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ppp_async.c

/*
 * PPP async serial channel driver for Linux.
 *
 * Copyright 1999 Paul Mackerras.
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 *
 * This driver provides the encapsulation and framing for sending
 * and receiving PPP frames over async serial lines.  It relies on
 * the generic PPP layer to give it frames to send and to process
 * received frames.  It implements the PPP line discipline.
 *
 * Part of the code in this driver was inspired by the old async-only
 * PPP driver, written by Michael Callahan and Al Longyear, and
 * subsequently hacked by Paul Mackerras.
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/tty.h>
#include <linux/netdevice.h>
#include <linux/poll.h>
#include <linux/crc-ccitt.h>
#include <linux/ppp_defs.h>
#include <linux/if_ppp.h>
#include <linux/ppp_channel.h>
#include <linux/spinlock.h>
#include <linux/init.h>
#include <linux/jiffies.h>
#include <asm/uaccess.h>
#include <asm/string.h>

#define PPP_VERSION     "2.4.2"

#define OBUFSIZE  256

/* Structure for storing local state. */
struct asyncppp {
      struct tty_struct *tty;
      unsigned int      flags;
      unsigned int      state;
      unsigned int      rbits;
      int         mru;
      spinlock_t  xmit_lock;
      spinlock_t  recv_lock;
      unsigned long     xmit_flags;
      u32         xaccm[8];
      u32         raccm;
      unsigned int      bytes_sent;
      unsigned int      bytes_rcvd;

      struct sk_buff    *tpkt;
      int         tpkt_pos;
      u16         tfcs;
      unsigned char     *optr;
      unsigned char     *olim;
      unsigned long     last_xmit;

      struct sk_buff    *rpkt;
      int         lcp_fcs;
      struct sk_buff_head rqueue;

      struct tasklet_struct tsk;

      atomic_t    refcnt;
      struct semaphore dead_sem;
      struct ppp_channel chan;      /* interface to generic ppp layer */
      unsigned char     obuf[OBUFSIZE];
};

/* Bit numbers in xmit_flags */
#define XMIT_WAKEUP     0
#define XMIT_FULL 1
#define XMIT_BUSY 2

/* State bits */
#define SC_TOSS         1
#define SC_ESCAPE 2
#define SC_PREV_ERROR   4

/* Bits in rbits */
#define SC_RCV_BITS     (SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)

static int flag_time = HZ;
module_param(flag_time, int, 0);
MODULE_PARM_DESC(flag_time, "ppp_async: interval between flagged packets (in clock ticks)");
MODULE_LICENSE("GPL");
MODULE_ALIAS_LDISC(N_PPP);

/*
 * Prototypes.
 */
static int ppp_async_encode(struct asyncppp *ap);
static int ppp_async_send(struct ppp_channel *chan, struct sk_buff *skb);
static int ppp_async_push(struct asyncppp *ap);
static void ppp_async_flush_output(struct asyncppp *ap);
static void ppp_async_input(struct asyncppp *ap, const unsigned char *buf,
                      char *flags, int count);
static int ppp_async_ioctl(struct ppp_channel *chan, unsigned int cmd,
                     unsigned long arg);
static void ppp_async_process(unsigned long arg);

static void async_lcp_peek(struct asyncppp *ap, unsigned char *data,
                     int len, int inbound);

static struct ppp_channel_ops async_ops = {
      ppp_async_send,
      ppp_async_ioctl
};

/*
 * Routines implementing the PPP line discipline.
 */

/*
 * We have a potential race on dereferencing tty->disc_data,
 * because the tty layer provides no locking at all - thus one
 * cpu could be running ppp_asynctty_receive while another
 * calls ppp_asynctty_close, which zeroes tty->disc_data and
 * frees the memory that ppp_asynctty_receive is using.  The best
 * way to fix this is to use a rwlock in the tty struct, but for now
 * we use a single global rwlock for all ttys in ppp line discipline.
 *
 * FIXME: this is no longer true. The _close path for the ldisc is
 * now guaranteed to be sane.
 */
static DEFINE_RWLOCK(disc_data_lock);

static struct asyncppp *ap_get(struct tty_struct *tty)
{
      struct asyncppp *ap;

      read_lock(&disc_data_lock);
      ap = tty->disc_data;
      if (ap != NULL)
            atomic_inc(&ap->refcnt);
      read_unlock(&disc_data_lock);
      return ap;
}

static void ap_put(struct asyncppp *ap)
{
      if (atomic_dec_and_test(&ap->refcnt))
            up(&ap->dead_sem);
}

/*
 * Called when a tty is put into PPP line discipline. Called in process
 * context.
 */
static int
ppp_asynctty_open(struct tty_struct *tty)
{
      struct asyncppp *ap;
      int err;

      err = -ENOMEM;
      ap = kzalloc(sizeof(*ap), GFP_KERNEL);
      if (!ap)
            goto out;

      /* initialize the asyncppp structure */
      ap->tty = tty;
      ap->mru = PPP_MRU;
      spin_lock_init(&ap->xmit_lock);
      spin_lock_init(&ap->recv_lock);
      ap->xaccm[0] = ~0U;
      ap->xaccm[3] = 0x60000000U;
      ap->raccm = ~0U;
      ap->optr = ap->obuf;
      ap->olim = ap->obuf;
      ap->lcp_fcs = -1;

      skb_queue_head_init(&ap->rqueue);
      tasklet_init(&ap->tsk, ppp_async_process, (unsigned long) ap);

      atomic_set(&ap->refcnt, 1);
      init_MUTEX_LOCKED(&ap->dead_sem);

      ap->chan.private = ap;
      ap->chan.ops = &async_ops;
      ap->chan.mtu = PPP_MRU;
      err = ppp_register_channel(&ap->chan);
      if (err)
            goto out_free;

      tty->disc_data = ap;
      tty->receive_room = 65536;
      return 0;

 out_free:
      kfree(ap);
 out:
      return err;
}

/*
 * Called when the tty is put into another line discipline
 * or it hangs up.  We have to wait for any cpu currently
 * executing in any of the other ppp_asynctty_* routines to
 * finish before we can call ppp_unregister_channel and free
 * the asyncppp struct.  This routine must be called from
 * process context, not interrupt or softirq context.
 */
static void
ppp_asynctty_close(struct tty_struct *tty)
{
      struct asyncppp *ap;

      write_lock_irq(&disc_data_lock);
      ap = tty->disc_data;
      tty->disc_data = NULL;
      write_unlock_irq(&disc_data_lock);
      if (!ap)
            return;

      /*
       * We have now ensured that nobody can start using ap from now
       * on, but we have to wait for all existing users to finish.
       * Note that ppp_unregister_channel ensures that no calls to
       * our channel ops (i.e. ppp_async_send/ioctl) are in progress
       * by the time it returns.
       */
      if (!atomic_dec_and_test(&ap->refcnt))
            down(&ap->dead_sem);
      tasklet_kill(&ap->tsk);

      ppp_unregister_channel(&ap->chan);
      if (ap->rpkt)
            kfree_skb(ap->rpkt);
      skb_queue_purge(&ap->rqueue);
      if (ap->tpkt)
            kfree_skb(ap->tpkt);
      kfree(ap);
}

/*
 * Called on tty hangup in process context.
 *
 * Wait for I/O to driver to complete and unregister PPP channel.
 * This is already done by the close routine, so just call that.
 */
static int ppp_asynctty_hangup(struct tty_struct *tty)
{
      ppp_asynctty_close(tty);
      return 0;
}

/*
 * Read does nothing - no data is ever available this way.
 * Pppd reads and writes packets via /dev/ppp instead.
 */
static ssize_t
ppp_asynctty_read(struct tty_struct *tty, struct file *file,
              unsigned char __user *buf, size_t count)
{
      return -EAGAIN;
}

/*
 * Write on the tty does nothing, the packets all come in
 * from the ppp generic stuff.
 */
static ssize_t
ppp_asynctty_write(struct tty_struct *tty, struct file *file,
               const unsigned char *buf, size_t count)
{
      return -EAGAIN;
}

/*
 * Called in process context only. May be re-entered by multiple
 * ioctl calling threads.
 */

static int
ppp_asynctty_ioctl(struct tty_struct *tty, struct file *file,
               unsigned int cmd, unsigned long arg)
{
      struct asyncppp *ap = ap_get(tty);
      int err, val;
      int __user *p = (int __user *)arg;

      if (!ap)
            return -ENXIO;
      err = -EFAULT;
      switch (cmd) {
      case PPPIOCGCHAN:
            err = -ENXIO;
            if (!ap)
                  break;
            err = -EFAULT;
            if (put_user(ppp_channel_index(&ap->chan), p))
                  break;
            err = 0;
            break;

      case PPPIOCGUNIT:
            err = -ENXIO;
            if (!ap)
                  break;
            err = -EFAULT;
            if (put_user(ppp_unit_number(&ap->chan), p))
                  break;
            err = 0;
            break;

      case TCFLSH:
            /* flush our buffers and the serial port's buffer */
            if (arg == TCIOFLUSH || arg == TCOFLUSH)
                  ppp_async_flush_output(ap);
            err = tty_perform_flush(tty, arg);
            break;

      case FIONREAD:
            val = 0;
            if (put_user(val, p))
                  break;
            err = 0;
            break;

      default:
            /* Try the various mode ioctls */
            err = tty_mode_ioctl(tty, file, cmd, arg);
      }

      ap_put(ap);
      return err;
}

/* No kernel lock - fine */
static unsigned int
ppp_asynctty_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
{
      return 0;
}

/*
 * This can now be called from hard interrupt level as well
 * as soft interrupt level or mainline.
 */
static void
ppp_asynctty_receive(struct tty_struct *tty, const unsigned char *buf,
              char *cflags, int count)
{
      struct asyncppp *ap = ap_get(tty);
      unsigned long flags;

      if (!ap)
            return;
      spin_lock_irqsave(&ap->recv_lock, flags);
      ppp_async_input(ap, buf, cflags, count);
      spin_unlock_irqrestore(&ap->recv_lock, flags);
      if (!skb_queue_empty(&ap->rqueue))
            tasklet_schedule(&ap->tsk);
      ap_put(ap);
      if (test_and_clear_bit(TTY_THROTTLED, &tty->flags)
          && tty->driver->unthrottle)
            tty->driver->unthrottle(tty);
}

static void
ppp_asynctty_wakeup(struct tty_struct *tty)
{
      struct asyncppp *ap = ap_get(tty);

      clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
      if (!ap)
            return;
      set_bit(XMIT_WAKEUP, &ap->xmit_flags);
      tasklet_schedule(&ap->tsk);
      ap_put(ap);
}


static struct tty_ldisc ppp_ldisc = {
      .owner  = THIS_MODULE,
      .magic      = TTY_LDISC_MAGIC,
      .name = "ppp",
      .open = ppp_asynctty_open,
      .close      = ppp_asynctty_close,
      .hangup     = ppp_asynctty_hangup,
      .read = ppp_asynctty_read,
      .write      = ppp_asynctty_write,
      .ioctl      = ppp_asynctty_ioctl,
      .poll = ppp_asynctty_poll,
      .receive_buf = ppp_asynctty_receive,
      .write_wakeup = ppp_asynctty_wakeup,
};

static int __init
ppp_async_init(void)
{
      int err;

      err = tty_register_ldisc(N_PPP, &ppp_ldisc);
      if (err != 0)
            printk(KERN_ERR "PPP_async: error %d registering line disc.\n",
                   err);
      return err;
}

/*
 * The following routines provide the PPP channel interface.
 */
static int
ppp_async_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
{
      struct asyncppp *ap = chan->private;
      void __user *argp = (void __user *)arg;
      int __user *p = argp;
      int err, val;
      u32 accm[8];

      err = -EFAULT;
      switch (cmd) {
      case PPPIOCGFLAGS:
            val = ap->flags | ap->rbits;
            if (put_user(val, p))
                  break;
            err = 0;
            break;
      case PPPIOCSFLAGS:
            if (get_user(val, p))
                  break;
            ap->flags = val & ~SC_RCV_BITS;
            spin_lock_irq(&ap->recv_lock);
            ap->rbits = val & SC_RCV_BITS;
            spin_unlock_irq(&ap->recv_lock);
            err = 0;
            break;

      case PPPIOCGASYNCMAP:
            if (put_user(ap->xaccm[0], (u32 __user *)argp))
                  break;
            err = 0;
            break;
      case PPPIOCSASYNCMAP:
            if (get_user(ap->xaccm[0], (u32 __user *)argp))
                  break;
            err = 0;
            break;

      case PPPIOCGRASYNCMAP:
            if (put_user(ap->raccm, (u32 __user *)argp))
                  break;
            err = 0;
            break;
      case PPPIOCSRASYNCMAP:
            if (get_user(ap->raccm, (u32 __user *)argp))
                  break;
            err = 0;
            break;

      case PPPIOCGXASYNCMAP:
            if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
                  break;
            err = 0;
            break;
      case PPPIOCSXASYNCMAP:
            if (copy_from_user(accm, argp, sizeof(accm)))
                  break;
            accm[2] &= ~0x40000000U;      /* can't escape 0x5e */
            accm[3] |= 0x60000000U;       /* must escape 0x7d, 0x7e */
            memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
            err = 0;
            break;

      case PPPIOCGMRU:
            if (put_user(ap->mru, p))
                  break;
            err = 0;
            break;
      case PPPIOCSMRU:
            if (get_user(val, p))
                  break;
            if (val < PPP_MRU)
                  val = PPP_MRU;
            ap->mru = val;
            err = 0;
            break;

      default:
            err = -ENOTTY;
      }

      return err;
}

/*
 * This is called at softirq level to deliver received packets
 * to the ppp_generic code, and to tell the ppp_generic code
 * if we can accept more output now.
 */
static void ppp_async_process(unsigned long arg)
{
      struct asyncppp *ap = (struct asyncppp *) arg;
      struct sk_buff *skb;

      /* process received packets */
      while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
            if (skb->cb[0])
                  ppp_input_error(&ap->chan, 0);
            ppp_input(&ap->chan, skb);
      }

      /* try to push more stuff out */
      if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_async_push(ap))
            ppp_output_wakeup(&ap->chan);
}

/*
 * Procedures for encapsulation and framing.
 */

/*
 * Procedure to encode the data for async serial transmission.
 * Does octet stuffing (escaping), puts the address/control bytes
 * on if A/C compression is disabled, and does protocol compression.
 * Assumes ap->tpkt != 0 on entry.
 * Returns 1 if we finished the current frame, 0 otherwise.
 */

#define PUT_BYTE(ap, buf, c, islcp) do {        \
      if ((islcp && c < 0x20) || (ap->xaccm[c >> 5] & (1 << (c & 0x1f)))) {\
            *buf++ = PPP_ESCAPE;                \
            *buf++ = c ^ 0x20;                  \
      } else                                    \
            *buf++ = c;                   \
} while (0)

static int
ppp_async_encode(struct asyncppp *ap)
{
      int fcs, i, count, c, proto;
      unsigned char *buf, *buflim;
      unsigned char *data;
      int islcp;

      buf = ap->obuf;
      ap->olim = buf;
      ap->optr = buf;
      i = ap->tpkt_pos;
      data = ap->tpkt->data;
      count = ap->tpkt->len;
      fcs = ap->tfcs;
      proto = (data[0] << 8) + data[1];

      /*
       * LCP packets with code values between 1 (configure-reqest)
       * and 7 (code-reject) must be sent as though no options
       * had been negotiated.
       */
      islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;

      if (i == 0) {
            if (islcp)
                  async_lcp_peek(ap, data, count, 0);

            /*
             * Start of a new packet - insert the leading FLAG
             * character if necessary.
             */
            if (islcp || flag_time == 0
                || time_after_eq(jiffies, ap->last_xmit + flag_time))
                  *buf++ = PPP_FLAG;
            ap->last_xmit = jiffies;
            fcs = PPP_INITFCS;

            /*
             * Put in the address/control bytes if necessary
             */
            if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
                  PUT_BYTE(ap, buf, 0xff, islcp);
                  fcs = PPP_FCS(fcs, 0xff);
                  PUT_BYTE(ap, buf, 0x03, islcp);
                  fcs = PPP_FCS(fcs, 0x03);
            }
      }

      /*
       * Once we put in the last byte, we need to put in the FCS
       * and closing flag, so make sure there is at least 7 bytes
       * of free space in the output buffer.
       */
      buflim = ap->obuf + OBUFSIZE - 6;
      while (i < count && buf < buflim) {
            c = data[i++];
            if (i == 1 && c == 0 && (ap->flags & SC_COMP_PROT))
                  continue;   /* compress protocol field */
            fcs = PPP_FCS(fcs, c);
            PUT_BYTE(ap, buf, c, islcp);
      }

      if (i < count) {
            /*
             * Remember where we are up to in this packet.
             */
            ap->olim = buf;
            ap->tpkt_pos = i;
            ap->tfcs = fcs;
            return 0;
      }

      /*
       * We have finished the packet.  Add the FCS and flag.
       */
      fcs = ~fcs;
      c = fcs & 0xff;
      PUT_BYTE(ap, buf, c, islcp);
      c = (fcs >> 8) & 0xff;
      PUT_BYTE(ap, buf, c, islcp);
      *buf++ = PPP_FLAG;
      ap->olim = buf;

      kfree_skb(ap->tpkt);
      ap->tpkt = NULL;
      return 1;
}

/*
 * Transmit-side routines.
 */

/*
 * Send a packet to the peer over an async tty line.
 * Returns 1 iff the packet was accepted.
 * If the packet was not accepted, we will call ppp_output_wakeup
 * at some later time.
 */
static int
ppp_async_send(struct ppp_channel *chan, struct sk_buff *skb)
{
      struct asyncppp *ap = chan->private;

      ppp_async_push(ap);

      if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
            return 0;   /* already full */
      ap->tpkt = skb;
      ap->tpkt_pos = 0;

      ppp_async_push(ap);
      return 1;
}

/*
 * Push as much data as possible out to the tty.
 */
static int
ppp_async_push(struct asyncppp *ap)
{
      int avail, sent, done = 0;
      struct tty_struct *tty = ap->tty;
      int tty_stuffed = 0;

      /*
       * We can get called recursively here if the tty write
       * function calls our wakeup function.  This can happen
       * for example on a pty with both the master and slave
       * set to PPP line discipline.
       * We use the XMIT_BUSY bit to detect this and get out,
       * leaving the XMIT_WAKEUP bit set to tell the other
       * instance that it may now be able to write more now.
       */
      if (test_and_set_bit(XMIT_BUSY, &ap->xmit_flags))
            return 0;
      spin_lock_bh(&ap->xmit_lock);
      for (;;) {
            if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
                  tty_stuffed = 0;
            if (!tty_stuffed && ap->optr < ap->olim) {
                  avail = ap->olim - ap->optr;
                  set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
                  sent = tty->driver->write(tty, ap->optr, avail);
                  if (sent < 0)
                        goto flush; /* error, e.g. loss of CD */
                  ap->optr += sent;
                  if (sent < avail)
                        tty_stuffed = 1;
                  continue;
            }
            if (ap->optr >= ap->olim && ap->tpkt) {
                  if (ppp_async_encode(ap)) {
                        /* finished processing ap->tpkt */
                        clear_bit(XMIT_FULL, &ap->xmit_flags);
                        done = 1;
                  }
                  continue;
            }
            /*
             * We haven't made any progress this time around.
             * Clear XMIT_BUSY to let other callers in, but
             * after doing so we have to check if anyone set
             * XMIT_WAKEUP since we last checked it.  If they
             * did, we should try again to set XMIT_BUSY and go
             * around again in case XMIT_BUSY was still set when
             * the other caller tried.
             */
            clear_bit(XMIT_BUSY, &ap->xmit_flags);
            /* any more work to do? if not, exit the loop */
            if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags)
                  || (!tty_stuffed && ap->tpkt)))
                  break;
            /* more work to do, see if we can do it now */
            if (test_and_set_bit(XMIT_BUSY, &ap->xmit_flags))
                  break;
      }
      spin_unlock_bh(&ap->xmit_lock);
      return done;

flush:
      clear_bit(XMIT_BUSY, &ap->xmit_flags);
      if (ap->tpkt) {
            kfree_skb(ap->tpkt);
            ap->tpkt = NULL;
            clear_bit(XMIT_FULL, &ap->xmit_flags);
            done = 1;
      }
      ap->optr = ap->olim;
      spin_unlock_bh(&ap->xmit_lock);
      return done;
}

/*
 * Flush output from our internal buffers.
 * Called for the TCFLSH ioctl. Can be entered in parallel
 * but this is covered by the xmit_lock.
 */
static void
ppp_async_flush_output(struct asyncppp *ap)
{
      int done = 0;

      spin_lock_bh(&ap->xmit_lock);
      ap->optr = ap->olim;
      if (ap->tpkt != NULL) {
            kfree_skb(ap->tpkt);
            ap->tpkt = NULL;
            clear_bit(XMIT_FULL, &ap->xmit_flags);
            done = 1;
      }
      spin_unlock_bh(&ap->xmit_lock);
      if (done)
            ppp_output_wakeup(&ap->chan);
}

/*
 * Receive-side routines.
 */

/* see how many ordinary chars there are at the start of buf */
static inline int
scan_ordinary(struct asyncppp *ap, const unsigned char *buf, int count)
{
      int i, c;

      for (i = 0; i < count; ++i) {
            c = buf[i];
            if (c == PPP_ESCAPE || c == PPP_FLAG
                || (c < 0x20 && (ap->raccm & (1 << c)) != 0))
                  break;
      }
      return i;
}

/* called when a flag is seen - do end-of-packet processing */
static void
process_input_packet(struct asyncppp *ap)
{
      struct sk_buff *skb;
      unsigned char *p;
      unsigned int len, fcs, proto;

      skb = ap->rpkt;
      if (ap->state & (SC_TOSS | SC_ESCAPE))
            goto err;

      if (skb == NULL)
            return;           /* 0-length packet */

      /* check the FCS */
      p = skb->data;
      len = skb->len;
      if (len < 3)
            goto err;   /* too short */
      fcs = PPP_INITFCS;
      for (; len > 0; --len)
            fcs = PPP_FCS(fcs, *p++);
      if (fcs != PPP_GOODFCS)
            goto err;   /* bad FCS */
      skb_trim(skb, skb->len - 2);

      /* check for address/control and protocol compression */
      p = skb->data;
      if (p[0] == PPP_ALLSTATIONS) {
            /* chop off address/control */
            if (p[1] != PPP_UI || skb->len < 3)
                  goto err;
            p = skb_pull(skb, 2);
      }
      proto = p[0];
      if (proto & 1) {
            /* protocol is compressed */
            skb_push(skb, 1)[0] = 0;
      } else {
            if (skb->len < 2)
                  goto err;
            proto = (proto << 8) + p[1];
            if (proto == PPP_LCP)
                  async_lcp_peek(ap, p, skb->len, 1);
      }

      /* queue the frame to be processed */
      skb->cb[0] = ap->state;
      skb_queue_tail(&ap->rqueue, skb);
      ap->rpkt = NULL;
      ap->state = 0;
      return;

 err:
      /* frame had an error, remember that, reset SC_TOSS & SC_ESCAPE */
      ap->state = SC_PREV_ERROR;
      if (skb) {
            /* make skb appear as freshly allocated */
            skb_trim(skb, 0);
            skb_reserve(skb, - skb_headroom(skb));
      }
}

/* Called when the tty driver has data for us. Runs parallel with the
   other ldisc functions but will not be re-entered */

static void
ppp_async_input(struct asyncppp *ap, const unsigned char *buf,
            char *flags, int count)
{
      struct sk_buff *skb;
      int c, i, j, n, s, f;
      unsigned char *sp;

      /* update bits used for 8-bit cleanness detection */
      if (~ap->rbits & SC_RCV_BITS) {
            s = 0;
            for (i = 0; i < count; ++i) {
                  c = buf[i];
                  if (flags && flags[i] != 0)
                        continue;
                  s |= (c & 0x80)? SC_RCV_B7_1: SC_RCV_B7_0;
                  c = ((c >> 4) ^ c) & 0xf;
                  s |= (0x6996 & (1 << c))? SC_RCV_ODDP: SC_RCV_EVNP;
            }
            ap->rbits |= s;
      }

      while (count > 0) {
            /* scan through and see how many chars we can do in bulk */
            if ((ap->state & SC_ESCAPE) && buf[0] == PPP_ESCAPE)
                  n = 1;
            else
                  n = scan_ordinary(ap, buf, count);

            f = 0;
            if (flags && (ap->state & SC_TOSS) == 0) {
                  /* check the flags to see if any char had an error */
                  for (j = 0; j < n; ++j)
                        if ((f = flags[j]) != 0)
                              break;
            }
            if (f != 0) {
                  /* start tossing */
                  ap->state |= SC_TOSS;

            } else if (n > 0 && (ap->state & SC_TOSS) == 0) {
                  /* stuff the chars in the skb */
                  skb = ap->rpkt;
                  if (!skb) {
                        skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2);
                        if (!skb)
                              goto nomem;
                        ap->rpkt = skb;
                  }
                  if (skb->len == 0) {
                        /* Try to get the payload 4-byte aligned.
                         * This should match the
                         * PPP_ALLSTATIONS/PPP_UI/compressed tests in
                         * process_input_packet, but we do not have
                         * enough chars here to test buf[1] and buf[2].
                         */
                        if (buf[0] != PPP_ALLSTATIONS)
                              skb_reserve(skb, 2 + (buf[0] & 1));
                  }
                  if (n > skb_tailroom(skb)) {
                        /* packet overflowed MRU */
                        ap->state |= SC_TOSS;
                  } else {
                        sp = skb_put(skb, n);
                        memcpy(sp, buf, n);
                        if (ap->state & SC_ESCAPE) {
                              sp[0] ^= 0x20;
                              ap->state &= ~SC_ESCAPE;
                        }
                  }
            }

            if (n >= count)
                  break;

            c = buf[n];
            if (flags != NULL && flags[n] != 0) {
                  ap->state |= SC_TOSS;
            } else if (c == PPP_FLAG) {
                  process_input_packet(ap);
            } else if (c == PPP_ESCAPE) {
                  ap->state |= SC_ESCAPE;
            } else if (I_IXON(ap->tty)) {
                  if (c == START_CHAR(ap->tty))
                        start_tty(ap->tty);
                  else if (c == STOP_CHAR(ap->tty))
                        stop_tty(ap->tty);
            }
            /* otherwise it's a char in the recv ACCM */
            ++n;

            buf += n;
            if (flags)
                  flags += n;
            count -= n;
      }
      return;

 nomem:
      printk(KERN_ERR "PPPasync: no memory (input pkt)\n");
      ap->state |= SC_TOSS;
}

/*
 * We look at LCP frames going past so that we can notice
 * and react to the LCP configure-ack from the peer.
 * In the situation where the peer has been sent a configure-ack
 * already, LCP is up once it has sent its configure-ack
 * so the immediately following packet can be sent with the
 * configured LCP options.  This allows us to process the following
 * packet correctly without pppd needing to respond quickly.
 *
 * We only respond to the received configure-ack if we have just
 * sent a configure-request, and the configure-ack contains the
 * same data (this is checked using a 16-bit crc of the data).
 */
#define CONFREQ         1     /* LCP code field values */
#define CONFACK         2
#define LCP_MRU         1     /* LCP option numbers */
#define LCP_ASYNCMAP    2

static void async_lcp_peek(struct asyncppp *ap, unsigned char *data,
                     int len, int inbound)
{
      int dlen, fcs, i, code;
      u32 val;

      data += 2;        /* skip protocol bytes */
      len -= 2;
      if (len < 4)            /* 4 = code, ID, length */
            return;
      code = data[0];
      if (code != CONFACK && code != CONFREQ)
            return;
      dlen = (data[2] << 8) + data[3];
      if (len < dlen)
            return;           /* packet got truncated or length is bogus */

      if (code == (inbound? CONFACK: CONFREQ)) {
            /*
             * sent confreq or received confack:
             * calculate the crc of the data from the ID field on.
             */
            fcs = PPP_INITFCS;
            for (i = 1; i < dlen; ++i)
                  fcs = PPP_FCS(fcs, data[i]);

            if (!inbound) {
                  /* outbound confreq - remember the crc for later */
                  ap->lcp_fcs = fcs;
                  return;
            }

            /* received confack, check the crc */
            fcs ^= ap->lcp_fcs;
            ap->lcp_fcs = -1;
            if (fcs != 0)
                  return;
      } else if (inbound)
            return;     /* not interested in received confreq */

      /* process the options in the confack */
      data += 4;
      dlen -= 4;
      /* data[0] is code, data[1] is length */
      while (dlen >= 2 && dlen >= data[1] && data[1] >= 2) {
            switch (data[0]) {
            case LCP_MRU:
                  val = (data[2] << 8) + data[3];
                  if (inbound)
                        ap->mru = val;
                  else
                        ap->chan.mtu = val;
                  break;
            case LCP_ASYNCMAP:
                  val = (data[2] << 24) + (data[3] << 16)
                        + (data[4] << 8) + data[5];
                  if (inbound)
                        ap->raccm = val;
                  else
                        ap->xaccm[0] = val;
                  break;
            }
            dlen -= data[1];
            data += data[1];
      }
}

static void __exit ppp_async_cleanup(void)
{
      if (tty_unregister_ldisc(N_PPP) != 0)
            printk(KERN_ERR "failed to unregister PPP line discipline\n");
}

module_init(ppp_async_init);
module_exit(ppp_async_cleanup);

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