sys/netinet/tcp_output.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-3-Clause
   3  *
   4  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  * 3. Neither the name of the University nor the names of its contributors
  16  *    may be used to endorse or promote products derived from this software
  17  *    without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  29  * SUCH DAMAGE.
  30  *
  31  *      @(#)tcp_output.c        8.4 (Berkeley) 5/24/95
  32  */
  33
  34 #include <sys/cdefs.h>
  35 __FBSDID("$FreeBSD$");
  36
  37 #include "opt_inet.h"
  38 #include "opt_inet6.h"
  39 #include "opt_ipsec.h"
  40 #include "opt_kern_tls.h"
  41
  42 #include <sys/param.h>
  43 #include <sys/systm.h>
  44 #include <sys/arb.h>
  45 #include <sys/domain.h>
  46 #ifdef TCP_HHOOK
  47 #include <sys/hhook.h>
  48 #endif
  49 #include <sys/kernel.h>
  50 #ifdef KERN_TLS
  51 #include <sys/ktls.h>
  52 #endif
  53 #include <sys/lock.h>
  54 #include <sys/mbuf.h>
  55 #include <sys/mutex.h>
  56 #include <sys/protosw.h>
  57 #include <sys/qmath.h>
  58 #include <sys/sdt.h>
  59 #include <sys/socket.h>
  60 #include <sys/socketvar.h>
  61 #include <sys/sysctl.h>
  62 #include <sys/stats.h>
  63
  64 #include <net/if.h>
  65 #include <net/route.h>
  66 #include <net/route/nhop.h>
  67 #include <net/vnet.h>
  68
  69 #include <netinet/in.h>
  70 #include <netinet/in_kdtrace.h>
  71 #include <netinet/in_systm.h>
  72 #include <netinet/ip.h>
  73 #include <netinet/in_pcb.h>
  74 #include <netinet/ip_var.h>
  75 #include <netinet/ip_options.h>
  76 #ifdef INET6
  77 #include <netinet6/in6_pcb.h>
  78 #include <netinet/ip6.h>
  79 #include <netinet6/ip6_var.h>
  80 #endif
  81 #include <netinet/tcp.h>
  82 #define TCPOUTFLAGS
  83 #include <netinet/tcp_fsm.h>
  84 #include <netinet/tcp_seq.h>
  85 #include <netinet/tcp_var.h>
  86 #include <netinet/tcp_log_buf.h>
  87 #include <netinet/tcp_syncache.h>
  88 #include <netinet/tcp_timer.h>
  89 #include <netinet/tcpip.h>
  90 #include <netinet/cc/cc.h>
  91 #include <netinet/tcp_fastopen.h>
  92 #ifdef TCPPCAP
  93 #include <netinet/tcp_pcap.h>
  94 #endif
  95 #ifdef TCP_OFFLOAD
  96 #include <netinet/tcp_offload.h>
  97 #endif
  98 #include <netinet/tcp_ecn.h>
  99
 100 #include <netipsec/ipsec_support.h>
 101
 102 #include <netinet/udp.h>
 103 #include <netinet/udp_var.h>
 104 #include <machine/in_cksum.h>
 105
 106 #include <security/mac/mac_framework.h>
 107
 108 VNET_DEFINE(int, path_mtu_discovery) = 1;
 109 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_VNET | CTLFLAG_RW,
 110         &VNET_NAME(path_mtu_discovery), 1,
 111         "Enable Path MTU Discovery");
 112
 113 VNET_DEFINE(int, tcp_do_tso) = 1;
 114 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_VNET | CTLFLAG_RW,
 115         &VNET_NAME(tcp_do_tso), 0,
 116         "Enable TCP Segmentation Offload");
 117
 118 VNET_DEFINE(int, tcp_sendspace) = 1024*32;
 119 #define V_tcp_sendspace VNET(tcp_sendspace)
 120 SYSCTL_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_VNET | CTLFLAG_RW,
 121         &VNET_NAME(tcp_sendspace), 0, "Initial send socket buffer size");
 122
 123 VNET_DEFINE(int, tcp_do_autosndbuf) = 1;
 124 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
 125         &VNET_NAME(tcp_do_autosndbuf), 0,
 126         "Enable automatic send buffer sizing");
 127
 128 VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024;
 129 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_VNET | CTLFLAG_RW,
 130         &VNET_NAME(tcp_autosndbuf_inc), 0,
 131         "Incrementor step size of automatic send buffer");
 132
 133 VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024;
 134 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
 135         &VNET_NAME(tcp_autosndbuf_max), 0,
 136         "Max size of automatic send buffer");
 137
 138 VNET_DEFINE(int, tcp_sendbuf_auto_lowat) = 0;
 139 #define V_tcp_sendbuf_auto_lowat        VNET(tcp_sendbuf_auto_lowat)
 140 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto_lowat, CTLFLAG_VNET | CTLFLAG_RW,
 141         &VNET_NAME(tcp_sendbuf_auto_lowat), 0,
 142         "Modify threshold for auto send buffer growth to account for SO_SNDLOWAT");
 143
 144 /*
 145  * Make sure that either retransmit or persist timer is set for SYN, FIN and
 146  * non-ACK.
 147  */
 148 #define TCP_XMIT_TIMER_ASSERT(tp, len, th_flags)                        \
 149         KASSERT(((len) == 0 && ((th_flags) & (TH_SYN | TH_FIN)) == 0) ||\
 150             tcp_timer_active((tp), TT_REXMT) ||                         \
 151             tcp_timer_active((tp), TT_PERSIST),                         \
 152             ("neither rexmt nor persist timer is set"))
 153
 154 #ifdef TCP_HHOOK
 155 /*
 156  * Wrapper for the TCP established output helper hook.
 157  */
 158 void
 159 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
 160     struct tcpopt *to, uint32_t len, int tso)
 161 {
 162         struct tcp_hhook_data hhook_data;
 163
 164         if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
 165                 hhook_data.tp = tp;
 166                 hhook_data.th = th;
 167                 hhook_data.to = to;
 168                 hhook_data.len = len;
 169                 hhook_data.tso = tso;
 170
 171                 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
 172                     &tp->t_osd);
 173         }
 174 }
 175 #endif
 176
 177 /*
 178  * CC wrapper hook functions
 179  */
 180 void
 181 cc_after_idle(struct tcpcb *tp)
 182 {
 183         INP_WLOCK_ASSERT(tptoinpcb(tp));
 184
 185         if (CC_ALGO(tp)->after_idle != NULL)
 186                 CC_ALGO(tp)->after_idle(&tp->t_ccv);
 187 }
 188
 189 /*
 190  * Tcp output routine: figure out what should be sent and send it.
 191  */
 192 int
 193 tcp_default_output(struct tcpcb *tp)
 194 {
 195         struct socket *so = tptosocket(tp);
 196         struct inpcb *inp = tptoinpcb(tp);
 197         int32_t len;
 198         uint32_t recwin, sendwin;
 199         uint16_t flags;
 200         int off, error = 0;     /* Keep compiler happy */
 201         u_int if_hw_tsomaxsegcount = 0;
 202         u_int if_hw_tsomaxsegsize = 0;
 203         struct mbuf *m;
 204         struct ip *ip = NULL;
 205         struct tcphdr *th;
 206         u_char opt[TCP_MAXOLEN];
 207         unsigned ipoptlen, optlen, hdrlen, ulen;
 208 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 209         unsigned ipsec_optlen = 0;
 210 #endif
 211         int idle, sendalot, curticks;
 212         int sack_rxmit, sack_bytes_rxmt;
 213         struct sackhole *p;
 214         int tso, mtu;
 215         struct tcpopt to;
 216         struct udphdr *udp = NULL;
 217         struct tcp_log_buffer *lgb;
 218         unsigned int wanted_cookie = 0;
 219         unsigned int dont_sendalot = 0;
 220 #if 0
 221         int maxburst = TCP_MAXBURST;
 222 #endif
 223 #ifdef INET6
 224         struct ip6_hdr *ip6 = NULL;
 225         const bool isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
 226 #endif
 227 #ifdef KERN_TLS
 228         const bool hw_tls = tp->t_nic_ktls_xmit != 0;
 229 #else
 230         const bool hw_tls = false;
 231 #endif
 232
 233         NET_EPOCH_ASSERT();
 234         INP_WLOCK_ASSERT(inp);
 235
 236 #ifdef TCP_OFFLOAD
 237         if (tp->t_flags & TF_TOE)
 238                 return (tcp_offload_output(tp));
 239 #endif
 240
 241         /*
 242          * For TFO connections in SYN_SENT or SYN_RECEIVED,
 243          * only allow the initial SYN or SYN|ACK and those sent
 244          * by the retransmit timer.
 245          */
 246         if (IS_FASTOPEN(tp->t_flags) &&
 247             ((tp->t_state == TCPS_SYN_SENT) ||
 248              (tp->t_state == TCPS_SYN_RECEIVED)) &&
 249             SEQ_GT(tp->snd_max, tp->snd_una) && /* initial SYN or SYN|ACK sent */
 250             (tp->snd_nxt != tp->snd_una))       /* not a retransmit */
 251                 return (0);
 252
 253         /*
 254          * Determine length of data that should be transmitted,
 255          * and flags that will be used.
 256          * If there is some data or critical controls (SYN, RST)
 257          * to send, then transmit; otherwise, investigate further.
 258          */
 259         idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
 260         if (idle && (((ticks - tp->t_rcvtime) >= tp->t_rxtcur) ||
 261             (tp->t_sndtime && ((ticks - tp->t_sndtime) >= tp->t_rxtcur))))
 262                 cc_after_idle(tp);
 263         tp->t_flags &= ~TF_LASTIDLE;
 264         if (idle) {
 265                 if (tp->t_flags & TF_MORETOCOME) {
 266                         tp->t_flags |= TF_LASTIDLE;
 267                         idle = 0;
 268                 }
 269         }
 270 again:
 271         /*
 272          * If we've recently taken a timeout, snd_max will be greater than
 273          * snd_nxt.  There may be SACK information that allows us to avoid
 274          * resending already delivered data.  Adjust snd_nxt accordingly.
 275          */
 276         if ((tp->t_flags & TF_SACK_PERMIT) &&
 277             SEQ_LT(tp->snd_nxt, tp->snd_max))
 278                 tcp_sack_adjust(tp);
 279         sendalot = 0;
 280         tso = 0;
 281         mtu = 0;
 282         off = tp->snd_nxt - tp->snd_una;
 283         sendwin = min(tp->snd_wnd, tp->snd_cwnd);
 284
 285         flags = tcp_outflags[tp->t_state];
 286         /*
 287          * Send any SACK-generated retransmissions.  If we're explicitly trying
 288          * to send out new data (when sendalot is 1), bypass this function.
 289          * If we retransmit in fast recovery mode, decrement snd_cwnd, since
 290          * we're replacing a (future) new transmission with a retransmission
 291          * now, and we previously incremented snd_cwnd in tcp_input().
 292          */
 293         /*
 294          * Still in sack recovery , reset rxmit flag to zero.
 295          */
 296         sack_rxmit = 0;
 297         sack_bytes_rxmt = 0;
 298         len = 0;
 299         p = NULL;
 300         if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
 301             (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
 302                 uint32_t cwin;
 303
 304                 cwin =
 305                     imax(min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt, 0);
 306                 /* Do not retransmit SACK segments beyond snd_recover */
 307                 if (SEQ_GT(p->end, tp->snd_recover)) {
 308                         /*
 309                          * (At least) part of sack hole extends beyond
 310                          * snd_recover. Check to see if we can rexmit data
 311                          * for this hole.
 312                          */
 313                         if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
 314                                 /*
 315                                  * Can't rexmit any more data for this hole.
 316                                  * That data will be rexmitted in the next
 317                                  * sack recovery episode, when snd_recover
 318                                  * moves past p->rxmit.
 319                                  */
 320                                 p = NULL;
 321                                 goto after_sack_rexmit;
 322                         } else {
 323                                 /* Can rexmit part of the current hole */
 324                                 len = ((int32_t)ulmin(cwin,
 325                                     SEQ_SUB(tp->snd_recover, p->rxmit)));
 326                         }
 327                 } else {
 328                         len = ((int32_t)ulmin(cwin,
 329                             SEQ_SUB(p->end, p->rxmit)));
 330                 }
 331                 if (len > 0) {
 332                         off = SEQ_SUB(p->rxmit, tp->snd_una);
 333                         KASSERT(off >= 0,("%s: sack block to the left of una : %d",
 334                             __func__, off));
 335                         sack_rxmit = 1;
 336                         sendalot = 1;
 337                         TCPSTAT_INC(tcps_sack_rexmits);
 338                         TCPSTAT_ADD(tcps_sack_rexmit_bytes,
 339                             min(len, tcp_maxseg(tp)));
 340                 }
 341         }
 342 after_sack_rexmit:
 343         /*
 344          * Get standard flags, and add SYN or FIN if requested by 'hidden'
 345          * state flags.
 346          */
 347         if (tp->t_flags & TF_NEEDFIN)
 348                 flags |= TH_FIN;
 349         if (tp->t_flags & TF_NEEDSYN)
 350                 flags |= TH_SYN;
 351
 352         SOCKBUF_LOCK(&so->so_snd);
 353         /*
 354          * If in persist timeout with window of 0, send 1 byte.
 355          * Otherwise, if window is small but nonzero
 356          * and timer expired, we will send what we can
 357          * and go to transmit state.
 358          */
 359         if (tp->t_flags & TF_FORCEDATA) {
 360                 if (sendwin == 0) {
 361                         /*
 362                          * If we still have some data to send, then
 363                          * clear the FIN bit.  Usually this would
 364                          * happen below when it realizes that we
 365                          * aren't sending all the data.  However,
 366                          * if we have exactly 1 byte of unsent data,
 367                          * then it won't clear the FIN bit below,
 368                          * and if we are in persist state, we wind
 369                          * up sending the packet without recording
 370                          * that we sent the FIN bit.
 371                          *
 372                          * We can't just blindly clear the FIN bit,
 373                          * because if we don't have any more data
 374                          * to send then the probe will be the FIN
 375                          * itself.
 376                          */
 377                         if (off < sbused(&so->so_snd))
 378                                 flags &= ~TH_FIN;
 379                         sendwin = 1;
 380                 } else {
 381                         tcp_timer_activate(tp, TT_PERSIST, 0);
 382                         tp->t_rxtshift = 0;
 383                 }
 384         }
 385
 386         /*
 387          * If snd_nxt == snd_max and we have transmitted a FIN, the
 388          * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
 389          * a negative length.  This can also occur when TCP opens up
 390          * its congestion window while receiving additional duplicate
 391          * acks after fast-retransmit because TCP will reset snd_nxt
 392          * to snd_max after the fast-retransmit.
 393          *
 394          * In the normal retransmit-FIN-only case, however, snd_nxt will
 395          * be set to snd_una, the offset will be 0, and the length may
 396          * wind up 0.
 397          *
 398          * If sack_rxmit is true we are retransmitting from the scoreboard
 399          * in which case len is already set.
 400          */
 401         if (sack_rxmit == 0) {
 402                 if (sack_bytes_rxmt == 0)
 403                         len = ((int32_t)min(sbavail(&so->so_snd), sendwin) -
 404                             off);
 405                 else {
 406                         int32_t cwin;
 407
 408                         /*
 409                          * We are inside of a SACK recovery episode and are
 410                          * sending new data, having retransmitted all the
 411                          * data possible in the scoreboard.
 412                          */
 413                         len = ((int32_t)min(sbavail(&so->so_snd), tp->snd_wnd) -
 414                             off);
 415                         /*
 416                          * Don't remove this (len > 0) check !
 417                          * We explicitly check for len > 0 here (although it
 418                          * isn't really necessary), to work around a gcc
 419                          * optimization issue - to force gcc to compute
 420                          * len above. Without this check, the computation
 421                          * of len is bungled by the optimizer.
 422                          */
 423                         if (len > 0) {
 424                                 cwin = tp->snd_cwnd - imax(0, (int32_t)
 425                                         (tp->snd_nxt - tp->snd_recover)) -
 426                                         sack_bytes_rxmt;
 427                                 if (cwin < 0)
 428                                         cwin = 0;
 429                                 len = imin(len, cwin);
 430                         }
 431                 }
 432         }
 433
 434         /*
 435          * Lop off SYN bit if it has already been sent.  However, if this
 436          * is SYN-SENT state and if segment contains data and if we don't
 437          * know that foreign host supports TAO, suppress sending segment.
 438          */
 439         if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
 440                 if (tp->t_state != TCPS_SYN_RECEIVED)
 441                         flags &= ~TH_SYN;
 442                 /*
 443                  * When sending additional segments following a TFO SYN|ACK,
 444                  * do not include the SYN bit.
 445                  */
 446                 if (IS_FASTOPEN(tp->t_flags) &&
 447                     (tp->t_state == TCPS_SYN_RECEIVED))
 448                         flags &= ~TH_SYN;
 449                 off--, len++;
 450         }
 451
 452         /*
 453          * Be careful not to send data and/or FIN on SYN segments.
 454          * This measure is needed to prevent interoperability problems
 455          * with not fully conformant TCP implementations.
 456          */
 457         if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
 458                 len = 0;
 459                 flags &= ~TH_FIN;
 460         }
 461
 462         /*
 463          * On TFO sockets, ensure no data is sent in the following cases:
 464          *
 465          *  - When retransmitting SYN|ACK on a passively-created socket
 466          *
 467          *  - When retransmitting SYN on an actively created socket
 468          *
 469          *  - When sending a zero-length cookie (cookie request) on an
 470          *    actively created socket
 471          *
 472          *  - When the socket is in the CLOSED state (RST is being sent)
 473          */
 474         if (IS_FASTOPEN(tp->t_flags) &&
 475             (((flags & TH_SYN) && (tp->t_rxtshift > 0)) ||
 476              ((tp->t_state == TCPS_SYN_SENT) &&
 477               (tp->t_tfo_client_cookie_len == 0)) ||
 478              (flags & TH_RST)))
 479                 len = 0;
 480         if (len <= 0) {
 481                 /*
 482                  * If FIN has been sent but not acked,
 483                  * but we haven't been called to retransmit,
 484                  * len will be < 0.  Otherwise, window shrank
 485                  * after we sent into it.  If window shrank to 0,
 486                  * cancel pending retransmit, pull snd_nxt back
 487                  * to (closed) window, and set the persist timer
 488                  * if it isn't already going.  If the window didn't
 489                  * close completely, just wait for an ACK.
 490                  *
 491                  * We also do a general check here to ensure that
 492                  * we will set the persist timer when we have data
 493                  * to send, but a 0-byte window. This makes sure
 494                  * the persist timer is set even if the packet
 495                  * hits one of the "goto send" lines below.
 496                  */
 497                 len = 0;
 498                 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
 499                     (off < (int) sbavail(&so->so_snd)) &&
 500                     !tcp_timer_active(tp, TT_PERSIST)) {
 501                         tcp_timer_activate(tp, TT_REXMT, 0);
 502                         tp->t_rxtshift = 0;
 503                         tp->snd_nxt = tp->snd_una;
 504                         if (!tcp_timer_active(tp, TT_PERSIST))
 505                                 tcp_setpersist(tp);
 506                 }
 507         }
 508
 509         /* len will be >= 0 after this point. */
 510         KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
 511
 512         tcp_sndbuf_autoscale(tp, so, sendwin);
 513
 514         /*
 515          * Decide if we can use TCP Segmentation Offloading (if supported by
 516          * hardware).
 517          *
 518          * TSO may only be used if we are in a pure bulk sending state.  The
 519          * presence of TCP-MD5, SACK retransmits, SACK advertizements and
 520          * IP options prevent using TSO.  With TSO the TCP header is the same
 521          * (except for the sequence number) for all generated packets.  This
 522          * makes it impossible to transmit any options which vary per generated
 523          * segment or packet.
 524          *
 525          * IPv4 handling has a clear separation of ip options and ip header
 526          * flags while IPv6 combines both in in6p_outputopts. ip6_optlen() does
 527          * the right thing below to provide length of just ip options and thus
 528          * checking for ipoptlen is enough to decide if ip options are present.
 529          */
 530 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 531         /*
 532          * Pre-calculate here as we save another lookup into the darknesses
 533          * of IPsec that way and can actually decide if TSO is ok.
 534          */
 535 #ifdef INET6
 536         if (isipv6 && IPSEC_ENABLED(ipv6))
 537                 ipsec_optlen = IPSEC_HDRSIZE(ipv6, inp);
 538 #ifdef INET
 539         else
 540 #endif
 541 #endif /* INET6 */
 542 #ifdef INET
 543         if (IPSEC_ENABLED(ipv4))
 544                 ipsec_optlen = IPSEC_HDRSIZE(ipv4, inp);
 545 #endif /* INET */
 546 #endif /* IPSEC */
 547 #ifdef INET6
 548         if (isipv6)
 549                 ipoptlen = ip6_optlen(inp);
 550         else
 551 #endif
 552         if (inp->inp_options)
 553                 ipoptlen = inp->inp_options->m_len -
 554                                 offsetof(struct ipoption, ipopt_list);
 555         else
 556                 ipoptlen = 0;
 557 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 558         ipoptlen += ipsec_optlen;
 559 #endif
 560
 561         if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
 562             (tp->t_port == 0) &&
 563             ((tp->t_flags & TF_SIGNATURE) == 0) &&
 564             tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
 565             ipoptlen == 0 && !(flags & TH_SYN))
 566                 tso = 1;
 567
 568         if (sack_rxmit) {
 569                 if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
 570                         flags &= ~TH_FIN;
 571         } else {
 572                 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
 573                     sbused(&so->so_snd)))
 574                         flags &= ~TH_FIN;
 575         }
 576
 577         recwin = lmin(lmax(sbspace(&so->so_rcv), 0),
 578             (long)TCP_MAXWIN << tp->rcv_scale);
 579
 580         /*
 581          * Sender silly window avoidance.   We transmit under the following
 582          * conditions when len is non-zero:
 583          *
 584          *      - We have a full segment (or more with TSO)
 585          *      - This is the last buffer in a write()/send() and we are
 586          *        either idle or running NODELAY
 587          *      - we've timed out (e.g. persist timer)
 588          *      - we have more then 1/2 the maximum send window's worth of
 589          *        data (receiver may be limited the window size)
 590          *      - we need to retransmit
 591          */
 592         if (len) {
 593                 if (len >= tp->t_maxseg)
 594                         goto send;
 595                 /*
 596                  * As the TCP header options are now
 597                  * considered when setting up the initial
 598                  * window, we would not send the last segment
 599                  * if we skip considering the option length here.
 600                  * Note: this may not work when tcp headers change
 601                  * very dynamically in the future.
 602                  */
 603                 if ((((tp->t_flags & TF_SIGNATURE) ?
 604                         PADTCPOLEN(TCPOLEN_SIGNATURE) : 0) +
 605                     ((tp->t_flags & TF_RCVD_TSTMP) ?
 606                         PADTCPOLEN(TCPOLEN_TIMESTAMP) : 0) +
 607                     len) >= tp->t_maxseg)
 608                         goto send;
 609                 /*
 610                  * NOTE! on localhost connections an 'ack' from the remote
 611                  * end may occur synchronously with the output and cause
 612                  * us to flush a buffer queued with moretocome.  XXX
 613                  *
 614                  * note: the len + off check is almost certainly unnecessary.
 615                  */
 616                 if (!(tp->t_flags & TF_MORETOCOME) &&   /* normal case */
 617                     (idle || (tp->t_flags & TF_NODELAY)) &&
 618                     (uint32_t)len + (uint32_t)off >= sbavail(&so->so_snd) &&
 619                     (tp->t_flags & TF_NOPUSH) == 0) {
 620                         goto send;
 621                 }
 622                 if (tp->t_flags & TF_FORCEDATA)         /* typ. timeout case */
 623                         goto send;
 624                 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
 625                         goto send;
 626                 if (SEQ_LT(tp->snd_nxt, tp->snd_max))   /* retransmit case */
 627                         goto send;
 628                 if (sack_rxmit)
 629                         goto send;
 630         }
 631
 632         /*
 633          * Sending of standalone window updates.
 634          *
 635          * Window updates are important when we close our window due to a
 636          * full socket buffer and are opening it again after the application
 637          * reads data from it.  Once the window has opened again and the
 638          * remote end starts to send again the ACK clock takes over and
 639          * provides the most current window information.
 640          *
 641          * We must avoid the silly window syndrome whereas every read
 642          * from the receive buffer, no matter how small, causes a window
 643          * update to be sent.  We also should avoid sending a flurry of
 644          * window updates when the socket buffer had queued a lot of data
 645          * and the application is doing small reads.
 646          *
 647          * Prevent a flurry of pointless window updates by only sending
 648          * an update when we can increase the advertized window by more
 649          * than 1/4th of the socket buffer capacity.  When the buffer is
 650          * getting full or is very small be more aggressive and send an
 651          * update whenever we can increase by two mss sized segments.
 652          * In all other situations the ACK's to new incoming data will
 653          * carry further window increases.
 654          *
 655          * Don't send an independent window update if a delayed
 656          * ACK is pending (it will get piggy-backed on it) or the
 657          * remote side already has done a half-close and won't send
 658          * more data.  Skip this if the connection is in T/TCP
 659          * half-open state.
 660          */
 661         if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
 662             !(tp->t_flags & TF_DELACK) &&
 663             !TCPS_HAVERCVDFIN(tp->t_state)) {
 664                 /*
 665                  * "adv" is the amount we could increase the window,
 666                  * taking into account that we are limited by
 667                  * TCP_MAXWIN << tp->rcv_scale.
 668                  */
 669                 int32_t adv;
 670                 int oldwin;
 671
 672                 adv = recwin;
 673                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
 674                         oldwin = (tp->rcv_adv - tp->rcv_nxt);
 675                         if (adv > oldwin)
 676                                 adv -= oldwin;
 677                         else
 678                                 adv = 0;
 679                 } else
 680                         oldwin = 0;
 681
 682                 /*
 683                  * If the new window size ends up being the same as or less
 684                  * than the old size when it is scaled, then don't force
 685                  * a window update.
 686                  */
 687                 if (oldwin >> tp->rcv_scale >= (adv + oldwin) >> tp->rcv_scale)
 688                         goto dontupdate;
 689
 690                 if (adv >= (int32_t)(2 * tp->t_maxseg) &&
 691                     (adv >= (int32_t)(so->so_rcv.sb_hiwat / 4) ||
 692                      recwin <= (so->so_rcv.sb_hiwat / 8) ||
 693                      so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg ||
 694                      adv >= TCP_MAXWIN << tp->rcv_scale))
 695                         goto send;
 696                 if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat)
 697                         goto send;
 698         }
 699 dontupdate:
 700
 701         /*
 702          * Send if we owe the peer an ACK, RST, SYN, or urgent data.  ACKNOW
 703          * is also a catch-all for the retransmit timer timeout case.
 704          */
 705         if (tp->t_flags & TF_ACKNOW)
 706                 goto send;
 707         if ((flags & TH_RST) ||
 708             ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
 709                 goto send;
 710         if (SEQ_GT(tp->snd_up, tp->snd_una))
 711                 goto send;
 712         /*
 713          * If our state indicates that FIN should be sent
 714          * and we have not yet done so, then we need to send.
 715          */
 716         if (flags & TH_FIN &&
 717             ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
 718                 goto send;
 719         /*
 720          * In SACK, it is possible for tcp_output to fail to send a segment
 721          * after the retransmission timer has been turned off.  Make sure
 722          * that the retransmission timer is set.
 723          */
 724         if ((tp->t_flags & TF_SACK_PERMIT) &&
 725             SEQ_GT(tp->snd_max, tp->snd_una) &&
 726             !tcp_timer_active(tp, TT_REXMT) &&
 727             !tcp_timer_active(tp, TT_PERSIST)) {
 728                 tcp_timer_activate(tp, TT_REXMT, TP_RXTCUR(tp));
 729                 goto just_return;
 730         }
 731         /*
 732          * TCP window updates are not reliable, rather a polling protocol
 733          * using ``persist'' packets is used to insure receipt of window
 734          * updates.  The three ``states'' for the output side are:
 735          *      idle                    not doing retransmits or persists
 736          *      persisting              to move a small or zero window
 737          *      (re)transmitting        and thereby not persisting
 738          *
 739          * tcp_timer_active(tp, TT_PERSIST)
 740          *      is true when we are in persist state.
 741          * (tp->t_flags & TF_FORCEDATA)
 742          *      is set when we are called to send a persist packet.
 743          * tcp_timer_active(tp, TT_REXMT)
 744          *      is set when we are retransmitting
 745          * The output side is idle when both timers are zero.
 746          *
 747          * If send window is too small, there is data to transmit, and no
 748          * retransmit or persist is pending, then go to persist state.
 749          * If nothing happens soon, send when timer expires:
 750          * if window is nonzero, transmit what we can,
 751          * otherwise force out a byte.
 752          */
 753         if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) &&
 754             !tcp_timer_active(tp, TT_PERSIST)) {
 755                 tp->t_rxtshift = 0;
 756                 tcp_setpersist(tp);
 757         }
 758
 759         /*
 760          * No reason to send a segment, just return.
 761          */
 762 just_return:
 763         SOCKBUF_UNLOCK(&so->so_snd);
 764         return (0);
 765
 766 send:
 767         SOCKBUF_LOCK_ASSERT(&so->so_snd);
 768         if (len > 0) {
 769                 if (len >= tp->t_maxseg)
 770                         tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
 771                 else
 772                         tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
 773         }
 774         /*
 775          * Before ESTABLISHED, force sending of initial options
 776          * unless TCP set not to do any options.
 777          * NOTE: we assume that the IP/TCP header plus TCP options
 778          * always fit in a single mbuf, leaving room for a maximum
 779          * link header, i.e.
 780          *      max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
 781          */
 782         optlen = 0;
 783 #ifdef INET6
 784         if (isipv6)
 785                 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
 786         else
 787 #endif
 788                 hdrlen = sizeof (struct tcpiphdr);
 789
 790         if (flags & TH_SYN) {
 791                 tp->snd_nxt = tp->iss;
 792         }
 793
 794         /*
 795          * Compute options for segment.
 796          * We only have to care about SYN and established connection
 797          * segments.  Options for SYN-ACK segments are handled in TCP
 798          * syncache.
 799          */
 800         to.to_flags = 0;
 801         if ((tp->t_flags & TF_NOOPT) == 0) {
 802                 /* Maximum segment size. */
 803                 if (flags & TH_SYN) {
 804                         to.to_mss = tcp_mssopt(&inp->inp_inc);
 805                         if (tp->t_port)
 806                                 to.to_mss -= V_tcp_udp_tunneling_overhead;
 807                         to.to_flags |= TOF_MSS;
 808
 809                         /*
 810                          * On SYN or SYN|ACK transmits on TFO connections,
 811                          * only include the TFO option if it is not a
 812                          * retransmit, as the presence of the TFO option may
 813                          * have caused the original SYN or SYN|ACK to have
 814                          * been dropped by a middlebox.
 815                          */
 816                         if (IS_FASTOPEN(tp->t_flags) &&
 817                             (tp->t_rxtshift == 0)) {
 818                                 if (tp->t_state == TCPS_SYN_RECEIVED) {
 819                                         to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
 820                                         to.to_tfo_cookie =
 821                                             (u_int8_t *)&tp->t_tfo_cookie.server;
 822                                         to.to_flags |= TOF_FASTOPEN;
 823                                         wanted_cookie = 1;
 824                                 } else if (tp->t_state == TCPS_SYN_SENT) {
 825                                         to.to_tfo_len =
 826                                             tp->t_tfo_client_cookie_len;
 827                                         to.to_tfo_cookie =
 828                                             tp->t_tfo_cookie.client;
 829                                         to.to_flags |= TOF_FASTOPEN;
 830                                         wanted_cookie = 1;
 831                                         /*
 832                                          * If we wind up having more data to
 833                                          * send with the SYN than can fit in
 834                                          * one segment, don't send any more
 835                                          * until the SYN|ACK comes back from
 836                                          * the other end.
 837                                          */
 838                                         dont_sendalot = 1;
 839                                 }
 840                         }
 841                 }
 842                 /* Window scaling. */
 843                 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
 844                         to.to_wscale = tp->request_r_scale;
 845                         to.to_flags |= TOF_SCALE;
 846                 }
 847                 /* Timestamps. */
 848                 if ((tp->t_flags & TF_RCVD_TSTMP) ||
 849                     ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
 850                         curticks = tcp_ts_getticks();
 851                         to.to_tsval = curticks + tp->ts_offset;
 852                         to.to_tsecr = tp->ts_recent;
 853                         to.to_flags |= TOF_TS;
 854                         if (tp->t_rxtshift == 1)
 855                                 tp->t_badrxtwin = curticks;
 856                 }
 857
 858                 /* Set receive buffer autosizing timestamp. */
 859                 if (tp->rfbuf_ts == 0 &&
 860                     (so->so_rcv.sb_flags & SB_AUTOSIZE))
 861                         tp->rfbuf_ts = tcp_ts_getticks();
 862
 863                 /* Selective ACK's. */
 864                 if (tp->t_flags & TF_SACK_PERMIT) {
 865                         if (flags & TH_SYN)
 866                                 to.to_flags |= TOF_SACKPERM;
 867                         else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
 868                             tp->rcv_numsacks > 0) {
 869                                 to.to_flags |= TOF_SACK;
 870                                 to.to_nsacks = tp->rcv_numsacks;
 871                                 to.to_sacks = (u_char *)tp->sackblks;
 872                         }
 873                 }
 874 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 875                 /* TCP-MD5 (RFC2385). */
 876                 /*
 877                  * Check that TCP_MD5SIG is enabled in tcpcb to
 878                  * account the size needed to set this TCP option.
 879                  */
 880                 if (tp->t_flags & TF_SIGNATURE)
 881                         to.to_flags |= TOF_SIGNATURE;
 882 #endif /* TCP_SIGNATURE */
 883
 884                 /* Processing the options. */
 885                 hdrlen += optlen = tcp_addoptions(&to, opt);
 886                 /*
 887                  * If we wanted a TFO option to be added, but it was unable
 888                  * to fit, ensure no data is sent.
 889                  */
 890                 if (IS_FASTOPEN(tp->t_flags) && wanted_cookie &&
 891                     !(to.to_flags & TOF_FASTOPEN))
 892                         len = 0;
 893         }
 894         if (tp->t_port) {
 895                 if (V_tcp_udp_tunneling_port == 0) {
 896                         /* The port was removed?? */
 897                         SOCKBUF_UNLOCK(&so->so_snd);
 898                         return (EHOSTUNREACH);
 899                 }
 900                 hdrlen += sizeof(struct udphdr);
 901         }
 902         /*
 903          * Adjust data length if insertion of options will
 904          * bump the packet length beyond the t_maxseg length.
 905          * Clear the FIN bit because we cut off the tail of
 906          * the segment.
 907          */
 908         if (len + optlen + ipoptlen > tp->t_maxseg) {
 909                 flags &= ~TH_FIN;
 910
 911                 if (tso) {
 912                         u_int if_hw_tsomax;
 913                         u_int moff;
 914                         int max_len;
 915
 916                         /* extract TSO information */
 917                         if_hw_tsomax = tp->t_tsomax;
 918                         if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
 919                         if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
 920
 921                         /*
 922                          * Limit a TSO burst to prevent it from
 923                          * overflowing or exceeding the maximum length
 924                          * allowed by the network interface:
 925                          */
 926                         KASSERT(ipoptlen == 0,
 927                             ("%s: TSO can't do IP options", __func__));
 928
 929                         /*
 930                          * Check if we should limit by maximum payload
 931                          * length:
 932                          */
 933                         if (if_hw_tsomax != 0) {
 934                                 /* compute maximum TSO length */
 935                                 max_len = (if_hw_tsomax - hdrlen -
 936                                     max_linkhdr);
 937                                 if (max_len <= 0) {
 938                                         len = 0;
 939                                 } else if (len > max_len) {
 940                                         sendalot = 1;
 941                                         len = max_len;
 942                                 }
 943                         }
 944
 945                         /*
 946                          * Prevent the last segment from being
 947                          * fractional unless the send sockbuf can be
 948                          * emptied:
 949                          */
 950                         max_len = (tp->t_maxseg - optlen);
 951                         if (((uint32_t)off + (uint32_t)len) <
 952                             sbavail(&so->so_snd)) {
 953                                 moff = len % max_len;
 954                                 if (moff != 0) {
 955                                         len -= moff;
 956                                         sendalot = 1;
 957                                 }
 958                         }
 959
 960                         /*
 961                          * In case there are too many small fragments
 962                          * don't use TSO:
 963                          */
 964                         if (len <= max_len) {
 965                                 len = max_len;
 966                                 sendalot = 1;
 967                                 tso = 0;
 968                         }
 969
 970                         /*
 971                          * Send the FIN in a separate segment
 972                          * after the bulk sending is done.
 973                          * We don't trust the TSO implementations
 974                          * to clear the FIN flag on all but the
 975                          * last segment.
 976                          */
 977                         if (tp->t_flags & TF_NEEDFIN)
 978                                 sendalot = 1;
 979                 } else {
 980                         if (optlen + ipoptlen >= tp->t_maxseg) {
 981                                 /*
 982                                  * Since we don't have enough space to put
 983                                  * the IP header chain and the TCP header in
 984                                  * one packet as required by RFC 7112, don't
 985                                  * send it. Also ensure that at least one
 986                                  * byte of the payload can be put into the
 987                                  * TCP segment.
 988                                  */
 989                                 SOCKBUF_UNLOCK(&so->so_snd);
 990                                 error = EMSGSIZE;
 991                                 sack_rxmit = 0;
 992                                 goto out;
 993                         }
 994                         len = tp->t_maxseg - optlen - ipoptlen;
 995                         sendalot = 1;
 996                         if (dont_sendalot)
 997                                 sendalot = 0;
 998                 }
 999         } else
1000                 tso = 0;
1001
1002         KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
1003             ("%s: len > IP_MAXPACKET", __func__));
1004
1005 /*#ifdef DIAGNOSTIC*/
1006 #ifdef INET6
1007         if (max_linkhdr + hdrlen > MCLBYTES)
1008 #else
1009         if (max_linkhdr + hdrlen > MHLEN)
1010 #endif
1011                 panic("tcphdr too big");
1012 /*#endif*/
1013
1014         /*
1015          * This KASSERT is here to catch edge cases at a well defined place.
1016          * Before, those had triggered (random) panic conditions further down.
1017          */
1018         KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
1019
1020         /*
1021          * Grab a header mbuf, attaching a copy of data to
1022          * be transmitted, and initialize the header from
1023          * the template for sends on this connection.
1024          */
1025         if (len) {
1026                 struct mbuf *mb;
1027                 struct sockbuf *msb;
1028                 u_int moff;
1029
1030                 if ((tp->t_flags & TF_FORCEDATA) && len == 1) {
1031                         TCPSTAT_INC(tcps_sndprobe);
1032 #ifdef STATS
1033                         if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1034                                 stats_voi_update_abs_u32(tp->t_stats,
1035                                 VOI_TCP_RETXPB, len);
1036                         else
1037                                 stats_voi_update_abs_u64(tp->t_stats,
1038                                     VOI_TCP_TXPB, len);
1039 #endif /* STATS */
1040                 } else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
1041                         tp->t_sndrexmitpack++;
1042                         TCPSTAT_INC(tcps_sndrexmitpack);
1043                         TCPSTAT_ADD(tcps_sndrexmitbyte, len);
1044 #ifdef STATS
1045                         stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_RETXPB,
1046                             len);
1047 #endif /* STATS */
1048                 } else {
1049                         TCPSTAT_INC(tcps_sndpack);
1050                         TCPSTAT_ADD(tcps_sndbyte, len);
1051 #ifdef STATS
1052                         stats_voi_update_abs_u64(tp->t_stats, VOI_TCP_TXPB,
1053                             len);
1054 #endif /* STATS */
1055                 }
1056 #ifdef INET6
1057                 if (MHLEN < hdrlen + max_linkhdr)
1058                         m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
1059                 else
1060 #endif
1061                         m = m_gethdr(M_NOWAIT, MT_DATA);
1062
1063                 if (m == NULL) {
1064                         SOCKBUF_UNLOCK(&so->so_snd);
1065                         error = ENOBUFS;
1066                         sack_rxmit = 0;
1067                         goto out;
1068                 }
1069
1070                 m->m_data += max_linkhdr;
1071                 m->m_len = hdrlen;
1072
1073                 /*
1074                  * Start the m_copy functions from the closest mbuf
1075                  * to the offset in the socket buffer chain.
1076                  */
1077                 mb = sbsndptr_noadv(&so->so_snd, off, &moff);
1078                 if (len <= MHLEN - hdrlen - max_linkhdr && !hw_tls) {
1079                         m_copydata(mb, moff, len,
1080                             mtod(m, caddr_t) + hdrlen);
1081                         if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1082                                 sbsndptr_adv(&so->so_snd, mb, len);
1083                         m->m_len += len;
1084                 } else {
1085                         if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1086                                 msb = NULL;
1087                         else
1088                                 msb = &so->so_snd;
1089                         m->m_next = tcp_m_copym(mb, moff,
1090                             &len, if_hw_tsomaxsegcount,
1091                             if_hw_tsomaxsegsize, msb, hw_tls);
1092                         if (len <= (tp->t_maxseg - optlen)) {
1093                                 /*
1094                                  * Must have ran out of mbufs for the copy
1095                                  * shorten it to no longer need tso. Lets
1096                                  * not put on sendalot since we are low on
1097                                  * mbufs.
1098                                  */
1099                                 tso = 0;
1100                         }
1101                         if (m->m_next == NULL) {
1102                                 SOCKBUF_UNLOCK(&so->so_snd);
1103                                 (void) m_free(m);
1104                                 error = ENOBUFS;
1105                                 sack_rxmit = 0;
1106                                 goto out;
1107                         }
1108                 }
1109
1110                 /*
1111                  * If we're sending everything we've got, set PUSH.
1112                  * (This will keep happy those implementations which only
1113                  * give data to the user when a buffer fills or
1114                  * a PUSH comes in.)
1115                  */
1116                 if (((uint32_t)off + (uint32_t)len == sbused(&so->so_snd)) &&
1117                     !(flags & TH_SYN))
1118                         flags |= TH_PUSH;
1119                 SOCKBUF_UNLOCK(&so->so_snd);
1120         } else {
1121                 SOCKBUF_UNLOCK(&so->so_snd);
1122                 if (tp->t_flags & TF_ACKNOW)
1123                         TCPSTAT_INC(tcps_sndacks);
1124                 else if (flags & (TH_SYN|TH_FIN|TH_RST))
1125                         TCPSTAT_INC(tcps_sndctrl);
1126                 else if (SEQ_GT(tp->snd_up, tp->snd_una))
1127                         TCPSTAT_INC(tcps_sndurg);
1128                 else
1129                         TCPSTAT_INC(tcps_sndwinup);
1130
1131                 m = m_gethdr(M_NOWAIT, MT_DATA);
1132                 if (m == NULL) {
1133                         error = ENOBUFS;
1134                         sack_rxmit = 0;
1135                         goto out;
1136                 }
1137 #ifdef INET6
1138                 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
1139                     MHLEN >= hdrlen) {
1140                         M_ALIGN(m, hdrlen);
1141                 } else
1142 #endif
1143                 m->m_data += max_linkhdr;
1144                 m->m_len = hdrlen;
1145         }
1146         SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
1147         m->m_pkthdr.rcvif = (struct ifnet *)0;
1148 #ifdef MAC
1149         mac_inpcb_create_mbuf(inp, m);
1150 #endif
1151 #ifdef INET6
1152         if (isipv6) {
1153                 ip6 = mtod(m, struct ip6_hdr *);
1154                 if (tp->t_port) {
1155                         udp = (struct udphdr *)((caddr_t)ip6 + sizeof(struct ip6_hdr));
1156                         udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1157                         udp->uh_dport = tp->t_port;
1158                         ulen = hdrlen + len - sizeof(struct ip6_hdr);
1159                         udp->uh_ulen = htons(ulen);
1160                         th = (struct tcphdr *)(udp + 1);
1161                 } else {
1162                         th = (struct tcphdr *)(ip6 + 1);
1163                 }
1164                 tcpip_fillheaders(inp, tp->t_port, ip6, th);
1165         } else
1166 #endif /* INET6 */
1167         {
1168                 ip = mtod(m, struct ip *);
1169                 if (tp->t_port) {
1170                         udp = (struct udphdr *)((caddr_t)ip + sizeof(struct ip));
1171                         udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1172                         udp->uh_dport = tp->t_port;
1173                         ulen = hdrlen + len - sizeof(struct ip);
1174                         udp->uh_ulen = htons(ulen);
1175                         th = (struct tcphdr *)(udp + 1);
1176                 } else
1177                         th = (struct tcphdr *)(ip + 1);
1178                 tcpip_fillheaders(inp, tp->t_port, ip, th);
1179         }
1180
1181         /*
1182          * Fill in fields, remembering maximum advertised
1183          * window for use in delaying messages about window sizes.
1184          * If resending a FIN, be sure not to use a new sequence number.
1185          */
1186         if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1187             tp->snd_nxt == tp->snd_max)
1188                 tp->snd_nxt--;
1189         /*
1190          * If we are starting a connection, send ECN setup
1191          * SYN packet. If we are on a retransmit, we may
1192          * resend those bits a number of times as per
1193          * RFC 3168.
1194          */
1195         if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn) {
1196                 flags |= tcp_ecn_output_syn_sent(tp);
1197         }
1198         /* Also handle parallel SYN for ECN */
1199         if ((TCPS_HAVERCVDSYN(tp->t_state)) &&
1200             (tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT))) {
1201                 int ect = tcp_ecn_output_established(tp, &flags, len, sack_rxmit);
1202                 if ((tp->t_state == TCPS_SYN_RECEIVED) &&
1203                     (tp->t_flags2 & TF2_ECN_SND_ECE))
1204                         tp->t_flags2 &= ~TF2_ECN_SND_ECE;
1205 #ifdef INET6
1206                 if (isipv6) {
1207                         ip6->ip6_flow &= ~htonl(IPTOS_ECN_MASK << IPV6_FLOWLABEL_LEN);
1208                         ip6->ip6_flow |= htonl(ect << IPV6_FLOWLABEL_LEN);
1209                 }
1210                 else
1211 #endif
1212                 {
1213                         ip->ip_tos &= ~IPTOS_ECN_MASK;
1214                         ip->ip_tos |= ect;
1215                 }
1216         }
1217
1218         /*
1219          * If we are doing retransmissions, then snd_nxt will
1220          * not reflect the first unsent octet.  For ACK only
1221          * packets, we do not want the sequence number of the
1222          * retransmitted packet, we want the sequence number
1223          * of the next unsent octet.  So, if there is no data
1224          * (and no SYN or FIN), use snd_max instead of snd_nxt
1225          * when filling in ti_seq.  But if we are in persist
1226          * state, snd_max might reflect one byte beyond the
1227          * right edge of the window, so use snd_nxt in that
1228          * case, since we know we aren't doing a retransmission.
1229          * (retransmit and persist are mutually exclusive...)
1230          */
1231         if (sack_rxmit == 0) {
1232                 if (len || (flags & (TH_SYN|TH_FIN)) ||
1233                     tcp_timer_active(tp, TT_PERSIST))
1234                         th->th_seq = htonl(tp->snd_nxt);
1235                 else
1236                         th->th_seq = htonl(tp->snd_max);
1237         } else {
1238                 th->th_seq = htonl(p->rxmit);
1239                 p->rxmit += len;
1240                 /*
1241                  * Lost Retransmission Detection
1242                  * trigger resending of a (then
1243                  * still existing) hole, when
1244                  * fack acks recoverypoint.
1245                  */
1246                 if ((tp->t_flags & TF_LRD) && SEQ_GEQ(p->rxmit, p->end))
1247                         p->rxmit = tp->snd_recover;
1248                 tp->sackhint.sack_bytes_rexmit += len;
1249         }
1250         if (IN_RECOVERY(tp->t_flags)) {
1251                 /*
1252                  * Account all bytes transmitted while
1253                  * IN_RECOVERY, simplifying PRR and
1254                  * Lost Retransmit Detection
1255                  */
1256                 tp->sackhint.prr_out += len;
1257         }
1258         th->th_ack = htonl(tp->rcv_nxt);
1259         if (optlen) {
1260                 bcopy(opt, th + 1, optlen);
1261                 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
1262         }
1263         tcp_set_flags(th, flags);
1264         /*
1265          * Calculate receive window.  Don't shrink window,
1266          * but avoid silly window syndrome.
1267          * If a RST segment is sent, advertise a window of zero.
1268          */
1269         if (flags & TH_RST) {
1270                 recwin = 0;
1271         } else {
1272                 if (recwin < (so->so_rcv.sb_hiwat / 4) &&
1273                     recwin < tp->t_maxseg)
1274                         recwin = 0;
1275                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
1276                     recwin < (tp->rcv_adv - tp->rcv_nxt))
1277                         recwin = (tp->rcv_adv - tp->rcv_nxt);
1278         }
1279         /*
1280          * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1281          * or <SYN,ACK>) segment itself is never scaled.  The <SYN,ACK>
1282          * case is handled in syncache.
1283          */
1284         if (flags & TH_SYN)
1285                 th->th_win = htons((u_short)
1286                                 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1287         else {
1288                 /* Avoid shrinking window with window scaling. */
1289                 recwin = roundup2(recwin, 1 << tp->rcv_scale);
1290                 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
1291         }
1292
1293         /*
1294          * Adjust the RXWIN0SENT flag - indicate that we have advertised
1295          * a 0 window.  This may cause the remote transmitter to stall.  This
1296          * flag tells soreceive() to disable delayed acknowledgements when
1297          * draining the buffer.  This can occur if the receiver is attempting
1298          * to read more data than can be buffered prior to transmitting on
1299          * the connection.
1300          */
1301         if (th->th_win == 0) {
1302                 tp->t_sndzerowin++;
1303                 tp->t_flags |= TF_RXWIN0SENT;
1304         } else
1305                 tp->t_flags &= ~TF_RXWIN0SENT;
1306         if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1307                 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1308                 th->th_flags |= TH_URG;
1309         } else
1310                 /*
1311                  * If no urgent pointer to send, then we pull
1312                  * the urgent pointer to the left edge of the send window
1313                  * so that it doesn't drift into the send window on sequence
1314                  * number wraparound.
1315                  */
1316                 tp->snd_up = tp->snd_una;               /* drag it along */
1317
1318         /*
1319          * Put TCP length in extended header, and then
1320          * checksum extended header and data.
1321          */
1322         m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1323
1324 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1325         if (to.to_flags & TOF_SIGNATURE) {
1326                 /*
1327                  * Calculate MD5 signature and put it into the place
1328                  * determined before.
1329                  * NOTE: since TCP options buffer doesn't point into
1330                  * mbuf's data, calculate offset and use it.
1331                  */
1332                 if (!TCPMD5_ENABLED() || (error = TCPMD5_OUTPUT(m, th,
1333                     (u_char *)(th + 1) + (to.to_signature - opt))) != 0) {
1334                         /*
1335                          * Do not send segment if the calculation of MD5
1336                          * digest has failed.
1337                          */
1338                         m_freem(m);
1339                         goto out;
1340                 }
1341         }
1342 #endif
1343 #ifdef INET6
1344         if (isipv6) {
1345                 /*
1346                  * There is no need to fill in ip6_plen right now.
1347                  * It will be filled later by ip6_output.
1348                  */
1349                 if (tp->t_port) {
1350                         m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
1351                         m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
1352                         udp->uh_sum = in6_cksum_pseudo(ip6, ulen, IPPROTO_UDP, 0);
1353                         th->th_sum = htons(0);
1354                         UDPSTAT_INC(udps_opackets);
1355                 } else {
1356                         m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1357                         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1358                         th->th_sum = in6_cksum_pseudo(ip6,
1359                             sizeof(struct tcphdr) + optlen + len, IPPROTO_TCP,
1360                             0);
1361                 }
1362         }
1363 #endif
1364 #if defined(INET6) && defined(INET)
1365         else
1366 #endif
1367 #ifdef INET
1368         {
1369                 if (tp->t_port) {
1370                         m->m_pkthdr.csum_flags = CSUM_UDP;
1371                         m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
1372                         udp->uh_sum = in_pseudo(ip->ip_src.s_addr,
1373                            ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP));
1374                         th->th_sum = htons(0);
1375                         UDPSTAT_INC(udps_opackets);
1376                 } else {
1377                         m->m_pkthdr.csum_flags = CSUM_TCP;
1378                         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1379                         th->th_sum = in_pseudo(ip->ip_src.s_addr,
1380                             ip->ip_dst.s_addr, htons(sizeof(struct tcphdr) +
1381                             IPPROTO_TCP + len + optlen));
1382                 }
1383
1384                 /* IP version must be set here for ipv4/ipv6 checking later */
1385                 KASSERT(ip->ip_v == IPVERSION,
1386                     ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1387         }
1388 #endif
1389
1390         /*
1391          * Enable TSO and specify the size of the segments.
1392          * The TCP pseudo header checksum is always provided.
1393          */
1394         if (tso) {
1395                 KASSERT(len > tp->t_maxseg - optlen,
1396                     ("%s: len <= tso_segsz", __func__));
1397                 m->m_pkthdr.csum_flags |= CSUM_TSO;
1398                 m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen;
1399         }
1400
1401         KASSERT(len + hdrlen == m_length(m, NULL),
1402             ("%s: mbuf chain shorter than expected: %d + %u != %u",
1403             __func__, len, hdrlen, m_length(m, NULL)));
1404
1405 #ifdef TCP_HHOOK
1406         /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1407         hhook_run_tcp_est_out(tp, th, &to, len, tso);
1408 #endif
1409
1410         TCP_PROBE3(debug__output, tp, th, m);
1411
1412         /* We're getting ready to send; log now. */
1413         /* XXXMT: We are not honoring verbose logging. */
1414
1415         if (tcp_bblogging_on(tp))
1416                 lgb = tcp_log_event(tp, th, &so->so_rcv, &so->so_snd,
1417                     TCP_LOG_OUT, ERRNO_UNK, len, NULL, false, NULL, NULL, 0,
1418                     NULL);
1419         else
1420                 lgb = NULL;
1421
1422         /*
1423          * Fill in IP length and desired time to live and
1424          * send to IP level.  There should be a better way
1425          * to handle ttl and tos; we could keep them in
1426          * the template, but need a way to checksum without them.
1427          */
1428         /*
1429          * m->m_pkthdr.len should have been set before checksum calculation,
1430          * because in6_cksum() need it.
1431          */
1432 #ifdef INET6
1433         if (isipv6) {
1434                 /*
1435                  * we separately set hoplimit for every segment, since the
1436                  * user might want to change the value via setsockopt.
1437                  * Also, desired default hop limit might be changed via
1438                  * Neighbor Discovery.
1439                  */
1440                 ip6->ip6_hlim = in6_selecthlim(inp, NULL);
1441
1442                 /*
1443                  * Set the packet size here for the benefit of DTrace probes.
1444                  * ip6_output() will set it properly; it's supposed to include
1445                  * the option header lengths as well.
1446                  */
1447                 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
1448
1449                 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss)
1450                         tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1451                 else
1452                         tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1453
1454                 if (tp->t_state == TCPS_SYN_SENT)
1455                         TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
1456
1457                 TCP_PROBE5(send, NULL, tp, ip6, tp, th);
1458
1459 #ifdef TCPPCAP
1460                 /* Save packet, if requested. */
1461                 tcp_pcap_add(th, m, &(tp->t_outpkts));
1462 #endif
1463
1464                 /* TODO: IPv6 IP6TOS_ECT bit on */
1465                 error = ip6_output(m, inp->in6p_outputopts, &inp->inp_route6,
1466                     ((so->so_options & SO_DONTROUTE) ?  IP_ROUTETOIF : 0),
1467                     NULL, NULL, inp);
1468
1469                 if (error == EMSGSIZE && inp->inp_route6.ro_nh != NULL)
1470                         mtu = inp->inp_route6.ro_nh->nh_mtu;
1471         }
1472 #endif /* INET6 */
1473 #if defined(INET) && defined(INET6)
1474         else
1475 #endif
1476 #ifdef INET
1477     {
1478         ip->ip_len = htons(m->m_pkthdr.len);
1479 #ifdef INET6
1480         if (inp->inp_vflag & INP_IPV6PROTO)
1481                 ip->ip_ttl = in6_selecthlim(inp, NULL);
1482 #endif /* INET6 */
1483         /*
1484          * If we do path MTU discovery, then we set DF on every packet.
1485          * This might not be the best thing to do according to RFC3390
1486          * Section 2. However the tcp hostcache migitates the problem
1487          * so it affects only the first tcp connection with a host.
1488          *
1489          * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1490          */
1491         if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) {
1492                 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1493                 if (tp->t_port == 0 || len < V_tcp_minmss) {
1494                         ip->ip_off |= htons(IP_DF);
1495                 }
1496         } else {
1497                 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1498         }
1499
1500         if (tp->t_state == TCPS_SYN_SENT)
1501                 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
1502
1503         TCP_PROBE5(send, NULL, tp, ip, tp, th);
1504
1505 #ifdef TCPPCAP
1506         /* Save packet, if requested. */
1507         tcp_pcap_add(th, m, &(tp->t_outpkts));
1508 #endif
1509
1510         error = ip_output(m, inp->inp_options, &inp->inp_route,
1511             ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0, inp);
1512
1513         if (error == EMSGSIZE && inp->inp_route.ro_nh != NULL)
1514                 mtu = inp->inp_route.ro_nh->nh_mtu;
1515     }
1516 #endif /* INET */
1517
1518         if (lgb != NULL) {
1519                 lgb->tlb_errno = error;
1520                 lgb = NULL;
1521         }
1522 out:
1523         if (error == 0)
1524                 tcp_account_for_send(tp, len, (tp->snd_nxt != tp->snd_max), 0, hw_tls);
1525         /*
1526          * In transmit state, time the transmission and arrange for
1527          * the retransmit.  In persist state, just set snd_max.
1528          */
1529         if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1530             !tcp_timer_active(tp, TT_PERSIST)) {
1531                 tcp_seq startseq = tp->snd_nxt;
1532
1533                 /*
1534                  * Advance snd_nxt over sequence space of this segment.
1535                  */
1536                 if (flags & (TH_SYN|TH_FIN)) {
1537                         if (flags & TH_SYN)
1538                                 tp->snd_nxt++;
1539                         if (flags & TH_FIN) {
1540                                 tp->snd_nxt++;
1541                                 tp->t_flags |= TF_SENTFIN;
1542                         }
1543                 }
1544                 if (sack_rxmit)
1545                         goto timer;
1546                 tp->snd_nxt += len;
1547                 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1548                         /*
1549                          * Update "made progress" indication if we just
1550                          * added new data to an empty socket buffer.
1551                          */
1552                         if (tp->snd_una == tp->snd_max)
1553                                 tp->t_acktime = ticks;
1554                         tp->snd_max = tp->snd_nxt;
1555                         /*
1556                          * Time this transmission if not a retransmission and
1557                          * not currently timing anything.
1558                          */
1559                         tp->t_sndtime = ticks;
1560                         if (tp->t_rtttime == 0) {
1561                                 tp->t_rtttime = ticks;
1562                                 tp->t_rtseq = startseq;
1563                                 TCPSTAT_INC(tcps_segstimed);
1564                         }
1565 #ifdef STATS
1566                         if (!(tp->t_flags & TF_GPUTINPROG) && len) {
1567                                 tp->t_flags |= TF_GPUTINPROG;
1568                                 tp->gput_seq = startseq;
1569                                 tp->gput_ack = startseq +
1570                                     ulmin(sbavail(&so->so_snd) - off, sendwin);
1571                                 tp->gput_ts = tcp_ts_getticks();
1572                         }
1573 #endif /* STATS */
1574                 }
1575
1576                 /*
1577                  * Set retransmit timer if not currently set,
1578                  * and not doing a pure ack or a keep-alive probe.
1579                  * Initial value for retransmit timer is smoothed
1580                  * round-trip time + 2 * round-trip time variance.
1581                  * Initialize shift counter which is used for backoff
1582                  * of retransmit time.
1583                  */
1584 timer:
1585                 if (!tcp_timer_active(tp, TT_REXMT) &&
1586                     ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1587                      (tp->snd_nxt != tp->snd_una))) {
1588                         if (tcp_timer_active(tp, TT_PERSIST)) {
1589                                 tcp_timer_activate(tp, TT_PERSIST, 0);
1590                                 tp->t_rxtshift = 0;
1591                         }
1592                         tcp_timer_activate(tp, TT_REXMT, TP_RXTCUR(tp));
1593                 } else if (len == 0 && sbavail(&so->so_snd) &&
1594                     !tcp_timer_active(tp, TT_REXMT) &&
1595                     !tcp_timer_active(tp, TT_PERSIST)) {
1596                         /*
1597                          * Avoid a situation where we do not set persist timer
1598                          * after a zero window condition. For example:
1599                          * 1) A -> B: packet with enough data to fill the window
1600                          * 2) B -> A: ACK for #1 + new data (0 window
1601                          *    advertisement)
1602                          * 3) A -> B: ACK for #2, 0 len packet
1603                          *
1604                          * In this case, A will not activate the persist timer,
1605                          * because it chose to send a packet. Unless tcp_output
1606                          * is called for some other reason (delayed ack timer,
1607                          * another input packet from B, socket syscall), A will
1608                          * not send zero window probes.
1609                          *
1610                          * So, if you send a 0-length packet, but there is data
1611                          * in the socket buffer, and neither the rexmt or
1612                          * persist timer is already set, then activate the
1613                          * persist timer.
1614                          */
1615                         tp->t_rxtshift = 0;
1616                         tcp_setpersist(tp);
1617                 }
1618         } else {
1619                 /*
1620                  * Persist case, update snd_max but since we are in
1621                  * persist mode (no window) we do not update snd_nxt.
1622                  */
1623                 int xlen = len;
1624                 if (flags & TH_SYN)
1625                         ++xlen;
1626                 if (flags & TH_FIN) {
1627                         ++xlen;
1628                         tp->t_flags |= TF_SENTFIN;
1629                 }
1630                 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1631                         tp->snd_max = tp->snd_nxt + xlen;
1632         }
1633         if ((error == 0) &&
1634             (TCPS_HAVEESTABLISHED(tp->t_state) &&
1635              (tp->t_flags & TF_SACK_PERMIT) &&
1636              tp->rcv_numsacks > 0)) {
1637                     /* Clean up any DSACK's sent */
1638                     tcp_clean_dsack_blocks(tp);
1639         }
1640         if (error) {
1641                 /*
1642                  * We know that the packet was lost, so back out the
1643                  * sequence number advance, if any.
1644                  *
1645                  * If the error is EPERM the packet got blocked by the
1646                  * local firewall.  Normally we should terminate the
1647                  * connection but the blocking may have been spurious
1648                  * due to a firewall reconfiguration cycle.  So we treat
1649                  * it like a packet loss and let the retransmit timer and
1650                  * timeouts do their work over time.
1651                  * XXX: It is a POLA question whether calling tcp_drop right
1652                  * away would be the really correct behavior instead.
1653                  */
1654                 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1655                     !tcp_timer_active(tp, TT_PERSIST)) &&
1656                     ((flags & TH_SYN) == 0) &&
1657                     (error != EPERM)) {
1658                         if (sack_rxmit) {
1659                                 p->rxmit -= len;
1660                                 tp->sackhint.sack_bytes_rexmit -= len;
1661                                 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1662                                     ("sackhint bytes rtx >= 0"));
1663                                 KASSERT((flags & TH_FIN) == 0,
1664                                     ("error while FIN with SACK rxmit"));
1665                         } else {
1666                                 tp->snd_nxt -= len;
1667                                 if (flags & TH_FIN)
1668                                         tp->snd_nxt--;
1669                         }
1670                 }
1671                 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);     /* Check gotos. */
1672                 switch (error) {
1673                 case EACCES:
1674                 case EPERM:
1675                         tp->t_softerror = error;
1676                         return (error);
1677                 case ENOBUFS:
1678                         TCP_XMIT_TIMER_ASSERT(tp, len, flags);
1679                         tp->snd_cwnd = tp->t_maxseg;
1680                         return (0);
1681                 case EMSGSIZE:
1682                         /*
1683                          * For some reason the interface we used initially
1684                          * to send segments changed to another or lowered
1685                          * its MTU.
1686                          * If TSO was active we either got an interface
1687                          * without TSO capabilits or TSO was turned off.
1688                          * If we obtained mtu from ip_output() then update
1689                          * it and try again.
1690                          */
1691                         if (tso)
1692                                 tp->t_flags &= ~TF_TSO;
1693                         if (mtu != 0) {
1694                                 tcp_mss_update(tp, -1, mtu, NULL, NULL);
1695                                 goto again;
1696                         }
1697                         return (error);
1698                 case EHOSTDOWN:
1699                 case EHOSTUNREACH:
1700                 case ENETDOWN:
1701                 case ENETUNREACH:
1702                         if (TCPS_HAVERCVDSYN(tp->t_state)) {
1703                                 tp->t_softerror = error;
1704                                 return (0);
1705                         }
1706                         /* FALLTHROUGH */
1707                 default:
1708                         return (error);
1709                 }
1710         }
1711         TCPSTAT_INC(tcps_sndtotal);
1712
1713         /*
1714          * Data sent (as far as we can tell).
1715          * If this advertises a larger window than any other segment,
1716          * then remember the size of the advertised window.
1717          * Any pending ACK has now been sent.
1718          */
1719         if (SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1720                 tp->rcv_adv = tp->rcv_nxt + recwin;
1721         tp->last_ack_sent = tp->rcv_nxt;
1722         tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1723         if (tcp_timer_active(tp, TT_DELACK))
1724                 tcp_timer_activate(tp, TT_DELACK, 0);
1725 #if 0
1726         /*
1727          * This completely breaks TCP if newreno is turned on.  What happens
1728          * is that if delayed-acks are turned on on the receiver, this code
1729          * on the transmitter effectively destroys the TCP window, forcing
1730          * it to four packets (1.5Kx4 = 6K window).
1731          */
1732         if (sendalot && --maxburst)
1733                 goto again;
1734 #endif
1735         if (sendalot)
1736                 goto again;
1737         return (0);
1738 }
1739
1740 void
1741 tcp_setpersist(struct tcpcb *tp)
1742 {
1743         int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1744         int tt;
1745         int maxunacktime;
1746
1747         tp->t_flags &= ~TF_PREVVALID;
1748         if (tcp_timer_active(tp, TT_REXMT))
1749                 panic("tcp_setpersist: retransmit pending");
1750         /*
1751          * If the state is already closed, don't bother.
1752          */
1753         if (tp->t_state == TCPS_CLOSED)
1754                 return;
1755
1756         /*
1757          * Start/restart persistence timer.
1758          */
1759         TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1760                       tcp_persmin, tcp_persmax);
1761         if (TP_MAXUNACKTIME(tp) && tp->t_acktime) {
1762                 maxunacktime = tp->t_acktime + TP_MAXUNACKTIME(tp) - ticks;
1763                 if (maxunacktime < 1)
1764                         maxunacktime = 1;
1765                 if (maxunacktime < tt)
1766                         tt = maxunacktime;
1767         }
1768         tcp_timer_activate(tp, TT_PERSIST, tt);
1769         if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1770                 tp->t_rxtshift++;
1771 }
1772
1773 /*
1774  * Insert TCP options according to the supplied parameters to the place
1775  * optp in a consistent way.  Can handle unaligned destinations.
1776  *
1777  * The order of the option processing is crucial for optimal packing and
1778  * alignment for the scarce option space.
1779  *
1780  * The optimal order for a SYN/SYN-ACK segment is:
1781  *   MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1782  *   Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1783  *
1784  * The SACK options should be last.  SACK blocks consume 8*n+2 bytes.
1785  * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1786  * At minimum we need 10 bytes (to generate 1 SACK block).  If both
1787  * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1788  * we only have 10 bytes for SACK options (40 - (12 + 18)).
1789  */
1790 int
1791 tcp_addoptions(struct tcpopt *to, u_char *optp)
1792 {
1793         u_int32_t mask, optlen = 0;
1794
1795         for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1796                 if ((to->to_flags & mask) != mask)
1797                         continue;
1798                 if (optlen == TCP_MAXOLEN)
1799                         break;
1800                 switch (to->to_flags & mask) {
1801                 case TOF_MSS:
1802                         while (optlen % 4) {
1803                                 optlen += TCPOLEN_NOP;
1804                                 *optp++ = TCPOPT_NOP;
1805                         }
1806                         if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1807                                 continue;
1808                         optlen += TCPOLEN_MAXSEG;
1809                         *optp++ = TCPOPT_MAXSEG;
1810                         *optp++ = TCPOLEN_MAXSEG;
1811                         to->to_mss = htons(to->to_mss);
1812                         bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1813                         optp += sizeof(to->to_mss);
1814                         break;
1815                 case TOF_SCALE:
1816                         while (!optlen || optlen % 2 != 1) {
1817                                 optlen += TCPOLEN_NOP;
1818                                 *optp++ = TCPOPT_NOP;
1819                         }
1820                         if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1821                                 continue;
1822                         optlen += TCPOLEN_WINDOW;
1823                         *optp++ = TCPOPT_WINDOW;
1824                         *optp++ = TCPOLEN_WINDOW;
1825                         *optp++ = to->to_wscale;
1826                         break;
1827                 case TOF_SACKPERM:
1828                         while (optlen % 2) {
1829                                 optlen += TCPOLEN_NOP;
1830                                 *optp++ = TCPOPT_NOP;
1831                         }
1832                         if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1833                                 continue;
1834                         optlen += TCPOLEN_SACK_PERMITTED;
1835                         *optp++ = TCPOPT_SACK_PERMITTED;
1836                         *optp++ = TCPOLEN_SACK_PERMITTED;
1837                         break;
1838                 case TOF_TS:
1839                         while (!optlen || optlen % 4 != 2) {
1840                                 optlen += TCPOLEN_NOP;
1841                                 *optp++ = TCPOPT_NOP;
1842                         }
1843                         if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1844                                 continue;
1845                         optlen += TCPOLEN_TIMESTAMP;
1846                         *optp++ = TCPOPT_TIMESTAMP;
1847                         *optp++ = TCPOLEN_TIMESTAMP;
1848                         to->to_tsval = htonl(to->to_tsval);
1849                         to->to_tsecr = htonl(to->to_tsecr);
1850                         bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1851                         optp += sizeof(to->to_tsval);
1852                         bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1853                         optp += sizeof(to->to_tsecr);
1854                         break;
1855                 case TOF_SIGNATURE:
1856                         {
1857                         int siglen = TCPOLEN_SIGNATURE - 2;
1858
1859                         while (!optlen || optlen % 4 != 2) {
1860                                 optlen += TCPOLEN_NOP;
1861                                 *optp++ = TCPOPT_NOP;
1862                         }
1863                         if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) {
1864                                 to->to_flags &= ~TOF_SIGNATURE;
1865                                 continue;
1866                         }
1867                         optlen += TCPOLEN_SIGNATURE;
1868                         *optp++ = TCPOPT_SIGNATURE;
1869                         *optp++ = TCPOLEN_SIGNATURE;
1870                         to->to_signature = optp;
1871                         while (siglen--)
1872                                  *optp++ = 0;
1873                         break;
1874                         }
1875                 case TOF_SACK:
1876                         {
1877                         int sackblks = 0;
1878                         struct sackblk *sack = (struct sackblk *)to->to_sacks;
1879                         tcp_seq sack_seq;
1880
1881                         while (!optlen || optlen % 4 != 2) {
1882                                 optlen += TCPOLEN_NOP;
1883                                 *optp++ = TCPOPT_NOP;
1884                         }
1885                         if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1886                                 continue;
1887                         optlen += TCPOLEN_SACKHDR;
1888                         *optp++ = TCPOPT_SACK;
1889                         sackblks = min(to->to_nsacks,
1890                                         (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1891                         *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1892                         while (sackblks--) {
1893                                 sack_seq = htonl(sack->start);
1894                                 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1895                                 optp += sizeof(sack_seq);
1896                                 sack_seq = htonl(sack->end);
1897                                 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1898                                 optp += sizeof(sack_seq);
1899                                 optlen += TCPOLEN_SACK;
1900                                 sack++;
1901                         }
1902                         TCPSTAT_INC(tcps_sack_send_blocks);
1903                         break;
1904                         }
1905                 case TOF_FASTOPEN:
1906                         {
1907                         int total_len;
1908
1909                         /* XXX is there any point to aligning this option? */
1910                         total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len;
1911                         if (TCP_MAXOLEN - optlen < total_len) {
1912                                 to->to_flags &= ~TOF_FASTOPEN;
1913                                 continue;
1914                         }
1915                         *optp++ = TCPOPT_FAST_OPEN;
1916                         *optp++ = total_len;
1917                         if (to->to_tfo_len > 0) {
1918                                 bcopy(to->to_tfo_cookie, optp, to->to_tfo_len);
1919                                 optp += to->to_tfo_len;
1920                         }
1921                         optlen += total_len;
1922                         break;
1923                         }
1924                 default:
1925                         panic("%s: unknown TCP option type", __func__);
1926                         break;
1927                 }
1928         }
1929
1930         /* Terminate and pad TCP options to a 4 byte boundary. */
1931         if (optlen % 4) {
1932                 optlen += TCPOLEN_EOL;
1933                 *optp++ = TCPOPT_EOL;
1934         }
1935         /*
1936          * According to RFC 793 (STD0007):
1937          *   "The content of the header beyond the End-of-Option option
1938          *    must be header padding (i.e., zero)."
1939          *   and later: "The padding is composed of zeros."
1940          */
1941         while (optlen % 4) {
1942                 optlen += TCPOLEN_PAD;
1943                 *optp++ = TCPOPT_PAD;
1944         }
1945
1946         KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));
1947         return (optlen);
1948 }
1949
1950 /*
1951  * This is a copy of m_copym(), taking the TSO segment size/limit
1952  * constraints into account, and advancing the sndptr as it goes.
1953  */
1954 struct mbuf *
1955 tcp_m_copym(struct mbuf *m, int32_t off0, int32_t *plen,
1956     int32_t seglimit, int32_t segsize, struct sockbuf *sb, bool hw_tls)
1957 {
1958 #ifdef KERN_TLS
1959         struct ktls_session *tls, *ntls;
1960         struct mbuf *start __diagused;
1961 #endif
1962         struct mbuf *n, **np;
1963         struct mbuf *top;
1964         int32_t off = off0;
1965         int32_t len = *plen;
1966         int32_t fragsize;
1967         int32_t len_cp = 0;
1968         int32_t *pkthdrlen;
1969         uint32_t mlen, frags;
1970         bool copyhdr;
1971
1972         KASSERT(off >= 0, ("tcp_m_copym, negative off %d", off));
1973         KASSERT(len >= 0, ("tcp_m_copym, negative len %d", len));
1974         if (off == 0 && m->m_flags & M_PKTHDR)
1975                 copyhdr = true;
1976         else
1977                 copyhdr = false;
1978         while (off > 0) {
1979                 KASSERT(m != NULL, ("tcp_m_copym, offset > size of mbuf chain"));
1980                 if (off < m->m_len)
1981                         break;
1982                 off -= m->m_len;
1983                 if ((sb) && (m == sb->sb_sndptr)) {
1984                         sb->sb_sndptroff += m->m_len;
1985                         sb->sb_sndptr = m->m_next;
1986                 }
1987                 m = m->m_next;
1988         }
1989         np = &top;
1990         top = NULL;
1991         pkthdrlen = NULL;
1992 #ifdef KERN_TLS
1993         if (hw_tls && (m->m_flags & M_EXTPG))
1994                 tls = m->m_epg_tls;
1995         else
1996                 tls = NULL;
1997         start = m;
1998 #endif
1999         while (len > 0) {
2000                 if (m == NULL) {
2001                         KASSERT(len == M_COPYALL,
2002                             ("tcp_m_copym, length > size of mbuf chain"));
2003                         *plen = len_cp;
2004                         if (pkthdrlen != NULL)
2005                                 *pkthdrlen = len_cp;
2006                         break;
2007                 }
2008 #ifdef KERN_TLS
2009                 if (hw_tls) {
2010                         if (m->m_flags & M_EXTPG)
2011                                 ntls = m->m_epg_tls;
2012                         else
2013                                 ntls = NULL;
2014
2015                         /*
2016                          * Avoid mixing TLS records with handshake
2017                          * data or TLS records from different
2018                          * sessions.
2019                          */
2020                         if (tls != ntls) {
2021                                 MPASS(m != start);
2022                                 *plen = len_cp;
2023                                 if (pkthdrlen != NULL)
2024                                         *pkthdrlen = len_cp;
2025                                 break;
2026                         }
2027                 }
2028 #endif
2029                 mlen = min(len, m->m_len - off);
2030                 if (seglimit) {
2031                         /*
2032                          * For M_EXTPG mbufs, add 3 segments
2033                          * + 1 in case we are crossing page boundaries
2034                          * + 2 in case the TLS hdr/trailer are used
2035                          * It is cheaper to just add the segments
2036                          * than it is to take the cache miss to look
2037                          * at the mbuf ext_pgs state in detail.
2038                          */
2039                         if (m->m_flags & M_EXTPG) {
2040                                 fragsize = min(segsize, PAGE_SIZE);
2041                                 frags = 3;
2042                         } else {
2043                                 fragsize = segsize;
2044                                 frags = 0;
2045                         }
2046
2047                         /* Break if we really can't fit anymore. */
2048                         if ((frags + 1) >= seglimit) {
2049                                 *plen = len_cp;
2050                                 if (pkthdrlen != NULL)
2051                                         *pkthdrlen = len_cp;
2052                                 break;
2053                         }
2054
2055                         /*
2056                          * Reduce size if you can't copy the whole
2057                          * mbuf. If we can't copy the whole mbuf, also
2058                          * adjust len so the loop will end after this
2059                          * mbuf.
2060                          */
2061                         if ((frags + howmany(mlen, fragsize)) >= seglimit) {
2062                                 mlen = (seglimit - frags - 1) * fragsize;
2063                                 len = mlen;
2064                                 *plen = len_cp + len;
2065                                 if (pkthdrlen != NULL)
2066                                         *pkthdrlen = *plen;
2067                         }
2068                         frags += howmany(mlen, fragsize);
2069                         if (frags == 0)
2070                                 frags++;
2071                         seglimit -= frags;
2072                         KASSERT(seglimit > 0,
2073                             ("%s: seglimit went too low", __func__));
2074                 }
2075                 if (copyhdr)
2076                         n = m_gethdr(M_NOWAIT, m->m_type);
2077                 else
2078                         n = m_get(M_NOWAIT, m->m_type);
2079                 *np = n;
2080                 if (n == NULL)
2081                         goto nospace;
2082                 if (copyhdr) {
2083                         if (!m_dup_pkthdr(n, m, M_NOWAIT))
2084                                 goto nospace;
2085                         if (len == M_COPYALL)
2086                                 n->m_pkthdr.len -= off0;
2087                         else
2088                                 n->m_pkthdr.len = len;
2089                         pkthdrlen = &n->m_pkthdr.len;
2090                         copyhdr = false;
2091                 }
2092                 n->m_len = mlen;
2093                 len_cp += n->m_len;
2094                 if (m->m_flags & (M_EXT|M_EXTPG)) {
2095                         n->m_data = m->m_data + off;
2096                         mb_dupcl(n, m);
2097                 } else
2098                         bcopy(mtod(m, caddr_t)+off, mtod(n, caddr_t),
2099                             (u_int)n->m_len);
2100
2101                 if (sb && (sb->sb_sndptr == m) &&
2102                     ((n->m_len + off) >= m->m_len) && m->m_next) {
2103                         sb->sb_sndptroff += m->m_len;
2104                         sb->sb_sndptr = m->m_next;
2105                 }
2106                 off = 0;
2107                 if (len != M_COPYALL) {
2108                         len -= n->m_len;
2109                 }
2110                 m = m->m_next;
2111                 np = &n->m_next;
2112         }
2113         return (top);
2114 nospace:
2115         m_freem(top);
2116         return (NULL);
2117 }
2118
2119 void
2120 tcp_sndbuf_autoscale(struct tcpcb *tp, struct socket *so, uint32_t sendwin)
2121 {
2122
2123         /*
2124          * Automatic sizing of send socket buffer.  Often the send buffer
2125          * size is not optimally adjusted to the actual network conditions
2126          * at hand (delay bandwidth product).  Setting the buffer size too
2127          * small limits throughput on links with high bandwidth and high
2128          * delay (eg. trans-continental/oceanic links).  Setting the
2129          * buffer size too big consumes too much real kernel memory,
2130          * especially with many connections on busy servers.
2131          *
2132          * The criteria to step up the send buffer one notch are:
2133          *  1. receive window of remote host is larger than send buffer
2134          *     (with a fudge factor of 5/4th);
2135          *  2. send buffer is filled to 7/8th with data (so we actually
2136          *     have data to make use of it);
2137          *  3. send buffer fill has not hit maximal automatic size;
2138          *  4. our send window (slow start and cogestion controlled) is
2139          *     larger than sent but unacknowledged data in send buffer.
2140          *
2141          * The remote host receive window scaling factor may limit the
2142          * growing of the send buffer before it reaches its allowed
2143          * maximum.
2144          *
2145          * It scales directly with slow start or congestion window
2146          * and does at most one step per received ACK.  This fast
2147          * scaling has the drawback of growing the send buffer beyond
2148          * what is strictly necessary to make full use of a given
2149          * delay*bandwidth product.  However testing has shown this not
2150          * to be much of an problem.  At worst we are trading wasting
2151          * of available bandwidth (the non-use of it) for wasting some
2152          * socket buffer memory.
2153          *
2154          * TODO: Shrink send buffer during idle periods together
2155          * with congestion window.  Requires another timer.  Has to
2156          * wait for upcoming tcp timer rewrite.
2157          *
2158          * XXXGL: should there be used sbused() or sbavail()?
2159          */
2160         if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
2161                 int lowat;
2162
2163                 lowat = V_tcp_sendbuf_auto_lowat ? so->so_snd.sb_lowat : 0;
2164                 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat - lowat &&
2165                     sbused(&so->so_snd) >=
2166                     (so->so_snd.sb_hiwat / 8 * 7) - lowat &&
2167                     sbused(&so->so_snd) < V_tcp_autosndbuf_max &&
2168                     sendwin >= (sbused(&so->so_snd) -
2169                     (tp->snd_nxt - tp->snd_una))) {
2170                         if (!sbreserve_locked(so, SO_SND,
2171                             min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
2172                              V_tcp_autosndbuf_max), curthread))
2173                                 so->so_snd.sb_flags &= ~SB_AUTOSIZE;
2174                 }
2175         }
2176 }