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Linux/net/ipv4/tcp_output.c

  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 four TSO segments */
 54 int sysctl_tcp_limit_output_bytes __read_mostly = 262144;
 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 /* By default, RFC2861 behavior.  */
 63 int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
 64 
 65 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
 66                            int push_one, gfp_t gfp);
 67 
 68 /* Account for new data that has been sent to the network. */
 69 static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
 70 {
 71         struct inet_connection_sock *icsk = inet_csk(sk);
 72         struct tcp_sock *tp = tcp_sk(sk);
 73         unsigned int prior_packets = tp->packets_out;
 74 
 75         tcp_advance_send_head(sk, skb);
 76         tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
 77 
 78         tp->packets_out += tcp_skb_pcount(skb);
 79         if (!prior_packets || icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
 80             icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
 81                 tcp_rearm_rto(sk);
 82         }
 83 
 84         NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT,
 85                       tcp_skb_pcount(skb));
 86 }
 87 
 88 /* SND.NXT, if window was not shrunk.
 89  * If window has been shrunk, what should we make? It is not clear at all.
 90  * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
 91  * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
 92  * invalid. OK, let's make this for now:
 93  */
 94 static inline __u32 tcp_acceptable_seq(const struct sock *sk)
 95 {
 96         const struct tcp_sock *tp = tcp_sk(sk);
 97 
 98         if (!before(tcp_wnd_end(tp), tp->snd_nxt))
 99                 return tp->snd_nxt;
100         else
101                 return tcp_wnd_end(tp);
102 }
103 
104 /* Calculate mss to advertise in SYN segment.
105  * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
106  *
107  * 1. It is independent of path mtu.
108  * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
109  * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
110  *    attached devices, because some buggy hosts are confused by
111  *    large MSS.
112  * 4. We do not make 3, we advertise MSS, calculated from first
113  *    hop device mtu, but allow to raise it to ip_rt_min_advmss.
114  *    This may be overridden via information stored in routing table.
115  * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
116  *    probably even Jumbo".
117  */
118 static __u16 tcp_advertise_mss(struct sock *sk)
119 {
120         struct tcp_sock *tp = tcp_sk(sk);
121         const struct dst_entry *dst = __sk_dst_get(sk);
122         int mss = tp->advmss;
123 
124         if (dst) {
125                 unsigned int metric = dst_metric_advmss(dst);
126 
127                 if (metric < mss) {
128                         mss = metric;
129                         tp->advmss = mss;
130                 }
131         }
132 
133         return (__u16)mss;
134 }
135 
136 /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
137  * This is the first part of cwnd validation mechanism.
138  */
139 void tcp_cwnd_restart(struct sock *sk, s32 delta)
140 {
141         struct tcp_sock *tp = tcp_sk(sk);
142         u32 restart_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
143         u32 cwnd = tp->snd_cwnd;
144 
145         tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
146 
147         tp->snd_ssthresh = tcp_current_ssthresh(sk);
148         restart_cwnd = min(restart_cwnd, cwnd);
149 
150         while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
151                 cwnd >>= 1;
152         tp->snd_cwnd = max(cwnd, restart_cwnd);
153         tp->snd_cwnd_stamp = tcp_time_stamp;
154         tp->snd_cwnd_used = 0;
155 }
156 
157 /* Congestion state accounting after a packet has been sent. */
158 static void tcp_event_data_sent(struct tcp_sock *tp,
159                                 struct sock *sk)
160 {
161         struct inet_connection_sock *icsk = inet_csk(sk);
162         const u32 now = tcp_time_stamp;
163 
164         if (tcp_packets_in_flight(tp) == 0)
165                 tcp_ca_event(sk, CA_EVENT_TX_START);
166 
167         tp->lsndtime = now;
168 
169         /* If it is a reply for ato after last received
170          * packet, enter pingpong mode.
171          */
172         if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
173                 icsk->icsk_ack.pingpong = 1;
174 }
175 
176 /* Account for an ACK we sent. */
177 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
178 {
179         tcp_dec_quickack_mode(sk, pkts);
180         inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
181 }
182 
183 
184 u32 tcp_default_init_rwnd(u32 mss)
185 {
186         /* Initial receive window should be twice of TCP_INIT_CWND to
187          * enable proper sending of new unsent data during fast recovery
188          * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a
189          * limit when mss is larger than 1460.
190          */
191         u32 init_rwnd = TCP_INIT_CWND * 2;
192 
193         if (mss > 1460)
194                 init_rwnd = max((1460 * init_rwnd) / mss, 2U);
195         return init_rwnd;
196 }
197 
198 /* Determine a window scaling and initial window to offer.
199  * Based on the assumption that the given amount of space
200  * will be offered. Store the results in the tp structure.
201  * NOTE: for smooth operation initial space offering should
202  * be a multiple of mss if possible. We assume here that mss >= 1.
203  * This MUST be enforced by all callers.
204  */
205 void tcp_select_initial_window(int __space, __u32 mss,
206                                __u32 *rcv_wnd, __u32 *window_clamp,
207                                int wscale_ok, __u8 *rcv_wscale,
208                                __u32 init_rcv_wnd)
209 {
210         unsigned int space = (__space < 0 ? 0 : __space);
211 
212         /* If no clamp set the clamp to the max possible scaled window */
213         if (*window_clamp == 0)
214                 (*window_clamp) = (65535 << 14);
215         space = min(*window_clamp, space);
216 
217         /* Quantize space offering to a multiple of mss if possible. */
218         if (space > mss)
219                 space = (space / mss) * mss;
220 
221         /* NOTE: offering an initial window larger than 32767
222          * will break some buggy TCP stacks. If the admin tells us
223          * it is likely we could be speaking with such a buggy stack
224          * we will truncate our initial window offering to 32K-1
225          * unless the remote has sent us a window scaling option,
226          * which we interpret as a sign the remote TCP is not
227          * misinterpreting the window field as a signed quantity.
228          */
229         if (sysctl_tcp_workaround_signed_windows)
230                 (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
231         else
232                 (*rcv_wnd) = space;
233 
234         (*rcv_wscale) = 0;
235         if (wscale_ok) {
236                 /* Set window scaling on max possible window
237                  * See RFC1323 for an explanation of the limit to 14
238                  */
239                 space = max_t(u32, space, sysctl_tcp_rmem[2]);
240                 space = max_t(u32, space, sysctl_rmem_max);
241                 space = min_t(u32, space, *window_clamp);
242                 while (space > 65535 && (*rcv_wscale) < 14) {
243                         space >>= 1;
244                         (*rcv_wscale)++;
245                 }
246         }
247 
248         if (mss > (1 << *rcv_wscale)) {
249                 if (!init_rcv_wnd) /* Use default unless specified otherwise */
250                         init_rcv_wnd = tcp_default_init_rwnd(mss);
251                 *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
252         }
253 
254         /* Set the clamp no higher than max representable value */
255         (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
256 }
257 EXPORT_SYMBOL(tcp_select_initial_window);
258 
259 /* Chose a new window to advertise, update state in tcp_sock for the
260  * socket, and return result with RFC1323 scaling applied.  The return
261  * value can be stuffed directly into th->window for an outgoing
262  * frame.
263  */
264 static u16 tcp_select_window(struct sock *sk)
265 {
266         struct tcp_sock *tp = tcp_sk(sk);
267         u32 old_win = tp->rcv_wnd;
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                 if (new_win == 0)
281                         NET_INC_STATS(sock_net(sk),
282                                       LINUX_MIB_TCPWANTZEROWINDOWADV);
283                 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
284         }
285         tp->rcv_wnd = new_win;
286         tp->rcv_wup = tp->rcv_nxt;
287 
288         /* Make sure we do not exceed the maximum possible
289          * scaled window.
290          */
291         if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
292                 new_win = min(new_win, MAX_TCP_WINDOW);
293         else
294                 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
295 
296         /* RFC1323 scaling applied */
297         new_win >>= tp->rx_opt.rcv_wscale;
298 
299         /* If we advertise zero window, disable fast path. */
300         if (new_win == 0) {
301                 tp->pred_flags = 0;
302                 if (old_win)
303                         NET_INC_STATS(sock_net(sk),
304                                       LINUX_MIB_TCPTOZEROWINDOWADV);
305         } else if (old_win == 0) {
306                 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
307         }
308 
309         return new_win;
310 }
311 
312 /* Packet ECN state for a SYN-ACK */
313 static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
314 {
315         const struct tcp_sock *tp = tcp_sk(sk);
316 
317         TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
318         if (!(tp->ecn_flags & TCP_ECN_OK))
319                 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
320         else if (tcp_ca_needs_ecn(sk))
321                 INET_ECN_xmit(sk);
322 }
323 
324 /* Packet ECN state for a SYN.  */
325 static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
326 {
327         struct tcp_sock *tp = tcp_sk(sk);
328         bool use_ecn = sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 ||
329                        tcp_ca_needs_ecn(sk);
330 
331         if (!use_ecn) {
332                 const struct dst_entry *dst = __sk_dst_get(sk);
333 
334                 if (dst && dst_feature(dst, RTAX_FEATURE_ECN))
335                         use_ecn = true;
336         }
337 
338         tp->ecn_flags = 0;
339 
340         if (use_ecn) {
341                 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
342                 tp->ecn_flags = TCP_ECN_OK;
343                 if (tcp_ca_needs_ecn(sk))
344                         INET_ECN_xmit(sk);
345         }
346 }
347 
348 static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
349 {
350         if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback)
351                 /* tp->ecn_flags are cleared at a later point in time when
352                  * SYN ACK is ultimatively being received.
353                  */
354                 TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR);
355 }
356 
357 static void
358 tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th)
359 {
360         if (inet_rsk(req)->ecn_ok)
361                 th->ece = 1;
362 }
363 
364 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
365  * be sent.
366  */
367 static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
368                          struct tcphdr *th, int tcp_header_len)
369 {
370         struct tcp_sock *tp = tcp_sk(sk);
371 
372         if (tp->ecn_flags & TCP_ECN_OK) {
373                 /* Not-retransmitted data segment: set ECT and inject CWR. */
374                 if (skb->len != tcp_header_len &&
375                     !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
376                         INET_ECN_xmit(sk);
377                         if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
378                                 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
379                                 th->cwr = 1;
380                                 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
381                         }
382                 } else if (!tcp_ca_needs_ecn(sk)) {
383                         /* ACK or retransmitted segment: clear ECT|CE */
384                         INET_ECN_dontxmit(sk);
385                 }
386                 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
387                         th->ece = 1;
388         }
389 }
390 
391 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
392  * auto increment end seqno.
393  */
394 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
395 {
396         skb->ip_summed = CHECKSUM_PARTIAL;
397         skb->csum = 0;
398 
399         TCP_SKB_CB(skb)->tcp_flags = flags;
400         TCP_SKB_CB(skb)->sacked = 0;
401 
402         tcp_skb_pcount_set(skb, 1);
403 
404         TCP_SKB_CB(skb)->seq = seq;
405         if (flags & (TCPHDR_SYN | TCPHDR_FIN))
406                 seq++;
407         TCP_SKB_CB(skb)->end_seq = seq;
408 }
409 
410 static inline bool tcp_urg_mode(const struct tcp_sock *tp)
411 {
412         return tp->snd_una != tp->snd_up;
413 }
414 
415 #define OPTION_SACK_ADVERTISE   (1 << 0)
416 #define OPTION_TS               (1 << 1)
417 #define OPTION_MD5              (1 << 2)
418 #define OPTION_WSCALE           (1 << 3)
419 #define OPTION_FAST_OPEN_COOKIE (1 << 8)
420 
421 struct tcp_out_options {
422         u16 options;            /* bit field of OPTION_* */
423         u16 mss;                /* 0 to disable */
424         u8 ws;                  /* window scale, 0 to disable */
425         u8 num_sack_blocks;     /* number of SACK blocks to include */
426         u8 hash_size;           /* bytes in hash_location */
427         __u8 *hash_location;    /* temporary pointer, overloaded */
428         __u32 tsval, tsecr;     /* need to include OPTION_TS */
429         struct tcp_fastopen_cookie *fastopen_cookie;    /* Fast open cookie */
430 };
431 
432 /* Write previously computed TCP options to the packet.
433  *
434  * Beware: Something in the Internet is very sensitive to the ordering of
435  * TCP options, we learned this through the hard way, so be careful here.
436  * Luckily we can at least blame others for their non-compliance but from
437  * inter-operability perspective it seems that we're somewhat stuck with
438  * the ordering which we have been using if we want to keep working with
439  * those broken things (not that it currently hurts anybody as there isn't
440  * particular reason why the ordering would need to be changed).
441  *
442  * At least SACK_PERM as the first option is known to lead to a disaster
443  * (but it may well be that other scenarios fail similarly).
444  */
445 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
446                               struct tcp_out_options *opts)
447 {
448         u16 options = opts->options;    /* mungable copy */
449 
450         if (unlikely(OPTION_MD5 & options)) {
451                 *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
452                                (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
453                 /* overload cookie hash location */
454                 opts->hash_location = (__u8 *)ptr;
455                 ptr += 4;
456         }
457 
458         if (unlikely(opts->mss)) {
459                 *ptr++ = htonl((TCPOPT_MSS << 24) |
460                                (TCPOLEN_MSS << 16) |
461                                opts->mss);
462         }
463 
464         if (likely(OPTION_TS & options)) {
465                 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
466                         *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
467                                        (TCPOLEN_SACK_PERM << 16) |
468                                        (TCPOPT_TIMESTAMP << 8) |
469                                        TCPOLEN_TIMESTAMP);
470                         options &= ~OPTION_SACK_ADVERTISE;
471                 } else {
472                         *ptr++ = htonl((TCPOPT_NOP << 24) |
473                                        (TCPOPT_NOP << 16) |
474                                        (TCPOPT_TIMESTAMP << 8) |
475                                        TCPOLEN_TIMESTAMP);
476                 }
477                 *ptr++ = htonl(opts->tsval);
478                 *ptr++ = htonl(opts->tsecr);
479         }
480 
481         if (unlikely(OPTION_SACK_ADVERTISE & options)) {
482                 *ptr++ = htonl((TCPOPT_NOP << 24) |
483                                (TCPOPT_NOP << 16) |
484                                (TCPOPT_SACK_PERM << 8) |
485                                TCPOLEN_SACK_PERM);
486         }
487 
488         if (unlikely(OPTION_WSCALE & options)) {
489                 *ptr++ = htonl((TCPOPT_NOP << 24) |
490                                (TCPOPT_WINDOW << 16) |
491                                (TCPOLEN_WINDOW << 8) |
492                                opts->ws);
493         }
494 
495         if (unlikely(opts->num_sack_blocks)) {
496                 struct tcp_sack_block *sp = tp->rx_opt.dsack ?
497                         tp->duplicate_sack : tp->selective_acks;
498                 int this_sack;
499 
500                 *ptr++ = htonl((TCPOPT_NOP  << 24) |
501                                (TCPOPT_NOP  << 16) |
502                                (TCPOPT_SACK <<  8) |
503                                (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
504                                                      TCPOLEN_SACK_PERBLOCK)));
505 
506                 for (this_sack = 0; this_sack < opts->num_sack_blocks;
507                      ++this_sack) {
508                         *ptr++ = htonl(sp[this_sack].start_seq);
509                         *ptr++ = htonl(sp[this_sack].end_seq);
510                 }
511 
512                 tp->rx_opt.dsack = 0;
513         }
514 
515         if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
516                 struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
517                 u8 *p = (u8 *)ptr;
518                 u32 len; /* Fast Open option length */
519 
520                 if (foc->exp) {
521                         len = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
522                         *ptr = htonl((TCPOPT_EXP << 24) | (len << 16) |
523                                      TCPOPT_FASTOPEN_MAGIC);
524                         p += TCPOLEN_EXP_FASTOPEN_BASE;
525                 } else {
526                         len = TCPOLEN_FASTOPEN_BASE + foc->len;
527                         *p++ = TCPOPT_FASTOPEN;
528                         *p++ = len;
529                 }
530 
531                 memcpy(p, foc->val, foc->len);
532                 if ((len & 3) == 2) {
533                         p[foc->len] = TCPOPT_NOP;
534                         p[foc->len + 1] = TCPOPT_NOP;
535                 }
536                 ptr += (len + 3) >> 2;
537         }
538 }
539 
540 /* Compute TCP options for SYN packets. This is not the final
541  * network wire format yet.
542  */
543 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
544                                 struct tcp_out_options *opts,
545                                 struct tcp_md5sig_key **md5)
546 {
547         struct tcp_sock *tp = tcp_sk(sk);
548         unsigned int remaining = MAX_TCP_OPTION_SPACE;
549         struct tcp_fastopen_request *fastopen = tp->fastopen_req;
550 
551 #ifdef CONFIG_TCP_MD5SIG
552         *md5 = tp->af_specific->md5_lookup(sk, sk);
553         if (*md5) {
554                 opts->options |= OPTION_MD5;
555                 remaining -= TCPOLEN_MD5SIG_ALIGNED;
556         }
557 #else
558         *md5 = NULL;
559 #endif
560 
561         /* We always get an MSS option.  The option bytes which will be seen in
562          * normal data packets should timestamps be used, must be in the MSS
563          * advertised.  But we subtract them from tp->mss_cache so that
564          * calculations in tcp_sendmsg are simpler etc.  So account for this
565          * fact here if necessary.  If we don't do this correctly, as a
566          * receiver we won't recognize data packets as being full sized when we
567          * should, and thus we won't abide by the delayed ACK rules correctly.
568          * SACKs don't matter, we never delay an ACK when we have any of those
569          * going out.  */
570         opts->mss = tcp_advertise_mss(sk);
571         remaining -= TCPOLEN_MSS_ALIGNED;
572 
573         if (likely(sysctl_tcp_timestamps && !*md5)) {
574                 opts->options |= OPTION_TS;
575                 opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
576                 opts->tsecr = tp->rx_opt.ts_recent;
577                 remaining -= TCPOLEN_TSTAMP_ALIGNED;
578         }
579         if (likely(sysctl_tcp_window_scaling)) {
580                 opts->ws = tp->rx_opt.rcv_wscale;
581                 opts->options |= OPTION_WSCALE;
582                 remaining -= TCPOLEN_WSCALE_ALIGNED;
583         }
584         if (likely(sysctl_tcp_sack)) {
585                 opts->options |= OPTION_SACK_ADVERTISE;
586                 if (unlikely(!(OPTION_TS & opts->options)))
587                         remaining -= TCPOLEN_SACKPERM_ALIGNED;
588         }
589 
590         if (fastopen && fastopen->cookie.len >= 0) {
591                 u32 need = fastopen->cookie.len;
592 
593                 need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE :
594                                                TCPOLEN_FASTOPEN_BASE;
595                 need = (need + 3) & ~3U;  /* Align to 32 bits */
596                 if (remaining >= need) {
597                         opts->options |= OPTION_FAST_OPEN_COOKIE;
598                         opts->fastopen_cookie = &fastopen->cookie;
599                         remaining -= need;
600                         tp->syn_fastopen = 1;
601                         tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0;
602                 }
603         }
604 
605         return MAX_TCP_OPTION_SPACE - remaining;
606 }
607 
608 /* Set up TCP options for SYN-ACKs. */
609 static unsigned int tcp_synack_options(struct request_sock *req,
610                                        unsigned int mss, struct sk_buff *skb,
611                                        struct tcp_out_options *opts,
612                                        const struct tcp_md5sig_key *md5,
613                                        struct tcp_fastopen_cookie *foc)
614 {
615         struct inet_request_sock *ireq = inet_rsk(req);
616         unsigned int remaining = MAX_TCP_OPTION_SPACE;
617 
618 #ifdef CONFIG_TCP_MD5SIG
619         if (md5) {
620                 opts->options |= OPTION_MD5;
621                 remaining -= TCPOLEN_MD5SIG_ALIGNED;
622 
623                 /* We can't fit any SACK blocks in a packet with MD5 + TS
624                  * options. There was discussion about disabling SACK
625                  * rather than TS in order to fit in better with old,
626                  * buggy kernels, but that was deemed to be unnecessary.
627                  */
628                 ireq->tstamp_ok &= !ireq->sack_ok;
629         }
630 #endif
631 
632         /* We always send an MSS option. */
633         opts->mss = mss;
634         remaining -= TCPOLEN_MSS_ALIGNED;
635 
636         if (likely(ireq->wscale_ok)) {
637                 opts->ws = ireq->rcv_wscale;
638                 opts->options |= OPTION_WSCALE;
639                 remaining -= TCPOLEN_WSCALE_ALIGNED;
640         }
641         if (likely(ireq->tstamp_ok)) {
642                 opts->options |= OPTION_TS;
643                 opts->tsval = tcp_skb_timestamp(skb) + tcp_rsk(req)->ts_off;
644                 opts->tsecr = req->ts_recent;
645                 remaining -= TCPOLEN_TSTAMP_ALIGNED;
646         }
647         if (likely(ireq->sack_ok)) {
648                 opts->options |= OPTION_SACK_ADVERTISE;
649                 if (unlikely(!ireq->tstamp_ok))
650                         remaining -= TCPOLEN_SACKPERM_ALIGNED;
651         }
652         if (foc != NULL && foc->len >= 0) {
653                 u32 need = foc->len;
654 
655                 need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE :
656                                    TCPOLEN_FASTOPEN_BASE;
657                 need = (need + 3) & ~3U;  /* Align to 32 bits */
658                 if (remaining >= need) {
659                         opts->options |= OPTION_FAST_OPEN_COOKIE;
660                         opts->fastopen_cookie = foc;
661                         remaining -= need;
662                 }
663         }
664 
665         return MAX_TCP_OPTION_SPACE - remaining;
666 }
667 
668 /* Compute TCP options for ESTABLISHED sockets. This is not the
669  * final wire format yet.
670  */
671 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
672                                         struct tcp_out_options *opts,
673                                         struct tcp_md5sig_key **md5)
674 {
675         struct tcp_sock *tp = tcp_sk(sk);
676         unsigned int size = 0;
677         unsigned int eff_sacks;
678 
679         opts->options = 0;
680 
681 #ifdef CONFIG_TCP_MD5SIG
682         *md5 = tp->af_specific->md5_lookup(sk, sk);
683         if (unlikely(*md5)) {
684                 opts->options |= OPTION_MD5;
685                 size += TCPOLEN_MD5SIG_ALIGNED;
686         }
687 #else
688         *md5 = NULL;
689 #endif
690 
691         if (likely(tp->rx_opt.tstamp_ok)) {
692                 opts->options |= OPTION_TS;
693                 opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
694                 opts->tsecr = tp->rx_opt.ts_recent;
695                 size += TCPOLEN_TSTAMP_ALIGNED;
696         }
697 
698         eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
699         if (unlikely(eff_sacks)) {
700                 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
701                 opts->num_sack_blocks =
702                         min_t(unsigned int, eff_sacks,
703                               (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
704                               TCPOLEN_SACK_PERBLOCK);
705                 size += TCPOLEN_SACK_BASE_ALIGNED +
706                         opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
707         }
708 
709         return size;
710 }
711 
712 
713 /* TCP SMALL QUEUES (TSQ)
714  *
715  * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
716  * to reduce RTT and bufferbloat.
717  * We do this using a special skb destructor (tcp_wfree).
718  *
719  * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
720  * needs to be reallocated in a driver.
721  * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
722  *
723  * Since transmit from skb destructor is forbidden, we use a tasklet
724  * to process all sockets that eventually need to send more skbs.
725  * We use one tasklet per cpu, with its own queue of sockets.
726  */
727 struct tsq_tasklet {
728         struct tasklet_struct   tasklet;
729         struct list_head        head; /* queue of tcp sockets */
730 };
731 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
732 
733 static void tcp_tsq_handler(struct sock *sk)
734 {
735         if ((1 << sk->sk_state) &
736             (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
737              TCPF_CLOSE_WAIT  | TCPF_LAST_ACK)) {
738                 struct tcp_sock *tp = tcp_sk(sk);
739 
740                 if (tp->lost_out > tp->retrans_out &&
741                     tp->snd_cwnd > tcp_packets_in_flight(tp))
742                         tcp_xmit_retransmit_queue(sk);
743 
744                 tcp_write_xmit(sk, tcp_current_mss(sk), tp->nonagle,
745                                0, GFP_ATOMIC);
746         }
747 }
748 /*
749  * One tasklet per cpu tries to send more skbs.
750  * We run in tasklet context but need to disable irqs when
751  * transferring tsq->head because tcp_wfree() might
752  * interrupt us (non NAPI drivers)
753  */
754 static void tcp_tasklet_func(unsigned long data)
755 {
756         struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
757         LIST_HEAD(list);
758         unsigned long flags;
759         struct list_head *q, *n;
760         struct tcp_sock *tp;
761         struct sock *sk;
762 
763         local_irq_save(flags);
764         list_splice_init(&tsq->head, &list);
765         local_irq_restore(flags);
766 
767         list_for_each_safe(q, n, &list) {
768                 tp = list_entry(q, struct tcp_sock, tsq_node);
769                 list_del(&tp->tsq_node);
770 
771                 sk = (struct sock *)tp;
772                 smp_mb__before_atomic();
773                 clear_bit(TSQ_QUEUED, &sk->sk_tsq_flags);
774 
775                 if (!sk->sk_lock.owned &&
776                     test_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags)) {
777                         bh_lock_sock(sk);
778                         if (!sock_owned_by_user(sk)) {
779                                 clear_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags);
780                                 tcp_tsq_handler(sk);
781                         }
782                         bh_unlock_sock(sk);
783                 }
784 
785                 sk_free(sk);
786         }
787 }
788 
789 #define TCP_DEFERRED_ALL (TCPF_TSQ_DEFERRED |           \
790                           TCPF_WRITE_TIMER_DEFERRED |   \
791                           TCPF_DELACK_TIMER_DEFERRED |  \
792                           TCPF_MTU_REDUCED_DEFERRED)
793 /**
794  * tcp_release_cb - tcp release_sock() callback
795  * @sk: socket
796  *
797  * called from release_sock() to perform protocol dependent
798  * actions before socket release.
799  */
800 void tcp_release_cb(struct sock *sk)
801 {
802         unsigned long flags, nflags;
803 
804         /* perform an atomic operation only if at least one flag is set */
805         do {
806                 flags = sk->sk_tsq_flags;
807                 if (!(flags & TCP_DEFERRED_ALL))
808                         return;
809                 nflags = flags & ~TCP_DEFERRED_ALL;
810         } while (cmpxchg(&sk->sk_tsq_flags, flags, nflags) != flags);
811 
812         if (flags & TCPF_TSQ_DEFERRED)
813                 tcp_tsq_handler(sk);
814 
815         /* Here begins the tricky part :
816          * We are called from release_sock() with :
817          * 1) BH disabled
818          * 2) sk_lock.slock spinlock held
819          * 3) socket owned by us (sk->sk_lock.owned == 1)
820          *
821          * But following code is meant to be called from BH handlers,
822          * so we should keep BH disabled, but early release socket ownership
823          */
824         sock_release_ownership(sk);
825 
826         if (flags & TCPF_WRITE_TIMER_DEFERRED) {
827                 tcp_write_timer_handler(sk);
828                 __sock_put(sk);
829         }
830         if (flags & TCPF_DELACK_TIMER_DEFERRED) {
831                 tcp_delack_timer_handler(sk);
832                 __sock_put(sk);
833         }
834         if (flags & TCPF_MTU_REDUCED_DEFERRED) {
835                 inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
836                 __sock_put(sk);
837         }
838 }
839 EXPORT_SYMBOL(tcp_release_cb);
840 
841 void __init tcp_tasklet_init(void)
842 {
843         int i;
844 
845         for_each_possible_cpu(i) {
846                 struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
847 
848                 INIT_LIST_HEAD(&tsq->head);
849                 tasklet_init(&tsq->tasklet,
850                              tcp_tasklet_func,
851                              (unsigned long)tsq);
852         }
853 }
854 
855 /*
856  * Write buffer destructor automatically called from kfree_skb.
857  * We can't xmit new skbs from this context, as we might already
858  * hold qdisc lock.
859  */
860 void tcp_wfree(struct sk_buff *skb)
861 {
862         struct sock *sk = skb->sk;
863         struct tcp_sock *tp = tcp_sk(sk);
864         unsigned long flags, nval, oval;
865         int wmem;
866 
867         /* Keep one reference on sk_wmem_alloc.
868          * Will be released by sk_free() from here or tcp_tasklet_func()
869          */
870         wmem = atomic_sub_return(skb->truesize - 1, &sk->sk_wmem_alloc);
871 
872         /* If this softirq is serviced by ksoftirqd, we are likely under stress.
873          * Wait until our queues (qdisc + devices) are drained.
874          * This gives :
875          * - less callbacks to tcp_write_xmit(), reducing stress (batches)
876          * - chance for incoming ACK (processed by another cpu maybe)
877          *   to migrate this flow (skb->ooo_okay will be eventually set)
878          */
879         if (wmem >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current)
880                 goto out;
881 
882         for (oval = READ_ONCE(sk->sk_tsq_flags);; oval = nval) {
883                 struct tsq_tasklet *tsq;
884                 bool empty;
885 
886                 if (!(oval & TSQF_THROTTLED) || (oval & TSQF_QUEUED))
887                         goto out;
888 
889                 nval = (oval & ~TSQF_THROTTLED) | TSQF_QUEUED | TCPF_TSQ_DEFERRED;
890                 nval = cmpxchg(&sk->sk_tsq_flags, oval, nval);
891                 if (nval != oval)
892                         continue;
893 
894                 /* queue this socket to tasklet queue */
895                 local_irq_save(flags);
896                 tsq = this_cpu_ptr(&tsq_tasklet);
897                 empty = list_empty(&tsq->head);
898                 list_add(&tp->tsq_node, &tsq->head);
899                 if (empty)
900                         tasklet_schedule(&tsq->tasklet);
901                 local_irq_restore(flags);
902                 return;
903         }
904 out:
905         sk_free(sk);
906 }
907 
908 /* This routine actually transmits TCP packets queued in by
909  * tcp_do_sendmsg().  This is used by both the initial
910  * transmission and possible later retransmissions.
911  * All SKB's seen here are completely headerless.  It is our
912  * job to build the TCP header, and pass the packet down to
913  * IP so it can do the same plus pass the packet off to the
914  * device.
915  *
916  * We are working here with either a clone of the original
917  * SKB, or a fresh unique copy made by the retransmit engine.
918  */
919 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
920                             gfp_t gfp_mask)
921 {
922         const struct inet_connection_sock *icsk = inet_csk(sk);
923         struct inet_sock *inet;
924         struct tcp_sock *tp;
925         struct tcp_skb_cb *tcb;
926         struct tcp_out_options opts;
927         unsigned int tcp_options_size, tcp_header_size;
928         struct tcp_md5sig_key *md5;
929         struct tcphdr *th;
930         int err;
931 
932         BUG_ON(!skb || !tcp_skb_pcount(skb));
933         tp = tcp_sk(sk);
934 
935         if (clone_it) {
936                 skb_mstamp_get(&skb->skb_mstamp);
937                 TCP_SKB_CB(skb)->tx.in_flight = TCP_SKB_CB(skb)->end_seq
938                         - tp->snd_una;
939                 tcp_rate_skb_sent(sk, skb);
940 
941                 if (unlikely(skb_cloned(skb)))
942                         skb = pskb_copy(skb, gfp_mask);
943                 else
944                         skb = skb_clone(skb, gfp_mask);
945                 if (unlikely(!skb))
946                         return -ENOBUFS;
947         }
948 
949         inet = inet_sk(sk);
950         tcb = TCP_SKB_CB(skb);
951         memset(&opts, 0, sizeof(opts));
952 
953         if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
954                 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
955         else
956                 tcp_options_size = tcp_established_options(sk, skb, &opts,
957                                                            &md5);
958         tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
959 
960         /* if no packet is in qdisc/device queue, then allow XPS to select
961          * another queue. We can be called from tcp_tsq_handler()
962          * which holds one reference to sk_wmem_alloc.
963          *
964          * TODO: Ideally, in-flight pure ACK packets should not matter here.
965          * One way to get this would be to set skb->truesize = 2 on them.
966          */
967         skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
968 
969         skb_push(skb, tcp_header_size);
970         skb_reset_transport_header(skb);
971 
972         skb_orphan(skb);
973         skb->sk = sk;
974         skb->destructor = skb_is_tcp_pure_ack(skb) ? __sock_wfree : tcp_wfree;
975         skb_set_hash_from_sk(skb, sk);
976         atomic_add(skb->truesize, &sk->sk_wmem_alloc);
977 
978         /* Build TCP header and checksum it. */
979         th = (struct tcphdr *)skb->data;
980         th->source              = inet->inet_sport;
981         th->dest                = inet->inet_dport;
982         th->seq                 = htonl(tcb->seq);
983         th->ack_seq             = htonl(tp->rcv_nxt);
984         *(((__be16 *)th) + 6)   = htons(((tcp_header_size >> 2) << 12) |
985                                         tcb->tcp_flags);
986 
987         th->check               = 0;
988         th->urg_ptr             = 0;
989 
990         /* The urg_mode check is necessary during a below snd_una win probe */
991         if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
992                 if (before(tp->snd_up, tcb->seq + 0x10000)) {
993                         th->urg_ptr = htons(tp->snd_up - tcb->seq);
994                         th->urg = 1;
995                 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
996                         th->urg_ptr = htons(0xFFFF);
997                         th->urg = 1;
998                 }
999         }
1000 
1001         tcp_options_write((__be32 *)(th + 1), tp, &opts);
1002         skb_shinfo(skb)->gso_type = sk->sk_gso_type;
1003         if (likely(!(tcb->tcp_flags & TCPHDR_SYN))) {
1004                 th->window      = htons(tcp_select_window(sk));
1005                 tcp_ecn_send(sk, skb, th, tcp_header_size);
1006         } else {
1007                 /* RFC1323: The window in SYN & SYN/ACK segments
1008                  * is never scaled.
1009                  */
1010                 th->window      = htons(min(tp->rcv_wnd, 65535U));
1011         }
1012 #ifdef CONFIG_TCP_MD5SIG
1013         /* Calculate the MD5 hash, as we have all we need now */
1014         if (md5) {
1015                 sk_nocaps_add(sk, NETIF_F_GSO_MASK);
1016                 tp->af_specific->calc_md5_hash(opts.hash_location,
1017                                                md5, sk, skb);
1018         }
1019 #endif
1020 
1021         icsk->icsk_af_ops->send_check(sk, skb);
1022 
1023         if (likely(tcb->tcp_flags & TCPHDR_ACK))
1024                 tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
1025 
1026         if (skb->len != tcp_header_size) {
1027                 tcp_event_data_sent(tp, sk);
1028                 tp->data_segs_out += tcp_skb_pcount(skb);
1029         }
1030 
1031         if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1032                 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
1033                               tcp_skb_pcount(skb));
1034 
1035         tp->segs_out += tcp_skb_pcount(skb);
1036         /* OK, its time to fill skb_shinfo(skb)->gso_{segs|size} */
1037         skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
1038         skb_shinfo(skb)->gso_size = tcp_skb_mss(skb);
1039 
1040         /* Our usage of tstamp should remain private */
1041         skb->tstamp = 0;
1042 
1043         /* Cleanup our debris for IP stacks */
1044         memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
1045                                sizeof(struct inet6_skb_parm)));
1046 
1047         err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
1048 
1049         if (likely(err <= 0))
1050                 return err;
1051 
1052         tcp_enter_cwr(sk);
1053 
1054         return net_xmit_eval(err);
1055 }
1056 
1057 /* This routine just queues the buffer for sending.
1058  *
1059  * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
1060  * otherwise socket can stall.
1061  */
1062 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
1063 {
1064         struct tcp_sock *tp = tcp_sk(sk);
1065 
1066         /* Advance write_seq and place onto the write_queue. */
1067         tp->write_seq = TCP_SKB_CB(skb)->end_seq;
1068         __skb_header_release(skb);
1069         tcp_add_write_queue_tail(sk, skb);
1070         sk->sk_wmem_queued += skb->truesize;
1071         sk_mem_charge(sk, skb->truesize);
1072 }
1073 
1074 /* Initialize TSO segments for a packet. */
1075 static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1076 {
1077         if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
1078                 /* Avoid the costly divide in the normal
1079                  * non-TSO case.
1080                  */
1081                 tcp_skb_pcount_set(skb, 1);
1082                 TCP_SKB_CB(skb)->tcp_gso_size = 0;
1083         } else {
1084                 tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
1085                 TCP_SKB_CB(skb)->tcp_gso_size = mss_now;
1086         }
1087 }
1088 
1089 /* When a modification to fackets out becomes necessary, we need to check
1090  * skb is counted to fackets_out or not.
1091  */
1092 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
1093                                    int decr)
1094 {
1095         struct tcp_sock *tp = tcp_sk(sk);
1096 
1097         if (!tp->sacked_out || tcp_is_reno(tp))
1098                 return;
1099 
1100         if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
1101                 tp->fackets_out -= decr;
1102 }
1103 
1104 /* Pcount in the middle of the write queue got changed, we need to do various
1105  * tweaks to fix counters
1106  */
1107 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1108 {
1109         struct tcp_sock *tp = tcp_sk(sk);
1110 
1111         tp->packets_out -= decr;
1112 
1113         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1114                 tp->sacked_out -= decr;
1115         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1116                 tp->retrans_out -= decr;
1117         if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
1118                 tp->lost_out -= decr;
1119 
1120         /* Reno case is special. Sigh... */
1121         if (tcp_is_reno(tp) && decr > 0)
1122                 tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
1123 
1124         tcp_adjust_fackets_out(sk, skb, decr);
1125 
1126         if (tp->lost_skb_hint &&
1127             before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
1128             (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1129                 tp->lost_cnt_hint -= decr;
1130 
1131         tcp_verify_left_out(tp);
1132 }
1133 
1134 static bool tcp_has_tx_tstamp(const struct sk_buff *skb)
1135 {
1136         return TCP_SKB_CB(skb)->txstamp_ack ||
1137                 (skb_shinfo(skb)->tx_flags & SKBTX_ANY_TSTAMP);
1138 }
1139 
1140 static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
1141 {
1142         struct skb_shared_info *shinfo = skb_shinfo(skb);
1143 
1144         if (unlikely(tcp_has_tx_tstamp(skb)) &&
1145             !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
1146                 struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
1147                 u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;
1148 
1149                 shinfo->tx_flags &= ~tsflags;
1150                 shinfo2->tx_flags |= tsflags;
1151                 swap(shinfo->tskey, shinfo2->tskey);
1152                 TCP_SKB_CB(skb2)->txstamp_ack = TCP_SKB_CB(skb)->txstamp_ack;
1153                 TCP_SKB_CB(skb)->txstamp_ack = 0;
1154         }
1155 }
1156 
1157 static void tcp_skb_fragment_eor(struct sk_buff *skb, struct sk_buff *skb2)
1158 {
1159         TCP_SKB_CB(skb2)->eor = TCP_SKB_CB(skb)->eor;
1160         TCP_SKB_CB(skb)->eor = 0;
1161 }
1162 
1163 /* Function to create two new TCP segments.  Shrinks the given segment
1164  * to the specified size and appends a new segment with the rest of the
1165  * packet to the list.  This won't be called frequently, I hope.
1166  * Remember, these are still headerless SKBs at this point.
1167  */
1168 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1169                  unsigned int mss_now, gfp_t gfp)
1170 {
1171         struct tcp_sock *tp = tcp_sk(sk);
1172         struct sk_buff *buff;
1173         int nsize, old_factor;
1174         int nlen;
1175         u8 flags;
1176 
1177         if (WARN_ON(len > skb->len))
1178                 return -EINVAL;
1179 
1180         nsize = skb_headlen(skb) - len;
1181         if (nsize < 0)
1182                 nsize = 0;
1183 
1184         if (skb_unclone(skb, gfp))
1185                 return -ENOMEM;
1186 
1187         /* Get a new skb... force flag on. */
1188         buff = sk_stream_alloc_skb(sk, nsize, gfp, true);
1189         if (!buff)
1190                 return -ENOMEM; /* We'll just try again later. */
1191 
1192         sk->sk_wmem_queued += buff->truesize;
1193         sk_mem_charge(sk, buff->truesize);
1194         nlen = skb->len - len - nsize;
1195         buff->truesize += nlen;
1196         skb->truesize -= nlen;
1197 
1198         /* Correct the sequence numbers. */
1199         TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1200         TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1201         TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1202 
1203         /* PSH and FIN should only be set in the second packet. */
1204         flags = TCP_SKB_CB(skb)->tcp_flags;
1205         TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1206         TCP_SKB_CB(buff)->tcp_flags = flags;
1207         TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1208         tcp_skb_fragment_eor(skb, buff);
1209 
1210         if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
1211                 /* Copy and checksum data tail into the new buffer. */
1212                 buff->csum = csum_partial_copy_nocheck(skb->data + len,
1213                                                        skb_put(buff, nsize),
1214                                                        nsize, 0);
1215 
1216                 skb_trim(skb, len);
1217 
1218                 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
1219         } else {
1220                 skb->ip_summed = CHECKSUM_PARTIAL;
1221                 skb_split(skb, buff, len);
1222         }
1223 
1224         buff->ip_summed = skb->ip_summed;
1225 
1226         buff->tstamp = skb->tstamp;
1227         tcp_fragment_tstamp(skb, buff);
1228 
1229         old_factor = tcp_skb_pcount(skb);
1230 
1231         /* Fix up tso_factor for both original and new SKB.  */
1232         tcp_set_skb_tso_segs(skb, mss_now);
1233         tcp_set_skb_tso_segs(buff, mss_now);
1234 
1235         /* Update delivered info for the new segment */
1236         TCP_SKB_CB(buff)->tx = TCP_SKB_CB(skb)->tx;
1237 
1238         /* If this packet has been sent out already, we must
1239          * adjust the various packet counters.
1240          */
1241         if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1242                 int diff = old_factor - tcp_skb_pcount(skb) -
1243                         tcp_skb_pcount(buff);
1244 
1245                 if (diff)
1246                         tcp_adjust_pcount(sk, skb, diff);
1247         }
1248 
1249         /* Link BUFF into the send queue. */
1250         __skb_header_release(buff);
1251         tcp_insert_write_queue_after(skb, buff, sk);
1252 
1253         return 0;
1254 }
1255 
1256 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
1257  * eventually). The difference is that pulled data not copied, but
1258  * immediately discarded.
1259  */
1260 static void __pskb_trim_head(struct sk_buff *skb, int len)
1261 {
1262         struct skb_shared_info *shinfo;
1263         int i, k, eat;
1264 
1265         eat = min_t(int, len, skb_headlen(skb));
1266         if (eat) {
1267                 __skb_pull(skb, eat);
1268                 len -= eat;
1269                 if (!len)
1270                         return;
1271         }
1272         eat = len;
1273         k = 0;
1274         shinfo = skb_shinfo(skb);
1275         for (i = 0; i < shinfo->nr_frags; i++) {
1276                 int size = skb_frag_size(&shinfo->frags[i]);
1277 
1278                 if (size <= eat) {
1279                         skb_frag_unref(skb, i);
1280                         eat -= size;
1281                 } else {
1282                         shinfo->frags[k] = shinfo->frags[i];
1283                         if (eat) {
1284                                 shinfo->frags[k].page_offset += eat;
1285                                 skb_frag_size_sub(&shinfo->frags[k], eat);
1286                                 eat = 0;
1287                         }
1288                         k++;
1289                 }
1290         }
1291         shinfo->nr_frags = k;
1292 
1293         skb_reset_tail_pointer(skb);
1294         skb->data_len -= len;
1295         skb->len = skb->data_len;
1296 }
1297 
1298 /* Remove acked data from a packet in the transmit queue. */
1299 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1300 {
1301         if (skb_unclone(skb, GFP_ATOMIC))
1302                 return -ENOMEM;
1303 
1304         __pskb_trim_head(skb, len);
1305 
1306         TCP_SKB_CB(skb)->seq += len;
1307         skb->ip_summed = CHECKSUM_PARTIAL;
1308 
1309         skb->truesize        -= len;
1310         sk->sk_wmem_queued   -= len;
1311         sk_mem_uncharge(sk, len);
1312         sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
1313 
1314         /* Any change of skb->len requires recalculation of tso factor. */
1315         if (tcp_skb_pcount(skb) > 1)
1316                 tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb));
1317 
1318         return 0;
1319 }
1320 
1321 /* Calculate MSS not accounting any TCP options.  */
1322 static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
1323 {
1324         const struct tcp_sock *tp = tcp_sk(sk);
1325         const struct inet_connection_sock *icsk = inet_csk(sk);
1326         int mss_now;
1327 
1328         /* Calculate base mss without TCP options:
1329            It is MMS_S - sizeof(tcphdr) of rfc1122
1330          */
1331         mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1332 
1333         /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1334         if (icsk->icsk_af_ops->net_frag_header_len) {
1335                 const struct dst_entry *dst = __sk_dst_get(sk);
1336 
1337                 if (dst && dst_allfrag(dst))
1338                         mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1339         }
1340 
1341         /* Clamp it (mss_clamp does not include tcp options) */
1342         if (mss_now > tp->rx_opt.mss_clamp)
1343                 mss_now = tp->rx_opt.mss_clamp;
1344 
1345         /* Now subtract optional transport overhead */
1346         mss_now -= icsk->icsk_ext_hdr_len;
1347 
1348         /* Then reserve room for full set of TCP options and 8 bytes of data */
1349         if (mss_now < 48)
1350                 mss_now = 48;
1351         return mss_now;
1352 }
1353 
1354 /* Calculate MSS. Not accounting for SACKs here.  */
1355 int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1356 {
1357         /* Subtract TCP options size, not including SACKs */
1358         return __tcp_mtu_to_mss(sk, pmtu) -
1359                (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
1360 }
1361 
1362 /* Inverse of above */
1363 int tcp_mss_to_mtu(struct sock *sk, int mss)
1364 {
1365         const struct tcp_sock *tp = tcp_sk(sk);
1366         const struct inet_connection_sock *icsk = inet_csk(sk);
1367         int mtu;
1368 
1369         mtu = mss +
1370               tp->tcp_header_len +
1371               icsk->icsk_ext_hdr_len +
1372               icsk->icsk_af_ops->net_header_len;
1373 
1374         /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1375         if (icsk->icsk_af_ops->net_frag_header_len) {
1376                 const struct dst_entry *dst = __sk_dst_get(sk);
1377 
1378                 if (dst && dst_allfrag(dst))
1379                         mtu += icsk->icsk_af_ops->net_frag_header_len;
1380         }
1381         return mtu;
1382 }
1383 EXPORT_SYMBOL(tcp_mss_to_mtu);
1384 
1385 /* MTU probing init per socket */
1386 void tcp_mtup_init(struct sock *sk)
1387 {
1388         struct tcp_sock *tp = tcp_sk(sk);
1389         struct inet_connection_sock *icsk = inet_csk(sk);
1390         struct net *net = sock_net(sk);
1391 
1392         icsk->icsk_mtup.enabled = net->ipv4.sysctl_tcp_mtu_probing > 1;
1393         icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1394                                icsk->icsk_af_ops->net_header_len;
1395         icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss);
1396         icsk->icsk_mtup.probe_size = 0;
1397         if (icsk->icsk_mtup.enabled)
1398                 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1399 }
1400 EXPORT_SYMBOL(tcp_mtup_init);
1401 
1402 /* This function synchronize snd mss to current pmtu/exthdr set.
1403 
1404    tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1405    for TCP options, but includes only bare TCP header.
1406 
1407    tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1408    It is minimum of user_mss and mss received with SYN.
1409    It also does not include TCP options.
1410 
1411    inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1412 
1413    tp->mss_cache is current effective sending mss, including
1414    all tcp options except for SACKs. It is evaluated,
1415    taking into account current pmtu, but never exceeds
1416    tp->rx_opt.mss_clamp.
1417 
1418    NOTE1. rfc1122 clearly states that advertised MSS
1419    DOES NOT include either tcp or ip options.
1420 
1421    NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1422    are READ ONLY outside this function.         --ANK (980731)
1423  */
1424 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1425 {
1426         struct tcp_sock *tp = tcp_sk(sk);
1427         struct inet_connection_sock *icsk = inet_csk(sk);
1428         int mss_now;
1429 
1430         if (icsk->icsk_mtup.search_high > pmtu)
1431                 icsk->icsk_mtup.search_high = pmtu;
1432 
1433         mss_now = tcp_mtu_to_mss(sk, pmtu);
1434         mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1435 
1436         /* And store cached results */
1437         icsk->icsk_pmtu_cookie = pmtu;
1438         if (icsk->icsk_mtup.enabled)
1439                 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1440         tp->mss_cache = mss_now;
1441 
1442         return mss_now;
1443 }
1444 EXPORT_SYMBOL(tcp_sync_mss);
1445 
1446 /* Compute the current effective MSS, taking SACKs and IP options,
1447  * and even PMTU discovery events into account.
1448  */
1449 unsigned int tcp_current_mss(struct sock *sk)
1450 {
1451         const struct tcp_sock *tp = tcp_sk(sk);
1452         const struct dst_entry *dst = __sk_dst_get(sk);
1453         u32 mss_now;
1454         unsigned int header_len;
1455         struct tcp_out_options opts;
1456         struct tcp_md5sig_key *md5;
1457 
1458         mss_now = tp->mss_cache;
1459 
1460         if (dst) {
1461                 u32 mtu = dst_mtu(dst);
1462                 if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1463                         mss_now = tcp_sync_mss(sk, mtu);
1464         }
1465 
1466         header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1467                      sizeof(struct tcphdr);
1468         /* The mss_cache is sized based on tp->tcp_header_len, which assumes
1469          * some common options. If this is an odd packet (because we have SACK
1470          * blocks etc) then our calculated header_len will be different, and
1471          * we have to adjust mss_now correspondingly */
1472         if (header_len != tp->tcp_header_len) {
1473                 int delta = (int) header_len - tp->tcp_header_len;
1474                 mss_now -= delta;
1475         }
1476 
1477         return mss_now;
1478 }
1479 
1480 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
1481  * As additional protections, we do not touch cwnd in retransmission phases,
1482  * and if application hit its sndbuf limit recently.
1483  */
1484 static void tcp_cwnd_application_limited(struct sock *sk)
1485 {
1486         struct tcp_sock *tp = tcp_sk(sk);
1487 
1488         if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
1489             sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
1490                 /* Limited by application or receiver window. */
1491                 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
1492                 u32 win_used = max(tp->snd_cwnd_used, init_win);
1493                 if (win_used < tp->snd_cwnd) {
1494                         tp->snd_ssthresh = tcp_current_ssthresh(sk);
1495                         tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
1496                 }
1497                 tp->snd_cwnd_used = 0;
1498         }
1499         tp->snd_cwnd_stamp = tcp_time_stamp;
1500 }
1501 
1502 static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
1503 {
1504         struct tcp_sock *tp = tcp_sk(sk);
1505 
1506         /* Track the maximum number of outstanding packets in each
1507          * window, and remember whether we were cwnd-limited then.
1508          */
1509         if (!before(tp->snd_una, tp->max_packets_seq) ||
1510             tp->packets_out > tp->max_packets_out) {
1511                 tp->max_packets_out = tp->packets_out;
1512                 tp->max_packets_seq = tp->snd_nxt;
1513                 tp->is_cwnd_limited = is_cwnd_limited;
1514         }
1515 
1516         if (tcp_is_cwnd_limited(sk)) {
1517                 /* Network is feed fully. */
1518                 tp->snd_cwnd_used = 0;
1519                 tp->snd_cwnd_stamp = tcp_time_stamp;
1520         } else {
1521                 /* Network starves. */
1522                 if (tp->packets_out > tp->snd_cwnd_used)
1523                         tp->snd_cwnd_used = tp->packets_out;
1524 
1525                 if (sysctl_tcp_slow_start_after_idle &&
1526                     (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1527                         tcp_cwnd_application_limited(sk);
1528 
1529                 /* The following conditions together indicate the starvation
1530                  * is caused by insufficient sender buffer:
1531                  * 1) just sent some data (see tcp_write_xmit)
1532                  * 2) not cwnd limited (this else condition)
1533                  * 3) no more data to send (null tcp_send_head )
1534                  * 4) application is hitting buffer limit (SOCK_NOSPACE)
1535                  */
1536                 if (!tcp_send_head(sk) && sk->sk_socket &&
1537                     test_bit(SOCK_NOSPACE, &sk->sk_socket->flags) &&
1538                     (1 << sk->sk_state) & (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT))
1539                         tcp_chrono_start(sk, TCP_CHRONO_SNDBUF_LIMITED);
1540         }
1541 }
1542 
1543 /* Minshall's variant of the Nagle send check. */
1544 static bool tcp_minshall_check(const struct tcp_sock *tp)
1545 {
1546         return after(tp->snd_sml, tp->snd_una) &&
1547                 !after(tp->snd_sml, tp->snd_nxt);
1548 }
1549 
1550 /* Update snd_sml if this skb is under mss
1551  * Note that a TSO packet might end with a sub-mss segment
1552  * The test is really :
1553  * if ((skb->len % mss) != 0)
1554  *        tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1555  * But we can avoid doing the divide again given we already have
1556  *  skb_pcount = skb->len / mss_now
1557  */
1558 static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now,
1559                                 const struct sk_buff *skb)
1560 {
1561         if (skb->len < tcp_skb_pcount(skb) * mss_now)
1562                 tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1563 }
1564 
1565 /* Return false, if packet can be sent now without violation Nagle's rules:
1566  * 1. It is full sized. (provided by caller in %partial bool)
1567  * 2. Or it contains FIN. (already checked by caller)
1568  * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1569  * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1570  *    With Minshall's modification: all sent small packets are ACKed.
1571  */
1572 static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
1573                             int nonagle)
1574 {
1575         return partial &&
1576                 ((nonagle & TCP_NAGLE_CORK) ||
1577                  (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1578 }
1579 
1580 /* Return how many segs we'd like on a TSO packet,
1581  * to send one TSO packet per ms
1582  */
1583 u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
1584                      int min_tso_segs)
1585 {
1586         u32 bytes, segs;
1587 
1588         bytes = min(sk->sk_pacing_rate >> 10,
1589                     sk->sk_gso_max_size - 1 - MAX_TCP_HEADER);
1590 
1591         /* Goal is to send at least one packet per ms,
1592          * not one big TSO packet every 100 ms.
1593          * This preserves ACK clocking and is consistent
1594          * with tcp_tso_should_defer() heuristic.
1595          */
1596         segs = max_t(u32, bytes / mss_now, min_tso_segs);
1597 
1598         return min_t(u32, segs, sk->sk_gso_max_segs);
1599 }
1600 EXPORT_SYMBOL(tcp_tso_autosize);
1601 
1602 /* Return the number of segments we want in the skb we are transmitting.
1603  * See if congestion control module wants to decide; otherwise, autosize.
1604  */
1605 static u32 tcp_tso_segs(struct sock *sk, unsigned int mss_now)
1606 {
1607         const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
1608         u32 tso_segs = ca_ops->tso_segs_goal ? ca_ops->tso_segs_goal(sk) : 0;
1609 
1610         return tso_segs ? :
1611                 tcp_tso_autosize(sk, mss_now, sysctl_tcp_min_tso_segs);
1612 }
1613 
1614 /* Returns the portion of skb which can be sent right away */
1615 static unsigned int tcp_mss_split_point(const struct sock *sk,
1616                                         const struct sk_buff *skb,
1617                                         unsigned int mss_now,
1618                                         unsigned int max_segs,
1619                                         int nonagle)
1620 {
1621         const struct tcp_sock *tp = tcp_sk(sk);
1622         u32 partial, needed, window, max_len;
1623 
1624         window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1625         max_len = mss_now * max_segs;
1626 
1627         if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
1628                 return max_len;
1629 
1630         needed = min(skb->len, window);
1631 
1632         if (max_len <= needed)
1633                 return max_len;
1634 
1635         partial = needed % mss_now;
1636         /* If last segment is not a full MSS, check if Nagle rules allow us
1637          * to include this last segment in this skb.
1638          * Otherwise, we'll split the skb at last MSS boundary
1639          */
1640         if (tcp_nagle_check(partial != 0, tp, nonagle))
1641                 return needed - partial;
1642 
1643         return needed;
1644 }
1645 
1646 /* Can at least one segment of SKB be sent right now, according to the
1647  * congestion window rules?  If so, return how many segments are allowed.
1648  */
1649 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
1650                                          const struct sk_buff *skb)
1651 {
1652         u32 in_flight, cwnd, halfcwnd;
1653 
1654         /* Don't be strict about the congestion window for the final FIN.  */
1655         if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
1656             tcp_skb_pcount(skb) == 1)
1657                 return 1;
1658 
1659         in_flight = tcp_packets_in_flight(tp);
1660         cwnd = tp->snd_cwnd;
1661         if (in_flight >= cwnd)
1662                 return 0;
1663 
1664         /* For better scheduling, ensure we have at least
1665          * 2 GSO packets in flight.
1666          */
1667         halfcwnd = max(cwnd >> 1, 1U);
1668         return min(halfcwnd, cwnd - in_flight);
1669 }
1670 
1671 /* Initialize TSO state of a skb.
1672  * This must be invoked the first time we consider transmitting
1673  * SKB onto the wire.
1674  */
1675 static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1676 {
1677         int tso_segs = tcp_skb_pcount(skb);
1678 
1679         if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1680                 tcp_set_skb_tso_segs(skb, mss_now);
1681                 tso_segs = tcp_skb_pcount(skb);
1682         }
1683         return tso_segs;
1684 }
1685 
1686 
1687 /* Return true if the Nagle test allows this packet to be
1688  * sent now.
1689  */
1690 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1691                                   unsigned int cur_mss, int nonagle)
1692 {
1693         /* Nagle rule does not apply to frames, which sit in the middle of the
1694          * write_queue (they have no chances to get new data).
1695          *
1696          * This is implemented in the callers, where they modify the 'nonagle'
1697          * argument based upon the location of SKB in the send queue.
1698          */
1699         if (nonagle & TCP_NAGLE_PUSH)
1700                 return true;
1701 
1702         /* Don't use the nagle rule for urgent data (or for the final FIN). */
1703         if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
1704                 return true;
1705 
1706         if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
1707                 return true;
1708 
1709         return false;
1710 }
1711 
1712 /* Does at least the first segment of SKB fit into the send window? */
1713 static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
1714                              const struct sk_buff *skb,
1715                              unsigned int cur_mss)
1716 {
1717         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1718 
1719         if (skb->len > cur_mss)
1720                 end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1721 
1722         return !after(end_seq, tcp_wnd_end(tp));
1723 }
1724 
1725 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1726  * should be put on the wire right now.  If so, it returns the number of
1727  * packets allowed by the congestion window.
1728  */
1729 static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1730                                  unsigned int cur_mss, int nonagle)
1731 {
1732         const struct tcp_sock *tp = tcp_sk(sk);
1733         unsigned int cwnd_quota;
1734 
1735         tcp_init_tso_segs(skb, cur_mss);
1736 
1737         if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
1738                 return 0;
1739 
1740         cwnd_quota = tcp_cwnd_test(tp, skb);
1741         if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1742                 cwnd_quota = 0;
1743 
1744         return cwnd_quota;
1745 }
1746 
1747 /* Test if sending is allowed right now. */
1748 bool tcp_may_send_now(struct sock *sk)
1749 {
1750         const struct tcp_sock *tp = tcp_sk(sk);
1751         struct sk_buff *skb = tcp_send_head(sk);
1752 
1753         return skb &&
1754                 tcp_snd_test(sk, skb, tcp_current_mss(sk),
1755                              (tcp_skb_is_last(sk, skb) ?
1756                               tp->nonagle : TCP_NAGLE_PUSH));
1757 }
1758 
1759 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1760  * which is put after SKB on the list.  It is very much like
1761  * tcp_fragment() except that it may make several kinds of assumptions
1762  * in order to speed up the splitting operation.  In particular, we
1763  * know that all the data is in scatter-gather pages, and that the
1764  * packet has never been sent out before (and thus is not cloned).
1765  */
1766 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1767                         unsigned int mss_now, gfp_t gfp)
1768 {
1769         struct sk_buff *buff;
1770         int nlen = skb->len - len;
1771         u8 flags;
1772 
1773         /* All of a TSO frame must be composed of paged data.  */
1774         if (skb->len != skb->data_len)
1775                 return tcp_fragment(sk, skb, len, mss_now, gfp);
1776 
1777         buff = sk_stream_alloc_skb(sk, 0, gfp, true);
1778         if (unlikely(!buff))
1779                 return -ENOMEM;
1780 
1781         sk->sk_wmem_queued += buff->truesize;
1782         sk_mem_charge(sk, buff->truesize);
1783         buff->truesize += nlen;
1784         skb->truesize -= nlen;
1785 
1786         /* Correct the sequence numbers. */
1787         TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1788         TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1789         TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1790 
1791         /* PSH and FIN should only be set in the second packet. */
1792         flags = TCP_SKB_CB(skb)->tcp_flags;
1793         TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1794         TCP_SKB_CB(buff)->tcp_flags = flags;
1795 
1796         /* This packet was never sent out yet, so no SACK bits. */
1797         TCP_SKB_CB(buff)->sacked = 0;
1798 
1799         tcp_skb_fragment_eor(skb, buff);
1800 
1801         buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1802         skb_split(skb, buff, len);
1803         tcp_fragment_tstamp(skb, buff);
1804 
1805         /* Fix up tso_factor for both original and new SKB.  */
1806         tcp_set_skb_tso_segs(skb, mss_now);
1807         tcp_set_skb_tso_segs(buff, mss_now);
1808 
1809         /* Link BUFF into the send queue. */
1810         __skb_header_release(buff);
1811         tcp_insert_write_queue_after(skb, buff, sk);
1812 
1813         return 0;
1814 }
1815 
1816 /* Try to defer sending, if possible, in order to minimize the amount
1817  * of TSO splitting we do.  View it as a kind of TSO Nagle test.
1818  *
1819  * This algorithm is from John Heffner.
1820  */
1821 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
1822                                  bool *is_cwnd_limited, u32 max_segs)
1823 {
1824         const struct inet_connection_sock *icsk = inet_csk(sk);
1825         u32 age, send_win, cong_win, limit, in_flight;
1826         struct tcp_sock *tp = tcp_sk(sk);
1827         struct skb_mstamp now;
1828         struct sk_buff *head;
1829         int win_divisor;
1830 
1831         if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1832                 goto send_now;
1833 
1834         if (icsk->icsk_ca_state >= TCP_CA_Recovery)
1835                 goto send_now;
1836 
1837         /* Avoid bursty behavior by allowing defer
1838          * only if the last write was recent.
1839          */
1840         if ((s32)(tcp_time_stamp - tp->lsndtime) > 0)
1841                 goto send_now;
1842 
1843         in_flight = tcp_packets_in_flight(tp);
1844 
1845         BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1846 
1847         send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1848 
1849         /* From in_flight test above, we know that cwnd > in_flight.  */
1850         cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1851 
1852         limit = min(send_win, cong_win);
1853 
1854         /* If a full-sized TSO skb can be sent, do it. */
1855         if (limit >= max_segs * tp->mss_cache)
1856                 goto send_now;
1857 
1858         /* Middle in queue won't get any more data, full sendable already? */
1859         if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
1860                 goto send_now;
1861 
1862         win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
1863         if (win_divisor) {
1864                 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1865 
1866                 /* If at least some fraction of a window is available,
1867                  * just use it.
1868                  */
1869                 chunk /= win_divisor;
1870                 if (limit >= chunk)
1871                         goto send_now;
1872         } else {
1873                 /* Different approach, try not to defer past a single
1874                  * ACK.  Receiver should ACK every other full sized
1875                  * frame, so if we have space for more than 3 frames
1876                  * then send now.
1877                  */
1878                 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
1879                         goto send_now;
1880         }
1881 
1882         head = tcp_write_queue_head(sk);
1883         skb_mstamp_get(&now);
1884         age = skb_mstamp_us_delta(&now, &head->skb_mstamp);
1885         /* If next ACK is likely to come too late (half srtt), do not defer */
1886         if (age < (tp->srtt_us >> 4))
1887                 goto send_now;
1888 
1889         /* Ok, it looks like it is advisable to defer. */
1890 
1891         if (cong_win < send_win && cong_win <= skb->len)
1892                 *is_cwnd_limited = true;
1893 
1894         return true;
1895 
1896 send_now:
1897         return false;
1898 }
1899 
1900 static inline void tcp_mtu_check_reprobe(struct sock *sk)
1901 {
1902         struct inet_connection_sock *icsk = inet_csk(sk);
1903         struct tcp_sock *tp = tcp_sk(sk);
1904         struct net *net = sock_net(sk);
1905         u32 interval;
1906         s32 delta;
1907 
1908         interval = net->ipv4.sysctl_tcp_probe_interval;
1909         delta = tcp_time_stamp - icsk->icsk_mtup.probe_timestamp;
1910         if (unlikely(delta >= interval * HZ)) {
1911                 int mss = tcp_current_mss(sk);
1912 
1913                 /* Update current search range */
1914                 icsk->icsk_mtup.probe_size = 0;
1915                 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp +
1916                         sizeof(struct tcphdr) +
1917                         icsk->icsk_af_ops->net_header_len;
1918                 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
1919 
1920                 /* Update probe time stamp */
1921                 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1922         }
1923 }
1924 
1925 /* Create a new MTU probe if we are ready.
1926  * MTU probe is regularly attempting to increase the path MTU by
1927  * deliberately sending larger packets.  This discovers routing
1928  * changes resulting in larger path MTUs.
1929  *
1930  * Returns 0 if we should wait to probe (no cwnd available),
1931  *         1 if a probe was sent,
1932  *         -1 otherwise
1933  */
1934 static int tcp_mtu_probe(struct sock *sk)
1935 {
1936         struct inet_connection_sock *icsk = inet_csk(sk);
1937         struct tcp_sock *tp = tcp_sk(sk);
1938         struct sk_buff *skb, *nskb, *next;
1939         struct net *net = sock_net(sk);
1940         int probe_size;
1941         int size_needed;
1942         int copy, len;
1943         int mss_now;
1944         int interval;
1945 
1946         /* Not currently probing/verifying,
1947          * not in recovery,
1948          * have enough cwnd, and
1949          * not SACKing (the variable headers throw things off)
1950          */
1951         if (likely(!icsk->icsk_mtup.enabled ||
1952                    icsk->icsk_mtup.probe_size ||
1953                    inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
1954                    tp->snd_cwnd < 11 ||
1955                    tp->rx_opt.num_sacks || tp->rx_opt.dsack))
1956                 return -1;
1957 
1958         /* Use binary search for probe_size between tcp_mss_base,
1959          * and current mss_clamp. if (search_high - search_low)
1960          * smaller than a threshold, backoff from probing.
1961          */
1962         mss_now = tcp_current_mss(sk);
1963         probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high +
1964                                     icsk->icsk_mtup.search_low) >> 1);
1965         size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1966         interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low;
1967         /* When misfortune happens, we are reprobing actively,
1968          * and then reprobe timer has expired. We stick with current
1969          * probing process by not resetting search range to its orignal.
1970          */
1971         if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) ||
1972                 interval < net->ipv4.sysctl_tcp_probe_threshold) {
1973                 /* Check whether enough time has elaplased for
1974                  * another round of probing.
1975                  */
1976                 tcp_mtu_check_reprobe(sk);
1977                 return -1;
1978         }
1979 
1980         /* Have enough data in the send queue to probe? */
1981         if (tp->write_seq - tp->snd_nxt < size_needed)
1982                 return -1;
1983 
1984         if (tp->snd_wnd < size_needed)
1985                 return -1;
1986         if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1987                 return 0;
1988 
1989         /* Do we need to wait to drain cwnd? With none in flight, don't stall */
1990         if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
1991                 if (!tcp_packets_in_flight(tp))
1992                         return -1;
1993                 else
1994                         return 0;
1995         }
1996 
1997         /* We're allowed to probe.  Build it now. */
1998         nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false);
1999         if (!nskb)
2000                 return -1;
2001         sk->sk_wmem_queued += nskb->truesize;
2002         sk_mem_charge(sk, nskb->truesize);
2003 
2004         skb = tcp_send_head(sk);
2005 
2006         TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
2007         TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
2008         TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
2009         TCP_SKB_CB(nskb)->sacked = 0;
2010         nskb->csum = 0;
2011         nskb->ip_summed = skb->ip_summed;
2012 
2013         tcp_insert_write_queue_before(nskb, skb, sk);
2014 
2015         len = 0;
2016         tcp_for_write_queue_from_safe(skb, next, sk) {
2017                 copy = min_t(int, skb->len, probe_size - len);
2018                 if (nskb->ip_summed) {
2019                         skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
2020                 } else {
2021                         __wsum csum = skb_copy_and_csum_bits(skb, 0,
2022                                                              skb_put(nskb, copy),
2023                                                              copy, 0);
2024                         nskb->csum = csum_block_add(nskb->csum, csum, len);
2025                 }
2026 
2027                 if (skb->len <= copy) {
2028                         /* We've eaten all the data from this skb.
2029                          * Throw it away. */
2030                         TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
2031                         tcp_unlink_write_queue(skb, sk);
2032                         sk_wmem_free_skb(sk, skb);
2033                 } else {
2034                         TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
2035                                                    ~(TCPHDR_FIN|TCPHDR_PSH);
2036                         if (!skb_shinfo(skb)->nr_frags) {
2037                                 skb_pull(skb, copy);
2038                                 if (skb->ip_summed != CHECKSUM_PARTIAL)
2039                                         skb->csum = csum_partial(skb->data,
2040                                                                  skb->len, 0);
2041                         } else {
2042                                 __pskb_trim_head(skb, copy);
2043                                 tcp_set_skb_tso_segs(skb, mss_now);
2044                         }
2045                         TCP_SKB_CB(skb)->seq += copy;
2046                 }
2047 
2048                 len += copy;
2049 
2050                 if (len >= probe_size)
2051                         break;
2052         }
2053         tcp_init_tso_segs(nskb, nskb->len);
2054 
2055         /* We're ready to send.  If this fails, the probe will
2056          * be resegmented into mss-sized pieces by tcp_write_xmit().
2057          */
2058         if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
2059                 /* Decrement cwnd here because we are sending
2060                  * effectively two packets. */
2061                 tp->snd_cwnd--;
2062                 tcp_event_new_data_sent(sk, nskb);
2063 
2064                 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
2065                 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
2066                 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
2067 
2068                 return 1;
2069         }
2070 
2071         return -1;
2072 }
2073 
2074 /* TCP Small Queues :
2075  * Control number of packets in qdisc/devices to two packets / or ~1 ms.
2076  * (These limits are doubled for retransmits)
2077  * This allows for :
2078  *  - better RTT estimation and ACK scheduling
2079  *  - faster recovery
2080  *  - high rates
2081  * Alas, some drivers / subsystems require a fair amount
2082  * of queued bytes to ensure line rate.
2083  * One example is wifi aggregation (802.11 AMPDU)
2084  */
2085 static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb,
2086                                   unsigned int factor)
2087 {
2088         unsigned int limit;
2089 
2090         limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10);
2091         limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes);
2092         limit <<= factor;
2093 
2094         if (atomic_read(&sk->sk_wmem_alloc) > limit) {
2095                 /* Always send the 1st or 2nd skb in write queue.
2096                  * No need to wait for TX completion to call us back,
2097                  * after softirq/tasklet schedule.
2098                  * This helps when TX completions are delayed too much.
2099                  */
2100                 if (skb == sk->sk_write_queue.next ||
2101                     skb->prev == sk->sk_write_queue.next)
2102                         return false;
2103 
2104                 set_bit(TSQ_THROTTLED, &sk->sk_tsq_flags);
2105                 /* It is possible TX completion already happened
2106                  * before we set TSQ_THROTTLED, so we must
2107                  * test again the condition.
2108                  */
2109                 smp_mb__after_atomic();
2110                 if (atomic_read(&sk->sk_wmem_alloc) > limit)
2111                         return true;
2112         }
2113         return false;
2114 }
2115 
2116 static void tcp_chrono_set(struct tcp_sock *tp, const enum tcp_chrono new)
2117 {
2118         const u32 now = tcp_time_stamp;
2119 
2120         if (tp->chrono_type > TCP_CHRONO_UNSPEC)
2121                 tp->chrono_stat[tp->chrono_type - 1] += now - tp->chrono_start;
2122         tp->chrono_start = now;
2123         tp->chrono_type = new;
2124 }
2125 
2126 void tcp_chrono_start(struct sock *sk, const enum tcp_chrono type)
2127 {
2128         struct tcp_sock *tp = tcp_sk(sk);
2129 
2130         /* If there are multiple conditions worthy of tracking in a
2131          * chronograph then the highest priority enum takes precedence
2132          * over the other conditions. So that if something "more interesting"
2133          * starts happening, stop the previous chrono and start a new one.
2134          */
2135         if (type > tp->chrono_type)
2136                 tcp_chrono_set(tp, type);
2137 }
2138 
2139 void tcp_chrono_stop(struct sock *sk, const enum tcp_chrono type)
2140 {
2141         struct tcp_sock *tp = tcp_sk(sk);
2142 
2143 
2144         /* There are multiple conditions worthy of tracking in a
2145          * chronograph, so that the highest priority enum takes
2146          * precedence over the other conditions (see tcp_chrono_start).
2147          * If a condition stops, we only stop chrono tracking if
2148          * it's the "most interesting" or current chrono we are
2149          * tracking and starts busy chrono if we have pending data.
2150          */
2151         if (tcp_write_queue_empty(sk))
2152                 tcp_chrono_set(tp, TCP_CHRONO_UNSPEC);
2153         else if (type == tp->chrono_type)
2154                 tcp_chrono_set(tp, TCP_CHRONO_BUSY);
2155 }
2156 
2157 /* This routine writes packets to the network.  It advances the
2158  * send_head.  This happens as incoming acks open up the remote
2159  * window for us.
2160  *
2161  * LARGESEND note: !tcp_urg_mode is overkill, only frames between
2162  * snd_up-64k-mss .. snd_up cannot be large. However, taking into
2163  * account rare use of URG, this is not a big flaw.
2164  *
2165  * Send at most one packet when push_one > 0. Temporarily ignore
2166  * cwnd limit to force at most one packet out when push_one == 2.
2167 
2168  * Returns true, if no segments are in flight and we have queued segments,
2169  * but cannot send anything now because of SWS or another problem.
2170  */
2171 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
2172                            int push_one, gfp_t gfp)
2173 {
2174         struct tcp_sock *tp = tcp_sk(sk);
2175         struct sk_buff *skb;
2176         unsigned int tso_segs, sent_pkts;
2177         int cwnd_quota;
2178         int result;
2179         bool is_cwnd_limited = false, is_rwnd_limited = false;
2180         u32 max_segs;
2181 
2182         sent_pkts = 0;
2183 
2184         if (!push_one) {
2185                 /* Do MTU probing. */
2186                 result = tcp_mtu_probe(sk);
2187                 if (!result) {
2188                         return false;
2189                 } else if (result > 0) {
2190                         sent_pkts = 1;
2191                 }
2192         }
2193 
2194         max_segs = tcp_tso_segs(sk, mss_now);
2195         while ((skb = tcp_send_head(sk))) {
2196                 unsigned int limit;
2197 
2198                 tso_segs = tcp_init_tso_segs(skb, mss_now);
2199                 BUG_ON(!tso_segs);
2200 
2201                 if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
2202                         /* "skb_mstamp" is used as a start point for the retransmit timer */
2203                         skb_mstamp_get(&skb->skb_mstamp);
2204                         goto repair; /* Skip network transmission */
2205                 }
2206 
2207                 cwnd_quota = tcp_cwnd_test(tp, skb);
2208                 if (!cwnd_quota) {
2209                         if (push_one == 2)
2210                                 /* Force out a loss probe pkt. */
2211                                 cwnd_quota = 1;
2212                         else
2213                                 break;
2214                 }
2215 
2216                 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now))) {
2217                         is_rwnd_limited = true;
2218                         break;
2219                 }
2220 
2221                 if (tso_segs == 1) {
2222                         if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
2223                                                      (tcp_skb_is_last(sk, skb) ?
2224                                                       nonagle : TCP_NAGLE_PUSH))))
2225                                 break;
2226                 } else {
2227                         if (!push_one &&
2228                             tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
2229                                                  max_segs))
2230                                 break;
2231                 }
2232 
2233                 limit = mss_now;
2234                 if (tso_segs > 1 && !tcp_urg_mode(tp))
2235                         limit = tcp_mss_split_point(sk, skb, mss_now,
2236                                                     min_t(unsigned int,
2237                                                           cwnd_quota,
2238                                                           max_segs),
2239                                                     nonagle);
2240 
2241                 if (skb->len > limit &&
2242                     unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
2243                         break;
2244 
2245                 if (test_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags))
2246                         clear_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags);
2247                 if (tcp_small_queue_check(sk, skb, 0))
2248                         break;
2249 
2250                 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2251                         break;
2252 
2253 repair:
2254                 /* Advance the send_head.  This one is sent out.
2255                  * This call will increment packets_out.
2256                  */
2257                 tcp_event_new_data_sent(sk, skb);
2258 
2259                 tcp_minshall_update(tp, mss_now, skb);
2260                 sent_pkts += tcp_skb_pcount(skb);
2261 
2262                 if (push_one)
2263                         break;
2264         }
2265 
2266         if (is_rwnd_limited)
2267                 tcp_chrono_start(sk, TCP_CHRONO_RWND_LIMITED);
2268         else
2269                 tcp_chrono_stop(sk, TCP_CHRONO_RWND_LIMITED);
2270 
2271         if (likely(sent_pkts)) {
2272                 if (tcp_in_cwnd_reduction(sk))
2273                         tp->prr_out += sent_pkts;
2274 
2275                 /* Send one loss probe per tail loss episode. */
2276                 if (push_one != 2)
2277                         tcp_schedule_loss_probe(sk);
2278                 is_cwnd_limited |= (tcp_packets_in_flight(tp) >= tp->snd_cwnd);
2279                 tcp_cwnd_validate(sk, is_cwnd_limited);
2280                 return false;
2281         }
2282         return !tp->packets_out && tcp_send_head(sk);
2283 }
2284 
2285 bool tcp_schedule_loss_probe(struct sock *sk)
2286 {
2287         struct inet_connection_sock *icsk = inet_csk(sk);
2288         struct tcp_sock *tp = tcp_sk(sk);
2289         u32 timeout, tlp_time_stamp, rto_time_stamp;
2290         u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
2291 
2292         if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS))
2293                 return false;
2294         /* No consecutive loss probes. */
2295         if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
2296                 tcp_rearm_rto(sk);
2297                 return false;
2298         }
2299         /* Don't do any loss probe on a Fast Open connection before 3WHS
2300          * finishes.
2301          */
2302         if (tp->fastopen_rsk)
2303                 return false;
2304 
2305         /* TLP is only scheduled when next timer event is RTO. */
2306         if (icsk->icsk_pending != ICSK_TIME_RETRANS)
2307                 return false;
2308 
2309         /* Schedule a loss probe in 2*RTT for SACK capable connections
2310          * in Open state, that are either limited by cwnd or application.
2311          */
2312         if (sysctl_tcp_early_retrans < 3 || !tp->packets_out ||
2313             !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
2314                 return false;
2315 
2316         if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
2317              tcp_send_head(sk))
2318                 return false;
2319 
2320         /* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
2321          * for delayed ack when there's one outstanding packet. If no RTT
2322          * sample is available then probe after TCP_TIMEOUT_INIT.
2323          */
2324         timeout = rtt << 1 ? : TCP_TIMEOUT_INIT;
2325         if (tp->packets_out == 1)
2326                 timeout = max_t(u32, timeout,
2327                                 (rtt + (rtt >> 1) + TCP_DELACK_MAX));
2328         timeout = max_t(u32, timeout, msecs_to_jiffies(10));
2329 
2330         /* If RTO is shorter, just schedule TLP in its place. */
2331         tlp_time_stamp = tcp_time_stamp + timeout;
2332         rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
2333         if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
2334                 s32 delta = rto_time_stamp - tcp_time_stamp;
2335                 if (delta > 0)
2336                         timeout = delta;
2337         }
2338 
2339         inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
2340                                   TCP_RTO_MAX);
2341         return true;
2342 }
2343 
2344 /* Thanks to skb fast clones, we can detect if a prior transmit of
2345  * a packet is still in a qdisc or driver queue.
2346  * In this case, there is very little point doing a retransmit !
2347  */
2348 static bool skb_still_in_host_queue(const struct sock *sk,
2349                                     const struct sk_buff *skb)
2350 {
2351         if (unlikely(skb_fclone_busy(sk, skb))) {
2352                 NET_INC_STATS(sock_net(sk),
2353                               LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
2354                 return true;
2355         }
2356         return false;
2357 }
2358 
2359 /* When probe timeout (PTO) fires, try send a new segment if possible, else
2360  * retransmit the last segment.
2361  */
2362 void tcp_send_loss_probe(struct sock *sk)
2363 {
2364         struct tcp_sock *tp = tcp_sk(sk);
2365         struct sk_buff *skb;
2366         int pcount;
2367         int mss = tcp_current_mss(sk);
2368 
2369         skb = tcp_send_head(sk);
2370         if (skb) {
2371                 if (tcp_snd_wnd_test(tp, skb, mss)) {
2372                         pcount = tp->packets_out;
2373                         tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
2374                         if (tp->packets_out > pcount)
2375                                 goto probe_sent;
2376                         goto rearm_timer;
2377                 }
2378                 skb = tcp_write_queue_prev(sk, skb);
2379         } else {
2380                 skb = tcp_write_queue_tail(sk);
2381         }
2382 
2383         /* At most one outstanding TLP retransmission. */
2384         if (tp->tlp_high_seq)
2385                 goto rearm_timer;
2386 
2387         /* Retransmit last segment. */
2388         if (WARN_ON(!skb))
2389                 goto rearm_timer;
2390 
2391         if (skb_still_in_host_queue(sk, skb))
2392                 goto rearm_timer;
2393 
2394         pcount = tcp_skb_pcount(skb);
2395         if (WARN_ON(!pcount))
2396                 goto rearm_timer;
2397 
2398         if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2399                 if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
2400                                           GFP_ATOMIC)))
2401                         goto rearm_timer;
2402                 skb = tcp_write_queue_next(sk, skb);
2403         }
2404 
2405         if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
2406                 goto rearm_timer;
2407 
2408         if (__tcp_retransmit_skb(sk, skb, 1))
2409                 goto rearm_timer;
2410 
2411         /* Record snd_nxt for loss detection. */
2412         tp->tlp_high_seq = tp->snd_nxt;
2413 
2414 probe_sent:
2415         NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
2416         /* Reset s.t. tcp_rearm_rto will restart timer from now */
2417         inet_csk(sk)->icsk_pending = 0;
2418 rearm_timer:
2419         tcp_rearm_rto(sk);
2420 }
2421 
2422 /* Push out any pending frames which were held back due to
2423  * TCP_CORK or attempt at coalescing tiny packets.
2424  * The socket must be locked by the caller.
2425  */
2426 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
2427                                int nonagle)
2428 {
2429         /* If we are closed, the bytes will have to remain here.
2430          * In time closedown will finish, we empty the write queue and
2431          * all will be happy.
2432          */
2433         if (unlikely(sk->sk_state == TCP_CLOSE))
2434                 return;
2435 
2436         if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2437                            sk_gfp_mask(sk, GFP_ATOMIC)))
2438                 tcp_check_probe_timer(sk);
2439 }
2440 
2441 /* Send _single_ skb sitting at the send head. This function requires
2442  * true push pending frames to setup probe timer etc.
2443  */
2444 void tcp_push_one(struct sock *sk, unsigned int mss_now)
2445 {
2446         struct sk_buff *skb = tcp_send_head(sk);
2447 
2448         BUG_ON(!skb || skb->len < mss_now);
2449 
2450         tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2451 }
2452 
2453 /* This function returns the amount that we can raise the
2454  * usable window based on the following constraints
2455  *
2456  * 1. The window can never be shrunk once it is offered (RFC 793)
2457  * 2. We limit memory per socket
2458  *
2459  * RFC 1122:
2460  * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2461  *  RECV.NEXT + RCV.WIN fixed until:
2462  *  RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2463  *
2464  * i.e. don't raise the right edge of the window until you can raise
2465  * it at least MSS bytes.
2466  *
2467  * Unfortunately, the recommended algorithm breaks header prediction,
2468  * since header prediction assumes th->window stays fixed.
2469  *
2470  * Strictly speaking, keeping th->window fixed violates the receiver
2471  * side SWS prevention criteria. The problem is that under this rule
2472  * a stream of single byte packets will cause the right side of the
2473  * window to always advance by a single byte.
2474  *
2475  * Of course, if the sender implements sender side SWS prevention
2476  * then this will not be a problem.
2477  *
2478  * BSD seems to make the following compromise:
2479  *
2480  *      If the free space is less than the 1/4 of the maximum
2481  *      space available and the free space is less than 1/2 mss,
2482  *      then set the window to 0.
2483  *      [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2484  *      Otherwise, just prevent the window from shrinking
2485  *      and from being larger than the largest representable value.
2486  *
2487  * This prevents incremental opening of the window in the regime
2488  * where TCP is limited by the speed of the reader side taking
2489  * data out of the TCP receive queue. It does nothing about
2490  * those cases where the window is constrained on the sender side
2491  * because the pipeline is full.
2492  *
2493  * BSD also seems to "accidentally" limit itself to windows that are a
2494  * multiple of MSS, at least until the free space gets quite small.
2495  * This would appear to be a side effect of the mbuf implementation.
2496  * Combining these two algorithms results in the observed behavior
2497  * of having a fixed window size at almost all times.
2498  *
2499  * Below we obtain similar behavior by forcing the offered window to
2500  * a multiple of the mss when it is feasible to do so.
2501  *
2502  * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2503  * Regular options like TIMESTAMP are taken into account.
2504  */
2505 u32 __tcp_select_window(struct sock *sk)
2506 {
2507         struct inet_connection_sock *icsk = inet_csk(sk);
2508         struct tcp_sock *tp = tcp_sk(sk);
2509         /* MSS for the peer's data.  Previous versions used mss_clamp
2510          * here.  I don't know if the value based on our guesses
2511          * of peer's MSS is better for the performance.  It's more correct
2512          * but may be worse for the performance because of rcv_mss
2513          * fluctuations.  --SAW  1998/11/1
2514          */
2515         int mss = icsk->icsk_ack.rcv_mss;
2516         int free_space = tcp_space(sk);
2517         int allowed_space = tcp_full_space(sk);
2518         int full_space = min_t(int, tp->window_clamp, allowed_space);
2519         int window;
2520 
2521         if (unlikely(mss > full_space)) {
2522                 mss = full_space;
2523                 if (mss <= 0)
2524                         return 0;
2525         }
2526         if (free_space < (full_space >> 1)) {
2527                 icsk->icsk_ack.quick = 0;
2528 
2529                 if (tcp_under_memory_pressure(sk))
2530                         tp->rcv_ssthresh = min(tp->rcv_ssthresh,
2531                                                4U * tp->advmss);
2532 
2533                 /* free_space might become our new window, make sure we don't
2534                  * increase it due to wscale.
2535                  */
2536                 free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale);
2537 
2538                 /* if free space is less than mss estimate, or is below 1/16th
2539                  * of the maximum allowed, try to move to zero-window, else
2540                  * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
2541                  * new incoming data is dropped due to memory limits.
2542                  * With large window, mss test triggers way too late in order
2543                  * to announce zero window in time before rmem limit kicks in.
2544                  */
2545                 if (free_space < (allowed_space >> 4) || free_space < mss)
2546                         return 0;
2547         }
2548 
2549         if (free_space > tp->rcv_ssthresh)
2550                 free_space = tp->rcv_ssthresh;
2551 
2552         /* Don't do rounding if we are using window scaling, since the
2553          * scaled window will not line up with the MSS boundary anyway.
2554          */
2555         window = tp->rcv_wnd;
2556         if (tp->rx_opt.rcv_wscale) {
2557                 window = free_space;
2558 
2559                 /* Advertise enough space so that it won't get scaled away.
2560                  * Import case: prevent zero window announcement if
2561                  * 1<<rcv_wscale > mss.
2562                  */
2563                 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
2564                         window = (((window >> tp->rx_opt.rcv_wscale) + 1)
2565                                   << tp->rx_opt.rcv_wscale);
2566         } else {
2567                 /* Get the largest window that is a nice multiple of mss.
2568                  * Window clamp already applied above.
2569                  * If our current window offering is within 1 mss of the
2570                  * free space we just keep it. This prevents the divide
2571                  * and multiply from happening most of the time.
2572                  * We also don't do any window rounding when the free space
2573                  * is too small.
2574                  */
2575                 if (window <= free_space - mss || window > free_space)
2576                         window = (free_space / mss) * mss;
2577                 else if (mss == full_space &&
2578                          free_space > window + (full_space >> 1))
2579                         window = free_space;
2580         }
2581 
2582         return window;
2583 }
2584 
2585 void tcp_skb_collapse_tstamp(struct sk_buff *skb,
2586                              const struct sk_buff *next_skb)
2587 {
2588         if (unlikely(tcp_has_tx_tstamp(next_skb))) {
2589                 const struct skb_shared_info *next_shinfo =
2590                         skb_shinfo(next_skb);
2591                 struct skb_shared_info *shinfo = skb_shinfo(skb);
2592 
2593                 shinfo->tx_flags |= next_shinfo->tx_flags & SKBTX_ANY_TSTAMP;
2594                 shinfo->tskey = next_shinfo->tskey;
2595                 TCP_SKB_CB(skb)->txstamp_ack |=
2596                         TCP_SKB_CB(next_skb)->txstamp_ack;
2597         }
2598 }
2599 
2600 /* Collapses two adjacent SKB's during retransmission. */
2601 static bool tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
2602 {
2603         struct tcp_sock *tp = tcp_sk(sk);
2604         struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2605         int skb_size, next_skb_size;
2606 
2607         skb_size = skb->len;
2608         next_skb_size = next_skb->len;
2609 
2610         BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2611 
2612         if (next_skb_size) {
2613                 if (next_skb_size <= skb_availroom(skb))
2614                         skb_copy_bits(next_skb, 0, skb_put(skb, next_skb_size),
2615                                       next_skb_size);
2616                 else if (!skb_shift(skb, next_skb, next_skb_size))
2617                         return false;
2618         }
2619         tcp_highest_sack_combine(sk, next_skb, skb);
2620 
2621         tcp_unlink_write_queue(next_skb, sk);
2622 
2623         if (next_skb->ip_summed == CHECKSUM_PARTIAL)
2624                 skb->ip_summed = CHECKSUM_PARTIAL;
2625 
2626         if (skb->ip_summed != CHECKSUM_PARTIAL)
2627                 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
2628 
2629         /* Update sequence range on original skb. */
2630         TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
2631 
2632         /* Merge over control information. This moves PSH/FIN etc. over */
2633         TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2634 
2635         /* All done, get rid of second SKB and account for it so
2636          * packet counting does not break.
2637          */
2638         TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2639         TCP_SKB_CB(skb)->eor = TCP_SKB_CB(next_skb)->eor;
2640 
2641         /* changed transmit queue under us so clear hints */
2642         tcp_clear_retrans_hints_partial(tp);
2643         if (next_skb == tp->retransmit_skb_hint)
2644                 tp->retransmit_skb_hint = skb;
2645 
2646         tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
2647 
2648         tcp_skb_collapse_tstamp(skb, next_skb);
2649 
2650         sk_wmem_free_skb(sk, next_skb);
2651         return true;
2652 }
2653 
2654 /* Check if coalescing SKBs is legal. */
2655 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2656 {
2657         if (tcp_skb_pcount(skb) > 1)
2658                 return false;
2659         if (skb_cloned(skb))
2660                 return false;
2661         if (skb == tcp_send_head(sk))
2662                 return false;
2663         /* Some heuristics for collapsing over SACK'd could be invented */
2664         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2665                 return false;
2666 
2667         return true;
2668 }
2669 
2670 /* Collapse packets in the retransmit queue to make to create
2671  * less packets on the wire. This is only done on retransmission.
2672  */
2673 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
2674                                      int space)
2675 {
2676         struct tcp_sock *tp = tcp_sk(sk);
2677         struct sk_buff *skb = to, *tmp;
2678         bool first = true;
2679 
2680         if (!sysctl_tcp_retrans_collapse)
2681                 return;
2682         if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2683                 return;
2684 
2685         tcp_for_write_queue_from_safe(skb, tmp, sk) {
2686                 if (!tcp_can_collapse(sk, skb))
2687                         break;
2688 
2689                 if (!tcp_skb_can_collapse_to(to))
2690                         break;
2691 
2692                 space -= skb->len;
2693 
2694                 if (first) {
2695                         first = false;
2696                         continue;
2697                 }
2698 
2699                 if (space < 0)
2700                         break;
2701 
2702                 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
2703                         break;
2704 
2705                 if (!tcp_collapse_retrans(sk, to))
2706                         break;
2707         }
2708 }
2709 
2710 /* This retransmits one SKB.  Policy decisions and retransmit queue
2711  * state updates are done by the caller.  Returns non-zero if an
2712  * error occurred which prevented the send.
2713  */
2714 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
2715 {
2716         struct inet_connection_sock *icsk = inet_csk(sk);
2717         struct tcp_sock *tp = tcp_sk(sk);
2718         unsigned int cur_mss;
2719         int diff, len, err;
2720 
2721 
2722         /* Inconclusive MTU probe */
2723         if (icsk->icsk_mtup.probe_size)
2724                 icsk->icsk_mtup.probe_size = 0;
2725 
2726         /* Do not sent more than we queued. 1/4 is reserved for possible
2727          * copying overhead: fragmentation, tunneling, mangling etc.
2728          */
2729         if (atomic_read(&sk->sk_wmem_alloc) >
2730             min_t(u32, sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2),
2731                   sk->sk_sndbuf))
2732                 return -EAGAIN;
2733 
2734         if (skb_still_in_host_queue(sk, skb))
2735                 return -EBUSY;
2736 
2737         if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
2738                 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
2739                         BUG();
2740                 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2741                         return -ENOMEM;
2742         }
2743 
2744         if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
2745                 return -EHOSTUNREACH; /* Routing failure or similar. */
2746 
2747         cur_mss = tcp_current_mss(sk);
2748 
2749         /* If receiver has shrunk his window, and skb is out of
2750          * new window, do not retransmit it. The exception is the
2751          * case, when window is shrunk to zero. In this case
2752          * our retransmit serves as a zero window probe.
2753          */
2754         if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
2755             TCP_SKB_CB(skb)->seq != tp->snd_una)
2756                 return -EAGAIN;
2757 
2758         len = cur_mss * segs;
2759         if (skb->len > len) {
2760                 if (tcp_fragment(sk, skb, len, cur_mss, GFP_ATOMIC))
2761                         return -ENOMEM; /* We'll try again later. */
2762         } else {
2763                 if (skb_unclone(skb, GFP_ATOMIC))
2764                         return -ENOMEM;
2765 
2766                 diff = tcp_skb_pcount(skb);
2767                 tcp_set_skb_tso_segs(skb, cur_mss);
2768                 diff -= tcp_skb_pcount(skb);
2769                 if (diff)
2770                         tcp_adjust_pcount(sk, skb, diff);
2771                 if (skb->len < cur_mss)
2772                         tcp_retrans_try_collapse(sk, skb, cur_mss);
2773         }
2774 
2775         /* RFC3168, section 6.1.1.1. ECN fallback */
2776         if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN)
2777                 tcp_ecn_clear_syn(sk, skb);
2778 
2779         /* make sure skb->data is aligned on arches that require it
2780          * and check if ack-trimming & collapsing extended the headroom
2781          * beyond what csum_start can cover.
2782          */
2783         if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
2784                      skb_headroom(skb) >= 0xFFFF)) {
2785                 struct sk_buff *nskb;
2786 
2787                 skb_mstamp_get(&skb->skb_mstamp);
2788                 nskb = __pskb_copy(skb, MAX_TCP_HEADER, GFP_ATOMIC);
2789                 err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
2790                              -ENOBUFS;
2791         } else {
2792                 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2793         }
2794 
2795         if (likely(!err)) {
2796                 segs = tcp_skb_pcount(skb);
2797 
2798                 TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
2799                 /* Update global TCP statistics. */
2800                 TCP_ADD_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS, segs);
2801                 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2802                         __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
2803                 tp->total_retrans += segs;
2804         }
2805         return err;
2806 }
2807 
2808 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
2809 {
2810         struct tcp_sock *tp = tcp_sk(sk);
2811         int err = __tcp_retransmit_skb(sk, skb, segs);
2812 
2813         if (err == 0) {
2814 #if FASTRETRANS_DEBUG > 0
2815                 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2816                         net_dbg_ratelimited("retrans_out leaked\n");
2817                 }
2818 #endif
2819                 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
2820                 tp->retrans_out += tcp_skb_pcount(skb);
2821 
2822                 /* Save stamp of the first retransmit. */
2823                 if (!tp->retrans_stamp)
2824                         tp->retrans_stamp = tcp_skb_timestamp(skb);
2825 
2826         } else if (err != -EBUSY) {
2827                 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
2828         }
2829 
2830         if (tp->undo_retrans < 0)
2831                 tp->undo_retrans = 0;
2832         tp->undo_retrans += tcp_skb_pcount(skb);
2833         return err;
2834 }
2835 
2836 /* Check if we forward retransmits are possible in the current
2837  * window/congestion state.
2838  */
2839 static bool tcp_can_forward_retransmit(struct sock *sk)
2840 {
2841         const struct inet_connection_sock *icsk = inet_csk(sk);
2842         const struct tcp_sock *tp = tcp_sk(sk);
2843 
2844         /* Forward retransmissions are possible only during Recovery. */
2845         if (icsk->icsk_ca_state != TCP_CA_Recovery)
2846                 return false;
2847 
2848         /* No forward retransmissions in Reno are possible. */
2849         if (tcp_is_reno(tp))
2850                 return false;
2851 
2852         /* Yeah, we have to make difficult choice between forward transmission
2853          * and retransmission... Both ways have their merits...
2854          *
2855          * For now we do not retransmit anything, while we have some new
2856          * segments to send. In the other cases, follow rule 3 for
2857          * NextSeg() specified in RFC3517.
2858          */
2859 
2860         if (tcp_may_send_now(sk))
2861                 return false;
2862 
2863         return true;
2864 }
2865 
2866 /* This gets called after a retransmit timeout, and the initially
2867  * retransmitted data is acknowledged.  It tries to continue
2868  * resending the rest of the retransmit queue, until either
2869  * we've sent it all or the congestion window limit is reached.
2870  * If doing SACK, the first ACK which comes back for a timeout
2871  * based retransmit packet might feed us FACK information again.
2872  * If so, we use it to avoid unnecessarily retransmissions.
2873  */
2874 void tcp_xmit_retransmit_queue(struct sock *sk)
2875 {
2876         const struct inet_connection_sock *icsk = inet_csk(sk);
2877         struct tcp_sock *tp = tcp_sk(sk);
2878         struct sk_buff *skb;
2879         struct sk_buff *hole = NULL;
2880         u32 max_segs, last_lost;
2881         int mib_idx;
2882         int fwd_rexmitting = 0;
2883 
2884         if (!tp->packets_out)
2885                 return;
2886 
2887         if (!tp->lost_out)
2888                 tp->retransmit_high = tp->snd_una;
2889 
2890         if (tp->retransmit_skb_hint) {
2891                 skb = tp->retransmit_skb_hint;
2892                 last_lost = TCP_SKB_CB(skb)->end_seq;
2893                 if (after(last_lost, tp->retransmit_high))
2894                         last_lost = tp->retransmit_high;
2895         } else {
2896                 skb = tcp_write_queue_head(sk);
2897                 last_lost = tp->snd_una;
2898         }
2899 
2900         max_segs = tcp_tso_segs(sk, tcp_current_mss(sk));
2901         tcp_for_write_queue_from(skb, sk) {
2902                 __u8 sacked;
2903                 int segs;
2904 
2905                 if (skb == tcp_send_head(sk))
2906                         break;
2907                 /* we could do better than to assign each time */
2908                 if (!hole)
2909                         tp->retransmit_skb_hint = skb;
2910 
2911                 segs = tp->snd_cwnd - tcp_packets_in_flight(tp);
2912                 if (segs <= 0)
2913                         return;
2914                 sacked = TCP_SKB_CB(skb)->sacked;
2915                 /* In case tcp_shift_skb_data() have aggregated large skbs,
2916                  * we need to make sure not sending too bigs TSO packets
2917                  */
2918                 segs = min_t(int, segs, max_segs);
2919 
2920                 if (fwd_rexmitting) {
2921 begin_fwd:
2922                         if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
2923                                 break;
2924                         mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2925 
2926                 } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2927                         tp->retransmit_high = last_lost;
2928                         if (!tcp_can_forward_retransmit(sk))
2929                                 break;
2930                         /* Backtrack if necessary to non-L'ed skb */
2931                         if (hole) {
2932                                 skb = hole;
2933                                 hole = NULL;
2934                         }
2935                         fwd_rexmitting = 1;
2936                         goto begin_fwd;
2937 
2938                 } else if (!(sacked & TCPCB_LOST)) {
2939                         if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2940                                 hole = skb;
2941                         continue;
2942 
2943                 } else {
2944                         last_lost = TCP_SKB_CB(skb)->end_seq;
2945                         if (icsk->icsk_ca_state != TCP_CA_Loss)
2946                                 mib_idx = LINUX_MIB_TCPFASTRETRANS;
2947                         else
2948                                 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2949                 }
2950 
2951                 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
2952                         continue;
2953 
2954                 if (tcp_small_queue_check(sk, skb, 1))
2955                         return;
2956 
2957                 if (tcp_retransmit_skb(sk, skb, segs))
2958                         return;
2959 
2960                 NET_ADD_STATS(sock_net(sk), mib_idx, tcp_skb_pcount(skb));
2961 
2962                 if (tcp_in_cwnd_reduction(sk))
2963                         tp->prr_out += tcp_skb_pcount(skb);
2964 
2965                 if (skb == tcp_write_queue_head(sk))
2966                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2967                                                   inet_csk(sk)->icsk_rto,
2968                                                   TCP_RTO_MAX);
2969         }
2970 }
2971 
2972 /* We allow to exceed memory limits for FIN packets to expedite
2973  * connection tear down and (memory) recovery.
2974  * Otherwise tcp_send_fin() could be tempted to either delay FIN
2975  * or even be forced to close flow without any FIN.
2976  * In general, we want to allow one skb per socket to avoid hangs
2977  * with edge trigger epoll()
2978  */
2979 void sk_forced_mem_schedule(struct sock *sk, int size)
2980 {
2981         int amt;
2982 
2983         if (size <= sk->sk_forward_alloc)
2984                 return;
2985         amt = sk_mem_pages(size);
2986         sk->sk_forward_alloc += amt * SK_MEM_QUANTUM;
2987         sk_memory_allocated_add(sk, amt);
2988 
2989         if (mem_cgroup_sockets_enabled && sk->sk_memcg)
2990                 mem_cgroup_charge_skmem(sk->sk_memcg, amt);
2991 }
2992 
2993 /* Send a FIN. The caller locks the socket for us.
2994  * We should try to send a FIN packet really hard, but eventually give up.
2995  */
2996 void tcp_send_fin(struct sock *sk)
2997 {
2998         struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk);
2999         struct tcp_sock *tp = tcp_sk(sk);
3000 
3001         /* Optimization, tack on the FIN if we have one skb in write queue and
3002          * this skb was not yet sent, or we are under memory pressure.
3003          * Note: in the latter case, FIN packet will be sent after a timeout,
3004          * as TCP stack thinks it has already been transmitted.
3005          */
3006         if (tskb && (tcp_send_head(sk) || tcp_under_memory_pressure(sk))) {
3007 coalesce:
3008                 TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;
3009                 TCP_SKB_CB(tskb)->end_seq++;
3010                 tp->write_seq++;
3011                 if (!tcp_send_head(sk)) {
3012                         /* This means tskb was already sent.
3013                          * Pretend we included the FIN on previous transmit.
3014                          * We need to set tp->snd_nxt to the value it would have
3015                          * if FIN had been sent. This is because retransmit path
3016                          * does not change tp->snd_nxt.
3017                          */
3018                         tp->snd_nxt++;
3019                         return;
3020                 }
3021         } else {
3022                 skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
3023                 if (unlikely(!skb)) {
3024                         if (tskb)
3025                                 goto coalesce;
3026                         return;
3027                 }
3028                 skb_reserve(skb, MAX_TCP_HEADER);
3029                 sk_forced_mem_schedule(sk, skb->truesize);
3030                 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
3031                 tcp_init_nondata_skb(skb, tp->write_seq,
3032                                      TCPHDR_ACK | TCPHDR_FIN);
3033                 tcp_queue_skb(sk, skb);
3034         }
3035         __tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF);
3036 }
3037 
3038 /* We get here when a process closes a file descriptor (either due to
3039  * an explicit close() or as a byproduct of exit()'ing) and there
3040  * was unread data in the receive queue.  This behavior is recommended
3041  * by RFC 2525, section 2.17.  -DaveM
3042  */
3043 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
3044 {
3045         struct sk_buff *skb;
3046 
3047         /* NOTE: No TCP options attached and we never retransmit this. */
3048         skb = alloc_skb(MAX_TCP_HEADER, priority);
3049         if (!skb) {
3050                 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
3051                 return;
3052         }
3053 
3054         /* Reserve space for headers and prepare control bits. */
3055         skb_reserve(skb, MAX_TCP_HEADER);
3056         tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
3057                              TCPHDR_ACK | TCPHDR_RST);
3058         skb_mstamp_get(&skb->skb_mstamp);
3059         /* Send it off. */
3060         if (tcp_transmit_skb(sk, skb, 0, priority))
3061                 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
3062 
3063         TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
3064 }
3065 
3066 /* Send a crossed SYN-ACK during socket establishment.
3067  * WARNING: This routine must only be called when we have already sent
3068  * a SYN packet that crossed the incoming SYN that caused this routine
3069  * to get called. If this assumption fails then the initial rcv_wnd
3070  * and rcv_wscale values will not be correct.
3071  */
3072 int tcp_send_synack(struct sock *sk)
3073 {
3074         struct sk_buff *skb;
3075 
3076         skb = tcp_write_queue_head(sk);
3077         if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
3078                 pr_debug("%s: wrong queue state\n", __func__);
3079                 return -EFAULT;
3080         }
3081         if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
3082                 if (skb_cloned(skb)) {
3083                         struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
3084                         if (!nskb)
3085                                 return -ENOMEM;
3086                         tcp_unlink_write_queue(skb, sk);
3087                         __skb_header_release(nskb);
3088                         __tcp_add_write_queue_head(sk, nskb);
3089                         sk_wmem_free_skb(sk, skb);
3090                         sk->sk_wmem_queued += nskb->truesize;
3091                         sk_mem_charge(sk, nskb->truesize);
3092                         skb = nskb;
3093                 }
3094 
3095                 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
3096                 tcp_ecn_send_synack(sk, skb);
3097         }
3098         return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3099 }
3100 
3101 /**
3102  * tcp_make_synack - Prepare a SYN-ACK.
3103  * sk: listener socket
3104  * dst: dst entry attached to the SYNACK
3105  * req: request_sock pointer
3106  *
3107  * Allocate one skb and build a SYNACK packet.
3108  * @dst is consumed : Caller should not use it again.
3109  */
3110 struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
3111                                 struct request_sock *req,
3112                                 struct tcp_fastopen_cookie *foc,
3113                                 enum tcp_synack_type synack_type)
3114 {
3115         struct inet_request_sock *ireq = inet_rsk(req);
3116         const struct tcp_sock *tp = tcp_sk(sk);
3117         struct tcp_md5sig_key *md5 = NULL;
3118         struct tcp_out_options opts;
3119         struct sk_buff *skb;
3120         int tcp_header_size;
3121         struct tcphdr *th;
3122         u16 user_mss;
3123         int mss;
3124 
3125         skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
3126         if (unlikely(!skb)) {
3127                 dst_release(dst);
3128                 return NULL;
3129         }
3130         /* Reserve space for headers. */
3131         skb_reserve(skb, MAX_TCP_HEADER);
3132 
3133         switch (synack_type) {
3134         case TCP_SYNACK_NORMAL:
3135                 skb_set_owner_w(skb, req_to_sk(req));
3136                 break;
3137         case TCP_SYNACK_COOKIE:
3138                 /* Under synflood, we do not attach skb to a socket,
3139                  * to avoid false sharing.
3140                  */
3141                 break;
3142         case TCP_SYNACK_FASTOPEN:
3143                 /* sk is a const pointer, because we want to express multiple
3144                  * cpu might call us concurrently.
3145                  * sk->sk_wmem_alloc in an atomic, we can promote to rw.
3146                  */
3147                 skb_set_owner_w(skb, (struct sock *)sk);
3148                 break;
3149         }
3150         skb_dst_set(skb, dst);
3151 
3152         mss = dst_metric_advmss(dst);
3153         user_mss = READ_ONCE(tp->rx_opt.user_mss);
3154         if (user_mss && user_mss < mss)
3155                 mss = user_mss;
3156 
3157         memset(&opts, 0, sizeof(opts));
3158 #ifdef CONFIG_SYN_COOKIES
3159         if (unlikely(req->cookie_ts))
3160                 skb->skb_mstamp.stamp_jiffies = cookie_init_timestamp(req);
3161         else
3162 #endif
3163         skb_mstamp_get(&skb->skb_mstamp);
3164 
3165 #ifdef CONFIG_TCP_MD5SIG
3166         rcu_read_lock();
3167         md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
3168 #endif
3169         skb_set_hash(skb, tcp_rsk(req)->txhash, PKT_HASH_TYPE_L4);
3170         tcp_header_size = tcp_synack_options(req, mss, skb, &opts, md5, foc) +
3171                           sizeof(*th);
3172 
3173         skb_push(skb, tcp_header_size);
3174         skb_reset_transport_header(skb);
3175 
3176         th = (struct tcphdr *)skb->data;
3177         memset(th, 0, sizeof(struct tcphdr));
3178         th->syn = 1;
3179         th->ack = 1;
3180         tcp_ecn_make_synack(req, th);
3181         th->source = htons(ireq->ir_num);
3182         th->dest = ireq->ir_rmt_port;
3183         /* Setting of flags are superfluous here for callers (and ECE is
3184          * not even correctly set)
3185          */
3186         tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
3187                              TCPHDR_SYN | TCPHDR_ACK);
3188 
3189         th->seq = htonl(TCP_SKB_CB(skb)->seq);
3190         /* XXX data is queued and acked as is. No buffer/window check */
3191         th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);
3192 
3193         /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
3194         th->window = htons(min(req->rsk_rcv_wnd, 65535U));
3195         tcp_options_write((__be32 *)(th + 1), NULL, &opts);
3196         th->doff = (tcp_header_size >> 2);
3197         __TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
3198 
3199 #ifdef CONFIG_TCP_MD5SIG
3200         /* Okay, we have all we need - do the md5 hash if needed */
3201         if (md5)
3202                 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
3203                                                md5, req_to_sk(req), skb);
3204         rcu_read_unlock();
3205 #endif
3206 
3207         /* Do not fool tcpdump (if any), clean our debris */
3208         skb->tstamp = 0;
3209         return skb;
3210 }
3211 EXPORT_SYMBOL(tcp_make_synack);
3212 
3213 static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst)
3214 {
3215         struct inet_connection_sock *icsk = inet_csk(sk);
3216         const struct tcp_congestion_ops *ca;
3217         u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
3218 
3219         if (ca_key == TCP_CA_UNSPEC)
3220                 return;
3221 
3222         rcu_read_lock();
3223         ca = tcp_ca_find_key(ca_key);
3224         if (likely(ca && try_module_get(ca->owner))) {
3225                 module_put(icsk->icsk_ca_ops->owner);
3226                 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
3227                 icsk->icsk_ca_ops = ca;
3228         }
3229         rcu_read_unlock();
3230 }
3231 
3232 /* Do all connect socket setups that can be done AF independent. */
3233 static void tcp_connect_init(struct sock *sk)
3234 {
3235         const struct dst_entry *dst = __sk_dst_get(sk);
3236         struct tcp_sock *tp = tcp_sk(sk);
3237         __u8 rcv_wscale;
3238 
3239         /* We'll fix this up when we get a response from the other end.
3240          * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
3241          */
3242         tp->tcp_header_len = sizeof(struct tcphdr) +
3243                 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
3244 
3245 #ifdef CONFIG_TCP_MD5SIG
3246         if (tp->af_specific->md5_lookup(sk, sk))
3247                 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
3248 #endif
3249 
3250         /* If user gave his TCP_MAXSEG, record it to clamp */
3251         if (tp->rx_opt.user_mss)
3252                 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3253         tp->max_window = 0;
3254         tcp_mtup_init(sk);
3255         tcp_sync_mss(sk, dst_mtu(dst));
3256 
3257         tcp_ca_dst_init(sk, dst);
3258 
3259         if (!tp->window_clamp)
3260                 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
3261         tp->advmss = dst_metric_advmss(dst);
3262         if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
3263                 tp->advmss = tp->rx_opt.user_mss;
3264 
3265         tcp_initialize_rcv_mss(sk);
3266 
3267         /* limit the window selection if the user enforce a smaller rx buffer */
3268         if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
3269             (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
3270                 tp->window_clamp = tcp_full_space(sk);
3271 
3272         tcp_select_initial_window(tcp_full_space(sk),
3273                                   tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
3274                                   &tp->rcv_wnd,
3275                                   &tp->window_clamp,
3276                                   sysctl_tcp_window_scaling,
3277                                   &rcv_wscale,
3278                                   dst_metric(dst, RTAX_INITRWND));
3279 
3280         tp->rx_opt.rcv_wscale = rcv_wscale;
3281         tp->rcv_ssthresh = tp->rcv_wnd;
3282 
3283         sk->sk_err = 0;
3284         sock_reset_flag(sk, SOCK_DONE);
3285         tp->snd_wnd = 0;
3286         tcp_init_wl(tp, 0);
3287         tp->snd_una = tp->write_seq;
3288         tp->snd_sml = tp->write_seq;
3289         tp->snd_up = tp->write_seq;
3290         tp->snd_nxt = tp->write_seq;
3291 
3292         if (likely(!tp->repair))
3293                 tp->rcv_nxt = 0;
3294         else
3295                 tp->rcv_tstamp = tcp_time_stamp;
3296         tp->rcv_wup = tp->rcv_nxt;
3297         tp->copied_seq = tp->rcv_nxt;
3298 
3299         inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
3300         inet_csk(sk)->icsk_retransmits = 0;
3301         tcp_clear_retrans(tp);
3302 }
3303 
3304 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
3305 {
3306         struct tcp_sock *tp = tcp_sk(sk);
3307         struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
3308 
3309         tcb->end_seq += skb->len;
3310         __skb_header_release(skb);
3311         __tcp_add_write_queue_tail(sk, skb);
3312         sk->sk_wmem_queued += skb->truesize;
3313         sk_mem_charge(sk, skb->truesize);
3314         tp->write_seq = tcb->end_seq;
3315         tp->packets_out += tcp_skb_pcount(skb);
3316 }
3317 
3318 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
3319  * queue a data-only packet after the regular SYN, such that regular SYNs
3320  * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
3321  * only the SYN sequence, the data are retransmitted in the first ACK.
3322  * If cookie is not cached or other error occurs, falls back to send a
3323  * regular SYN with Fast Open cookie request option.
3324  */
3325 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
3326 {
3327         struct tcp_sock *tp = tcp_sk(sk);
3328         struct tcp_fastopen_request *fo = tp->fastopen_req;
3329         int syn_loss = 0, space, err = 0;
3330         unsigned long last_syn_loss = 0;
3331         struct sk_buff *syn_data;
3332 
3333         tp->rx_opt.mss_clamp = tp->advmss;  /* If MSS is not cached */
3334         tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
3335                                &syn_loss, &last_syn_loss);
3336         /* Recurring FO SYN losses: revert to regular handshake temporarily */
3337         if (syn_loss > 1 &&
3338             time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
3339                 fo->cookie.len = -1;
3340                 goto fallback;
3341         }
3342 
3343         if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
3344                 fo->cookie.len = -1;
3345         else if (fo->cookie.len <= 0)
3346                 goto fallback;
3347 
3348         /* MSS for SYN-data is based on cached MSS and bounded by PMTU and
3349          * user-MSS. Reserve maximum option space for middleboxes that add
3350          * private TCP options. The cost is reduced data space in SYN :(
3351          */
3352         if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
3353                 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3354         space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
3355                 MAX_TCP_OPTION_SPACE;
3356 
3357         space = min_t(size_t, space, fo->size);
3358 
3359         /* limit to order-0 allocations */
3360         space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));
3361 
3362         syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation, false);
3363         if (!syn_data)
3364                 goto fallback;
3365         syn_data->ip_summed = CHECKSUM_PARTIAL;
3366         memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
3367         if (space) {
3368                 int copied = copy_from_iter(skb_put(syn_data, space), space,
3369                                             &fo->data->msg_iter);
3370                 if (unlikely(!copied)) {
3371                         kfree_skb(syn_data);
3372                         goto fallback;
3373                 }
3374                 if (copied != space) {
3375                         skb_trim(syn_data, copied);
3376                         space = copied;
3377                 }
3378         }
3379         /* No more data pending in inet_wait_for_connect() */
3380         if (space == fo->size)
3381                 fo->data = NULL;
3382         fo->copied = space;
3383 
3384         tcp_connect_queue_skb(sk, syn_data);
3385         if (syn_data->len)
3386                 tcp_chrono_start(sk, TCP_CHRONO_BUSY);
3387 
3388         err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
3389 
3390         syn->skb_mstamp = syn_data->skb_mstamp;
3391 
3392         /* Now full SYN+DATA was cloned and sent (or not),
3393          * remove the SYN from the original skb (syn_data)
3394          * we keep in write queue in case of a retransmit, as we
3395          * also have the SYN packet (with no data) in the same queue.
3396          */
3397         TCP_SKB_CB(syn_data)->seq++;
3398         TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH;
3399         if (!err) {
3400                 tp->syn_data = (fo->copied > 0);
3401                 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
3402                 goto done;
3403         }
3404 
3405 fallback:
3406         /* Send a regular SYN with Fast Open cookie request option */
3407         if (fo->cookie.len > 0)
3408                 fo->cookie.len = 0;
3409         err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
3410         if (err)
3411                 tp->syn_fastopen = 0;
3412 done:
3413         fo->cookie.len = -1;  /* Exclude Fast Open option for SYN retries */
3414         return err;
3415 }
3416 
3417 /* Build a SYN and send it off. */
3418 int tcp_connect(struct sock *sk)
3419 {
3420         struct tcp_sock *tp = tcp_sk(sk);
3421         struct sk_buff *buff;
3422         int err;
3423 
3424         tcp_connect_init(sk);
3425 
3426         if (unlikely(tp->repair)) {
3427                 tcp_finish_connect(sk, NULL);
3428                 return 0;
3429         }
3430 
3431         buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation, true);
3432         if (unlikely(!buff))
3433                 return -ENOBUFS;
3434 
3435         tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
3436         tp->retrans_stamp = tcp_time_stamp;
3437         tcp_connect_queue_skb(sk, buff);
3438         tcp_ecn_send_syn(sk, buff);
3439 
3440         /* Send off SYN; include data in Fast Open. */
3441         err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
3442               tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
3443         if (err == -ECONNREFUSED)
3444                 return err;
3445 
3446         /* We change tp->snd_nxt after the tcp_transmit_skb() call
3447          * in order to make this packet get counted in tcpOutSegs.
3448          */
3449         tp->snd_nxt = tp->write_seq;
3450         tp->pushed_seq = tp->write_seq;
3451         TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
3452 
3453         /* Timer for repeating the SYN until an answer. */
3454         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3455                                   inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3456         return 0;
3457 }
3458 EXPORT_SYMBOL(tcp_connect);
3459 
3460 /* Send out a delayed ack, the caller does the policy checking
3461  * to see if we should even be here.  See tcp_input.c:tcp_ack_snd_check()
3462  * for details.
3463  */
3464 void tcp_send_delayed_ack(struct sock *sk)
3465 {
3466         struct inet_connection_sock *icsk = inet_csk(sk);
3467         int ato = icsk->icsk_ack.ato;
3468         unsigned long timeout;
3469 
3470         tcp_ca_event(sk, CA_EVENT_DELAYED_ACK);
3471 
3472         if (ato > TCP_DELACK_MIN) {
3473                 const struct tcp_sock *tp = tcp_sk(sk);
3474                 int max_ato = HZ / 2;
3475 
3476                 if (icsk->icsk_ack.pingpong ||
3477                     (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
3478                         max_ato = TCP_DELACK_MAX;
3479 
3480                 /* Slow path, intersegment interval is "high". */
3481 
3482                 /* If some rtt estimate is known, use it to bound delayed ack.
3483                  * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
3484                  * directly.
3485                  */
3486                 if (tp->srtt_us) {
3487                         int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3),
3488                                         TCP_DELACK_MIN);
3489 
3490                         if (rtt < max_ato)
3491                                 max_ato = rtt;
3492                 }
3493 
3494                 ato = min(ato, max_ato);
3495         }
3496 
3497         /* Stay within the limit we were given */
3498         timeout = jiffies + ato;
3499 
3500         /* Use new timeout only if there wasn't a older one earlier. */
3501         if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
3502                 /* If delack timer was blocked or is about to expire,
3503                  * send ACK now.
3504                  */
3505                 if (icsk->icsk_ack.blocked ||
3506                     time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
3507                         tcp_send_ack(sk);
3508                         return;
3509                 }
3510 
3511                 if (!time_before(timeout, icsk->icsk_ack.timeout))
3512                         timeout = icsk->icsk_ack.timeout;
3513         }
3514         icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
3515         icsk->icsk_ack.timeout = timeout;
3516         sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
3517 }
3518 
3519 /* This routine sends an ack and also updates the window. */
3520 void tcp_send_ack(struct sock *sk)
3521 {
3522         struct sk_buff *buff;
3523 
3524         /* If we have been reset, we may not send again. */
3525         if (sk->sk_state == TCP_CLOSE)
3526                 return;
3527 
3528         tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);
3529 
3530         /* We are not putting this on the write queue, so
3531          * tcp_transmit_skb() will set the ownership to this
3532          * sock.
3533          */
3534         buff = alloc_skb(MAX_TCP_HEADER,
3535                          sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
3536         if (unlikely(!buff)) {
3537                 inet_csk_schedule_ack(sk);
3538                 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
3539                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
3540                                           TCP_DELACK_MAX, TCP_RTO_MAX);
3541                 return;
3542         }
3543 
3544         /* Reserve space for headers and prepare control bits. */
3545         skb_reserve(buff, MAX_TCP_HEADER);
3546         tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3547 
3548         /* We do not want pure acks influencing TCP Small Queues or fq/pacing
3549          * too much.
3550          * SKB_TRUESIZE(max(1 .. 66, MAX_TCP_HEADER)) is unfortunately ~784
3551          */
3552         skb_set_tcp_pure_ack(buff);
3553 
3554         /* Send it off, this clears delayed acks for us. */
3555         skb_mstamp_get(&buff->skb_mstamp);
3556         tcp_transmit_skb(sk, buff, 0, (__force gfp_t)0);
3557 }
3558 EXPORT_SYMBOL_GPL(tcp_send_ack);
3559 
3560 /* This routine sends a packet with an out of date sequence
3561  * number. It assumes the other end will try to ack it.
3562  *
3563  * Question: what should we make while urgent mode?
3564  * 4.4BSD forces sending single byte of data. We cannot send
3565  * out of window data, because we have SND.NXT==SND.MAX...
3566  *
3567  * Current solution: to send TWO zero-length segments in urgent mode:
3568  * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
3569  * out-of-date with SND.UNA-1 to probe window.
3570  */
3571 static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib)
3572 {
3573         struct tcp_sock *tp = tcp_sk(sk);
3574         struct sk_buff *skb;
3575 
3576         /* We don't queue it, tcp_transmit_skb() sets ownership. */
3577         skb = alloc_skb(MAX_TCP_HEADER,
3578                         sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
3579         if (!skb)
3580                 return -1;
3581 
3582         /* Reserve space for headers and set control bits. */
3583         skb_reserve(skb, MAX_TCP_HEADER);
3584         /* Use a previous sequence.  This should cause the other
3585          * end to send an ack.  Don't queue or clone SKB, just
3586          * send it.
3587          */
3588         tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
3589         skb_mstamp_get(&skb->skb_mstamp);
3590         NET_INC_STATS(sock_net(sk), mib);
3591         return tcp_transmit_skb(sk, skb, 0, (__force gfp_t)0);
3592 }
3593 
3594 void tcp_send_window_probe(struct sock *sk)
3595 {
3596         if (sk->sk_state == TCP_ESTABLISHED) {
3597                 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
3598                 tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE);
3599         }
3600 }
3601 
3602 /* Initiate keepalive or window probe from timer. */
3603 int tcp_write_wakeup(struct sock *sk, int mib)
3604 {
3605         struct tcp_sock *tp = tcp_sk(sk);
3606         struct sk_buff *skb;
3607 
3608         if (sk->sk_state == TCP_CLOSE)
3609                 return -1;
3610 
3611         skb = tcp_send_head(sk);
3612         if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3613                 int err;
3614                 unsigned int mss = tcp_current_mss(sk);
3615                 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
3616 
3617                 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
3618                         tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
3619 
3620                 /* We are probing the opening of a window
3621                  * but the window size is != 0
3622                  * must have been a result SWS avoidance ( sender )
3623                  */
3624                 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
3625                     skb->len > mss) {
3626                         seg_size = min(seg_size, mss);
3627                         TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3628                         if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC))
3629                                 return -1;
3630                 } else if (!tcp_skb_pcount(skb))
3631                         tcp_set_skb_tso_segs(skb, mss);
3632 
3633                 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3634                 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3635                 if (!err)
3636                         tcp_event_new_data_sent(sk, skb);
3637                 return err;
3638         } else {
3639                 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3640                         tcp_xmit_probe_skb(sk, 1, mib);
3641                 return tcp_xmit_probe_skb(sk, 0, mib);
3642         }
3643 }
3644 
3645 /* A window probe timeout has occurred.  If window is not closed send
3646  * a partial packet else a zero probe.
3647  */
3648 void tcp_send_probe0(struct sock *sk)
3649 {
3650         struct inet_connection_sock *icsk = inet_csk(sk);
3651         struct tcp_sock *tp = tcp_sk(sk);
3652         struct net *net = sock_net(sk);
3653         unsigned long probe_max;
3654         int err;
3655 
3656         err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE);
3657 
3658         if (tp->packets_out || !tcp_send_head(sk)) {
3659                 /* Cancel probe timer, if it is not required. */
3660                 icsk->icsk_probes_out = 0;
3661                 icsk->icsk_backoff = 0;
3662                 return;
3663         }
3664 
3665         if (err <= 0) {
3666                 if (icsk->icsk_backoff < net->ipv4.sysctl_tcp_retries2)
3667                         icsk->icsk_backoff++;
3668                 icsk->icsk_probes_out++;
3669                 probe_max = TCP_RTO_MAX;
3670         } else {
3671                 /* If packet was not sent due to local congestion,
3672                  * do not backoff and do not remember icsk_probes_out.
3673                  * Let local senders to fight for local resources.
3674                  *
3675                  * Use accumulated backoff yet.
3676                  */
3677                 if (!icsk->icsk_probes_out)
3678                         icsk->icsk_probes_out = 1;
3679                 probe_max = TCP_RESOURCE_PROBE_INTERVAL;
3680         }
3681         inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3682                                   tcp_probe0_when(sk, probe_max),
3683                                   TCP_RTO_MAX);
3684 }
3685 
3686 int tcp_rtx_synack(const struct sock *sk, struct request_sock *req)
3687 {
3688         const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
3689         struct flowi fl;
3690         int res;
3691 
3692         tcp_rsk(req)->txhash = net_tx_rndhash();
3693         res = af_ops->send_synack(sk, NULL, &fl, req, NULL, TCP_SYNACK_NORMAL);
3694         if (!res) {
3695                 __TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
3696                 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
3697                 if (unlikely(tcp_passive_fastopen(sk)))
3698                         tcp_sk(sk)->total_retrans++;
3699         }
3700         return res;
3701 }
3702 EXPORT_SYMBOL(tcp_rtx_synack);
3703 

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