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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/cryptohash.h>
 31 #include <linux/kref.h>
 32 #include <linux/ktime.h>
 33 
 34 #include <net/inet_connection_sock.h>
 35 #include <net/inet_timewait_sock.h>
 36 #include <net/inet_hashtables.h>
 37 #include <net/checksum.h>
 38 #include <net/request_sock.h>
 39 #include <net/sock.h>
 40 #include <net/snmp.h>
 41 #include <net/ip.h>
 42 #include <net/tcp_states.h>
 43 #include <net/inet_ecn.h>
 44 #include <net/dst.h>
 45 
 46 #include <linux/seq_file.h>
 47 #include <linux/memcontrol.h>
 48 
 49 extern struct inet_hashinfo tcp_hashinfo;
 50 
 51 extern struct percpu_counter tcp_orphan_count;
 52 void tcp_time_wait(struct sock *sk, int state, int timeo);
 53 
 54 #define MAX_TCP_HEADER  (128 + MAX_HEADER)
 55 #define MAX_TCP_OPTION_SPACE 40
 56 
 57 /*
 58  * Never offer a window over 32767 without using window scaling. Some
 59  * poor stacks do signed 16bit maths!
 60  */
 61 #define MAX_TCP_WINDOW          32767U
 62 
 63 /* Minimal accepted MSS. It is (60+60+8) - (20+20). */
 64 #define TCP_MIN_MSS             88U
 65 
 66 /* The least MTU to use for probing */
 67 #define TCP_BASE_MSS            1024
 68 
 69 /* probing interval, default to 10 minutes as per RFC4821 */
 70 #define TCP_PROBE_INTERVAL      600
 71 
 72 /* Specify interval when tcp mtu probing will stop */
 73 #define TCP_PROBE_THRESHOLD     8
 74 
 75 /* After receiving this amount of duplicate ACKs fast retransmit starts. */
 76 #define TCP_FASTRETRANS_THRESH 3
 77 
 78 /* Maximal number of ACKs sent quickly to accelerate slow-start. */
 79 #define TCP_MAX_QUICKACKS       16U
 80 
 81 /* urg_data states */
 82 #define TCP_URG_VALID   0x0100
 83 #define TCP_URG_NOTYET  0x0200
 84 #define TCP_URG_READ    0x0400
 85 
 86 #define TCP_RETR1       3       /*
 87                                  * This is how many retries it does before it
 88                                  * tries to figure out if the gateway is
 89                                  * down. Minimal RFC value is 3; it corresponds
 90                                  * to ~3sec-8min depending on RTO.
 91                                  */
 92 
 93 #define TCP_RETR2       15      /*
 94                                  * This should take at least
 95                                  * 90 minutes to time out.
 96                                  * RFC1122 says that the limit is 100 sec.
 97                                  * 15 is ~13-30min depending on RTO.
 98                                  */
 99 
100 #define TCP_SYN_RETRIES  6      /* This is how many retries are done
101                                  * when active opening a connection.
102                                  * RFC1122 says the minimum retry MUST
103                                  * be at least 180secs.  Nevertheless
104                                  * this value is corresponding to
105                                  * 63secs of retransmission with the
106                                  * current initial RTO.
107                                  */
108 
109 #define TCP_SYNACK_RETRIES 5    /* This is how may retries are done
110                                  * when passive opening a connection.
111                                  * This is corresponding to 31secs of
112                                  * retransmission with the current
113                                  * initial RTO.
114                                  */
115 
116 #define TCP_TIMEWAIT_LEN (60*HZ) /* how long to wait to destroy TIME-WAIT
117                                   * state, about 60 seconds     */
118 #define TCP_FIN_TIMEOUT TCP_TIMEWAIT_LEN
119                                  /* BSD style FIN_WAIT2 deadlock breaker.
120                                   * It used to be 3min, new value is 60sec,
121                                   * to combine FIN-WAIT-2 timeout with
122                                   * TIME-WAIT timer.
123                                   */
124 
125 #define TCP_DELACK_MAX  ((unsigned)(HZ/5))      /* maximal time to delay before sending an ACK */
126 #if HZ >= 100
127 #define TCP_DELACK_MIN  ((unsigned)(HZ/25))     /* minimal time to delay before sending an ACK */
128 #define TCP_ATO_MIN     ((unsigned)(HZ/25))
129 #else
130 #define TCP_DELACK_MIN  4U
131 #define TCP_ATO_MIN     4U
132 #endif
133 #define TCP_RTO_MAX     ((unsigned)(120*HZ))
134 #define TCP_RTO_MIN     ((unsigned)(HZ/5))
135 #define TCP_TIMEOUT_INIT ((unsigned)(1*HZ))     /* RFC6298 2.1 initial RTO value        */
136 #define TCP_TIMEOUT_FALLBACK ((unsigned)(3*HZ)) /* RFC 1122 initial RTO value, now
137                                                  * used as a fallback RTO for the
138                                                  * initial data transmission if no
139                                                  * valid RTT sample has been acquired,
140                                                  * most likely due to retrans in 3WHS.
141                                                  */
142 
143 #define TCP_RESOURCE_PROBE_INTERVAL ((unsigned)(HZ/2U)) /* Maximal interval between probes
144                                                          * for local resources.
145                                                          */
146 
147 #define TCP_KEEPALIVE_TIME      (120*60*HZ)     /* two hours */
148 #define TCP_KEEPALIVE_PROBES    9               /* Max of 9 keepalive probes    */
149 #define TCP_KEEPALIVE_INTVL     (75*HZ)
150 
151 #define MAX_TCP_KEEPIDLE        32767
152 #define MAX_TCP_KEEPINTVL       32767
153 #define MAX_TCP_KEEPCNT         127
154 #define MAX_TCP_SYNCNT          127
155 
156 #define TCP_SYNQ_INTERVAL       (HZ/5)  /* Period of SYNACK timer */
157 
158 #define TCP_PAWS_24DAYS (60 * 60 * 24 * 24)
159 #define TCP_PAWS_MSL    60              /* Per-host timestamps are invalidated
160                                          * after this time. It should be equal
161                                          * (or greater than) TCP_TIMEWAIT_LEN
162                                          * to provide reliability equal to one
163                                          * provided by timewait state.
164                                          */
165 #define TCP_PAWS_WINDOW 1               /* Replay window for per-host
166                                          * timestamps. It must be less than
167                                          * minimal timewait lifetime.
168                                          */
169 /*
170  *      TCP option
171  */
172 
173 #define TCPOPT_NOP              1       /* Padding */
174 #define TCPOPT_EOL              0       /* End of options */
175 #define TCPOPT_MSS              2       /* Segment size negotiating */
176 #define TCPOPT_WINDOW           3       /* Window scaling */
177 #define TCPOPT_SACK_PERM        4       /* SACK Permitted */
178 #define TCPOPT_SACK             5       /* SACK Block */
179 #define TCPOPT_TIMESTAMP        8       /* Better RTT estimations/PAWS */
180 #define TCPOPT_MD5SIG           19      /* MD5 Signature (RFC2385) */
181 #define TCPOPT_FASTOPEN         34      /* Fast open (RFC7413) */
182 #define TCPOPT_EXP              254     /* Experimental */
183 /* Magic number to be after the option value for sharing TCP
184  * experimental options. See draft-ietf-tcpm-experimental-options-00.txt
185  */
186 #define TCPOPT_FASTOPEN_MAGIC   0xF989
187 
188 /*
189  *     TCP option lengths
190  */
191 
192 #define TCPOLEN_MSS            4
193 #define TCPOLEN_WINDOW         3
194 #define TCPOLEN_SACK_PERM      2
195 #define TCPOLEN_TIMESTAMP      10
196 #define TCPOLEN_MD5SIG         18
197 #define TCPOLEN_FASTOPEN_BASE  2
198 #define TCPOLEN_EXP_FASTOPEN_BASE  4
199 
200 /* But this is what stacks really send out. */
201 #define TCPOLEN_TSTAMP_ALIGNED          12
202 #define TCPOLEN_WSCALE_ALIGNED          4
203 #define TCPOLEN_SACKPERM_ALIGNED        4
204 #define TCPOLEN_SACK_BASE               2
205 #define TCPOLEN_SACK_BASE_ALIGNED       4
206 #define TCPOLEN_SACK_PERBLOCK           8
207 #define TCPOLEN_MD5SIG_ALIGNED          20
208 #define TCPOLEN_MSS_ALIGNED             4
209 
210 /* Flags in tp->nonagle */
211 #define TCP_NAGLE_OFF           1       /* Nagle's algo is disabled */
212 #define TCP_NAGLE_CORK          2       /* Socket is corked         */
213 #define TCP_NAGLE_PUSH          4       /* Cork is overridden for already queued data */
214 
215 /* TCP thin-stream limits */
216 #define TCP_THIN_LINEAR_RETRIES 6       /* After 6 linear retries, do exp. backoff */
217 
218 /* TCP initial congestion window as per rfc6928 */
219 #define TCP_INIT_CWND           10
220 
221 /* Bit Flags for sysctl_tcp_fastopen */
222 #define TFO_CLIENT_ENABLE       1
223 #define TFO_SERVER_ENABLE       2
224 #define TFO_CLIENT_NO_COOKIE    4       /* Data in SYN w/o cookie option */
225 
226 /* Accept SYN data w/o any cookie option */
227 #define TFO_SERVER_COOKIE_NOT_REQD      0x200
228 
229 /* Force enable TFO on all listeners, i.e., not requiring the
230  * TCP_FASTOPEN socket option. SOCKOPT1/2 determine how to set max_qlen.
231  */
232 #define TFO_SERVER_WO_SOCKOPT1  0x400
233 #define TFO_SERVER_WO_SOCKOPT2  0x800
234 
235 extern struct inet_timewait_death_row tcp_death_row;
236 
237 /* sysctl variables for tcp */
238 extern int sysctl_tcp_timestamps;
239 extern int sysctl_tcp_window_scaling;
240 extern int sysctl_tcp_sack;
241 extern int sysctl_tcp_fastopen;
242 extern int sysctl_tcp_retrans_collapse;
243 extern int sysctl_tcp_stdurg;
244 extern int sysctl_tcp_rfc1337;
245 extern int sysctl_tcp_abort_on_overflow;
246 extern int sysctl_tcp_max_orphans;
247 extern int sysctl_tcp_fack;
248 extern int sysctl_tcp_reordering;
249 extern int sysctl_tcp_max_reordering;
250 extern int sysctl_tcp_dsack;
251 extern long sysctl_tcp_mem[3];
252 extern int sysctl_tcp_wmem[3];
253 extern int sysctl_tcp_rmem[3];
254 extern int sysctl_tcp_app_win;
255 extern int sysctl_tcp_adv_win_scale;
256 extern int sysctl_tcp_tw_reuse;
257 extern int sysctl_tcp_frto;
258 extern int sysctl_tcp_low_latency;
259 extern int sysctl_tcp_nometrics_save;
260 extern int sysctl_tcp_moderate_rcvbuf;
261 extern int sysctl_tcp_tso_win_divisor;
262 extern int sysctl_tcp_workaround_signed_windows;
263 extern int sysctl_tcp_slow_start_after_idle;
264 extern int sysctl_tcp_thin_linear_timeouts;
265 extern int sysctl_tcp_thin_dupack;
266 extern int sysctl_tcp_early_retrans;
267 extern int sysctl_tcp_limit_output_bytes;
268 extern int sysctl_tcp_challenge_ack_limit;
269 extern int sysctl_tcp_min_tso_segs;
270 extern int sysctl_tcp_min_rtt_wlen;
271 extern int sysctl_tcp_autocorking;
272 extern int sysctl_tcp_invalid_ratelimit;
273 extern int sysctl_tcp_pacing_ss_ratio;
274 extern int sysctl_tcp_pacing_ca_ratio;
275 
276 extern atomic_long_t tcp_memory_allocated;
277 extern struct percpu_counter tcp_sockets_allocated;
278 extern int tcp_memory_pressure;
279 
280 /* optimized version of sk_under_memory_pressure() for TCP sockets */
281 static inline bool tcp_under_memory_pressure(const struct sock *sk)
282 {
283         if (mem_cgroup_sockets_enabled && sk->sk_memcg &&
284             mem_cgroup_under_socket_pressure(sk->sk_memcg))
285                 return true;
286 
287         return tcp_memory_pressure;
288 }
289 /*
290  * The next routines deal with comparing 32 bit unsigned ints
291  * and worry about wraparound (automatic with unsigned arithmetic).
292  */
293 
294 static inline bool before(__u32 seq1, __u32 seq2)
295 {
296         return (__s32)(seq1-seq2) < 0;
297 }
298 #define after(seq2, seq1)       before(seq1, seq2)
299 
300 /* is s2<=s1<=s3 ? */
301 static inline bool between(__u32 seq1, __u32 seq2, __u32 seq3)
302 {
303         return seq3 - seq2 >= seq1 - seq2;
304 }
305 
306 static inline bool tcp_out_of_memory(struct sock *sk)
307 {
308         if (sk->sk_wmem_queued > SOCK_MIN_SNDBUF &&
309             sk_memory_allocated(sk) > sk_prot_mem_limits(sk, 2))
310                 return true;
311         return false;
312 }
313 
314 void sk_forced_mem_schedule(struct sock *sk, int size);
315 
316 static inline bool tcp_too_many_orphans(struct sock *sk, int shift)
317 {
318         struct percpu_counter *ocp = sk->sk_prot->orphan_count;
319         int orphans = percpu_counter_read_positive(ocp);
320 
321         if (orphans << shift > sysctl_tcp_max_orphans) {
322                 orphans = percpu_counter_sum_positive(ocp);
323                 if (orphans << shift > sysctl_tcp_max_orphans)
324                         return true;
325         }
326         return false;
327 }
328 
329 bool tcp_check_oom(struct sock *sk, int shift);
330 
331 
332 extern struct proto tcp_prot;
333 
334 #define TCP_INC_STATS(net, field)       SNMP_INC_STATS((net)->mib.tcp_statistics, field)
335 #define __TCP_INC_STATS(net, field)     __SNMP_INC_STATS((net)->mib.tcp_statistics, field)
336 #define TCP_DEC_STATS(net, field)       SNMP_DEC_STATS((net)->mib.tcp_statistics, field)
337 #define TCP_ADD_STATS(net, field, val)  SNMP_ADD_STATS((net)->mib.tcp_statistics, field, val)
338 
339 void tcp_tasklet_init(void);
340 
341 void tcp_v4_err(struct sk_buff *skb, u32);
342 
343 void tcp_shutdown(struct sock *sk, int how);
344 
345 void tcp_v4_early_demux(struct sk_buff *skb);
346 int tcp_v4_rcv(struct sk_buff *skb);
347 
348 int tcp_v4_tw_remember_stamp(struct inet_timewait_sock *tw);
349 int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size);
350 int tcp_sendpage(struct sock *sk, struct page *page, int offset, size_t size,
351                  int flags);
352 void tcp_release_cb(struct sock *sk);
353 void tcp_wfree(struct sk_buff *skb);
354 void tcp_write_timer_handler(struct sock *sk);
355 void tcp_delack_timer_handler(struct sock *sk);
356 int tcp_ioctl(struct sock *sk, int cmd, unsigned long arg);
357 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb);
358 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
359                          const struct tcphdr *th, unsigned int len);
360 void tcp_rcv_space_adjust(struct sock *sk);
361 int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp);
362 void tcp_twsk_destructor(struct sock *sk);
363 ssize_t tcp_splice_read(struct socket *sk, loff_t *ppos,
364                         struct pipe_inode_info *pipe, size_t len,
365                         unsigned int flags);
366 
367 static inline void tcp_dec_quickack_mode(struct sock *sk,
368                                          const unsigned int pkts)
369 {
370         struct inet_connection_sock *icsk = inet_csk(sk);
371 
372         if (icsk->icsk_ack.quick) {
373                 if (pkts >= icsk->icsk_ack.quick) {
374                         icsk->icsk_ack.quick = 0;
375                         /* Leaving quickack mode we deflate ATO. */
376                         icsk->icsk_ack.ato   = TCP_ATO_MIN;
377                 } else
378                         icsk->icsk_ack.quick -= pkts;
379         }
380 }
381 
382 #define TCP_ECN_OK              1
383 #define TCP_ECN_QUEUE_CWR       2
384 #define TCP_ECN_DEMAND_CWR      4
385 #define TCP_ECN_SEEN            8
386 
387 enum tcp_tw_status {
388         TCP_TW_SUCCESS = 0,
389         TCP_TW_RST = 1,
390         TCP_TW_ACK = 2,
391         TCP_TW_SYN = 3
392 };
393 
394 
395 enum tcp_tw_status tcp_timewait_state_process(struct inet_timewait_sock *tw,
396                                               struct sk_buff *skb,
397                                               const struct tcphdr *th);
398 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
399                            struct request_sock *req, bool fastopen);
400 int tcp_child_process(struct sock *parent, struct sock *child,
401                       struct sk_buff *skb);
402 void tcp_enter_loss(struct sock *sk);
403 void tcp_clear_retrans(struct tcp_sock *tp);
404 void tcp_update_metrics(struct sock *sk);
405 void tcp_init_metrics(struct sock *sk);
406 void tcp_metrics_init(void);
407 bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst,
408                         bool paws_check, bool timestamps);
409 bool tcp_remember_stamp(struct sock *sk);
410 bool tcp_tw_remember_stamp(struct inet_timewait_sock *tw);
411 void tcp_fetch_timewait_stamp(struct sock *sk, struct dst_entry *dst);
412 void tcp_disable_fack(struct tcp_sock *tp);
413 void tcp_close(struct sock *sk, long timeout);
414 void tcp_init_sock(struct sock *sk);
415 unsigned int tcp_poll(struct file *file, struct socket *sock,
416                       struct poll_table_struct *wait);
417 int tcp_getsockopt(struct sock *sk, int level, int optname,
418                    char __user *optval, int __user *optlen);
419 int tcp_setsockopt(struct sock *sk, int level, int optname,
420                    char __user *optval, unsigned int optlen);
421 int compat_tcp_getsockopt(struct sock *sk, int level, int optname,
422                           char __user *optval, int __user *optlen);
423 int compat_tcp_setsockopt(struct sock *sk, int level, int optname,
424                           char __user *optval, unsigned int optlen);
425 void tcp_set_keepalive(struct sock *sk, int val);
426 void tcp_syn_ack_timeout(const struct request_sock *req);
427 int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
428                 int flags, int *addr_len);
429 void tcp_parse_options(const struct sk_buff *skb,
430                        struct tcp_options_received *opt_rx,
431                        int estab, struct tcp_fastopen_cookie *foc);
432 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th);
433 
434 /*
435  *      TCP v4 functions exported for the inet6 API
436  */
437 
438 void tcp_v4_send_check(struct sock *sk, struct sk_buff *skb);
439 void tcp_v4_mtu_reduced(struct sock *sk);
440 void tcp_req_err(struct sock *sk, u32 seq, bool abort);
441 int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb);
442 struct sock *tcp_create_openreq_child(const struct sock *sk,
443                                       struct request_sock *req,
444                                       struct sk_buff *skb);
445 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst);
446 struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
447                                   struct request_sock *req,
448                                   struct dst_entry *dst,
449                                   struct request_sock *req_unhash,
450                                   bool *own_req);
451 int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb);
452 int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
453 int tcp_connect(struct sock *sk);
454 enum tcp_synack_type {
455         TCP_SYNACK_NORMAL,
456         TCP_SYNACK_FASTOPEN,
457         TCP_SYNACK_COOKIE,
458 };
459 struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
460                                 struct request_sock *req,
461                                 struct tcp_fastopen_cookie *foc,
462                                 enum tcp_synack_type synack_type);
463 int tcp_disconnect(struct sock *sk, int flags);
464 
465 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb);
466 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size);
467 void inet_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb);
468 
469 /* From syncookies.c */
470 struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
471                                  struct request_sock *req,
472                                  struct dst_entry *dst);
473 int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th,
474                       u32 cookie);
475 struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb);
476 #ifdef CONFIG_SYN_COOKIES
477 
478 /* Syncookies use a monotonic timer which increments every 60 seconds.
479  * This counter is used both as a hash input and partially encoded into
480  * the cookie value.  A cookie is only validated further if the delta
481  * between the current counter value and the encoded one is less than this,
482  * i.e. a sent cookie is valid only at most for 2*60 seconds (or less if
483  * the counter advances immediately after a cookie is generated).
484  */
485 #define MAX_SYNCOOKIE_AGE       2
486 #define TCP_SYNCOOKIE_PERIOD    (60 * HZ)
487 #define TCP_SYNCOOKIE_VALID     (MAX_SYNCOOKIE_AGE * TCP_SYNCOOKIE_PERIOD)
488 
489 /* syncookies: remember time of last synqueue overflow
490  * But do not dirty this field too often (once per second is enough)
491  * It is racy as we do not hold a lock, but race is very minor.
492  */
493 static inline void tcp_synq_overflow(const struct sock *sk)
494 {
495         unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
496         unsigned long now = jiffies;
497 
498         if (time_after(now, last_overflow + HZ))
499                 tcp_sk(sk)->rx_opt.ts_recent_stamp = now;
500 }
501 
502 /* syncookies: no recent synqueue overflow on this listening socket? */
503 static inline bool tcp_synq_no_recent_overflow(const struct sock *sk)
504 {
505         unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
506 
507         return time_after(jiffies, last_overflow + TCP_SYNCOOKIE_VALID);
508 }
509 
510 static inline u32 tcp_cookie_time(void)
511 {
512         u64 val = get_jiffies_64();
513 
514         do_div(val, TCP_SYNCOOKIE_PERIOD);
515         return val;
516 }
517 
518 u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,
519                               u16 *mssp);
520 __u32 cookie_v4_init_sequence(const struct sk_buff *skb, __u16 *mss);
521 __u32 cookie_init_timestamp(struct request_sock *req);
522 bool cookie_timestamp_decode(struct tcp_options_received *opt);
523 bool cookie_ecn_ok(const struct tcp_options_received *opt,
524                    const struct net *net, const struct dst_entry *dst);
525 
526 /* From net/ipv6/syncookies.c */
527 int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th,
528                       u32 cookie);
529 struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb);
530 
531 u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
532                               const struct tcphdr *th, u16 *mssp);
533 __u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mss);
534 #endif
535 /* tcp_output.c */
536 
537 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
538                                int nonagle);
539 bool tcp_may_send_now(struct sock *sk);
540 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs);
541 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs);
542 void tcp_retransmit_timer(struct sock *sk);
543 void tcp_xmit_retransmit_queue(struct sock *);
544 void tcp_simple_retransmit(struct sock *);
545 int tcp_trim_head(struct sock *, struct sk_buff *, u32);
546 int tcp_fragment(struct sock *, struct sk_buff *, u32, unsigned int, gfp_t);
547 
548 void tcp_send_probe0(struct sock *);
549 void tcp_send_partial(struct sock *);
550 int tcp_write_wakeup(struct sock *, int mib);
551 void tcp_send_fin(struct sock *sk);
552 void tcp_send_active_reset(struct sock *sk, gfp_t priority);
553 int tcp_send_synack(struct sock *);
554 void tcp_push_one(struct sock *, unsigned int mss_now);
555 void tcp_send_ack(struct sock *sk);
556 void tcp_send_delayed_ack(struct sock *sk);
557 void tcp_send_loss_probe(struct sock *sk);
558 bool tcp_schedule_loss_probe(struct sock *sk);
559 void tcp_skb_collapse_tstamp(struct sk_buff *skb,
560                              const struct sk_buff *next_skb);
561 
562 /* tcp_input.c */
563 void tcp_resume_early_retransmit(struct sock *sk);
564 void tcp_rearm_rto(struct sock *sk);
565 void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req);
566 void tcp_reset(struct sock *sk);
567 void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb);
568 void tcp_fin(struct sock *sk);
569 
570 /* tcp_timer.c */
571 void tcp_init_xmit_timers(struct sock *);
572 static inline void tcp_clear_xmit_timers(struct sock *sk)
573 {
574         inet_csk_clear_xmit_timers(sk);
575 }
576 
577 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu);
578 unsigned int tcp_current_mss(struct sock *sk);
579 
580 /* Bound MSS / TSO packet size with the half of the window */
581 static inline int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
582 {
583         int cutoff;
584 
585         /* When peer uses tiny windows, there is no use in packetizing
586          * to sub-MSS pieces for the sake of SWS or making sure there
587          * are enough packets in the pipe for fast recovery.
588          *
589          * On the other hand, for extremely large MSS devices, handling
590          * smaller than MSS windows in this way does make sense.
591          */
592         if (tp->max_window > TCP_MSS_DEFAULT)
593                 cutoff = (tp->max_window >> 1);
594         else
595                 cutoff = tp->max_window;
596 
597         if (cutoff && pktsize > cutoff)
598                 return max_t(int, cutoff, 68U - tp->tcp_header_len);
599         else
600                 return pktsize;
601 }
602 
603 /* tcp.c */
604 void tcp_get_info(struct sock *, struct tcp_info *);
605 
606 /* Read 'sendfile()'-style from a TCP socket */
607 typedef int (*sk_read_actor_t)(read_descriptor_t *, struct sk_buff *,
608                                 unsigned int, size_t);
609 int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
610                   sk_read_actor_t recv_actor);
611 
612 void tcp_initialize_rcv_mss(struct sock *sk);
613 
614 int tcp_mtu_to_mss(struct sock *sk, int pmtu);
615 int tcp_mss_to_mtu(struct sock *sk, int mss);
616 void tcp_mtup_init(struct sock *sk);
617 void tcp_init_buffer_space(struct sock *sk);
618 
619 static inline void tcp_bound_rto(const struct sock *sk)
620 {
621         if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
622                 inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
623 }
624 
625 static inline u32 __tcp_set_rto(const struct tcp_sock *tp)
626 {
627         return usecs_to_jiffies((tp->srtt_us >> 3) + tp->rttvar_us);
628 }
629 
630 static inline void __tcp_fast_path_on(struct tcp_sock *tp, u32 snd_wnd)
631 {
632         tp->pred_flags = htonl((tp->tcp_header_len << 26) |
633                                ntohl(TCP_FLAG_ACK) |
634                                snd_wnd);
635 }
636 
637 static inline void tcp_fast_path_on(struct tcp_sock *tp)
638 {
639         __tcp_fast_path_on(tp, tp->snd_wnd >> tp->rx_opt.snd_wscale);
640 }
641 
642 static inline void tcp_fast_path_check(struct sock *sk)
643 {
644         struct tcp_sock *tp = tcp_sk(sk);
645 
646         if (skb_queue_empty(&tp->out_of_order_queue) &&
647             tp->rcv_wnd &&
648             atomic_read(&sk->sk_rmem_alloc) < sk->sk_rcvbuf &&
649             !tp->urg_data)
650                 tcp_fast_path_on(tp);
651 }
652 
653 /* Compute the actual rto_min value */
654 static inline u32 tcp_rto_min(struct sock *sk)
655 {
656         const struct dst_entry *dst = __sk_dst_get(sk);
657         u32 rto_min = TCP_RTO_MIN;
658 
659         if (dst && dst_metric_locked(dst, RTAX_RTO_MIN))
660                 rto_min = dst_metric_rtt(dst, RTAX_RTO_MIN);
661         return rto_min;
662 }
663 
664 static inline u32 tcp_rto_min_us(struct sock *sk)
665 {
666         return jiffies_to_usecs(tcp_rto_min(sk));
667 }
668 
669 static inline bool tcp_ca_dst_locked(const struct dst_entry *dst)
670 {
671         return dst_metric_locked(dst, RTAX_CC_ALGO);
672 }
673 
674 /* Minimum RTT in usec. ~0 means not available. */
675 static inline u32 tcp_min_rtt(const struct tcp_sock *tp)
676 {
677         return tp->rtt_min[0].rtt;
678 }
679 
680 /* Compute the actual receive window we are currently advertising.
681  * Rcv_nxt can be after the window if our peer push more data
682  * than the offered window.
683  */
684 static inline u32 tcp_receive_window(const struct tcp_sock *tp)
685 {
686         s32 win = tp->rcv_wup + tp->rcv_wnd - tp->rcv_nxt;
687 
688         if (win < 0)
689                 win = 0;
690         return (u32) win;
691 }
692 
693 /* Choose a new window, without checks for shrinking, and without
694  * scaling applied to the result.  The caller does these things
695  * if necessary.  This is a "raw" window selection.
696  */
697 u32 __tcp_select_window(struct sock *sk);
698 
699 void tcp_send_window_probe(struct sock *sk);
700 
701 /* TCP timestamps are only 32-bits, this causes a slight
702  * complication on 64-bit systems since we store a snapshot
703  * of jiffies in the buffer control blocks below.  We decided
704  * to use only the low 32-bits of jiffies and hide the ugly
705  * casts with the following macro.
706  */
707 #define tcp_time_stamp          ((__u32)(jiffies))
708 
709 static inline u32 tcp_skb_timestamp(const struct sk_buff *skb)
710 {
711         return skb->skb_mstamp.stamp_jiffies;
712 }
713 
714 
715 #define tcp_flag_byte(th) (((u_int8_t *)th)[13])
716 
717 #define TCPHDR_FIN 0x01
718 #define TCPHDR_SYN 0x02
719 #define TCPHDR_RST 0x04
720 #define TCPHDR_PSH 0x08
721 #define TCPHDR_ACK 0x10
722 #define TCPHDR_URG 0x20
723 #define TCPHDR_ECE 0x40
724 #define TCPHDR_CWR 0x80
725 
726 #define TCPHDR_SYN_ECN  (TCPHDR_SYN | TCPHDR_ECE | TCPHDR_CWR)
727 
728 /* This is what the send packet queuing engine uses to pass
729  * TCP per-packet control information to the transmission code.
730  * We also store the host-order sequence numbers in here too.
731  * This is 44 bytes if IPV6 is enabled.
732  * If this grows please adjust skbuff.h:skbuff->cb[xxx] size appropriately.
733  */
734 struct tcp_skb_cb {
735         __u32           seq;            /* Starting sequence number     */
736         __u32           end_seq;        /* SEQ + FIN + SYN + datalen    */
737         union {
738                 /* Note : tcp_tw_isn is used in input path only
739                  *        (isn chosen by tcp_timewait_state_process())
740                  *
741                  *        tcp_gso_segs/size are used in write queue only,
742                  *        cf tcp_skb_pcount()/tcp_skb_mss()
743                  */
744                 __u32           tcp_tw_isn;
745                 struct {
746                         u16     tcp_gso_segs;
747                         u16     tcp_gso_size;
748                 };
749         };
750         __u8            tcp_flags;      /* TCP header flags. (tcp[13])  */
751 
752         __u8            sacked;         /* State flags for SACK/FACK.   */
753 #define TCPCB_SACKED_ACKED      0x01    /* SKB ACK'd by a SACK block    */
754 #define TCPCB_SACKED_RETRANS    0x02    /* SKB retransmitted            */
755 #define TCPCB_LOST              0x04    /* SKB is lost                  */
756 #define TCPCB_TAGBITS           0x07    /* All tag bits                 */
757 #define TCPCB_REPAIRED          0x10    /* SKB repaired (no skb_mstamp) */
758 #define TCPCB_EVER_RETRANS      0x80    /* Ever retransmitted frame     */
759 #define TCPCB_RETRANS           (TCPCB_SACKED_RETRANS|TCPCB_EVER_RETRANS| \
760                                 TCPCB_REPAIRED)
761 
762         __u8            ip_dsfield;     /* IPv4 tos or IPv6 dsfield     */
763         __u8            txstamp_ack:1,  /* Record TX timestamp for ack? */
764                         eor:1,          /* Is skb MSG_EOR marked? */
765                         unused:6;
766         __u32           ack_seq;        /* Sequence number ACK'd        */
767         union {
768                 struct {
769                         /* There is space for up to 20 bytes */
770                         __u32 in_flight;/* Bytes in flight when packet sent */
771                 } tx;   /* only used for outgoing skbs */
772                 union {
773                         struct inet_skb_parm    h4;
774 #if IS_ENABLED(CONFIG_IPV6)
775                         struct inet6_skb_parm   h6;
776 #endif
777                 } header;       /* For incoming skbs */
778         };
779 };
780 
781 #define TCP_SKB_CB(__skb)       ((struct tcp_skb_cb *)&((__skb)->cb[0]))
782 
783 
784 #if IS_ENABLED(CONFIG_IPV6)
785 /* This is the variant of inet6_iif() that must be used by TCP,
786  * as TCP moves IP6CB into a different location in skb->cb[]
787  */
788 static inline int tcp_v6_iif(const struct sk_buff *skb)
789 {
790         bool l3_slave = skb_l3mdev_slave(TCP_SKB_CB(skb)->header.h6.flags);
791 
792         return l3_slave ? skb->skb_iif : TCP_SKB_CB(skb)->header.h6.iif;
793 }
794 #endif
795 
796 /* Due to TSO, an SKB can be composed of multiple actual
797  * packets.  To keep these tracked properly, we use this.
798  */
799 static inline int tcp_skb_pcount(const struct sk_buff *skb)
800 {
801         return TCP_SKB_CB(skb)->tcp_gso_segs;
802 }
803 
804 static inline void tcp_skb_pcount_set(struct sk_buff *skb, int segs)
805 {
806         TCP_SKB_CB(skb)->tcp_gso_segs = segs;
807 }
808 
809 static inline void tcp_skb_pcount_add(struct sk_buff *skb, int segs)
810 {
811         TCP_SKB_CB(skb)->tcp_gso_segs += segs;
812 }
813 
814 /* This is valid iff skb is in write queue and tcp_skb_pcount() > 1. */
815 static inline int tcp_skb_mss(const struct sk_buff *skb)
816 {
817         return TCP_SKB_CB(skb)->tcp_gso_size;
818 }
819 
820 static inline bool tcp_skb_can_collapse_to(const struct sk_buff *skb)
821 {
822         return likely(!TCP_SKB_CB(skb)->eor);
823 }
824 
825 /* Events passed to congestion control interface */
826 enum tcp_ca_event {
827         CA_EVENT_TX_START,      /* first transmit when no packets in flight */
828         CA_EVENT_CWND_RESTART,  /* congestion window restart */
829         CA_EVENT_COMPLETE_CWR,  /* end of congestion recovery */
830         CA_EVENT_LOSS,          /* loss timeout */
831         CA_EVENT_ECN_NO_CE,     /* ECT set, but not CE marked */
832         CA_EVENT_ECN_IS_CE,     /* received CE marked IP packet */
833         CA_EVENT_DELAYED_ACK,   /* Delayed ack is sent */
834         CA_EVENT_NON_DELAYED_ACK,
835 };
836 
837 /* Information about inbound ACK, passed to cong_ops->in_ack_event() */
838 enum tcp_ca_ack_event_flags {
839         CA_ACK_SLOWPATH         = (1 << 0),     /* In slow path processing */
840         CA_ACK_WIN_UPDATE       = (1 << 1),     /* ACK updated window */
841         CA_ACK_ECE              = (1 << 2),     /* ECE bit is set on ack */
842 };
843 
844 /*
845  * Interface for adding new TCP congestion control handlers
846  */
847 #define TCP_CA_NAME_MAX 16
848 #define TCP_CA_MAX      128
849 #define TCP_CA_BUF_MAX  (TCP_CA_NAME_MAX*TCP_CA_MAX)
850 
851 #define TCP_CA_UNSPEC   0
852 
853 /* Algorithm can be set on socket without CAP_NET_ADMIN privileges */
854 #define TCP_CONG_NON_RESTRICTED 0x1
855 /* Requires ECN/ECT set on all packets */
856 #define TCP_CONG_NEEDS_ECN      0x2
857 
858 union tcp_cc_info;
859 
860 struct ack_sample {
861         u32 pkts_acked;
862         s32 rtt_us;
863         u32 in_flight;
864 };
865 
866 struct tcp_congestion_ops {
867         struct list_head        list;
868         u32 key;
869         u32 flags;
870 
871         /* initialize private data (optional) */
872         void (*init)(struct sock *sk);
873         /* cleanup private data  (optional) */
874         void (*release)(struct sock *sk);
875 
876         /* return slow start threshold (required) */
877         u32 (*ssthresh)(struct sock *sk);
878         /* do new cwnd calculation (required) */
879         void (*cong_avoid)(struct sock *sk, u32 ack, u32 acked);
880         /* call before changing ca_state (optional) */
881         void (*set_state)(struct sock *sk, u8 new_state);
882         /* call when cwnd event occurs (optional) */
883         void (*cwnd_event)(struct sock *sk, enum tcp_ca_event ev);
884         /* call when ack arrives (optional) */
885         void (*in_ack_event)(struct sock *sk, u32 flags);
886         /* new value of cwnd after loss (optional) */
887         u32  (*undo_cwnd)(struct sock *sk);
888         /* hook for packet ack accounting (optional) */
889         void (*pkts_acked)(struct sock *sk, const struct ack_sample *sample);
890         /* get info for inet_diag (optional) */
891         size_t (*get_info)(struct sock *sk, u32 ext, int *attr,
892                            union tcp_cc_info *info);
893 
894         char            name[TCP_CA_NAME_MAX];
895         struct module   *owner;
896 };
897 
898 int tcp_register_congestion_control(struct tcp_congestion_ops *type);
899 void tcp_unregister_congestion_control(struct tcp_congestion_ops *type);
900 
901 void tcp_assign_congestion_control(struct sock *sk);
902 void tcp_init_congestion_control(struct sock *sk);
903 void tcp_cleanup_congestion_control(struct sock *sk);
904 int tcp_set_default_congestion_control(const char *name);
905 void tcp_get_default_congestion_control(char *name);
906 void tcp_get_available_congestion_control(char *buf, size_t len);
907 void tcp_get_allowed_congestion_control(char *buf, size_t len);
908 int tcp_set_allowed_congestion_control(char *allowed);
909 int tcp_set_congestion_control(struct sock *sk, const char *name);
910 u32 tcp_slow_start(struct tcp_sock *tp, u32 acked);
911 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked);
912 
913 u32 tcp_reno_ssthresh(struct sock *sk);
914 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked);
915 extern struct tcp_congestion_ops tcp_reno;
916 
917 struct tcp_congestion_ops *tcp_ca_find_key(u32 key);
918 u32 tcp_ca_get_key_by_name(const char *name, bool *ecn_ca);
919 #ifdef CONFIG_INET
920 char *tcp_ca_get_name_by_key(u32 key, char *buffer);
921 #else
922 static inline char *tcp_ca_get_name_by_key(u32 key, char *buffer)
923 {
924         return NULL;
925 }
926 #endif
927 
928 static inline bool tcp_ca_needs_ecn(const struct sock *sk)
929 {
930         const struct inet_connection_sock *icsk = inet_csk(sk);
931 
932         return icsk->icsk_ca_ops->flags & TCP_CONG_NEEDS_ECN;
933 }
934 
935 static inline void tcp_set_ca_state(struct sock *sk, const u8 ca_state)
936 {
937         struct inet_connection_sock *icsk = inet_csk(sk);
938 
939         if (icsk->icsk_ca_ops->set_state)
940                 icsk->icsk_ca_ops->set_state(sk, ca_state);
941         icsk->icsk_ca_state = ca_state;
942 }
943 
944 static inline void tcp_ca_event(struct sock *sk, const enum tcp_ca_event event)
945 {
946         const struct inet_connection_sock *icsk = inet_csk(sk);
947 
948         if (icsk->icsk_ca_ops->cwnd_event)
949                 icsk->icsk_ca_ops->cwnd_event(sk, event);
950 }
951 
952 /* These functions determine how the current flow behaves in respect of SACK
953  * handling. SACK is negotiated with the peer, and therefore it can vary
954  * between different flows.
955  *
956  * tcp_is_sack - SACK enabled
957  * tcp_is_reno - No SACK
958  * tcp_is_fack - FACK enabled, implies SACK enabled
959  */
960 static inline int tcp_is_sack(const struct tcp_sock *tp)
961 {
962         return tp->rx_opt.sack_ok;
963 }
964 
965 static inline bool tcp_is_reno(const struct tcp_sock *tp)
966 {
967         return !tcp_is_sack(tp);
968 }
969 
970 static inline bool tcp_is_fack(const struct tcp_sock *tp)
971 {
972         return tp->rx_opt.sack_ok & TCP_FACK_ENABLED;
973 }
974 
975 static inline void tcp_enable_fack(struct tcp_sock *tp)
976 {
977         tp->rx_opt.sack_ok |= TCP_FACK_ENABLED;
978 }
979 
980 /* TCP early-retransmit (ER) is similar to but more conservative than
981  * the thin-dupack feature.  Enable ER only if thin-dupack is disabled.
982  */
983 static inline void tcp_enable_early_retrans(struct tcp_sock *tp)
984 {
985         struct net *net = sock_net((struct sock *)tp);
986 
987         tp->do_early_retrans = sysctl_tcp_early_retrans &&
988                 sysctl_tcp_early_retrans < 4 && !sysctl_tcp_thin_dupack &&
989                 net->ipv4.sysctl_tcp_reordering == 3;
990 }
991 
992 static inline void tcp_disable_early_retrans(struct tcp_sock *tp)
993 {
994         tp->do_early_retrans = 0;
995 }
996 
997 static inline unsigned int tcp_left_out(const struct tcp_sock *tp)
998 {
999         return tp->sacked_out + tp->lost_out;
1000 }
1001 
1002 /* This determines how many packets are "in the network" to the best
1003  * of our knowledge.  In many cases it is conservative, but where
1004  * detailed information is available from the receiver (via SACK
1005  * blocks etc.) we can make more aggressive calculations.
1006  *
1007  * Use this for decisions involving congestion control, use just
1008  * tp->packets_out to determine if the send queue is empty or not.
1009  *
1010  * Read this equation as:
1011  *
1012  *      "Packets sent once on transmission queue" MINUS
1013  *      "Packets left network, but not honestly ACKed yet" PLUS
1014  *      "Packets fast retransmitted"
1015  */
1016 static inline unsigned int tcp_packets_in_flight(const struct tcp_sock *tp)
1017 {
1018         return tp->packets_out - tcp_left_out(tp) + tp->retrans_out;
1019 }
1020 
1021 #define TCP_INFINITE_SSTHRESH   0x7fffffff
1022 
1023 static inline bool tcp_in_slow_start(const struct tcp_sock *tp)
1024 {
1025         return tp->snd_cwnd < tp->snd_ssthresh;
1026 }
1027 
1028 static inline bool tcp_in_initial_slowstart(const struct tcp_sock *tp)
1029 {
1030         return tp->snd_ssthresh >= TCP_INFINITE_SSTHRESH;
1031 }
1032 
1033 static inline bool tcp_in_cwnd_reduction(const struct sock *sk)
1034 {
1035         return (TCPF_CA_CWR | TCPF_CA_Recovery) &
1036                (1 << inet_csk(sk)->icsk_ca_state);
1037 }
1038 
1039 /* If cwnd > ssthresh, we may raise ssthresh to be half-way to cwnd.
1040  * The exception is cwnd reduction phase, when cwnd is decreasing towards
1041  * ssthresh.
1042  */
1043 static inline __u32 tcp_current_ssthresh(const struct sock *sk)
1044 {
1045         const struct tcp_sock *tp = tcp_sk(sk);
1046 
1047         if (tcp_in_cwnd_reduction(sk))
1048                 return tp->snd_ssthresh;
1049         else
1050                 return max(tp->snd_ssthresh,
1051                            ((tp->snd_cwnd >> 1) +
1052                             (tp->snd_cwnd >> 2)));
1053 }
1054 
1055 /* Use define here intentionally to get WARN_ON location shown at the caller */
1056 #define tcp_verify_left_out(tp) WARN_ON(tcp_left_out(tp) > tp->packets_out)
1057 
1058 void tcp_enter_cwr(struct sock *sk);
1059 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst);
1060 
1061 /* The maximum number of MSS of available cwnd for which TSO defers
1062  * sending if not using sysctl_tcp_tso_win_divisor.
1063  */
1064 static inline __u32 tcp_max_tso_deferred_mss(const struct tcp_sock *tp)
1065 {
1066         return 3;
1067 }
1068 
1069 /* Returns end sequence number of the receiver's advertised window */
1070 static inline u32 tcp_wnd_end(const struct tcp_sock *tp)
1071 {
1072         return tp->snd_una + tp->snd_wnd;
1073 }
1074 
1075 /* We follow the spirit of RFC2861 to validate cwnd but implement a more
1076  * flexible approach. The RFC suggests cwnd should not be raised unless
1077  * it was fully used previously. And that's exactly what we do in
1078  * congestion avoidance mode. But in slow start we allow cwnd to grow
1079  * as long as the application has used half the cwnd.
1080  * Example :
1081  *    cwnd is 10 (IW10), but application sends 9 frames.
1082  *    We allow cwnd to reach 18 when all frames are ACKed.
1083  * This check is safe because it's as aggressive as slow start which already
1084  * risks 100% overshoot. The advantage is that we discourage application to
1085  * either send more filler packets or data to artificially blow up the cwnd
1086  * usage, and allow application-limited process to probe bw more aggressively.
1087  */
1088 static inline bool tcp_is_cwnd_limited(const struct sock *sk)
1089 {
1090         const struct tcp_sock *tp = tcp_sk(sk);
1091 
1092         /* If in slow start, ensure cwnd grows to twice what was ACKed. */
1093         if (tcp_in_slow_start(tp))
1094                 return tp->snd_cwnd < 2 * tp->max_packets_out;
1095 
1096         return tp->is_cwnd_limited;
1097 }
1098 
1099 /* Something is really bad, we could not queue an additional packet,
1100  * because qdisc is full or receiver sent a 0 window.
1101  * We do not want to add fuel to the fire, or abort too early,
1102  * so make sure the timer we arm now is at least 200ms in the future,
1103  * regardless of current icsk_rto value (as it could be ~2ms)
1104  */
1105 static inline unsigned long tcp_probe0_base(const struct sock *sk)
1106 {
1107         return max_t(unsigned long, inet_csk(sk)->icsk_rto, TCP_RTO_MIN);
1108 }
1109 
1110 /* Variant of inet_csk_rto_backoff() used for zero window probes */
1111 static inline unsigned long tcp_probe0_when(const struct sock *sk,
1112                                             unsigned long max_when)
1113 {
1114         u64 when = (u64)tcp_probe0_base(sk) << inet_csk(sk)->icsk_backoff;
1115 
1116         return (unsigned long)min_t(u64, when, max_when);
1117 }
1118 
1119 static inline void tcp_check_probe_timer(struct sock *sk)
1120 {
1121         if (!tcp_sk(sk)->packets_out && !inet_csk(sk)->icsk_pending)
1122                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
1123                                           tcp_probe0_base(sk), TCP_RTO_MAX);
1124 }
1125 
1126 static inline void tcp_init_wl(struct tcp_sock *tp, u32 seq)
1127 {
1128         tp->snd_wl1 = seq;
1129 }
1130 
1131 static inline void tcp_update_wl(struct tcp_sock *tp, u32 seq)
1132 {
1133         tp->snd_wl1 = seq;
1134 }
1135 
1136 /*
1137  * Calculate(/check) TCP checksum
1138  */
1139 static inline __sum16 tcp_v4_check(int len, __be32 saddr,
1140                                    __be32 daddr, __wsum base)
1141 {
1142         return csum_tcpudp_magic(saddr,daddr,len,IPPROTO_TCP,base);
1143 }
1144 
1145 static inline __sum16 __tcp_checksum_complete(struct sk_buff *skb)
1146 {
1147         return __skb_checksum_complete(skb);
1148 }
1149 
1150 static inline bool tcp_checksum_complete(struct sk_buff *skb)
1151 {
1152         return !skb_csum_unnecessary(skb) &&
1153                 __tcp_checksum_complete(skb);
1154 }
1155 
1156 /* Prequeue for VJ style copy to user, combined with checksumming. */
1157 
1158 static inline void tcp_prequeue_init(struct tcp_sock *tp)
1159 {
1160         tp->ucopy.task = NULL;
1161         tp->ucopy.len = 0;
1162         tp->ucopy.memory = 0;
1163         skb_queue_head_init(&tp->ucopy.prequeue);
1164 }
1165 
1166 bool tcp_prequeue(struct sock *sk, struct sk_buff *skb);
1167 
1168 #undef STATE_TRACE
1169 
1170 #ifdef STATE_TRACE
1171 static const char *statename[]={
1172         "Unused","Established","Syn Sent","Syn Recv",
1173         "Fin Wait 1","Fin Wait 2","Time Wait", "Close",
1174         "Close Wait","Last ACK","Listen","Closing"
1175 };
1176 #endif
1177 void tcp_set_state(struct sock *sk, int state);
1178 
1179 void tcp_done(struct sock *sk);
1180 
1181 int tcp_abort(struct sock *sk, int err);
1182 
1183 static inline void tcp_sack_reset(struct tcp_options_received *rx_opt)
1184 {
1185         rx_opt->dsack = 0;
1186         rx_opt->num_sacks = 0;
1187 }
1188 
1189 u32 tcp_default_init_rwnd(u32 mss);
1190 void tcp_cwnd_restart(struct sock *sk, s32 delta);
1191 
1192 static inline void tcp_slow_start_after_idle_check(struct sock *sk)
1193 {
1194         struct tcp_sock *tp = tcp_sk(sk);
1195         s32 delta;
1196 
1197         if (!sysctl_tcp_slow_start_after_idle || tp->packets_out)
1198                 return;
1199         delta = tcp_time_stamp - tp->lsndtime;
1200         if (delta > inet_csk(sk)->icsk_rto)
1201                 tcp_cwnd_restart(sk, delta);
1202 }
1203 
1204 /* Determine a window scaling and initial window to offer. */
1205 void tcp_select_initial_window(int __space, __u32 mss, __u32 *rcv_wnd,
1206                                __u32 *window_clamp, int wscale_ok,
1207                                __u8 *rcv_wscale, __u32 init_rcv_wnd);
1208 
1209 static inline int tcp_win_from_space(int space)
1210 {
1211         return sysctl_tcp_adv_win_scale<=0 ?
1212                 (space>>(-sysctl_tcp_adv_win_scale)) :
1213                 space - (space>>sysctl_tcp_adv_win_scale);
1214 }
1215 
1216 /* Note: caller must be prepared to deal with negative returns */
1217 static inline int tcp_space(const struct sock *sk)
1218 {
1219         return tcp_win_from_space(sk->sk_rcvbuf -
1220                                   atomic_read(&sk->sk_rmem_alloc));
1221 }
1222 
1223 static inline int tcp_full_space(const struct sock *sk)
1224 {
1225         return tcp_win_from_space(sk->sk_rcvbuf);
1226 }
1227 
1228 extern void tcp_openreq_init_rwin(struct request_sock *req,
1229                                   const struct sock *sk_listener,
1230                                   const struct dst_entry *dst);
1231 
1232 void tcp_enter_memory_pressure(struct sock *sk);
1233 
1234 static inline int keepalive_intvl_when(const struct tcp_sock *tp)
1235 {
1236         struct net *net = sock_net((struct sock *)tp);
1237 
1238         return tp->keepalive_intvl ? : net->ipv4.sysctl_tcp_keepalive_intvl;
1239 }
1240 
1241 static inline int keepalive_time_when(const struct tcp_sock *tp)
1242 {
1243         struct net *net = sock_net((struct sock *)tp);
1244 
1245         return tp->keepalive_time ? : net->ipv4.sysctl_tcp_keepalive_time;
1246 }
1247 
1248 static inline int keepalive_probes(const struct tcp_sock *tp)
1249 {
1250         struct net *net = sock_net((struct sock *)tp);
1251 
1252         return tp->keepalive_probes ? : net->ipv4.sysctl_tcp_keepalive_probes;
1253 }
1254 
1255 static inline u32 keepalive_time_elapsed(const struct tcp_sock *tp)
1256 {
1257         const struct inet_connection_sock *icsk = &tp->inet_conn;
1258 
1259         return min_t(u32, tcp_time_stamp - icsk->icsk_ack.lrcvtime,
1260                           tcp_time_stamp - tp->rcv_tstamp);
1261 }
1262 
1263 static inline int tcp_fin_time(const struct sock *sk)
1264 {
1265         int fin_timeout = tcp_sk(sk)->linger2 ? : sock_net(sk)->ipv4.sysctl_tcp_fin_timeout;
1266         const int rto = inet_csk(sk)->icsk_rto;
1267 
1268         if (fin_timeout < (rto << 2) - (rto >> 1))
1269                 fin_timeout = (rto << 2) - (rto >> 1);
1270 
1271         return fin_timeout;
1272 }
1273 
1274 static inline bool tcp_paws_check(const struct tcp_options_received *rx_opt,
1275                                   int paws_win)
1276 {
1277         if ((s32)(rx_opt->ts_recent - rx_opt->rcv_tsval) <= paws_win)
1278                 return true;
1279         if (unlikely(get_seconds() >= rx_opt->ts_recent_stamp + TCP_PAWS_24DAYS))
1280                 return true;
1281         /*
1282          * Some OSes send SYN and SYNACK messages with tsval=0 tsecr=0,
1283          * then following tcp messages have valid values. Ignore 0 value,
1284          * or else 'negative' tsval might forbid us to accept their packets.
1285          */
1286         if (!rx_opt->ts_recent)
1287                 return true;
1288         return false;
1289 }
1290 
1291 static inline bool tcp_paws_reject(const struct tcp_options_received *rx_opt,
1292                                    int rst)
1293 {
1294         if (tcp_paws_check(rx_opt, 0))
1295                 return false;
1296 
1297         /* RST segments are not recommended to carry timestamp,
1298            and, if they do, it is recommended to ignore PAWS because
1299            "their cleanup function should take precedence over timestamps."
1300            Certainly, it is mistake. It is necessary to understand the reasons
1301            of this constraint to relax it: if peer reboots, clock may go
1302            out-of-sync and half-open connections will not be reset.
1303            Actually, the problem would be not existing if all
1304            the implementations followed draft about maintaining clock
1305            via reboots. Linux-2.2 DOES NOT!
1306 
1307            However, we can relax time bounds for RST segments to MSL.
1308          */
1309         if (rst && get_seconds() >= rx_opt->ts_recent_stamp + TCP_PAWS_MSL)
1310                 return false;
1311         return true;
1312 }
1313 
1314 bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
1315                           int mib_idx, u32 *last_oow_ack_time);
1316 
1317 static inline void tcp_mib_init(struct net *net)
1318 {
1319         /* See RFC 2012 */
1320         TCP_ADD_STATS(net, TCP_MIB_RTOALGORITHM, 1);
1321         TCP_ADD_STATS(net, TCP_MIB_RTOMIN, TCP_RTO_MIN*1000/HZ);
1322         TCP_ADD_STATS(net, TCP_MIB_RTOMAX, TCP_RTO_MAX*1000/HZ);
1323         TCP_ADD_STATS(net, TCP_MIB_MAXCONN, -1);
1324 }
1325 
1326 /* from STCP */
1327 static inline void tcp_clear_retrans_hints_partial(struct tcp_sock *tp)
1328 {
1329         tp->lost_skb_hint = NULL;
1330 }
1331 
1332 static inline void tcp_clear_all_retrans_hints(struct tcp_sock *tp)
1333 {
1334         tcp_clear_retrans_hints_partial(tp);
1335         tp->retransmit_skb_hint = NULL;
1336 }
1337 
1338 union tcp_md5_addr {
1339         struct in_addr  a4;
1340 #if IS_ENABLED(CONFIG_IPV6)
1341         struct in6_addr a6;
1342 #endif
1343 };
1344 
1345 /* - key database */
1346 struct tcp_md5sig_key {
1347         struct hlist_node       node;
1348         u8                      keylen;
1349         u8                      family; /* AF_INET or AF_INET6 */
1350         union tcp_md5_addr      addr;
1351         u8                      key[TCP_MD5SIG_MAXKEYLEN];
1352         struct rcu_head         rcu;
1353 };
1354 
1355 /* - sock block */
1356 struct tcp_md5sig_info {
1357         struct hlist_head       head;
1358         struct rcu_head         rcu;
1359 };
1360 
1361 /* - pseudo header */
1362 struct tcp4_pseudohdr {
1363         __be32          saddr;
1364         __be32          daddr;
1365         __u8            pad;
1366         __u8            protocol;
1367         __be16          len;
1368 };
1369 
1370 struct tcp6_pseudohdr {
1371         struct in6_addr saddr;
1372         struct in6_addr daddr;
1373         __be32          len;
1374         __be32          protocol;       /* including padding */
1375 };
1376 
1377 union tcp_md5sum_block {
1378         struct tcp4_pseudohdr ip4;
1379 #if IS_ENABLED(CONFIG_IPV6)
1380         struct tcp6_pseudohdr ip6;
1381 #endif
1382 };
1383 
1384 /* - pool: digest algorithm, hash description and scratch buffer */
1385 struct tcp_md5sig_pool {
1386         struct ahash_request    *md5_req;
1387         void                    *scratch;
1388 };
1389 
1390 /* - functions */
1391 int tcp_v4_md5_hash_skb(char *md5_hash, const struct tcp_md5sig_key *key,
1392                         const struct sock *sk, const struct sk_buff *skb);
1393 int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
1394                    int family, const u8 *newkey, u8 newkeylen, gfp_t gfp);
1395 int tcp_md5_do_del(struct sock *sk, const union tcp_md5_addr *addr,
1396                    int family);
1397 struct tcp_md5sig_key *tcp_v4_md5_lookup(const struct sock *sk,
1398                                          const struct sock *addr_sk);
1399 
1400 #ifdef CONFIG_TCP_MD5SIG
1401 struct tcp_md5sig_key *tcp_md5_do_lookup(const struct sock *sk,
1402                                          const union tcp_md5_addr *addr,
1403                                          int family);
1404 #define tcp_twsk_md5_key(twsk)  ((twsk)->tw_md5_key)
1405 #else
1406 static inline struct tcp_md5sig_key *tcp_md5_do_lookup(const struct sock *sk,
1407                                          const union tcp_md5_addr *addr,
1408                                          int family)
1409 {
1410         return NULL;
1411 }
1412 #define tcp_twsk_md5_key(twsk)  NULL
1413 #endif
1414 
1415 bool tcp_alloc_md5sig_pool(void);
1416 
1417 struct tcp_md5sig_pool *tcp_get_md5sig_pool(void);
1418 static inline void tcp_put_md5sig_pool(void)
1419 {
1420         local_bh_enable();
1421 }
1422 
1423 int tcp_md5_hash_skb_data(struct tcp_md5sig_pool *, const struct sk_buff *,
1424                           unsigned int header_len);
1425 int tcp_md5_hash_key(struct tcp_md5sig_pool *hp,
1426                      const struct tcp_md5sig_key *key);
1427 
1428 /* From tcp_fastopen.c */
1429 void tcp_fastopen_cache_get(struct sock *sk, u16 *mss,
1430                             struct tcp_fastopen_cookie *cookie, int *syn_loss,
1431                             unsigned long *last_syn_loss);
1432 void tcp_fastopen_cache_set(struct sock *sk, u16 mss,
1433                             struct tcp_fastopen_cookie *cookie, bool syn_lost,
1434                             u16 try_exp);
1435 struct tcp_fastopen_request {
1436         /* Fast Open cookie. Size 0 means a cookie request */
1437         struct tcp_fastopen_cookie      cookie;
1438         struct msghdr                   *data;  /* data in MSG_FASTOPEN */
1439         size_t                          size;
1440         int                             copied; /* queued in tcp_connect() */
1441 };
1442 void tcp_free_fastopen_req(struct tcp_sock *tp);
1443 
1444 extern struct tcp_fastopen_context __rcu *tcp_fastopen_ctx;
1445 int tcp_fastopen_reset_cipher(void *key, unsigned int len);
1446 void tcp_fastopen_add_skb(struct sock *sk, struct sk_buff *skb);
1447 struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
1448                               struct request_sock *req,
1449                               struct tcp_fastopen_cookie *foc,
1450                               struct dst_entry *dst);
1451 void tcp_fastopen_init_key_once(bool publish);
1452 #define TCP_FASTOPEN_KEY_LENGTH 16
1453 
1454 /* Fastopen key context */
1455 struct tcp_fastopen_context {
1456         struct crypto_cipher    *tfm;
1457         __u8                    key[TCP_FASTOPEN_KEY_LENGTH];
1458         struct rcu_head         rcu;
1459 };
1460 
1461 /* write queue abstraction */
1462 static inline void tcp_write_queue_purge(struct sock *sk)
1463 {
1464         struct sk_buff *skb;
1465 
1466         while ((skb = __skb_dequeue(&sk->sk_write_queue)) != NULL)
1467                 sk_wmem_free_skb(sk, skb);
1468         sk_mem_reclaim(sk);
1469         tcp_clear_all_retrans_hints(tcp_sk(sk));
1470 }
1471 
1472 static inline struct sk_buff *tcp_write_queue_head(const struct sock *sk)
1473 {
1474         return skb_peek(&sk->sk_write_queue);
1475 }
1476 
1477 static inline struct sk_buff *tcp_write_queue_tail(const struct sock *sk)
1478 {
1479         return skb_peek_tail(&sk->sk_write_queue);
1480 }
1481 
1482 static inline struct sk_buff *tcp_write_queue_next(const struct sock *sk,
1483                                                    const struct sk_buff *skb)
1484 {
1485         return skb_queue_next(&sk->sk_write_queue, skb);
1486 }
1487 
1488 static inline struct sk_buff *tcp_write_queue_prev(const struct sock *sk,
1489                                                    const struct sk_buff *skb)
1490 {
1491         return skb_queue_prev(&sk->sk_write_queue, skb);
1492 }
1493 
1494 #define tcp_for_write_queue(skb, sk)                                    \
1495         skb_queue_walk(&(sk)->sk_write_queue, skb)
1496 
1497 #define tcp_for_write_queue_from(skb, sk)                               \
1498         skb_queue_walk_from(&(sk)->sk_write_queue, skb)
1499 
1500 #define tcp_for_write_queue_from_safe(skb, tmp, sk)                     \
1501         skb_queue_walk_from_safe(&(sk)->sk_write_queue, skb, tmp)
1502 
1503 static inline struct sk_buff *tcp_send_head(const struct sock *sk)
1504 {
1505         return sk->sk_send_head;
1506 }
1507 
1508 static inline bool tcp_skb_is_last(const struct sock *sk,
1509                                    const struct sk_buff *skb)
1510 {
1511         return skb_queue_is_last(&sk->sk_write_queue, skb);
1512 }
1513 
1514 static inline void tcp_advance_send_head(struct sock *sk, const struct sk_buff *skb)
1515 {
1516         if (tcp_skb_is_last(sk, skb))
1517                 sk->sk_send_head = NULL;
1518         else
1519                 sk->sk_send_head = tcp_write_queue_next(sk, skb);
1520 }
1521 
1522 static inline void tcp_check_send_head(struct sock *sk, struct sk_buff *skb_unlinked)
1523 {
1524         if (sk->sk_send_head == skb_unlinked)
1525                 sk->sk_send_head = NULL;
1526         if (tcp_sk(sk)->highest_sack == skb_unlinked)
1527                 tcp_sk(sk)->highest_sack = NULL;
1528 }
1529 
1530 static inline void tcp_init_send_head(struct sock *sk)
1531 {
1532         sk->sk_send_head = NULL;
1533 }
1534 
1535 static inline void __tcp_add_write_queue_tail(struct sock *sk, struct sk_buff *skb)
1536 {
1537         __skb_queue_tail(&sk->sk_write_queue, skb);
1538 }
1539 
1540 static inline void tcp_add_write_queue_tail(struct sock *sk, struct sk_buff *skb)
1541 {
1542         __tcp_add_write_queue_tail(sk, skb);
1543 
1544         /* Queue it, remembering where we must start sending. */
1545         if (sk->sk_send_head == NULL) {
1546                 sk->sk_send_head = skb;
1547 
1548                 if (tcp_sk(sk)->highest_sack == NULL)
1549                         tcp_sk(sk)->highest_sack = skb;
1550         }
1551 }
1552 
1553 static inline void __tcp_add_write_queue_head(struct sock *sk, struct sk_buff *skb)
1554 {
1555         __skb_queue_head(&sk->sk_write_queue, skb);
1556 }
1557 
1558 /* Insert buff after skb on the write queue of sk.  */
1559 static inline void tcp_insert_write_queue_after(struct sk_buff *skb,
1560                                                 struct sk_buff *buff,
1561                                                 struct sock *sk)
1562 {
1563         __skb_queue_after(&sk->sk_write_queue, skb, buff);
1564 }
1565 
1566 /* Insert new before skb on the write queue of sk.  */
1567 static inline void tcp_insert_write_queue_before(struct sk_buff *new,
1568                                                   struct sk_buff *skb,
1569                                                   struct sock *sk)
1570 {
1571         __skb_queue_before(&sk->sk_write_queue, skb, new);
1572 
1573         if (sk->sk_send_head == skb)
1574                 sk->sk_send_head = new;
1575 }
1576 
1577 static inline void tcp_unlink_write_queue(struct sk_buff *skb, struct sock *sk)
1578 {
1579         __skb_unlink(skb, &sk->sk_write_queue);
1580 }
1581 
1582 static inline bool tcp_write_queue_empty(struct sock *sk)
1583 {
1584         return skb_queue_empty(&sk->sk_write_queue);
1585 }
1586 
1587 static inline void tcp_push_pending_frames(struct sock *sk)
1588 {
1589         if (tcp_send_head(sk)) {
1590                 struct tcp_sock *tp = tcp_sk(sk);
1591 
1592                 __tcp_push_pending_frames(sk, tcp_current_mss(sk), tp->nonagle);
1593         }
1594 }
1595 
1596 /* Start sequence of the skb just after the highest skb with SACKed
1597  * bit, valid only if sacked_out > 0 or when the caller has ensured
1598  * validity by itself.
1599  */
1600 static inline u32 tcp_highest_sack_seq(struct tcp_sock *tp)
1601 {
1602         if (!tp->sacked_out)
1603                 return tp->snd_una;
1604 
1605         if (tp->highest_sack == NULL)
1606                 return tp->snd_nxt;
1607 
1608         return TCP_SKB_CB(tp->highest_sack)->seq;
1609 }
1610 
1611 static inline void tcp_advance_highest_sack(struct sock *sk, struct sk_buff *skb)
1612 {
1613         tcp_sk(sk)->highest_sack = tcp_skb_is_last(sk, skb) ? NULL :
1614                                                 tcp_write_queue_next(sk, skb);
1615 }
1616 
1617 static inline struct sk_buff *tcp_highest_sack(struct sock *sk)
1618 {
1619         return tcp_sk(sk)->highest_sack;
1620 }
1621 
1622 static inline void tcp_highest_sack_reset(struct sock *sk)
1623 {
1624         tcp_sk(sk)->highest_sack = tcp_write_queue_head(sk);
1625 }
1626 
1627 /* Called when old skb is about to be deleted (to be combined with new skb) */
1628 static inline void tcp_highest_sack_combine(struct sock *sk,
1629                                             struct sk_buff *old,
1630                                             struct sk_buff *new)
1631 {
1632         if (tcp_sk(sk)->sacked_out && (old == tcp_sk(sk)->highest_sack))
1633                 tcp_sk(sk)->highest_sack = new;
1634 }
1635 
1636 /* This helper checks if socket has IP_TRANSPARENT set */
1637 static inline bool inet_sk_transparent(const struct sock *sk)
1638 {
1639         switch (sk->sk_state) {
1640         case TCP_TIME_WAIT:
1641                 return inet_twsk(sk)->tw_transparent;
1642         case TCP_NEW_SYN_RECV:
1643                 return inet_rsk(inet_reqsk(sk))->no_srccheck;
1644         }
1645         return inet_sk(sk)->transparent;
1646 }
1647 
1648 /* Determines whether this is a thin stream (which may suffer from
1649  * increased latency). Used to trigger latency-reducing mechanisms.
1650  */
1651 static inline bool tcp_stream_is_thin(struct tcp_sock *tp)
1652 {
1653         return tp->packets_out < 4 && !tcp_in_initial_slowstart(tp);
1654 }
1655 
1656 /* /proc */
1657 enum tcp_seq_states {
1658         TCP_SEQ_STATE_LISTENING,
1659         TCP_SEQ_STATE_ESTABLISHED,
1660 };
1661 
1662 int tcp_seq_open(struct inode *inode, struct file *file);
1663 
1664 struct tcp_seq_afinfo {
1665         char                            *name;
1666         sa_family_t                     family;
1667         const struct file_operations    *seq_fops;
1668         struct seq_operations           seq_ops;
1669 };
1670 
1671 struct tcp_iter_state {
1672         struct seq_net_private  p;
1673         sa_family_t             family;
1674         enum tcp_seq_states     state;
1675         struct sock             *syn_wait_sk;
1676         int                     bucket, offset, sbucket, num;
1677         loff_t                  last_pos;
1678 };
1679 
1680 int tcp_proc_register(struct net *net, struct tcp_seq_afinfo *afinfo);
1681 void tcp_proc_unregister(struct net *net, struct tcp_seq_afinfo *afinfo);
1682 
1683 extern struct request_sock_ops tcp_request_sock_ops;
1684 extern struct request_sock_ops tcp6_request_sock_ops;
1685 
1686 void tcp_v4_destroy_sock(struct sock *sk);
1687 
1688 struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
1689                                 netdev_features_t features);
1690 struct sk_buff **tcp_gro_receive(struct sk_buff **head, struct sk_buff *skb);
1691 int tcp_gro_complete(struct sk_buff *skb);
1692 
1693 void __tcp_v4_send_check(struct sk_buff *skb, __be32 saddr, __be32 daddr);
1694 
1695 static inline u32 tcp_notsent_lowat(const struct tcp_sock *tp)
1696 {
1697         struct net *net = sock_net((struct sock *)tp);
1698         return tp->notsent_lowat ?: net->ipv4.sysctl_tcp_notsent_lowat;
1699 }
1700 
1701 static inline bool tcp_stream_memory_free(const struct sock *sk)
1702 {
1703         const struct tcp_sock *tp = tcp_sk(sk);
1704         u32 notsent_bytes = tp->write_seq - tp->snd_nxt;
1705 
1706         return notsent_bytes < tcp_notsent_lowat(tp);
1707 }
1708 
1709 #ifdef CONFIG_PROC_FS
1710 int tcp4_proc_init(void);
1711 void tcp4_proc_exit(void);
1712 #endif
1713 
1714 int tcp_rtx_synack(const struct sock *sk, struct request_sock *req);
1715 int tcp_conn_request(struct request_sock_ops *rsk_ops,
1716                      const struct tcp_request_sock_ops *af_ops,
1717                      struct sock *sk, struct sk_buff *skb);
1718 
1719 /* TCP af-specific functions */
1720 struct tcp_sock_af_ops {
1721 #ifdef CONFIG_TCP_MD5SIG
1722         struct tcp_md5sig_key   *(*md5_lookup) (const struct sock *sk,
1723                                                 const struct sock *addr_sk);
1724         int             (*calc_md5_hash)(char *location,
1725                                          const struct tcp_md5sig_key *md5,
1726                                          const struct sock *sk,
1727                                          const struct sk_buff *skb);
1728         int             (*md5_parse)(struct sock *sk,
1729                                      char __user *optval,
1730                                      int optlen);
1731 #endif
1732 };
1733 
1734 struct tcp_request_sock_ops {
1735         u16 mss_clamp;
1736 #ifdef CONFIG_TCP_MD5SIG
1737         struct tcp_md5sig_key *(*req_md5_lookup)(const struct sock *sk,
1738                                                  const struct sock *addr_sk);
1739         int             (*calc_md5_hash) (char *location,
1740                                           const struct tcp_md5sig_key *md5,
1741                                           const struct sock *sk,
1742                                           const struct sk_buff *skb);
1743 #endif
1744         void (*init_req)(struct request_sock *req,
1745                          const struct sock *sk_listener,
1746                          struct sk_buff *skb);
1747 #ifdef CONFIG_SYN_COOKIES
1748         __u32 (*cookie_init_seq)(const struct sk_buff *skb,
1749                                  __u16 *mss);
1750 #endif
1751         struct dst_entry *(*route_req)(const struct sock *sk, struct flowi *fl,
1752                                        const struct request_sock *req,
1753                                        bool *strict);
1754         __u32 (*init_seq)(const struct sk_buff *skb);
1755         int (*send_synack)(const struct sock *sk, struct dst_entry *dst,
1756                            struct flowi *fl, struct request_sock *req,
1757                            struct tcp_fastopen_cookie *foc,
1758                            enum tcp_synack_type synack_type);
1759 };
1760 
1761 #ifdef CONFIG_SYN_COOKIES
1762 static inline __u32 cookie_init_sequence(const struct tcp_request_sock_ops *ops,
1763                                          const struct sock *sk, struct sk_buff *skb,
1764                                          __u16 *mss)
1765 {
1766         tcp_synq_overflow(sk);
1767         __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
1768         return ops->cookie_init_seq(skb, mss);
1769 }
1770 #else
1771 static inline __u32 cookie_init_sequence(const struct tcp_request_sock_ops *ops,
1772                                          const struct sock *sk, struct sk_buff *skb,
1773                                          __u16 *mss)
1774 {
1775         return 0;
1776 }
1777 #endif
1778 
1779 int tcpv4_offload_init(void);
1780 
1781 void tcp_v4_init(void);
1782 void tcp_init(void);
1783 
1784 /* tcp_recovery.c */
1785 
1786 /* Flags to enable various loss recovery features. See below */
1787 extern int sysctl_tcp_recovery;
1788 
1789 /* Use TCP RACK to detect (some) tail and retransmit losses */
1790 #define TCP_RACK_LOST_RETRANS  0x1
1791 
1792 extern int tcp_rack_mark_lost(struct sock *sk);
1793 
1794 extern void tcp_rack_advance(struct tcp_sock *tp,
1795                              const struct skb_mstamp *xmit_time, u8 sacked);
1796 
1797 /*
1798  * Save and compile IPv4 options, return a pointer to it
1799  */
1800 static inline struct ip_options_rcu *tcp_v4_save_options(struct sk_buff *skb)
1801 {
1802         const struct ip_options *opt = &TCP_SKB_CB(skb)->header.h4.opt;
1803         struct ip_options_rcu *dopt = NULL;
1804 
1805         if (opt->optlen) {
1806                 int opt_size = sizeof(*dopt) + opt->optlen;
1807 
1808                 dopt = kmalloc(opt_size, GFP_ATOMIC);
1809                 if (dopt && __ip_options_echo(&dopt->opt, skb, opt)) {
1810                         kfree(dopt);
1811                         dopt = NULL;
1812                 }
1813         }
1814         return dopt;
1815 }
1816 
1817 /* locally generated TCP pure ACKs have skb->truesize == 2
1818  * (check tcp_send_ack() in net/ipv4/tcp_output.c )
1819  * This is much faster than dissecting the packet to find out.
1820  * (Think of GRE encapsulations, IPv4, IPv6, ...)
1821  */
1822 static inline bool skb_is_tcp_pure_ack(const struct sk_buff *skb)
1823 {
1824         return skb->truesize == 2;
1825 }
1826 
1827 static inline void skb_set_tcp_pure_ack(struct sk_buff *skb)
1828 {
1829         skb->truesize = 2;
1830 }
1831 
1832 static inline int tcp_inq(struct sock *sk)
1833 {
1834         struct tcp_sock *tp = tcp_sk(sk);
1835         int answ;
1836 
1837         if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
1838                 answ = 0;
1839         } else if (sock_flag(sk, SOCK_URGINLINE) ||
1840                    !tp->urg_data ||
1841                    before(tp->urg_seq, tp->copied_seq) ||
1842                    !before(tp->urg_seq, tp->rcv_nxt)) {
1843 
1844                 answ = tp->rcv_nxt - tp->copied_seq;
1845 
1846                 /* Subtract 1, if FIN was received */
1847                 if (answ && sock_flag(sk, SOCK_DONE))
1848                         answ--;
1849         } else {
1850                 answ = tp->urg_seq - tp->copied_seq;
1851         }
1852 
1853         return answ;
1854 }
1855 
1856 static inline void tcp_segs_in(struct tcp_sock *tp, const struct sk_buff *skb)
1857 {
1858         u16 segs_in;
1859 
1860         segs_in = max_t(u16, 1, skb_shinfo(skb)->gso_segs);
1861         tp->segs_in += segs_in;
1862         if (skb->len > tcp_hdrlen(skb))
1863                 tp->data_segs_in += segs_in;
1864 }
1865 
1866 /*
1867  * TCP listen path runs lockless.
1868  * We forced "struct sock" to be const qualified to make sure
1869  * we don't modify one of its field by mistake.
1870  * Here, we increment sk_drops which is an atomic_t, so we can safely
1871  * make sock writable again.
1872  */
1873 static inline void tcp_listendrop(const struct sock *sk)
1874 {
1875         atomic_inc(&((struct sock *)sk)->sk_drops);
1876         __NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENDROPS);
1877 }
1878 
1879 #endif  /* _TCP_H */
1880 

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