/*      $NetBSD: if_sl.c,v 1.136 2022/10/26 23:42:42 riastradh Exp $    */

/*
 * Copyright (c) 1987, 1989, 1992, 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. 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.
 *
 *      @(#)if_sl.c     8.9 (Berkeley) 1/9/95
 */

/*
 * Serial Line interface
 *
 * Rick Adams
 * Center for Seismic Studies
 * 1300 N 17th Street, Suite 1450
 * Arlington, Virginia 22209
 * (703)276-7900
 * rick@seismo.ARPA
 * seismo!rick
 *
 * Pounded on heavily by Chris Torek (chris@mimsy.umd.edu, umcp-cs!chris).
 * N.B.: this belongs in netinet, not net, the way it stands now.
 * Should have a link-layer type designation, but wouldn't be
 * backwards-compatible.
 *
 * Converted to 4.3BSD Beta by Chris Torek.
 * Other changes made at Berkeley, based in part on code by Kirk Smith.
 * W. Jolitz added slip abort.
 *
 * Hacked almost beyond recognition by Van Jacobson (van@helios.ee.lbl.gov).
 * Added priority queuing for "interactive" traffic; hooks for TCP
 * header compression; ICMP filtering (at 2400 baud, some cretin
 * pinging you can use up all your bandwidth).  Made low clist behavior
 * more robust and slightly less likely to hang serial line.
 * Sped up a bunch of things.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: if_sl.c,v 1.136 2022/10/26 23:42:42 riastradh Exp $");

#ifdef _KERNEL_OPT
#include "opt_inet.h"
#endif

#include <sys/param.h>
#include <sys/proc.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/buf.h>
#include <sys/dkstat.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/file.h>
#include <sys/conf.h>
#include <sys/tty.h>
#include <sys/kernel.h>
#include <sys/socketvar.h>
#if __NetBSD__
#include <sys/systm.h>
#include <sys/kauth.h>
#endif
#include <sys/cpu.h>
#include <sys/intr.h>
#include <sys/device.h>
#include <sys/module.h>

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

#ifdef INET
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/in_var.h>
#include <netinet/ip.h>
#endif

#include <net/slcompress.h>
#include <net/if_slvar.h>
#include <net/slip.h>
#include <net/ppp_defs.h>
#include <net/if_ppp.h>

#include <sys/time.h>
#include <net/bpf.h>

#include "ioconf.h"

/*
 * SLMAX is a hard limit on input packet size.  To simplify the code
 * and improve performance, we require that packets fit in an mbuf
 * cluster, and if we get a compressed packet, there's enough extra
 * room to expand the header into a max length tcp/ip header (128
 * bytes).  So, SLMAX can be at most
 *      MCLBYTES - 128
 *
 * SLMTU is a hard limit on output packet size.  To insure good
 * interactive response, SLMTU wants to be the smallest size that
 * amortizes the header cost.  (Remember that even with
 * type-of-service queuing, we have to wait for any in-progress
 * packet to finish.  I.e., we wait, on the average, 1/2 * mtu /
 * cps, where cps is the line speed in characters per second.
 * E.g., 533ms wait for a 1024 byte MTU on a 9600 baud line.  The
 * average compressed header size is 6-8 bytes so any MTU > 90
 * bytes will give us 90% of the line bandwidth.  A 100ms wait is
 * tolerable (500ms is not), so want an MTU around 296.  (Since TCP
 * will send 256 byte segments (to allow for 40 byte headers), the
 * typical packet size on the wire will be around 260 bytes).  In
 * 4.3tahoe+ systems, we can set an MTU in a route so we do that &
 * leave the interface MTU relatively high (so we don't IP fragment
 * when acting as a gateway to someone using a stupid MTU).
 *
 * Similar considerations apply to SLIP_HIWAT:  It's the amount of
 * data that will be queued 'downstream' of us (i.e., in clists
 * waiting to be picked up by the tty output interrupt).  If we
 * queue a lot of data downstream, it's immune to our t.o.s. queuing.
 * E.g., if SLIP_HIWAT is 1024, the interactive traffic in mixed
 * telnet/ftp will see a 1 sec wait, independent of the mtu (the
 * wait is dependent on the ftp window size but that's typically
 * 1k - 4k).  So, we want SLIP_HIWAT just big enough to amortize
 * the cost (in idle time on the wire) of the tty driver running
 * off the end of its clists & having to call back slstart for a
 * new packet.  For a tty interface with any buffering at all, this
 * cost will be zero.  Even with a totally brain dead interface (like
 * the one on a typical workstation), the cost will be <= 1 character
 * time.  So, setting SLIP_HIWAT to ~100 guarantees that we'll lose
 * at most 1% while maintaining good interactive response.
 */
#define BUFOFFSET       (128+sizeof(struct ifnet **)+SLIP_HDRLEN)
#define SLMAX           (MCLBYTES - BUFOFFSET)
#define SLBUFSIZE       (SLMAX + BUFOFFSET)
#ifndef SLMTU
#define SLMTU           296
#endif
#if (SLMTU < 3)
#error SLMTU way too small.
#endif
#define SLIP_HIWAT      roundup(50, TTROUND)
#ifndef __NetBSD__                                      /* XXX - cgd */
#define CLISTRESERVE    1024    /* Can't let clists get too low */
#endif  /* !__NetBSD__ */

/*
 * SLIP ABORT ESCAPE MECHANISM:
 *      (inspired by HAYES modem escape arrangement)
 *      1sec escape 1sec escape 1sec escape { 1sec escape 1sec escape }
 *      within window time signals a "soft" exit from slip mode by remote end
 *      if the IFF_DEBUG flag is on.
 */
#define ABT_ESC         '\033'  /* can't be t_intr - distant host must know it*/
#define ABT_IDLE        1       /* in seconds - idle before an escape */
#define ABT_COUNT       3       /* count of escapes for abort */
#define ABT_WINDOW      (ABT_COUNT*2+2) /* in seconds - time to count */

static int              sl_clone_create(struct if_clone *, int);
static int              sl_clone_destroy(struct ifnet *);

static LIST_HEAD(, sl_softc) sl_softc_list;

struct if_clone sl_cloner =
    IF_CLONE_INITIALIZER("sl", sl_clone_create, sl_clone_destroy);

#define FRAME_END               0xc0            /* Frame End */
#define FRAME_ESCAPE            0xdb            /* Frame Esc */
#define TRANS_FRAME_END         0xdc            /* transposed frame end */
#define TRANS_FRAME_ESCAPE      0xdd            /* transposed frame esc */

static void     slintr(void *);

static int      slcreate(struct sl_softc *);
static struct mbuf *sl_btom(struct sl_softc *, int);

static int      slclose(struct tty *, int);
static int      slinput(int, struct tty *);
static int      slioctl(struct ifnet *, u_long, void *);
static int      slopen(dev_t, struct tty *);
static int      sloutput(struct ifnet *, struct mbuf *, const struct sockaddr *,
                         const struct rtentry *);
static int      slstart(struct tty *);
static int      sltioctl(struct tty *, u_long, void *, int, struct lwp *);

static struct linesw slip_disc = {
        .l_name = "slip",
        .l_open = slopen,
        .l_close = slclose,
        .l_read = ttyerrio,
        .l_write = ttyerrio,
        .l_ioctl = sltioctl,
        .l_rint = slinput,
        .l_start = slstart,
        .l_modem = nullmodem,
        .l_poll = ttyerrpoll
};

void
slattach(int n __unused)
{

        /*
         * Nothing to do here, initialization is handled by the
         * module initialization code in slinit() below).
         */
}

static void
slinit(void)
{

        if (ttyldisc_attach(&slip_disc) != 0)
                panic("%s", __func__);
        LIST_INIT(&sl_softc_list);
        if_clone_attach(&sl_cloner);
}

static int
sldetach(void)
{
        int error = 0;

        if (!LIST_EMPTY(&sl_softc_list))
                error = EBUSY;

        if (error == 0)
                error = ttyldisc_detach(&slip_disc);

        if (error == 0)
                if_clone_detach(&sl_cloner);

        return error;
}

static int
sl_clone_create(struct if_clone *ifc, int unit)
{
        struct sl_softc *sc;

        sc = malloc(sizeof(*sc), M_DEVBUF, M_WAIT|M_ZERO);
        sc->sc_unit = unit;
        if_initname(&sc->sc_if, ifc->ifc_name, unit);
        sc->sc_if.if_softc = sc;
        sc->sc_if.if_mtu = SLMTU;
        sc->sc_if.if_flags = IFF_POINTOPOINT | SC_AUTOCOMP | IFF_MULTICAST;
        sc->sc_if.if_type = IFT_SLIP;
        sc->sc_if.if_ioctl = slioctl;
        sc->sc_if.if_output = sloutput;
        sc->sc_if.if_dlt = DLT_SLIP;
        IFQ_SET_MAXLEN(&sc->sc_fastq, 32);
        IFQ_LOCK_INIT(&sc->sc_fastq);
        IFQ_SET_READY(&sc->sc_if.if_snd);
        if_attach(&sc->sc_if);
        if_alloc_sadl(&sc->sc_if);
        bpf_attach(&sc->sc_if, DLT_SLIP, SLIP_HDRLEN);
        LIST_INSERT_HEAD(&sl_softc_list, sc, sc_iflist);
        return 0;
}

static int
sl_clone_destroy(struct ifnet *ifp)
{
        struct sl_softc *sc = (struct sl_softc *)ifp->if_softc;

        if (sc->sc_ttyp != NULL)
                return EBUSY;   /* Not removing it */

        LIST_REMOVE(sc, sc_iflist);

        bpf_detach(ifp);
        if_detach(ifp);

        IFQ_LOCK_DESTROY(&sc->sc_fastq);

        free(sc, M_DEVBUF);
        return 0;
}

static int
slcreate(struct sl_softc *sc)
{

        if (sc->sc_mbuf == NULL) {
                sc->sc_mbuf = m_gethdr(M_WAIT, MT_DATA);
                m_clget(sc->sc_mbuf, M_WAIT);
        }
        sc->sc_ep = (u_char *)sc->sc_mbuf->m_ext.ext_buf +
            sc->sc_mbuf->m_ext.ext_size;
        sc->sc_mp = sc->sc_pktstart = (u_char *)sc->sc_mbuf->m_ext.ext_buf +
            BUFOFFSET;

#ifdef INET
        sl_compress_init(&sc->sc_comp);
#endif

        return 1;
}

/*
 * Line specific open routine.
 * Attach the given tty to the first available sl unit.
 */
/* ARGSUSED */
static int
slopen(dev_t dev, struct tty *tp)
{
        struct lwp *l = curlwp;         /* XXX */
        struct sl_softc *sc;
        int error;

        error = kauth_authorize_network(l->l_cred, KAUTH_NETWORK_INTERFACE_SLIP,
            KAUTH_REQ_NETWORK_INTERFACE_SLIP_ADD, NULL, NULL, NULL);
        if (error)
                return error;

        if (tp->t_linesw == &slip_disc)
                return 0;

        LIST_FOREACH(sc, &sl_softc_list, sc_iflist)
                if (sc->sc_ttyp == NULL) {
                        sc->sc_si = softint_establish(SOFTINT_NET,
                            slintr, sc);
                        if (sc->sc_si == NULL)
                                return ENOMEM;
                        if (slcreate(sc) == 0) {
                                softint_disestablish(sc->sc_si);
                                return ENOBUFS;
                        }
                        tp->t_sc = (void *)sc;
                        sc->sc_ttyp = tp;
                        sc->sc_if.if_baudrate = tp->t_ospeed;
                        ttylock(tp);
                        tp->t_state |= TS_ISOPEN | TS_XCLUDE;
                        ttyflush(tp, FREAD | FWRITE);
                        /*
                         * make sure tty output queue is large enough
                         * to hold a full-sized packet (including frame
                         * end, and a possible extra frame end).  full-sized
                         * packet occupies a max of 2*SLMAX bytes (because
                         * of possible escapes), and add two on for frame
                         * ends.
                         */
                        if (tp->t_outq.c_cn < 2 * SLMAX + 2) {
                                sc->sc_oldbufsize = tp->t_outq.c_cn;
                                sc->sc_oldbufquot = tp->t_outq.c_cq != 0;

                                clfree(&tp->t_outq);
                                ttyunlock(tp);
                                error = clalloc(&tp->t_outq, 2 * SLMAX + 2, 0);
                                if (error) {
                                        softint_disestablish(sc->sc_si);
                                        /*
                                         * clalloc() might return -1 which
                                         * is no good, so we need to return
                                         * something else.
                                         */
                                        return ENOMEM; /* XXX ?! */
                                }
                        } else {
                                sc->sc_oldbufsize = sc->sc_oldbufquot = 0;
                                ttyunlock(tp);
                        }
                        return 0;
                }
        return ENXIO;
}

/*
 * Line specific close routine.
 * Detach the tty from the sl unit.
 */
static int
slclose(struct tty *tp, int flag)
{
        struct sl_softc *sc;
        int s;

        ttywflush(tp);
        sc = tp->t_sc;

        if (sc != NULL) {
                softint_disestablish(sc->sc_si);
                s = splnet();
                if_down(&sc->sc_if);
                IF_PURGE(&sc->sc_fastq);
                splx(s);

                s = spltty();
                ttyldisc_release(tp->t_linesw);
                tp->t_linesw = ttyldisc_default();
                tp->t_state = 0;

                sc->sc_ttyp = NULL;
                tp->t_sc = NULL;

                m_freem(sc->sc_mbuf);
                sc->sc_mbuf = NULL;
                sc->sc_ep = sc->sc_mp = sc->sc_pktstart = NULL;
                IF_PURGE(&sc->sc_inq);

                /*
                 * If necessary, install a new outq buffer of the
                 * appropriate size.
                 */
                if (sc->sc_oldbufsize != 0) {
                        clfree(&tp->t_outq);
                        clalloc(&tp->t_outq, sc->sc_oldbufsize,
                            sc->sc_oldbufquot);
                }
                splx(s);
        }

        return 0;
}

/*
 * Line specific (tty) ioctl routine.
 * Provide a way to get the sl unit number.
 */
/* ARGSUSED */
static int
sltioctl(struct tty *tp, u_long cmd, void *data, int flag,
    struct lwp *l)
{
        struct sl_softc *sc = (struct sl_softc *)tp->t_sc;

        /*
         * XXX
         * This function can be called without KERNEL_LOCK when caller's
         * struct cdevsw is set D_MPSAFE. Is KERNEL_LOCK required?
         */

        switch (cmd) {
        case SLIOCGUNIT:
                *(int *)data = sc->sc_unit;     /* XXX */
                break;

        default:
                return EPASSTHROUGH;
        }
        return 0;
}

/*
 * Queue a packet.  Start transmission if not active.
 * Compression happens in slintr(); if we do it here, IP TOS
 * will cause us to not compress "background" packets, because
 * ordering gets trashed.  It can be done for all packets in slintr().
 */
static int
sloutput(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst,
    const struct rtentry *rtp)
{
        struct sl_softc *sc = ifp->if_softc;
        struct ip *ip;
        struct ifqueue *ifq = NULL;
        int s, error;

        IFQ_CLASSIFY(&ifp->if_snd, m, dst->sa_family);

        /*
         * `Cannot happen' (see slioctl).  Someday we will extend
         * the line protocol to support other address families.
         */
        if (dst->sa_family != AF_INET) {
                printf("%s: af%d not supported\n", sc->sc_if.if_xname,
                    dst->sa_family);
                m_freem(m);
                if_statinc(&sc->sc_if, if_noproto);
                return EAFNOSUPPORT;
        }

        if (sc->sc_ttyp == NULL) {
                m_freem(m);
                return ENETDOWN;        /* sort of */
        }
        if ((sc->sc_ttyp->t_state & TS_CARR_ON) == 0 &&
            (sc->sc_ttyp->t_cflag & CLOCAL) == 0) {
                m_freem(m);
                printf("%s: no carrier and not local\n", sc->sc_if.if_xname);
                return EHOSTUNREACH;
        }
        ip = mtod(m, struct ip *);
#ifdef INET
        if (sc->sc_if.if_flags & SC_NOICMP && ip->ip_p == IPPROTO_ICMP) {
                m_freem(m);
                return ENETRESET;               /* XXX ? */
        }
#endif

        s = spltty();
        if (sc->sc_oqlen && sc->sc_ttyp->t_outq.c_cc == sc->sc_oqlen) {
                struct bintime bt;

                /* if output's been stalled for too long, and restart */
                getbinuptime(&bt);
                bintime_sub(&bt, &sc->sc_lastpacket);
                if (bt.sec > 0) {
                        sc->sc_otimeout++;
                        slstart(sc->sc_ttyp);
                }
        }
        splx(s);

        s = splnet();
#ifdef INET
        if ((ip->ip_tos & IPTOS_LOWDELAY) != 0)
                ifq = &sc->sc_fastq;
#endif
        if ((error = ifq_enqueue2(ifp, ifq, m)) != 0) {
                splx(s);
                return error;
        }
        getbinuptime(&sc->sc_lastpacket);
        splx(s);

        s = spltty();
        if ((sc->sc_oqlen = sc->sc_ttyp->t_outq.c_cc) == 0)
                slstart(sc->sc_ttyp);
        splx(s);

        return 0;
}

/*
 * Start output on interface.  Get another datagram
 * to send from the interface queue and map it to
 * the interface before starting output.
 */
static int
slstart(struct tty *tp)
{
        struct sl_softc *sc = tp->t_sc;

        /*
         * If there is more in the output queue, just send it now.
         * We are being called in lieu of ttstart and must do what
         * it would.
         */
        if (tp->t_outq.c_cc != 0) {
                (*tp->t_oproc)(tp);
                if (tp->t_outq.c_cc > SLIP_HIWAT)
                        return 0;
        }

        /*
         * This happens briefly when the line shuts down.
         */
        if (sc == NULL)
                return 0;
        softint_schedule(sc->sc_si);
        return 0;
}

/*
 * Copy data buffer to mbuf chain; add ifnet pointer.
 */
static struct mbuf *
sl_btom(struct sl_softc *sc, int len)
{
        struct mbuf *m;

        /*
         * Allocate a new input buffer and swap.
         */
        m = sc->sc_mbuf;
        MGETHDR(sc->sc_mbuf, M_DONTWAIT, MT_DATA);
        if (sc->sc_mbuf == NULL) {
                sc->sc_mbuf = m;
                return NULL;
        }
        MCLGET(sc->sc_mbuf, M_DONTWAIT);
        if ((sc->sc_mbuf->m_flags & M_EXT) == 0) {
                m_freem(sc->sc_mbuf);
                sc->sc_mbuf = m;
                return NULL;
        }
        sc->sc_ep = (u_char *)sc->sc_mbuf->m_ext.ext_buf +
            sc->sc_mbuf->m_ext.ext_size;

        m->m_data = sc->sc_pktstart;

        m->m_pkthdr.len = m->m_len = len;
        m_set_rcvif(m, &sc->sc_if);
        return m;
}

/*
 * tty interface receiver interrupt.
 */
static int
slinput(int c, struct tty *tp)
{
        struct sl_softc *sc;
        struct mbuf *m;
        int len;

        tk_nin++;
        sc = (struct sl_softc *)tp->t_sc;
        if (sc == NULL)
                return 0;
        if ((c & TTY_ERRORMASK) || ((tp->t_state & TS_CARR_ON) == 0 &&
            (tp->t_cflag & CLOCAL) == 0)) {
                sc->sc_flags |= SC_ERROR;
                return 0;
        }
        c &= TTY_CHARMASK;

        if_statinc(&sc->sc_if, if_ibytes);

        if (sc->sc_if.if_flags & IFF_DEBUG) {
                if (c == ABT_ESC) {
                        /*
                         * If we have a previous abort, see whether
                         * this one is within the time limit.
                         */
                        if (sc->sc_abortcount &&
                            time_second >= sc->sc_starttime + ABT_WINDOW)
                                sc->sc_abortcount = 0;
                        /*
                         * If we see an abort after "idle" time, count it;
                         * record when the first abort escape arrived.
                         */
                        if (time_second >= sc->sc_lasttime + ABT_IDLE) {
                                if (++sc->sc_abortcount == 1)
                                        sc->sc_starttime = time_second;
                                if (sc->sc_abortcount >= ABT_COUNT) {
                                        slclose(tp, 0);
                                        return 0;
                                }
                        }
                } else
                        sc->sc_abortcount = 0;
                sc->sc_lasttime = time_second;
        }

        switch (c) {

        case TRANS_FRAME_ESCAPE:
                if (sc->sc_escape)
                        c = FRAME_ESCAPE;
                break;

        case TRANS_FRAME_END:
                if (sc->sc_escape)
                        c = FRAME_END;
                break;

        case FRAME_ESCAPE:
                sc->sc_escape = 1;
                return 0;

        case FRAME_END:
                if (sc->sc_flags & SC_ERROR) {
                        sc->sc_flags &= ~SC_ERROR;
                        goto newpack;
                }
                len = sc->sc_mp - sc->sc_pktstart;
                if (len < 3)
                        /* less than min length packet - ignore */
                        goto newpack;

                m = sl_btom(sc, len);
                if (m == NULL)
                        goto error;

                IF_ENQUEUE(&sc->sc_inq, m);
                softint_schedule(sc->sc_si);
                goto newpack;
        }
        if (sc->sc_mp < sc->sc_ep) {
                *sc->sc_mp++ = c;
                sc->sc_escape = 0;
                return 0;
        }

        /* can't put lower; would miss an extra frame */
        sc->sc_flags |= SC_ERROR;

error:
        if_statinc(&sc->sc_if, if_ierrors);
newpack:
        sc->sc_mp = sc->sc_pktstart = (u_char *)sc->sc_mbuf->m_ext.ext_buf +
            BUFOFFSET;
        sc->sc_escape = 0;

        return 0;
}

static void
slintr(void *arg)
{
        struct sl_softc *sc = arg;
        struct tty *tp = sc->sc_ttyp;
        struct mbuf *m, *n;
        int s, len;
        u_char *pktstart;
        u_char chdr[CHDR_LEN];

        KASSERT(tp != NULL);

        /*
         * Output processing loop.
         */
        mutex_enter(softnet_lock);
        for (;;) {
                struct mbuf *m2;
                struct mbuf *bpf_m;

                /*
                 * Do not remove the packet from the queue if it
                 * doesn't look like it will fit into the current
                 * serial output queue.  With a packet full of
                 * escapes, this could be as bad as MTU*2+2.
                 */
                s = spltty();
                if (tp->t_outq.c_cn - tp->t_outq.c_cc <
                    2 * sc->sc_if.if_mtu + 2) {
                        splx(s);
                        break;
                }
                splx(s);

                /*
                 * Get a packet and send it to the interface.
                 */
                s = splnet();
                IF_DEQUEUE(&sc->sc_fastq, m);
                if (m)
                        if_statinc(&sc->sc_if, if_omcasts);     /* XXX */
                else
                        IFQ_DEQUEUE(&sc->sc_if.if_snd, m);
                splx(s);

                if (m == NULL)
                        break;

                /*
                 * We do the header compression here rather than in
                 * sloutput() because the packets will be out of order
                 * if we are using TOS queueing, and the connection
                 * ID compression will get munged when this happens.
                 */
                if (sc->sc_if.if_bpf) {
                        /*
                         * We need to save the TCP/IP header before
                         * it's compressed.  To avoid complicated
                         * code, we just make a deep copy of the
                         * entire packet (since this is a serial
                         * line, packets should be short and/or the
                         * copy should be negligible cost compared
                         * to the packet transmission time).
                         */
                        bpf_m = m_dup(m, 0, M_COPYALL, M_DONTWAIT);
                } else
                        bpf_m = NULL;
#ifdef INET
                struct ip *ip;
                if ((ip = mtod(m, struct ip *))->ip_p == IPPROTO_TCP) {
                        if (sc->sc_if.if_flags & SC_COMPRESS)
                                *mtod(m, u_char *) |=
                                    sl_compress_tcp(m, ip, &sc->sc_comp, 1);
                }
#endif
                if (bpf_m)
                        bpf_mtap_sl_out(&sc->sc_if, mtod(m, u_char *), bpf_m);
                getbinuptime(&sc->sc_lastpacket);

                s = spltty();

                /*
                 * The extra FRAME_END will start up a new packet,
                 * and thus will flush any accumulated garbage.  We
                 * do this whenever the line may have been idle for
                 * some time.
                 */
                if (tp->t_outq.c_cc == 0) {
                        if_statinc(&sc->sc_if, if_obytes);
                        (void)putc(FRAME_END, &tp->t_outq);
                }

                while (m) {
                        u_char *bp, *cp, *ep;

                        bp = cp = mtod(m, u_char *);
                        ep = cp + m->m_len;
                        while (cp < ep) {
                                /*
                                 * Find out how many bytes in the
                                 * string we can handle without
                                 * doing something special.
                                 */
                                while (cp < ep) {
                                        switch (*cp++) {
                                        case FRAME_ESCAPE:
                                        case FRAME_END:
                                                cp--;
                                                goto out;
                                        }
                                }
                                out:
                                if (cp > bp) {
                                        /*
                                         * Put N characters at once
                                         * into the tty output queue.
                                         */
                                        if (b_to_q(bp, cp - bp, &tp->t_outq))
                                                break;
                                        if_statadd(&sc->sc_if, if_obytes,
                                            cp - bp);
                                }
                                /*
                                 * If there are characters left in
                                 * the mbuf, the first one must be
                                 * special..  Put it out in a different
                                 * form.
                                 */
                                if (cp < ep) {
                                        if (putc(FRAME_ESCAPE, &tp->t_outq))
                                                break;
                                        if (putc(*cp++ == FRAME_ESCAPE ?
                                            TRANS_FRAME_ESCAPE :
                                            TRANS_FRAME_END,
                                            &tp->t_outq)) {
                                                (void)unputc(&tp->t_outq);
                                                break;
                                        }
                                        if_statadd(&sc->sc_if, if_obytes, 2);
                                }
                                bp = cp;
                        }
                        m = m2 = m_free(m);
                }

                if (putc(FRAME_END, &tp->t_outq)) {
                        /*
                         * Not enough room.  Remove a char to make
                         * room and end the packet normally.  If
                         * you get many collisions (more than one
                         * or two a day), you probably do not have
                         * enough clists and you should increase
                         * "nclist" in param.c
                         */
                        (void)unputc(&tp->t_outq);
                        (void)putc(FRAME_END, &tp->t_outq);
                        if_statinc(&sc->sc_if, if_collisions);
                } else {
                        if_statadd2(&sc->sc_if, if_obytes, 1, if_opackets, 1);
                }

                /*
                 * We now have characters in the output queue,
                 * kick the serial port.
                 */
                (*tp->t_oproc)(tp);
                splx(s);
        }

        /*
         * Input processing loop.
         */
        for (;;) {
                s = spltty();
                IF_DEQUEUE(&sc->sc_inq, m);
                splx(s);
                if (m == NULL)
                        break;
                pktstart = mtod(m, u_char *);
                len = m->m_pkthdr.len;
                if (sc->sc_if.if_bpf) {
                        /*
                         * Save the compressed header, so we
                         * can tack it on later.  Note that we
                         * will end up copying garbage in some
                         * cases but this is okay.  We remember
                         * where the buffer started so we can
                         * compute the new header length.
                         */
                        memcpy(chdr, pktstart, CHDR_LEN);
                }
#ifdef INET
                u_char c;
                if ((c = (*pktstart & 0xf0)) != (IPVERSION << 4)) {
                        if (c & 0x80)
                                c = TYPE_COMPRESSED_TCP;
                        else if (c == TYPE_UNCOMPRESSED_TCP)
                                *pktstart &= 0x4f; /* XXX */
                        /*
                         * We've got something that's not an IP
                         * packet.  If compression is enabled,
                         * try to decompress it.  Otherwise, if
                         * `auto-enable' compression is on and
                         * it's a reasonable packet, decompress
                         * it and then enable compression.
                         * Otherwise, drop it.
                         */
                        if (sc->sc_if.if_flags & SC_COMPRESS) {
                                len = sl_uncompress_tcp(&pktstart, len,
                                    (u_int)c, &sc->sc_comp);
                                if (len <= 0) {
                                        m_freem(m);
                                        continue;
                                }
                        } else if ((sc->sc_if.if_flags & SC_AUTOCOMP) &&
                            c == TYPE_UNCOMPRESSED_TCP && len >= 40) {
                                len = sl_uncompress_tcp(&pktstart, len,
                                    (u_int)c, &sc->sc_comp);
                                if (len <= 0) {
                                        m_freem(m);
                                        continue;
                                }
                                sc->sc_if.if_flags |= SC_COMPRESS;
                        } else {
                                m_freem(m);
                                continue;
                        }
                }
#endif
                m->m_data = (void *) pktstart;
                m->m_pkthdr.len = m->m_len = len;
                if (sc->sc_if.if_bpf) {
                        bpf_mtap_sl_in(&sc->sc_if, chdr, &m);
                        if (m == NULL)
                                continue;
                }
                /*
                 * If the packet will fit into a single
                 * header mbuf, try to copy it into one,
                 * to save memory.
                 */
                if ((m->m_pkthdr.len < MHLEN) &&
                    (n = m_gethdr(M_DONTWAIT, MT_DATA))) {
                        int pktlen;

                        pktlen = m->m_pkthdr.len;
                        m_move_pkthdr(n, m);
                        memcpy(mtod(n, void *), mtod(m, void *), pktlen);
                        n->m_len = m->m_len;
                        m_freem(m);
                        m = n;
                }

                if_statinc(&sc->sc_if, if_ipackets);
                getbinuptime(&sc->sc_lastpacket);

#ifdef INET
                s = splnet();
                if (__predict_false(!pktq_enqueue(ip_pktq, m, 0))) {
                        if_statadd2(&sc->sc_if, if_ierrors, 1, if_iqdrops, 1);
                        m_freem(m);
                }
                splx(s);
#endif
        }
        mutex_exit(softnet_lock);
}

/*
 * Process an ioctl request.
 */
static int
slioctl(struct ifnet *ifp, u_long cmd, void *data)
{
        struct ifaddr *ifa = (struct ifaddr *)data;
        struct ifreq *ifr = (struct ifreq *)data;
        int s = splnet(), error = 0;
        struct sl_softc *sc = ifp->if_softc;
        struct ppp_stats *psp;
        struct ppp_comp_stats *pcp;

        switch (cmd) {

        case SIOCINITIFADDR:
                if (ifa->ifa_addr->sa_family == AF_INET)
                        ifp->if_flags |= IFF_UP;
                else
                        error = EAFNOSUPPORT;
                break;

        case SIOCSIFDSTADDR:
                if (ifreq_getaddr(cmd, ifr)->sa_family != AF_INET)
                        error = EAFNOSUPPORT;
                break;

        case SIOCSIFMTU:
                if ((ifr->ifr_mtu < 3) || (ifr->ifr_mtu > SLMAX)) {
                    error = EINVAL;
                    break;
                }
                /*FALLTHROUGH*/
        case SIOCGIFMTU:
                if ((error = ifioctl_common(&sc->sc_if, cmd, data)) == ENETRESET)
                        error = 0;
                break;

        case SIOCADDMULTI:
        case SIOCDELMULTI:
                if (ifr == 0) {
                        error = EAFNOSUPPORT;           /* XXX */
                        break;
                }
                switch (ifreq_getaddr(cmd, ifr)->sa_family) {

#ifdef INET
                case AF_INET:
                        break;
#endif

                default:
                        error = EAFNOSUPPORT;
                        break;
                }
                break;

        case SIOCGPPPSTATS: {
                struct if_data ifi;

                if_export_if_data(&sc->sc_if, &ifi, false);
                psp = &((struct ifpppstatsreq *) data)->stats;
                (void)memset(psp, 0, sizeof(*psp));
                psp->p.ppp_ibytes = ifi.ifi_ibytes;
                psp->p.ppp_ipackets = ifi.ifi_ipackets;
                psp->p.ppp_ierrors = ifi.ifi_ierrors;
                psp->p.ppp_obytes = ifi.ifi_obytes;
                psp->p.ppp_opackets = ifi.ifi_opackets;
                psp->p.ppp_oerrors = ifi.ifi_oerrors;
#ifdef INET
                psp->vj.vjs_packets = sc->sc_comp.sls_packets;
                psp->vj.vjs_compressed = sc->sc_comp.sls_compressed;
                psp->vj.vjs_searches = sc->sc_comp.sls_searches;
                psp->vj.vjs_misses = sc->sc_comp.sls_misses;
                psp->vj.vjs_uncompressedin = sc->sc_comp.sls_uncompressedin;
                psp->vj.vjs_compressedin = sc->sc_comp.sls_compressedin;
                psp->vj.vjs_errorin = sc->sc_comp.sls_errorin;
                psp->vj.vjs_tossed = sc->sc_comp.sls_tossed;
#endif
            }
                break;

        case SIOCGPPPCSTATS:
                pcp = &((struct ifpppcstatsreq *) data)->stats;
                (void)memset(pcp, 0, sizeof(*pcp));
                break;

        default:
                error = ifioctl_common(ifp, cmd, data);
                break;
        }
        splx(s);
        return error;
}


/*
 * Module infrastructure
 */

#include "if_module.h"

IF_MODULE(MODULE_CLASS_DRIVER, sl, "slcompress");