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tcp.h

/*
 * 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>
 *
 *          This program is free software; you can redistribute it and/or
 *          modify it under the terms of the GNU General Public License
 *          as published by the Free Software Foundation; either version
 *          2 of the License, or (at your option) any later version.
 */
#ifndef _TCP_H
#define _TCP_H

#define TCP_DEBUG 1
#define FASTRETRANS_DEBUG 1

#include <linux/list.h>
#include <linux/tcp.h>
#include <linux/slab.h>
#include <linux/cache.h>
#include <linux/percpu.h>
#include <linux/skbuff.h>
#include <linux/dmaengine.h>
#include <linux/crypto.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.h>
#include <net/snmp.h>
#include <net/ip.h>
#include <net/tcp_states.h>
#include <net/inet_ecn.h>

#include <linux/seq_file.h>

extern struct inet_hashinfo tcp_hashinfo;

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

#define MAX_TCP_HEADER  (128 + MAX_HEADER)

/* 
 * 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

/* Minimal RCV_MSS. */
#define TCP_MIN_RCVMSS        536U

/* The least MTU to use for probing */
#define TCP_BASE_MSS          512

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

/* Maximal reordering. */
#define TCP_MAX_REORDERING    127

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

/* 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  5    /* number of times to retry active opening a
                         * connection: ~180sec is RFC minimum     */

#define TCP_SYNACK_RETRIES 5  /* number of times to retry passive opening a
                         * connection: ~180sec is RFC minimum     */


#define TCP_ORPHAN_RETRIES 7  /* number of times to retry on an orphaned
                         * socket. 7 is ~50sec-16min.
                         */


#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_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_INIT ((unsigned)(3*HZ))     /* RFC 1122 initial RTO value */

#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) */

/*
 *     TCP option lengths
 */

#define TCPOLEN_MSS            4
#define TCPOLEN_WINDOW         3
#define TCPOLEN_SACK_PERM      2
#define TCPOLEN_TIMESTAMP      10
#define TCPOLEN_MD5SIG         18

/* 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

/* 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 */

extern struct inet_timewait_death_row tcp_death_row;

/* sysctl variables for tcp */
extern int sysctl_tcp_timestamps;
extern int sysctl_tcp_window_scaling;
extern int sysctl_tcp_sack;
extern int sysctl_tcp_fin_timeout;
extern int sysctl_tcp_keepalive_time;
extern int sysctl_tcp_keepalive_probes;
extern int sysctl_tcp_keepalive_intvl;
extern int sysctl_tcp_syn_retries;
extern int sysctl_tcp_synack_retries;
extern int sysctl_tcp_retries1;
extern int sysctl_tcp_retries2;
extern int sysctl_tcp_orphan_retries;
extern int sysctl_tcp_syncookies;
extern int sysctl_tcp_retrans_collapse;
extern int sysctl_tcp_stdurg;
extern int sysctl_tcp_rfc1337;
extern int sysctl_tcp_abort_on_overflow;
extern int sysctl_tcp_max_orphans;
extern int sysctl_tcp_fack;
extern int sysctl_tcp_reordering;
extern int sysctl_tcp_ecn;
extern int sysctl_tcp_dsack;
extern int sysctl_tcp_mem[3];
extern int sysctl_tcp_wmem[3];
extern int sysctl_tcp_rmem[3];
extern int sysctl_tcp_app_win;
extern int sysctl_tcp_adv_win_scale;
extern int sysctl_tcp_tw_reuse;
extern int sysctl_tcp_frto;
extern int sysctl_tcp_frto_response;
extern int sysctl_tcp_low_latency;
extern int sysctl_tcp_dma_copybreak;
extern int sysctl_tcp_nometrics_save;
extern int sysctl_tcp_moderate_rcvbuf;
extern int sysctl_tcp_tso_win_divisor;
extern int sysctl_tcp_abc;
extern int sysctl_tcp_mtu_probing;
extern int sysctl_tcp_base_mss;
extern int sysctl_tcp_workaround_signed_windows;
extern int sysctl_tcp_slow_start_after_idle;
extern int sysctl_tcp_max_ssthresh;

extern atomic_t tcp_memory_allocated;
extern atomic_t tcp_sockets_allocated;
extern int tcp_memory_pressure;

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

static inline int before(__u32 seq1, __u32 seq2)
{
        return (__s32)(seq1-seq2) < 0;
}
#define after(seq2, seq1)     before(seq1, seq2)

/* is s2<=s1<=s3 ? */
static inline int between(__u32 seq1, __u32 seq2, __u32 seq3)
{
      return seq3 - seq2 >= seq1 - seq2;
}

static inline int tcp_too_many_orphans(struct sock *sk, int num)
{
      return (num > sysctl_tcp_max_orphans) ||
            (sk->sk_wmem_queued > SOCK_MIN_SNDBUF &&
             atomic_read(&tcp_memory_allocated) > sysctl_tcp_mem[2]);
}

extern struct proto tcp_prot;

DECLARE_SNMP_STAT(struct tcp_mib, tcp_statistics);
#define TCP_INC_STATS(field)        SNMP_INC_STATS(tcp_statistics, field)
#define TCP_INC_STATS_BH(field)           SNMP_INC_STATS_BH(tcp_statistics, field)
#define TCP_INC_STATS_USER(field)   SNMP_INC_STATS_USER(tcp_statistics, field)
#define TCP_DEC_STATS(field)        SNMP_DEC_STATS(tcp_statistics, field)
#define TCP_ADD_STATS_BH(field, val)      SNMP_ADD_STATS_BH(tcp_statistics, field, val)
#define TCP_ADD_STATS_USER(field, val)    SNMP_ADD_STATS_USER(tcp_statistics, field, val)

extern void             tcp_v4_err(struct sk_buff *skb, u32);

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

extern int              tcp_v4_rcv(struct sk_buff *skb);

extern int              tcp_v4_remember_stamp(struct sock *sk);

extern int              tcp_v4_tw_remember_stamp(struct inet_timewait_sock *tw);

extern int              tcp_sendmsg(struct kiocb *iocb, struct socket *sock,
                                  struct msghdr *msg, size_t size);
extern ssize_t                tcp_sendpage(struct socket *sock, struct page *page, int offset, size_t size, int flags);

extern int              tcp_ioctl(struct sock *sk, 
                                int cmd, 
                                unsigned long arg);

extern int              tcp_rcv_state_process(struct sock *sk, 
                                          struct sk_buff *skb,
                                          struct tcphdr *th,
                                          unsigned len);

extern int              tcp_rcv_established(struct sock *sk, 
                                        struct sk_buff *skb,
                                        struct tcphdr *th, 
                                        unsigned len);

extern void             tcp_rcv_space_adjust(struct sock *sk);

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

extern int              tcp_twsk_unique(struct sock *sk,
                                    struct sock *sktw, void *twp);

extern void             tcp_twsk_destructor(struct sock *sk);

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;
      }
}

extern void tcp_enter_quickack_mode(struct sock *sk);

static inline void tcp_clear_options(struct tcp_options_received *rx_opt)
{
      rx_opt->tstamp_ok = rx_opt->sack_ok = rx_opt->wscale_ok = rx_opt->snd_wscale = 0;
}

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

static __inline__ void
TCP_ECN_create_request(struct request_sock *req, struct tcphdr *th)
{
      if (sysctl_tcp_ecn && th->ece && th->cwr)
            inet_rsk(req)->ecn_ok = 1;
}

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


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

extern struct sock *          tcp_check_req(struct sock *sk,struct sk_buff *skb,
                                    struct request_sock *req,
                                    struct request_sock **prev);
extern int              tcp_child_process(struct sock *parent,
                                      struct sock *child,
                                      struct sk_buff *skb);
extern int              tcp_use_frto(struct sock *sk);
extern void             tcp_enter_frto(struct sock *sk);
extern void             tcp_enter_loss(struct sock *sk, int how);
extern void             tcp_clear_retrans(struct tcp_sock *tp);
extern void             tcp_update_metrics(struct sock *sk);

extern void             tcp_close(struct sock *sk, 
                                long timeout);
extern unsigned int           tcp_poll(struct file * file, struct socket *sock, struct poll_table_struct *wait);

extern int              tcp_getsockopt(struct sock *sk, int level, 
                                     int optname,
                                     char __user *optval, 
                                     int __user *optlen);
extern int              tcp_setsockopt(struct sock *sk, int level, 
                                     int optname, char __user *optval, 
                                     int optlen);
extern int              compat_tcp_getsockopt(struct sock *sk,
                              int level, int optname,
                              char __user *optval, int __user *optlen);
extern int              compat_tcp_setsockopt(struct sock *sk,
                              int level, int optname,
                              char __user *optval, int optlen);
extern void             tcp_set_keepalive(struct sock *sk, int val);
extern int              tcp_recvmsg(struct kiocb *iocb, struct sock *sk,
                                  struct msghdr *msg,
                                  size_t len, int nonblock, 
                                  int flags, int *addr_len);

extern void             tcp_parse_options(struct sk_buff *skb,
                                      struct tcp_options_received *opt_rx,
                                      int estab);

/*
 *    TCP v4 functions exported for the inet6 API
 */

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

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

extern struct sock *          tcp_create_openreq_child(struct sock *sk,
                                           struct request_sock *req,
                                           struct sk_buff *skb);

extern struct sock *          tcp_v4_syn_recv_sock(struct sock *sk,
                                         struct sk_buff *skb,
                                         struct request_sock *req,
                                          struct dst_entry *dst);

extern int              tcp_v4_do_rcv(struct sock *sk,
                                    struct sk_buff *skb);

extern int              tcp_v4_connect(struct sock *sk,
                                     struct sockaddr *uaddr,
                                     int addr_len);

extern int              tcp_connect(struct sock *sk);

extern struct sk_buff *       tcp_make_synack(struct sock *sk,
                                    struct dst_entry *dst,
                                    struct request_sock *req);

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

extern void             tcp_unhash(struct sock *sk);

/* From syncookies.c */
extern struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb, 
                            struct ip_options *opt);
extern __u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb, 
                             __u16 *mss);

/* tcp_output.c */

extern void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
                              int nonagle);
extern int tcp_may_send_now(struct sock *sk);
extern int tcp_retransmit_skb(struct sock *, struct sk_buff *);
extern void tcp_xmit_retransmit_queue(struct sock *);
extern void tcp_simple_retransmit(struct sock *);
extern int tcp_trim_head(struct sock *, struct sk_buff *, u32);
extern int tcp_fragment(struct sock *, struct sk_buff *, u32, unsigned int);

extern void tcp_send_probe0(struct sock *);
extern void tcp_send_partial(struct sock *);
extern int  tcp_write_wakeup(struct sock *);
extern void tcp_send_fin(struct sock *sk);
extern void tcp_send_active_reset(struct sock *sk, gfp_t priority);
extern int  tcp_send_synack(struct sock *);
extern void tcp_push_one(struct sock *, unsigned int mss_now);
extern void tcp_send_ack(struct sock *sk);
extern void tcp_send_delayed_ack(struct sock *sk);

/* tcp_input.c */
extern void tcp_cwnd_application_limited(struct sock *sk);

/* tcp_timer.c */
extern void tcp_init_xmit_timers(struct sock *);
static inline void tcp_clear_xmit_timers(struct sock *sk)
{
      inet_csk_clear_xmit_timers(sk);
}

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

/* tcp.c */
extern void tcp_get_info(struct sock *, struct tcp_info *);

/* Read 'sendfile()'-style from a TCP socket */
typedef int (*sk_read_actor_t)(read_descriptor_t *, struct sk_buff *,
                        unsigned int, size_t);
extern int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
                   sk_read_actor_t recv_actor);

extern void tcp_initialize_rcv_mss(struct sock *sk);

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

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 (skb_queue_empty(&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 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.
 */
extern u32  __tcp_select_window(struct sock *sk);

/* TCP timestamps are only 32-bits, this causes a slight
 * complication on 64-bit systems since we store a snapshot
 * of jiffies in the buffer control blocks below.  We decided
 * to use only the low 32-bits of jiffies and hide the ugly
 * casts with the following macro.
 */
#define tcp_time_stamp        ((__u32)(jiffies))

/* 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 36 bytes on 32-bit architectures,
 * 40 bytes on 64-bit machines, if this grows please adjust
 * skbuff.h:skbuff->cb[xxx] size appropriately.
 */
struct tcp_skb_cb {
      union {
            struct inet_skb_parm    h4;
#if defined(CONFIG_IPV6) || defined (CONFIG_IPV6_MODULE)
            struct inet6_skb_parm   h6;
#endif
      } header;   /* For incoming frames        */
      __u32       seq;        /* Starting sequence number   */
      __u32       end_seq;    /* SEQ + FIN + SYN + datalen  */
      __u32       when;       /* used to compute rtt's      */
      __u8        flags;            /* TCP header flags.          */

      /* NOTE: These must match up to the flags byte in a
       *       real TCP header.
       */
#define TCPCB_FLAG_FIN        0x01
#define TCPCB_FLAG_SYN        0x02
#define TCPCB_FLAG_RST        0x04
#define TCPCB_FLAG_PSH        0x08
#define TCPCB_FLAG_ACK        0x10
#define TCPCB_FLAG_URG        0x20
#define TCPCB_FLAG_ECE        0x40
#define TCPCB_FLAG_CWR        0x80

      __u8        sacked;           /* State flags for SACK/FACK. */
#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_EVER_RETRANS    0x80  /* Ever retransmitted frame   */
#define TCPCB_RETRANS         (TCPCB_SACKED_RETRANS|TCPCB_EVER_RETRANS)

#define TCPCB_URG       0x20  /* Urgent pointer advanced here     */

#define TCPCB_AT_TAIL         (TCPCB_URG)

      __u16       urg_ptr;    /* Valid w/URG flags is set.  */
      __u32       ack_seq;    /* Sequence number ACK'd      */
};

#define TCP_SKB_CB(__skb)     ((struct tcp_skb_cb *)&((__skb)->cb[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 skb_shinfo(skb)->gso_segs;
}

/* This is valid iff tcp_skb_pcount() > 1. */
static inline int tcp_skb_mss(const struct sk_buff *skb)
{
      return skb_shinfo(skb)->gso_size;
}

static inline void tcp_dec_pcount_approx_int(__u32 *count, const int decr)
{
      if (*count) {
            *count -= decr;
            if ((int)*count < 0)
                  *count = 0;
      }
}

static inline void tcp_dec_pcount_approx(__u32 *count,
                               const struct sk_buff *skb)
{
      tcp_dec_pcount_approx_int(count, tcp_skb_pcount(skb));
}

/* 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_FRTO,          /* fast recovery timeout */
      CA_EVENT_LOSS,          /* loss timeout */
      CA_EVENT_FAST_ACK,      /* in sequence ack */
      CA_EVENT_SLOW_ACK,      /* other 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_CONG_NON_RESTRICTED 0x1
#define TCP_CONG_RTT_STAMP    0x2

struct tcp_congestion_ops {
      struct list_head  list;
      unsigned long 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);
      /* lower bound for congestion window (optional) */
      u32 (*min_cwnd)(const struct sock *sk);
      /* do new cwnd calculation (required) */
      void (*cong_avoid)(struct sock *sk, u32 ack, u32 in_flight, int good_ack);
      /* 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);
      /* new value of cwnd after loss (optional) */
      u32  (*undo_cwnd)(struct sock *sk);
      /* hook for packet ack accounting (optional) */
      void (*pkts_acked)(struct sock *sk, u32 num_acked, s32 rtt_us);
      /* get info for inet_diag (optional) */
      void (*get_info)(struct sock *sk, u32 ext, struct sk_buff *skb);

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

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

extern void tcp_init_congestion_control(struct sock *sk);
extern void tcp_cleanup_congestion_control(struct sock *sk);
extern int tcp_set_default_congestion_control(const char *name);
extern void tcp_get_default_congestion_control(char *name);
extern void tcp_get_available_congestion_control(char *buf, size_t len);
extern void tcp_get_allowed_congestion_control(char *buf, size_t len);
extern int tcp_set_allowed_congestion_control(char *allowed);
extern int tcp_set_congestion_control(struct sock *sk, const char *name);
extern void tcp_slow_start(struct tcp_sock *tp);

extern struct tcp_congestion_ops tcp_init_congestion_ops;
extern u32 tcp_reno_ssthresh(struct sock *sk);
extern void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight, int flag);
extern u32 tcp_reno_min_cwnd(const struct sock *sk);
extern struct tcp_congestion_ops tcp_reno;

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);
}

/* 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
 * tcp_is_fack - FACK enabled, implies SACK enabled
 */
static inline int tcp_is_sack(const struct tcp_sock *tp)
{
      return tp->rx_opt.sack_ok;
}

static inline int tcp_is_reno(const struct tcp_sock *tp)
{
      return !tcp_is_sack(tp);
}

static inline int tcp_is_fack(const struct tcp_sock *tp)
{
      return tp->rx_opt.sack_ok & 2;
}

static inline void tcp_enable_fack(struct tcp_sock *tp)
{
      tp->rx_opt.sack_ok |= 2;
}

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;
}

/* If cwnd > ssthresh, we may raise ssthresh to be half-way to cwnd.
 * The exception is rate halving 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 ((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_CWR | TCPF_CA_Recovery))
            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)

extern void tcp_enter_cwr(struct sock *sk, const int set_ssthresh);
extern __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst);

/* Slow start with delack produces 3 packets of burst, so that
 * it is safe "de facto".
 */
static __inline__ __u32 tcp_max_burst(const struct tcp_sock *tp)
{
      return 3;
}

/* RFC2861 Check whether we are limited by application or congestion window
 * This is the inverse of cwnd check in tcp_tso_should_defer
 */
static inline int tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
{
      const struct tcp_sock *tp = tcp_sk(sk);
      u32 left;

      if (in_flight >= tp->snd_cwnd)
            return 1;

      if (!sk_can_gso(sk))
            return 0;

      left = tp->snd_cwnd - in_flight;
      if (sysctl_tcp_tso_win_divisor)
            return left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd;
      else
            return left <= tcp_max_burst(tp);
}

static inline void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss,
                               const struct sk_buff *skb)
{
      if (skb->len < mss)
            tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
}

static inline void tcp_check_probe_timer(struct sock *sk)
{
      struct tcp_sock *tp = tcp_sk(sk);
      const struct inet_connection_sock *icsk = inet_csk(sk);

      if (!tp->packets_out && !icsk->icsk_pending)
            inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
                                icsk->icsk_rto, TCP_RTO_MAX);
}

static inline void tcp_push_pending_frames(struct sock *sk)
{
      struct tcp_sock *tp = tcp_sk(sk);

      __tcp_push_pending_frames(sk, tcp_current_mss(sk, 1), tp->nonagle);
}

static inline void tcp_init_wl(struct tcp_sock *tp, u32 ack, u32 seq)
{
      tp->snd_wl1 = seq;
}

static inline void tcp_update_wl(struct tcp_sock *tp, u32 ack, 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 __sum16 __tcp_checksum_complete(struct sk_buff *skb)
{
      return __skb_checksum_complete(skb);
}

static inline int tcp_checksum_complete(struct sk_buff *skb)
{
      return !skb_csum_unnecessary(skb) &&
            __tcp_checksum_complete(skb);
}

/* Prequeue for VJ style copy to user, combined with checksumming. */

static inline void tcp_prequeue_init(struct tcp_sock *tp)
{
      tp->ucopy.task = NULL;
      tp->ucopy.len = 0;
      tp->ucopy.memory = 0;
      skb_queue_head_init(&tp->ucopy.prequeue);
#ifdef CONFIG_NET_DMA
      tp->ucopy.dma_chan = NULL;
      tp->ucopy.wakeup = 0;
      tp->ucopy.pinned_list = NULL;
      tp->ucopy.dma_cookie = 0;
#endif
}

/* Packet is added to VJ-style prequeue for processing in process
 * context, if a reader task is waiting. Apparently, this exciting
 * idea (VJ's mail "Re: query about TCP header on tcp-ip" of 07 Sep 93)
 * failed somewhere. Latency? Burstiness? Well, at least now we will
 * see, why it failed. 8)8)                       --ANK
 *
 * NOTE: is this not too big to inline?
 */
static inline int tcp_prequeue(struct sock *sk, struct sk_buff *skb)
{
      struct tcp_sock *tp = tcp_sk(sk);

      if (!sysctl_tcp_low_latency && tp->ucopy.task) {
            __skb_queue_tail(&tp->ucopy.prequeue, skb);
            tp->ucopy.memory += skb->truesize;
            if (tp->ucopy.memory > sk->sk_rcvbuf) {
                  struct sk_buff *skb1;

                  BUG_ON(sock_owned_by_user(sk));

                  while ((skb1 = __skb_dequeue(&tp->ucopy.prequeue)) != NULL) {
                        sk->sk_backlog_rcv(sk, skb1);
                        NET_INC_STATS_BH(LINUX_MIB_TCPPREQUEUEDROPPED);
                  }

                  tp->ucopy.memory = 0;
            } else if (skb_queue_len(&tp->ucopy.prequeue) == 1) {
                  wake_up_interruptible(sk->sk_sleep);
                  if (!inet_csk_ack_scheduled(sk))
                        inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
                                              (3 * TCP_RTO_MIN) / 4,
                                            TCP_RTO_MAX);
            }
            return 1;
      }
      return 0;
}


#undef STATE_TRACE

#ifdef STATE_TRACE
static const char *statename[]={
      "Unused","Established","Syn Sent","Syn Recv",
      "Fin Wait 1","Fin Wait 2","Time Wait", "Close",
      "Close Wait","Last ACK","Listen","Closing"
};
#endif

static inline void tcp_set_state(struct sock *sk, int state)
{
      int oldstate = sk->sk_state;

      switch (state) {
      case TCP_ESTABLISHED:
            if (oldstate != TCP_ESTABLISHED)
                  TCP_INC_STATS(TCP_MIB_CURRESTAB);
            break;

      case TCP_CLOSE:
            if (oldstate == TCP_CLOSE_WAIT || oldstate == TCP_ESTABLISHED)
                  TCP_INC_STATS(TCP_MIB_ESTABRESETS);

            sk->sk_prot->unhash(sk);
            if (inet_csk(sk)->icsk_bind_hash &&
                !(sk->sk_userlocks & SOCK_BINDPORT_LOCK))
                  inet_put_port(&tcp_hashinfo, sk);
            /* fall through */
      default:
            if (oldstate==TCP_ESTABLISHED)
                  TCP_DEC_STATS(TCP_MIB_CURRESTAB);
      }

      /* Change state AFTER socket is unhashed to avoid closed
       * socket sitting in hash tables.
       */
      sk->sk_state = state;

#ifdef STATE_TRACE
      SOCK_DEBUG(sk, "TCP sk=%p, State %s -> %s\n",sk, statename[oldstate],statename[state]);
#endif      
}

extern void tcp_done(struct sock *sk);

static inline void tcp_sack_reset(struct tcp_options_received *rx_opt)
{
      rx_opt->dsack = 0;
      rx_opt->eff_sacks = 0;
      rx_opt->num_sacks = 0;
}

/* Determine a window scaling and initial window to offer. */
extern void tcp_select_initial_window(int __space, __u32 mss,
                              __u32 *rcv_wnd, __u32 *window_clamp,
                              int wscale_ok, __u8 *rcv_wscale);

static inline int tcp_win_from_space(int space)
{
      return sysctl_tcp_adv_win_scale<=0 ?
            (space>>(-sysctl_tcp_adv_win_scale)) :
            space - (space>>sysctl_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->sk_rcvbuf -
                          atomic_read(&sk->sk_rmem_alloc));
} 

static inline int tcp_full_space(const struct sock *sk)
{
      return tcp_win_from_space(sk->sk_rcvbuf); 
}

static inline void tcp_openreq_init(struct request_sock *req,
                            struct tcp_options_received *rx_opt,
                            struct sk_buff *skb)
{
      struct inet_request_sock *ireq = inet_rsk(req);

      req->rcv_wnd = 0;       /* So that tcp_send_synack() knows! */
      tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
      req->mss = rx_opt->mss_clamp;
      req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
      ireq->tstamp_ok = rx_opt->tstamp_ok;
      ireq->sack_ok = rx_opt->sack_ok;
      ireq->snd_wscale = rx_opt->snd_wscale;
      ireq->wscale_ok = rx_opt->wscale_ok;
      ireq->acked = 0;
      ireq->ecn_ok = 0;
      ireq->rmt_port = tcp_hdr(skb)->source;
}

extern void tcp_enter_memory_pressure(void);

static inline int keepalive_intvl_when(const struct tcp_sock *tp)
{
      return tp->keepalive_intvl ? : sysctl_tcp_keepalive_intvl;
}

static inline int keepalive_time_when(const struct tcp_sock *tp)
{
      return tp->keepalive_time ? : sysctl_tcp_keepalive_time;
}

static inline int tcp_fin_time(const struct sock *sk)
{
      int fin_timeout = tcp_sk(sk)->linger2 ? : sysctl_tcp_fin_timeout;
      const int rto = inet_csk(sk)->icsk_rto;

      if (fin_timeout < (rto << 2) - (rto >> 1))
            fin_timeout = (rto << 2) - (rto >> 1);

      return fin_timeout;
}

static inline int tcp_paws_check(const struct tcp_options_received *rx_opt, int rst)
{
      if ((s32)(rx_opt->rcv_tsval - rx_opt->ts_recent) >= 0)
            return 0;
      if (get_seconds() >= rx_opt->ts_recent_stamp + TCP_PAWS_24DAYS)
            return 0;

      /* RST segments are not recommended to carry timestamp,
         and, if they do, it is recommended to ignore PAWS because
         "their cleanup function should take precedence over timestamps."
         Certainly, it is mistake. It is necessary to understand the reasons
         of this constraint to relax it: if peer reboots, clock may go
         out-of-sync and half-open connections will not be reset.
         Actually, the problem would be not existing if all
         the implementations followed draft about maintaining clock
         via reboots. Linux-2.2 DOES NOT!

         However, we can relax time bounds for RST segments to MSL.
       */
      if (rst && get_seconds() >= rx_opt->ts_recent_stamp + TCP_PAWS_MSL)
            return 0;
      return 1;
}

#define TCP_CHECK_TIMER(sk) do { } while (0)

static inline void tcp_mib_init(void)
{
      /* See RFC 2012 */
      TCP_ADD_STATS_USER(TCP_MIB_RTOALGORITHM, 1);
      TCP_ADD_STATS_USER(TCP_MIB_RTOMIN, TCP_RTO_MIN*1000/HZ);
      TCP_ADD_STATS_USER(TCP_MIB_RTOMAX, TCP_RTO_MAX*1000/HZ);
      TCP_ADD_STATS_USER(TCP_MIB_MAXCONN, -1);
}

/* from STCP */
static inline void tcp_clear_retrans_hints_partial(struct tcp_sock *tp)
{
      tp->lost_skb_hint = NULL;
      tp->scoreboard_skb_hint = NULL;
      tp->retransmit_skb_hint = NULL;
      tp->forward_skb_hint = NULL;
}

static inline void tcp_clear_all_retrans_hints(struct tcp_sock *tp)
{
      tcp_clear_retrans_hints_partial(tp);
      tp->fastpath_skb_hint = NULL;
}

/* MD5 Signature */
struct crypto_hash;

/* - key database */
struct tcp_md5sig_key {
      u8                *key;
      u8                keylen;
};

struct tcp4_md5sig_key {
      struct tcp_md5sig_key   base;
      __be32                  addr;
};

struct tcp6_md5sig_key {
      struct tcp_md5sig_key   base;
#if 0
      u32               scope_id;   /* XXX */
#endif
      struct in6_addr         addr;
};

/* - sock block */
struct tcp_md5sig_info {
      struct tcp4_md5sig_key  *keys4;
#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
      struct tcp6_md5sig_key  *keys6;
      u32               entries6;
      u32               alloced6;
#endif
      u32               entries4;
      u32               alloced4;
};

/* - pseudo header */
struct tcp4_pseudohdr {
      __be32            saddr;
      __be32            daddr;
      __u8        pad;
      __u8        protocol;
      __be16            len;
};

struct tcp6_pseudohdr {
      struct in6_addr   saddr;
      struct in6_addr daddr;
      __be32            len;
      __be32            protocol;   /* including padding */
};

union tcp_md5sum_block {
      struct tcp4_pseudohdr ip4;
#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
      struct tcp6_pseudohdr ip6;
#endif
};

/* - pool: digest algorithm, hash description and scratch buffer */
struct tcp_md5sig_pool {
      struct hash_desc  md5_desc;
      union tcp_md5sum_block  md5_blk;
};

#define TCP_MD5SIG_MAXKEYS    (~(u32)0)   /* really?! */

/* - functions */
extern int              tcp_v4_calc_md5_hash(char *md5_hash,
                                         struct tcp_md5sig_key *key,
                                         struct sock *sk,
                                         struct dst_entry *dst,
                                         struct request_sock *req,
                                         struct tcphdr *th,
                                         int protocol, int tcplen);
extern struct tcp_md5sig_key  *tcp_v4_md5_lookup(struct sock *sk,
                                       struct sock *addr_sk);

extern int              tcp_v4_md5_do_add(struct sock *sk,
                                      __be32 addr,
                                      u8 *newkey,
                                      u8 newkeylen);

extern int              tcp_v4_md5_do_del(struct sock *sk,
                                      __be32 addr);

extern struct tcp_md5sig_pool **tcp_alloc_md5sig_pool(void);
extern void             tcp_free_md5sig_pool(void);

extern struct tcp_md5sig_pool *__tcp_get_md5sig_pool(int cpu);
extern void             __tcp_put_md5sig_pool(void);

static inline
struct tcp_md5sig_pool        *tcp_get_md5sig_pool(void)
{
      int cpu = get_cpu();
      struct tcp_md5sig_pool *ret = __tcp_get_md5sig_pool(cpu);
      if (!ret)
            put_cpu();
      return ret;
}

static inline void            tcp_put_md5sig_pool(void)
{
      __tcp_put_md5sig_pool();
      put_cpu();
}

/* write queue abstraction */
static inline void tcp_write_queue_purge(struct sock *sk)
{
      struct sk_buff *skb;

      while ((skb = __skb_dequeue(&sk->sk_write_queue)) != NULL)
            sk_stream_free_skb(sk, skb);
      sk_stream_mem_reclaim(sk);
}

static inline struct sk_buff *tcp_write_queue_head(struct sock *sk)
{
      struct sk_buff *skb = sk->sk_write_queue.next;
      if (skb == (struct sk_buff *) &sk->sk_write_queue)
            return NULL;
      return skb;
}

static inline struct sk_buff *tcp_write_queue_tail(struct sock *sk)
{
      struct sk_buff *skb = sk->sk_write_queue.prev;
      if (skb == (struct sk_buff *) &sk->sk_write_queue)
            return NULL;
      return skb;
}

static inline struct sk_buff *tcp_write_queue_next(struct sock *sk, struct sk_buff *skb)
{
      return skb->next;
}

#define tcp_for_write_queue(skb, sk)                              \
            for (skb = (sk)->sk_write_queue.next;                 \
                 (skb != (struct sk_buff *)&(sk)->sk_write_queue);      \
                 skb = skb->next)

#define tcp_for_write_queue_from(skb, sk)                   \
            for (; (skb != (struct sk_buff *)&(sk)->sk_write_queue);\
                 skb = skb->next)

static inline struct sk_buff *tcp_send_head(struct sock *sk)
{
      return sk->sk_send_head;
}

static inline void tcp_advance_send_head(struct sock *sk, struct sk_buff *skb)
{
      struct tcp_sock *tp = tcp_sk(sk);

      sk->sk_send_head = skb->next;
      if (sk->sk_send_head == (struct sk_buff *)&sk->sk_write_queue)
            sk->sk_send_head = NULL;
      /* Don't override Nagle indefinately with F-RTO */
      if (tp->frto_counter == 2)
            tp->frto_counter = 3;
}

static inline void tcp_check_send_head(struct sock *sk, struct sk_buff *skb_unlinked)
{
      if (sk->sk_send_head == skb_unlinked)
            sk->sk_send_head = NULL;
}

static inline void tcp_init_send_head(struct sock *sk)
{
      sk->sk_send_head = NULL;
}

static inline void __tcp_add_write_queue_tail(struct sock *sk, struct sk_buff *skb)
{
      __skb_queue_tail(&sk->sk_write_queue, skb);
}

static inline void tcp_add_write_queue_tail(struct sock *sk, struct sk_buff *skb)
{
      __tcp_add_write_queue_tail(sk, skb);

      /* Queue it, remembering where we must start sending. */
      if (sk->sk_send_head == NULL)
            sk->sk_send_head = skb;
}

static inline void __tcp_add_write_queue_head(struct sock *sk, struct sk_buff *skb)
{
      __skb_queue_head(&sk->sk_write_queue, skb);
}

/* Insert buff after skb on the write queue of sk.  */
static inline void tcp_insert_write_queue_after(struct sk_buff *skb,
                                    struct sk_buff *buff,
                                    struct sock *sk)
{
      __skb_append(skb, buff, &sk->sk_write_queue);
}

/* Insert skb between prev and next on the write queue of sk.  */
static inline void tcp_insert_write_queue_before(struct sk_buff *new,
                                      struct sk_buff *skb,
                                      struct sock *sk)
{
      __skb_insert(new, skb->prev, skb, &sk->sk_write_queue);

      if (sk->sk_send_head == skb)
            sk->sk_send_head = new;
}

static inline void tcp_unlink_write_queue(struct sk_buff *skb, struct sock *sk)
{
      __skb_unlink(skb, &sk->sk_write_queue);
}

static inline int tcp_skb_is_last(const struct sock *sk,
                          const struct sk_buff *skb)
{
      return skb->next == (struct sk_buff *)&sk->sk_write_queue;
}

static inline int tcp_write_queue_empty(struct sock *sk)
{
      return skb_queue_empty(&sk->sk_write_queue);
}

/* /proc */
enum tcp_seq_states {
      TCP_SEQ_STATE_LISTENING,
      TCP_SEQ_STATE_OPENREQ,
      TCP_SEQ_STATE_ESTABLISHED,
      TCP_SEQ_STATE_TIME_WAIT,
};

struct tcp_seq_afinfo {
      struct module           *owner;
      char              *name;
      sa_family_t       family;
      int               (*seq_show) (struct seq_file *m, void *v);
      struct file_operations  *seq_fops;
};

struct tcp_iter_state {
      sa_family_t       family;
      enum tcp_seq_states     state;
      struct sock       *syn_wait_sk;
      int               bucket, sbucket, num, uid;
      struct seq_operations   seq_ops;
};

extern int tcp_proc_register(struct tcp_seq_afinfo *afinfo);
extern void tcp_proc_unregister(struct tcp_seq_afinfo *afinfo);

extern struct request_sock_ops tcp_request_sock_ops;

extern int tcp_v4_destroy_sock(struct sock *sk);

extern int tcp_v4_gso_send_check(struct sk_buff *skb);
extern struct sk_buff *tcp_tso_segment(struct sk_buff *skb, int features);

#ifdef CONFIG_PROC_FS
extern int  tcp4_proc_init(void);
extern void tcp4_proc_exit(void);
#endif

/* TCP af-specific functions */
struct tcp_sock_af_ops {
#ifdef CONFIG_TCP_MD5SIG
      struct tcp_md5sig_key   *(*md5_lookup) (struct sock *sk,
                                    struct sock *addr_sk);
      int               (*calc_md5_hash) (char *location,
                                      struct tcp_md5sig_key *md5,
                                      struct sock *sk,
                                      struct dst_entry *dst,
                                      struct request_sock *req,
                                      struct tcphdr *th,
                                      int protocol, int len);
      int               (*md5_add) (struct sock *sk,
                                  struct sock *addr_sk,
                                  u8 *newkey,
                                  u8 len);
      int               (*md5_parse) (struct sock *sk,
                                    char __user *optval,
                                    int optlen);
#endif
};

struct tcp_request_sock_ops {
#ifdef CONFIG_TCP_MD5SIG
      struct tcp_md5sig_key   *(*md5_lookup) (struct sock *sk,
                                    struct request_sock *req);
#endif
};

extern void tcp_v4_init(struct net_proto_family *ops);
extern void tcp_init(void);

#endif      /* _TCP_H */

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