FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_var.h

     /*-
      * SPDX-License-Identifier: BSD-3-Clause
      *
      * Copyright (c) 1982, 1986, 1993, 1994, 1995
      *      The Regents of the University of California.  All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)tcp_var.h   8.4 (Berkeley) 5/24/95
     * $FreeBSD: releng/12.0/sys/netinet/tcp_var.h 338102 2018-08-20 12:43:18Z rrs $
     */
    
    #ifndef _NETINET_TCP_VAR_H_
    #define _NETINET_TCP_VAR_H_
    
    #include <netinet/tcp.h>
    #include <netinet/tcp_fsm.h>
    
    #ifdef _KERNEL
    #include <net/vnet.h>
    #include <sys/mbuf.h>
    #endif
    
    #if defined(_KERNEL) || defined(_WANT_TCPCB)
    /* TCP segment queue entry */
    struct tseg_qent {
            TAILQ_ENTRY(tseg_qent) tqe_q;
            struct  mbuf   *tqe_m;          /* mbuf contains packet */
            struct  mbuf   *tqe_last;       /* last mbuf in chain */
            tcp_seq tqe_start;              /* TCP Sequence number start */
            int     tqe_len;                /* TCP segment data length */
            uint32_t tqe_flags;             /* The flags from the th->th_flags */
            uint32_t tqe_mbuf_cnt;          /* Count of mbuf overhead */
    };
    TAILQ_HEAD(tsegqe_head, tseg_qent);
    
    struct sackblk {
            tcp_seq start;          /* start seq no. of sack block */
            tcp_seq end;            /* end seq no. */
    };
    
    struct sackhole {
            tcp_seq start;          /* start seq no. of hole */
            tcp_seq end;            /* end seq no. */
            tcp_seq rxmit;          /* next seq. no in hole to be retransmitted */
            TAILQ_ENTRY(sackhole) scblink;  /* scoreboard linkage */
    };
    
    struct sackhint {
            struct sackhole *nexthole;
            int             sack_bytes_rexmit;
            tcp_seq         last_sack_ack;  /* Most recent/largest sacked ack */
    
            int             ispare;         /* explicit pad for 64bit alignment */
            int             sacked_bytes;   /*
                                             * Total sacked bytes reported by the
                                             * receiver via sack option
                                             */
            uint32_t        _pad1[1];       /* TBD */
            uint64_t        _pad[1];        /* TBD */
    };
    
    #define SEGQ_EMPTY(tp) TAILQ_EMPTY(&(tp)->t_segq)
    
    STAILQ_HEAD(tcp_log_stailq, tcp_log_mem);
    
    /*
     * Tcp control block, one per tcp; fields:
     * Organized for 64 byte cacheline efficiency based
     * on common tcp_input/tcp_output processing.
     */
    struct tcpcb {
            /* Cache line 1 */
            struct  inpcb *t_inpcb;         /* back pointer to internet pcb */
            struct tcp_function_block *t_fb;/* TCP function call block */
            void    *t_fb_ptr;              /* Pointer to t_fb specific data */
            uint32_t t_maxseg:24,           /* maximum segment size */
                   t_logstate:8;           /* State of "black box" logging */
           uint32_t t_port:16,             /* Tunneling (over udp) port */
                   t_state:4,              /* state of this connection */
                   t_idle_reduce : 1,
                   t_delayed_ack: 7,       /* Delayed ack variable */
                   bits_spare : 4;
           u_int   t_flags;
           tcp_seq snd_una;                /* sent but unacknowledged */
           tcp_seq snd_max;                /* highest sequence number sent;
                                            * used to recognize retransmits
                                            */
           tcp_seq snd_nxt;                /* send next */
           tcp_seq snd_up;                 /* send urgent pointer */
           uint32_t  snd_wnd;              /* send window */
           uint32_t  snd_cwnd;             /* congestion-controlled window */
           uint32_t t_peakrate_thr;        /* pre-calculated peak rate threshold */
           /* Cache line 2 */
           u_int32_t  ts_offset;           /* our timestamp offset */
           u_int32_t       rfbuf_ts;       /* recv buffer autoscaling timestamp */
           int     rcv_numsacks;           /* # distinct sack blks present */
           u_int   t_tsomax;               /* TSO total burst length limit in bytes */
           u_int   t_tsomaxsegcount;       /* TSO maximum segment count */
           u_int   t_tsomaxsegsize;        /* TSO maximum segment size in bytes */
           tcp_seq rcv_nxt;                /* receive next */
           tcp_seq rcv_adv;                /* advertised window */
           uint32_t  rcv_wnd;              /* receive window */
           u_int   t_flags2;               /* More tcpcb flags storage */
           int     t_srtt;                 /* smoothed round-trip time */
           int     t_rttvar;               /* variance in round-trip time */
           u_int32_t  ts_recent;           /* timestamp echo data */
           u_char  snd_scale;              /* window scaling for send window */
           u_char  rcv_scale;              /* window scaling for recv window */
           u_char  snd_limited;            /* segments limited transmitted */
           u_char  request_r_scale;        /* pending window scaling */
           tcp_seq last_ack_sent;
           u_int   t_rcvtime;              /* inactivity time */
           /* Cache line 3 */
           tcp_seq rcv_up;                 /* receive urgent pointer */
           int     t_segqlen;              /* segment reassembly queue length */
           uint32_t t_segqmbuflen;         /* Count of bytes mbufs on all entries */
           struct  tsegqe_head t_segq;     /* segment reassembly queue */
           struct mbuf      *t_in_pkt;
           struct mbuf      *t_tail_pkt;
           struct tcp_timer *t_timers;     /* All the TCP timers in one struct */
           struct  vnet *t_vnet;           /* back pointer to parent vnet */
           uint32_t  snd_ssthresh;         /* snd_cwnd size threshold for
                                            * for slow start exponential to
                                            * linear switch
                                            */
           tcp_seq snd_wl1;                /* window update seg seq number */
           /* Cache line 4 */
           tcp_seq snd_wl2;                /* window update seg ack number */
   
           tcp_seq irs;                    /* initial receive sequence number */
           tcp_seq iss;                    /* initial send sequence number */
           u_int   t_acktime;
           u_int   ts_recent_age;          /* when last updated */
           tcp_seq snd_recover;            /* for use in NewReno Fast Recovery */
           uint16_t cl4_spare;             /* Spare to adjust CL 4 */
           char    t_oobflags;             /* have some */
           char    t_iobc;                 /* input character */
           int     t_rxtcur;               /* current retransmit value (ticks) */
   
           int     t_rxtshift;             /* log(2) of rexmt exp. backoff */
           u_int   t_rtttime;              /* RTT measurement start time */
   
           tcp_seq t_rtseq;                /* sequence number being timed */
           u_int   t_starttime;            /* time connection was established */
   
           u_int   t_pmtud_saved_maxseg;   /* pre-blackhole MSS */
           u_int   t_rttmin;               /* minimum rtt allowed */
   
           u_int   t_rttbest;              /* best rtt we've seen */
   
           int     t_softerror;            /* possible error not yet reported */
           uint32_t  max_sndwnd;           /* largest window peer has offered */
           /* Cache line 5 */
           uint32_t  snd_cwnd_prev;        /* cwnd prior to retransmit */
           uint32_t  snd_ssthresh_prev;    /* ssthresh prior to retransmit */
           tcp_seq snd_recover_prev;       /* snd_recover prior to retransmit */
           int     t_sndzerowin;           /* zero-window updates sent */
           u_long  t_rttupdated;           /* number of times rtt sampled */
           int     snd_numholes;           /* number of holes seen by sender */
           u_int   t_badrxtwin;            /* window for retransmit recovery */
           TAILQ_HEAD(sackhole_head, sackhole) snd_holes;
                                           /* SACK scoreboard (sorted) */
           tcp_seq snd_fack;               /* last seq number(+1) sack'd by rcv'r*/
           tcp_seq sack_newdata;           /* New data xmitted in this recovery
                                              episode starts at this seq number */
           struct sackblk sackblks[MAX_SACK_BLKS]; /* seq nos. of sack blocks */
           struct sackhint sackhint;       /* SACK scoreboard hint */
           int     t_rttlow;               /* smallest observerved RTT */
           int     rfbuf_cnt;              /* recv buffer autoscaling byte count */
           struct toedev   *tod;           /* toedev handling this connection */
           int     t_sndrexmitpack;        /* retransmit packets sent */
           int     t_rcvoopack;            /* out-of-order packets received */
           void    *t_toe;                 /* TOE pcb pointer */
           struct cc_algo  *cc_algo;       /* congestion control algorithm */
           struct cc_var   *ccv;           /* congestion control specific vars */
           struct osd      *osd;           /* storage for Khelp module data */
           int     t_bytes_acked;          /* # bytes acked during current RTT */
           u_int   t_maxunacktime;
           u_int   t_keepinit;             /* time to establish connection */
           u_int   t_keepidle;             /* time before keepalive probes begin */
           u_int   t_keepintvl;            /* interval between keepalives */
           u_int   t_keepcnt;              /* number of keepalives before close */
           int     t_dupacks;              /* consecutive dup acks recd */
           int     t_lognum;               /* Number of log entries */
           struct tcp_log_stailq t_logs;   /* Log buffer */
           struct tcp_log_id_node *t_lin;
           struct tcp_log_id_bucket *t_lib;
           const char *t_output_caller;    /* Function that called tcp_output */
           uint32_t t_logsn;               /* Log "serial number" */
           uint8_t t_tfo_client_cookie_len; /* TCP Fast Open client cookie length */
           unsigned int *t_tfo_pending;    /* TCP Fast Open server pending counter */
           union {
                   uint8_t client[TCP_FASTOPEN_MAX_COOKIE_LEN];
                   uint64_t server;
           } t_tfo_cookie;                 /* TCP Fast Open cookie to send */
   #ifdef TCPPCAP
           struct mbufq t_inpkts;          /* List of saved input packets. */
           struct mbufq t_outpkts;         /* List of saved output packets. */
   #endif
   };
   #endif  /* _KERNEL || _WANT_TCPCB */
   
   #ifdef _KERNEL
   struct tcptemp {
           u_char  tt_ipgen[40]; /* the size must be of max ip header, now IPv6 */
           struct  tcphdr tt_t;
   };
   
   /* 
    * TODO: We yet need to brave plowing in
    * to tcp_input() and the pru_usrreq() block.
    * Right now these go to the old standards which
    * are somewhat ok, but in the long term may
    * need to be changed. If we do tackle tcp_input()
    * then we need to get rid of the tcp_do_segment()
    * function below.
    */
   /* Flags for tcp functions */
   #define TCP_FUNC_BEING_REMOVED 0x01     /* Can no longer be referenced */
   
   /*
    * If defining the optional tcp_timers, in the
    * tfb_tcp_timer_stop call you must use the
    * callout_async_drain() function with the
    * tcp_timer_discard callback. You should check
    * the return of callout_async_drain() and if 0
    * increment tt_draincnt. Since the timer sub-system
    * does not know your callbacks you must provide a
    * stop_all function that loops through and calls
    * tcp_timer_stop() with each of your defined timers.
    * Adding a tfb_tcp_handoff_ok function allows the socket
    * option to change stacks to query you even if the
    * connection is in a later stage. You return 0 to
    * say you can take over and run your stack, you return
    * non-zero (an error number) to say no you can't.
    * If the function is undefined you can only change
    * in the early states (before connect or listen).
    * tfb_tcp_fb_fini is changed to add a flag to tell
    * the old stack if the tcb is being destroyed or
    * not. A one in the flag means the TCB is being
    * destroyed, a zero indicates its transitioning to
    * another stack (via socket option).
    */
   struct tcp_function_block {
           char tfb_tcp_block_name[TCP_FUNCTION_NAME_LEN_MAX];
           int     (*tfb_tcp_output)(struct tcpcb *);
           int     (*tfb_tcp_output_wtime)(struct tcpcb *, const struct timeval *);
           void    (*tfb_tcp_do_segment)(struct mbuf *, struct tcphdr *,
                               struct socket *, struct tcpcb *,
                           int, int, uint8_t);
           void    (*tfb_tcp_hpts_do_segment)(struct mbuf *, struct tcphdr *,
                               struct socket *, struct tcpcb *,
                               int, int, uint8_t,
                               int, struct timeval *);
           int     (*tfb_tcp_ctloutput)(struct socket *so, struct sockopt *sopt,
                               struct inpcb *inp, struct tcpcb *tp);
           /* Optional memory allocation/free routine */
           int     (*tfb_tcp_fb_init)(struct tcpcb *);
           void    (*tfb_tcp_fb_fini)(struct tcpcb *, int);
           /* Optional timers, must define all if you define one */
           int     (*tfb_tcp_timer_stop_all)(struct tcpcb *);
           void    (*tfb_tcp_timer_activate)(struct tcpcb *,
                               uint32_t, u_int);
           int     (*tfb_tcp_timer_active)(struct tcpcb *, uint32_t);
           void    (*tfb_tcp_timer_stop)(struct tcpcb *, uint32_t);
           void    (*tfb_tcp_rexmit_tmr)(struct tcpcb *);
           int     (*tfb_tcp_handoff_ok)(struct tcpcb *);
           void    (*tfb_tcp_mtu_chg)(struct tcpcb *);
           volatile uint32_t tfb_refcnt;
           uint32_t  tfb_flags;
           uint8_t tfb_id;
   };
   
   struct tcp_function {
           TAILQ_ENTRY(tcp_function)       tf_next;
           char                            tf_name[TCP_FUNCTION_NAME_LEN_MAX];
           struct tcp_function_block       *tf_fb;
   };
   
   TAILQ_HEAD(tcp_funchead, tcp_function);
   #endif  /* _KERNEL */
   
   /*
    * Flags and utility macros for the t_flags field.
    */
   #define TF_ACKNOW       0x000001        /* ack peer immediately */
   #define TF_DELACK       0x000002        /* ack, but try to delay it */
   #define TF_NODELAY      0x000004        /* don't delay packets to coalesce */
   #define TF_NOOPT        0x000008        /* don't use tcp options */
   #define TF_SENTFIN      0x000010        /* have sent FIN */
   #define TF_REQ_SCALE    0x000020        /* have/will request window scaling */
   #define TF_RCVD_SCALE   0x000040        /* other side has requested scaling */
   #define TF_REQ_TSTMP    0x000080        /* have/will request timestamps */
   #define TF_RCVD_TSTMP   0x000100        /* a timestamp was received in SYN */
   #define TF_SACK_PERMIT  0x000200        /* other side said I could SACK */
   #define TF_NEEDSYN      0x000400        /* send SYN (implicit state) */
   #define TF_NEEDFIN      0x000800        /* send FIN (implicit state) */
   #define TF_NOPUSH       0x001000        /* don't push */
   #define TF_PREVVALID    0x002000        /* saved values for bad rxmit valid */
   #define TF_MORETOCOME   0x010000        /* More data to be appended to sock */
   #define TF_LQ_OVERFLOW  0x020000        /* listen queue overflow */
   #define TF_LASTIDLE     0x040000        /* connection was previously idle */
   #define TF_RXWIN0SENT   0x080000        /* sent a receiver win 0 in response */
   #define TF_FASTRECOVERY 0x100000        /* in NewReno Fast Recovery */
   #define TF_WASFRECOVERY 0x200000        /* was in NewReno Fast Recovery */
   #define TF_SIGNATURE    0x400000        /* require MD5 digests (RFC2385) */
   #define TF_FORCEDATA    0x800000        /* force out a byte */
   #define TF_TSO          0x1000000       /* TSO enabled on this connection */
   #define TF_TOE          0x2000000       /* this connection is offloaded */
   #define TF_ECN_PERMIT   0x4000000       /* connection ECN-ready */
   #define TF_ECN_SND_CWR  0x8000000       /* ECN CWR in queue */
   #define TF_ECN_SND_ECE  0x10000000      /* ECN ECE in queue */
   #define TF_CONGRECOVERY 0x20000000      /* congestion recovery mode */
   #define TF_WASCRECOVERY 0x40000000      /* was in congestion recovery */
   #define TF_FASTOPEN     0x80000000      /* TCP Fast Open indication */
   
   #define IN_FASTRECOVERY(t_flags)        (t_flags & TF_FASTRECOVERY)
   #define ENTER_FASTRECOVERY(t_flags)     t_flags |= TF_FASTRECOVERY
   #define EXIT_FASTRECOVERY(t_flags)      t_flags &= ~TF_FASTRECOVERY
   
   #define IN_CONGRECOVERY(t_flags)        (t_flags & TF_CONGRECOVERY)
   #define ENTER_CONGRECOVERY(t_flags)     t_flags |= TF_CONGRECOVERY
   #define EXIT_CONGRECOVERY(t_flags)      t_flags &= ~TF_CONGRECOVERY
   
   #define IN_RECOVERY(t_flags) (t_flags & (TF_CONGRECOVERY | TF_FASTRECOVERY))
   #define ENTER_RECOVERY(t_flags) t_flags |= (TF_CONGRECOVERY | TF_FASTRECOVERY)
   #define EXIT_RECOVERY(t_flags) t_flags &= ~(TF_CONGRECOVERY | TF_FASTRECOVERY)
   
   #if defined(_KERNEL) && !defined(TCP_RFC7413)
   #define IS_FASTOPEN(t_flags)            (false)
   #else
   #define IS_FASTOPEN(t_flags)            (t_flags & TF_FASTOPEN)
   #endif
   
   #define BYTES_THIS_ACK(tp, th)  (th->th_ack - tp->snd_una)
   
   /*
    * Flags for the t_oobflags field.
    */
   #define TCPOOB_HAVEDATA 0x01
   #define TCPOOB_HADDATA  0x02
   
   /*
    * Flags for the extended TCP flags field, t_flags2
    */
   #define TF2_PLPMTU_BLACKHOLE    0x00000001 /* Possible PLPMTUD Black Hole. */
   #define TF2_PLPMTU_PMTUD        0x00000002 /* Allowed to attempt PLPMTUD. */
   #define TF2_PLPMTU_MAXSEGSNT    0x00000004 /* Last seg sent was full seg. */
   #define TF2_LOG_AUTO            0x00000008 /* Session is auto-logging. */
   #define TF2_DROP_AF_DATA        0x00000010 /* Drop after all data ack'd */
   
   /*
    * Structure to hold TCP options that are only used during segment
    * processing (in tcp_input), but not held in the tcpcb.
    * It's basically used to reduce the number of parameters
    * to tcp_dooptions and tcp_addoptions.
    * The binary order of the to_flags is relevant for packing of the
    * options in tcp_addoptions.
    */
   struct tcpopt {
           u_int32_t       to_flags;       /* which options are present */
   #define TOF_MSS         0x0001          /* maximum segment size */
   #define TOF_SCALE       0x0002          /* window scaling */
   #define TOF_SACKPERM    0x0004          /* SACK permitted */
   #define TOF_TS          0x0010          /* timestamp */
   #define TOF_SIGNATURE   0x0040          /* TCP-MD5 signature option (RFC2385) */
   #define TOF_SACK        0x0080          /* Peer sent SACK option */
   #define TOF_FASTOPEN    0x0100          /* TCP Fast Open (TFO) cookie */
   #define TOF_MAXOPT      0x0200
           u_int32_t       to_tsval;       /* new timestamp */
           u_int32_t       to_tsecr;       /* reflected timestamp */
           u_char          *to_sacks;      /* pointer to the first SACK blocks */
           u_char          *to_signature;  /* pointer to the TCP-MD5 signature */
           u_int8_t        *to_tfo_cookie; /* pointer to the TFO cookie */
           u_int16_t       to_mss;         /* maximum segment size */
           u_int8_t        to_wscale;      /* window scaling */
           u_int8_t        to_nsacks;      /* number of SACK blocks */
           u_int8_t        to_tfo_len;     /* TFO cookie length */
           u_int32_t       to_spare;       /* UTO */
   };
   
   /*
    * Flags for tcp_dooptions.
    */
   #define TO_SYN          0x01            /* parse SYN-only options */
   
   struct hc_metrics_lite {        /* must stay in sync with hc_metrics */
           uint32_t        rmx_mtu;        /* MTU for this path */
           uint32_t        rmx_ssthresh;   /* outbound gateway buffer limit */
           uint32_t        rmx_rtt;        /* estimated round trip time */
           uint32_t        rmx_rttvar;     /* estimated rtt variance */
           uint32_t        rmx_cwnd;       /* congestion window */
           uint32_t        rmx_sendpipe;   /* outbound delay-bandwidth product */
           uint32_t        rmx_recvpipe;   /* inbound delay-bandwidth product */
   };
   
   /*
    * Used by tcp_maxmtu() to communicate interface specific features
    * and limits at the time of connection setup.
    */
   struct tcp_ifcap {
           int     ifcap;
           u_int   tsomax;
           u_int   tsomaxsegcount;
           u_int   tsomaxsegsize;
   };
   
   #ifndef _NETINET_IN_PCB_H_
   struct in_conninfo;
   #endif /* _NETINET_IN_PCB_H_ */
   
   struct tcptw {
           struct inpcb    *tw_inpcb;      /* XXX back pointer to internet pcb */
           tcp_seq         snd_nxt;
           tcp_seq         rcv_nxt;
           tcp_seq         iss;
           tcp_seq         irs;
           u_short         last_win;       /* cached window value */
           short           tw_so_options;  /* copy of so_options */
           struct ucred    *tw_cred;       /* user credentials */
           u_int32_t       t_recent;
           u_int32_t       ts_offset;      /* our timestamp offset */
           u_int           t_starttime;
           int             tw_time;
           TAILQ_ENTRY(tcptw) tw_2msl;
           void            *tw_pspare;     /* TCP_SIGNATURE */
           u_int           *tw_spare;      /* TCP_SIGNATURE */
   };
   
   #define intotcpcb(ip)   ((struct tcpcb *)(ip)->inp_ppcb)
   #define intotw(ip)      ((struct tcptw *)(ip)->inp_ppcb)
   #define sototcpcb(so)   (intotcpcb(sotoinpcb(so)))
   
   /*
    * The smoothed round-trip time and estimated variance
    * are stored as fixed point numbers scaled by the values below.
    * For convenience, these scales are also used in smoothing the average
    * (smoothed = (1/scale)sample + ((scale-1)/scale)smoothed).
    * With these scales, srtt has 3 bits to the right of the binary point,
    * and thus an "ALPHA" of 0.875.  rttvar has 2 bits to the right of the
    * binary point, and is smoothed with an ALPHA of 0.75.
    */
   #define TCP_RTT_SCALE           32      /* multiplier for srtt; 3 bits frac. */
   #define TCP_RTT_SHIFT           5       /* shift for srtt; 3 bits frac. */
   #define TCP_RTTVAR_SCALE        16      /* multiplier for rttvar; 2 bits */
   #define TCP_RTTVAR_SHIFT        4       /* shift for rttvar; 2 bits */
   #define TCP_DELTA_SHIFT         2       /* see tcp_input.c */
   
   /*
    * The initial retransmission should happen at rtt + 4 * rttvar.
    * Because of the way we do the smoothing, srtt and rttvar
    * will each average +1/2 tick of bias.  When we compute
    * the retransmit timer, we want 1/2 tick of rounding and
    * 1 extra tick because of +-1/2 tick uncertainty in the
    * firing of the timer.  The bias will give us exactly the
    * 1.5 tick we need.  But, because the bias is
    * statistical, we have to test that we don't drop below
    * the minimum feasible timer (which is 2 ticks).
    * This version of the macro adapted from a paper by Lawrence
    * Brakmo and Larry Peterson which outlines a problem caused
    * by insufficient precision in the original implementation,
    * which results in inappropriately large RTO values for very
    * fast networks.
    */
   #define TCP_REXMTVAL(tp) \
           max((tp)->t_rttmin, (((tp)->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT))  \
             + (tp)->t_rttvar) >> TCP_DELTA_SHIFT)
   
   /*
    * TCP statistics.
    * Many of these should be kept per connection,
    * but that's inconvenient at the moment.
    */
   struct  tcpstat {
           uint64_t tcps_connattempt;      /* connections initiated */
           uint64_t tcps_accepts;          /* connections accepted */
           uint64_t tcps_connects;         /* connections established */
           uint64_t tcps_drops;            /* connections dropped */
           uint64_t tcps_conndrops;        /* embryonic connections dropped */
           uint64_t tcps_minmssdrops;      /* average minmss too low drops */
           uint64_t tcps_closed;           /* conn. closed (includes drops) */
           uint64_t tcps_segstimed;        /* segs where we tried to get rtt */
           uint64_t tcps_rttupdated;       /* times we succeeded */
           uint64_t tcps_delack;           /* delayed acks sent */
           uint64_t tcps_timeoutdrop;      /* conn. dropped in rxmt timeout */
           uint64_t tcps_rexmttimeo;       /* retransmit timeouts */
           uint64_t tcps_persisttimeo;     /* persist timeouts */
           uint64_t tcps_keeptimeo;        /* keepalive timeouts */
           uint64_t tcps_keepprobe;        /* keepalive probes sent */
           uint64_t tcps_keepdrops;        /* connections dropped in keepalive */
   
           uint64_t tcps_sndtotal;         /* total packets sent */
           uint64_t tcps_sndpack;          /* data packets sent */
           uint64_t tcps_sndbyte;          /* data bytes sent */
           uint64_t tcps_sndrexmitpack;    /* data packets retransmitted */
           uint64_t tcps_sndrexmitbyte;    /* data bytes retransmitted */
           uint64_t tcps_sndrexmitbad;     /* unnecessary packet retransmissions */
           uint64_t tcps_sndacks;          /* ack-only packets sent */
           uint64_t tcps_sndprobe;         /* window probes sent */
           uint64_t tcps_sndurg;           /* packets sent with URG only */
           uint64_t tcps_sndwinup;         /* window update-only packets sent */
           uint64_t tcps_sndctrl;          /* control (SYN|FIN|RST) packets sent */
   
           uint64_t tcps_rcvtotal;         /* total packets received */
           uint64_t tcps_rcvpack;          /* packets received in sequence */
           uint64_t tcps_rcvbyte;          /* bytes received in sequence */
           uint64_t tcps_rcvbadsum;        /* packets received with ccksum errs */
           uint64_t tcps_rcvbadoff;        /* packets received with bad offset */
           uint64_t tcps_rcvreassfull;     /* packets dropped for no reass space */
           uint64_t tcps_rcvshort;         /* packets received too short */
           uint64_t tcps_rcvduppack;       /* duplicate-only packets received */
           uint64_t tcps_rcvdupbyte;       /* duplicate-only bytes received */
           uint64_t tcps_rcvpartduppack;   /* packets with some duplicate data */
           uint64_t tcps_rcvpartdupbyte;   /* dup. bytes in part-dup. packets */
           uint64_t tcps_rcvoopack;        /* out-of-order packets received */
           uint64_t tcps_rcvoobyte;        /* out-of-order bytes received */
           uint64_t tcps_rcvpackafterwin;  /* packets with data after window */
           uint64_t tcps_rcvbyteafterwin;  /* bytes rcvd after window */
           uint64_t tcps_rcvafterclose;    /* packets rcvd after "close" */
           uint64_t tcps_rcvwinprobe;      /* rcvd window probe packets */
           uint64_t tcps_rcvdupack;        /* rcvd duplicate acks */
           uint64_t tcps_rcvacktoomuch;    /* rcvd acks for unsent data */
           uint64_t tcps_rcvackpack;       /* rcvd ack packets */
           uint64_t tcps_rcvackbyte;       /* bytes acked by rcvd acks */
           uint64_t tcps_rcvwinupd;        /* rcvd window update packets */
           uint64_t tcps_pawsdrop;         /* segments dropped due to PAWS */
           uint64_t tcps_predack;          /* times hdr predict ok for acks */
           uint64_t tcps_preddat;          /* times hdr predict ok for data pkts */
           uint64_t tcps_pcbcachemiss;
           uint64_t tcps_cachedrtt;        /* times cached RTT in route updated */
           uint64_t tcps_cachedrttvar;     /* times cached rttvar updated */
           uint64_t tcps_cachedssthresh;   /* times cached ssthresh updated */
           uint64_t tcps_usedrtt;          /* times RTT initialized from route */
           uint64_t tcps_usedrttvar;       /* times RTTVAR initialized from rt */
           uint64_t tcps_usedssthresh;     /* times ssthresh initialized from rt*/
           uint64_t tcps_persistdrop;      /* timeout in persist state */
           uint64_t tcps_badsyn;           /* bogus SYN, e.g. premature ACK */
           uint64_t tcps_mturesent;        /* resends due to MTU discovery */
           uint64_t tcps_listendrop;       /* listen queue overflows */
           uint64_t tcps_badrst;           /* ignored RSTs in the window */
   
           uint64_t tcps_sc_added;         /* entry added to syncache */
           uint64_t tcps_sc_retransmitted; /* syncache entry was retransmitted */
           uint64_t tcps_sc_dupsyn;        /* duplicate SYN packet */
           uint64_t tcps_sc_dropped;       /* could not reply to packet */
           uint64_t tcps_sc_completed;     /* successful extraction of entry */
           uint64_t tcps_sc_bucketoverflow;/* syncache per-bucket limit hit */
           uint64_t tcps_sc_cacheoverflow; /* syncache cache limit hit */
           uint64_t tcps_sc_reset;         /* RST removed entry from syncache */
           uint64_t tcps_sc_stale;         /* timed out or listen socket gone */
           uint64_t tcps_sc_aborted;       /* syncache entry aborted */
           uint64_t tcps_sc_badack;        /* removed due to bad ACK */
           uint64_t tcps_sc_unreach;       /* ICMP unreachable received */
           uint64_t tcps_sc_zonefail;      /* zalloc() failed */
           uint64_t tcps_sc_sendcookie;    /* SYN cookie sent */
           uint64_t tcps_sc_recvcookie;    /* SYN cookie received */
   
           uint64_t tcps_hc_added;         /* entry added to hostcache */
           uint64_t tcps_hc_bucketoverflow;/* hostcache per bucket limit hit */
   
           uint64_t tcps_finwait2_drops;    /* Drop FIN_WAIT_2 connection after time limit */
   
           /* SACK related stats */
           uint64_t tcps_sack_recovery_episode; /* SACK recovery episodes */
           uint64_t tcps_sack_rexmits;         /* SACK rexmit segments   */
           uint64_t tcps_sack_rexmit_bytes;    /* SACK rexmit bytes      */
           uint64_t tcps_sack_rcv_blocks;      /* SACK blocks (options) received */
           uint64_t tcps_sack_send_blocks;     /* SACK blocks (options) sent     */
           uint64_t tcps_sack_sboverflow;      /* times scoreboard overflowed */
           
           /* ECN related stats */
           uint64_t tcps_ecn_ce;           /* ECN Congestion Experienced */
           uint64_t tcps_ecn_ect0;         /* ECN Capable Transport */
           uint64_t tcps_ecn_ect1;         /* ECN Capable Transport */
           uint64_t tcps_ecn_shs;          /* ECN successful handshakes */
           uint64_t tcps_ecn_rcwnd;        /* # times ECN reduced the cwnd */
   
           /* TCP_SIGNATURE related stats */
           uint64_t tcps_sig_rcvgoodsig;   /* Total matching signature received */
           uint64_t tcps_sig_rcvbadsig;    /* Total bad signature received */
           uint64_t tcps_sig_err_buildsig; /* Failed to make signature */
           uint64_t tcps_sig_err_sigopt;   /* No signature expected by socket */
           uint64_t tcps_sig_err_nosigopt; /* No signature provided by segment */
   
           /* Path MTU Discovery Black Hole Detection related stats */
           uint64_t tcps_pmtud_blackhole_activated;         /* Black Hole Count */
           uint64_t tcps_pmtud_blackhole_activated_min_mss; /* BH at min MSS Count */
           uint64_t tcps_pmtud_blackhole_failed;            /* Black Hole Failure Count */
   
           uint64_t _pad[12];              /* 6 UTO, 6 TBD */
   };
   
   #define tcps_rcvmemdrop tcps_rcvreassfull       /* compat */
   
   #ifdef _KERNEL
   #define TI_UNLOCKED     1
   #define TI_RLOCKED      2
   #include <sys/counter.h>
   
   VNET_PCPUSTAT_DECLARE(struct tcpstat, tcpstat); /* tcp statistics */
   /*
    * In-kernel consumers can use these accessor macros directly to update
    * stats.
    */
   #define TCPSTAT_ADD(name, val)  \
       VNET_PCPUSTAT_ADD(struct tcpstat, tcpstat, name, (val))
   #define TCPSTAT_INC(name)       TCPSTAT_ADD(name, 1)
   
   /*
    * Kernel module consumers must use this accessor macro.
    */
   void    kmod_tcpstat_inc(int statnum);
   #define KMOD_TCPSTAT_INC(name)                                          \
       kmod_tcpstat_inc(offsetof(struct tcpstat, name) / sizeof(uint64_t))
   
   /*
    * Running TCP connection count by state.
    */
   VNET_DECLARE(counter_u64_t, tcps_states[TCP_NSTATES]);
   #define V_tcps_states   VNET(tcps_states)
   #define TCPSTATES_INC(state)    counter_u64_add(V_tcps_states[state], 1)
   #define TCPSTATES_DEC(state)    counter_u64_add(V_tcps_states[state], -1)
   
   /*
    * TCP specific helper hook point identifiers.
    */
   #define HHOOK_TCP_EST_IN                0
   #define HHOOK_TCP_EST_OUT               1
   #define HHOOK_TCP_LAST                  HHOOK_TCP_EST_OUT
   
   struct tcp_hhook_data {
           struct tcpcb    *tp;
           struct tcphdr   *th;
           struct tcpopt   *to;
           uint32_t        len;
           int             tso;
           tcp_seq         curack;
   };
   #ifdef TCP_HHOOK
   void hhook_run_tcp_est_out(struct tcpcb *tp,
           struct tcphdr *th, struct tcpopt *to,
           uint32_t len, int tso);
   #endif
   #endif
   
   /*
    * TCB structure exported to user-land via sysctl(3).
    *
    * Fields prefixed with "xt_" are unique to the export structure, and fields
    * with "t_" or other prefixes match corresponding fields of 'struct tcpcb'.
    *
    * Legend:
    * (s) - used by userland utilities in src
    * (p) - used by utilities in ports
    * (3) - is known to be used by third party software not in ports
    * (n) - no known usage
    *
    * Evil hack: declare only if in_pcb.h and sys/socketvar.h have been
    * included.  Not all of our clients do.
    */
   #if defined(_NETINET_IN_PCB_H_) && defined(_SYS_SOCKETVAR_H_)
   struct xtcpcb {
           ksize_t xt_len;         /* length of this structure */
           struct xinpcb   xt_inp;
           char            xt_stack[TCP_FUNCTION_NAME_LEN_MAX];    /* (s) */
           char            xt_logid[TCP_LOG_ID_LEN];       /* (s) */
           int64_t         spare64[8];
           int32_t         t_state;                /* (s,p) */
           uint32_t        t_flags;                /* (s,p) */
           int32_t         t_sndzerowin;           /* (s) */
           int32_t         t_sndrexmitpack;        /* (s) */
           int32_t         t_rcvoopack;            /* (s) */
           int32_t         t_rcvtime;              /* (s) */
           int32_t         tt_rexmt;               /* (s) */
           int32_t         tt_persist;             /* (s) */
           int32_t         tt_keep;                /* (s) */
           int32_t         tt_2msl;                /* (s) */
           int32_t         tt_delack;              /* (s) */
           int32_t         t_logstate;             /* (3) */
           int32_t         spare32[32];
   } __aligned(8);
   
   #ifdef _KERNEL
   void    tcp_inptoxtp(const struct inpcb *, struct xtcpcb *);
   #endif
   #endif
   
   /*
    * TCP function information (name-to-id mapping, aliases, and refcnt)
    * exported to user-land via sysctl(3).
    */
   struct tcp_function_info {
           uint32_t        tfi_refcnt;
           uint8_t         tfi_id;
           char            tfi_name[TCP_FUNCTION_NAME_LEN_MAX];
           char            tfi_alias[TCP_FUNCTION_NAME_LEN_MAX];
   };
   
   /*
    * Identifiers for TCP sysctl nodes
    */
   #define TCPCTL_DO_RFC1323       1       /* use RFC-1323 extensions */
   #define TCPCTL_MSSDFLT          3       /* MSS default */
   #define TCPCTL_STATS            4       /* statistics */
   #define TCPCTL_RTTDFLT          5       /* default RTT estimate */
   #define TCPCTL_KEEPIDLE         6       /* keepalive idle timer */
   #define TCPCTL_KEEPINTVL        7       /* interval to send keepalives */
   #define TCPCTL_SENDSPACE        8       /* send buffer space */
   #define TCPCTL_RECVSPACE        9       /* receive buffer space */
   #define TCPCTL_KEEPINIT         10      /* timeout for establishing syn */
   #define TCPCTL_PCBLIST          11      /* list of all outstanding PCBs */
   #define TCPCTL_DELACKTIME       12      /* time before sending delayed ACK */
   #define TCPCTL_V6MSSDFLT        13      /* MSS default for IPv6 */
   #define TCPCTL_SACK             14      /* Selective Acknowledgement,rfc 2018 */
   #define TCPCTL_DROP             15      /* drop tcp connection */
   #define TCPCTL_STATES           16      /* connection counts by TCP state */
   
   #ifdef _KERNEL
   #ifdef SYSCTL_DECL
   SYSCTL_DECL(_net_inet_tcp);
   SYSCTL_DECL(_net_inet_tcp_sack);
   MALLOC_DECLARE(M_TCPLOG);
   #endif
   
   extern  int tcp_log_in_vain;
   
   /*
    * Global TCP tunables shared between different stacks.
    * Please keep the list sorted.
    */
   VNET_DECLARE(int, drop_synfin);
   VNET_DECLARE(int, path_mtu_discovery);
   VNET_DECLARE(int, tcp_abc_l_var);
   VNET_DECLARE(int, tcp_autorcvbuf_inc);
   VNET_DECLARE(int, tcp_autorcvbuf_max);
   VNET_DECLARE(int, tcp_autosndbuf_inc);
   VNET_DECLARE(int, tcp_autosndbuf_max);
   VNET_DECLARE(int, tcp_delack_enabled);
   VNET_DECLARE(int, tcp_do_autorcvbuf);
   VNET_DECLARE(int, tcp_do_autosndbuf);
   VNET_DECLARE(int, tcp_do_ecn);
   VNET_DECLARE(int, tcp_do_rfc1323);
   VNET_DECLARE(int, tcp_do_rfc3042);
   VNET_DECLARE(int, tcp_do_rfc3390);
   VNET_DECLARE(int, tcp_do_rfc3465);
   VNET_DECLARE(int, tcp_do_rfc6675_pipe);
   VNET_DECLARE(int, tcp_do_sack);
   VNET_DECLARE(int, tcp_do_tso);
   VNET_DECLARE(int, tcp_ecn_maxretries);
   VNET_DECLARE(int, tcp_initcwnd_segments);
   VNET_DECLARE(int, tcp_insecure_rst);
   VNET_DECLARE(int, tcp_insecure_syn);
   VNET_DECLARE(int, tcp_minmss);
   VNET_DECLARE(int, tcp_mssdflt);
   VNET_DECLARE(int, tcp_recvspace);
   VNET_DECLARE(int, tcp_sack_globalholes);
   VNET_DECLARE(int, tcp_sack_globalmaxholes);
   VNET_DECLARE(int, tcp_sack_maxholes);
   VNET_DECLARE(int, tcp_sc_rst_sock_fail);
   VNET_DECLARE(int, tcp_sendspace);
   VNET_DECLARE(struct inpcbhead, tcb);
   VNET_DECLARE(struct inpcbinfo, tcbinfo);
   
   #define V_drop_synfin                   VNET(drop_synfin)
   #define V_path_mtu_discovery            VNET(path_mtu_discovery)
   #define V_tcb                           VNET(tcb)
   #define V_tcbinfo                       VNET(tcbinfo)
   #define V_tcp_abc_l_var                 VNET(tcp_abc_l_var)
   #define V_tcp_autorcvbuf_inc            VNET(tcp_autorcvbuf_inc)
   #define V_tcp_autorcvbuf_max            VNET(tcp_autorcvbuf_max)
   #define V_tcp_autosndbuf_inc            VNET(tcp_autosndbuf_inc)
   #define V_tcp_autosndbuf_max            VNET(tcp_autosndbuf_max)
   #define V_tcp_delack_enabled            VNET(tcp_delack_enabled)
   #define V_tcp_do_autorcvbuf             VNET(tcp_do_autorcvbuf)
   #define V_tcp_do_autosndbuf             VNET(tcp_do_autosndbuf)
   #define V_tcp_do_ecn                    VNET(tcp_do_ecn)
   #define V_tcp_do_rfc1323                VNET(tcp_do_rfc1323)
   #define V_tcp_do_rfc3042                VNET(tcp_do_rfc3042)
   #define V_tcp_do_rfc3390                VNET(tcp_do_rfc3390)
   #define V_tcp_do_rfc3465                VNET(tcp_do_rfc3465)
   #define V_tcp_do_rfc6675_pipe           VNET(tcp_do_rfc6675_pipe)
   #define V_tcp_do_sack                   VNET(tcp_do_sack)
   #define V_tcp_do_tso                    VNET(tcp_do_tso)
   #define V_tcp_ecn_maxretries            VNET(tcp_ecn_maxretries)
   #define V_tcp_initcwnd_segments         VNET(tcp_initcwnd_segments)
   #define V_tcp_insecure_rst              VNET(tcp_insecure_rst)
   #define V_tcp_insecure_syn              VNET(tcp_insecure_syn)
   #define V_tcp_minmss                    VNET(tcp_minmss)
   #define V_tcp_mssdflt                   VNET(tcp_mssdflt)
   #define V_tcp_recvspace                 VNET(tcp_recvspace)
   #define V_tcp_sack_globalholes          VNET(tcp_sack_globalholes)
   #define V_tcp_sack_globalmaxholes       VNET(tcp_sack_globalmaxholes)
   #define V_tcp_sack_maxholes             VNET(tcp_sack_maxholes)
   #define V_tcp_sc_rst_sock_fail          VNET(tcp_sc_rst_sock_fail)
   #define V_tcp_sendspace                 VNET(tcp_sendspace)
   #define V_tcp_udp_tunneling_overhead    VNET(tcp_udp_tunneling_overhead)
   #define V_tcp_udp_tunneling_port        VNET(tcp_udp_tunneling_port)
   
   
   #ifdef TCP_HHOOK
   VNET_DECLARE(struct hhook_head *, tcp_hhh[HHOOK_TCP_LAST + 1]);
   #define V_tcp_hhh               VNET(tcp_hhh)
   #endif
   
   int      tcp_addoptions(struct tcpopt *, u_char *);
   int      tcp_ccalgounload(struct cc_algo *unload_algo);
   struct tcpcb *
            tcp_close(struct tcpcb *);
   void     tcp_discardcb(struct tcpcb *);
   void     tcp_twstart(struct tcpcb *);
   void     tcp_twclose(struct tcptw *, int);
   void     tcp_ctlinput(int, struct sockaddr *, void *);
   int      tcp_ctloutput(struct socket *, struct sockopt *);
   struct tcpcb *
            tcp_drop(struct tcpcb *, int);
   void     tcp_drain(void);
   void     tcp_init(void);
   void     tcp_fini(void *);
   char    *tcp_log_addrs(struct in_conninfo *, struct tcphdr *, void *,
               const void *);
   char    *tcp_log_vain(struct in_conninfo *, struct tcphdr *, void *,
               const void *);
   int      tcp_reass(struct tcpcb *, struct tcphdr *, tcp_seq *, int *, struct mbuf *);
   void     tcp_reass_global_init(void);
   void     tcp_reass_flush(struct tcpcb *);
   void     tcp_dooptions(struct tcpopt *, u_char *, int, int);
   void    tcp_dropwithreset(struct mbuf *, struct tcphdr *,
                        struct tcpcb *, int, int);
   void    tcp_pulloutofband(struct socket *,
                        struct tcphdr *, struct mbuf *, int);
   void    tcp_xmit_timer(struct tcpcb *, int);
   void    tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
   void    cc_ack_received(struct tcpcb *tp, struct tcphdr *th,
                               uint16_t nsegs, uint16_t type);
   void    cc_conn_init(struct tcpcb *tp);
   void    cc_post_recovery(struct tcpcb *tp, struct tcphdr *th);
   void    cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type);
   #ifdef TCP_HHOOK
   void    hhook_run_tcp_est_in(struct tcpcb *tp,
                               struct tcphdr *th, struct tcpopt *to);
   #endif
   
   int      tcp_input(struct mbuf **, int *, int);
   int      tcp_autorcvbuf(struct mbuf *, struct tcphdr *, struct socket *,
               struct tcpcb *, int);
   void     tcp_do_segment(struct mbuf *, struct tcphdr *,
                           struct socket *, struct tcpcb *, int, int, uint8_t);
   
   int register_tcp_functions(struct tcp_function_block *blk, int wait);
   int register_tcp_functions_as_names(struct tcp_function_block *blk,
       int wait, const char *names[], int *num_names);
   int register_tcp_functions_as_name(struct tcp_function_block *blk,
       const char *name, int wait);
   int deregister_tcp_functions(struct tcp_function_block *blk, bool quiesce,
       bool force);
   struct tcp_function_block *find_and_ref_tcp_functions(struct tcp_function_set *fs);
   void tcp_switch_back_to_default(struct tcpcb *tp);
   struct tcp_function_block *
   find_and_ref_tcp_fb(struct tcp_function_block *fs);
   int tcp_default_ctloutput(struct socket *so, struct sockopt *sopt, struct inpcb *inp, struct tcpcb *tp);
   
   uint32_t tcp_maxmtu(struct in_conninfo *, struct tcp_ifcap *);
   uint32_t tcp_maxmtu6(struct in_conninfo *, struct tcp_ifcap *);
   u_int    tcp_maxseg(const struct tcpcb *);
   void     tcp_mss_update(struct tcpcb *, int, int, struct hc_metrics_lite *,
               struct tcp_ifcap *);
   void     tcp_mss(struct tcpcb *, int);
   int      tcp_mssopt(struct in_conninfo *);
   struct inpcb *
            tcp_drop_syn_sent(struct inpcb *, int);
   struct tcpcb *
            tcp_newtcpcb(struct inpcb *);
   int      tcp_output(struct tcpcb *);
   void     tcp_state_change(struct tcpcb *, int);
   void     tcp_respond(struct tcpcb *, void *,
               struct tcphdr *, struct mbuf *, tcp_seq, tcp_seq, int);
   void     tcp_tw_init(void);
   #ifdef VIMAGE
   void     tcp_tw_destroy(void);
   #endif
   void     tcp_tw_zone_change(void);
   int      tcp_twcheck(struct inpcb *, struct tcpopt *, struct tcphdr *,
               struct mbuf *, int);
   void     tcp_setpersist(struct tcpcb *);
   void     tcp_slowtimo(void);
   struct tcptemp *
            tcpip_maketemplate(struct inpcb *);
   void     tcpip_fillheaders(struct inpcb *, void *, void *);
   void     tcp_timer_activate(struct tcpcb *, uint32_t, u_int);
   int      tcp_timer_suspend(struct tcpcb *, uint32_t);
   void     tcp_timers_unsuspend(struct tcpcb *, uint32_t);
   int      tcp_timer_active(struct tcpcb *, uint32_t);
   void     tcp_timer_stop(struct tcpcb *, uint32_t);
   void     tcp_trace(short, short, struct tcpcb *, void *, struct tcphdr *, int);
   int      inp_to_cpuid(struct inpcb *inp);
   /*
    * All tcp_hc_* functions are IPv4 and IPv6 (via in_conninfo)
    */
   void     tcp_hc_init(void);
   #ifdef VIMAGE
   void     tcp_hc_destroy(void);
   #endif
   void     tcp_hc_get(struct in_conninfo *, struct hc_metrics_lite *);
   uint32_t tcp_hc_getmtu(struct in_conninfo *);
   void     tcp_hc_updatemtu(struct in_conninfo *, uint32_t);
   void     tcp_hc_update(struct in_conninfo *, struct hc_metrics_lite *);
   
   extern  struct pr_usrreqs tcp_usrreqs;
   
   uint32_t tcp_new_ts_offset(struct in_conninfo *);
   tcp_seq  tcp_new_isn(struct in_conninfo *);
   
   int      tcp_sack_doack(struct tcpcb *, struct tcpopt *, tcp_seq);
   void     tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_laststart, tcp_seq rcv_lastend);
   void     tcp_clean_sackreport(struct tcpcb *tp);
   void     tcp_sack_adjust(struct tcpcb *tp);
   struct sackhole *tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt);
   void     tcp_sack_partialack(struct tcpcb *, struct tcphdr *);
   void     tcp_free_sackholes(struct tcpcb *tp);
   int      tcp_newreno(struct tcpcb *, struct tcphdr *);
   int      tcp_compute_pipe(struct tcpcb *);
   void     tcp_sndbuf_autoscale(struct tcpcb *, struct socket *, uint32_t);
   struct mbuf *
            tcp_m_copym(struct mbuf *m, int32_t off0, int32_t *plen,
              int32_t seglimit, int32_t segsize, struct sockbuf *sb);
   
   
   static inline void
   tcp_fields_to_host(struct tcphdr *th)
   {
   
           th->th_seq = ntohl(th->th_seq);
           th->th_ack = ntohl(th->th_ack);
           th->th_win = ntohs(th->th_win);
           th->th_urp = ntohs(th->th_urp);
   }
   
   static inline void
   tcp_fields_to_net(struct tcphdr *th)
   {
   
           th->th_seq = htonl(th->th_seq);
           th->th_ack = htonl(th->th_ack);
           th->th_win = htons(th->th_win);
           th->th_urp = htons(th->th_urp);
   }
   #endif /* _KERNEL */
   
   #endif /* _NETINET_TCP_VAR_H_ */

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