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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_BH(net, field)    SNMP_INC_STATS_BH((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_USER(net, field, val) SNMP_ADD_STATS_USER((net)->mib.tcp_statistics, field, val)
338 #define TCP_ADD_STATS(net, field, val)  SNMP_ADD_STATS((net)->mib.tcp_statistics, field, val)
339 
340 void tcp_tasklet_init(void);
341 
342 void tcp_v4_err(struct sk_buff *skb, u32);
343 
344 void tcp_shutdown(struct sock *sk, int how);
345 
346 void tcp_v4_early_demux(struct sk_buff *skb);
347 int tcp_v4_rcv(struct sk_buff *skb);
348 
349 int tcp_v4_tw_remember_stamp(struct inet_timewait_sock *tw);
350 int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size);
351 int tcp_sendpage(struct sock *sk, struct page *page, int offset, size_t size,
352                  int flags);
353 void tcp_release_cb(struct sock *sk);
354 void tcp_wfree(struct sk_buff *skb);
355 void tcp_write_timer_handler(struct sock *sk);
356 void tcp_delack_timer_handler(struct sock *sk);
357 int tcp_ioctl(struct sock *sk, int cmd, unsigned long arg);
358 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb);
359 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
360                          const struct tcphdr *th, unsigned int len);
361 void tcp_rcv_space_adjust(struct sock *sk);
362 int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp);
363 void tcp_twsk_destructor(struct sock *sk);
364 ssize_t tcp_splice_read(struct socket *sk, loff_t *ppos,
365                         struct pipe_inode_info *pipe, size_t len,
366                         unsigned int flags);
367 
368 static inline void tcp_dec_quickack_mode(struct sock *sk,
369                                          const unsigned int pkts)
370 {
371         struct inet_connection_sock *icsk = inet_csk(sk);
372 
373         if (icsk->icsk_ack.quick) {
374                 if (pkts >= icsk->icsk_ack.quick) {
375                         icsk->icsk_ack.quick = 0;
376                         /* Leaving quickack mode we deflate ATO. */
377                         icsk->icsk_ack.ato   = TCP_ATO_MIN;
378                 } else
379                         icsk->icsk_ack.quick -= pkts;
380         }
381 }
382 
383 #define TCP_ECN_OK              1
384 #define TCP_ECN_QUEUE_CWR       2
385 #define TCP_ECN_DEMAND_CWR      4
386 #define TCP_ECN_SEEN            8
387 
388 enum tcp_tw_status {
389         TCP_TW_SUCCESS = 0,
390         TCP_TW_RST = 1,
391         TCP_TW_ACK = 2,
392         TCP_TW_SYN = 3
393 };
394 
395 
396 enum tcp_tw_status tcp_timewait_state_process(struct inet_timewait_sock *tw,
397                                               struct sk_buff *skb,
398                                               const struct tcphdr *th);
399 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
400                            struct request_sock *req, bool fastopen);
401 int tcp_child_process(struct sock *parent, struct sock *child,
402                       struct sk_buff *skb);
403 void tcp_enter_loss(struct sock *sk);
404 void tcp_clear_retrans(struct tcp_sock *tp);
405 void tcp_update_metrics(struct sock *sk);
406 void tcp_init_metrics(struct sock *sk);
407 void tcp_metrics_init(void);
408 bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst,
409                         bool paws_check, bool timestamps);
410 bool tcp_remember_stamp(struct sock *sk);
411 bool tcp_tw_remember_stamp(struct inet_timewait_sock *tw);
412 void tcp_fetch_timewait_stamp(struct sock *sk, struct dst_entry *dst);
413 void tcp_disable_fack(struct tcp_sock *tp);
414 void tcp_close(struct sock *sk, long timeout);
415 void tcp_init_sock(struct sock *sk);
416 unsigned int tcp_poll(struct file *file, struct socket *sock,
417                       struct poll_table_struct *wait);
418 int tcp_getsockopt(struct sock *sk, int level, int optname,
419                    char __user *optval, int __user *optlen);
420 int tcp_setsockopt(struct sock *sk, int level, int optname,
421                    char __user *optval, unsigned int optlen);
422 int compat_tcp_getsockopt(struct sock *sk, int level, int optname,
423                           char __user *optval, int __user *optlen);
424 int compat_tcp_setsockopt(struct sock *sk, int level, int optname,
425                           char __user *optval, unsigned int optlen);
426 void tcp_set_keepalive(struct sock *sk, int val);
427 void tcp_syn_ack_timeout(const struct request_sock *req);
428 int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
429                 int flags, int *addr_len);
430 void tcp_parse_options(const struct sk_buff *skb,
431                        struct tcp_options_received *opt_rx,
432                        int estab, struct tcp_fastopen_cookie *foc);
433 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th);
434 
435 /*
436  *      TCP v4 functions exported for the inet6 API
437  */
438 
439 void tcp_v4_send_check(struct sock *sk, struct sk_buff *skb);
440 void tcp_v4_mtu_reduced(struct sock *sk);
441 void tcp_req_err(struct sock *sk, u32 seq, bool abort);
442 int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb);
443 struct sock *tcp_create_openreq_child(const struct sock *sk,
444                                       struct request_sock *req,
445                                       struct sk_buff *skb);
446 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst);
447 struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
448                                   struct request_sock *req,
449                                   struct dst_entry *dst,
450                                   struct request_sock *req_unhash,
451                                   bool *own_req);
452 int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb);
453 int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
454 int tcp_connect(struct sock *sk);
455 struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
456                                 struct request_sock *req,
457                                 struct tcp_fastopen_cookie *foc,
458                                 bool attach_req);
459 int tcp_disconnect(struct sock *sk, int flags);
460 
461 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb);
462 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size);
463 void inet_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb);
464 
465 /* From syncookies.c */
466 struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
467                                  struct request_sock *req,
468                                  struct dst_entry *dst);
469 int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th,
470                       u32 cookie);
471 struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb);
472 #ifdef CONFIG_SYN_COOKIES
473 
474 /* Syncookies use a monotonic timer which increments every 60 seconds.
475  * This counter is used both as a hash input and partially encoded into
476  * the cookie value.  A cookie is only validated further if the delta
477  * between the current counter value and the encoded one is less than this,
478  * i.e. a sent cookie is valid only at most for 2*60 seconds (or less if
479  * the counter advances immediately after a cookie is generated).
480  */
481 #define MAX_SYNCOOKIE_AGE       2
482 #define TCP_SYNCOOKIE_PERIOD    (60 * HZ)
483 #define TCP_SYNCOOKIE_VALID     (MAX_SYNCOOKIE_AGE * TCP_SYNCOOKIE_PERIOD)
484 
485 /* syncookies: remember time of last synqueue overflow
486  * But do not dirty this field too often (once per second is enough)
487  * It is racy as we do not hold a lock, but race is very minor.
488  */
489 static inline void tcp_synq_overflow(const struct sock *sk)
490 {
491         unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
492         unsigned long now = jiffies;
493 
494         if (time_after(now, last_overflow + HZ))
495                 tcp_sk(sk)->rx_opt.ts_recent_stamp = now;
496 }
497 
498 /* syncookies: no recent synqueue overflow on this listening socket? */
499 static inline bool tcp_synq_no_recent_overflow(const struct sock *sk)
500 {
501         unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
502 
503         return time_after(jiffies, last_overflow + TCP_SYNCOOKIE_VALID);
504 }
505 
506 static inline u32 tcp_cookie_time(void)
507 {
508         u64 val = get_jiffies_64();
509 
510         do_div(val, TCP_SYNCOOKIE_PERIOD);
511         return val;
512 }
513 
514 u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,
515                               u16 *mssp);
516 __u32 cookie_v4_init_sequence(const struct sk_buff *skb, __u16 *mss);
517 __u32 cookie_init_timestamp(struct request_sock *req);
518 bool cookie_timestamp_decode(struct tcp_options_received *opt);
519 bool cookie_ecn_ok(const struct tcp_options_received *opt,
520                    const struct net *net, const struct dst_entry *dst);
521 
522 /* From net/ipv6/syncookies.c */
523 int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th,
524                       u32 cookie);
525 struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb);
526 
527 u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
528                               const struct tcphdr *th, u16 *mssp);
529 __u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mss);
530 #endif
531 /* tcp_output.c */
532 
533 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
534                                int nonagle);
535 bool tcp_may_send_now(struct sock *sk);
536 int __tcp_retransmit_skb(struct sock *, struct sk_buff *);
537 int tcp_retransmit_skb(struct sock *, struct sk_buff *);
538 void tcp_retransmit_timer(struct sock *sk);
539 void tcp_xmit_retransmit_queue(struct sock *);
540 void tcp_simple_retransmit(struct sock *);
541 int tcp_trim_head(struct sock *, struct sk_buff *, u32);
542 int tcp_fragment(struct sock *, struct sk_buff *, u32, unsigned int, gfp_t);
543 
544 void tcp_send_probe0(struct sock *);
545 void tcp_send_partial(struct sock *);
546 int tcp_write_wakeup(struct sock *, int mib);
547 void tcp_send_fin(struct sock *sk);
548 void tcp_send_active_reset(struct sock *sk, gfp_t priority);
549 int tcp_send_synack(struct sock *);
550 void tcp_push_one(struct sock *, unsigned int mss_now);
551 void tcp_send_ack(struct sock *sk);
552 void tcp_send_delayed_ack(struct sock *sk);
553 void tcp_send_loss_probe(struct sock *sk);
554 bool tcp_schedule_loss_probe(struct sock *sk);
555 void tcp_skb_collapse_tstamp(struct sk_buff *skb,
556                              const struct sk_buff *next_skb);
557 
558 /* tcp_input.c */
559 void tcp_resume_early_retransmit(struct sock *sk);
560 void tcp_rearm_rto(struct sock *sk);
561 void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req);
562 void tcp_reset(struct sock *sk);
563 void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb);
564 void tcp_fin(struct sock *sk);
565 
566 /* tcp_timer.c */
567 void tcp_init_xmit_timers(struct sock *);
568 static inline void tcp_clear_xmit_timers(struct sock *sk)
569 {
570         inet_csk_clear_xmit_timers(sk);
571 }
572 
573 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu);
574 unsigned int tcp_current_mss(struct sock *sk);
575 
576 /* Bound MSS / TSO packet size with the half of the window */
577 static inline int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
578 {
579         int cutoff;
580 
581         /* When peer uses tiny windows, there is no use in packetizing
582          * to sub-MSS pieces for the sake of SWS or making sure there
583          * are enough packets in the pipe for fast recovery.
584          *
585          * On the other hand, for extremely large MSS devices, handling
586          * smaller than MSS windows in this way does make sense.
587          */
588         if (tp->max_window >= 512)
589                 cutoff = (tp->max_window >> 1);
590         else
591                 cutoff = tp->max_window;
592 
593         if (cutoff && pktsize > cutoff)
594                 return max_t(int, cutoff, 68U - tp->tcp_header_len);
595         else
596                 return pktsize;
597 }
598 
599 /* tcp.c */
600 void tcp_get_info(struct sock *, struct tcp_info *);
601 
602 /* Read 'sendfile()'-style from a TCP socket */
603 typedef int (*sk_read_actor_t)(read_descriptor_t *, struct sk_buff *,
604                                 unsigned int, size_t);
605 int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
606                   sk_read_actor_t recv_actor);
607 
608 void tcp_initialize_rcv_mss(struct sock *sk);
609 
610 int tcp_mtu_to_mss(struct sock *sk, int pmtu);
611 int tcp_mss_to_mtu(struct sock *sk, int mss);
612 void tcp_mtup_init(struct sock *sk);
613 void tcp_init_buffer_space(struct sock *sk);
614 
615 static inline void tcp_bound_rto(const struct sock *sk)
616 {
617         if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
618                 inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
619 }
620 
621 static inline u32 __tcp_set_rto(const struct tcp_sock *tp)
622 {
623         return usecs_to_jiffies((tp->srtt_us >> 3) + tp->rttvar_us);
624 }
625 
626 static inline void __tcp_fast_path_on(struct tcp_sock *tp, u32 snd_wnd)
627 {
628         tp->pred_flags = htonl((tp->tcp_header_len << 26) |
629                                ntohl(TCP_FLAG_ACK) |
630                                snd_wnd);
631 }
632 
633 static inline void tcp_fast_path_on(struct tcp_sock *tp)
634 {
635         __tcp_fast_path_on(tp, tp->snd_wnd >> tp->rx_opt.snd_wscale);
636 }
637 
638 static inline void tcp_fast_path_check(struct sock *sk)
639 {
640         struct tcp_sock *tp = tcp_sk(sk);
641 
642         if (skb_queue_empty(&tp->out_of_order_queue) &&
643             tp->rcv_wnd &&
644             atomic_read(&sk->sk_rmem_alloc) < sk->sk_rcvbuf &&
645             !tp->urg_data)
646                 tcp_fast_path_on(tp);
647 }
648 
649 /* Compute the actual rto_min value */
650 static inline u32 tcp_rto_min(struct sock *sk)
651 {
652         const struct dst_entry *dst = __sk_dst_get(sk);
653         u32 rto_min = TCP_RTO_MIN;
654 
655         if (dst && dst_metric_locked(dst, RTAX_RTO_MIN))
656                 rto_min = dst_metric_rtt(dst, RTAX_RTO_MIN);
657         return rto_min;
658 }
659 
660 static inline u32 tcp_rto_min_us(struct sock *sk)
661 {
662         return jiffies_to_usecs(tcp_rto_min(sk));
663 }
664 
665 static inline bool tcp_ca_dst_locked(const struct dst_entry *dst)
666 {
667         return dst_metric_locked(dst, RTAX_CC_ALGO);
668 }
669 
670 /* Minimum RTT in usec. ~0 means not available. */
671 static inline u32 tcp_min_rtt(const struct tcp_sock *tp)
672 {
673         return tp->rtt_min[0].rtt;
674 }
675 
676 /* Compute the actual receive window we are currently advertising.
677  * Rcv_nxt can be after the window if our peer push more data
678  * than the offered window.
679  */
680 static inline u32 tcp_receive_window(const struct tcp_sock *tp)
681 {
682         s32 win = tp->rcv_wup + tp->rcv_wnd - tp->rcv_nxt;
683 
684         if (win < 0)
685                 win = 0;
686         return (u32) win;
687 }
688 
689 /* Choose a new window, without checks for shrinking, and without
690  * scaling applied to the result.  The caller does these things
691  * if necessary.  This is a "raw" window selection.
692  */
693 u32 __tcp_select_window(struct sock *sk);
694 
695 void tcp_send_window_probe(struct sock *sk);
696 
697 /* TCP timestamps are only 32-bits, this causes a slight
698  * complication on 64-bit systems since we store a snapshot
699  * of jiffies in the buffer control blocks below.  We decided
700  * to use only the low 32-bits of jiffies and hide the ugly
701  * casts with the following macro.
702  */
703 #define tcp_time_stamp          ((__u32)(jiffies))
704 
705 static inline u32 tcp_skb_timestamp(const struct sk_buff *skb)
706 {
707         return skb->skb_mstamp.stamp_jiffies;
708 }
709 
710 
711 #define tcp_flag_byte(th) (((u_int8_t *)th)[13])
712 
713 #define TCPHDR_FIN 0x01
714 #define TCPHDR_SYN 0x02
715 #define TCPHDR_RST 0x04
716 #define TCPHDR_PSH 0x08
717 #define TCPHDR_ACK 0x10
718 #define TCPHDR_URG 0x20
719 #define TCPHDR_ECE 0x40
720 #define TCPHDR_CWR 0x80
721 
722 #define TCPHDR_SYN_ECN  (TCPHDR_SYN | TCPHDR_ECE | TCPHDR_CWR)
723 
724 /* This is what the send packet queuing engine uses to pass
725  * TCP per-packet control information to the transmission code.
726  * We also store the host-order sequence numbers in here too.
727  * This is 44 bytes if IPV6 is enabled.
728  * If this grows please adjust skbuff.h:skbuff->cb[xxx] size appropriately.
729  */
730 struct tcp_skb_cb {
731         __u32           seq;            /* Starting sequence number     */
732         __u32           end_seq;        /* SEQ + FIN + SYN + datalen    */
733         union {
734                 /* Note : tcp_tw_isn is used in input path only
735                  *        (isn chosen by tcp_timewait_state_process())
736                  *
737                  *        tcp_gso_segs/size are used in write queue only,
738                  *        cf tcp_skb_pcount()/tcp_skb_mss()
739                  */
740                 __u32           tcp_tw_isn;
741                 struct {
742                         u16     tcp_gso_segs;
743                         u16     tcp_gso_size;
744                 };
745         };
746         __u8            tcp_flags;      /* TCP header flags. (tcp[13])  */
747 
748         __u8            sacked;         /* State flags for SACK/FACK.   */
749 #define TCPCB_SACKED_ACKED      0x01    /* SKB ACK'd by a SACK block    */
750 #define TCPCB_SACKED_RETRANS    0x02    /* SKB retransmitted            */
751 #define TCPCB_LOST              0x04    /* SKB is lost                  */
752 #define TCPCB_TAGBITS           0x07    /* All tag bits                 */
753 #define TCPCB_REPAIRED          0x10    /* SKB repaired (no skb_mstamp) */
754 #define TCPCB_EVER_RETRANS      0x80    /* Ever retransmitted frame     */
755 #define TCPCB_RETRANS           (TCPCB_SACKED_RETRANS|TCPCB_EVER_RETRANS| \
756                                 TCPCB_REPAIRED)
757 
758         __u8            ip_dsfield;     /* IPv4 tos or IPv6 dsfield     */
759         /* 1 byte hole */
760         __u32           ack_seq;        /* Sequence number ACK'd        */
761         union {
762                 struct inet_skb_parm    h4;
763 #if IS_ENABLED(CONFIG_IPV6)
764                 struct inet6_skb_parm   h6;
765 #endif
766         } header;       /* For incoming frames          */
767 };
768 
769 #define TCP_SKB_CB(__skb)       ((struct tcp_skb_cb *)&((__skb)->cb[0]))
770 
771 
772 #if IS_ENABLED(CONFIG_IPV6)
773 /* This is the variant of inet6_iif() that must be used by TCP,
774  * as TCP moves IP6CB into a different location in skb->cb[]
775  */
776 static inline int tcp_v6_iif(const struct sk_buff *skb)
777 {
778         return TCP_SKB_CB(skb)->header.h6.iif;
779 }
780 #endif
781 
782 /* Due to TSO, an SKB can be composed of multiple actual
783  * packets.  To keep these tracked properly, we use this.
784  */
785 static inline int tcp_skb_pcount(const struct sk_buff *skb)
786 {
787         return TCP_SKB_CB(skb)->tcp_gso_segs;
788 }
789 
790 static inline void tcp_skb_pcount_set(struct sk_buff *skb, int segs)
791 {
792         TCP_SKB_CB(skb)->tcp_gso_segs = segs;
793 }
794 
795 static inline void tcp_skb_pcount_add(struct sk_buff *skb, int segs)
796 {
797         TCP_SKB_CB(skb)->tcp_gso_segs += segs;
798 }
799 
800 /* This is valid iff skb is in write queue and tcp_skb_pcount() > 1. */
801 static inline int tcp_skb_mss(const struct sk_buff *skb)
802 {
803         return TCP_SKB_CB(skb)->tcp_gso_size;
804 }
805 
806 /* Events passed to congestion control interface */
807 enum tcp_ca_event {
808         CA_EVENT_TX_START,      /* first transmit when no packets in flight */
809         CA_EVENT_CWND_RESTART,  /* congestion window restart */
810         CA_EVENT_COMPLETE_CWR,  /* end of congestion recovery */
811         CA_EVENT_LOSS,          /* loss timeout */
812         CA_EVENT_ECN_NO_CE,     /* ECT set, but not CE marked */
813         CA_EVENT_ECN_IS_CE,     /* received CE marked IP packet */
814         CA_EVENT_DELAYED_ACK,   /* Delayed ack is sent */
815         CA_EVENT_NON_DELAYED_ACK,
816 };
817 
818 /* Information about inbound ACK, passed to cong_ops->in_ack_event() */
819 enum tcp_ca_ack_event_flags {
820         CA_ACK_SLOWPATH         = (1 << 0),     /* In slow path processing */
821         CA_ACK_WIN_UPDATE       = (1 << 1),     /* ACK updated window */
822         CA_ACK_ECE              = (1 << 2),     /* ECE bit is set on ack */
823 };
824 
825 /*
826  * Interface for adding new TCP congestion control handlers
827  */
828 #define TCP_CA_NAME_MAX 16
829 #define TCP_CA_MAX      128
830 #define TCP_CA_BUF_MAX  (TCP_CA_NAME_MAX*TCP_CA_MAX)
831 
832 #define TCP_CA_UNSPEC   0
833 
834 /* Algorithm can be set on socket without CAP_NET_ADMIN privileges */
835 #define TCP_CONG_NON_RESTRICTED 0x1
836 /* Requires ECN/ECT set on all packets */
837 #define TCP_CONG_NEEDS_ECN      0x2
838 
839 union tcp_cc_info;
840 
841 struct tcp_congestion_ops {
842         struct list_head        list;
843         u32 key;
844         u32 flags;
845 
846         /* initialize private data (optional) */
847         void (*init)(struct sock *sk);
848         /* cleanup private data  (optional) */
849         void (*release)(struct sock *sk);
850 
851         /* return slow start threshold (required) */
852         u32 (*ssthresh)(struct sock *sk);
853         /* do new cwnd calculation (required) */
854         void (*cong_avoid)(struct sock *sk, u32 ack, u32 acked);
855         /* call before changing ca_state (optional) */
856         void (*set_state)(struct sock *sk, u8 new_state);
857         /* call when cwnd event occurs (optional) */
858         void (*cwnd_event)(struct sock *sk, enum tcp_ca_event ev);
859         /* call when ack arrives (optional) */
860         void (*in_ack_event)(struct sock *sk, u32 flags);
861         /* new value of cwnd after loss (optional) */
862         u32  (*undo_cwnd)(struct sock *sk);
863         /* hook for packet ack accounting (optional) */
864         void (*pkts_acked)(struct sock *sk, u32 num_acked, s32 rtt_us);
865         /* get info for inet_diag (optional) */
866         size_t (*get_info)(struct sock *sk, u32 ext, int *attr,
867                            union tcp_cc_info *info);
868 
869         char            name[TCP_CA_NAME_MAX];
870         struct module   *owner;
871 };
872 
873 int tcp_register_congestion_control(struct tcp_congestion_ops *type);
874 void tcp_unregister_congestion_control(struct tcp_congestion_ops *type);
875 
876 void tcp_assign_congestion_control(struct sock *sk);
877 void tcp_init_congestion_control(struct sock *sk);
878 void tcp_cleanup_congestion_control(struct sock *sk);
879 int tcp_set_default_congestion_control(const char *name);
880 void tcp_get_default_congestion_control(char *name);
881 void tcp_get_available_congestion_control(char *buf, size_t len);
882 void tcp_get_allowed_congestion_control(char *buf, size_t len);
883 int tcp_set_allowed_congestion_control(char *allowed);
884 int tcp_set_congestion_control(struct sock *sk, const char *name);
885 u32 tcp_slow_start(struct tcp_sock *tp, u32 acked);
886 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked);
887 
888 u32 tcp_reno_ssthresh(struct sock *sk);
889 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked);
890 extern struct tcp_congestion_ops tcp_reno;
891 
892 struct tcp_congestion_ops *tcp_ca_find_key(u32 key);
893 u32 tcp_ca_get_key_by_name(const char *name, bool *ecn_ca);
894 #ifdef CONFIG_INET
895 char *tcp_ca_get_name_by_key(u32 key, char *buffer);
896 #else
897 static inline char *tcp_ca_get_name_by_key(u32 key, char *buffer)
898 {
899         return NULL;
900 }
901 #endif
902 
903 static inline bool tcp_ca_needs_ecn(const struct sock *sk)
904 {
905         const struct inet_connection_sock *icsk = inet_csk(sk);
906 
907         return icsk->icsk_ca_ops->flags & TCP_CONG_NEEDS_ECN;
908 }
909 
910 static inline void tcp_set_ca_state(struct sock *sk, const u8 ca_state)
911 {
912         struct inet_connection_sock *icsk = inet_csk(sk);
913 
914         if (icsk->icsk_ca_ops->set_state)
915                 icsk->icsk_ca_ops->set_state(sk, ca_state);
916         icsk->icsk_ca_state = ca_state;
917 }
918 
919 static inline void tcp_ca_event(struct sock *sk, const enum tcp_ca_event event)
920 {
921         const struct inet_connection_sock *icsk = inet_csk(sk);
922 
923         if (icsk->icsk_ca_ops->cwnd_event)
924                 icsk->icsk_ca_ops->cwnd_event(sk, event);
925 }
926 
927 /* These functions determine how the current flow behaves in respect of SACK
928  * handling. SACK is negotiated with the peer, and therefore it can vary
929  * between different flows.
930  *
931  * tcp_is_sack - SACK enabled
932  * tcp_is_reno - No SACK
933  * tcp_is_fack - FACK enabled, implies SACK enabled
934  */
935 static inline int tcp_is_sack(const struct tcp_sock *tp)
936 {
937         return tp->rx_opt.sack_ok;
938 }
939 
940 static inline bool tcp_is_reno(const struct tcp_sock *tp)
941 {
942         return !tcp_is_sack(tp);
943 }
944 
945 static inline bool tcp_is_fack(const struct tcp_sock *tp)
946 {
947         return tp->rx_opt.sack_ok & TCP_FACK_ENABLED;
948 }
949 
950 static inline void tcp_enable_fack(struct tcp_sock *tp)
951 {
952         tp->rx_opt.sack_ok |= TCP_FACK_ENABLED;
953 }
954 
955 /* TCP early-retransmit (ER) is similar to but more conservative than
956  * the thin-dupack feature.  Enable ER only if thin-dupack is disabled.
957  */
958 static inline void tcp_enable_early_retrans(struct tcp_sock *tp)
959 {
960         struct net *net = sock_net((struct sock *)tp);
961 
962         tp->do_early_retrans = sysctl_tcp_early_retrans &&
963                 sysctl_tcp_early_retrans < 4 && !sysctl_tcp_thin_dupack &&
964                 net->ipv4.sysctl_tcp_reordering == 3;
965 }
966 
967 static inline void tcp_disable_early_retrans(struct tcp_sock *tp)
968 {
969         tp->do_early_retrans = 0;
970 }
971 
972 static inline unsigned int tcp_left_out(const struct tcp_sock *tp)
973 {
974         return tp->sacked_out + tp->lost_out;
975 }
976 
977 /* This determines how many packets are "in the network" to the best
978  * of our knowledge.  In many cases it is conservative, but where
979  * detailed information is available from the receiver (via SACK
980  * blocks etc.) we can make more aggressive calculations.
981  *
982  * Use this for decisions involving congestion control, use just
983  * tp->packets_out to determine if the send queue is empty or not.
984  *
985  * Read this equation as:
986  *
987  *      "Packets sent once on transmission queue" MINUS
988  *      "Packets left network, but not honestly ACKed yet" PLUS
989  *      "Packets fast retransmitted"
990  */
991 static inline unsigned int tcp_packets_in_flight(const struct tcp_sock *tp)
992 {
993         return tp->packets_out - tcp_left_out(tp) + tp->retrans_out;
994 }
995 
996 #define TCP_INFINITE_SSTHRESH   0x7fffffff
997 
998 static inline bool tcp_in_slow_start(const struct tcp_sock *tp)
999 {
1000         return tp->snd_cwnd < tp->snd_ssthresh;
1001 }
1002 
1003 static inline bool tcp_in_initial_slowstart(const struct tcp_sock *tp)
1004 {
1005         return tp->snd_ssthresh >= TCP_INFINITE_SSTHRESH;
1006 }
1007 
1008 static inline bool tcp_in_cwnd_reduction(const struct sock *sk)
1009 {
1010         return (TCPF_CA_CWR | TCPF_CA_Recovery) &
1011                (1 << inet_csk(sk)->icsk_ca_state);
1012 }
1013 
1014 /* If cwnd > ssthresh, we may raise ssthresh to be half-way to cwnd.
1015  * The exception is cwnd reduction phase, when cwnd is decreasing towards
1016  * ssthresh.
1017  */
1018 static inline __u32 tcp_current_ssthresh(const struct sock *sk)
1019 {
1020         const struct tcp_sock *tp = tcp_sk(sk);
1021 
1022         if (tcp_in_cwnd_reduction(sk))
1023                 return tp->snd_ssthresh;
1024         else
1025                 return max(tp->snd_ssthresh,
1026                            ((tp->snd_cwnd >> 1) +
1027                             (tp->snd_cwnd >> 2)));
1028 }
1029 
1030 /* Use define here intentionally to get WARN_ON location shown at the caller */
1031 #define tcp_verify_left_out(tp) WARN_ON(tcp_left_out(tp) > tp->packets_out)
1032 
1033 void tcp_enter_cwr(struct sock *sk);
1034 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst);
1035 
1036 /* The maximum number of MSS of available cwnd for which TSO defers
1037  * sending if not using sysctl_tcp_tso_win_divisor.
1038  */
1039 static inline __u32 tcp_max_tso_deferred_mss(const struct tcp_sock *tp)
1040 {
1041         return 3;
1042 }
1043 
1044 /* Slow start with delack produces 3 packets of burst, so that
1045  * it is safe "de facto".  This will be the default - same as
1046  * the default reordering threshold - but if reordering increases,
1047  * we must be able to allow cwnd to burst at least this much in order
1048  * to not pull it back when holes are filled.
1049  */
1050 static __inline__ __u32 tcp_max_burst(const struct tcp_sock *tp)
1051 {
1052         return tp->reordering;
1053 }
1054 
1055 /* Returns end sequence number of the receiver's advertised window */
1056 static inline u32 tcp_wnd_end(const struct tcp_sock *tp)
1057 {
1058         return tp->snd_una + tp->snd_wnd;
1059 }
1060 
1061 /* We follow the spirit of RFC2861 to validate cwnd but implement a more
1062  * flexible approach. The RFC suggests cwnd should not be raised unless
1063  * it was fully used previously. And that's exactly what we do in
1064  * congestion avoidance mode. But in slow start we allow cwnd to grow
1065  * as long as the application has used half the cwnd.
1066  * Example :
1067  *    cwnd is 10 (IW10), but application sends 9 frames.
1068  *    We allow cwnd to reach 18 when all frames are ACKed.
1069  * This check is safe because it's as aggressive as slow start which already
1070  * risks 100% overshoot. The advantage is that we discourage application to
1071  * either send more filler packets or data to artificially blow up the cwnd
1072  * usage, and allow application-limited process to probe bw more aggressively.
1073  */
1074 static inline bool tcp_is_cwnd_limited(const struct sock *sk)
1075 {
1076         const struct tcp_sock *tp = tcp_sk(sk);
1077 
1078         /* If in slow start, ensure cwnd grows to twice what was ACKed. */
1079         if (tcp_in_slow_start(tp))
1080                 return tp->snd_cwnd < 2 * tp->max_packets_out;
1081 
1082         return tp->is_cwnd_limited;
1083 }
1084 
1085 /* Something is really bad, we could not queue an additional packet,
1086  * because qdisc is full or receiver sent a 0 window.
1087  * We do not want to add fuel to the fire, or abort too early,
1088  * so make sure the timer we arm now is at least 200ms in the future,
1089  * regardless of current icsk_rto value (as it could be ~2ms)
1090  */
1091 static inline unsigned long tcp_probe0_base(const struct sock *sk)
1092 {
1093         return max_t(unsigned long, inet_csk(sk)->icsk_rto, TCP_RTO_MIN);
1094 }
1095 
1096 /* Variant of inet_csk_rto_backoff() used for zero window probes */
1097 static inline unsigned long tcp_probe0_when(const struct sock *sk,
1098                                             unsigned long max_when)
1099 {
1100         u64 when = (u64)tcp_probe0_base(sk) << inet_csk(sk)->icsk_backoff;
1101 
1102         return (unsigned long)min_t(u64, when, max_when);
1103 }
1104 
1105 static inline void tcp_check_probe_timer(struct sock *sk)
1106 {
1107         if (!tcp_sk(sk)->packets_out && !inet_csk(sk)->icsk_pending)
1108                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
1109                                           tcp_probe0_base(sk), TCP_RTO_MAX);
1110 }
1111 
1112 static inline void tcp_init_wl(struct tcp_sock *tp, u32 seq)
1113 {
1114         tp->snd_wl1 = seq;
1115 }
1116 
1117 static inline void tcp_update_wl(struct tcp_sock *tp, u32 seq)
1118 {
1119         tp->snd_wl1 = seq;
1120 }
1121 
1122 /*
1123  * Calculate(/check) TCP checksum
1124  */
1125 static inline __sum16 tcp_v4_check(int len, __be32 saddr,
1126                                    __be32 daddr, __wsum base)
1127 {
1128         return csum_tcpudp_magic(saddr,daddr,len,IPPROTO_TCP,base);
1129 }
1130 
1131 static inline __sum16 __tcp_checksum_complete(struct sk_buff *skb)
1132 {
1133         return __skb_checksum_complete(skb);
1134 }
1135 
1136 static inline bool tcp_checksum_complete(struct sk_buff *skb)
1137 {
1138         return !skb_csum_unnecessary(skb) &&
1139                 __tcp_checksum_complete(skb);
1140 }
1141 
1142 /* Prequeue for VJ style copy to user, combined with checksumming. */
1143 
1144 static inline void tcp_prequeue_init(struct tcp_sock *tp)
1145 {
1146         tp->ucopy.task = NULL;
1147         tp->ucopy.len = 0;
1148         tp->ucopy.memory = 0;
1149         skb_queue_head_init(&tp->ucopy.prequeue);
1150 }
1151 
1152 bool tcp_prequeue(struct sock *sk, struct sk_buff *skb);
1153 
1154 #undef STATE_TRACE
1155 
1156 #ifdef STATE_TRACE
1157 static const char *statename[]={
1158         "Unused","Established","Syn Sent","Syn Recv",
1159         "Fin Wait 1","Fin Wait 2","Time Wait", "Close",
1160         "Close Wait","Last ACK","Listen","Closing"
1161 };
1162 #endif
1163 void tcp_set_state(struct sock *sk, int state);
1164 
1165 void tcp_done(struct sock *sk);
1166 
1167 int tcp_abort(struct sock *sk, int err);
1168 
1169 static inline void tcp_sack_reset(struct tcp_options_received *rx_opt)
1170 {
1171         rx_opt->dsack = 0;
1172         rx_opt->num_sacks = 0;
1173 }
1174 
1175 u32 tcp_default_init_rwnd(u32 mss);
1176 void tcp_cwnd_restart(struct sock *sk, s32 delta);
1177 
1178 static inline void tcp_slow_start_after_idle_check(struct sock *sk)
1179 {
1180         struct tcp_sock *tp = tcp_sk(sk);
1181         s32 delta;
1182 
1183         if (!sysctl_tcp_slow_start_after_idle || tp->packets_out)
1184                 return;
1185         delta = tcp_time_stamp - tp->lsndtime;
1186         if (delta > inet_csk(sk)->icsk_rto)
1187                 tcp_cwnd_restart(sk, delta);
1188 }
1189 
1190 /* Determine a window scaling and initial window to offer. */
1191 void tcp_select_initial_window(int __space, __u32 mss, __u32 *rcv_wnd,
1192                                __u32 *window_clamp, int wscale_ok,
1193                                __u8 *rcv_wscale, __u32 init_rcv_wnd);
1194 
1195 static inline int tcp_win_from_space(int space)
1196 {
1197         return sysctl_tcp_adv_win_scale<=0 ?
1198                 (space>>(-sysctl_tcp_adv_win_scale)) :
1199                 space - (space>>sysctl_tcp_adv_win_scale);
1200 }
1201 
1202 /* Note: caller must be prepared to deal with negative returns */
1203 static inline int tcp_space(const struct sock *sk)
1204 {
1205         return tcp_win_from_space(sk->sk_rcvbuf -
1206                                   atomic_read(&sk->sk_rmem_alloc));
1207 }
1208 
1209 static inline int tcp_full_space(const struct sock *sk)
1210 {
1211         return tcp_win_from_space(sk->sk_rcvbuf);
1212 }
1213 
1214 extern void tcp_openreq_init_rwin(struct request_sock *req,
1215                                   const struct sock *sk_listener,
1216                                   const struct dst_entry *dst);
1217 
1218 void tcp_enter_memory_pressure(struct sock *sk);
1219 
1220 static inline int keepalive_intvl_when(const struct tcp_sock *tp)
1221 {
1222         struct net *net = sock_net((struct sock *)tp);
1223 
1224         return tp->keepalive_intvl ? : net->ipv4.sysctl_tcp_keepalive_intvl;
1225 }
1226 
1227 static inline int keepalive_time_when(const struct tcp_sock *tp)
1228 {
1229         struct net *net = sock_net((struct sock *)tp);
1230 
1231         return tp->keepalive_time ? : net->ipv4.sysctl_tcp_keepalive_time;
1232 }
1233 
1234 static inline int keepalive_probes(const struct tcp_sock *tp)
1235 {
1236         struct net *net = sock_net((struct sock *)tp);
1237 
1238         return tp->keepalive_probes ? : net->ipv4.sysctl_tcp_keepalive_probes;
1239 }
1240 
1241 static inline u32 keepalive_time_elapsed(const struct tcp_sock *tp)
1242 {
1243         const struct inet_connection_sock *icsk = &tp->inet_conn;
1244 
1245         return min_t(u32, tcp_time_stamp - icsk->icsk_ack.lrcvtime,
1246                           tcp_time_stamp - tp->rcv_tstamp);
1247 }
1248 
1249 static inline int tcp_fin_time(const struct sock *sk)
1250 {
1251         int fin_timeout = tcp_sk(sk)->linger2 ? : sock_net(sk)->ipv4.sysctl_tcp_fin_timeout;
1252         const int rto = inet_csk(sk)->icsk_rto;
1253 
1254         if (fin_timeout < (rto << 2) - (rto >> 1))
1255                 fin_timeout = (rto << 2) - (rto >> 1);
1256 
1257         return fin_timeout;
1258 }
1259 
1260 static inline bool tcp_paws_check(const struct tcp_options_received *rx_opt,
1261                                   int paws_win)
1262 {
1263         if ((s32)(rx_opt->ts_recent - rx_opt->rcv_tsval) <= paws_win)
1264                 return true;
1265         if (unlikely(get_seconds() >= rx_opt->ts_recent_stamp + TCP_PAWS_24DAYS))
1266                 return true;
1267         /*
1268          * Some OSes send SYN and SYNACK messages with tsval=0 tsecr=0,
1269          * then following tcp messages have valid values. Ignore 0 value,
1270          * or else 'negative' tsval might forbid us to accept their packets.
1271          */
1272         if (!rx_opt->ts_recent)
1273                 return true;
1274         return false;
1275 }
1276 
1277 static inline bool tcp_paws_reject(const struct tcp_options_received *rx_opt,
1278                                    int rst)
1279 {
1280         if (tcp_paws_check(rx_opt, 0))
1281                 return false;
1282 
1283         /* RST segments are not recommended to carry timestamp,
1284            and, if they do, it is recommended to ignore PAWS because
1285            "their cleanup function should take precedence over timestamps."
1286            Certainly, it is mistake. It is necessary to understand the reasons
1287            of this constraint to relax it: if peer reboots, clock may go
1288            out-of-sync and half-open connections will not be reset.
1289            Actually, the problem would be not existing if all
1290            the implementations followed draft about maintaining clock
1291            via reboots. Linux-2.2 DOES NOT!
1292 
1293            However, we can relax time bounds for RST segments to MSL.
1294          */
1295         if (rst && get_seconds() >= rx_opt->ts_recent_stamp + TCP_PAWS_MSL)
1296                 return false;
1297         return true;
1298 }
1299 
1300 bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
1301                           int mib_idx, u32 *last_oow_ack_time);
1302 
1303 static inline void tcp_mib_init(struct net *net)
1304 {
1305         /* See RFC 2012 */
1306         TCP_ADD_STATS_USER(net, TCP_MIB_RTOALGORITHM, 1);
1307         TCP_ADD_STATS_USER(net, TCP_MIB_RTOMIN, TCP_RTO_MIN*1000/HZ);
1308         TCP_ADD_STATS_USER(net, TCP_MIB_RTOMAX, TCP_RTO_MAX*1000/HZ);
1309         TCP_ADD_STATS_USER(net, TCP_MIB_MAXCONN, -1);
1310 }
1311 
1312 /* from STCP */
1313 static inline void tcp_clear_retrans_hints_partial(struct tcp_sock *tp)
1314 {
1315         tp->lost_skb_hint = NULL;
1316 }
1317 
1318 static inline void tcp_clear_all_retrans_hints(struct tcp_sock *tp)
1319 {
1320         tcp_clear_retrans_hints_partial(tp);
1321         tp->retransmit_skb_hint = NULL;
1322 }
1323 
1324 union tcp_md5_addr {
1325         struct in_addr  a4;
1326 #if IS_ENABLED(CONFIG_IPV6)
1327         struct in6_addr a6;
1328 #endif
1329 };
1330 
1331 /* - key database */
1332 struct tcp_md5sig_key {
1333         struct hlist_node       node;
1334         u8                      keylen;
1335         u8                      family; /* AF_INET or AF_INET6 */
1336         union tcp_md5_addr      addr;
1337         u8                      key[TCP_MD5SIG_MAXKEYLEN];
1338         struct rcu_head         rcu;
1339 };
1340 
1341 /* - sock block */
1342 struct tcp_md5sig_info {
1343         struct hlist_head       head;
1344         struct rcu_head         rcu;
1345 };
1346 
1347 /* - pseudo header */
1348 struct tcp4_pseudohdr {
1349         __be32          saddr;
1350         __be32          daddr;
1351         __u8            pad;
1352         __u8            protocol;
1353         __be16          len;
1354 };
1355 
1356 struct tcp6_pseudohdr {
1357         struct in6_addr saddr;
1358         struct in6_addr daddr;
1359         __be32          len;
1360         __be32          protocol;       /* including padding */
1361 };
1362 
1363 union tcp_md5sum_block {
1364         struct tcp4_pseudohdr ip4;
1365 #if IS_ENABLED(CONFIG_IPV6)
1366         struct tcp6_pseudohdr ip6;
1367 #endif
1368 };
1369 
1370 /* - pool: digest algorithm, hash description and scratch buffer */
1371 struct tcp_md5sig_pool {
1372         struct ahash_request    *md5_req;
1373         union tcp_md5sum_block  md5_blk;
1374 };
1375 
1376 /* - functions */
1377 int tcp_v4_md5_hash_skb(char *md5_hash, const struct tcp_md5sig_key *key,
1378                         const struct sock *sk, const struct sk_buff *skb);
1379 int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
1380                    int family, const u8 *newkey, u8 newkeylen, gfp_t gfp);
1381 int tcp_md5_do_del(struct sock *sk, const union tcp_md5_addr *addr,
1382                    int family);
1383 struct tcp_md5sig_key *tcp_v4_md5_lookup(const struct sock *sk,
1384                                          const struct sock *addr_sk);
1385 
1386 #ifdef CONFIG_TCP_MD5SIG
1387 struct tcp_md5sig_key *tcp_md5_do_lookup(const struct sock *sk,
1388                                          const union tcp_md5_addr *addr,
1389                                          int family);
1390 #define tcp_twsk_md5_key(twsk)  ((twsk)->tw_md5_key)
1391 #else
1392 static inline struct tcp_md5sig_key *tcp_md5_do_lookup(const struct sock *sk,
1393                                          const union tcp_md5_addr *addr,
1394                                          int family)
1395 {
1396         return NULL;
1397 }
1398 #define tcp_twsk_md5_key(twsk)  NULL
1399 #endif
1400 
1401 bool tcp_alloc_md5sig_pool(void);
1402 
1403 struct tcp_md5sig_pool *tcp_get_md5sig_pool(void);
1404 static inline void tcp_put_md5sig_pool(void)
1405 {
1406         local_bh_enable();
1407 }
1408 
1409 int tcp_md5_hash_header(struct tcp_md5sig_pool *, const struct tcphdr *);
1410 int tcp_md5_hash_skb_data(struct tcp_md5sig_pool *, const struct sk_buff *,
1411                           unsigned int header_len);
1412 int tcp_md5_hash_key(struct tcp_md5sig_pool *hp,
1413                      const struct tcp_md5sig_key *key);
1414 
1415 /* From tcp_fastopen.c */
1416 void tcp_fastopen_cache_get(struct sock *sk, u16 *mss,
1417                             struct tcp_fastopen_cookie *cookie, int *syn_loss,
1418                             unsigned long *last_syn_loss);
1419 void tcp_fastopen_cache_set(struct sock *sk, u16 mss,
1420                             struct tcp_fastopen_cookie *cookie, bool syn_lost,
1421                             u16 try_exp);
1422 struct tcp_fastopen_request {
1423         /* Fast Open cookie. Size 0 means a cookie request */
1424         struct tcp_fastopen_cookie      cookie;
1425         struct msghdr                   *data;  /* data in MSG_FASTOPEN */
1426         size_t                          size;
1427         int                             copied; /* queued in tcp_connect() */
1428 };
1429 void tcp_free_fastopen_req(struct tcp_sock *tp);
1430 
1431 extern struct tcp_fastopen_context __rcu *tcp_fastopen_ctx;
1432 int tcp_fastopen_reset_cipher(void *key, unsigned int len);
1433 void tcp_fastopen_add_skb(struct sock *sk, struct sk_buff *skb);
1434 struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
1435                               struct request_sock *req,
1436                               struct tcp_fastopen_cookie *foc,
1437                               struct dst_entry *dst);
1438 void tcp_fastopen_init_key_once(bool publish);
1439 #define TCP_FASTOPEN_KEY_LENGTH 16
1440 
1441 /* Fastopen key context */
1442 struct tcp_fastopen_context {
1443         struct crypto_cipher    *tfm;
1444         __u8                    key[TCP_FASTOPEN_KEY_LENGTH];
1445         struct rcu_head         rcu;
1446 };
1447 
1448 /* write queue abstraction */
1449 static inline void tcp_write_queue_purge(struct sock *sk)
1450 {
1451         struct sk_buff *skb;
1452 
1453         while ((skb = __skb_dequeue(&sk->sk_write_queue)) != NULL)
1454                 sk_wmem_free_skb(sk, skb);
1455         sk_mem_reclaim(sk);
1456         tcp_clear_all_retrans_hints(tcp_sk(sk));
1457 }
1458 
1459 static inline struct sk_buff *tcp_write_queue_head(const struct sock *sk)
1460 {
1461         return skb_peek(&sk->sk_write_queue);
1462 }
1463 
1464 static inline struct sk_buff *tcp_write_queue_tail(const struct sock *sk)
1465 {
1466         return skb_peek_tail(&sk->sk_write_queue);
1467 }
1468 
1469 static inline struct sk_buff *tcp_write_queue_next(const struct sock *sk,
1470                                                    const struct sk_buff *skb)
1471 {
1472         return skb_queue_next(&sk->sk_write_queue, skb);
1473 }
1474 
1475 static inline struct sk_buff *tcp_write_queue_prev(const struct sock *sk,
1476                                                    const struct sk_buff *skb)
1477 {
1478         return skb_queue_prev(&sk->sk_write_queue, skb);
1479 }
1480 
1481 #define tcp_for_write_queue(skb, sk)                                    \
1482         skb_queue_walk(&(sk)->sk_write_queue, skb)
1483 
1484 #define tcp_for_write_queue_from(skb, sk)                               \
1485         skb_queue_walk_from(&(sk)->sk_write_queue, skb)
1486 
1487 #define tcp_for_write_queue_from_safe(skb, tmp, sk)                     \
1488         skb_queue_walk_from_safe(&(sk)->sk_write_queue, skb, tmp)
1489 
1490 static inline struct sk_buff *tcp_send_head(const struct sock *sk)
1491 {
1492         return sk->sk_send_head;
1493 }
1494 
1495 static inline bool tcp_skb_is_last(const struct sock *sk,
1496                                    const struct sk_buff *skb)
1497 {
1498         return skb_queue_is_last(&sk->sk_write_queue, skb);
1499 }
1500 
1501 static inline void tcp_advance_send_head(struct sock *sk, const struct sk_buff *skb)
1502 {
1503         if (tcp_skb_is_last(sk, skb))
1504                 sk->sk_send_head = NULL;
1505         else
1506                 sk->sk_send_head = tcp_write_queue_next(sk, skb);
1507 }
1508 
1509 static inline void tcp_check_send_head(struct sock *sk, struct sk_buff *skb_unlinked)
1510 {
1511         if (sk->sk_send_head == skb_unlinked)
1512                 sk->sk_send_head = NULL;
1513 }
1514 
1515 static inline void tcp_init_send_head(struct sock *sk)
1516 {
1517         sk->sk_send_head = NULL;
1518 }
1519 
1520 static inline void __tcp_add_write_queue_tail(struct sock *sk, struct sk_buff *skb)
1521 {
1522         __skb_queue_tail(&sk->sk_write_queue, skb);
1523 }
1524 
1525 static inline void tcp_add_write_queue_tail(struct sock *sk, struct sk_buff *skb)
1526 {
1527         __tcp_add_write_queue_tail(sk, skb);
1528 
1529         /* Queue it, remembering where we must start sending. */
1530         if (sk->sk_send_head == NULL) {
1531                 sk->sk_send_head = skb;
1532 
1533                 if (tcp_sk(sk)->highest_sack == NULL)
1534                         tcp_sk(sk)->highest_sack = skb;
1535         }
1536 }
1537 
1538 static inline void __tcp_add_write_queue_head(struct sock *sk, struct sk_buff *skb)
1539 {
1540         __skb_queue_head(&sk->sk_write_queue, skb);
1541 }
1542 
1543 /* Insert buff after skb on the write queue of sk.  */
1544 static inline void tcp_insert_write_queue_after(struct sk_buff *skb,
1545                                                 struct sk_buff *buff,
1546                                                 struct sock *sk)
1547 {
1548         __skb_queue_after(&sk->sk_write_queue, skb, buff);
1549 }
1550 
1551 /* Insert new before skb on the write queue of sk.  */
1552 static inline void tcp_insert_write_queue_before(struct sk_buff *new,
1553                                                   struct sk_buff *skb,
1554                                                   struct sock *sk)
1555 {
1556         __skb_queue_before(&sk->sk_write_queue, skb, new);
1557 
1558         if (sk->sk_send_head == skb)
1559                 sk->sk_send_head = new;
1560 }
1561 
1562 static inline void tcp_unlink_write_queue(struct sk_buff *skb, struct sock *sk)
1563 {
1564         __skb_unlink(skb, &sk->sk_write_queue);
1565 }
1566 
1567 static inline bool tcp_write_queue_empty(struct sock *sk)
1568 {
1569         return skb_queue_empty(&sk->sk_write_queue);
1570 }
1571 
1572 static inline void tcp_push_pending_frames(struct sock *sk)
1573 {
1574         if (tcp_send_head(sk)) {
1575                 struct tcp_sock *tp = tcp_sk(sk);
1576 
1577                 __tcp_push_pending_frames(sk, tcp_current_mss(sk), tp->nonagle);
1578         }
1579 }
1580 
1581 /* Start sequence of the skb just after the highest skb with SACKed
1582  * bit, valid only if sacked_out > 0 or when the caller has ensured
1583  * validity by itself.
1584  */
1585 static inline u32 tcp_highest_sack_seq(struct tcp_sock *tp)
1586 {
1587         if (!tp->sacked_out)
1588                 return tp->snd_una;
1589 
1590         if (tp->highest_sack == NULL)
1591                 return tp->snd_nxt;
1592 
1593         return TCP_SKB_CB(tp->highest_sack)->seq;
1594 }
1595 
1596 static inline void tcp_advance_highest_sack(struct sock *sk, struct sk_buff *skb)
1597 {
1598         tcp_sk(sk)->highest_sack = tcp_skb_is_last(sk, skb) ? NULL :
1599                                                 tcp_write_queue_next(sk, skb);
1600 }
1601 
1602 static inline struct sk_buff *tcp_highest_sack(struct sock *sk)
1603 {
1604         return tcp_sk(sk)->highest_sack;
1605 }
1606 
1607 static inline void tcp_highest_sack_reset(struct sock *sk)
1608 {
1609         tcp_sk(sk)->highest_sack = tcp_write_queue_head(sk);
1610 }
1611 
1612 /* Called when old skb is about to be deleted (to be combined with new skb) */
1613 static inline void tcp_highest_sack_combine(struct sock *sk,
1614                                             struct sk_buff *old,
1615                                             struct sk_buff *new)
1616 {
1617         if (tcp_sk(sk)->sacked_out && (old == tcp_sk(sk)->highest_sack))
1618                 tcp_sk(sk)->highest_sack = new;
1619 }
1620 
1621 /* This helper checks if socket has IP_TRANSPARENT set */
1622 static inline bool inet_sk_transparent(const struct sock *sk)
1623 {
1624         switch (sk->sk_state) {
1625         case TCP_TIME_WAIT:
1626                 return inet_twsk(sk)->tw_transparent;
1627         case TCP_NEW_SYN_RECV:
1628                 return inet_rsk(inet_reqsk(sk))->no_srccheck;
1629         }
1630         return inet_sk(sk)->transparent;
1631 }
1632 
1633 /* Determines whether this is a thin stream (which may suffer from
1634  * increased latency). Used to trigger latency-reducing mechanisms.
1635  */
1636 static inline bool tcp_stream_is_thin(struct tcp_sock *tp)
1637 {
1638         return tp->packets_out < 4 && !tcp_in_initial_slowstart(tp);
1639 }
1640 
1641 /* /proc */
1642 enum tcp_seq_states {
1643         TCP_SEQ_STATE_LISTENING,
1644         TCP_SEQ_STATE_ESTABLISHED,
1645 };
1646 
1647 int tcp_seq_open(struct inode *inode, struct file *file);
1648 
1649 struct tcp_seq_afinfo {
1650         char                            *name;
1651         sa_family_t                     family;
1652         const struct file_operations    *seq_fops;
1653         struct seq_operations           seq_ops;
1654 };
1655 
1656 struct tcp_iter_state {
1657         struct seq_net_private  p;
1658         sa_family_t             family;
1659         enum tcp_seq_states     state;
1660         struct sock             *syn_wait_sk;
1661         int                     bucket, offset, sbucket, num;
1662         loff_t                  last_pos;
1663 };
1664 
1665 int tcp_proc_register(struct net *net, struct tcp_seq_afinfo *afinfo);
1666 void tcp_proc_unregister(struct net *net, struct tcp_seq_afinfo *afinfo);
1667 
1668 extern struct request_sock_ops tcp_request_sock_ops;
1669 extern struct request_sock_ops tcp6_request_sock_ops;
1670 
1671 void tcp_v4_destroy_sock(struct sock *sk);
1672 
1673 struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
1674                                 netdev_features_t features);
1675 struct sk_buff **tcp_gro_receive(struct sk_buff **head, struct sk_buff *skb);
1676 int tcp_gro_complete(struct sk_buff *skb);
1677 
1678 void __tcp_v4_send_check(struct sk_buff *skb, __be32 saddr, __be32 daddr);
1679 
1680 static inline u32 tcp_notsent_lowat(const struct tcp_sock *tp)
1681 {
1682         struct net *net = sock_net((struct sock *)tp);
1683         return tp->notsent_lowat ?: net->ipv4.sysctl_tcp_notsent_lowat;
1684 }
1685 
1686 static inline bool tcp_stream_memory_free(const struct sock *sk)
1687 {
1688         const struct tcp_sock *tp = tcp_sk(sk);
1689         u32 notsent_bytes = tp->write_seq - tp->snd_nxt;
1690 
1691         return notsent_bytes < tcp_notsent_lowat(tp);
1692 }
1693 
1694 #ifdef CONFIG_PROC_FS
1695 int tcp4_proc_init(void);
1696 void tcp4_proc_exit(void);
1697 #endif
1698 
1699 int tcp_rtx_synack(const struct sock *sk, struct request_sock *req);
1700 int tcp_conn_request(struct request_sock_ops *rsk_ops,
1701                      const struct tcp_request_sock_ops *af_ops,
1702                      struct sock *sk, struct sk_buff *skb);
1703 
1704 /* TCP af-specific functions */
1705 struct tcp_sock_af_ops {
1706 #ifdef CONFIG_TCP_MD5SIG
1707         struct tcp_md5sig_key   *(*md5_lookup) (const struct sock *sk,
1708                                                 const struct sock *addr_sk);
1709         int             (*calc_md5_hash)(char *location,
1710                                          const struct tcp_md5sig_key *md5,
1711                                          const struct sock *sk,
1712                                          const struct sk_buff *skb);
1713         int             (*md5_parse)(struct sock *sk,
1714                                      char __user *optval,
1715                                      int optlen);
1716 #endif
1717 };
1718 
1719 struct tcp_request_sock_ops {
1720         u16 mss_clamp;
1721 #ifdef CONFIG_TCP_MD5SIG
1722         struct tcp_md5sig_key *(*req_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 #endif
1729         void (*init_req)(struct request_sock *req,
1730                          const struct sock *sk_listener,
1731                          struct sk_buff *skb);
1732 #ifdef CONFIG_SYN_COOKIES
1733         __u32 (*cookie_init_seq)(const struct sk_buff *skb,
1734                                  __u16 *mss);
1735 #endif
1736         struct dst_entry *(*route_req)(const struct sock *sk, struct flowi *fl,
1737                                        const struct request_sock *req,
1738                                        bool *strict);
1739         __u32 (*init_seq)(const struct sk_buff *skb);
1740         int (*send_synack)(const struct sock *sk, struct dst_entry *dst,
1741                            struct flowi *fl, struct request_sock *req,
1742                            struct tcp_fastopen_cookie *foc,
1743                            bool attach_req);
1744 };
1745 
1746 #ifdef CONFIG_SYN_COOKIES
1747 static inline __u32 cookie_init_sequence(const struct tcp_request_sock_ops *ops,
1748                                          const struct sock *sk, struct sk_buff *skb,
1749                                          __u16 *mss)
1750 {
1751         tcp_synq_overflow(sk);
1752         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
1753         return ops->cookie_init_seq(skb, mss);
1754 }
1755 #else
1756 static inline __u32 cookie_init_sequence(const struct tcp_request_sock_ops *ops,
1757                                          const struct sock *sk, struct sk_buff *skb,
1758                                          __u16 *mss)
1759 {
1760         return 0;
1761 }
1762 #endif
1763 
1764 int tcpv4_offload_init(void);
1765 
1766 void tcp_v4_init(void);
1767 void tcp_init(void);
1768 
1769 /* tcp_recovery.c */
1770 
1771 /* Flags to enable various loss recovery features. See below */
1772 extern int sysctl_tcp_recovery;
1773 
1774 /* Use TCP RACK to detect (some) tail and retransmit losses */
1775 #define TCP_RACK_LOST_RETRANS  0x1
1776 
1777 extern int tcp_rack_mark_lost(struct sock *sk);
1778 
1779 extern void tcp_rack_advance(struct tcp_sock *tp,
1780                              const struct skb_mstamp *xmit_time, u8 sacked);
1781 
1782 /*
1783  * Save and compile IPv4 options, return a pointer to it
1784  */
1785 static inline struct ip_options_rcu *tcp_v4_save_options(struct sk_buff *skb)
1786 {
1787         const struct ip_options *opt = &TCP_SKB_CB(skb)->header.h4.opt;
1788         struct ip_options_rcu *dopt = NULL;
1789 
1790         if (opt->optlen) {
1791                 int opt_size = sizeof(*dopt) + opt->optlen;
1792 
1793                 dopt = kmalloc(opt_size, GFP_ATOMIC);
1794                 if (dopt && __ip_options_echo(&dopt->opt, skb, opt)) {
1795                         kfree(dopt);
1796                         dopt = NULL;
1797                 }
1798         }
1799         return dopt;
1800 }
1801 
1802 /* locally generated TCP pure ACKs have skb->truesize == 2
1803  * (check tcp_send_ack() in net/ipv4/tcp_output.c )
1804  * This is much faster than dissecting the packet to find out.
1805  * (Think of GRE encapsulations, IPv4, IPv6, ...)
1806  */
1807 static inline bool skb_is_tcp_pure_ack(const struct sk_buff *skb)
1808 {
1809         return skb->truesize == 2;
1810 }
1811 
1812 static inline void skb_set_tcp_pure_ack(struct sk_buff *skb)
1813 {
1814         skb->truesize = 2;
1815 }
1816 
1817 static inline int tcp_inq(struct sock *sk)
1818 {
1819         struct tcp_sock *tp = tcp_sk(sk);
1820         int answ;
1821 
1822         if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
1823                 answ = 0;
1824         } else if (sock_flag(sk, SOCK_URGINLINE) ||
1825                    !tp->urg_data ||
1826                    before(tp->urg_seq, tp->copied_seq) ||
1827                    !before(tp->urg_seq, tp->rcv_nxt)) {
1828 
1829                 answ = tp->rcv_nxt - tp->copied_seq;
1830 
1831                 /* Subtract 1, if FIN was received */
1832                 if (answ && sock_flag(sk, SOCK_DONE))
1833                         answ--;
1834         } else {
1835                 answ = tp->urg_seq - tp->copied_seq;
1836         }
1837 
1838         return answ;
1839 }
1840 
1841 static inline void tcp_segs_in(struct tcp_sock *tp, const struct sk_buff *skb)
1842 {
1843         u16 segs_in;
1844 
1845         segs_in = max_t(u16, 1, skb_shinfo(skb)->gso_segs);
1846         tp->segs_in += segs_in;
1847         if (skb->len > tcp_hdrlen(skb))
1848                 tp->data_segs_in += segs_in;
1849 }
1850 
1851 #endif  /* _TCP_H */
1852 

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