The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/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  * Authors:     Ross Biro
    9  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
   10  *              Mark Evans, <evansmp@uhura.aston.ac.uk>
   11  *              Corey Minyard <wf-rch!minyard@relay.EU.net>
   12  *              Florian La Roche, <flla@stud.uni-sb.de>
   13  *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
   14  *              Linus Torvalds, <torvalds@cs.helsinki.fi>
   15  *              Alan Cox, <gw4pts@gw4pts.ampr.org>
   16  *              Matthew Dillon, <dillon@apollo.west.oic.com>
   17  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
   18  *              Jorge Cwik, <jorge@laser.satlink.net>
   19  */
   20 
   21 /*
   22  * Changes:     Pedro Roque     :       Retransmit queue handled by TCP.
   23  *                              :       Fragmentation on mtu decrease
   24  *                              :       Segment collapse on retransmit
   25  *                              :       AF independence
   26  *
   27  *              Linus Torvalds  :       send_delayed_ack
   28  *              David S. Miller :       Charge memory using the right skb
   29  *                                      during syn/ack processing.
   30  *              David S. Miller :       Output engine completely rewritten.
   31  *              Andrea Arcangeli:       SYNACK carry ts_recent in tsecr.
   32  *              Cacophonix Gaul :       draft-minshall-nagle-01
   33  *              J Hadi Salim    :       ECN support
   34  *
   35  */
   36 
   37 #define pr_fmt(fmt) "TCP: " fmt
   38 
   39 #include <net/tcp.h>
   40 
   41 #include <linux/compiler.h>
   42 #include <linux/gfp.h>
   43 #include <linux/module.h>
   44 
   45 /* People can turn this off for buggy TCP's found in printers etc. */
   46 int 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  */
   51 int sysctl_tcp_workaround_signed_windows __read_mostly = 0;
   52 
   53 /* Default TSQ limit of two TSO segments */
   54 int sysctl_tcp_limit_output_bytes __read_mostly = 131072;
   55 
   56 /* This limits the percentage of the congestion window which we
   57  * will allow a single TSO frame to consume.  Building TSO frames
   58  * which are too large can cause TCP streams to be bursty.
   59  */
   60 int sysctl_tcp_tso_win_divisor __read_mostly = 3;
   61 
   62 int sysctl_tcp_mtu_probing __read_mostly = 0;
   63 int sysctl_tcp_base_mss __read_mostly = TCP_BASE_MSS;
   64 
   65 /* By default, RFC2861 behavior.  */
   66 int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
   67 
   68 int sysctl_tcp_cookie_size __read_mostly = 0; /* TCP_COOKIE_MAX */
   69 EXPORT_SYMBOL_GPL(sysctl_tcp_cookie_size);
   70 
   71 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
   72                            int push_one, gfp_t gfp);
   73 
   74 /* Account for new data that has been sent to the network. */
   75 static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
   76 {
   77         struct tcp_sock *tp = tcp_sk(sk);
   78         unsigned int prior_packets = tp->packets_out;
   79 
   80         tcp_advance_send_head(sk, skb);
   81         tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
   82 
   83         /* Don't override Nagle indefinitely with F-RTO */
   84         if (tp->frto_counter == 2)
   85                 tp->frto_counter = 3;
   86 
   87         tp->packets_out += tcp_skb_pcount(skb);
   88         if (!prior_packets || tp->early_retrans_delayed)
   89                 tcp_rearm_rto(sk);
   90 }
   91 
   92 /* SND.NXT, if window was not shrunk.
   93  * If window has been shrunk, what should we make? It is not clear at all.
   94  * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
   95  * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
   96  * invalid. OK, let's make this for now:
   97  */
   98 static inline __u32 tcp_acceptable_seq(const struct sock *sk)
   99 {
  100         const struct tcp_sock *tp = tcp_sk(sk);
  101 
  102         if (!before(tcp_wnd_end(tp), tp->snd_nxt))
  103                 return tp->snd_nxt;
  104         else
  105                 return tcp_wnd_end(tp);
  106 }
  107 
  108 /* Calculate mss to advertise in SYN segment.
  109  * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
  110  *
  111  * 1. It is independent of path mtu.
  112  * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
  113  * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
  114  *    attached devices, because some buggy hosts are confused by
  115  *    large MSS.
  116  * 4. We do not make 3, we advertise MSS, calculated from first
  117  *    hop device mtu, but allow to raise it to ip_rt_min_advmss.
  118  *    This may be overridden via information stored in routing table.
  119  * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
  120  *    probably even Jumbo".
  121  */
  122 static __u16 tcp_advertise_mss(struct sock *sk)
  123 {
  124         struct tcp_sock *tp = tcp_sk(sk);
  125         const struct dst_entry *dst = __sk_dst_get(sk);
  126         int mss = tp->advmss;
  127 
  128         if (dst) {
  129                 unsigned int metric = dst_metric_advmss(dst);
  130 
  131                 if (metric < mss) {
  132                         mss = metric;
  133                         tp->advmss = mss;
  134                 }
  135         }
  136 
  137         return (__u16)mss;
  138 }
  139 
  140 /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
  141  * This is the first part of cwnd validation mechanism. */
  142 static void tcp_cwnd_restart(struct sock *sk, const struct dst_entry *dst)
  143 {
  144         struct tcp_sock *tp = tcp_sk(sk);
  145         s32 delta = tcp_time_stamp - tp->lsndtime;
  146         u32 restart_cwnd = tcp_init_cwnd(tp, dst);
  147         u32 cwnd = tp->snd_cwnd;
  148 
  149         tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
  150 
  151         tp->snd_ssthresh = tcp_current_ssthresh(sk);
  152         restart_cwnd = min(restart_cwnd, cwnd);
  153 
  154         while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
  155                 cwnd >>= 1;
  156         tp->snd_cwnd = max(cwnd, restart_cwnd);
  157         tp->snd_cwnd_stamp = tcp_time_stamp;
  158         tp->snd_cwnd_used = 0;
  159 }
  160 
  161 /* Congestion state accounting after a packet has been sent. */
  162 static void tcp_event_data_sent(struct tcp_sock *tp,
  163                                 struct sock *sk)
  164 {
  165         struct inet_connection_sock *icsk = inet_csk(sk);
  166         const u32 now = tcp_time_stamp;
  167 
  168         if (sysctl_tcp_slow_start_after_idle &&
  169             (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto))
  170                 tcp_cwnd_restart(sk, __sk_dst_get(sk));
  171 
  172         tp->lsndtime = now;
  173 
  174         /* If it is a reply for ato after last received
  175          * packet, enter pingpong mode.
  176          */
  177         if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
  178                 icsk->icsk_ack.pingpong = 1;
  179 }
  180 
  181 /* Account for an ACK we sent. */
  182 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
  183 {
  184         tcp_dec_quickack_mode(sk, pkts);
  185         inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
  186 }
  187 
  188 /* Determine a window scaling and initial window to offer.
  189  * Based on the assumption that the given amount of space
  190  * will be offered. Store the results in the tp structure.
  191  * NOTE: for smooth operation initial space offering should
  192  * be a multiple of mss if possible. We assume here that mss >= 1.
  193  * This MUST be enforced by all callers.
  194  */
  195 void tcp_select_initial_window(int __space, __u32 mss,
  196                                __u32 *rcv_wnd, __u32 *window_clamp,
  197                                int wscale_ok, __u8 *rcv_wscale,
  198                                __u32 init_rcv_wnd)
  199 {
  200         unsigned int space = (__space < 0 ? 0 : __space);
  201 
  202         /* If no clamp set the clamp to the max possible scaled window */
  203         if (*window_clamp == 0)
  204                 (*window_clamp) = (65535 << 14);
  205         space = min(*window_clamp, space);
  206 
  207         /* Quantize space offering to a multiple of mss if possible. */
  208         if (space > mss)
  209                 space = (space / mss) * mss;
  210 
  211         /* NOTE: offering an initial window larger than 32767
  212          * will break some buggy TCP stacks. If the admin tells us
  213          * it is likely we could be speaking with such a buggy stack
  214          * we will truncate our initial window offering to 32K-1
  215          * unless the remote has sent us a window scaling option,
  216          * which we interpret as a sign the remote TCP is not
  217          * misinterpreting the window field as a signed quantity.
  218          */
  219         if (sysctl_tcp_workaround_signed_windows)
  220                 (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
  221         else
  222                 (*rcv_wnd) = space;
  223 
  224         (*rcv_wscale) = 0;
  225         if (wscale_ok) {
  226                 /* Set window scaling on max possible window
  227                  * See RFC1323 for an explanation of the limit to 14
  228                  */
  229                 space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max);
  230                 space = min_t(u32, space, *window_clamp);
  231                 while (space > 65535 && (*rcv_wscale) < 14) {
  232                         space >>= 1;
  233                         (*rcv_wscale)++;
  234                 }
  235         }
  236 
  237         /* Set initial window to a value enough for senders starting with
  238          * initial congestion window of TCP_DEFAULT_INIT_RCVWND. Place
  239          * a limit on the initial window when mss is larger than 1460.
  240          */
  241         if (mss > (1 << *rcv_wscale)) {
  242                 int init_cwnd = TCP_DEFAULT_INIT_RCVWND;
  243                 if (mss > 1460)
  244                         init_cwnd =
  245                         max_t(u32, (1460 * TCP_DEFAULT_INIT_RCVWND) / mss, 2);
  246                 /* when initializing use the value from init_rcv_wnd
  247                  * rather than the default from above
  248                  */
  249                 if (init_rcv_wnd)
  250                         *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
  251                 else
  252                         *rcv_wnd = min(*rcv_wnd, init_cwnd * mss);
  253         }
  254 
  255         /* Set the clamp no higher than max representable value */
  256         (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
  257 }
  258 EXPORT_SYMBOL(tcp_select_initial_window);
  259 
  260 /* Chose a new window to advertise, update state in tcp_sock for the
  261  * socket, and return result with RFC1323 scaling applied.  The return
  262  * value can be stuffed directly into th->window for an outgoing
  263  * frame.
  264  */
  265 static u16 tcp_select_window(struct sock *sk)
  266 {
  267         struct tcp_sock *tp = tcp_sk(sk);
  268         u32 cur_win = tcp_receive_window(tp);
  269         u32 new_win = __tcp_select_window(sk);
  270 
  271         /* Never shrink the offered window */
  272         if (new_win < cur_win) {
  273                 /* Danger Will Robinson!
  274                  * Don't update rcv_wup/rcv_wnd here or else
  275                  * we will not be able to advertise a zero
  276                  * window in time.  --DaveM
  277                  *
  278                  * Relax Will Robinson.
  279                  */
  280                 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
  281         }
  282         tp->rcv_wnd = new_win;
  283         tp->rcv_wup = tp->rcv_nxt;
  284 
  285         /* Make sure we do not exceed the maximum possible
  286          * scaled window.
  287          */
  288         if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
  289                 new_win = min(new_win, MAX_TCP_WINDOW);
  290         else
  291                 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
  292 
  293         /* RFC1323 scaling applied */
  294         new_win >>= tp->rx_opt.rcv_wscale;
  295 
  296         /* If we advertise zero window, disable fast path. */
  297         if (new_win == 0)
  298                 tp->pred_flags = 0;
  299 
  300         return new_win;
  301 }
  302 
  303 /* Packet ECN state for a SYN-ACK */
  304 static inline void TCP_ECN_send_synack(const struct tcp_sock *tp, struct sk_buff *skb)
  305 {
  306         TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
  307         if (!(tp->ecn_flags & TCP_ECN_OK))
  308                 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
  309 }
  310 
  311 /* Packet ECN state for a SYN.  */
  312 static inline void TCP_ECN_send_syn(struct sock *sk, struct sk_buff *skb)
  313 {
  314         struct tcp_sock *tp = tcp_sk(sk);
  315 
  316         tp->ecn_flags = 0;
  317         if (sysctl_tcp_ecn == 1) {
  318                 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
  319                 tp->ecn_flags = TCP_ECN_OK;
  320         }
  321 }
  322 
  323 static __inline__ void
  324 TCP_ECN_make_synack(const struct request_sock *req, struct tcphdr *th)
  325 {
  326         if (inet_rsk(req)->ecn_ok)
  327                 th->ece = 1;
  328 }
  329 
  330 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
  331  * be sent.
  332  */
  333 static inline void TCP_ECN_send(struct sock *sk, struct sk_buff *skb,
  334                                 int tcp_header_len)
  335 {
  336         struct tcp_sock *tp = tcp_sk(sk);
  337 
  338         if (tp->ecn_flags & TCP_ECN_OK) {
  339                 /* Not-retransmitted data segment: set ECT and inject CWR. */
  340                 if (skb->len != tcp_header_len &&
  341                     !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
  342                         INET_ECN_xmit(sk);
  343                         if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
  344                                 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
  345                                 tcp_hdr(skb)->cwr = 1;
  346                                 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
  347                         }
  348                 } else {
  349                         /* ACK or retransmitted segment: clear ECT|CE */
  350                         INET_ECN_dontxmit(sk);
  351                 }
  352                 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
  353                         tcp_hdr(skb)->ece = 1;
  354         }
  355 }
  356 
  357 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
  358  * auto increment end seqno.
  359  */
  360 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
  361 {
  362         skb->ip_summed = CHECKSUM_PARTIAL;
  363         skb->csum = 0;
  364 
  365         TCP_SKB_CB(skb)->tcp_flags = flags;
  366         TCP_SKB_CB(skb)->sacked = 0;
  367 
  368         skb_shinfo(skb)->gso_segs = 1;
  369         skb_shinfo(skb)->gso_size = 0;
  370         skb_shinfo(skb)->gso_type = 0;
  371 
  372         TCP_SKB_CB(skb)->seq = seq;
  373         if (flags & (TCPHDR_SYN | TCPHDR_FIN))
  374                 seq++;
  375         TCP_SKB_CB(skb)->end_seq = seq;
  376 }
  377 
  378 static inline bool tcp_urg_mode(const struct tcp_sock *tp)
  379 {
  380         return tp->snd_una != tp->snd_up;
  381 }
  382 
  383 #define OPTION_SACK_ADVERTISE   (1 << 0)
  384 #define OPTION_TS               (1 << 1)
  385 #define OPTION_MD5              (1 << 2)
  386 #define OPTION_WSCALE           (1 << 3)
  387 #define OPTION_COOKIE_EXTENSION (1 << 4)
  388 #define OPTION_FAST_OPEN_COOKIE (1 << 8)
  389 
  390 struct tcp_out_options {
  391         u16 options;            /* bit field of OPTION_* */
  392         u16 mss;                /* 0 to disable */
  393         u8 ws;                  /* window scale, 0 to disable */
  394         u8 num_sack_blocks;     /* number of SACK blocks to include */
  395         u8 hash_size;           /* bytes in hash_location */
  396         __u8 *hash_location;    /* temporary pointer, overloaded */
  397         __u32 tsval, tsecr;     /* need to include OPTION_TS */
  398         struct tcp_fastopen_cookie *fastopen_cookie;    /* Fast open cookie */
  399 };
  400 
  401 /* The sysctl int routines are generic, so check consistency here.
  402  */
  403 static u8 tcp_cookie_size_check(u8 desired)
  404 {
  405         int cookie_size;
  406 
  407         if (desired > 0)
  408                 /* previously specified */
  409                 return desired;
  410 
  411         cookie_size = ACCESS_ONCE(sysctl_tcp_cookie_size);
  412         if (cookie_size <= 0)
  413                 /* no default specified */
  414                 return 0;
  415 
  416         if (cookie_size <= TCP_COOKIE_MIN)
  417                 /* value too small, specify minimum */
  418                 return TCP_COOKIE_MIN;
  419 
  420         if (cookie_size >= TCP_COOKIE_MAX)
  421                 /* value too large, specify maximum */
  422                 return TCP_COOKIE_MAX;
  423 
  424         if (cookie_size & 1)
  425                 /* 8-bit multiple, illegal, fix it */
  426                 cookie_size++;
  427 
  428         return (u8)cookie_size;
  429 }
  430 
  431 /* Write previously computed TCP options to the packet.
  432  *
  433  * Beware: Something in the Internet is very sensitive to the ordering of
  434  * TCP options, we learned this through the hard way, so be careful here.
  435  * Luckily we can at least blame others for their non-compliance but from
  436  * inter-operatibility perspective it seems that we're somewhat stuck with
  437  * the ordering which we have been using if we want to keep working with
  438  * those broken things (not that it currently hurts anybody as there isn't
  439  * particular reason why the ordering would need to be changed).
  440  *
  441  * At least SACK_PERM as the first option is known to lead to a disaster
  442  * (but it may well be that other scenarios fail similarly).
  443  */
  444 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
  445                               struct tcp_out_options *opts)
  446 {
  447         u16 options = opts->options;    /* mungable copy */
  448 
  449         /* Having both authentication and cookies for security is redundant,
  450          * and there's certainly not enough room.  Instead, the cookie-less
  451          * extension variant is proposed.
  452          *
  453          * Consider the pessimal case with authentication.  The options
  454          * could look like:
  455          *   COOKIE|MD5(20) + MSS(4) + SACK|TS(12) + WSCALE(4) == 40
  456          */
  457         if (unlikely(OPTION_MD5 & options)) {
  458                 if (unlikely(OPTION_COOKIE_EXTENSION & options)) {
  459                         *ptr++ = htonl((TCPOPT_COOKIE << 24) |
  460                                        (TCPOLEN_COOKIE_BASE << 16) |
  461                                        (TCPOPT_MD5SIG << 8) |
  462                                        TCPOLEN_MD5SIG);
  463                 } else {
  464                         *ptr++ = htonl((TCPOPT_NOP << 24) |
  465                                        (TCPOPT_NOP << 16) |
  466                                        (TCPOPT_MD5SIG << 8) |
  467                                        TCPOLEN_MD5SIG);
  468                 }
  469                 options &= ~OPTION_COOKIE_EXTENSION;
  470                 /* overload cookie hash location */
  471                 opts->hash_location = (__u8 *)ptr;
  472                 ptr += 4;
  473         }
  474 
  475         if (unlikely(opts->mss)) {
  476                 *ptr++ = htonl((TCPOPT_MSS << 24) |
  477                                (TCPOLEN_MSS << 16) |
  478                                opts->mss);
  479         }
  480 
  481         if (likely(OPTION_TS & options)) {
  482                 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
  483                         *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
  484                                        (TCPOLEN_SACK_PERM << 16) |
  485                                        (TCPOPT_TIMESTAMP << 8) |
  486                                        TCPOLEN_TIMESTAMP);
  487                         options &= ~OPTION_SACK_ADVERTISE;
  488                 } else {
  489                         *ptr++ = htonl((TCPOPT_NOP << 24) |
  490                                        (TCPOPT_NOP << 16) |
  491                                        (TCPOPT_TIMESTAMP << 8) |
  492                                        TCPOLEN_TIMESTAMP);
  493                 }
  494                 *ptr++ = htonl(opts->tsval);
  495                 *ptr++ = htonl(opts->tsecr);
  496         }
  497 
  498         /* Specification requires after timestamp, so do it now.
  499          *
  500          * Consider the pessimal case without authentication.  The options
  501          * could look like:
  502          *   MSS(4) + SACK|TS(12) + COOKIE(20) + WSCALE(4) == 40
  503          */
  504         if (unlikely(OPTION_COOKIE_EXTENSION & options)) {
  505                 __u8 *cookie_copy = opts->hash_location;
  506                 u8 cookie_size = opts->hash_size;
  507 
  508                 /* 8-bit multiple handled in tcp_cookie_size_check() above,
  509                  * and elsewhere.
  510                  */
  511                 if (0x2 & cookie_size) {
  512                         __u8 *p = (__u8 *)ptr;
  513 
  514                         /* 16-bit multiple */
  515                         *p++ = TCPOPT_COOKIE;
  516                         *p++ = TCPOLEN_COOKIE_BASE + cookie_size;
  517                         *p++ = *cookie_copy++;
  518                         *p++ = *cookie_copy++;
  519                         ptr++;
  520                         cookie_size -= 2;
  521                 } else {
  522                         /* 32-bit multiple */
  523                         *ptr++ = htonl(((TCPOPT_NOP << 24) |
  524                                         (TCPOPT_NOP << 16) |
  525                                         (TCPOPT_COOKIE << 8) |
  526                                         TCPOLEN_COOKIE_BASE) +
  527                                        cookie_size);
  528                 }
  529 
  530                 if (cookie_size > 0) {
  531                         memcpy(ptr, cookie_copy, cookie_size);
  532                         ptr += (cookie_size / 4);
  533                 }
  534         }
  535 
  536         if (unlikely(OPTION_SACK_ADVERTISE & options)) {
  537                 *ptr++ = htonl((TCPOPT_NOP << 24) |
  538                                (TCPOPT_NOP << 16) |
  539                                (TCPOPT_SACK_PERM << 8) |
  540                                TCPOLEN_SACK_PERM);
  541         }
  542 
  543         if (unlikely(OPTION_WSCALE & options)) {
  544                 *ptr++ = htonl((TCPOPT_NOP << 24) |
  545                                (TCPOPT_WINDOW << 16) |
  546                                (TCPOLEN_WINDOW << 8) |
  547                                opts->ws);
  548         }
  549 
  550         if (unlikely(opts->num_sack_blocks)) {
  551                 struct tcp_sack_block *sp = tp->rx_opt.dsack ?
  552                         tp->duplicate_sack : tp->selective_acks;
  553                 int this_sack;
  554 
  555                 *ptr++ = htonl((TCPOPT_NOP  << 24) |
  556                                (TCPOPT_NOP  << 16) |
  557                                (TCPOPT_SACK <<  8) |
  558                                (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
  559                                                      TCPOLEN_SACK_PERBLOCK)));
  560 
  561                 for (this_sack = 0; this_sack < opts->num_sack_blocks;
  562                      ++this_sack) {
  563                         *ptr++ = htonl(sp[this_sack].start_seq);
  564                         *ptr++ = htonl(sp[this_sack].end_seq);
  565                 }
  566 
  567                 tp->rx_opt.dsack = 0;
  568         }
  569 
  570         if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
  571                 struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
  572 
  573                 *ptr++ = htonl((TCPOPT_EXP << 24) |
  574                                ((TCPOLEN_EXP_FASTOPEN_BASE + foc->len) << 16) |
  575                                TCPOPT_FASTOPEN_MAGIC);
  576 
  577                 memcpy(ptr, foc->val, foc->len);
  578                 if ((foc->len & 3) == 2) {
  579                         u8 *align = ((u8 *)ptr) + foc->len;
  580                         align[0] = align[1] = TCPOPT_NOP;
  581                 }
  582                 ptr += (foc->len + 3) >> 2;
  583         }
  584 }
  585 
  586 /* Compute TCP options for SYN packets. This is not the final
  587  * network wire format yet.
  588  */
  589 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
  590                                 struct tcp_out_options *opts,
  591                                 struct tcp_md5sig_key **md5)
  592 {
  593         struct tcp_sock *tp = tcp_sk(sk);
  594         struct tcp_cookie_values *cvp = tp->cookie_values;
  595         unsigned int remaining = MAX_TCP_OPTION_SPACE;
  596         u8 cookie_size = (!tp->rx_opt.cookie_out_never && cvp != NULL) ?
  597                          tcp_cookie_size_check(cvp->cookie_desired) :
  598                          0;
  599         struct tcp_fastopen_request *fastopen = tp->fastopen_req;
  600 
  601 #ifdef CONFIG_TCP_MD5SIG
  602         *md5 = tp->af_specific->md5_lookup(sk, sk);
  603         if (*md5) {
  604                 opts->options |= OPTION_MD5;
  605                 remaining -= TCPOLEN_MD5SIG_ALIGNED;
  606         }
  607 #else
  608         *md5 = NULL;
  609 #endif
  610 
  611         /* We always get an MSS option.  The option bytes which will be seen in
  612          * normal data packets should timestamps be used, must be in the MSS
  613          * advertised.  But we subtract them from tp->mss_cache so that
  614          * calculations in tcp_sendmsg are simpler etc.  So account for this
  615          * fact here if necessary.  If we don't do this correctly, as a
  616          * receiver we won't recognize data packets as being full sized when we
  617          * should, and thus we won't abide by the delayed ACK rules correctly.
  618          * SACKs don't matter, we never delay an ACK when we have any of those
  619          * going out.  */
  620         opts->mss = tcp_advertise_mss(sk);
  621         remaining -= TCPOLEN_MSS_ALIGNED;
  622 
  623         if (likely(sysctl_tcp_timestamps && *md5 == NULL)) {
  624                 opts->options |= OPTION_TS;
  625                 opts->tsval = TCP_SKB_CB(skb)->when;
  626                 opts->tsecr = tp->rx_opt.ts_recent;
  627                 remaining -= TCPOLEN_TSTAMP_ALIGNED;
  628         }
  629         if (likely(sysctl_tcp_window_scaling)) {
  630                 opts->ws = tp->rx_opt.rcv_wscale;
  631                 opts->options |= OPTION_WSCALE;
  632                 remaining -= TCPOLEN_WSCALE_ALIGNED;
  633         }
  634         if (likely(sysctl_tcp_sack)) {
  635                 opts->options |= OPTION_SACK_ADVERTISE;
  636                 if (unlikely(!(OPTION_TS & opts->options)))
  637                         remaining -= TCPOLEN_SACKPERM_ALIGNED;
  638         }
  639 
  640         if (fastopen && fastopen->cookie.len >= 0) {
  641                 u32 need = TCPOLEN_EXP_FASTOPEN_BASE + fastopen->cookie.len;
  642                 need = (need + 3) & ~3U;  /* Align to 32 bits */
  643                 if (remaining >= need) {
  644                         opts->options |= OPTION_FAST_OPEN_COOKIE;
  645                         opts->fastopen_cookie = &fastopen->cookie;
  646                         remaining -= need;
  647                         tp->syn_fastopen = 1;
  648                 }
  649         }
  650         /* Note that timestamps are required by the specification.
  651          *
  652          * Odd numbers of bytes are prohibited by the specification, ensuring
  653          * that the cookie is 16-bit aligned, and the resulting cookie pair is
  654          * 32-bit aligned.
  655          */
  656         if (*md5 == NULL &&
  657             (OPTION_TS & opts->options) &&
  658             cookie_size > 0) {
  659                 int need = TCPOLEN_COOKIE_BASE + cookie_size;
  660 
  661                 if (0x2 & need) {
  662                         /* 32-bit multiple */
  663                         need += 2; /* NOPs */
  664 
  665                         if (need > remaining) {
  666                                 /* try shrinking cookie to fit */
  667                                 cookie_size -= 2;
  668                                 need -= 4;
  669                         }
  670                 }
  671                 while (need > remaining && TCP_COOKIE_MIN <= cookie_size) {
  672                         cookie_size -= 4;
  673                         need -= 4;
  674                 }
  675                 if (TCP_COOKIE_MIN <= cookie_size) {
  676                         opts->options |= OPTION_COOKIE_EXTENSION;
  677                         opts->hash_location = (__u8 *)&cvp->cookie_pair[0];
  678                         opts->hash_size = cookie_size;
  679 
  680                         /* Remember for future incarnations. */
  681                         cvp->cookie_desired = cookie_size;
  682 
  683                         if (cvp->cookie_desired != cvp->cookie_pair_size) {
  684                                 /* Currently use random bytes as a nonce,
  685                                  * assuming these are completely unpredictable
  686                                  * by hostile users of the same system.
  687                                  */
  688                                 get_random_bytes(&cvp->cookie_pair[0],
  689                                                  cookie_size);
  690                                 cvp->cookie_pair_size = cookie_size;
  691                         }
  692 
  693                         remaining -= need;
  694                 }
  695         }
  696         return MAX_TCP_OPTION_SPACE - remaining;
  697 }
  698 
  699 /* Set up TCP options for SYN-ACKs. */
  700 static unsigned int tcp_synack_options(struct sock *sk,
  701                                    struct request_sock *req,
  702                                    unsigned int mss, struct sk_buff *skb,
  703                                    struct tcp_out_options *opts,
  704                                    struct tcp_md5sig_key **md5,
  705                                    struct tcp_extend_values *xvp,
  706                                    struct tcp_fastopen_cookie *foc)
  707 {
  708         struct inet_request_sock *ireq = inet_rsk(req);
  709         unsigned int remaining = MAX_TCP_OPTION_SPACE;
  710         u8 cookie_plus = (xvp != NULL && !xvp->cookie_out_never) ?
  711                          xvp->cookie_plus :
  712                          0;
  713 
  714 #ifdef CONFIG_TCP_MD5SIG
  715         *md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
  716         if (*md5) {
  717                 opts->options |= OPTION_MD5;
  718                 remaining -= TCPOLEN_MD5SIG_ALIGNED;
  719 
  720                 /* We can't fit any SACK blocks in a packet with MD5 + TS
  721                  * options. There was discussion about disabling SACK
  722                  * rather than TS in order to fit in better with old,
  723                  * buggy kernels, but that was deemed to be unnecessary.
  724                  */
  725                 ireq->tstamp_ok &= !ireq->sack_ok;
  726         }
  727 #else
  728         *md5 = NULL;
  729 #endif
  730 
  731         /* We always send an MSS option. */
  732         opts->mss = mss;
  733         remaining -= TCPOLEN_MSS_ALIGNED;
  734 
  735         if (likely(ireq->wscale_ok)) {
  736                 opts->ws = ireq->rcv_wscale;
  737                 opts->options |= OPTION_WSCALE;
  738                 remaining -= TCPOLEN_WSCALE_ALIGNED;
  739         }
  740         if (likely(ireq->tstamp_ok)) {
  741                 opts->options |= OPTION_TS;
  742                 opts->tsval = TCP_SKB_CB(skb)->when;
  743                 opts->tsecr = req->ts_recent;
  744                 remaining -= TCPOLEN_TSTAMP_ALIGNED;
  745         }
  746         if (likely(ireq->sack_ok)) {
  747                 opts->options |= OPTION_SACK_ADVERTISE;
  748                 if (unlikely(!ireq->tstamp_ok))
  749                         remaining -= TCPOLEN_SACKPERM_ALIGNED;
  750         }
  751         if (foc != NULL) {
  752                 u32 need = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
  753                 need = (need + 3) & ~3U;  /* Align to 32 bits */
  754                 if (remaining >= need) {
  755                         opts->options |= OPTION_FAST_OPEN_COOKIE;
  756                         opts->fastopen_cookie = foc;
  757                         remaining -= need;
  758                 }
  759         }
  760         /* Similar rationale to tcp_syn_options() applies here, too.
  761          * If the <SYN> options fit, the same options should fit now!
  762          */
  763         if (*md5 == NULL &&
  764             ireq->tstamp_ok &&
  765             cookie_plus > TCPOLEN_COOKIE_BASE) {
  766                 int need = cookie_plus; /* has TCPOLEN_COOKIE_BASE */
  767 
  768                 if (0x2 & need) {
  769                         /* 32-bit multiple */
  770                         need += 2; /* NOPs */
  771                 }
  772                 if (need <= remaining) {
  773                         opts->options |= OPTION_COOKIE_EXTENSION;
  774                         opts->hash_size = cookie_plus - TCPOLEN_COOKIE_BASE;
  775                         remaining -= need;
  776                 } else {
  777                         /* There's no error return, so flag it. */
  778                         xvp->cookie_out_never = 1; /* true */
  779                         opts->hash_size = 0;
  780                 }
  781         }
  782         return MAX_TCP_OPTION_SPACE - remaining;
  783 }
  784 
  785 /* Compute TCP options for ESTABLISHED sockets. This is not the
  786  * final wire format yet.
  787  */
  788 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
  789                                         struct tcp_out_options *opts,
  790                                         struct tcp_md5sig_key **md5)
  791 {
  792         struct tcp_skb_cb *tcb = skb ? TCP_SKB_CB(skb) : NULL;
  793         struct tcp_sock *tp = tcp_sk(sk);
  794         unsigned int size = 0;
  795         unsigned int eff_sacks;
  796 
  797 #ifdef CONFIG_TCP_MD5SIG
  798         *md5 = tp->af_specific->md5_lookup(sk, sk);
  799         if (unlikely(*md5)) {
  800                 opts->options |= OPTION_MD5;
  801                 size += TCPOLEN_MD5SIG_ALIGNED;
  802         }
  803 #else
  804         *md5 = NULL;
  805 #endif
  806 
  807         if (likely(tp->rx_opt.tstamp_ok)) {
  808                 opts->options |= OPTION_TS;
  809                 opts->tsval = tcb ? tcb->when : 0;
  810                 opts->tsecr = tp->rx_opt.ts_recent;
  811                 size += TCPOLEN_TSTAMP_ALIGNED;
  812         }
  813 
  814         eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
  815         if (unlikely(eff_sacks)) {
  816                 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
  817                 opts->num_sack_blocks =
  818                         min_t(unsigned int, eff_sacks,
  819                               (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
  820                               TCPOLEN_SACK_PERBLOCK);
  821                 size += TCPOLEN_SACK_BASE_ALIGNED +
  822                         opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
  823         }
  824 
  825         return size;
  826 }
  827 
  828 
  829 /* TCP SMALL QUEUES (TSQ)
  830  *
  831  * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
  832  * to reduce RTT and bufferbloat.
  833  * We do this using a special skb destructor (tcp_wfree).
  834  *
  835  * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
  836  * needs to be reallocated in a driver.
  837  * The invariant being skb->truesize substracted from sk->sk_wmem_alloc
  838  *
  839  * Since transmit from skb destructor is forbidden, we use a tasklet
  840  * to process all sockets that eventually need to send more skbs.
  841  * We use one tasklet per cpu, with its own queue of sockets.
  842  */
  843 struct tsq_tasklet {
  844         struct tasklet_struct   tasklet;
  845         struct list_head        head; /* queue of tcp sockets */
  846 };
  847 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
  848 
  849 static void tcp_tsq_handler(struct sock *sk)
  850 {
  851         if ((1 << sk->sk_state) &
  852             (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
  853              TCPF_CLOSE_WAIT  | TCPF_LAST_ACK))
  854                 tcp_write_xmit(sk, tcp_current_mss(sk), 0, 0, GFP_ATOMIC);
  855 }
  856 /*
  857  * One tasklest per cpu tries to send more skbs.
  858  * We run in tasklet context but need to disable irqs when
  859  * transfering tsq->head because tcp_wfree() might
  860  * interrupt us (non NAPI drivers)
  861  */
  862 static void tcp_tasklet_func(unsigned long data)
  863 {
  864         struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
  865         LIST_HEAD(list);
  866         unsigned long flags;
  867         struct list_head *q, *n;
  868         struct tcp_sock *tp;
  869         struct sock *sk;
  870 
  871         local_irq_save(flags);
  872         list_splice_init(&tsq->head, &list);
  873         local_irq_restore(flags);
  874 
  875         list_for_each_safe(q, n, &list) {
  876                 tp = list_entry(q, struct tcp_sock, tsq_node);
  877                 list_del(&tp->tsq_node);
  878 
  879                 sk = (struct sock *)tp;
  880                 bh_lock_sock(sk);
  881 
  882                 if (!sock_owned_by_user(sk)) {
  883                         tcp_tsq_handler(sk);
  884                 } else {
  885                         /* defer the work to tcp_release_cb() */
  886                         set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
  887                 }
  888                 bh_unlock_sock(sk);
  889 
  890                 clear_bit(TSQ_QUEUED, &tp->tsq_flags);
  891                 sk_free(sk);
  892         }
  893 }
  894 
  895 #define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) |           \
  896                           (1UL << TCP_WRITE_TIMER_DEFERRED) |   \
  897                           (1UL << TCP_DELACK_TIMER_DEFERRED) |  \
  898                           (1UL << TCP_MTU_REDUCED_DEFERRED))
  899 /**
  900  * tcp_release_cb - tcp release_sock() callback
  901  * @sk: socket
  902  *
  903  * called from release_sock() to perform protocol dependent
  904  * actions before socket release.
  905  */
  906 void tcp_release_cb(struct sock *sk)
  907 {
  908         struct tcp_sock *tp = tcp_sk(sk);
  909         unsigned long flags, nflags;
  910 
  911         /* perform an atomic operation only if at least one flag is set */
  912         do {
  913                 flags = tp->tsq_flags;
  914                 if (!(flags & TCP_DEFERRED_ALL))
  915                         return;
  916                 nflags = flags & ~TCP_DEFERRED_ALL;
  917         } while (cmpxchg(&tp->tsq_flags, flags, nflags) != flags);
  918 
  919         if (flags & (1UL << TCP_TSQ_DEFERRED))
  920                 tcp_tsq_handler(sk);
  921 
  922         if (flags & (1UL << TCP_WRITE_TIMER_DEFERRED)) {
  923                 tcp_write_timer_handler(sk);
  924                 __sock_put(sk);
  925         }
  926         if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED)) {
  927                 tcp_delack_timer_handler(sk);
  928                 __sock_put(sk);
  929         }
  930         if (flags & (1UL << TCP_MTU_REDUCED_DEFERRED)) {
  931                 sk->sk_prot->mtu_reduced(sk);
  932                 __sock_put(sk);
  933         }
  934 }
  935 EXPORT_SYMBOL(tcp_release_cb);
  936 
  937 void __init tcp_tasklet_init(void)
  938 {
  939         int i;
  940 
  941         for_each_possible_cpu(i) {
  942                 struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
  943 
  944                 INIT_LIST_HEAD(&tsq->head);
  945                 tasklet_init(&tsq->tasklet,
  946                              tcp_tasklet_func,
  947                              (unsigned long)tsq);
  948         }
  949 }
  950 
  951 /*
  952  * Write buffer destructor automatically called from kfree_skb.
  953  * We cant xmit new skbs from this context, as we might already
  954  * hold qdisc lock.
  955  */
  956 static void tcp_wfree(struct sk_buff *skb)
  957 {
  958         struct sock *sk = skb->sk;
  959         struct tcp_sock *tp = tcp_sk(sk);
  960 
  961         if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) &&
  962             !test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) {
  963                 unsigned long flags;
  964                 struct tsq_tasklet *tsq;
  965 
  966                 /* Keep a ref on socket.
  967                  * This last ref will be released in tcp_tasklet_func()
  968                  */
  969                 atomic_sub(skb->truesize - 1, &sk->sk_wmem_alloc);
  970 
  971                 /* queue this socket to tasklet queue */
  972                 local_irq_save(flags);
  973                 tsq = &__get_cpu_var(tsq_tasklet);
  974                 list_add(&tp->tsq_node, &tsq->head);
  975                 tasklet_schedule(&tsq->tasklet);
  976                 local_irq_restore(flags);
  977         } else {
  978                 sock_wfree(skb);
  979         }
  980 }
  981 
  982 /* This routine actually transmits TCP packets queued in by
  983  * tcp_do_sendmsg().  This is used by both the initial
  984  * transmission and possible later retransmissions.
  985  * All SKB's seen here are completely headerless.  It is our
  986  * job to build the TCP header, and pass the packet down to
  987  * IP so it can do the same plus pass the packet off to the
  988  * device.
  989  *
  990  * We are working here with either a clone of the original
  991  * SKB, or a fresh unique copy made by the retransmit engine.
  992  */
  993 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
  994                             gfp_t gfp_mask)
  995 {
  996         const struct inet_connection_sock *icsk = inet_csk(sk);
  997         struct inet_sock *inet;
  998         struct tcp_sock *tp;
  999         struct tcp_skb_cb *tcb;
 1000         struct tcp_out_options opts;
 1001         unsigned int tcp_options_size, tcp_header_size;
 1002         struct tcp_md5sig_key *md5;
 1003         struct tcphdr *th;
 1004         int err;
 1005 
 1006         BUG_ON(!skb || !tcp_skb_pcount(skb));
 1007 
 1008         /* If congestion control is doing timestamping, we must
 1009          * take such a timestamp before we potentially clone/copy.
 1010          */
 1011         if (icsk->icsk_ca_ops->flags & TCP_CONG_RTT_STAMP)
 1012                 __net_timestamp(skb);
 1013 
 1014         if (likely(clone_it)) {
 1015                 if (unlikely(skb_cloned(skb)))
 1016                         skb = pskb_copy(skb, gfp_mask);
 1017                 else
 1018                         skb = skb_clone(skb, gfp_mask);
 1019                 if (unlikely(!skb))
 1020                         return -ENOBUFS;
 1021         }
 1022 
 1023         inet = inet_sk(sk);
 1024         tp = tcp_sk(sk);
 1025         tcb = TCP_SKB_CB(skb);
 1026         memset(&opts, 0, sizeof(opts));
 1027 
 1028         if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
 1029                 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
 1030         else
 1031                 tcp_options_size = tcp_established_options(sk, skb, &opts,
 1032                                                            &md5);
 1033         tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
 1034 
 1035         if (tcp_packets_in_flight(tp) == 0) {
 1036                 tcp_ca_event(sk, CA_EVENT_TX_START);
 1037                 skb->ooo_okay = 1;
 1038         } else
 1039                 skb->ooo_okay = 0;
 1040 
 1041         skb_push(skb, tcp_header_size);
 1042         skb_reset_transport_header(skb);
 1043 
 1044         skb_orphan(skb);
 1045         skb->sk = sk;
 1046         skb->destructor = (sysctl_tcp_limit_output_bytes > 0) ?
 1047                           tcp_wfree : sock_wfree;
 1048         atomic_add(skb->truesize, &sk->sk_wmem_alloc);
 1049 
 1050         /* Build TCP header and checksum it. */
 1051         th = tcp_hdr(skb);
 1052         th->source              = inet->inet_sport;
 1053         th->dest                = inet->inet_dport;
 1054         th->seq                 = htonl(tcb->seq);
 1055         th->ack_seq             = htonl(tp->rcv_nxt);
 1056         *(((__be16 *)th) + 6)   = htons(((tcp_header_size >> 2) << 12) |
 1057                                         tcb->tcp_flags);
 1058 
 1059         if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
 1060                 /* RFC1323: The window in SYN & SYN/ACK segments
 1061                  * is never scaled.
 1062                  */
 1063                 th->window      = htons(min(tp->rcv_wnd, 65535U));
 1064         } else {
 1065                 th->window      = htons(tcp_select_window(sk));
 1066         }
 1067         th->check               = 0;
 1068         th->urg_ptr             = 0;
 1069 
 1070         /* The urg_mode check is necessary during a below snd_una win probe */
 1071         if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
 1072                 if (before(tp->snd_up, tcb->seq + 0x10000)) {
 1073                         th->urg_ptr = htons(tp->snd_up - tcb->seq);
 1074                         th->urg = 1;
 1075                 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
 1076                         th->urg_ptr = htons(0xFFFF);
 1077                         th->urg = 1;
 1078                 }
 1079         }
 1080 
 1081         tcp_options_write((__be32 *)(th + 1), tp, &opts);
 1082         if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0))
 1083                 TCP_ECN_send(sk, skb, tcp_header_size);
 1084 
 1085 #ifdef CONFIG_TCP_MD5SIG
 1086         /* Calculate the MD5 hash, as we have all we need now */
 1087         if (md5) {
 1088                 sk_nocaps_add(sk, NETIF_F_GSO_MASK);
 1089                 tp->af_specific->calc_md5_hash(opts.hash_location,
 1090                                                md5, sk, NULL, skb);
 1091         }
 1092 #endif
 1093 
 1094         icsk->icsk_af_ops->send_check(sk, skb);
 1095 
 1096         if (likely(tcb->tcp_flags & TCPHDR_ACK))
 1097                 tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
 1098 
 1099         if (skb->len != tcp_header_size)
 1100                 tcp_event_data_sent(tp, sk);
 1101 
 1102         if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
 1103                 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
 1104                               tcp_skb_pcount(skb));
 1105 
 1106         err = icsk->icsk_af_ops->queue_xmit(skb, &inet->cork.fl);
 1107         if (likely(err <= 0))
 1108                 return err;
 1109 
 1110         tcp_enter_cwr(sk, 1);
 1111 
 1112         return net_xmit_eval(err);
 1113 }
 1114 
 1115 /* This routine just queues the buffer for sending.
 1116  *
 1117  * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
 1118  * otherwise socket can stall.
 1119  */
 1120 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
 1121 {
 1122         struct tcp_sock *tp = tcp_sk(sk);
 1123 
 1124         /* Advance write_seq and place onto the write_queue. */
 1125         tp->write_seq = TCP_SKB_CB(skb)->end_seq;
 1126         skb_header_release(skb);
 1127         tcp_add_write_queue_tail(sk, skb);
 1128         sk->sk_wmem_queued += skb->truesize;
 1129         sk_mem_charge(sk, skb->truesize);
 1130 }
 1131 
 1132 /* Initialize TSO segments for a packet. */
 1133 static void tcp_set_skb_tso_segs(const struct sock *sk, struct sk_buff *skb,
 1134                                  unsigned int mss_now)
 1135 {
 1136         if (skb->len <= mss_now || !sk_can_gso(sk) ||
 1137             skb->ip_summed == CHECKSUM_NONE) {
 1138                 /* Avoid the costly divide in the normal
 1139                  * non-TSO case.
 1140                  */
 1141                 skb_shinfo(skb)->gso_segs = 1;
 1142                 skb_shinfo(skb)->gso_size = 0;
 1143                 skb_shinfo(skb)->gso_type = 0;
 1144         } else {
 1145                 skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len, mss_now);
 1146                 skb_shinfo(skb)->gso_size = mss_now;
 1147                 skb_shinfo(skb)->gso_type = sk->sk_gso_type;
 1148         }
 1149 }
 1150 
 1151 /* When a modification to fackets out becomes necessary, we need to check
 1152  * skb is counted to fackets_out or not.
 1153  */
 1154 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
 1155                                    int decr)
 1156 {
 1157         struct tcp_sock *tp = tcp_sk(sk);
 1158 
 1159         if (!tp->sacked_out || tcp_is_reno(tp))
 1160                 return;
 1161 
 1162         if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
 1163                 tp->fackets_out -= decr;
 1164 }
 1165 
 1166 /* Pcount in the middle of the write queue got changed, we need to do various
 1167  * tweaks to fix counters
 1168  */
 1169 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
 1170 {
 1171         struct tcp_sock *tp = tcp_sk(sk);
 1172 
 1173         tp->packets_out -= decr;
 1174 
 1175         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
 1176                 tp->sacked_out -= decr;
 1177         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
 1178                 tp->retrans_out -= decr;
 1179         if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
 1180                 tp->lost_out -= decr;
 1181 
 1182         /* Reno case is special. Sigh... */
 1183         if (tcp_is_reno(tp) && decr > 0)
 1184                 tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
 1185 
 1186         tcp_adjust_fackets_out(sk, skb, decr);
 1187 
 1188         if (tp->lost_skb_hint &&
 1189             before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
 1190             (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
 1191                 tp->lost_cnt_hint -= decr;
 1192 
 1193         tcp_verify_left_out(tp);
 1194 }
 1195 
 1196 /* Function to create two new TCP segments.  Shrinks the given segment
 1197  * to the specified size and appends a new segment with the rest of the
 1198  * packet to the list.  This won't be called frequently, I hope.
 1199  * Remember, these are still headerless SKBs at this point.
 1200  */
 1201 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
 1202                  unsigned int mss_now)
 1203 {
 1204         struct tcp_sock *tp = tcp_sk(sk);
 1205         struct sk_buff *buff;
 1206         int nsize, old_factor;
 1207         int nlen;
 1208         u8 flags;
 1209 
 1210         if (WARN_ON(len > skb->len))
 1211                 return -EINVAL;
 1212 
 1213         nsize = skb_headlen(skb) - len;
 1214         if (nsize < 0)
 1215                 nsize = 0;
 1216 
 1217         if (skb_cloned(skb) &&
 1218             skb_is_nonlinear(skb) &&
 1219             pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
 1220                 return -ENOMEM;
 1221 
 1222         /* Get a new skb... force flag on. */
 1223         buff = sk_stream_alloc_skb(sk, nsize, GFP_ATOMIC);
 1224         if (buff == NULL)
 1225                 return -ENOMEM; /* We'll just try again later. */
 1226 
 1227         sk->sk_wmem_queued += buff->truesize;
 1228         sk_mem_charge(sk, buff->truesize);
 1229         nlen = skb->len - len - nsize;
 1230         buff->truesize += nlen;
 1231         skb->truesize -= nlen;
 1232 
 1233         /* Correct the sequence numbers. */
 1234         TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
 1235         TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
 1236         TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
 1237 
 1238         /* PSH and FIN should only be set in the second packet. */
 1239         flags = TCP_SKB_CB(skb)->tcp_flags;
 1240         TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
 1241         TCP_SKB_CB(buff)->tcp_flags = flags;
 1242         TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
 1243 
 1244         if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
 1245                 /* Copy and checksum data tail into the new buffer. */
 1246                 buff->csum = csum_partial_copy_nocheck(skb->data + len,
 1247                                                        skb_put(buff, nsize),
 1248                                                        nsize, 0);
 1249 
 1250                 skb_trim(skb, len);
 1251 
 1252                 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
 1253         } else {
 1254                 skb->ip_summed = CHECKSUM_PARTIAL;
 1255                 skb_split(skb, buff, len);
 1256         }
 1257 
 1258         buff->ip_summed = skb->ip_summed;
 1259 
 1260         /* Looks stupid, but our code really uses when of
 1261          * skbs, which it never sent before. --ANK
 1262          */
 1263         TCP_SKB_CB(buff)->when = TCP_SKB_CB(skb)->when;
 1264         buff->tstamp = skb->tstamp;
 1265 
 1266         old_factor = tcp_skb_pcount(skb);
 1267 
 1268         /* Fix up tso_factor for both original and new SKB.  */
 1269         tcp_set_skb_tso_segs(sk, skb, mss_now);
 1270         tcp_set_skb_tso_segs(sk, buff, mss_now);
 1271 
 1272         /* If this packet has been sent out already, we must
 1273          * adjust the various packet counters.
 1274          */
 1275         if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
 1276                 int diff = old_factor - tcp_skb_pcount(skb) -
 1277                         tcp_skb_pcount(buff);
 1278 
 1279                 if (diff)
 1280                         tcp_adjust_pcount(sk, skb, diff);
 1281         }
 1282 
 1283         /* Link BUFF into the send queue. */
 1284         skb_header_release(buff);
 1285         tcp_insert_write_queue_after(skb, buff, sk);
 1286 
 1287         return 0;
 1288 }
 1289 
 1290 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
 1291  * eventually). The difference is that pulled data not copied, but
 1292  * immediately discarded.
 1293  */
 1294 static void __pskb_trim_head(struct sk_buff *skb, int len)
 1295 {
 1296         int i, k, eat;
 1297 
 1298         eat = min_t(int, len, skb_headlen(skb));
 1299         if (eat) {
 1300                 __skb_pull(skb, eat);
 1301                 skb->avail_size -= eat;
 1302                 len -= eat;
 1303                 if (!len)
 1304                         return;
 1305         }
 1306         eat = len;
 1307         k = 0;
 1308         for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
 1309                 int size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
 1310 
 1311                 if (size <= eat) {
 1312                         skb_frag_unref(skb, i);
 1313                         eat -= size;
 1314                 } else {
 1315                         skb_shinfo(skb)->frags[k] = skb_shinfo(skb)->frags[i];
 1316                         if (eat) {
 1317                                 skb_shinfo(skb)->frags[k].page_offset += eat;
 1318                                 skb_frag_size_sub(&skb_shinfo(skb)->frags[k], eat);
 1319                                 eat = 0;
 1320                         }
 1321                         k++;
 1322                 }
 1323         }
 1324         skb_shinfo(skb)->nr_frags = k;
 1325 
 1326         skb_reset_tail_pointer(skb);
 1327         skb->data_len -= len;
 1328         skb->len = skb->data_len;
 1329 }
 1330 
 1331 /* Remove acked data from a packet in the transmit queue. */
 1332 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
 1333 {
 1334         if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
 1335                 return -ENOMEM;
 1336 
 1337         __pskb_trim_head(skb, len);
 1338 
 1339         TCP_SKB_CB(skb)->seq += len;
 1340         skb->ip_summed = CHECKSUM_PARTIAL;
 1341 
 1342         skb->truesize        -= len;
 1343         sk->sk_wmem_queued   -= len;
 1344         sk_mem_uncharge(sk, len);
 1345         sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
 1346 
 1347         /* Any change of skb->len requires recalculation of tso factor. */
 1348         if (tcp_skb_pcount(skb) > 1)
 1349                 tcp_set_skb_tso_segs(sk, skb, tcp_skb_mss(skb));
 1350 
 1351         return 0;
 1352 }
 1353 
 1354 /* Calculate MSS. Not accounting for SACKs here.  */
 1355 int tcp_mtu_to_mss(struct sock *sk, int pmtu)
 1356 {
 1357         const struct tcp_sock *tp = tcp_sk(sk);
 1358         const struct inet_connection_sock *icsk = inet_csk(sk);
 1359         int mss_now;
 1360 
 1361         /* Calculate base mss without TCP options:
 1362            It is MMS_S - sizeof(tcphdr) of rfc1122
 1363          */
 1364         mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
 1365 
 1366         /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
 1367         if (icsk->icsk_af_ops->net_frag_header_len) {
 1368                 const struct dst_entry *dst = __sk_dst_get(sk);
 1369 
 1370                 if (dst && dst_allfrag(dst))
 1371                         mss_now -= icsk->icsk_af_ops->net_frag_header_len;
 1372         }
 1373 
 1374         /* Clamp it (mss_clamp does not include tcp options) */
 1375         if (mss_now > tp->rx_opt.mss_clamp)
 1376                 mss_now = tp->rx_opt.mss_clamp;
 1377 
 1378         /* Now subtract optional transport overhead */
 1379         mss_now -= icsk->icsk_ext_hdr_len;
 1380 
 1381         /* Then reserve room for full set of TCP options and 8 bytes of data */
 1382         if (mss_now < 48)
 1383                 mss_now = 48;
 1384 
 1385         /* Now subtract TCP options size, not including SACKs */
 1386         mss_now -= tp->tcp_header_len - sizeof(struct tcphdr);
 1387 
 1388         return mss_now;
 1389 }
 1390 
 1391 /* Inverse of above */
 1392 int tcp_mss_to_mtu(struct sock *sk, int mss)
 1393 {
 1394         const struct tcp_sock *tp = tcp_sk(sk);
 1395         const struct inet_connection_sock *icsk = inet_csk(sk);
 1396         int mtu;
 1397 
 1398         mtu = mss +
 1399               tp->tcp_header_len +
 1400               icsk->icsk_ext_hdr_len +
 1401               icsk->icsk_af_ops->net_header_len;
 1402 
 1403         /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
 1404         if (icsk->icsk_af_ops->net_frag_header_len) {
 1405                 const struct dst_entry *dst = __sk_dst_get(sk);
 1406 
 1407                 if (dst && dst_allfrag(dst))
 1408                         mtu += icsk->icsk_af_ops->net_frag_header_len;
 1409         }
 1410         return mtu;
 1411 }
 1412 
 1413 /* MTU probing init per socket */
 1414 void tcp_mtup_init(struct sock *sk)
 1415 {
 1416         struct tcp_sock *tp = tcp_sk(sk);
 1417         struct inet_connection_sock *icsk = inet_csk(sk);
 1418 
 1419         icsk->icsk_mtup.enabled = sysctl_tcp_mtu_probing > 1;
 1420         icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
 1421                                icsk->icsk_af_ops->net_header_len;
 1422         icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, sysctl_tcp_base_mss);
 1423         icsk->icsk_mtup.probe_size = 0;
 1424 }
 1425 EXPORT_SYMBOL(tcp_mtup_init);
 1426 
 1427 /* This function synchronize snd mss to current pmtu/exthdr set.
 1428 
 1429    tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
 1430    for TCP options, but includes only bare TCP header.
 1431 
 1432    tp->rx_opt.mss_clamp is mss negotiated at connection setup.
 1433    It is minimum of user_mss and mss received with SYN.
 1434    It also does not include TCP options.
 1435 
 1436    inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
 1437 
 1438    tp->mss_cache is current effective sending mss, including
 1439    all tcp options except for SACKs. It is evaluated,
 1440    taking into account current pmtu, but never exceeds
 1441    tp->rx_opt.mss_clamp.
 1442 
 1443    NOTE1. rfc1122 clearly states that advertised MSS
 1444    DOES NOT include either tcp or ip options.
 1445 
 1446    NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
 1447    are READ ONLY outside this function.         --ANK (980731)
 1448  */
 1449 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
 1450 {
 1451         struct tcp_sock *tp = tcp_sk(sk);
 1452         struct inet_connection_sock *icsk = inet_csk(sk);
 1453         int mss_now;
 1454 
 1455         if (icsk->icsk_mtup.search_high > pmtu)
 1456                 icsk->icsk_mtup.search_high = pmtu;
 1457 
 1458         mss_now = tcp_mtu_to_mss(sk, pmtu);
 1459         mss_now = tcp_bound_to_half_wnd(tp, mss_now);
 1460 
 1461         /* And store cached results */
 1462         icsk->icsk_pmtu_cookie = pmtu;
 1463         if (icsk->icsk_mtup.enabled)
 1464                 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
 1465         tp->mss_cache = mss_now;
 1466 
 1467         return mss_now;
 1468 }
 1469 EXPORT_SYMBOL(tcp_sync_mss);
 1470 
 1471 /* Compute the current effective MSS, taking SACKs and IP options,
 1472  * and even PMTU discovery events into account.
 1473  */
 1474 unsigned int tcp_current_mss(struct sock *sk)
 1475 {
 1476         const struct tcp_sock *tp = tcp_sk(sk);
 1477         const struct dst_entry *dst = __sk_dst_get(sk);
 1478         u32 mss_now;
 1479         unsigned int header_len;
 1480         struct tcp_out_options opts;
 1481         struct tcp_md5sig_key *md5;
 1482 
 1483         mss_now = tp->mss_cache;
 1484 
 1485         if (dst) {
 1486                 u32 mtu = dst_mtu(dst);
 1487                 if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
 1488                         mss_now = tcp_sync_mss(sk, mtu);
 1489         }
 1490 
 1491         header_len = tcp_established_options(sk, NULL, &opts, &md5) +
 1492                      sizeof(struct tcphdr);
 1493         /* The mss_cache is sized based on tp->tcp_header_len, which assumes
 1494          * some common options. If this is an odd packet (because we have SACK
 1495          * blocks etc) then our calculated header_len will be different, and
 1496          * we have to adjust mss_now correspondingly */
 1497         if (header_len != tp->tcp_header_len) {
 1498                 int delta = (int) header_len - tp->tcp_header_len;
 1499                 mss_now -= delta;
 1500         }
 1501 
 1502         return mss_now;
 1503 }
 1504 
 1505 /* Congestion window validation. (RFC2861) */
 1506 static void tcp_cwnd_validate(struct sock *sk)
 1507 {
 1508         struct tcp_sock *tp = tcp_sk(sk);
 1509 
 1510         if (tp->packets_out >= tp->snd_cwnd) {
 1511                 /* Network is feed fully. */
 1512                 tp->snd_cwnd_used = 0;
 1513                 tp->snd_cwnd_stamp = tcp_time_stamp;
 1514         } else {
 1515                 /* Network starves. */
 1516                 if (tp->packets_out > tp->snd_cwnd_used)
 1517                         tp->snd_cwnd_used = tp->packets_out;
 1518 
 1519                 if (sysctl_tcp_slow_start_after_idle &&
 1520                     (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
 1521                         tcp_cwnd_application_limited(sk);
 1522         }
 1523 }
 1524 
 1525 /* Returns the portion of skb which can be sent right away without
 1526  * introducing MSS oddities to segment boundaries. In rare cases where
 1527  * mss_now != mss_cache, we will request caller to create a small skb
 1528  * per input skb which could be mostly avoided here (if desired).
 1529  *
 1530  * We explicitly want to create a request for splitting write queue tail
 1531  * to a small skb for Nagle purposes while avoiding unnecessary modulos,
 1532  * thus all the complexity (cwnd_len is always MSS multiple which we
 1533  * return whenever allowed by the other factors). Basically we need the
 1534  * modulo only when the receiver window alone is the limiting factor or
 1535  * when we would be allowed to send the split-due-to-Nagle skb fully.
 1536  */
 1537 static unsigned int tcp_mss_split_point(const struct sock *sk, const struct sk_buff *skb,
 1538                                         unsigned int mss_now, unsigned int max_segs)
 1539 {
 1540         const struct tcp_sock *tp = tcp_sk(sk);
 1541         u32 needed, window, max_len;
 1542 
 1543         window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
 1544         max_len = mss_now * max_segs;
 1545 
 1546         if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
 1547                 return max_len;
 1548 
 1549         needed = min(skb->len, window);
 1550 
 1551         if (max_len <= needed)
 1552                 return max_len;
 1553 
 1554         return needed - needed % mss_now;
 1555 }
 1556 
 1557 /* Can at least one segment of SKB be sent right now, according to the
 1558  * congestion window rules?  If so, return how many segments are allowed.
 1559  */
 1560 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
 1561                                          const struct sk_buff *skb)
 1562 {
 1563         u32 in_flight, cwnd;
 1564 
 1565         /* Don't be strict about the congestion window for the final FIN.  */
 1566         if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
 1567             tcp_skb_pcount(skb) == 1)
 1568                 return 1;
 1569 
 1570         in_flight = tcp_packets_in_flight(tp);
 1571         cwnd = tp->snd_cwnd;
 1572         if (in_flight < cwnd)
 1573                 return (cwnd - in_flight);
 1574 
 1575         return 0;
 1576 }
 1577 
 1578 /* Initialize TSO state of a skb.
 1579  * This must be invoked the first time we consider transmitting
 1580  * SKB onto the wire.
 1581  */
 1582 static int tcp_init_tso_segs(const struct sock *sk, struct sk_buff *skb,
 1583                              unsigned int mss_now)
 1584 {
 1585         int tso_segs = tcp_skb_pcount(skb);
 1586 
 1587         if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
 1588                 tcp_set_skb_tso_segs(sk, skb, mss_now);
 1589                 tso_segs = tcp_skb_pcount(skb);
 1590         }
 1591         return tso_segs;
 1592 }
 1593 
 1594 /* Minshall's variant of the Nagle send check. */
 1595 static inline bool tcp_minshall_check(const struct tcp_sock *tp)
 1596 {
 1597         return after(tp->snd_sml, tp->snd_una) &&
 1598                 !after(tp->snd_sml, tp->snd_nxt);
 1599 }
 1600 
 1601 /* Return false, if packet can be sent now without violation Nagle's rules:
 1602  * 1. It is full sized.
 1603  * 2. Or it contains FIN. (already checked by caller)
 1604  * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
 1605  * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
 1606  *    With Minshall's modification: all sent small packets are ACKed.
 1607  */
 1608 static inline bool tcp_nagle_check(const struct tcp_sock *tp,
 1609                                   const struct sk_buff *skb,
 1610                                   unsigned int mss_now, int nonagle)
 1611 {
 1612         return skb->len < mss_now &&
 1613                 ((nonagle & TCP_NAGLE_CORK) ||
 1614                  (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
 1615 }
 1616 
 1617 /* Return true if the Nagle test allows this packet to be
 1618  * sent now.
 1619  */
 1620 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
 1621                                   unsigned int cur_mss, int nonagle)
 1622 {
 1623         /* Nagle rule does not apply to frames, which sit in the middle of the
 1624          * write_queue (they have no chances to get new data).
 1625          *
 1626          * This is implemented in the callers, where they modify the 'nonagle'
 1627          * argument based upon the location of SKB in the send queue.
 1628          */
 1629         if (nonagle & TCP_NAGLE_PUSH)
 1630                 return true;
 1631 
 1632         /* Don't use the nagle rule for urgent data (or for the final FIN).
 1633          * Nagle can be ignored during F-RTO too (see RFC4138).
 1634          */
 1635         if (tcp_urg_mode(tp) || (tp->frto_counter == 2) ||
 1636             (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
 1637                 return true;
 1638 
 1639         if (!tcp_nagle_check(tp, skb, cur_mss, nonagle))
 1640                 return true;
 1641 
 1642         return false;
 1643 }
 1644 
 1645 /* Does at least the first segment of SKB fit into the send window? */
 1646 static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
 1647                              const struct sk_buff *skb,
 1648                              unsigned int cur_mss)
 1649 {
 1650         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
 1651 
 1652         if (skb->len > cur_mss)
 1653                 end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
 1654 
 1655         return !after(end_seq, tcp_wnd_end(tp));
 1656 }
 1657 
 1658 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
 1659  * should be put on the wire right now.  If so, it returns the number of
 1660  * packets allowed by the congestion window.
 1661  */
 1662 static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
 1663                                  unsigned int cur_mss, int nonagle)
 1664 {
 1665         const struct tcp_sock *tp = tcp_sk(sk);
 1666         unsigned int cwnd_quota;
 1667 
 1668         tcp_init_tso_segs(sk, skb, cur_mss);
 1669 
 1670         if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
 1671                 return 0;
 1672 
 1673         cwnd_quota = tcp_cwnd_test(tp, skb);
 1674         if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
 1675                 cwnd_quota = 0;
 1676 
 1677         return cwnd_quota;
 1678 }
 1679 
 1680 /* Test if sending is allowed right now. */
 1681 bool tcp_may_send_now(struct sock *sk)
 1682 {
 1683         const struct tcp_sock *tp = tcp_sk(sk);
 1684         struct sk_buff *skb = tcp_send_head(sk);
 1685 
 1686         return skb &&
 1687                 tcp_snd_test(sk, skb, tcp_current_mss(sk),
 1688                              (tcp_skb_is_last(sk, skb) ?
 1689                               tp->nonagle : TCP_NAGLE_PUSH));
 1690 }
 1691 
 1692 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
 1693  * which is put after SKB on the list.  It is very much like
 1694  * tcp_fragment() except that it may make several kinds of assumptions
 1695  * in order to speed up the splitting operation.  In particular, we
 1696  * know that all the data is in scatter-gather pages, and that the
 1697  * packet has never been sent out before (and thus is not cloned).
 1698  */
 1699 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
 1700                         unsigned int mss_now, gfp_t gfp)
 1701 {
 1702         struct sk_buff *buff;
 1703         int nlen = skb->len - len;
 1704         u8 flags;
 1705 
 1706         /* All of a TSO frame must be composed of paged data.  */
 1707         if (skb->len != skb->data_len)
 1708                 return tcp_fragment(sk, skb, len, mss_now);
 1709 
 1710         buff = sk_stream_alloc_skb(sk, 0, gfp);
 1711         if (unlikely(buff == NULL))
 1712                 return -ENOMEM;
 1713 
 1714         sk->sk_wmem_queued += buff->truesize;
 1715         sk_mem_charge(sk, buff->truesize);
 1716         buff->truesize += nlen;
 1717         skb->truesize -= nlen;
 1718 
 1719         /* Correct the sequence numbers. */
 1720         TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
 1721         TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
 1722         TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
 1723 
 1724         /* PSH and FIN should only be set in the second packet. */
 1725         flags = TCP_SKB_CB(skb)->tcp_flags;
 1726         TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
 1727         TCP_SKB_CB(buff)->tcp_flags = flags;
 1728 
 1729         /* This packet was never sent out yet, so no SACK bits. */
 1730         TCP_SKB_CB(buff)->sacked = 0;
 1731 
 1732         buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
 1733         skb_split(skb, buff, len);
 1734 
 1735         /* Fix up tso_factor for both original and new SKB.  */
 1736         tcp_set_skb_tso_segs(sk, skb, mss_now);
 1737         tcp_set_skb_tso_segs(sk, buff, mss_now);
 1738 
 1739         /* Link BUFF into the send queue. */
 1740         skb_header_release(buff);
 1741         tcp_insert_write_queue_after(skb, buff, sk);
 1742 
 1743         return 0;
 1744 }
 1745 
 1746 /* Try to defer sending, if possible, in order to minimize the amount
 1747  * of TSO splitting we do.  View it as a kind of TSO Nagle test.
 1748  *
 1749  * This algorithm is from John Heffner.
 1750  */
 1751 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb)
 1752 {
 1753         struct tcp_sock *tp = tcp_sk(sk);
 1754         const struct inet_connection_sock *icsk = inet_csk(sk);
 1755         u32 send_win, cong_win, limit, in_flight;
 1756         int win_divisor;
 1757 
 1758         if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
 1759                 goto send_now;
 1760 
 1761         if (icsk->icsk_ca_state != TCP_CA_Open)
 1762                 goto send_now;
 1763 
 1764         /* Defer for less than two clock ticks. */
 1765         if (tp->tso_deferred &&
 1766             (((u32)jiffies << 1) >> 1) - (tp->tso_deferred >> 1) > 1)
 1767                 goto send_now;
 1768 
 1769         in_flight = tcp_packets_in_flight(tp);
 1770 
 1771         BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
 1772 
 1773         send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
 1774 
 1775         /* From in_flight test above, we know that cwnd > in_flight.  */
 1776         cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
 1777 
 1778         limit = min(send_win, cong_win);
 1779 
 1780         /* If a full-sized TSO skb can be sent, do it. */
 1781         if (limit >= min_t(unsigned int, sk->sk_gso_max_size,
 1782                            sk->sk_gso_max_segs * tp->mss_cache))
 1783                 goto send_now;
 1784 
 1785         /* Middle in queue won't get any more data, full sendable already? */
 1786         if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
 1787                 goto send_now;
 1788 
 1789         win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
 1790         if (win_divisor) {
 1791                 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
 1792 
 1793                 /* If at least some fraction of a window is available,
 1794                  * just use it.
 1795                  */
 1796                 chunk /= win_divisor;
 1797                 if (limit >= chunk)
 1798                         goto send_now;
 1799         } else {
 1800                 /* Different approach, try not to defer past a single
 1801                  * ACK.  Receiver should ACK every other full sized
 1802                  * frame, so if we have space for more than 3 frames
 1803                  * then send now.
 1804                  */
 1805                 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
 1806                         goto send_now;
 1807         }
 1808 
 1809         /* Ok, it looks like it is advisable to defer.  */
 1810         tp->tso_deferred = 1 | (jiffies << 1);
 1811 
 1812         return true;
 1813 
 1814 send_now:
 1815         tp->tso_deferred = 0;
 1816         return false;
 1817 }
 1818 
 1819 /* Create a new MTU probe if we are ready.
 1820  * MTU probe is regularly attempting to increase the path MTU by
 1821  * deliberately sending larger packets.  This discovers routing
 1822  * changes resulting in larger path MTUs.
 1823  *
 1824  * Returns 0 if we should wait to probe (no cwnd available),
 1825  *         1 if a probe was sent,
 1826  *         -1 otherwise
 1827  */
 1828 static int tcp_mtu_probe(struct sock *sk)
 1829 {
 1830         struct tcp_sock *tp = tcp_sk(sk);
 1831         struct inet_connection_sock *icsk = inet_csk(sk);
 1832         struct sk_buff *skb, *nskb, *next;
 1833         int len;
 1834         int probe_size;
 1835         int size_needed;
 1836         int copy;
 1837         int mss_now;
 1838 
 1839         /* Not currently probing/verifying,
 1840          * not in recovery,
 1841          * have enough cwnd, and
 1842          * not SACKing (the variable headers throw things off) */
 1843         if (!icsk->icsk_mtup.enabled ||
 1844             icsk->icsk_mtup.probe_size ||
 1845             inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
 1846             tp->snd_cwnd < 11 ||
 1847             tp->rx_opt.num_sacks || tp->rx_opt.dsack)
 1848                 return -1;
 1849 
 1850         /* Very simple search strategy: just double the MSS. */
 1851         mss_now = tcp_current_mss(sk);
 1852         probe_size = 2 * tp->mss_cache;
 1853         size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
 1854         if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high)) {
 1855                 /* TODO: set timer for probe_converge_event */
 1856                 return -1;
 1857         }
 1858 
 1859         /* Have enough data in the send queue to probe? */
 1860         if (tp->write_seq - tp->snd_nxt < size_needed)
 1861                 return -1;
 1862 
 1863         if (tp->snd_wnd < size_needed)
 1864                 return -1;
 1865         if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
 1866                 return 0;
 1867 
 1868         /* Do we need to wait to drain cwnd? With none in flight, don't stall */
 1869         if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
 1870                 if (!tcp_packets_in_flight(tp))
 1871                         return -1;
 1872                 else
 1873                         return 0;
 1874         }
 1875 
 1876         /* We're allowed to probe.  Build it now. */
 1877         if ((nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC)) == NULL)
 1878                 return -1;
 1879         sk->sk_wmem_queued += nskb->truesize;
 1880         sk_mem_charge(sk, nskb->truesize);
 1881 
 1882         skb = tcp_send_head(sk);
 1883 
 1884         TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
 1885         TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
 1886         TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
 1887         TCP_SKB_CB(nskb)->sacked = 0;
 1888         nskb->csum = 0;
 1889         nskb->ip_summed = skb->ip_summed;
 1890 
 1891         tcp_insert_write_queue_before(nskb, skb, sk);
 1892 
 1893         len = 0;
 1894         tcp_for_write_queue_from_safe(skb, next, sk) {
 1895                 copy = min_t(int, skb->len, probe_size - len);
 1896                 if (nskb->ip_summed)
 1897                         skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
 1898                 else
 1899                         nskb->csum = skb_copy_and_csum_bits(skb, 0,
 1900                                                             skb_put(nskb, copy),
 1901                                                             copy, nskb->csum);
 1902 
 1903                 if (skb->len <= copy) {
 1904                         /* We've eaten all the data from this skb.
 1905                          * Throw it away. */
 1906                         TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
 1907                         tcp_unlink_write_queue(skb, sk);
 1908                         sk_wmem_free_skb(sk, skb);
 1909                 } else {
 1910                         TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
 1911                                                    ~(TCPHDR_FIN|TCPHDR_PSH);
 1912                         if (!skb_shinfo(skb)->nr_frags) {
 1913                                 skb_pull(skb, copy);
 1914                                 if (skb->ip_summed != CHECKSUM_PARTIAL)
 1915                                         skb->csum = csum_partial(skb->data,
 1916                                                                  skb->len, 0);
 1917                         } else {
 1918                                 __pskb_trim_head(skb, copy);
 1919                                 tcp_set_skb_tso_segs(sk, skb, mss_now);
 1920                         }
 1921                         TCP_SKB_CB(skb)->seq += copy;
 1922                 }
 1923 
 1924                 len += copy;
 1925 
 1926                 if (len >= probe_size)
 1927                         break;
 1928         }
 1929         tcp_init_tso_segs(sk, nskb, nskb->len);
 1930 
 1931         /* We're ready to send.  If this fails, the probe will
 1932          * be resegmented into mss-sized pieces by tcp_write_xmit(). */
 1933         TCP_SKB_CB(nskb)->when = tcp_time_stamp;
 1934         if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
 1935                 /* Decrement cwnd here because we are sending
 1936                  * effectively two packets. */
 1937                 tp->snd_cwnd--;
 1938                 tcp_event_new_data_sent(sk, nskb);
 1939 
 1940                 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
 1941                 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
 1942                 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
 1943 
 1944                 return 1;
 1945         }
 1946 
 1947         return -1;
 1948 }
 1949 
 1950 /* This routine writes packets to the network.  It advances the
 1951  * send_head.  This happens as incoming acks open up the remote
 1952  * window for us.
 1953  *
 1954  * LARGESEND note: !tcp_urg_mode is overkill, only frames between
 1955  * snd_up-64k-mss .. snd_up cannot be large. However, taking into
 1956  * account rare use of URG, this is not a big flaw.
 1957  *
 1958  * Returns true, if no segments are in flight and we have queued segments,
 1959  * but cannot send anything now because of SWS or another problem.
 1960  */
 1961 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
 1962                            int push_one, gfp_t gfp)
 1963 {
 1964         struct tcp_sock *tp = tcp_sk(sk);
 1965         struct sk_buff *skb;
 1966         unsigned int tso_segs, sent_pkts;
 1967         int cwnd_quota;
 1968         int result;
 1969 
 1970         sent_pkts = 0;
 1971 
 1972         if (!push_one) {
 1973                 /* Do MTU probing. */
 1974                 result = tcp_mtu_probe(sk);
 1975                 if (!result) {
 1976                         return false;
 1977                 } else if (result > 0) {
 1978                         sent_pkts = 1;
 1979                 }
 1980         }
 1981 
 1982         while ((skb = tcp_send_head(sk))) {
 1983                 unsigned int limit;
 1984 
 1985 
 1986                 tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
 1987                 BUG_ON(!tso_segs);
 1988 
 1989                 if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE)
 1990                         goto repair; /* Skip network transmission */
 1991 
 1992                 cwnd_quota = tcp_cwnd_test(tp, skb);
 1993                 if (!cwnd_quota)
 1994                         break;
 1995 
 1996                 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
 1997                         break;
 1998 
 1999                 if (tso_segs == 1) {
 2000                         if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
 2001                                                      (tcp_skb_is_last(sk, skb) ?
 2002                                                       nonagle : TCP_NAGLE_PUSH))))
 2003                                 break;
 2004                 } else {
 2005                         if (!push_one && tcp_tso_should_defer(sk, skb))
 2006                                 break;
 2007                 }
 2008 
 2009                 /* TSQ : sk_wmem_alloc accounts skb truesize,
 2010                  * including skb overhead. But thats OK.
 2011                  */
 2012                 if (atomic_read(&sk->sk_wmem_alloc) >= sysctl_tcp_limit_output_bytes) {
 2013                         set_bit(TSQ_THROTTLED, &tp->tsq_flags);
 2014                         break;
 2015                 }
 2016                 limit = mss_now;
 2017                 if (tso_segs > 1 && !tcp_urg_mode(tp))
 2018                         limit = tcp_mss_split_point(sk, skb, mss_now,
 2019                                                     min_t(unsigned int,
 2020                                                           cwnd_quota,
 2021                                                           sk->sk_gso_max_segs));
 2022 
 2023                 if (skb->len > limit &&
 2024                     unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
 2025                         break;
 2026 
 2027                 TCP_SKB_CB(skb)->when = tcp_time_stamp;
 2028 
 2029                 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
 2030                         break;
 2031 
 2032 repair:
 2033                 /* Advance the send_head.  This one is sent out.
 2034                  * This call will increment packets_out.
 2035                  */
 2036                 tcp_event_new_data_sent(sk, skb);
 2037 
 2038                 tcp_minshall_update(tp, mss_now, skb);
 2039                 sent_pkts += tcp_skb_pcount(skb);
 2040 
 2041                 if (push_one)
 2042                         break;
 2043         }
 2044 
 2045         if (likely(sent_pkts)) {
 2046                 if (tcp_in_cwnd_reduction(sk))
 2047                         tp->prr_out += sent_pkts;
 2048                 tcp_cwnd_validate(sk);
 2049                 return false;
 2050         }
 2051         return !tp->packets_out && tcp_send_head(sk);
 2052 }
 2053 
 2054 /* Push out any pending frames which were held back due to
 2055  * TCP_CORK or attempt at coalescing tiny packets.
 2056  * The socket must be locked by the caller.
 2057  */
 2058 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
 2059                                int nonagle)
 2060 {
 2061         /* If we are closed, the bytes will have to remain here.
 2062          * In time closedown will finish, we empty the write queue and
 2063          * all will be happy.
 2064          */
 2065         if (unlikely(sk->sk_state == TCP_CLOSE))
 2066                 return;
 2067 
 2068         if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
 2069                            sk_gfp_atomic(sk, GFP_ATOMIC)))
 2070                 tcp_check_probe_timer(sk);
 2071 }
 2072 
 2073 /* Send _single_ skb sitting at the send head. This function requires
 2074  * true push pending frames to setup probe timer etc.
 2075  */
 2076 void tcp_push_one(struct sock *sk, unsigned int mss_now)
 2077 {
 2078         struct sk_buff *skb = tcp_send_head(sk);
 2079 
 2080         BUG_ON(!skb || skb->len < mss_now);
 2081 
 2082         tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
 2083 }
 2084 
 2085 /* This function returns the amount that we can raise the
 2086  * usable window based on the following constraints
 2087  *
 2088  * 1. The window can never be shrunk once it is offered (RFC 793)
 2089  * 2. We limit memory per socket
 2090  *
 2091  * RFC 1122:
 2092  * "the suggested [SWS] avoidance algorithm for the receiver is to keep
 2093  *  RECV.NEXT + RCV.WIN fixed until:
 2094  *  RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
 2095  *
 2096  * i.e. don't raise the right edge of the window until you can raise
 2097  * it at least MSS bytes.
 2098  *
 2099  * Unfortunately, the recommended algorithm breaks header prediction,
 2100  * since header prediction assumes th->window stays fixed.
 2101  *
 2102  * Strictly speaking, keeping th->window fixed violates the receiver
 2103  * side SWS prevention criteria. The problem is that under this rule
 2104  * a stream of single byte packets will cause the right side of the
 2105  * window to always advance by a single byte.
 2106  *
 2107  * Of course, if the sender implements sender side SWS prevention
 2108  * then this will not be a problem.
 2109  *
 2110  * BSD seems to make the following compromise:
 2111  *
 2112  *      If the free space is less than the 1/4 of the maximum
 2113  *      space available and the free space is less than 1/2 mss,
 2114  *      then set the window to 0.
 2115  *      [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
 2116  *      Otherwise, just prevent the window from shrinking
 2117  *      and from being larger than the largest representable value.
 2118  *
 2119  * This prevents incremental opening of the window in the regime
 2120  * where TCP is limited by the speed of the reader side taking
 2121  * data out of the TCP receive queue. It does nothing about
 2122  * those cases where the window is constrained on the sender side
 2123  * because the pipeline is full.
 2124  *
 2125  * BSD also seems to "accidentally" limit itself to windows that are a
 2126  * multiple of MSS, at least until the free space gets quite small.
 2127  * This would appear to be a side effect of the mbuf implementation.
 2128  * Combining these two algorithms results in the observed behavior
 2129  * of having a fixed window size at almost all times.
 2130  *
 2131  * Below we obtain similar behavior by forcing the offered window to
 2132  * a multiple of the mss when it is feasible to do so.
 2133  *
 2134  * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
 2135  * Regular options like TIMESTAMP are taken into account.
 2136  */
 2137 u32 __tcp_select_window(struct sock *sk)
 2138 {
 2139         struct inet_connection_sock *icsk = inet_csk(sk);
 2140         struct tcp_sock *tp = tcp_sk(sk);
 2141         /* MSS for the peer's data.  Previous versions used mss_clamp
 2142          * here.  I don't know if the value based on our guesses
 2143          * of peer's MSS is better for the performance.  It's more correct
 2144          * but may be worse for the performance because of rcv_mss
 2145          * fluctuations.  --SAW  1998/11/1
 2146          */
 2147         int mss = icsk->icsk_ack.rcv_mss;
 2148         int free_space = tcp_space(sk);
 2149         int full_space = min_t(int, tp->window_clamp, tcp_full_space(sk));
 2150         int window;
 2151 
 2152         if (mss > full_space)
 2153                 mss = full_space;
 2154 
 2155         if (free_space < (full_space >> 1)) {
 2156                 icsk->icsk_ack.quick = 0;
 2157 
 2158                 if (sk_under_memory_pressure(sk))
 2159                         tp->rcv_ssthresh = min(tp->rcv_ssthresh,
 2160                                                4U * tp->advmss);
 2161 
 2162                 if (free_space < mss)
 2163                         return 0;
 2164         }
 2165 
 2166         if (free_space > tp->rcv_ssthresh)
 2167                 free_space = tp->rcv_ssthresh;
 2168 
 2169         /* Don't do rounding if we are using window scaling, since the
 2170          * scaled window will not line up with the MSS boundary anyway.
 2171          */
 2172         window = tp->rcv_wnd;
 2173         if (tp->rx_opt.rcv_wscale) {
 2174                 window = free_space;
 2175 
 2176                 /* Advertise enough space so that it won't get scaled away.
 2177                  * Import case: prevent zero window announcement if
 2178                  * 1<<rcv_wscale > mss.
 2179                  */
 2180                 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
 2181                         window = (((window >> tp->rx_opt.rcv_wscale) + 1)
 2182                                   << tp->rx_opt.rcv_wscale);
 2183         } else {
 2184                 /* Get the largest window that is a nice multiple of mss.
 2185                  * Window clamp already applied above.
 2186                  * If our current window offering is within 1 mss of the
 2187                  * free space we just keep it. This prevents the divide
 2188                  * and multiply from happening most of the time.
 2189                  * We also don't do any window rounding when the free space
 2190                  * is too small.
 2191                  */
 2192                 if (window <= free_space - mss || window > free_space)
 2193                         window = (free_space / mss) * mss;
 2194                 else if (mss == full_space &&
 2195                          free_space > window + (full_space >> 1))
 2196                         window = free_space;
 2197         }
 2198 
 2199         return window;
 2200 }
 2201 
 2202 /* Collapses two adjacent SKB's during retransmission. */
 2203 static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
 2204 {
 2205         struct tcp_sock *tp = tcp_sk(sk);
 2206         struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
 2207         int skb_size, next_skb_size;
 2208 
 2209         skb_size = skb->len;
 2210         next_skb_size = next_skb->len;
 2211 
 2212         BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
 2213 
 2214         tcp_highest_sack_combine(sk, next_skb, skb);
 2215 
 2216         tcp_unlink_write_queue(next_skb, sk);
 2217 
 2218         skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
 2219                                   next_skb_size);
 2220 
 2221         if (next_skb->ip_summed == CHECKSUM_PARTIAL)
 2222                 skb->ip_summed = CHECKSUM_PARTIAL;
 2223 
 2224         if (skb->ip_summed != CHECKSUM_PARTIAL)
 2225                 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
 2226 
 2227         /* Update sequence range on original skb. */
 2228         TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
 2229 
 2230         /* Merge over control information. This moves PSH/FIN etc. over */
 2231         TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
 2232 
 2233         /* All done, get rid of second SKB and account for it so
 2234          * packet counting does not break.
 2235          */
 2236         TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
 2237 
 2238         /* changed transmit queue under us so clear hints */
 2239         tcp_clear_retrans_hints_partial(tp);
 2240         if (next_skb == tp->retransmit_skb_hint)
 2241                 tp->retransmit_skb_hint = skb;
 2242 
 2243         tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
 2244 
 2245         sk_wmem_free_skb(sk, next_skb);
 2246 }
 2247 
 2248 /* Check if coalescing SKBs is legal. */
 2249 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
 2250 {
 2251         if (tcp_skb_pcount(skb) > 1)
 2252                 return false;
 2253         /* TODO: SACK collapsing could be used to remove this condition */
 2254         if (skb_shinfo(skb)->nr_frags != 0)
 2255                 return false;
 2256         if (skb_cloned(skb))
 2257                 return false;
 2258         if (skb == tcp_send_head(sk))
 2259                 return false;
 2260         /* Some heurestics for collapsing over SACK'd could be invented */
 2261         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
 2262                 return false;
 2263 
 2264         return true;
 2265 }
 2266 
 2267 /* Collapse packets in the retransmit queue to make to create
 2268  * less packets on the wire. This is only done on retransmission.
 2269  */
 2270 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
 2271                                      int space)
 2272 {
 2273         struct tcp_sock *tp = tcp_sk(sk);
 2274         struct sk_buff *skb = to, *tmp;
 2275         bool first = true;
 2276 
 2277         if (!sysctl_tcp_retrans_collapse)
 2278                 return;
 2279         if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
 2280                 return;
 2281 
 2282         tcp_for_write_queue_from_safe(skb, tmp, sk) {
 2283                 if (!tcp_can_collapse(sk, skb))
 2284                         break;
 2285 
 2286                 space -= skb->len;
 2287 
 2288                 if (first) {
 2289                         first = false;
 2290                         continue;
 2291                 }
 2292 
 2293                 if (space < 0)
 2294                         break;
 2295                 /* Punt if not enough space exists in the first SKB for
 2296                  * the data in the second
 2297                  */
 2298                 if (skb->len > skb_availroom(to))
 2299                         break;
 2300 
 2301                 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
 2302                         break;
 2303 
 2304                 tcp_collapse_retrans(sk, to);
 2305         }
 2306 }
 2307 
 2308 /* This retransmits one SKB.  Policy decisions and retransmit queue
 2309  * state updates are done by the caller.  Returns non-zero if an
 2310  * error occurred which prevented the send.
 2311  */
 2312 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
 2313 {
 2314         struct tcp_sock *tp = tcp_sk(sk);
 2315         struct inet_connection_sock *icsk = inet_csk(sk);
 2316         unsigned int cur_mss;
 2317 
 2318         /* Inconslusive MTU probe */
 2319         if (icsk->icsk_mtup.probe_size) {
 2320                 icsk->icsk_mtup.probe_size = 0;
 2321         }
 2322 
 2323         /* Do not sent more than we queued. 1/4 is reserved for possible
 2324          * copying overhead: fragmentation, tunneling, mangling etc.
 2325          */
 2326         if (atomic_read(&sk->sk_wmem_alloc) >
 2327             min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
 2328                 return -EAGAIN;
 2329 
 2330         if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
 2331                 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
 2332                         BUG();
 2333                 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
 2334                         return -ENOMEM;
 2335         }
 2336 
 2337         if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
 2338                 return -EHOSTUNREACH; /* Routing failure or similar. */
 2339 
 2340         cur_mss = tcp_current_mss(sk);
 2341 
 2342         /* If receiver has shrunk his window, and skb is out of
 2343          * new window, do not retransmit it. The exception is the
 2344          * case, when window is shrunk to zero. In this case
 2345          * our retransmit serves as a zero window probe.
 2346          */
 2347         if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
 2348             TCP_SKB_CB(skb)->seq != tp->snd_una)
 2349                 return -EAGAIN;
 2350 
 2351         if (skb->len > cur_mss) {
 2352                 if (tcp_fragment(sk, skb, cur_mss, cur_mss))
 2353                         return -ENOMEM; /* We'll try again later. */
 2354         } else {
 2355                 int oldpcount = tcp_skb_pcount(skb);
 2356 
 2357                 if (unlikely(oldpcount > 1)) {
 2358                         tcp_init_tso_segs(sk, skb, cur_mss);
 2359                         tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
 2360                 }
 2361         }
 2362 
 2363         tcp_retrans_try_collapse(sk, skb, cur_mss);
 2364 
 2365         /* Some Solaris stacks overoptimize and ignore the FIN on a
 2366          * retransmit when old data is attached.  So strip it off
 2367          * since it is cheap to do so and saves bytes on the network.
 2368          */
 2369         if (skb->len > 0 &&
 2370             (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
 2371             tp->snd_una == (TCP_SKB_CB(skb)->end_seq - 1)) {
 2372                 if (!pskb_trim(skb, 0)) {
 2373                         /* Reuse, even though it does some unnecessary work */
 2374                         tcp_init_nondata_skb(skb, TCP_SKB_CB(skb)->end_seq - 1,
 2375                                              TCP_SKB_CB(skb)->tcp_flags);
 2376                         skb->ip_summed = CHECKSUM_NONE;
 2377                 }
 2378         }
 2379 
 2380         /* Make a copy, if the first transmission SKB clone we made
 2381          * is still in somebody's hands, else make a clone.
 2382          */
 2383         TCP_SKB_CB(skb)->when = tcp_time_stamp;
 2384 
 2385         /* make sure skb->data is aligned on arches that require it */
 2386         if (unlikely(NET_IP_ALIGN && ((unsigned long)skb->data & 3))) {
 2387                 struct sk_buff *nskb = __pskb_copy(skb, MAX_TCP_HEADER,
 2388                                                    GFP_ATOMIC);
 2389                 return nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
 2390                               -ENOBUFS;
 2391         } else {
 2392                 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
 2393         }
 2394 }
 2395 
 2396 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
 2397 {
 2398         struct tcp_sock *tp = tcp_sk(sk);
 2399         int err = __tcp_retransmit_skb(sk, skb);
 2400 
 2401         if (err == 0) {
 2402                 /* Update global TCP statistics. */
 2403                 TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
 2404 
 2405                 tp->total_retrans++;
 2406 
 2407 #if FASTRETRANS_DEBUG > 0
 2408                 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
 2409                         net_dbg_ratelimited("retrans_out leaked\n");
 2410                 }
 2411 #endif
 2412                 if (!tp->retrans_out)
 2413                         tp->lost_retrans_low = tp->snd_nxt;
 2414                 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
 2415                 tp->retrans_out += tcp_skb_pcount(skb);
 2416 
 2417                 /* Save stamp of the first retransmit. */
 2418                 if (!tp->retrans_stamp)
 2419                         tp->retrans_stamp = TCP_SKB_CB(skb)->when;
 2420 
 2421                 tp->undo_retrans += tcp_skb_pcount(skb);
 2422 
 2423                 /* snd_nxt is stored to detect loss of retransmitted segment,
 2424                  * see tcp_input.c tcp_sacktag_write_queue().
 2425                  */
 2426                 TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
 2427         }
 2428         return err;
 2429 }
 2430 
 2431 /* Check if we forward retransmits are possible in the current
 2432  * window/congestion state.
 2433  */
 2434 static bool tcp_can_forward_retransmit(struct sock *sk)
 2435 {
 2436         const struct inet_connection_sock *icsk = inet_csk(sk);
 2437         const struct tcp_sock *tp = tcp_sk(sk);
 2438 
 2439         /* Forward retransmissions are possible only during Recovery. */
 2440         if (icsk->icsk_ca_state != TCP_CA_Recovery)
 2441                 return false;
 2442 
 2443         /* No forward retransmissions in Reno are possible. */
 2444         if (tcp_is_reno(tp))
 2445                 return false;
 2446 
 2447         /* Yeah, we have to make difficult choice between forward transmission
 2448          * and retransmission... Both ways have their merits...
 2449          *
 2450          * For now we do not retransmit anything, while we have some new
 2451          * segments to send. In the other cases, follow rule 3 for
 2452          * NextSeg() specified in RFC3517.
 2453          */
 2454 
 2455         if (tcp_may_send_now(sk))
 2456                 return false;
 2457 
 2458         return true;
 2459 }
 2460 
 2461 /* This gets called after a retransmit timeout, and the initially
 2462  * retransmitted data is acknowledged.  It tries to continue
 2463  * resending the rest of the retransmit queue, until either
 2464  * we've sent it all or the congestion window limit is reached.
 2465  * If doing SACK, the first ACK which comes back for a timeout
 2466  * based retransmit packet might feed us FACK information again.
 2467  * If so, we use it to avoid unnecessarily retransmissions.
 2468  */
 2469 void tcp_xmit_retransmit_queue(struct sock *sk)
 2470 {
 2471         const struct inet_connection_sock *icsk = inet_csk(sk);
 2472         struct tcp_sock *tp = tcp_sk(sk);
 2473         struct sk_buff *skb;
 2474         struct sk_buff *hole = NULL;
 2475         u32 last_lost;
 2476         int mib_idx;
 2477         int fwd_rexmitting = 0;
 2478 
 2479         if (!tp->packets_out)
 2480                 return;
 2481 
 2482         if (!tp->lost_out)
 2483                 tp->retransmit_high = tp->snd_una;
 2484 
 2485         if (tp->retransmit_skb_hint) {
 2486                 skb = tp->retransmit_skb_hint;
 2487                 last_lost = TCP_SKB_CB(skb)->end_seq;
 2488                 if (after(last_lost, tp->retransmit_high))
 2489                         last_lost = tp->retransmit_high;
 2490         } else {
 2491                 skb = tcp_write_queue_head(sk);
 2492                 last_lost = tp->snd_una;
 2493         }
 2494 
 2495         tcp_for_write_queue_from(skb, sk) {
 2496                 __u8 sacked = TCP_SKB_CB(skb)->sacked;
 2497 
 2498                 if (skb == tcp_send_head(sk))
 2499                         break;
 2500                 /* we could do better than to assign each time */
 2501                 if (hole == NULL)
 2502                         tp->retransmit_skb_hint = skb;
 2503 
 2504                 /* Assume this retransmit will generate
 2505                  * only one packet for congestion window
 2506                  * calculation purposes.  This works because
 2507                  * tcp_retransmit_skb() will chop up the
 2508                  * packet to be MSS sized and all the
 2509                  * packet counting works out.
 2510                  */
 2511                 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
 2512                         return;
 2513 
 2514                 if (fwd_rexmitting) {
 2515 begin_fwd:
 2516                         if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
 2517                                 break;
 2518                         mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
 2519 
 2520                 } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
 2521                         tp->retransmit_high = last_lost;
 2522                         if (!tcp_can_forward_retransmit(sk))
 2523                                 break;
 2524                         /* Backtrack if necessary to non-L'ed skb */
 2525                         if (hole != NULL) {
 2526                                 skb = hole;
 2527                                 hole = NULL;
 2528                         }
 2529                         fwd_rexmitting = 1;
 2530                         goto begin_fwd;
 2531 
 2532                 } else if (!(sacked & TCPCB_LOST)) {
 2533                         if (hole == NULL && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
 2534                                 hole = skb;
 2535                         continue;
 2536 
 2537                 } else {
 2538                         last_lost = TCP_SKB_CB(skb)->end_seq;
 2539                         if (icsk->icsk_ca_state != TCP_CA_Loss)
 2540                                 mib_idx = LINUX_MIB_TCPFASTRETRANS;
 2541                         else
 2542                                 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
 2543                 }
 2544 
 2545                 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
 2546                         continue;
 2547 
 2548                 if (tcp_retransmit_skb(sk, skb)) {
 2549                         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
 2550                         return;
 2551                 }
 2552                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
 2553 
 2554                 if (tcp_in_cwnd_reduction(sk))
 2555                         tp->prr_out += tcp_skb_pcount(skb);
 2556 
 2557                 if (skb == tcp_write_queue_head(sk))
 2558                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 2559                                                   inet_csk(sk)->icsk_rto,
 2560                                                   TCP_RTO_MAX);
 2561         }
 2562 }
 2563 
 2564 /* Send a fin.  The caller locks the socket for us.  This cannot be
 2565  * allowed to fail queueing a FIN frame under any circumstances.
 2566  */
 2567 void tcp_send_fin(struct sock *sk)
 2568 {
 2569         struct tcp_sock *tp = tcp_sk(sk);
 2570         struct sk_buff *skb = tcp_write_queue_tail(sk);
 2571         int mss_now;
 2572 
 2573         /* Optimization, tack on the FIN if we have a queue of
 2574          * unsent frames.  But be careful about outgoing SACKS
 2575          * and IP options.
 2576          */
 2577         mss_now = tcp_current_mss(sk);
 2578 
 2579         if (tcp_send_head(sk) != NULL) {
 2580                 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_FIN;
 2581                 TCP_SKB_CB(skb)->end_seq++;
 2582                 tp->write_seq++;
 2583         } else {
 2584                 /* Socket is locked, keep trying until memory is available. */
 2585                 for (;;) {
 2586                         skb = alloc_skb_fclone(MAX_TCP_HEADER,
 2587                                                sk->sk_allocation);
 2588                         if (skb)
 2589                                 break;
 2590                         yield();
 2591                 }
 2592 
 2593                 /* Reserve space for headers and prepare control bits. */
 2594                 skb_reserve(skb, MAX_TCP_HEADER);
 2595                 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
 2596                 tcp_init_nondata_skb(skb, tp->write_seq,
 2597                                      TCPHDR_ACK | TCPHDR_FIN);
 2598                 tcp_queue_skb(sk, skb);
 2599         }
 2600         __tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_OFF);
 2601 }
 2602 
 2603 /* We get here when a process closes a file descriptor (either due to
 2604  * an explicit close() or as a byproduct of exit()'ing) and there
 2605  * was unread data in the receive queue.  This behavior is recommended
 2606  * by RFC 2525, section 2.17.  -DaveM
 2607  */
 2608 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
 2609 {
 2610         struct sk_buff *skb;
 2611 
 2612         /* NOTE: No TCP options attached and we never retransmit this. */
 2613         skb = alloc_skb(MAX_TCP_HEADER, priority);
 2614         if (!skb) {
 2615                 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
 2616                 return;
 2617         }
 2618 
 2619         /* Reserve space for headers and prepare control bits. */
 2620         skb_reserve(skb, MAX_TCP_HEADER);
 2621         tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
 2622                              TCPHDR_ACK | TCPHDR_RST);
 2623         /* Send it off. */
 2624         TCP_SKB_CB(skb)->when = tcp_time_stamp;
 2625         if (tcp_transmit_skb(sk, skb, 0, priority))
 2626                 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
 2627 
 2628         TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
 2629 }
 2630 
 2631 /* Send a crossed SYN-ACK during socket establishment.
 2632  * WARNING: This routine must only be called when we have already sent
 2633  * a SYN packet that crossed the incoming SYN that caused this routine
 2634  * to get called. If this assumption fails then the initial rcv_wnd
 2635  * and rcv_wscale values will not be correct.
 2636  */
 2637 int tcp_send_synack(struct sock *sk)
 2638 {
 2639         struct sk_buff *skb;
 2640 
 2641         skb = tcp_write_queue_head(sk);
 2642         if (skb == NULL || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
 2643                 pr_debug("%s: wrong queue state\n", __func__);
 2644                 return -EFAULT;
 2645         }
 2646         if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
 2647                 if (skb_cloned(skb)) {
 2648                         struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
 2649                         if (nskb == NULL)
 2650                                 return -ENOMEM;
 2651                         tcp_unlink_write_queue(skb, sk);
 2652                         skb_header_release(nskb);
 2653                         __tcp_add_write_queue_head(sk, nskb);
 2654                         sk_wmem_free_skb(sk, skb);
 2655                         sk->sk_wmem_queued += nskb->truesize;
 2656                         sk_mem_charge(sk, nskb->truesize);
 2657                         skb = nskb;
 2658                 }
 2659 
 2660                 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
 2661                 TCP_ECN_send_synack(tcp_sk(sk), skb);
 2662         }
 2663         TCP_SKB_CB(skb)->when = tcp_time_stamp;
 2664         return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
 2665 }
 2666 
 2667 /**
 2668  * tcp_make_synack - Prepare a SYN-ACK.
 2669  * sk: listener socket
 2670  * dst: dst entry attached to the SYNACK
 2671  * req: request_sock pointer
 2672  * rvp: request_values pointer
 2673  *
 2674  * Allocate one skb and build a SYNACK packet.
 2675  * @dst is consumed : Caller should not use it again.
 2676  */
 2677 struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
 2678                                 struct request_sock *req,
 2679                                 struct request_values *rvp,
 2680                                 struct tcp_fastopen_cookie *foc)
 2681 {
 2682         struct tcp_out_options opts;
 2683         struct tcp_extend_values *xvp = tcp_xv(rvp);
 2684         struct inet_request_sock *ireq = inet_rsk(req);
 2685         struct tcp_sock *tp = tcp_sk(sk);
 2686         const struct tcp_cookie_values *cvp = tp->cookie_values;
 2687         struct tcphdr *th;
 2688         struct sk_buff *skb;
 2689         struct tcp_md5sig_key *md5;
 2690         int tcp_header_size;
 2691         int mss;
 2692         int s_data_desired = 0;
 2693 
 2694         if (cvp != NULL && cvp->s_data_constant && cvp->s_data_desired)
 2695                 s_data_desired = cvp->s_data_desired;
 2696         skb = alloc_skb(MAX_TCP_HEADER + 15 + s_data_desired,
 2697                         sk_gfp_atomic(sk, GFP_ATOMIC));
 2698         if (unlikely(!skb)) {
 2699                 dst_release(dst);
 2700                 return NULL;
 2701         }
 2702         /* Reserve space for headers. */
 2703         skb_reserve(skb, MAX_TCP_HEADER);
 2704 
 2705         skb_dst_set(skb, dst);
 2706 
 2707         mss = dst_metric_advmss(dst);
 2708         if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
 2709                 mss = tp->rx_opt.user_mss;
 2710 
 2711         if (req->rcv_wnd == 0) { /* ignored for retransmitted syns */
 2712                 __u8 rcv_wscale;
 2713                 /* Set this up on the first call only */
 2714                 req->window_clamp = tp->window_clamp ? : dst_metric(dst, RTAX_WINDOW);
 2715 
 2716                 /* limit the window selection if the user enforce a smaller rx buffer */
 2717                 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
 2718                     (req->window_clamp > tcp_full_space(sk) || req->window_clamp == 0))
 2719                         req->window_clamp = tcp_full_space(sk);
 2720 
 2721                 /* tcp_full_space because it is guaranteed to be the first packet */
 2722                 tcp_select_initial_window(tcp_full_space(sk),
 2723                         mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
 2724                         &req->rcv_wnd,
 2725                         &req->window_clamp,
 2726                         ireq->wscale_ok,
 2727                         &rcv_wscale,
 2728                         dst_metric(dst, RTAX_INITRWND));
 2729                 ireq->rcv_wscale = rcv_wscale;
 2730         }
 2731 
 2732         memset(&opts, 0, sizeof(opts));
 2733 #ifdef CONFIG_SYN_COOKIES
 2734         if (unlikely(req->cookie_ts))
 2735                 TCP_SKB_CB(skb)->when = cookie_init_timestamp(req);
 2736         else
 2737 #endif
 2738         TCP_SKB_CB(skb)->when = tcp_time_stamp;
 2739         tcp_header_size = tcp_synack_options(sk, req, mss,
 2740                                              skb, &opts, &md5, xvp, foc)
 2741                         + sizeof(*th);
 2742 
 2743         skb_push(skb, tcp_header_size);
 2744         skb_reset_transport_header(skb);
 2745 
 2746         th = tcp_hdr(skb);
 2747         memset(th, 0, sizeof(struct tcphdr));
 2748         th->syn = 1;
 2749         th->ack = 1;
 2750         TCP_ECN_make_synack(req, th);
 2751         th->source = ireq->loc_port;
 2752         th->dest = ireq->rmt_port;
 2753         /* Setting of flags are superfluous here for callers (and ECE is
 2754          * not even correctly set)
 2755          */
 2756         tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
 2757                              TCPHDR_SYN | TCPHDR_ACK);
 2758 
 2759         if (OPTION_COOKIE_EXTENSION & opts.options) {
 2760                 if (s_data_desired) {
 2761                         u8 *buf = skb_put(skb, s_data_desired);
 2762 
 2763                         /* copy data directly from the listening socket. */
 2764                         memcpy(buf, cvp->s_data_payload, s_data_desired);
 2765                         TCP_SKB_CB(skb)->end_seq += s_data_desired;
 2766                 }
 2767 
 2768                 if (opts.hash_size > 0) {
 2769                         __u32 workspace[SHA_WORKSPACE_WORDS];
 2770                         u32 *mess = &xvp->cookie_bakery[COOKIE_DIGEST_WORDS];
 2771                         u32 *tail = &mess[COOKIE_MESSAGE_WORDS-1];
 2772 
 2773                         /* Secret recipe depends on the Timestamp, (future)
 2774                          * Sequence and Acknowledgment Numbers, Initiator
 2775                          * Cookie, and others handled by IP variant caller.
 2776                          */
 2777                         *tail-- ^= opts.tsval;
 2778                         *tail-- ^= tcp_rsk(req)->rcv_isn + 1;
 2779                         *tail-- ^= TCP_SKB_CB(skb)->seq + 1;
 2780 
 2781                         /* recommended */
 2782                         *tail-- ^= (((__force u32)th->dest << 16) | (__force u32)th->source);
 2783                         *tail-- ^= (u32)(unsigned long)cvp; /* per sockopt */
 2784 
 2785                         sha_transform((__u32 *)&xvp->cookie_bakery[0],
 2786                                       (char *)mess,
 2787                                       &workspace[0]);
 2788                         opts.hash_location =
 2789                                 (__u8 *)&xvp->cookie_bakery[0];
 2790                 }
 2791         }
 2792 
 2793         th->seq = htonl(TCP_SKB_CB(skb)->seq);
 2794         /* XXX data is queued and acked as is. No buffer/window check */
 2795         th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);
 2796 
 2797         /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
 2798         th->window = htons(min(req->rcv_wnd, 65535U));
 2799         tcp_options_write((__be32 *)(th + 1), tp, &opts);
 2800         th->doff = (tcp_header_size >> 2);
 2801         TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS, tcp_skb_pcount(skb));
 2802 
 2803 #ifdef CONFIG_TCP_MD5SIG
 2804         /* Okay, we have all we need - do the md5 hash if needed */
 2805         if (md5) {
 2806                 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
 2807                                                md5, NULL, req, skb);
 2808         }
 2809 #endif
 2810 
 2811         return skb;
 2812 }
 2813 EXPORT_SYMBOL(tcp_make_synack);
 2814 
 2815 /* Do all connect socket setups that can be done AF independent. */
 2816 void tcp_connect_init(struct sock *sk)
 2817 {
 2818         const struct dst_entry *dst = __sk_dst_get(sk);
 2819         struct tcp_sock *tp = tcp_sk(sk);
 2820         __u8 rcv_wscale;
 2821 
 2822         /* We'll fix this up when we get a response from the other end.
 2823          * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
 2824          */
 2825         tp->tcp_header_len = sizeof(struct tcphdr) +
 2826                 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
 2827 
 2828 #ifdef CONFIG_TCP_MD5SIG
 2829         if (tp->af_specific->md5_lookup(sk, sk) != NULL)
 2830                 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
 2831 #endif
 2832 
 2833         /* If user gave his TCP_MAXSEG, record it to clamp */
 2834         if (tp->rx_opt.user_mss)
 2835                 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
 2836         tp->max_window = 0;
 2837         tcp_mtup_init(sk);
 2838         tcp_sync_mss(sk, dst_mtu(dst));
 2839 
 2840         if (!tp->window_clamp)
 2841                 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
 2842         tp->advmss = dst_metric_advmss(dst);
 2843         if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
 2844                 tp->advmss = tp->rx_opt.user_mss;
 2845 
 2846         tcp_initialize_rcv_mss(sk);
 2847 
 2848         /* limit the window selection if the user enforce a smaller rx buffer */
 2849         if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
 2850             (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
 2851                 tp->window_clamp = tcp_full_space(sk);
 2852 
 2853         tcp_select_initial_window(tcp_full_space(sk),
 2854                                   tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
 2855                                   &tp->rcv_wnd,
 2856                                   &tp->window_clamp,
 2857                                   sysctl_tcp_window_scaling,
 2858                                   &rcv_wscale,
 2859                                   dst_metric(dst, RTAX_INITRWND));
 2860 
 2861         tp->rx_opt.rcv_wscale = rcv_wscale;
 2862         tp->rcv_ssthresh = tp->rcv_wnd;
 2863 
 2864         sk->sk_err = 0;
 2865         sock_reset_flag(sk, SOCK_DONE);
 2866         tp->snd_wnd = 0;
 2867         tcp_init_wl(tp, 0);
 2868         tp->snd_una = tp->write_seq;
 2869         tp->snd_sml = tp->write_seq;
 2870         tp->snd_up = tp->write_seq;
 2871         tp->snd_nxt = tp->write_seq;
 2872 
 2873         if (likely(!tp->repair))
 2874                 tp->rcv_nxt = 0;
 2875         tp->rcv_wup = tp->rcv_nxt;
 2876         tp->copied_seq = tp->rcv_nxt;
 2877 
 2878         inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
 2879         inet_csk(sk)->icsk_retransmits = 0;
 2880         tcp_clear_retrans(tp);
 2881 }
 2882 
 2883 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
 2884 {
 2885         struct tcp_sock *tp = tcp_sk(sk);
 2886         struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
 2887 
 2888         tcb->end_seq += skb->len;
 2889         skb_header_release(skb);
 2890         __tcp_add_write_queue_tail(sk, skb);
 2891         sk->sk_wmem_queued += skb->truesize;
 2892         sk_mem_charge(sk, skb->truesize);
 2893         tp->write_seq = tcb->end_seq;
 2894         tp->packets_out += tcp_skb_pcount(skb);
 2895 }
 2896 
 2897 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
 2898  * queue a data-only packet after the regular SYN, such that regular SYNs
 2899  * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
 2900  * only the SYN sequence, the data are retransmitted in the first ACK.
 2901  * If cookie is not cached or other error occurs, falls back to send a
 2902  * regular SYN with Fast Open cookie request option.
 2903  */
 2904 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
 2905 {
 2906         struct tcp_sock *tp = tcp_sk(sk);
 2907         struct tcp_fastopen_request *fo = tp->fastopen_req;
 2908         int syn_loss = 0, space, i, err = 0, iovlen = fo->data->msg_iovlen;
 2909         struct sk_buff *syn_data = NULL, *data;
 2910         unsigned long last_syn_loss = 0;
 2911 
 2912         tp->rx_opt.mss_clamp = tp->advmss;  /* If MSS is not cached */
 2913         tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
 2914                                &syn_loss, &last_syn_loss);
 2915         /* Recurring FO SYN losses: revert to regular handshake temporarily */
 2916         if (syn_loss > 1 &&
 2917             time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
 2918                 fo->cookie.len = -1;
 2919                 goto fallback;
 2920         }
 2921 
 2922         if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
 2923                 fo->cookie.len = -1;
 2924         else if (fo->cookie.len <= 0)
 2925                 goto fallback;
 2926 
 2927         /* MSS for SYN-data is based on cached MSS and bounded by PMTU and
 2928          * user-MSS. Reserve maximum option space for middleboxes that add
 2929          * private TCP options. The cost is reduced data space in SYN :(
 2930          */
 2931         if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
 2932                 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
 2933         space = tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
 2934                 MAX_TCP_OPTION_SPACE;
 2935 
 2936         syn_data = skb_copy_expand(syn, skb_headroom(syn), space,
 2937                                    sk->sk_allocation);
 2938         if (syn_data == NULL)
 2939                 goto fallback;
 2940 
 2941         for (i = 0; i < iovlen && syn_data->len < space; ++i) {
 2942                 struct iovec *iov = &fo->data->msg_iov[i];
 2943                 unsigned char __user *from = iov->iov_base;
 2944                 int len = iov->iov_len;
 2945 
 2946                 if (syn_data->len + len > space)
 2947                         len = space - syn_data->len;
 2948                 else if (i + 1 == iovlen)
 2949                         /* No more data pending in inet_wait_for_connect() */
 2950                         fo->data = NULL;
 2951 
 2952                 if (skb_add_data(syn_data, from, len))
 2953                         goto fallback;
 2954         }
 2955 
 2956         /* Queue a data-only packet after the regular SYN for retransmission */
 2957         data = pskb_copy(syn_data, sk->sk_allocation);
 2958         if (data == NULL)
 2959                 goto fallback;
 2960         TCP_SKB_CB(data)->seq++;
 2961         TCP_SKB_CB(data)->tcp_flags &= ~TCPHDR_SYN;
 2962         TCP_SKB_CB(data)->tcp_flags = (TCPHDR_ACK|TCPHDR_PSH);
 2963         tcp_connect_queue_skb(sk, data);
 2964         fo->copied = data->len;
 2965 
 2966         if (tcp_transmit_skb(sk, syn_data, 0, sk->sk_allocation) == 0) {
 2967                 tp->syn_data = (fo->copied > 0);
 2968                 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
 2969                 goto done;
 2970         }
 2971         syn_data = NULL;
 2972 
 2973 fallback:
 2974         /* Send a regular SYN with Fast Open cookie request option */
 2975         if (fo->cookie.len > 0)
 2976                 fo->cookie.len = 0;
 2977         err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
 2978         if (err)
 2979                 tp->syn_fastopen = 0;
 2980         kfree_skb(syn_data);
 2981 done:
 2982         fo->cookie.len = -1;  /* Exclude Fast Open option for SYN retries */
 2983         return err;
 2984 }
 2985 
 2986 /* Build a SYN and send it off. */
 2987 int tcp_connect(struct sock *sk)
 2988 {
 2989         struct tcp_sock *tp = tcp_sk(sk);
 2990         struct sk_buff *buff;
 2991         int err;
 2992 
 2993         tcp_connect_init(sk);
 2994 
 2995         if (unlikely(tp->repair)) {
 2996                 tcp_finish_connect(sk, NULL);
 2997                 return 0;
 2998         }
 2999 
 3000         buff = alloc_skb_fclone(MAX_TCP_HEADER + 15, sk->sk_allocation);
 3001         if (unlikely(buff == NULL))
 3002                 return -ENOBUFS;
 3003 
 3004         /* Reserve space for headers. */
 3005         skb_reserve(buff, MAX_TCP_HEADER);
 3006 
 3007         tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
 3008         tp->retrans_stamp = TCP_SKB_CB(buff)->when = tcp_time_stamp;
 3009         tcp_connect_queue_skb(sk, buff);
 3010         TCP_ECN_send_syn(sk, buff);
 3011 
 3012         /* Send off SYN; include data in Fast Open. */
 3013         err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
 3014               tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
 3015         if (err == -ECONNREFUSED)
 3016                 return err;
 3017 
 3018         /* We change tp->snd_nxt after the tcp_transmit_skb() call
 3019          * in order to make this packet get counted in tcpOutSegs.
 3020          */
 3021         tp->snd_nxt = tp->write_seq;
 3022         tp->pushed_seq = tp->write_seq;
 3023         TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
 3024 
 3025         /* Timer for repeating the SYN until an answer. */
 3026         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 3027                                   inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
 3028         return 0;
 3029 }
 3030 EXPORT_SYMBOL(tcp_connect);
 3031 
 3032 /* Send out a delayed ack, the caller does the policy checking
 3033  * to see if we should even be here.  See tcp_input.c:tcp_ack_snd_check()
 3034  * for details.
 3035  */
 3036 void tcp_send_delayed_ack(struct sock *sk)
 3037 {
 3038         struct inet_connection_sock *icsk = inet_csk(sk);
 3039         int ato = icsk->icsk_ack.ato;
 3040         unsigned long timeout;
 3041 
 3042         if (ato > TCP_DELACK_MIN) {
 3043                 const struct tcp_sock *tp = tcp_sk(sk);
 3044                 int max_ato = HZ / 2;
 3045 
 3046                 if (icsk->icsk_ack.pingpong ||
 3047                     (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
 3048                         max_ato = TCP_DELACK_MAX;
 3049 
 3050                 /* Slow path, intersegment interval is "high". */
 3051 
 3052                 /* If some rtt estimate is known, use it to bound delayed ack.
 3053                  * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
 3054                  * directly.
 3055                  */
 3056                 if (tp->srtt) {
 3057                         int rtt = max(tp->srtt >> 3, TCP_DELACK_MIN);
 3058 
 3059                         if (rtt < max_ato)
 3060                                 max_ato = rtt;
 3061                 }
 3062 
 3063                 ato = min(ato, max_ato);
 3064         }
 3065 
 3066         /* Stay within the limit we were given */
 3067         timeout = jiffies + ato;
 3068 
 3069         /* Use new timeout only if there wasn't a older one earlier. */
 3070         if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
 3071                 /* If delack timer was blocked or is about to expire,
 3072                  * send ACK now.
 3073                  */
 3074                 if (icsk->icsk_ack.blocked ||
 3075                     time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
 3076                         tcp_send_ack(sk);
 3077                         return;
 3078                 }
 3079 
 3080                 if (!time_before(timeout, icsk->icsk_ack.timeout))
 3081                         timeout = icsk->icsk_ack.timeout;
 3082         }
 3083         icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
 3084         icsk->icsk_ack.timeout = timeout;
 3085         sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
 3086 }
 3087 
 3088 /* This routine sends an ack and also updates the window. */
 3089 void tcp_send_ack(struct sock *sk)
 3090 {
 3091         struct sk_buff *buff;
 3092 
 3093         /* If we have been reset, we may not send again. */
 3094         if (sk->sk_state == TCP_CLOSE)
 3095                 return;
 3096 
 3097         /* We are not putting this on the write queue, so
 3098          * tcp_transmit_skb() will set the ownership to this
 3099          * sock.
 3100          */
 3101         buff = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
 3102         if (buff == NULL) {
 3103                 inet_csk_schedule_ack(sk);
 3104                 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
 3105                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
 3106                                           TCP_DELACK_MAX, TCP_RTO_MAX);
 3107                 return;
 3108         }
 3109 
 3110         /* Reserve space for headers and prepare control bits. */
 3111         skb_reserve(buff, MAX_TCP_HEADER);
 3112         tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
 3113 
 3114         /* Send it off, this clears delayed acks for us. */
 3115         TCP_SKB_CB(buff)->when = tcp_time_stamp;
 3116         tcp_transmit_skb(sk, buff, 0, sk_gfp_atomic(sk, GFP_ATOMIC));
 3117 }
 3118 
 3119 /* This routine sends a packet with an out of date sequence
 3120  * number. It assumes the other end will try to ack it.
 3121  *
 3122  * Question: what should we make while urgent mode?
 3123  * 4.4BSD forces sending single byte of data. We cannot send
 3124  * out of window data, because we have SND.NXT==SND.MAX...
 3125  *
 3126  * Current solution: to send TWO zero-length segments in urgent mode:
 3127  * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
 3128  * out-of-date with SND.UNA-1 to probe window.
 3129  */
 3130 static int tcp_xmit_probe_skb(struct sock *sk, int urgent)
 3131 {
 3132         struct tcp_sock *tp = tcp_sk(sk);
 3133         struct sk_buff *skb;
 3134 
 3135         /* We don't queue it, tcp_transmit_skb() sets ownership. */
 3136         skb = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
 3137         if (skb == NULL)
 3138                 return -1;
 3139 
 3140         /* Reserve space for headers and set control bits. */
 3141         skb_reserve(skb, MAX_TCP_HEADER);
 3142         /* Use a previous sequence.  This should cause the other
 3143          * end to send an ack.  Don't queue or clone SKB, just
 3144          * send it.
 3145          */
 3146         tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
 3147         TCP_SKB_CB(skb)->when = tcp_time_stamp;
 3148         return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
 3149 }
 3150 
 3151 void tcp_send_window_probe(struct sock *sk)
 3152 {
 3153         if (sk->sk_state == TCP_ESTABLISHED) {
 3154                 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
 3155                 tcp_sk(sk)->snd_nxt = tcp_sk(sk)->write_seq;
 3156                 tcp_xmit_probe_skb(sk, 0);
 3157         }
 3158 }
 3159 
 3160 /* Initiate keepalive or window probe from timer. */
 3161 int tcp_write_wakeup(struct sock *sk)
 3162 {
 3163         struct tcp_sock *tp = tcp_sk(sk);
 3164         struct sk_buff *skb;
 3165 
 3166         if (sk->sk_state == TCP_CLOSE)
 3167                 return -1;
 3168 
 3169         if ((skb = tcp_send_head(sk)) != NULL &&
 3170             before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
 3171                 int err;
 3172                 unsigned int mss = tcp_current_mss(sk);
 3173                 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
 3174 
 3175                 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
 3176                         tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
 3177 
 3178                 /* We are probing the opening of a window
 3179                  * but the window size is != 0
 3180                  * must have been a result SWS avoidance ( sender )
 3181                  */
 3182                 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
 3183                     skb->len > mss) {
 3184                         seg_size = min(seg_size, mss);
 3185                         TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
 3186                         if (tcp_fragment(sk, skb, seg_size, mss))
 3187                                 return -1;
 3188                 } else if (!tcp_skb_pcount(skb))
 3189                         tcp_set_skb_tso_segs(sk, skb, mss);
 3190 
 3191                 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
 3192                 TCP_SKB_CB(skb)->when = tcp_time_stamp;
 3193                 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
 3194                 if (!err)
 3195                         tcp_event_new_data_sent(sk, skb);
 3196                 return err;
 3197         } else {
 3198                 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
 3199                         tcp_xmit_probe_skb(sk, 1);
 3200                 return tcp_xmit_probe_skb(sk, 0);
 3201         }
 3202 }
 3203 
 3204 /* A window probe timeout has occurred.  If window is not closed send
 3205  * a partial packet else a zero probe.
 3206  */
 3207 void tcp_send_probe0(struct sock *sk)
 3208 {
 3209         struct inet_connection_sock *icsk = inet_csk(sk);
 3210         struct tcp_sock *tp = tcp_sk(sk);
 3211         int err;
 3212 
 3213         err = tcp_write_wakeup(sk);
 3214 
 3215         if (tp->packets_out || !tcp_send_head(sk)) {
 3216                 /* Cancel probe timer, if it is not required. */
 3217                 icsk->icsk_probes_out = 0;
 3218                 icsk->icsk_backoff = 0;
 3219                 return;
 3220         }
 3221 
 3222         if (err <= 0) {
 3223                 if (icsk->icsk_backoff < sysctl_tcp_retries2)
 3224                         icsk->icsk_backoff++;
 3225                 icsk->icsk_probes_out++;
 3226                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
 3227                                           min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
 3228                                           TCP_RTO_MAX);
 3229         } else {
 3230                 /* If packet was not sent due to local congestion,
 3231                  * do not backoff and do not remember icsk_probes_out.
 3232                  * Let local senders to fight for local resources.
 3233                  *
 3234                  * Use accumulated backoff yet.
 3235                  */
 3236                 if (!icsk->icsk_probes_out)
 3237                         icsk->icsk_probes_out = 1;
 3238                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
 3239                                           min(icsk->icsk_rto << icsk->icsk_backoff,
 3240                                               TCP_RESOURCE_PROBE_INTERVAL),
 3241                                           TCP_RTO_MAX);
 3242         }
 3243 }

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