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Linux/include/net/tcp.h

  1 /*
  2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
  3  *              operating system.  INET is implemented using the  BSD Socket
  4  *              interface as the means of communication with the user level.
  5  *
  6  *              Definitions for the TCP module.
  7  *
  8  * Version:     @(#)tcp.h       1.0.5   05/23/93
  9  *
 10  * Authors:     Ross Biro
 11  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 12  *
 13  *              This program is free software; you can redistribute it and/or
 14  *              modify it under the terms of the GNU General Public License
 15  *              as published by the Free Software Foundation; either version
 16  *              2 of the License, or (at your option) any later version.
 17  */
 18 #ifndef _TCP_H
 19 #define _TCP_H
 20 
 21 #define FASTRETRANS_DEBUG 1
 22 
 23 #include <linux/list.h>
 24 #include <linux/tcp.h>
 25 #include <linux/bug.h>
 26 #include <linux/slab.h>
 27 #include <linux/cache.h>
 28 #include <linux/percpu.h>
 29 #include <linux/skbuff.h>
 30 #include <linux/crypto.h>
 31 #include <linux/cryptohash.h>
 32 #include <linux/kref.h>
 33 #include <linux/ktime.h>
 34 
 35 #include <net/inet_connection_sock.h>
 36 #include <net/inet_timewait_sock.h>
 37 #include <net/inet_hashtables.h>
 38 #include <net/checksum.h>
 39 #include <net/request_sock.h>
 40 #include <net/sock.h>
 41 #include <net/snmp.h>
 42 #include <net/ip.h>
 43 #include <net/tcp_states.h>
 44 #include <net/inet_ecn.h>
 45 #include <net/dst.h>
 46 
 47 #include <linux/seq_file.h>
 48 #include <linux/memcontrol.h>
 49 
 50 extern struct inet_hashinfo tcp_hashinfo;
 51 
 52 extern struct percpu_counter tcp_orphan_count;
 53 void tcp_time_wait(struct sock *sk, int state, int timeo);
 54 
 55 #define MAX_TCP_HEADER  (128 + MAX_HEADER)
 56 #define MAX_TCP_OPTION_SPACE 40
 57 
 58 /*
 59  * Never offer a window over 32767 without using window scaling. Some
 60  * poor stacks do signed 16bit maths!
 61  */
 62 #define MAX_TCP_WINDOW          32767U
 63 
 64 /* Minimal accepted MSS. It is (60+60+8) - (20+20). */
 65 #define TCP_MIN_MSS             88U
 66 
 67 /* The least MTU to use for probing */
 68 #define TCP_BASE_MSS            512
 69 
 70 /* After receiving this amount of duplicate ACKs fast retransmit starts. */
 71 #define TCP_FASTRETRANS_THRESH 3
 72 
 73 /* Maximal number of ACKs sent quickly to accelerate slow-start. */
 74 #define TCP_MAX_QUICKACKS       16U
 75 
 76 /* urg_data states */
 77 #define TCP_URG_VALID   0x0100
 78 #define TCP_URG_NOTYET  0x0200
 79 #define TCP_URG_READ    0x0400
 80 
 81 #define TCP_RETR1       3       /*
 82                                  * This is how many retries it does before it
 83                                  * tries to figure out if the gateway is
 84                                  * down. Minimal RFC value is 3; it corresponds
 85                                  * to ~3sec-8min depending on RTO.
 86                                  */
 87 
 88 #define TCP_RETR2       15      /*
 89                                  * This should take at least
 90                                  * 90 minutes to time out.
 91                                  * RFC1122 says that the limit is 100 sec.
 92                                  * 15 is ~13-30min depending on RTO.
 93                                  */
 94 
 95 #define TCP_SYN_RETRIES  6      /* This is how many retries are done
 96                                  * when active opening a connection.
 97                                  * RFC1122 says the minimum retry MUST
 98                                  * be at least 180secs.  Nevertheless
 99                                  * this value is corresponding to
100                                  * 63secs of retransmission with the
101                                  * current initial RTO.
102                                  */
103 
104 #define TCP_SYNACK_RETRIES 5    /* This is how may retries are done
105                                  * when passive opening a connection.
106                                  * This is corresponding to 31secs of
107                                  * retransmission with the current
108                                  * initial RTO.
109                                  */
110 
111 #define TCP_TIMEWAIT_LEN (60*HZ) /* how long to wait to destroy TIME-WAIT
112                                   * state, about 60 seconds     */
113 #define TCP_FIN_TIMEOUT TCP_TIMEWAIT_LEN
114                                  /* BSD style FIN_WAIT2 deadlock breaker.
115                                   * It used to be 3min, new value is 60sec,
116                                   * to combine FIN-WAIT-2 timeout with
117                                   * TIME-WAIT timer.
118                                   */
119 
120 #define TCP_DELACK_MAX  ((unsigned)(HZ/5))      /* maximal time to delay before sending an ACK */
121 #if HZ >= 100
122 #define TCP_DELACK_MIN  ((unsigned)(HZ/25))     /* minimal time to delay before sending an ACK */
123 #define TCP_ATO_MIN     ((unsigned)(HZ/25))
124 #else
125 #define TCP_DELACK_MIN  4U
126 #define TCP_ATO_MIN     4U
127 #endif
128 #define TCP_RTO_MAX     ((unsigned)(120*HZ))
129 #define TCP_RTO_MIN     ((unsigned)(HZ/5))
130 #define TCP_TIMEOUT_INIT ((unsigned)(1*HZ))     /* RFC6298 2.1 initial RTO value        */
131 #define TCP_TIMEOUT_FALLBACK ((unsigned)(3*HZ)) /* RFC 1122 initial RTO value, now
132                                                  * used as a fallback RTO for the
133                                                  * initial data transmission if no
134                                                  * valid RTT sample has been acquired,
135                                                  * most likely due to retrans in 3WHS.
136                                                  */
137 
138 #define TCP_RESOURCE_PROBE_INTERVAL ((unsigned)(HZ/2U)) /* Maximal interval between probes
139                                                          * for local resources.
140                                                          */
141 
142 #define TCP_KEEPALIVE_TIME      (120*60*HZ)     /* two hours */
143 #define TCP_KEEPALIVE_PROBES    9               /* Max of 9 keepalive probes    */
144 #define TCP_KEEPALIVE_INTVL     (75*HZ)
145 
146 #define MAX_TCP_KEEPIDLE        32767
147 #define MAX_TCP_KEEPINTVL       32767
148 #define MAX_TCP_KEEPCNT         127
149 #define MAX_TCP_SYNCNT          127
150 
151 #define TCP_SYNQ_INTERVAL       (HZ/5)  /* Period of SYNACK timer */
152 
153 #define TCP_PAWS_24DAYS (60 * 60 * 24 * 24)
154 #define TCP_PAWS_MSL    60              /* Per-host timestamps are invalidated
155                                          * after this time. It should be equal
156                                          * (or greater than) TCP_TIMEWAIT_LEN
157                                          * to provide reliability equal to one
158                                          * provided by timewait state.
159                                          */
160 #define TCP_PAWS_WINDOW 1               /* Replay window for per-host
161                                          * timestamps. It must be less than
162                                          * minimal timewait lifetime.
163                                          */
164 /*
165  *      TCP option
166  */
167 
168 #define TCPOPT_NOP              1       /* Padding */
169 #define TCPOPT_EOL              0       /* End of options */
170 #define TCPOPT_MSS              2       /* Segment size negotiating */
171 #define TCPOPT_WINDOW           3       /* Window scaling */
172 #define TCPOPT_SACK_PERM        4       /* SACK Permitted */
173 #define TCPOPT_SACK             5       /* SACK Block */
174 #define TCPOPT_TIMESTAMP        8       /* Better RTT estimations/PAWS */
175 #define TCPOPT_MD5SIG           19      /* MD5 Signature (RFC2385) */
176 #define TCPOPT_EXP              254     /* Experimental */
177 /* Magic number to be after the option value for sharing TCP
178  * experimental options. See draft-ietf-tcpm-experimental-options-00.txt
179  */
180 #define TCPOPT_FASTOPEN_MAGIC   0xF989
181 
182 /*
183  *     TCP option lengths
184  */
185 
186 #define TCPOLEN_MSS            4
187 #define TCPOLEN_WINDOW         3
188 #define TCPOLEN_SACK_PERM      2
189 #define TCPOLEN_TIMESTAMP      10
190 #define TCPOLEN_MD5SIG         18
191 #define TCPOLEN_EXP_FASTOPEN_BASE  4
192 
193 /* But this is what stacks really send out. */
194 #define TCPOLEN_TSTAMP_ALIGNED          12
195 #define TCPOLEN_WSCALE_ALIGNED          4
196 #define TCPOLEN_SACKPERM_ALIGNED        4
197 #define TCPOLEN_SACK_BASE               2
198 #define TCPOLEN_SACK_BASE_ALIGNED       4
199 #define TCPOLEN_SACK_PERBLOCK           8
200 #define TCPOLEN_MD5SIG_ALIGNED          20
201 #define TCPOLEN_MSS_ALIGNED             4
202 
203 /* Flags in tp->nonagle */
204 #define TCP_NAGLE_OFF           1       /* Nagle's algo is disabled */
205 #define TCP_NAGLE_CORK          2       /* Socket is corked         */
206 #define TCP_NAGLE_PUSH          4       /* Cork is overridden for already queued data */
207 
208 /* TCP thin-stream limits */
209 #define TCP_THIN_LINEAR_RETRIES 6       /* After 6 linear retries, do exp. backoff */
210 
211 /* TCP initial congestion window as per draft-hkchu-tcpm-initcwnd-01 */
212 #define TCP_INIT_CWND           10
213 
214 /* Bit Flags for sysctl_tcp_fastopen */
215 #define TFO_CLIENT_ENABLE       1
216 #define TFO_SERVER_ENABLE       2
217 #define TFO_CLIENT_NO_COOKIE    4       /* Data in SYN w/o cookie option */
218 
219 /* Accept SYN data w/o any cookie option */
220 #define TFO_SERVER_COOKIE_NOT_REQD      0x200
221 
222 /* Force enable TFO on all listeners, i.e., not requiring the
223  * TCP_FASTOPEN socket option. SOCKOPT1/2 determine how to set max_qlen.
224  */
225 #define TFO_SERVER_WO_SOCKOPT1  0x400
226 #define TFO_SERVER_WO_SOCKOPT2  0x800
227 
228 extern struct inet_timewait_death_row tcp_death_row;
229 
230 /* sysctl variables for tcp */
231 extern int sysctl_tcp_timestamps;
232 extern int sysctl_tcp_window_scaling;
233 extern int sysctl_tcp_sack;
234 extern int sysctl_tcp_fin_timeout;
235 extern int sysctl_tcp_keepalive_time;
236 extern int sysctl_tcp_keepalive_probes;
237 extern int sysctl_tcp_keepalive_intvl;
238 extern int sysctl_tcp_syn_retries;
239 extern int sysctl_tcp_synack_retries;
240 extern int sysctl_tcp_retries1;
241 extern int sysctl_tcp_retries2;
242 extern int sysctl_tcp_orphan_retries;
243 extern int sysctl_tcp_syncookies;
244 extern int sysctl_tcp_fastopen;
245 extern int sysctl_tcp_retrans_collapse;
246 extern int sysctl_tcp_stdurg;
247 extern int sysctl_tcp_rfc1337;
248 extern int sysctl_tcp_abort_on_overflow;
249 extern int sysctl_tcp_max_orphans;
250 extern int sysctl_tcp_fack;
251 extern int sysctl_tcp_reordering;
252 extern int sysctl_tcp_max_reordering;
253 extern int sysctl_tcp_dsack;
254 extern long sysctl_tcp_mem[3];
255 extern int sysctl_tcp_wmem[3];
256 extern int sysctl_tcp_rmem[3];
257 extern int sysctl_tcp_app_win;
258 extern int sysctl_tcp_adv_win_scale;
259 extern int sysctl_tcp_tw_reuse;
260 extern int sysctl_tcp_frto;
261 extern int sysctl_tcp_low_latency;
262 extern int sysctl_tcp_nometrics_save;
263 extern int sysctl_tcp_moderate_rcvbuf;
264 extern int sysctl_tcp_tso_win_divisor;
265 extern int sysctl_tcp_mtu_probing;
266 extern int sysctl_tcp_base_mss;
267 extern int sysctl_tcp_workaround_signed_windows;
268 extern int sysctl_tcp_slow_start_after_idle;
269 extern int sysctl_tcp_thin_linear_timeouts;
270 extern int sysctl_tcp_thin_dupack;
271 extern int sysctl_tcp_early_retrans;
272 extern int sysctl_tcp_limit_output_bytes;
273 extern int sysctl_tcp_challenge_ack_limit;
274 extern unsigned int sysctl_tcp_notsent_lowat;
275 extern int sysctl_tcp_min_tso_segs;
276 extern int sysctl_tcp_autocorking;
277 
278 extern atomic_long_t tcp_memory_allocated;
279 extern struct percpu_counter tcp_sockets_allocated;
280 extern int tcp_memory_pressure;
281 
282 /*
283  * The next routines deal with comparing 32 bit unsigned ints
284  * and worry about wraparound (automatic with unsigned arithmetic).
285  */
286 
287 static inline bool before(__u32 seq1, __u32 seq2)
288 {
289         return (__s32)(seq1-seq2) < 0;
290 }
291 #define after(seq2, seq1)       before(seq1, seq2)
292 
293 /* is s2<=s1<=s3 ? */
294 static inline bool between(__u32 seq1, __u32 seq2, __u32 seq3)
295 {
296         return seq3 - seq2 >= seq1 - seq2;
297 }
298 
299 static inline bool tcp_out_of_memory(struct sock *sk)
300 {
301         if (sk->sk_wmem_queued > SOCK_MIN_SNDBUF &&
302             sk_memory_allocated(sk) > sk_prot_mem_limits(sk, 2))
303                 return true;
304         return false;
305 }
306 
307 static inline bool tcp_too_many_orphans(struct sock *sk, int shift)
308 {
309         struct percpu_counter *ocp = sk->sk_prot->orphan_count;
310         int orphans = percpu_counter_read_positive(ocp);
311 
312         if (orphans << shift > sysctl_tcp_max_orphans) {
313                 orphans = percpu_counter_sum_positive(ocp);
314                 if (orphans << shift > sysctl_tcp_max_orphans)
315                         return true;
316         }
317         return false;
318 }
319 
320 bool tcp_check_oom(struct sock *sk, int shift);
321 
322 /* syncookies: remember time of last synqueue overflow */
323 static inline void tcp_synq_overflow(struct sock *sk)
324 {
325         tcp_sk(sk)->rx_opt.ts_recent_stamp = jiffies;
326 }
327 
328 /* syncookies: no recent synqueue overflow on this listening socket? */
329 static inline bool tcp_synq_no_recent_overflow(const struct sock *sk)
330 {
331         unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
332         return time_after(jiffies, last_overflow + TCP_TIMEOUT_FALLBACK);
333 }
334 
335 extern struct proto tcp_prot;
336 
337 #define TCP_INC_STATS(net, field)       SNMP_INC_STATS((net)->mib.tcp_statistics, field)
338 #define TCP_INC_STATS_BH(net, field)    SNMP_INC_STATS_BH((net)->mib.tcp_statistics, field)
339 #define TCP_DEC_STATS(net, field)       SNMP_DEC_STATS((net)->mib.tcp_statistics, field)
340 #define TCP_ADD_STATS_USER(net, field, val) SNMP_ADD_STATS_USER((net)->mib.tcp_statistics, field, val)
341 #define TCP_ADD_STATS(net, field, val)  SNMP_ADD_STATS((net)->mib.tcp_statistics, field, val)
342 
343 void tcp_tasklet_init(void);
344 
345 void tcp_v4_err(struct sk_buff *skb, u32);
346 
347 void tcp_shutdown(struct sock *sk, int how);
348 
349 void tcp_v4_early_demux(struct sk_buff *skb);
350 int tcp_v4_rcv(struct sk_buff *skb);
351 
352 int tcp_v4_tw_remember_stamp(struct inet_timewait_sock *tw);
353 int tcp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
354                 size_t size);
355 int tcp_sendpage(struct sock *sk, struct page *page, int offset, size_t size,
356                  int flags);
357 void tcp_release_cb(struct sock *sk);
358 void tcp_wfree(struct sk_buff *skb);
359 void tcp_write_timer_handler(struct sock *sk);
360 void tcp_delack_timer_handler(struct sock *sk);
361 int tcp_ioctl(struct sock *sk, int cmd, unsigned long arg);
362 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
363                           const struct tcphdr *th, unsigned int len);
364 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
365                          const struct tcphdr *th, unsigned int len);
366 void tcp_rcv_space_adjust(struct sock *sk);
367 int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp);
368 void tcp_twsk_destructor(struct sock *sk);
369 ssize_t tcp_splice_read(struct socket *sk, loff_t *ppos,
370                         struct pipe_inode_info *pipe, size_t len,
371                         unsigned int flags);
372 
373 static inline void tcp_dec_quickack_mode(struct sock *sk,
374                                          const unsigned int pkts)
375 {
376         struct inet_connection_sock *icsk = inet_csk(sk);
377 
378         if (icsk->icsk_ack.quick) {
379                 if (pkts >= icsk->icsk_ack.quick) {
380                         icsk->icsk_ack.quick = 0;
381                         /* Leaving quickack mode we deflate ATO. */
382                         icsk->icsk_ack.ato   = TCP_ATO_MIN;
383                 } else
384                         icsk->icsk_ack.quick -= pkts;
385         }
386 }
387 
388 #define TCP_ECN_OK              1
389 #define TCP_ECN_QUEUE_CWR       2
390 #define TCP_ECN_DEMAND_CWR      4
391 #define TCP_ECN_SEEN            8
392 
393 enum tcp_tw_status {
394         TCP_TW_SUCCESS = 0,
395         TCP_TW_RST = 1,
396         TCP_TW_ACK = 2,
397         TCP_TW_SYN = 3
398 };
399 
400 
401 enum tcp_tw_status tcp_timewait_state_process(struct inet_timewait_sock *tw,
402                                               struct sk_buff *skb,
403                                               const struct tcphdr *th);
404 struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
405                            struct request_sock *req, struct request_sock **prev,
406                            bool fastopen);
407 int tcp_child_process(struct sock *parent, struct sock *child,
408                       struct sk_buff *skb);
409 void tcp_enter_loss(struct sock *sk);
410 void tcp_clear_retrans(struct tcp_sock *tp);
411 void tcp_update_metrics(struct sock *sk);
412 void tcp_init_metrics(struct sock *sk);
413 void tcp_metrics_init(void);
414 bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst,
415                         bool paws_check, bool timestamps);
416 bool tcp_remember_stamp(struct sock *sk);
417 bool tcp_tw_remember_stamp(struct inet_timewait_sock *tw);
418 void tcp_fetch_timewait_stamp(struct sock *sk, struct dst_entry *dst);
419 void tcp_disable_fack(struct tcp_sock *tp);
420 void tcp_close(struct sock *sk, long timeout);
421 void tcp_init_sock(struct sock *sk);
422 unsigned int tcp_poll(struct file *file, struct socket *sock,
423                       struct poll_table_struct *wait);
424 int tcp_getsockopt(struct sock *sk, int level, int optname,
425                    char __user *optval, int __user *optlen);
426 int tcp_setsockopt(struct sock *sk, int level, int optname,
427                    char __user *optval, unsigned int optlen);
428 int compat_tcp_getsockopt(struct sock *sk, int level, int optname,
429                           char __user *optval, int __user *optlen);
430 int compat_tcp_setsockopt(struct sock *sk, int level, int optname,
431                           char __user *optval, unsigned int optlen);
432 void tcp_set_keepalive(struct sock *sk, int val);
433 void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req);
434 int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
435                 size_t len, int nonblock, int flags, int *addr_len);
436 void tcp_parse_options(const struct sk_buff *skb,
437                        struct tcp_options_received *opt_rx,
438                        int estab, struct tcp_fastopen_cookie *foc);
439 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th);
440 
441 /*
442  *      TCP v4 functions exported for the inet6 API
443  */
444 
445 void tcp_v4_send_check(struct sock *sk, struct sk_buff *skb);
446 void tcp_v4_mtu_reduced(struct sock *sk);
447 int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb);
448 struct sock *tcp_create_openreq_child(struct sock *sk,
449                                       struct request_sock *req,
450                                       struct sk_buff *skb);
451 struct sock *tcp_v4_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
452                                   struct request_sock *req,
453                                   struct dst_entry *dst);
454 int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb);
455 int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
456 int tcp_connect(struct sock *sk);
457 struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
458                                 struct request_sock *req,
459                                 struct tcp_fastopen_cookie *foc);
460 int tcp_disconnect(struct sock *sk, int flags);
461 
462 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb);
463 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size);
464 void inet_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb);
465 
466 /* From syncookies.c */
467 int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th,
468                       u32 cookie);
469 struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb);
470 #ifdef CONFIG_SYN_COOKIES
471 
472 /* Syncookies use a monotonic timer which increments every 60 seconds.
473  * This counter is used both as a hash input and partially encoded into
474  * the cookie value.  A cookie is only validated further if the delta
475  * between the current counter value and the encoded one is less than this,
476  * i.e. a sent cookie is valid only at most for 2*60 seconds (or less if
477  * the counter advances immediately after a cookie is generated).
478  */
479 #define MAX_SYNCOOKIE_AGE 2
480 
481 static inline u32 tcp_cookie_time(void)
482 {
483         u64 val = get_jiffies_64();
484 
485         do_div(val, 60 * HZ);
486         return val;
487 }
488 
489 u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,
490                               u16 *mssp);
491 __u32 cookie_v4_init_sequence(struct sock *sk, const struct sk_buff *skb,
492                               __u16 *mss);
493 __u32 cookie_init_timestamp(struct request_sock *req);
494 bool cookie_timestamp_decode(struct tcp_options_received *opt);
495 bool cookie_ecn_ok(const struct tcp_options_received *opt,
496                    const struct net *net, const struct dst_entry *dst);
497 
498 /* From net/ipv6/syncookies.c */
499 int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th,
500                       u32 cookie);
501 struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb);
502 
503 u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
504                               const struct tcphdr *th, u16 *mssp);
505 __u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb,
506                               __u16 *mss);
507 #endif
508 /* tcp_output.c */
509 
510 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
511                                int nonagle);
512 bool tcp_may_send_now(struct sock *sk);
513 int __tcp_retransmit_skb(struct sock *, struct sk_buff *);
514 int tcp_retransmit_skb(struct sock *, struct sk_buff *);
515 void tcp_retransmit_timer(struct sock *sk);
516 void tcp_xmit_retransmit_queue(struct sock *);
517 void tcp_simple_retransmit(struct sock *);
518 int tcp_trim_head(struct sock *, struct sk_buff *, u32);
519 int tcp_fragment(struct sock *, struct sk_buff *, u32, unsigned int, gfp_t);
520 
521 void tcp_send_probe0(struct sock *);
522 void tcp_send_partial(struct sock *);
523 int tcp_write_wakeup(struct sock *);
524 void tcp_send_fin(struct sock *sk);
525 void tcp_send_active_reset(struct sock *sk, gfp_t priority);
526 int tcp_send_synack(struct sock *);
527 bool tcp_syn_flood_action(struct sock *sk, const struct sk_buff *skb,
528                           const char *proto);
529 void tcp_push_one(struct sock *, unsigned int mss_now);
530 void tcp_send_ack(struct sock *sk);
531 void tcp_send_delayed_ack(struct sock *sk);
532 void tcp_send_loss_probe(struct sock *sk);
533 bool tcp_schedule_loss_probe(struct sock *sk);
534 
535 /* tcp_input.c */
536 void tcp_resume_early_retransmit(struct sock *sk);
537 void tcp_rearm_rto(struct sock *sk);
538 void tcp_reset(struct sock *sk);
539 
540 /* tcp_timer.c */
541 void tcp_init_xmit_timers(struct sock *);
542 static inline void tcp_clear_xmit_timers(struct sock *sk)
543 {
544         inet_csk_clear_xmit_timers(sk);
545 }
546 
547 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu);
548 unsigned int tcp_current_mss(struct sock *sk);
549 
550 /* Bound MSS / TSO packet size with the half of the window */
551 static inline int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
552 {
553         int cutoff;
554 
555         /* When peer uses tiny windows, there is no use in packetizing
556          * to sub-MSS pieces for the sake of SWS or making sure there
557          * are enough packets in the pipe for fast recovery.
558          *
559          * On the other hand, for extremely large MSS devices, handling
560          * smaller than MSS windows in this way does make sense.
561          */
562         if (tp->max_window >= 512)
563                 cutoff = (tp->max_window >> 1);
564         else
565                 cutoff = tp->max_window;
566 
567         if (cutoff && pktsize > cutoff)
568                 return max_t(int, cutoff, 68U - tp->tcp_header_len);
569         else
570                 return pktsize;
571 }
572 
573 /* tcp.c */
574 void tcp_get_info(const struct sock *, struct tcp_info *);
575 
576 /* Read 'sendfile()'-style from a TCP socket */
577 typedef int (*sk_read_actor_t)(read_descriptor_t *, struct sk_buff *,
578                                 unsigned int, size_t);
579 int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
580                   sk_read_actor_t recv_actor);
581 
582 void tcp_initialize_rcv_mss(struct sock *sk);
583 
584 int tcp_mtu_to_mss(struct sock *sk, int pmtu);
585 int tcp_mss_to_mtu(struct sock *sk, int mss);
586 void tcp_mtup_init(struct sock *sk);
587 void tcp_init_buffer_space(struct sock *sk);
588 
589 static inline void tcp_bound_rto(const struct sock *sk)
590 {
591         if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
592                 inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
593 }
594 
595 static inline u32 __tcp_set_rto(const struct tcp_sock *tp)
596 {
597         return usecs_to_jiffies((tp->srtt_us >> 3) + tp->rttvar_us);
598 }
599 
600 static inline void __tcp_fast_path_on(struct tcp_sock *tp, u32 snd_wnd)
601 {
602         tp->pred_flags = htonl((tp->tcp_header_len << 26) |
603                                ntohl(TCP_FLAG_ACK) |
604                                snd_wnd);
605 }
606 
607 static inline void tcp_fast_path_on(struct tcp_sock *tp)
608 {
609         __tcp_fast_path_on(tp, tp->snd_wnd >> tp->rx_opt.snd_wscale);
610 }
611 
612 static inline void tcp_fast_path_check(struct sock *sk)
613 {
614         struct tcp_sock *tp = tcp_sk(sk);
615 
616         if (skb_queue_empty(&tp->out_of_order_queue) &&
617             tp->rcv_wnd &&
618             atomic_read(&sk->sk_rmem_alloc) < sk->sk_rcvbuf &&
619             !tp->urg_data)
620                 tcp_fast_path_on(tp);
621 }
622 
623 /* Compute the actual rto_min value */
624 static inline u32 tcp_rto_min(struct sock *sk)
625 {
626         const struct dst_entry *dst = __sk_dst_get(sk);
627         u32 rto_min = TCP_RTO_MIN;
628 
629         if (dst && dst_metric_locked(dst, RTAX_RTO_MIN))
630                 rto_min = dst_metric_rtt(dst, RTAX_RTO_MIN);
631         return rto_min;
632 }
633 
634 static inline u32 tcp_rto_min_us(struct sock *sk)
635 {
636         return jiffies_to_usecs(tcp_rto_min(sk));
637 }
638 
639 /* Compute the actual receive window we are currently advertising.
640  * Rcv_nxt can be after the window if our peer push more data
641  * than the offered window.
642  */
643 static inline u32 tcp_receive_window(const struct tcp_sock *tp)
644 {
645         s32 win = tp->rcv_wup + tp->rcv_wnd - tp->rcv_nxt;
646 
647         if (win < 0)
648                 win = 0;
649         return (u32) win;
650 }
651 
652 /* Choose a new window, without checks for shrinking, and without
653  * scaling applied to the result.  The caller does these things
654  * if necessary.  This is a "raw" window selection.
655  */
656 u32 __tcp_select_window(struct sock *sk);
657 
658 void tcp_send_window_probe(struct sock *sk);
659 
660 /* TCP timestamps are only 32-bits, this causes a slight
661  * complication on 64-bit systems since we store a snapshot
662  * of jiffies in the buffer control blocks below.  We decided
663  * to use only the low 32-bits of jiffies and hide the ugly
664  * casts with the following macro.
665  */
666 #define tcp_time_stamp          ((__u32)(jiffies))
667 
668 static inline u32 tcp_skb_timestamp(const struct sk_buff *skb)
669 {
670         return skb->skb_mstamp.stamp_jiffies;
671 }
672 
673 
674 #define tcp_flag_byte(th) (((u_int8_t *)th)[13])
675 
676 #define TCPHDR_FIN 0x01
677 #define TCPHDR_SYN 0x02
678 #define TCPHDR_RST 0x04
679 #define TCPHDR_PSH 0x08
680 #define TCPHDR_ACK 0x10
681 #define TCPHDR_URG 0x20
682 #define TCPHDR_ECE 0x40
683 #define TCPHDR_CWR 0x80
684 
685 /* This is what the send packet queuing engine uses to pass
686  * TCP per-packet control information to the transmission code.
687  * We also store the host-order sequence numbers in here too.
688  * This is 44 bytes if IPV6 is enabled.
689  * If this grows please adjust skbuff.h:skbuff->cb[xxx] size appropriately.
690  */
691 struct tcp_skb_cb {
692         __u32           seq;            /* Starting sequence number     */
693         __u32           end_seq;        /* SEQ + FIN + SYN + datalen    */
694         union {
695                 /* Note : tcp_tw_isn is used in input path only
696                  *        (isn chosen by tcp_timewait_state_process())
697                  *
698                  *        tcp_gso_segs is used in write queue only,
699                  *        cf tcp_skb_pcount()
700                  */
701                 __u32           tcp_tw_isn;
702                 __u32           tcp_gso_segs;
703         };
704         __u8            tcp_flags;      /* TCP header flags. (tcp[13])  */
705 
706         __u8            sacked;         /* State flags for SACK/FACK.   */
707 #define TCPCB_SACKED_ACKED      0x01    /* SKB ACK'd by a SACK block    */
708 #define TCPCB_SACKED_RETRANS    0x02    /* SKB retransmitted            */
709 #define TCPCB_LOST              0x04    /* SKB is lost                  */
710 #define TCPCB_TAGBITS           0x07    /* All tag bits                 */
711 #define TCPCB_REPAIRED          0x10    /* SKB repaired (no skb_mstamp) */
712 #define TCPCB_EVER_RETRANS      0x80    /* Ever retransmitted frame     */
713 #define TCPCB_RETRANS           (TCPCB_SACKED_RETRANS|TCPCB_EVER_RETRANS| \
714                                 TCPCB_REPAIRED)
715 
716         __u8            ip_dsfield;     /* IPv4 tos or IPv6 dsfield     */
717         /* 1 byte hole */
718         __u32           ack_seq;        /* Sequence number ACK'd        */
719         union {
720                 struct inet_skb_parm    h4;
721 #if IS_ENABLED(CONFIG_IPV6)
722                 struct inet6_skb_parm   h6;
723 #endif
724         } header;       /* For incoming frames          */
725 };
726 
727 #define TCP_SKB_CB(__skb)       ((struct tcp_skb_cb *)&((__skb)->cb[0]))
728 
729 
730 #if IS_ENABLED(CONFIG_IPV6)
731 /* This is the variant of inet6_iif() that must be used by TCP,
732  * as TCP moves IP6CB into a different location in skb->cb[]
733  */
734 static inline int tcp_v6_iif(const struct sk_buff *skb)
735 {
736         return TCP_SKB_CB(skb)->header.h6.iif;
737 }
738 #endif
739 
740 /* Due to TSO, an SKB can be composed of multiple actual
741  * packets.  To keep these tracked properly, we use this.
742  */
743 static inline int tcp_skb_pcount(const struct sk_buff *skb)
744 {
745         return TCP_SKB_CB(skb)->tcp_gso_segs;
746 }
747 
748 static inline void tcp_skb_pcount_set(struct sk_buff *skb, int segs)
749 {
750         TCP_SKB_CB(skb)->tcp_gso_segs = segs;
751 }
752 
753 static inline void tcp_skb_pcount_add(struct sk_buff *skb, int segs)
754 {
755         TCP_SKB_CB(skb)->tcp_gso_segs += segs;
756 }
757 
758 /* This is valid iff tcp_skb_pcount() > 1. */
759 static inline int tcp_skb_mss(const struct sk_buff *skb)
760 {
761         return skb_shinfo(skb)->gso_size;
762 }
763 
764 /* Events passed to congestion control interface */
765 enum tcp_ca_event {
766         CA_EVENT_TX_START,      /* first transmit when no packets in flight */
767         CA_EVENT_CWND_RESTART,  /* congestion window restart */
768         CA_EVENT_COMPLETE_CWR,  /* end of congestion recovery */
769         CA_EVENT_LOSS,          /* loss timeout */
770         CA_EVENT_ECN_NO_CE,     /* ECT set, but not CE marked */
771         CA_EVENT_ECN_IS_CE,     /* received CE marked IP packet */
772         CA_EVENT_DELAYED_ACK,   /* Delayed ack is sent */
773         CA_EVENT_NON_DELAYED_ACK,
774 };
775 
776 /* Information about inbound ACK, passed to cong_ops->in_ack_event() */
777 enum tcp_ca_ack_event_flags {
778         CA_ACK_SLOWPATH         = (1 << 0),     /* In slow path processing */
779         CA_ACK_WIN_UPDATE       = (1 << 1),     /* ACK updated window */
780         CA_ACK_ECE              = (1 << 2),     /* ECE bit is set on ack */
781 };
782 
783 /*
784  * Interface for adding new TCP congestion control handlers
785  */
786 #define TCP_CA_NAME_MAX 16
787 #define TCP_CA_MAX      128
788 #define TCP_CA_BUF_MAX  (TCP_CA_NAME_MAX*TCP_CA_MAX)
789 
790 /* Algorithm can be set on socket without CAP_NET_ADMIN privileges */
791 #define TCP_CONG_NON_RESTRICTED 0x1
792 /* Requires ECN/ECT set on all packets */
793 #define TCP_CONG_NEEDS_ECN      0x2
794 
795 struct tcp_congestion_ops {
796         struct list_head        list;
797         unsigned long flags;
798 
799         /* initialize private data (optional) */
800         void (*init)(struct sock *sk);
801         /* cleanup private data  (optional) */
802         void (*release)(struct sock *sk);
803 
804         /* return slow start threshold (required) */
805         u32 (*ssthresh)(struct sock *sk);
806         /* do new cwnd calculation (required) */
807         void (*cong_avoid)(struct sock *sk, u32 ack, u32 acked);
808         /* call before changing ca_state (optional) */
809         void (*set_state)(struct sock *sk, u8 new_state);
810         /* call when cwnd event occurs (optional) */
811         void (*cwnd_event)(struct sock *sk, enum tcp_ca_event ev);
812         /* call when ack arrives (optional) */
813         void (*in_ack_event)(struct sock *sk, u32 flags);
814         /* new value of cwnd after loss (optional) */
815         u32  (*undo_cwnd)(struct sock *sk);
816         /* hook for packet ack accounting (optional) */
817         void (*pkts_acked)(struct sock *sk, u32 num_acked, s32 rtt_us);
818         /* get info for inet_diag (optional) */
819         void (*get_info)(struct sock *sk, u32 ext, struct sk_buff *skb);
820 
821         char            name[TCP_CA_NAME_MAX];
822         struct module   *owner;
823 };
824 
825 int tcp_register_congestion_control(struct tcp_congestion_ops *type);
826 void tcp_unregister_congestion_control(struct tcp_congestion_ops *type);
827 
828 void tcp_assign_congestion_control(struct sock *sk);
829 void tcp_init_congestion_control(struct sock *sk);
830 void tcp_cleanup_congestion_control(struct sock *sk);
831 int tcp_set_default_congestion_control(const char *name);
832 void tcp_get_default_congestion_control(char *name);
833 void tcp_get_available_congestion_control(char *buf, size_t len);
834 void tcp_get_allowed_congestion_control(char *buf, size_t len);
835 int tcp_set_allowed_congestion_control(char *allowed);
836 int tcp_set_congestion_control(struct sock *sk, const char *name);
837 u32 tcp_slow_start(struct tcp_sock *tp, u32 acked);
838 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked);
839 
840 u32 tcp_reno_ssthresh(struct sock *sk);
841 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked);
842 extern struct tcp_congestion_ops tcp_reno;
843 
844 static inline bool tcp_ca_needs_ecn(const struct sock *sk)
845 {
846         const struct inet_connection_sock *icsk = inet_csk(sk);
847 
848         return icsk->icsk_ca_ops->flags & TCP_CONG_NEEDS_ECN;
849 }
850 
851 static inline void tcp_set_ca_state(struct sock *sk, const u8 ca_state)
852 {
853         struct inet_connection_sock *icsk = inet_csk(sk);
854 
855         if (icsk->icsk_ca_ops->set_state)
856                 icsk->icsk_ca_ops->set_state(sk, ca_state);
857         icsk->icsk_ca_state = ca_state;
858 }
859 
860 static inline void tcp_ca_event(struct sock *sk, const enum tcp_ca_event event)
861 {
862         const struct inet_connection_sock *icsk = inet_csk(sk);
863 
864         if (icsk->icsk_ca_ops->cwnd_event)
865                 icsk->icsk_ca_ops->cwnd_event(sk, event);
866 }
867 
868 /* These functions determine how the current flow behaves in respect of SACK
869  * handling. SACK is negotiated with the peer, and therefore it can vary
870  * between different flows.
871  *
872  * tcp_is_sack - SACK enabled
873  * tcp_is_reno - No SACK
874  * tcp_is_fack - FACK enabled, implies SACK enabled
875  */
876 static inline int tcp_is_sack(const struct tcp_sock *tp)
877 {
878         return tp->rx_opt.sack_ok;
879 }
880 
881 static inline bool tcp_is_reno(const struct tcp_sock *tp)
882 {
883         return !tcp_is_sack(tp);
884 }
885 
886 static inline bool tcp_is_fack(const struct tcp_sock *tp)
887 {
888         return tp->rx_opt.sack_ok & TCP_FACK_ENABLED;
889 }
890 
891 static inline void tcp_enable_fack(struct tcp_sock *tp)
892 {
893         tp->rx_opt.sack_ok |= TCP_FACK_ENABLED;
894 }
895 
896 /* TCP early-retransmit (ER) is similar to but more conservative than
897  * the thin-dupack feature.  Enable ER only if thin-dupack is disabled.
898  */
899 static inline void tcp_enable_early_retrans(struct tcp_sock *tp)
900 {
901         tp->do_early_retrans = sysctl_tcp_early_retrans &&
902                 sysctl_tcp_early_retrans < 4 && !sysctl_tcp_thin_dupack &&
903                 sysctl_tcp_reordering == 3;
904 }
905 
906 static inline void tcp_disable_early_retrans(struct tcp_sock *tp)
907 {
908         tp->do_early_retrans = 0;
909 }
910 
911 static inline unsigned int tcp_left_out(const struct tcp_sock *tp)
912 {
913         return tp->sacked_out + tp->lost_out;
914 }
915 
916 /* This determines how many packets are "in the network" to the best
917  * of our knowledge.  In many cases it is conservative, but where
918  * detailed information is available from the receiver (via SACK
919  * blocks etc.) we can make more aggressive calculations.
920  *
921  * Use this for decisions involving congestion control, use just
922  * tp->packets_out to determine if the send queue is empty or not.
923  *
924  * Read this equation as:
925  *
926  *      "Packets sent once on transmission queue" MINUS
927  *      "Packets left network, but not honestly ACKed yet" PLUS
928  *      "Packets fast retransmitted"
929  */
930 static inline unsigned int tcp_packets_in_flight(const struct tcp_sock *tp)
931 {
932         return tp->packets_out - tcp_left_out(tp) + tp->retrans_out;
933 }
934 
935 #define TCP_INFINITE_SSTHRESH   0x7fffffff
936 
937 static inline bool tcp_in_initial_slowstart(const struct tcp_sock *tp)
938 {
939         return tp->snd_ssthresh >= TCP_INFINITE_SSTHRESH;
940 }
941 
942 static inline bool tcp_in_cwnd_reduction(const struct sock *sk)
943 {
944         return (TCPF_CA_CWR | TCPF_CA_Recovery) &
945                (1 << inet_csk(sk)->icsk_ca_state);
946 }
947 
948 /* If cwnd > ssthresh, we may raise ssthresh to be half-way to cwnd.
949  * The exception is cwnd reduction phase, when cwnd is decreasing towards
950  * ssthresh.
951  */
952 static inline __u32 tcp_current_ssthresh(const struct sock *sk)
953 {
954         const struct tcp_sock *tp = tcp_sk(sk);
955 
956         if (tcp_in_cwnd_reduction(sk))
957                 return tp->snd_ssthresh;
958         else
959                 return max(tp->snd_ssthresh,
960                            ((tp->snd_cwnd >> 1) +
961                             (tp->snd_cwnd >> 2)));
962 }
963 
964 /* Use define here intentionally to get WARN_ON location shown at the caller */
965 #define tcp_verify_left_out(tp) WARN_ON(tcp_left_out(tp) > tp->packets_out)
966 
967 void tcp_enter_cwr(struct sock *sk);
968 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst);
969 
970 /* The maximum number of MSS of available cwnd for which TSO defers
971  * sending if not using sysctl_tcp_tso_win_divisor.
972  */
973 static inline __u32 tcp_max_tso_deferred_mss(const struct tcp_sock *tp)
974 {
975         return 3;
976 }
977 
978 /* Slow start with delack produces 3 packets of burst, so that
979  * it is safe "de facto".  This will be the default - same as
980  * the default reordering threshold - but if reordering increases,
981  * we must be able to allow cwnd to burst at least this much in order
982  * to not pull it back when holes are filled.
983  */
984 static __inline__ __u32 tcp_max_burst(const struct tcp_sock *tp)
985 {
986         return tp->reordering;
987 }
988 
989 /* Returns end sequence number of the receiver's advertised window */
990 static inline u32 tcp_wnd_end(const struct tcp_sock *tp)
991 {
992         return tp->snd_una + tp->snd_wnd;
993 }
994 
995 /* We follow the spirit of RFC2861 to validate cwnd but implement a more
996  * flexible approach. The RFC suggests cwnd should not be raised unless
997  * it was fully used previously. And that's exactly what we do in
998  * congestion avoidance mode. But in slow start we allow cwnd to grow
999  * as long as the application has used half the cwnd.
1000  * Example :
1001  *    cwnd is 10 (IW10), but application sends 9 frames.
1002  *    We allow cwnd to reach 18 when all frames are ACKed.
1003  * This check is safe because it's as aggressive as slow start which already
1004  * risks 100% overshoot. The advantage is that we discourage application to
1005  * either send more filler packets or data to artificially blow up the cwnd
1006  * usage, and allow application-limited process to probe bw more aggressively.
1007  */
1008 static inline bool tcp_is_cwnd_limited(const struct sock *sk)
1009 {
1010         const struct tcp_sock *tp = tcp_sk(sk);
1011 
1012         /* If in slow start, ensure cwnd grows to twice what was ACKed. */
1013         if (tp->snd_cwnd <= tp->snd_ssthresh)
1014                 return tp->snd_cwnd < 2 * tp->max_packets_out;
1015 
1016         return tp->is_cwnd_limited;
1017 }
1018 
1019 static inline void tcp_check_probe_timer(struct sock *sk)
1020 {
1021         const struct tcp_sock *tp = tcp_sk(sk);
1022         const struct inet_connection_sock *icsk = inet_csk(sk);
1023 
1024         if (!tp->packets_out && !icsk->icsk_pending)
1025                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
1026                                           icsk->icsk_rto, TCP_RTO_MAX);
1027 }
1028 
1029 static inline void tcp_init_wl(struct tcp_sock *tp, u32 seq)
1030 {
1031         tp->snd_wl1 = seq;
1032 }
1033 
1034 static inline void tcp_update_wl(struct tcp_sock *tp, u32 seq)
1035 {
1036         tp->snd_wl1 = seq;
1037 }
1038 
1039 /*
1040  * Calculate(/check) TCP checksum
1041  */
1042 static inline __sum16 tcp_v4_check(int len, __be32 saddr,
1043                                    __be32 daddr, __wsum base)
1044 {
1045         return csum_tcpudp_magic(saddr,daddr,len,IPPROTO_TCP,base);
1046 }
1047 
1048 static inline __sum16 __tcp_checksum_complete(struct sk_buff *skb)
1049 {
1050         return __skb_checksum_complete(skb);
1051 }
1052 
1053 static inline bool tcp_checksum_complete(struct sk_buff *skb)
1054 {
1055         return !skb_csum_unnecessary(skb) &&
1056                 __tcp_checksum_complete(skb);
1057 }
1058 
1059 /* Prequeue for VJ style copy to user, combined with checksumming. */
1060 
1061 static inline void tcp_prequeue_init(struct tcp_sock *tp)
1062 {
1063         tp->ucopy.task = NULL;
1064         tp->ucopy.len = 0;
1065         tp->ucopy.memory = 0;
1066         skb_queue_head_init(&tp->ucopy.prequeue);
1067 }
1068 
1069 bool tcp_prequeue(struct sock *sk, struct sk_buff *skb);
1070 
1071 #undef STATE_TRACE
1072 
1073 #ifdef STATE_TRACE
1074 static const char *statename[]={
1075         "Unused","Established","Syn Sent","Syn Recv",
1076         "Fin Wait 1","Fin Wait 2","Time Wait", "Close",
1077         "Close Wait","Last ACK","Listen","Closing"
1078 };
1079 #endif
1080 void tcp_set_state(struct sock *sk, int state);
1081 
1082 void tcp_done(struct sock *sk);
1083 
1084 static inline void tcp_sack_reset(struct tcp_options_received *rx_opt)
1085 {
1086         rx_opt->dsack = 0;
1087         rx_opt->num_sacks = 0;
1088 }
1089 
1090 u32 tcp_default_init_rwnd(u32 mss);
1091 
1092 /* Determine a window scaling and initial window to offer. */
1093 void tcp_select_initial_window(int __space, __u32 mss, __u32 *rcv_wnd,
1094                                __u32 *window_clamp, int wscale_ok,
1095                                __u8 *rcv_wscale, __u32 init_rcv_wnd);
1096 
1097 static inline int tcp_win_from_space(int space)
1098 {
1099         return sysctl_tcp_adv_win_scale<=0 ?
1100                 (space>>(-sysctl_tcp_adv_win_scale)) :
1101                 space - (space>>sysctl_tcp_adv_win_scale);
1102 }
1103 
1104 /* Note: caller must be prepared to deal with negative returns */
1105 static inline int tcp_space(const struct sock *sk)
1106 {
1107         return tcp_win_from_space(sk->sk_rcvbuf -
1108                                   atomic_read(&sk->sk_rmem_alloc));
1109 }
1110 
1111 static inline int tcp_full_space(const struct sock *sk)
1112 {
1113         return tcp_win_from_space(sk->sk_rcvbuf);
1114 }
1115 
1116 static inline void tcp_openreq_init(struct request_sock *req,
1117                                     struct tcp_options_received *rx_opt,
1118                                     struct sk_buff *skb, struct sock *sk)
1119 {
1120         struct inet_request_sock *ireq = inet_rsk(req);
1121 
1122         req->rcv_wnd = 0;               /* So that tcp_send_synack() knows! */
1123         req->cookie_ts = 0;
1124         tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
1125         tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
1126         tcp_rsk(req)->snt_synack = tcp_time_stamp;
1127         req->mss = rx_opt->mss_clamp;
1128         req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
1129         ireq->tstamp_ok = rx_opt->tstamp_ok;
1130         ireq->sack_ok = rx_opt->sack_ok;
1131         ireq->snd_wscale = rx_opt->snd_wscale;
1132         ireq->wscale_ok = rx_opt->wscale_ok;
1133         ireq->acked = 0;
1134         ireq->ecn_ok = 0;
1135         ireq->ir_rmt_port = tcp_hdr(skb)->source;
1136         ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
1137         ireq->ir_mark = inet_request_mark(sk, skb);
1138 }
1139 
1140 extern void tcp_openreq_init_rwin(struct request_sock *req,
1141                                   struct sock *sk, struct dst_entry *dst);
1142 
1143 void tcp_enter_memory_pressure(struct sock *sk);
1144 
1145 static inline int keepalive_intvl_when(const struct tcp_sock *tp)
1146 {
1147         return tp->keepalive_intvl ? : sysctl_tcp_keepalive_intvl;
1148 }
1149 
1150 static inline int keepalive_time_when(const struct tcp_sock *tp)
1151 {
1152         return tp->keepalive_time ? : sysctl_tcp_keepalive_time;
1153 }
1154 
1155 static inline int keepalive_probes(const struct tcp_sock *tp)
1156 {
1157         return tp->keepalive_probes ? : sysctl_tcp_keepalive_probes;
1158 }
1159 
1160 static inline u32 keepalive_time_elapsed(const struct tcp_sock *tp)
1161 {
1162         const struct inet_connection_sock *icsk = &tp->inet_conn;
1163 
1164         return min_t(u32, tcp_time_stamp - icsk->icsk_ack.lrcvtime,
1165                           tcp_time_stamp - tp->rcv_tstamp);
1166 }
1167 
1168 static inline int tcp_fin_time(const struct sock *sk)
1169 {
1170         int fin_timeout = tcp_sk(sk)->linger2 ? : sysctl_tcp_fin_timeout;
1171         const int rto = inet_csk(sk)->icsk_rto;
1172 
1173         if (fin_timeout < (rto << 2) - (rto >> 1))
1174                 fin_timeout = (rto << 2) - (rto >> 1);
1175 
1176         return fin_timeout;
1177 }
1178 
1179 static inline bool tcp_paws_check(const struct tcp_options_received *rx_opt,
1180                                   int paws_win)
1181 {
1182         if ((s32)(rx_opt->ts_recent - rx_opt->rcv_tsval) <= paws_win)
1183                 return true;
1184         if (unlikely(get_seconds() >= rx_opt->ts_recent_stamp + TCP_PAWS_24DAYS))
1185                 return true;
1186         /*
1187          * Some OSes send SYN and SYNACK messages with tsval=0 tsecr=0,
1188          * then following tcp messages have valid values. Ignore 0 value,
1189          * or else 'negative' tsval might forbid us to accept their packets.
1190          */
1191         if (!rx_opt->ts_recent)
1192                 return true;
1193         return false;
1194 }
1195 
1196 static inline bool tcp_paws_reject(const struct tcp_options_received *rx_opt,
1197                                    int rst)
1198 {
1199         if (tcp_paws_check(rx_opt, 0))
1200                 return false;
1201 
1202         /* RST segments are not recommended to carry timestamp,
1203            and, if they do, it is recommended to ignore PAWS because
1204            "their cleanup function should take precedence over timestamps."
1205            Certainly, it is mistake. It is necessary to understand the reasons
1206            of this constraint to relax it: if peer reboots, clock may go
1207            out-of-sync and half-open connections will not be reset.
1208            Actually, the problem would be not existing if all
1209            the implementations followed draft about maintaining clock
1210            via reboots. Linux-2.2 DOES NOT!
1211 
1212            However, we can relax time bounds for RST segments to MSL.
1213          */
1214         if (rst && get_seconds() >= rx_opt->ts_recent_stamp + TCP_PAWS_MSL)
1215                 return false;
1216         return true;
1217 }
1218 
1219 static inline void tcp_mib_init(struct net *net)
1220 {
1221         /* See RFC 2012 */
1222         TCP_ADD_STATS_USER(net, TCP_MIB_RTOALGORITHM, 1);
1223         TCP_ADD_STATS_USER(net, TCP_MIB_RTOMIN, TCP_RTO_MIN*1000/HZ);
1224         TCP_ADD_STATS_USER(net, TCP_MIB_RTOMAX, TCP_RTO_MAX*1000/HZ);
1225         TCP_ADD_STATS_USER(net, TCP_MIB_MAXCONN, -1);
1226 }
1227 
1228 /* from STCP */
1229 static inline void tcp_clear_retrans_hints_partial(struct tcp_sock *tp)
1230 {
1231         tp->lost_skb_hint = NULL;
1232 }
1233 
1234 static inline void tcp_clear_all_retrans_hints(struct tcp_sock *tp)
1235 {
1236         tcp_clear_retrans_hints_partial(tp);
1237         tp->retransmit_skb_hint = NULL;
1238 }
1239 
1240 /* MD5 Signature */
1241 struct crypto_hash;
1242 
1243 union tcp_md5_addr {
1244         struct in_addr  a4;
1245 #if IS_ENABLED(CONFIG_IPV6)
1246         struct in6_addr a6;
1247 #endif
1248 };
1249 
1250 /* - key database */
1251 struct tcp_md5sig_key {
1252         struct hlist_node       node;
1253         u8                      keylen;
1254         u8                      family; /* AF_INET or AF_INET6 */
1255         union tcp_md5_addr      addr;
1256         u8                      key[TCP_MD5SIG_MAXKEYLEN];
1257         struct rcu_head         rcu;
1258 };
1259 
1260 /* - sock block */
1261 struct tcp_md5sig_info {
1262         struct hlist_head       head;
1263         struct rcu_head         rcu;
1264 };
1265 
1266 /* - pseudo header */
1267 struct tcp4_pseudohdr {
1268         __be32          saddr;
1269         __be32          daddr;
1270         __u8            pad;
1271         __u8            protocol;
1272         __be16          len;
1273 };
1274 
1275 struct tcp6_pseudohdr {
1276         struct in6_addr saddr;
1277         struct in6_addr daddr;
1278         __be32          len;
1279         __be32          protocol;       /* including padding */
1280 };
1281 
1282 union tcp_md5sum_block {
1283         struct tcp4_pseudohdr ip4;
1284 #if IS_ENABLED(CONFIG_IPV6)
1285         struct tcp6_pseudohdr ip6;
1286 #endif
1287 };
1288 
1289 /* - pool: digest algorithm, hash description and scratch buffer */
1290 struct tcp_md5sig_pool {
1291         struct hash_desc        md5_desc;
1292         union tcp_md5sum_block  md5_blk;
1293 };
1294 
1295 /* - functions */
1296 int tcp_v4_md5_hash_skb(char *md5_hash, struct tcp_md5sig_key *key,
1297                         const struct sock *sk, const struct request_sock *req,
1298                         const struct sk_buff *skb);
1299 int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
1300                    int family, const u8 *newkey, u8 newkeylen, gfp_t gfp);
1301 int tcp_md5_do_del(struct sock *sk, const union tcp_md5_addr *addr,
1302                    int family);
1303 struct tcp_md5sig_key *tcp_v4_md5_lookup(struct sock *sk,
1304                                          struct sock *addr_sk);
1305 
1306 #ifdef CONFIG_TCP_MD5SIG
1307 struct tcp_md5sig_key *tcp_md5_do_lookup(struct sock *sk,
1308                                          const union tcp_md5_addr *addr,
1309                                          int family);
1310 #define tcp_twsk_md5_key(twsk)  ((twsk)->tw_md5_key)
1311 #else
1312 static inline struct tcp_md5sig_key *tcp_md5_do_lookup(struct sock *sk,
1313                                          const union tcp_md5_addr *addr,
1314                                          int family)
1315 {
1316         return NULL;
1317 }
1318 #define tcp_twsk_md5_key(twsk)  NULL
1319 #endif
1320 
1321 bool tcp_alloc_md5sig_pool(void);
1322 
1323 struct tcp_md5sig_pool *tcp_get_md5sig_pool(void);
1324 static inline void tcp_put_md5sig_pool(void)
1325 {
1326         local_bh_enable();
1327 }
1328 
1329 int tcp_md5_hash_header(struct tcp_md5sig_pool *, const struct tcphdr *);
1330 int tcp_md5_hash_skb_data(struct tcp_md5sig_pool *, const struct sk_buff *,
1331                           unsigned int header_len);
1332 int tcp_md5_hash_key(struct tcp_md5sig_pool *hp,
1333                      const struct tcp_md5sig_key *key);
1334 
1335 /* From tcp_fastopen.c */
1336 void tcp_fastopen_cache_get(struct sock *sk, u16 *mss,
1337                             struct tcp_fastopen_cookie *cookie, int *syn_loss,
1338                             unsigned long *last_syn_loss);
1339 void tcp_fastopen_cache_set(struct sock *sk, u16 mss,
1340                             struct tcp_fastopen_cookie *cookie, bool syn_lost);
1341 struct tcp_fastopen_request {
1342         /* Fast Open cookie. Size 0 means a cookie request */
1343         struct tcp_fastopen_cookie      cookie;
1344         struct msghdr                   *data;  /* data in MSG_FASTOPEN */
1345         size_t                          size;
1346         int                             copied; /* queued in tcp_connect() */
1347 };
1348 void tcp_free_fastopen_req(struct tcp_sock *tp);
1349 
1350 extern struct tcp_fastopen_context __rcu *tcp_fastopen_ctx;
1351 int tcp_fastopen_reset_cipher(void *key, unsigned int len);
1352 bool tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
1353                       struct request_sock *req,
1354                       struct tcp_fastopen_cookie *foc,
1355                       struct dst_entry *dst);
1356 void tcp_fastopen_init_key_once(bool publish);
1357 #define TCP_FASTOPEN_KEY_LENGTH 16
1358 
1359 /* Fastopen key context */
1360 struct tcp_fastopen_context {
1361         struct crypto_cipher    *tfm;
1362         __u8                    key[TCP_FASTOPEN_KEY_LENGTH];
1363         struct rcu_head         rcu;
1364 };
1365 
1366 /* write queue abstraction */
1367 static inline void tcp_write_queue_purge(struct sock *sk)
1368 {
1369         struct sk_buff *skb;
1370 
1371         while ((skb = __skb_dequeue(&sk->sk_write_queue)) != NULL)
1372                 sk_wmem_free_skb(sk, skb);
1373         sk_mem_reclaim(sk);
1374         tcp_clear_all_retrans_hints(tcp_sk(sk));
1375 }
1376 
1377 static inline struct sk_buff *tcp_write_queue_head(const struct sock *sk)
1378 {
1379         return skb_peek(&sk->sk_write_queue);
1380 }
1381 
1382 static inline struct sk_buff *tcp_write_queue_tail(const struct sock *sk)
1383 {
1384         return skb_peek_tail(&sk->sk_write_queue);
1385 }
1386 
1387 static inline struct sk_buff *tcp_write_queue_next(const struct sock *sk,
1388                                                    const struct sk_buff *skb)
1389 {
1390         return skb_queue_next(&sk->sk_write_queue, skb);
1391 }
1392 
1393 static inline struct sk_buff *tcp_write_queue_prev(const struct sock *sk,
1394                                                    const struct sk_buff *skb)
1395 {
1396         return skb_queue_prev(&sk->sk_write_queue, skb);
1397 }
1398 
1399 #define tcp_for_write_queue(skb, sk)                                    \
1400         skb_queue_walk(&(sk)->sk_write_queue, skb)
1401 
1402 #define tcp_for_write_queue_from(skb, sk)                               \
1403         skb_queue_walk_from(&(sk)->sk_write_queue, skb)
1404 
1405 #define tcp_for_write_queue_from_safe(skb, tmp, sk)                     \
1406         skb_queue_walk_from_safe(&(sk)->sk_write_queue, skb, tmp)
1407 
1408 static inline struct sk_buff *tcp_send_head(const struct sock *sk)
1409 {
1410         return sk->sk_send_head;
1411 }
1412 
1413 static inline bool tcp_skb_is_last(const struct sock *sk,
1414                                    const struct sk_buff *skb)
1415 {
1416         return skb_queue_is_last(&sk->sk_write_queue, skb);
1417 }
1418 
1419 static inline void tcp_advance_send_head(struct sock *sk, const struct sk_buff *skb)
1420 {
1421         if (tcp_skb_is_last(sk, skb))
1422                 sk->sk_send_head = NULL;
1423         else
1424                 sk->sk_send_head = tcp_write_queue_next(sk, skb);
1425 }
1426 
1427 static inline void tcp_check_send_head(struct sock *sk, struct sk_buff *skb_unlinked)
1428 {
1429         if (sk->sk_send_head == skb_unlinked)
1430                 sk->sk_send_head = NULL;
1431 }
1432 
1433 static inline void tcp_init_send_head(struct sock *sk)
1434 {
1435         sk->sk_send_head = NULL;
1436 }
1437 
1438 static inline void __tcp_add_write_queue_tail(struct sock *sk, struct sk_buff *skb)
1439 {
1440         __skb_queue_tail(&sk->sk_write_queue, skb);
1441 }
1442 
1443 static inline void tcp_add_write_queue_tail(struct sock *sk, struct sk_buff *skb)
1444 {
1445         __tcp_add_write_queue_tail(sk, skb);
1446 
1447         /* Queue it, remembering where we must start sending. */
1448         if (sk->sk_send_head == NULL) {
1449                 sk->sk_send_head = skb;
1450 
1451                 if (tcp_sk(sk)->highest_sack == NULL)
1452                         tcp_sk(sk)->highest_sack = skb;
1453         }
1454 }
1455 
1456 static inline void __tcp_add_write_queue_head(struct sock *sk, struct sk_buff *skb)
1457 {
1458         __skb_queue_head(&sk->sk_write_queue, skb);
1459 }
1460 
1461 /* Insert buff after skb on the write queue of sk.  */
1462 static inline void tcp_insert_write_queue_after(struct sk_buff *skb,
1463                                                 struct sk_buff *buff,
1464                                                 struct sock *sk)
1465 {
1466         __skb_queue_after(&sk->sk_write_queue, skb, buff);
1467 }
1468 
1469 /* Insert new before skb on the write queue of sk.  */
1470 static inline void tcp_insert_write_queue_before(struct sk_buff *new,
1471                                                   struct sk_buff *skb,
1472                                                   struct sock *sk)
1473 {
1474         __skb_queue_before(&sk->sk_write_queue, skb, new);
1475 
1476         if (sk->sk_send_head == skb)
1477                 sk->sk_send_head = new;
1478 }
1479 
1480 static inline void tcp_unlink_write_queue(struct sk_buff *skb, struct sock *sk)
1481 {
1482         __skb_unlink(skb, &sk->sk_write_queue);
1483 }
1484 
1485 static inline bool tcp_write_queue_empty(struct sock *sk)
1486 {
1487         return skb_queue_empty(&sk->sk_write_queue);
1488 }
1489 
1490 static inline void tcp_push_pending_frames(struct sock *sk)
1491 {
1492         if (tcp_send_head(sk)) {
1493                 struct tcp_sock *tp = tcp_sk(sk);
1494 
1495                 __tcp_push_pending_frames(sk, tcp_current_mss(sk), tp->nonagle);
1496         }
1497 }
1498 
1499 /* Start sequence of the skb just after the highest skb with SACKed
1500  * bit, valid only if sacked_out > 0 or when the caller has ensured
1501  * validity by itself.
1502  */
1503 static inline u32 tcp_highest_sack_seq(struct tcp_sock *tp)
1504 {
1505         if (!tp->sacked_out)
1506                 return tp->snd_una;
1507 
1508         if (tp->highest_sack == NULL)
1509                 return tp->snd_nxt;
1510 
1511         return TCP_SKB_CB(tp->highest_sack)->seq;
1512 }
1513 
1514 static inline void tcp_advance_highest_sack(struct sock *sk, struct sk_buff *skb)
1515 {
1516         tcp_sk(sk)->highest_sack = tcp_skb_is_last(sk, skb) ? NULL :
1517                                                 tcp_write_queue_next(sk, skb);
1518 }
1519 
1520 static inline struct sk_buff *tcp_highest_sack(struct sock *sk)
1521 {
1522         return tcp_sk(sk)->highest_sack;
1523 }
1524 
1525 static inline void tcp_highest_sack_reset(struct sock *sk)
1526 {
1527         tcp_sk(sk)->highest_sack = tcp_write_queue_head(sk);
1528 }
1529 
1530 /* Called when old skb is about to be deleted (to be combined with new skb) */
1531 static inline void tcp_highest_sack_combine(struct sock *sk,
1532                                             struct sk_buff *old,
1533                                             struct sk_buff *new)
1534 {
1535         if (tcp_sk(sk)->sacked_out && (old == tcp_sk(sk)->highest_sack))
1536                 tcp_sk(sk)->highest_sack = new;
1537 }
1538 
1539 /* Determines whether this is a thin stream (which may suffer from
1540  * increased latency). Used to trigger latency-reducing mechanisms.
1541  */
1542 static inline bool tcp_stream_is_thin(struct tcp_sock *tp)
1543 {
1544         return tp->packets_out < 4 && !tcp_in_initial_slowstart(tp);
1545 }
1546 
1547 /* /proc */
1548 enum tcp_seq_states {
1549         TCP_SEQ_STATE_LISTENING,
1550         TCP_SEQ_STATE_OPENREQ,
1551         TCP_SEQ_STATE_ESTABLISHED,
1552 };
1553 
1554 int tcp_seq_open(struct inode *inode, struct file *file);
1555 
1556 struct tcp_seq_afinfo {
1557         char                            *name;
1558         sa_family_t                     family;
1559         const struct file_operations    *seq_fops;
1560         struct seq_operations           seq_ops;
1561 };
1562 
1563 struct tcp_iter_state {
1564         struct seq_net_private  p;
1565         sa_family_t             family;
1566         enum tcp_seq_states     state;
1567         struct sock             *syn_wait_sk;
1568         int                     bucket, offset, sbucket, num;
1569         kuid_t                  uid;
1570         loff_t                  last_pos;
1571 };
1572 
1573 int tcp_proc_register(struct net *net, struct tcp_seq_afinfo *afinfo);
1574 void tcp_proc_unregister(struct net *net, struct tcp_seq_afinfo *afinfo);
1575 
1576 extern struct request_sock_ops tcp_request_sock_ops;
1577 extern struct request_sock_ops tcp6_request_sock_ops;
1578 
1579 void tcp_v4_destroy_sock(struct sock *sk);
1580 
1581 struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
1582                                 netdev_features_t features);
1583 struct sk_buff **tcp_gro_receive(struct sk_buff **head, struct sk_buff *skb);
1584 int tcp_gro_complete(struct sk_buff *skb);
1585 
1586 void __tcp_v4_send_check(struct sk_buff *skb, __be32 saddr, __be32 daddr);
1587 
1588 static inline u32 tcp_notsent_lowat(const struct tcp_sock *tp)
1589 {
1590         return tp->notsent_lowat ?: sysctl_tcp_notsent_lowat;
1591 }
1592 
1593 static inline bool tcp_stream_memory_free(const struct sock *sk)
1594 {
1595         const struct tcp_sock *tp = tcp_sk(sk);
1596         u32 notsent_bytes = tp->write_seq - tp->snd_nxt;
1597 
1598         return notsent_bytes < tcp_notsent_lowat(tp);
1599 }
1600 
1601 #ifdef CONFIG_PROC_FS
1602 int tcp4_proc_init(void);
1603 void tcp4_proc_exit(void);
1604 #endif
1605 
1606 int tcp_rtx_synack(struct sock *sk, struct request_sock *req);
1607 int tcp_conn_request(struct request_sock_ops *rsk_ops,
1608                      const struct tcp_request_sock_ops *af_ops,
1609                      struct sock *sk, struct sk_buff *skb);
1610 
1611 /* TCP af-specific functions */
1612 struct tcp_sock_af_ops {
1613 #ifdef CONFIG_TCP_MD5SIG
1614         struct tcp_md5sig_key   *(*md5_lookup) (struct sock *sk,
1615                                                 struct sock *addr_sk);
1616         int                     (*calc_md5_hash) (char *location,
1617                                                   struct tcp_md5sig_key *md5,
1618                                                   const struct sock *sk,
1619                                                   const struct request_sock *req,
1620                                                   const struct sk_buff *skb);
1621         int                     (*md5_parse) (struct sock *sk,
1622                                               char __user *optval,
1623                                               int optlen);
1624 #endif
1625 };
1626 
1627 struct tcp_request_sock_ops {
1628         u16 mss_clamp;
1629 #ifdef CONFIG_TCP_MD5SIG
1630         struct tcp_md5sig_key   *(*md5_lookup) (struct sock *sk,
1631                                                 struct request_sock *req);
1632         int                     (*calc_md5_hash) (char *location,
1633                                                   struct tcp_md5sig_key *md5,
1634                                                   const struct sock *sk,
1635                                                   const struct request_sock *req,
1636                                                   const struct sk_buff *skb);
1637 #endif
1638         void (*init_req)(struct request_sock *req, struct sock *sk,
1639                          struct sk_buff *skb);
1640 #ifdef CONFIG_SYN_COOKIES
1641         __u32 (*cookie_init_seq)(struct sock *sk, const struct sk_buff *skb,
1642                                  __u16 *mss);
1643 #endif
1644         struct dst_entry *(*route_req)(struct sock *sk, struct flowi *fl,
1645                                        const struct request_sock *req,
1646                                        bool *strict);
1647         __u32 (*init_seq)(const struct sk_buff *skb);
1648         int (*send_synack)(struct sock *sk, struct dst_entry *dst,
1649                            struct flowi *fl, struct request_sock *req,
1650                            u16 queue_mapping, struct tcp_fastopen_cookie *foc);
1651         void (*queue_hash_add)(struct sock *sk, struct request_sock *req,
1652                                const unsigned long timeout);
1653 };
1654 
1655 #ifdef CONFIG_SYN_COOKIES
1656 static inline __u32 cookie_init_sequence(const struct tcp_request_sock_ops *ops,
1657                                          struct sock *sk, struct sk_buff *skb,
1658                                          __u16 *mss)
1659 {
1660         return ops->cookie_init_seq(sk, skb, mss);
1661 }
1662 #else
1663 static inline __u32 cookie_init_sequence(const struct tcp_request_sock_ops *ops,
1664                                          struct sock *sk, struct sk_buff *skb,
1665                                          __u16 *mss)
1666 {
1667         return 0;
1668 }
1669 #endif
1670 
1671 int tcpv4_offload_init(void);
1672 
1673 void tcp_v4_init(void);
1674 void tcp_init(void);
1675 
1676 /*
1677  * Save and compile IPv4 options, return a pointer to it
1678  */
1679 static inline struct ip_options_rcu *tcp_v4_save_options(struct sk_buff *skb)
1680 {
1681         const struct ip_options *opt = &TCP_SKB_CB(skb)->header.h4.opt;
1682         struct ip_options_rcu *dopt = NULL;
1683 
1684         if (opt->optlen) {
1685                 int opt_size = sizeof(*dopt) + opt->optlen;
1686 
1687                 dopt = kmalloc(opt_size, GFP_ATOMIC);
1688                 if (dopt && __ip_options_echo(&dopt->opt, skb, opt)) {
1689                         kfree(dopt);
1690                         dopt = NULL;
1691                 }
1692         }
1693         return dopt;
1694 }
1695 
1696 #endif  /* _TCP_H */
1697 

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