text: /*
   * (MPSAFE)
   *
   * 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	8.6 (Berkeley) 2/1/94
   * $FreeBSD: src/sys/net/if_sl.c,v 1.84.2.2 2002/02/13 00:43:10 dillon Exp $
   */
  
  /*
   * 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/priv.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;
  
  	lwkt_gettoken(&tty_token);
  	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_mp(&sc->sc_oftimeout);
  		callout_init_mp(&sc->sc_katimeout);
  		if_attach(&sc->sc_if, NULL);
  		bpfattach(&sc->sc_if, DLT_SLIP, SLIP_HDRLEN);
  	}
  	lwkt_reltoken(&tty_token);
  }
  
  static int
  slinit(struct sl_softc *sc)
  {
  	lwkt_gettoken(&tty_token);
  	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);
  	lwkt_reltoken(&tty_token);
  	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 = priv_check(td, PRIV_ROOT);
  	if (error)
  		return (error);
  
  	lwkt_gettoken(&tty_token);
  	if (tp->t_line == SLIPDISC) {
  		lwkt_reltoken(&tty_token);
  		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) {
  				lwkt_reltoken(&tty_token);
  				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();
  			lwkt_reltoken(&tty_token);
  			return (0);
  		}
  	lwkt_reltoken(&tty_token);
  	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;
  
  	lwkt_gettoken(&tty_token);
  	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();
  	lwkt_reltoken(&tty_token);
  	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();
  	lwkt_gettoken(&tty_token);
  
  	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;
  				}
  			}
  			lwkt_reltoken(&tty_token);
  			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:
  		lwkt_reltoken(&tty_token);
  		crit_exit();
  		return (ENOIOCTL);
  	}
  	lwkt_reltoken(&tty_token);
  	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 ifaltq_subque *ifsq,
      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);
  		IFNET_STAT_INC(&sc->sc_if, noproto, 1);
  		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 = ifsq_enqueue(ifsq, m, &pktattr);
  	}
  	if (error) {
  		IFNET_STAT_INC(&sc->sc_if, oerrors, 1);
  		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)
  {
  	struct ifaltq_subque *ifsq = ifq_get_subq_default(&ifp->if_snd);
  	int error;
  
  	ifsq_serialize_hw(ifsq);
  	error = sloutput_serialized(ifp, ifsq, m, dst, rtp);
  	ifsq_deserialize_hw(ifsq);
  
  	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 ifaltq_subque *ifsq = ifq_get_subq_default(&sc->sc_if.if_snd);
  	struct mbuf *m;
  	u_char *cp;
  	struct ip *ip;
  	u_char bpfbuf[SLTMAX + SLIP_HDRLEN];
  	int len = 0;
  
  	lwkt_gettoken(&tty_token);
  	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) {
  				lwkt_reltoken(&tty_token);
  				return 0;
  			}
  		}
  
  		/*
  		 * This happens briefly when the line shuts down.
  		 */
  		if (sc == NULL) {
  			lwkt_reltoken(&tty_token);
  			return 0;
  		}
  
  		/*
  		 * Get a packet and send it to the interface.
  		 */
  		crit_enter();
  		IF_DEQUEUE(&sc->sc_fastq, m);
  		if (m)
  			IFNET_STAT_INC(&sc->sc_if, omcasts, 1);	/* XXX */
  		else
  			m = ifsq_dequeue(ifsq);
  		crit_exit();
  		if (m == NULL) {
  			lwkt_reltoken(&tty_token);
  			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) {
  			bpf_gettoken();
  
  			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);
  			}
  
  			bpf_reltoken();
  		}
  
  		/*
  		 * 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);
  			IFNET_STAT_INC(&sc->sc_if, collisions, 1);
  			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) {
  			IFNET_STAT_INC(&sc->sc_if, obytes, 1);
  			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;
  					IFNET_STAT_INC(&sc->sc_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;
  					}
  					IFNET_STAT_INC(&sc->sc_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);
  			IFNET_STAT_INC(&sc->sc_if, collisions, 1);
  		} else {
  			IFNET_STAT_INC(&sc->sc_if, obytes, 1);
  			IFNET_STAT_INC(&sc->sc_if, opackets, 1);
  		}
  	}
  	lwkt_reltoken(&tty_token);
  	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, M_NOWAIT, 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_NOWAIT);
  		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];
  
  	lwkt_gettoken(&tty_token);
  	tk_nin++;
  	sc = (struct sl_softc *)tp->t_sc;
  	if (sc == NULL) {
  		lwkt_reltoken(&tty_token);
  		return 0;
  	}
  	if (c & TTY_ERRORMASK || (tp->t_state & TS_CONNECTED) == 0) {
  		sc->sc_flags |= SC_ERROR;
  		lwkt_reltoken(&tty_token);
  		return 0;
  	}
  	c &= TTY_CHARMASK;
  
  	IFNET_STAT_INC(&sc->sc_if, ibytes, 1);
  
  	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_uptime >= 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_uptime >= sc->sc_lasttime + ABT_IDLE) {
  				if (++sc->sc_abortcount == 1)
  					sc->sc_starttime = time_uptime;
  				if (sc->sc_abortcount >= ABT_COUNT) {
  					slclose(tp,0);
  					lwkt_reltoken(&tty_token);
  					return 0;
  				}
  			}
  		} else
  			sc->sc_abortcount = 0;
  		sc->sc_lasttime = time_uptime;
  	}
  
  	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;
  		lwkt_reltoken(&tty_token);
  		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) {
  			bpf_gettoken();
  
  			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);
  			}
  
  			bpf_reltoken();
  		}
  		m = sl_btom(sc, len);
  		if (m == NULL)
  			goto error;
  
  		IFNET_STAT_INC(&sc->sc_if, ipackets, 1);
  
  		if ((sc->sc_if.if_flags & IFF_UP) == 0) {
  			m_freem(m);
  			goto newpack;
  		}
  
  		if (netisr_queue(NETISR_IP, m)) {
  			IFNET_STAT_INC(&sc->sc_if, ierrors, 1);
  			IFNET_STAT_INC(&sc->sc_if, iqdrops, 1);
  		}
  
  		goto newpack;
  	}
  	if (sc->sc_mp < sc->sc_ep + SLBUFSIZE) {
  		*sc->sc_mp++ = c;
  		sc->sc_escape = 0;
  		lwkt_reltoken(&tty_token);
  		return 0;
  	}
  
  	/* can't put lower; would miss an extra frame */
  	sc->sc_flags |= SC_ERROR;
  
  error:
  	IFNET_STAT_INC(&sc->sc_if, ierrors, 1);
  newpack:
  	sc->sc_mp = sc->sc_buf = sc->sc_ep + SLBUFSIZE - SLRMAX;
  	sc->sc_escape = 0;
  	lwkt_reltoken(&tty_token);
  	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;
  	struct pgrp *pg;
  
  	lwkt_gettoken(&tty_token);
  	if (sc->sc_keepalive) {
  		if (sc->sc_flags & SC_KEEPALIVE) {
  			pg = sc->sc_ttyp->t_pgrp;
  			if (pg) {
  				pgref(pg);
  				pgsignal (pg, SIGURG, 1);
  				pgrel(pg);
  			}
  		} else {
  			sc->sc_flags |= SC_KEEPALIVE;
  		}
  		callout_reset(&sc->sc_katimeout, sc->sc_keepalive,
  				sl_keepalive, sc);
  	} else {
  		sc->sc_flags &= ~SC_KEEPALIVE;
  	}
  	lwkt_reltoken(&tty_token);
  }
  
  static void
  sl_outfill(void *chan)
  {
  	struct sl_softc *sc = chan;
  	struct tty *tp = sc->sc_ttyp;
  
  	lwkt_gettoken(&tty_token);
  
  	if (sc->sc_outfill && tp != NULL) {
  		if (sc->sc_flags & SC_OUTWAIT) {
  			crit_enter();
  			IFNET_STAT_INC(&sc->sc_if, obytes, 1);
  			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;
  	}
  	lwkt_reltoken(&tty_token);
  }
  