IPV6 - Attempt to fix tcp46 compatibility listen sockets

[dragonfly.git] / sys / netinet / tcp_usrreq.c

/*
 * Copyright (c) 2003, 2004 Jeffrey M. Hsu.  All rights reserved.
 * Copyright (c) 2003, 2004 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Jeffrey M. Hsu.
 *
 * 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 DragonFly 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 COPYRIGHT HOLDERS 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
 * COPYRIGHT HOLDERS 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, 1993
 *      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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. 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.
 *
 *      From: @(#)tcp_usrreq.c  8.2 (Berkeley) 1/3/94
 * $FreeBSD: src/sys/netinet/tcp_usrreq.c,v 1.51.2.17 2002/10/11 11:46:44 ume Exp $
 * $DragonFly: src/sys/netinet/tcp_usrreq.c,v 1.51 2008/09/29 20:52:23 dillon Exp $
 */

#include "opt_ipsec.h"
#include "opt_inet6.h"
#include "opt_tcpdebug.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/sysctl.h>
#include <sys/globaldata.h>
#include <sys/thread.h>

#include <sys/mbuf.h>
#ifdef INET6
#include <sys/domain.h>
#endif /* INET6 */
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/protosw.h>

#include <sys/thread2.h>
#include <sys/msgport2.h>

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

#include <net/netmsg2.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#ifdef INET6
#include <netinet/ip6.h>
#endif
#include <netinet/in_pcb.h>
#ifdef INET6
#include <netinet6/in6_pcb.h>
#endif
#include <netinet/in_var.h>
#include <netinet/ip_var.h>
#ifdef INET6
#include <netinet6/ip6_var.h>
#include <netinet6/tcp6_var.h>
#endif
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_timer2.h>
#include <netinet/tcp_var.h>
#include <netinet/tcpip.h>
#ifdef TCPDEBUG
#include <netinet/tcp_debug.h>
#endif

#ifdef IPSEC
#include <netinet6/ipsec.h>
#endif /*IPSEC*/

/*
 * TCP protocol interface to socket abstraction.
 */
extern  char *tcpstates[];      /* XXX ??? */

static int      tcp_attach (struct socket *, struct pru_attach_info *);
static int      tcp_connect (struct tcpcb *, struct sockaddr *,
                                struct thread *);
#ifdef INET6
static int      tcp6_connect (struct tcpcb *, struct sockaddr *,
                                struct thread *);
static int      tcp6_connect_oncpu(struct tcpcb *tp, struct sockaddr_in6 *sin6,
                                struct in6_addr *addr6);
#endif /* INET6 */
static struct tcpcb *
                tcp_disconnect (struct tcpcb *);
static struct tcpcb *
                tcp_usrclosed (struct tcpcb *);

#ifdef TCPDEBUG
#define TCPDEBUG0       int ostate = 0
#define TCPDEBUG1()     ostate = tp ? tp->t_state : 0
#define TCPDEBUG2(req)  if (tp && (so->so_options & SO_DEBUG)) \
                                tcp_trace(TA_USER, ostate, tp, 0, 0, req)
#else
#define TCPDEBUG0
#define TCPDEBUG1()
#define TCPDEBUG2(req)
#endif

/*
 * TCP attaches to socket via pru_attach(), reserving space,
 * and an internet control block.
 */
static int
tcp_usr_attach(struct socket *so, int proto, struct pru_attach_info *ai)
{
        int error;
        struct inpcb *inp;
        struct tcpcb *tp = 0;
        TCPDEBUG0;

        crit_enter();
        inp = so->so_pcb;
        TCPDEBUG1();
        if (inp) {
                error = EISCONN;
                goto out;
        }

        error = tcp_attach(so, ai);
        if (error)
                goto out;

        if ((so->so_options & SO_LINGER) && so->so_linger == 0)
                so->so_linger = TCP_LINGERTIME;
        tp = sototcpcb(so);
out:
        TCPDEBUG2(PRU_ATTACH);
        crit_exit();
        return error;
}

/*
 * pru_detach() detaches the TCP protocol from the socket.
 * If the protocol state is non-embryonic, then can't
 * do this directly: have to initiate a pru_disconnect(),
 * which may finish later; embryonic TCB's can just
 * be discarded here.
 */
static int
tcp_usr_detach(struct socket *so)
{
        int error = 0;
        struct inpcb *inp;
        struct tcpcb *tp;
        TCPDEBUG0;

        crit_enter();
        inp = so->so_pcb;

        /*
         * If the inp is already detached it may have been due to an async
         * close.  Just return as if no error occured.
         */
        if (inp == NULL) {
                crit_exit();
                return 0;
        }

        /*
         * It's possible for the tcpcb (tp) to disconnect from the inp due
         * to tcp_drop()->tcp_close() being called.  This may occur *after*
         * the detach message has been queued so we may find a NULL tp here.
         */
        if ((tp = intotcpcb(inp)) != NULL) {
                TCPDEBUG1();
                tp = tcp_disconnect(tp);
                TCPDEBUG2(PRU_DETACH);
        }
        crit_exit();
        return error;
}

/*
 * Note: ignore_error is non-zero for certain disconnection races
 * which we want to silently allow, otherwise close() may return
 * an unexpected error.
 */
#define COMMON_START(so, inp, ignore_error)                     \
        TCPDEBUG0;              \
                                \
        crit_enter();           \
        inp = so->so_pcb;       \
        do {                    \
                 if (inp == NULL) {                             \
                         crit_exit();                           \
                         return (ignore_error ? 0 : EINVAL);    \
                 }                                              \
                 tp = intotcpcb(inp);                           \
                 TCPDEBUG1();                                   \
        } while(0)

#define COMMON_END(req) out: TCPDEBUG2(req); crit_exit(); return error; goto out


/*
 * Give the socket an address.
 */
static int
tcp_usr_bind(struct socket *so, struct sockaddr *nam, struct thread *td)
{
        int error = 0;
        struct inpcb *inp;
        struct tcpcb *tp;
        struct sockaddr_in *sinp;

        COMMON_START(so, inp, 0);

        /*
         * Must check for multicast addresses and disallow binding
         * to them.
         */
        sinp = (struct sockaddr_in *)nam;
        if (sinp->sin_family == AF_INET &&
            IN_MULTICAST(ntohl(sinp->sin_addr.s_addr))) {
                error = EAFNOSUPPORT;
                goto out;
        }
        error = in_pcbbind(inp, nam, td);
        if (error)
                goto out;
        COMMON_END(PRU_BIND);

}

#ifdef INET6
static int
tcp6_usr_bind(struct socket *so, struct sockaddr *nam, struct thread *td)
{
        int error = 0;
        struct inpcb *inp;
        struct tcpcb *tp;
        struct sockaddr_in6 *sin6p;

        COMMON_START(so, inp, 0);

        /*
         * Must check for multicast addresses and disallow binding
         * to them.
         */
        sin6p = (struct sockaddr_in6 *)nam;
        if (sin6p->sin6_family == AF_INET6 &&
            IN6_IS_ADDR_MULTICAST(&sin6p->sin6_addr)) {
                error = EAFNOSUPPORT;
                goto out;
        }
        inp->inp_vflag &= ~INP_IPV4;
        inp->inp_vflag |= INP_IPV6;
        if ((inp->inp_flags & IN6P_IPV6_V6ONLY) == 0) {
                if (IN6_IS_ADDR_UNSPECIFIED(&sin6p->sin6_addr))
                        inp->inp_vflag |= INP_IPV4;
                else if (IN6_IS_ADDR_V4MAPPED(&sin6p->sin6_addr)) {
                        struct sockaddr_in sin;

                        in6_sin6_2_sin(&sin, sin6p);
                        inp->inp_vflag |= INP_IPV4;
                        inp->inp_vflag &= ~INP_IPV6;
                        error = in_pcbbind(inp, (struct sockaddr *)&sin, td);
                        goto out;
                }
        }
        error = in6_pcbbind(inp, nam, td);
        if (error)
                goto out;
        COMMON_END(PRU_BIND);
}
#endif /* INET6 */

#ifdef SMP
struct netmsg_inswildcard {
        struct netmsg           nm_netmsg;
        struct inpcb            *nm_inp;
        struct inpcbinfo        *nm_pcbinfo;
};

static void
in_pcbinswildcardhash_handler(struct netmsg *msg0)
{
        struct netmsg_inswildcard *msg = (struct netmsg_inswildcard *)msg0;

        in_pcbinswildcardhash_oncpu(msg->nm_inp, msg->nm_pcbinfo);
        lwkt_replymsg(&msg->nm_netmsg.nm_lmsg, 0);
}
#endif

/*
 * Prepare to accept connections.
 */
static int
tcp_usr_listen(struct socket *so, struct thread *td)
{
        int error = 0;
        struct inpcb *inp;
        struct tcpcb *tp;
#ifdef SMP
        int cpu;
#endif

        COMMON_START(so, inp, 0);
        if (inp->inp_lport == 0) {
                error = in_pcbbind(inp, NULL, td);
                if (error != 0)
                        goto out;
        }

        tp->t_state = TCPS_LISTEN;
        tp->tt_msg = NULL; /* Catch any invalid timer usage */
#ifdef SMP
        /*
         * We have to set the flag because we can't have other cpus
         * messing with our inp's flags.
         */
        inp->inp_flags |= INP_WILDCARD_MP;
        for (cpu = 0; cpu < ncpus2; cpu++) {
                struct netmsg_inswildcard *msg;

                if (cpu == mycpu->gd_cpuid) {
                        in_pcbinswildcardhash(inp);
                        continue;
                }

                msg = kmalloc(sizeof(struct netmsg_inswildcard), M_LWKTMSG,
                              M_INTWAIT);
                netmsg_init(&msg->nm_netmsg, &netisr_afree_rport, 0,
                            in_pcbinswildcardhash_handler);
                msg->nm_inp = inp;
                msg->nm_pcbinfo = &tcbinfo[cpu];
                lwkt_sendmsg(tcp_cport(cpu), &msg->nm_netmsg.nm_lmsg);
        }
#else
        in_pcbinswildcardhash(inp);
#endif
        COMMON_END(PRU_LISTEN);
}

#ifdef INET6
static int
tcp6_usr_listen(struct socket *so, struct thread *td)
{
        int error = 0;
        struct inpcb *inp;
        struct tcpcb *tp;
#ifdef SMP
        int cpu;
#endif

        COMMON_START(so, inp, 0);
        if (inp->inp_lport == 0) {
                if (!(inp->inp_flags & IN6P_IPV6_V6ONLY))
                        inp->inp_vflag |= INP_IPV4;
                else
                        inp->inp_vflag &= ~INP_IPV4;
                error = in6_pcbbind(inp, NULL, td);
        }
        if (error == 0)
                tp->t_state = TCPS_LISTEN;
#ifdef SMP
        /*
         * We have to set the flag because we can't have other cpus
         * messing with our inp's flags.
         */
        inp->inp_flags |= INP_WILDCARD_MP;
        for (cpu = 0; cpu < ncpus2; cpu++) {
                struct netmsg_inswildcard *msg;

                if (cpu == mycpu->gd_cpuid) {
                        in_pcbinswildcardhash(inp);
                        continue;
                }

                msg = kmalloc(sizeof(struct netmsg_inswildcard), M_LWKTMSG,
                              M_INTWAIT);
                netmsg_init(&msg->nm_netmsg, &netisr_afree_rport, 0,
                            in_pcbinswildcardhash_handler);
                msg->nm_inp = inp;
                msg->nm_pcbinfo = &tcbinfo[cpu];
                lwkt_sendmsg(tcp_cport(cpu), &msg->nm_netmsg.nm_lmsg);
        }
#else
        in_pcbinswildcardhash(inp);
#endif
        COMMON_END(PRU_LISTEN);
}
#endif /* INET6 */

#ifdef SMP
static void
tcp_output_dispatch(struct netmsg *nmsg)
{
        struct lwkt_msg *msg = &nmsg->nm_lmsg;
        struct tcpcb *tp = msg->u.ms_resultp;
        int error;

        error = tcp_output(tp);
        lwkt_replymsg(msg, error);
}
#endif

static int
tcp_conn_output(struct tcpcb *tp)
{
        int error;
#ifdef SMP
        struct inpcb *inp = tp->t_inpcb;
        lwkt_port_t port;

        port = tcp_addrport(inp->inp_faddr.s_addr, inp->inp_fport,
                            inp->inp_laddr.s_addr, inp->inp_lport);
        if (port != &curthread->td_msgport) {
                struct netmsg nmsg;
                struct lwkt_msg *msg;

                netmsg_init(&nmsg, &curthread->td_msgport, 0,
                            tcp_output_dispatch);
                msg = &nmsg.nm_lmsg;
                msg->u.ms_resultp = tp;

                error = lwkt_domsg(port, msg, 0);
        } else
#endif
                error = tcp_output(tp);
        return error;
}

/*
 * Initiate connection to peer.
 * Create a template for use in transmissions on this connection.
 * Enter SYN_SENT state, and mark socket as connecting.
 * Start keep-alive timer, and seed output sequence space.
 * Send initial segment on connection.
 */
static int
tcp_usr_connect(struct socket *so, struct sockaddr *nam, struct thread *td)
{
        int error = 0;
        struct inpcb *inp;
        struct tcpcb *tp;
        struct sockaddr_in *sinp;

        COMMON_START(so, inp, 0);

        /*
         * Must disallow TCP ``connections'' to multicast addresses.
         */
        sinp = (struct sockaddr_in *)nam;
        if (sinp->sin_family == AF_INET
            && IN_MULTICAST(ntohl(sinp->sin_addr.s_addr))) {
                error = EAFNOSUPPORT;
                goto out;
        }

        if (!prison_remote_ip(td, (struct sockaddr*)sinp)) {
                error = EAFNOSUPPORT; /* IPv6 only jail */
                goto out;
        }

        if ((error = tcp_connect(tp, nam, td)) != 0)
                goto out;

        error = tcp_conn_output(tp);

        COMMON_END(PRU_CONNECT);
}

#ifdef INET6
static int
tcp6_usr_connect(struct socket *so, struct sockaddr *nam, struct thread *td)
{
        int error = 0;
        struct inpcb *inp;
        struct tcpcb *tp;
        struct sockaddr_in6 *sin6p;

        COMMON_START(so, inp, 0);

        /*
         * Must disallow TCP ``connections'' to multicast addresses.
         */
        sin6p = (struct sockaddr_in6 *)nam;
        if (sin6p->sin6_family == AF_INET6
            && IN6_IS_ADDR_MULTICAST(&sin6p->sin6_addr)) {
                error = EAFNOSUPPORT;
                goto out;
        }

        if (!prison_remote_ip(td, nam)) {
                error = EAFNOSUPPORT; /* IPv4 only jail */
                goto out;
        }

        if (IN6_IS_ADDR_V4MAPPED(&sin6p->sin6_addr)) {
                struct sockaddr_in sin;

                if ((inp->inp_flags & IN6P_IPV6_V6ONLY) != 0) {
                        error = EINVAL;
                        goto out;
                }

                in6_sin6_2_sin(&sin, sin6p);
                inp->inp_vflag |= INP_IPV4;
                inp->inp_vflag &= ~INP_IPV6;
                if ((error = tcp_connect(tp, (struct sockaddr *)&sin, td)) != 0)
                        goto out;
                error = tcp_conn_output(tp);
                goto out;
        }
        inp->inp_vflag &= ~INP_IPV4;
        inp->inp_vflag |= INP_IPV6;
        inp->inp_inc.inc_isipv6 = 1;
        if ((error = tcp6_connect(tp, nam, td)) != 0)
                goto out;
        error = tcp_output(tp);
        COMMON_END(PRU_CONNECT);
}
#endif /* INET6 */

/*
 * Initiate disconnect from peer.
 * If connection never passed embryonic stage, just drop;
 * else if don't need to let data drain, then can just drop anyways,
 * else have to begin TCP shutdown process: mark socket disconnecting,
 * drain unread data, state switch to reflect user close, and
 * send segment (e.g. FIN) to peer.  Socket will be really disconnected
 * when peer sends FIN and acks ours.
 *
 * SHOULD IMPLEMENT LATER PRU_CONNECT VIA REALLOC TCPCB.
 */
static int
tcp_usr_disconnect(struct socket *so)
{
        int error = 0;
        struct inpcb *inp;
        struct tcpcb *tp;

        COMMON_START(so, inp, 1);
        tp = tcp_disconnect(tp);
        COMMON_END(PRU_DISCONNECT);
}

/*
 * Accept a connection.  Essentially all the work is
 * done at higher levels; just return the address
 * of the peer, storing through addr.
 */
static int
tcp_usr_accept(struct socket *so, struct sockaddr **nam)
{
        int error = 0;
        struct inpcb *inp;
        struct tcpcb *tp = NULL;
        TCPDEBUG0;

        crit_enter();
        inp = so->so_pcb;
        if (so->so_state & SS_ISDISCONNECTED) {
                error = ECONNABORTED;
                goto out;
        }
        if (inp == 0) {
                crit_exit();
                return (EINVAL);
        }
        tp = intotcpcb(inp);
        TCPDEBUG1();
        in_setpeeraddr(so, nam);
        COMMON_END(PRU_ACCEPT);
}

#ifdef INET6
static int
tcp6_usr_accept(struct socket *so, struct sockaddr **nam)
{
        int error = 0;
        struct inpcb *inp;
        struct tcpcb *tp = NULL;
        TCPDEBUG0;

        crit_enter();
        inp = so->so_pcb;

        if (so->so_state & SS_ISDISCONNECTED) {
                error = ECONNABORTED;
                goto out;
        }
        if (inp == 0) {
                crit_exit();
                return (EINVAL);
        }
        tp = intotcpcb(inp);
        TCPDEBUG1();
        in6_mapped_peeraddr(so, nam);
        COMMON_END(PRU_ACCEPT);
}
#endif /* INET6 */
/*
 * Mark the connection as being incapable of further output.
 */
static int
tcp_usr_shutdown(struct socket *so)
{
        int error = 0;
        struct inpcb *inp;
        struct tcpcb *tp;

        COMMON_START(so, inp, 0);
        socantsendmore(so);
        tp = tcp_usrclosed(tp);
        if (tp)
                error = tcp_output(tp);
        COMMON_END(PRU_SHUTDOWN);
}

/*
 * After a receive, possibly send window update to peer.
 */
static int
tcp_usr_rcvd(struct socket *so, int flags)
{
        int error = 0;
        struct inpcb *inp;
        struct tcpcb *tp;

        COMMON_START(so, inp, 0);
        tcp_output(tp);
        COMMON_END(PRU_RCVD);
}

/*
 * Do a send by putting data in output queue and updating urgent
 * marker if URG set.  Possibly send more data.  Unlike the other
 * pru_*() routines, the mbuf chains are our responsibility.  We
 * must either enqueue them or free them.  The other pru_* routines
 * generally are caller-frees.
 */
static int
tcp_usr_send(struct socket *so, int flags, struct mbuf *m,
             struct sockaddr *nam, struct mbuf *control, struct thread *td)
{
        int error = 0;
        struct inpcb *inp;
        struct tcpcb *tp;
#ifdef INET6
        int isipv6;
#endif
        TCPDEBUG0;

        crit_enter();
        inp = so->so_pcb;

        if (inp == NULL) {
                /*
                 * OOPS! we lost a race, the TCP session got reset after
                 * we checked SS_CANTSENDMORE, eg: while doing uiomove or a
                 * network interrupt in the non-critical section of sosend().
                 */
                if (m)
                        m_freem(m);
                if (control)
                        m_freem(control);
                error = ECONNRESET;     /* XXX EPIPE? */
                tp = NULL;
                TCPDEBUG1();
                goto out;
        }
#ifdef INET6
        isipv6 = nam && nam->sa_family == AF_INET6;
#endif /* INET6 */
        tp = intotcpcb(inp);
        TCPDEBUG1();
        if (control) {
                /* TCP doesn't do control messages (rights, creds, etc) */
                if (control->m_len) {
                        m_freem(control);
                        if (m)
                                m_freem(m);
                        error = EINVAL;
                        goto out;
                }
                m_freem(control);       /* empty control, just free it */
        }
        if(!(flags & PRUS_OOB)) {
                ssb_appendstream(&so->so_snd, m);
                if (nam && tp->t_state < TCPS_SYN_SENT) {
                        /*
                         * Do implied connect if not yet connected,
                         * initialize window to default value, and
                         * initialize maxseg/maxopd using peer's cached
                         * MSS.
                         */
#ifdef INET6
                        if (isipv6)
                                error = tcp6_connect(tp, nam, td);
                        else
#endif /* INET6 */
                        error = tcp_connect(tp, nam, td);
                        if (error)
                                goto out;
                        tp->snd_wnd = TTCP_CLIENT_SND_WND;
                        tcp_mss(tp, -1);
                }

                if (flags & PRUS_EOF) {
                        /*
                         * Close the send side of the connection after
                         * the data is sent.
                         */
                        socantsendmore(so);
                        tp = tcp_usrclosed(tp);
                }
                if (tp != NULL) {
                        if (flags & PRUS_MORETOCOME)
                                tp->t_flags |= TF_MORETOCOME;
                        error = tcp_output(tp);
                        if (flags & PRUS_MORETOCOME)
                                tp->t_flags &= ~TF_MORETOCOME;
                }
        } else {
                if (ssb_space(&so->so_snd) < -512) {
                        m_freem(m);
                        error = ENOBUFS;
                        goto out;
                }
                /*
                 * According to RFC961 (Assigned Protocols),
                 * the urgent pointer points to the last octet
                 * of urgent data.  We continue, however,
                 * to consider it to indicate the first octet
                 * of data past the urgent section.
                 * Otherwise, snd_up should be one lower.
                 */
                ssb_appendstream(&so->so_snd, m);
                if (nam && tp->t_state < TCPS_SYN_SENT) {
                        /*
                         * Do implied connect if not yet connected,
                         * initialize window to default value, and
                         * initialize maxseg/maxopd using peer's cached
                         * MSS.
                         */
#ifdef INET6
                        if (isipv6)
                                error = tcp6_connect(tp, nam, td);
                        else
#endif /* INET6 */
                        error = tcp_connect(tp, nam, td);
                        if (error)
                                goto out;
                        tp->snd_wnd = TTCP_CLIENT_SND_WND;
                        tcp_mss(tp, -1);
                }
                tp->snd_up = tp->snd_una + so->so_snd.ssb_cc;
                tp->t_flags |= TF_FORCE;
                error = tcp_output(tp);
                tp->t_flags &= ~TF_FORCE;
        }
        COMMON_END((flags & PRUS_OOB) ? PRU_SENDOOB :
                   ((flags & PRUS_EOF) ? PRU_SEND_EOF : PRU_SEND));
}

/*
 * Abort the TCP.
 */
static int
tcp_usr_abort(struct socket *so)
{
        int error = 0;
        struct inpcb *inp;
        struct tcpcb *tp;

        COMMON_START(so, inp, 1);
        tp = tcp_drop(tp, ECONNABORTED);
        COMMON_END(PRU_ABORT);
}

/*
 * Receive out-of-band data.
 */
static int
tcp_usr_rcvoob(struct socket *so, struct mbuf *m, int flags)
{
        int error = 0;
        struct inpcb *inp;
        struct tcpcb *tp;

        COMMON_START(so, inp, 0);
        if ((so->so_oobmark == 0 &&
             (so->so_state & SS_RCVATMARK) == 0) ||
            so->so_options & SO_OOBINLINE ||
            tp->t_oobflags & TCPOOB_HADDATA) {
                error = EINVAL;
                goto out;
        }
        if ((tp->t_oobflags & TCPOOB_HAVEDATA) == 0) {
                error = EWOULDBLOCK;
                goto out;
        }
        m->m_len = 1;
        *mtod(m, caddr_t) = tp->t_iobc;
        if ((flags & MSG_PEEK) == 0)
                tp->t_oobflags ^= (TCPOOB_HAVEDATA | TCPOOB_HADDATA);
        COMMON_END(PRU_RCVOOB);
}

/* xxx - should be const */
struct pr_usrreqs tcp_usrreqs = {
        .pru_abort = tcp_usr_abort,
        .pru_accept = tcp_usr_accept,
        .pru_attach = tcp_usr_attach,
        .pru_bind = tcp_usr_bind,
        .pru_connect = tcp_usr_connect,
        .pru_connect2 = pru_connect2_notsupp,
        .pru_control = in_control,
        .pru_detach = tcp_usr_detach,
        .pru_disconnect = tcp_usr_disconnect,
        .pru_listen = tcp_usr_listen,
        .pru_peeraddr = in_setpeeraddr,
        .pru_rcvd = tcp_usr_rcvd,
        .pru_rcvoob = tcp_usr_rcvoob,
        .pru_send = tcp_usr_send,
        .pru_sense = pru_sense_null,
        .pru_shutdown = tcp_usr_shutdown,
        .pru_sockaddr = in_setsockaddr,
        .pru_sosend = sosend,
        .pru_soreceive = soreceive,
        .pru_sopoll = sopoll
};

#ifdef INET6
struct pr_usrreqs tcp6_usrreqs = {
        .pru_abort = tcp_usr_abort,
        .pru_accept = tcp6_usr_accept,
        .pru_attach = tcp_usr_attach,
        .pru_bind = tcp6_usr_bind,
        .pru_connect = tcp6_usr_connect,
        .pru_connect2 = pru_connect2_notsupp,
        .pru_control = in6_control,
        .pru_detach = tcp_usr_detach,
        .pru_disconnect = tcp_usr_disconnect,
        .pru_listen = tcp6_usr_listen,
        .pru_peeraddr = in6_mapped_peeraddr,
        .pru_rcvd = tcp_usr_rcvd,
        .pru_rcvoob = tcp_usr_rcvoob,
        .pru_send = tcp_usr_send,
        .pru_sense = pru_sense_null,
        .pru_shutdown = tcp_usr_shutdown,
        .pru_sockaddr = in6_mapped_sockaddr,
        .pru_sosend = sosend,
        .pru_soreceive = soreceive,
        .pru_sopoll = sopoll
};
#endif /* INET6 */

static int
tcp_connect_oncpu(struct tcpcb *tp, struct sockaddr_in *sin,
                  struct sockaddr_in *if_sin)
{
        struct inpcb *inp = tp->t_inpcb, *oinp;
        struct socket *so = inp->inp_socket;
        struct route *ro = &inp->inp_route;
        struct tcpcb *otp;
        struct rmxp_tao *taop;
        struct rmxp_tao tao_noncached;

        oinp = in_pcblookup_hash(&tcbinfo[mycpu->gd_cpuid],
            sin->sin_addr, sin->sin_port,
            inp->inp_laddr.s_addr != INADDR_ANY ?
                inp->inp_laddr : if_sin->sin_addr,
            inp->inp_lport, 0, NULL);
        if (oinp != NULL) {
                if (oinp != inp && (otp = intotcpcb(oinp)) != NULL &&
                    otp->t_state == TCPS_TIME_WAIT &&
                    (ticks - otp->t_starttime) < tcp_msl &&
                    (otp->t_flags & TF_RCVD_CC))
                        tcp_close(otp);
                else
                        return (EADDRINUSE);
        }
        if (inp->inp_laddr.s_addr == INADDR_ANY)
                inp->inp_laddr = if_sin->sin_addr;
        inp->inp_faddr = sin->sin_addr;
        inp->inp_fport = sin->sin_port;
        inp->inp_cpcbinfo = &tcbinfo[mycpu->gd_cpuid];
        in_pcbinsconnhash(inp);

        /*
         * We are now on the inpcb's owner CPU, if the cached route was
         * freed because the rtentry's owner CPU is not the current CPU
         * (e.g. in tcp_connect()), then we try to reallocate it here with
         * the hope that a rtentry may be cloned from a RTF_PRCLONING
         * rtentry.
         */
        if (!(inp->inp_socket->so_options & SO_DONTROUTE) && /*XXX*/
            ro->ro_rt == NULL) {
                bzero(&ro->ro_dst, sizeof(struct sockaddr_in));
                ro->ro_dst.sa_family = AF_INET;
                ro->ro_dst.sa_len = sizeof(struct sockaddr_in);
                ((struct sockaddr_in *)&ro->ro_dst)->sin_addr =
                        sin->sin_addr;
                rtalloc(ro);
        }

        /*
         * Create TCP timer message now; we are on the tcpcb's owner
         * CPU/thread.
         */
        tcp_create_timermsg(tp, &curthread->td_msgport);

        /*
         * Compute window scaling to request.  Use a larger scaling then
         * needed for the initial receive buffer in case the receive buffer
         * gets expanded.
         */
        if (tp->request_r_scale < TCP_MIN_WINSHIFT)
                tp->request_r_scale = TCP_MIN_WINSHIFT;
        while (tp->request_r_scale < TCP_MAX_WINSHIFT &&
               (TCP_MAXWIN << tp->request_r_scale) < so->so_rcv.ssb_hiwat
        ) {
                tp->request_r_scale++;
        }

        soisconnecting(so);
        tcpstat.tcps_connattempt++;
        tp->t_state = TCPS_SYN_SENT;
        tcp_callout_reset(tp, tp->tt_keep, tcp_keepinit, tcp_timer_keep);
        tp->iss = tcp_new_isn(tp);
        tcp_sendseqinit(tp);

        /*
         * Generate a CC value for this connection and
         * check whether CC or CCnew should be used.
         */
        if ((taop = tcp_gettaocache(&tp->t_inpcb->inp_inc)) == NULL) {
                taop = &tao_noncached;
                bzero(taop, sizeof *taop);
        }

        tp->cc_send = CC_INC(tcp_ccgen);
        if (taop->tao_ccsent != 0 &&
            CC_GEQ(tp->cc_send, taop->tao_ccsent)) {
                taop->tao_ccsent = tp->cc_send;
        } else {
                taop->tao_ccsent = 0;
                tp->t_flags |= TF_SENDCCNEW;
        }

        return (0);
}

#ifdef SMP

struct netmsg_tcp_connect {
        struct netmsg           nm_netmsg;
        struct tcpcb            *nm_tp;
        struct sockaddr_in      *nm_sin;
        struct sockaddr_in      *nm_ifsin;
};

static void
tcp_connect_handler(netmsg_t netmsg)
{
        struct netmsg_tcp_connect *msg = (void *)netmsg;
        int error;

        error = tcp_connect_oncpu(msg->nm_tp, msg->nm_sin, msg->nm_ifsin);
        lwkt_replymsg(&msg->nm_netmsg.nm_lmsg, error);
}

struct netmsg_tcp6_connect {
        struct netmsg           nm_netmsg;
        struct tcpcb            *nm_tp;
        struct sockaddr_in6     *nm_sin6;
        struct in6_addr         *nm_addr6;
};

static void
tcp6_connect_handler(netmsg_t netmsg)
{
        struct netmsg_tcp6_connect *msg = (void *)netmsg;
        int error;

        error = tcp6_connect_oncpu(msg->nm_tp, msg->nm_sin6, msg->nm_addr6);
        lwkt_replymsg(&msg->nm_netmsg.nm_lmsg, error);
}

#endif

/*
 * Common subroutine to open a TCP connection to remote host specified
 * by struct sockaddr_in in mbuf *nam.  Call in_pcbbind to assign a local
 * port number if needed.  Call in_pcbladdr to do the routing and to choose
 * a local host address (interface).  If there is an existing incarnation
 * of the same connection in TIME-WAIT state and if the remote host was
 * sending CC options and if the connection duration was < MSL, then
 * truncate the previous TIME-WAIT state and proceed.
 * Initialize connection parameters and enter SYN-SENT state.
 */
static int
tcp_connect(struct tcpcb *tp, struct sockaddr *nam, struct thread *td)
{
        struct inpcb *inp = tp->t_inpcb;
        struct sockaddr_in *sin = (struct sockaddr_in *)nam;
        struct sockaddr_in *if_sin;
        int error;
#ifdef SMP
        lwkt_port_t port;
#endif

        if (inp->inp_lport == 0) {
                error = in_pcbbind(inp, NULL, td);
                if (error)
                        return (error);
        }

        /*
         * Cannot simply call in_pcbconnect, because there might be an
         * earlier incarnation of this same connection still in
         * TIME_WAIT state, creating an ADDRINUSE error.
         */
        error = in_pcbladdr(inp, nam, &if_sin, td);
        if (error)
                return (error);

#ifdef SMP
        port = tcp_addrport(sin->sin_addr.s_addr, sin->sin_port,
            inp->inp_laddr.s_addr ?
                inp->inp_laddr.s_addr : if_sin->sin_addr.s_addr,
            inp->inp_lport);

        if (port != &curthread->td_msgport) {
                struct netmsg_tcp_connect msg;
                struct route *ro = &inp->inp_route;

                /*
                 * in_pcbladdr() may have allocated a route entry for us
                 * on the current CPU, but we need a route entry on the
                 * inpcb's owner CPU, so free it here.
                 */
                if (ro->ro_rt != NULL)
                        RTFREE(ro->ro_rt);
                bzero(ro, sizeof(*ro));

                netmsg_init(&msg.nm_netmsg, &curthread->td_msgport, 0,
                            tcp_connect_handler);
                msg.nm_tp = tp;
                msg.nm_sin = sin;
                msg.nm_ifsin = if_sin;
                error = lwkt_domsg(port, &msg.nm_netmsg.nm_lmsg, 0);
        } else
#endif
                error = tcp_connect_oncpu(tp, sin, if_sin);

        return (error);
}

#ifdef INET6

static int
tcp6_connect(struct tcpcb *tp, struct sockaddr *nam, struct thread *td)
{
        struct inpcb *inp = tp->t_inpcb;
        struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *)nam;
        struct in6_addr *addr6;
        lwkt_port_t port;
        int error;

        if (inp->inp_lport == 0) {
                error = in6_pcbbind(inp, NULL, td);
                if (error)
                        return error;
        }

        /*
         * Cannot simply call in_pcbconnect, because there might be an
         * earlier incarnation of this same connection still in
         * TIME_WAIT state, creating an ADDRINUSE error.
         */
        error = in6_pcbladdr(inp, nam, &addr6, td);
        if (error)
                return error;

#ifdef SMP
        port = tcp6_addrport(); /* XXX hack for now, always cpu0 */

        if (port != &curthread->td_msgport) {
                struct netmsg_tcp6_connect msg;
                struct route *ro = &inp->inp_route;

                /*
                 * in_pcbladdr() may have allocated a route entry for us
                 * on the current CPU, but we need a route entry on the
                 * inpcb's owner CPU, so free it here.
                 */
                if (ro->ro_rt != NULL)
                        RTFREE(ro->ro_rt);
                bzero(ro, sizeof(*ro));

                netmsg_init(&msg.nm_netmsg, &curthread->td_msgport, 0,
                            tcp6_connect_handler);
                msg.nm_tp = tp;
                msg.nm_sin6 = sin6;
                msg.nm_addr6 = addr6;
                error = lwkt_domsg(port, &msg.nm_netmsg.nm_lmsg, 0);
        } else
#endif
                error = tcp6_connect_oncpu(tp, sin6, addr6);

        return (error);
}

static int
tcp6_connect_oncpu(struct tcpcb *tp, struct sockaddr_in6 *sin6,
                   struct in6_addr *addr6)
{
        struct inpcb *inp = tp->t_inpcb;
        struct socket *so = inp->inp_socket;
        struct inpcb *oinp;
        struct tcpcb *otp;
        struct rmxp_tao *taop;
        struct rmxp_tao tao_noncached;

        oinp = in6_pcblookup_hash(inp->inp_cpcbinfo,
                                  &sin6->sin6_addr, sin6->sin6_port,
                                  IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr) ?
                                      addr6 : &inp->in6p_laddr,
                                  inp->inp_lport,  0, NULL);
        if (oinp) {
                if (oinp != inp && (otp = intotcpcb(oinp)) != NULL &&
                    otp->t_state == TCPS_TIME_WAIT &&
                    (ticks - otp->t_starttime) < tcp_msl &&
                    (otp->t_flags & TF_RCVD_CC))
                        otp = tcp_close(otp);
                else
                        return (EADDRINUSE);
        }
        if (IN6_IS_ADDR_UNSPECIFIED(&inp->in6p_laddr))
                inp->in6p_laddr = *addr6;
        inp->in6p_faddr = sin6->sin6_addr;
        inp->inp_fport = sin6->sin6_port;
        if ((sin6->sin6_flowinfo & IPV6_FLOWINFO_MASK) != 0)
                inp->in6p_flowinfo = sin6->sin6_flowinfo;
        in_pcbinsconnhash(inp);

        /* NOTE: must be done in tcpcb's owner thread */
        tcp_create_timermsg(tp, &curthread->td_msgport);

        /* Compute window scaling to request.  */
        if (tp->request_r_scale < TCP_MIN_WINSHIFT)
                tp->request_r_scale = TCP_MIN_WINSHIFT;
        while (tp->request_r_scale < TCP_MAX_WINSHIFT &&
            (TCP_MAXWIN << tp->request_r_scale) < so->so_rcv.ssb_hiwat) {
                tp->request_r_scale++;
        }

        soisconnecting(so);
        tcpstat.tcps_connattempt++;
        tp->t_state = TCPS_SYN_SENT;
        tcp_callout_reset(tp, tp->tt_keep, tcp_keepinit, tcp_timer_keep);
        tp->iss = tcp_new_isn(tp);
        tcp_sendseqinit(tp);

        /*
         * Generate a CC value for this connection and
         * check whether CC or CCnew should be used.
         */
        if ((taop = tcp_gettaocache(&tp->t_inpcb->inp_inc)) == NULL) {
                taop = &tao_noncached;
                bzero(taop, sizeof *taop);
        }

        tp->cc_send = CC_INC(tcp_ccgen);
        if (taop->tao_ccsent != 0 &&
            CC_GEQ(tp->cc_send, taop->tao_ccsent)) {
                taop->tao_ccsent = tp->cc_send;
        } else {
                taop->tao_ccsent = 0;
                tp->t_flags |= TF_SENDCCNEW;
        }

        return (0);
}

#endif /* INET6 */

/*
 * The new sockopt interface makes it possible for us to block in the
 * copyin/out step (if we take a page fault).  Taking a page fault while
 * in a critical section is probably a Bad Thing.  (Since sockets and pcbs
 * both now use TSM, there probably isn't any need for this function to 
 * run in a critical section any more.  This needs more examination.)
 */
int
tcp_ctloutput(struct socket *so, struct sockopt *sopt)
{
        int     error, opt, optval;
        struct  inpcb *inp;
        struct  tcpcb *tp;

        error = 0;
        crit_enter();           /* XXX */
        inp = so->so_pcb;
        if (inp == NULL) {
                crit_exit();
                return (ECONNRESET);
        }
        if (sopt->sopt_level != IPPROTO_TCP) {
#ifdef INET6
                if (INP_CHECK_SOCKAF(so, AF_INET6))
                        error = ip6_ctloutput(so, sopt);
                else
#endif /* INET6 */
                error = ip_ctloutput(so, sopt);
                crit_exit();
                return (error);
        }
        tp = intotcpcb(inp);

        switch (sopt->sopt_dir) {
        case SOPT_SET:
                error = soopt_to_kbuf(sopt, &optval, sizeof optval,
                                      sizeof optval);
                if (error)
                        break;
                switch (sopt->sopt_name) {
                case TCP_NODELAY:
                case TCP_NOOPT:
                        switch (sopt->sopt_name) {
                        case TCP_NODELAY:
                                opt = TF_NODELAY;
                                break;
                        case TCP_NOOPT:
                                opt = TF_NOOPT;
                                break;
                        default:
                                opt = 0; /* dead code to fool gcc */
                                break;
                        }

                        if (optval)
                                tp->t_flags |= opt;
                        else
                                tp->t_flags &= ~opt;
                        break;

                case TCP_NOPUSH:
                        if (optval)
                                tp->t_flags |= TF_NOPUSH;
                        else {
                                tp->t_flags &= ~TF_NOPUSH;
                                error = tcp_output(tp);
                        }
                        break;

                case TCP_MAXSEG:
                        /*
                         * Must be between 0 and maxseg.  If the requested
                         * maxseg is too small to satisfy the desired minmss,
                         * pump it up (silently so sysctl modifications of
                         * minmss do not create unexpected program failures).
                         * Handle degenerate cases.
                         */
                        if (optval > 0 && optval <= tp->t_maxseg) {
                                if (optval + 40 < tcp_minmss) {
                                        optval = tcp_minmss - 40;
                                        if (optval < 0)
                                                optval = 1;
                                }
                                tp->t_maxseg = optval;
                        } else {
                                error = EINVAL;
                        }
                        break;

                default:
                        error = ENOPROTOOPT;
                        break;
                }
                break;

        case SOPT_GET:
                switch (sopt->sopt_name) {
                case TCP_NODELAY:
                        optval = tp->t_flags & TF_NODELAY;
                        break;
                case TCP_MAXSEG:
                        optval = tp->t_maxseg;
                        break;
                case TCP_NOOPT:
                        optval = tp->t_flags & TF_NOOPT;
                        break;
                case TCP_NOPUSH:
                        optval = tp->t_flags & TF_NOPUSH;
                        break;
                default:
                        error = ENOPROTOOPT;
                        break;
                }
                if (error == 0)
                        soopt_from_kbuf(sopt, &optval, sizeof optval);
                break;
        }
        crit_exit();
        return (error);
}

/*
 * tcp_sendspace and tcp_recvspace are the default send and receive window
 * sizes, respectively.  These are obsolescent (this information should
 * be set by the route).
 *
 * Use a default that does not require tcp window scaling to be turned
 * on.  Individual programs or the administrator can increase the default.
 */
u_long  tcp_sendspace = 57344;  /* largest multiple of PAGE_SIZE < 64k */
SYSCTL_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_RW,
    &tcp_sendspace , 0, "Maximum outgoing TCP datagram size");
u_long  tcp_recvspace = 57344;  /* largest multiple of PAGE_SIZE < 64k */
SYSCTL_INT(_net_inet_tcp, TCPCTL_RECVSPACE, recvspace, CTLFLAG_RW,
    &tcp_recvspace , 0, "Maximum incoming TCP datagram size");

/*
 * Attach TCP protocol to socket, allocating
 * internet protocol control block, tcp control block,
 * bufer space, and entering LISTEN state if to accept connections.
 */
static int
tcp_attach(struct socket *so, struct pru_attach_info *ai)
{
        struct tcpcb *tp;
        struct inpcb *inp;
        int error;
        int cpu;
#ifdef INET6
        int isipv6 = INP_CHECK_SOCKAF(so, AF_INET6) != 0;
#endif

        if (so->so_snd.ssb_hiwat == 0 || so->so_rcv.ssb_hiwat == 0) {
                error = soreserve(so, tcp_sendspace, tcp_recvspace,
                                  ai->sb_rlimit);
                if (error)
                        return (error);
        }
        so->so_rcv.ssb_flags |= SSB_AUTOSIZE;
        so->so_snd.ssb_flags |= SSB_AUTOSIZE;
        cpu = mycpu->gd_cpuid;
        error = in_pcballoc(so, &tcbinfo[cpu]);
        if (error)
                return (error);
        inp = so->so_pcb;
#ifdef INET6
        if (isipv6) {
                inp->inp_vflag |= INP_IPV6;
                inp->in6p_hops = -1;    /* use kernel default */
        }
        else
#endif
        inp->inp_vflag |= INP_IPV4;
        tp = tcp_newtcpcb(inp);
        if (tp == 0) {
                int nofd = so->so_state & SS_NOFDREF;   /* XXX */

                so->so_state &= ~SS_NOFDREF;    /* don't free the socket yet */
#ifdef INET6
                if (isipv6)
                        in6_pcbdetach(inp);
                else
#endif
                in_pcbdetach(inp);
                so->so_state |= nofd;
                return (ENOBUFS);
        }
        tp->t_state = TCPS_CLOSED;
        return (0);
}

/*
 * Initiate (or continue) disconnect.
 * If embryonic state, just send reset (once).
 * If in ``let data drain'' option and linger null, just drop.
 * Otherwise (hard), mark socket disconnecting and drop
 * current input data; switch states based on user close, and
 * send segment to peer (with FIN).
 */
static struct tcpcb *
tcp_disconnect(struct tcpcb *tp)
{
        struct socket *so = tp->t_inpcb->inp_socket;

        if (tp->t_state < TCPS_ESTABLISHED)
                tp = tcp_close(tp);
        else if ((so->so_options & SO_LINGER) && so->so_linger == 0)
                tp = tcp_drop(tp, 0);
        else {
                soisdisconnecting(so);
                sbflush(&so->so_rcv.sb);
                tp = tcp_usrclosed(tp);
                if (tp)
                        tcp_output(tp);
        }
        return (tp);
}

/*
 * User issued close, and wish to trail through shutdown states:
 * if never received SYN, just forget it.  If got a SYN from peer,
 * but haven't sent FIN, then go to FIN_WAIT_1 state to send peer a FIN.
 * If already got a FIN from peer, then almost done; go to LAST_ACK
 * state.  In all other cases, have already sent FIN to peer (e.g.
 * after PRU_SHUTDOWN), and just have to play tedious game waiting
 * for peer to send FIN or not respond to keep-alives, etc.
 * We can let the user exit from the close as soon as the FIN is acked.
 */
static struct tcpcb *
tcp_usrclosed(struct tcpcb *tp)
{

        switch (tp->t_state) {

        case TCPS_CLOSED:
        case TCPS_LISTEN:
                tp->t_state = TCPS_CLOSED;
                tp = tcp_close(tp);
                break;

        case TCPS_SYN_SENT:
        case TCPS_SYN_RECEIVED:
                tp->t_flags |= TF_NEEDFIN;
                break;

        case TCPS_ESTABLISHED:
                tp->t_state = TCPS_FIN_WAIT_1;
                break;

        case TCPS_CLOSE_WAIT:
                tp->t_state = TCPS_LAST_ACK;
                break;
        }
        if (tp && tp->t_state >= TCPS_FIN_WAIT_2) {
                soisdisconnected(tp->t_inpcb->inp_socket);
                /* To prevent the connection hanging in FIN_WAIT_2 forever. */
                if (tp->t_state == TCPS_FIN_WAIT_2) {
                        tcp_callout_reset(tp, tp->tt_2msl, tcp_maxidle,
                            tcp_timer_2msl);
                }
        }
        return (tp);
}