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Linux/include/net/tcp.h

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

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