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Linux/include/net/tcp.h

  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  *              Definitions for the TCP module.
  7  *
  8  * Version:     @(#)tcp.h       1.0.5   05/23/93
  9  *
 10  * Authors:     Ross Biro
 11  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 12  *
 13  *              This program is free software; you can redistribute it and/or
 14  *              modify it under the terms of the GNU General Public License
 15  *              as published by the Free Software Foundation; either version
 16  *              2 of the License, or (at your option) any later version.
 17  */
 18 #ifndef _TCP_H
 19 #define _TCP_H
 20 
 21 #define FASTRETRANS_DEBUG 1
 22 
 23 #include <linux/list.h>
 24 #include <linux/tcp.h>
 25 #include <linux/bug.h>
 26 #include <linux/slab.h>
 27 #include <linux/cache.h>
 28 #include <linux/percpu.h>
 29 #include <linux/skbuff.h>
 30 #include <linux/crypto.h>
 31 #include <linux/cryptohash.h>
 32 #include <linux/kref.h>
 33 #include <linux/ktime.h>
 34 
 35 #include <net/inet_connection_sock.h>
 36 #include <net/inet_timewait_sock.h>
 37 #include <net/inet_hashtables.h>
 38 #include <net/checksum.h>
 39 #include <net/request_sock.h>
 40 #include <net/sock.h>
 41 #include <net/snmp.h>
 42 #include <net/ip.h>
 43 #include <net/tcp_states.h>
 44 #include <net/inet_ecn.h>
 45 #include <net/dst.h>
 46 
 47 #include <linux/seq_file.h>
 48 #include <linux/memcontrol.h>
 49 
 50 extern struct inet_hashinfo tcp_hashinfo;
 51 
 52 extern struct percpu_counter tcp_orphan_count;
 53 void tcp_time_wait(struct sock *sk, int state, int timeo);
 54 
 55 #define MAX_TCP_HEADER  (128 + MAX_HEADER)
 56 #define MAX_TCP_OPTION_SPACE 40
 57 
 58 /*
 59  * Never offer a window over 32767 without using window scaling. Some
 60  * poor stacks do signed 16bit maths!
 61  */
 62 #define MAX_TCP_WINDOW          32767U
 63 
 64 /* Minimal accepted MSS. It is (60+60+8) - (20+20). */
 65 #define TCP_MIN_MSS             88U
 66 
 67 /* The least MTU to use for probing */
 68 #define TCP_BASE_MSS            1024
 69 
 70 /* probing interval, default to 10 minutes as per RFC4821 */
 71 #define TCP_PROBE_INTERVAL      600
 72 
 73 /* Specify interval when tcp mtu probing will stop */
 74 #define TCP_PROBE_THRESHOLD     8
 75 
 76 /* After receiving this amount of duplicate ACKs fast retransmit starts. */
 77 #define TCP_FASTRETRANS_THRESH 3
 78 
 79 /* Maximal number of ACKs sent quickly to accelerate slow-start. */
 80 #define TCP_MAX_QUICKACKS       16U
 81 
 82 /* urg_data states */
 83 #define TCP_URG_VALID   0x0100
 84 #define TCP_URG_NOTYET  0x0200
 85 #define TCP_URG_READ    0x0400
 86 
 87 #define TCP_RETR1       3       /*
 88                                  * This is how many retries it does before it
 89                                  * tries to figure out if the gateway is
 90                                  * down. Minimal RFC value is 3; it corresponds
 91                                  * to ~3sec-8min depending on RTO.
 92                                  */
 93 
 94 #define TCP_RETR2       15      /*
 95                                  * This should take at least
 96                                  * 90 minutes to time out.
 97                                  * RFC1122 says that the limit is 100 sec.
 98                                  * 15 is ~13-30min depending on RTO.
 99                                  */
100 
101 #define TCP_SYN_RETRIES  6      /* This is how many retries are done
102                                  * when active opening a connection.
103                                  * RFC1122 says the minimum retry MUST
104                                  * be at least 180secs.  Nevertheless
105                                  * this value is corresponding to
106                                  * 63secs of retransmission with the
107                                  * current initial RTO.
108                                  */
109 
110 #define TCP_SYNACK_RETRIES 5    /* This is how may retries are done
111                                  * when passive opening a connection.
112                                  * This is corresponding to 31secs of
113                                  * retransmission with the current
114                                  * initial RTO.
115                                  */
116 
117 #define TCP_TIMEWAIT_LEN (60*HZ) /* how long to wait to destroy TIME-WAIT
118                                   * state, about 60 seconds     */
119 #define TCP_FIN_TIMEOUT TCP_TIMEWAIT_LEN
120                                  /* BSD style FIN_WAIT2 deadlock breaker.
121                                   * It used to be 3min, new value is 60sec,
122                                   * to combine FIN-WAIT-2 timeout with
123                                   * TIME-WAIT timer.
124                                   */
125 
126 #define TCP_DELACK_MAX  ((unsigned)(HZ/5))      /* maximal time to delay before sending an ACK */
127 #if HZ >= 100
128 #define TCP_DELACK_MIN  ((unsigned)(HZ/25))     /* minimal time to delay before sending an ACK */
129 #define TCP_ATO_MIN     ((unsigned)(HZ/25))
130 #else
131 #define TCP_DELACK_MIN  4U
132 #define TCP_ATO_MIN     4U
133 #endif
134 #define TCP_RTO_MAX     ((unsigned)(120*HZ))
135 #define TCP_RTO_MIN     ((unsigned)(HZ/5))
136 #define TCP_TIMEOUT_INIT ((unsigned)(1*HZ))     /* RFC6298 2.1 initial RTO value        */
137 #define TCP_TIMEOUT_FALLBACK ((unsigned)(3*HZ)) /* RFC 1122 initial RTO value, now
138                                                  * used as a fallback RTO for the
139                                                  * initial data transmission if no
140                                                  * valid RTT sample has been acquired,
141                                                  * most likely due to retrans in 3WHS.
142                                                  */
143 
144 #define TCP_RESOURCE_PROBE_INTERVAL ((unsigned)(HZ/2U)) /* Maximal interval between probes
145                                                          * for local resources.
146                                                          */
147 
148 #define TCP_KEEPALIVE_TIME      (120*60*HZ)     /* two hours */
149 #define TCP_KEEPALIVE_PROBES    9               /* Max of 9 keepalive probes    */
150 #define TCP_KEEPALIVE_INTVL     (75*HZ)
151 
152 #define MAX_TCP_KEEPIDLE        32767
153 #define MAX_TCP_KEEPINTVL       32767
154 #define MAX_TCP_KEEPCNT         127
155 #define MAX_TCP_SYNCNT          127
156 
157 #define TCP_SYNQ_INTERVAL       (HZ/5)  /* Period of SYNACK timer */
158 
159 #define TCP_PAWS_24DAYS (60 * 60 * 24 * 24)
160 #define TCP_PAWS_MSL    60              /* Per-host timestamps are invalidated
161                                          * after this time. It should be equal
162                                          * (or greater than) TCP_TIMEWAIT_LEN
163                                          * to provide reliability equal to one
164                                          * provided by timewait state.
165                                          */
166 #define TCP_PAWS_WINDOW 1               /* Replay window for per-host
167                                          * timestamps. It must be less than
168                                          * minimal timewait lifetime.
169                                          */
170 /*
171  *      TCP option
172  */
173 
174 #define TCPOPT_NOP              1       /* Padding */
175 #define TCPOPT_EOL              0       /* End of options */
176 #define TCPOPT_MSS              2       /* Segment size negotiating */
177 #define TCPOPT_WINDOW           3       /* Window scaling */
178 #define TCPOPT_SACK_PERM        4       /* SACK Permitted */
179 #define TCPOPT_SACK             5       /* SACK Block */
180 #define TCPOPT_TIMESTAMP        8       /* Better RTT estimations/PAWS */
181 #define TCPOPT_MD5SIG           19      /* MD5 Signature (RFC2385) */
182 #define TCPOPT_FASTOPEN         34      /* Fast open (RFC7413) */
183 #define TCPOPT_EXP              254     /* Experimental */
184 /* Magic number to be after the option value for sharing TCP
185  * experimental options. See draft-ietf-tcpm-experimental-options-00.txt
186  */
187 #define TCPOPT_FASTOPEN_MAGIC   0xF989
188 
189 /*
190  *     TCP option lengths
191  */
192 
193 #define TCPOLEN_MSS            4
194 #define TCPOLEN_WINDOW         3
195 #define TCPOLEN_SACK_PERM      2
196 #define TCPOLEN_TIMESTAMP      10
197 #define TCPOLEN_MD5SIG         18
198 #define TCPOLEN_FASTOPEN_BASE  2
199 #define TCPOLEN_EXP_FASTOPEN_BASE  4
200 
201 /* But this is what stacks really send out. */
202 #define TCPOLEN_TSTAMP_ALIGNED          12
203 #define TCPOLEN_WSCALE_ALIGNED          4
204 #define TCPOLEN_SACKPERM_ALIGNED        4
205 #define TCPOLEN_SACK_BASE               2
206 #define TCPOLEN_SACK_BASE_ALIGNED       4
207 #define TCPOLEN_SACK_PERBLOCK           8
208 #define TCPOLEN_MD5SIG_ALIGNED          20
209 #define TCPOLEN_MSS_ALIGNED             4
210 
211 /* Flags in tp->nonagle */
212 #define TCP_NAGLE_OFF           1       /* Nagle's algo is disabled */
213 #define TCP_NAGLE_CORK          2       /* Socket is corked         */
214 #define TCP_NAGLE_PUSH          4       /* Cork is overridden for already queued data */
215 
216 /* TCP thin-stream limits */
217 #define TCP_THIN_LINEAR_RETRIES 6       /* After 6 linear retries, do exp. backoff */
218 
219 /* TCP initial congestion window as per draft-hkchu-tcpm-initcwnd-01 */
220 #define TCP_INIT_CWND           10
221 
222 /* Bit Flags for sysctl_tcp_fastopen */
223 #define TFO_CLIENT_ENABLE       1
224 #define TFO_SERVER_ENABLE       2
225 #define TFO_CLIENT_NO_COOKIE    4       /* Data in SYN w/o cookie option */
226 
227 /* Accept SYN data w/o any cookie option */
228 #define TFO_SERVER_COOKIE_NOT_REQD      0x200
229 
230 /* Force enable TFO on all listeners, i.e., not requiring the
231  * TCP_FASTOPEN socket option. SOCKOPT1/2 determine how to set max_qlen.
232  */
233 #define TFO_SERVER_WO_SOCKOPT1  0x400
234 #define TFO_SERVER_WO_SOCKOPT2  0x800
235 
236 extern struct inet_timewait_death_row tcp_death_row;
237 
238 /* sysctl variables for tcp */
239 extern int sysctl_tcp_timestamps;
240 extern int sysctl_tcp_window_scaling;
241 extern int sysctl_tcp_sack;
242 extern int sysctl_tcp_fin_timeout;
243 extern int sysctl_tcp_keepalive_time;
244 extern int sysctl_tcp_keepalive_probes;
245 extern int sysctl_tcp_keepalive_intvl;
246 extern int sysctl_tcp_syn_retries;
247 extern int sysctl_tcp_synack_retries;
248 extern int sysctl_tcp_retries1;
249 extern int sysctl_tcp_retries2;
250 extern int sysctl_tcp_orphan_retries;
251 extern int sysctl_tcp_syncookies;
252 extern int sysctl_tcp_fastopen;
253 extern int sysctl_tcp_retrans_collapse;
254 extern int sysctl_tcp_stdurg;
255 extern int sysctl_tcp_rfc1337;
256 extern int sysctl_tcp_abort_on_overflow;
257 extern int sysctl_tcp_max_orphans;
258 extern int sysctl_tcp_fack;
259 extern int sysctl_tcp_reordering;
260 extern int sysctl_tcp_max_reordering;
261 extern int sysctl_tcp_dsack;
262 extern long sysctl_tcp_mem[3];
263 extern int sysctl_tcp_wmem[3];
264 extern int sysctl_tcp_rmem[3];
265 extern int sysctl_tcp_app_win;
266 extern int sysctl_tcp_adv_win_scale;
267 extern int sysctl_tcp_tw_reuse;
268 extern int sysctl_tcp_frto;
269 extern int sysctl_tcp_low_latency;
270 extern int sysctl_tcp_nometrics_save;
271 extern int sysctl_tcp_moderate_rcvbuf;
272 extern int sysctl_tcp_tso_win_divisor;
273 extern int sysctl_tcp_workaround_signed_windows;
274 extern int sysctl_tcp_slow_start_after_idle;
275 extern int sysctl_tcp_thin_linear_timeouts;
276 extern int sysctl_tcp_thin_dupack;
277 extern int sysctl_tcp_early_retrans;
278 extern int sysctl_tcp_limit_output_bytes;
279 extern int sysctl_tcp_challenge_ack_limit;
280 extern unsigned int sysctl_tcp_notsent_lowat;
281 extern int sysctl_tcp_min_tso_segs;
282 extern int sysctl_tcp_autocorking;
283 extern int sysctl_tcp_invalid_ratelimit;
284 
285 extern atomic_long_t tcp_memory_allocated;
286 extern struct percpu_counter tcp_sockets_allocated;
287 extern int tcp_memory_pressure;
288 
289 /* optimized version of sk_under_memory_pressure() for TCP sockets */
290 static inline bool tcp_under_memory_pressure(const struct sock *sk)
291 {
292         if (mem_cgroup_sockets_enabled && sk->sk_cgrp)
293                 return !!sk->sk_cgrp->memory_pressure;
294 
295         return tcp_memory_pressure;
296 }
297 /*
298  * The next routines deal with comparing 32 bit unsigned ints
299  * and worry about wraparound (automatic with unsigned arithmetic).
300  */
301 
302 static inline bool before(__u32 seq1, __u32 seq2)
303 {
304         return (__s32)(seq1-seq2) < 0;
305 }
306 #define after(seq2, seq1)       before(seq1, seq2)
307 
308 /* is s2<=s1<=s3 ? */
309 static inline bool between(__u32 seq1, __u32 seq2, __u32 seq3)
310 {
311         return seq3 - seq2 >= seq1 - seq2;
312 }
313 
314 static inline bool tcp_out_of_memory(struct sock *sk)
315 {
316         if (sk->sk_wmem_queued > SOCK_MIN_SNDBUF &&
317             sk_memory_allocated(sk) > sk_prot_mem_limits(sk, 2))
318                 return true;
319         return false;
320 }
321 
322 void sk_forced_mem_schedule(struct sock *sk, int size);
323 
324 static inline bool tcp_too_many_orphans(struct sock *sk, int shift)
325 {
326         struct percpu_counter *ocp = sk->sk_prot->orphan_count;
327         int orphans = percpu_counter_read_positive(ocp);
328 
329         if (orphans << shift > sysctl_tcp_max_orphans) {
330                 orphans = percpu_counter_sum_positive(ocp);
331                 if (orphans << shift > sysctl_tcp_max_orphans)
332                         return true;
333         }
334         return false;
335 }
336 
337 bool tcp_check_oom(struct sock *sk, int shift);
338 
339 
340 extern struct proto tcp_prot;
341 
342 #define TCP_INC_STATS(net, field)       SNMP_INC_STATS((net)->mib.tcp_statistics, field)
343 #define TCP_INC_STATS_BH(net, field)    SNMP_INC_STATS_BH((net)->mib.tcp_statistics, field)
344 #define TCP_DEC_STATS(net, field)       SNMP_DEC_STATS((net)->mib.tcp_statistics, field)
345 #define TCP_ADD_STATS_USER(net, field, val) SNMP_ADD_STATS_USER((net)->mib.tcp_statistics, field, val)
346 #define TCP_ADD_STATS(net, field, val)  SNMP_ADD_STATS((net)->mib.tcp_statistics, field, val)
347 
348 void tcp_tasklet_init(void);
349 
350 void tcp_v4_err(struct sk_buff *skb, u32);
351 
352 void tcp_shutdown(struct sock *sk, int how);
353 
354 void tcp_v4_early_demux(struct sk_buff *skb);
355 int tcp_v4_rcv(struct sk_buff *skb);
356 
357 int tcp_v4_tw_remember_stamp(struct inet_timewait_sock *tw);
358 int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size);
359 int tcp_sendpage(struct sock *sk, struct page *page, int offset, size_t size,
360                  int flags);
361 void tcp_release_cb(struct sock *sk);
362 void tcp_wfree(struct sk_buff *skb);
363 void tcp_write_timer_handler(struct sock *sk);
364 void tcp_delack_timer_handler(struct sock *sk);
365 int tcp_ioctl(struct sock *sk, int cmd, unsigned long arg);
366 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
367                           const struct tcphdr *th, unsigned int len);
368 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
369                          const struct tcphdr *th, unsigned int len);
370 void tcp_rcv_space_adjust(struct sock *sk);
371 int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp);
372 void tcp_twsk_destructor(struct sock *sk);
373 ssize_t tcp_splice_read(struct socket *sk, loff_t *ppos,
374                         struct pipe_inode_info *pipe, size_t len,
375                         unsigned int flags);
376 
377 static inline void tcp_dec_quickack_mode(struct sock *sk,
378                                          const unsigned int pkts)
379 {
380         struct inet_connection_sock *icsk = inet_csk(sk);
381 
382         if (icsk->icsk_ack.quick) {
383                 if (pkts >= icsk->icsk_ack.quick) {
384                         icsk->icsk_ack.quick = 0;
385                         /* Leaving quickack mode we deflate ATO. */
386                         icsk->icsk_ack.ato   = TCP_ATO_MIN;
387                 } else
388                         icsk->icsk_ack.quick -= pkts;
389         }
390 }
391 
392 #define TCP_ECN_OK              1
393 #define TCP_ECN_QUEUE_CWR       2
394 #define TCP_ECN_DEMAND_CWR      4
395 #define TCP_ECN_SEEN            8
396 
397 enum tcp_tw_status {
398         TCP_TW_SUCCESS = 0,
399         TCP_TW_RST = 1,
400         TCP_TW_ACK = 2,
401         TCP_TW_SYN = 3
402 };
403 
404 
405 enum tcp_tw_status tcp_timewait_state_process(struct inet_timewait_sock *tw,
406                                               struct sk_buff *skb,
407                                               const struct tcphdr *th);
408 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
409                            struct request_sock *req, bool fastopen);
410 int tcp_child_process(struct sock *parent, struct sock *child,
411                       struct sk_buff *skb);
412 void tcp_enter_loss(struct sock *sk);
413 void tcp_clear_retrans(struct tcp_sock *tp);
414 void tcp_update_metrics(struct sock *sk);
415 void tcp_init_metrics(struct sock *sk);
416 void tcp_metrics_init(void);
417 bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst,
418                         bool paws_check, bool timestamps);
419 bool tcp_remember_stamp(struct sock *sk);
420 bool tcp_tw_remember_stamp(struct inet_timewait_sock *tw);
421 void tcp_fetch_timewait_stamp(struct sock *sk, struct dst_entry *dst);
422 void tcp_disable_fack(struct tcp_sock *tp);
423 void tcp_close(struct sock *sk, long timeout);
424 void tcp_init_sock(struct sock *sk);
425 unsigned int tcp_poll(struct file *file, struct socket *sock,
426                       struct poll_table_struct *wait);
427 int tcp_getsockopt(struct sock *sk, int level, int optname,
428                    char __user *optval, int __user *optlen);
429 int tcp_setsockopt(struct sock *sk, int level, int optname,
430                    char __user *optval, unsigned int optlen);
431 int compat_tcp_getsockopt(struct sock *sk, int level, int optname,
432                           char __user *optval, int __user *optlen);
433 int compat_tcp_setsockopt(struct sock *sk, int level, int optname,
434                           char __user *optval, unsigned int optlen);
435 void tcp_set_keepalive(struct sock *sk, int val);
436 void tcp_syn_ack_timeout(const struct request_sock *req);
437 int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
438                 int flags, int *addr_len);
439 void tcp_parse_options(const struct sk_buff *skb,
440                        struct tcp_options_received *opt_rx,
441                        int estab, struct tcp_fastopen_cookie *foc);
442 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th);
443 
444 /*
445  *      TCP v4 functions exported for the inet6 API
446  */
447 
448 void tcp_v4_send_check(struct sock *sk, struct sk_buff *skb);
449 void tcp_v4_mtu_reduced(struct sock *sk);
450 void tcp_req_err(struct sock *sk, u32 seq);
451 int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb);
452 struct sock *tcp_create_openreq_child(struct sock *sk,
453                                       struct request_sock *req,
454                                       struct sk_buff *skb);
455 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst);
456 struct sock *tcp_v4_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
457                                   struct request_sock *req,
458                                   struct dst_entry *dst);
459 int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb);
460 int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
461 int tcp_connect(struct sock *sk);
462 struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
463                                 struct request_sock *req,
464                                 struct tcp_fastopen_cookie *foc);
465 int tcp_disconnect(struct sock *sk, int flags);
466 
467 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb);
468 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size);
469 void inet_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb);
470 
471 /* From syncookies.c */
472 struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
473                                  struct request_sock *req,
474                                  struct dst_entry *dst);
475 int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th,
476                       u32 cookie);
477 struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb);
478 #ifdef CONFIG_SYN_COOKIES
479 
480 /* Syncookies use a monotonic timer which increments every 60 seconds.
481  * This counter is used both as a hash input and partially encoded into
482  * the cookie value.  A cookie is only validated further if the delta
483  * between the current counter value and the encoded one is less than this,
484  * i.e. a sent cookie is valid only at most for 2*60 seconds (or less if
485  * the counter advances immediately after a cookie is generated).
486  */
487 #define MAX_SYNCOOKIE_AGE       2
488 #define TCP_SYNCOOKIE_PERIOD    (60 * HZ)
489 #define TCP_SYNCOOKIE_VALID     (MAX_SYNCOOKIE_AGE * TCP_SYNCOOKIE_PERIOD)
490 
491 /* syncookies: remember time of last synqueue overflow
492  * But do not dirty this field too often (once per second is enough)
493  */
494 static inline void tcp_synq_overflow(struct sock *sk)
495 {
496         unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
497         unsigned long now = jiffies;
498 
499         if (time_after(now, last_overflow + HZ))
500                 tcp_sk(sk)->rx_opt.ts_recent_stamp = now;
501 }
502 
503 /* syncookies: no recent synqueue overflow on this listening socket? */
504 static inline bool tcp_synq_no_recent_overflow(const struct sock *sk)
505 {
506         unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
507 
508         return time_after(jiffies, last_overflow + TCP_SYNCOOKIE_VALID);
509 }
510 
511 static inline u32 tcp_cookie_time(void)
512 {
513         u64 val = get_jiffies_64();
514 
515         do_div(val, TCP_SYNCOOKIE_PERIOD);
516         return val;
517 }
518 
519 u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,
520                               u16 *mssp);
521 __u32 cookie_v4_init_sequence(struct sock *sk, const struct sk_buff *skb,
522                               __u16 *mss);
523 __u32 cookie_init_timestamp(struct request_sock *req);
524 bool cookie_timestamp_decode(struct tcp_options_received *opt);
525 bool cookie_ecn_ok(const struct tcp_options_received *opt,
526                    const struct net *net, const struct dst_entry *dst);
527 
528 /* From net/ipv6/syncookies.c */
529 int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th,
530                       u32 cookie);
531 struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb);
532 
533 u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
534                               const struct tcphdr *th, u16 *mssp);
535 __u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb,
536                               __u16 *mss);
537 #endif
538 /* tcp_output.c */
539 
540 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
541                                int nonagle);
542 bool tcp_may_send_now(struct sock *sk);
543 int __tcp_retransmit_skb(struct sock *, struct sk_buff *);
544 int tcp_retransmit_skb(struct sock *, struct sk_buff *);
545 void tcp_retransmit_timer(struct sock *sk);
546 void tcp_xmit_retransmit_queue(struct sock *);
547 void tcp_simple_retransmit(struct sock *);
548 int tcp_trim_head(struct sock *, struct sk_buff *, u32);
549 int tcp_fragment(struct sock *, struct sk_buff *, u32, unsigned int, gfp_t);
550 
551 void tcp_send_probe0(struct sock *);
552 void tcp_send_partial(struct sock *);
553 int tcp_write_wakeup(struct sock *, int mib);
554 void tcp_send_fin(struct sock *sk);
555 void tcp_send_active_reset(struct sock *sk, gfp_t priority);
556 int tcp_send_synack(struct sock *);
557 void tcp_push_one(struct sock *, unsigned int mss_now);
558 void tcp_send_ack(struct sock *sk);
559 void tcp_send_delayed_ack(struct sock *sk);
560 void tcp_send_loss_probe(struct sock *sk);
561 bool tcp_schedule_loss_probe(struct sock *sk);
562 
563 /* tcp_input.c */
564 void tcp_resume_early_retransmit(struct sock *sk);
565 void tcp_rearm_rto(struct sock *sk);
566 void tcp_reset(struct sock *sk);
567 
568 /* tcp_timer.c */
569 void tcp_init_xmit_timers(struct sock *);
570 static inline void tcp_clear_xmit_timers(struct sock *sk)
571 {
572         inet_csk_clear_xmit_timers(sk);
573 }
574 
575 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu);
576 unsigned int tcp_current_mss(struct sock *sk);
577 
578 /* Bound MSS / TSO packet size with the half of the window */
579 static inline int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
580 {
581         int cutoff;
582 
583         /* When peer uses tiny windows, there is no use in packetizing
584          * to sub-MSS pieces for the sake of SWS or making sure there
585          * are enough packets in the pipe for fast recovery.
586          *
587          * On the other hand, for extremely large MSS devices, handling
588          * smaller than MSS windows in this way does make sense.
589          */
590         if (tp->max_window >= 512)
591                 cutoff = (tp->max_window >> 1);
592         else
593                 cutoff = tp->max_window;
594 
595         if (cutoff && pktsize > cutoff)
596                 return max_t(int, cutoff, 68U - tp->tcp_header_len);
597         else
598                 return pktsize;
599 }
600 
601 /* tcp.c */
602 void tcp_get_info(struct sock *, struct tcp_info *);
603 
604 /* Read 'sendfile()'-style from a TCP socket */
605 typedef int (*sk_read_actor_t)(read_descriptor_t *, struct sk_buff *,
606                                 unsigned int, size_t);
607 int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
608                   sk_read_actor_t recv_actor);
609 
610 void tcp_initialize_rcv_mss(struct sock *sk);
611 
612 int tcp_mtu_to_mss(struct sock *sk, int pmtu);
613 int tcp_mss_to_mtu(struct sock *sk, int mss);
614 void tcp_mtup_init(struct sock *sk);
615 void tcp_init_buffer_space(struct sock *sk);
616 
617 static inline void tcp_bound_rto(const struct sock *sk)
618 {
619         if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
620                 inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
621 }
622 
623 static inline u32 __tcp_set_rto(const struct tcp_sock *tp)
624 {
625         return usecs_to_jiffies((tp->srtt_us >> 3) + tp->rttvar_us);
626 }
627 
628 static inline void __tcp_fast_path_on(struct tcp_sock *tp, u32 snd_wnd)
629 {
630         tp->pred_flags = htonl((tp->tcp_header_len << 26) |
631                                ntohl(TCP_FLAG_ACK) |
632                                snd_wnd);
633 }
634 
635 static inline void tcp_fast_path_on(struct tcp_sock *tp)
636 {
637         __tcp_fast_path_on(tp, tp->snd_wnd >> tp->rx_opt.snd_wscale);
638 }
639 
640 static inline void tcp_fast_path_check(struct sock *sk)
641 {
642         struct tcp_sock *tp = tcp_sk(sk);
643 
644         if (skb_queue_empty(&tp->out_of_order_queue) &&
645             tp->rcv_wnd &&
646             atomic_read(&sk->sk_rmem_alloc) < sk->sk_rcvbuf &&
647             !tp->urg_data)
648                 tcp_fast_path_on(tp);
649 }
650 
651 /* Compute the actual rto_min value */
652 static inline u32 tcp_rto_min(struct sock *sk)
653 {
654         const struct dst_entry *dst = __sk_dst_get(sk);
655         u32 rto_min = TCP_RTO_MIN;
656 
657         if (dst && dst_metric_locked(dst, RTAX_RTO_MIN))
658                 rto_min = dst_metric_rtt(dst, RTAX_RTO_MIN);
659         return rto_min;
660 }
661 
662 static inline u32 tcp_rto_min_us(struct sock *sk)
663 {
664         return jiffies_to_usecs(tcp_rto_min(sk));
665 }
666 
667 static inline bool tcp_ca_dst_locked(const struct dst_entry *dst)
668 {
669         return dst_metric_locked(dst, RTAX_CC_ALGO);
670 }
671 
672 /* Compute the actual receive window we are currently advertising.
673  * Rcv_nxt can be after the window if our peer push more data
674  * than the offered window.
675  */
676 static inline u32 tcp_receive_window(const struct tcp_sock *tp)
677 {
678         s32 win = tp->rcv_wup + tp->rcv_wnd - tp->rcv_nxt;
679 
680         if (win < 0)
681                 win = 0;
682         return (u32) win;
683 }
684 
685 /* Choose a new window, without checks for shrinking, and without
686  * scaling applied to the result.  The caller does these things
687  * if necessary.  This is a "raw" window selection.
688  */
689 u32 __tcp_select_window(struct sock *sk);
690 
691 void tcp_send_window_probe(struct sock *sk);
692 
693 /* TCP timestamps are only 32-bits, this causes a slight
694  * complication on 64-bit systems since we store a snapshot
695  * of jiffies in the buffer control blocks below.  We decided
696  * to use only the low 32-bits of jiffies and hide the ugly
697  * casts with the following macro.
698  */
699 #define tcp_time_stamp          ((__u32)(jiffies))
700 
701 static inline u32 tcp_skb_timestamp(const struct sk_buff *skb)
702 {
703         return skb->skb_mstamp.stamp_jiffies;
704 }
705 
706 
707 #define tcp_flag_byte(th) (((u_int8_t *)th)[13])
708 
709 #define TCPHDR_FIN 0x01
710 #define TCPHDR_SYN 0x02
711 #define TCPHDR_RST 0x04
712 #define TCPHDR_PSH 0x08
713 #define TCPHDR_ACK 0x10
714 #define TCPHDR_URG 0x20
715 #define TCPHDR_ECE 0x40
716 #define TCPHDR_CWR 0x80
717 
718 #define TCPHDR_SYN_ECN  (TCPHDR_SYN | TCPHDR_ECE | TCPHDR_CWR)
719 
720 /* This is what the send packet queuing engine uses to pass
721  * TCP per-packet control information to the transmission code.
722  * We also store the host-order sequence numbers in here too.
723  * This is 44 bytes if IPV6 is enabled.
724  * If this grows please adjust skbuff.h:skbuff->cb[xxx] size appropriately.
725  */
726 struct tcp_skb_cb {
727         __u32           seq;            /* Starting sequence number     */
728         __u32           end_seq;        /* SEQ + FIN + SYN + datalen    */
729         union {
730                 /* Note : tcp_tw_isn is used in input path only
731                  *        (isn chosen by tcp_timewait_state_process())
732                  *
733                  *        tcp_gso_segs/size are used in write queue only,
734                  *        cf tcp_skb_pcount()/tcp_skb_mss()
735                  */
736                 __u32           tcp_tw_isn;
737                 struct {
738                         u16     tcp_gso_segs;
739                         u16     tcp_gso_size;
740                 };
741         };
742         __u8            tcp_flags;      /* TCP header flags. (tcp[13])  */
743 
744         __u8            sacked;         /* State flags for SACK/FACK.   */
745 #define TCPCB_SACKED_ACKED      0x01    /* SKB ACK'd by a SACK block    */
746 #define TCPCB_SACKED_RETRANS    0x02    /* SKB retransmitted            */
747 #define TCPCB_LOST              0x04    /* SKB is lost                  */
748 #define TCPCB_TAGBITS           0x07    /* All tag bits                 */
749 #define TCPCB_REPAIRED          0x10    /* SKB repaired (no skb_mstamp) */
750 #define TCPCB_EVER_RETRANS      0x80    /* Ever retransmitted frame     */
751 #define TCPCB_RETRANS           (TCPCB_SACKED_RETRANS|TCPCB_EVER_RETRANS| \
752                                 TCPCB_REPAIRED)
753 
754         __u8            ip_dsfield;     /* IPv4 tos or IPv6 dsfield     */
755         /* 1 byte hole */
756         __u32           ack_seq;        /* Sequence number ACK'd        */
757         union {
758                 struct inet_skb_parm    h4;
759 #if IS_ENABLED(CONFIG_IPV6)
760                 struct inet6_skb_parm   h6;
761 #endif
762         } header;       /* For incoming frames          */
763 };
764 
765 #define TCP_SKB_CB(__skb)       ((struct tcp_skb_cb *)&((__skb)->cb[0]))
766 
767 
768 #if IS_ENABLED(CONFIG_IPV6)
769 /* This is the variant of inet6_iif() that must be used by TCP,
770  * as TCP moves IP6CB into a different location in skb->cb[]
771  */
772 static inline int tcp_v6_iif(const struct sk_buff *skb)
773 {
774         return TCP_SKB_CB(skb)->header.h6.iif;
775 }
776 #endif
777 
778 /* Due to TSO, an SKB can be composed of multiple actual
779  * packets.  To keep these tracked properly, we use this.
780  */
781 static inline int tcp_skb_pcount(const struct sk_buff *skb)
782 {
783         return TCP_SKB_CB(skb)->tcp_gso_segs;
784 }
785 
786 static inline void tcp_skb_pcount_set(struct sk_buff *skb, int segs)
787 {
788         TCP_SKB_CB(skb)->tcp_gso_segs = segs;
789 }
790 
791 static inline void tcp_skb_pcount_add(struct sk_buff *skb, int segs)
792 {
793         TCP_SKB_CB(skb)->tcp_gso_segs += segs;
794 }
795 
796 /* This is valid iff skb is in write queue and tcp_skb_pcount() > 1. */
797 static inline int tcp_skb_mss(const struct sk_buff *skb)
798 {
799         return TCP_SKB_CB(skb)->tcp_gso_size;
800 }
801 
802 /* Events passed to congestion control interface */
803 enum tcp_ca_event {
804         CA_EVENT_TX_START,      /* first transmit when no packets in flight */
805         CA_EVENT_CWND_RESTART,  /* congestion window restart */
806         CA_EVENT_COMPLETE_CWR,  /* end of congestion recovery */
807         CA_EVENT_LOSS,          /* loss timeout */
808         CA_EVENT_ECN_NO_CE,     /* ECT set, but not CE marked */
809         CA_EVENT_ECN_IS_CE,     /* received CE marked IP packet */
810         CA_EVENT_DELAYED_ACK,   /* Delayed ack is sent */
811         CA_EVENT_NON_DELAYED_ACK,
812 };
813 
814 /* Information about inbound ACK, passed to cong_ops->in_ack_event() */
815 enum tcp_ca_ack_event_flags {
816         CA_ACK_SLOWPATH         = (1 << 0),     /* In slow path processing */
817         CA_ACK_WIN_UPDATE       = (1 << 1),     /* ACK updated window */
818         CA_ACK_ECE              = (1 << 2),     /* ECE bit is set on ack */
819 };
820 
821 /*
822  * Interface for adding new TCP congestion control handlers
823  */
824 #define TCP_CA_NAME_MAX 16
825 #define TCP_CA_MAX      128
826 #define TCP_CA_BUF_MAX  (TCP_CA_NAME_MAX*TCP_CA_MAX)
827 
828 #define TCP_CA_UNSPEC   0
829 
830 /* Algorithm can be set on socket without CAP_NET_ADMIN privileges */
831 #define TCP_CONG_NON_RESTRICTED 0x1
832 /* Requires ECN/ECT set on all packets */
833 #define TCP_CONG_NEEDS_ECN      0x2
834 
835 union tcp_cc_info;
836 
837 struct tcp_congestion_ops {
838         struct list_head        list;
839         u32 key;
840         u32 flags;
841 
842         /* initialize private data (optional) */
843         void (*init)(struct sock *sk);
844         /* cleanup private data  (optional) */
845         void (*release)(struct sock *sk);
846 
847         /* return slow start threshold (required) */
848         u32 (*ssthresh)(struct sock *sk);
849         /* do new cwnd calculation (required) */
850         void (*cong_avoid)(struct sock *sk, u32 ack, u32 acked);
851         /* call before changing ca_state (optional) */
852         void (*set_state)(struct sock *sk, u8 new_state);
853         /* call when cwnd event occurs (optional) */
854         void (*cwnd_event)(struct sock *sk, enum tcp_ca_event ev);
855         /* call when ack arrives (optional) */
856         void (*in_ack_event)(struct sock *sk, u32 flags);
857         /* new value of cwnd after loss (optional) */
858         u32  (*undo_cwnd)(struct sock *sk);
859         /* hook for packet ack accounting (optional) */
860         void (*pkts_acked)(struct sock *sk, u32 num_acked, s32 rtt_us);
861         /* get info for inet_diag (optional) */
862         size_t (*get_info)(struct sock *sk, u32 ext, int *attr,
863                            union tcp_cc_info *info);
864 
865         char            name[TCP_CA_NAME_MAX];
866         struct module   *owner;
867 };
868 
869 int tcp_register_congestion_control(struct tcp_congestion_ops *type);
870 void tcp_unregister_congestion_control(struct tcp_congestion_ops *type);
871 
872 void tcp_assign_congestion_control(struct sock *sk);
873 void tcp_init_congestion_control(struct sock *sk);
874 void tcp_cleanup_congestion_control(struct sock *sk);
875 int tcp_set_default_congestion_control(const char *name);
876 void tcp_get_default_congestion_control(char *name);
877 void tcp_get_available_congestion_control(char *buf, size_t len);
878 void tcp_get_allowed_congestion_control(char *buf, size_t len);
879 int tcp_set_allowed_congestion_control(char *allowed);
880 int tcp_set_congestion_control(struct sock *sk, const char *name);
881 u32 tcp_slow_start(struct tcp_sock *tp, u32 acked);
882 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked);
883 
884 u32 tcp_reno_ssthresh(struct sock *sk);
885 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked);
886 extern struct tcp_congestion_ops tcp_reno;
887 
888 struct tcp_congestion_ops *tcp_ca_find_key(u32 key);
889 u32 tcp_ca_get_key_by_name(const char *name);
890 #ifdef CONFIG_INET
891 char *tcp_ca_get_name_by_key(u32 key, char *buffer);
892 #else
893 static inline char *tcp_ca_get_name_by_key(u32 key, char *buffer)
894 {
895         return NULL;
896 }
897 #endif
898 
899 static inline bool tcp_ca_needs_ecn(const struct sock *sk)
900 {
901         const struct inet_connection_sock *icsk = inet_csk(sk);
902 
903         return icsk->icsk_ca_ops->flags & TCP_CONG_NEEDS_ECN;
904 }
905 
906 static inline void tcp_set_ca_state(struct sock *sk, const u8 ca_state)
907 {
908         struct inet_connection_sock *icsk = inet_csk(sk);
909 
910         if (icsk->icsk_ca_ops->set_state)
911                 icsk->icsk_ca_ops->set_state(sk, ca_state);
912         icsk->icsk_ca_state = ca_state;
913 }
914 
915 static inline void tcp_ca_event(struct sock *sk, const enum tcp_ca_event event)
916 {
917         const struct inet_connection_sock *icsk = inet_csk(sk);
918 
919         if (icsk->icsk_ca_ops->cwnd_event)
920                 icsk->icsk_ca_ops->cwnd_event(sk, event);
921 }
922 
923 /* These functions determine how the current flow behaves in respect of SACK
924  * handling. SACK is negotiated with the peer, and therefore it can vary
925  * between different flows.
926  *
927  * tcp_is_sack - SACK enabled
928  * tcp_is_reno - No SACK
929  * tcp_is_fack - FACK enabled, implies SACK enabled
930  */
931 static inline int tcp_is_sack(const struct tcp_sock *tp)
932 {
933         return tp->rx_opt.sack_ok;
934 }
935 
936 static inline bool tcp_is_reno(const struct tcp_sock *tp)
937 {
938         return !tcp_is_sack(tp);
939 }
940 
941 static inline bool tcp_is_fack(const struct tcp_sock *tp)
942 {
943         return tp->rx_opt.sack_ok & TCP_FACK_ENABLED;
944 }
945 
946 static inline void tcp_enable_fack(struct tcp_sock *tp)
947 {
948         tp->rx_opt.sack_ok |= TCP_FACK_ENABLED;
949 }
950 
951 /* TCP early-retransmit (ER) is similar to but more conservative than
952  * the thin-dupack feature.  Enable ER only if thin-dupack is disabled.
953  */
954 static inline void tcp_enable_early_retrans(struct tcp_sock *tp)
955 {
956         tp->do_early_retrans = sysctl_tcp_early_retrans &&
957                 sysctl_tcp_early_retrans < 4 && !sysctl_tcp_thin_dupack &&
958                 sysctl_tcp_reordering == 3;
959 }
960 
961 static inline void tcp_disable_early_retrans(struct tcp_sock *tp)
962 {
963         tp->do_early_retrans = 0;
964 }
965 
966 static inline unsigned int tcp_left_out(const struct tcp_sock *tp)
967 {
968         return tp->sacked_out + tp->lost_out;
969 }
970 
971 /* This determines how many packets are "in the network" to the best
972  * of our knowledge.  In many cases it is conservative, but where
973  * detailed information is available from the receiver (via SACK
974  * blocks etc.) we can make more aggressive calculations.
975  *
976  * Use this for decisions involving congestion control, use just
977  * tp->packets_out to determine if the send queue is empty or not.
978  *
979  * Read this equation as:
980  *
981  *      "Packets sent once on transmission queue" MINUS
982  *      "Packets left network, but not honestly ACKed yet" PLUS
983  *      "Packets fast retransmitted"
984  */
985 static inline unsigned int tcp_packets_in_flight(const struct tcp_sock *tp)
986 {
987         return tp->packets_out - tcp_left_out(tp) + tp->retrans_out;
988 }
989 
990 #define TCP_INFINITE_SSTHRESH   0x7fffffff
991 
992 static inline bool tcp_in_initial_slowstart(const struct tcp_sock *tp)
993 {
994         return tp->snd_ssthresh >= TCP_INFINITE_SSTHRESH;
995 }
996 
997 static inline bool tcp_in_cwnd_reduction(const struct sock *sk)
998 {
999         return (TCPF_CA_CWR | TCPF_CA_Recovery) &
1000                (1 << inet_csk(sk)->icsk_ca_state);
1001 }
1002 
1003 /* If cwnd > ssthresh, we may raise ssthresh to be half-way to cwnd.
1004  * The exception is cwnd reduction phase, when cwnd is decreasing towards
1005  * ssthresh.
1006  */
1007 static inline __u32 tcp_current_ssthresh(const struct sock *sk)
1008 {
1009         const struct tcp_sock *tp = tcp_sk(sk);
1010 
1011         if (tcp_in_cwnd_reduction(sk))
1012                 return tp->snd_ssthresh;
1013         else
1014                 return max(tp->snd_ssthresh,
1015                            ((tp->snd_cwnd >> 1) +
1016                             (tp->snd_cwnd >> 2)));
1017 }
1018 
1019 /* Use define here intentionally to get WARN_ON location shown at the caller */
1020 #define tcp_verify_left_out(tp) WARN_ON(tcp_left_out(tp) > tp->packets_out)
1021 
1022 void tcp_enter_cwr(struct sock *sk);
1023 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst);
1024 
1025 /* The maximum number of MSS of available cwnd for which TSO defers
1026  * sending if not using sysctl_tcp_tso_win_divisor.
1027  */
1028 static inline __u32 tcp_max_tso_deferred_mss(const struct tcp_sock *tp)
1029 {
1030         return 3;
1031 }
1032 
1033 /* Slow start with delack produces 3 packets of burst, so that
1034  * it is safe "de facto".  This will be the default - same as
1035  * the default reordering threshold - but if reordering increases,
1036  * we must be able to allow cwnd to burst at least this much in order
1037  * to not pull it back when holes are filled.
1038  */
1039 static __inline__ __u32 tcp_max_burst(const struct tcp_sock *tp)
1040 {
1041         return tp->reordering;
1042 }
1043 
1044 /* Returns end sequence number of the receiver's advertised window */
1045 static inline u32 tcp_wnd_end(const struct tcp_sock *tp)
1046 {
1047         return tp->snd_una + tp->snd_wnd;
1048 }
1049 
1050 /* We follow the spirit of RFC2861 to validate cwnd but implement a more
1051  * flexible approach. The RFC suggests cwnd should not be raised unless
1052  * it was fully used previously. And that's exactly what we do in
1053  * congestion avoidance mode. But in slow start we allow cwnd to grow
1054  * as long as the application has used half the cwnd.
1055  * Example :
1056  *    cwnd is 10 (IW10), but application sends 9 frames.
1057  *    We allow cwnd to reach 18 when all frames are ACKed.
1058  * This check is safe because it's as aggressive as slow start which already
1059  * risks 100% overshoot. The advantage is that we discourage application to
1060  * either send more filler packets or data to artificially blow up the cwnd
1061  * usage, and allow application-limited process to probe bw more aggressively.
1062  */
1063 static inline bool tcp_is_cwnd_limited(const struct sock *sk)
1064 {
1065         const struct tcp_sock *tp = tcp_sk(sk);
1066 
1067         /* If in slow start, ensure cwnd grows to twice what was ACKed. */
1068         if (tp->snd_cwnd <= tp->snd_ssthresh)
1069                 return tp->snd_cwnd < 2 * tp->max_packets_out;
1070 
1071         return tp->is_cwnd_limited;
1072 }
1073 
1074 /* Something is really bad, we could not queue an additional packet,
1075  * because qdisc is full or receiver sent a 0 window.
1076  * We do not want to add fuel to the fire, or abort too early,
1077  * so make sure the timer we arm now is at least 200ms in the future,
1078  * regardless of current icsk_rto value (as it could be ~2ms)
1079  */
1080 static inline unsigned long tcp_probe0_base(const struct sock *sk)
1081 {
1082         return max_t(unsigned long, inet_csk(sk)->icsk_rto, TCP_RTO_MIN);
1083 }
1084 
1085 /* Variant of inet_csk_rto_backoff() used for zero window probes */
1086 static inline unsigned long tcp_probe0_when(const struct sock *sk,
1087                                             unsigned long max_when)
1088 {
1089         u64 when = (u64)tcp_probe0_base(sk) << inet_csk(sk)->icsk_backoff;
1090 
1091         return (unsigned long)min_t(u64, when, max_when);
1092 }
1093 
1094 static inline void tcp_check_probe_timer(struct sock *sk)
1095 {
1096         if (!tcp_sk(sk)->packets_out && !inet_csk(sk)->icsk_pending)
1097                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
1098                                           tcp_probe0_base(sk), TCP_RTO_MAX);
1099 }
1100 
1101 static inline void tcp_init_wl(struct tcp_sock *tp, u32 seq)
1102 {
1103         tp->snd_wl1 = seq;
1104 }
1105 
1106 static inline void tcp_update_wl(struct tcp_sock *tp, u32 seq)
1107 {
1108         tp->snd_wl1 = seq;
1109 }
1110 
1111 /*
1112  * Calculate(/check) TCP checksum
1113  */
1114 static inline __sum16 tcp_v4_check(int len, __be32 saddr,
1115                                    __be32 daddr, __wsum base)
1116 {
1117         return csum_tcpudp_magic(saddr,daddr,len,IPPROTO_TCP,base);
1118 }
1119 
1120 static inline __sum16 __tcp_checksum_complete(struct sk_buff *skb)
1121 {
1122         return __skb_checksum_complete(skb);
1123 }
1124 
1125 static inline bool tcp_checksum_complete(struct sk_buff *skb)
1126 {
1127         return !skb_csum_unnecessary(skb) &&
1128                 __tcp_checksum_complete(skb);
1129 }
1130 
1131 /* Prequeue for VJ style copy to user, combined with checksumming. */
1132 
1133 static inline void tcp_prequeue_init(struct tcp_sock *tp)
1134 {
1135         tp->ucopy.task = NULL;
1136         tp->ucopy.len = 0;
1137         tp->ucopy.memory = 0;
1138         skb_queue_head_init(&tp->ucopy.prequeue);
1139 }
1140 
1141 bool tcp_prequeue(struct sock *sk, struct sk_buff *skb);
1142 
1143 #undef STATE_TRACE
1144 
1145 #ifdef STATE_TRACE
1146 static const char *statename[]={
1147         "Unused","Established","Syn Sent","Syn Recv",
1148         "Fin Wait 1","Fin Wait 2","Time Wait", "Close",
1149         "Close Wait","Last ACK","Listen","Closing"
1150 };
1151 #endif
1152 void tcp_set_state(struct sock *sk, int state);
1153 
1154 void tcp_done(struct sock *sk);
1155 
1156 static inline void tcp_sack_reset(struct tcp_options_received *rx_opt)
1157 {
1158         rx_opt->dsack = 0;
1159         rx_opt->num_sacks = 0;
1160 }
1161 
1162 u32 tcp_default_init_rwnd(u32 mss);
1163 
1164 /* Determine a window scaling and initial window to offer. */
1165 void tcp_select_initial_window(int __space, __u32 mss, __u32 *rcv_wnd,
1166                                __u32 *window_clamp, int wscale_ok,
1167                                __u8 *rcv_wscale, __u32 init_rcv_wnd);
1168 
1169 static inline int tcp_win_from_space(int space)
1170 {
1171         return sysctl_tcp_adv_win_scale<=0 ?
1172                 (space>>(-sysctl_tcp_adv_win_scale)) :
1173                 space - (space>>sysctl_tcp_adv_win_scale);
1174 }
1175 
1176 /* Note: caller must be prepared to deal with negative returns */
1177 static inline int tcp_space(const struct sock *sk)
1178 {
1179         return tcp_win_from_space(sk->sk_rcvbuf -
1180                                   atomic_read(&sk->sk_rmem_alloc));
1181 }
1182 
1183 static inline int tcp_full_space(const struct sock *sk)
1184 {
1185         return tcp_win_from_space(sk->sk_rcvbuf);
1186 }
1187 
1188 extern void tcp_openreq_init_rwin(struct request_sock *req,
1189                                   struct sock *sk, struct dst_entry *dst);
1190 
1191 void tcp_enter_memory_pressure(struct sock *sk);
1192 
1193 static inline int keepalive_intvl_when(const struct tcp_sock *tp)
1194 {
1195         return tp->keepalive_intvl ? : sysctl_tcp_keepalive_intvl;
1196 }
1197 
1198 static inline int keepalive_time_when(const struct tcp_sock *tp)
1199 {
1200         return tp->keepalive_time ? : sysctl_tcp_keepalive_time;
1201 }
1202 
1203 static inline int keepalive_probes(const struct tcp_sock *tp)
1204 {
1205         return tp->keepalive_probes ? : sysctl_tcp_keepalive_probes;
1206 }
1207 
1208 static inline u32 keepalive_time_elapsed(const struct tcp_sock *tp)
1209 {
1210         const struct inet_connection_sock *icsk = &tp->inet_conn;
1211 
1212         return min_t(u32, tcp_time_stamp - icsk->icsk_ack.lrcvtime,
1213                           tcp_time_stamp - tp->rcv_tstamp);
1214 }
1215 
1216 static inline int tcp_fin_time(const struct sock *sk)
1217 {
1218         int fin_timeout = tcp_sk(sk)->linger2 ? : sysctl_tcp_fin_timeout;
1219         const int rto = inet_csk(sk)->icsk_rto;
1220 
1221         if (fin_timeout < (rto << 2) - (rto >> 1))
1222                 fin_timeout = (rto << 2) - (rto >> 1);
1223 
1224         return fin_timeout;
1225 }
1226 
1227 static inline bool tcp_paws_check(const struct tcp_options_received *rx_opt,
1228                                   int paws_win)
1229 {
1230         if ((s32)(rx_opt->ts_recent - rx_opt->rcv_tsval) <= paws_win)
1231                 return true;
1232         if (unlikely(get_seconds() >= rx_opt->ts_recent_stamp + TCP_PAWS_24DAYS))
1233                 return true;
1234         /*
1235          * Some OSes send SYN and SYNACK messages with tsval=0 tsecr=0,
1236          * then following tcp messages have valid values. Ignore 0 value,
1237          * or else 'negative' tsval might forbid us to accept their packets.
1238          */
1239         if (!rx_opt->ts_recent)
1240                 return true;
1241         return false;
1242 }
1243 
1244 static inline bool tcp_paws_reject(const struct tcp_options_received *rx_opt,
1245                                    int rst)
1246 {
1247         if (tcp_paws_check(rx_opt, 0))
1248                 return false;
1249 
1250         /* RST segments are not recommended to carry timestamp,
1251            and, if they do, it is recommended to ignore PAWS because
1252            "their cleanup function should take precedence over timestamps."
1253            Certainly, it is mistake. It is necessary to understand the reasons
1254            of this constraint to relax it: if peer reboots, clock may go
1255            out-of-sync and half-open connections will not be reset.
1256            Actually, the problem would be not existing if all
1257            the implementations followed draft about maintaining clock
1258            via reboots. Linux-2.2 DOES NOT!
1259 
1260            However, we can relax time bounds for RST segments to MSL.
1261          */
1262         if (rst && get_seconds() >= rx_opt->ts_recent_stamp + TCP_PAWS_MSL)
1263                 return false;
1264         return true;
1265 }
1266 
1267 bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
1268                           int mib_idx, u32 *last_oow_ack_time);
1269 
1270 static inline void tcp_mib_init(struct net *net)
1271 {
1272         /* See RFC 2012 */
1273         TCP_ADD_STATS_USER(net, TCP_MIB_RTOALGORITHM, 1);
1274         TCP_ADD_STATS_USER(net, TCP_MIB_RTOMIN, TCP_RTO_MIN*1000/HZ);
1275         TCP_ADD_STATS_USER(net, TCP_MIB_RTOMAX, TCP_RTO_MAX*1000/HZ);
1276         TCP_ADD_STATS_USER(net, TCP_MIB_MAXCONN, -1);
1277 }
1278 
1279 /* from STCP */
1280 static inline void tcp_clear_retrans_hints_partial(struct tcp_sock *tp)
1281 {
1282         tp->lost_skb_hint = NULL;
1283 }
1284 
1285 static inline void tcp_clear_all_retrans_hints(struct tcp_sock *tp)
1286 {
1287         tcp_clear_retrans_hints_partial(tp);
1288         tp->retransmit_skb_hint = NULL;
1289 }
1290 
1291 /* MD5 Signature */
1292 struct crypto_hash;
1293 
1294 union tcp_md5_addr {
1295         struct in_addr  a4;
1296 #if IS_ENABLED(CONFIG_IPV6)
1297         struct in6_addr a6;
1298 #endif
1299 };
1300 
1301 /* - key database */
1302 struct tcp_md5sig_key {
1303         struct hlist_node       node;
1304         u8                      keylen;
1305         u8                      family; /* AF_INET or AF_INET6 */
1306         union tcp_md5_addr      addr;
1307         u8                      key[TCP_MD5SIG_MAXKEYLEN];
1308         struct rcu_head         rcu;
1309 };
1310 
1311 /* - sock block */
1312 struct tcp_md5sig_info {
1313         struct hlist_head       head;
1314         struct rcu_head         rcu;
1315 };
1316 
1317 /* - pseudo header */
1318 struct tcp4_pseudohdr {
1319         __be32          saddr;
1320         __be32          daddr;
1321         __u8            pad;
1322         __u8            protocol;
1323         __be16          len;
1324 };
1325 
1326 struct tcp6_pseudohdr {
1327         struct in6_addr saddr;
1328         struct in6_addr daddr;
1329         __be32          len;
1330         __be32          protocol;       /* including padding */
1331 };
1332 
1333 union tcp_md5sum_block {
1334         struct tcp4_pseudohdr ip4;
1335 #if IS_ENABLED(CONFIG_IPV6)
1336         struct tcp6_pseudohdr ip6;
1337 #endif
1338 };
1339 
1340 /* - pool: digest algorithm, hash description and scratch buffer */
1341 struct tcp_md5sig_pool {
1342         struct hash_desc        md5_desc;
1343         union tcp_md5sum_block  md5_blk;
1344 };
1345 
1346 /* - functions */
1347 int tcp_v4_md5_hash_skb(char *md5_hash, const struct tcp_md5sig_key *key,
1348                         const struct sock *sk, const struct sk_buff *skb);
1349 int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
1350                    int family, const u8 *newkey, u8 newkeylen, gfp_t gfp);
1351 int tcp_md5_do_del(struct sock *sk, const union tcp_md5_addr *addr,
1352                    int family);
1353 struct tcp_md5sig_key *tcp_v4_md5_lookup(struct sock *sk,
1354                                          const struct sock *addr_sk);
1355 
1356 #ifdef CONFIG_TCP_MD5SIG
1357 struct tcp_md5sig_key *tcp_md5_do_lookup(struct sock *sk,
1358                                          const union tcp_md5_addr *addr,
1359                                          int family);
1360 #define tcp_twsk_md5_key(twsk)  ((twsk)->tw_md5_key)
1361 #else
1362 static inline struct tcp_md5sig_key *tcp_md5_do_lookup(struct sock *sk,
1363                                          const union tcp_md5_addr *addr,
1364                                          int family)
1365 {
1366         return NULL;
1367 }
1368 #define tcp_twsk_md5_key(twsk)  NULL
1369 #endif
1370 
1371 bool tcp_alloc_md5sig_pool(void);
1372 
1373 struct tcp_md5sig_pool *tcp_get_md5sig_pool(void);
1374 static inline void tcp_put_md5sig_pool(void)
1375 {
1376         local_bh_enable();
1377 }
1378 
1379 int tcp_md5_hash_header(struct tcp_md5sig_pool *, const struct tcphdr *);
1380 int tcp_md5_hash_skb_data(struct tcp_md5sig_pool *, const struct sk_buff *,
1381                           unsigned int header_len);
1382 int tcp_md5_hash_key(struct tcp_md5sig_pool *hp,
1383                      const struct tcp_md5sig_key *key);
1384 
1385 /* From tcp_fastopen.c */
1386 void tcp_fastopen_cache_get(struct sock *sk, u16 *mss,
1387                             struct tcp_fastopen_cookie *cookie, int *syn_loss,
1388                             unsigned long *last_syn_loss);
1389 void tcp_fastopen_cache_set(struct sock *sk, u16 mss,
1390                             struct tcp_fastopen_cookie *cookie, bool syn_lost,
1391                             u16 try_exp);
1392 struct tcp_fastopen_request {
1393         /* Fast Open cookie. Size 0 means a cookie request */
1394         struct tcp_fastopen_cookie      cookie;
1395         struct msghdr                   *data;  /* data in MSG_FASTOPEN */
1396         size_t                          size;
1397         int                             copied; /* queued in tcp_connect() */
1398 };
1399 void tcp_free_fastopen_req(struct tcp_sock *tp);
1400 
1401 extern struct tcp_fastopen_context __rcu *tcp_fastopen_ctx;
1402 int tcp_fastopen_reset_cipher(void *key, unsigned int len);
1403 bool tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
1404                       struct request_sock *req,
1405                       struct tcp_fastopen_cookie *foc,
1406                       struct dst_entry *dst);
1407 void tcp_fastopen_init_key_once(bool publish);
1408 #define TCP_FASTOPEN_KEY_LENGTH 16
1409 
1410 /* Fastopen key context */
1411 struct tcp_fastopen_context {
1412         struct crypto_cipher    *tfm;
1413         __u8                    key[TCP_FASTOPEN_KEY_LENGTH];
1414         struct rcu_head         rcu;
1415 };
1416 
1417 /* write queue abstraction */
1418 static inline void tcp_write_queue_purge(struct sock *sk)
1419 {
1420         struct sk_buff *skb;
1421 
1422         while ((skb = __skb_dequeue(&sk->sk_write_queue)) != NULL)
1423                 sk_wmem_free_skb(sk, skb);
1424         sk_mem_reclaim(sk);
1425         tcp_clear_all_retrans_hints(tcp_sk(sk));
1426 }
1427 
1428 static inline struct sk_buff *tcp_write_queue_head(const struct sock *sk)
1429 {
1430         return skb_peek(&sk->sk_write_queue);
1431 }
1432 
1433 static inline struct sk_buff *tcp_write_queue_tail(const struct sock *sk)
1434 {
1435         return skb_peek_tail(&sk->sk_write_queue);
1436 }
1437 
1438 static inline struct sk_buff *tcp_write_queue_next(const struct sock *sk,
1439                                                    const struct sk_buff *skb)
1440 {
1441         return skb_queue_next(&sk->sk_write_queue, skb);
1442 }
1443 
1444 static inline struct sk_buff *tcp_write_queue_prev(const struct sock *sk,
1445                                                    const struct sk_buff *skb)
1446 {
1447         return skb_queue_prev(&sk->sk_write_queue, skb);
1448 }
1449 
1450 #define tcp_for_write_queue(skb, sk)                                    \
1451         skb_queue_walk(&(sk)->sk_write_queue, skb)
1452 
1453 #define tcp_for_write_queue_from(skb, sk)                               \
1454         skb_queue_walk_from(&(sk)->sk_write_queue, skb)
1455 
1456 #define tcp_for_write_queue_from_safe(skb, tmp, sk)                     \
1457         skb_queue_walk_from_safe(&(sk)->sk_write_queue, skb, tmp)
1458 
1459 static inline struct sk_buff *tcp_send_head(const struct sock *sk)
1460 {
1461         return sk->sk_send_head;
1462 }
1463 
1464 static inline bool tcp_skb_is_last(const struct sock *sk,
1465                                    const struct sk_buff *skb)
1466 {
1467         return skb_queue_is_last(&sk->sk_write_queue, skb);
1468 }
1469 
1470 static inline void tcp_advance_send_head(struct sock *sk, const struct sk_buff *skb)
1471 {
1472         if (tcp_skb_is_last(sk, skb))
1473                 sk->sk_send_head = NULL;
1474         else
1475                 sk->sk_send_head = tcp_write_queue_next(sk, skb);
1476 }
1477 
1478 static inline void tcp_check_send_head(struct sock *sk, struct sk_buff *skb_unlinked)
1479 {
1480         if (sk->sk_send_head == skb_unlinked)
1481                 sk->sk_send_head = NULL;
1482 }
1483 
1484 static inline void tcp_init_send_head(struct sock *sk)
1485 {
1486         sk->sk_send_head = NULL;
1487 }
1488 
1489 static inline void __tcp_add_write_queue_tail(struct sock *sk, struct sk_buff *skb)
1490 {
1491         __skb_queue_tail(&sk->sk_write_queue, skb);
1492 }
1493 
1494 static inline void tcp_add_write_queue_tail(struct sock *sk, struct sk_buff *skb)
1495 {
1496         __tcp_add_write_queue_tail(sk, skb);
1497 
1498         /* Queue it, remembering where we must start sending. */
1499         if (sk->sk_send_head == NULL) {
1500                 sk->sk_send_head = skb;
1501 
1502                 if (tcp_sk(sk)->highest_sack == NULL)
1503                         tcp_sk(sk)->highest_sack = skb;
1504         }
1505 }
1506 
1507 static inline void __tcp_add_write_queue_head(struct sock *sk, struct sk_buff *skb)
1508 {
1509         __skb_queue_head(&sk->sk_write_queue, skb);
1510 }
1511 
1512 /* Insert buff after skb on the write queue of sk.  */
1513 static inline void tcp_insert_write_queue_after(struct sk_buff *skb,
1514                                                 struct sk_buff *buff,
1515                                                 struct sock *sk)
1516 {
1517         __skb_queue_after(&sk->sk_write_queue, skb, buff);
1518 }
1519 
1520 /* Insert new before skb on the write queue of sk.  */
1521 static inline void tcp_insert_write_queue_before(struct sk_buff *new,
1522                                                   struct sk_buff *skb,
1523                                                   struct sock *sk)
1524 {
1525         __skb_queue_before(&sk->sk_write_queue, skb, new);
1526 
1527         if (sk->sk_send_head == skb)
1528                 sk->sk_send_head = new;
1529 }
1530 
1531 static inline void tcp_unlink_write_queue(struct sk_buff *skb, struct sock *sk)
1532 {
1533         __skb_unlink(skb, &sk->sk_write_queue);
1534 }
1535 
1536 static inline bool tcp_write_queue_empty(struct sock *sk)
1537 {
1538         return skb_queue_empty(&sk->sk_write_queue);
1539 }
1540 
1541 static inline void tcp_push_pending_frames(struct sock *sk)
1542 {
1543         if (tcp_send_head(sk)) {
1544                 struct tcp_sock *tp = tcp_sk(sk);
1545 
1546                 __tcp_push_pending_frames(sk, tcp_current_mss(sk), tp->nonagle);
1547         }
1548 }
1549 
1550 /* Start sequence of the skb just after the highest skb with SACKed
1551  * bit, valid only if sacked_out > 0 or when the caller has ensured
1552  * validity by itself.
1553  */
1554 static inline u32 tcp_highest_sack_seq(struct tcp_sock *tp)
1555 {
1556         if (!tp->sacked_out)
1557                 return tp->snd_una;
1558 
1559         if (tp->highest_sack == NULL)
1560                 return tp->snd_nxt;
1561 
1562         return TCP_SKB_CB(tp->highest_sack)->seq;
1563 }
1564 
1565 static inline void tcp_advance_highest_sack(struct sock *sk, struct sk_buff *skb)
1566 {
1567         tcp_sk(sk)->highest_sack = tcp_skb_is_last(sk, skb) ? NULL :
1568                                                 tcp_write_queue_next(sk, skb);
1569 }
1570 
1571 static inline struct sk_buff *tcp_highest_sack(struct sock *sk)
1572 {
1573         return tcp_sk(sk)->highest_sack;
1574 }
1575 
1576 static inline void tcp_highest_sack_reset(struct sock *sk)
1577 {
1578         tcp_sk(sk)->highest_sack = tcp_write_queue_head(sk);
1579 }
1580 
1581 /* Called when old skb is about to be deleted (to be combined with new skb) */
1582 static inline void tcp_highest_sack_combine(struct sock *sk,
1583                                             struct sk_buff *old,
1584                                             struct sk_buff *new)
1585 {
1586         if (tcp_sk(sk)->sacked_out && (old == tcp_sk(sk)->highest_sack))
1587                 tcp_sk(sk)->highest_sack = new;
1588 }
1589 
1590 /* Determines whether this is a thin stream (which may suffer from
1591  * increased latency). Used to trigger latency-reducing mechanisms.
1592  */
1593 static inline bool tcp_stream_is_thin(struct tcp_sock *tp)
1594 {
1595         return tp->packets_out < 4 && !tcp_in_initial_slowstart(tp);
1596 }
1597 
1598 /* /proc */
1599 enum tcp_seq_states {
1600         TCP_SEQ_STATE_LISTENING,
1601         TCP_SEQ_STATE_OPENREQ,
1602         TCP_SEQ_STATE_ESTABLISHED,
1603 };
1604 
1605 int tcp_seq_open(struct inode *inode, struct file *file);
1606 
1607 struct tcp_seq_afinfo {
1608         char                            *name;
1609         sa_family_t                     family;
1610         const struct file_operations    *seq_fops;
1611         struct seq_operations           seq_ops;
1612 };
1613 
1614 struct tcp_iter_state {
1615         struct seq_net_private  p;
1616         sa_family_t             family;
1617         enum tcp_seq_states     state;
1618         struct sock             *syn_wait_sk;
1619         int                     bucket, offset, sbucket, num;
1620         kuid_t                  uid;
1621         loff_t                  last_pos;
1622 };
1623 
1624 int tcp_proc_register(struct net *net, struct tcp_seq_afinfo *afinfo);
1625 void tcp_proc_unregister(struct net *net, struct tcp_seq_afinfo *afinfo);
1626 
1627 extern struct request_sock_ops tcp_request_sock_ops;
1628 extern struct request_sock_ops tcp6_request_sock_ops;
1629 
1630 void tcp_v4_destroy_sock(struct sock *sk);
1631 
1632 struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
1633                                 netdev_features_t features);
1634 struct sk_buff **tcp_gro_receive(struct sk_buff **head, struct sk_buff *skb);
1635 int tcp_gro_complete(struct sk_buff *skb);
1636 
1637 void __tcp_v4_send_check(struct sk_buff *skb, __be32 saddr, __be32 daddr);
1638 
1639 static inline u32 tcp_notsent_lowat(const struct tcp_sock *tp)
1640 {
1641         return tp->notsent_lowat ?: sysctl_tcp_notsent_lowat;
1642 }
1643 
1644 static inline bool tcp_stream_memory_free(const struct sock *sk)
1645 {
1646         const struct tcp_sock *tp = tcp_sk(sk);
1647         u32 notsent_bytes = tp->write_seq - tp->snd_nxt;
1648 
1649         return notsent_bytes < tcp_notsent_lowat(tp);
1650 }
1651 
1652 #ifdef CONFIG_PROC_FS
1653 int tcp4_proc_init(void);
1654 void tcp4_proc_exit(void);
1655 #endif
1656 
1657 int tcp_rtx_synack(struct sock *sk, struct request_sock *req);
1658 int tcp_conn_request(struct request_sock_ops *rsk_ops,
1659                      const struct tcp_request_sock_ops *af_ops,
1660                      struct sock *sk, struct sk_buff *skb);
1661 
1662 /* TCP af-specific functions */
1663 struct tcp_sock_af_ops {
1664 #ifdef CONFIG_TCP_MD5SIG
1665         struct tcp_md5sig_key   *(*md5_lookup) (struct sock *sk,
1666                                                 const struct sock *addr_sk);
1667         int             (*calc_md5_hash)(char *location,
1668                                          const struct tcp_md5sig_key *md5,
1669                                          const struct sock *sk,
1670                                          const struct sk_buff *skb);
1671         int             (*md5_parse)(struct sock *sk,
1672                                      char __user *optval,
1673                                      int optlen);
1674 #endif
1675 };
1676 
1677 struct tcp_request_sock_ops {
1678         u16 mss_clamp;
1679 #ifdef CONFIG_TCP_MD5SIG
1680         struct tcp_md5sig_key *(*req_md5_lookup)(struct sock *sk,
1681                                                  const struct sock *addr_sk);
1682         int             (*calc_md5_hash) (char *location,
1683                                           const struct tcp_md5sig_key *md5,
1684                                           const struct sock *sk,
1685                                           const struct sk_buff *skb);
1686 #endif
1687         void (*init_req)(struct request_sock *req, struct sock *sk,
1688                          struct sk_buff *skb);
1689 #ifdef CONFIG_SYN_COOKIES
1690         __u32 (*cookie_init_seq)(struct sock *sk, const struct sk_buff *skb,
1691                                  __u16 *mss);
1692 #endif
1693         struct dst_entry *(*route_req)(struct sock *sk, struct flowi *fl,
1694                                        const struct request_sock *req,
1695                                        bool *strict);
1696         __u32 (*init_seq)(const struct sk_buff *skb);
1697         int (*send_synack)(struct sock *sk, struct dst_entry *dst,
1698                            struct flowi *fl, struct request_sock *req,
1699                            u16 queue_mapping, struct tcp_fastopen_cookie *foc);
1700         void (*queue_hash_add)(struct sock *sk, struct request_sock *req,
1701                                const unsigned long timeout);
1702 };
1703 
1704 #ifdef CONFIG_SYN_COOKIES
1705 static inline __u32 cookie_init_sequence(const struct tcp_request_sock_ops *ops,
1706                                          struct sock *sk, struct sk_buff *skb,
1707                                          __u16 *mss)
1708 {
1709         return ops->cookie_init_seq(sk, skb, mss);
1710 }
1711 #else
1712 static inline __u32 cookie_init_sequence(const struct tcp_request_sock_ops *ops,
1713                                          struct sock *sk, struct sk_buff *skb,
1714                                          __u16 *mss)
1715 {
1716         return 0;
1717 }
1718 #endif
1719 
1720 int tcpv4_offload_init(void);
1721 
1722 void tcp_v4_init(void);
1723 void tcp_init(void);
1724 
1725 /*
1726  * Save and compile IPv4 options, return a pointer to it
1727  */
1728 static inline struct ip_options_rcu *tcp_v4_save_options(struct sk_buff *skb)
1729 {
1730         const struct ip_options *opt = &TCP_SKB_CB(skb)->header.h4.opt;
1731         struct ip_options_rcu *dopt = NULL;
1732 
1733         if (opt->optlen) {
1734                 int opt_size = sizeof(*dopt) + opt->optlen;
1735 
1736                 dopt = kmalloc(opt_size, GFP_ATOMIC);
1737                 if (dopt && __ip_options_echo(&dopt->opt, skb, opt)) {
1738                         kfree(dopt);
1739                         dopt = NULL;
1740                 }
1741         }
1742         return dopt;
1743 }
1744 
1745 /* locally generated TCP pure ACKs have skb->truesize == 2
1746  * (check tcp_send_ack() in net/ipv4/tcp_output.c )
1747  * This is much faster than dissecting the packet to find out.
1748  * (Think of GRE encapsulations, IPv4, IPv6, ...)
1749  */
1750 static inline bool skb_is_tcp_pure_ack(const struct sk_buff *skb)
1751 {
1752         return skb->truesize == 2;
1753 }
1754 
1755 static inline void skb_set_tcp_pure_ack(struct sk_buff *skb)
1756 {
1757         skb->truesize = 2;
1758 }
1759 
1760 #endif  /* _TCP_H */
1761 

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