/* SPDX-License-Identifier: GPL-2.0-or-later */

  /*
   * INET		An implementation of the TCP/IP protocol suite for the LINUX
   *		operating system.  INET is implemented using the  BSD Socket
   *		interface as the means of communication with the user level.
   *
   *		Definitions for the TCP module.
   *
   * Version:	@(#)tcp.h	1.0.5	05/23/93
   *

   * Authors:	Ross Biro

   *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>

   */
  #ifndef _TCP_H
  #define _TCP_H

  #define FASTRETRANS_DEBUG 1

  #include <linux/list.h>
  #include <linux/tcp.h>

  #include <linux/bug.h>

  #include <linux/slab.h>
  #include <linux/cache.h>
  #include <linux/percpu.h>

  #include <linux/skbuff.h>

  #include <linux/kref.h>

  #include <linux/ktime.h>

  #include <linux/indirect_call_wrapper.h>

  
  #include <net/inet_connection_sock.h>

  #include <net/inet_timewait_sock.h>

  #include <net/inet_hashtables.h>

  #include <net/checksum.h>

  #include <net/request_sock.h>

  #include <net/sock_reuseport.h>

  #include <net/sock.h>
  #include <net/snmp.h>
  #include <net/ip.h>

  #include <net/tcp_states.h>

  #include <net/inet_ecn.h>

  #include <net/dst.h>

  #include <net/mptcp.h>

  #include <linux/seq_file.h>

  #include <linux/memcontrol.h>

  #include <linux/bpf-cgroup.h>

  #include <linux/siphash.h>

  extern struct inet_hashinfo tcp_hashinfo;

  extern struct percpu_counter tcp_orphan_count;

  void tcp_time_wait(struct sock *sk, int state, int timeo);

  #define MAX_TCP_HEADER	L1_CACHE_ALIGN(128 + MAX_HEADER)

  #define MAX_TCP_OPTION_SPACE 40

  #define TCP_MIN_SND_MSS		48
  #define TCP_MIN_GSO_SIZE	(TCP_MIN_SND_MSS - MAX_TCP_OPTION_SPACE)

  /*

   * Never offer a window over 32767 without using window scaling. Some

   * poor stacks do signed 16bit maths!

   */
  #define MAX_TCP_WINDOW		32767U
  
  /* Minimal accepted MSS. It is (60+60+8) - (20+20). */
  #define TCP_MIN_MSS		88U

  /* The initial MTU to use for probing */

  #define TCP_BASE_MSS		1024

  /* probing interval, default to 10 minutes as per RFC4821 */
  #define TCP_PROBE_INTERVAL	600

  /* Specify interval when tcp mtu probing will stop */
  #define TCP_PROBE_THRESHOLD	8

  /* After receiving this amount of duplicate ACKs fast retransmit starts. */
  #define TCP_FASTRETRANS_THRESH 3

  /* Maximal number of ACKs sent quickly to accelerate slow-start. */
  #define TCP_MAX_QUICKACKS	16U

  /* Maximal number of window scale according to RFC1323 */
  #define TCP_MAX_WSCALE		14U

  /* urg_data states */
  #define TCP_URG_VALID	0x0100
  #define TCP_URG_NOTYET	0x0200
  #define TCP_URG_READ	0x0400
  
  #define TCP_RETR1	3	/*
  				 * This is how many retries it does before it
  				 * tries to figure out if the gateway is
  				 * down. Minimal RFC value is 3; it corresponds
  				 * to ~3sec-8min depending on RTO.
  				 */
  
  #define TCP_RETR2	15	/*
  				 * This should take at least
  				 * 90 minutes to time out.
  				 * RFC1122 says that the limit is 100 sec.
  				 * 15 is ~13-30min depending on RTO.
  				 */

  #define TCP_SYN_RETRIES	 6	/* This is how many retries are done
  				 * when active opening a connection.
  				 * RFC1122 says the minimum retry MUST
  				 * be at least 180secs.  Nevertheless
  				 * this value is corresponding to
  				 * 63secs of retransmission with the
  				 * current initial RTO.
  				 */

  #define TCP_SYNACK_RETRIES 5	/* This is how may retries are done
  				 * when passive opening a connection.
  				 * This is corresponding to 31secs of
  				 * retransmission with the current
  				 * initial RTO.
  				 */

  #define TCP_TIMEWAIT_LEN (60*HZ) /* how long to wait to destroy TIME-WAIT
  				  * state, about 60 seconds	*/
  #define TCP_FIN_TIMEOUT	TCP_TIMEWAIT_LEN
                                   /* BSD style FIN_WAIT2 deadlock breaker.
  				  * It used to be 3min, new value is 60sec,
  				  * to combine FIN-WAIT-2 timeout with
  				  * TIME-WAIT timer.
  				  */

  #define TCP_FIN_TIMEOUT_MAX (120 * HZ) /* max TCP_LINGER2 value (two minutes) */

  
  #define TCP_DELACK_MAX	((unsigned)(HZ/5))	/* maximal time to delay before sending an ACK */
  #if HZ >= 100
  #define TCP_DELACK_MIN	((unsigned)(HZ/25))	/* minimal time to delay before sending an ACK */
  #define TCP_ATO_MIN	((unsigned)(HZ/25))
  #else
  #define TCP_DELACK_MIN	4U
  #define TCP_ATO_MIN	4U
  #endif
  #define TCP_RTO_MAX	((unsigned)(120*HZ))
  #define TCP_RTO_MIN	((unsigned)(HZ/5))

  #define TCP_TIMEOUT_MIN	(2U) /* Min timeout for TCP timers in jiffies */

  #define TCP_TIMEOUT_INIT ((unsigned)(1*HZ))	/* RFC6298 2.1 initial RTO value	*/

  #define TCP_TIMEOUT_FALLBACK ((unsigned)(3*HZ))	/* RFC 1122 initial RTO value, now
  						 * used as a fallback RTO for the
  						 * initial data transmission if no
  						 * valid RTT sample has been acquired,
  						 * most likely due to retrans in 3WHS.
  						 */

  
  #define TCP_RESOURCE_PROBE_INTERVAL ((unsigned)(HZ/2U)) /* Maximal interval between probes
  					                 * for local resources.
  					                 */

  #define TCP_KEEPALIVE_TIME	(120*60*HZ)	/* two hours */
  #define TCP_KEEPALIVE_PROBES	9		/* Max of 9 keepalive probes	*/
  #define TCP_KEEPALIVE_INTVL	(75*HZ)
  
  #define MAX_TCP_KEEPIDLE	32767
  #define MAX_TCP_KEEPINTVL	32767
  #define MAX_TCP_KEEPCNT		127
  #define MAX_TCP_SYNCNT		127
  
  #define TCP_SYNQ_INTERVAL	(HZ/5)	/* Period of SYNACK timer */

  
  #define TCP_PAWS_24DAYS	(60 * 60 * 24 * 24)
  #define TCP_PAWS_MSL	60		/* Per-host timestamps are invalidated
  					 * after this time. It should be equal
  					 * (or greater than) TCP_TIMEWAIT_LEN
  					 * to provide reliability equal to one
  					 * provided by timewait state.
  					 */
  #define TCP_PAWS_WINDOW	1		/* Replay window for per-host
  					 * timestamps. It must be less than
  					 * minimal timewait lifetime.
  					 */

  /*
   *	TCP option
   */

  #define TCPOPT_NOP		1	/* Padding */
  #define TCPOPT_EOL		0	/* End of options */
  #define TCPOPT_MSS		2	/* Segment size negotiating */
  #define TCPOPT_WINDOW		3	/* Window scaling */
  #define TCPOPT_SACK_PERM        4       /* SACK Permitted */
  #define TCPOPT_SACK             5       /* SACK Block */
  #define TCPOPT_TIMESTAMP	8	/* Better RTT estimations/PAWS */

  #define TCPOPT_MD5SIG		19	/* MD5 Signature (RFC2385) */

  #define TCPOPT_MPTCP		30	/* Multipath TCP (RFC6824) */

  #define TCPOPT_FASTOPEN		34	/* Fast open (RFC7413) */

  #define TCPOPT_EXP		254	/* Experimental */
  /* Magic number to be after the option value for sharing TCP
   * experimental options. See draft-ietf-tcpm-experimental-options-00.txt
   */
  #define TCPOPT_FASTOPEN_MAGIC	0xF989

  #define TCPOPT_SMC_MAGIC	0xE2D4C3D9

  
  /*
   *     TCP option lengths
   */
  
  #define TCPOLEN_MSS            4
  #define TCPOLEN_WINDOW         3
  #define TCPOLEN_SACK_PERM      2
  #define TCPOLEN_TIMESTAMP      10

  #define TCPOLEN_MD5SIG         18

  #define TCPOLEN_FASTOPEN_BASE  2

  #define TCPOLEN_EXP_FASTOPEN_BASE  4

  #define TCPOLEN_EXP_SMC_BASE   6

  
  /* But this is what stacks really send out. */
  #define TCPOLEN_TSTAMP_ALIGNED		12
  #define TCPOLEN_WSCALE_ALIGNED		4
  #define TCPOLEN_SACKPERM_ALIGNED	4
  #define TCPOLEN_SACK_BASE		2
  #define TCPOLEN_SACK_BASE_ALIGNED	4
  #define TCPOLEN_SACK_PERBLOCK		8

  #define TCPOLEN_MD5SIG_ALIGNED		20

  #define TCPOLEN_MSS_ALIGNED		4

  #define TCPOLEN_EXP_SMC_BASE_ALIGNED	8

  /* Flags in tp->nonagle */
  #define TCP_NAGLE_OFF		1	/* Nagle's algo is disabled */
  #define TCP_NAGLE_CORK		2	/* Socket is corked	    */

  #define TCP_NAGLE_PUSH		4	/* Cork is overridden for already queued data */

  /* TCP thin-stream limits */
  #define TCP_THIN_LINEAR_RETRIES 6       /* After 6 linear retries, do exp. backoff */

  /* TCP initial congestion window as per rfc6928 */

  #define TCP_INIT_CWND		10

  /* Bit Flags for sysctl_tcp_fastopen */
  #define	TFO_CLIENT_ENABLE	1

  #define	TFO_SERVER_ENABLE	2

  #define	TFO_CLIENT_NO_COOKIE	4	/* Data in SYN w/o cookie option */

  /* Accept SYN data w/o any cookie option */
  #define	TFO_SERVER_COOKIE_NOT_REQD	0x200
  
  /* Force enable TFO on all listeners, i.e., not requiring the

   * TCP_FASTOPEN socket option.

   */
  #define	TFO_SERVER_WO_SOCKOPT1	0x400

  /* sysctl variables for tcp */

  extern int sysctl_tcp_max_orphans;

  extern long sysctl_tcp_mem[3];

  #define TCP_RACK_LOSS_DETECTION  0x1 /* Use RACK to detect losses */

  #define TCP_RACK_STATIC_REO_WND  0x2 /* Use static RACK reo wnd */

  #define TCP_RACK_NO_DUPTHRESH    0x4 /* Do not use DUPACK threshold in RACK */

  extern atomic_long_t tcp_memory_allocated;

  extern struct percpu_counter tcp_sockets_allocated;

  extern unsigned long tcp_memory_pressure;

  /* optimized version of sk_under_memory_pressure() for TCP sockets */
  static inline bool tcp_under_memory_pressure(const struct sock *sk)
  {

  	if (mem_cgroup_sockets_enabled && sk->sk_memcg &&
  	    mem_cgroup_under_socket_pressure(sk->sk_memcg))

  		return true;

  	return READ_ONCE(tcp_memory_pressure);

  }

  /*

   * The next routines deal with comparing 32 bit unsigned ints
   * and worry about wraparound (automatic with unsigned arithmetic).
   */

  static inline bool before(__u32 seq1, __u32 seq2)

  {

          return (__s32)(seq1-seq2) < 0;

  }

  #define after(seq2, seq1) 	before(seq1, seq2)

  
  /* is s2<=s1<=s3 ? */

  static inline bool between(__u32 seq1, __u32 seq2, __u32 seq3)

  {
  	return seq3 - seq2 >= seq1 - seq2;
  }

  static inline bool tcp_out_of_memory(struct sock *sk)
  {
  	if (sk->sk_wmem_queued > SOCK_MIN_SNDBUF &&
  	    sk_memory_allocated(sk) > sk_prot_mem_limits(sk, 2))
  		return true;
  	return false;
  }

  void sk_forced_mem_schedule(struct sock *sk, int size);

  static inline bool tcp_too_many_orphans(struct sock *sk, int shift)

  {

  	struct percpu_counter *ocp = sk->sk_prot->orphan_count;
  	int orphans = percpu_counter_read_positive(ocp);
  
  	if (orphans << shift > sysctl_tcp_max_orphans) {
  		orphans = percpu_counter_sum_positive(ocp);
  		if (orphans << shift > sysctl_tcp_max_orphans)
  			return true;
  	}

  	return false;

  }

  bool tcp_check_oom(struct sock *sk, int shift);

  extern struct proto tcp_prot;

  #define TCP_INC_STATS(net, field)	SNMP_INC_STATS((net)->mib.tcp_statistics, field)

  #define __TCP_INC_STATS(net, field)	__SNMP_INC_STATS((net)->mib.tcp_statistics, field)

  #define TCP_DEC_STATS(net, field)	SNMP_DEC_STATS((net)->mib.tcp_statistics, field)

  #define TCP_ADD_STATS(net, field, val)	SNMP_ADD_STATS((net)->mib.tcp_statistics, field, val)

  void tcp_tasklet_init(void);

  int tcp_v4_err(struct sk_buff *skb, u32);

  
  void tcp_shutdown(struct sock *sk, int how);

  int tcp_v4_early_demux(struct sk_buff *skb);

  int tcp_v4_rcv(struct sk_buff *skb);
  
  int tcp_v4_tw_remember_stamp(struct inet_timewait_sock *tw);

  int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size);

  int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size);

  int tcp_sendpage(struct sock *sk, struct page *page, int offset, size_t size,
  		 int flags);

  int tcp_sendpage_locked(struct sock *sk, struct page *page, int offset,
  			size_t size, int flags);

  ssize_t do_tcp_sendpages(struct sock *sk, struct page *page, int offset,
  		 size_t size, int flags);

  int tcp_send_mss(struct sock *sk, int *size_goal, int flags);
  void tcp_push(struct sock *sk, int flags, int mss_now, int nonagle,
  	      int size_goal);

  void tcp_release_cb(struct sock *sk);
  void tcp_wfree(struct sk_buff *skb);
  void tcp_write_timer_handler(struct sock *sk);
  void tcp_delack_timer_handler(struct sock *sk);
  int tcp_ioctl(struct sock *sk, int cmd, unsigned long arg);

  int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb);

  void tcp_rcv_established(struct sock *sk, struct sk_buff *skb);

  void tcp_rcv_space_adjust(struct sock *sk);

  int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp);
  void tcp_twsk_destructor(struct sock *sk);
  ssize_t tcp_splice_read(struct socket *sk, loff_t *ppos,
  			struct pipe_inode_info *pipe, size_t len,
  			unsigned int flags);

  void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks);

  static inline void tcp_dec_quickack_mode(struct sock *sk,
  					 const unsigned int pkts)

  {

  	struct inet_connection_sock *icsk = inet_csk(sk);

  	if (icsk->icsk_ack.quick) {
  		if (pkts >= icsk->icsk_ack.quick) {
  			icsk->icsk_ack.quick = 0;

  			/* Leaving quickack mode we deflate ATO. */

  			icsk->icsk_ack.ato   = TCP_ATO_MIN;

  		} else

  			icsk->icsk_ack.quick -= pkts;

  	}
  }

  #define	TCP_ECN_OK		1
  #define	TCP_ECN_QUEUE_CWR	2
  #define	TCP_ECN_DEMAND_CWR	4

  #define	TCP_ECN_SEEN		8

  enum tcp_tw_status {

  	TCP_TW_SUCCESS = 0,
  	TCP_TW_RST = 1,
  	TCP_TW_ACK = 2,
  	TCP_TW_SYN = 3
  };

  enum tcp_tw_status tcp_timewait_state_process(struct inet_timewait_sock *tw,
  					      struct sk_buff *skb,
  					      const struct tcphdr *th);
  struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,

  			   struct request_sock *req, bool fastopen,
  			   bool *lost_race);

  int tcp_child_process(struct sock *parent, struct sock *child,
  		      struct sk_buff *skb);

  void tcp_enter_loss(struct sock *sk);

  void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int flag);

  void tcp_clear_retrans(struct tcp_sock *tp);
  void tcp_update_metrics(struct sock *sk);
  void tcp_init_metrics(struct sock *sk);
  void tcp_metrics_init(void);

  bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst);

  void tcp_close(struct sock *sk, long timeout);
  void tcp_init_sock(struct sock *sk);

  void tcp_init_transfer(struct sock *sk, int bpf_op, struct sk_buff *skb);

  __poll_t tcp_poll(struct file *file, struct socket *sock,
  		      struct poll_table_struct *wait);

  int tcp_getsockopt(struct sock *sk, int level, int optname,
  		   char __user *optval, int __user *optlen);

  int tcp_setsockopt(struct sock *sk, int level, int optname, sockptr_t optval,
  		   unsigned int optlen);

  void tcp_set_keepalive(struct sock *sk, int val);

  void tcp_syn_ack_timeout(const struct request_sock *req);

  int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
  		int flags, int *addr_len);

  int tcp_set_rcvlowat(struct sock *sk, int val);

  void tcp_data_ready(struct sock *sk);

  #ifdef CONFIG_MMU

  int tcp_mmap(struct file *file, struct socket *sock,
  	     struct vm_area_struct *vma);

  #endif

  void tcp_parse_options(const struct net *net, const struct sk_buff *skb,

  		       struct tcp_options_received *opt_rx,
  		       int estab, struct tcp_fastopen_cookie *foc);
  const u8 *tcp_parse_md5sig_option(const struct tcphdr *th);

  /*

   *	BPF SKB-less helpers
   */
  u16 tcp_v4_get_syncookie(struct sock *sk, struct iphdr *iph,
  			 struct tcphdr *th, u32 *cookie);
  u16 tcp_v6_get_syncookie(struct sock *sk, struct ipv6hdr *iph,
  			 struct tcphdr *th, u32 *cookie);
  u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops,
  			  const struct tcp_request_sock_ops *af_ops,
  			  struct sock *sk, struct tcphdr *th);
  /*

   *	TCP v4 functions exported for the inet6 API
   */

  void tcp_v4_send_check(struct sock *sk, struct sk_buff *skb);

  void tcp_v4_mtu_reduced(struct sock *sk);

  void tcp_req_err(struct sock *sk, u32 seq, bool abort);

  void tcp_ld_RTO_revert(struct sock *sk, u32 seq);

  int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb);

  struct sock *tcp_create_openreq_child(const struct sock *sk,

  				      struct request_sock *req,
  				      struct sk_buff *skb);

  void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst);

  struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,

  				  struct request_sock *req,

  				  struct dst_entry *dst,
  				  struct request_sock *req_unhash,
  				  bool *own_req);

  int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb);
  int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
  int tcp_connect(struct sock *sk);

  enum tcp_synack_type {
  	TCP_SYNACK_NORMAL,
  	TCP_SYNACK_FASTOPEN,
  	TCP_SYNACK_COOKIE,
  };

  struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,

  				struct request_sock *req,

  				struct tcp_fastopen_cookie *foc,

  				enum tcp_synack_type synack_type,
  				struct sk_buff *syn_skb);

  int tcp_disconnect(struct sock *sk, int flags);

  void tcp_finish_connect(struct sock *sk, struct sk_buff *skb);

  int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size);

  void inet_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb);

  /* From syncookies.c */

  struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
  				 struct request_sock *req,

  				 struct dst_entry *dst, u32 tsoff);

  int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th,
  		      u32 cookie);

  struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb);

  struct request_sock *cookie_tcp_reqsk_alloc(const struct request_sock_ops *ops,
  					    struct sock *sk, struct sk_buff *skb);

  #ifdef CONFIG_SYN_COOKIES

  /* Syncookies use a monotonic timer which increments every 60 seconds.

   * This counter is used both as a hash input and partially encoded into
   * the cookie value.  A cookie is only validated further if the delta
   * between the current counter value and the encoded one is less than this,

   * i.e. a sent cookie is valid only at most for 2*60 seconds (or less if

   * the counter advances immediately after a cookie is generated).
   */

  #define MAX_SYNCOOKIE_AGE	2
  #define TCP_SYNCOOKIE_PERIOD	(60 * HZ)
  #define TCP_SYNCOOKIE_VALID	(MAX_SYNCOOKIE_AGE * TCP_SYNCOOKIE_PERIOD)
  
  /* syncookies: remember time of last synqueue overflow
   * But do not dirty this field too often (once per second is enough)

   * It is racy as we do not hold a lock, but race is very minor.

   */

  static inline void tcp_synq_overflow(const struct sock *sk)

  {

  	unsigned int last_overflow;

  	unsigned int now = jiffies;

  	if (sk->sk_reuseport) {
  		struct sock_reuseport *reuse;
  
  		reuse = rcu_dereference(sk->sk_reuseport_cb);
  		if (likely(reuse)) {
  			last_overflow = READ_ONCE(reuse->synq_overflow_ts);

  			if (!time_between32(now, last_overflow,
  					    last_overflow + HZ))

  				WRITE_ONCE(reuse->synq_overflow_ts, now);
  			return;
  		}
  	}

  	last_overflow = READ_ONCE(tcp_sk(sk)->rx_opt.ts_recent_stamp);

  	if (!time_between32(now, last_overflow, last_overflow + HZ))

  		WRITE_ONCE(tcp_sk(sk)->rx_opt.ts_recent_stamp, now);

  }
  
  /* syncookies: no recent synqueue overflow on this listening socket? */
  static inline bool tcp_synq_no_recent_overflow(const struct sock *sk)
  {

  	unsigned int last_overflow;

  	unsigned int now = jiffies;

  	if (sk->sk_reuseport) {
  		struct sock_reuseport *reuse;
  
  		reuse = rcu_dereference(sk->sk_reuseport_cb);
  		if (likely(reuse)) {
  			last_overflow = READ_ONCE(reuse->synq_overflow_ts);

  			return !time_between32(now, last_overflow - HZ,
  					       last_overflow +
  					       TCP_SYNCOOKIE_VALID);

  		}
  	}

  	last_overflow = READ_ONCE(tcp_sk(sk)->rx_opt.ts_recent_stamp);

  
  	/* If last_overflow <= jiffies <= last_overflow + TCP_SYNCOOKIE_VALID,
  	 * then we're under synflood. However, we have to use
  	 * 'last_overflow - HZ' as lower bound. That's because a concurrent
  	 * tcp_synq_overflow() could update .ts_recent_stamp after we read
  	 * jiffies but before we store .ts_recent_stamp into last_overflow,
  	 * which could lead to rejecting a valid syncookie.
  	 */
  	return !time_between32(now, last_overflow - HZ,
  			       last_overflow + TCP_SYNCOOKIE_VALID);

  }

  
  static inline u32 tcp_cookie_time(void)
  {

  	u64 val = get_jiffies_64();

  	do_div(val, TCP_SYNCOOKIE_PERIOD);

  	return val;

  }

  u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,
  			      u16 *mssp);

  __u32 cookie_v4_init_sequence(const struct sk_buff *skb, __u16 *mss);

  u64 cookie_init_timestamp(struct request_sock *req, u64 now);

  bool cookie_timestamp_decode(const struct net *net,
  			     struct tcp_options_received *opt);

  bool cookie_ecn_ok(const struct tcp_options_received *opt,

  		   const struct net *net, const struct dst_entry *dst);

  /* From net/ipv6/syncookies.c */

  int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th,
  		      u32 cookie);
  struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb);

  u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
  			      const struct tcphdr *th, u16 *mssp);

  __u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mss);

  #endif

  /* tcp_output.c */

  void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
  			       int nonagle);

  int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs);
  int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs);

  void tcp_retransmit_timer(struct sock *sk);
  void tcp_xmit_retransmit_queue(struct sock *);
  void tcp_simple_retransmit(struct sock *);

  void tcp_enter_recovery(struct sock *sk, bool ece_ack);

  int tcp_trim_head(struct sock *, struct sk_buff *, u32);

  enum tcp_queue {
  	TCP_FRAG_IN_WRITE_QUEUE,
  	TCP_FRAG_IN_RTX_QUEUE,
  };
  int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue,
  		 struct sk_buff *skb, u32 len,
  		 unsigned int mss_now, gfp_t gfp);

  
  void tcp_send_probe0(struct sock *);
  void tcp_send_partial(struct sock *);

  int tcp_write_wakeup(struct sock *, int mib);

  void tcp_send_fin(struct sock *sk);
  void tcp_send_active_reset(struct sock *sk, gfp_t priority);
  int tcp_send_synack(struct sock *);

  void tcp_push_one(struct sock *, unsigned int mss_now);

  void __tcp_send_ack(struct sock *sk, u32 rcv_nxt);

  void tcp_send_ack(struct sock *sk);
  void tcp_send_delayed_ack(struct sock *sk);
  void tcp_send_loss_probe(struct sock *sk);

  bool tcp_schedule_loss_probe(struct sock *sk, bool advancing_rto);

  void tcp_skb_collapse_tstamp(struct sk_buff *skb,
  			     const struct sk_buff *next_skb);

  /* tcp_input.c */

  void tcp_rearm_rto(struct sock *sk);

  void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req);

  void tcp_reset(struct sock *sk);

  void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb);

  void tcp_fin(struct sock *sk);

  /* tcp_timer.c */

  void tcp_init_xmit_timers(struct sock *);

  static inline void tcp_clear_xmit_timers(struct sock *sk)
  {

  	if (hrtimer_try_to_cancel(&tcp_sk(sk)->pacing_timer) == 1)

  		__sock_put(sk);

  	if (hrtimer_try_to_cancel(&tcp_sk(sk)->compressed_ack_timer) == 1)
  		__sock_put(sk);

  	inet_csk_clear_xmit_timers(sk);
  }

  unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu);
  unsigned int tcp_current_mss(struct sock *sk);

  
  /* Bound MSS / TSO packet size with the half of the window */
  static inline int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
  {

  	int cutoff;
  
  	/* When peer uses tiny windows, there is no use in packetizing
  	 * to sub-MSS pieces for the sake of SWS or making sure there
  	 * are enough packets in the pipe for fast recovery.
  	 *
  	 * On the other hand, for extremely large MSS devices, handling
  	 * smaller than MSS windows in this way does make sense.
  	 */

  	if (tp->max_window > TCP_MSS_DEFAULT)

  		cutoff = (tp->max_window >> 1);
  	else
  		cutoff = tp->max_window;
  
  	if (cutoff && pktsize > cutoff)
  		return max_t(int, cutoff, 68U - tp->tcp_header_len);

  	else
  		return pktsize;
  }

  /* tcp.c */

  void tcp_get_info(struct sock *, struct tcp_info *);

  
  /* Read 'sendfile()'-style from a TCP socket */

  int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
  		  sk_read_actor_t recv_actor);

  void tcp_initialize_rcv_mss(struct sock *sk);

  int tcp_mtu_to_mss(struct sock *sk, int pmtu);
  int tcp_mss_to_mtu(struct sock *sk, int mss);
  void tcp_mtup_init(struct sock *sk);

  static inline void tcp_bound_rto(const struct sock *sk)
  {
  	if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
  		inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
  }
  
  static inline u32 __tcp_set_rto(const struct tcp_sock *tp)
  {

  	return usecs_to_jiffies((tp->srtt_us >> 3) + tp->rttvar_us);

  }

  static inline void __tcp_fast_path_on(struct tcp_sock *tp, u32 snd_wnd)
  {
  	tp->pred_flags = htonl((tp->tcp_header_len << 26) |
  			       ntohl(TCP_FLAG_ACK) |
  			       snd_wnd);
  }
  
  static inline void tcp_fast_path_on(struct tcp_sock *tp)
  {
  	__tcp_fast_path_on(tp, tp->snd_wnd >> tp->rx_opt.snd_wscale);
  }
  
  static inline void tcp_fast_path_check(struct sock *sk)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  
  	if (RB_EMPTY_ROOT(&tp->out_of_order_queue) &&
  	    tp->rcv_wnd &&
  	    atomic_read(&sk->sk_rmem_alloc) < sk->sk_rcvbuf &&
  	    !tp->urg_data)
  		tcp_fast_path_on(tp);
  }

  /* Compute the actual rto_min value */
  static inline u32 tcp_rto_min(struct sock *sk)
  {

  	const struct dst_entry *dst = __sk_dst_get(sk);

  	u32 rto_min = inet_csk(sk)->icsk_rto_min;

  
  	if (dst && dst_metric_locked(dst, RTAX_RTO_MIN))
  		rto_min = dst_metric_rtt(dst, RTAX_RTO_MIN);
  	return rto_min;
  }

  static inline u32 tcp_rto_min_us(struct sock *sk)
  {
  	return jiffies_to_usecs(tcp_rto_min(sk));
  }

  static inline bool tcp_ca_dst_locked(const struct dst_entry *dst)
  {
  	return dst_metric_locked(dst, RTAX_CC_ALGO);
  }

  /* Minimum RTT in usec. ~0 means not available. */
  static inline u32 tcp_min_rtt(const struct tcp_sock *tp)
  {

  	return minmax_get(&tp->rtt_min);

  }

  /* Compute the actual receive window we are currently advertising.
   * Rcv_nxt can be after the window if our peer push more data
   * than the offered window.
   */

  static inline u32 tcp_receive_window(const struct tcp_sock *tp)

  {
  	s32 win = tp->rcv_wup + tp->rcv_wnd - tp->rcv_nxt;
  
  	if (win < 0)
  		win = 0;
  	return (u32) win;
  }
  
  /* Choose a new window, without checks for shrinking, and without
   * scaling applied to the result.  The caller does these things
   * if necessary.  This is a "raw" window selection.
   */

  u32 __tcp_select_window(struct sock *sk);

  void tcp_send_window_probe(struct sock *sk);

  /* TCP uses 32bit jiffies to save some space.
   * Note that this is different from tcp_time_stamp, which
   * historically has been the same until linux-4.13.
   */
  #define tcp_jiffies32 ((u32)jiffies)

  /*
   * Deliver a 32bit value for TCP timestamp option (RFC 7323)
   * It is no longer tied to jiffies, but to 1 ms clock.
   * Note: double check if you want to use tcp_jiffies32 instead of this.
   */
  #define TCP_TS_HZ	1000
  
  static inline u64 tcp_clock_ns(void)
  {

  	return ktime_get_ns();

  }
  
  static inline u64 tcp_clock_us(void)
  {
  	return div_u64(tcp_clock_ns(), NSEC_PER_USEC);
  }
  
  /* This should only be used in contexts where tp->tcp_mstamp is up to date */
  static inline u32 tcp_time_stamp(const struct tcp_sock *tp)
  {
  	return div_u64(tp->tcp_mstamp, USEC_PER_SEC / TCP_TS_HZ);
  }

  /* Convert a nsec timestamp into TCP TSval timestamp (ms based currently) */
  static inline u32 tcp_ns_to_ts(u64 ns)
  {
  	return div_u64(ns, NSEC_PER_SEC / TCP_TS_HZ);
  }

  /* Could use tcp_clock_us() / 1000, but this version uses a single divide */
  static inline u32 tcp_time_stamp_raw(void)
  {

  	return tcp_ns_to_ts(tcp_clock_ns());

  }

  void tcp_mstamp_refresh(struct tcp_sock *tp);

  
  static inline u32 tcp_stamp_us_delta(u64 t1, u64 t0)
  {
  	return max_t(s64, t1 - t0, 0);
  }

  static inline u32 tcp_skb_timestamp(const struct sk_buff *skb)
  {

  	return tcp_ns_to_ts(skb->skb_mstamp_ns);

  }

  /* provide the departure time in us unit */
  static inline u64 tcp_skb_timestamp_us(const struct sk_buff *skb)
  {

  	return div_u64(skb->skb_mstamp_ns, NSEC_PER_USEC);

  }

  #define tcp_flag_byte(th) (((u_int8_t *)th)[13])
  
  #define TCPHDR_FIN 0x01
  #define TCPHDR_SYN 0x02
  #define TCPHDR_RST 0x04
  #define TCPHDR_PSH 0x08
  #define TCPHDR_ACK 0x10
  #define TCPHDR_URG 0x20
  #define TCPHDR_ECE 0x40
  #define TCPHDR_CWR 0x80

  #define TCPHDR_SYN_ECN	(TCPHDR_SYN | TCPHDR_ECE | TCPHDR_CWR)

  /* This is what the send packet queuing engine uses to pass

   * TCP per-packet control information to the transmission code.
   * We also store the host-order sequence numbers in here too.
   * This is 44 bytes if IPV6 is enabled.
   * If this grows please adjust skbuff.h:skbuff->cb[xxx] size appropriately.

   */
  struct tcp_skb_cb {

  	__u32		seq;		/* Starting sequence number	*/
  	__u32		end_seq;	/* SEQ + FIN + SYN + datalen	*/

  	union {
  		/* Note : tcp_tw_isn is used in input path only
  		 *	  (isn chosen by tcp_timewait_state_process())
  		 *

  		 * 	  tcp_gso_segs/size are used in write queue only,
  		 *	  cf tcp_skb_pcount()/tcp_skb_mss()

  		 */
  		__u32		tcp_tw_isn;

  		struct {
  			u16	tcp_gso_segs;
  			u16	tcp_gso_size;
  		};

  	};

  	__u8		tcp_flags;	/* TCP header flags. (tcp[13])	*/

  	__u8		sacked;		/* State flags for SACK.	*/

  #define TCPCB_SACKED_ACKED	0x01	/* SKB ACK'd by a SACK block	*/
  #define TCPCB_SACKED_RETRANS	0x02	/* SKB retransmitted		*/
  #define TCPCB_LOST		0x04	/* SKB is lost			*/
  #define TCPCB_TAGBITS		0x07	/* All tag bits			*/

  #define TCPCB_REPAIRED		0x10	/* SKB repaired (no skb_mstamp_ns)	*/

  #define TCPCB_EVER_RETRANS	0x80	/* Ever retransmitted frame	*/

  #define TCPCB_RETRANS		(TCPCB_SACKED_RETRANS|TCPCB_EVER_RETRANS| \
  				TCPCB_REPAIRED)

  	__u8		ip_dsfield;	/* IPv4 tos or IPv6 dsfield	*/

  	__u8		txstamp_ack:1,	/* Record TX timestamp for ack? */

  			eor:1,		/* Is skb MSG_EOR marked? */

  			has_rxtstamp:1,	/* SKB has a RX timestamp	*/
  			unused:5;

  	__u32		ack_seq;	/* Sequence number ACK'd	*/

  	union {

  		struct {

  			/* There is space for up to 24 bytes */

  			__u32 in_flight:30,/* Bytes in flight at transmit */
  			      is_app_limited:1, /* cwnd not fully used? */
  			      unused:1;

  			/* pkts S/ACKed so far upon tx of skb, incl retrans: */
  			__u32 delivered;
  			/* start of send pipeline phase */

  			u64 first_tx_mstamp;

  			/* when we reached the "delivered" count */

  			u64 delivered_mstamp;

  		} tx;   /* only used for outgoing skbs */
  		union {
  			struct inet_skb_parm	h4;

  #if IS_ENABLED(CONFIG_IPV6)

  			struct inet6_skb_parm	h6;

  #endif

  		} header;	/* For incoming skbs */

  		struct {

  			__u32 flags;

  			struct sock *sk_redir;

  			void *data_end;

  		} bpf;

  	};

  };
  
  #define TCP_SKB_CB(__skb)	((struct tcp_skb_cb *)&((__skb)->cb[0]))

  static inline void bpf_compute_data_end_sk_skb(struct sk_buff *skb)
  {
  	TCP_SKB_CB(skb)->bpf.data_end = skb->data + skb_headlen(skb);
  }

  static inline bool tcp_skb_bpf_ingress(const struct sk_buff *skb)
  {
  	return TCP_SKB_CB(skb)->bpf.flags & BPF_F_INGRESS;
  }
  
  static inline struct sock *tcp_skb_bpf_redirect_fetch(struct sk_buff *skb)
  {
  	return TCP_SKB_CB(skb)->bpf.sk_redir;
  }
  
  static inline void tcp_skb_bpf_redirect_clear(struct sk_buff *skb)
  {
  	TCP_SKB_CB(skb)->bpf.sk_redir = NULL;
  }

  extern const struct inet_connection_sock_af_ops ipv4_specific;

  #if IS_ENABLED(CONFIG_IPV6)

  /* This is the variant of inet6_iif() that must be used by TCP,
   * as TCP moves IP6CB into a different location in skb->cb[]
   */
  static inline int tcp_v6_iif(const struct sk_buff *skb)
  {

  	return TCP_SKB_CB(skb)->header.h6.iif;
  }
  
  static inline int tcp_v6_iif_l3_slave(const struct sk_buff *skb)
  {

  	bool l3_slave = ipv6_l3mdev_skb(TCP_SKB_CB(skb)->header.h6.flags);

  
  	return l3_slave ? skb->skb_iif : TCP_SKB_CB(skb)->header.h6.iif;

  }

  
  /* TCP_SKB_CB reference means this can not be used from early demux */
  static inline int tcp_v6_sdif(const struct sk_buff *skb)
  {
  #if IS_ENABLED(CONFIG_NET_L3_MASTER_DEV)
  	if (skb && ipv6_l3mdev_skb(TCP_SKB_CB(skb)->header.h6.flags))
  		return TCP_SKB_CB(skb)->header.h6.iif;
  #endif
  	return 0;
  }

  extern const struct inet_connection_sock_af_ops ipv6_specific;

  INDIRECT_CALLABLE_DECLARE(void tcp_v6_send_check(struct sock *sk, struct sk_buff *skb));

  INDIRECT_CALLABLE_DECLARE(int tcp_v6_rcv(struct sk_buff *skb));
  INDIRECT_CALLABLE_DECLARE(void tcp_v6_early_demux(struct sk_buff *skb));

  #endif

  /* TCP_SKB_CB reference means this can not be used from early demux */
  static inline int tcp_v4_sdif(struct sk_buff *skb)
  {
  #if IS_ENABLED(CONFIG_NET_L3_MASTER_DEV)
  	if (skb && ipv4_l3mdev_skb(TCP_SKB_CB(skb)->header.h4.flags))
  		return TCP_SKB_CB(skb)->header.h4.iif;
  #endif
  	return 0;
  }

  /* Due to TSO, an SKB can be composed of multiple actual
   * packets.  To keep these tracked properly, we use this.

   */

  static inline int tcp_skb_pcount(const struct sk_buff *skb)

  {

  	return TCP_SKB_CB(skb)->tcp_gso_segs;
  }

  static inline void tcp_skb_pcount_set(struct sk_buff *skb, int segs)
  {
  	TCP_SKB_CB(skb)->tcp_gso_segs = segs;

  }

  static inline void tcp_skb_pcount_add(struct sk_buff *skb, int segs)

  {

  	TCP_SKB_CB(skb)->tcp_gso_segs += segs;

  }

  /* This is valid iff skb is in write queue and tcp_skb_pcount() > 1. */

  static inline int tcp_skb_mss(const struct sk_buff *skb)
  {

  	return TCP_SKB_CB(skb)->tcp_gso_size;

  }

  static inline bool tcp_skb_can_collapse_to(const struct sk_buff *skb)
  {
  	return likely(!TCP_SKB_CB(skb)->eor);
  }

  static inline bool tcp_skb_can_collapse(const struct sk_buff *to,
  					const struct sk_buff *from)
  {
  	return likely(tcp_skb_can_collapse_to(to) &&
  		      mptcp_skb_can_collapse(to, from));
  }

  /* Events passed to congestion control interface */
  enum tcp_ca_event {
  	CA_EVENT_TX_START,	/* first transmit when no packets in flight */
  	CA_EVENT_CWND_RESTART,	/* congestion window restart */
  	CA_EVENT_COMPLETE_CWR,	/* end of congestion recovery */

  	CA_EVENT_LOSS,		/* loss timeout */

  	CA_EVENT_ECN_NO_CE,	/* ECT set, but not CE marked */
  	CA_EVENT_ECN_IS_CE,	/* received CE marked IP packet */

  };

  /* Information about inbound ACK, passed to cong_ops->in_ack_event() */

  enum tcp_ca_ack_event_flags {

  	CA_ACK_SLOWPATH		= (1 << 0),	/* In slow path processing */
  	CA_ACK_WIN_UPDATE	= (1 << 1),	/* ACK updated window */
  	CA_ACK_ECE		= (1 << 2),	/* ECE bit is set on ack */

  };
  
  /*
   * Interface for adding new TCP congestion control handlers
   */
  #define TCP_CA_NAME_MAX	16

  #define TCP_CA_MAX	128
  #define TCP_CA_BUF_MAX	(TCP_CA_NAME_MAX*TCP_CA_MAX)

  #define TCP_CA_UNSPEC	0

  /* Algorithm can be set on socket without CAP_NET_ADMIN privileges */

  #define TCP_CONG_NON_RESTRICTED 0x1

  /* Requires ECN/ECT set on all packets */
  #define TCP_CONG_NEEDS_ECN	0x2

  #define TCP_CONG_MASK	(TCP_CONG_NON_RESTRICTED | TCP_CONG_NEEDS_ECN)

  union tcp_cc_info;

  struct ack_sample {
  	u32 pkts_acked;
  	s32 rtt_us;

  	u32 in_flight;

  };

  /* A rate sample measures the number of (original/retransmitted) data
   * packets delivered "delivered" over an interval of time "interval_us".
   * The tcp_rate.c code fills in the rate sample, and congestion
   * control modules that define a cong_control function to run at the end
   * of ACK processing can optionally chose to consult this sample when
   * setting cwnd and pacing rate.
   * A sample is invalid if "delivered" or "interval_us" is negative.
   */
  struct rate_sample {

  	u64  prior_mstamp; /* starting timestamp for interval */

  	u32  prior_delivered;	/* tp->delivered at "prior_mstamp" */
  	s32  delivered;		/* number of packets delivered over interval */
  	long interval_us;	/* time for tp->delivered to incr "delivered" */

  	u32 snd_interval_us;	/* snd interval for delivered packets */
  	u32 rcv_interval_us;	/* rcv interval for delivered packets */

  	long rtt_us;		/* RTT of last (S)ACKed packet (or -1) */
  	int  losses;		/* number of packets marked lost upon ACK */
  	u32  acked_sacked;	/* number of packets newly (S)ACKed upon ACK */
  	u32  prior_in_flight;	/* in flight before this ACK */

  	bool is_app_limited;	/* is sample from packet with bubble in pipe? */

  	bool is_retrans;	/* is sample from retransmission? */

  	bool is_ack_delayed;	/* is this (likely) a delayed ACK? */

  };

  struct tcp_congestion_ops {
  	struct list_head	list;

  	u32 key;
  	u32 flags;

  
  	/* initialize private data (optional) */

  	void (*init)(struct sock *sk);

  	/* cleanup private data  (optional) */

  	void (*release)(struct sock *sk);

  
  	/* return slow start threshold (required) */

  	u32 (*ssthresh)(struct sock *sk);

  	/* do new cwnd calculation (required) */

  	void (*cong_avoid)(struct sock *sk, u32 ack, u32 acked);

  	/* call before changing ca_state (optional) */

  	void (*set_state)(struct sock *sk, u8 new_state);

  	/* call when cwnd event occurs (optional) */

  	void (*cwnd_event)(struct sock *sk, enum tcp_ca_event ev);

  	/* call when ack arrives (optional) */
  	void (*in_ack_event)(struct sock *sk, u32 flags);

  	/* new value of cwnd after loss (required) */

  	u32  (*undo_cwnd)(struct sock *sk);

  	/* hook for packet ack accounting (optional) */

  	void (*pkts_acked)(struct sock *sk, const struct ack_sample *sample);

  	/* override sysctl_tcp_min_tso_segs */
  	u32 (*min_tso_segs)(struct sock *sk);

  	/* returns the multiplier used in tcp_sndbuf_expand (optional) */
  	u32 (*sndbuf_expand)(struct sock *sk);

  	/* call when packets are delivered to update cwnd and pacing rate,
  	 * after all the ca_state processing. (optional)
  	 */
  	void (*cong_control)(struct sock *sk, const struct rate_sample *rs);

  	/* get info for inet_diag (optional) */

  	size_t (*get_info)(struct sock *sk, u32 ext, int *attr,
  			   union tcp_cc_info *info);

  
  	char 		name[TCP_CA_NAME_MAX];
  	struct module 	*owner;
  };

  int tcp_register_congestion_control(struct tcp_congestion_ops *type);
  void tcp_unregister_congestion_control(struct tcp_congestion_ops *type);

  void tcp_assign_congestion_control(struct sock *sk);

  void tcp_init_congestion_control(struct sock *sk);
  void tcp_cleanup_congestion_control(struct sock *sk);

  int tcp_set_default_congestion_control(struct net *net, const char *name);
  void tcp_get_default_congestion_control(struct net *net, char *name);

  void tcp_get_available_congestion_control(char *buf, size_t len);
  void tcp_get_allowed_congestion_control(char *buf, size_t len);
  int tcp_set_allowed_congestion_control(char *allowed);

  int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,

  			       bool cap_net_admin);

  u32 tcp_slow_start(struct tcp_sock *tp, u32 acked);
  void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked);

  u32 tcp_reno_ssthresh(struct sock *sk);

  u32 tcp_reno_undo_cwnd(struct sock *sk);

  void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked);

  extern struct tcp_congestion_ops tcp_reno;

  struct tcp_congestion_ops *tcp_ca_find(const char *name);

  struct tcp_congestion_ops *tcp_ca_find_key(u32 key);

  u32 tcp_ca_get_key_by_name(struct net *net, const char *name, bool *ecn_ca);

  #ifdef CONFIG_INET

  char *tcp_ca_get_name_by_key(u32 key, char *buffer);

  #else
  static inline char *tcp_ca_get_name_by_key(u32 key, char *buffer)
  {
  	return NULL;
  }
  #endif

  static inline bool tcp_ca_needs_ecn(const struct sock *sk)
  {
  	const struct inet_connection_sock *icsk = inet_csk(sk);
  
  	return icsk->icsk_ca_ops->flags & TCP_CONG_NEEDS_ECN;
  }

  static inline void tcp_set_ca_state(struct sock *sk, const u8 ca_state)

  {

  	struct inet_connection_sock *icsk = inet_csk(sk);
  
  	if (icsk->icsk_ca_ops->set_state)
  		icsk->icsk_ca_ops->set_state(sk, ca_state);
  	icsk->icsk_ca_state = ca_state;

  }

  static inline void tcp_ca_event(struct sock *sk, const enum tcp_ca_event event)

  {

  	const struct inet_connection_sock *icsk = inet_csk(sk);
  
  	if (icsk->icsk_ca_ops->cwnd_event)
  		icsk->icsk_ca_ops->cwnd_event(sk, event);

  }

  /* From tcp_rate.c */
  void tcp_rate_skb_sent(struct sock *sk, struct sk_buff *skb);
  void tcp_rate_skb_delivered(struct sock *sk, struct sk_buff *skb,
  			    struct rate_sample *rs);
  void tcp_rate_gen(struct sock *sk, u32 delivered, u32 lost,

  		  bool is_sack_reneg, struct rate_sample *rs);

  void tcp_rate_check_app_limited(struct sock *sk);

  /* These functions determine how the current flow behaves in respect of SACK
   * handling. SACK is negotiated with the peer, and therefore it can vary
   * between different flows.
   *
   * tcp_is_sack - SACK enabled
   * tcp_is_reno - No SACK

   */
  static inline int tcp_is_sack(const struct tcp_sock *tp)
  {

  	return likely(tp->rx_opt.sack_ok);

  }

  static inline bool tcp_is_reno(const struct tcp_sock *tp)

  {
  	return !tcp_is_sack(tp);
  }

  static inline unsigned int tcp_left_out(const struct tcp_sock *tp)
  {
  	return tp->sacked_out + tp->lost_out;
  }

  /* This determines how many packets are "in the network" to the best
   * of our knowledge.  In many cases it is conservative, but where
   * detailed information is available from the receiver (via SACK
   * blocks etc.) we can make more aggressive calculations.
   *
   * Use this for decisions involving congestion control, use just
   * tp->packets_out to determine if the send queue is empty or not.
   *
   * Read this equation as:
   *
   *	"Packets sent once on transmission queue" MINUS
   *	"Packets left network, but not honestly ACKed yet" PLUS
   *	"Packets fast retransmitted"
   */

  static inline unsigned int tcp_packets_in_flight(const struct tcp_sock *tp)

  {

  	return tp->packets_out - tcp_left_out(tp) + tp->retrans_out;

  }

  #define TCP_INFINITE_SSTHRESH	0x7fffffff

  static inline bool tcp_in_slow_start(const struct tcp_sock *tp)
  {

  	return tp->snd_cwnd < tp->snd_ssthresh;

  }

  static inline bool tcp_in_initial_slowstart(const struct tcp_sock *tp)
  {
  	return tp->snd_ssthresh >= TCP_INFINITE_SSTHRESH;
  }

  static inline bool tcp_in_cwnd_reduction(const struct sock *sk)
  {
  	return (TCPF_CA_CWR | TCPF_CA_Recovery) &
  	       (1 << inet_csk(sk)->icsk_ca_state);
  }

  /* If cwnd > ssthresh, we may raise ssthresh to be half-way to cwnd.

   * The exception is cwnd reduction phase, when cwnd is decreasing towards

   * ssthresh.
   */

  static inline __u32 tcp_current_ssthresh(const struct sock *sk)

  {

  	const struct tcp_sock *tp = tcp_sk(sk);

  	if (tcp_in_cwnd_reduction(sk))

  		return tp->snd_ssthresh;
  	else
  		return max(tp->snd_ssthresh,
  			   ((tp->snd_cwnd >> 1) +
  			    (tp->snd_cwnd >> 2)));
  }

  /* Use define here intentionally to get WARN_ON location shown at the caller */
  #define tcp_verify_left_out(tp)	WARN_ON(tcp_left_out(tp) > tp->packets_out)

  void tcp_enter_cwr(struct sock *sk);

  __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst);

  /* The maximum number of MSS of available cwnd for which TSO defers
   * sending if not using sysctl_tcp_tso_win_divisor.
   */
  static inline __u32 tcp_max_tso_deferred_mss(const struct tcp_sock *tp)
  {
  	return 3;
  }

  /* Returns end sequence number of the receiver's advertised window */
  static inline u32 tcp_wnd_end(const struct tcp_sock *tp)
  {
  	return tp->snd_una + tp->snd_wnd;
  }

  
  /* We follow the spirit of RFC2861 to validate cwnd but implement a more
   * flexible approach. The RFC suggests cwnd should not be raised unless

   * it was fully used previously. And that's exactly what we do in
   * congestion avoidance mode. But in slow start we allow cwnd to grow
   * as long as the application has used half the cwnd.

   * Example :
   *    cwnd is 10 (IW10), but application sends 9 frames.
   *    We allow cwnd to reach 18 when all frames are ACKed.
   * This check is safe because it's as aggressive as slow start which already
   * risks 100% overshoot. The advantage is that we discourage application to
   * either send more filler packets or data to artificially blow up the cwnd
   * usage, and allow application-limited process to probe bw more aggressively.

   */

  static inline bool tcp_is_cwnd_limited(const struct sock *sk)

  {
  	const struct tcp_sock *tp = tcp_sk(sk);

  	/* If in slow start, ensure cwnd grows to twice what was ACKed. */

  	if (tcp_in_slow_start(tp))

  		return tp->snd_cwnd < 2 * tp->max_packets_out;
  
  	return tp->is_cwnd_limited;

  }

  /* BBR congestion control needs pacing.
   * Same remark for SO_MAX_PACING_RATE.
   * sch_fq packet scheduler is efficiently handling pacing,
   * but is not always installed/used.
   * Return true if TCP stack should pace packets itself.
   */
  static inline bool tcp_needs_internal_pacing(const struct sock *sk)
  {
  	return smp_load_acquire(&sk->sk_pacing_status) == SK_PACING_NEEDED;
  }

  /* Estimates in how many jiffies next packet for this flow can be sent.
   * Scheduling a retransmit timer too early would be silly.

   */

  static inline unsigned long tcp_pacing_delay(const struct sock *sk)

  {

  	s64 delay = tcp_sk(sk)->tcp_wstamp_ns - tcp_sk(sk)->tcp_clock_cache;

  	return delay > 0 ? nsecs_to_jiffies(delay) : 0;

  }
  
  static inline void tcp_reset_xmit_timer(struct sock *sk,
  					const int what,
  					unsigned long when,

  					const unsigned long max_when)

  {

  	inet_csk_reset_xmit_timer(sk, what, when + tcp_pacing_delay(sk),

  				  max_when);
  }

  /* Something is really bad, we could not queue an additional packet,

   * because qdisc is full or receiver sent a 0 window, or we are paced.

   * We do not want to add fuel to the fire, or abort too early,
   * so make sure the timer we arm now is at least 200ms in the future,
   * regardless of current icsk_rto value (as it could be ~2ms)
   */
  static inline unsigned long tcp_probe0_base(const struct sock *sk)

  {

  	return max_t(unsigned long, inet_csk(sk)->icsk_rto, TCP_RTO_MIN);
  }

  /* Variant of inet_csk_rto_backoff() used for zero window probes */
  static inline unsigned long tcp_probe0_when(const struct sock *sk,
  					    unsigned long max_when)
  {
  	u64 when = (u64)tcp_probe0_base(sk) << inet_csk(sk)->icsk_backoff;
  
  	return (unsigned long)min_t(u64, when, max_when);
  }
  
  static inline void tcp_check_probe_timer(struct sock *sk)
  {
  	if (!tcp_sk(sk)->packets_out && !inet_csk(sk)->icsk_pending)

  		tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0,

  				     tcp_probe0_base(sk), TCP_RTO_MAX);

  }

  static inline void tcp_init_wl(struct tcp_sock *tp, u32 seq)

  {
  	tp->snd_wl1 = seq;
  }

  static inline void tcp_update_wl(struct tcp_sock *tp, u32 seq)

  {
  	tp->snd_wl1 = seq;
  }

  /*
   * Calculate(/check) TCP checksum
   */

  static inline __sum16 tcp_v4_check(int len, __be32 saddr,
  				   __be32 daddr, __wsum base)

  {

  	return csum_tcpudp_magic(saddr, daddr, len, IPPROTO_TCP, base);

  }

  static inline bool tcp_checksum_complete(struct sk_buff *skb)

  {

  	return !skb_csum_unnecessary(skb) &&

  		__skb_checksum_complete(skb);

  }

  bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb);

  int tcp_filter(struct sock *sk, struct sk_buff *skb);

  void tcp_set_state(struct sock *sk, int state);

  void tcp_done(struct sock *sk);

  int tcp_abort(struct sock *sk, int err);

  static inline void tcp_sack_reset(struct tcp_options_received *rx_opt)

  {
  	rx_opt->dsack = 0;

  	rx_opt->num_sacks = 0;
  }

  void tcp_cwnd_restart(struct sock *sk, s32 delta);
  
  static inline void tcp_slow_start_after_idle_check(struct sock *sk)
  {

  	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;

  	struct tcp_sock *tp = tcp_sk(sk);
  	s32 delta;

  	if (!sock_net(sk)->ipv4.sysctl_tcp_slow_start_after_idle || tp->packets_out ||

  	    ca_ops->cong_control)

  		return;

  	delta = tcp_jiffies32 - tp->lsndtime;

  	if (delta > inet_csk(sk)->icsk_rto)
  		tcp_cwnd_restart(sk, delta);
  }

  /* Determine a window scaling and initial window to offer. */

  void tcp_select_initial_window(const struct sock *sk, int __space,
  			       __u32 mss, __u32 *rcv_wnd,

  			       __u32 *window_clamp, int wscale_ok,
  			       __u8 *rcv_wscale, __u32 init_rcv_wnd);

  static inline int tcp_win_from_space(const struct sock *sk, int space)

  {

  	int tcp_adv_win_scale = sock_net(sk)->ipv4.sysctl_tcp_adv_win_scale;

  
  	return tcp_adv_win_scale <= 0 ?
  		(space>>(-tcp_adv_win_scale)) :
  		space - (space>>tcp_adv_win_scale);

  }

  /* Note: caller must be prepared to deal with negative returns */

  static inline int tcp_space(const struct sock *sk)
  {

  	return tcp_win_from_space(sk, READ_ONCE(sk->sk_rcvbuf) -

  				  READ_ONCE(sk->sk_backlog.len) -

  				  atomic_read(&sk->sk_rmem_alloc));

  }

  
  static inline int tcp_full_space(const struct sock *sk)
  {

  	return tcp_win_from_space(sk, READ_ONCE(sk->sk_rcvbuf));

  }

  void tcp_cleanup_rbuf(struct sock *sk, int copied);

  /* We provision sk_rcvbuf around 200% of sk_rcvlowat.
   * If 87.5 % (7/8) of the space has been consumed, we want to override
   * SO_RCVLOWAT constraint, since we are receiving skbs with too small
   * len/truesize ratio.
   */
  static inline bool tcp_rmem_pressure(const struct sock *sk)
  {
  	int rcvbuf = READ_ONCE(sk->sk_rcvbuf);
  	int threshold = rcvbuf - (rcvbuf >> 3);
  
  	return atomic_read(&sk->sk_rmem_alloc) > threshold;
  }

  extern void tcp_openreq_init_rwin(struct request_sock *req,

  				  const struct sock *sk_listener,
  				  const struct dst_entry *dst);

  void tcp_enter_memory_pressure(struct sock *sk);

  void tcp_leave_memory_pressure(struct sock *sk);

  static inline int keepalive_intvl_when(const struct tcp_sock *tp)
  {

  	struct net *net = sock_net((struct sock *)tp);
  
  	return tp->keepalive_intvl ? : net->ipv4.sysctl_tcp_keepalive_intvl;

  }
  
  static inline int keepalive_time_when(const struct tcp_sock *tp)
  {

  	struct net *net = sock_net((struct sock *)tp);
  
  	return tp->keepalive_time ? : net->ipv4.sysctl_tcp_keepalive_time;

  }