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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            512
 69 
 70 /* After receiving this amount of duplicate ACKs fast retransmit starts. */
 71 #define TCP_FASTRETRANS_THRESH 3
 72 
 73 /* Maximal number of ACKs sent quickly to accelerate slow-start. */
 74 #define TCP_MAX_QUICKACKS       16U
 75 
 76 /* urg_data states */
 77 #define TCP_URG_VALID   0x0100
 78 #define TCP_URG_NOTYET  0x0200
 79 #define TCP_URG_READ    0x0400
 80 
 81 #define TCP_RETR1       3       /*
 82                                  * This is how many retries it does before it
 83                                  * tries to figure out if the gateway is
 84                                  * down. Minimal RFC value is 3; it corresponds
 85                                  * to ~3sec-8min depending on RTO.
 86                                  */
 87 
 88 #define TCP_RETR2       15      /*
 89                                  * This should take at least
 90                                  * 90 minutes to time out.
 91                                  * RFC1122 says that the limit is 100 sec.
 92                                  * 15 is ~13-30min depending on RTO.
 93                                  */
 94 
 95 #define TCP_SYN_RETRIES  6      /* This is how many retries are done
 96                                  * when active opening a connection.
 97                                  * RFC1122 says the minimum retry MUST
 98                                  * be at least 180secs.  Nevertheless
 99                                  * this value is corresponding to
100                                  * 63secs of retransmission with the
101                                  * current initial RTO.
102                                  */
103 
104 #define TCP_SYNACK_RETRIES 5    /* This is how may retries are done
105                                  * when passive opening a connection.
106                                  * This is corresponding to 31secs of
107                                  * retransmission with the current
108                                  * initial RTO.
109                                  */
110 
111 #define TCP_TIMEWAIT_LEN (60*HZ) /* how long to wait to destroy TIME-WAIT
112                                   * state, about 60 seconds     */
113 #define TCP_FIN_TIMEOUT TCP_TIMEWAIT_LEN
114                                  /* BSD style FIN_WAIT2 deadlock breaker.
115                                   * It used to be 3min, new value is 60sec,
116                                   * to combine FIN-WAIT-2 timeout with
117                                   * TIME-WAIT timer.
118                                   */
119 
120 #define TCP_DELACK_MAX  ((unsigned)(HZ/5))      /* maximal time to delay before sending an ACK */
121 #if HZ >= 100
122 #define TCP_DELACK_MIN  ((unsigned)(HZ/25))     /* minimal time to delay before sending an ACK */
123 #define TCP_ATO_MIN     ((unsigned)(HZ/25))
124 #else
125 #define TCP_DELACK_MIN  4U
126 #define TCP_ATO_MIN     4U
127 #endif
128 #define TCP_RTO_MAX     ((unsigned)(120*HZ))
129 #define TCP_RTO_MIN     ((unsigned)(HZ/5))
130 #define TCP_TIMEOUT_INIT ((unsigned)(1*HZ))     /* RFC6298 2.1 initial RTO value        */
131 #define TCP_TIMEOUT_FALLBACK ((unsigned)(3*HZ)) /* RFC 1122 initial RTO value, now
132                                                  * used as a fallback RTO for the
133                                                  * initial data transmission if no
134                                                  * valid RTT sample has been acquired,
135                                                  * most likely due to retrans in 3WHS.
136                                                  */
137 
138 #define TCP_RESOURCE_PROBE_INTERVAL ((unsigned)(HZ/2U)) /* Maximal interval between probes
139                                                          * for local resources.
140                                                          */
141 
142 #define TCP_KEEPALIVE_TIME      (120*60*HZ)     /* two hours */
143 #define TCP_KEEPALIVE_PROBES    9               /* Max of 9 keepalive probes    */
144 #define TCP_KEEPALIVE_INTVL     (75*HZ)
145 
146 #define MAX_TCP_KEEPIDLE        32767
147 #define MAX_TCP_KEEPINTVL       32767
148 #define MAX_TCP_KEEPCNT         127
149 #define MAX_TCP_SYNCNT          127
150 
151 #define TCP_SYNQ_INTERVAL       (HZ/5)  /* Period of SYNACK timer */
152 
153 #define TCP_PAWS_24DAYS (60 * 60 * 24 * 24)
154 #define TCP_PAWS_MSL    60              /* Per-host timestamps are invalidated
155                                          * after this time. It should be equal
156                                          * (or greater than) TCP_TIMEWAIT_LEN
157                                          * to provide reliability equal to one
158                                          * provided by timewait state.
159                                          */
160 #define TCP_PAWS_WINDOW 1               /* Replay window for per-host
161                                          * timestamps. It must be less than
162                                          * minimal timewait lifetime.
163                                          */
164 /*
165  *      TCP option
166  */
167 
168 #define TCPOPT_NOP              1       /* Padding */
169 #define TCPOPT_EOL              0       /* End of options */
170 #define TCPOPT_MSS              2       /* Segment size negotiating */
171 #define TCPOPT_WINDOW           3       /* Window scaling */
172 #define TCPOPT_SACK_PERM        4       /* SACK Permitted */
173 #define TCPOPT_SACK             5       /* SACK Block */
174 #define TCPOPT_TIMESTAMP        8       /* Better RTT estimations/PAWS */
175 #define TCPOPT_MD5SIG           19      /* MD5 Signature (RFC2385) */
176 #define TCPOPT_EXP              254     /* Experimental */
177 /* Magic number to be after the option value for sharing TCP
178  * experimental options. See draft-ietf-tcpm-experimental-options-00.txt
179  */
180 #define TCPOPT_FASTOPEN_MAGIC   0xF989
181 
182 /*
183  *     TCP option lengths
184  */
185 
186 #define TCPOLEN_MSS            4
187 #define TCPOLEN_WINDOW         3
188 #define TCPOLEN_SACK_PERM      2
189 #define TCPOLEN_TIMESTAMP      10
190 #define TCPOLEN_MD5SIG         18
191 #define TCPOLEN_EXP_FASTOPEN_BASE  4
192 
193 /* But this is what stacks really send out. */
194 #define TCPOLEN_TSTAMP_ALIGNED          12
195 #define TCPOLEN_WSCALE_ALIGNED          4
196 #define TCPOLEN_SACKPERM_ALIGNED        4
197 #define TCPOLEN_SACK_BASE               2
198 #define TCPOLEN_SACK_BASE_ALIGNED       4
199 #define TCPOLEN_SACK_PERBLOCK           8
200 #define TCPOLEN_MD5SIG_ALIGNED          20
201 #define TCPOLEN_MSS_ALIGNED             4
202 
203 /* Flags in tp->nonagle */
204 #define TCP_NAGLE_OFF           1       /* Nagle's algo is disabled */
205 #define TCP_NAGLE_CORK          2       /* Socket is corked         */
206 #define TCP_NAGLE_PUSH          4       /* Cork is overridden for already queued data */
207 
208 /* TCP thin-stream limits */
209 #define TCP_THIN_LINEAR_RETRIES 6       /* After 6 linear retries, do exp. backoff */
210 
211 /* TCP initial congestion window as per draft-hkchu-tcpm-initcwnd-01 */
212 #define TCP_INIT_CWND           10
213 
214 /* Bit Flags for sysctl_tcp_fastopen */
215 #define TFO_CLIENT_ENABLE       1
216 #define TFO_SERVER_ENABLE       2
217 #define TFO_CLIENT_NO_COOKIE    4       /* Data in SYN w/o cookie option */
218 
219 /* Accept SYN data w/o any cookie option */
220 #define TFO_SERVER_COOKIE_NOT_REQD      0x200
221 
222 /* Force enable TFO on all listeners, i.e., not requiring the
223  * TCP_FASTOPEN socket option. SOCKOPT1/2 determine how to set max_qlen.
224  */
225 #define TFO_SERVER_WO_SOCKOPT1  0x400
226 #define TFO_SERVER_WO_SOCKOPT2  0x800
227 
228 extern struct inet_timewait_death_row tcp_death_row;
229 
230 /* sysctl variables for tcp */
231 extern int sysctl_tcp_timestamps;
232 extern int sysctl_tcp_window_scaling;
233 extern int sysctl_tcp_sack;
234 extern int sysctl_tcp_fin_timeout;
235 extern int sysctl_tcp_keepalive_time;
236 extern int sysctl_tcp_keepalive_probes;
237 extern int sysctl_tcp_keepalive_intvl;
238 extern int sysctl_tcp_syn_retries;
239 extern int sysctl_tcp_synack_retries;
240 extern int sysctl_tcp_retries1;
241 extern int sysctl_tcp_retries2;
242 extern int sysctl_tcp_orphan_retries;
243 extern int sysctl_tcp_syncookies;
244 extern int sysctl_tcp_fastopen;
245 extern int sysctl_tcp_retrans_collapse;
246 extern int sysctl_tcp_stdurg;
247 extern int sysctl_tcp_rfc1337;
248 extern int sysctl_tcp_abort_on_overflow;
249 extern int sysctl_tcp_max_orphans;
250 extern int sysctl_tcp_fack;
251 extern int sysctl_tcp_reordering;
252 extern int sysctl_tcp_max_reordering;
253 extern int sysctl_tcp_dsack;
254 extern long sysctl_tcp_mem[3];
255 extern int sysctl_tcp_wmem[3];
256 extern int sysctl_tcp_rmem[3];
257 extern int sysctl_tcp_app_win;
258 extern int sysctl_tcp_adv_win_scale;
259 extern int sysctl_tcp_tw_reuse;
260 extern int sysctl_tcp_frto;
261 extern int sysctl_tcp_low_latency;
262 extern int sysctl_tcp_nometrics_save;
263 extern int sysctl_tcp_moderate_rcvbuf;
264 extern int sysctl_tcp_tso_win_divisor;
265 extern int sysctl_tcp_workaround_signed_windows;
266 extern int sysctl_tcp_slow_start_after_idle;
267 extern int sysctl_tcp_thin_linear_timeouts;
268 extern int sysctl_tcp_thin_dupack;
269 extern int sysctl_tcp_early_retrans;
270 extern int sysctl_tcp_limit_output_bytes;
271 extern int sysctl_tcp_challenge_ack_limit;
272 extern unsigned int sysctl_tcp_notsent_lowat;
273 extern int sysctl_tcp_min_tso_segs;
274 extern int sysctl_tcp_autocorking;
275 extern int sysctl_tcp_invalid_ratelimit;
276 
277 extern atomic_long_t tcp_memory_allocated;
278 extern struct percpu_counter tcp_sockets_allocated;
279 extern int tcp_memory_pressure;
280 
281 /*
282  * The next routines deal with comparing 32 bit unsigned ints
283  * and worry about wraparound (automatic with unsigned arithmetic).
284  */
285 
286 static inline bool before(__u32 seq1, __u32 seq2)
287 {
288         return (__s32)(seq1-seq2) < 0;
289 }
290 #define after(seq2, seq1)       before(seq1, seq2)
291 
292 /* is s2<=s1<=s3 ? */
293 static inline bool between(__u32 seq1, __u32 seq2, __u32 seq3)
294 {
295         return seq3 - seq2 >= seq1 - seq2;
296 }
297 
298 static inline bool tcp_out_of_memory(struct sock *sk)
299 {
300         if (sk->sk_wmem_queued > SOCK_MIN_SNDBUF &&
301             sk_memory_allocated(sk) > sk_prot_mem_limits(sk, 2))
302                 return true;
303         return false;
304 }
305 
306 static inline bool tcp_too_many_orphans(struct sock *sk, int shift)
307 {
308         struct percpu_counter *ocp = sk->sk_prot->orphan_count;
309         int orphans = percpu_counter_read_positive(ocp);
310 
311         if (orphans << shift > sysctl_tcp_max_orphans) {
312                 orphans = percpu_counter_sum_positive(ocp);
313                 if (orphans << shift > sysctl_tcp_max_orphans)
314                         return true;
315         }
316         return false;
317 }
318 
319 bool tcp_check_oom(struct sock *sk, int shift);
320 
321 /* syncookies: remember time of last synqueue overflow */
322 static inline void tcp_synq_overflow(struct sock *sk)
323 {
324         tcp_sk(sk)->rx_opt.ts_recent_stamp = jiffies;
325 }
326 
327 /* syncookies: no recent synqueue overflow on this listening socket? */
328 static inline bool tcp_synq_no_recent_overflow(const struct sock *sk)
329 {
330         unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
331         return time_after(jiffies, last_overflow + TCP_TIMEOUT_FALLBACK);
332 }
333 
334 extern struct proto tcp_prot;
335 
336 #define TCP_INC_STATS(net, field)       SNMP_INC_STATS((net)->mib.tcp_statistics, field)
337 #define TCP_INC_STATS_BH(net, field)    SNMP_INC_STATS_BH((net)->mib.tcp_statistics, field)
338 #define TCP_DEC_STATS(net, field)       SNMP_DEC_STATS((net)->mib.tcp_statistics, field)
339 #define TCP_ADD_STATS_USER(net, field, val) SNMP_ADD_STATS_USER((net)->mib.tcp_statistics, field, val)
340 #define TCP_ADD_STATS(net, field, val)  SNMP_ADD_STATS((net)->mib.tcp_statistics, field, val)
341 
342 void tcp_tasklet_init(void);
343 
344 void tcp_v4_err(struct sk_buff *skb, u32);
345 
346 void tcp_shutdown(struct sock *sk, int how);
347 
348 void tcp_v4_early_demux(struct sk_buff *skb);
349 int tcp_v4_rcv(struct sk_buff *skb);
350 
351 int tcp_v4_tw_remember_stamp(struct inet_timewait_sock *tw);
352 int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
353                 size_t size);
354 int tcp_sendpage(struct sock *sk, struct page *page, int offset, size_t size,
355                  int flags);
356 void tcp_release_cb(struct sock *sk);
357 void tcp_wfree(struct sk_buff *skb);
358 void tcp_write_timer_handler(struct sock *sk);
359 void tcp_delack_timer_handler(struct sock *sk);
360 int tcp_ioctl(struct sock *sk, int cmd, unsigned long arg);
361 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
362                           const struct tcphdr *th, unsigned int len);
363 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
364                          const struct tcphdr *th, unsigned int len);
365 void tcp_rcv_space_adjust(struct sock *sk);
366 int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp);
367 void tcp_twsk_destructor(struct sock *sk);
368 ssize_t tcp_splice_read(struct socket *sk, loff_t *ppos,
369                         struct pipe_inode_info *pipe, size_t len,
370                         unsigned int flags);
371 
372 static inline void tcp_dec_quickack_mode(struct sock *sk,
373                                          const unsigned int pkts)
374 {
375         struct inet_connection_sock *icsk = inet_csk(sk);
376 
377         if (icsk->icsk_ack.quick) {
378                 if (pkts >= icsk->icsk_ack.quick) {
379                         icsk->icsk_ack.quick = 0;
380                         /* Leaving quickack mode we deflate ATO. */
381                         icsk->icsk_ack.ato   = TCP_ATO_MIN;
382                 } else
383                         icsk->icsk_ack.quick -= pkts;
384         }
385 }
386 
387 #define TCP_ECN_OK              1
388 #define TCP_ECN_QUEUE_CWR       2
389 #define TCP_ECN_DEMAND_CWR      4
390 #define TCP_ECN_SEEN            8
391 
392 enum tcp_tw_status {
393         TCP_TW_SUCCESS = 0,
394         TCP_TW_RST = 1,
395         TCP_TW_ACK = 2,
396         TCP_TW_SYN = 3
397 };
398 
399 
400 enum tcp_tw_status tcp_timewait_state_process(struct inet_timewait_sock *tw,
401                                               struct sk_buff *skb,
402                                               const struct tcphdr *th);
403 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
404                            struct request_sock *req, struct request_sock **prev,
405                            bool fastopen);
406 int tcp_child_process(struct sock *parent, struct sock *child,
407                       struct sk_buff *skb);
408 void tcp_enter_loss(struct sock *sk);
409 void tcp_clear_retrans(struct tcp_sock *tp);
410 void tcp_update_metrics(struct sock *sk);
411 void tcp_init_metrics(struct sock *sk);
412 void tcp_metrics_init(void);
413 bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst,
414                         bool paws_check, bool timestamps);
415 bool tcp_remember_stamp(struct sock *sk);
416 bool tcp_tw_remember_stamp(struct inet_timewait_sock *tw);
417 void tcp_fetch_timewait_stamp(struct sock *sk, struct dst_entry *dst);
418 void tcp_disable_fack(struct tcp_sock *tp);
419 void tcp_close(struct sock *sk, long timeout);
420 void tcp_init_sock(struct sock *sk);
421 unsigned int tcp_poll(struct file *file, struct socket *sock,
422                       struct poll_table_struct *wait);
423 int tcp_getsockopt(struct sock *sk, int level, int optname,
424                    char __user *optval, int __user *optlen);
425 int tcp_setsockopt(struct sock *sk, int level, int optname,
426                    char __user *optval, unsigned int optlen);
427 int compat_tcp_getsockopt(struct sock *sk, int level, int optname,
428                           char __user *optval, int __user *optlen);
429 int compat_tcp_setsockopt(struct sock *sk, int level, int optname,
430                           char __user *optval, unsigned int optlen);
431 void tcp_set_keepalive(struct sock *sk, int val);
432 void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req);
433 int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
434                 size_t len, int nonblock, int flags, int *addr_len);
435 void tcp_parse_options(const struct sk_buff *skb,
436                        struct tcp_options_received *opt_rx,
437                        int estab, struct tcp_fastopen_cookie *foc);
438 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th);
439 
440 /*
441  *      TCP v4 functions exported for the inet6 API
442  */
443 
444 void tcp_v4_send_check(struct sock *sk, struct sk_buff *skb);
445 void tcp_v4_mtu_reduced(struct sock *sk);
446 int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb);
447 struct sock *tcp_create_openreq_child(struct sock *sk,
448                                       struct request_sock *req,
449                                       struct sk_buff *skb);
450 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst);
451 struct sock *tcp_v4_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
452                                   struct request_sock *req,
453                                   struct dst_entry *dst);
454 int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb);
455 int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
456 int tcp_connect(struct sock *sk);
457 struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
458                                 struct request_sock *req,
459                                 struct tcp_fastopen_cookie *foc);
460 int tcp_disconnect(struct sock *sk, int flags);
461 
462 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb);
463 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size);
464 void inet_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb);
465 
466 /* From syncookies.c */
467 int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th,
468                       u32 cookie);
469 struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb);
470 #ifdef CONFIG_SYN_COOKIES
471 
472 /* Syncookies use a monotonic timer which increments every 60 seconds.
473  * This counter is used both as a hash input and partially encoded into
474  * the cookie value.  A cookie is only validated further if the delta
475  * between the current counter value and the encoded one is less than this,
476  * i.e. a sent cookie is valid only at most for 2*60 seconds (or less if
477  * the counter advances immediately after a cookie is generated).
478  */
479 #define MAX_SYNCOOKIE_AGE 2
480 
481 static inline u32 tcp_cookie_time(void)
482 {
483         u64 val = get_jiffies_64();
484 
485         do_div(val, 60 * HZ);
486         return val;
487 }
488 
489 u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,
490                               u16 *mssp);
491 __u32 cookie_v4_init_sequence(struct sock *sk, const struct sk_buff *skb,
492                               __u16 *mss);
493 __u32 cookie_init_timestamp(struct request_sock *req);
494 bool cookie_timestamp_decode(struct tcp_options_received *opt);
495 bool cookie_ecn_ok(const struct tcp_options_received *opt,
496                    const struct net *net, const struct dst_entry *dst);
497 
498 /* From net/ipv6/syncookies.c */
499 int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th,
500                       u32 cookie);
501 struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb);
502 
503 u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
504                               const struct tcphdr *th, u16 *mssp);
505 __u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb,
506                               __u16 *mss);
507 #endif
508 /* tcp_output.c */
509 
510 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
511                                int nonagle);
512 bool tcp_may_send_now(struct sock *sk);
513 int __tcp_retransmit_skb(struct sock *, struct sk_buff *);
514 int tcp_retransmit_skb(struct sock *, struct sk_buff *);
515 void tcp_retransmit_timer(struct sock *sk);
516 void tcp_xmit_retransmit_queue(struct sock *);
517 void tcp_simple_retransmit(struct sock *);
518 int tcp_trim_head(struct sock *, struct sk_buff *, u32);
519 int tcp_fragment(struct sock *, struct sk_buff *, u32, unsigned int, gfp_t);
520 
521 void tcp_send_probe0(struct sock *);
522 void tcp_send_partial(struct sock *);
523 int tcp_write_wakeup(struct sock *);
524 void tcp_send_fin(struct sock *sk);
525 void tcp_send_active_reset(struct sock *sk, gfp_t priority);
526 int tcp_send_synack(struct sock *);
527 bool tcp_syn_flood_action(struct sock *sk, const struct sk_buff *skb,
528                           const char *proto);
529 void tcp_push_one(struct sock *, unsigned int mss_now);
530 void tcp_send_ack(struct sock *sk);
531 void tcp_send_delayed_ack(struct sock *sk);
532 void tcp_send_loss_probe(struct sock *sk);
533 bool tcp_schedule_loss_probe(struct sock *sk);
534 
535 /* tcp_input.c */
536 void tcp_resume_early_retransmit(struct sock *sk);
537 void tcp_rearm_rto(struct sock *sk);
538 void tcp_reset(struct sock *sk);
539 
540 /* tcp_timer.c */
541 void tcp_init_xmit_timers(struct sock *);
542 static inline void tcp_clear_xmit_timers(struct sock *sk)
543 {
544         inet_csk_clear_xmit_timers(sk);
545 }
546 
547 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu);
548 unsigned int tcp_current_mss(struct sock *sk);
549 
550 /* Bound MSS / TSO packet size with the half of the window */
551 static inline int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
552 {
553         int cutoff;
554 
555         /* When peer uses tiny windows, there is no use in packetizing
556          * to sub-MSS pieces for the sake of SWS or making sure there
557          * are enough packets in the pipe for fast recovery.
558          *
559          * On the other hand, for extremely large MSS devices, handling
560          * smaller than MSS windows in this way does make sense.
561          */
562         if (tp->max_window >= 512)
563                 cutoff = (tp->max_window >> 1);
564         else
565                 cutoff = tp->max_window;
566 
567         if (cutoff && pktsize > cutoff)
568                 return max_t(int, cutoff, 68U - tp->tcp_header_len);
569         else
570                 return pktsize;
571 }
572 
573 /* tcp.c */
574 void tcp_get_info(const struct sock *, struct tcp_info *);
575 
576 /* Read 'sendfile()'-style from a TCP socket */
577 typedef int (*sk_read_actor_t)(read_descriptor_t *, struct sk_buff *,
578                                 unsigned int, size_t);
579 int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
580                   sk_read_actor_t recv_actor);
581 
582 void tcp_initialize_rcv_mss(struct sock *sk);
583 
584 int tcp_mtu_to_mss(struct sock *sk, int pmtu);
585 int tcp_mss_to_mtu(struct sock *sk, int mss);
586 void tcp_mtup_init(struct sock *sk);
587 void tcp_init_buffer_space(struct sock *sk);
588 
589 static inline void tcp_bound_rto(const struct sock *sk)
590 {
591         if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
592                 inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
593 }
594 
595 static inline u32 __tcp_set_rto(const struct tcp_sock *tp)
596 {
597         return usecs_to_jiffies((tp->srtt_us >> 3) + tp->rttvar_us);
598 }
599 
600 static inline void __tcp_fast_path_on(struct tcp_sock *tp, u32 snd_wnd)
601 {
602         tp->pred_flags = htonl((tp->tcp_header_len << 26) |
603                                ntohl(TCP_FLAG_ACK) |
604                                snd_wnd);
605 }
606 
607 static inline void tcp_fast_path_on(struct tcp_sock *tp)
608 {
609         __tcp_fast_path_on(tp, tp->snd_wnd >> tp->rx_opt.snd_wscale);
610 }
611 
612 static inline void tcp_fast_path_check(struct sock *sk)
613 {
614         struct tcp_sock *tp = tcp_sk(sk);
615 
616         if (skb_queue_empty(&tp->out_of_order_queue) &&
617             tp->rcv_wnd &&
618             atomic_read(&sk->sk_rmem_alloc) < sk->sk_rcvbuf &&
619             !tp->urg_data)
620                 tcp_fast_path_on(tp);
621 }
622 
623 /* Compute the actual rto_min value */
624 static inline u32 tcp_rto_min(struct sock *sk)
625 {
626         const struct dst_entry *dst = __sk_dst_get(sk);
627         u32 rto_min = TCP_RTO_MIN;
628 
629         if (dst && dst_metric_locked(dst, RTAX_RTO_MIN))
630                 rto_min = dst_metric_rtt(dst, RTAX_RTO_MIN);
631         return rto_min;
632 }
633 
634 static inline u32 tcp_rto_min_us(struct sock *sk)
635 {
636         return jiffies_to_usecs(tcp_rto_min(sk));
637 }
638 
639 static inline bool tcp_ca_dst_locked(const struct dst_entry *dst)
640 {
641         return dst_metric_locked(dst, RTAX_CC_ALGO);
642 }
643 
644 /* Compute the actual receive window we are currently advertising.
645  * Rcv_nxt can be after the window if our peer push more data
646  * than the offered window.
647  */
648 static inline u32 tcp_receive_window(const struct tcp_sock *tp)
649 {
650         s32 win = tp->rcv_wup + tp->rcv_wnd - tp->rcv_nxt;
651 
652         if (win < 0)
653                 win = 0;
654         return (u32) win;
655 }
656 
657 /* Choose a new window, without checks for shrinking, and without
658  * scaling applied to the result.  The caller does these things
659  * if necessary.  This is a "raw" window selection.
660  */
661 u32 __tcp_select_window(struct sock *sk);
662 
663 void tcp_send_window_probe(struct sock *sk);
664 
665 /* TCP timestamps are only 32-bits, this causes a slight
666  * complication on 64-bit systems since we store a snapshot
667  * of jiffies in the buffer control blocks below.  We decided
668  * to use only the low 32-bits of jiffies and hide the ugly
669  * casts with the following macro.
670  */
671 #define tcp_time_stamp          ((__u32)(jiffies))
672 
673 static inline u32 tcp_skb_timestamp(const struct sk_buff *skb)
674 {
675         return skb->skb_mstamp.stamp_jiffies;
676 }
677 
678 
679 #define tcp_flag_byte(th) (((u_int8_t *)th)[13])
680 
681 #define TCPHDR_FIN 0x01
682 #define TCPHDR_SYN 0x02
683 #define TCPHDR_RST 0x04
684 #define TCPHDR_PSH 0x08
685 #define TCPHDR_ACK 0x10
686 #define TCPHDR_URG 0x20
687 #define TCPHDR_ECE 0x40
688 #define TCPHDR_CWR 0x80
689 
690 /* This is what the send packet queuing engine uses to pass
691  * TCP per-packet control information to the transmission code.
692  * We also store the host-order sequence numbers in here too.
693  * This is 44 bytes if IPV6 is enabled.
694  * If this grows please adjust skbuff.h:skbuff->cb[xxx] size appropriately.
695  */
696 struct tcp_skb_cb {
697         __u32           seq;            /* Starting sequence number     */
698         __u32           end_seq;        /* SEQ + FIN + SYN + datalen    */
699         union {
700                 /* Note : tcp_tw_isn is used in input path only
701                  *        (isn chosen by tcp_timewait_state_process())
702                  *
703                  *        tcp_gso_segs is used in write queue only,
704                  *        cf tcp_skb_pcount()
705                  */
706                 __u32           tcp_tw_isn;
707                 __u32           tcp_gso_segs;
708         };
709         __u8            tcp_flags;      /* TCP header flags. (tcp[13])  */
710 
711         __u8            sacked;         /* State flags for SACK/FACK.   */
712 #define TCPCB_SACKED_ACKED      0x01    /* SKB ACK'd by a SACK block    */
713 #define TCPCB_SACKED_RETRANS    0x02    /* SKB retransmitted            */
714 #define TCPCB_LOST              0x04    /* SKB is lost                  */
715 #define TCPCB_TAGBITS           0x07    /* All tag bits                 */
716 #define TCPCB_REPAIRED          0x10    /* SKB repaired (no skb_mstamp) */
717 #define TCPCB_EVER_RETRANS      0x80    /* Ever retransmitted frame     */
718 #define TCPCB_RETRANS           (TCPCB_SACKED_RETRANS|TCPCB_EVER_RETRANS| \
719                                 TCPCB_REPAIRED)
720 
721         __u8            ip_dsfield;     /* IPv4 tos or IPv6 dsfield     */
722         /* 1 byte hole */
723         __u32           ack_seq;        /* Sequence number ACK'd        */
724         union {
725                 struct inet_skb_parm    h4;
726 #if IS_ENABLED(CONFIG_IPV6)
727                 struct inet6_skb_parm   h6;
728 #endif
729         } header;       /* For incoming frames          */
730 };
731 
732 #define TCP_SKB_CB(__skb)       ((struct tcp_skb_cb *)&((__skb)->cb[0]))
733 
734 
735 #if IS_ENABLED(CONFIG_IPV6)
736 /* This is the variant of inet6_iif() that must be used by TCP,
737  * as TCP moves IP6CB into a different location in skb->cb[]
738  */
739 static inline int tcp_v6_iif(const struct sk_buff *skb)
740 {
741         return TCP_SKB_CB(skb)->header.h6.iif;
742 }
743 #endif
744 
745 /* Due to TSO, an SKB can be composed of multiple actual
746  * packets.  To keep these tracked properly, we use this.
747  */
748 static inline int tcp_skb_pcount(const struct sk_buff *skb)
749 {
750         return TCP_SKB_CB(skb)->tcp_gso_segs;
751 }
752 
753 static inline void tcp_skb_pcount_set(struct sk_buff *skb, int segs)
754 {
755         TCP_SKB_CB(skb)->tcp_gso_segs = segs;
756 }
757 
758 static inline void tcp_skb_pcount_add(struct sk_buff *skb, int segs)
759 {
760         TCP_SKB_CB(skb)->tcp_gso_segs += segs;
761 }
762 
763 /* This is valid iff tcp_skb_pcount() > 1. */
764 static inline int tcp_skb_mss(const struct sk_buff *skb)
765 {
766         return skb_shinfo(skb)->gso_size;
767 }
768 
769 /* Events passed to congestion control interface */
770 enum tcp_ca_event {
771         CA_EVENT_TX_START,      /* first transmit when no packets in flight */
772         CA_EVENT_CWND_RESTART,  /* congestion window restart */
773         CA_EVENT_COMPLETE_CWR,  /* end of congestion recovery */
774         CA_EVENT_LOSS,          /* loss timeout */
775         CA_EVENT_ECN_NO_CE,     /* ECT set, but not CE marked */
776         CA_EVENT_ECN_IS_CE,     /* received CE marked IP packet */
777         CA_EVENT_DELAYED_ACK,   /* Delayed ack is sent */
778         CA_EVENT_NON_DELAYED_ACK,
779 };
780 
781 /* Information about inbound ACK, passed to cong_ops->in_ack_event() */
782 enum tcp_ca_ack_event_flags {
783         CA_ACK_SLOWPATH         = (1 << 0),     /* In slow path processing */
784         CA_ACK_WIN_UPDATE       = (1 << 1),     /* ACK updated window */
785         CA_ACK_ECE              = (1 << 2),     /* ECE bit is set on ack */
786 };
787 
788 /*
789  * Interface for adding new TCP congestion control handlers
790  */
791 #define TCP_CA_NAME_MAX 16
792 #define TCP_CA_MAX      128
793 #define TCP_CA_BUF_MAX  (TCP_CA_NAME_MAX*TCP_CA_MAX)
794 
795 #define TCP_CA_UNSPEC   0
796 
797 /* Algorithm can be set on socket without CAP_NET_ADMIN privileges */
798 #define TCP_CONG_NON_RESTRICTED 0x1
799 /* Requires ECN/ECT set on all packets */
800 #define TCP_CONG_NEEDS_ECN      0x2
801 
802 struct tcp_congestion_ops {
803         struct list_head        list;
804         u32 key;
805         u32 flags;
806 
807         /* initialize private data (optional) */
808         void (*init)(struct sock *sk);
809         /* cleanup private data  (optional) */
810         void (*release)(struct sock *sk);
811 
812         /* return slow start threshold (required) */
813         u32 (*ssthresh)(struct sock *sk);
814         /* do new cwnd calculation (required) */
815         void (*cong_avoid)(struct sock *sk, u32 ack, u32 acked);
816         /* call before changing ca_state (optional) */
817         void (*set_state)(struct sock *sk, u8 new_state);
818         /* call when cwnd event occurs (optional) */
819         void (*cwnd_event)(struct sock *sk, enum tcp_ca_event ev);
820         /* call when ack arrives (optional) */
821         void (*in_ack_event)(struct sock *sk, u32 flags);
822         /* new value of cwnd after loss (optional) */
823         u32  (*undo_cwnd)(struct sock *sk);
824         /* hook for packet ack accounting (optional) */
825         void (*pkts_acked)(struct sock *sk, u32 num_acked, s32 rtt_us);
826         /* get info for inet_diag (optional) */
827         void (*get_info)(struct sock *sk, u32 ext, struct sk_buff *skb);
828 
829         char            name[TCP_CA_NAME_MAX];
830         struct module   *owner;
831 };
832 
833 int tcp_register_congestion_control(struct tcp_congestion_ops *type);
834 void tcp_unregister_congestion_control(struct tcp_congestion_ops *type);
835 
836 void tcp_assign_congestion_control(struct sock *sk);
837 void tcp_init_congestion_control(struct sock *sk);
838 void tcp_cleanup_congestion_control(struct sock *sk);
839 int tcp_set_default_congestion_control(const char *name);
840 void tcp_get_default_congestion_control(char *name);
841 void tcp_get_available_congestion_control(char *buf, size_t len);
842 void tcp_get_allowed_congestion_control(char *buf, size_t len);
843 int tcp_set_allowed_congestion_control(char *allowed);
844 int tcp_set_congestion_control(struct sock *sk, const char *name);
845 u32 tcp_slow_start(struct tcp_sock *tp, u32 acked);
846 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked);
847 
848 u32 tcp_reno_ssthresh(struct sock *sk);
849 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked);
850 extern struct tcp_congestion_ops tcp_reno;
851 
852 struct tcp_congestion_ops *tcp_ca_find_key(u32 key);
853 u32 tcp_ca_get_key_by_name(const char *name);
854 #ifdef CONFIG_INET
855 char *tcp_ca_get_name_by_key(u32 key, char *buffer);
856 #else
857 static inline char *tcp_ca_get_name_by_key(u32 key, char *buffer)
858 {
859         return NULL;
860 }
861 #endif
862 
863 static inline bool tcp_ca_needs_ecn(const struct sock *sk)
864 {
865         const struct inet_connection_sock *icsk = inet_csk(sk);
866 
867         return icsk->icsk_ca_ops->flags & TCP_CONG_NEEDS_ECN;
868 }
869 
870 static inline void tcp_set_ca_state(struct sock *sk, const u8 ca_state)
871 {
872         struct inet_connection_sock *icsk = inet_csk(sk);
873 
874         if (icsk->icsk_ca_ops->set_state)
875                 icsk->icsk_ca_ops->set_state(sk, ca_state);
876         icsk->icsk_ca_state = ca_state;
877 }
878 
879 static inline void tcp_ca_event(struct sock *sk, const enum tcp_ca_event event)
880 {
881         const struct inet_connection_sock *icsk = inet_csk(sk);
882 
883         if (icsk->icsk_ca_ops->cwnd_event)
884                 icsk->icsk_ca_ops->cwnd_event(sk, event);
885 }
886 
887 /* These functions determine how the current flow behaves in respect of SACK
888  * handling. SACK is negotiated with the peer, and therefore it can vary
889  * between different flows.
890  *
891  * tcp_is_sack - SACK enabled
892  * tcp_is_reno - No SACK
893  * tcp_is_fack - FACK enabled, implies SACK enabled
894  */
895 static inline int tcp_is_sack(const struct tcp_sock *tp)
896 {
897         return tp->rx_opt.sack_ok;
898 }
899 
900 static inline bool tcp_is_reno(const struct tcp_sock *tp)
901 {
902         return !tcp_is_sack(tp);
903 }
904 
905 static inline bool tcp_is_fack(const struct tcp_sock *tp)
906 {
907         return tp->rx_opt.sack_ok & TCP_FACK_ENABLED;
908 }
909 
910 static inline void tcp_enable_fack(struct tcp_sock *tp)
911 {
912         tp->rx_opt.sack_ok |= TCP_FACK_ENABLED;
913 }
914 
915 /* TCP early-retransmit (ER) is similar to but more conservative than
916  * the thin-dupack feature.  Enable ER only if thin-dupack is disabled.
917  */
918 static inline void tcp_enable_early_retrans(struct tcp_sock *tp)
919 {
920         tp->do_early_retrans = sysctl_tcp_early_retrans &&
921                 sysctl_tcp_early_retrans < 4 && !sysctl_tcp_thin_dupack &&
922                 sysctl_tcp_reordering == 3;
923 }
924 
925 static inline void tcp_disable_early_retrans(struct tcp_sock *tp)
926 {
927         tp->do_early_retrans = 0;
928 }
929 
930 static inline unsigned int tcp_left_out(const struct tcp_sock *tp)
931 {
932         return tp->sacked_out + tp->lost_out;
933 }
934 
935 /* This determines how many packets are "in the network" to the best
936  * of our knowledge.  In many cases it is conservative, but where
937  * detailed information is available from the receiver (via SACK
938  * blocks etc.) we can make more aggressive calculations.
939  *
940  * Use this for decisions involving congestion control, use just
941  * tp->packets_out to determine if the send queue is empty or not.
942  *
943  * Read this equation as:
944  *
945  *      "Packets sent once on transmission queue" MINUS
946  *      "Packets left network, but not honestly ACKed yet" PLUS
947  *      "Packets fast retransmitted"
948  */
949 static inline unsigned int tcp_packets_in_flight(const struct tcp_sock *tp)
950 {
951         return tp->packets_out - tcp_left_out(tp) + tp->retrans_out;
952 }
953 
954 #define TCP_INFINITE_SSTHRESH   0x7fffffff
955 
956 static inline bool tcp_in_initial_slowstart(const struct tcp_sock *tp)
957 {
958         return tp->snd_ssthresh >= TCP_INFINITE_SSTHRESH;
959 }
960 
961 static inline bool tcp_in_cwnd_reduction(const struct sock *sk)
962 {
963         return (TCPF_CA_CWR | TCPF_CA_Recovery) &
964                (1 << inet_csk(sk)->icsk_ca_state);
965 }
966 
967 /* If cwnd > ssthresh, we may raise ssthresh to be half-way to cwnd.
968  * The exception is cwnd reduction phase, when cwnd is decreasing towards
969  * ssthresh.
970  */
971 static inline __u32 tcp_current_ssthresh(const struct sock *sk)
972 {
973         const struct tcp_sock *tp = tcp_sk(sk);
974 
975         if (tcp_in_cwnd_reduction(sk))
976                 return tp->snd_ssthresh;
977         else
978                 return max(tp->snd_ssthresh,
979                            ((tp->snd_cwnd >> 1) +
980                             (tp->snd_cwnd >> 2)));
981 }
982 
983 /* Use define here intentionally to get WARN_ON location shown at the caller */
984 #define tcp_verify_left_out(tp) WARN_ON(tcp_left_out(tp) > tp->packets_out)
985 
986 void tcp_enter_cwr(struct sock *sk);
987 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst);
988 
989 /* The maximum number of MSS of available cwnd for which TSO defers
990  * sending if not using sysctl_tcp_tso_win_divisor.
991  */
992 static inline __u32 tcp_max_tso_deferred_mss(const struct tcp_sock *tp)
993 {
994         return 3;
995 }
996 
997 /* Slow start with delack produces 3 packets of burst, so that
998  * it is safe "de facto".  This will be the default - same as
999  * the default reordering threshold - but if reordering increases,
1000  * we must be able to allow cwnd to burst at least this much in order
1001  * to not pull it back when holes are filled.
1002  */
1003 static __inline__ __u32 tcp_max_burst(const struct tcp_sock *tp)
1004 {
1005         return tp->reordering;
1006 }
1007 
1008 /* Returns end sequence number of the receiver's advertised window */
1009 static inline u32 tcp_wnd_end(const struct tcp_sock *tp)
1010 {
1011         return tp->snd_una + tp->snd_wnd;
1012 }
1013 
1014 /* We follow the spirit of RFC2861 to validate cwnd but implement a more
1015  * flexible approach. The RFC suggests cwnd should not be raised unless
1016  * it was fully used previously. And that's exactly what we do in
1017  * congestion avoidance mode. But in slow start we allow cwnd to grow
1018  * as long as the application has used half the cwnd.
1019  * Example :
1020  *    cwnd is 10 (IW10), but application sends 9 frames.
1021  *    We allow cwnd to reach 18 when all frames are ACKed.
1022  * This check is safe because it's as aggressive as slow start which already
1023  * risks 100% overshoot. The advantage is that we discourage application to
1024  * either send more filler packets or data to artificially blow up the cwnd
1025  * usage, and allow application-limited process to probe bw more aggressively.
1026  */
1027 static inline bool tcp_is_cwnd_limited(const struct sock *sk)
1028 {
1029         const struct tcp_sock *tp = tcp_sk(sk);
1030 
1031         /* If in slow start, ensure cwnd grows to twice what was ACKed. */
1032         if (tp->snd_cwnd <= tp->snd_ssthresh)
1033                 return tp->snd_cwnd < 2 * tp->max_packets_out;
1034 
1035         return tp->is_cwnd_limited;
1036 }
1037 
1038 static inline void tcp_check_probe_timer(struct sock *sk)
1039 {
1040         const struct tcp_sock *tp = tcp_sk(sk);
1041         const struct inet_connection_sock *icsk = inet_csk(sk);
1042 
1043         if (!tp->packets_out && !icsk->icsk_pending)
1044                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
1045                                           icsk->icsk_rto, TCP_RTO_MAX);
1046 }
1047 
1048 static inline void tcp_init_wl(struct tcp_sock *tp, u32 seq)
1049 {
1050         tp->snd_wl1 = seq;
1051 }
1052 
1053 static inline void tcp_update_wl(struct tcp_sock *tp, u32 seq)
1054 {
1055         tp->snd_wl1 = seq;
1056 }
1057 
1058 /*
1059  * Calculate(/check) TCP checksum
1060  */
1061 static inline __sum16 tcp_v4_check(int len, __be32 saddr,
1062                                    __be32 daddr, __wsum base)
1063 {
1064         return csum_tcpudp_magic(saddr,daddr,len,IPPROTO_TCP,base);
1065 }
1066 
1067 static inline __sum16 __tcp_checksum_complete(struct sk_buff *skb)
1068 {
1069         return __skb_checksum_complete(skb);
1070 }
1071 
1072 static inline bool tcp_checksum_complete(struct sk_buff *skb)
1073 {
1074         return !skb_csum_unnecessary(skb) &&
1075                 __tcp_checksum_complete(skb);
1076 }
1077 
1078 /* Prequeue for VJ style copy to user, combined with checksumming. */
1079 
1080 static inline void tcp_prequeue_init(struct tcp_sock *tp)
1081 {
1082         tp->ucopy.task = NULL;
1083         tp->ucopy.len = 0;
1084         tp->ucopy.memory = 0;
1085         skb_queue_head_init(&tp->ucopy.prequeue);
1086 }
1087 
1088 bool tcp_prequeue(struct sock *sk, struct sk_buff *skb);
1089 
1090 #undef STATE_TRACE
1091 
1092 #ifdef STATE_TRACE
1093 static const char *statename[]={
1094         "Unused","Established","Syn Sent","Syn Recv",
1095         "Fin Wait 1","Fin Wait 2","Time Wait", "Close",
1096         "Close Wait","Last ACK","Listen","Closing"
1097 };
1098 #endif
1099 void tcp_set_state(struct sock *sk, int state);
1100 
1101 void tcp_done(struct sock *sk);
1102 
1103 static inline void tcp_sack_reset(struct tcp_options_received *rx_opt)
1104 {
1105         rx_opt->dsack = 0;
1106         rx_opt->num_sacks = 0;
1107 }
1108 
1109 u32 tcp_default_init_rwnd(u32 mss);
1110 
1111 /* Determine a window scaling and initial window to offer. */
1112 void tcp_select_initial_window(int __space, __u32 mss, __u32 *rcv_wnd,
1113                                __u32 *window_clamp, int wscale_ok,
1114                                __u8 *rcv_wscale, __u32 init_rcv_wnd);
1115 
1116 static inline int tcp_win_from_space(int space)
1117 {
1118         return sysctl_tcp_adv_win_scale<=0 ?
1119                 (space>>(-sysctl_tcp_adv_win_scale)) :
1120                 space - (space>>sysctl_tcp_adv_win_scale);
1121 }
1122 
1123 /* Note: caller must be prepared to deal with negative returns */
1124 static inline int tcp_space(const struct sock *sk)
1125 {
1126         return tcp_win_from_space(sk->sk_rcvbuf -
1127                                   atomic_read(&sk->sk_rmem_alloc));
1128 }
1129 
1130 static inline int tcp_full_space(const struct sock *sk)
1131 {
1132         return tcp_win_from_space(sk->sk_rcvbuf);
1133 }
1134 
1135 static inline void tcp_openreq_init(struct request_sock *req,
1136                                     struct tcp_options_received *rx_opt,
1137                                     struct sk_buff *skb, struct sock *sk)
1138 {
1139         struct inet_request_sock *ireq = inet_rsk(req);
1140 
1141         req->rcv_wnd = 0;               /* So that tcp_send_synack() knows! */
1142         req->cookie_ts = 0;
1143         tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
1144         tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
1145         tcp_rsk(req)->snt_synack = tcp_time_stamp;
1146         tcp_rsk(req)->last_oow_ack_time = 0;
1147         req->mss = rx_opt->mss_clamp;
1148         req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
1149         ireq->tstamp_ok = rx_opt->tstamp_ok;
1150         ireq->sack_ok = rx_opt->sack_ok;
1151         ireq->snd_wscale = rx_opt->snd_wscale;
1152         ireq->wscale_ok = rx_opt->wscale_ok;
1153         ireq->acked = 0;
1154         ireq->ecn_ok = 0;
1155         ireq->ir_rmt_port = tcp_hdr(skb)->source;
1156         ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
1157         ireq->ir_mark = inet_request_mark(sk, skb);
1158 }
1159 
1160 extern void tcp_openreq_init_rwin(struct request_sock *req,
1161                                   struct sock *sk, struct dst_entry *dst);
1162 
1163 void tcp_enter_memory_pressure(struct sock *sk);
1164 
1165 static inline int keepalive_intvl_when(const struct tcp_sock *tp)
1166 {
1167         return tp->keepalive_intvl ? : sysctl_tcp_keepalive_intvl;
1168 }
1169 
1170 static inline int keepalive_time_when(const struct tcp_sock *tp)
1171 {
1172         return tp->keepalive_time ? : sysctl_tcp_keepalive_time;
1173 }
1174 
1175 static inline int keepalive_probes(const struct tcp_sock *tp)
1176 {
1177         return tp->keepalive_probes ? : sysctl_tcp_keepalive_probes;
1178 }
1179 
1180 static inline u32 keepalive_time_elapsed(const struct tcp_sock *tp)
1181 {
1182         const struct inet_connection_sock *icsk = &tp->inet_conn;
1183 
1184         return min_t(u32, tcp_time_stamp - icsk->icsk_ack.lrcvtime,
1185                           tcp_time_stamp - tp->rcv_tstamp);
1186 }
1187 
1188 static inline int tcp_fin_time(const struct sock *sk)
1189 {
1190         int fin_timeout = tcp_sk(sk)->linger2 ? : sysctl_tcp_fin_timeout;
1191         const int rto = inet_csk(sk)->icsk_rto;
1192 
1193         if (fin_timeout < (rto << 2) - (rto >> 1))
1194                 fin_timeout = (rto << 2) - (rto >> 1);
1195 
1196         return fin_timeout;
1197 }
1198 
1199 static inline bool tcp_paws_check(const struct tcp_options_received *rx_opt,
1200                                   int paws_win)
1201 {
1202         if ((s32)(rx_opt->ts_recent - rx_opt->rcv_tsval) <= paws_win)
1203                 return true;
1204         if (unlikely(get_seconds() >= rx_opt->ts_recent_stamp + TCP_PAWS_24DAYS))
1205                 return true;
1206         /*
1207          * Some OSes send SYN and SYNACK messages with tsval=0 tsecr=0,
1208          * then following tcp messages have valid values. Ignore 0 value,
1209          * or else 'negative' tsval might forbid us to accept their packets.
1210          */
1211         if (!rx_opt->ts_recent)
1212                 return true;
1213         return false;
1214 }
1215 
1216 static inline bool tcp_paws_reject(const struct tcp_options_received *rx_opt,
1217                                    int rst)
1218 {
1219         if (tcp_paws_check(rx_opt, 0))
1220                 return false;
1221 
1222         /* RST segments are not recommended to carry timestamp,
1223            and, if they do, it is recommended to ignore PAWS because
1224            "their cleanup function should take precedence over timestamps."
1225            Certainly, it is mistake. It is necessary to understand the reasons
1226            of this constraint to relax it: if peer reboots, clock may go
1227            out-of-sync and half-open connections will not be reset.
1228            Actually, the problem would be not existing if all
1229            the implementations followed draft about maintaining clock
1230            via reboots. Linux-2.2 DOES NOT!
1231 
1232            However, we can relax time bounds for RST segments to MSL.
1233          */
1234         if (rst && get_seconds() >= rx_opt->ts_recent_stamp + TCP_PAWS_MSL)
1235                 return false;
1236         return true;
1237 }
1238 
1239 /* Return true if we're currently rate-limiting out-of-window ACKs and
1240  * thus shouldn't send a dupack right now. We rate-limit dupacks in
1241  * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
1242  * attacks that send repeated SYNs or ACKs for the same connection. To
1243  * do this, we do not send a duplicate SYNACK or ACK if the remote
1244  * endpoint is sending out-of-window SYNs or pure ACKs at a high rate.
1245  */
1246 static inline bool tcp_oow_rate_limited(struct net *net,
1247                                         const struct sk_buff *skb,
1248                                         int mib_idx, u32 *last_oow_ack_time)
1249 {
1250         /* Data packets without SYNs are not likely part of an ACK loop. */
1251         if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
1252             !tcp_hdr(skb)->syn)
1253                 goto not_rate_limited;
1254 
1255         if (*last_oow_ack_time) {
1256                 s32 elapsed = (s32)(tcp_time_stamp - *last_oow_ack_time);
1257 
1258                 if (0 <= elapsed && elapsed < sysctl_tcp_invalid_ratelimit) {
1259                         NET_INC_STATS_BH(net, mib_idx);
1260                         return true;    /* rate-limited: don't send yet! */
1261                 }
1262         }
1263 
1264         *last_oow_ack_time = tcp_time_stamp;
1265 
1266 not_rate_limited:
1267         return false;   /* not rate-limited: go ahead, send dupack now! */
1268 }
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, struct tcp_md5sig_key *key,
1348                         const struct sock *sk, const struct request_sock *req,
1349                         const struct sk_buff *skb);
1350 int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
1351                    int family, const u8 *newkey, u8 newkeylen, gfp_t gfp);
1352 int tcp_md5_do_del(struct sock *sk, const union tcp_md5_addr *addr,
1353                    int family);
1354 struct tcp_md5sig_key *tcp_v4_md5_lookup(struct sock *sk,
1355                                          struct sock *addr_sk);
1356 
1357 #ifdef CONFIG_TCP_MD5SIG
1358 struct tcp_md5sig_key *tcp_md5_do_lookup(struct sock *sk,
1359                                          const union tcp_md5_addr *addr,
1360                                          int family);
1361 #define tcp_twsk_md5_key(twsk)  ((twsk)->tw_md5_key)
1362 #else
1363 static inline struct tcp_md5sig_key *tcp_md5_do_lookup(struct sock *sk,
1364                                          const union tcp_md5_addr *addr,
1365                                          int family)
1366 {
1367         return NULL;
1368 }
1369 #define tcp_twsk_md5_key(twsk)  NULL
1370 #endif
1371 
1372 bool tcp_alloc_md5sig_pool(void);
1373 
1374 struct tcp_md5sig_pool *tcp_get_md5sig_pool(void);
1375 static inline void tcp_put_md5sig_pool(void)
1376 {
1377         local_bh_enable();
1378 }
1379 
1380 int tcp_md5_hash_header(struct tcp_md5sig_pool *, const struct tcphdr *);
1381 int tcp_md5_hash_skb_data(struct tcp_md5sig_pool *, const struct sk_buff *,
1382                           unsigned int header_len);
1383 int tcp_md5_hash_key(struct tcp_md5sig_pool *hp,
1384                      const struct tcp_md5sig_key *key);
1385 
1386 /* From tcp_fastopen.c */
1387 void tcp_fastopen_cache_get(struct sock *sk, u16 *mss,
1388                             struct tcp_fastopen_cookie *cookie, int *syn_loss,
1389                             unsigned long *last_syn_loss);
1390 void tcp_fastopen_cache_set(struct sock *sk, u16 mss,
1391                             struct tcp_fastopen_cookie *cookie, bool syn_lost);
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                                                 struct sock *addr_sk);
1667         int                     (*calc_md5_hash) (char *location,
1668                                                   struct tcp_md5sig_key *md5,
1669                                                   const struct sock *sk,
1670                                                   const struct request_sock *req,
1671                                                   const struct sk_buff *skb);
1672         int                     (*md5_parse) (struct sock *sk,
1673                                               char __user *optval,
1674                                               int optlen);
1675 #endif
1676 };
1677 
1678 struct tcp_request_sock_ops {
1679         u16 mss_clamp;
1680 #ifdef CONFIG_TCP_MD5SIG
1681         struct tcp_md5sig_key   *(*md5_lookup) (struct sock *sk,
1682                                                 struct request_sock *req);
1683         int                     (*calc_md5_hash) (char *location,
1684                                                   struct tcp_md5sig_key *md5,
1685                                                   const struct sock *sk,
1686                                                   const struct request_sock *req,
1687                                                   const struct sk_buff *skb);
1688 #endif
1689         void (*init_req)(struct request_sock *req, struct sock *sk,
1690                          struct sk_buff *skb);
1691 #ifdef CONFIG_SYN_COOKIES
1692         __u32 (*cookie_init_seq)(struct sock *sk, const struct sk_buff *skb,
1693                                  __u16 *mss);
1694 #endif
1695         struct dst_entry *(*route_req)(struct sock *sk, struct flowi *fl,
1696                                        const struct request_sock *req,
1697                                        bool *strict);
1698         __u32 (*init_seq)(const struct sk_buff *skb);
1699         int (*send_synack)(struct sock *sk, struct dst_entry *dst,
1700                            struct flowi *fl, struct request_sock *req,
1701                            u16 queue_mapping, struct tcp_fastopen_cookie *foc);
1702         void (*queue_hash_add)(struct sock *sk, struct request_sock *req,
1703                                const unsigned long timeout);
1704 };
1705 
1706 #ifdef CONFIG_SYN_COOKIES
1707 static inline __u32 cookie_init_sequence(const struct tcp_request_sock_ops *ops,
1708                                          struct sock *sk, struct sk_buff *skb,
1709                                          __u16 *mss)
1710 {
1711         return ops->cookie_init_seq(sk, skb, mss);
1712 }
1713 #else
1714 static inline __u32 cookie_init_sequence(const struct tcp_request_sock_ops *ops,
1715                                          struct sock *sk, struct sk_buff *skb,
1716                                          __u16 *mss)
1717 {
1718         return 0;
1719 }
1720 #endif
1721 
1722 int tcpv4_offload_init(void);
1723 
1724 void tcp_v4_init(void);
1725 void tcp_init(void);
1726 
1727 /*
1728  * Save and compile IPv4 options, return a pointer to it
1729  */
1730 static inline struct ip_options_rcu *tcp_v4_save_options(struct sk_buff *skb)
1731 {
1732         const struct ip_options *opt = &TCP_SKB_CB(skb)->header.h4.opt;
1733         struct ip_options_rcu *dopt = NULL;
1734 
1735         if (opt->optlen) {
1736                 int opt_size = sizeof(*dopt) + opt->optlen;
1737 
1738                 dopt = kmalloc(opt_size, GFP_ATOMIC);
1739                 if (dopt && __ip_options_echo(&dopt->opt, skb, opt)) {
1740                         kfree(dopt);
1741                         dopt = NULL;
1742                 }
1743         }
1744         return dopt;
1745 }
1746 
1747 /* locally generated TCP pure ACKs have skb->truesize == 2
1748  * (check tcp_send_ack() in net/ipv4/tcp_output.c )
1749  * This is much faster than dissecting the packet to find out.
1750  * (Think of GRE encapsulations, IPv4, IPv6, ...)
1751  */
1752 static inline bool skb_is_tcp_pure_ack(const struct sk_buff *skb)
1753 {
1754         return skb->truesize == 2;
1755 }
1756 
1757 static inline void skb_set_tcp_pure_ack(struct sk_buff *skb)
1758 {
1759         skb->truesize = 2;
1760 }
1761 
1762 #endif  /* _TCP_H */
1763 

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