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Linux/include/net/tcp.h

  1 /*
  2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
  3  *              operating system.  INET is implemented using the  BSD Socket
  4  *              interface as the means of communication with the user level.
  5  *
  6  *              Definitions for the TCP module.
  7  *
  8  * Version:     @(#)tcp.h       1.0.5   05/23/93
  9  *
 10  * Authors:     Ross Biro
 11  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 12  *
 13  *              This program is free software; you can redistribute it and/or
 14  *              modify it under the terms of the GNU General Public License
 15  *              as published by the Free Software Foundation; either version
 16  *              2 of the License, or (at your option) any later version.
 17  */
 18 #ifndef _TCP_H
 19 #define _TCP_H
 20 
 21 #define FASTRETRANS_DEBUG 1
 22 
 23 #include <linux/list.h>
 24 #include <linux/tcp.h>
 25 #include <linux/bug.h>
 26 #include <linux/slab.h>
 27 #include <linux/cache.h>
 28 #include <linux/percpu.h>
 29 #include <linux/skbuff.h>
 30 #include <linux/crypto.h>
 31 #include <linux/cryptohash.h>
 32 #include <linux/kref.h>
 33 #include <linux/ktime.h>
 34 
 35 #include <net/inet_connection_sock.h>
 36 #include <net/inet_timewait_sock.h>
 37 #include <net/inet_hashtables.h>
 38 #include <net/checksum.h>
 39 #include <net/request_sock.h>
 40 #include <net/sock.h>
 41 #include <net/snmp.h>
 42 #include <net/ip.h>
 43 #include <net/tcp_states.h>
 44 #include <net/inet_ecn.h>
 45 #include <net/dst.h>
 46 
 47 #include <linux/seq_file.h>
 48 #include <linux/memcontrol.h>
 49 
 50 extern struct inet_hashinfo tcp_hashinfo;
 51 
 52 extern struct percpu_counter tcp_orphan_count;
 53 void tcp_time_wait(struct sock *sk, int state, int timeo);
 54 
 55 #define MAX_TCP_HEADER  (128 + MAX_HEADER)
 56 #define MAX_TCP_OPTION_SPACE 40
 57 
 58 /*
 59  * Never offer a window over 32767 without using window scaling. Some
 60  * poor stacks do signed 16bit maths!
 61  */
 62 #define MAX_TCP_WINDOW          32767U
 63 
 64 /* Minimal accepted MSS. It is (60+60+8) - (20+20). */
 65 #define TCP_MIN_MSS             88U
 66 
 67 /* The least MTU to use for probing */
 68 #define TCP_BASE_MSS            1024
 69 
 70 /* probing interval, default to 10 minutes as per RFC4821 */
 71 #define TCP_PROBE_INTERVAL      600
 72 
 73 /* Specify interval when tcp mtu probing will stop */
 74 #define TCP_PROBE_THRESHOLD     8
 75 
 76 /* After receiving this amount of duplicate ACKs fast retransmit starts. */
 77 #define TCP_FASTRETRANS_THRESH 3
 78 
 79 /* Maximal number of ACKs sent quickly to accelerate slow-start. */
 80 #define TCP_MAX_QUICKACKS       16U
 81 
 82 /* urg_data states */
 83 #define TCP_URG_VALID   0x0100
 84 #define TCP_URG_NOTYET  0x0200
 85 #define TCP_URG_READ    0x0400
 86 
 87 #define TCP_RETR1       3       /*
 88                                  * This is how many retries it does before it
 89                                  * tries to figure out if the gateway is
 90                                  * down. Minimal RFC value is 3; it corresponds
 91                                  * to ~3sec-8min depending on RTO.
 92                                  */
 93 
 94 #define TCP_RETR2       15      /*
 95                                  * This should take at least
 96                                  * 90 minutes to time out.
 97                                  * RFC1122 says that the limit is 100 sec.
 98                                  * 15 is ~13-30min depending on RTO.
 99                                  */
100 
101 #define TCP_SYN_RETRIES  6      /* This is how many retries are done
102                                  * when active opening a connection.
103                                  * RFC1122 says the minimum retry MUST
104                                  * be at least 180secs.  Nevertheless
105                                  * this value is corresponding to
106                                  * 63secs of retransmission with the
107                                  * current initial RTO.
108                                  */
109 
110 #define TCP_SYNACK_RETRIES 5    /* This is how may retries are done
111                                  * when passive opening a connection.
112                                  * This is corresponding to 31secs of
113                                  * retransmission with the current
114                                  * initial RTO.
115                                  */
116 
117 #define TCP_TIMEWAIT_LEN (60*HZ) /* how long to wait to destroy TIME-WAIT
118                                   * state, about 60 seconds     */
119 #define TCP_FIN_TIMEOUT TCP_TIMEWAIT_LEN
120                                  /* BSD style FIN_WAIT2 deadlock breaker.
121                                   * It used to be 3min, new value is 60sec,
122                                   * to combine FIN-WAIT-2 timeout with
123                                   * TIME-WAIT timer.
124                                   */
125 
126 #define TCP_DELACK_MAX  ((unsigned)(HZ/5))      /* maximal time to delay before sending an ACK */
127 #if HZ >= 100
128 #define TCP_DELACK_MIN  ((unsigned)(HZ/25))     /* minimal time to delay before sending an ACK */
129 #define TCP_ATO_MIN     ((unsigned)(HZ/25))
130 #else
131 #define TCP_DELACK_MIN  4U
132 #define TCP_ATO_MIN     4U
133 #endif
134 #define TCP_RTO_MAX     ((unsigned)(120*HZ))
135 #define TCP_RTO_MIN     ((unsigned)(HZ/5))
136 #define TCP_TIMEOUT_INIT ((unsigned)(1*HZ))     /* RFC6298 2.1 initial RTO value        */
137 #define TCP_TIMEOUT_FALLBACK ((unsigned)(3*HZ)) /* RFC 1122 initial RTO value, now
138                                                  * used as a fallback RTO for the
139                                                  * initial data transmission if no
140                                                  * valid RTT sample has been acquired,
141                                                  * most likely due to retrans in 3WHS.
142                                                  */
143 
144 #define TCP_RESOURCE_PROBE_INTERVAL ((unsigned)(HZ/2U)) /* Maximal interval between probes
145                                                          * for local resources.
146                                                          */
147 
148 #define TCP_KEEPALIVE_TIME      (120*60*HZ)     /* two hours */
149 #define TCP_KEEPALIVE_PROBES    9               /* Max of 9 keepalive probes    */
150 #define TCP_KEEPALIVE_INTVL     (75*HZ)
151 
152 #define MAX_TCP_KEEPIDLE        32767
153 #define MAX_TCP_KEEPINTVL       32767
154 #define MAX_TCP_KEEPCNT         127
155 #define MAX_TCP_SYNCNT          127
156 
157 #define TCP_SYNQ_INTERVAL       (HZ/5)  /* Period of SYNACK timer */
158 
159 #define TCP_PAWS_24DAYS (60 * 60 * 24 * 24)
160 #define TCP_PAWS_MSL    60              /* Per-host timestamps are invalidated
161                                          * after this time. It should be equal
162                                          * (or greater than) TCP_TIMEWAIT_LEN
163                                          * to provide reliability equal to one
164                                          * provided by timewait state.
165                                          */
166 #define TCP_PAWS_WINDOW 1               /* Replay window for per-host
167                                          * timestamps. It must be less than
168                                          * minimal timewait lifetime.
169                                          */
170 /*
171  *      TCP option
172  */
173 
174 #define TCPOPT_NOP              1       /* Padding */
175 #define TCPOPT_EOL              0       /* End of options */
176 #define TCPOPT_MSS              2       /* Segment size negotiating */
177 #define TCPOPT_WINDOW           3       /* Window scaling */
178 #define TCPOPT_SACK_PERM        4       /* SACK Permitted */
179 #define TCPOPT_SACK             5       /* SACK Block */
180 #define TCPOPT_TIMESTAMP        8       /* Better RTT estimations/PAWS */
181 #define TCPOPT_MD5SIG           19      /* MD5 Signature (RFC2385) */
182 #define TCPOPT_FASTOPEN         34      /* Fast open (RFC7413) */
183 #define TCPOPT_EXP              254     /* Experimental */
184 /* Magic number to be after the option value for sharing TCP
185  * experimental options. See draft-ietf-tcpm-experimental-options-00.txt
186  */
187 #define TCPOPT_FASTOPEN_MAGIC   0xF989
188 
189 /*
190  *     TCP option lengths
191  */
192 
193 #define TCPOLEN_MSS            4
194 #define TCPOLEN_WINDOW         3
195 #define TCPOLEN_SACK_PERM      2
196 #define TCPOLEN_TIMESTAMP      10
197 #define TCPOLEN_MD5SIG         18
198 #define TCPOLEN_FASTOPEN_BASE  2
199 #define TCPOLEN_EXP_FASTOPEN_BASE  4
200 
201 /* But this is what stacks really send out. */
202 #define TCPOLEN_TSTAMP_ALIGNED          12
203 #define TCPOLEN_WSCALE_ALIGNED          4
204 #define TCPOLEN_SACKPERM_ALIGNED        4
205 #define TCPOLEN_SACK_BASE               2
206 #define TCPOLEN_SACK_BASE_ALIGNED       4
207 #define TCPOLEN_SACK_PERBLOCK           8
208 #define TCPOLEN_MD5SIG_ALIGNED          20
209 #define TCPOLEN_MSS_ALIGNED             4
210 
211 /* Flags in tp->nonagle */
212 #define TCP_NAGLE_OFF           1       /* Nagle's algo is disabled */
213 #define TCP_NAGLE_CORK          2       /* Socket is corked         */
214 #define TCP_NAGLE_PUSH          4       /* Cork is overridden for already queued data */
215 
216 /* TCP thin-stream limits */
217 #define TCP_THIN_LINEAR_RETRIES 6       /* After 6 linear retries, do exp. backoff */
218 
219 /* TCP initial congestion window as per rfc6928 */
220 #define TCP_INIT_CWND           10
221 
222 /* Bit Flags for sysctl_tcp_fastopen */
223 #define TFO_CLIENT_ENABLE       1
224 #define TFO_SERVER_ENABLE       2
225 #define TFO_CLIENT_NO_COOKIE    4       /* Data in SYN w/o cookie option */
226 
227 /* Accept SYN data w/o any cookie option */
228 #define TFO_SERVER_COOKIE_NOT_REQD      0x200
229 
230 /* Force enable TFO on all listeners, i.e., not requiring the
231  * TCP_FASTOPEN socket option. SOCKOPT1/2 determine how to set max_qlen.
232  */
233 #define TFO_SERVER_WO_SOCKOPT1  0x400
234 #define TFO_SERVER_WO_SOCKOPT2  0x800
235 
236 extern struct inet_timewait_death_row tcp_death_row;
237 
238 /* sysctl variables for tcp */
239 extern int sysctl_tcp_timestamps;
240 extern int sysctl_tcp_window_scaling;
241 extern int sysctl_tcp_sack;
242 extern int sysctl_tcp_fin_timeout;
243 extern int sysctl_tcp_syn_retries;
244 extern int sysctl_tcp_synack_retries;
245 extern int sysctl_tcp_retries1;
246 extern int sysctl_tcp_retries2;
247 extern int sysctl_tcp_orphan_retries;
248 extern int sysctl_tcp_syncookies;
249 extern int sysctl_tcp_fastopen;
250 extern int sysctl_tcp_retrans_collapse;
251 extern int sysctl_tcp_stdurg;
252 extern int sysctl_tcp_rfc1337;
253 extern int sysctl_tcp_abort_on_overflow;
254 extern int sysctl_tcp_max_orphans;
255 extern int sysctl_tcp_fack;
256 extern int sysctl_tcp_reordering;
257 extern int sysctl_tcp_max_reordering;
258 extern int sysctl_tcp_dsack;
259 extern long sysctl_tcp_mem[3];
260 extern int sysctl_tcp_wmem[3];
261 extern int sysctl_tcp_rmem[3];
262 extern int sysctl_tcp_app_win;
263 extern int sysctl_tcp_adv_win_scale;
264 extern int sysctl_tcp_tw_reuse;
265 extern int sysctl_tcp_frto;
266 extern int sysctl_tcp_low_latency;
267 extern int sysctl_tcp_nometrics_save;
268 extern int sysctl_tcp_moderate_rcvbuf;
269 extern int sysctl_tcp_tso_win_divisor;
270 extern int sysctl_tcp_workaround_signed_windows;
271 extern int sysctl_tcp_slow_start_after_idle;
272 extern int sysctl_tcp_thin_linear_timeouts;
273 extern int sysctl_tcp_thin_dupack;
274 extern int sysctl_tcp_early_retrans;
275 extern int sysctl_tcp_limit_output_bytes;
276 extern int sysctl_tcp_challenge_ack_limit;
277 extern unsigned int sysctl_tcp_notsent_lowat;
278 extern int sysctl_tcp_min_tso_segs;
279 extern int sysctl_tcp_min_rtt_wlen;
280 extern int sysctl_tcp_autocorking;
281 extern int sysctl_tcp_invalid_ratelimit;
282 extern int sysctl_tcp_pacing_ss_ratio;
283 extern int sysctl_tcp_pacing_ca_ratio;
284 
285 extern atomic_long_t tcp_memory_allocated;
286 extern struct percpu_counter tcp_sockets_allocated;
287 extern int tcp_memory_pressure;
288 
289 /* optimized version of sk_under_memory_pressure() for TCP sockets */
290 static inline bool tcp_under_memory_pressure(const struct sock *sk)
291 {
292         if (mem_cgroup_sockets_enabled && sk->sk_memcg &&
293             mem_cgroup_under_socket_pressure(sk->sk_memcg))
294                 return true;
295 
296         return tcp_memory_pressure;
297 }
298 /*
299  * The next routines deal with comparing 32 bit unsigned ints
300  * and worry about wraparound (automatic with unsigned arithmetic).
301  */
302 
303 static inline bool before(__u32 seq1, __u32 seq2)
304 {
305         return (__s32)(seq1-seq2) < 0;
306 }
307 #define after(seq2, seq1)       before(seq1, seq2)
308 
309 /* is s2<=s1<=s3 ? */
310 static inline bool between(__u32 seq1, __u32 seq2, __u32 seq3)
311 {
312         return seq3 - seq2 >= seq1 - seq2;
313 }
314 
315 static inline bool tcp_out_of_memory(struct sock *sk)
316 {
317         if (sk->sk_wmem_queued > SOCK_MIN_SNDBUF &&
318             sk_memory_allocated(sk) > sk_prot_mem_limits(sk, 2))
319                 return true;
320         return false;
321 }
322 
323 void sk_forced_mem_schedule(struct sock *sk, int size);
324 
325 static inline bool tcp_too_many_orphans(struct sock *sk, int shift)
326 {
327         struct percpu_counter *ocp = sk->sk_prot->orphan_count;
328         int orphans = percpu_counter_read_positive(ocp);
329 
330         if (orphans << shift > sysctl_tcp_max_orphans) {
331                 orphans = percpu_counter_sum_positive(ocp);
332                 if (orphans << shift > sysctl_tcp_max_orphans)
333                         return true;
334         }
335         return false;
336 }
337 
338 bool tcp_check_oom(struct sock *sk, int shift);
339 
340 
341 extern struct proto tcp_prot;
342 
343 #define TCP_INC_STATS(net, field)       SNMP_INC_STATS((net)->mib.tcp_statistics, field)
344 #define TCP_INC_STATS_BH(net, field)    SNMP_INC_STATS_BH((net)->mib.tcp_statistics, field)
345 #define TCP_DEC_STATS(net, field)       SNMP_DEC_STATS((net)->mib.tcp_statistics, field)
346 #define TCP_ADD_STATS_USER(net, field, val) SNMP_ADD_STATS_USER((net)->mib.tcp_statistics, field, val)
347 #define TCP_ADD_STATS(net, field, val)  SNMP_ADD_STATS((net)->mib.tcp_statistics, field, val)
348 
349 void tcp_tasklet_init(void);
350 
351 void tcp_v4_err(struct sk_buff *skb, u32);
352 
353 void tcp_shutdown(struct sock *sk, int how);
354 
355 void tcp_v4_early_demux(struct sk_buff *skb);
356 int tcp_v4_rcv(struct sk_buff *skb);
357 
358 int tcp_v4_tw_remember_stamp(struct inet_timewait_sock *tw);
359 int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size);
360 int tcp_sendpage(struct sock *sk, struct page *page, int offset, size_t size,
361                  int flags);
362 void tcp_release_cb(struct sock *sk);
363 void tcp_wfree(struct sk_buff *skb);
364 void tcp_write_timer_handler(struct sock *sk);
365 void tcp_delack_timer_handler(struct sock *sk);
366 int tcp_ioctl(struct sock *sk, int cmd, unsigned long arg);
367 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb);
368 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
369                          const struct tcphdr *th, unsigned int len);
370 void tcp_rcv_space_adjust(struct sock *sk);
371 int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp);
372 void tcp_twsk_destructor(struct sock *sk);
373 ssize_t tcp_splice_read(struct socket *sk, loff_t *ppos,
374                         struct pipe_inode_info *pipe, size_t len,
375                         unsigned int flags);
376 
377 static inline void tcp_dec_quickack_mode(struct sock *sk,
378                                          const unsigned int pkts)
379 {
380         struct inet_connection_sock *icsk = inet_csk(sk);
381 
382         if (icsk->icsk_ack.quick) {
383                 if (pkts >= icsk->icsk_ack.quick) {
384                         icsk->icsk_ack.quick = 0;
385                         /* Leaving quickack mode we deflate ATO. */
386                         icsk->icsk_ack.ato   = TCP_ATO_MIN;
387                 } else
388                         icsk->icsk_ack.quick -= pkts;
389         }
390 }
391 
392 #define TCP_ECN_OK              1
393 #define TCP_ECN_QUEUE_CWR       2
394 #define TCP_ECN_DEMAND_CWR      4
395 #define TCP_ECN_SEEN            8
396 
397 enum tcp_tw_status {
398         TCP_TW_SUCCESS = 0,
399         TCP_TW_RST = 1,
400         TCP_TW_ACK = 2,
401         TCP_TW_SYN = 3
402 };
403 
404 
405 enum tcp_tw_status tcp_timewait_state_process(struct inet_timewait_sock *tw,
406                                               struct sk_buff *skb,
407                                               const struct tcphdr *th);
408 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
409                            struct request_sock *req, bool fastopen);
410 int tcp_child_process(struct sock *parent, struct sock *child,
411                       struct sk_buff *skb);
412 void tcp_enter_loss(struct sock *sk);
413 void tcp_clear_retrans(struct tcp_sock *tp);
414 void tcp_update_metrics(struct sock *sk);
415 void tcp_init_metrics(struct sock *sk);
416 void tcp_metrics_init(void);
417 bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst,
418                         bool paws_check, bool timestamps);
419 bool tcp_remember_stamp(struct sock *sk);
420 bool tcp_tw_remember_stamp(struct inet_timewait_sock *tw);
421 void tcp_fetch_timewait_stamp(struct sock *sk, struct dst_entry *dst);
422 void tcp_disable_fack(struct tcp_sock *tp);
423 void tcp_close(struct sock *sk, long timeout);
424 void tcp_init_sock(struct sock *sk);
425 unsigned int tcp_poll(struct file *file, struct socket *sock,
426                       struct poll_table_struct *wait);
427 int tcp_getsockopt(struct sock *sk, int level, int optname,
428                    char __user *optval, int __user *optlen);
429 int tcp_setsockopt(struct sock *sk, int level, int optname,
430                    char __user *optval, unsigned int optlen);
431 int compat_tcp_getsockopt(struct sock *sk, int level, int optname,
432                           char __user *optval, int __user *optlen);
433 int compat_tcp_setsockopt(struct sock *sk, int level, int optname,
434                           char __user *optval, unsigned int optlen);
435 void tcp_set_keepalive(struct sock *sk, int val);
436 void tcp_syn_ack_timeout(const struct request_sock *req);
437 int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
438                 int flags, int *addr_len);
439 void tcp_parse_options(const struct sk_buff *skb,
440                        struct tcp_options_received *opt_rx,
441                        int estab, struct tcp_fastopen_cookie *foc);
442 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th);
443 
444 /*
445  *      TCP v4 functions exported for the inet6 API
446  */
447 
448 void tcp_v4_send_check(struct sock *sk, struct sk_buff *skb);
449 void tcp_v4_mtu_reduced(struct sock *sk);
450 void tcp_req_err(struct sock *sk, u32 seq, bool abort);
451 int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb);
452 struct sock *tcp_create_openreq_child(const struct sock *sk,
453                                       struct request_sock *req,
454                                       struct sk_buff *skb);
455 void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst);
456 struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
457                                   struct request_sock *req,
458                                   struct dst_entry *dst,
459                                   struct request_sock *req_unhash,
460                                   bool *own_req);
461 int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb);
462 int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
463 int tcp_connect(struct sock *sk);
464 struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
465                                 struct request_sock *req,
466                                 struct tcp_fastopen_cookie *foc,
467                                 bool attach_req);
468 int tcp_disconnect(struct sock *sk, int flags);
469 
470 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb);
471 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size);
472 void inet_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb);
473 
474 /* From syncookies.c */
475 struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
476                                  struct request_sock *req,
477                                  struct dst_entry *dst);
478 int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th,
479                       u32 cookie);
480 struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb);
481 #ifdef CONFIG_SYN_COOKIES
482 
483 /* Syncookies use a monotonic timer which increments every 60 seconds.
484  * This counter is used both as a hash input and partially encoded into
485  * the cookie value.  A cookie is only validated further if the delta
486  * between the current counter value and the encoded one is less than this,
487  * i.e. a sent cookie is valid only at most for 2*60 seconds (or less if
488  * the counter advances immediately after a cookie is generated).
489  */
490 #define MAX_SYNCOOKIE_AGE       2
491 #define TCP_SYNCOOKIE_PERIOD    (60 * HZ)
492 #define TCP_SYNCOOKIE_VALID     (MAX_SYNCOOKIE_AGE * TCP_SYNCOOKIE_PERIOD)
493 
494 /* syncookies: remember time of last synqueue overflow
495  * But do not dirty this field too often (once per second is enough)
496  * It is racy as we do not hold a lock, but race is very minor.
497  */
498 static inline void tcp_synq_overflow(const struct sock *sk)
499 {
500         unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
501         unsigned long now = jiffies;
502 
503         if (time_after(now, last_overflow + HZ))
504                 tcp_sk(sk)->rx_opt.ts_recent_stamp = now;
505 }
506 
507 /* syncookies: no recent synqueue overflow on this listening socket? */
508 static inline bool tcp_synq_no_recent_overflow(const struct sock *sk)
509 {
510         unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
511 
512         return time_after(jiffies, last_overflow + TCP_SYNCOOKIE_VALID);
513 }
514 
515 static inline u32 tcp_cookie_time(void)
516 {
517         u64 val = get_jiffies_64();
518 
519         do_div(val, TCP_SYNCOOKIE_PERIOD);
520         return val;
521 }
522 
523 u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,
524                               u16 *mssp);
525 __u32 cookie_v4_init_sequence(const struct sk_buff *skb, __u16 *mss);
526 __u32 cookie_init_timestamp(struct request_sock *req);
527 bool cookie_timestamp_decode(struct tcp_options_received *opt);
528 bool cookie_ecn_ok(const struct tcp_options_received *opt,
529                    const struct net *net, const struct dst_entry *dst);
530 
531 /* From net/ipv6/syncookies.c */
532 int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th,
533                       u32 cookie);
534 struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb);
535 
536 u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
537                               const struct tcphdr *th, u16 *mssp);
538 __u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mss);
539 #endif
540 /* tcp_output.c */
541 
542 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
543                                int nonagle);
544 bool tcp_may_send_now(struct sock *sk);
545 int __tcp_retransmit_skb(struct sock *, struct sk_buff *);
546 int tcp_retransmit_skb(struct sock *, struct sk_buff *);
547 void tcp_retransmit_timer(struct sock *sk);
548 void tcp_xmit_retransmit_queue(struct sock *);
549 void tcp_simple_retransmit(struct sock *);
550 int tcp_trim_head(struct sock *, struct sk_buff *, u32);
551 int tcp_fragment(struct sock *, struct sk_buff *, u32, unsigned int, gfp_t);
552 
553 void tcp_send_probe0(struct sock *);
554 void tcp_send_partial(struct sock *);
555 int tcp_write_wakeup(struct sock *, int mib);
556 void tcp_send_fin(struct sock *sk);
557 void tcp_send_active_reset(struct sock *sk, gfp_t priority);
558 int tcp_send_synack(struct sock *);
559 void tcp_push_one(struct sock *, unsigned int mss_now);
560 void tcp_send_ack(struct sock *sk);
561 void tcp_send_delayed_ack(struct sock *sk);
562 void tcp_send_loss_probe(struct sock *sk);
563 bool tcp_schedule_loss_probe(struct sock *sk);
564 
565 /* tcp_input.c */
566 void tcp_resume_early_retransmit(struct sock *sk);
567 void tcp_rearm_rto(struct sock *sk);
568 void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req);
569 void tcp_reset(struct sock *sk);
570 void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb);
571 
572 /* tcp_timer.c */
573 void tcp_init_xmit_timers(struct sock *);
574 static inline void tcp_clear_xmit_timers(struct sock *sk)
575 {
576         inet_csk_clear_xmit_timers(sk);
577 }
578 
579 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu);
580 unsigned int tcp_current_mss(struct sock *sk);
581 
582 /* Bound MSS / TSO packet size with the half of the window */
583 static inline int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
584 {
585         int cutoff;
586 
587         /* When peer uses tiny windows, there is no use in packetizing
588          * to sub-MSS pieces for the sake of SWS or making sure there
589          * are enough packets in the pipe for fast recovery.
590          *
591          * On the other hand, for extremely large MSS devices, handling
592          * smaller than MSS windows in this way does make sense.
593          */
594         if (tp->max_window >= 512)
595                 cutoff = (tp->max_window >> 1);
596         else
597                 cutoff = tp->max_window;
598 
599         if (cutoff && pktsize > cutoff)
600                 return max_t(int, cutoff, 68U - tp->tcp_header_len);
601         else
602                 return pktsize;
603 }
604 
605 /* tcp.c */
606 void tcp_get_info(struct sock *, struct tcp_info *);
607 
608 /* Read 'sendfile()'-style from a TCP socket */
609 typedef int (*sk_read_actor_t)(read_descriptor_t *, struct sk_buff *,
610                                 unsigned int, size_t);
611 int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
612                   sk_read_actor_t recv_actor);
613 
614 void tcp_initialize_rcv_mss(struct sock *sk);
615 
616 int tcp_mtu_to_mss(struct sock *sk, int pmtu);
617 int tcp_mss_to_mtu(struct sock *sk, int mss);
618 void tcp_mtup_init(struct sock *sk);
619 void tcp_init_buffer_space(struct sock *sk);
620 
621 static inline void tcp_bound_rto(const struct sock *sk)
622 {
623         if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
624                 inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
625 }
626 
627 static inline u32 __tcp_set_rto(const struct tcp_sock *tp)
628 {
629         return usecs_to_jiffies((tp->srtt_us >> 3) + tp->rttvar_us);
630 }
631 
632 static inline void __tcp_fast_path_on(struct tcp_sock *tp, u32 snd_wnd)
633 {
634         tp->pred_flags = htonl((tp->tcp_header_len << 26) |
635                                ntohl(TCP_FLAG_ACK) |
636                                snd_wnd);
637 }
638 
639 static inline void tcp_fast_path_on(struct tcp_sock *tp)
640 {
641         __tcp_fast_path_on(tp, tp->snd_wnd >> tp->rx_opt.snd_wscale);
642 }
643 
644 static inline void tcp_fast_path_check(struct sock *sk)
645 {
646         struct tcp_sock *tp = tcp_sk(sk);
647 
648         if (skb_queue_empty(&tp->out_of_order_queue) &&
649             tp->rcv_wnd &&
650             atomic_read(&sk->sk_rmem_alloc) < sk->sk_rcvbuf &&
651             !tp->urg_data)
652                 tcp_fast_path_on(tp);
653 }
654 
655 /* Compute the actual rto_min value */
656 static inline u32 tcp_rto_min(struct sock *sk)
657 {
658         const struct dst_entry *dst = __sk_dst_get(sk);
659         u32 rto_min = TCP_RTO_MIN;
660 
661         if (dst && dst_metric_locked(dst, RTAX_RTO_MIN))
662                 rto_min = dst_metric_rtt(dst, RTAX_RTO_MIN);
663         return rto_min;
664 }
665 
666 static inline u32 tcp_rto_min_us(struct sock *sk)
667 {
668         return jiffies_to_usecs(tcp_rto_min(sk));
669 }
670 
671 static inline bool tcp_ca_dst_locked(const struct dst_entry *dst)
672 {
673         return dst_metric_locked(dst, RTAX_CC_ALGO);
674 }
675 
676 /* Minimum RTT in usec. ~0 means not available. */
677 static inline u32 tcp_min_rtt(const struct tcp_sock *tp)
678 {
679         return tp->rtt_min[0].rtt;
680 }
681 
682 /* Compute the actual receive window we are currently advertising.
683  * Rcv_nxt can be after the window if our peer push more data
684  * than the offered window.
685  */
686 static inline u32 tcp_receive_window(const struct tcp_sock *tp)
687 {
688         s32 win = tp->rcv_wup + tp->rcv_wnd - tp->rcv_nxt;
689 
690         if (win < 0)
691                 win = 0;
692         return (u32) win;
693 }
694 
695 /* Choose a new window, without checks for shrinking, and without
696  * scaling applied to the result.  The caller does these things
697  * if necessary.  This is a "raw" window selection.
698  */
699 u32 __tcp_select_window(struct sock *sk);
700 
701 void tcp_send_window_probe(struct sock *sk);
702 
703 /* TCP timestamps are only 32-bits, this causes a slight
704  * complication on 64-bit systems since we store a snapshot
705  * of jiffies in the buffer control blocks below.  We decided
706  * to use only the low 32-bits of jiffies and hide the ugly
707  * casts with the following macro.
708  */
709 #define tcp_time_stamp          ((__u32)(jiffies))
710 
711 static inline u32 tcp_skb_timestamp(const struct sk_buff *skb)
712 {
713         return skb->skb_mstamp.stamp_jiffies;
714 }
715 
716 
717 #define tcp_flag_byte(th) (((u_int8_t *)th)[13])
718 
719 #define TCPHDR_FIN 0x01
720 #define TCPHDR_SYN 0x02
721 #define TCPHDR_RST 0x04
722 #define TCPHDR_PSH 0x08
723 #define TCPHDR_ACK 0x10
724 #define TCPHDR_URG 0x20
725 #define TCPHDR_ECE 0x40
726 #define TCPHDR_CWR 0x80
727 
728 #define TCPHDR_SYN_ECN  (TCPHDR_SYN | TCPHDR_ECE | TCPHDR_CWR)
729 
730 /* This is what the send packet queuing engine uses to pass
731  * TCP per-packet control information to the transmission code.
732  * We also store the host-order sequence numbers in here too.
733  * This is 44 bytes if IPV6 is enabled.
734  * If this grows please adjust skbuff.h:skbuff->cb[xxx] size appropriately.
735  */
736 struct tcp_skb_cb {
737         __u32           seq;            /* Starting sequence number     */
738         __u32           end_seq;        /* SEQ + FIN + SYN + datalen    */
739         union {
740                 /* Note : tcp_tw_isn is used in input path only
741                  *        (isn chosen by tcp_timewait_state_process())
742                  *
743                  *        tcp_gso_segs/size are used in write queue only,
744                  *        cf tcp_skb_pcount()/tcp_skb_mss()
745                  */
746                 __u32           tcp_tw_isn;
747                 struct {
748                         u16     tcp_gso_segs;
749                         u16     tcp_gso_size;
750                 };
751         };
752         __u8            tcp_flags;      /* TCP header flags. (tcp[13])  */
753 
754         __u8            sacked;         /* State flags for SACK/FACK.   */
755 #define TCPCB_SACKED_ACKED      0x01    /* SKB ACK'd by a SACK block    */
756 #define TCPCB_SACKED_RETRANS    0x02    /* SKB retransmitted            */
757 #define TCPCB_LOST              0x04    /* SKB is lost                  */
758 #define TCPCB_TAGBITS           0x07    /* All tag bits                 */
759 #define TCPCB_REPAIRED          0x10    /* SKB repaired (no skb_mstamp) */
760 #define TCPCB_EVER_RETRANS      0x80    /* Ever retransmitted frame     */
761 #define TCPCB_RETRANS           (TCPCB_SACKED_RETRANS|TCPCB_EVER_RETRANS| \
762                                 TCPCB_REPAIRED)
763 
764         __u8            ip_dsfield;     /* IPv4 tos or IPv6 dsfield     */
765         /* 1 byte hole */
766         __u32           ack_seq;        /* Sequence number ACK'd        */
767         union {
768                 struct inet_skb_parm    h4;
769 #if IS_ENABLED(CONFIG_IPV6)
770                 struct inet6_skb_parm   h6;
771 #endif
772         } header;       /* For incoming frames          */
773 };
774 
775 #define TCP_SKB_CB(__skb)       ((struct tcp_skb_cb *)&((__skb)->cb[0]))
776 
777 
778 #if IS_ENABLED(CONFIG_IPV6)
779 /* This is the variant of inet6_iif() that must be used by TCP,
780  * as TCP moves IP6CB into a different location in skb->cb[]
781  */
782 static inline int tcp_v6_iif(const struct sk_buff *skb)
783 {
784         return TCP_SKB_CB(skb)->header.h6.iif;
785 }
786 #endif
787 
788 /* Due to TSO, an SKB can be composed of multiple actual
789  * packets.  To keep these tracked properly, we use this.
790  */
791 static inline int tcp_skb_pcount(const struct sk_buff *skb)
792 {
793         return TCP_SKB_CB(skb)->tcp_gso_segs;
794 }
795 
796 static inline void tcp_skb_pcount_set(struct sk_buff *skb, int segs)
797 {
798         TCP_SKB_CB(skb)->tcp_gso_segs = segs;
799 }
800 
801 static inline void tcp_skb_pcount_add(struct sk_buff *skb, int segs)
802 {
803         TCP_SKB_CB(skb)->tcp_gso_segs += segs;
804 }
805 
806 /* This is valid iff skb is in write queue and tcp_skb_pcount() > 1. */
807 static inline int tcp_skb_mss(const struct sk_buff *skb)
808 {
809         return TCP_SKB_CB(skb)->tcp_gso_size;
810 }
811 
812 /* Events passed to congestion control interface */
813 enum tcp_ca_event {
814         CA_EVENT_TX_START,      /* first transmit when no packets in flight */
815         CA_EVENT_CWND_RESTART,  /* congestion window restart */
816         CA_EVENT_COMPLETE_CWR,  /* end of congestion recovery */
817         CA_EVENT_LOSS,          /* loss timeout */
818         CA_EVENT_ECN_NO_CE,     /* ECT set, but not CE marked */
819         CA_EVENT_ECN_IS_CE,     /* received CE marked IP packet */
820         CA_EVENT_DELAYED_ACK,   /* Delayed ack is sent */
821         CA_EVENT_NON_DELAYED_ACK,
822 };
823 
824 /* Information about inbound ACK, passed to cong_ops->in_ack_event() */
825 enum tcp_ca_ack_event_flags {
826         CA_ACK_SLOWPATH         = (1 << 0),     /* In slow path processing */
827         CA_ACK_WIN_UPDATE       = (1 << 1),     /* ACK updated window */
828         CA_ACK_ECE              = (1 << 2),     /* ECE bit is set on ack */
829 };
830 
831 /*
832  * Interface for adding new TCP congestion control handlers
833  */
834 #define TCP_CA_NAME_MAX 16
835 #define TCP_CA_MAX      128
836 #define TCP_CA_BUF_MAX  (TCP_CA_NAME_MAX*TCP_CA_MAX)
837 
838 #define TCP_CA_UNSPEC   0
839 
840 /* Algorithm can be set on socket without CAP_NET_ADMIN privileges */
841 #define TCP_CONG_NON_RESTRICTED 0x1
842 /* Requires ECN/ECT set on all packets */
843 #define TCP_CONG_NEEDS_ECN      0x2
844 
845 union tcp_cc_info;
846 
847 struct tcp_congestion_ops {
848         struct list_head        list;
849         u32 key;
850         u32 flags;
851 
852         /* initialize private data (optional) */
853         void (*init)(struct sock *sk);
854         /* cleanup private data  (optional) */
855         void (*release)(struct sock *sk);
856 
857         /* return slow start threshold (required) */
858         u32 (*ssthresh)(struct sock *sk);
859         /* do new cwnd calculation (required) */
860         void (*cong_avoid)(struct sock *sk, u32 ack, u32 acked);
861         /* call before changing ca_state (optional) */
862         void (*set_state)(struct sock *sk, u8 new_state);
863         /* call when cwnd event occurs (optional) */
864         void (*cwnd_event)(struct sock *sk, enum tcp_ca_event ev);
865         /* call when ack arrives (optional) */
866         void (*in_ack_event)(struct sock *sk, u32 flags);
867         /* new value of cwnd after loss (optional) */
868         u32  (*undo_cwnd)(struct sock *sk);
869         /* hook for packet ack accounting (optional) */
870         void (*pkts_acked)(struct sock *sk, u32 num_acked, s32 rtt_us);
871         /* get info for inet_diag (optional) */
872         size_t (*get_info)(struct sock *sk, u32 ext, int *attr,
873                            union tcp_cc_info *info);
874 
875         char            name[TCP_CA_NAME_MAX];
876         struct module   *owner;
877 };
878 
879 int tcp_register_congestion_control(struct tcp_congestion_ops *type);
880 void tcp_unregister_congestion_control(struct tcp_congestion_ops *type);
881 
882 void tcp_assign_congestion_control(struct sock *sk);
883 void tcp_init_congestion_control(struct sock *sk);
884 void tcp_cleanup_congestion_control(struct sock *sk);
885 int tcp_set_default_congestion_control(const char *name);
886 void tcp_get_default_congestion_control(char *name);
887 void tcp_get_available_congestion_control(char *buf, size_t len);
888 void tcp_get_allowed_congestion_control(char *buf, size_t len);
889 int tcp_set_allowed_congestion_control(char *allowed);
890 int tcp_set_congestion_control(struct sock *sk, const char *name);
891 u32 tcp_slow_start(struct tcp_sock *tp, u32 acked);
892 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked);
893 
894 u32 tcp_reno_ssthresh(struct sock *sk);
895 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked);
896 extern struct tcp_congestion_ops tcp_reno;
897 
898 struct tcp_congestion_ops *tcp_ca_find_key(u32 key);
899 u32 tcp_ca_get_key_by_name(const char *name, bool *ecn_ca);
900 #ifdef CONFIG_INET
901 char *tcp_ca_get_name_by_key(u32 key, char *buffer);
902 #else
903 static inline char *tcp_ca_get_name_by_key(u32 key, char *buffer)
904 {
905         return NULL;
906 }
907 #endif
908 
909 static inline bool tcp_ca_needs_ecn(const struct sock *sk)
910 {
911         const struct inet_connection_sock *icsk = inet_csk(sk);
912 
913         return icsk->icsk_ca_ops->flags & TCP_CONG_NEEDS_ECN;
914 }
915 
916 static inline void tcp_set_ca_state(struct sock *sk, const u8 ca_state)
917 {
918         struct inet_connection_sock *icsk = inet_csk(sk);
919 
920         if (icsk->icsk_ca_ops->set_state)
921                 icsk->icsk_ca_ops->set_state(sk, ca_state);
922         icsk->icsk_ca_state = ca_state;
923 }
924 
925 static inline void tcp_ca_event(struct sock *sk, const enum tcp_ca_event event)
926 {
927         const struct inet_connection_sock *icsk = inet_csk(sk);
928 
929         if (icsk->icsk_ca_ops->cwnd_event)
930                 icsk->icsk_ca_ops->cwnd_event(sk, event);
931 }
932 
933 /* These functions determine how the current flow behaves in respect of SACK
934  * handling. SACK is negotiated with the peer, and therefore it can vary
935  * between different flows.
936  *
937  * tcp_is_sack - SACK enabled
938  * tcp_is_reno - No SACK
939  * tcp_is_fack - FACK enabled, implies SACK enabled
940  */
941 static inline int tcp_is_sack(const struct tcp_sock *tp)
942 {
943         return tp->rx_opt.sack_ok;
944 }
945 
946 static inline bool tcp_is_reno(const struct tcp_sock *tp)
947 {
948         return !tcp_is_sack(tp);
949 }
950 
951 static inline bool tcp_is_fack(const struct tcp_sock *tp)
952 {
953         return tp->rx_opt.sack_ok & TCP_FACK_ENABLED;
954 }
955 
956 static inline void tcp_enable_fack(struct tcp_sock *tp)
957 {
958         tp->rx_opt.sack_ok |= TCP_FACK_ENABLED;
959 }
960 
961 /* TCP early-retransmit (ER) is similar to but more conservative than
962  * the thin-dupack feature.  Enable ER only if thin-dupack is disabled.
963  */
964 static inline void tcp_enable_early_retrans(struct tcp_sock *tp)
965 {
966         tp->do_early_retrans = sysctl_tcp_early_retrans &&
967                 sysctl_tcp_early_retrans < 4 && !sysctl_tcp_thin_dupack &&
968                 sysctl_tcp_reordering == 3;
969 }
970 
971 static inline void tcp_disable_early_retrans(struct tcp_sock *tp)
972 {
973         tp->do_early_retrans = 0;
974 }
975 
976 static inline unsigned int tcp_left_out(const struct tcp_sock *tp)
977 {
978         return tp->sacked_out + tp->lost_out;
979 }
980 
981 /* This determines how many packets are "in the network" to the best
982  * of our knowledge.  In many cases it is conservative, but where
983  * detailed information is available from the receiver (via SACK
984  * blocks etc.) we can make more aggressive calculations.
985  *
986  * Use this for decisions involving congestion control, use just
987  * tp->packets_out to determine if the send queue is empty or not.
988  *
989  * Read this equation as:
990  *
991  *      "Packets sent once on transmission queue" MINUS
992  *      "Packets left network, but not honestly ACKed yet" PLUS
993  *      "Packets fast retransmitted"
994  */
995 static inline unsigned int tcp_packets_in_flight(const struct tcp_sock *tp)
996 {
997         return tp->packets_out - tcp_left_out(tp) + tp->retrans_out;
998 }
999 
1000 #define TCP_INFINITE_SSTHRESH   0x7fffffff
1001 
1002 static inline bool tcp_in_slow_start(const struct tcp_sock *tp)
1003 {
1004         return tp->snd_cwnd < tp->snd_ssthresh;
1005 }
1006 
1007 static inline bool tcp_in_initial_slowstart(const struct tcp_sock *tp)
1008 {
1009         return tp->snd_ssthresh >= TCP_INFINITE_SSTHRESH;
1010 }
1011 
1012 static inline bool tcp_in_cwnd_reduction(const struct sock *sk)
1013 {
1014         return (TCPF_CA_CWR | TCPF_CA_Recovery) &
1015                (1 << inet_csk(sk)->icsk_ca_state);
1016 }
1017 
1018 /* If cwnd > ssthresh, we may raise ssthresh to be half-way to cwnd.
1019  * The exception is cwnd reduction phase, when cwnd is decreasing towards
1020  * ssthresh.
1021  */
1022 static inline __u32 tcp_current_ssthresh(const struct sock *sk)
1023 {
1024         const struct tcp_sock *tp = tcp_sk(sk);
1025 
1026         if (tcp_in_cwnd_reduction(sk))
1027                 return tp->snd_ssthresh;
1028         else
1029                 return max(tp->snd_ssthresh,
1030                            ((tp->snd_cwnd >> 1) +
1031                             (tp->snd_cwnd >> 2)));
1032 }
1033 
1034 /* Use define here intentionally to get WARN_ON location shown at the caller */
1035 #define tcp_verify_left_out(tp) WARN_ON(tcp_left_out(tp) > tp->packets_out)
1036 
1037 void tcp_enter_cwr(struct sock *sk);
1038 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst);
1039 
1040 /* The maximum number of MSS of available cwnd for which TSO defers
1041  * sending if not using sysctl_tcp_tso_win_divisor.
1042  */
1043 static inline __u32 tcp_max_tso_deferred_mss(const struct tcp_sock *tp)
1044 {
1045         return 3;
1046 }
1047 
1048 /* Slow start with delack produces 3 packets of burst, so that
1049  * it is safe "de facto".  This will be the default - same as
1050  * the default reordering threshold - but if reordering increases,
1051  * we must be able to allow cwnd to burst at least this much in order
1052  * to not pull it back when holes are filled.
1053  */
1054 static __inline__ __u32 tcp_max_burst(const struct tcp_sock *tp)
1055 {
1056         return tp->reordering;
1057 }
1058 
1059 /* Returns end sequence number of the receiver's advertised window */
1060 static inline u32 tcp_wnd_end(const struct tcp_sock *tp)
1061 {
1062         return tp->snd_una + tp->snd_wnd;
1063 }
1064 
1065 /* We follow the spirit of RFC2861 to validate cwnd but implement a more
1066  * flexible approach. The RFC suggests cwnd should not be raised unless
1067  * it was fully used previously. And that's exactly what we do in
1068  * congestion avoidance mode. But in slow start we allow cwnd to grow
1069  * as long as the application has used half the cwnd.
1070  * Example :
1071  *    cwnd is 10 (IW10), but application sends 9 frames.
1072  *    We allow cwnd to reach 18 when all frames are ACKed.
1073  * This check is safe because it's as aggressive as slow start which already
1074  * risks 100% overshoot. The advantage is that we discourage application to
1075  * either send more filler packets or data to artificially blow up the cwnd
1076  * usage, and allow application-limited process to probe bw more aggressively.
1077  */
1078 static inline bool tcp_is_cwnd_limited(const struct sock *sk)
1079 {
1080         const struct tcp_sock *tp = tcp_sk(sk);
1081 
1082         /* If in slow start, ensure cwnd grows to twice what was ACKed. */
1083         if (tcp_in_slow_start(tp))
1084                 return tp->snd_cwnd < 2 * tp->max_packets_out;
1085 
1086         return tp->is_cwnd_limited;
1087 }
1088 
1089 /* Something is really bad, we could not queue an additional packet,
1090  * because qdisc is full or receiver sent a 0 window.
1091  * We do not want to add fuel to the fire, or abort too early,
1092  * so make sure the timer we arm now is at least 200ms in the future,
1093  * regardless of current icsk_rto value (as it could be ~2ms)
1094  */
1095 static inline unsigned long tcp_probe0_base(const struct sock *sk)
1096 {
1097         return max_t(unsigned long, inet_csk(sk)->icsk_rto, TCP_RTO_MIN);
1098 }
1099 
1100 /* Variant of inet_csk_rto_backoff() used for zero window probes */
1101 static inline unsigned long tcp_probe0_when(const struct sock *sk,
1102                                             unsigned long max_when)
1103 {
1104         u64 when = (u64)tcp_probe0_base(sk) << inet_csk(sk)->icsk_backoff;
1105 
1106         return (unsigned long)min_t(u64, when, max_when);
1107 }
1108 
1109 static inline void tcp_check_probe_timer(struct sock *sk)
1110 {
1111         if (!tcp_sk(sk)->packets_out && !inet_csk(sk)->icsk_pending)
1112                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
1113                                           tcp_probe0_base(sk), TCP_RTO_MAX);
1114 }
1115 
1116 static inline void tcp_init_wl(struct tcp_sock *tp, u32 seq)
1117 {
1118         tp->snd_wl1 = seq;
1119 }
1120 
1121 static inline void tcp_update_wl(struct tcp_sock *tp, u32 seq)
1122 {
1123         tp->snd_wl1 = seq;
1124 }
1125 
1126 /*
1127  * Calculate(/check) TCP checksum
1128  */
1129 static inline __sum16 tcp_v4_check(int len, __be32 saddr,
1130                                    __be32 daddr, __wsum base)
1131 {
1132         return csum_tcpudp_magic(saddr,daddr,len,IPPROTO_TCP,base);
1133 }
1134 
1135 static inline __sum16 __tcp_checksum_complete(struct sk_buff *skb)
1136 {
1137         return __skb_checksum_complete(skb);
1138 }
1139 
1140 static inline bool tcp_checksum_complete(struct sk_buff *skb)
1141 {
1142         return !skb_csum_unnecessary(skb) &&
1143                 __tcp_checksum_complete(skb);
1144 }
1145 
1146 /* Prequeue for VJ style copy to user, combined with checksumming. */
1147 
1148 static inline void tcp_prequeue_init(struct tcp_sock *tp)
1149 {
1150         tp->ucopy.task = NULL;
1151         tp->ucopy.len = 0;
1152         tp->ucopy.memory = 0;
1153         skb_queue_head_init(&tp->ucopy.prequeue);
1154 }
1155 
1156 bool tcp_prequeue(struct sock *sk, struct sk_buff *skb);
1157 
1158 #undef STATE_TRACE
1159 
1160 #ifdef STATE_TRACE
1161 static const char *statename[]={
1162         "Unused","Established","Syn Sent","Syn Recv",
1163         "Fin Wait 1","Fin Wait 2","Time Wait", "Close",
1164         "Close Wait","Last ACK","Listen","Closing"
1165 };
1166 #endif
1167 void tcp_set_state(struct sock *sk, int state);
1168 
1169 void tcp_done(struct sock *sk);
1170 
1171 int tcp_abort(struct sock *sk, int err);
1172 
1173 static inline void tcp_sack_reset(struct tcp_options_received *rx_opt)
1174 {
1175         rx_opt->dsack = 0;
1176         rx_opt->num_sacks = 0;
1177 }
1178 
1179 u32 tcp_default_init_rwnd(u32 mss);
1180 void tcp_cwnd_restart(struct sock *sk, s32 delta);
1181 
1182 static inline void tcp_slow_start_after_idle_check(struct sock *sk)
1183 {
1184         struct tcp_sock *tp = tcp_sk(sk);
1185         s32 delta;
1186 
1187         if (!sysctl_tcp_slow_start_after_idle || tp->packets_out)
1188                 return;
1189         delta = tcp_time_stamp - tp->lsndtime;
1190         if (delta > inet_csk(sk)->icsk_rto)
1191                 tcp_cwnd_restart(sk, delta);
1192 }
1193 
1194 /* Determine a window scaling and initial window to offer. */
1195 void tcp_select_initial_window(int __space, __u32 mss, __u32 *rcv_wnd,
1196                                __u32 *window_clamp, int wscale_ok,
1197                                __u8 *rcv_wscale, __u32 init_rcv_wnd);
1198 
1199 static inline int tcp_win_from_space(int space)
1200 {
1201         return sysctl_tcp_adv_win_scale<=0 ?
1202                 (space>>(-sysctl_tcp_adv_win_scale)) :
1203                 space - (space>>sysctl_tcp_adv_win_scale);
1204 }
1205 
1206 /* Note: caller must be prepared to deal with negative returns */
1207 static inline int tcp_space(const struct sock *sk)
1208 {
1209         return tcp_win_from_space(sk->sk_rcvbuf -
1210                                   atomic_read(&sk->sk_rmem_alloc));
1211 }
1212 
1213 static inline int tcp_full_space(const struct sock *sk)
1214 {
1215         return tcp_win_from_space(sk->sk_rcvbuf);
1216 }
1217 
1218 extern void tcp_openreq_init_rwin(struct request_sock *req,
1219                                   const struct sock *sk_listener,
1220                                   const struct dst_entry *dst);
1221 
1222 void tcp_enter_memory_pressure(struct sock *sk);
1223 
1224 static inline int keepalive_intvl_when(const struct tcp_sock *tp)
1225 {
1226         struct net *net = sock_net((struct sock *)tp);
1227 
1228         return tp->keepalive_intvl ? : net->ipv4.sysctl_tcp_keepalive_intvl;
1229 }
1230 
1231 static inline int keepalive_time_when(const struct tcp_sock *tp)
1232 {
1233         struct net *net = sock_net((struct sock *)tp);
1234 
1235         return tp->keepalive_time ? : net->ipv4.sysctl_tcp_keepalive_time;
1236 }
1237 
1238 static inline int keepalive_probes(const struct tcp_sock *tp)
1239 {
1240         struct net *net = sock_net((struct sock *)tp);
1241 
1242         return tp->keepalive_probes ? : net->ipv4.sysctl_tcp_keepalive_probes;
1243 }
1244 
1245 static inline u32 keepalive_time_elapsed(const struct tcp_sock *tp)
1246 {
1247         const struct inet_connection_sock *icsk = &tp->inet_conn;
1248 
1249         return min_t(u32, tcp_time_stamp - icsk->icsk_ack.lrcvtime,
1250                           tcp_time_stamp - tp->rcv_tstamp);
1251 }
1252 
1253 static inline int tcp_fin_time(const struct sock *sk)
1254 {
1255         int fin_timeout = tcp_sk(sk)->linger2 ? : sysctl_tcp_fin_timeout;
1256         const int rto = inet_csk(sk)->icsk_rto;
1257 
1258         if (fin_timeout < (rto << 2) - (rto >> 1))
1259                 fin_timeout = (rto << 2) - (rto >> 1);
1260 
1261         return fin_timeout;
1262 }
1263 
1264 static inline bool tcp_paws_check(const struct tcp_options_received *rx_opt,
1265                                   int paws_win)
1266 {
1267         if ((s32)(rx_opt->ts_recent - rx_opt->rcv_tsval) <= paws_win)
1268                 return true;
1269         if (unlikely(get_seconds() >= rx_opt->ts_recent_stamp + TCP_PAWS_24DAYS))
1270                 return true;
1271         /*
1272          * Some OSes send SYN and SYNACK messages with tsval=0 tsecr=0,
1273          * then following tcp messages have valid values. Ignore 0 value,
1274          * or else 'negative' tsval might forbid us to accept their packets.
1275          */
1276         if (!rx_opt->ts_recent)
1277                 return true;
1278         return false;
1279 }
1280 
1281 static inline bool tcp_paws_reject(const struct tcp_options_received *rx_opt,
1282                                    int rst)
1283 {
1284         if (tcp_paws_check(rx_opt, 0))
1285                 return false;
1286 
1287         /* RST segments are not recommended to carry timestamp,
1288            and, if they do, it is recommended to ignore PAWS because
1289            "their cleanup function should take precedence over timestamps."
1290            Certainly, it is mistake. It is necessary to understand the reasons
1291            of this constraint to relax it: if peer reboots, clock may go
1292            out-of-sync and half-open connections will not be reset.
1293            Actually, the problem would be not existing if all
1294            the implementations followed draft about maintaining clock
1295            via reboots. Linux-2.2 DOES NOT!
1296 
1297            However, we can relax time bounds for RST segments to MSL.
1298          */
1299         if (rst && get_seconds() >= rx_opt->ts_recent_stamp + TCP_PAWS_MSL)
1300                 return false;
1301         return true;
1302 }
1303 
1304 bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
1305                           int mib_idx, u32 *last_oow_ack_time);
1306 
1307 static inline void tcp_mib_init(struct net *net)
1308 {
1309         /* See RFC 2012 */
1310         TCP_ADD_STATS_USER(net, TCP_MIB_RTOALGORITHM, 1);
1311         TCP_ADD_STATS_USER(net, TCP_MIB_RTOMIN, TCP_RTO_MIN*1000/HZ);
1312         TCP_ADD_STATS_USER(net, TCP_MIB_RTOMAX, TCP_RTO_MAX*1000/HZ);
1313         TCP_ADD_STATS_USER(net, TCP_MIB_MAXCONN, -1);
1314 }
1315 
1316 /* from STCP */
1317 static inline void tcp_clear_retrans_hints_partial(struct tcp_sock *tp)
1318 {
1319         tp->lost_skb_hint = NULL;
1320 }
1321 
1322 static inline void tcp_clear_all_retrans_hints(struct tcp_sock *tp)
1323 {
1324         tcp_clear_retrans_hints_partial(tp);
1325         tp->retransmit_skb_hint = NULL;
1326 }
1327 
1328 /* MD5 Signature */
1329 struct crypto_hash;
1330 
1331 union tcp_md5_addr {
1332         struct in_addr  a4;
1333 #if IS_ENABLED(CONFIG_IPV6)
1334         struct in6_addr a6;
1335 #endif
1336 };
1337 
1338 /* - key database */
1339 struct tcp_md5sig_key {
1340         struct hlist_node       node;
1341         u8                      keylen;
1342         u8                      family; /* AF_INET or AF_INET6 */
1343         union tcp_md5_addr      addr;
1344         u8                      key[TCP_MD5SIG_MAXKEYLEN];
1345         struct rcu_head         rcu;
1346 };
1347 
1348 /* - sock block */
1349 struct tcp_md5sig_info {
1350         struct hlist_head       head;
1351         struct rcu_head         rcu;
1352 };
1353 
1354 /* - pseudo header */
1355 struct tcp4_pseudohdr {
1356         __be32          saddr;
1357         __be32          daddr;
1358         __u8            pad;
1359         __u8            protocol;
1360         __be16          len;
1361 };
1362 
1363 struct tcp6_pseudohdr {
1364         struct in6_addr saddr;
1365         struct in6_addr daddr;
1366         __be32          len;
1367         __be32          protocol;       /* including padding */
1368 };
1369 
1370 union tcp_md5sum_block {
1371         struct tcp4_pseudohdr ip4;
1372 #if IS_ENABLED(CONFIG_IPV6)
1373         struct tcp6_pseudohdr ip6;
1374 #endif
1375 };
1376 
1377 /* - pool: digest algorithm, hash description and scratch buffer */
1378 struct tcp_md5sig_pool {
1379         struct hash_desc        md5_desc;
1380         union tcp_md5sum_block  md5_blk;
1381 };
1382 
1383 /* - functions */
1384 int tcp_v4_md5_hash_skb(char *md5_hash, const struct tcp_md5sig_key *key,
1385                         const struct sock *sk, const struct sk_buff *skb);
1386 int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
1387                    int family, const u8 *newkey, u8 newkeylen, gfp_t gfp);
1388 int tcp_md5_do_del(struct sock *sk, const union tcp_md5_addr *addr,
1389                    int family);
1390 struct tcp_md5sig_key *tcp_v4_md5_lookup(const struct sock *sk,
1391                                          const struct sock *addr_sk);
1392 
1393 #ifdef CONFIG_TCP_MD5SIG
1394 struct tcp_md5sig_key *tcp_md5_do_lookup(const struct sock *sk,
1395                                          const union tcp_md5_addr *addr,
1396                                          int family);
1397 #define tcp_twsk_md5_key(twsk)  ((twsk)->tw_md5_key)
1398 #else
1399 static inline struct tcp_md5sig_key *tcp_md5_do_lookup(const struct sock *sk,
1400                                          const union tcp_md5_addr *addr,
1401                                          int family)
1402 {
1403         return NULL;
1404 }
1405 #define tcp_twsk_md5_key(twsk)  NULL
1406 #endif
1407 
1408 bool tcp_alloc_md5sig_pool(void);
1409 
1410 struct tcp_md5sig_pool *tcp_get_md5sig_pool(void);
1411 static inline void tcp_put_md5sig_pool(void)
1412 {
1413         local_bh_enable();
1414 }
1415 
1416 int tcp_md5_hash_header(struct tcp_md5sig_pool *, const struct tcphdr *);
1417 int tcp_md5_hash_skb_data(struct tcp_md5sig_pool *, const struct sk_buff *,
1418                           unsigned int header_len);
1419 int tcp_md5_hash_key(struct tcp_md5sig_pool *hp,
1420                      const struct tcp_md5sig_key *key);
1421 
1422 /* From tcp_fastopen.c */
1423 void tcp_fastopen_cache_get(struct sock *sk, u16 *mss,
1424                             struct tcp_fastopen_cookie *cookie, int *syn_loss,
1425                             unsigned long *last_syn_loss);
1426 void tcp_fastopen_cache_set(struct sock *sk, u16 mss,
1427                             struct tcp_fastopen_cookie *cookie, bool syn_lost,
1428                             u16 try_exp);
1429 struct tcp_fastopen_request {
1430         /* Fast Open cookie. Size 0 means a cookie request */
1431         struct tcp_fastopen_cookie      cookie;
1432         struct msghdr                   *data;  /* data in MSG_FASTOPEN */
1433         size_t                          size;
1434         int                             copied; /* queued in tcp_connect() */
1435 };
1436 void tcp_free_fastopen_req(struct tcp_sock *tp);
1437 
1438 extern struct tcp_fastopen_context __rcu *tcp_fastopen_ctx;
1439 int tcp_fastopen_reset_cipher(void *key, unsigned int len);
1440 struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
1441                               struct request_sock *req,
1442                               struct tcp_fastopen_cookie *foc,
1443                               struct dst_entry *dst);
1444 void tcp_fastopen_init_key_once(bool publish);
1445 #define TCP_FASTOPEN_KEY_LENGTH 16
1446 
1447 /* Fastopen key context */
1448 struct tcp_fastopen_context {
1449         struct crypto_cipher    *tfm;
1450         __u8                    key[TCP_FASTOPEN_KEY_LENGTH];
1451         struct rcu_head         rcu;
1452 };
1453 
1454 /* write queue abstraction */
1455 static inline void tcp_write_queue_purge(struct sock *sk)
1456 {
1457         struct sk_buff *skb;
1458 
1459         while ((skb = __skb_dequeue(&sk->sk_write_queue)) != NULL)
1460                 sk_wmem_free_skb(sk, skb);
1461         sk_mem_reclaim(sk);
1462         tcp_clear_all_retrans_hints(tcp_sk(sk));
1463 }
1464 
1465 static inline struct sk_buff *tcp_write_queue_head(const struct sock *sk)
1466 {
1467         return skb_peek(&sk->sk_write_queue);
1468 }
1469 
1470 static inline struct sk_buff *tcp_write_queue_tail(const struct sock *sk)
1471 {
1472         return skb_peek_tail(&sk->sk_write_queue);
1473 }
1474 
1475 static inline struct sk_buff *tcp_write_queue_next(const struct sock *sk,
1476                                                    const struct sk_buff *skb)
1477 {
1478         return skb_queue_next(&sk->sk_write_queue, skb);
1479 }
1480 
1481 static inline struct sk_buff *tcp_write_queue_prev(const struct sock *sk,
1482                                                    const struct sk_buff *skb)
1483 {
1484         return skb_queue_prev(&sk->sk_write_queue, skb);
1485 }
1486 
1487 #define tcp_for_write_queue(skb, sk)                                    \
1488         skb_queue_walk(&(sk)->sk_write_queue, skb)
1489 
1490 #define tcp_for_write_queue_from(skb, sk)                               \
1491         skb_queue_walk_from(&(sk)->sk_write_queue, skb)
1492 
1493 #define tcp_for_write_queue_from_safe(skb, tmp, sk)                     \
1494         skb_queue_walk_from_safe(&(sk)->sk_write_queue, skb, tmp)
1495 
1496 static inline struct sk_buff *tcp_send_head(const struct sock *sk)
1497 {
1498         return sk->sk_send_head;
1499 }
1500 
1501 static inline bool tcp_skb_is_last(const struct sock *sk,
1502                                    const struct sk_buff *skb)
1503 {
1504         return skb_queue_is_last(&sk->sk_write_queue, skb);
1505 }
1506 
1507 static inline void tcp_advance_send_head(struct sock *sk, const struct sk_buff *skb)
1508 {
1509         if (tcp_skb_is_last(sk, skb))
1510                 sk->sk_send_head = NULL;
1511         else
1512                 sk->sk_send_head = tcp_write_queue_next(sk, skb);
1513 }
1514 
1515 static inline void tcp_check_send_head(struct sock *sk, struct sk_buff *skb_unlinked)
1516 {
1517         if (sk->sk_send_head == skb_unlinked)
1518                 sk->sk_send_head = NULL;
1519 }
1520 
1521 static inline void tcp_init_send_head(struct sock *sk)
1522 {
1523         sk->sk_send_head = NULL;
1524 }
1525 
1526 static inline void __tcp_add_write_queue_tail(struct sock *sk, struct sk_buff *skb)
1527 {
1528         __skb_queue_tail(&sk->sk_write_queue, skb);
1529 }
1530 
1531 static inline void tcp_add_write_queue_tail(struct sock *sk, struct sk_buff *skb)
1532 {
1533         __tcp_add_write_queue_tail(sk, skb);
1534 
1535         /* Queue it, remembering where we must start sending. */
1536         if (sk->sk_send_head == NULL) {
1537                 sk->sk_send_head = skb;
1538 
1539                 if (tcp_sk(sk)->highest_sack == NULL)
1540                         tcp_sk(sk)->highest_sack = skb;
1541         }
1542 }
1543 
1544 static inline void __tcp_add_write_queue_head(struct sock *sk, struct sk_buff *skb)
1545 {
1546         __skb_queue_head(&sk->sk_write_queue, skb);
1547 }
1548 
1549 /* Insert buff after skb on the write queue of sk.  */
1550 static inline void tcp_insert_write_queue_after(struct sk_buff *skb,
1551                                                 struct sk_buff *buff,
1552                                                 struct sock *sk)
1553 {
1554         __skb_queue_after(&sk->sk_write_queue, skb, buff);
1555 }
1556 
1557 /* Insert new before skb on the write queue of sk.  */
1558 static inline void tcp_insert_write_queue_before(struct sk_buff *new,
1559                                                   struct sk_buff *skb,
1560                                                   struct sock *sk)
1561 {
1562         __skb_queue_before(&sk->sk_write_queue, skb, new);
1563 
1564         if (sk->sk_send_head == skb)
1565                 sk->sk_send_head = new;
1566 }
1567 
1568 static inline void tcp_unlink_write_queue(struct sk_buff *skb, struct sock *sk)
1569 {
1570         __skb_unlink(skb, &sk->sk_write_queue);
1571 }
1572 
1573 static inline bool tcp_write_queue_empty(struct sock *sk)
1574 {
1575         return skb_queue_empty(&sk->sk_write_queue);
1576 }
1577 
1578 static inline void tcp_push_pending_frames(struct sock *sk)
1579 {
1580         if (tcp_send_head(sk)) {
1581                 struct tcp_sock *tp = tcp_sk(sk);
1582 
1583                 __tcp_push_pending_frames(sk, tcp_current_mss(sk), tp->nonagle);
1584         }
1585 }
1586 
1587 /* Start sequence of the skb just after the highest skb with SACKed
1588  * bit, valid only if sacked_out > 0 or when the caller has ensured
1589  * validity by itself.
1590  */
1591 static inline u32 tcp_highest_sack_seq(struct tcp_sock *tp)
1592 {
1593         if (!tp->sacked_out)
1594                 return tp->snd_una;
1595 
1596         if (tp->highest_sack == NULL)
1597                 return tp->snd_nxt;
1598 
1599         return TCP_SKB_CB(tp->highest_sack)->seq;
1600 }
1601 
1602 static inline void tcp_advance_highest_sack(struct sock *sk, struct sk_buff *skb)
1603 {
1604         tcp_sk(sk)->highest_sack = tcp_skb_is_last(sk, skb) ? NULL :
1605                                                 tcp_write_queue_next(sk, skb);
1606 }
1607 
1608 static inline struct sk_buff *tcp_highest_sack(struct sock *sk)
1609 {
1610         return tcp_sk(sk)->highest_sack;
1611 }
1612 
1613 static inline void tcp_highest_sack_reset(struct sock *sk)
1614 {
1615         tcp_sk(sk)->highest_sack = tcp_write_queue_head(sk);
1616 }
1617 
1618 /* Called when old skb is about to be deleted (to be combined with new skb) */
1619 static inline void tcp_highest_sack_combine(struct sock *sk,
1620                                             struct sk_buff *old,
1621                                             struct sk_buff *new)
1622 {
1623         if (tcp_sk(sk)->sacked_out && (old == tcp_sk(sk)->highest_sack))
1624                 tcp_sk(sk)->highest_sack = new;
1625 }
1626 
1627 /* This helper checks if socket has IP_TRANSPARENT set */
1628 static inline bool inet_sk_transparent(const struct sock *sk)
1629 {
1630         switch (sk->sk_state) {
1631         case TCP_TIME_WAIT:
1632                 return inet_twsk(sk)->tw_transparent;
1633         case TCP_NEW_SYN_RECV:
1634                 return inet_rsk(inet_reqsk(sk))->no_srccheck;
1635         }
1636         return inet_sk(sk)->transparent;
1637 }
1638 
1639 /* Determines whether this is a thin stream (which may suffer from
1640  * increased latency). Used to trigger latency-reducing mechanisms.
1641  */
1642 static inline bool tcp_stream_is_thin(struct tcp_sock *tp)
1643 {
1644         return tp->packets_out < 4 && !tcp_in_initial_slowstart(tp);
1645 }
1646 
1647 /* /proc */
1648 enum tcp_seq_states {
1649         TCP_SEQ_STATE_LISTENING,
1650         TCP_SEQ_STATE_ESTABLISHED,
1651 };
1652 
1653 int tcp_seq_open(struct inode *inode, struct file *file);
1654 
1655 struct tcp_seq_afinfo {
1656         char                            *name;
1657         sa_family_t                     family;
1658         const struct file_operations    *seq_fops;
1659         struct seq_operations           seq_ops;
1660 };
1661 
1662 struct tcp_iter_state {
1663         struct seq_net_private  p;
1664         sa_family_t             family;
1665         enum tcp_seq_states     state;
1666         struct sock             *syn_wait_sk;
1667         int                     bucket, offset, sbucket, num;
1668         loff_t                  last_pos;
1669 };
1670 
1671 int tcp_proc_register(struct net *net, struct tcp_seq_afinfo *afinfo);
1672 void tcp_proc_unregister(struct net *net, struct tcp_seq_afinfo *afinfo);
1673 
1674 extern struct request_sock_ops tcp_request_sock_ops;
1675 extern struct request_sock_ops tcp6_request_sock_ops;
1676 
1677 void tcp_v4_destroy_sock(struct sock *sk);
1678 
1679 struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
1680                                 netdev_features_t features);
1681 struct sk_buff **tcp_gro_receive(struct sk_buff **head, struct sk_buff *skb);
1682 int tcp_gro_complete(struct sk_buff *skb);
1683 
1684 void __tcp_v4_send_check(struct sk_buff *skb, __be32 saddr, __be32 daddr);
1685 
1686 static inline u32 tcp_notsent_lowat(const struct tcp_sock *tp)
1687 {
1688         return tp->notsent_lowat ?: sysctl_tcp_notsent_lowat;
1689 }
1690 
1691 static inline bool tcp_stream_memory_free(const struct sock *sk)
1692 {
1693         const struct tcp_sock *tp = tcp_sk(sk);
1694         u32 notsent_bytes = tp->write_seq - tp->snd_nxt;
1695 
1696         return notsent_bytes < tcp_notsent_lowat(tp);
1697 }
1698 
1699 #ifdef CONFIG_PROC_FS
1700 int tcp4_proc_init(void);
1701 void tcp4_proc_exit(void);
1702 #endif
1703 
1704 int tcp_rtx_synack(const struct sock *sk, struct request_sock *req);
1705 int tcp_conn_request(struct request_sock_ops *rsk_ops,
1706                      const struct tcp_request_sock_ops *af_ops,
1707                      struct sock *sk, struct sk_buff *skb);
1708 
1709 /* TCP af-specific functions */
1710 struct tcp_sock_af_ops {
1711 #ifdef CONFIG_TCP_MD5SIG
1712         struct tcp_md5sig_key   *(*md5_lookup) (const struct sock *sk,
1713                                                 const struct sock *addr_sk);
1714         int             (*calc_md5_hash)(char *location,
1715                                          const struct tcp_md5sig_key *md5,
1716                                          const struct sock *sk,
1717                                          const struct sk_buff *skb);
1718         int             (*md5_parse)(struct sock *sk,
1719                                      char __user *optval,
1720                                      int optlen);
1721 #endif
1722 };
1723 
1724 struct tcp_request_sock_ops {
1725         u16 mss_clamp;
1726 #ifdef CONFIG_TCP_MD5SIG
1727         struct tcp_md5sig_key *(*req_md5_lookup)(const struct sock *sk,
1728                                                  const struct sock *addr_sk);
1729         int             (*calc_md5_hash) (char *location,
1730                                           const struct tcp_md5sig_key *md5,
1731                                           const struct sock *sk,
1732                                           const struct sk_buff *skb);
1733 #endif
1734         void (*init_req)(struct request_sock *req,
1735                          const struct sock *sk_listener,
1736                          struct sk_buff *skb);
1737 #ifdef CONFIG_SYN_COOKIES
1738         __u32 (*cookie_init_seq)(const struct sk_buff *skb,
1739                                  __u16 *mss);
1740 #endif
1741         struct dst_entry *(*route_req)(const struct sock *sk, struct flowi *fl,
1742                                        const struct request_sock *req,
1743                                        bool *strict);
1744         __u32 (*init_seq)(const struct sk_buff *skb);
1745         int (*send_synack)(const struct sock *sk, struct dst_entry *dst,
1746                            struct flowi *fl, struct request_sock *req,
1747                            struct tcp_fastopen_cookie *foc,
1748                            bool attach_req);
1749 };
1750 
1751 #ifdef CONFIG_SYN_COOKIES
1752 static inline __u32 cookie_init_sequence(const struct tcp_request_sock_ops *ops,
1753                                          const struct sock *sk, struct sk_buff *skb,
1754                                          __u16 *mss)
1755 {
1756         tcp_synq_overflow(sk);
1757         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
1758         return ops->cookie_init_seq(skb, mss);
1759 }
1760 #else
1761 static inline __u32 cookie_init_sequence(const struct tcp_request_sock_ops *ops,
1762                                          const struct sock *sk, struct sk_buff *skb,
1763                                          __u16 *mss)
1764 {
1765         return 0;
1766 }
1767 #endif
1768 
1769 int tcpv4_offload_init(void);
1770 
1771 void tcp_v4_init(void);
1772 void tcp_init(void);
1773 
1774 /* tcp_recovery.c */
1775 
1776 /* Flags to enable various loss recovery features. See below */
1777 extern int sysctl_tcp_recovery;
1778 
1779 /* Use TCP RACK to detect (some) tail and retransmit losses */
1780 #define TCP_RACK_LOST_RETRANS  0x1
1781 
1782 extern int tcp_rack_mark_lost(struct sock *sk);
1783 
1784 extern void tcp_rack_advance(struct tcp_sock *tp,
1785                              const struct skb_mstamp *xmit_time, u8 sacked);
1786 
1787 /*
1788  * Save and compile IPv4 options, return a pointer to it
1789  */
1790 static inline struct ip_options_rcu *tcp_v4_save_options(struct sk_buff *skb)
1791 {
1792         const struct ip_options *opt = &TCP_SKB_CB(skb)->header.h4.opt;
1793         struct ip_options_rcu *dopt = NULL;
1794 
1795         if (opt->optlen) {
1796                 int opt_size = sizeof(*dopt) + opt->optlen;
1797 
1798                 dopt = kmalloc(opt_size, GFP_ATOMIC);
1799                 if (dopt && __ip_options_echo(&dopt->opt, skb, opt)) {
1800                         kfree(dopt);
1801                         dopt = NULL;
1802                 }
1803         }
1804         return dopt;
1805 }
1806 
1807 /* locally generated TCP pure ACKs have skb->truesize == 2
1808  * (check tcp_send_ack() in net/ipv4/tcp_output.c )
1809  * This is much faster than dissecting the packet to find out.
1810  * (Think of GRE encapsulations, IPv4, IPv6, ...)
1811  */
1812 static inline bool skb_is_tcp_pure_ack(const struct sk_buff *skb)
1813 {
1814         return skb->truesize == 2;
1815 }
1816 
1817 static inline void skb_set_tcp_pure_ack(struct sk_buff *skb)
1818 {
1819         skb->truesize = 2;
1820 }
1821 
1822 #endif  /* _TCP_H */
1823 

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