xref: /openbmc/linux/include/net/tcp.h (revision c819e2cf)
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 void tcp_slow_start(struct tcp_sock *tp, u32 acked);
838 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w);
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