1 /* SPDX-License-Identifier: GPL-2.0-or-later */
2 /*
3  * INET		An implementation of the TCP/IP protocol suite for the LINUX
4  *		operating system.  INET is implemented using the  BSD Socket
5  *		interface as the means of communication with the user level.
6  *
7  *		Definitions for the TCP protocol.
8  *
9  * Version:	@(#)tcp.h	1.0.2	04/28/93
10  *
11  * Author:	Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
12  */
13 #ifndef _LINUX_TCP_H
14 #define _LINUX_TCP_H
15 
16 
17 #include <linux/skbuff.h>
18 #include <linux/win_minmax.h>
19 #include <net/sock.h>
20 #include <net/inet_connection_sock.h>
21 #include <net/inet_timewait_sock.h>
22 #include <uapi/linux/tcp.h>
23 
tcp_hdr(const struct sk_buff * skb)24 static inline struct tcphdr *tcp_hdr(const struct sk_buff *skb)
25 {
26 	return (struct tcphdr *)skb_transport_header(skb);
27 }
28 
__tcp_hdrlen(const struct tcphdr * th)29 static inline unsigned int __tcp_hdrlen(const struct tcphdr *th)
30 {
31 	return th->doff * 4;
32 }
33 
tcp_hdrlen(const struct sk_buff * skb)34 static inline unsigned int tcp_hdrlen(const struct sk_buff *skb)
35 {
36 	return __tcp_hdrlen(tcp_hdr(skb));
37 }
38 
inner_tcp_hdr(const struct sk_buff * skb)39 static inline struct tcphdr *inner_tcp_hdr(const struct sk_buff *skb)
40 {
41 	return (struct tcphdr *)skb_inner_transport_header(skb);
42 }
43 
inner_tcp_hdrlen(const struct sk_buff * skb)44 static inline unsigned int inner_tcp_hdrlen(const struct sk_buff *skb)
45 {
46 	return inner_tcp_hdr(skb)->doff * 4;
47 }
48 
tcp_optlen(const struct sk_buff * skb)49 static inline unsigned int tcp_optlen(const struct sk_buff *skb)
50 {
51 	return (tcp_hdr(skb)->doff - 5) * 4;
52 }
53 
54 /* TCP Fast Open */
55 #define TCP_FASTOPEN_COOKIE_MIN	4	/* Min Fast Open Cookie size in bytes */
56 #define TCP_FASTOPEN_COOKIE_MAX	16	/* Max Fast Open Cookie size in bytes */
57 #define TCP_FASTOPEN_COOKIE_SIZE 8	/* the size employed by this impl. */
58 
59 /* TCP Fast Open Cookie as stored in memory */
60 struct tcp_fastopen_cookie {
61 	__le64	val[DIV_ROUND_UP(TCP_FASTOPEN_COOKIE_MAX, sizeof(u64))];
62 	s8	len;
63 	bool	exp;	/* In RFC6994 experimental option format */
64 };
65 
66 /* This defines a selective acknowledgement block. */
67 struct tcp_sack_block_wire {
68 	__be32	start_seq;
69 	__be32	end_seq;
70 };
71 
72 struct tcp_sack_block {
73 	u32	start_seq;
74 	u32	end_seq;
75 };
76 
77 /*These are used to set the sack_ok field in struct tcp_options_received */
78 #define TCP_SACK_SEEN     (1 << 0)   /*1 = peer is SACK capable, */
79 #define TCP_DSACK_SEEN    (1 << 2)   /*1 = DSACK was received from peer*/
80 
81 struct tcp_options_received {
82 /*	PAWS/RTTM data	*/
83 	int	ts_recent_stamp;/* Time we stored ts_recent (for aging) */
84 	u32	ts_recent;	/* Time stamp to echo next		*/
85 	u32	rcv_tsval;	/* Time stamp value             	*/
86 	u32	rcv_tsecr;	/* Time stamp echo reply        	*/
87 	u16 	saw_tstamp : 1,	/* Saw TIMESTAMP on last packet		*/
88 		tstamp_ok : 1,	/* TIMESTAMP seen on SYN packet		*/
89 		dsack : 1,	/* D-SACK is scheduled			*/
90 		wscale_ok : 1,	/* Wscale seen on SYN packet		*/
91 		sack_ok : 3,	/* SACK seen on SYN packet		*/
92 		smc_ok : 1,	/* SMC seen on SYN packet		*/
93 		snd_wscale : 4,	/* Window scaling received from sender	*/
94 		rcv_wscale : 4;	/* Window scaling to send to receiver	*/
95 	u8	saw_unknown:1,	/* Received unknown option		*/
96 		unused:7;
97 	u8	num_sacks;	/* Number of SACK blocks		*/
98 	u16	user_mss;	/* mss requested by user in ioctl	*/
99 	u16	mss_clamp;	/* Maximal mss, negotiated at connection setup */
100 };
101 
tcp_clear_options(struct tcp_options_received * rx_opt)102 static inline void tcp_clear_options(struct tcp_options_received *rx_opt)
103 {
104 	rx_opt->tstamp_ok = rx_opt->sack_ok = 0;
105 	rx_opt->wscale_ok = rx_opt->snd_wscale = 0;
106 #if IS_ENABLED(CONFIG_SMC)
107 	rx_opt->smc_ok = 0;
108 #endif
109 }
110 
111 /* This is the max number of SACKS that we'll generate and process. It's safe
112  * to increase this, although since:
113  *   size = TCPOLEN_SACK_BASE_ALIGNED (4) + n * TCPOLEN_SACK_PERBLOCK (8)
114  * only four options will fit in a standard TCP header */
115 #define TCP_NUM_SACKS 4
116 
117 struct tcp_request_sock_ops;
118 
119 struct tcp_request_sock {
120 	struct inet_request_sock 	req;
121 	const struct tcp_request_sock_ops *af_specific;
122 	u64				snt_synack; /* first SYNACK sent time */
123 	bool				tfo_listener;
124 	bool				is_mptcp;
125 #if IS_ENABLED(CONFIG_MPTCP)
126 	bool				drop_req;
127 #endif
128 	u32				txhash;
129 	u32				rcv_isn;
130 	u32				snt_isn;
131 	u32				ts_off;
132 	u32				last_oow_ack_time; /* last SYNACK */
133 	u32				rcv_nxt; /* the ack # by SYNACK. For
134 						  * FastOpen it's the seq#
135 						  * after data-in-SYN.
136 						  */
137 	u8				syn_tos;
138 };
139 
tcp_rsk(const struct request_sock * req)140 static inline struct tcp_request_sock *tcp_rsk(const struct request_sock *req)
141 {
142 	return (struct tcp_request_sock *)req;
143 }
144 
145 struct tcp_sock {
146 	/* inet_connection_sock has to be the first member of tcp_sock */
147 	struct inet_connection_sock	inet_conn;
148 	u16	tcp_header_len;	/* Bytes of tcp header to send		*/
149 	u16	gso_segs;	/* Max number of segs per GSO packet	*/
150 
151 /*
152  *	Header prediction flags
153  *	0x5?10 << 16 + snd_wnd in net byte order
154  */
155 	__be32	pred_flags;
156 
157 /*
158  *	RFC793 variables by their proper names. This means you can
159  *	read the code and the spec side by side (and laugh ...)
160  *	See RFC793 and RFC1122. The RFC writes these in capitals.
161  */
162 	u64	bytes_received;	/* RFC4898 tcpEStatsAppHCThruOctetsReceived
163 				 * sum(delta(rcv_nxt)), or how many bytes
164 				 * were acked.
165 				 */
166 	u32	segs_in;	/* RFC4898 tcpEStatsPerfSegsIn
167 				 * total number of segments in.
168 				 */
169 	u32	data_segs_in;	/* RFC4898 tcpEStatsPerfDataSegsIn
170 				 * total number of data segments in.
171 				 */
172  	u32	rcv_nxt;	/* What we want to receive next 	*/
173 	u32	copied_seq;	/* Head of yet unread data		*/
174 	u32	rcv_wup;	/* rcv_nxt on last window update sent	*/
175  	u32	snd_nxt;	/* Next sequence we send		*/
176 	u32	segs_out;	/* RFC4898 tcpEStatsPerfSegsOut
177 				 * The total number of segments sent.
178 				 */
179 	u32	data_segs_out;	/* RFC4898 tcpEStatsPerfDataSegsOut
180 				 * total number of data segments sent.
181 				 */
182 	u64	bytes_sent;	/* RFC4898 tcpEStatsPerfHCDataOctetsOut
183 				 * total number of data bytes sent.
184 				 */
185 	u64	bytes_acked;	/* RFC4898 tcpEStatsAppHCThruOctetsAcked
186 				 * sum(delta(snd_una)), or how many bytes
187 				 * were acked.
188 				 */
189 	u32	dsack_dups;	/* RFC4898 tcpEStatsStackDSACKDups
190 				 * total number of DSACK blocks received
191 				 */
192  	u32	snd_una;	/* First byte we want an ack for	*/
193  	u32	snd_sml;	/* Last byte of the most recently transmitted small packet */
194 	u32	rcv_tstamp;	/* timestamp of last received ACK (for keepalives) */
195 	u32	lsndtime;	/* timestamp of last sent data packet (for restart window) */
196 	u32	last_oow_ack_time;  /* timestamp of last out-of-window ACK */
197 	u32	compressed_ack_rcv_nxt;
198 
199 	u32	tsoffset;	/* timestamp offset */
200 
201 	struct list_head tsq_node; /* anchor in tsq_tasklet.head list */
202 	struct list_head tsorted_sent_queue; /* time-sorted sent but un-SACKed skbs */
203 
204 	u32	snd_wl1;	/* Sequence for window update		*/
205 	u32	snd_wnd;	/* The window we expect to receive	*/
206 	u32	max_window;	/* Maximal window ever seen from peer	*/
207 	u32	mss_cache;	/* Cached effective mss, not including SACKS */
208 
209 	u32	window_clamp;	/* Maximal window to advertise		*/
210 	u32	rcv_ssthresh;	/* Current window clamp			*/
211 
212 	/* Information of the most recently (s)acked skb */
213 	struct tcp_rack {
214 		u64 mstamp; /* (Re)sent time of the skb */
215 		u32 rtt_us;  /* Associated RTT */
216 		u32 end_seq; /* Ending TCP sequence of the skb */
217 		u32 last_delivered; /* tp->delivered at last reo_wnd adj */
218 		u8 reo_wnd_steps;   /* Allowed reordering window */
219 #define TCP_RACK_RECOVERY_THRESH 16
220 		u8 reo_wnd_persist:5, /* No. of recovery since last adj */
221 		   dsack_seen:1, /* Whether DSACK seen after last adj */
222 		   advanced:1;	 /* mstamp advanced since last lost marking */
223 	} rack;
224 	u16	advmss;		/* Advertised MSS			*/
225 	u8	compressed_ack;
226 	u8	dup_ack_counter:2,
227 		tlp_retrans:1,	/* TLP is a retransmission */
228 		unused:5;
229 	u32	chrono_start;	/* Start time in jiffies of a TCP chrono */
230 	u32	chrono_stat[3];	/* Time in jiffies for chrono_stat stats */
231 	u8	chrono_type:2,	/* current chronograph type */
232 		rate_app_limited:1,  /* rate_{delivered,interval_us} limited? */
233 		fastopen_connect:1, /* FASTOPEN_CONNECT sockopt */
234 		fastopen_no_cookie:1, /* Allow send/recv SYN+data without a cookie */
235 		is_sack_reneg:1,    /* in recovery from loss with SACK reneg? */
236 		fastopen_client_fail:2; /* reason why fastopen failed */
237 	u8	nonagle     : 4,/* Disable Nagle algorithm?             */
238 		thin_lto    : 1,/* Use linear timeouts for thin streams */
239 		recvmsg_inq : 1,/* Indicate # of bytes in queue upon recvmsg */
240 		repair      : 1,
241 		frto        : 1;/* F-RTO (RFC5682) activated in CA_Loss */
242 	u8	repair_queue;
243 	u8	save_syn:2,	/* Save headers of SYN packet */
244 		syn_data:1,	/* SYN includes data */
245 		syn_fastopen:1,	/* SYN includes Fast Open option */
246 		syn_fastopen_exp:1,/* SYN includes Fast Open exp. option */
247 		syn_fastopen_ch:1, /* Active TFO re-enabling probe */
248 		syn_data_acked:1,/* data in SYN is acked by SYN-ACK */
249 		is_cwnd_limited:1;/* forward progress limited by snd_cwnd? */
250 	u32	tlp_high_seq;	/* snd_nxt at the time of TLP */
251 
252 	u32	tcp_tx_delay;	/* delay (in usec) added to TX packets */
253 	u64	tcp_wstamp_ns;	/* departure time for next sent data packet */
254 	u64	tcp_clock_cache; /* cache last tcp_clock_ns() (see tcp_mstamp_refresh()) */
255 
256 /* RTT measurement */
257 	u64	tcp_mstamp;	/* most recent packet received/sent */
258 	u32	srtt_us;	/* smoothed round trip time << 3 in usecs */
259 	u32	mdev_us;	/* medium deviation			*/
260 	u32	mdev_max_us;	/* maximal mdev for the last rtt period	*/
261 	u32	rttvar_us;	/* smoothed mdev_max			*/
262 	u32	rtt_seq;	/* sequence number to update rttvar	*/
263 	struct  minmax rtt_min;
264 
265 	u32	packets_out;	/* Packets which are "in flight"	*/
266 	u32	retrans_out;	/* Retransmitted packets out		*/
267 	u32	max_packets_out;  /* max packets_out in last window */
268 	u32	max_packets_seq;  /* right edge of max_packets_out flight */
269 
270 	u16	urg_data;	/* Saved octet of OOB data and control flags */
271 	u8	ecn_flags;	/* ECN status bits.			*/
272 	u8	keepalive_probes; /* num of allowed keep alive probes	*/
273 	u32	reordering;	/* Packet reordering metric.		*/
274 	u32	reord_seen;	/* number of data packet reordering events */
275 	u32	snd_up;		/* Urgent pointer		*/
276 
277 /*
278  *      Options received (usually on last packet, some only on SYN packets).
279  */
280 	struct tcp_options_received rx_opt;
281 
282 /*
283  *	Slow start and congestion control (see also Nagle, and Karn & Partridge)
284  */
285  	u32	snd_ssthresh;	/* Slow start size threshold		*/
286  	u32	snd_cwnd;	/* Sending congestion window		*/
287 	u32	snd_cwnd_cnt;	/* Linear increase counter		*/
288 	u32	snd_cwnd_clamp; /* Do not allow snd_cwnd to grow above this */
289 	u32	snd_cwnd_used;
290 	u32	snd_cwnd_stamp;
291 	u32	prior_cwnd;	/* cwnd right before starting loss recovery */
292 	u32	prr_delivered;	/* Number of newly delivered packets to
293 				 * receiver in Recovery. */
294 	u32	prr_out;	/* Total number of pkts sent during Recovery. */
295 	u32	delivered;	/* Total data packets delivered incl. rexmits */
296 	u32	delivered_ce;	/* Like the above but only ECE marked packets */
297 	u32	lost;		/* Total data packets lost incl. rexmits */
298 	u32	app_limited;	/* limited until "delivered" reaches this val */
299 	u64	first_tx_mstamp;  /* start of window send phase */
300 	u64	delivered_mstamp; /* time we reached "delivered" */
301 	u32	rate_delivered;    /* saved rate sample: packets delivered */
302 	u32	rate_interval_us;  /* saved rate sample: time elapsed */
303 
304  	u32	rcv_wnd;	/* Current receiver window		*/
305 	u32	write_seq;	/* Tail(+1) of data held in tcp send buffer */
306 	u32	notsent_lowat;	/* TCP_NOTSENT_LOWAT */
307 	u32	pushed_seq;	/* Last pushed seq, required to talk to windows */
308 	u32	lost_out;	/* Lost packets			*/
309 	u32	sacked_out;	/* SACK'd packets			*/
310 
311 	struct hrtimer	pacing_timer;
312 	struct hrtimer	compressed_ack_timer;
313 
314 	/* from STCP, retrans queue hinting */
315 	struct sk_buff* lost_skb_hint;
316 	struct sk_buff *retransmit_skb_hint;
317 
318 	/* OOO segments go in this rbtree. Socket lock must be held. */
319 	struct rb_root	out_of_order_queue;
320 	struct sk_buff	*ooo_last_skb; /* cache rb_last(out_of_order_queue) */
321 
322 	/* SACKs data, these 2 need to be together (see tcp_options_write) */
323 	struct tcp_sack_block duplicate_sack[1]; /* D-SACK block */
324 	struct tcp_sack_block selective_acks[4]; /* The SACKS themselves*/
325 
326 	struct tcp_sack_block recv_sack_cache[4];
327 
328 	struct sk_buff *highest_sack;   /* skb just after the highest
329 					 * skb with SACKed bit set
330 					 * (validity guaranteed only if
331 					 * sacked_out > 0)
332 					 */
333 
334 	int     lost_cnt_hint;
335 
336 	u32	prior_ssthresh; /* ssthresh saved at recovery start	*/
337 	u32	high_seq;	/* snd_nxt at onset of congestion	*/
338 
339 	u32	retrans_stamp;	/* Timestamp of the last retransmit,
340 				 * also used in SYN-SENT to remember stamp of
341 				 * the first SYN. */
342 	u32	undo_marker;	/* snd_una upon a new recovery episode. */
343 	int	undo_retrans;	/* number of undoable retransmissions. */
344 	u64	bytes_retrans;	/* RFC4898 tcpEStatsPerfOctetsRetrans
345 				 * Total data bytes retransmitted
346 				 */
347 	u32	total_retrans;	/* Total retransmits for entire connection */
348 
349 	u32	urg_seq;	/* Seq of received urgent pointer */
350 	unsigned int		keepalive_time;	  /* time before keep alive takes place */
351 	unsigned int		keepalive_intvl;  /* time interval between keep alive probes */
352 
353 	int			linger2;
354 
355 
356 /* Sock_ops bpf program related variables */
357 #ifdef CONFIG_BPF
358 	u8	bpf_sock_ops_cb_flags;  /* Control calling BPF programs
359 					 * values defined in uapi/linux/tcp.h
360 					 */
361 #define BPF_SOCK_OPS_TEST_FLAG(TP, ARG) (TP->bpf_sock_ops_cb_flags & ARG)
362 #else
363 #define BPF_SOCK_OPS_TEST_FLAG(TP, ARG) 0
364 #endif
365 
366 	u16 timeout_rehash;	/* Timeout-triggered rehash attempts */
367 
368 	u32 rcv_ooopack; /* Received out-of-order packets, for tcpinfo */
369 
370 /* Receiver side RTT estimation */
371 	u32 rcv_rtt_last_tsecr;
372 	struct {
373 		u32	rtt_us;
374 		u32	seq;
375 		u64	time;
376 	} rcv_rtt_est;
377 
378 /* Receiver queue space */
379 	struct {
380 		u32	space;
381 		u32	seq;
382 		u64	time;
383 	} rcvq_space;
384 
385 /* TCP-specific MTU probe information. */
386 	struct {
387 		u32		  probe_seq_start;
388 		u32		  probe_seq_end;
389 	} mtu_probe;
390 	u32	mtu_info; /* We received an ICMP_FRAG_NEEDED / ICMPV6_PKT_TOOBIG
391 			   * while socket was owned by user.
392 			   */
393 #if IS_ENABLED(CONFIG_MPTCP)
394 	bool	is_mptcp;
395 #endif
396 #if IS_ENABLED(CONFIG_SMC)
397 	bool	(*smc_hs_congested)(const struct sock *sk);
398 	bool	syn_smc;	/* SYN includes SMC */
399 #endif
400 
401 #ifdef CONFIG_TCP_MD5SIG
402 /* TCP AF-Specific parts; only used by MD5 Signature support so far */
403 	const struct tcp_sock_af_ops	*af_specific;
404 
405 /* TCP MD5 Signature Option information */
406 	struct tcp_md5sig_info	__rcu *md5sig_info;
407 #endif
408 
409 /* TCP fastopen related information */
410 	struct tcp_fastopen_request *fastopen_req;
411 	/* fastopen_rsk points to request_sock that resulted in this big
412 	 * socket. Used to retransmit SYNACKs etc.
413 	 */
414 	struct request_sock __rcu *fastopen_rsk;
415 	struct saved_syn *saved_syn;
416 };
417 
418 enum tsq_enum {
419 	TSQ_THROTTLED,
420 	TSQ_QUEUED,
421 	TCP_TSQ_DEFERRED,	   /* tcp_tasklet_func() found socket was owned */
422 	TCP_WRITE_TIMER_DEFERRED,  /* tcp_write_timer() found socket was owned */
423 	TCP_DELACK_TIMER_DEFERRED, /* tcp_delack_timer() found socket was owned */
424 	TCP_MTU_REDUCED_DEFERRED,  /* tcp_v{4|6}_err() could not call
425 				    * tcp_v{4|6}_mtu_reduced()
426 				    */
427 };
428 
429 enum tsq_flags {
430 	TSQF_THROTTLED			= (1UL << TSQ_THROTTLED),
431 	TSQF_QUEUED			= (1UL << TSQ_QUEUED),
432 	TCPF_TSQ_DEFERRED		= (1UL << TCP_TSQ_DEFERRED),
433 	TCPF_WRITE_TIMER_DEFERRED	= (1UL << TCP_WRITE_TIMER_DEFERRED),
434 	TCPF_DELACK_TIMER_DEFERRED	= (1UL << TCP_DELACK_TIMER_DEFERRED),
435 	TCPF_MTU_REDUCED_DEFERRED	= (1UL << TCP_MTU_REDUCED_DEFERRED),
436 };
437 
tcp_sk(const struct sock * sk)438 static inline struct tcp_sock *tcp_sk(const struct sock *sk)
439 {
440 	return (struct tcp_sock *)sk;
441 }
442 
443 struct tcp_timewait_sock {
444 	struct inet_timewait_sock tw_sk;
445 #define tw_rcv_nxt tw_sk.__tw_common.skc_tw_rcv_nxt
446 #define tw_snd_nxt tw_sk.__tw_common.skc_tw_snd_nxt
447 	u32			  tw_rcv_wnd;
448 	u32			  tw_ts_offset;
449 	u32			  tw_ts_recent;
450 
451 	/* The time we sent the last out-of-window ACK: */
452 	u32			  tw_last_oow_ack_time;
453 
454 	int			  tw_ts_recent_stamp;
455 	u32			  tw_tx_delay;
456 #ifdef CONFIG_TCP_MD5SIG
457 	struct tcp_md5sig_key	  *tw_md5_key;
458 #endif
459 };
460 
tcp_twsk(const struct sock * sk)461 static inline struct tcp_timewait_sock *tcp_twsk(const struct sock *sk)
462 {
463 	return (struct tcp_timewait_sock *)sk;
464 }
465 
tcp_passive_fastopen(const struct sock * sk)466 static inline bool tcp_passive_fastopen(const struct sock *sk)
467 {
468 	return sk->sk_state == TCP_SYN_RECV &&
469 	       rcu_access_pointer(tcp_sk(sk)->fastopen_rsk) != NULL;
470 }
471 
fastopen_queue_tune(struct sock * sk,int backlog)472 static inline void fastopen_queue_tune(struct sock *sk, int backlog)
473 {
474 	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
475 	int somaxconn = READ_ONCE(sock_net(sk)->core.sysctl_somaxconn);
476 
477 	queue->fastopenq.max_qlen = min_t(unsigned int, backlog, somaxconn);
478 }
479 
tcp_move_syn(struct tcp_sock * tp,struct request_sock * req)480 static inline void tcp_move_syn(struct tcp_sock *tp,
481 				struct request_sock *req)
482 {
483 	tp->saved_syn = req->saved_syn;
484 	req->saved_syn = NULL;
485 }
486 
tcp_saved_syn_free(struct tcp_sock * tp)487 static inline void tcp_saved_syn_free(struct tcp_sock *tp)
488 {
489 	kfree(tp->saved_syn);
490 	tp->saved_syn = NULL;
491 }
492 
tcp_saved_syn_len(const struct saved_syn * saved_syn)493 static inline u32 tcp_saved_syn_len(const struct saved_syn *saved_syn)
494 {
495 	return saved_syn->mac_hdrlen + saved_syn->network_hdrlen +
496 		saved_syn->tcp_hdrlen;
497 }
498 
499 struct sk_buff *tcp_get_timestamping_opt_stats(const struct sock *sk,
500 					       const struct sk_buff *orig_skb,
501 					       const struct sk_buff *ack_skb);
502 
tcp_mss_clamp(const struct tcp_sock * tp,u16 mss)503 static inline u16 tcp_mss_clamp(const struct tcp_sock *tp, u16 mss)
504 {
505 	/* We use READ_ONCE() here because socket might not be locked.
506 	 * This happens for listeners.
507 	 */
508 	u16 user_mss = READ_ONCE(tp->rx_opt.user_mss);
509 
510 	return (user_mss && user_mss < mss) ? user_mss : mss;
511 }
512 
513 int tcp_skb_shift(struct sk_buff *to, struct sk_buff *from, int pcount,
514 		  int shiftlen);
515 
516 void __tcp_sock_set_cork(struct sock *sk, bool on);
517 void tcp_sock_set_cork(struct sock *sk, bool on);
518 int tcp_sock_set_keepcnt(struct sock *sk, int val);
519 int tcp_sock_set_keepidle_locked(struct sock *sk, int val);
520 int tcp_sock_set_keepidle(struct sock *sk, int val);
521 int tcp_sock_set_keepintvl(struct sock *sk, int val);
522 void __tcp_sock_set_nodelay(struct sock *sk, bool on);
523 void tcp_sock_set_nodelay(struct sock *sk);
524 void tcp_sock_set_quickack(struct sock *sk, int val);
525 int tcp_sock_set_syncnt(struct sock *sk, int val);
526 void tcp_sock_set_user_timeout(struct sock *sk, u32 val);
527 
528 #endif	/* _LINUX_TCP_H */
529