[apple/xnu.git] / bsd / net / if_sl.c

/*
 * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This Original Code and all software distributed under the License are
 * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/* Copyright (c) 1995 NeXT Computer, Inc. All Rights Reserved */
/*
 * 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. 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.
 *
 *      @(#)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.
 * 
 * Note that splimp() is used throughout to block both (tty) input
 * interrupts and network activity; thus, splimp must be >= spltty.
 */

#include "sl.h"
#if NSL > 0

#include "bpfilter.h"

#include <sys/param.h>
#include <sys/proc.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/tty.h>
#include <sys/kernel.h>
#include <sys/conf.h>

#include <kern/cpu_number.h>

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

#if INET
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/in_var.h>
#include <netinet/ip.h>
#else
Huh? Slip without inet?
#endif

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

#if NBPFILTER > 0
#include <sys/time.h>
#include <net/bpf.h>
#endif

/*
 * 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.
 */
#if NBPFILTER > 0
#define BUFOFFSET       (128+sizeof(struct ifnet **)+SLIP_HDRLEN)
#else
#define BUFOFFSET       (128+sizeof(struct ifnet **))
#endif
#define SLMAX           (MCLBYTES - BUFOFFSET)
#define SLBUFSIZE       (SLMAX + BUFOFFSET)
#define SLMTU           296
#define SLIP_HIWAT      roundup(50,CBSIZE)

/*
 * 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 */

struct sl_softc sl_softc[NSL];

#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 int slinit __P((struct sl_softc *));
static struct mbuf *sl_btom __P((struct sl_softc *, int));

/*
 * Called from boot code to establish sl interfaces.
 */
void
slattach()
{
        register struct sl_softc *sc;
        register int i = 0;

        for (sc = sl_softc; i < NSL; sc++) {
                sc->sc_if.if_name = "sl";
                sc->sc_if.if_family = APPLE_IF_FAM_SLIP;
                sc->sc_if.if_next = NULL;
                sc->sc_if.if_unit = i++;
                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_snd.ifq_maxlen = 50;
                sc->sc_fastq.ifq_maxlen = 32;
                if_attach(&sc->sc_if);
#if NBPFILTER > 0
                bpfattach(&sc->sc_bpf, &sc->sc_if, DLT_SLIP, SLIP_HDRLEN);
#endif
        }
}

static int
slinit(sc)
        register struct sl_softc *sc;
{
        register caddr_t p;

        if (sc->sc_ep == (u_char *) 0) {
                MCLALLOC(p, M_WAIT);
                if (p)
                        sc->sc_ep = (u_char *)p + SLBUFSIZE;
                else {
                        printf("sl%d: can't allocate buffer\n", sc - sl_softc);
                        sc->sc_if.if_flags &= ~IFF_UP;
                        return (0);
                }
        }
        sc->sc_buf = sc->sc_ep - SLMAX;
        sc->sc_mp = sc->sc_buf;
        sl_compress_init(&sc->sc_comp, -1);
        return (1);
}

/*
 * Line specific open routine.
 * Attach the given tty to the first available sl unit.
 */
/* ARGSUSED */
int
slopen(dev, tp)
        dev_t dev;
        register struct tty *tp;
{
        struct proc *p = curproc;               /* XXX */
        register struct sl_softc *sc;
        register int nsl;
        int error;
        int s;

        if (error = suser(p->p_ucred, &p->p_acflag))
                return (error);

        if (tp->t_line == SLIPDISC)
                return (0);

        for (nsl = NSL, sc = sl_softc; --nsl >= 0; sc++)
                if (sc->sc_ttyp == NULL) {
                        if (slinit(sc) == 0)
                                return (ENOBUFS);
                        tp->t_sc = (caddr_t)sc;
                        sc->sc_ttyp = tp;
                        sc->sc_if.if_baudrate = tp->t_ospeed;
                        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*SLMTU bytes (because
                         * of possible escapes), and add two on for frame
                         * ends.
                         */
                        s = spltty();
                        if (tp->t_outq.c_cn < 2*SLMTU+2) {
                                sc->sc_oldbufsize = tp->t_outq.c_cn;
                                sc->sc_oldbufquot = tp->t_outq.c_cq != 0;

                                clfree(&tp->t_outq);
                                error = clalloc(&tp->t_outq, 3*SLMTU, 0);
                                if (error) {
                                        splx(s);
                                        return(error);
                                }
                        } else
                                sc->sc_oldbufsize = sc->sc_oldbufquot = 0;
                        splx(s);

                        return (0);
                }
        return (ENXIO);
}

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

        ttywflush(tp);
        s = splimp();           /* actually, max(spltty, splnet) */
        tp->t_line = 0;
        tp->t_state = 0;
        sc = (struct sl_softc *)tp->t_sc;
        if (sc != NULL) {
                if_down(&sc->sc_if);
                sc->sc_ttyp = NULL;
                tp->t_sc = NULL;
                MCLFREE((caddr_t)(sc->sc_ep - SLBUFSIZE));
                sc->sc_ep = 0;
                sc->sc_mp = 0;
                sc->sc_buf = 0;
        }
        /* 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);
}

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

        switch (cmd) {
        case SLIOCGUNIT:
                *(int *)data = sc->sc_if.if_unit;
                break;

        default:
                return (-1);
        }
        return (0);
}

/*
 * Queue a packet.  Start transmission if not active.
 * Compression happens in slstart; 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 slstart.
 */
int
sloutput(ifp, m, dst, rtp)
        struct ifnet *ifp;
        register struct mbuf *m;
        struct sockaddr *dst;
        struct rtentry *rtp;
{
        register struct sl_softc *sc = &sl_softc[ifp->if_unit];
        register struct ip *ip;
        register struct ifqueue *ifq;
        int s;

        /*
         * `Cannot happen' (see slioctl).  Someday we will extend
         * the line protocol to support other address families.
         */
        if (dst->sa_family != AF_INET) {
                printf("sl%d: af%d not supported\n", sc->sc_if.if_unit,
                        dst->sa_family);
                m_freem(m);
                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);
                return (EHOSTUNREACH);
        }
        ifq = &sc->sc_if.if_snd;
        ip = mtod(m, struct ip *);
        if (sc->sc_if.if_flags & SC_NOICMP && ip->ip_p == IPPROTO_ICMP) {
                m_freem(m);
                return (ENETRESET);             /* XXX ? */
        }
        if (ip->ip_tos & IPTOS_LOWDELAY)
                ifq = &sc->sc_fastq;
        s = splimp();
        if (sc->sc_oqlen && sc->sc_ttyp->t_outq.c_cc == sc->sc_oqlen) {
                /* if output's been stalled for too long, and restart */
                timersub(&time, &sc->sc_if.if_lastchange, &tv);
                if (tv.tv_sec > 0) {
                        sc->sc_otimeout++;
                        slstart(sc->sc_ttyp);
                }
        }
        if (IF_QFULL(ifq)) {
                IF_DROP(ifq);
                m_freem(m);
                splx(s);
                sc->sc_if.if_oerrors++;
                return (ENOBUFS);
        }
        IF_ENQUEUE(ifq, m);
        sc->sc_if.if_lastchange = time;
        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.
 */
void
slstart(tp)
        register struct tty *tp;
{
        register struct sl_softc *sc = (struct sl_softc *)tp->t_sc;
        register struct mbuf *m;
        register u_char *cp;
        register struct ip *ip;
        int s;
        struct mbuf *m2;
#if NBPFILTER > 0
        u_char bpfbuf[SLMTU + SLIP_HDRLEN];
        register int len;
#endif

        for (;;) {
                /*
                 * 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;
                }
                /*
                 * This happens briefly when the line shuts down.
                 */
                if (sc == NULL)
                        return;

                /*
                 * Do not remove the packet from the IP queue if it
                 * doesn't look like the packet will fit into the
                 * current serial output queue, with a packet full of
                 * escapes this could be as bad as SLMTU*2+2.
                 */
                if (tp->t_outq.c_cn - tp->t_outq.c_cc < 2*SLMTU+2)
                        return;

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

                /*
                 * 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 NBPFILTER > 0
                if (sc->sc_bpf) {
                        /*
                         * We need to save the TCP/IP header before it's
                         * compressed.  To avoid complicated code, we just
                         * copy the entire packet into a stack buffer (since
                         * this is a serial line, packets should be short
                         * and/or the copy should be negligible cost compared
                         * to the packet transmission time).
                         */
                        register struct mbuf *m1 = m;
                        register u_char *cp = bpfbuf + SLIP_HDRLEN;

                        len = 0;
                        do {
                                register int mlen = m1->m_len;

                                bcopy(mtod(m1, caddr_t), cp, mlen);
                                cp += mlen;
                                len += mlen;
                        } while (m1 = m1->m_next);
                }
#endif
                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);
                }
#if NBPFILTER > 0
                if (sc->sc_bpf) {
                        /*
                         * Put the SLIP pseudo-"link header" in place.  The
                         * compressed header is now at the beginning of the
                         * mbuf.
                         */
                        bpfbuf[SLX_DIR] = SLIPDIR_OUT;
                        bcopy(mtod(m, caddr_t), &bpfbuf[SLX_CHDR], CHDR_LEN);
                        BPF_TAP(sc->sc_bpf, bpfbuf, len + SLIP_HDRLEN);
                }
#endif
                sc->sc_if.if_lastchange = time;

                /*
                 * 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) {
                        ++sc->sc_if.if_obytes;
                        (void) putc(FRAME_END, &tp->t_outq);
                }

                while (m) {
                        register u_char *ep;

                        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.
                                 */
                                register u_char *bp = cp;

                                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((u_char *)bp, cp - bp,
                                            &tp->t_outq))
                                                break;
                                        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;
                                        }
                                        sc->sc_if.if_obytes += 2;
                                }
                        }
                        MFREE(m, m2);
                        m = m2;
                }

                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);
                        sc->sc_if.if_collisions++;
                } else {
                        ++sc->sc_if.if_obytes;
                        sc->sc_if.if_opackets++;
                }
        }
}

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

        MGETHDR(m, M_DONTWAIT, MT_DATA);
        if (m == NULL)
                return (NULL);

        /*
         * If we have more than MHLEN bytes, it's cheaper to
         * queue the cluster we just filled & allocate a new one
         * for the input buffer.  Otherwise, fill the mbuf we
         * allocated above.  Note that code in the input routine
         * guarantees that packet will fit in a cluster.
         */
        if (len >= MHLEN) {
                MCLGET(m, M_DONTWAIT);
                if ((m->m_flags & M_EXT) == 0) {
                        /*
                         * we couldn't get a cluster - if memory's this
                         * low, it's time to start dropping packets.
                         */
                        (void) m_free(m);
                        return (NULL);
                }
                sc->sc_ep = mtod(m, u_char *) + SLBUFSIZE;
                m->m_data = (caddr_t)sc->sc_buf;
                m->m_ext.ext_buf = (caddr_t)((long)sc->sc_buf &~ MCLOFSET);
        } else
                bcopy((caddr_t)sc->sc_buf, mtod(m, caddr_t), len);

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

/*
 * tty interface receiver interrupt.
 */
void
slinput(c, tp)
        register int c;
        register struct tty *tp;
{
        register struct sl_softc *sc;
        register struct mbuf *m;
        register int len;
        int s;
#if NBPFILTER > 0
        u_char chdr[CHDR_LEN];
#endif

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

        ++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.tv_sec >= 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.tv_sec >= sc->sc_lasttime + ABT_IDLE) {
                                if (++sc->sc_abortcount == 1)
                                        sc->sc_starttime = time.tv_sec;
                                if (sc->sc_abortcount >= ABT_COUNT) {
                                        slclose(tp);
                                        return;
                                }
                        }
                } else
                        sc->sc_abortcount = 0;
                sc->sc_lasttime = time.tv_sec;
        }

        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;

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

#if NBPFILTER > 0
                if (sc->sc_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.
                         */
                        bcopy(sc->sc_buf, chdr, CHDR_LEN);
                }
#endif

                if ((c = (*sc->sc_buf & 0xf0)) != (IPVERSION << 4)) {
                        if (c & 0x80)
                                c = TYPE_COMPRESSED_TCP;
                        else if (c == TYPE_UNCOMPRESSED_TCP)
                                *sc->sc_buf &= 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(&sc->sc_buf, len,
                                                        (u_int)c, &sc->sc_comp);
                                if (len <= 0)
                                        goto error;
                        } else if ((sc->sc_if.if_flags & SC_AUTOCOMP) &&
                            c == TYPE_UNCOMPRESSED_TCP && len >= 40) {
                                len = sl_uncompress_tcp(&sc->sc_buf, len,
                                                        (u_int)c, &sc->sc_comp);
                                if (len <= 0)
                                        goto error;
                                sc->sc_if.if_flags |= SC_COMPRESS;
                        } else
                                goto error;
                }
#if NBPFILTER > 0
                if (sc->sc_bpf) {
                        /*
                         * Put the SLIP pseudo-"link header" in place.
                         * We couldn't do this any earlier since
                         * decompression probably moved the buffer
                         * pointer.  Then, invoke BPF.
                         */
                        register u_char *hp = sc->sc_buf - SLIP_HDRLEN;

                        hp[SLX_DIR] = SLIPDIR_IN;
                        bcopy(chdr, &hp[SLX_CHDR], CHDR_LEN);
                        BPF_TAP(sc->sc_bpf, hp, len + SLIP_HDRLEN);
                }
#endif
                m = sl_btom(sc, len);
                if (m == NULL)
                        goto error;

                sc->sc_if.if_ipackets++;
                sc->sc_if.if_lastchange = time;
                s = splimp();
                if (IF_QFULL(&ipintrq)) {
                        IF_DROP(&ipintrq);
                        sc->sc_if.if_ierrors++;
                        sc->sc_if.if_iqdrops++;
                        m_freem(m);
                } else {
                        IF_ENQUEUE(&ipintrq, m);
                        schednetisr(NETISR_IP);
                }
                splx(s);
                goto newpack;
        }
        if (sc->sc_mp < sc->sc_ep) {
                *sc->sc_mp++ = c;
                sc->sc_escape = 0;
                return;
        }

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

error:
        sc->sc_if.if_ierrors++;
newpack:
        sc->sc_mp = sc->sc_buf = sc->sc_ep - SLMAX;
        sc->sc_escape = 0;
}

/*
 * Process an ioctl request.
 */
int
slioctl(ifp, cmd, data)
        register struct ifnet *ifp;
        u_long cmd;
        caddr_t data;
{
        register struct ifaddr *ifa = (struct ifaddr *)data;
        register struct ifreq *ifr;
        register int s = splimp(), error = 0;

        switch (cmd) {

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

        case SIOCSIFDSTADDR:
                if (ifa->ifa_addr->sa_family != AF_INET)
                        error = EAFNOSUPPORT;
                break;

        case SIOCADDMULTI:
        case SIOCDELMULTI:
                ifr = (struct ifreq *)data;
                if (ifr == 0) {
                        error = EAFNOSUPPORT;           /* XXX */
                        break;
                }
                switch (ifr->ifr_addr.sa_family) {

#if INET
                case AF_INET:
                        break;
#endif

                default:
                        error = EAFNOSUPPORT;
                        break;
                }
                break;

        default:
                error = EINVAL;
        }
        splx(s);
        return (error);
}
#endif