linux/net/ipv4/tcp_output.c
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   1/*
   2 * INET         An implementation of the TCP/IP protocol suite for the LINUX
   3 *              operating system.  INET is implemented using the  BSD Socket
   4 *              interface as the means of communication with the user level.
   5 *
   6 *              Implementation of the Transmission Control Protocol(TCP).
   7 *
   8 * Version:     $Id: tcp_output.c,v 1.146 2002/02/01 22:01:04 davem Exp $
   9 *
  10 * Authors:     Ross Biro
  11 *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
  12 *              Mark Evans, <evansmp@uhura.aston.ac.uk>
  13 *              Corey Minyard <wf-rch!minyard@relay.EU.net>
  14 *              Florian La Roche, <flla@stud.uni-sb.de>
  15 *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
  16 *              Linus Torvalds, <torvalds@cs.helsinki.fi>
  17 *              Alan Cox, <gw4pts@gw4pts.ampr.org>
  18 *              Matthew Dillon, <dillon@apollo.west.oic.com>
  19 *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
  20 *              Jorge Cwik, <jorge@laser.satlink.net>
  21 */
  22
  23/*
  24 * Changes:     Pedro Roque     :       Retransmit queue handled by TCP.
  25 *                              :       Fragmentation on mtu decrease
  26 *                              :       Segment collapse on retransmit
  27 *                              :       AF independence
  28 *
  29 *              Linus Torvalds  :       send_delayed_ack
  30 *              David S. Miller :       Charge memory using the right skb
  31 *                                      during syn/ack processing.
  32 *              David S. Miller :       Output engine completely rewritten.
  33 *              Andrea Arcangeli:       SYNACK carry ts_recent in tsecr.
  34 *              Cacophonix Gaul :       draft-minshall-nagle-01
  35 *              J Hadi Salim    :       ECN support
  36 *
  37 */
  38
  39#include <net/tcp.h>
  40
  41#include <linux/compiler.h>
  42#include <linux/module.h>
  43#include <linux/smp_lock.h>
  44
  45/* People can turn this off for buggy TCP's found in printers etc. */
  46int sysctl_tcp_retrans_collapse __read_mostly = 1;
  47
  48/* People can turn this on to  work with those rare, broken TCPs that
  49 * interpret the window field as a signed quantity.
  50 */
  51int sysctl_tcp_workaround_signed_windows __read_mostly = 0;
  52
  53/* This limits the percentage of the congestion window which we
  54 * will allow a single TSO frame to consume.  Building TSO frames
  55 * which are too large can cause TCP streams to be bursty.
  56 */
  57int sysctl_tcp_tso_win_divisor __read_mostly = 3;
  58
  59int sysctl_tcp_mtu_probing __read_mostly = 0;
  60int sysctl_tcp_base_mss __read_mostly = 512;
  61
  62/* By default, RFC2861 behavior.  */
  63int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
  64
  65static void update_send_head(struct sock *sk, struct tcp_sock *tp,
  66                             struct sk_buff *skb)
  67{
  68        sk->sk_send_head = skb->next;
  69        if (sk->sk_send_head == (struct sk_buff *)&sk->sk_write_queue)
  70                sk->sk_send_head = NULL;
  71        tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
  72        tcp_packets_out_inc(sk, tp, skb);
  73}
  74
  75/* SND.NXT, if window was not shrunk.
  76 * If window has been shrunk, what should we make? It is not clear at all.
  77 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
  78 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
  79 * invalid. OK, let's make this for now:
  80 */
  81static inline __u32 tcp_acceptable_seq(struct sock *sk, struct tcp_sock *tp)
  82{
  83        if (!before(tp->snd_una+tp->snd_wnd, tp->snd_nxt))
  84                return tp->snd_nxt;
  85        else
  86                return tp->snd_una+tp->snd_wnd;
  87}
  88
  89/* Calculate mss to advertise in SYN segment.
  90 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
  91 *
  92 * 1. It is independent of path mtu.
  93 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
  94 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
  95 *    attached devices, because some buggy hosts are confused by
  96 *    large MSS.
  97 * 4. We do not make 3, we advertise MSS, calculated from first
  98 *    hop device mtu, but allow to raise it to ip_rt_min_advmss.
  99 *    This may be overridden via information stored in routing table.
 100 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
 101 *    probably even Jumbo".
 102 */
 103static __u16 tcp_advertise_mss(struct sock *sk)
 104{
 105        struct tcp_sock *tp = tcp_sk(sk);
 106        struct dst_entry *dst = __sk_dst_get(sk);
 107        int mss = tp->advmss;
 108
 109        if (dst && dst_metric(dst, RTAX_ADVMSS) < mss) {
 110                mss = dst_metric(dst, RTAX_ADVMSS);
 111                tp->advmss = mss;
 112        }
 113
 114        return (__u16)mss;
 115}
 116
 117/* RFC2861. Reset CWND after idle period longer RTO to "restart window".
 118 * This is the first part of cwnd validation mechanism. */
 119static void tcp_cwnd_restart(struct sock *sk, struct dst_entry *dst)
 120{
 121        struct tcp_sock *tp = tcp_sk(sk);
 122        s32 delta = tcp_time_stamp - tp->lsndtime;
 123        u32 restart_cwnd = tcp_init_cwnd(tp, dst);
 124        u32 cwnd = tp->snd_cwnd;
 125
 126        tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
 127
 128        tp->snd_ssthresh = tcp_current_ssthresh(sk);
 129        restart_cwnd = min(restart_cwnd, cwnd);
 130
 131        while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
 132                cwnd >>= 1;
 133        tp->snd_cwnd = max(cwnd, restart_cwnd);
 134        tp->snd_cwnd_stamp = tcp_time_stamp;
 135        tp->snd_cwnd_used = 0;
 136}
 137
 138static void tcp_event_data_sent(struct tcp_sock *tp,
 139                                struct sk_buff *skb, struct sock *sk)
 140{
 141        struct inet_connection_sock *icsk = inet_csk(sk);
 142        const u32 now = tcp_time_stamp;
 143
 144        if (sysctl_tcp_slow_start_after_idle &&
 145            (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto))
 146                tcp_cwnd_restart(sk, __sk_dst_get(sk));
 147
 148        tp->lsndtime = now;
 149
 150        /* If it is a reply for ato after last received
 151         * packet, enter pingpong mode.
 152         */
 153        if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
 154                icsk->icsk_ack.pingpong = 1;
 155}
 156
 157static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
 158{
 159        tcp_dec_quickack_mode(sk, pkts);
 160        inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
 161}
 162
 163/* Determine a window scaling and initial window to offer.
 164 * Based on the assumption that the given amount of space
 165 * will be offered. Store the results in the tp structure.
 166 * NOTE: for smooth operation initial space offering should
 167 * be a multiple of mss if possible. We assume here that mss >= 1.
 168 * This MUST be enforced by all callers.
 169 */
 170void tcp_select_initial_window(int __space, __u32 mss,
 171                               __u32 *rcv_wnd, __u32 *window_clamp,
 172                               int wscale_ok, __u8 *rcv_wscale)
 173{
 174        unsigned int space = (__space < 0 ? 0 : __space);
 175
 176        /* If no clamp set the clamp to the max possible scaled window */
 177        if (*window_clamp == 0)
 178                (*window_clamp) = (65535 << 14);
 179        space = min(*window_clamp, space);
 180
 181        /* Quantize space offering to a multiple of mss if possible. */
 182        if (space > mss)
 183                space = (space / mss) * mss;
 184
 185        /* NOTE: offering an initial window larger than 32767
 186         * will break some buggy TCP stacks. If the admin tells us
 187         * it is likely we could be speaking with such a buggy stack
 188         * we will truncate our initial window offering to 32K-1
 189         * unless the remote has sent us a window scaling option,
 190         * which we interpret as a sign the remote TCP is not
 191         * misinterpreting the window field as a signed quantity.
 192         */
 193        if (sysctl_tcp_workaround_signed_windows)
 194                (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
 195        else
 196                (*rcv_wnd) = space;
 197
 198        (*rcv_wscale) = 0;
 199        if (wscale_ok) {
 200                /* Set window scaling on max possible window
 201                 * See RFC1323 for an explanation of the limit to 14 
 202                 */
 203                space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max);
 204                space = min_t(u32, space, *window_clamp);
 205                while (space > 65535 && (*rcv_wscale) < 14) {
 206                        space >>= 1;
 207                        (*rcv_wscale)++;
 208                }
 209        }
 210
 211        /* Set initial window to value enough for senders,
 212         * following RFC2414. Senders, not following this RFC,
 213         * will be satisfied with 2.
 214         */
 215        if (mss > (1<<*rcv_wscale)) {
 216                int init_cwnd = 4;
 217                if (mss > 1460*3)
 218                        init_cwnd = 2;
 219                else if (mss > 1460)
 220                        init_cwnd = 3;
 221                if (*rcv_wnd > init_cwnd*mss)
 222                        *rcv_wnd = init_cwnd*mss;
 223        }
 224
 225        /* Set the clamp no higher than max representable value */
 226        (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
 227}
 228
 229/* Chose a new window to advertise, update state in tcp_sock for the
 230 * socket, and return result with RFC1323 scaling applied.  The return
 231 * value can be stuffed directly into th->window for an outgoing
 232 * frame.
 233 */
 234static u16 tcp_select_window(struct sock *sk)
 235{
 236        struct tcp_sock *tp = tcp_sk(sk);
 237        u32 cur_win = tcp_receive_window(tp);
 238        u32 new_win = __tcp_select_window(sk);
 239
 240        /* Never shrink the offered window */
 241        if(new_win < cur_win) {
 242                /* Danger Will Robinson!
 243                 * Don't update rcv_wup/rcv_wnd here or else
 244                 * we will not be able to advertise a zero
 245                 * window in time.  --DaveM
 246                 *
 247                 * Relax Will Robinson.
 248                 */
 249                new_win = cur_win;
 250        }
 251        tp->rcv_wnd = new_win;
 252        tp->rcv_wup = tp->rcv_nxt;
 253
 254        /* Make sure we do not exceed the maximum possible
 255         * scaled window.
 256         */
 257        if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
 258                new_win = min(new_win, MAX_TCP_WINDOW);
 259        else
 260                new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
 261
 262        /* RFC1323 scaling applied */
 263        new_win >>= tp->rx_opt.rcv_wscale;
 264
 265        /* If we advertise zero window, disable fast path. */
 266        if (new_win == 0)
 267                tp->pred_flags = 0;
 268
 269        return new_win;
 270}
 271
 272static void tcp_build_and_update_options(__be32 *ptr, struct tcp_sock *tp,
 273                                         __u32 tstamp, __u8 **md5_hash)
 274{
 275        if (tp->rx_opt.tstamp_ok) {
 276                *ptr++ = htonl((TCPOPT_NOP << 24) |
 277                               (TCPOPT_NOP << 16) |
 278                               (TCPOPT_TIMESTAMP << 8) |
 279                               TCPOLEN_TIMESTAMP);
 280                *ptr++ = htonl(tstamp);
 281                *ptr++ = htonl(tp->rx_opt.ts_recent);
 282        }
 283        if (tp->rx_opt.eff_sacks) {
 284                struct tcp_sack_block *sp = tp->rx_opt.dsack ? tp->duplicate_sack : tp->selective_acks;
 285                int this_sack;
 286
 287                *ptr++ = htonl((TCPOPT_NOP  << 24) |
 288                               (TCPOPT_NOP  << 16) |
 289                               (TCPOPT_SACK <<  8) |
 290                               (TCPOLEN_SACK_BASE + (tp->rx_opt.eff_sacks *
 291                                                     TCPOLEN_SACK_PERBLOCK)));
 292                for(this_sack = 0; this_sack < tp->rx_opt.eff_sacks; this_sack++) {
 293                        *ptr++ = htonl(sp[this_sack].start_seq);
 294                        *ptr++ = htonl(sp[this_sack].end_seq);
 295                }
 296                if (tp->rx_opt.dsack) {
 297                        tp->rx_opt.dsack = 0;
 298                        tp->rx_opt.eff_sacks--;
 299                }
 300        }
 301#ifdef CONFIG_TCP_MD5SIG
 302        if (md5_hash) {
 303                *ptr++ = htonl((TCPOPT_NOP << 24) |
 304                               (TCPOPT_NOP << 16) |
 305                               (TCPOPT_MD5SIG << 8) |
 306                               TCPOLEN_MD5SIG);
 307                *md5_hash = (__u8 *)ptr;
 308        }
 309#endif
 310}
 311
 312/* Construct a tcp options header for a SYN or SYN_ACK packet.
 313 * If this is every changed make sure to change the definition of
 314 * MAX_SYN_SIZE to match the new maximum number of options that you
 315 * can generate.
 316 *
 317 * Note - that with the RFC2385 TCP option, we make room for the
 318 * 16 byte MD5 hash. This will be filled in later, so the pointer for the
 319 * location to be filled is passed back up.
 320 */
 321static void tcp_syn_build_options(__be32 *ptr, int mss, int ts, int sack,
 322                                  int offer_wscale, int wscale, __u32 tstamp,
 323                                  __u32 ts_recent, __u8 **md5_hash)
 324{
 325        /* We always get an MSS option.
 326         * The option bytes which will be seen in normal data
 327         * packets should timestamps be used, must be in the MSS
 328         * advertised.  But we subtract them from tp->mss_cache so
 329         * that calculations in tcp_sendmsg are simpler etc.
 330         * So account for this fact here if necessary.  If we
 331         * don't do this correctly, as a receiver we won't
 332         * recognize data packets as being full sized when we
 333         * should, and thus we won't abide by the delayed ACK
 334         * rules correctly.
 335         * SACKs don't matter, we never delay an ACK when we
 336         * have any of those going out.
 337         */
 338        *ptr++ = htonl((TCPOPT_MSS << 24) | (TCPOLEN_MSS << 16) | mss);
 339        if (ts) {
 340                if(sack)
 341                        *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
 342                                       (TCPOLEN_SACK_PERM << 16) |
 343                                       (TCPOPT_TIMESTAMP << 8) |
 344                                       TCPOLEN_TIMESTAMP);
 345                else
 346                        *ptr++ = htonl((TCPOPT_NOP << 24) |
 347                                       (TCPOPT_NOP << 16) |
 348                                       (TCPOPT_TIMESTAMP << 8) |
 349                                       TCPOLEN_TIMESTAMP);
 350                *ptr++ = htonl(tstamp);         /* TSVAL */
 351                *ptr++ = htonl(ts_recent);      /* TSECR */
 352        } else if(sack)
 353                *ptr++ = htonl((TCPOPT_NOP << 24) |
 354                               (TCPOPT_NOP << 16) |
 355                               (TCPOPT_SACK_PERM << 8) |
 356                               TCPOLEN_SACK_PERM);
 357        if (offer_wscale)
 358                *ptr++ = htonl((TCPOPT_NOP << 24) |
 359                               (TCPOPT_WINDOW << 16) |
 360                               (TCPOLEN_WINDOW << 8) |
 361                               (wscale));
 362#ifdef CONFIG_TCP_MD5SIG
 363        /*
 364         * If MD5 is enabled, then we set the option, and include the size
 365         * (always 18). The actual MD5 hash is added just before the
 366         * packet is sent.
 367         */
 368        if (md5_hash) {
 369                *ptr++ = htonl((TCPOPT_NOP << 24) |
 370                               (TCPOPT_NOP << 16) |
 371                               (TCPOPT_MD5SIG << 8) |
 372                               TCPOLEN_MD5SIG);
 373                *md5_hash = (__u8 *) ptr;
 374        }
 375#endif
 376}
 377
 378/* This routine actually transmits TCP packets queued in by
 379 * tcp_do_sendmsg().  This is used by both the initial
 380 * transmission and possible later retransmissions.
 381 * All SKB's seen here are completely headerless.  It is our
 382 * job to build the TCP header, and pass the packet down to
 383 * IP so it can do the same plus pass the packet off to the
 384 * device.
 385 *
 386 * We are working here with either a clone of the original
 387 * SKB, or a fresh unique copy made by the retransmit engine.
 388 */
 389static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it, gfp_t gfp_mask)
 390{
 391        const struct inet_connection_sock *icsk = inet_csk(sk);
 392        struct inet_sock *inet;
 393        struct tcp_sock *tp;
 394        struct tcp_skb_cb *tcb;
 395        int tcp_header_size;
 396#ifdef CONFIG_TCP_MD5SIG
 397        struct tcp_md5sig_key *md5;
 398        __u8 *md5_hash_location;
 399#endif
 400        struct tcphdr *th;
 401        int sysctl_flags;
 402        int err;
 403
 404        BUG_ON(!skb || !tcp_skb_pcount(skb));
 405
 406        /* If congestion control is doing timestamping, we must
 407         * take such a timestamp before we potentially clone/copy.
 408         */
 409        if (icsk->icsk_ca_ops->rtt_sample)
 410                __net_timestamp(skb);
 411
 412        if (likely(clone_it)) {
 413                if (unlikely(skb_cloned(skb)))
 414                        skb = pskb_copy(skb, gfp_mask);
 415                else
 416                        skb = skb_clone(skb, gfp_mask);
 417                if (unlikely(!skb))
 418                        return -ENOBUFS;
 419        }
 420
 421        inet = inet_sk(sk);
 422        tp = tcp_sk(sk);
 423        tcb = TCP_SKB_CB(skb);
 424        tcp_header_size = tp->tcp_header_len;
 425
 426#define SYSCTL_FLAG_TSTAMPS     0x1
 427#define SYSCTL_FLAG_WSCALE      0x2
 428#define SYSCTL_FLAG_SACK        0x4
 429
 430        sysctl_flags = 0;
 431        if (unlikely(tcb->flags & TCPCB_FLAG_SYN)) {
 432                tcp_header_size = sizeof(struct tcphdr) + TCPOLEN_MSS;
 433                if(sysctl_tcp_timestamps) {
 434                        tcp_header_size += TCPOLEN_TSTAMP_ALIGNED;
 435                        sysctl_flags |= SYSCTL_FLAG_TSTAMPS;
 436                }
 437                if (sysctl_tcp_window_scaling) {
 438                        tcp_header_size += TCPOLEN_WSCALE_ALIGNED;
 439                        sysctl_flags |= SYSCTL_FLAG_WSCALE;
 440                }
 441                if (sysctl_tcp_sack) {
 442                        sysctl_flags |= SYSCTL_FLAG_SACK;
 443                        if (!(sysctl_flags & SYSCTL_FLAG_TSTAMPS))
 444                                tcp_header_size += TCPOLEN_SACKPERM_ALIGNED;
 445                }
 446        } else if (unlikely(tp->rx_opt.eff_sacks)) {
 447                /* A SACK is 2 pad bytes, a 2 byte header, plus
 448                 * 2 32-bit sequence numbers for each SACK block.
 449                 */
 450                tcp_header_size += (TCPOLEN_SACK_BASE_ALIGNED +
 451                                    (tp->rx_opt.eff_sacks *
 452                                     TCPOLEN_SACK_PERBLOCK));
 453        }
 454                
 455        if (tcp_packets_in_flight(tp) == 0)
 456                tcp_ca_event(sk, CA_EVENT_TX_START);
 457
 458#ifdef CONFIG_TCP_MD5SIG
 459        /*
 460         * Are we doing MD5 on this segment? If so - make
 461         * room for it.
 462         */
 463        md5 = tp->af_specific->md5_lookup(sk, sk);
 464        if (md5)
 465                tcp_header_size += TCPOLEN_MD5SIG_ALIGNED;
 466#endif
 467
 468        th = (struct tcphdr *) skb_push(skb, tcp_header_size);
 469        skb->h.th = th;
 470        skb_set_owner_w(skb, sk);
 471
 472        /* Build TCP header and checksum it. */
 473        th->source              = inet->sport;
 474        th->dest                = inet->dport;
 475        th->seq                 = htonl(tcb->seq);
 476        th->ack_seq             = htonl(tp->rcv_nxt);
 477        *(((__be16 *)th) + 6)   = htons(((tcp_header_size >> 2) << 12) |
 478                                        tcb->flags);
 479
 480        if (unlikely(tcb->flags & TCPCB_FLAG_SYN)) {
 481                /* RFC1323: The window in SYN & SYN/ACK segments
 482                 * is never scaled.
 483                 */
 484                th->window      = htons(tp->rcv_wnd);
 485        } else {
 486                th->window      = htons(tcp_select_window(sk));
 487        }
 488        th->check               = 0;
 489        th->urg_ptr             = 0;
 490
 491        if (unlikely(tp->urg_mode &&
 492                     between(tp->snd_up, tcb->seq+1, tcb->seq+0xFFFF))) {
 493                th->urg_ptr             = htons(tp->snd_up-tcb->seq);
 494                th->urg                 = 1;
 495        }
 496
 497        if (unlikely(tcb->flags & TCPCB_FLAG_SYN)) {
 498                tcp_syn_build_options((__be32 *)(th + 1),
 499                                      tcp_advertise_mss(sk),
 500                                      (sysctl_flags & SYSCTL_FLAG_TSTAMPS),
 501                                      (sysctl_flags & SYSCTL_FLAG_SACK),
 502                                      (sysctl_flags & SYSCTL_FLAG_WSCALE),
 503                                      tp->rx_opt.rcv_wscale,
 504                                      tcb->when,
 505                                      tp->rx_opt.ts_recent,
 506
 507#ifdef CONFIG_TCP_MD5SIG
 508                                      md5 ? &md5_hash_location :
 509#endif
 510                                      NULL);
 511        } else {
 512                tcp_build_and_update_options((__be32 *)(th + 1),
 513                                             tp, tcb->when,
 514#ifdef CONFIG_TCP_MD5SIG
 515                                             md5 ? &md5_hash_location :
 516#endif
 517                                             NULL);
 518                TCP_ECN_send(sk, tp, skb, tcp_header_size);
 519        }
 520
 521#ifdef CONFIG_TCP_MD5SIG
 522        /* Calculate the MD5 hash, as we have all we need now */
 523        if (md5) {
 524                tp->af_specific->calc_md5_hash(md5_hash_location,
 525                                               md5,
 526                                               sk, NULL, NULL,
 527                                               skb->h.th,
 528                                               sk->sk_protocol,
 529                                               skb->len);
 530        }
 531#endif
 532
 533        icsk->icsk_af_ops->send_check(sk, skb->len, skb);
 534
 535        if (likely(tcb->flags & TCPCB_FLAG_ACK))
 536                tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
 537
 538        if (skb->len != tcp_header_size)
 539                tcp_event_data_sent(tp, skb, sk);
 540
 541        if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
 542                TCP_INC_STATS(TCP_MIB_OUTSEGS);
 543
 544        err = icsk->icsk_af_ops->queue_xmit(skb, 0);
 545        if (likely(err <= 0))
 546                return err;
 547
 548        tcp_enter_cwr(sk);
 549
 550        return net_xmit_eval(err);
 551
 552#undef SYSCTL_FLAG_TSTAMPS
 553#undef SYSCTL_FLAG_WSCALE
 554#undef SYSCTL_FLAG_SACK
 555}
 556
 557
 558/* This routine just queue's the buffer 
 559 *
 560 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
 561 * otherwise socket can stall.
 562 */
 563static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
 564{
 565        struct tcp_sock *tp = tcp_sk(sk);
 566
 567        /* Advance write_seq and place onto the write_queue. */
 568        tp->write_seq = TCP_SKB_CB(skb)->end_seq;
 569        skb_header_release(skb);
 570        __skb_queue_tail(&sk->sk_write_queue, skb);
 571        sk_charge_skb(sk, skb);
 572
 573        /* Queue it, remembering where we must start sending. */
 574        if (sk->sk_send_head == NULL)
 575                sk->sk_send_head = skb;
 576}
 577
 578static void tcp_set_skb_tso_segs(struct sock *sk, struct sk_buff *skb, unsigned int mss_now)
 579{
 580        if (skb->len <= mss_now || !sk_can_gso(sk)) {
 581                /* Avoid the costly divide in the normal
 582                 * non-TSO case.
 583                 */
 584                skb_shinfo(skb)->gso_segs = 1;
 585                skb_shinfo(skb)->gso_size = 0;
 586                skb_shinfo(skb)->gso_type = 0;
 587        } else {
 588                unsigned int factor;
 589
 590                factor = skb->len + (mss_now - 1);
 591                factor /= mss_now;
 592                skb_shinfo(skb)->gso_segs = factor;
 593                skb_shinfo(skb)->gso_size = mss_now;
 594                skb_shinfo(skb)->gso_type = sk->sk_gso_type;
 595        }
 596}
 597
 598/* Function to create two new TCP segments.  Shrinks the given segment
 599 * to the specified size and appends a new segment with the rest of the
 600 * packet to the list.  This won't be called frequently, I hope. 
 601 * Remember, these are still headerless SKBs at this point.
 602 */
 603int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len, unsigned int mss_now)
 604{
 605        struct tcp_sock *tp = tcp_sk(sk);
 606        struct sk_buff *buff;
 607        int nsize, old_factor;
 608        int nlen;
 609        u16 flags;
 610
 611        BUG_ON(len > skb->len);
 612
 613        clear_all_retrans_hints(tp);
 614        nsize = skb_headlen(skb) - len;
 615        if (nsize < 0)
 616                nsize = 0;
 617
 618        if (skb_cloned(skb) &&
 619            skb_is_nonlinear(skb) &&
 620            pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
 621                return -ENOMEM;
 622
 623        /* Get a new skb... force flag on. */
 624        buff = sk_stream_alloc_skb(sk, nsize, GFP_ATOMIC);
 625        if (buff == NULL)
 626                return -ENOMEM; /* We'll just try again later. */
 627
 628        sk_charge_skb(sk, buff);
 629        nlen = skb->len - len - nsize;
 630        buff->truesize += nlen;
 631        skb->truesize -= nlen;
 632
 633        /* Correct the sequence numbers. */
 634        TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
 635        TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
 636        TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
 637
 638        /* PSH and FIN should only be set in the second packet. */
 639        flags = TCP_SKB_CB(skb)->flags;
 640        TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH);
 641        TCP_SKB_CB(buff)->flags = flags;
 642        TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
 643        TCP_SKB_CB(skb)->sacked &= ~TCPCB_AT_TAIL;
 644
 645        if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
 646                /* Copy and checksum data tail into the new buffer. */
 647                buff->csum = csum_partial_copy_nocheck(skb->data + len, skb_put(buff, nsize),
 648                                                       nsize, 0);
 649
 650                skb_trim(skb, len);
 651
 652                skb->csum = csum_block_sub(skb->csum, buff->csum, len);
 653        } else {
 654                skb->ip_summed = CHECKSUM_PARTIAL;
 655                skb_split(skb, buff, len);
 656        }
 657
 658        buff->ip_summed = skb->ip_summed;
 659
 660        /* Looks stupid, but our code really uses when of
 661         * skbs, which it never sent before. --ANK
 662         */
 663        TCP_SKB_CB(buff)->when = TCP_SKB_CB(skb)->when;
 664        buff->tstamp = skb->tstamp;
 665
 666        old_factor = tcp_skb_pcount(skb);
 667
 668        /* Fix up tso_factor for both original and new SKB.  */
 669        tcp_set_skb_tso_segs(sk, skb, mss_now);
 670        tcp_set_skb_tso_segs(sk, buff, mss_now);
 671
 672        /* If this packet has been sent out already, we must
 673         * adjust the various packet counters.
 674         */
 675        if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
 676                int diff = old_factor - tcp_skb_pcount(skb) -
 677                        tcp_skb_pcount(buff);
 678
 679                tp->packets_out -= diff;
 680
 681                if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
 682                        tp->sacked_out -= diff;
 683                if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
 684                        tp->retrans_out -= diff;
 685
 686                if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) {
 687                        tp->lost_out -= diff;
 688                        tp->left_out -= diff;
 689                }
 690
 691                if (diff > 0) {
 692                        /* Adjust Reno SACK estimate. */
 693                        if (!tp->rx_opt.sack_ok) {
 694                                tp->sacked_out -= diff;
 695                                if ((int)tp->sacked_out < 0)
 696                                        tp->sacked_out = 0;
 697                                tcp_sync_left_out(tp);
 698                        }
 699
 700                        tp->fackets_out -= diff;
 701                        if ((int)tp->fackets_out < 0)
 702                                tp->fackets_out = 0;
 703                }
 704        }
 705
 706        /* Link BUFF into the send queue. */
 707        skb_header_release(buff);
 708        __skb_append(skb, buff, &sk->sk_write_queue);
 709
 710        return 0;
 711}
 712
 713/* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
 714 * eventually). The difference is that pulled data not copied, but
 715 * immediately discarded.
 716 */
 717static void __pskb_trim_head(struct sk_buff *skb, int len)
 718{
 719        int i, k, eat;
 720
 721        eat = len;
 722        k = 0;
 723        for (i=0; i<skb_shinfo(skb)->nr_frags; i++) {
 724                if (skb_shinfo(skb)->frags[i].size <= eat) {
 725                        put_page(skb_shinfo(skb)->frags[i].page);
 726                        eat -= skb_shinfo(skb)->frags[i].size;
 727                } else {
 728                        skb_shinfo(skb)->frags[k] = skb_shinfo(skb)->frags[i];
 729                        if (eat) {
 730                                skb_shinfo(skb)->frags[k].page_offset += eat;
 731                                skb_shinfo(skb)->frags[k].size -= eat;
 732                                eat = 0;
 733                        }
 734                        k++;
 735                }
 736        }
 737        skb_shinfo(skb)->nr_frags = k;
 738
 739        skb->tail = skb->data;
 740        skb->data_len -= len;
 741        skb->len = skb->data_len;
 742}
 743
 744int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
 745{
 746        if (skb_cloned(skb) &&
 747            pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
 748                return -ENOMEM;
 749
 750        /* If len == headlen, we avoid __skb_pull to preserve alignment. */
 751        if (unlikely(len < skb_headlen(skb)))
 752                __skb_pull(skb, len);
 753        else
 754                __pskb_trim_head(skb, len - skb_headlen(skb));
 755
 756        TCP_SKB_CB(skb)->seq += len;
 757        skb->ip_summed = CHECKSUM_PARTIAL;
 758
 759        skb->truesize        -= len;
 760        sk->sk_wmem_queued   -= len;
 761        sk->sk_forward_alloc += len;
 762        sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
 763
 764        /* Any change of skb->len requires recalculation of tso
 765         * factor and mss.
 766         */
 767        if (tcp_skb_pcount(skb) > 1)
 768                tcp_set_skb_tso_segs(sk, skb, tcp_current_mss(sk, 1));
 769
 770        return 0;
 771}
 772
 773/* Not accounting for SACKs here. */
 774int tcp_mtu_to_mss(struct sock *sk, int pmtu)
 775{
 776        struct tcp_sock *tp = tcp_sk(sk);
 777        struct inet_connection_sock *icsk = inet_csk(sk);
 778        int mss_now;
 779
 780        /* Calculate base mss without TCP options:
 781           It is MMS_S - sizeof(tcphdr) of rfc1122
 782         */
 783        mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
 784
 785        /* Clamp it (mss_clamp does not include tcp options) */
 786        if (mss_now > tp->rx_opt.mss_clamp)
 787                mss_now = tp->rx_opt.mss_clamp;
 788
 789        /* Now subtract optional transport overhead */
 790        mss_now -= icsk->icsk_ext_hdr_len;
 791
 792        /* Then reserve room for full set of TCP options and 8 bytes of data */
 793        if (mss_now < 48)
 794                mss_now = 48;
 795
 796        /* Now subtract TCP options size, not including SACKs */
 797        mss_now -= tp->tcp_header_len - sizeof(struct tcphdr);
 798
 799        return mss_now;
 800}
 801
 802/* Inverse of above */
 803int tcp_mss_to_mtu(struct sock *sk, int mss)
 804{
 805        struct tcp_sock *tp = tcp_sk(sk);
 806        struct inet_connection_sock *icsk = inet_csk(sk);
 807        int mtu;
 808
 809        mtu = mss +
 810              tp->tcp_header_len +
 811              icsk->icsk_ext_hdr_len +
 812              icsk->icsk_af_ops->net_header_len;
 813
 814        return mtu;
 815}
 816
 817void tcp_mtup_init(struct sock *sk)
 818{
 819        struct tcp_sock *tp = tcp_sk(sk);
 820        struct inet_connection_sock *icsk = inet_csk(sk);
 821
 822        icsk->icsk_mtup.enabled = sysctl_tcp_mtu_probing > 1;
 823        icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
 824                               icsk->icsk_af_ops->net_header_len;
 825        icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, sysctl_tcp_base_mss);
 826        icsk->icsk_mtup.probe_size = 0;
 827}
 828
 829/* This function synchronize snd mss to current pmtu/exthdr set.
 830
 831   tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
 832   for TCP options, but includes only bare TCP header.
 833
 834   tp->rx_opt.mss_clamp is mss negotiated at connection setup.
 835   It is minimum of user_mss and mss received with SYN.
 836   It also does not include TCP options.
 837
 838   inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
 839
 840   tp->mss_cache is current effective sending mss, including
 841   all tcp options except for SACKs. It is evaluated,
 842   taking into account current pmtu, but never exceeds
 843   tp->rx_opt.mss_clamp.
 844
 845   NOTE1. rfc1122 clearly states that advertised MSS
 846   DOES NOT include either tcp or ip options.
 847
 848   NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
 849   are READ ONLY outside this function.         --ANK (980731)
 850 */
 851
 852unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
 853{
 854        struct tcp_sock *tp = tcp_sk(sk);
 855        struct inet_connection_sock *icsk = inet_csk(sk);
 856        int mss_now;
 857
 858        if (icsk->icsk_mtup.search_high > pmtu)
 859                icsk->icsk_mtup.search_high = pmtu;
 860
 861        mss_now = tcp_mtu_to_mss(sk, pmtu);
 862
 863        /* Bound mss with half of window */
 864        if (tp->max_window && mss_now > (tp->max_window>>1))
 865                mss_now = max((tp->max_window>>1), 68U - tp->tcp_header_len);
 866
 867        /* And store cached results */
 868        icsk->icsk_pmtu_cookie = pmtu;
 869        if (icsk->icsk_mtup.enabled)
 870                mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
 871        tp->mss_cache = mss_now;
 872
 873        return mss_now;
 874}
 875
 876/* Compute the current effective MSS, taking SACKs and IP options,
 877 * and even PMTU discovery events into account.
 878 *
 879 * LARGESEND note: !urg_mode is overkill, only frames up to snd_up
 880 * cannot be large. However, taking into account rare use of URG, this
 881 * is not a big flaw.
 882 */
 883unsigned int tcp_current_mss(struct sock *sk, int large_allowed)
 884{
 885        struct tcp_sock *tp = tcp_sk(sk);
 886        struct dst_entry *dst = __sk_dst_get(sk);
 887        u32 mss_now;
 888        u16 xmit_size_goal;
 889        int doing_tso = 0;
 890
 891        mss_now = tp->mss_cache;
 892
 893        if (large_allowed && sk_can_gso(sk) && !tp->urg_mode)
 894                doing_tso = 1;
 895
 896        if (dst) {
 897                u32 mtu = dst_mtu(dst);
 898                if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
 899                        mss_now = tcp_sync_mss(sk, mtu);
 900        }
 901
 902        if (tp->rx_opt.eff_sacks)
 903                mss_now -= (TCPOLEN_SACK_BASE_ALIGNED +
 904                            (tp->rx_opt.eff_sacks * TCPOLEN_SACK_PERBLOCK));
 905
 906#ifdef CONFIG_TCP_MD5SIG
 907        if (tp->af_specific->md5_lookup(sk, sk))
 908                mss_now -= TCPOLEN_MD5SIG_ALIGNED;
 909#endif
 910
 911        xmit_size_goal = mss_now;
 912
 913        if (doing_tso) {
 914                xmit_size_goal = (65535 -
 915                                  inet_csk(sk)->icsk_af_ops->net_header_len -
 916                                  inet_csk(sk)->icsk_ext_hdr_len -
 917                                  tp->tcp_header_len);
 918
 919                if (tp->max_window &&
 920                    (xmit_size_goal > (tp->max_window >> 1)))
 921                        xmit_size_goal = max((tp->max_window >> 1),
 922                                             68U - tp->tcp_header_len);
 923
 924                xmit_size_goal -= (xmit_size_goal % mss_now);
 925        }
 926        tp->xmit_size_goal = xmit_size_goal;
 927
 928        return mss_now;
 929}
 930
 931/* Congestion window validation. (RFC2861) */
 932
 933static void tcp_cwnd_validate(struct sock *sk, struct tcp_sock *tp)
 934{
 935        __u32 packets_out = tp->packets_out;
 936
 937        if (packets_out >= tp->snd_cwnd) {
 938                /* Network is feed fully. */
 939                tp->snd_cwnd_used = 0;
 940                tp->snd_cwnd_stamp = tcp_time_stamp;
 941        } else {
 942                /* Network starves. */
 943                if (tp->packets_out > tp->snd_cwnd_used)
 944                        tp->snd_cwnd_used = tp->packets_out;
 945
 946                if ((s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
 947                        tcp_cwnd_application_limited(sk);
 948        }
 949}
 950
 951static unsigned int tcp_window_allows(struct tcp_sock *tp, struct sk_buff *skb, unsigned int mss_now, unsigned int cwnd)
 952{
 953        u32 window, cwnd_len;
 954
 955        window = (tp->snd_una + tp->snd_wnd - TCP_SKB_CB(skb)->seq);
 956        cwnd_len = mss_now * cwnd;
 957        return min(window, cwnd_len);
 958}
 959
 960/* Can at least one segment of SKB be sent right now, according to the
 961 * congestion window rules?  If so, return how many segments are allowed.
 962 */
 963static inline unsigned int tcp_cwnd_test(struct tcp_sock *tp, struct sk_buff *skb)
 964{
 965        u32 in_flight, cwnd;
 966
 967        /* Don't be strict about the congestion window for the final FIN.  */
 968        if (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN)
 969                return 1;
 970
 971        in_flight = tcp_packets_in_flight(tp);
 972        cwnd = tp->snd_cwnd;
 973        if (in_flight < cwnd)
 974                return (cwnd - in_flight);
 975
 976        return 0;
 977}
 978
 979/* This must be invoked the first time we consider transmitting
 980 * SKB onto the wire.
 981 */
 982static int tcp_init_tso_segs(struct sock *sk, struct sk_buff *skb, unsigned int mss_now)
 983{
 984        int tso_segs = tcp_skb_pcount(skb);
 985
 986        if (!tso_segs ||
 987            (tso_segs > 1 &&
 988             tcp_skb_mss(skb) != mss_now)) {
 989                tcp_set_skb_tso_segs(sk, skb, mss_now);
 990                tso_segs = tcp_skb_pcount(skb);
 991        }
 992        return tso_segs;
 993}
 994
 995static inline int tcp_minshall_check(const struct tcp_sock *tp)
 996{
 997        return after(tp->snd_sml,tp->snd_una) &&
 998                !after(tp->snd_sml, tp->snd_nxt);
 999}
1000
1001/* Return 0, if packet can be sent now without violation Nagle's rules:
1002 * 1. It is full sized.
1003 * 2. Or it contains FIN. (already checked by caller)
1004 * 3. Or TCP_NODELAY was set.
1005 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1006 *    With Minshall's modification: all sent small packets are ACKed.
1007 */
1008
1009static inline int tcp_nagle_check(const struct tcp_sock *tp,
1010                                  const struct sk_buff *skb, 
1011                                  unsigned mss_now, int nonagle)
1012{
1013        return (skb->len < mss_now &&
1014                ((nonagle&TCP_NAGLE_CORK) ||
1015                 (!nonagle &&
1016                  tp->packets_out &&
1017                  tcp_minshall_check(tp))));
1018}
1019
1020/* Return non-zero if the Nagle test allows this packet to be
1021 * sent now.
1022 */
1023static inline int tcp_nagle_test(struct tcp_sock *tp, struct sk_buff *skb,
1024                                 unsigned int cur_mss, int nonagle)
1025{
1026        /* Nagle rule does not apply to frames, which sit in the middle of the
1027         * write_queue (they have no chances to get new data).
1028         *
1029         * This is implemented in the callers, where they modify the 'nonagle'
1030         * argument based upon the location of SKB in the send queue.
1031         */
1032        if (nonagle & TCP_NAGLE_PUSH)
1033                return 1;
1034
1035        /* Don't use the nagle rule for urgent data (or for the final FIN).  */
1036        if (tp->urg_mode ||
1037            (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN))
1038                return 1;
1039
1040        if (!tcp_nagle_check(tp, skb, cur_mss, nonagle))
1041                return 1;
1042
1043        return 0;
1044}
1045
1046/* Does at least the first segment of SKB fit into the send window? */
1047static inline int tcp_snd_wnd_test(struct tcp_sock *tp, struct sk_buff *skb, unsigned int cur_mss)
1048{
1049        u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1050
1051        if (skb->len > cur_mss)
1052                end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1053
1054        return !after(end_seq, tp->snd_una + tp->snd_wnd);
1055}
1056
1057/* This checks if the data bearing packet SKB (usually sk->sk_send_head)
1058 * should be put on the wire right now.  If so, it returns the number of
1059 * packets allowed by the congestion window.
1060 */
1061static unsigned int tcp_snd_test(struct sock *sk, struct sk_buff *skb,
1062                                 unsigned int cur_mss, int nonagle)
1063{
1064        struct tcp_sock *tp = tcp_sk(sk);
1065        unsigned int cwnd_quota;
1066
1067        tcp_init_tso_segs(sk, skb, cur_mss);
1068
1069        if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
1070                return 0;
1071
1072        cwnd_quota = tcp_cwnd_test(tp, skb);
1073        if (cwnd_quota &&
1074            !tcp_snd_wnd_test(tp, skb, cur_mss))
1075                cwnd_quota = 0;
1076
1077        return cwnd_quota;
1078}
1079
1080static inline int tcp_skb_is_last(const struct sock *sk, 
1081                                  const struct sk_buff *skb)
1082{
1083        return skb->next == (struct sk_buff *)&sk->sk_write_queue;
1084}
1085
1086int tcp_may_send_now(struct sock *sk, struct tcp_sock *tp)
1087{
1088        struct sk_buff *skb = sk->sk_send_head;
1089
1090        return (skb &&
1091                tcp_snd_test(sk, skb, tcp_current_mss(sk, 1),
1092                             (tcp_skb_is_last(sk, skb) ?
1093                              TCP_NAGLE_PUSH :
1094                              tp->nonagle)));
1095}
1096
1097/* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1098 * which is put after SKB on the list.  It is very much like
1099 * tcp_fragment() except that it may make several kinds of assumptions
1100 * in order to speed up the splitting operation.  In particular, we
1101 * know that all the data is in scatter-gather pages, and that the
1102 * packet has never been sent out before (and thus is not cloned).
1103 */
1104static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len, unsigned int mss_now)
1105{
1106        struct sk_buff *buff;
1107        int nlen = skb->len - len;
1108        u16 flags;
1109
1110        /* All of a TSO frame must be composed of paged data.  */
1111        if (skb->len != skb->data_len)
1112                return tcp_fragment(sk, skb, len, mss_now);
1113
1114        buff = sk_stream_alloc_pskb(sk, 0, 0, GFP_ATOMIC);
1115        if (unlikely(buff == NULL))
1116                return -ENOMEM;
1117
1118        sk_charge_skb(sk, buff);
1119        buff->truesize += nlen;
1120        skb->truesize -= nlen;
1121
1122        /* Correct the sequence numbers. */
1123        TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1124        TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1125        TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1126
1127        /* PSH and FIN should only be set in the second packet. */
1128        flags = TCP_SKB_CB(skb)->flags;
1129        TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH);
1130        TCP_SKB_CB(buff)->flags = flags;
1131
1132        /* This packet was never sent out yet, so no SACK bits. */
1133        TCP_SKB_CB(buff)->sacked = 0;
1134
1135        buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1136        skb_split(skb, buff, len);
1137
1138        /* Fix up tso_factor for both original and new SKB.  */
1139        tcp_set_skb_tso_segs(sk, skb, mss_now);
1140        tcp_set_skb_tso_segs(sk, buff, mss_now);
1141
1142        /* Link BUFF into the send queue. */
1143        skb_header_release(buff);
1144        __skb_append(skb, buff, &sk->sk_write_queue);
1145
1146        return 0;
1147}
1148
1149/* Try to defer sending, if possible, in order to minimize the amount
1150 * of TSO splitting we do.  View it as a kind of TSO Nagle test.
1151 *
1152 * This algorithm is from John Heffner.
1153 */
1154static int tcp_tso_should_defer(struct sock *sk, struct tcp_sock *tp, struct sk_buff *skb)
1155{
1156        const struct inet_connection_sock *icsk = inet_csk(sk);
1157        u32 send_win, cong_win, limit, in_flight;
1158
1159        if (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN)
1160                goto send_now;
1161
1162        if (icsk->icsk_ca_state != TCP_CA_Open)
1163                goto send_now;
1164
1165        /* Defer for less than two clock ticks. */
1166        if (!tp->tso_deferred && ((jiffies<<1)>>1) - (tp->tso_deferred>>1) > 1)
1167                goto send_now;
1168
1169        in_flight = tcp_packets_in_flight(tp);
1170
1171        BUG_ON(tcp_skb_pcount(skb) <= 1 ||
1172               (tp->snd_cwnd <= in_flight));
1173
1174        send_win = (tp->snd_una + tp->snd_wnd) - TCP_SKB_CB(skb)->seq;
1175
1176        /* From in_flight test above, we know that cwnd > in_flight.  */
1177        cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1178
1179        limit = min(send_win, cong_win);
1180
1181        /* If a full-sized TSO skb can be sent, do it. */
1182        if (limit >= 65536)
1183                goto send_now;
1184
1185        if (sysctl_tcp_tso_win_divisor) {
1186                u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1187
1188                /* If at least some fraction of a window is available,
1189                 * just use it.
1190                 */
1191                chunk /= sysctl_tcp_tso_win_divisor;
1192                if (limit >= chunk)
1193                        goto send_now;
1194        } else {
1195                /* Different approach, try not to defer past a single
1196                 * ACK.  Receiver should ACK every other full sized
1197                 * frame, so if we have space for more than 3 frames
1198                 * then send now.
1199                 */
1200                if (limit > tcp_max_burst(tp) * tp->mss_cache)
1201                        goto send_now;
1202        }
1203
1204        /* Ok, it looks like it is advisable to defer.  */
1205        tp->tso_deferred = 1 | (jiffies<<1);
1206
1207        return 1;
1208
1209send_now:
1210        tp->tso_deferred = 0;
1211        return 0;
1212}
1213
1214/* Create a new MTU probe if we are ready.
1215 * Returns 0 if we should wait to probe (no cwnd available),
1216 *         1 if a probe was sent,
1217 *         -1 otherwise */
1218static int tcp_mtu_probe(struct sock *sk)
1219{
1220        struct tcp_sock *tp = tcp_sk(sk);
1221        struct inet_connection_sock *icsk = inet_csk(sk);
1222        struct sk_buff *skb, *nskb, *next;
1223        int len;
1224        int probe_size;
1225        unsigned int pif;
1226        int copy;
1227        int mss_now;
1228
1229        /* Not currently probing/verifying,
1230         * not in recovery,
1231         * have enough cwnd, and
1232         * not SACKing (the variable headers throw things off) */
1233        if (!icsk->icsk_mtup.enabled ||
1234            icsk->icsk_mtup.probe_size ||
1235            inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
1236            tp->snd_cwnd < 11 ||
1237            tp->rx_opt.eff_sacks)
1238                return -1;
1239
1240        /* Very simple search strategy: just double the MSS. */
1241        mss_now = tcp_current_mss(sk, 0);
1242        probe_size = 2*tp->mss_cache;
1243        if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high)) {
1244                /* TODO: set timer for probe_converge_event */
1245                return -1;
1246        }
1247
1248        /* Have enough data in the send queue to probe? */
1249        len = 0;
1250        if ((skb = sk->sk_send_head) == NULL)
1251                return -1;
1252        while ((len += skb->len) < probe_size && !tcp_skb_is_last(sk, skb))
1253                skb = skb->next;
1254        if (len < probe_size)
1255                return -1;
1256
1257        /* Receive window check. */
1258        if (after(TCP_SKB_CB(skb)->seq + probe_size, tp->snd_una + tp->snd_wnd)) {
1259                if (tp->snd_wnd < probe_size)
1260                        return -1;
1261                else
1262                        return 0;
1263        }
1264
1265        /* Do we need to wait to drain cwnd? */
1266        pif = tcp_packets_in_flight(tp);
1267        if (pif + 2 > tp->snd_cwnd) {
1268                /* With no packets in flight, don't stall. */
1269                if (pif == 0)
1270                        return -1;
1271                else
1272                        return 0;
1273        }
1274
1275        /* We're allowed to probe.  Build it now. */
1276        if ((nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC)) == NULL)
1277                return -1;
1278        sk_charge_skb(sk, nskb);
1279
1280        skb = sk->sk_send_head;
1281        __skb_insert(nskb, skb->prev, skb, &sk->sk_write_queue);
1282        sk->sk_send_head = nskb;
1283
1284        TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
1285        TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
1286        TCP_SKB_CB(nskb)->flags = TCPCB_FLAG_ACK;
1287        TCP_SKB_CB(nskb)->sacked = 0;
1288        nskb->csum = 0;
1289        nskb->ip_summed = skb->ip_summed;
1290
1291        len = 0;
1292        while (len < probe_size) {
1293                next = skb->next;
1294
1295                copy = min_t(int, skb->len, probe_size - len);
1296                if (nskb->ip_summed)
1297                        skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
1298                else
1299                        nskb->csum = skb_copy_and_csum_bits(skb, 0,
1300                                         skb_put(nskb, copy), copy, nskb->csum);
1301
1302                if (skb->len <= copy) {
1303                        /* We've eaten all the data from this skb.
1304                         * Throw it away. */
1305                        TCP_SKB_CB(nskb)->flags |= TCP_SKB_CB(skb)->flags;
1306                        __skb_unlink(skb, &sk->sk_write_queue);
1307                        sk_stream_free_skb(sk, skb);
1308                } else {
1309                        TCP_SKB_CB(nskb)->flags |= TCP_SKB_CB(skb)->flags &
1310                                                   ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH);
1311                        if (!skb_shinfo(skb)->nr_frags) {
1312                                skb_pull(skb, copy);
1313                                if (skb->ip_summed != CHECKSUM_PARTIAL)
1314                                        skb->csum = csum_partial(skb->data, skb->len, 0);
1315                        } else {
1316                                __pskb_trim_head(skb, copy);
1317                                tcp_set_skb_tso_segs(sk, skb, mss_now);
1318                        }
1319                        TCP_SKB_CB(skb)->seq += copy;
1320                }
1321
1322                len += copy;
1323                skb = next;
1324        }
1325        tcp_init_tso_segs(sk, nskb, nskb->len);
1326
1327        /* We're ready to send.  If this fails, the probe will
1328         * be resegmented into mss-sized pieces by tcp_write_xmit(). */
1329        TCP_SKB_CB(nskb)->when = tcp_time_stamp;
1330        if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
1331                /* Decrement cwnd here because we are sending
1332                * effectively two packets. */
1333                tp->snd_cwnd--;
1334                update_send_head(sk, tp, nskb);
1335
1336                icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
1337                tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
1338                tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
1339
1340                return 1;
1341        }
1342
1343        return -1;
1344}
1345
1346
1347/* This routine writes packets to the network.  It advances the
1348 * send_head.  This happens as incoming acks open up the remote
1349 * window for us.
1350 *
1351 * Returns 1, if no segments are in flight and we have queued segments, but
1352 * cannot send anything now because of SWS or another problem.
1353 */
1354static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle)
1355{
1356        struct tcp_sock *tp = tcp_sk(sk);
1357        struct sk_buff *skb;
1358        unsigned int tso_segs, sent_pkts;
1359        int cwnd_quota;
1360        int result;
1361
1362        /* If we are closed, the bytes will have to remain here.
1363         * In time closedown will finish, we empty the write queue and all
1364         * will be happy.
1365         */
1366        if (unlikely(sk->sk_state == TCP_CLOSE))
1367                return 0;
1368
1369        sent_pkts = 0;
1370
1371        /* Do MTU probing. */
1372        if ((result = tcp_mtu_probe(sk)) == 0) {
1373                return 0;
1374        } else if (result > 0) {
1375                sent_pkts = 1;
1376        }
1377
1378        while ((skb = sk->sk_send_head)) {
1379                unsigned int limit;
1380
1381                tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
1382                BUG_ON(!tso_segs);
1383
1384                cwnd_quota = tcp_cwnd_test(tp, skb);
1385                if (!cwnd_quota)
1386                        break;
1387
1388                if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
1389                        break;
1390
1391                if (tso_segs == 1) {
1392                        if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
1393                                                     (tcp_skb_is_last(sk, skb) ?
1394                                                      nonagle : TCP_NAGLE_PUSH))))
1395                                break;
1396                } else {
1397                        if (tcp_tso_should_defer(sk, tp, skb))
1398                                break;
1399                }
1400
1401                limit = mss_now;
1402                if (tso_segs > 1) {
1403                        limit = tcp_window_allows(tp, skb,
1404                                                  mss_now, cwnd_quota);
1405
1406                        if (skb->len < limit) {
1407                                unsigned int trim = skb->len % mss_now;
1408
1409                                if (trim)
1410                                        limit = skb->len - trim;
1411                        }
1412                }
1413
1414                if (skb->len > limit &&
1415                    unlikely(tso_fragment(sk, skb, limit, mss_now)))
1416                        break;
1417
1418                TCP_SKB_CB(skb)->when = tcp_time_stamp;
1419
1420                if (unlikely(tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC)))
1421                        break;
1422
1423                /* Advance the send_head.  This one is sent out.
1424                 * This call will increment packets_out.
1425                 */
1426                update_send_head(sk, tp, skb);
1427
1428                tcp_minshall_update(tp, mss_now, skb);
1429                sent_pkts++;
1430        }
1431
1432        if (likely(sent_pkts)) {
1433                tcp_cwnd_validate(sk, tp);
1434                return 0;
1435        }
1436        return !tp->packets_out && sk->sk_send_head;
1437}
1438
1439/* Push out any pending frames which were held back due to
1440 * TCP_CORK or attempt at coalescing tiny packets.
1441 * The socket must be locked by the caller.
1442 */
1443void __tcp_push_pending_frames(struct sock *sk, struct tcp_sock *tp,
1444                               unsigned int cur_mss, int nonagle)
1445{
1446        struct sk_buff *skb = sk->sk_send_head;
1447
1448        if (skb) {
1449                if (tcp_write_xmit(sk, cur_mss, nonagle))
1450                        tcp_check_probe_timer(sk, tp);
1451        }
1452}
1453
1454/* Send _single_ skb sitting at the send head. This function requires
1455 * true push pending frames to setup probe timer etc.
1456 */
1457void tcp_push_one(struct sock *sk, unsigned int mss_now)
1458{
1459        struct tcp_sock *tp = tcp_sk(sk);
1460        struct sk_buff *skb = sk->sk_send_head;
1461        unsigned int tso_segs, cwnd_quota;
1462
1463        BUG_ON(!skb || skb->len < mss_now);
1464
1465        tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
1466        cwnd_quota = tcp_snd_test(sk, skb, mss_now, TCP_NAGLE_PUSH);
1467
1468        if (likely(cwnd_quota)) {
1469                unsigned int limit;
1470
1471                BUG_ON(!tso_segs);
1472
1473                limit = mss_now;
1474                if (tso_segs > 1) {
1475                        limit = tcp_window_allows(tp, skb,
1476                                                  mss_now, cwnd_quota);
1477
1478                        if (skb->len < limit) {
1479                                unsigned int trim = skb->len % mss_now;
1480
1481                                if (trim)
1482                                        limit = skb->len - trim;
1483                        }
1484                }
1485
1486                if (skb->len > limit &&
1487                    unlikely(tso_fragment(sk, skb, limit, mss_now)))
1488                        return;
1489
1490                /* Send it out now. */
1491                TCP_SKB_CB(skb)->when = tcp_time_stamp;
1492
1493                if (likely(!tcp_transmit_skb(sk, skb, 1, sk->sk_allocation))) {
1494                        update_send_head(sk, tp, skb);
1495                        tcp_cwnd_validate(sk, tp);
1496                        return;
1497                }
1498        }
1499}
1500
1501/* This function returns the amount that we can raise the
1502 * usable window based on the following constraints
1503 *  
1504 * 1. The window can never be shrunk once it is offered (RFC 793)
1505 * 2. We limit memory per socket
1506 *
1507 * RFC 1122:
1508 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
1509 *  RECV.NEXT + RCV.WIN fixed until:
1510 *  RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
1511 *
1512 * i.e. don't raise the right edge of the window until you can raise
1513 * it at least MSS bytes.
1514 *
1515 * Unfortunately, the recommended algorithm breaks header prediction,
1516 * since header prediction assumes th->window stays fixed.
1517 *
1518 * Strictly speaking, keeping th->window fixed violates the receiver
1519 * side SWS prevention criteria. The problem is that under this rule
1520 * a stream of single byte packets will cause the right side of the
1521 * window to always advance by a single byte.
1522 * 
1523 * Of course, if the sender implements sender side SWS prevention
1524 * then this will not be a problem.
1525 * 
1526 * BSD seems to make the following compromise:
1527 * 
1528 *      If the free space is less than the 1/4 of the maximum
1529 *      space available and the free space is less than 1/2 mss,
1530 *      then set the window to 0.
1531 *      [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
1532 *      Otherwise, just prevent the window from shrinking
1533 *      and from being larger than the largest representable value.
1534 *
1535 * This prevents incremental opening of the window in the regime
1536 * where TCP is limited by the speed of the reader side taking
1537 * data out of the TCP receive queue. It does nothing about
1538 * those cases where the window is constrained on the sender side
1539 * because the pipeline is full.
1540 *
1541 * BSD also seems to "accidentally" limit itself to windows that are a
1542 * multiple of MSS, at least until the free space gets quite small.
1543 * This would appear to be a side effect of the mbuf implementation.
1544 * Combining these two algorithms results in the observed behavior
1545 * of having a fixed window size at almost all times.
1546 *
1547 * Below we obtain similar behavior by forcing the offered window to
1548 * a multiple of the mss when it is feasible to do so.
1549 *
1550 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
1551 * Regular options like TIMESTAMP are taken into account.
1552 */
1553u32 __tcp_select_window(struct sock *sk)
1554{
1555        struct inet_connection_sock *icsk = inet_csk(sk);
1556        struct tcp_sock *tp = tcp_sk(sk);
1557        /* MSS for the peer's data.  Previous versions used mss_clamp
1558         * here.  I don't know if the value based on our guesses
1559         * of peer's MSS is better for the performance.  It's more correct
1560         * but may be worse for the performance because of rcv_mss
1561         * fluctuations.  --SAW  1998/11/1
1562         */
1563        int mss = icsk->icsk_ack.rcv_mss;
1564        int free_space = tcp_space(sk);
1565        int full_space = min_t(int, tp->window_clamp, tcp_full_space(sk));
1566        int window;
1567
1568        if (mss > full_space)
1569                mss = full_space; 
1570
1571        if (free_space < full_space/2) {
1572                icsk->icsk_ack.quick = 0;
1573
1574                if (tcp_memory_pressure)
1575                        tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U*tp->advmss);
1576
1577                if (free_space < mss)
1578                        return 0;
1579        }
1580
1581        if (free_space > tp->rcv_ssthresh)
1582                free_space = tp->rcv_ssthresh;
1583
1584        /* Don't do rounding if we are using window scaling, since the
1585         * scaled window will not line up with the MSS boundary anyway.
1586         */
1587        window = tp->rcv_wnd;
1588        if (tp->rx_opt.rcv_wscale) {
1589                window = free_space;
1590
1591                /* Advertise enough space so that it won't get scaled away.
1592                 * Import case: prevent zero window announcement if
1593                 * 1<<rcv_wscale > mss.
1594                 */
1595                if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
1596                        window = (((window >> tp->rx_opt.rcv_wscale) + 1)
1597                                  << tp->rx_opt.rcv_wscale);
1598        } else {
1599                /* Get the largest window that is a nice multiple of mss.
1600                 * Window clamp already applied above.
1601                 * If our current window offering is within 1 mss of the
1602                 * free space we just keep it. This prevents the divide
1603                 * and multiply from happening most of the time.
1604                 * We also don't do any window rounding when the free space
1605                 * is too small.
1606                 */
1607                if (window <= free_space - mss || window > free_space)
1608                        window = (free_space/mss)*mss;
1609        }
1610
1611        return window;
1612}
1613
1614/* Attempt to collapse two adjacent SKB's during retransmission. */
1615static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *skb, int mss_now)
1616{
1617        struct tcp_sock *tp = tcp_sk(sk);
1618        struct sk_buff *next_skb = skb->next;
1619
1620        /* The first test we must make is that neither of these two
1621         * SKB's are still referenced by someone else.
1622         */
1623        if (!skb_cloned(skb) && !skb_cloned(next_skb)) {
1624                int skb_size = skb->len, next_skb_size = next_skb->len;
1625                u16 flags = TCP_SKB_CB(skb)->flags;
1626
1627                /* Also punt if next skb has been SACK'd. */
1628                if(TCP_SKB_CB(next_skb)->sacked & TCPCB_SACKED_ACKED)
1629                        return;
1630
1631                /* Next skb is out of window. */
1632                if (after(TCP_SKB_CB(next_skb)->end_seq, tp->snd_una+tp->snd_wnd))
1633                        return;
1634
1635                /* Punt if not enough space exists in the first SKB for
1636                 * the data in the second, or the total combined payload
1637                 * would exceed the MSS.
1638                 */
1639                if ((next_skb_size > skb_tailroom(skb)) ||
1640                    ((skb_size + next_skb_size) > mss_now))
1641                        return;
1642
1643                BUG_ON(tcp_skb_pcount(skb) != 1 ||
1644                       tcp_skb_pcount(next_skb) != 1);
1645
1646                /* changing transmit queue under us so clear hints */
1647                clear_all_retrans_hints(tp);
1648
1649                /* Ok.  We will be able to collapse the packet. */
1650                __skb_unlink(next_skb, &sk->sk_write_queue);
1651
1652                memcpy(skb_put(skb, next_skb_size), next_skb->data, next_skb_size);
1653
1654                if (next_skb->ip_summed == CHECKSUM_PARTIAL)
1655                        skb->ip_summed = CHECKSUM_PARTIAL;
1656
1657                if (skb->ip_summed != CHECKSUM_PARTIAL)
1658                        skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
1659
1660                /* Update sequence range on original skb. */
1661                TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
1662
1663                /* Merge over control information. */
1664                flags |= TCP_SKB_CB(next_skb)->flags; /* This moves PSH/FIN etc. over */
1665                TCP_SKB_CB(skb)->flags = flags;
1666
1667                /* All done, get rid of second SKB and account for it so
1668                 * packet counting does not break.
1669                 */
1670                TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked&(TCPCB_EVER_RETRANS|TCPCB_AT_TAIL);
1671                if (TCP_SKB_CB(next_skb)->sacked&TCPCB_SACKED_RETRANS)
1672                        tp->retrans_out -= tcp_skb_pcount(next_skb);
1673                if (TCP_SKB_CB(next_skb)->sacked&TCPCB_LOST) {
1674                        tp->lost_out -= tcp_skb_pcount(next_skb);
1675                        tp->left_out -= tcp_skb_pcount(next_skb);
1676                }
1677                /* Reno case is special. Sigh... */
1678                if (!tp->rx_opt.sack_ok && tp->sacked_out) {
1679                        tcp_dec_pcount_approx(&tp->sacked_out, next_skb);
1680                        tp->left_out -= tcp_skb_pcount(next_skb);
1681                }
1682
1683                /* Not quite right: it can be > snd.fack, but
1684                 * it is better to underestimate fackets.
1685                 */
1686                tcp_dec_pcount_approx(&tp->fackets_out, next_skb);
1687                tcp_packets_out_dec(tp, next_skb);
1688                sk_stream_free_skb(sk, next_skb);
1689        }
1690}
1691
1692/* Do a simple retransmit without using the backoff mechanisms in
1693 * tcp_timer. This is used for path mtu discovery. 
1694 * The socket is already locked here.
1695 */ 
1696void tcp_simple_retransmit(struct sock *sk)
1697{
1698        const struct inet_connection_sock *icsk = inet_csk(sk);
1699        struct tcp_sock *tp = tcp_sk(sk);
1700        struct sk_buff *skb;
1701        unsigned int mss = tcp_current_mss(sk, 0);
1702        int lost = 0;
1703
1704        sk_stream_for_retrans_queue(skb, sk) {
1705                if (skb->len > mss && 
1706                    !(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) {
1707                        if (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) {
1708                                TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1709                                tp->retrans_out -= tcp_skb_pcount(skb);
1710                        }
1711                        if (!(TCP_SKB_CB(skb)->sacked&TCPCB_LOST)) {
1712                                TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1713                                tp->lost_out += tcp_skb_pcount(skb);
1714                                lost = 1;
1715                        }
1716                }
1717        }
1718
1719        clear_all_retrans_hints(tp);
1720
1721        if (!lost)
1722                return;
1723
1724        tcp_sync_left_out(tp);
1725
1726        /* Don't muck with the congestion window here.
1727         * Reason is that we do not increase amount of _data_
1728         * in network, but units changed and effective
1729         * cwnd/ssthresh really reduced now.
1730         */
1731        if (icsk->icsk_ca_state != TCP_CA_Loss) {
1732                tp->high_seq = tp->snd_nxt;
1733                tp->snd_ssthresh = tcp_current_ssthresh(sk);
1734                tp->prior_ssthresh = 0;
1735                tp->undo_marker = 0;
1736                tcp_set_ca_state(sk, TCP_CA_Loss);
1737        }
1738        tcp_xmit_retransmit_queue(sk);
1739}
1740
1741/* This retransmits one SKB.  Policy decisions and retransmit queue
1742 * state updates are done by the caller.  Returns non-zero if an
1743 * error occurred which prevented the send.
1744 */
1745int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
1746{
1747        struct tcp_sock *tp = tcp_sk(sk);
1748        struct inet_connection_sock *icsk = inet_csk(sk);
1749        unsigned int cur_mss = tcp_current_mss(sk, 0);
1750        int err;
1751
1752        /* Inconslusive MTU probe */
1753        if (icsk->icsk_mtup.probe_size) {
1754                icsk->icsk_mtup.probe_size = 0;
1755        }
1756
1757        /* Do not sent more than we queued. 1/4 is reserved for possible
1758         * copying overhead: fragmentation, tunneling, mangling etc.
1759         */
1760        if (atomic_read(&sk->sk_wmem_alloc) >
1761            min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
1762                return -EAGAIN;
1763
1764        if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
1765                if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1766                        BUG();
1767                if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
1768                        return -ENOMEM;
1769        }
1770
1771        /* If receiver has shrunk his window, and skb is out of
1772         * new window, do not retransmit it. The exception is the
1773         * case, when window is shrunk to zero. In this case
1774         * our retransmit serves as a zero window probe.
1775         */
1776        if (!before(TCP_SKB_CB(skb)->seq, tp->snd_una+tp->snd_wnd)
1777            && TCP_SKB_CB(skb)->seq != tp->snd_una)
1778                return -EAGAIN;
1779
1780        if (skb->len > cur_mss) {
1781                if (tcp_fragment(sk, skb, cur_mss, cur_mss))
1782                        return -ENOMEM; /* We'll try again later. */
1783        }
1784
1785        /* Collapse two adjacent packets if worthwhile and we can. */
1786        if(!(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_SYN) &&
1787           (skb->len < (cur_mss >> 1)) &&
1788           (skb->next != sk->sk_send_head) &&
1789           (skb->next != (struct sk_buff *)&sk->sk_write_queue) &&
1790           (skb_shinfo(skb)->nr_frags == 0 && skb_shinfo(skb->next)->nr_frags == 0) &&
1791           (tcp_skb_pcount(skb) == 1 && tcp_skb_pcount(skb->next) == 1) &&
1792           (sysctl_tcp_retrans_collapse != 0))
1793                tcp_retrans_try_collapse(sk, skb, cur_mss);
1794
1795        if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
1796                return -EHOSTUNREACH; /* Routing failure or similar. */
1797
1798        /* Some Solaris stacks overoptimize and ignore the FIN on a
1799         * retransmit when old data is attached.  So strip it off
1800         * since it is cheap to do so and saves bytes on the network.
1801         */
1802        if(skb->len > 0 &&
1803           (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) &&
1804           tp->snd_una == (TCP_SKB_CB(skb)->end_seq - 1)) {
1805                if (!pskb_trim(skb, 0)) {
1806                        TCP_SKB_CB(skb)->seq = TCP_SKB_CB(skb)->end_seq - 1;
1807                        skb_shinfo(skb)->gso_segs = 1;
1808                        skb_shinfo(skb)->gso_size = 0;
1809                        skb_shinfo(skb)->gso_type = 0;
1810                        skb->ip_summed = CHECKSUM_NONE;
1811                        skb->csum = 0;
1812                }
1813        }
1814
1815        /* Make a copy, if the first transmission SKB clone we made
1816         * is still in somebody's hands, else make a clone.
1817         */
1818        TCP_SKB_CB(skb)->when = tcp_time_stamp;
1819
1820        err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
1821
1822        if (err == 0) {
1823                /* Update global TCP statistics. */
1824                TCP_INC_STATS(TCP_MIB_RETRANSSEGS);
1825
1826                tp->total_retrans++;
1827
1828#if FASTRETRANS_DEBUG > 0
1829                if (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) {
1830                        if (net_ratelimit())
1831                                printk(KERN_DEBUG "retrans_out leaked.\n");
1832                }
1833#endif
1834                TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
1835                tp->retrans_out += tcp_skb_pcount(skb);
1836
1837                /* Save stamp of the first retransmit. */
1838                if (!tp->retrans_stamp)
1839                        tp->retrans_stamp = TCP_SKB_CB(skb)->when;
1840
1841                tp->undo_retrans++;
1842
1843                /* snd_nxt is stored to detect loss of retransmitted segment,
1844                 * see tcp_input.c tcp_sacktag_write_queue().
1845                 */
1846                TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
1847        }
1848        return err;
1849}
1850
1851/* This gets called after a retransmit timeout, and the initially
1852 * retransmitted data is acknowledged.  It tries to continue
1853 * resending the rest of the retransmit queue, until either
1854 * we've sent it all or the congestion window limit is reached.
1855 * If doing SACK, the first ACK which comes back for a timeout
1856 * based retransmit packet might feed us FACK information again.
1857 * If so, we use it to avoid unnecessarily retransmissions.
1858 */
1859void tcp_xmit_retransmit_queue(struct sock *sk)
1860{
1861        const struct inet_connection_sock *icsk = inet_csk(sk);
1862        struct tcp_sock *tp = tcp_sk(sk);
1863        struct sk_buff *skb;
1864        int packet_cnt;
1865
1866        if (tp->retransmit_skb_hint) {
1867                skb = tp->retransmit_skb_hint;
1868                packet_cnt = tp->retransmit_cnt_hint;
1869        }else{
1870                skb = sk->sk_write_queue.next;
1871                packet_cnt = 0;
1872        }
1873
1874        /* First pass: retransmit lost packets. */
1875        if (tp->lost_out) {
1876                sk_stream_for_retrans_queue_from(skb, sk) {
1877                        __u8 sacked = TCP_SKB_CB(skb)->sacked;
1878
1879                        /* we could do better than to assign each time */
1880                        tp->retransmit_skb_hint = skb;
1881                        tp->retransmit_cnt_hint = packet_cnt;
1882
1883                        /* Assume this retransmit will generate
1884                         * only one packet for congestion window
1885                         * calculation purposes.  This works because
1886                         * tcp_retransmit_skb() will chop up the
1887                         * packet to be MSS sized and all the
1888                         * packet counting works out.
1889                         */
1890                        if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
1891                                return;
1892
1893                        if (sacked & TCPCB_LOST) {
1894                                if (!(sacked&(TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))) {
1895                                        if (tcp_retransmit_skb(sk, skb)) {
1896                                                tp->retransmit_skb_hint = NULL;
1897                                                return;
1898                                        }
1899                                        if (icsk->icsk_ca_state != TCP_CA_Loss)
1900                                                NET_INC_STATS_BH(LINUX_MIB_TCPFASTRETRANS);
1901                                        else
1902                                                NET_INC_STATS_BH(LINUX_MIB_TCPSLOWSTARTRETRANS);
1903
1904                                        if (skb ==
1905                                            skb_peek(&sk->sk_write_queue))
1906                                                inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1907                                                                          inet_csk(sk)->icsk_rto,
1908                                                                          TCP_RTO_MAX);
1909                                }
1910
1911                                packet_cnt += tcp_skb_pcount(skb);
1912                                if (packet_cnt >= tp->lost_out)
1913                                        break;
1914                        }
1915                }
1916        }
1917
1918        /* OK, demanded retransmission is finished. */
1919
1920        /* Forward retransmissions are possible only during Recovery. */
1921        if (icsk->icsk_ca_state != TCP_CA_Recovery)
1922                return;
1923
1924        /* No forward retransmissions in Reno are possible. */
1925        if (!tp->rx_opt.sack_ok)
1926                return;
1927
1928        /* Yeah, we have to make difficult choice between forward transmission
1929         * and retransmission... Both ways have their merits...
1930         *
1931         * For now we do not retransmit anything, while we have some new
1932         * segments to send.
1933         */
1934
1935        if (tcp_may_send_now(sk, tp))
1936                return;
1937
1938        if (tp->forward_skb_hint) {
1939                skb = tp->forward_skb_hint;
1940                packet_cnt = tp->forward_cnt_hint;
1941        } else{
1942                skb = sk->sk_write_queue.next;
1943                packet_cnt = 0;
1944        }
1945
1946        sk_stream_for_retrans_queue_from(skb, sk) {
1947                tp->forward_cnt_hint = packet_cnt;
1948                tp->forward_skb_hint = skb;
1949
1950                /* Similar to the retransmit loop above we
1951                 * can pretend that the retransmitted SKB
1952                 * we send out here will be composed of one
1953                 * real MSS sized packet because tcp_retransmit_skb()
1954                 * will fragment it if necessary.
1955                 */
1956                if (++packet_cnt > tp->fackets_out)
1957                        break;
1958
1959                if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
1960                        break;
1961
1962                if (TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS)
1963                        continue;
1964
1965                /* Ok, retransmit it. */
1966                if (tcp_retransmit_skb(sk, skb)) {
1967                        tp->forward_skb_hint = NULL;
1968                        break;
1969                }
1970
1971                if (skb == skb_peek(&sk->sk_write_queue))
1972                        inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1973                                                  inet_csk(sk)->icsk_rto,
1974                                                  TCP_RTO_MAX);
1975
1976                NET_INC_STATS_BH(LINUX_MIB_TCPFORWARDRETRANS);
1977        }
1978}
1979
1980
1981/* Send a fin.  The caller locks the socket for us.  This cannot be
1982 * allowed to fail queueing a FIN frame under any circumstances.
1983 */
1984void tcp_send_fin(struct sock *sk)
1985{
1986        struct tcp_sock *tp = tcp_sk(sk);       
1987        struct sk_buff *skb = skb_peek_tail(&sk->sk_write_queue);
1988        int mss_now;
1989        
1990        /* Optimization, tack on the FIN if we have a queue of
1991         * unsent frames.  But be careful about outgoing SACKS
1992         * and IP options.
1993         */
1994        mss_now = tcp_current_mss(sk, 1);
1995
1996        if (sk->sk_send_head != NULL) {
1997                TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_FIN;
1998                TCP_SKB_CB(skb)->end_seq++;
1999                tp->write_seq++;
2000        } else {
2001                /* Socket is locked, keep trying until memory is available. */
2002                for (;;) {
2003                        skb = alloc_skb_fclone(MAX_TCP_HEADER, GFP_KERNEL);
2004                        if (skb)
2005                                break;
2006                        yield();
2007                }
2008
2009                /* Reserve space for headers and prepare control bits. */
2010                skb_reserve(skb, MAX_TCP_HEADER);
2011                skb->csum = 0;
2012                TCP_SKB_CB(skb)->flags = (TCPCB_FLAG_ACK | TCPCB_FLAG_FIN);
2013                TCP_SKB_CB(skb)->sacked = 0;
2014                skb_shinfo(skb)->gso_segs = 1;
2015                skb_shinfo(skb)->gso_size = 0;
2016                skb_shinfo(skb)->gso_type = 0;
2017
2018                /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
2019                TCP_SKB_CB(skb)->seq = tp->write_seq;
2020                TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + 1;
2021                tcp_queue_skb(sk, skb);
2022        }
2023        __tcp_push_pending_frames(sk, tp, mss_now, TCP_NAGLE_OFF);
2024}
2025
2026/* We get here when a process closes a file descriptor (either due to
2027 * an explicit close() or as a byproduct of exit()'ing) and there
2028 * was unread data in the receive queue.  This behavior is recommended
2029 * by draft-ietf-tcpimpl-prob-03.txt section 3.10.  -DaveM
2030 */
2031void tcp_send_active_reset(struct sock *sk, gfp_t priority)
2032{
2033        struct tcp_sock *tp = tcp_sk(sk);
2034        struct sk_buff *skb;
2035
2036        /* NOTE: No TCP options attached and we never retransmit this. */
2037        skb = alloc_skb(MAX_TCP_HEADER, priority);
2038        if (!skb) {
2039                NET_INC_STATS(LINUX_MIB_TCPABORTFAILED);
2040                return;
2041        }
2042
2043        /* Reserve space for headers and prepare control bits. */
2044        skb_reserve(skb, MAX_TCP_HEADER);
2045        skb->csum = 0;
2046        TCP_SKB_CB(skb)->flags = (TCPCB_FLAG_ACK | TCPCB_FLAG_RST);
2047        TCP_SKB_CB(skb)->sacked = 0;
2048        skb_shinfo(skb)->gso_segs = 1;
2049        skb_shinfo(skb)->gso_size = 0;
2050        skb_shinfo(skb)->gso_type = 0;
2051
2052        /* Send it off. */
2053        TCP_SKB_CB(skb)->seq = tcp_acceptable_seq(sk, tp);
2054        TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq;
2055        TCP_SKB_CB(skb)->when = tcp_time_stamp;
2056        if (tcp_transmit_skb(sk, skb, 0, priority))
2057                NET_INC_STATS(LINUX_MIB_TCPABORTFAILED);
2058}
2059
2060/* WARNING: This routine must only be called when we have already sent
2061 * a SYN packet that crossed the incoming SYN that caused this routine
2062 * to get called. If this assumption fails then the initial rcv_wnd
2063 * and rcv_wscale values will not be correct.
2064 */
2065int tcp_send_synack(struct sock *sk)
2066{
2067        struct sk_buff* skb;
2068
2069        skb = skb_peek(&sk->sk_write_queue);
2070        if (skb == NULL || !(TCP_SKB_CB(skb)->flags&TCPCB_FLAG_SYN)) {
2071                printk(KERN_DEBUG "tcp_send_synack: wrong queue state\n");
2072                return -EFAULT;
2073        }
2074        if (!(TCP_SKB_CB(skb)->flags&TCPCB_FLAG_ACK)) {
2075                if (skb_cloned(skb)) {
2076                        struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
2077                        if (nskb == NULL)
2078                                return -ENOMEM;
2079                        __skb_unlink(skb, &sk->sk_write_queue);
2080                        skb_header_release(nskb);
2081                        __skb_queue_head(&sk->sk_write_queue, nskb);
2082                        sk_stream_free_skb(sk, skb);
2083                        sk_charge_skb(sk, nskb);
2084                        skb = nskb;
2085                }
2086
2087                TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_ACK;
2088                TCP_ECN_send_synack(tcp_sk(sk), skb);
2089        }
2090        TCP_SKB_CB(skb)->when = tcp_time_stamp;
2091        return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2092}
2093
2094/*
2095 * Prepare a SYN-ACK.
2096 */
2097struct sk_buff * tcp_make_synack(struct sock *sk, struct dst_entry *dst,
2098                                 struct request_sock *req)
2099{
2100        struct inet_request_sock *ireq = inet_rsk(req);
2101        struct tcp_sock *tp = tcp_sk(sk);
2102        struct tcphdr *th;
2103        int tcp_header_size;
2104        struct sk_buff *skb;
2105#ifdef CONFIG_TCP_MD5SIG
2106        struct tcp_md5sig_key *md5;
2107        __u8 *md5_hash_location;
2108#endif
2109
2110        skb = sock_wmalloc(sk, MAX_TCP_HEADER + 15, 1, GFP_ATOMIC);
2111        if (skb == NULL)
2112                return NULL;
2113
2114        /* Reserve space for headers. */
2115        skb_reserve(skb, MAX_TCP_HEADER);
2116
2117        skb->dst = dst_clone(dst);
2118
2119        tcp_header_size = (sizeof(struct tcphdr) + TCPOLEN_MSS +
2120                           (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0) +
2121                           (ireq->wscale_ok ? TCPOLEN_WSCALE_ALIGNED : 0) +
2122                           /* SACK_PERM is in the place of NOP NOP of TS */
2123                           ((ireq->sack_ok && !ireq->tstamp_ok) ? TCPOLEN_SACKPERM_ALIGNED : 0));
2124
2125#ifdef CONFIG_TCP_MD5SIG
2126        /* Are we doing MD5 on this segment? If so - make room for it */
2127        md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
2128        if (md5)
2129                tcp_header_size += TCPOLEN_MD5SIG_ALIGNED;
2130#endif
2131        skb->h.th = th = (struct tcphdr *) skb_push(skb, tcp_header_size);
2132
2133        memset(th, 0, sizeof(struct tcphdr));
2134        th->syn = 1;
2135        th->ack = 1;
2136        TCP_ECN_make_synack(req, th);
2137        th->source = inet_sk(sk)->sport;
2138        th->dest = ireq->rmt_port;
2139        TCP_SKB_CB(skb)->seq = tcp_rsk(req)->snt_isn;
2140        TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + 1;
2141        TCP_SKB_CB(skb)->sacked = 0;
2142        skb_shinfo(skb)->gso_segs = 1;
2143        skb_shinfo(skb)->gso_size = 0;
2144        skb_shinfo(skb)->gso_type = 0;
2145        th->seq = htonl(TCP_SKB_CB(skb)->seq);
2146        th->ack_seq = htonl(tcp_rsk(req)->rcv_isn + 1);
2147        if (req->rcv_wnd == 0) { /* ignored for retransmitted syns */
2148                __u8 rcv_wscale; 
2149                /* Set this up on the first call only */
2150                req->window_clamp = tp->window_clamp ? : dst_metric(dst, RTAX_WINDOW);
2151                /* tcp_full_space because it is guaranteed to be the first packet */
2152                tcp_select_initial_window(tcp_full_space(sk), 
2153                        dst_metric(dst, RTAX_ADVMSS) - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
2154                        &req->rcv_wnd,
2155                        &req->window_clamp,
2156                        ireq->wscale_ok,
2157                        &rcv_wscale);
2158                ireq->rcv_wscale = rcv_wscale; 
2159        }
2160
2161        /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
2162        th->window = htons(req->rcv_wnd);
2163
2164        TCP_SKB_CB(skb)->when = tcp_time_stamp;
2165        tcp_syn_build_options((__be32 *)(th + 1), dst_metric(dst, RTAX_ADVMSS), ireq->tstamp_ok,
2166                              ireq->sack_ok, ireq->wscale_ok, ireq->rcv_wscale,
2167                              TCP_SKB_CB(skb)->when,
2168                              req->ts_recent,
2169                              (
2170#ifdef CONFIG_TCP_MD5SIG
2171                               md5 ? &md5_hash_location :
2172#endif
2173                               NULL)
2174                              );
2175
2176        skb->csum = 0;
2177        th->doff = (tcp_header_size >> 2);
2178        TCP_INC_STATS(TCP_MIB_OUTSEGS);
2179
2180#ifdef CONFIG_TCP_MD5SIG
2181        /* Okay, we have all we need - do the md5 hash if needed */
2182        if (md5) {
2183                tp->af_specific->calc_md5_hash(md5_hash_location,
2184                                               md5,
2185                                               NULL, dst, req,
2186                                               skb->h.th, sk->sk_protocol,
2187                                               skb->len);
2188        }
2189#endif
2190
2191        return skb;
2192}
2193
2194/* 
2195 * Do all connect socket setups that can be done AF independent.
2196 */ 
2197static void tcp_connect_init(struct sock *sk)
2198{
2199        struct dst_entry *dst = __sk_dst_get(sk);
2200        struct tcp_sock *tp = tcp_sk(sk);
2201        __u8 rcv_wscale;
2202
2203        /* We'll fix this up when we get a response from the other end.
2204         * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
2205         */
2206        tp->tcp_header_len = sizeof(struct tcphdr) +
2207                (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
2208
2209#ifdef CONFIG_TCP_MD5SIG
2210        if (tp->af_specific->md5_lookup(sk, sk) != NULL)
2211                tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
2212#endif
2213
2214        /* If user gave his TCP_MAXSEG, record it to clamp */
2215        if (tp->rx_opt.user_mss)
2216                tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
2217        tp->max_window = 0;
2218        tcp_mtup_init(sk);
2219        tcp_sync_mss(sk, dst_mtu(dst));
2220
2221        if (!tp->window_clamp)
2222                tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
2223        tp->advmss = dst_metric(dst, RTAX_ADVMSS);
2224        tcp_initialize_rcv_mss(sk);
2225
2226        tcp_select_initial_window(tcp_full_space(sk),
2227                                  tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
2228                                  &tp->rcv_wnd,
2229                                  &tp->window_clamp,
2230                                  sysctl_tcp_window_scaling,
2231                                  &rcv_wscale);
2232
2233        tp->rx_opt.rcv_wscale = rcv_wscale;
2234        tp->rcv_ssthresh = tp->rcv_wnd;
2235
2236        sk->sk_err = 0;
2237        sock_reset_flag(sk, SOCK_DONE);
2238        tp->snd_wnd = 0;
2239        tcp_init_wl(tp, tp->write_seq, 0);
2240        tp->snd_una = tp->write_seq;
2241        tp->snd_sml = tp->write_seq;
2242        tp->rcv_nxt = 0;
2243        tp->rcv_wup = 0;
2244        tp->copied_seq = 0;
2245
2246        inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
2247        inet_csk(sk)->icsk_retransmits = 0;
2248        tcp_clear_retrans(tp);
2249}
2250
2251/*
2252 * Build a SYN and send it off.
2253 */ 
2254int tcp_connect(struct sock *sk)
2255{
2256        struct tcp_sock *tp = tcp_sk(sk);
2257        struct sk_buff *buff;
2258
2259        tcp_connect_init(sk);
2260
2261        buff = alloc_skb_fclone(MAX_TCP_HEADER + 15, sk->sk_allocation);
2262        if (unlikely(buff == NULL))
2263                return -ENOBUFS;
2264
2265        /* Reserve space for headers. */
2266        skb_reserve(buff, MAX_TCP_HEADER);
2267
2268        TCP_SKB_CB(buff)->flags = TCPCB_FLAG_SYN;
2269        TCP_ECN_send_syn(sk, tp, buff);
2270        TCP_SKB_CB(buff)->sacked = 0;
2271        skb_shinfo(buff)->gso_segs = 1;
2272        skb_shinfo(buff)->gso_size = 0;
2273        skb_shinfo(buff)->gso_type = 0;
2274        buff->csum = 0;
2275        tp->snd_nxt = tp->write_seq;
2276        TCP_SKB_CB(buff)->seq = tp->write_seq++;
2277        TCP_SKB_CB(buff)->end_seq = tp->write_seq;
2278
2279        /* Send it off. */
2280        TCP_SKB_CB(buff)->when = tcp_time_stamp;
2281        tp->retrans_stamp = TCP_SKB_CB(buff)->when;
2282        skb_header_release(buff);
2283        __skb_queue_tail(&sk->sk_write_queue, buff);
2284        sk_charge_skb(sk, buff);
2285        tp->packets_out += tcp_skb_pcount(buff);
2286        tcp_transmit_skb(sk, buff, 1, GFP_KERNEL);
2287
2288        /* We change tp->snd_nxt after the tcp_transmit_skb() call
2289         * in order to make this packet get counted in tcpOutSegs.
2290         */
2291        tp->snd_nxt = tp->write_seq;
2292        tp->pushed_seq = tp->write_seq;
2293        TCP_INC_STATS(TCP_MIB_ACTIVEOPENS);
2294
2295        /* Timer for repeating the SYN until an answer. */
2296        inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2297                                  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
2298        return 0;
2299}
2300
2301/* Send out a delayed ack, the caller does the policy checking
2302 * to see if we should even be here.  See tcp_input.c:tcp_ack_snd_check()
2303 * for details.
2304 */
2305void tcp_send_delayed_ack(struct sock *sk)
2306{
2307        struct inet_connection_sock *icsk = inet_csk(sk);
2308        int ato = icsk->icsk_ack.ato;
2309        unsigned long timeout;
2310
2311        if (ato > TCP_DELACK_MIN) {
2312                const struct tcp_sock *tp = tcp_sk(sk);
2313                int max_ato = HZ/2;
2314
2315                if (icsk->icsk_ack.pingpong || (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
2316                        max_ato = TCP_DELACK_MAX;
2317
2318                /* Slow path, intersegment interval is "high". */
2319
2320                /* If some rtt estimate is known, use it to bound delayed ack.
2321                 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
2322                 * directly.
2323                 */
2324                if (tp->srtt) {
2325                        int rtt = max(tp->srtt>>3, TCP_DELACK_MIN);
2326
2327                        if (rtt < max_ato)
2328                                max_ato = rtt;
2329                }
2330
2331                ato = min(ato, max_ato);
2332        }
2333
2334        /* Stay within the limit we were given */
2335        timeout = jiffies + ato;
2336
2337        /* Use new timeout only if there wasn't a older one earlier. */
2338        if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
2339                /* If delack timer was blocked or is about to expire,
2340                 * send ACK now.
2341                 */
2342                if (icsk->icsk_ack.blocked ||
2343                    time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
2344                        tcp_send_ack(sk);
2345                        return;
2346                }
2347
2348                if (!time_before(timeout, icsk->icsk_ack.timeout))
2349                        timeout = icsk->icsk_ack.timeout;
2350        }
2351        icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
2352        icsk->icsk_ack.timeout = timeout;
2353        sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
2354}
2355
2356/* This routine sends an ack and also updates the window. */
2357void tcp_send_ack(struct sock *sk)
2358{
2359        /* If we have been reset, we may not send again. */
2360        if (sk->sk_state != TCP_CLOSE) {
2361                struct tcp_sock *tp = tcp_sk(sk);
2362                struct sk_buff *buff;
2363
2364                /* We are not putting this on the write queue, so
2365                 * tcp_transmit_skb() will set the ownership to this
2366                 * sock.
2367                 */
2368                buff = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
2369                if (buff == NULL) {
2370                        inet_csk_schedule_ack(sk);
2371                        inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
2372                        inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
2373                                                  TCP_DELACK_MAX, TCP_RTO_MAX);
2374                        return;
2375                }
2376
2377                /* Reserve space for headers and prepare control bits. */
2378                skb_reserve(buff, MAX_TCP_HEADER);
2379                buff->csum = 0;
2380                TCP_SKB_CB(buff)->flags = TCPCB_FLAG_ACK;
2381                TCP_SKB_CB(buff)->sacked = 0;
2382                skb_shinfo(buff)->gso_segs = 1;
2383                skb_shinfo(buff)->gso_size = 0;
2384                skb_shinfo(buff)->gso_type = 0;
2385
2386                /* Send it off, this clears delayed acks for us. */
2387                TCP_SKB_CB(buff)->seq = TCP_SKB_CB(buff)->end_seq = tcp_acceptable_seq(sk, tp);
2388                TCP_SKB_CB(buff)->when = tcp_time_stamp;
2389                tcp_transmit_skb(sk, buff, 0, GFP_ATOMIC);
2390        }
2391}
2392
2393/* This routine sends a packet with an out of date sequence
2394 * number. It assumes the other end will try to ack it.
2395 *
2396 * Question: what should we make while urgent mode?
2397 * 4.4BSD forces sending single byte of data. We cannot send
2398 * out of window data, because we have SND.NXT==SND.MAX...
2399 *
2400 * Current solution: to send TWO zero-length segments in urgent mode:
2401 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
2402 * out-of-date with SND.UNA-1 to probe window.
2403 */
2404static int tcp_xmit_probe_skb(struct sock *sk, int urgent)
2405{
2406        struct tcp_sock *tp = tcp_sk(sk);
2407        struct sk_buff *skb;
2408
2409        /* We don't queue it, tcp_transmit_skb() sets ownership. */
2410        skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
2411        if (skb == NULL) 
2412                return -1;
2413
2414        /* Reserve space for headers and set control bits. */
2415        skb_reserve(skb, MAX_TCP_HEADER);
2416        skb->csum = 0;
2417        TCP_SKB_CB(skb)->flags = TCPCB_FLAG_ACK;
2418        TCP_SKB_CB(skb)->sacked = urgent;
2419        skb_shinfo(skb)->gso_segs = 1;
2420        skb_shinfo(skb)->gso_size = 0;
2421        skb_shinfo(skb)->gso_type = 0;
2422
2423        /* Use a previous sequence.  This should cause the other
2424         * end to send an ack.  Don't queue or clone SKB, just
2425         * send it.
2426         */
2427        TCP_SKB_CB(skb)->seq = urgent ? tp->snd_una : tp->snd_una - 1;
2428        TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq;
2429        TCP_SKB_CB(skb)->when = tcp_time_stamp;
2430        return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
2431}
2432
2433int tcp_write_wakeup(struct sock *sk)
2434{
2435        if (sk->sk_state != TCP_CLOSE) {
2436                struct tcp_sock *tp = tcp_sk(sk);
2437                struct sk_buff *skb;
2438
2439                if ((skb = sk->sk_send_head) != NULL &&
2440                    before(TCP_SKB_CB(skb)->seq, tp->snd_una+tp->snd_wnd)) {
2441                        int err;
2442                        unsigned int mss = tcp_current_mss(sk, 0);
2443                        unsigned int seg_size = tp->snd_una+tp->snd_wnd-TCP_SKB_CB(skb)->seq;
2444
2445                        if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
2446                                tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
2447
2448                        /* We are probing the opening of a window
2449                         * but the window size is != 0
2450                         * must have been a result SWS avoidance ( sender )
2451                         */
2452                        if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
2453                            skb->len > mss) {
2454                                seg_size = min(seg_size, mss);
2455                                TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
2456                                if (tcp_fragment(sk, skb, seg_size, mss))
2457                                        return -1;
2458                        } else if (!tcp_skb_pcount(skb))
2459                                tcp_set_skb_tso_segs(sk, skb, mss);
2460
2461                        TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
2462                        TCP_SKB_CB(skb)->when = tcp_time_stamp;
2463                        err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2464                        if (!err) {
2465                                update_send_head(sk, tp, skb);
2466                        }
2467                        return err;
2468                } else {
2469                        if (tp->urg_mode &&
2470                            between(tp->snd_up, tp->snd_una+1, tp->snd_una+0xFFFF))
2471                                tcp_xmit_probe_skb(sk, TCPCB_URG);
2472                        return tcp_xmit_probe_skb(sk, 0);
2473                }
2474        }
2475        return -1;
2476}
2477
2478/* A window probe timeout has occurred.  If window is not closed send
2479 * a partial packet else a zero probe.
2480 */
2481void tcp_send_probe0(struct sock *sk)
2482{
2483        struct inet_connection_sock *icsk = inet_csk(sk);
2484        struct tcp_sock *tp = tcp_sk(sk);
2485        int err;
2486
2487        err = tcp_write_wakeup(sk);
2488
2489        if (tp->packets_out || !sk->sk_send_head) {
2490                /* Cancel probe timer, if it is not required. */
2491                icsk->icsk_probes_out = 0;
2492                icsk->icsk_backoff = 0;
2493                return;
2494        }
2495
2496        if (err <= 0) {
2497                if (icsk->icsk_backoff < sysctl_tcp_retries2)
2498                        icsk->icsk_backoff++;
2499                icsk->icsk_probes_out++;
2500                inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0, 
2501                                          min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
2502                                          TCP_RTO_MAX);
2503        } else {
2504                /* If packet was not sent due to local congestion,
2505                 * do not backoff and do not remember icsk_probes_out.
2506                 * Let local senders to fight for local resources.
2507                 *
2508                 * Use accumulated backoff yet.
2509                 */
2510                if (!icsk->icsk_probes_out)
2511                        icsk->icsk_probes_out = 1;
2512                inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0, 
2513                                          min(icsk->icsk_rto << icsk->icsk_backoff,
2514                                              TCP_RESOURCE_PROBE_INTERVAL),
2515                                          TCP_RTO_MAX);
2516        }
2517}
2518
2519EXPORT_SYMBOL(tcp_connect);
2520EXPORT_SYMBOL(tcp_make_synack);
2521EXPORT_SYMBOL(tcp_simple_retransmit);
2522EXPORT_SYMBOL(tcp_sync_mss);
2523EXPORT_SYMBOL(sysctl_tcp_tso_win_divisor);
2524EXPORT_SYMBOL(tcp_mtup_init);
2525
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