ADD(tcps_sack_rexmit_bytes,
 335                             min(len, tcp_maxseg(tp)));
 336                 }
 337         }
 338 after_sack_rexmit:
 339         /*
 340          * Get standard flags, and add SYN or FIN if requested by 'hidden'
 341          * state flags.
 342          */
 343         if (tp->t_flags & TF_NEEDFIN)
 344                 flags |= TH_FIN;
 345         if (tp->t_flags & TF_NEEDSYN)
 346                 flags |= TH_SYN;
 347
 348         SOCKBUF_LOCK(&so->so_snd);
 349         /*
 350          * If in persist timeout with window of 0, send 1 byte.
 351          * Otherwise, if window is small but nonzero
 352          * and timer expired, we will send what we can
 353          * and go to transmit state.
 354          */
 355         if (tp->t_flags & TF_FORCEDATA) {
 356                 if (sendwin == 0) {
 357                         /*
 358                          * If we still have some data to send, then
 359                          * clear the FIN bit.  Usually this would
 360                          * happen below when it realizes that we
 361                          * aren't sending all the data.  However,
 362                          * if we have exactly 1 byte of unsent data,
 363                          * then it won't clear the FIN bit below,
 364                          * and if we are in persist state, we wind
 365                          * up sending the packet without recording
 366                          * that we sent the FIN bit.
 367                          *
 368                          * We can't just blindly clear the FIN bit,
 369                          * because if we don't have any more data
 370                          * to send then the probe will be the FIN
 371                          * itself.
 372                          */
 373                         if (off < sbused(&so->so_snd))
 374                                 flags &= ~TH_FIN;
 375                         sendwin = 1;
 376                 } else {
 377                         tcp_timer_activate(tp, TT_PERSIST, 0);
 378                         tp->t_rxtshift = 0;
 379                 }
 380         }
 381
 382         /*
 383          * If snd_nxt == snd_max and we have transmitted a FIN, the
 384          * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
 385          * a negative length.  This can also occur when TCP opens up
 386          * its congestion window while receiving additional duplicate
 387          * acks after fast-retransmit because TCP will reset snd_nxt
 388          * to snd_max after the fast-retransmit.
 389          *
 390          * In the normal retransmit-FIN-only case, however, snd_nxt will
 391          * be set to snd_una, the offset will be 0, and the length may
 392          * wind up 0.
 393          *
 394          * If sack_rxmit is true we are retransmitting from the scoreboard
 395          * in which case len is already set.
 396          */
 397         if (sack_rxmit == 0) {
 398                 if (sack_bytes_rxmt == 0)
 399                         len = ((int32_t)min(sbavail(&so->so_snd), sendwin) -
 400                             off);
 401                 else {
 402                         int32_t cwin;
 403
 404                         /*
 405                          * We are inside of a SACK recovery episode and are
 406                          * sending new data, having retransmitted all the
 407                          * data possible in the scoreboard.
 408                          */
 409                         len = ((int32_t)min(sbavail(&so->so_snd), tp->snd_wnd) -
 410                             off);
 411                         /*
 412                          * Don't remove this (len > 0) check !
 413                          * We explicitly check for len > 0 here (although it
 414                          * isn't really necessary), to work around a gcc
 415                          * optimization issue - to force gcc to compute
 416                          * len above. Without this check, the computation
 417                          * of len is bungled by the optimizer.
 418                          */
 419                         if (len > 0) {
 420                                 cwin = tp->snd_cwnd - imax(0, (int32_t)
 421                                         (tp->snd_nxt - tp->snd_recover)) -
 422                                         sack_bytes_rxmt;
 423                                 if (cwin < 0)
 424                                         cwin = 0;
 425                                 len = imin(len, cwin);
 426                         }
 427                 }
 428         }
 429
 430         /*
 431          * Lop off SYN bit if it has already been sent.  However, if this
 432          * is SYN-SENT state and if segment contains data and if we don't
 433          * know that foreign host supports TAO, suppress sending segment.
 434          */
 435         if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
 436                 if (tp->t_state != TCPS_SYN_RECEIVED)
 437                         flags &= ~TH_SYN;
 438                 /*
 439                  * When sending additional segments following a TFO SYN|ACK,
 440                  * do not include the SYN bit.
 441                  */
 442                 if (IS_FASTOPEN(tp->t_flags) &&
 443                     (tp->t_state == TCPS_SYN_RECEIVED))
 444                         flags &= ~TH_SYN;
 445                 off--, len++;
 446         }
 447
 448         /*
 449          * Be careful not to send data and/or FIN on SYN segments.
 450          * This measure is needed to prevent interoperability problems
 451          * with not fully conformant TCP implementations.
 452          */
 453         if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
 454                 len = 0;
 455                 flags &= ~TH_FIN;
 456         }
 457
 458         /*
 459          * On TFO sockets, ensure no data is sent in the following cases:
 460          *
 461          *  - When retransmitting SYN|ACK on a passively-created socket
 462          *
 463          *  - When retransmitting SYN on an actively created socket
 464          *
 465          *  - When sending a zero-length cookie (cookie request) on an
 466          *    actively created socket
 467          *
 468          *  - When the socket is in the CLOSED state (RST is being sent)
 469          */
 470         if (IS_FASTOPEN(tp->t_flags) &&
 471             (((flags & TH_SYN) && (tp->t_rxtshift > 0)) ||
 472              ((tp->t_state == TCPS_SYN_SENT) &&
 473               (tp->t_tfo_client_cookie_len == 0)) ||
 474              (flags & TH_RST)))
 475                 len = 0;
 476         if (len <= 0) {
 477                 /*
 478                  * If FIN has been sent but not acked,
 479                  * but we haven't been called to retransmit,
 480                  * len will be < 0.  Otherwise, window shrank
 481                  * after we sent into it.  If window shrank to 0,
 482                  * cancel pending retransmit, pull snd_nxt back
 483                  * to (closed) window, and set the persist timer
 484                  * if it isn't already going.  If the window didn't
 485                  * close completely, just wait for an ACK.
 486                  *
 487                  * We also do a general check here to ensure that
 488                  * we will set the persist timer when we have data
 489                  * to send, but a 0-byte window. This makes sure
 490                  * the persist timer is set even if the packet
 491                  * hits one of the "goto send" lines below.
 492                  */
 493                 len = 0;
 494                 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
 495                     (off < (int) sbavail(&so->so_snd)) &&
 496                     !tcp_timer_active(tp, TT_PERSIST)) {
 497                         tcp_timer_activate(tp, TT_REXMT, 0);
 498                         tp->t_rxtshift = 0;
 499                         tp->snd_nxt = tp->snd_una;
 500                         if (!tcp_timer_active(tp, TT_PERSIST))
 501                                 tcp_setpersist(tp);
 502                 }
 503         }
 504
 505         /* len will be >= 0 after this point. */
 506         KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
 507
 508         tcp_sndbuf_autoscale(tp, so, sendwin);
 509
 510         /*
 511          * Decide if we can use TCP Segmentation Offloading (if supported by
 512          * hardware).
 513          *
 514          * TSO may only be used if we are in a pure bulk sending state.  The
 515          * presence of TCP-MD5, SACK retransmits, SACK advertizements and
 516          * IP options prevent using TSO.  With TSO the TCP header is the same
 517          * (except for the sequence number) for all generated packets.  This
 518          * makes it impossible to transmit any options which vary per generated
 519          * segment or packet.
 520          *
 521          * IPv4 handling has a clear separation of ip options and ip header
 522          * flags while IPv6 combines both in in6p_outputopts. ip6_optlen() does
 523          * the right thing below to provide length of just ip options and thus
 524          * checking for ipoptlen is enough to decide if ip options are present.
 525          */
 526 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 527         /*
 528          * Pre-calculate here as we save another lookup into the darknesses
 529          * of IPsec that way and can actually decide if TSO is ok.
 530          */
 531 #ifdef INET6
 532         if (isipv6 && IPSEC_ENABLED(ipv6))
 533                 ipsec_optlen = IPSEC_HDRSIZE(ipv6, inp);
 534 #ifdef INET
 535         else
 536 #endif
 537 #endif /* INET6 */
 538 #ifdef INET
 539         if (IPSEC_ENABLED(ipv4))
 540                 ipsec_optlen = IPSEC_HDRSIZE(ipv4, inp);
 541 #endif /* INET */
 542 #endif /* IPSEC */
 543 #ifdef INET6
 544         if (isipv6)
 545                 ipoptlen = ip6_optlen(inp);
 546         else
 547 #endif
 548         if (inp->inp_options)
 549                 ipoptlen = inp->inp_options->m_len -
 550                                 offsetof(struct ipoption, ipopt_list);
 551         else
 552                 ipoptlen = 0;
 553 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 554         ipoptlen += ipsec_optlen;
 555 #endif
 556
 557         if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
 558             (tp->t_port == 0) &&
 559             ((tp->t_flags & TF_SIGNATURE) == 0) &&
 560             tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
 561             ipoptlen == 0 && !(flags & TH_SYN))
 562                 tso = 1;
 563
 564         if (sack_rxmit) {
 565                 if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
 566                         flags &= ~TH_FIN;
 567         } else {
 568                 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
 569                     sbused(&so->so_snd)))
 570                         flags &= ~TH_FIN;
 571         }
 572
 573         recwin = lmin(lmax(sbspace(&so->so_rcv), 0),
 574             (long)TCP_MAXWIN << tp->rcv_scale);
 575
 576         /*
 577          * Sender silly window avoidance.   We transmit under the following
 578          * conditions when len is non-zero:
 579          *
 580          *      - We have a full segment (or more with TSO)
 581          *      - This is the last buffer in a write()/send() and we are
 582          *        either idle or running NODELAY
 583          *      - we've timed out (e.g. persist timer)
 584          *      - we have more then 1/2 the maximum send window's worth of
 585          *        data (receiver may be limited the window size)
 586          *      - we need to retransmit
 587          */
 588         if (len) {
 589                 if (len >= tp->t_maxseg)
 590                         goto send;
 591                 /*
 592                  * As the TCP header options are now
 593                  * considered when setting up the initial
 594                  * window, we would not send the last segment
 595                  * if we skip considering the option length here.
 596                  * Note: this may not work when tcp headers change
 597                  * very dynamically in the future.
 598                  */
 599                 if ((((tp->t_flags & TF_SIGNATURE) ?
 600                         PADTCPOLEN(TCPOLEN_SIGNATURE) : 0) +
 601                     ((tp->t_flags & TF_RCVD_TSTMP) ?
 602                         PADTCPOLEN(TCPOLEN_TIMESTAMP) : 0) +
 603                     len) >= tp->t_maxseg)
 604                         goto send;
 605                 /*
 606                  * NOTE! on localhost connections an 'ack' from the remote
 607                  * end may occur synchronously with the output and cause
 608                  * us to flush a buffer queued with moretocome.  XXX
 609                  *
 610                  * note: the len + off check is almost certainly unnecessary.
 611                  */
 612                 if (!(tp->t_flags & TF_MORETOCOME) &&   /* normal case */
 613                     (idle || (tp->t_flags & TF_NODELAY)) &&
 614                     (uint32_t)len + (uint32_t)off >= sbavail(&so->so_snd) &&
 615                     (tp->t_flags & TF_NOPUSH) == 0) {
 616                         goto send;
 617                 }
 618                 if (tp->t_flags & TF_FORCEDATA)         /* typ. timeout case */
 619                         goto send;
 620                 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
 621                         goto send;
 622                 if (SEQ_LT(tp->snd_nxt, tp->snd_max))   /* retransmit case */
 623                         goto send;
 624                 if (sack_rxmit)
 625                         goto send;
 626         }
 627
 628         /*
 629          * Sending of standalone window updates.
 630          *
 631          * Window updates are important when we close our window due to a
 632          * full socket buffer and are opening it again after the application
 633          * reads data from it.  Once the window has opened again and the
 634          * remote end starts to send again the ACK clock takes over and
 635          * provides the most current window information.
 636          *
 637          * We must avoid the silly window syndrome whereas every read
 638          * from the receive buffer, no matter how small, causes a window
 639          * update to be sent.  We also should avoid sending a flurry of
 640          * window updates when the socket buffer had queued a lot of data
 641          * and the application is doing small reads.
 642          *
 643          * Prevent a flurry of pointless window updates by only sending
 644          * an update when we can increase the advertized window by more
 645          * than 1/4th of the socket buffer capacity.  When the buffer is
 646          * getting full or is very small be more aggressive and send an
 647          * update whenever we can increase by two mss sized segments.
 648          * In all other situations the ACK's to new incoming data will
 649          * carry further window increases.
 650          *
 651          * Don't send an independent window update if a delayed
 652          * ACK is pending (it will get piggy-backed on it) or the
 653          * remote side already has done a half-close and won't send
 654          * more data.  Skip this if the connection is in T/TCP
 655          * half-open state.
 656          */
 657         if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
 658             !(tp->t_flags & TF_DELACK) &&
 659             !TCPS_HAVERCVDFIN(tp->t_state)) {
 660                 /*
 661                  * "adv" is the amount we could increase the window,
 662                  * taking into account that we are limited by
 663                  * TCP_MAXWIN << tp->rcv_scale.
 664                  */
 665                 int32_t adv;
 666                 int oldwin;
 667
 668                 adv = recwin;
 669                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
 670                         oldwin = (tp->rcv_adv - tp->rcv_nxt);
 671                         if (adv > oldwin)
 672                                 adv -= oldwin;
 673                         else
 674                                 adv = 0;
 675                 } else
 676                         oldwin = 0;
 677
 678                 /*
 679                  * If the new window size ends up being the same as or less
 680                  * than the old size when it is scaled, then don't force
 681                  * a window update.
 682                  */
 683                 if (oldwin >> tp->rcv_scale >= (adv + oldwin) >> tp->rcv_scale)
 684                         goto dontupdate;
 685
 686                 if (adv >= (int32_t)(2 * tp->t_maxseg) &&
 687                     (adv >= (int32_t)(so->so_rcv.sb_hiwat / 4) ||
 688                      recwin <= (so->so_rcv.sb_hiwat / 8) ||
 689                      so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg ||
 690                      adv >= TCP_MAXWIN << tp->rcv_scale))
 691                         goto send;
 692                 if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat)
 693                         goto send;
 694         }
 695 dontupdate:
 696
 697         /*
 698          * Send if we owe the peer an ACK, RST, SYN, or urgent data.  ACKNOW
 699          * is also a catch-all for the retransmit timer timeout case.
 700          */
 701         if (tp->t_flags & TF_ACKNOW)
 702                 goto send;
 703         if ((flags & TH_RST) ||
 704             ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
 705                 goto send;
 706         if (SEQ_GT(tp->snd_up, tp->snd_una))
 707                 goto send;
 708         /*
 709          * If our state indicates that FIN should be sent
 710          * and we have not yet done so, then we need to send.
 711          */
 712         if (flags & TH_FIN &&
 713             ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
 714                 goto send;
 715         /*
 716          * In SACK, it is possible for tcp_output to fail to send a segment
 717          * after the retransmission timer has been turned off.  Make sure
 718          * that the retransmission timer is set.
 719          */
 720         if ((tp->t_flags & TF_SACK_PERMIT) &&
 721             SEQ_GT(tp->snd_max, tp->snd_una) &&
 722             !tcp_timer_active(tp, TT_REXMT) &&
 723             !tcp_timer_active(tp, TT_PERSIST)) {
 724                 tcp_timer_activate(tp, TT_REXMT, TP_RXTCUR(tp));
 725                 goto just_return;
 726         }
 727         /*
 728          * TCP window updates are not reliable, rather a polling protocol
 729          * using ``persist'' packets is used to insure receipt of window
 730          * updates.  The three ``states'' for the output side are:
 731          *      idle                    not doing retransmits or persists
 732          *      persisting              to move a small or zero window
 733          *      (re)transmitting        and thereby not persisting
 734          *
 735          * tcp_timer_active(tp, TT_PERSIST)
 736          *      is true when we are in persist state.
 737          * (tp->t_flags & TF_FORCEDATA)
 738          *      is set when we are called to send a persist packet.
 739          * tcp_timer_active(tp, TT_REXMT)
 740          *      is set when we are retransmitting
 741          * The output side is idle when both timers are zero.
 742          *
 743          * If send window is too small, there is data to transmit, and no
 744          * retransmit or persist is pending, then go to persist state.
 745          * If nothing happens soon, send when timer expires:
 746          * if window is nonzero, transmit what we can,
 747          * otherwise force out a byte.
 748          */
 749         if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) &&
 750             !tcp_timer_active(tp, TT_PERSIST)) {
 751                 tp->t_rxtshift = 0;
 752                 tcp_setpersist(tp);
 753         }
 754
 755         /*
 756          * No reason to send a segment, just return.
 757          */
 758 just_return:
 759         SOCKBUF_UNLOCK(&so->so_snd);
 760         return (0);
 761
 762 send:
 763         SOCKBUF_LOCK_ASSERT(&so->so_snd);
 764         if (len > 0) {
 765                 if (len >= tp->t_maxseg)
 766                         tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
 767                 else
 768                         tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
 769         }
 770         /*
 771          * Before ESTABLISHED, force sending of initial options
 772          * unless TCP set not to do any options.
 773          * NOTE: we assume that the IP/TCP header plus TCP options
 774          * always fit in a single mbuf, leaving room for a maximum
 775          * link header, i.e.
 776          *      max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
 777          */
 778         optlen = 0;
 779 #ifdef INET6
 780         if (isipv6)
 781                 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
 782         else
 783 #endif
 784                 hdrlen = sizeof (struct tcpiphdr);
 785
 786         if (flags & TH_SYN) {
 787                 tp->snd_nxt = tp->iss;
 788         }
 789
 790         /*
 791          * Compute options for segment.
 792          * We only have to care about SYN and established connection
 793          * segments.  Options for SYN-ACK segments are handled in TCP
 794          * syncache.
 795          */
 796         to.to_flags = 0;
 797         if ((tp->t_flags & TF_NOOPT) == 0) {
 798                 /* Maximum segment size. */
 799                 if (flags & TH_SYN) {
 800                         to.to_mss = tcp_mssopt(&inp->inp_inc);
 801                         if (tp->t_port)
 802                                 to.to_mss -= V_tcp_udp_tunneling_overhead;
 803                         to.to_flags |= TOF_MSS;
 804
 805                         /*
 806                          * On SYN or SYN|ACK transmits on TFO connections,
 807                          * only include the TFO option if it is not a
 808                          * retransmit, as the presence of the TFO option may
 809                          * have caused the original SYN or SYN|ACK to have
 810                          * been dropped by a middlebox.
 811                          */
 812                         if (IS_FASTOPEN(tp->t_flags) &&
 813                             (tp->t_rxtshift == 0)) {
 814                                 if (tp->t_state == TCPS_SYN_RECEIVED) {
 815                                         to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
 816                                         to.to_tfo_cookie =
 817                                             (u_int8_t *)&tp->t_tfo_cookie.server;
 818                                         to.to_flags |= TOF_FASTOPEN;
 819                                         wanted_cookie = 1;
 820                                 } else if (tp->t_state == TCPS_SYN_SENT) {
 821                                         to.to_tfo_len =
 822                                             tp->t_tfo_client_cookie_len;
 823                                         to.to_tfo_cookie =
 824                                             tp->t_tfo_cookie.client;
 825                                         to.to_flags |= TOF_FASTOPEN;
 826                                         wanted_cookie = 1;
 827                                         /*
 828                                          * If we wind up having more data to
 829                                          * send with the SYN than can fit in
 830                                          * one segment, don't send any more
 831                                          * until the SYN|ACK comes back from
 832                                          * the other end.
 833                                          */
 834                                         dont_sendalot = 1;
 835                                 }
 836                         }
 837                 }
 838                 /* Window scaling. */
 839                 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
 840                         to.to_wscale = tp->request_r_scale;
 841                         to.to_flags |= TOF_SCALE;
 842                 }
 843                 /* Timestamps. */
 844                 if ((tp->t_flags & TF_RCVD_TSTMP) ||
 845                     ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
 846                         curticks = tcp_ts_getticks();
 847                         to.to_tsval = curticks + tp->ts_offset;
 848                         to.to_tsecr = tp->ts_recent;
 849                         to.to_flags |= TOF_TS;
 850                         if (tp->t_rxtshift == 1)
 851                                 tp->t_badrxtwin = curticks;
 852                 }
 853
 854                 /* Set receive buffer autosizing timestamp. */
 855                 if (tp->rfbuf_ts == 0 &&
 856                     (so->so_rcv.sb_flags & SB_AUTOSIZE))
 857                         tp->rfbuf_ts = tcp_ts_getticks();
 858
 859                 /* Selective ACK's. */
 860                 if (tp->t_flags & TF_SACK_PERMIT) {
 861                         if (flags & TH_SYN)
 862                                 to.to_flags |= TOF_SACKPERM;
 863                         else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
 864                             tp->rcv_numsacks > 0) {
 865                                 to.to_flags |= TOF_SACK;
 866                                 to.to_nsacks = tp->rcv_numsacks;
 867                                 to.to_sacks = (u_char *)tp->sackblks;
 868                         }
 869                 }
 870 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 871                 /* TCP-MD5 (RFC2385). */
 872                 /*
 873                  * Check that TCP_MD5SIG is enabled in tcpcb to
 874                  * account the size needed to set this TCP option.
 875                  */
 876                 if (tp->t_flags & TF_SIGNATURE)
 877                         to.to_flags |= TOF_SIGNATURE;
 878 #endif /* TCP_SIGNATURE */
 879
 880                 /* Processing the options. */
 881                 hdrlen += optlen = tcp_addoptions(&to, opt);
 882                 /*
 883                  * If we wanted a TFO option to be added, but it was unable
 884                  * to fit, ensure no data is sent.
 885                  */
 886                 if (IS_FASTOPEN(tp->t_flags) && wanted_cookie &&
 887                     !(to.to_flags & TOF_FASTOPEN))
 888                         len = 0;
 889         }
 890         if (tp->t_port) {
 891                 if (V_tcp_udp_tunneling_port == 0) {
 892                         /* The port was removed?? */
 893                         SOCKBUF_UNLOCK(&so->so_snd);
 894                         return (EHOSTUNREACH);
 895                 }
 896                 hdrlen += sizeof(struct udphdr);
 897         }
 898         /*
 899          * Adjust data length if insertion of options will
 900          * bump the packet length beyond the t_maxseg length.
 901          * Clear the FIN bit because we cut off the tail of
 902          * the segment.
 903          */
 904         if (len + optlen + ipoptlen > tp->t_maxseg) {
 905                 flags &= ~TH_FIN;
 906
 907                 if (tso) {
 908                         u_int if_hw_tsomax;
 909                         u_int moff;
 910                         int max_len;
 911
 912                         /* extract TSO information */
 913                         if_hw_tsomax = tp->t_tsomax;
 914                         if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
 915                         if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
 916
 917                         /*
 918                          * Limit a TSO burst to prevent it from
 919                          * overflowing or exceeding the maximum length
 920                          * allowed by the network interface:
 921                          */
 922                         KASSERT(ipoptlen == 0,
 923                             ("%s: TSO can't do IP options", __func__));
 924
 925                         /*
 926                          * Check if we should limit by maximum payload
 927                          * length:
 928                          */
 929                         if (if_hw_tsomax != 0) {
 930                                 /* compute maximum TSO length */
 931                                 max_len = (if_hw_tsomax - hdrlen -
 932                                     max_linkhdr);
 933                                 if (max_len <= 0) {
 934                                         len = 0;
 935                                 } else if (len > max_len) {
 936                                         sendalot = 1;
 937                                         len = max_len;
 938                                 }
 939                         }
 940
 941                         /*
 942                          * Prevent the last segment from being
 943                          * fractional unless the send sockbuf can be
 944                          * emptied:
 945                          */
 946                         max_len = (tp->t_maxseg - optlen);
 947                         if (((uint32_t)off + (uint32_t)len) <
 948                             sbavail(&so->so_snd)) {
 949                                 moff = len % max_len;
 950                                 if (moff != 0) {
 951                                         len -= moff;
 952                                         sendalot = 1;
 953                                 }
 954                         }
 955
 956                         /*
 957                          * In case there are too many small fragments
 958                          * don't use TSO:
 959                          */
 960                         if (len <= max_len) {
 961                                 len = max_len;
 962                                 sendalot = 1;
 963                                 tso = 0;
 964                         }
 965
 966                         /*
 967                          * Send the FIN in a separate segment
 968                          * after the bulk sending is done.
 969                          * We don't trust the TSO implementations
 970                          * to clear the FIN flag on all but the
 971                          * last segment.
 972                          */
 973                         if (tp->t_flags & TF_NEEDFIN)
 974                                 sendalot = 1;
 975                 } else {
 976                         if (optlen + ipoptlen >= tp->t_maxseg) {
 977                                 /*
 978                                  * Since we don't have enough space to put
 979                                  * the IP header chain and the TCP header in
 980                                  * one packet as required by RFC 7112, don't
 981                                  * send it. Also ensure that at least one
 982                                  * byte of the payload can be put into the
 983                                  * TCP segment.
 984                                  */
 985                                 SOCKBUF_UNLOCK(&so->so_snd);
 986                                 error = EMSGSIZE;
 987                                 sack_rxmit = 0;
 988                                 goto out;
 989                         }
 990                         len = tp->t_maxseg - optlen - ipoptlen;
 991                         sendalot = 1;
 992                         if (dont_sendalot)
 993                                 sendalot = 0;
 994                 }
 995         } else
 996                 tso = 0;
 997
 998         KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
 999             ("%s: len > IP_MAXPACKET", __func__));
1000
1001 /*#ifdef DIAGNOSTIC*/
1002 #ifdef INET6
1003         if (max_linkhdr + hdrlen > MCLBYTES)
1004 #else
1005         if (max_linkhdr + hdrlen > MHLEN)
1006 #endif
1007                 panic("tcphdr too big");
1008 /*#endif*/
1009
1010         /*
1011          * This KASSERT is here to catch edge cases at a well defined place.
1012          * Before, those had triggered (random) panic conditions further down.
1013          */
1014         KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
1015
1016         /*
1017          * Grab a header mbuf, attaching a copy of data to
1018          * be transmitted, and initialize the header from
1019          * the template for sends on this connection.
1020          */
1021         if (len) {
1022                 struct mbuf *mb;
1023                 struct sockbuf *msb;
1024                 u_int moff;
1025
1026                 if ((tp->t_flags & TF_FORCEDATA) && len == 1) {
1027                         TCPSTAT_INC(tcps_sndprobe);
1028 #ifdef STATS
1029                         if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1030                                 stats_voi_update_abs_u32(tp->t_stats,
1031                                 VOI_TCP_RETXPB, len);
1032                         else
1033                                 stats_voi_update_abs_u64(tp->t_stats,
1034                                     VOI_TCP_TXPB, len);
1035 #endif /* STATS */
1036                 } else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
1037                         tp->t_sndrexmitpack++;
1038                         TCPSTAT_INC(tcps_sndrexmitpack);
1039                         TCPSTAT_ADD(tcps_sndrexmitbyte, len);
1040 #ifdef STATS
1041                         stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_RETXPB,
1042                             len);
1043 #endif /* STATS */
1044                 } else {
1045                         TCPSTAT_INC(tcps_sndpack);
1046                         TCPSTAT_ADD(tcps_sndbyte, len);
1047 #ifdef STATS
1048                         stats_voi_update_abs_u64(tp->t_stats, VOI_TCP_TXPB,
1049                             len);
1050 #endif /* STATS */
1051                 }
1052 #ifdef INET6
1053                 if (MHLEN < hdrlen + max_linkhdr)
1054                         m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
1055                 else
1056 #endif
1057                         m = m_gethdr(M_NOWAIT, MT_DATA);
1058
1059                 if (m == NULL) {
1060                         SOCKBUF_UNLOCK(&so->so_snd);
1061                         error = ENOBUFS;
1062                         sack_rxmit = 0;
1063                         goto out;
1064                 }
1065
1066                 m->m_data += max_linkhdr;
1067                 m->m_len = hdrlen;
1068
1069                 /*
1070                  * Start the m_copy functions from the closest mbuf
1071                  * to the offset in the socket buffer chain.
1072                  */
1073                 mb = sbsndptr_noadv(&so->so_snd, off, &moff);
1074                 if (len <= MHLEN - hdrlen - max_linkhdr && !hw_tls) {
1075                         m_copydata(mb, moff, len,
1076                             mtod(m, caddr_t) + hdrlen);
1077                         if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1078                                 sbsndptr_adv(&so->so_snd, mb, len);
1079                         m->m_len += len;
1080                 } else {
1081                         if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1082                                 msb = NULL;
1083                         else
1084                                 msb = &so->so_snd;
1085                         m->m_next = tcp_m_copym(mb, moff,
1086                             &len, if_hw_tsomaxsegcount,
1087                             if_hw_tsomaxsegsize, msb, hw_tls);
1088                         if (len <= (tp->t_maxseg - optlen)) {
1089                                 /*
1090                                  * Must have ran out of mbufs for the copy
1091                                  * shorten it to no longer need tso. Lets
1092                                  * not put on sendalot since we are low on
1093                                  * mbufs.
1094                                  */
1095                                 tso = 0;
1096                         }
1097                         if (m->m_next == NULL) {
1098                                 SOCKBUF_UNLOCK(&so->so_snd);
1099                                 (void) m_free(m);
1100                                 error = ENOBUFS;
1101                                 sack_rxmit = 0;
1102                                 goto out;
1103                         }
1104                 }
1105
1106                 /*
1107                  * If we're sending everything we've got, set PUSH.
1108                  * (This will keep happy those implementations which only
1109                  * give data to the user when a buffer fills or
1110                  * a PUSH comes in.)
1111                  */
1112                 if (((uint32_t)off + (uint32_t)len == sbused(&so->so_snd)) &&
1113                     !(flags & TH_SYN))
1114                         flags |= TH_PUSH;
1115                 SOCKBUF_UNLOCK(&so->so_snd);
1116         } else {
1117                 SOCKBUF_UNLOCK(&so->so_snd);
1118                 if (tp->t_flags & TF_ACKNOW)
1119                         TCPSTAT_INC(tcps_sndacks);
1120                 else if (flags & (TH_SYN|TH_FIN|TH_RST))
1121                         TCPSTAT_INC(tcps_sndctrl);
1122                 else if (SEQ_GT(tp->snd_up, tp->snd_una))
1123                         TCPSTAT_INC(tcps_sndurg);
1124                 else
1125                         TCPSTAT_INC(tcps_sndwinup);
1126
1127                 m = m_gethdr(M_NOWAIT, MT_DATA);
1128                 if (m == NULL) {
1129                         error = ENOBUFS;
1130                         sack_rxmit = 0;
1131                         goto out;
1132                 }
1133 #ifdef INET6
1134                 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
1135                     MHLEN >= hdrlen) {
1136                         M_ALIGN(m, hdrlen);
1137                 } else
1138 #endif
1139                 m->m_data += max_linkhdr;
1140                 m->m_len = hdrlen;
1141         }
1142         SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
1143         m->m_pkthdr.rcvif = (struct ifnet *)0;
1144 #ifdef MAC
1145         mac_inpcb_create_mbuf(inp, m);
1146 #endif
1147 #ifdef INET6
1148         if (isipv6) {
1149                 ip6 = mtod(m, struct ip6_hdr *);
1150                 if (tp->t_port) {
1151                         udp = (struct udphdr *)((caddr_t)ip6 + sizeof(struct ip6_hdr));
1152                         udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1153                         udp->uh_dport = tp->t_port;
1154                         ulen = hdrlen + len - sizeof(struct ip6_hdr);
1155                         udp->uh_ulen = htons(ulen);
1156                         th = (struct tcphdr *)(udp + 1);
1157                 } else {
1158                         th = (struct tcphdr *)(ip6 + 1);
1159                 }
1160                 tcpip_fillheaders(inp, tp->t_port, ip6, th);
1161         } else
1162 #endif /* INET6 */
1163         {
1164                 ip = mtod(m, struct ip *);
1165                 if (tp->t_port) {
1166                         udp = (struct udphdr *)((caddr_t)ip + sizeof(struct ip));
1167                         udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1168                         udp->uh_dport = tp->t_port;
1169                         ulen = hdrlen + len - sizeof(struct ip);
1170                         udp->uh_ulen = htons(ulen);
1171                         th = (struct tcphdr *)(udp + 1);
1172                 } else
1173                         th = (struct tcphdr *)(ip + 1);
1174                 tcpip_fillheaders(inp, tp->t_port, ip, th);
1175         }
1176
1177         /*
1178          * Fill in fields, remembering maximum advertised
1179          * window for use in delaying messages about window sizes.
1180          * If resending a FIN, be sure not to use a new sequence number.
1181          */
1182         if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1183             tp->snd_nxt == tp->snd_max)
1184                 tp->snd_nxt--;
1185         /*
1186          * If we are starting a connection, send ECN setup
1187          * SYN packet. If we are on a retransmit, we may
1188          * resend those bits a number of times as per
1189          * RFC 3168.
1190          */
1191         if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn) {
1192                 flags |= tcp_ecn_output_syn_sent(tp);
1193         }
1194         /* Also handle parallel SYN for ECN */
1195         if ((TCPS_HAVERCVDSYN(tp->t_state)) &&
1196             (tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT))) {
1197                 int ect = tcp_ecn_output_established(tp, &flags, len, sack_rxmit);
1198                 if ((tp->t_state == TCPS_SYN_RECEIVED) &&
1199                     (tp->t_flags2 & TF2_ECN_SND_ECE))
1200                         tp->t_flags2 &= ~TF2_ECN_SND_ECE;
1201 #ifdef INET6
1202                 if (isipv6) {
1203                         ip6->ip6_flow &= ~htonl(IPTOS_ECN_MASK << IPV6_FLOWLABEL_LEN);
1204                         ip6->ip6_flow |= htonl(ect << IPV6_FLOWLABEL_LEN);
1205                 }
1206                 else
1207 #endif
1208                 {
1209                         ip->ip_tos &= ~IPTOS_ECN_MASK;
1210                         ip->ip_tos |= ect;
1211                 }
1212         }
1213
1214         /*
1215          * If we are doing retransmissions, then snd_nxt will
1216          * not reflect the first unsent octet.  For ACK only
1217          * packets, we do not want the sequence number of the
1218          * retransmitted packet, we want the sequence number
1219          * of the next unsent octet.  So, if there is no data
1220          * (and no SYN or FIN), use snd_max instead of snd_nxt
1221          * when filling in ti_seq.  But if we are in persist
1222          * state, snd_max might reflect one byte beyond the
1223          * right edge of the window, so use snd_nxt in that
1224          * case, since we know we aren't doing a retransmission.
1225          * (retransmit and persist are mutually exclusive...)
1226          */
1227         if (sack_rxmit == 0) {
1228                 if (len || (flags & (TH_SYN|TH_FIN)) ||
1229                     tcp_timer_active(tp, TT_PERSIST))
1230                         th->th_seq = htonl(tp->snd_nxt);
1231                 else
1232                         th->th_seq = htonl(tp->snd_max);
1233         } else {
1234                 th->th_seq = htonl(p->rxmit);
1235                 p->rxmit += len;
1236                 /*
1237                  * Lost Retransmission Detection
1238                  * trigger resending of a (then
1239                  * still existing) hole, when
1240                  * fack acks recoverypoint.
1241                  */
1242                 if ((tp->t_flags & TF_LRD) && SEQ_GEQ(p->rxmit, p->end))
1243                         p->rxmit = tp->snd_recover;
1244                 tp->sackhint.sack_bytes_rexmit += len;
1245         }
1246         if (IN_RECOVERY(tp->t_flags)) {
1247                 /*
1248                  * Account all bytes transmitted while
1249                  * IN_RECOVERY, simplifying PRR and
1250                  * Lost Retransmit Detection
1251                  */
1252                 tp->sackhint.prr_out += len;
1253         }
1254         th->th_ack = htonl(tp->rcv_nxt);
1255         if (optlen) {
1256                 bcopy(opt, th + 1, optlen);
1257                 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
1258         }
1259         tcp_set_flags(th, flags);
1260         /*
1261          * Calculate receive window.  Don't shrink window,
1262          * but avoid silly window syndrome.
1263          * If a RST segment is sent, advertise a window of zero.
1264          */
1265         if (flags & TH_RST) {
1266                 recwin = 0;
1267         } else {
1268                 if (recwin < (so->so_rcv.sb_hiwat / 4) &&
1269                     recwin < tp->t_maxseg)
1270                         recwin = 0;
1271                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
1272                     recwin < (tp->rcv_adv - tp->rcv_nxt))
1273                         recwin = (tp->rcv_adv - tp->rcv_nxt);
1274         }
1275         /*
1276          * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1277          * or <SYN,ACK>) segment itself is never scaled.  The <SYN,ACK>
1278          * case is handled in syncache.
1279          */
1280         if (flags & TH_SYN)
1281                 th->th_win = htons((u_short)
1282                                 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1283         else {
1284                 /* Avoid shrinking window with window scaling. */
1285                 recwin = roundup2(recwin, 1 << tp->rcv_scale);
1286                 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
1287         }
1288
1289         /*
1290          * Adjust the RXWIN0SENT flag - indicate that we have advertised
1291          * a 0 window.  This may cause the remote transmitter to stall.  This
1292          * flag tells soreceive() to disable delayed acknowledgements when
1293          * draining the buffer.  This can occur if the receiver is attempting
1294          * to read more data than can be buffered prior to transmitting on
1295          * the connection.
1296          */
1297         if (th->th_win == 0) {
1298                 tp->t_sndzerowin++;
1299                 tp->t_flags |= TF_RXWIN0SENT;
1300         } else
1301                 tp->t_flags &= ~TF_RXWIN0SENT;
1302         if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1303                 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1304                 th->th_flags |= TH_URG;
1305         } else
1306                 /*
1307                  * If no urgent pointer to send, then we pull
1308                  * the urgent pointer to the left edge of the send window
1309                  * so that it doesn't drift into the send window on sequence
1310                  * number wraparound.
1311                  */
1312                 tp->snd_up = tp->snd_una;               /* drag it along */
1313
1314         /*
1315          * Put TCP length in extended header, and then
1316          * checksum extended header and data.
1317          */
1318         m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1319
1320 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1321         if (to.to_flags & TOF_SIGNATURE) {
1322                 /*
1323                  * Calculate MD5 signature and put it into the place
1324                  * determined before.
1325                  * NOTE: since TCP options buffer doesn't point into
1326                  * mbuf's data, calculate offset and use it.
1327                  */
1328                 if (!TCPMD5_ENABLED() || (error = TCPMD5_OUTPUT(m, th,
1329                     (u_char *)(th + 1) + (to.to_signature - opt))) != 0) {
1330                         /*
1331                          * Do not send segment if the calculation of MD5
1332                          * digest has failed.
1333                          */
1334                         m_freem(m);
1335                         goto out;
1336                 }
1337         }
1338 #endif
1339 #ifdef INET6
1340         if (isipv6) {
1341                 /*
1342                  * There is no need to fill in ip6_plen right now.
1343                  * It will be filled later by ip6_output.
1344                  */
1345                 if (tp->t_port) {
1346                         m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
1347                         m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
1348                         udp->uh_sum = in6_cksum_pseudo(ip6, ulen, IPPROTO_UDP, 0);
1349                         th->th_sum = htons(0);
1350                         UDPSTAT_INC(udps_opackets);
1351                 } else {
1352                         m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1353                         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1354                         th->th_sum = in6_cksum_pseudo(ip6,
1355                             sizeof(struct tcphdr) + optlen + len, IPPROTO_TCP,
1356                             0);
1357                 }
1358         }
1359 #endif
1360 #if defined(INET6) && defined(INET)
1361         else
1362 #endif
1363 #ifdef INET
1364         {
1365                 if (tp->t_port) {
1366                         m->m_pkthdr.csum_flags = CSUM_UDP;
1367                         m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
1368                         udp->uh_sum = in_pseudo(ip->ip_src.s_addr,
1369                            ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP));
1370                         th->th_sum = htons(0);
1371                         UDPSTAT_INC(udps_opackets);
1372                 } else {
1373                         m->m_pkthdr.csum_flags = CSUM_TCP;
1374                         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1375                         th->th_sum = in_pseudo(ip->ip_src.s_addr,
1376                             ip->ip_dst.s_addr, htons(sizeof(struct tcphdr) +
1377                             IPPROTO_TCP + len + optlen));
1378                 }
1379
1380                 /* IP version must be set here for ipv4/ipv6 checking later */
1381                 KASSERT(ip->ip_v == IPVERSION,
1382                     ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1383         }
1384 #endif
1385
1386         /*
1387          * Enable TSO and specify the size of the segments.
1388          * The TCP pseudo header checksum is always provided.
1389          */
1390         if (tso) {
1391                 KASSERT(len > tp->t_maxseg - optlen,
1392                     ("%s: len <= tso_segsz", __func__));
1393                 m->m_pkthdr.csum_flags |= CSUM_TSO;
1394                 m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen;
1395         }
1396
1397         KASSERT(len + hdrlen == m_length(m, NULL),
1398             ("%s: mbuf chain shorter than expected: %d + %u != %u",
1399             __func__, len, hdrlen, m_length(m, NULL)));
1400
1401 #ifdef TCP_HHOOK
1402         /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1403         hhook_run_tcp_est_out(tp, th, &to, len, tso);
1404 #endif
1405
1406         TCP_PROBE3(debug__output, tp, th, m);
1407
1408         /* We're getting ready to send; log now. */
1409         /* XXXMT: We are not honoring verbose logging. */
1410
1411         if (tcp_bblogging_on(tp))
1412                 lgb = tcp_log_event(tp, th, &so->so_rcv, &so->so_snd,
1413                     TCP_LOG_OUT, ERRNO_UNK, len, NULL, false, NULL, NULL, 0,
1414                     NULL);
1415         else
1416                 lgb = NULL;
1417
1418         /*
1419          * Fill in IP length and desired time to live and
1420          * send to IP level.  There should be a better way
1421          * to handle ttl and tos; we could keep them in
1422          * the template, but need a way to checksum without them.
1423          */
1424         /*
1425          * m->m_pkthdr.len should have been set before checksum calculation,
1426          * because in6_cksum() need it.
1427          */
1428 #ifdef INET6
1429         if (isipv6) {
1430                 /*
1431                  * we separately set hoplimit for every segment, since the
1432                  * user might want to change the value via setsockopt.
1433                  * Also, desired default hop limit might be changed via
1434                  * Neighbor Discovery.
1435                  */
1436                 ip6->ip6_hlim = in6_selecthlim(inp, NULL);
1437
1438                 /*
1439                  * Set the packet size here for the benefit of DTrace probes.
1440                  * ip6_output() will set it properly; it's supposed to include
1441                  * the option header lengths as well.
1442                  */
1443                 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
1444
1445                 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss)
1446                         tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1447                 else
1448                         tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1449
1450                 if (tp->t_state == TCPS_SYN_SENT)
1451                         TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
1452
1453                 TCP_PROBE5(send, NULL, tp, ip6, tp, th);
1454
1455 #ifdef TCPPCAP
1456                 /* Save packet, if requested. */
1457                 tcp_pcap_add(th, m, &(tp->t_outpkts));
1458 #endif
1459
1460                 /* TODO: IPv6 IP6TOS_ECT bit on */
1461                 error = ip6_output(m, inp->in6p_outputopts, &inp->inp_route6,
1462                     ((so->so_options & SO_DONTROUTE) ?  IP_ROUTETOIF : 0),
1463                     NULL, NULL, inp);
1464
1465                 if (error == EMSGSIZE && inp->inp_route6.ro_nh != NULL)
1466                         mtu = inp->inp_route6.ro_nh->nh_mtu;
1467         }
1468 #endif /* INET6 */
1469 #if defined(INET) && defined(INET6)
1470         else
1471 #endif
1472 #ifdef INET
1473     {
1474         ip->ip_len = htons(m->m_pkthdr.len);
1475 #ifdef INET6
1476         if (inp->inp_vflag & INP_IPV6PROTO)
1477                 ip->ip_ttl = in6_selecthlim(inp, NULL);
1478 #endif /* INET6 */
1479         /*
1480          * If we do path MTU discovery, then we set DF on every packet.
1481          * This might not be the best thing to do according to RFC3390
1482          * Section 2. However the tcp hostcache migitates the problem
1483          * so it affects only the first tcp connection with a host.
1484          *
1485          * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1486          */
1487         if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) {
1488                 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1489                 if (tp->t_port == 0 || len < V_tcp_minmss) {
1490                         ip->ip_off |= htons(IP_DF);
1491                 }
1492         } else {
1493                 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1494         }
1495
1496         if (tp->t_state == TCPS_SYN_SENT)
1497                 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
1498
1499         TCP_PROBE5(send, NULL, tp, ip, tp, th);
1500
1501 #ifdef TCPPCAP
1502         /* Save packet, if requested. */
1503         tcp_pcap_add(th, m, &(tp->t_outpkts));
1504 #endif
1505
1506         error = ip_output(m, inp->inp_options, &inp->inp_route,
1507             ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0, inp);
1508
1509         if (error == EMSGSIZE && inp->inp_route.ro_nh != NULL)
1510                 mtu = inp->inp_route.ro_nh->nh_mtu;
1511     }
1512 #endif /* INET */
1513
1514         if (lgb != NULL) {
1515                 lgb->tlb_errno = error;
1516                 lgb = NULL;
1517         }
1518 out:
1519         if (error == 0)
1520                 tcp_account_for_send(tp, len, (tp->snd_nxt != tp->snd_max), 0, hw_tls);
1521         /*
1522          * In transmit state, time the transmission and arrange for
1523          * the retransmit.  In persist state, just set snd_max.
1524          */
1525         if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1526             !tcp_timer_active(tp, TT_PERSIST)) {
1527                 tcp_seq startseq = tp->snd_nxt;
1528
1529                 /*
1530                  * Advance snd_nxt over sequence space of this segment.
1531                  */
1532                 if (flags & (TH_SYN|TH_FIN)) {
1533                         if (flags & TH_SYN)
1534                                 tp->snd_nxt++;
1535                         if (flags & TH_FIN) {
1536                                 tp->snd_nxt++;
1537                                 tp->t_flags |= TF_SENTFIN;
1538                         }
1539                 }
1540                 if (sack_rxmit)
1541                         goto timer;
1542                 tp->snd_nxt += len;
1543                 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1544                         /*
1545                          * Update "made progress" indication if we just
1546                          * added new data to an empty socket buffer.
1547                          */
1548                         if (tp->snd_una == tp->snd_max)
1549                                 tp->t_acktime = ticks;
1550                         tp->snd_max = tp->snd_nxt;
1551                         /*
1552                          * Time this transmission if not a retransmission and
1553                          * not currently timing anything.
1554                          */
1555                         tp->t_sndtime = ticks;
1556                         if (tp->t_rtttime == 0) {
1557                                 tp->t_rtttime = ticks;
1558                                 tp->t_rtseq = startseq;
1559                                 TCPSTAT_INC(tcps_segstimed);
1560                         }
1561 #ifdef STATS
1562                         if (!(tp->t_flags & TF_GPUTINPROG) && len) {
1563                                 tp->t_flags |= TF_GPUTINPROG;
1564                                 tp->gput_seq = startseq;
1565                                 tp->gput_ack = startseq +
1566                                     ulmin(sbavail(&so->so_snd) - off, sendwin);
1567                                 tp->gput_ts = tcp_ts_getticks();
1568                         }
1569 #endif /* STATS */
1570                 }
1571
1572                 /*
1573                  * Set retransmit timer if not currently set,
1574                  * and not doing a pure ack or a keep-alive probe.
1575                  * Initial value for retransmit timer is smoothed
1576                  * round-trip time + 2 * round-trip time variance.
1577                  * Initialize shift counter which is used for backoff
1578                  * of retransmit time.
1579                  */
1580 timer:
1581                 if (!tcp_timer_active(tp, TT_REXMT) &&
1582                     ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1583                      (tp->snd_nxt != tp->snd_una))) {
1584                         if (tcp_timer_active(tp, TT_PERSIST)) {
1585                                 tcp_timer_activate(tp, TT_PERSIST, 0);
1586                                 tp->t_rxtshift = 0;
1587                         }
1588                         tcp_timer_activate(tp, TT_REXMT, TP_RXTCUR(tp));
1589                 } else if (len == 0 && sbavail(&so->so_snd) &&
1590                     !tcp_timer_active(tp, TT_REXMT) &&
1591                     !tcp_timer_active(tp, TT_PERSIST)) {
1592                         /*
1593                          * Avoid a situation where we do not set persist timer
1594                          * after a zero window condition. For example:
1595                          * 1) A -> B: packet with enough data to fill the window
1596                          * 2) B -> A: ACK for #1 + new data (0 window
1597                          *    advertisement)
1598                          * 3) A -> B: ACK for #2, 0 len packet
1599                          *
1600                          * In this case, A will not activate the persist timer,
1601                          * because it chose to send a packet. Unless tcp_output
1602                          * is called for some other reason (delayed ack timer,
1603                          * another input packet from B, socket syscall), A will
1604                          * not send zero window probes.
1605                          *
1606                          * So, if you send a 0-length packet, but there is data
1607                          * in the socket buffer, and neither the rexmt or
1608                          * persist timer is already set, then activate the
1609                          * persist timer.
1610                          */
1611                         tp->t_rxtshift = 0;
1612                         tcp_setpersist(tp);
1613                 }
1614         } else {
1615                 /*
1616                  * Persist case, update snd_max but since we are in
1617                  * persist mode (no window) we do not update snd_nxt.
1618                  */
1619                 int xlen = len;
1620                 if (flags & TH_SYN)
1621                         ++xlen;
1622                 if (flags & TH_FIN) {
1623                         ++xlen;
1624                         tp->t_flags |= TF_SENTFIN;
1625                 }
1626                 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1627                         tp->snd_max = tp->snd_nxt + xlen;
1628         }
1629         if ((error == 0) &&
1630             (TCPS_HAVEESTABLISHED(tp->t_state) &&
1631              (tp->t_flags & TF_SACK_PERMIT) &&
1632              tp->rcv_numsacks > 0)) {
1633                     /* Clean up any DSACK's sent */
1634                     tcp_clean_dsack_blocks(tp);
1635         }
1636         if (error) {
1637                 /*
1638                  * We know that the packet was lost, so back out the
1639                  * sequence number advance, if any.
1640                  *
1641                  * If the error is EPERM the packet got blocked by the
1642                  * local firewall.  Normally we should terminate the
1643                  * connection but the blocking may have been spurious
1644                  * due to a firewall reconfiguration cycle.  So we treat
1645                  * it like a packet loss and let the retransmit timer and
1646                  * timeouts do their work over time.
1647                  * XXX: It is a POLA question whether calling tcp_drop right
1648                  * away would be the really correct behavior instead.
1649                  */
1650                 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1651                     !tcp_timer_active(tp, TT_PERSIST)) &&
1652                     ((flags & TH_SYN) == 0) &&
1653                     (error != EPERM)) {
1654                         if (sack_rxmit) {
1655                                 p->rxmit -= len;
1656                                 tp->sackhint.sack_bytes_rexmit -= len;
1657                                 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1658                                     ("sackhint bytes rtx >= 0"));
1659                                 KASSERT((flags & TH_FIN) == 0,
1660                                     ("error while FIN with SACK rxmit"));
1661                         } else {
1662                                 tp->snd_nxt -= len;
1663                                 if (flags & TH_FIN)
1664                                         tp->snd_nxt--;
1665                         }
1666                 }
1667                 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);     /* Check gotos. */
1668                 switch (error) {
1669                 case EACCES:
1670                 case EPERM:
1671                         tp->t_softerror = error;
1672                         return (error);
1673                 case ENOBUFS:
1674                         TCP_XMIT_TIMER_ASSERT(tp, len, flags);
1675                         tp->snd_cwnd = tp->t_maxseg;
1676                         return (0);
1677                 case EMSGSIZE:
1678                         /*
1679                          * For some reason the interface we used initially
1680                          * to send segments changed to another or lowered
1681                          * its MTU.
1682                          * If TSO was active we either got an interface
1683                          * without TSO capabilits or TSO was turned off.
1684                          * If we obtained mtu from ip_output() then update
1685                          * it and try again.
1686                          */
1687                         if (tso)
1688                                 tp->t_flags &= ~TF_TSO;
1689                         if (mtu != 0) {
1690                                 tcp_mss_update(tp, -1, mtu, NULL, NULL);
1691                                 goto again;
1692                         }
1693                         return (error);
1694                 case EHOSTDOWN:
1695                 case EHOSTUNREACH:
1696                 case ENETDOWN:
1697                 case ENETUNREACH:
1698                         if (TCPS_HAVERCVDSYN(tp->t_state)) {
1699                                 tp->t_softerror = error;
1700                                 return (0);
1701                         }
1702                         /* FALLTHROUGH */
1703                 default:
1704                         return (error);
1705                 }
1706         }
1707         TCPSTAT_INC(tcps_sndtotal);
1708
1709         /*
1710          * Data sent (as far as we can tell).
1711          * If this advertises a larger window than any other segment,
1712          * then remember the size of the advertised window.
1713          * Any pending ACK has now been sent.
1714          */
1715         if (SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1716                 tp->rcv_adv = tp->rcv_nxt + recwin;
1717         tp->last_ack_sent = tp->rcv_nxt;
1718         tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1719         if (tcp_timer_active(tp, TT_DELACK))
1720                 tcp_timer_activate(tp, TT_DELACK, 0);
1721 #if 0
1722         /*
1723          * This completely breaks TCP if newreno is turned on.  What happens
1724          * is that if delayed-acks are turned on on the receiver, this code
1725          * on the transmitter effectively destroys the TCP window, forcing
1726          * it to four packets (1.5Kx4 = 6K window).
1727          */
1728         if (sendalot && --maxburst)
1729                 goto again;
1730 #endif
1731         if (sendalot)
1732                 goto again;
1733         return (0);
1734 }
1735
1736 void
1737 tcp_setpersist(struct tcpcb *tp)
1738 {
1739         int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1740         int tt;
1741         int maxunacktime;
1742
1743         tp->t_flags &= ~TF_PREVVALID;
1744         if (tcp_timer_active(tp, TT_REXMT))
1745                 panic("tcp_setpersist: retransmit pending");
1746         /*
1747          * If the state is already closed, don't bother.
1748          */
1749         if (tp->t_state == TCPS_CLOSED)
1750                 return;
1751
1752         /*
1753          * Start/restart persistence timer.
1754          */
1755         TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1756                       tcp_persmin, tcp_persmax);
1757         if (TP_MAXUNACKTIME(tp) && tp->t_acktime) {
1758                 maxunacktime = tp->t_acktime + TP_MAXUNACKTIME(tp) - ticks;
1759                 if (maxunacktime < 1)
1760                         maxunacktime = 1;
1761                 if (maxunacktime < tt)
1762                         tt = maxunacktime;
1763         }
1764         tcp_timer_activate(tp, TT_PERSIST, tt);
1765         if (tp->t_rxtshift < V_tcp_retries)
1766                 tp->t_rxtshift++;
1767 }
1768
1769 /*
1770  * Insert TCP options according to the supplied parameters to the place
1771  * optp in a consistent way.  Can handle unaligned destinations.
1772  *
1773  * The order of the option processing is crucial for optimal packing and
1774  * alignment for the scarce option space.
1775  *
1776  * The optimal order for a SYN/SYN-ACK segment is:
1777  *   MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1778  *   Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1779  *
1780  * The SACK options should be last.  SACK blocks consume 8*n+2 bytes.
1781  * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1782  * At minimum we need 10 bytes (to generate 1 SACK block).  If both
1783  * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1784  * we only have 10 bytes for SACK options (40 - (12 + 18)).
1785  */
1786 int
1787 tcp_addoptions(struct tcpopt *to, u_char *optp)
1788 {
1789         u_int32_t mask, optlen = 0;
1790
1791         for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1792                 if ((to->to_flags & mask) != mask)
1793                         continue;
1794                 if (optlen == TCP_MAXOLEN)
1795                         break;
1796                 switch (to->to_flags & mask) {
1797                 case TOF_MSS:
1798                         while (optlen % 4) {
1799                                 optlen += TCPOLEN_NOP;
1800                                 *optp++ = TCPOPT_NOP;
1801                         }
1802                         if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1803                                 continue;
1804                         optlen += TCPOLEN_MAXSEG;
1805                         *optp++ = TCPOPT_MAXSEG;
1806                         *optp++ = TCPOLEN_MAXSEG;
1807                         to->to_mss = htons(to->to_mss);
1808                         bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1809                         optp += sizeof(to->to_mss);
1810                         break;
1811                 case TOF_SCALE:
1812                         while (!optlen || optlen % 2 != 1) {
1813                                 optlen += TCPOLEN_NOP;
1814                                 *optp++ = TCPOPT_NOP;
1815                         }
1816                         if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1817                                 continue;
1818                         optlen += TCPOLEN_WINDOW;
1819                         *optp++ = TCPOPT_WINDOW;
1820                         *optp++ = TCPOLEN_WINDOW;
1821                         *optp++ = to->to_wscale;
1822                         break;
1823                 case TOF_SACKPERM:
1824                         while (optlen % 2) {
1825                                 optlen += TCPOLEN_NOP;
1826                                 *optp++ = TCPOPT_NOP;
1827                         }
1828                         if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1829                                 continue;
1830                         optlen += TCPOLEN_SACK_PERMITTED;
1831                         *optp++ = TCPOPT_SACK_PERMITTED;
1832                         *optp++ = TCPOLEN_SACK_PERMITTED;
1833                         break;
1834                 case TOF_TS:
1835                         while (!optlen || optlen % 4 != 2) {
1836                                 optlen += TCPOLEN_NOP;
1837                                 *optp++ = TCPOPT_NOP;
1838                         }
1839                         if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1840                                 continue;
1841                         optlen += TCPOLEN_TIMESTAMP;
1842                         *optp++ = TCPOPT_TIMESTAMP;
1843                         *optp++ = TCPOLEN_TIMESTAMP;
1844                         to->to_tsval = htonl(to->to_tsval);
1845                         to->to_tsecr = htonl(to->to_tsecr);
1846                         bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1847                         optp += sizeof(to->to_tsval);
1848                         bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1849                         optp += sizeof(to->to_tsecr);
1850                         break;
1851                 case TOF_SIGNATURE:
1852                         {
1853                         int siglen = TCPOLEN_SIGNATURE - 2;
1854
1855                         while (!optlen || optlen % 4 != 2) {
1856                                 optlen += TCPOLEN_NOP;
1857                                 *optp++ = TCPOPT_NOP;
1858                         }
1859                         if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) {
1860                                 to->to_flags &= ~TOF_SIGNATURE;
1861                                 continue;
1862                         }
1863                         optlen += TCPOLEN_SIGNATURE;
1864                         *optp++ = TCPOPT_SIGNATURE;
1865                         *optp++ = TCPOLEN_SIGNATURE;
1866                         to->to_signature = optp;
1867                         while (siglen--)
1868                                  *optp++ = 0;
1869                         break;
1870                         }
1871                 case TOF_SACK:
1872                         {
1873                         int sackblks = 0;
1874                         struct sackblk *sack = (struct sackblk *)to->to_sacks;
1875                         tcp_seq sack_seq;
1876
1877                         while (!optlen || optlen % 4 != 2) {
1878                                 optlen += TCPOLEN_NOP;
1879                                 *optp++ = TCPOPT_NOP;
1880                         }
1881                         if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1882                                 continue;
1883                         optlen += TCPOLEN_SACKHDR;
1884                         *optp++ = TCPOPT_SACK;
1885                         sackblks = min(to->to_nsacks,
1886                                         (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1887                         *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1888                         while (sackblks--) {
1889                                 sack_seq = htonl(sack->start);
1890                                 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1891                                 optp += sizeof(sack_seq);
1892                                 sack_seq = htonl(sack->end);
1893                                 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1894                                 optp += sizeof(sack_seq);
1895                                 optlen += TCPOLEN_SACK;
1896                                 sack++;
1897                         }
1898                         TCPSTAT_INC(tcps_sack_send_blocks);
1899                         break;
1900                         }
1901                 case TOF_FASTOPEN:
1902                         {
1903                         int total_len;
1904
1905                         /* XXX is there any point to aligning this option? */
1906                         total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len;
1907                         if (TCP_MAXOLEN - optlen < total_len) {
1908                                 to->to_flags &= ~TOF_FASTOPEN;
1909                                 continue;
1910                         }
1911                         *optp++ = TCPOPT_FAST_OPEN;
1912                         *optp++ = total_len;
1913                         if (to->to_tfo_len > 0) {
1914                                 bcopy(to->to_tfo_cookie, optp, to->to_tfo_len);
1915                                 optp += to->to_tfo_len;
1916                         }
1917                         optlen += total_len;
1918                         break;
1919                         }
1920                 default:
1921                         panic("%s: unknown TCP option type", __func__);
1922                         break;
1923                 }
1924         }
1925
1926         /* Terminate and pad TCP options to a 4 byte boundary. */
1927         if (optlen % 4) {
1928                 optlen += TCPOLEN_EOL;
1929                 *optp++ = TCPOPT_EOL;
1930         }
1931         /*
1932          * According to RFC 793 (STD0007):
1933          *   "The content of the header beyond the End-of-Option option
1934          *    must be header padding (i.e., zero)."
1935          *   and later: "The padding is composed of zeros."
1936          */
1937         while (optlen % 4) {
1938                 optlen += TCPOLEN_PAD;
1939                 *optp++ = TCPOPT_PAD;
1940         }
1941
1942         KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));
1943         return (optlen);
1944 }
1945
1946 /*
1947  * This is a copy of m_copym(), taking the TSO segment size/limit
1948  * constraints into account, and advancing the sndptr as it goes.
1949  */
1950 struct mbuf *
1951 tcp_m_copym(struct mbuf *m, int32_t off0, int32_t *plen,
1952     int32_t seglimit, int32_t segsize, struct sockbuf *sb, bool hw_tls)
1953 {
1954 #ifdef KERN_TLS
1955         struct ktls_session *tls, *ntls;
1956         struct mbuf *start __diagused;
1957 #endif
1958         struct mbuf *n, **np;
1959         struct mbuf *top;
1960         int32_t off = off0;
1961         int32_t len = *plen;
1962         int32_t fragsize;
1963         int32_t len_cp = 0;
1964         int32_t *pkthdrlen;
1965         uint32_t mlen, frags;
1966         bool copyhdr;
1967
1968         KASSERT(off >= 0, ("tcp_m_copym, negative off %d", off));
1969         KASSERT(len >= 0, ("tcp_m_copym, negative len %d", len));
1970         if (off == 0 && m->m_flags & M_PKTHDR)
1971                 copyhdr = true;
1972         else
1973                 copyhdr = false;
1974         while (off > 0) {
1975                 KASSERT(m != NULL, ("tcp_m_copym, offset > size of mbuf chain"));
1976                 if (off < m->m_len)
1977                         break;
1978                 off -= m->m_len;
1979                 if ((sb) && (m == sb->sb_sndptr)) {
1980                         sb->sb_sndptroff += m->m_len;
1981                         sb->sb_sndptr = m->m_next;
1982                 }
1983                 m = m->m_next;
1984         }
1985         np = &top;
1986         top = NULL;
1987         pkthdrlen = NULL;
1988 #ifdef KERN_TLS
1989         if (hw_tls && (m->m_flags & M_EXTPG))
1990                 tls = m->m_epg_tls;
1991         else
1992                 tls = NULL;
1993         start = m;
1994 #endif
1995         while (len > 0) {
1996                 if (m == NULL) {
1997                         KASSERT(len == M_COPYALL,
1998                             ("tcp_m_copym, length > size of mbuf chain"));
1999                         *plen = len_cp;
2000                         if (pkthdrlen != NULL)
2001                                 *pkthdrlen = len_cp;
2002                         break;
2003                 }
2004 #ifdef KERN_TLS
2005                 if (hw_tls) {
2006                         if (m->m_flags & M_EXTPG)
2007                                 ntls = m->m_epg_tls;
2008                         else
2009                                 ntls = NULL;
2010
2011                         /*
2012                          * Avoid mixing TLS records with handshake
2013                          * data or TLS records from different
2014                          * sessions.
2015                          */
2016                         if (tls != ntls) {
2017                                 MPASS(m != start);
2018                                 *plen = len_cp;
2019                                 if (pkthdrlen != NULL)
2020                                         *pkthdrlen = len_cp;
2021                                 break;
2022                         }
2023                 }
2024 #endif
2025                 mlen = min(len, m->m_len - off);
2026                 if (seglimit) {
2027                         /*
2028                          * For M_EXTPG mbufs, add 3 segments
2029                          * + 1 in case we are crossing page boundaries
2030                          * + 2 in case the TLS hdr/trailer are used
2031                          * It is cheaper to just add the segments
2032                          * than it is to take the cache miss to look
2033                          * at the mbuf ext_pgs state in detail.
2034                          */
2035                         if (m->m_flags & M_EXTPG) {
2036                                 fragsize = min(segsize, PAGE_SIZE);
2037                                 frags = 3;
2038                         } else {
2039                                 fragsize = segsize;
2040                                 frags = 0;
2041                         }
2042
2043                         /* Break if we really can't fit anymore. */
2044                         if ((frags + 1) >= seglimit) {
2045                                 *plen = len_cp;
2046                                 if (pkthdrlen != NULL)
2047                                         *pkthdrlen = len_cp;
2048                                 break;
2049                         }
2050
2051                         /*
2052                          * Reduce size if you can't copy the whole
2053                          * mbuf. If we can't copy the whole mbuf, also
2054                          * adjust len so the loop will end after this
2055                          * mbuf.
2056                          */
2057                         if ((frags + howmany(mlen, fragsize)) >= seglimit) {
2058                                 mlen = (seglimit - frags - 1) * fragsize;
2059                                 len = mlen;
2060                                 *plen = len_cp + len;
2061                                 if (pkthdrlen != NULL)
2062                                         *pkthdrlen = *plen;
2063                         }
2064                         frags += howmany(mlen, fragsize);
2065                         if (frags == 0)
2066                                 frags++;
2067                         seglimit -= frags;
2068                         KASSERT(seglimit > 0,
2069                             ("%s: seglimit went too low", __func__));
2070                 }
2071                 if (copyhdr)
2072                         n = m_gethdr(M_NOWAIT, m->m_type);
2073                 else
2074                         n = m_get(M_NOWAIT, m->m_type);
2075                 *np = n;
2076                 if (n == NULL)
2077                         goto nospace;
2078                 if (copyhdr) {
2079                         if (!m_dup_pkthdr(n, m, M_NOWAIT))
2080                                 goto nospace;
2081                         if (len == M_COPYALL)
2082                                 n->m_pkthdr.len -= off0;
2083                         else
2084                                 n->m_pkthdr.len = len;
2085                         pkthdrlen = &n->m_pkthdr.len;
2086                         copyhdr = false;
2087                 }
2088                 n->m_len = mlen;
2089                 len_cp += n->m_len;
2090                 if (m->m_flags & (M_EXT|M_EXTPG)) {
2091                         n->m_data = m->m_data + off;
2092                         mb_dupcl(n, m);
2093                 } else
2094                         bcopy(mtod(m, caddr_t)+off, mtod(n, caddr_t),
2095                             (u_int)n->m_len);
2096
2097                 if (sb && (sb->sb_sndptr == m) &&
2098                     ((n->m_len + off) >= m->m_len) && m->m_next) {
2099                         sb->sb_sndptroff += m->m_len;
2100                         sb->sb_sndptr = m->m_next;
2101                 }
2102                 off = 0;
2103                 if (len != M_COPYALL) {
2104                         len -= n->m_len;
2105                 }
2106                 m = m->m_next;
2107                 np = &n->m_next;
2108         }
2109         return (top);
2110 nospace:
2111         m_freem(top);
2112         return (NULL);
2113 }
2114
2115 void
2116 tcp_sndbuf_autoscale(struct tcpcb *tp, struct socket *so, uint32_t sendwin)
2117 {
2118
2119         /*
2120          * Automatic sizing of send socket buffer.  Often the send buffer
2121          * size is not optimally adjusted to the actual network conditions
2122          * at hand (delay bandwidth product).  Setting the buffer size too
2123          * small limits throughput on links with high bandwidth and high
2124          * delay (eg. trans-continental/oceanic links).  Setting the
2125          * buffer size too big consumes too much real kernel memory,
2126          * especially with many connections on busy servers.
2127          *
2128          * The criteria to step up the send buffer one notch are:
2129          *  1. receive window of remote host is larger than send buffer
2130          *     (with a fudge factor of 5/4th);
2131          *  2. send buffer is filled to 7/8th with data (so we actually
2132          *     have data to make use of it);
2133          *  3. send buffer fill has not hit maximal automatic size;
2134          *  4. our send window (slow start and cogestion controlled) is
2135          *     larger than sent but unacknowledged data in send buffer.
2136          *
2137          * The remote host receive window scaling factor may limit the
2138          * growing of the send buffer before it reaches its allowed
2139          * maximum.
2140          *
2141          * It scales directly with slow start or congestion window
2142          * and does at most one step per received ACK.  This fast
2143          * scaling has the drawback of growing the send buffer beyond
2144          * what is strictly necessary to make full use of a given
2145          * delay*bandwidth product.  However testing has shown this not
2146          * to be much of an problem.  At worst we are trading wasting
2147          * of available bandwidth (the non-use of it) for wasting some
2148          * socket buffer memory.
2149          *
2150          * TODO: Shrink send buffer during idle periods together
2151          * with congestion window.  Requires another timer.  Has to
2152          * wait for upcoming tcp timer rewrite.
2153          *
2154          * XXXGL: should there be used sbused() or sbavail()?
2155          */
2156         if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
2157                 int lowat;
2158
2159                 lowat = V_tcp_sendbuf_auto_lowat ? so->so_snd.sb_lowat : 0;
2160                 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat - lowat &&
2161                     sbused(&so->so_snd) >=
2162                     (so->so_snd.sb_hiwat / 8 * 7) - lowat &&
2163                     sbused(&so->so_snd) < V_tcp_autosndbuf_max &&
2164                     sendwin >= (sbused(&so->so_snd) -
2165                     (tp->snd_nxt - tp->snd_una))) {
2166                         if (!sbreserve_locked(so, SO_SND,
2167                             min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
2168                              V_tcp_autosndbuf_max), curthread))
2169                                 so->so_snd.sb_flags &= ~SB_AUTOSIZE;
2170                 }
2171         }
2172 }