Remove /* within block comment.

[dragonfly/netmp.git] / sys / net / sl / if_sl.c

/*
 * 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     8.6 (Berkeley) 2/1/94
 * $FreeBSD: src/sys/net/if_sl.c,v 1.84.2.2 2002/02/13 00:43:10 dillon Exp $
 * $DragonFly: src/sys/net/sl/if_sl.c,v 1.32 2008/05/14 11:59:23 sephe Exp $
 */

/*
 * 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 "use_sl.h"

#include "opt_inet.h"
#if !defined(KLD_MODULE)
#include "opt_slip.h"
#endif
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/dkstat.h>
#include <sys/socket.h>
#include <sys/sockio.h>
#include <sys/fcntl.h>
#include <sys/signalvar.h>
#include <sys/tty.h>
#include <sys/clist.h>
#include <sys/kernel.h>
#include <sys/conf.h>
#include <sys/thread2.h>

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

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

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

#include <net/bpf.h>

static void slattach (void *);
PSEUDO_SET(slattach, if_sl);

/*
 * SLRMAX 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, SLRMAX can be at most
 *      MCLBYTES - 128
 *
 * SLMTU is the default transmit MTU. The transmit MTU should be kept
 * small enough so that interactive use doesn't suffer, but large
 * enough to provide good performance. 552 is a good choice for SLMTU
 * because it is high enough to not fragment TCP packets being routed
 * through this host. Packet fragmentation is bad with SLIP because
 * fragment headers aren't compressed. The previous assumptions about
 * the best MTU value don't really hold when using modern modems with
 * BTLZ data compression because the modem buffers play a much larger
 * role in interactive performance than the MTU. The MTU can be changed
 * at any time to suit the specific environment with ifconfig(8), and
 * its maximum value is defined as SLTMAX. SLTMAX must not be so large
 * that it would overflow the stack if BPF is configured (XXX; if_ppp.c
 * handles this better).
 *
 * SLIP_HIWAT is 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 SLRMAX          (MCLBYTES - BUFOFFSET)
#define SLBUFSIZE       (SLRMAX + BUFOFFSET)
#ifndef SLMTU
#define SLMTU           552             /* default MTU */
#endif
#define SLTMAX          1500            /* maximum MTU */
#define SLIP_HIWAT      roundup(50,CBSIZE)
#define CLISTRESERVE    1024            /* Can't let clists get too low */

/*
 * 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 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 (struct sl_softc *);
static struct mbuf *sl_btom (struct sl_softc *, int);
static timeout_t sl_keepalive;
static timeout_t sl_outfill;
static int      slclose (struct tty *,int);
static int      slinput (int, struct tty *);
static int      slioctl (struct ifnet *, u_long, caddr_t, struct ucred *);
static int      sltioctl (struct tty *, u_long, caddr_t, int, struct ucred *);
static int      slopen (cdev_t, struct tty *);
static int      sloutput (struct ifnet *,
            struct mbuf *, struct sockaddr *, struct rtentry *);
static int      slstart (struct tty *);

static struct linesw slipdisc = {
        slopen,         slclose,        l_noread,       l_nowrite,
        sltioctl,       slinput,        slstart,        ttymodem,
        FRAME_END
};

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

        linesw[SLIPDISC] = slipdisc;

        for (sc = sl_softc; i < NSL; sc++) {
                if_initname(&(sc->sc_if), "sl", i++);
                sc->sc_if.if_mtu = SLMTU;
                sc->sc_if.if_flags =
#ifdef SLIP_IFF_OPTS
                    SLIP_IFF_OPTS;
#else
                    IFF_POINTOPOINT | SC_AUTOCOMP | IFF_MULTICAST;
#endif
                sc->sc_if.if_type = IFT_SLIP;
                sc->sc_if.if_ioctl = slioctl;
                sc->sc_if.if_output = sloutput;
                ifq_set_maxlen(&sc->sc_if.if_snd, 50);
                ifq_set_ready(&sc->sc_if.if_snd);
                sc->sc_fastq.ifq_maxlen = 32;
                sc->sc_if.if_linkmib = sc;
                sc->sc_if.if_linkmiblen = sizeof *sc;
                callout_init(&sc->sc_oftimeout);
                callout_init(&sc->sc_katimeout);
                if_attach(&sc->sc_if, NULL);
                bpfattach(&sc->sc_if, DLT_SLIP, SLIP_HDRLEN);
        }
}

static int
slinit(struct sl_softc *sc)
{
        if (sc->sc_ep == NULL)
                sc->sc_ep = kmalloc(SLBUFSIZE, M_DEVBUF, M_WAITOK);
        sc->sc_buf = sc->sc_ep + SLBUFSIZE - SLRMAX;
        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 */
static int
slopen(cdev_t dev, struct tty *tp)
{
        struct sl_softc *sc;
        int nsl;
        int error;
        struct thread *td = curthread;  /* XXX */

        error = suser(td);
        if (error)
                return (error);

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

        for (nsl = NSL, sc = sl_softc; --nsl >= 0; sc++)
                if (sc->sc_ttyp == NULL && !(sc->sc_flags & SC_STATIC)) {
                        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);

                        tp->t_line = SLIPDISC;
                        /*
                         * We don't use t_canq or t_rawq, so reduce their
                         * cblock resources to 0.  Reserve enough cblocks
                         * for t_outq to guarantee that we can fit a full
                         * packet if the SLIP_HIWAT check allows slstart()
                         * to loop.  Use the same value for the cblock
                         * limit since the reserved blocks should always
                         * be enough.  Reserving cblocks probably makes
                         * the CLISTRESERVE check unnecessary and wasteful.
                         */
                        clist_alloc_cblocks(&tp->t_canq, 0, 0);
                        clist_alloc_cblocks(&tp->t_outq,
                            SLIP_HIWAT + 2 * sc->sc_if.if_mtu + 1,
                            SLIP_HIWAT + 2 * sc->sc_if.if_mtu + 1);
                        clist_alloc_cblocks(&tp->t_rawq, 0, 0);

                        crit_enter();
                        if_up(&sc->sc_if);
                        crit_exit();
                        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;

        ttyflush(tp, FREAD | FWRITE);
        crit_enter();

        clist_free_cblocks(&tp->t_outq);
        tp->t_line = 0;
        sc = (struct sl_softc *)tp->t_sc;
        if (sc != NULL) {
                if (sc->sc_outfill) {
                        sc->sc_outfill = 0;
                        callout_stop(&sc->sc_oftimeout);
                }
                if (sc->sc_keepalive) {
                        sc->sc_keepalive = 0;
                        callout_stop(&sc->sc_katimeout);
                }
                if_down(&sc->sc_if);
                sc->sc_flags &= SC_STATIC;
                sc->sc_ttyp = NULL;
                tp->t_sc = NULL;
                if (sc->sc_ep) {
                        kfree(sc->sc_ep, M_DEVBUF);
                        sc->sc_ep = NULL;
                }
                sc->sc_mp = 0;
                sc->sc_buf = 0;
        }
        crit_exit();
        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, caddr_t data, int flag, struct ucred *cred)
{
        struct sl_softc *sc = (struct sl_softc *)tp->t_sc, *nc, *tmpnc;
        int nsl;

        crit_enter();

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

        case SLIOCSUNIT:
                if (sc->sc_if.if_dunit != *(u_int *)data) {
                        for (nsl = NSL, nc = sl_softc; --nsl >= 0; nc++) {
                                if (   nc->sc_if.if_dunit == *(u_int *)data
                                    && nc->sc_ttyp == NULL
                                   ) {
                                        tmpnc = kmalloc(sizeof *tmpnc, M_TEMP,
                                                       M_WAITOK);
                                        *tmpnc = *nc;
                                        *nc = *sc;
                                        nc->sc_if = tmpnc->sc_if;
                                        tmpnc->sc_if = sc->sc_if;
                                        *sc = *tmpnc;
                                        kfree(tmpnc, M_TEMP);
                                        if (sc->sc_if.if_flags & IFF_UP) {
                                                if_down(&sc->sc_if);
                                                if (!(nc->sc_if.if_flags & IFF_UP))
                                                        if_up(&nc->sc_if);
                                        } else if (nc->sc_if.if_flags & IFF_UP)
                                                if_down(&nc->sc_if);
                                        sc->sc_flags &= ~SC_STATIC;
                                        sc->sc_flags |= (nc->sc_flags & SC_STATIC);
                                        tp->t_sc = sc = nc;
                                        clist_alloc_cblocks(&tp->t_outq,
                                            SLIP_HIWAT + 2 * sc->sc_if.if_mtu + 1,
                                            SLIP_HIWAT + 2 * sc->sc_if.if_mtu + 1);
                                        sl_compress_init(&sc->sc_comp, -1);
                                        goto slfound;
                                }
                        }
                        crit_exit();
                        return (ENXIO);
                }
        slfound:
                sc->sc_flags |= SC_STATIC;
                break;

        case SLIOCSKEEPAL:
                sc->sc_keepalive = *(u_int *)data * hz;
                if (sc->sc_keepalive) {
                        sc->sc_flags |= SC_KEEPALIVE;
                        callout_reset(&sc->sc_katimeout, sc->sc_keepalive,
                                        sl_keepalive, sc);
                } else {
                        if ((sc->sc_flags & SC_KEEPALIVE) != 0) {
                                callout_stop(&sc->sc_katimeout);
                                sc->sc_flags &= ~SC_KEEPALIVE;
                        }
                }
                break;

        case SLIOCGKEEPAL:
                *(int *)data = sc->sc_keepalive / hz;
                break;

        case SLIOCSOUTFILL:
                sc->sc_outfill = *(u_int *)data * hz;
                if (sc->sc_outfill) {
                        sc->sc_flags |= SC_OUTWAIT;
                        callout_reset(&sc->sc_oftimeout, sc->sc_outfill, 
                                        sl_outfill, sc);
                } else {
                        if ((sc->sc_flags & SC_OUTWAIT) != 0) {
                                callout_stop(&sc->sc_oftimeout);
                                sc->sc_flags &= ~SC_OUTWAIT;
                        }
                }
                break;

        case SLIOCGOUTFILL:
                *(int *)data = sc->sc_outfill / hz;
                break;

        default:
                crit_exit();
                return (ENOIOCTL);
        }
        crit_exit();
        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.
 */
static int
sloutput_serialized(struct ifnet *ifp, struct mbuf *m, struct sockaddr *dst,
                    struct rtentry *rtp)
{
        struct sl_softc *sc = &sl_softc[ifp->if_dunit];
        struct ip *ip;
        int error;
        struct altq_pktattr pktattr;

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

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

        if (sc->sc_ttyp == NULL || !(ifp->if_flags & IFF_UP)) {
                m_freem(m);
                return (ENETDOWN);
        }
        if ((sc->sc_ttyp->t_state & TS_CONNECTED) == 0) {
                m_freem(m);
                return (EHOSTUNREACH);
        }
        ip = mtod(m, struct ip *);
        if (sc->sc_if.if_flags & SC_NOICMP && ip->ip_p == IPPROTO_ICMP) {
                m_freem(m);
                return (ENETRESET);             /* XXX ? */
        }

        crit_enter();

        if ((ip->ip_tos & IPTOS_LOWDELAY) && !ifq_is_enabled(&sc->sc_if.if_snd)) {
                if (IF_QFULL(&sc->sc_fastq)) {
                        IF_DROP(&sc->sc_fastq);
                        m_freem(m);
                        error = ENOBUFS;
                } else {
                        IF_ENQUEUE(&sc->sc_fastq, m);
                        error = 0;
                }
        } else {
                error = ifq_enqueue(&sc->sc_if.if_snd, m, &pktattr);
        }
        if (error) {
                sc->sc_if.if_oerrors++;
                crit_exit();
                return (error);
        }
        if (sc->sc_ttyp->t_outq.c_cc == 0)
                slstart(sc->sc_ttyp);
        crit_exit();
        return (0);
}

static int
sloutput(struct ifnet *ifp, struct mbuf *m, struct sockaddr *dst,
         struct rtentry *rtp)
{
        int error;

        lwkt_serialize_enter(ifp->if_serializer);
        error = sloutput_serialized(ifp, m, dst, rtp);
        lwkt_serialize_exit(ifp->if_serializer);

        return error;
}

/*
 * 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 = (struct sl_softc *)tp->t_sc;
        struct mbuf *m;
        u_char *cp;
        struct ip *ip;
        u_char bpfbuf[SLTMAX + SLIP_HDRLEN];
        int len = 0;

        for (;;) {
                /*
                 * Call output process whether or not there is more in the
                 * output queue.  We are being called in lieu of ttstart
                 * and must do what it would.
                 */
                (*tp->t_oproc)(tp);

                if (tp->t_outq.c_cc != 0) {
                        if (sc != NULL)
                                sc->sc_flags &= ~SC_OUTWAIT;
                        if (tp->t_outq.c_cc > SLIP_HIWAT)
                                return 0;
                }

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

                /*
                 * Get a packet and send it to the interface.
                 */
                crit_enter();
                IF_DEQUEUE(&sc->sc_fastq, m);
                if (m)
                        sc->sc_if.if_omcasts++;         /* XXX */
                else
                        m = ifq_dequeue(&sc->sc_if.if_snd, NULL);
                crit_exit();
                if (m == NULL)
                        return 0;

                /*
                 * 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
                         * 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).
                         */
                        struct mbuf *m1 = m;
                        u_char *cp = bpfbuf + SLIP_HDRLEN;

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

                                bcopy(mtod(m1, caddr_t), cp, mlen);
                                cp += mlen;
                                len += mlen;
                        } while ((m1 = m1->m_next) != NULL);
                }
                ip = mtod(m, struct ip *);
                if (ip->ip_v == IPVERSION && 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 (sc->sc_if.if_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_if.if_bpf, bpfbuf, len + SLIP_HDRLEN);
                }

                /*
                 * If system is getting low on clists, just flush our
                 * output queue (if the stuff was important, it'll get
                 * retransmitted). Note that SLTMAX is used instead of
                 * the current if_mtu setting because connections that
                 * have already been established still use the original
                 * (possibly larger) mss.
                 */
                if (cfreecount < CLISTRESERVE + SLTMAX) {
                        m_freem(m);
                        sc->sc_if.if_collisions++;
                        continue;
                }

                sc->sc_flags &= ~SC_OUTWAIT;
                /*
                 * 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;
                        clist_putc(FRAME_END, &tp->t_outq);
                }

                while (m) {
                        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.
                                 */
                                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((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 (clist_putc(FRAME_ESCAPE, &tp->t_outq))
                                                break;
                                        if (clist_putc(*cp++ == FRAME_ESCAPE ?
                                           TRANS_FRAME_ESCAPE : TRANS_FRAME_END,
                                           &tp->t_outq)) {
                                                clist_unputc(&tp->t_outq);
                                                break;
                                        }
                                        sc->sc_if.if_obytes += 2;
                                }
                        }
                        m = m_free(m);
                }

                if (clist_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.
                         */
                        clist_unputc(&tp->t_outq);
                        clist_putc(FRAME_END, &tp->t_outq);
                        sc->sc_if.if_collisions++;
                } else {
                        ++sc->sc_if.if_obytes;
                        sc->sc_if.if_opackets++;
                }
        }
        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;

        if (len >= MCLBYTES)
                return (NULL);

        MGETHDR(m, MB_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, MB_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.
                         */
                        m_free(m);
                        return (NULL);
                }
        }
        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.
 */
static int
slinput(int c, struct tty *tp)
{
        struct sl_softc *sc;
        struct mbuf *m;
        int len;
        u_char chdr[CHDR_LEN];

        tk_nin++;
        sc = (struct sl_softc *)tp->t_sc;
        if (sc == NULL)
                return 0;
        if (c & TTY_ERRORMASK || (tp->t_state & TS_CONNECTED) == 0) {
                sc->sc_flags |= SC_ERROR;
                return 0;
        }
        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_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:
                sc->sc_flags &= ~SC_KEEPALIVE;
                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 (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.
                         */
                        bcopy(sc->sc_buf, chdr, CHDR_LEN);
                }

                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 (sc->sc_if.if_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.
                         */
                        u_char *hp = sc->sc_buf - SLIP_HDRLEN;

                        hp[SLX_DIR] = SLIPDIR_IN;
                        bcopy(chdr, &hp[SLX_CHDR], CHDR_LEN);
                        bpf_tap(sc->sc_if.if_bpf, hp, len + SLIP_HDRLEN);
                }
                m = sl_btom(sc, len);
                if (m == NULL)
                        goto error;

                sc->sc_if.if_ipackets++;

                if ((sc->sc_if.if_flags & IFF_UP) == 0) {
                        m_freem(m);
                        goto newpack;
                }

                if (netisr_queue(NETISR_IP, m)) {
                        sc->sc_if.if_ierrors++;
                        sc->sc_if.if_iqdrops++;
                }

                goto newpack;
        }
        if (sc->sc_mp < sc->sc_ep + SLBUFSIZE) {
                *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:
        sc->sc_if.if_ierrors++;
newpack:
        sc->sc_mp = sc->sc_buf = sc->sc_ep + SLBUFSIZE - SLRMAX;
        sc->sc_escape = 0;
        return 0;
}

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

        crit_enter();

        switch (cmd) {

        case SIOCSIFFLAGS:
                /*
                 * if.c will set the interface up even if we
                 * don't want it to.
                 */
                if (sl_softc[ifp->if_dunit].sc_ttyp == NULL) {
                        ifp->if_flags &= ~IFF_UP;
                }
                break;
        case SIOCSIFADDR:
                /*
                 * This is "historical" - set the interface up when
                 * setting the address.
                 */
                if (ifa->ifa_addr->sa_family == AF_INET) {
                        if (sl_softc[ifp->if_dunit].sc_ttyp != NULL)
                                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:
                break;

        case SIOCSIFMTU:
                /*
                 * Set the interface MTU.
                 */
                if (ifr->ifr_mtu > SLTMAX)
                        error = EINVAL;
                else {
                        struct tty *tp;

                        ifp->if_mtu = ifr->ifr_mtu;
                        tp = sl_softc[ifp->if_dunit].sc_ttyp;
                        if (tp != NULL)
                                clist_alloc_cblocks(&tp->t_outq,
                                    SLIP_HIWAT + 2 * ifp->if_mtu + 1,
                                    SLIP_HIWAT + 2 * ifp->if_mtu + 1);
                }
                break;

        default:
                error = EINVAL;
        }

        crit_exit();
        return (error);
}

static void
sl_keepalive(void *chan)
{
        struct sl_softc *sc = chan;

        if (sc->sc_keepalive) {
                if (sc->sc_flags & SC_KEEPALIVE)
                        pgsignal (sc->sc_ttyp->t_pgrp, SIGURG, 1);
                else
                        sc->sc_flags |= SC_KEEPALIVE;
                callout_reset(&sc->sc_katimeout, sc->sc_keepalive,
                                sl_keepalive, sc);
        } else {
                sc->sc_flags &= ~SC_KEEPALIVE;
        }
}

static void
sl_outfill(void *chan)
{
        struct sl_softc *sc = chan;
        struct tty *tp = sc->sc_ttyp;

        if (sc->sc_outfill && tp != NULL) {
                if (sc->sc_flags & SC_OUTWAIT) {
                        crit_enter();
                        ++sc->sc_if.if_obytes;
                        clist_putc(FRAME_END, &tp->t_outq);
                        (*tp->t_oproc)(tp);
                        crit_exit();
                } else
                        sc->sc_flags |= SC_OUTWAIT;
                callout_reset(&sc->sc_oftimeout, sc->sc_outfill,
                                sl_outfill, sc);
        } else {
                sc->sc_flags &= ~SC_OUTWAIT;
        }
}