/*      $NetBSD: ppp_tty.c,v 1.73 2024/07/05 04:31:53 rin Exp $ */
/*      Id: ppp_tty.c,v 1.3 1996/07/01 01:04:11 paulus Exp      */

/*
 * ppp_tty.c - Point-to-Point Protocol (PPP) driver for asynchronous
 *             tty devices.
 *
 * Copyright (c) 1984-2000 Carnegie Mellon University. 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. The name "Carnegie Mellon University" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For permission or any legal
 *    details, please contact
 *      Office of Technology Transfer
 *      Carnegie Mellon University
 *      5000 Forbes Avenue
 *      Pittsburgh, PA  15213-3890
 *      (412) 268-4387, fax: (412) 268-7395
 *      tech-transfer@andrew.cmu.edu
 *
 * 4. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by Computing Services
 *     at Carnegie Mellon University (http://www.cmu.edu/computing/)."
 *
 * CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO
 * THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS, IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY BE LIABLE
 * FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
 * AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 * Based on:
 *      @(#)if_sl.c     7.6.1.2 (Berkeley) 2/15/89
 *
 * Copyright (c) 1987 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * 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).
 * Converted to 4.3BSD Beta by Chris Torek.
 * Other changes made at Berkeley, based in part on code by Kirk Smith.
 *
 * Converted to 4.3BSD+ 386BSD by Brad Parker (brad@cayman.com)
 * Added VJ tcp header compression; more unified ioctls
 *
 * Extensively modified by Paul Mackerras (paulus@cs.anu.edu.au).
 * Cleaned up a lot of the mbuf-related code to fix bugs that
 * caused system crashes and packet corruption.  Changed pppstart
 * so that it doesn't just give up with a "collision" if the whole
 * packet doesn't fit in the output ring buffer.
 *
 * Added priority queueing for interactive IP packets, following
 * the model of if_sl.c, plus hooks for bpf.
 * Paul Mackerras (paulus@cs.anu.edu.au).
 */

/* from if_sl.c,v 1.11 84/10/04 12:54:47 rick Exp */
/* from NetBSD: if_ppp.c,v 1.15.2.2 1994/07/28 05:17:58 cgd Exp */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: ppp_tty.c,v 1.73 2024/07/05 04:31:53 rin Exp $");

#ifdef _KERNEL_OPT
#include "ppp.h"
#include "opt_ppp.h"
#endif
#define VJC
#define PPP_COMPRESS

#include <sys/param.h>
#include <sys/proc.h>
#include <sys/mbuf.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 <sys/vnode.h>
#include <sys/systm.h>
#include <sys/kauth.h>

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

#ifdef VJC
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <net/slcompress.h>
#endif

#include <net/bpf.h>
#include <net/ppp_defs.h>
#include <net/if_ppp.h>
#include <net/if_pppvar.h>

static int      pppopen(dev_t dev, struct tty *tp);
static int      pppclose(struct tty *tp, int flag);
static int      pppread(struct tty *tp, struct uio *uio, int flag);
static int      pppwrite(struct tty *tp, struct uio *uio, int flag);
static int      ppptioctl(struct tty *tp, u_long cmd, void *data, int flag,
                          struct lwp *);
static int      pppinput(int c, struct tty *tp);
static int      pppstart(struct tty *tp);

struct linesw ppp_disc = {      /* XXX should be static */
        .l_name = "ppp",
        .l_open = pppopen,
        .l_close = pppclose,
        .l_read = pppread,
        .l_write = pppwrite,
        .l_ioctl = ppptioctl,
        .l_rint = pppinput,
        .l_start = pppstart,
        .l_modem = ttymodem,
        .l_poll = ttpoll
};

static uint16_t pppfcs(uint16_t fcs, const uint8_t *cp, int len);
static void     pppasyncstart(struct ppp_softc *);
static void     pppasyncctlp(struct ppp_softc *);
static void     pppasyncrelinq(struct ppp_softc *);
static void     ppp_timeout(void *);
static void     pppgetm(struct ppp_softc *sc);
static void     pppdumpb(u_char *b, int l);
static void     ppplogchar(struct ppp_softc *, int);

/*
 * Does c need to be escaped?
 */
#define ESCAPE_P(c)     (sc->sc_asyncmap[(c) >> 5] & (1U << ((c) & 0x1F)))

/*
 * Procedures for using an async tty interface for PPP.
 */

/* This is a NetBSD-1.0 or later kernel. */
#define CCOUNT(q)       ((q)->c_cc)

#define PPP_LOWAT       100     /* Process more output when < LOWAT on queue */
#define PPP_HIWAT       400     /* Don't start a new packet if HIWAT on que */

/*
 * Line specific open routine for async tty devices.
 * Attach the given tty to the first available ppp unit.
 * Called from device open routine or ttioctl.
 */
/* ARGSUSED */
static int
pppopen(dev_t dev, struct tty *tp)
{
    struct lwp *l = curlwp;             /* XXX */
    struct ppp_softc *sc;
    int error, s;

    error = kauth_authorize_network(l->l_cred, KAUTH_NETWORK_INTERFACE_PPP,
        KAUTH_REQ_NETWORK_INTERFACE_PPP_ADD, NULL, NULL, NULL);
    if (error)
        return (error);

    s = spltty();

    if (tp->t_linesw == &ppp_disc) {
        sc = (struct ppp_softc *) tp->t_sc;
        if (sc != NULL && sc->sc_devp == (void *) tp) {
            splx(s);
            return (0);
        }
    }

    if ((sc = pppalloc(l->l_proc->p_pid)) == NULL) {
        splx(s);
        return ENXIO;
    }

    if (sc->sc_relinq)
        (*sc->sc_relinq)(sc);   /* get previous owner to relinquish the unit */

    /* Switch DLT to PPP-over-serial. */
    bpf_change_type(&sc->sc_if, DLT_PPP_SERIAL, PPP_HDRLEN);

    sc->sc_ilen = 0;
    sc->sc_m = NULL;
    memset(sc->sc_asyncmap, 0, sizeof(sc->sc_asyncmap));
    sc->sc_asyncmap[0] = 0xffffffff;
    sc->sc_asyncmap[3] = 0x60000000;
    sc->sc_rasyncmap = 0;
    sc->sc_devp = (void *) tp;
    sc->sc_start = pppasyncstart;
    sc->sc_ctlp = pppasyncctlp;
    sc->sc_relinq = pppasyncrelinq;
    sc->sc_outm = NULL;
    pppgetm(sc);
    sc->sc_if.if_flags |= IFF_RUNNING;
    sc->sc_if.if_baudrate = tp->t_ospeed;

    tp->t_sc = (void *) sc;
    ttylock(tp);
    ttyflush(tp, FREAD | FWRITE);
    ttyunlock(tp);

    splx(s);
    return (0);
}

/*
 * Line specific close routine, called from device close routine
 * and from ttioctl.
 * Detach the tty from the ppp unit.
 * Mimics part of ttyclose().
 */
static int
pppclose(struct tty *tp, int flag)
{
    struct ppp_softc *sc;
    int s;

    s = spltty();
    ttylock(tp);
    ttyflush(tp, FREAD|FWRITE);
    ttyunlock(tp);      /* XXX */
    ttyldisc_release(tp->t_linesw);
    tp->t_linesw = ttyldisc_default();
    sc = (struct ppp_softc *) tp->t_sc;
    if (sc != NULL) {
        tp->t_sc = NULL;
        if (tp == (struct tty *) sc->sc_devp) {
            pppasyncrelinq(sc);
            pppdealloc(sc);
        }
    }
    splx(s);
    return 0;
}

/*
 * Relinquish the interface unit to another device.
 */
static void
pppasyncrelinq(struct ppp_softc *sc)
{
    int s;

    /* Change DLT to back none. */
    bpf_change_type(&sc->sc_if, DLT_NULL, 0);

    s = spltty();
    m_freem(sc->sc_outm);
    sc->sc_outm = NULL;
    m_freem(sc->sc_m);
    sc->sc_m = NULL;
    if (sc->sc_flags & SC_TIMEOUT) {
        callout_stop(&sc->sc_timo_ch);
        sc->sc_flags &= ~SC_TIMEOUT;
    }
    splx(s);
}

/*
 * Line specific (tty) read routine.
 */
static int
pppread(struct tty *tp, struct uio *uio, int flag)
{
    struct ppp_softc *sc = (struct ppp_softc *)tp->t_sc;
    struct mbuf *m, *m0;
    int error = 0;

    if (sc == NULL)
        return 0;
    /*
     * Loop waiting for input, checking that nothing disastrous
     * happens in the meantime.
     */
    ttylock(tp);
    for (;;) {
        if (tp != (struct tty *) sc->sc_devp ||
            tp->t_linesw != &ppp_disc) {
            ttyunlock(tp);
            return 0;
        }
        if (sc->sc_inq.ifq_head != NULL)
            break;
        if ((tp->t_state & TS_CARR_ON) == 0 && (tp->t_cflag & CLOCAL) == 0
            && (tp->t_state & TS_ISOPEN)) {
            ttyunlock(tp);
            return 0;           /* end of file */
        }
        if (tp->t_state & TS_ASYNC || flag & IO_NDELAY) {
            ttyunlock(tp);
            return (EWOULDBLOCK);
        }
        error = ttysleep(tp, &tp->t_rawcv, true, 0);
        if (error) {
            ttyunlock(tp);
            return error;
        }
    }

    /* Pull place-holder byte out of canonical queue */
    getc(&tp->t_canq);

    /* Get the packet from the input queue */
    IF_DEQUEUE(&sc->sc_inq, m0);
    ttyunlock(tp);

    for (m = m0; m && uio->uio_resid; m = m->m_next)
        if ((error = uiomove(mtod(m, u_char *), m->m_len, uio)) != 0)
            break;
    m_freem(m0);
    return (error);
}

/*
 * Line specific (tty) write routine.
 */
static int
pppwrite(struct tty *tp, struct uio *uio, int flag)
{
    struct ppp_softc *sc = (struct ppp_softc *)tp->t_sc;
    struct mbuf *m, *m0;
    struct sockaddr dst;
    int len, error;

    if ((tp->t_state & TS_CARR_ON) == 0 && (tp->t_cflag & CLOCAL) == 0)
        return 0;               /* wrote 0 bytes */
    if (tp->t_linesw != &ppp_disc)
        return (EINVAL);
    if (sc == NULL || tp != (struct tty *) sc->sc_devp)
        return EIO;
    if (uio->uio_resid > sc->sc_if.if_mtu + PPP_HDRLEN ||
        uio->uio_resid < PPP_HDRLEN)
        return (EMSGSIZE);

    MGETHDR(m0, M_WAIT, MT_DATA);
    if (m0 == NULL)
        return ENOBUFS;

    m0->m_len = 0;
    m0->m_pkthdr.len = uio->uio_resid;
    m_reset_rcvif(m0);

    if (uio->uio_resid >= MCLBYTES / 2)
        MCLGET(m0, M_DONTWAIT);

    for (m = m0; uio->uio_resid;) {
        len = M_TRAILINGSPACE(m);
        if (len > uio->uio_resid)
            len = uio->uio_resid;
        if ((error = uiomove(mtod(m, u_char *), len, uio)) != 0) {
            m_freem(m0);
            return (error);
        }
        m->m_len = len;

        if (uio->uio_resid == 0)
            break;

        MGET(m->m_next, M_WAIT, MT_DATA);
        if (m->m_next == NULL) {
            m_freem(m0);
            return ENOBUFS;
        }
        m = m->m_next;
        m->m_len = 0;
    }
    dst.sa_family = AF_UNSPEC;
    bcopy(mtod(m0, u_char *), dst.sa_data, PPP_HDRLEN);
    m_adj(m0, PPP_HDRLEN);
    return if_output_lock(&sc->sc_if, &sc->sc_if, m0, &dst, (struct rtentry *)0);
}

/*
 * Line specific (tty) ioctl routine.
 * This discipline requires that tty device drivers call
 * the line specific l_ioctl routine from their ioctl routines.
 */
/* ARGSUSED */
static int
ppptioctl(struct tty *tp, u_long cmd, void *data, int flag, struct lwp *l)
{
    struct ppp_softc *sc = (struct ppp_softc *) tp->t_sc;
    int error, s;

    if (sc == NULL)
        return (EPASSTHROUGH);

    KERNEL_LOCK(1, NULL);

    if (tp != (struct tty *) sc->sc_devp) {
        error = EPASSTHROUGH;
        goto out;
    }

    error = 0;
    switch (cmd) {
    case PPPIOCSASYNCMAP:
        if ((error = kauth_authorize_device_tty(l->l_cred,
          KAUTH_DEVICE_TTY_PRIVSET, tp)) != 0)
            break;
        sc->sc_asyncmap[0] = *(u_int *)data;
        break;

    case PPPIOCGASYNCMAP:
        *(u_int *)data = sc->sc_asyncmap[0];
        break;

    case PPPIOCSRASYNCMAP:
        if ((error = kauth_authorize_device_tty(l->l_cred,
          KAUTH_DEVICE_TTY_PRIVSET, tp)) != 0)
            break;
        sc->sc_rasyncmap = *(u_int *)data;
        break;

    case PPPIOCGRASYNCMAP:
        *(u_int *)data = sc->sc_rasyncmap;
        break;

    case PPPIOCSXASYNCMAP:
        if ((error = kauth_authorize_device_tty(l->l_cred,
          KAUTH_DEVICE_TTY_PRIVSET, tp)) != 0)
            break;
        s = spltty();
        bcopy(data, sc->sc_asyncmap, sizeof(sc->sc_asyncmap));
        sc->sc_asyncmap[1] = 0;             /* mustn't escape 0x20 - 0x3f */
        sc->sc_asyncmap[2] &= ~0x40000000;  /* mustn't escape 0x5e */
        sc->sc_asyncmap[3] |= 0x60000000;   /* must escape 0x7d, 0x7e */
        splx(s);
        break;

    case PPPIOCGXASYNCMAP:
        bcopy(sc->sc_asyncmap, data, sizeof(sc->sc_asyncmap));
        break;

    default:
        error = pppioctl(sc, cmd, data, flag, l);
        if (error == 0 && cmd == PPPIOCSMRU)
            pppgetm(sc);
    }

 out:
    KERNEL_UNLOCK_ONE(NULL);
    return error;
}

/*
 * FCS lookup table as calculated by genfcstab.
 */
static const uint16_t fcstab[256] = {
        0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
        0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
        0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
        0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
        0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
        0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
        0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
        0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
        0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
        0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
        0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
        0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
        0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
        0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
        0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
        0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
        0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
        0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
        0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
        0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
        0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
        0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
        0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,
        0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
        0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,
        0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
        0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
        0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
        0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
        0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
        0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
        0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
};

/*
 * Calculate a new FCS given the current FCS and the new data.
 */
static uint16_t
pppfcs(uint16_t fcs, const uint8_t *cp, int len)
{
    while (len--)
        fcs = PPP_FCS(fcs, *cp++);
    return (fcs);
}

/*
 * This gets called at splsoftnet from if_ppp.c at various times
 * when there is data ready to be sent.
 */
static void
pppasyncstart(struct ppp_softc *sc)
{
    struct tty *tp = (struct tty *) sc->sc_devp;
    struct mbuf *m;
    int len;
    u_char *start, *stop, *cp;
    int n, ndone, done, idle;
    struct mbuf *m2;

    ttylock(tp);

    idle = 0;
    while (CCOUNT(&tp->t_outq) < PPP_HIWAT) {
        /*
         * See if we have an existing packet partly sent.
         * If not, get a new packet and start sending it.
         */
        m = sc->sc_outm;
        if (m == NULL) {
            /*
             * Get another packet to be sent.
             */
            m = ppp_dequeue(sc);
            if (m == NULL) {
                idle = 1;
                break;
            }

            /*
             * The extra PPP_FLAG 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 (CCOUNT(&tp->t_outq) == 0) {
                ++sc->sc_stats.ppp_obytes;
                (void) putc(PPP_FLAG, &tp->t_outq);
            }

            /* Calculate the FCS for the first mbuf's worth. */
            sc->sc_outfcs = pppfcs(PPP_INITFCS, mtod(m, uint8_t *), m->m_len);
        }

        for (;;) {
            start = mtod(m, u_char *);
            len = m->m_len;
            stop = start + len;
            while (len > 0) {
                /*
                 * Find out how many bytes in the string we can
                 * handle without doing something special.
                 */
                for (cp = start; cp < stop; cp++)
                    if (ESCAPE_P(*cp))
                        break;
                n = cp - start;
                if (n) {
                    /* NetBSD (0.9 or later), 4.3-Reno or similar. */
                    ndone = n - b_to_q(start, n, &tp->t_outq);
                    len -= ndone;
                    start += ndone;
                    sc->sc_stats.ppp_obytes += ndone;

                    if (ndone < n)
                        break;  /* packet doesn't fit */
                }
                /*
                 * If there are characters left in the mbuf,
                 * the first one must be special.
                 * Put it out in a different form.
                 */
                if (len) {
                    if (putc(PPP_ESCAPE, &tp->t_outq))
                        break;
                    if (putc(*start ^ PPP_TRANS, &tp->t_outq)) {
                        (void) unputc(&tp->t_outq);
                        break;
                    }
                    sc->sc_stats.ppp_obytes += 2;
                    start++;
                    len--;
                }
            }

            /*
             * If we didn't empty this mbuf, remember where we're up to.
             * If we emptied the last mbuf, try to add the FCS and closing
             * flag, and if we can't, leave sc_outm pointing to m, but with
             * m->m_len == 0, to remind us to output the FCS and flag later.
             */
            done = len == 0;
            if (done && m->m_next == NULL) {
                u_char *p, *q;
                int c;
                u_char endseq[8];

                /*
                 * We may have to escape the bytes in the FCS.
                 */
                p = endseq;
                c = ~sc->sc_outfcs & 0xFF;
                if (ESCAPE_P(c)) {
                    *p++ = PPP_ESCAPE;
                    *p++ = c ^ PPP_TRANS;
                } else
                    *p++ = c;
                c = (~sc->sc_outfcs >> 8) & 0xFF;
                if (ESCAPE_P(c)) {
                    *p++ = PPP_ESCAPE;
                    *p++ = c ^ PPP_TRANS;
                } else
                    *p++ = c;
                *p++ = PPP_FLAG;

                /*
                 * Try to output the FCS and flag.  If the bytes
                 * don't all fit, back out.
                 */
                for (q = endseq; q < p; ++q)
                    if (putc(*q, &tp->t_outq)) {
                        done = 0;
                        for (; q > endseq; --q)
                            unputc(&tp->t_outq);
                        break;
                    }
                if (done)
                    sc->sc_stats.ppp_obytes += q - endseq;
            }

            if (!done) {
                /* remember where we got to */
                m->m_data = start;
                m->m_len = len;
                break;
            }

            /* Finished with this mbuf; free it and move on. */
            m = m2 = m_free(m);
            if (m == NULL) {
                /* Finished a packet */
                break;
            }
            sc->sc_outfcs = pppfcs(sc->sc_outfcs, mtod(m, uint8_t *), m->m_len);
        }

        /*
         * If m == NULL, we have finished a packet.
         * If m != NULL, we've either done as much work this time
         * as we need to, or else we've filled up the output queue.
         */
        sc->sc_outm = m;
        if (m)
            break;
    }

    /* Call pppstart to start output again if necessary. */
    pppstart(tp);

    /*
     * This timeout is needed for operation on a pseudo-tty,
     * because the pty code doesn't call pppstart after it has
     * drained the t_outq.
     */
    if (!idle && (sc->sc_flags & SC_TIMEOUT) == 0) {
        callout_reset(&sc->sc_timo_ch, 1, ppp_timeout, sc);
        sc->sc_flags |= SC_TIMEOUT;
    }

    ttyunlock(tp);
}

/*
 * This gets called when a received packet is placed on
 * the inq, at splsoftnet.
 */
static void
pppasyncctlp(struct ppp_softc *sc)
{
    struct tty *tp;

    /* Put a placeholder byte in canq for ttselect()/ttnread(). */
    tp = (struct tty *) sc->sc_devp;
    ttylock(tp);
    putc(0, &tp->t_canq);
    ttwakeup(tp);
    ttyunlock(tp);
}

/*
 * Start output on async tty interface.  If the transmit queue
 * has drained sufficiently, arrange for pppasyncstart to be
 * called later at splsoftnet.
 * Called at spltty or higher.
 */
static int
pppstart(struct tty *tp)
{
    struct ppp_softc *sc = (struct ppp_softc *) tp->t_sc;

    /*
     * If there is stuff in the output queue, send it now.
     * We are being called in lieu of ttstart and must do what it would.
     */
    if (tp->t_oproc != NULL)
        (*tp->t_oproc)(tp);

    /*
     * If the transmit queue has drained and the tty has not hung up
     * or been disconnected from the ppp unit, then tell if_ppp.c that
     * we need more output.
     */
    if ((CCOUNT(&tp->t_outq) >= PPP_LOWAT)
        && ((sc == NULL) || (sc->sc_flags & SC_TIMEOUT)))
        return 0;
#ifdef ALTQ
    /*
     * if ALTQ is enabled, don't invoke NETISR_PPP.
     * pppintr() could loop without doing anything useful
     * under rate-limiting.
     */
    if (ALTQ_IS_ENABLED(&sc->sc_if.if_snd))
        return 0;
#endif
    if (!((tp->t_state & TS_CARR_ON) == 0 && (tp->t_cflag & CLOCAL) == 0)
        && sc != NULL && tp == (struct tty *) sc->sc_devp) {
        ppp_restart(sc);
    }

    return 0;
}

/*
 * Timeout routine - try to start some more output.
 */
static void
ppp_timeout(void *x)
{
    struct ppp_softc *sc = (struct ppp_softc *) x;
    struct tty *tp = (struct tty *) sc->sc_devp;

    ttylock(tp);
    sc->sc_flags &= ~SC_TIMEOUT;
    pppstart(tp);
    ttyunlock(tp);
}

/*
 * Allocate enough mbuf to handle current MRU.
 */
static void
pppgetm(struct ppp_softc *sc)
{
    struct mbuf *m, **mp;
    int len;

    mp = &sc->sc_m;
    for (len = sc->sc_mru + PPP_HDRLEN + PPP_FCSLEN; len > 0; ){
        if ((m = *mp) == NULL) {
            MGETHDR(m, M_DONTWAIT, MT_DATA);
            if (m == NULL)
                break;
            *mp = m;
            MCLGET(m, M_DONTWAIT);
        }
        len -= M_BUFSIZE(m);
        mp = &m->m_next;
    }
}

/*
 * tty interface receiver interrupt.
 */
static const unsigned paritytab[8] = {
    0x96696996, 0x69969669, 0x69969669, 0x96696996,
    0x69969669, 0x96696996, 0x96696996, 0x69969669
};

static int
pppinput(int c, struct tty *tp)
{
    struct ppp_softc *sc;
    struct mbuf *m;
    int ilen, s;
    int result;

    sc = (struct ppp_softc *) tp->t_sc;
    if (sc == NULL || tp != (struct tty *) sc->sc_devp)
        return 0;

    ++tk_nin;
    ++sc->sc_stats.ppp_ibytes;

    if (c & TTY_FE) {
        /* framing error or overrun on this char - abort packet */
        if (sc->sc_flags & SC_DEBUG)
            printf("%s: bad char %x\n", sc->sc_if.if_xname, c);
        goto flush;
    }

    c &= 0xff;

    /*
     * Handle software flow control of output.
     */
    result = tty_try_xonxoff(tp, c);
    if (result == 0) {
            /* Character was recognized and consumed. */
            return 0;
    }
    /* Character wasn't consumed, continue processing it. */

    s = spltty();
    if (c & 0x80)
        sc->sc_flags |= SC_RCV_B7_1;
    else
        sc->sc_flags |= SC_RCV_B7_0;
    if (paritytab[c >> 5] & (1U << (c & 0x1F)))
        sc->sc_flags |= SC_RCV_ODDP;
    else
        sc->sc_flags |= SC_RCV_EVNP;
    splx(s);

    ppplogchar(sc, c);

    if (c == PPP_FLAG) {
        ilen = sc->sc_ilen;
        sc->sc_ilen = 0;

        if ((sc->sc_flags & SC_LOG_RAWIN) && sc->sc_rawin.count > 0)
            ppplogchar(sc, -1);

        /*
         * If SC_ESCAPED is set, then we've seen the packet
         * abort sequence "}~".
         */
        if (sc->sc_flags & (SC_FLUSH | SC_ESCAPED)
            || (ilen > 0 && sc->sc_fcs != PPP_GOODFCS)) {
            s = spltty();
            sc->sc_flags |= SC_PKTLOST; /* note the dropped packet */
            if ((sc->sc_flags & (SC_FLUSH | SC_ESCAPED)) == 0){
                if (sc->sc_flags & SC_DEBUG)
                    printf("%s: bad fcs %x\n", sc->sc_if.if_xname,
                        sc->sc_fcs);
                if_statinc(&sc->sc_if, if_ierrors);
                sc->sc_stats.ppp_ierrors++;
            } else
                sc->sc_flags &= ~(SC_FLUSH | SC_ESCAPED);
            splx(s);
            return 0;
        }

        if (ilen < PPP_HDRLEN + PPP_FCSLEN) {
            if (ilen) {
                if (sc->sc_flags & SC_DEBUG)
                    printf("%s: too short (%d)\n", sc->sc_if.if_xname, ilen);
                s = spltty();
                if_statinc(&sc->sc_if, if_ierrors);
                sc->sc_stats.ppp_ierrors++;
                sc->sc_flags |= SC_PKTLOST;
                splx(s);
            }
            return 0;
        }

        /*
         * Remove FCS trailer.  Somewhat painful...
         */
        ilen -= 2;
        if (--sc->sc_mc->m_len == 0) {
            for (m = sc->sc_m; m->m_next != sc->sc_mc; m = m->m_next)
                ;
            sc->sc_mc = m;
        }
        sc->sc_mc->m_len--;

        /* excise this mbuf chain */
        m = sc->sc_m;
        sc->sc_m = sc->sc_mc->m_next;
        sc->sc_mc->m_next = NULL;

        ppppktin(sc, m, sc->sc_flags & SC_PKTLOST);
        if (sc->sc_flags & SC_PKTLOST) {
            s = spltty();
            sc->sc_flags &= ~SC_PKTLOST;
            splx(s);
        }

        pppgetm(sc);
        return 0;
    }

    if (sc->sc_flags & SC_FLUSH) {
        if (sc->sc_flags & SC_LOG_FLUSH)
            ppplogchar(sc, c);
        return 0;
    }

    if (c < 0x20 && (sc->sc_rasyncmap & (1U << c)))
        return 0;

    s = spltty();
    if (sc->sc_flags & SC_ESCAPED) {
        sc->sc_flags &= ~SC_ESCAPED;
        c ^= PPP_TRANS;
    } else if (c == PPP_ESCAPE) {
        sc->sc_flags |= SC_ESCAPED;
        splx(s);
        return 0;
    }
    splx(s);

    /*
     * Initialize buffer on first octet received.
     * First octet could be address or protocol (when compressing
     * address/control).
     * Second octet is control.
     * Third octet is first or second (when compressing protocol)
     * octet of protocol.
     * Fourth octet is second octet of protocol.
     */
    if (sc->sc_ilen == 0) {
        /* reset the first input mbuf */
        if (sc->sc_m == NULL) {
            pppgetm(sc);
            if (sc->sc_m == NULL) {
                if (sc->sc_flags & SC_DEBUG)
                    printf("%s: no input mbufs!\n", sc->sc_if.if_xname);
                goto flush;
            }
        }
        m = sc->sc_m;
        m->m_len = 0;
        MRESETDATA(m);
        sc->sc_mc = m;
        sc->sc_mp = mtod(m, char *);
        sc->sc_fcs = PPP_INITFCS;
        if (c != PPP_ALLSTATIONS) {
            if (sc->sc_flags & SC_REJ_COMP_AC) {
                if (sc->sc_flags & SC_DEBUG)
                    printf("%s: garbage received: 0x%x (need 0xFF)\n",
                    sc->sc_if.if_xname, c);
                goto flush;
            }
            *sc->sc_mp++ = PPP_ALLSTATIONS;
            *sc->sc_mp++ = PPP_UI;
            sc->sc_ilen += 2;
            m->m_len += 2;
        }
    }
    if (sc->sc_ilen == 1 && c != PPP_UI) {
        if (sc->sc_flags & SC_DEBUG)
            printf("%s: missing UI (0x3), got 0x%x\n",
                sc->sc_if.if_xname, c);
        goto flush;
    }
    if (sc->sc_ilen == 2 && (c & 1) == 1) {
        /* a compressed protocol */
        *sc->sc_mp++ = 0;
        sc->sc_ilen++;
        sc->sc_mc->m_len++;
    }
    if (sc->sc_ilen == 3 && (c & 1) == 0) {
        if (sc->sc_flags & SC_DEBUG)
            printf("%s: bad protocol %x\n", sc->sc_if.if_xname,
                (sc->sc_mp[-1] << 8) + c);
        goto flush;
    }

    /* packet beyond configured mru? */
    if (++sc->sc_ilen > sc->sc_mru + PPP_HDRLEN + PPP_FCSLEN) {
        if (sc->sc_flags & SC_DEBUG)
            printf("%s: packet too big\n", sc->sc_if.if_xname);
        goto flush;
    }

    /* is this mbuf full? */
    m = sc->sc_mc;
    if (M_TRAILINGSPACE(m) <= 0) {
        if (m->m_next == NULL) {
            pppgetm(sc);
            if (m->m_next == NULL) {
                if (sc->sc_flags & SC_DEBUG)
                    printf("%s: too few input mbufs!\n", sc->sc_if.if_xname);
                goto flush;
            }
        }
        sc->sc_mc = m = m->m_next;
        m->m_len = 0;
        MRESETDATA(m);
        sc->sc_mp = mtod(m, char *);
    }

    ++m->m_len;
    *sc->sc_mp++ = c;
    sc->sc_fcs = PPP_FCS(sc->sc_fcs, c);
    return 0;

 flush:
    if (!(sc->sc_flags & SC_FLUSH)) {
        s = spltty();
        if_statinc(&sc->sc_if, if_ierrors);
        sc->sc_stats.ppp_ierrors++;
        sc->sc_flags |= SC_FLUSH;
        splx(s);
        if (sc->sc_flags & SC_LOG_FLUSH)
            ppplogchar(sc, c);
    }
    return 0;
}

#define MAX_DUMP_BYTES  128

static void
ppplogchar(struct ppp_softc *sc, int c)
{
    if (c >= 0) {
        sc->sc_rawin.buf[sc->sc_rawin_start++] = c;
        if (sc->sc_rawin.count < sizeof(sc->sc_rawin.buf))
            sc->sc_rawin.count++;
    }
    if (sc->sc_rawin_start >= sizeof(sc->sc_rawin.buf)
        || (c < 0 && sc->sc_rawin_start > 0)) {
        if (sc->sc_flags & (SC_LOG_FLUSH|SC_LOG_RAWIN)) {
            printf("%s input: ", sc->sc_if.if_xname);
            pppdumpb(sc->sc_rawin.buf, sc->sc_rawin_start);
        }
        if (c < 0)
            sc->sc_rawin.count = 0;
        sc->sc_rawin_start = 0;
    }
}

static void
pppdumpb(u_char *b, int l)
{
    char bf[3*MAX_DUMP_BYTES+4];
    char *bp = bf;

    while (l--) {
        if (bp >= bf + sizeof(bf) - 3) {
            *bp++ = '>';
            break;
        }
        *bp++ = hexdigits[*b >> 4]; /* convert byte to ascii hex */
        *bp++ = hexdigits[*b++ & 0xf];
        *bp++ = ' ';
    }

    *bp = 0;
    printf("%s\n", bf);
}