Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1021 insertions, 0 deletions

diff --git a/drivers/net/ppp/ppp_async.c b/drivers/net/ppp/ppp_async.c
new file mode 100644
index 000000000..15a179631
--- /dev/null
+++ b/drivers/net/ppp/ppp_async.c
@@ -0,0 +1,1021 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * PPP async serial channel driver for Linux.
+ *
+ * Copyright 1999 Paul Mackerras.
+ *
+ * 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/ppp-ioctl.h>
+#include <linux/ppp_channel.h>
+#include <linux/spinlock.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/jiffies.h>
+#include <linux/slab.h>
+#include <asm/unaligned.h>
+#include <linux/uaccess.h>
+#include <asm/string.h>
+
+#define PPP_VERSION	"2.4.2"
+
+#define OBUFSIZE	4096
+
+/* 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;
+
+	refcount_t	refcnt;
+	struct completion dead;
+	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,
+			    const char *flags, int count);
+static int ppp_async_ioctl(struct ppp_channel *chan, unsigned int cmd,
+			   unsigned long arg);
+static void ppp_async_process(struct tasklet_struct *t);
+
+static void async_lcp_peek(struct asyncppp *ap, unsigned char *data,
+			   int len, int inbound);
+
+static const struct ppp_channel_ops async_ops = {
+	.start_xmit = ppp_async_send,
+	.ioctl      = 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)
+		refcount_inc(&ap->refcnt);
+	read_unlock(&disc_data_lock);
+	return ap;
+}
+
+static void ap_put(struct asyncppp *ap)
+{
+	if (refcount_dec_and_test(&ap->refcnt))
+		complete(&ap->dead);
+}
+
+/*
+ * 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;
+	int speed;
+
+	if (tty->ops->write == NULL)
+		return -EOPNOTSUPP;
+
+	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_setup(&ap->tsk, ppp_async_process);
+
+	refcount_set(&ap->refcnt, 1);
+	init_completion(&ap->dead);
+
+	ap->chan.private = ap;
+	ap->chan.ops = &async_ops;
+	ap->chan.mtu = PPP_MRU;
+	speed = tty_get_baud_rate(tty);
+	ap->chan.speed = speed;
+	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 (!refcount_dec_and_test(&ap->refcnt))
+		wait_for_completion(&ap->dead);
+	tasklet_kill(&ap->tsk);
+
+	ppp_unregister_channel(&ap->chan);
+	kfree_skb(ap->rpkt);
+	skb_queue_purge(&ap->rqueue);
+	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 void ppp_asynctty_hangup(struct tty_struct *tty)
+{
+	ppp_asynctty_close(tty);
+}
+
+/*
+ * 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 *buf, size_t count,
+		  void **cookie, unsigned long offset)
+{
+	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, 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 = -EFAULT;
+		if (put_user(ppp_channel_index(&ap->chan), p))
+			break;
+		err = 0;
+		break;
+
+	case PPPIOCGUNIT:
+		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 = n_tty_ioctl_helper(tty, cmd, 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, cmd, arg);
+	}
+
+	ap_put(ap);
+	return err;
+}
+
+/* No kernel lock - fine */
+static __poll_t
+ppp_asynctty_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
+{
+	return 0;
+}
+
+/* May sleep, don't call from interrupt level or with interrupts disabled */
+static void
+ppp_asynctty_receive(struct tty_struct *tty, const unsigned char *buf,
+		  const 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);
+	tty_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_ops ppp_ldisc = {
+	.owner  = THIS_MODULE,
+	.num	= N_PPP,
+	.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(&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(struct tasklet_struct *t)
+{
+	struct asyncppp *ap = from_tasklet(ap, t, tsk);
+	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 ^ PPP_TRANS;			\
+	} 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 = get_unaligned_be16(data);
+
+	/*
+	 * 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;
+
+	consume_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->ops->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;
+
+	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);
+	}
+
+	/* If protocol field is not compressed, it can be LCP packet */
+	if (!(p[0] & 0x01)) {
+		unsigned int proto;
+
+		if (skb->len < 2)
+			goto err;
+		proto = (p[0] << 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,
+		const 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_data(skb, buf, n);
+				if (ap->state & SC_ESCAPE) {
+					sp[0] ^= PPP_TRANS;
+					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 = get_unaligned_be16(data + 2);
+	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 = get_unaligned_be16(data + 2);
+			if (inbound)
+				ap->mru = val;
+			else
+				ap->chan.mtu = val;
+			break;
+		case LCP_ASYNCMAP:
+			val = get_unaligned_be32(data + 2);
+			if (inbound)
+				ap->raccm = val;
+			else
+				ap->xaccm[0] = val;
+			break;
+		}
+		dlen -= data[1];
+		data += data[1];
+	}
+}
+
+static void __exit ppp_async_cleanup(void)
+{
+	tty_unregister_ldisc(&ppp_ldisc);
+}
+
+module_init(ppp_async_init);
+module_exit(ppp_async_cleanup);