source: rtems/cpukit/libnetworking/netinet/tcp_usrreq.c @ 657e6c93

/*
 * 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.
 * 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 1.120 2005/05/01 14:01:38 rwatson Exp $
 */
 

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "opt_tcpdebug.h"

#include <sys/param.h>
#include <sys/queue.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/protosw.h>
#include <errno.h>
#include <sys/stat.h>

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

#include <netinet/in.h>
#include <rtems/rtems_netinet_in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/in_pcb.h>
#include <netinet/in_var.h>
#include <netinet/ip_var.h>
#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/tcpip.h>
#ifdef TCPDEBUG
#include <netinet/tcp_debug.h>
#endif

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

static int      tcp_attach(struct socket *);
static int      tcp_connect(struct tcpcb *, struct mbuf *);
static struct tcpcb *
                tcp_disconnect(struct tcpcb *);
static struct tcpcb *
                tcp_usrclosed(struct tcpcb *);

#ifdef TCPDEBUG
#define TCPDEBUG0       int ostate
#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, 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, intptr_t proto)
{
        int s = splnet();
        int error;
        struct inpcb *inp = sotoinpcb(so);
        struct tcpcb *tp = 0;
        TCPDEBUG0;

        TCPDEBUG1();
        if (inp) {
                error = EISCONN;
                goto out;
        }

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

        if ((so->so_options & SO_LINGER) && so->so_linger == 0)
                so->so_linger = TCP_LINGERTIME * hz;
        tp = sototcpcb(so);
out:
        TCPDEBUG2(PRU_ATTACH);
        splx(s);
        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 s = splnet();
        int error = 0;
        struct inpcb *inp = sotoinpcb(so);
        struct tcpcb *tp;
        TCPDEBUG0;

        if (inp == 0) {
                splx(s);
                return EINVAL;  /* XXX */
        }
        tp = intotcpcb(inp);
        TCPDEBUG1();
        if (tp->t_state > TCPS_LISTEN)
                tp = tcp_disconnect(tp);
        else
                tp = tcp_close(tp);

        TCPDEBUG2(PRU_DETACH);
        splx(s);
        return error;
}

#define COMMON_START()  TCPDEBUG0; \
                        do { \
                                     if (inp == 0) { \
                                             splx(s); \
                                             return EINVAL; \
                                     } \
                                     tp = intotcpcb(inp); \
                                     TCPDEBUG1(); \
                     } while(0)
                             
#define COMMON_END(req) out: TCPDEBUG2(req); splx(s); return error; goto out


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

        COMMON_START();

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

}

/*
 * Prepare to accept connections.
 */
static int
tcp_usr_listen(struct socket *so)
{
        int s = splnet();
        int error = 0;
        struct inpcb *inp = sotoinpcb(so);
        struct tcpcb *tp;

        COMMON_START();
        if (inp->inp_lport == 0)
                error = in_pcbbind(inp, NULL);
        if (error == 0)
                tp->t_state = TCPS_LISTEN;
        COMMON_END(PRU_LISTEN);
}

/*
 * 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 mbuf *nam)
{
        int s = splnet();
        int error = 0;
        struct inpcb *inp = sotoinpcb(so);
        struct tcpcb *tp;
        struct sockaddr_in *sinp;

        COMMON_START();

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

        if ((error = tcp_connect(tp, nam)) != 0)
                goto out;
        error = tcp_output(tp);
        COMMON_END(PRU_CONNECT);
}

/*
 * 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 s = splnet();
        int error = 0;
        struct inpcb *inp = sotoinpcb(so);
        struct tcpcb *tp;

        COMMON_START();
        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 mbuf *nam)
{
        int s = splnet();
        int error = 0;
        struct inpcb *inp = sotoinpcb(so);
        struct tcpcb *tp;

        COMMON_START();
        in_setpeeraddr(inp, nam);
        COMMON_END(PRU_ACCEPT);
}

/*
 * Mark the connection as being incapable of further output.
 */
static int
tcp_usr_shutdown(struct socket *so)
{
        int s = splnet();
        int error = 0;
        struct inpcb *inp = sotoinpcb(so);
        struct tcpcb *tp;

        COMMON_START();
        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, intptr_t flags)
{
        int s = splnet();
        int error = 0;
        struct inpcb *inp = sotoinpcb(so);
        struct tcpcb *tp;

        COMMON_START();
        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.
 */
static int
tcp_usr_send(struct socket *so, int flags, struct mbuf *m, struct mbuf *nam,
             struct mbuf *control)
{
        int s = splnet();
        int error = 0;
        struct inpcb *inp = sotoinpcb(so);
        struct tcpcb *tp;

        COMMON_START();
        if (control && control->m_len) {
                m_freem(control); /* XXX shouldn't caller do this??? */
                if (m)
                        m_freem(m);
                error = EINVAL;
                goto out;
        }

        if(!(flags & PRUS_OOB)) {
                sbappend(&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.
                         */
                        error = tcp_connect(tp, nam);
                        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)
                        error = tcp_output(tp);
        } else {
                if (sbspace(&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.
                 */
                sbappend(&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.
                         */
                        error = tcp_connect(tp, nam);
                        if (error)
                                goto out;
                        tp->snd_wnd = TTCP_CLIENT_SND_WND;
                        tcp_mss(tp, -1);
                }
                tp->snd_up = tp->snd_una + so->so_snd.sb_cc;
                tp->t_force = 1;
                error = tcp_output(tp);
                tp->t_force = 0;
        }
        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 s = splnet();
        int error = 0;
        struct inpcb *inp = sotoinpcb(so);
        struct tcpcb *tp;

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

/*
 * Fill in st_bklsize for fstat() operations on a socket.
 */
static int
tcp_usr_sense(struct socket *so, struct stat *sb)
{
        int s = splnet();

        sb->st_blksize = so->so_snd.sb_hiwat;
        splx(s);
        return 0;
}

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

        COMMON_START();
        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);
}

static int
tcp_usr_sockaddr(struct socket *so, struct mbuf *nam)
{
        int s = splnet();
        int error = 0;
        struct inpcb *inp = sotoinpcb(so);
        struct tcpcb *tp;

        COMMON_START();
        in_setsockaddr(inp, nam);
        COMMON_END(PRU_SOCKADDR);
}

static int
tcp_usr_peeraddr(struct socket *so, struct mbuf *nam)
{
        int s = splnet();
        int error = 0;
        struct inpcb *inp = sotoinpcb(so);
        struct tcpcb *tp;

        COMMON_START();
        in_setpeeraddr(inp, nam);
        COMMON_END(PRU_PEERADDR);
}

/*
 * XXX - this should just be a call to in_control, but we need to get
 * the types worked out.
 */
static int
tcp_usr_control(struct socket *so, intptr_t cmd, caddr_t arg, struct ifnet *ifp)
{
        return in_control(so, cmd, arg, ifp);
}

/* xxx - should be const */
struct pr_usrreqs tcp_usrreqs = {
        tcp_usr_abort, tcp_usr_accept, tcp_usr_attach, tcp_usr_bind,
        tcp_usr_connect, pru_connect2_notsupp, tcp_usr_control, tcp_usr_detach,
        tcp_usr_disconnect, tcp_usr_listen, tcp_usr_peeraddr, tcp_usr_rcvd,
        tcp_usr_rcvoob, tcp_usr_send, tcp_usr_sense, tcp_usr_shutdown,
        tcp_usr_sockaddr
};

/*
 * 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 mbuf *nam)
{
        struct inpcb *inp = tp->t_inpcb, *oinp;
        struct socket *so = inp->inp_socket;
        struct tcpcb *otp;
        struct sockaddr_in *sin = mtod(nam, struct sockaddr_in *);
        struct sockaddr_in *ifaddr;
        int error;
        struct rmxp_tao *taop;
        struct rmxp_tao tao_noncached;

        if (inp->inp_lport == 0) {
                error = in_pcbbind(inp, NULL);
                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, &ifaddr);
        if (error)
                return error;
        oinp = in_pcblookuphash(inp->inp_pcbinfo,
            sin->sin_addr, sin->sin_port,
            inp->inp_laddr.s_addr != INADDR_ANY ? inp->inp_laddr
                                                : ifaddr->sin_addr,
            inp->inp_lport,  0);
        if (oinp) {
                if (oinp != inp && (otp = intotcpcb(oinp)) != NULL &&
                otp->t_state == TCPS_TIME_WAIT &&
                    otp->t_duration < TCPTV_MSL &&
                    (otp->t_flags & TF_RCVD_CC))
                        otp = tcp_close(otp);
                else
                        return EADDRINUSE;
        }
        if (inp->inp_laddr.s_addr == INADDR_ANY)
                inp->inp_laddr = ifaddr->sin_addr;
        inp->inp_faddr = sin->sin_addr;
        inp->inp_fport = sin->sin_port;
        in_pcbrehash(inp);

        tp->t_template = tcp_template(tp);
        if (tp->t_template == 0) {
                in_pcbdisconnect(inp);
                return ENOBUFS;
        }

        /* Compute window scaling to request.  */
        while (tp->request_r_scale < TCP_MAX_WINSHIFT &&
            (TCP_MAXWIN << tp->request_r_scale) < so->so_rcv.sb_hiwat)
                tp->request_r_scale++;

        soisconnecting(so);
        tcpstat.tcps_connattempt++;
        tp->t_state = TCPS_SYN_SENT;
        tp->t_timer[TCPT_KEEP] = tcp_keepinit;
        tp->iss = tcp_iss; tcp_iss += TCP_ISSINCR/2;
        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)) == 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;
}

int
tcp_ctloutput(int op, struct socket *so, int level, int optname,
    struct mbuf **mp)
{
        int error = 0, s;
        struct inpcb *inp;
        register struct tcpcb *tp;
        register struct mbuf *m;
        register int i;

        s = splnet();
        inp = sotoinpcb(so);
        if (inp == NULL) {
                splx(s);
                if (op == PRCO_SETOPT && *mp)
                        (void) m_free(*mp);
                return (ECONNRESET);
        }
        if (level != IPPROTO_TCP) {
                error = ip_ctloutput(op, so, level, optname, mp);
                splx(s);
                return (error);
        }
        tp = intotcpcb(inp);

        switch (op) {

        case PRCO_SETOPT:
                m = *mp;
                switch (optname) {

                case TCP_NODELAY:
                        if (m == NULL || m->m_len < sizeof (int))
                                error = EINVAL;
                        else if (*mtod(m, int *))
                                tp->t_flags |= TF_NODELAY;
                        else
                                tp->t_flags &= ~TF_NODELAY;
                        break;

                case TCP_MAXSEG:
                        if (m && (i = *mtod(m, int *)) > 0 && i <= tp->t_maxseg)
                                tp->t_maxseg = i;
                        else
                                error = EINVAL;
                        break;

                case TCP_NOOPT:
                        if (m == NULL || m->m_len < sizeof (int))
                                error = EINVAL;
                        else if (*mtod(m, int *))
                                tp->t_flags |= TF_NOOPT;
                        else
                                tp->t_flags &= ~TF_NOOPT;
                        break;

                case TCP_NOPUSH:
                        if (m == NULL || m->m_len < sizeof (int))
                                error = EINVAL;
                        else if (*mtod(m, int *))
                                tp->t_flags |= TF_NOPUSH;
                        else
                                tp->t_flags &= ~TF_NOPUSH;
                        break;

                default:
                        error = ENOPROTOOPT;
                        break;
                }
                if (m)
                        (void) m_free(m);
                break;

        case PRCO_GETOPT:
                *mp = m = m_get(M_WAIT, MT_SOOPTS);
                m->m_len = sizeof(int);

                switch (optname) {
                case TCP_NODELAY:
                        *mtod(m, int *) = tp->t_flags & TF_NODELAY;
                        break;
                case TCP_MAXSEG:
                        *mtod(m, int *) = tp->t_maxseg;
                        break;
                case TCP_NOOPT:
                        *mtod(m, int *) = tp->t_flags & TF_NOOPT;
                        break;
                case TCP_NOPUSH:
                        *mtod(m, int *) = tp->t_flags & TF_NOPUSH;
                        break;
                default:
                        error = ENOPROTOOPT;
                        break;
                }
                break;
        }
        splx(s);
        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).
 */
u_long  tcp_sendspace = 1024*16;
SYSCTL_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace,
        CTLFLAG_RW, &tcp_sendspace , 0, "");
u_long  tcp_recvspace = 1024*16;
SYSCTL_INT(_net_inet_tcp, TCPCTL_RECVSPACE, recvspace,
        CTLFLAG_RW, &tcp_recvspace , 0, "");

#if defined(__rtems__)
void rtems_set_tcp_buffer_sizes(u_long sendspace, u_long recvspace)
{
    if ( sendspace != 0 )
      tcp_sendspace = sendspace;
    if ( recvspace != 0 )
      tcp_recvspace = recvspace;
}
#endif

/*
 * 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)
{
        register struct tcpcb *tp;
        struct inpcb *inp;
        int error;

        if (so->so_snd.sb_hiwat == 0 || so->so_rcv.sb_hiwat == 0) {
                error = soreserve(so, tcp_sendspace, tcp_recvspace);
                if (error)
                        return (error);
        }
        error = in_pcballoc(so, &tcbinfo);
        if (error)
                return (error);
        inp = sotoinpcb(so);
        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 */
                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);
                tp = tcp_usrclosed(tp);
                if (tp)
                        (void) 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)
                        tp->t_timer[TCPT_2MSL] = tcp_maxidle;
        }
        return (tp);
}