/*      $NetBSD: tcp_subr.c,v 1.300 2026/05/20 21:12:36 kbowling Exp $  */

/*
 * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
 * 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 project 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 PROJECT 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 PROJECT 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.
 */

/*
 * Copyright (c) 1997, 1998, 2000, 2001, 2008 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Jason R. Thorpe and Kevin M. Lahey of the Numerical Aerospace Simulation
 * Facility, NASA Ames Research Center.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
 */

/*
 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 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_subr.c  8.2 (Berkeley) 5/24/95
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: tcp_subr.c,v 1.300 2026/05/20 21:12:36 kbowling Exp $");

#ifdef _KERNEL_OPT
#include "opt_inet.h"
#include "opt_ipsec.h"
#include "opt_inet_csum.h"
#include "opt_mbuftrace.h"
#endif

#include <sys/param.h>
#include <sys/atomic.h>
#include <sys/proc.h>
#include <sys/systm.h>
#include <sys/mbuf.h>
#include <sys/once.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/protosw.h>
#include <sys/errno.h>
#include <sys/kernel.h>
#include <sys/pool.h>
#include <sys/md5.h>
#include <sys/cprng.h>

#include <net/route.h>
#include <net/if.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/in_pcb.h>
#include <netinet/ip_var.h>
#include <netinet/ip_icmp.h>

#ifdef INET6
#include <netinet/ip6.h>
#include <netinet6/in6_pcb.h>
#include <netinet6/ip6_var.h>
#include <netinet6/in6_var.h>
#include <netinet6/ip6protosw.h>
#include <netinet/icmp6.h>
#include <netinet6/nd6.h>
#endif

#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet/tcp_vtw.h>
#include <netinet/tcp_private.h>
#include <netinet/tcp_congctl.h>
#include <netinet/tcp_syncache.h>

#ifdef IPSEC
#include <netipsec/ipsec.h>
#ifdef INET6
#include <netipsec/ipsec6.h>
#endif
#include <netipsec/key.h>
#endif


struct  inpcbtable tcbtable;    /* head of queue of active tcpcb's */
u_int32_t tcp_now;              /* slow ticks, for RFC 1323 timestamps */

percpu_t *tcpstat_percpu;

/* patchable/settable parameters for tcp */
int     tcp_mssdflt = TCP_MSS;
int     tcp_minmss = TCP_MINMSS;
int     tcp_rttdflt = TCPTV_SRTTDFLT / PR_SLOWHZ;
int     tcp_do_rfc1323 = 1;     /* window scaling / timestamps (obsolete) */
int     tcp_do_rfc1948 = 0;     /* ISS by cryptographic hash */
int     tcp_do_sack = 1;        /* selective acknowledgement */
int     tcp_do_win_scale = 1;   /* RFC1323 window scaling */
int     tcp_do_timestamps = 1;  /* RFC1323 timestamps */
int     tcp_ack_on_push = 0;    /* set to enable immediate ACK-on-PUSH */
int     tcp_do_ecn = 0;         /* Explicit Congestion Notification */
#ifndef TCP_INIT_WIN
#define TCP_INIT_WIN    4       /* initial slow start window */
#endif
#ifndef TCP_INIT_WIN_LOCAL
#define TCP_INIT_WIN_LOCAL 4    /* initial slow start window for local nets */
#endif
/*
 * Up to 5 we scale linearly, to reach 3 * 1460; then (iw) * 1460.
 * This is to simulate current behavior for iw == 4
 */
int tcp_init_win_max[] = {
         1 * 1460,
         1 * 1460,
         2 * 1460,
         2 * 1460,
         3 * 1460,
         5 * 1460,
         6 * 1460,
         7 * 1460,
         8 * 1460,
         9 * 1460,
        10 * 1460
};
int     tcp_init_win = TCP_INIT_WIN;
int     tcp_init_win_local = TCP_INIT_WIN_LOCAL;
int     tcp_mss_ifmtu = 0;
int     tcp_rst_ppslim = 100;   /* 100pps */
int     tcp_ackdrop_ppslim = 100;       /* 100pps */
int     tcp_do_loopback_cksum = 0;
int     tcp_do_abc = 1;         /* RFC3465 Appropriate byte counting. */
int     tcp_abc_aggressive = 1; /* 1: L=2*SMSS  0: L=1*SMSS */
int     tcp_sack_tp_maxholes = 32;
int     tcp_sack_globalmaxholes = 1024;
int     tcp_sack_globalholes = 0;
int     tcp_ecn_maxretries = 1;
int     tcp_msl_enable = 1;             /* enable TIME_WAIT truncation  */
int     tcp_msl_loop   = PR_SLOWHZ;     /* MSL for loopback             */
int     tcp_msl_local  = 5 * PR_SLOWHZ; /* MSL for 'local'              */
int     tcp_msl_remote = TCPTV_MSL;     /* MSL otherwise                */
int     tcp_msl_remote_threshold = 3*PR_SLOWHZ;         /* RTT threshold */
int     tcp_rttlocal = 0;               /* Use RTT to decide who's 'local' */

int     tcp4_vtw_enable = 0;            /* 1 to enable */
int     tcp6_vtw_enable = 0;            /* 1 to enable */
int     tcp_vtw_was_enabled = 0;
int     tcp_vtw_entries = 1 << 4;       /* 16 vestigial TIME_WAIT entries */

/* tcb hash */
#ifndef TCBHASHSIZE
#define TCBHASHSIZE     128
#endif
int     tcbhashsize = TCBHASHSIZE;

int     tcp_freeq(struct tcpcb *);
static int      tcp_iss_secret_init(void);

static void     tcp_mtudisc_callback(struct in_addr);

#ifdef INET6
static void     tcp6_mtudisc(struct inpcb *, int);
#endif

static struct pool tcpcb_pool;

static int tcp_drainwanted;

#ifdef TCP_CSUM_COUNTERS
#include <sys/device.h>

struct evcnt tcp_hwcsum_bad = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    NULL, "tcp", "hwcsum bad");
struct evcnt tcp_hwcsum_ok = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    NULL, "tcp", "hwcsum ok");
struct evcnt tcp_hwcsum_data = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    NULL, "tcp", "hwcsum data");
struct evcnt tcp_swcsum = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    NULL, "tcp", "swcsum");

EVCNT_ATTACH_STATIC(tcp_hwcsum_bad);
EVCNT_ATTACH_STATIC(tcp_hwcsum_ok);
EVCNT_ATTACH_STATIC(tcp_hwcsum_data);
EVCNT_ATTACH_STATIC(tcp_swcsum);

#if defined(INET6)
struct evcnt tcp6_hwcsum_bad = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    NULL, "tcp6", "hwcsum bad");
struct evcnt tcp6_hwcsum_ok = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    NULL, "tcp6", "hwcsum ok");
struct evcnt tcp6_hwcsum_data = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    NULL, "tcp6", "hwcsum data");
struct evcnt tcp6_swcsum = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    NULL, "tcp6", "swcsum");

EVCNT_ATTACH_STATIC(tcp6_hwcsum_bad);
EVCNT_ATTACH_STATIC(tcp6_hwcsum_ok);
EVCNT_ATTACH_STATIC(tcp6_hwcsum_data);
EVCNT_ATTACH_STATIC(tcp6_swcsum);
#endif /* defined(INET6) */
#endif /* TCP_CSUM_COUNTERS */


#ifdef TCP_OUTPUT_COUNTERS
#include <sys/device.h>

struct evcnt tcp_output_bigheader = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    NULL, "tcp", "output big header");
struct evcnt tcp_output_predict_hit = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    NULL, "tcp", "output predict hit");
struct evcnt tcp_output_predict_miss = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    NULL, "tcp", "output predict miss");
struct evcnt tcp_output_copysmall = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    NULL, "tcp", "output copy small");
struct evcnt tcp_output_copybig = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    NULL, "tcp", "output copy big");
struct evcnt tcp_output_refbig = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    NULL, "tcp", "output reference big");

EVCNT_ATTACH_STATIC(tcp_output_bigheader);
EVCNT_ATTACH_STATIC(tcp_output_predict_hit);
EVCNT_ATTACH_STATIC(tcp_output_predict_miss);
EVCNT_ATTACH_STATIC(tcp_output_copysmall);
EVCNT_ATTACH_STATIC(tcp_output_copybig);
EVCNT_ATTACH_STATIC(tcp_output_refbig);

#endif /* TCP_OUTPUT_COUNTERS */

#ifdef TCP_REASS_COUNTERS
#include <sys/device.h>

struct evcnt tcp_reass_ = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    NULL, "tcp_reass", "calls");
struct evcnt tcp_reass_empty = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    &tcp_reass_, "tcp_reass", "insert into empty queue");
struct evcnt tcp_reass_iteration[8] = {
    EVCNT_INITIALIZER(EVCNT_TYPE_MISC, &tcp_reass_, "tcp_reass", ">7 iterations"),
    EVCNT_INITIALIZER(EVCNT_TYPE_MISC, &tcp_reass_, "tcp_reass", "1 iteration"),
    EVCNT_INITIALIZER(EVCNT_TYPE_MISC, &tcp_reass_, "tcp_reass", "2 iterations"),
    EVCNT_INITIALIZER(EVCNT_TYPE_MISC, &tcp_reass_, "tcp_reass", "3 iterations"),
    EVCNT_INITIALIZER(EVCNT_TYPE_MISC, &tcp_reass_, "tcp_reass", "4 iterations"),
    EVCNT_INITIALIZER(EVCNT_TYPE_MISC, &tcp_reass_, "tcp_reass", "5 iterations"),
    EVCNT_INITIALIZER(EVCNT_TYPE_MISC, &tcp_reass_, "tcp_reass", "6 iterations"),
    EVCNT_INITIALIZER(EVCNT_TYPE_MISC, &tcp_reass_, "tcp_reass", "7 iterations"),
};
struct evcnt tcp_reass_prependfirst = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    &tcp_reass_, "tcp_reass", "prepend to first");
struct evcnt tcp_reass_prepend = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    &tcp_reass_, "tcp_reass", "prepend");
struct evcnt tcp_reass_insert = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    &tcp_reass_, "tcp_reass", "insert");
struct evcnt tcp_reass_inserttail = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    &tcp_reass_, "tcp_reass", "insert at tail");
struct evcnt tcp_reass_append = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    &tcp_reass_, "tcp_reass", "append");
struct evcnt tcp_reass_appendtail = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    &tcp_reass_, "tcp_reass", "append to tail fragment");
struct evcnt tcp_reass_overlaptail = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    &tcp_reass_, "tcp_reass", "overlap at end");
struct evcnt tcp_reass_overlapfront = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    &tcp_reass_, "tcp_reass", "overlap at start");
struct evcnt tcp_reass_segdup = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    &tcp_reass_, "tcp_reass", "duplicate segment");
struct evcnt tcp_reass_fragdup = EVCNT_INITIALIZER(EVCNT_TYPE_MISC,
    &tcp_reass_, "tcp_reass", "duplicate fragment");

EVCNT_ATTACH_STATIC(tcp_reass_);
EVCNT_ATTACH_STATIC(tcp_reass_empty);
EVCNT_ATTACH_STATIC2(tcp_reass_iteration, 0);
EVCNT_ATTACH_STATIC2(tcp_reass_iteration, 1);
EVCNT_ATTACH_STATIC2(tcp_reass_iteration, 2);
EVCNT_ATTACH_STATIC2(tcp_reass_iteration, 3);
EVCNT_ATTACH_STATIC2(tcp_reass_iteration, 4);
EVCNT_ATTACH_STATIC2(tcp_reass_iteration, 5);
EVCNT_ATTACH_STATIC2(tcp_reass_iteration, 6);
EVCNT_ATTACH_STATIC2(tcp_reass_iteration, 7);
EVCNT_ATTACH_STATIC(tcp_reass_prependfirst);
EVCNT_ATTACH_STATIC(tcp_reass_prepend);
EVCNT_ATTACH_STATIC(tcp_reass_insert);
EVCNT_ATTACH_STATIC(tcp_reass_inserttail);
EVCNT_ATTACH_STATIC(tcp_reass_append);
EVCNT_ATTACH_STATIC(tcp_reass_appendtail);
EVCNT_ATTACH_STATIC(tcp_reass_overlaptail);
EVCNT_ATTACH_STATIC(tcp_reass_overlapfront);
EVCNT_ATTACH_STATIC(tcp_reass_segdup);
EVCNT_ATTACH_STATIC(tcp_reass_fragdup);

#endif /* TCP_REASS_COUNTERS */

#ifdef MBUFTRACE
struct mowner tcp_mowner = MOWNER_INIT("tcp", "");
struct mowner tcp_rx_mowner = MOWNER_INIT("tcp", "rx");
struct mowner tcp_tx_mowner = MOWNER_INIT("tcp", "tx");
struct mowner tcp_sock_mowner = MOWNER_INIT("tcp", "sock");
struct mowner tcp_sock_rx_mowner = MOWNER_INIT("tcp", "sock rx");
struct mowner tcp_sock_tx_mowner = MOWNER_INIT("tcp", "sock tx");
#endif

static int
do_tcpinit(void)
{

        inpcb_init(&tcbtable, tcbhashsize, tcbhashsize);
        pool_init(&tcpcb_pool, sizeof(struct tcpcb), 0, 0, 0, "tcpcbpl",
            NULL, IPL_SOFTNET);

        tcp_usrreq_init();

        /* Initialize timer state. */
        tcp_timer_init();

        /* Initialize the compressed state engine. */
        syn_cache_init();

        /* Initialize the congestion control algorithms. */
        tcp_congctl_init();

        /* Initialize the TCPCB template. */
        tcp_tcpcb_template();

        /* Initialize reassembly queue */
        tcpipqent_init();

        /* SACK */
        tcp_sack_init();

        MOWNER_ATTACH(&tcp_tx_mowner);
        MOWNER_ATTACH(&tcp_rx_mowner);
        MOWNER_ATTACH(&tcp_reass_mowner);
        MOWNER_ATTACH(&tcp_sock_mowner);
        MOWNER_ATTACH(&tcp_sock_tx_mowner);
        MOWNER_ATTACH(&tcp_sock_rx_mowner);
        MOWNER_ATTACH(&tcp_mowner);

        tcpstat_percpu = percpu_alloc(sizeof(uint64_t) * TCP_NSTATS);

        vtw_earlyinit();

        tcp_slowtimo_init();

        return 0;
}

void
tcp_init_common(unsigned basehlen)
{
        static ONCE_DECL(dotcpinit);
        unsigned hlen = basehlen + sizeof(struct tcphdr);
        unsigned oldhlen;

        if (max_linkhdr + hlen > MHLEN)
                panic("tcp_init");
        while ((oldhlen = max_protohdr) < hlen)
                atomic_cas_uint(&max_protohdr, oldhlen, hlen);

        RUN_ONCE(&dotcpinit, do_tcpinit);
}

/*
 * Tcp initialization
 */
void
tcp_init(void)
{

        icmp_mtudisc_callback_register(tcp_mtudisc_callback);

        tcp_init_common(sizeof(struct ip));
}

/*
 * Create template to be used to send tcp packets on a connection.
 * Call after host entry created, allocates an mbuf and fills
 * in a skeletal tcp/ip header, minimizing the amount of work
 * necessary when the connection is used.
 */
struct mbuf *
tcp_template(struct tcpcb *tp)
{
        struct inpcb *inp = tp->t_inpcb;
        struct tcphdr *n;
        struct mbuf *m;
        int hlen;

        switch (tp->t_family) {
        case AF_INET:
                hlen = sizeof(struct ip);
                if (inp->inp_af == AF_INET)
                        break;
#ifdef INET6
                if (inp->inp_af == AF_INET6) {
                        /* mapped addr case */
                        if (IN6_IS_ADDR_V4MAPPED(&in6p_laddr(inp))
                         && IN6_IS_ADDR_V4MAPPED(&in6p_faddr(inp)))
                                break;
                }
#endif
                return NULL;    /*EINVAL*/
#ifdef INET6
        case AF_INET6:
                hlen = sizeof(struct ip6_hdr);
                if (inp != NULL) {
                        /* more sainty check? */
                        break;
                }
                return NULL;    /*EINVAL*/
#endif
        default:
                return NULL;    /*EAFNOSUPPORT*/
        }

        KASSERT(hlen + sizeof(struct tcphdr) <= MCLBYTES);

        m = tp->t_template;
        if (m && m->m_len == hlen + sizeof(struct tcphdr)) {
                ;
        } else {
                m_freem(m);
                m = tp->t_template = NULL;
                MGETHDR(m, M_DONTWAIT, MT_HEADER);
                if (m && hlen + sizeof(struct tcphdr) > MHLEN) {
                        MCLGET(m, M_DONTWAIT);
                        if ((m->m_flags & M_EXT) == 0) {
                                m_free(m);
                                m = NULL;
                        }
                }
                if (m == NULL)
                        return NULL;
                MCLAIM(m, &tcp_mowner);
                m->m_pkthdr.len = m->m_len = hlen + sizeof(struct tcphdr);
        }

        memset(mtod(m, void *), 0, m->m_len);

        n = (struct tcphdr *)(mtod(m, char *) + hlen);

        switch (tp->t_family) {
        case AF_INET:
            {
                struct ipovly *ipov;
                mtod(m, struct ip *)->ip_v = 4;
                mtod(m, struct ip *)->ip_hl = hlen >> 2;
                ipov = mtod(m, struct ipovly *);
                ipov->ih_pr = IPPROTO_TCP;
                ipov->ih_len = htons(sizeof(struct tcphdr));
                if (inp->inp_af == AF_INET) {
                        ipov->ih_src = in4p_laddr(inp);
                        ipov->ih_dst = in4p_faddr(inp);
                }
#ifdef INET6
                else if (inp->inp_af == AF_INET6) {
                        /* mapped addr case */
                        bcopy(&in6p_laddr(inp).s6_addr32[3], &ipov->ih_src,
                                sizeof(ipov->ih_src));
                        bcopy(&in6p_faddr(inp).s6_addr32[3], &ipov->ih_dst,
                                sizeof(ipov->ih_dst));
                }
#endif

                /*
                 * Compute the pseudo-header portion of the checksum
                 * now.  We incrementally add in the TCP option and
                 * payload lengths later, and then compute the TCP
                 * checksum right before the packet is sent off onto
                 * the wire.
                 */
                n->th_sum = in_cksum_phdr(ipov->ih_src.s_addr,
                    ipov->ih_dst.s_addr,
                    htons(sizeof(struct tcphdr) + IPPROTO_TCP));
                break;
            }
#ifdef INET6
        case AF_INET6:
            {
                struct ip6_hdr *ip6;
                mtod(m, struct ip *)->ip_v = 6;
                ip6 = mtod(m, struct ip6_hdr *);
                ip6->ip6_nxt = IPPROTO_TCP;
                ip6->ip6_plen = htons(sizeof(struct tcphdr));
                ip6->ip6_src = in6p_laddr(inp);
                ip6->ip6_dst = in6p_faddr(inp);
                ip6->ip6_flow = in6p_flowinfo(inp) & IPV6_FLOWINFO_MASK;
                if (ip6_auto_flowlabel) {
                        ip6->ip6_flow &= ~IPV6_FLOWLABEL_MASK;
                        ip6->ip6_flow |=
                            (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK);
                }
                ip6->ip6_vfc &= ~IPV6_VERSION_MASK;
                ip6->ip6_vfc |= IPV6_VERSION;

                /*
                 * Compute the pseudo-header portion of the checksum
                 * now.  We incrementally add in the TCP option and
                 * payload lengths later, and then compute the TCP
                 * checksum right before the packet is sent off onto
                 * the wire.
                 */
                n->th_sum = in6_cksum_phdr(&in6p_laddr(inp),
                    &in6p_faddr(inp), htonl(sizeof(struct tcphdr)),
                    htonl(IPPROTO_TCP));
                break;
            }
#endif
        }

        n->th_sport = inp->inp_lport;
        n->th_dport = inp->inp_fport;

        n->th_seq = 0;
        n->th_ack = 0;
        n->th_x2 = 0;
        n->th_off = 5;
        n->th_flags = 0;
        n->th_win = 0;
        n->th_urp = 0;
        return m;
}

/*
 * Send a single message to the TCP at address specified by
 * the given TCP/IP header.  If m == 0, then we make a copy
 * of the tcpiphdr at ti and send directly to the addressed host.
 * This is used to force keep alive messages out using the TCP
 * template for a connection tp->t_template.  If flags are given
 * then we send a message back to the TCP which originated the
 * segment ti, and discard the mbuf containing it and any other
 * attached mbufs.
 *
 * In any case the ack and sequence number of the transmitted
 * segment are as specified by the parameters.
 */
int
tcp_respond(struct tcpcb *tp, struct mbuf *mtemplate, struct mbuf *m,
    struct tcphdr *th0, tcp_seq ack, tcp_seq seq, int flags)
{
        struct route *ro;
        int error, tlen, win = 0;
        int hlen;
        struct ip *ip;
#ifdef INET6
        struct ip6_hdr *ip6;
#endif
        int family;     /* family on packet, not inpcb! */
        struct tcphdr *th;

        if (tp != NULL && (flags & TH_RST) == 0) {
                KASSERT(tp->t_inpcb != NULL);

                win = sbspace(&tp->t_inpcb->inp_socket->so_rcv);
        }

        th = NULL;      /* Quell uninitialized warning */
        ip = NULL;
#ifdef INET6
        ip6 = NULL;
#endif
        if (m == NULL) {
                if (!mtemplate)
                        return EINVAL;

                /* get family information from template */
                switch (mtod(mtemplate, struct ip *)->ip_v) {
                case 4:
                        family = AF_INET;
                        hlen = sizeof(struct ip);
                        break;
#ifdef INET6
                case 6:
                        family = AF_INET6;
                        hlen = sizeof(struct ip6_hdr);
                        break;
#endif
                default:
                        return EAFNOSUPPORT;
                }

                MGETHDR(m, M_DONTWAIT, MT_HEADER);
                if (m) {
                        MCLAIM(m, &tcp_tx_mowner);
                        MCLGET(m, M_DONTWAIT);
                        if ((m->m_flags & M_EXT) == 0) {
                                m_free(m);
                                m = NULL;
                        }
                }
                if (m == NULL)
                        return ENOBUFS;

                tlen = 0;

                m->m_data += max_linkhdr;
                bcopy(mtod(mtemplate, void *), mtod(m, void *),
                        mtemplate->m_len);
                switch (family) {
                case AF_INET:
                        ip = mtod(m, struct ip *);
                        th = (struct tcphdr *)(ip + 1);
                        break;
#ifdef INET6
                case AF_INET6:
                        ip6 = mtod(m, struct ip6_hdr *);
                        th = (struct tcphdr *)(ip6 + 1);
                        break;
#endif
                }
                flags = TH_ACK;
        } else {
                if ((m->m_flags & M_PKTHDR) == 0) {
                        m_freem(m);
                        return EINVAL;
                }
                KASSERT(th0 != NULL);

                /* get family information from m */
                switch (mtod(m, struct ip *)->ip_v) {
                case 4:
                        family = AF_INET;
                        hlen = sizeof(struct ip);
                        ip = mtod(m, struct ip *);
                        break;
#ifdef INET6
                case 6:
                        family = AF_INET6;
                        hlen = sizeof(struct ip6_hdr);
                        ip6 = mtod(m, struct ip6_hdr *);
                        break;
#endif
                default:
                        m_freem(m);
                        return EAFNOSUPPORT;
                }
                /* clear h/w csum flags inherited from rx packet */
                m->m_pkthdr.csum_flags = 0;

                if ((flags & TH_SYN) == 0 || sizeof(*th0) > (th0->th_off << 2))
                        tlen = sizeof(*th0);
                else
                        tlen = th0->th_off << 2;

                if (m->m_len > hlen + tlen && (m->m_flags & M_EXT) == 0 &&
                    mtod(m, char *) + hlen == (char *)th0) {
                        m->m_len = hlen + tlen;
                        m_freem(m->m_next);
                        m->m_next = NULL;
                } else {
                        struct mbuf *n;

                        KASSERT(max_linkhdr + hlen + tlen <= MCLBYTES);

                        MGETHDR(n, M_DONTWAIT, MT_HEADER);
                        if (n && max_linkhdr + hlen + tlen > MHLEN) {
                                MCLGET(n, M_DONTWAIT);
                                if ((n->m_flags & M_EXT) == 0) {
                                        m_freem(n);
                                        n = NULL;
                                }
                        }
                        if (!n) {
                                m_freem(m);
                                return ENOBUFS;
                        }

                        MCLAIM(n, &tcp_tx_mowner);
                        n->m_data += max_linkhdr;
                        n->m_len = hlen + tlen;
                        m_copyback(n, 0, hlen, mtod(m, void *));
                        m_copyback(n, hlen, tlen, (void *)th0);

                        m_freem(m);
                        m = n;
                        n = NULL;
                }

#define xchg(a,b,type) { type t; t=a; a=b; b=t; }
                switch (family) {
                case AF_INET:
                        ip = mtod(m, struct ip *);
                        th = (struct tcphdr *)(ip + 1);
                        ip->ip_p = IPPROTO_TCP;
                        xchg(ip->ip_dst, ip->ip_src, struct in_addr);
                        ip->ip_p = IPPROTO_TCP;
                        break;
#ifdef INET6
                case AF_INET6:
                        ip6 = mtod(m, struct ip6_hdr *);
                        th = (struct tcphdr *)(ip6 + 1);
                        ip6->ip6_nxt = IPPROTO_TCP;
                        xchg(ip6->ip6_dst, ip6->ip6_src, struct in6_addr);
                        ip6->ip6_nxt = IPPROTO_TCP;
                        break;
#endif
                }
                xchg(th->th_dport, th->th_sport, u_int16_t);
#undef xchg
                tlen = 0;       /*be friendly with the following code*/
        }
        th->th_seq = htonl(seq);
        th->th_ack = htonl(ack);
        th->th_x2 = 0;
        if ((flags & TH_SYN) == 0) {
                if (tp)
                        win >>= tp->rcv_scale;
                if (win > TCP_MAXWIN)
                        win = TCP_MAXWIN;
                th->th_win = htons((u_int16_t)win);
                th->th_off = sizeof (struct tcphdr) >> 2;
                tlen += sizeof(*th);
        } else {
                tlen += th->th_off << 2;
        }
        m->m_len = hlen + tlen;
        m->m_pkthdr.len = hlen + tlen;
        m_reset_rcvif(m);
        th->th_flags = flags;
        th->th_urp = 0;

        switch (family) {
        case AF_INET:
            {
                struct ipovly *ipov = (struct ipovly *)ip;
                memset(ipov->ih_x1, 0, sizeof ipov->ih_x1);
                ipov->ih_len = htons((u_int16_t)tlen);

                th->th_sum = 0;
                th->th_sum = in_cksum(m, hlen + tlen);
                ip->ip_len = htons(hlen + tlen);
                ip->ip_ttl = ip_defttl;
                break;
            }
#ifdef INET6
        case AF_INET6:
            {
                th->th_sum = 0;
                th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr),
                    tlen);
                ip6->ip6_plen = htons(tlen);
                if (tp && tp->t_inpcb->inp_af == AF_INET6)
                        ip6->ip6_hlim = in6pcb_selecthlim_rt(tp->t_inpcb);
                else
                        ip6->ip6_hlim = ip6_defhlim;
                ip6->ip6_flow &= ~IPV6_FLOWINFO_MASK;
                if (ip6_auto_flowlabel) {
                        ip6->ip6_flow |=
                            (htonl(ip6_randomflowlabel()) & IPV6_FLOWLABEL_MASK);
                }
                break;
            }
#endif
        }

        if (tp != NULL && tp->t_inpcb->inp_af == AF_INET) {
                ro = &tp->t_inpcb->inp_route;
                KASSERT(family == AF_INET);
                KASSERT(in_hosteq(ip->ip_dst, in4p_faddr(tp->t_inpcb)));
        }
#ifdef INET6
        else if (tp != NULL && tp->t_inpcb->inp_af == AF_INET6) {
                ro = (struct route *)&tp->t_inpcb->inp_route;

#ifdef DIAGNOSTIC
                if (family == AF_INET) {
                        if (!IN6_IS_ADDR_V4MAPPED(&in6p_faddr(tp->t_inpcb)))
                                panic("tcp_respond: not mapped addr");
                        if (memcmp(&ip->ip_dst,
                            &in6p_faddr(tp->t_inpcb).s6_addr32[3],
                            sizeof(ip->ip_dst)) != 0) {
                                panic("tcp_respond: ip_dst != in6p_faddr");
                        }
                } else if (family == AF_INET6) {
                        if (!IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst,
                            &in6p_faddr(tp->t_inpcb)))
                                panic("tcp_respond: ip6_dst != in6p_faddr");
                } else
                        panic("tcp_respond: address family mismatch");
#endif
        }
#endif
        else
                ro = NULL;

        switch (family) {
        case AF_INET:
                error = ip_output(m, NULL, ro,
                    (tp && tp->t_mtudisc ? IP_MTUDISC : 0), NULL,
                    tp ? tp->t_inpcb : NULL);
                break;
#ifdef INET6
        case AF_INET6:
                error = ip6_output(m, NULL, ro, 0, NULL,
                    tp ? tp->t_inpcb : NULL, NULL);
                break;
#endif
        default:
                m_freem(m);
                error = EAFNOSUPPORT;
                break;
        }

        return error;
}

/*
 * Template TCPCB.  Rather than zeroing a new TCPCB and initializing
 * a bunch of members individually, we maintain this template for the
 * static and mostly-static components of the TCPCB, and copy it into
 * the new TCPCB instead.
 */
static struct tcpcb tcpcb_template = {
        .t_srtt = TCPTV_SRTTBASE,
        .t_rttmin = TCPTV_MIN,

        .snd_cwnd = TCP_MAXWIN << TCP_MAX_WINSHIFT,
        .snd_ssthresh = TCP_MAXWIN << TCP_MAX_WINSHIFT,
        .snd_numholes = 0,
        .snd_cubic_wmax = 0,
        .snd_cubic_wmax_last = 0,
        .snd_cubic_ctime = 0,

        .t_partialacks = -1,
        .t_bytes_acked = 0,
        .t_sndrexmitpack = 0,
        .t_rcvoopack = 0,
        .t_sndzerowin = 0,
};

/*
 * Updates the TCPCB template whenever a parameter that would affect
 * the template is changed.
 */
void
tcp_tcpcb_template(void)
{
        struct tcpcb *tp = &tcpcb_template;
        int flags;

        tp->t_peermss = tcp_mssdflt;
        tp->t_ourmss = tcp_mssdflt;
        tp->t_segsz = tcp_mssdflt;

        flags = 0;
        if (tcp_do_rfc1323 && tcp_do_win_scale)
                flags |= TF_REQ_SCALE;
        if (tcp_do_rfc1323 && tcp_do_timestamps)
                flags |= TF_REQ_TSTMP;
        tp->t_flags = flags;

        /*
         * Init srtt to TCPTV_SRTTBASE (0), so we can tell that we have no
         * rtt estimate.  Seed rttvar so the initial RTO computed by
         * TCP_REXMTVAL() equals TCPTV_SRTTDFLT (RFC 6298 section 2.1).
         */
        tp->t_rttvar = tcp_rttdflt * PR_SLOWHZ << TCP_RTTVAR_SHIFT;
        TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
            TCPTV_MIN, TCPTV_REXMTMAX);

        /* Keep Alive */
        tp->t_keepinit = MIN(tcp_keepinit, TCP_TIMER_MAXTICKS);
        tp->t_keepidle = MIN(tcp_keepidle, TCP_TIMER_MAXTICKS);
        tp->t_keepintvl = MIN(tcp_keepintvl, TCP_TIMER_MAXTICKS);
        tp->t_keepcnt = MAX(1, MIN(tcp_keepcnt, TCP_TIMER_MAXTICKS));
        tp->t_maxidle = tp->t_keepcnt * MIN(tp->t_keepintvl,
            TCP_TIMER_MAXTICKS/tp->t_keepcnt);

        /* MSL */
        tp->t_msl = TCPTV_MSL;
}

/*
 * Create a new TCP control block, making an
 * empty reassembly queue and hooking it to the argument
 * protocol control block.
 */
struct tcpcb *
tcp_newtcpcb(int family, struct inpcb *inp)
{
        struct tcpcb *tp;
        int i;

        /* XXX Consider using a pool_cache for speed. */
        tp = pool_get(&tcpcb_pool, PR_NOWAIT);  /* splsoftnet via tcp_usrreq */
        if (tp == NULL)
                return NULL;
        memcpy(tp, &tcpcb_template, sizeof(*tp));
        TAILQ_INIT(&tp->segq);
        TAILQ_INIT(&tp->timeq);
        tp->t_family = family;          /* may be overridden later on */
        TAILQ_INIT(&tp->snd_holes);
        LIST_INIT(&tp->t_sc);           /* XXX can template this */

        /* Don't sweat this loop; hopefully the compiler will unroll it. */
        for (i = 0; i < TCPT_NTIMERS; i++) {
                callout_init(&tp->t_timer[i], CALLOUT_MPSAFE);
                TCP_TIMER_INIT(tp, i);
        }
        callout_init(&tp->t_delack_ch, CALLOUT_MPSAFE);

        switch (family) {
        case AF_INET:
                in4p_ip(inp).ip_ttl = ip_defttl;
                inp->inp_ppcb = (void *)tp;

                tp->t_inpcb = inp;
                tp->t_mtudisc = ip_mtudisc;
                break;
#ifdef INET6
        case AF_INET6:
                in6p_ip6(inp).ip6_hlim = in6pcb_selecthlim_rt(inp);
                inp->inp_ppcb = (void *)tp;

                tp->t_inpcb = inp;
                /* for IPv6, always try to run path MTU discovery */
                tp->t_mtudisc = 1;
                break;
#endif /* INET6 */
        default:
                for (i = 0; i < TCPT_NTIMERS; i++)
                        callout_destroy(&tp->t_timer[i]);
                callout_destroy(&tp->t_delack_ch);
                pool_put(&tcpcb_pool, tp);      /* splsoftnet via tcp_usrreq */
                return NULL;
        }

        /*
         * Initialize our timebase.  When we send timestamps, we take
         * the delta from tcp_now -- this means each connection always
         * gets a timebase of 1, which makes it, among other things,
         * more difficult to determine how long a system has been up,
         * and thus how many TCP sequence increments have occurred.
         *
         * We start with 1, because 0 doesn't work with linux, which
         * considers timestamp 0 in a SYN packet as a bug and disables
         * timestamps.
         */
        tp->ts_timebase = tcp_now - 1;

        tcp_congctl_select(tp, tcp_congctl_global_name);

        return tp;
}

/*
 * Drop a TCP connection, reporting
 * the specified error.  If connection is synchronized,
 * then send a RST to peer.
 */
struct tcpcb *
tcp_drop(struct tcpcb *tp, int errno)
{
        struct socket *so;

        KASSERT(tp->t_inpcb != NULL);

        so = tp->t_inpcb->inp_socket;
        if (so == NULL)
                return NULL;

        if (TCPS_HAVERCVDSYN(tp->t_state)) {
                tp->t_state = TCPS_CLOSED;
                (void) tcp_output(tp);
                TCP_STATINC(TCP_STAT_DROPS);
        } else
                TCP_STATINC(TCP_STAT_CONNDROPS);
        if (errno == ETIMEDOUT && tp->t_softerror)
                errno = tp->t_softerror;
        so->so_error = errno;
        return (tcp_close(tp));
}

/*
 * Close a TCP control block:
 *      discard all space held by the tcp
 *      discard internet protocol block
 *      wake up any sleepers
 */
struct tcpcb *
tcp_close(struct tcpcb *tp)
{
        struct inpcb *inp;
        struct socket *so;
#ifdef RTV_RTT
        struct rtentry *rt = NULL;
#endif
        struct route *ro;
        int j;

        inp = tp->t_inpcb;
        so = inp->inp_socket;
        ro = &inp->inp_route;

#ifdef RTV_RTT
        /*
         * If we sent enough data to get some meaningful characteristics,
         * save them in the routing entry.  'Enough' is arbitrarily
         * defined as the sendpipesize (default 4K) * 16.  This would
         * give us 16 rtt samples assuming we only get one sample per
         * window (the usual case on a long haul net).  16 samples is
         * enough for the srtt filter to converge to within 5% of the correct
         * value; fewer samples and we could save a very bogus rtt.
         *
         * Don't update the default route's characteristics and don't
         * update anything that the user "locked".
         */
        if (SEQ_LT(tp->iss + so->so_snd.sb_hiwat * 16, tp->snd_max) &&
            ro && (rt = rtcache_validate(ro)) != NULL &&
            !in_nullhost(satocsin(rt_getkey(rt))->sin_addr)) {
                u_long i = 0;

                if ((rt->rt_rmx.rmx_locks & RTV_RTT) == 0) {
                        i = tp->t_srtt *
                            ((RTM_RTTUNIT / PR_SLOWHZ) >> (TCP_RTT_SHIFT + 2));
                        if (rt->rt_rmx.rmx_rtt && i)
                                /*
                                 * filter this update to half the old & half
                                 * the new values, converting scale.
                                 * See route.h and tcp_var.h for a
                                 * description of the scaling constants.
                                 */
                                rt->rt_rmx.rmx_rtt =
                                    (rt->rt_rmx.rmx_rtt + i) / 2;
                        else
                                rt->rt_rmx.rmx_rtt = i;
                }
                if ((rt->rt_rmx.rmx_locks & RTV_RTTVAR) == 0) {
                        i = tp->t_rttvar *
                            ((RTM_RTTUNIT / PR_SLOWHZ) >> (TCP_RTTVAR_SHIFT + 2));
                        if (rt->rt_rmx.rmx_rttvar && i)
                                rt->rt_rmx.rmx_rttvar =
                                    (rt->rt_rmx.rmx_rttvar + i) / 2;
                        else
                                rt->rt_rmx.rmx_rttvar = i;
                }
                /*
                 * update the pipelimit (ssthresh) if it has been updated
                 * already or if a pipesize was specified & the threshold
                 * got below half the pipesize.  I.e., wait for bad news
                 * before we start updating, then update on both good
                 * and bad news.
                 */
                if (((rt->rt_rmx.rmx_locks & RTV_SSTHRESH) == 0 &&
                    (i = tp->snd_ssthresh) && rt->rt_rmx.rmx_ssthresh) ||
                    i < (rt->rt_rmx.rmx_sendpipe / 2)) {
                        /*
                         * convert the limit from user data bytes to
                         * packets then to packet data bytes.
                         */
                        i = (i + tp->t_segsz / 2) / tp->t_segsz;
                        if (i < 2)
                                i = 2;
                        i *= (u_long)(tp->t_segsz + sizeof (struct tcpiphdr));
                        if (rt->rt_rmx.rmx_ssthresh)
                                rt->rt_rmx.rmx_ssthresh =
                                    (rt->rt_rmx.rmx_ssthresh + i) / 2;
                        else
                                rt->rt_rmx.rmx_ssthresh = i;
                }
        }
        rtcache_unref(rt, ro);
#endif /* RTV_RTT */
        /* free the reassembly queue, if any */
        TCP_REASS_LOCK(tp);
        (void) tcp_freeq(tp);
        TCP_REASS_UNLOCK(tp);

        /* free the SACK holes list. */
        tcp_free_sackholes(tp);
        tcp_congctl_release(tp);
        syn_cache_cleanup(tp);

        if (tp->t_template) {
                m_free(tp->t_template);
                tp->t_template = NULL;
        }

        /*
         * Detaching the pcb will unlock the socket/tcpcb, and stopping
         * the timers can also drop the lock.  We need to prevent access
         * to the tcpcb as it's half torn down.  Flag the pcb as dead
         * (prevents access by timers) and only then detach it.
         */
        tp->t_flags |= TF_DEAD;
        inp->inp_ppcb = NULL;
        soisdisconnected(so);
        inpcb_destroy(inp);
        /*
         * pcb is no longer visble elsewhere, so we can safely release
         * the lock in callout_halt() if needed.
         */
        TCP_STATINC(TCP_STAT_CLOSED);
        for (j = 0; j < TCPT_NTIMERS; j++) {
                callout_halt(&tp->t_timer[j], softnet_lock);
                callout_destroy(&tp->t_timer[j]);
        }
        callout_halt(&tp->t_delack_ch, softnet_lock);
        callout_destroy(&tp->t_delack_ch);
        pool_put(&tcpcb_pool, tp);

        return NULL;
}

int
tcp_freeq(struct tcpcb *tp)
{
        struct ipqent *qe;
        int rv = 0;

        TCP_REASS_LOCK_CHECK(tp);

        while ((qe = TAILQ_FIRST(&tp->segq)) != NULL) {
                TAILQ_REMOVE(&tp->segq, qe, ipqe_q);
                TAILQ_REMOVE(&tp->timeq, qe, ipqe_timeq);
                m_freem(qe->ipqe_m);
                tcpipqent_free(qe);
                rv = 1;
        }
        tp->t_segqlen = 0;
        KASSERT(TAILQ_EMPTY(&tp->timeq));
        return (rv);
}

void
tcp_fasttimo(void)
{
        if (tcp_drainwanted) {
                tcp_drain();
                tcp_drainwanted = 0;
        }
}

void
tcp_drainstub(void)
{
        tcp_drainwanted = 1;
}

/*
 * Protocol drain routine.  Called when memory is in short supply.
 * Called from pr_fasttimo thus a callout context.
 */
void
tcp_drain(void)
{
        struct inpcb *inp;
        struct tcpcb *tp;

        mutex_enter(softnet_lock);
        KERNEL_LOCK(1, NULL);

        /*
         * Free the sequence queue of all TCP connections.
         */
        TAILQ_FOREACH(inp, &tcbtable.inpt_queue, inp_queue) {
                tp = intotcpcb(inp);
                if (tp != NULL) {
                        /*
                         * If the tcpcb is already busy,
                         * just bail out now.
                         */
                        if (tcp_reass_lock_try(tp) == 0)
                                continue;
                        if (tcp_freeq(tp))
                                TCP_STATINC(TCP_STAT_CONNSDRAINED);
                        TCP_REASS_UNLOCK(tp);
                }
        }

        KERNEL_UNLOCK_ONE(NULL);
        mutex_exit(softnet_lock);
}

/*
 * Notify a tcp user of an asynchronous error;
 * store error as soft error, but wake up user
 * (for now, won't do anything until can select for soft error).
 */
void
tcp_notify(struct inpcb *inp, int error)
{
        struct tcpcb *tp = (struct tcpcb *)inp->inp_ppcb;
        struct socket *so = inp->inp_socket;

        /*
         * Ignore some errors if we are hooked up.
         * If connection hasn't completed, has retransmitted several times,
         * and receives a second error, give up now.  This is better
         * than waiting a long time to establish a connection that
         * can never complete.
         */
        if (tp->t_state == TCPS_ESTABLISHED &&
             (error == EHOSTUNREACH || error == ENETUNREACH ||
              error == EHOSTDOWN)) {
                return;
        } else if (TCPS_HAVEESTABLISHED(tp->t_state) == 0 &&
            tp->t_rxtshift > 3 && tp->t_softerror)
                so->so_error = error;
        else
                tp->t_softerror = error;
        cv_broadcast(&so->so_cv);
        sorwakeup(so);
        sowwakeup(so);
}

#ifdef INET6
void *
tcp6_ctlinput(int cmd, const struct sockaddr *sa, void *d)
{
        struct tcphdr th;
        void (*notify)(struct inpcb *, int) = tcp_notify;
        int nmatch;
        struct ip6_hdr *ip6;
        const struct sockaddr_in6 *sa6_src = NULL;
        const struct sockaddr_in6 *sa6 = (const struct sockaddr_in6 *)sa;
        struct mbuf *m;
        int off;

        if (sa->sa_family != AF_INET6 ||
            sa->sa_len != sizeof(struct sockaddr_in6))
                return NULL;
        if ((unsigned)cmd >= PRC_NCMDS)
                return NULL;
        else if (cmd == PRC_QUENCH) {
                /*
                 * Don't honor ICMP Source Quench messages meant for
                 * TCP connections.
                 */
                return NULL;
        } else if (PRC_IS_REDIRECT(cmd))
                notify = in6pcb_rtchange, d = NULL;
        else if (cmd == PRC_MSGSIZE)
                ; /* special code is present, see below */
        else if (cmd == PRC_HOSTDEAD)
                d = NULL;
        else if (inet6ctlerrmap[cmd] == 0)
                return NULL;

        /* if the parameter is from icmp6, decode it. */
        if (d != NULL) {
                struct ip6ctlparam *ip6cp = (struct ip6ctlparam *)d;
                m = ip6cp->ip6c_m;
                ip6 = ip6cp->ip6c_ip6;
                off = ip6cp->ip6c_off;
                sa6_src = ip6cp->ip6c_src;
        } else {
                m = NULL;
                ip6 = NULL;
                sa6_src = &sa6_any;
                off = 0;
        }

        if (ip6) {
                /* check if we can safely examine src and dst ports */
                if (m->m_pkthdr.len < off + sizeof(th)) {
                        if (cmd == PRC_MSGSIZE)
                                icmp6_mtudisc_update((struct ip6ctlparam *)d, 0);
                        return NULL;
                }

                memset(&th, 0, sizeof(th));
                m_copydata(m, off, sizeof(th), (void *)&th);

                if (cmd == PRC_MSGSIZE) {
                        int valid = 0;

                        /*
                         * Check to see if we have a valid TCP connection
                         * corresponding to the address in the ICMPv6 message
                         * payload.
                         */
                        if (in6pcb_lookup(&tcbtable, &sa6->sin6_addr,
                            th.th_dport,
                            (const struct in6_addr *)&sa6_src->sin6_addr,
                                                  th.th_sport, 0, 0))
                                valid++;

                        /*
                         * Depending on the value of "valid" and routing table
                         * size (mtudisc_{hi,lo}wat), we will:
                         * - recalculate the new MTU and create the
                         *   corresponding routing entry, or
                         * - ignore the MTU change notification.
                         */
                        icmp6_mtudisc_update((struct ip6ctlparam *)d, valid);

                        /*
                         * no need to call in6pcb_notify, it should have been
                         * called via callback if necessary
                         */
                        return NULL;
                }

                nmatch = in6pcb_notify(&tcbtable, sa, th.th_dport,
                    (const struct sockaddr *)sa6_src, th.th_sport, cmd, NULL, notify);
                if (nmatch == 0 && syn_cache_count &&
                    (inet6ctlerrmap[cmd] == EHOSTUNREACH ||
                     inet6ctlerrmap[cmd] == ENETUNREACH ||
                     inet6ctlerrmap[cmd] == EHOSTDOWN))
                        syn_cache_unreach((const struct sockaddr *)sa6_src,
                                          sa, &th);
        } else {
                (void) in6pcb_notify(&tcbtable, sa, 0,
                    (const struct sockaddr *)sa6_src, 0, cmd, NULL, notify);
        }

        return NULL;
}
#endif

/* assumes that ip header and tcp header are contiguous on mbuf */
void *
tcp_ctlinput(int cmd, const struct sockaddr *sa, void *v)
{
        struct ip *ip = v;
        struct tcphdr *th;
        struct icmp *icp;
        extern const int inetctlerrmap[];
        void (*notify)(struct inpcb *, int) = tcp_notify;
        int errno;
        int nmatch;
        struct tcpcb *tp;
        u_int mtu;
        tcp_seq seq;
        struct inpcb *inp;
#ifdef INET6
        struct in6_addr src6, dst6;
#endif

        if (sa->sa_family != AF_INET ||
            sa->sa_len != sizeof(struct sockaddr_in))
                return NULL;
        if ((unsigned)cmd >= PRC_NCMDS)
                return NULL;
        errno = inetctlerrmap[cmd];
        if (cmd == PRC_QUENCH)
                /*
                 * Don't honor ICMP Source Quench messages meant for
                 * TCP connections.
                 */
                return NULL;
        else if (PRC_IS_REDIRECT(cmd))
                notify = inpcb_rtchange, ip = 0;
        else if (cmd == PRC_MSGSIZE && ip && ip->ip_v == 4) {
                /*
                 * Check to see if we have a valid TCP connection
                 * corresponding to the address in the ICMP message
                 * payload.
                 *
                 * Boundary check is made in icmp_input(), with ICMP_ADVLENMIN.
                 */
                th = (struct tcphdr *)((char *)ip + (ip->ip_hl << 2));
#ifdef INET6
                in6_in_2_v4mapin6(&ip->ip_src, &src6);
                in6_in_2_v4mapin6(&ip->ip_dst, &dst6);
#endif
                if ((inp = inpcb_lookup(&tcbtable, ip->ip_dst,
                    th->th_dport, ip->ip_src, th->th_sport, 0)) != NULL)
                        ;
#ifdef INET6
                else if ((inp = in6pcb_lookup(&tcbtable, &dst6,
                    th->th_dport, &src6, th->th_sport, 0, 0)) != NULL)
                        ;
#endif
                else
                        return NULL;

                /*
                 * Now that we've validated that we are actually communicating
                 * with the host indicated in the ICMP message, locate the
                 * ICMP header, recalculate the new MTU, and create the
                 * corresponding routing entry.
                 */
                icp = (struct icmp *)((char *)ip -
                    offsetof(struct icmp, icmp_ip));
                tp = intotcpcb(inp);
                if (tp == NULL)
                        return NULL;
                seq = ntohl(th->th_seq);
                if (SEQ_LT(seq, tp->snd_una) || SEQ_GT(seq, tp->snd_max))
                        return NULL;
                /*
                 * If the ICMP message advertises a Next-Hop MTU
                 * equal or larger than the maximum packet size we have
                 * ever sent, drop the message.
                 */
                mtu = (u_int)ntohs(icp->icmp_nextmtu);
                if (mtu >= tp->t_pmtud_mtu_sent)
                        return NULL;
                if (mtu >= tcp_hdrsz(tp) + tp->t_pmtud_mss_acked) {
                        /*
                         * Calculate new MTU, and create corresponding
                         * route (traditional PMTUD).
                         */
                        tp->t_flags &= ~TF_PMTUD_PEND;
                        icmp_mtudisc(icp, ip->ip_dst);
                } else {
                        /*
                         * Record the information got in the ICMP
                         * message; act on it later.
                         * If we had already recorded an ICMP message,
                         * replace the old one only if the new message
                         * refers to an older TCP segment
                         */
                        if (tp->t_flags & TF_PMTUD_PEND) {
                                if (SEQ_LT(tp->t_pmtud_th_seq, seq))
                                        return NULL;
                        } else
                                tp->t_flags |= TF_PMTUD_PEND;
                        tp->t_pmtud_th_seq = seq;
                        tp->t_pmtud_nextmtu = icp->icmp_nextmtu;
                        tp->t_pmtud_ip_len = icp->icmp_ip.ip_len;
                        tp->t_pmtud_ip_hl = icp->icmp_ip.ip_hl;
                }
                return NULL;
        } else if (cmd == PRC_HOSTDEAD)
                ip = 0;
        else if (errno == 0)
                return NULL;
        if (ip && ip->ip_v == 4 && sa->sa_family == AF_INET) {
                th = (struct tcphdr *)((char *)ip + (ip->ip_hl << 2));
                nmatch = inpcb_notify(&tcbtable, satocsin(sa)->sin_addr,
                    th->th_dport, ip->ip_src, th->th_sport, errno, notify);
                if (nmatch == 0 && syn_cache_count &&
                    (inetctlerrmap[cmd] == EHOSTUNREACH ||
                    inetctlerrmap[cmd] == ENETUNREACH ||
                    inetctlerrmap[cmd] == EHOSTDOWN)) {
                        struct sockaddr_in sin;
                        memset(&sin, 0, sizeof(sin));
                        sin.sin_len = sizeof(sin);
                        sin.sin_family = AF_INET;
                        sin.sin_port = th->th_sport;
                        sin.sin_addr = ip->ip_src;
                        syn_cache_unreach((struct sockaddr *)&sin, sa, th);
                }

                /* XXX mapped address case */
        } else
                inpcb_notifyall(&tcbtable, satocsin(sa)->sin_addr, errno,
                    notify);
        return NULL;
}

/*
 * When a source quench is received, we are being notified of congestion.
 * Close the congestion window down to the Loss Window (one segment).
 * We will gradually open it again as we proceed.
 */
void
tcp_quench(struct inpcb *inp)
{
        struct tcpcb *tp = intotcpcb(inp);

        if (tp) {
                tp->snd_cwnd = tp->t_segsz;
                tp->t_bytes_acked = 0;
        }
}

/*
 * Path MTU Discovery handlers.
 */
void
tcp_mtudisc_callback(struct in_addr faddr)
{
#ifdef INET6
        struct in6_addr in6;
#endif

        inpcb_notifyall(&tcbtable, faddr, EMSGSIZE, tcp_mtudisc);
#ifdef INET6
        in6_in_2_v4mapin6(&faddr, &in6);
        tcp6_mtudisc_callback(&in6);
#endif
}

/*
 * On receipt of path MTU corrections, flush old route and replace it
 * with the new one.  Retransmit all unacknowledged packets, to ensure
 * that all packets will be received.
 */
void
tcp_mtudisc(struct inpcb *inp, int errno)
{
        struct tcpcb *tp = intotcpcb(inp);
        struct rtentry *rt;

        if (tp == NULL)
                return;

        rt = inpcb_rtentry(inp);
        if (rt != NULL) {
                /*
                 * If this was not a host route, remove and realloc.
                 */
                if ((rt->rt_flags & RTF_HOST) == 0) {
                        inpcb_rtentry_unref(rt, inp);
                        inpcb_rtchange(inp, errno);
                        if ((rt = inpcb_rtentry(inp)) == NULL)
                                return;
                }

                /*
                 * Slow start out of the error condition.  We
                 * use the MTU because we know it's smaller
                 * than the previously transmitted segment.
                 *
                 * Note: This is more conservative than the
                 * suggestion in draft-floyd-incr-init-win-03.
                 */
                if (rt->rt_rmx.rmx_mtu != 0)
                        tp->snd_cwnd =
                            TCP_INITIAL_WINDOW(tcp_init_win,
                            rt->rt_rmx.rmx_mtu);
                inpcb_rtentry_unref(rt, inp);
        }

        /*
         * Resend unacknowledged packets.
         */
        tp->snd_nxt = tp->sack_newdata = tp->snd_una;
        tcp_output(tp);
}

#ifdef INET6
/*
 * Path MTU Discovery handlers.
 */
void
tcp6_mtudisc_callback(struct in6_addr *faddr)
{
        struct sockaddr_in6 sin6;

        memset(&sin6, 0, sizeof(sin6));
        sin6.sin6_family = AF_INET6;
        sin6.sin6_len = sizeof(struct sockaddr_in6);
        sin6.sin6_addr = *faddr;
        (void) in6pcb_notify(&tcbtable, (struct sockaddr *)&sin6, 0,
            (const struct sockaddr *)&sa6_any, 0, PRC_MSGSIZE, NULL, tcp6_mtudisc);
}

void
tcp6_mtudisc(struct inpcb *inp, int errno)
{
        struct tcpcb *tp = intotcpcb(inp);
        struct rtentry *rt;

        if (tp == NULL)
                return;

        rt = in6pcb_rtentry(inp);
        if (rt != NULL) {
                /*
                 * If this was not a host route, remove and realloc.
                 */
                if ((rt->rt_flags & RTF_HOST) == 0) {
                        in6pcb_rtentry_unref(rt, inp);
                        in6pcb_rtchange(inp, errno);
                        rt = in6pcb_rtentry(inp);
                        if (rt == NULL)
                                return;
                }

                /*
                 * Slow start out of the error condition.  We
                 * use the MTU because we know it's smaller
                 * than the previously transmitted segment.
                 *
                 * Note: This is more conservative than the
                 * suggestion in draft-floyd-incr-init-win-03.
                 */
                if (rt->rt_rmx.rmx_mtu != 0) {
                        tp->snd_cwnd = TCP_INITIAL_WINDOW(tcp_init_win,
                            rt->rt_rmx.rmx_mtu);
                }
                in6pcb_rtentry_unref(rt, inp);
        }

        /*
         * Resend unacknowledged packets.
         */
        tp->snd_nxt = tp->sack_newdata = tp->snd_una;
        tcp_output(tp);
}
#endif /* INET6 */

/*
 * Compute the MSS to advertise to the peer.  Called only during
 * the 3-way handshake.  If we are the server (peer initiated
 * connection), we are called with a pointer to the interface
 * on which the SYN packet arrived.  If we are the client (we
 * initiated connection), we are called with a pointer to the
 * interface out which this connection should go.
 *
 * NOTE: Do not subtract IP option/extension header size nor IPsec
 * header size from MSS advertisement.  MSS option must hold the maximum
 * segment size we can accept, so it must always be:
 *       max(if mtu) - ip header - tcp header
 */
u_long
tcp_mss_to_advertise(const struct ifnet *ifp, int af)
{
        extern u_long in_maxmtu;
        u_long mss = 0;
        u_long hdrsiz;

        /*
         * In order to avoid defeating path MTU discovery on the peer,
         * we advertise the max MTU of all attached networks as our MSS,
         * per RFC 1191, section 3.1.
         *
         * We provide the option to advertise just the MTU of
         * the interface on which we hope this connection will
         * be receiving.  If we are responding to a SYN, we
         * will have a pretty good idea about this, but when
         * initiating a connection there is a bit more doubt.
         *
         * We also need to ensure that loopback has a large enough
         * MSS, as the loopback MTU is never included in in_maxmtu.
         */

        if (ifp != NULL)
                switch (af) {
#ifdef INET6
                case AF_INET6:  /* FALLTHROUGH */
#endif
                case AF_INET:
                        mss = ifp->if_mtu;
                        break;
                }

        if (tcp_mss_ifmtu == 0)
                switch (af) {
#ifdef INET6
                case AF_INET6:  /* FALLTHROUGH */
#endif
                case AF_INET:
                        mss = uimax(in_maxmtu, mss);
                        break;
                }

        switch (af) {
        case AF_INET:
                hdrsiz = sizeof(struct ip);
                break;
#ifdef INET6
        case AF_INET6:
                hdrsiz = sizeof(struct ip6_hdr);
                break;
#endif
        default:
                hdrsiz = 0;
                break;
        }
        hdrsiz += sizeof(struct tcphdr);
        if (mss > hdrsiz)
                mss -= hdrsiz;

        mss = uimax(tcp_mssdflt, mss);
        return (mss);
}

/*
 * Set connection variables based on the peer's advertised MSS.
 * We are passed the TCPCB for the actual connection.  If we
 * are the server, we are called by the compressed state engine
 * when the 3-way handshake is complete.  If we are the client,
 * we are called when we receive the SYN,ACK from the server.
 *
 * NOTE: Our advertised MSS value must be initialized in the TCPCB
 * before this routine is called!
 */
void
tcp_mss_from_peer(struct tcpcb *tp, int offer)
{
        struct socket *so;
#if defined(RTV_SPIPE) || defined(RTV_SSTHRESH)
        struct rtentry *rt;
#endif
        u_long bufsize;
        int mss;

        KASSERT(tp->t_inpcb != NULL);

        so = NULL;
        rt = NULL;

        so = tp->t_inpcb->inp_socket;
#if defined(RTV_SPIPE) || defined(RTV_SSTHRESH)
        rt = inpcb_rtentry(tp->t_inpcb);
#endif

        /*
         * As per RFC1122, use the default MSS value, unless they
         * sent us an offer.  Do not accept offers less than 256 bytes.
         */
        mss = tcp_mssdflt;
        if (offer)
                mss = offer;
        mss = uimax(mss, 256);          /* sanity */
        tp->t_peermss = mss;
        mss -= tcp_optlen(tp);
        if (tp->t_inpcb->inp_af == AF_INET)
                mss -= ip_optlen(tp->t_inpcb);
#ifdef INET6
        if (tp->t_inpcb->inp_af == AF_INET6)
                mss -= ip6_optlen(tp->t_inpcb);
#endif
        /*
         * XXX XXX What if mss goes negative or zero? This can happen if a
         * socket has large IPv6 options. We crash below.
         */

        /*
         * If there's a pipesize, change the socket buffer to that size.
         * Make the socket buffer an integral number of MSS units.  If
         * the MSS is larger than the socket buffer, artificially decrease
         * the MSS.
         */
#ifdef RTV_SPIPE
        if (rt != NULL && rt->rt_rmx.rmx_sendpipe != 0)
                bufsize = rt->rt_rmx.rmx_sendpipe;
        else
#endif
        {
                KASSERT(so != NULL);
                bufsize = so->so_snd.sb_hiwat;
        }
        if (bufsize < mss)
                mss = bufsize;
        else {
                bufsize = roundup(bufsize, mss);
                if (bufsize > sb_max)
                        bufsize = sb_max;
                (void) sbreserve(&so->so_snd, bufsize, so);
        }
        tp->t_segsz = mss;

#ifdef RTV_SSTHRESH
        if (rt != NULL && rt->rt_rmx.rmx_ssthresh) {
                /*
                 * There's some sort of gateway or interface buffer
                 * limit on the path.  Use this to set the slow
                 * start threshold, but set the threshold to no less
                 * than 2 * MSS.
                 */
                tp->snd_ssthresh = uimax(2 * mss, rt->rt_rmx.rmx_ssthresh);
        }
#endif
#if defined(RTV_SPIPE) || defined(RTV_SSTHRESH)
        inpcb_rtentry_unref(rt, tp->t_inpcb);
#endif
}

/*
 * Processing necessary when a TCP connection is established.
 */
void
tcp_established(struct tcpcb *tp)
{
        struct socket *so;
#ifdef RTV_RPIPE
        struct rtentry *rt;
#endif
        u_long bufsize;

        KASSERT(tp->t_inpcb != NULL);

        so = NULL;
        rt = NULL;

        /* This is a while() to reduce the dreadful stairstepping below */
        while (tp->t_inpcb->inp_af == AF_INET) {
                so = tp->t_inpcb->inp_socket;
#if defined(RTV_RPIPE)
                rt = inpcb_rtentry(tp->t_inpcb);
#endif
                if (__predict_true(tcp_msl_enable)) {
                        if (in4p_laddr(tp->t_inpcb).s_addr == INADDR_LOOPBACK) {
                                tp->t_msl = tcp_msl_loop ? tcp_msl_loop : (TCPTV_MSL >> 2);
                                break;
                        }

                        if (__predict_false(tcp_rttlocal)) {
                                /* This may be adjusted by tcp_input */
                                tp->t_msl = tcp_msl_local ? tcp_msl_local : (TCPTV_MSL >> 1);
                                break;
                        }
                        if (in_localaddr(in4p_faddr(tp->t_inpcb))) {
                                tp->t_msl = tcp_msl_local ? tcp_msl_local : (TCPTV_MSL >> 1);
                                break;
                        }
                }
                tp->t_msl = tcp_msl_remote ? tcp_msl_remote : TCPTV_MSL;
                break;
        }

        /* Clamp to a reasonable range.  */
        tp->t_msl = MIN(tp->t_msl, TCP_MAXMSL);

#ifdef INET6
        while (tp->t_inpcb->inp_af == AF_INET6) {
                so = tp->t_inpcb->inp_socket;
#if defined(RTV_RPIPE)
                rt = in6pcb_rtentry(tp->t_inpcb);
#endif
                if (__predict_true(tcp_msl_enable)) {
                        extern const struct in6_addr in6addr_loopback;

                        if (IN6_ARE_ADDR_EQUAL(&in6p_laddr(tp->t_inpcb),
                            &in6addr_loopback)) {
                                tp->t_msl = tcp_msl_loop ? tcp_msl_loop : (TCPTV_MSL >> 2);
                                break;
                        }

                        if (__predict_false(tcp_rttlocal)) {
                                /* This may be adjusted by tcp_input */
                                tp->t_msl = tcp_msl_local ? tcp_msl_local : (TCPTV_MSL >> 1);
                                break;
                        }
                        if (in6_localaddr(&in6p_faddr(tp->t_inpcb))) {
                                tp->t_msl = tcp_msl_local ? tcp_msl_local : (TCPTV_MSL >> 1);
                                break;
                        }
                }
                tp->t_msl = tcp_msl_remote ? tcp_msl_remote : TCPTV_MSL;
                break;
        }

        /* Clamp to a reasonable range.  */
        tp->t_msl = MIN(tp->t_msl, TCP_MAXMSL);
#endif

        tp->t_state = TCPS_ESTABLISHED;
        TCP_TIMER_ARM(tp, TCPT_KEEP, tp->t_keepidle);

#ifdef RTV_RPIPE
        if (rt != NULL && rt->rt_rmx.rmx_recvpipe != 0)
                bufsize = rt->rt_rmx.rmx_recvpipe;
        else
#endif
        {
                KASSERT(so != NULL);
                bufsize = so->so_rcv.sb_hiwat;
        }
        if (bufsize > tp->t_ourmss) {
                bufsize = roundup(bufsize, tp->t_ourmss);
                if (bufsize > sb_max)
                        bufsize = sb_max;
                (void) sbreserve(&so->so_rcv, bufsize, so);
        }
#ifdef RTV_RPIPE
        inpcb_rtentry_unref(rt, tp->t_inpcb);
#endif
}

/*
 * Check if there's an initial rtt or rttvar.  Convert from the
 * route-table units to scaled multiples of the slow timeout timer.
 * Called only during the 3-way handshake.
 */
void
tcp_rmx_rtt(struct tcpcb *tp)
{
#ifdef RTV_RTT
        struct rtentry *rt = NULL;
        int rtt;

        KASSERT(tp->t_inpcb != NULL);

        rt = inpcb_rtentry(tp->t_inpcb);
        if (rt == NULL)
                return;

        if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
                /*
                 * XXX The lock bit for MTU indicates that the value
                 * is also a minimum value; this is subject to time.
                 */
                if (rt->rt_rmx.rmx_locks & RTV_RTT)
                        TCPT_RANGESET(tp->t_rttmin,
                            rtt / (RTM_RTTUNIT / PR_SLOWHZ),
                            TCPTV_MIN, TCPTV_REXMTMAX);
                tp->t_srtt = rtt /
                    ((RTM_RTTUNIT / PR_SLOWHZ) >> (TCP_RTT_SHIFT + 2));
                if (rt->rt_rmx.rmx_rttvar) {
                        tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
                            ((RTM_RTTUNIT / PR_SLOWHZ) >>
                                (TCP_RTTVAR_SHIFT + 2));
                } else {
                        /* Default variation is +- 1 rtt */
                        tp->t_rttvar =
                            tp->t_srtt >> (TCP_RTT_SHIFT - TCP_RTTVAR_SHIFT);
                }
                TCPT_RANGESET(tp->t_rxtcur,
                    ((tp->t_srtt >> 2) + tp->t_rttvar) >> (1 + 2),
                    tp->t_rttmin, TCPTV_REXMTMAX);
        }
        inpcb_rtentry_unref(rt, tp->t_inpcb);
#endif
}

tcp_seq  tcp_iss_seq = 0;       /* tcp initial seq # */

/*
 * Get a new sequence value given a tcp control block
 */
tcp_seq
tcp_new_iss(struct tcpcb *tp)
{

        if (tp->t_inpcb->inp_af == AF_INET) {
                return tcp_new_iss1(&in4p_laddr(tp->t_inpcb),
                    &in4p_faddr(tp->t_inpcb), tp->t_inpcb->inp_lport,
                    tp->t_inpcb->inp_fport, sizeof(in4p_laddr(tp->t_inpcb)));
        }
#ifdef INET6
        if (tp->t_inpcb->inp_af == AF_INET6) {
                return tcp_new_iss1(&in6p_laddr(tp->t_inpcb),
                    &in6p_faddr(tp->t_inpcb), tp->t_inpcb->inp_lport,
                    tp->t_inpcb->inp_fport, sizeof(in6p_laddr(tp->t_inpcb)));
        }
#endif

        panic("tcp_new_iss: unreachable");
}

static u_int8_t tcp_iss_secret[16];     /* 128 bits; should be plenty */

/*
 * Initialize RFC 1948 ISS Secret
 */
static int
tcp_iss_secret_init(void)
{
        cprng_strong(kern_cprng,
            tcp_iss_secret, sizeof(tcp_iss_secret), 0);

        return 0;
}

/*
 * This routine actually generates a new TCP initial sequence number.
 */
tcp_seq
tcp_new_iss1(void *laddr, void *faddr, u_int16_t lport, u_int16_t fport,
    size_t addrsz)
{
        tcp_seq tcp_iss;

        if (tcp_do_rfc1948) {
                MD5_CTX ctx;
                u_int8_t hash[16];      /* XXX MD5 knowledge */
                static ONCE_DECL(tcp_iss_secret_control);

                /*
                 * If we haven't been here before, initialize our cryptographic
                 * hash secret.
                 */
                RUN_ONCE(&tcp_iss_secret_control, tcp_iss_secret_init);

                /*
                 * Compute the base value of the ISS.  It is a hash
                 * of (saddr, sport, daddr, dport, secret).
                 */
                MD5Init(&ctx);

                MD5Update(&ctx, (u_char *) laddr, addrsz);
                MD5Update(&ctx, (u_char *) &lport, sizeof(lport));

                MD5Update(&ctx, (u_char *) faddr, addrsz);
                MD5Update(&ctx, (u_char *) &fport, sizeof(fport));

                MD5Update(&ctx, tcp_iss_secret, sizeof(tcp_iss_secret));

                MD5Final(hash, &ctx);

                memcpy(&tcp_iss, hash, sizeof(tcp_iss));

#ifdef TCPISS_DEBUG
                printf("ISS hash 0x%08x, ", tcp_iss);
#endif
        } else {
                /*
                 * Randomize.
                 */
                tcp_iss = cprng_fast32() & TCP_ISS_RANDOM_MASK;
#ifdef TCPISS_DEBUG
                printf("ISS random 0x%08x, ", tcp_iss);
#endif
        }

        /*
         * Add the offset in to the computed value.
         */
        tcp_iss += tcp_iss_seq;
#ifdef TCPISS_DEBUG
        printf("ISS %08x\n", tcp_iss);
#endif
        return tcp_iss;
}

#if defined(IPSEC)
/* compute ESP/AH header size for TCP, including outer IP header. */
size_t
ipsec4_hdrsiz_tcp(struct tcpcb *tp)
{
        struct inpcb *inp;
        size_t hdrsiz;

        /* XXX mapped addr case (tp->t_inpcb) */
        if (!tp || !tp->t_template || !(inp = tp->t_inpcb))
                return 0;
        switch (tp->t_family) {
        case AF_INET:
                /* XXX: should use correct direction. */
                hdrsiz = ipsec_hdrsiz(tp->t_template, IPSEC_DIR_OUTBOUND, inp);
                break;
        default:
                hdrsiz = 0;
                break;
        }

        return hdrsiz;
}

#ifdef INET6
size_t
ipsec6_hdrsiz_tcp(struct tcpcb *tp)
{
        struct inpcb *inp;
        size_t hdrsiz;

        if (!tp || !tp->t_template || !(inp = tp->t_inpcb))
                return 0;
        switch (tp->t_family) {
        case AF_INET6:
                /* XXX: should use correct direction. */
                hdrsiz = ipsec_hdrsiz(tp->t_template, IPSEC_DIR_OUTBOUND, inp);
                break;
        case AF_INET:
                /* mapped address case - tricky */
        default:
                hdrsiz = 0;
                break;
        }

        return hdrsiz;
}
#endif
#endif /*IPSEC*/

/*
 * Determine the length of the TCP options for this connection.
 *
 * XXX:  What do we do for SACK, when we add that?  Just reserve
 *       all of the space?  Otherwise we can't exactly be incrementing
 *       cwnd by an amount that varies depending on the amount we last
 *       had to SACK!
 */

u_int
tcp_optlen(struct tcpcb *tp)
{
        u_int optlen;

        optlen = 0;
        if ((tp->t_flags & (TF_REQ_TSTMP|TF_RCVD_TSTMP|TF_NOOPT)) ==
            (TF_REQ_TSTMP | TF_RCVD_TSTMP))
                optlen += TCPOLEN_TSTAMP_APPA;

#ifdef TCP_SIGNATURE
        if (tp->t_flags & TF_SIGNATURE)
                optlen += TCPOLEN_SIGLEN;
#endif

        return optlen;
}

u_int
tcp_hdrsz(struct tcpcb *tp)
{
        u_int hlen;

        switch (tp->t_family) {
#ifdef INET6
        case AF_INET6:
                hlen = sizeof(struct ip6_hdr);
                break;
#endif
        case AF_INET:
                hlen = sizeof(struct ip);
                break;
        default:
                hlen = 0;
                break;
        }
        hlen += sizeof(struct tcphdr);

        if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
            (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP)
                hlen += TCPOLEN_TSTAMP_APPA;
#ifdef TCP_SIGNATURE
        if (tp->t_flags & TF_SIGNATURE)
                hlen += TCPOLEN_SIGLEN;
#endif
        return hlen;
}

void
tcp_statinc(u_int stat)
{

        KASSERT(stat < TCP_NSTATS);
        TCP_STATINC(stat);
}

void
tcp_statadd(u_int stat, uint64_t val)
{

        KASSERT(stat < TCP_NSTATS);
        TCP_STATADD(stat, val);
}