[net-next-2.6.git] / drivers / net / ppp_synctty.c

/*
 * PPP synchronous tty channel driver for Linux.
 *
 * This is a ppp channel driver that can be used with tty device drivers
 * that are frame oriented, such as synchronous HDLC devices.
 *
 * Complete PPP frames without encoding/decoding are exchanged between
 * the channel driver and the device driver.
 *
 * The async map IOCTL codes are implemented to keep the user mode
 * applications happy if they call them. Synchronous PPP does not use
 * the async maps.
 *
 * Copyright 1999 Paul Mackerras.
 *
 * Also touched by the grubby hands of Paul Fulghum paulkf@microgate.com
 *
 *  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 sync 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.
 *
 * ==FILEVERSION 20040616==
 */

#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/ppp_defs.h>
#include <linux/if_ppp.h>
#include <linux/ppp_channel.h>
#include <linux/spinlock.h>
#include <linux/completion.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <asm/uaccess.h>

#define PPP_VERSION	"2.4.2"

/* Structure for storing local state. */
struct syncppp {
	struct tty_struct *tty;
	unsigned int	flags;
	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;
	unsigned long	last_xmit;

	struct sk_buff_head rqueue;

	struct tasklet_struct tsk;

	atomic_t	refcnt;
	struct completion dead_cmp;
	struct ppp_channel chan;	/* interface to generic ppp layer */
};

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

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

#define PPPSYNC_MAX_RQLEN	32	/* arbitrary */

/*
 * Prototypes.
 */
static struct sk_buff* ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *);
static int ppp_sync_send(struct ppp_channel *chan, struct sk_buff *skb);
static int ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd,
			  unsigned long arg);
static void ppp_sync_process(unsigned long arg);
static int ppp_sync_push(struct syncppp *ap);
static void ppp_sync_flush_output(struct syncppp *ap);
static void ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
			   char *flags, int count);

static const struct ppp_channel_ops sync_ops = {
	.start_xmit = ppp_sync_send,
	.ioctl      = ppp_sync_ioctl,
};

/*
 * Utility procedures to print a buffer in hex/ascii
 */
static void
ppp_print_hex (register __u8 * out, const __u8 * in, int count)
{
	register __u8 next_ch;
	static const char hex[] = "0123456789ABCDEF";

	while (count-- > 0) {
		next_ch = *in++;
		*out++ = hex[(next_ch >> 4) & 0x0F];
		*out++ = hex[next_ch & 0x0F];
		++out;
	}
}

static void
ppp_print_char (register __u8 * out, const __u8 * in, int count)
{
	register __u8 next_ch;

	while (count-- > 0) {
		next_ch = *in++;

		if (next_ch < 0x20 || next_ch > 0x7e)
			*out++ = '.';
		else {
			*out++ = next_ch;
			if (next_ch == '%')   /* printk/syslogd has a bug !! */
				*out++ = '%';
		}
	}
	*out = '\0';
}

static void
ppp_print_buffer (const char *name, const __u8 *buf, int count)
{
	__u8 line[44];

	if (name != NULL)
		printk(KERN_DEBUG "ppp_synctty: %s, count = %d\n", name, count);

	while (count > 8) {
		memset (line, 32, 44);
		ppp_print_hex (line, buf, 8);
		ppp_print_char (&line[8 * 3], buf, 8);
		printk(KERN_DEBUG "%s\n", line);
		count -= 8;
		buf += 8;
	}

	if (count > 0) {
		memset (line, 32, 44);
		ppp_print_hex (line, buf, count);
		ppp_print_char (&line[8 * 3], buf, count);
		printk(KERN_DEBUG "%s\n", line);
	}
}


/*
 * Routines implementing the synchronous 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_synctty_receive while another
 * calls ppp_synctty_close, which zeroes tty->disc_data and
 * frees the memory that ppp_synctty_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: Fixed in tty_io nowdays.
 */
static DEFINE_RWLOCK(disc_data_lock);

static struct syncppp *sp_get(struct tty_struct *tty)
{
	struct syncppp *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 sp_put(struct syncppp *ap)
{
	if (atomic_dec_and_test(&ap->refcnt))
		complete(&ap->dead_cmp);
}

/*
 * Called when a tty is put into sync-PPP line discipline.
 */
static int
ppp_sync_open(struct tty_struct *tty)
{
	struct syncppp *ap;
	int err;
	int speed;

	if (tty->ops->write == NULL)
		return -EOPNOTSUPP;

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

	/* initialize the syncppp 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;

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

	atomic_set(&ap->refcnt, 1);
	init_completion(&ap->dead_cmp);

	ap->chan.private = ap;
	ap->chan.ops = &sync_ops;
	ap->chan.mtu = PPP_MRU;
	ap->chan.hdrlen = 2;	/* for A/C bytes */
	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_synctty_* routines to
 * finish before we can call ppp_unregister_channel and free
 * the syncppp struct.  This routine must be called from
 * process context, not interrupt or softirq context.
 */
static void
ppp_sync_close(struct tty_struct *tty)
{
	struct syncppp *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_sync_send/ioctl) are in progress
	 * by the time it returns.
	 */
	if (!atomic_dec_and_test(&ap->refcnt))
		wait_for_completion(&ap->dead_cmp);
	tasklet_kill(&ap->tsk);

	ppp_unregister_channel(&ap->chan);
	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 int ppp_sync_hangup(struct tty_struct *tty)
{
	ppp_sync_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_sync_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_sync_write(struct tty_struct *tty, struct file *file,
		const unsigned char *buf, size_t count)
{
	return -EAGAIN;
}

static int
ppp_synctty_ioctl(struct tty_struct *tty, struct file *file,
		  unsigned int cmd, unsigned long arg)
{
	struct syncppp *ap = sp_get(tty);
	int __user *p = (int __user *)arg;
	int err, val;

	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_sync_flush_output(ap);
		err = tty_perform_flush(tty, arg);
		break;

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

	default:
		err = tty_mode_ioctl(tty, file, cmd, arg);
		break;
	}

	sp_put(ap);
	return err;
}

/* No kernel lock - fine */
static unsigned int
ppp_sync_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_sync_receive(struct tty_struct *tty, const unsigned char *buf,
		  char *cflags, int count)
{
	struct syncppp *ap = sp_get(tty);
	unsigned long flags;

	if (!ap)
		return;
	spin_lock_irqsave(&ap->recv_lock, flags);
	ppp_sync_input(ap, buf, cflags, count);
	spin_unlock_irqrestore(&ap->recv_lock, flags);
	if (!skb_queue_empty(&ap->rqueue))
		tasklet_schedule(&ap->tsk);
	sp_put(ap);
	tty_unthrottle(tty);
}

static void
ppp_sync_wakeup(struct tty_struct *tty)
{
	struct syncppp *ap = sp_get(tty);

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


static struct tty_ldisc_ops ppp_sync_ldisc = {
	.owner	= THIS_MODULE,
	.magic	= TTY_LDISC_MAGIC,
	.name	= "pppsync",
	.open	= ppp_sync_open,
	.close	= ppp_sync_close,
	.hangup	= ppp_sync_hangup,
	.read	= ppp_sync_read,
	.write	= ppp_sync_write,
	.ioctl	= ppp_synctty_ioctl,
	.poll	= ppp_sync_poll,
	.receive_buf = ppp_sync_receive,
	.write_wakeup = ppp_sync_wakeup,
};

static int __init
ppp_sync_init(void)
{
	int err;

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

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

	err = -EFAULT;
	switch (cmd) {
	case PPPIOCGFLAGS:
		val = ap->flags | ap->rbits;
		if (put_user(val, (int __user *) argp))
			break;
		err = 0;
		break;
	case PPPIOCSFLAGS:
		if (get_user(val, (int __user *) argp))
			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], p))
			break;
		err = 0;
		break;
	case PPPIOCSASYNCMAP:
		if (get_user(ap->xaccm[0], p))
			break;
		err = 0;
		break;

	case PPPIOCGRASYNCMAP:
		if (put_user(ap->raccm, p))
			break;
		err = 0;
		break;
	case PPPIOCSRASYNCMAP:
		if (get_user(ap->raccm, p))
			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, (int __user *) argp))
			break;
		err = 0;
		break;
	case PPPIOCSMRU:
		if (get_user(val, (int __user *) argp))
			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_sync_process(unsigned long arg)
{
	struct syncppp *ap = (struct syncppp *) arg;
	struct sk_buff *skb;

	/* process received packets */
	while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
		if (skb->len == 0) {
			/* zero length buffers indicate error */
			ppp_input_error(&ap->chan, 0);
			kfree_skb(skb);
		}
		else
			ppp_input(&ap->chan, skb);
	}

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

/*
 * Procedures for encapsulation and framing.
 */

static struct sk_buff*
ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb)
{
	int proto;
	unsigned char *data;
	int islcp;

	data  = skb->data;
	proto = (data[0] << 8) + data[1];

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

	/* compress protocol field if option enabled */
	if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp)
		skb_pull(skb,1);

	/* prepend address/control fields if necessary */
	if ((ap->flags & SC_COMP_AC) == 0 || islcp) {
		if (skb_headroom(skb) < 2) {
			struct sk_buff *npkt = dev_alloc_skb(skb->len + 2);
			if (npkt == NULL) {
				kfree_skb(skb);
				return NULL;
			}
			skb_reserve(npkt,2);
			skb_copy_from_linear_data(skb,
				      skb_put(npkt, skb->len), skb->len);
			kfree_skb(skb);
			skb = npkt;
		}
		skb_push(skb,2);
		skb->data[0] = PPP_ALLSTATIONS;
		skb->data[1] = PPP_UI;
	}

	ap->last_xmit = jiffies;

	if (skb && ap->flags & SC_LOG_OUTPKT)
		ppp_print_buffer ("send buffer", skb->data, skb->len);

	return skb;
}

/*
 * Transmit-side routines.
 */

/*
 * Send a packet to the peer over an sync 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_sync_send(struct ppp_channel *chan, struct sk_buff *skb)
{
	struct syncppp *ap = chan->private;

	ppp_sync_push(ap);

	if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
		return 0;	/* already full */
	skb = ppp_sync_txmunge(ap, skb);
	if (skb != NULL)
		ap->tpkt = skb;
	else
		clear_bit(XMIT_FULL, &ap->xmit_flags);

	ppp_sync_push(ap);
	return 1;
}

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

	if (!spin_trylock_bh(&ap->xmit_lock))
		return 0;
	for (;;) {
		if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
			tty_stuffed = 0;
		if (!tty_stuffed && ap->tpkt) {
			set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
			sent = tty->ops->write(tty, ap->tpkt->data, ap->tpkt->len);
			if (sent < 0)
				goto flush;	/* error, e.g. loss of CD */
			if (sent < ap->tpkt->len) {
				tty_stuffed = 1;
			} else {
				kfree_skb(ap->tpkt);
				ap->tpkt = NULL;
				clear_bit(XMIT_FULL, &ap->xmit_flags);
				done = 1;
			}
			continue;
		}
		/* haven't made any progress */
		spin_unlock_bh(&ap->xmit_lock);
		if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags) ||
		      (!tty_stuffed && ap->tpkt)))
			break;
		if (!spin_trylock_bh(&ap->xmit_lock))
			break;
	}
	return done;

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

/*
 * Flush output from our internal buffers.
 * Called for the TCFLSH ioctl.
 */
static void
ppp_sync_flush_output(struct syncppp *ap)
{
	int done = 0;

	spin_lock_bh(&ap->xmit_lock);
	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.
 */

/* called when the tty driver has data for us.
 *
 * Data is frame oriented: each call to ppp_sync_input is considered
 * a whole frame. If the 1st flag byte is non-zero then the whole
 * frame is considered to be in error and is tossed.
 */
static void
ppp_sync_input(struct syncppp *ap, const unsigned char *buf,
		char *flags, int count)
{
	struct sk_buff *skb;
	unsigned char *p;

	if (count == 0)
		return;

	if (ap->flags & SC_LOG_INPKT)
		ppp_print_buffer ("receive buffer", buf, count);

	/* stuff the chars in the skb */
	skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2);
	if (!skb) {
		printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
		goto err;
	}
	/* Try to get the payload 4-byte aligned */
	if (buf[0] != PPP_ALLSTATIONS)
		skb_reserve(skb, 2 + (buf[0] & 1));

	if (flags && *flags) {
		/* error flag set, ignore frame */
		goto err;
	} else if (count > skb_tailroom(skb)) {
		/* packet overflowed MRU */
		goto err;
	}

	p = skb_put(skb, count);
	memcpy(p, buf, count);

	/* strip address/control field if present */
	p = skb->data;
	if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
		/* chop off address/control */
		if (skb->len < 3)
			goto err;
		p = skb_pull(skb, 2);
	}

	/* decompress protocol field if compressed */
	if (p[0] & 1) {
		/* protocol is compressed */
		skb_push(skb, 1)[0] = 0;
	} else if (skb->len < 2)
		goto err;

	/* queue the frame to be processed */
	skb_queue_tail(&ap->rqueue, skb);
	return;

err:
	/* queue zero length packet as error indication */
	if (skb || (skb = dev_alloc_skb(0))) {
		skb_trim(skb, 0);
		skb_queue_tail(&ap->rqueue, skb);
	}
}

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

module_init(ppp_sync_init);
module_exit(ppp_sync_cleanup);
MODULE_LICENSE("GPL");
MODULE_ALIAS_LDISC(N_SYNC_PPP);
Commit	Line	Data
1da177e4 LT	1	/*
	2	* PPP synchronous tty channel driver for Linux.
	3	*
	4	* This is a ppp channel driver that can be used with tty device drivers
	5	* that are frame oriented, such as synchronous HDLC devices.
	6	*
	7	* Complete PPP frames without encoding/decoding are exchanged between
	8	* the channel driver and the device driver.
6aa20a22	9	*
1da177e4 LT	10	* The async map IOCTL codes are implemented to keep the user mode
	11	* applications happy if they call them. Synchronous PPP does not use
	12	* the async maps.
	13	*
	14	* Copyright 1999 Paul Mackerras.
	15	*
	16	* Also touched by the grubby hands of Paul Fulghum paulkf@microgate.com
	17	*
	18	* This program is free software; you can redistribute it and/or
	19	* modify it under the terms of the GNU General Public License
	20	* as published by the Free Software Foundation; either version
	21	* 2 of the License, or (at your option) any later version.
	22	*
	23	* This driver provides the encapsulation and framing for sending
	24	* and receiving PPP frames over sync serial lines. It relies on
	25	* the generic PPP layer to give it frames to send and to process
	26	* received frames. It implements the PPP line discipline.
	27	*
	28	* Part of the code in this driver was inspired by the old async-only
	29	* PPP driver, written by Michael Callahan and Al Longyear, and
	30	* subsequently hacked by Paul Mackerras.
	31	*
	32	* ==FILEVERSION 20040616==
	33	*/
	34
	35	#include <linux/module.h>
	36	#include <linux/kernel.h>
	37	#include <linux/skbuff.h>
	38	#include <linux/tty.h>
	39	#include <linux/netdevice.h>
	40	#include <linux/poll.h>
	41	#include <linux/ppp_defs.h>
	42	#include <linux/if_ppp.h>
	43	#include <linux/ppp_channel.h>
	44	#include <linux/spinlock.h>
5e41fb83	45	#include <linux/completion.h>
1da177e4	46	#include <linux/init.h>
5a0e3ad6	47	#include <linux/slab.h>
1da177e4	48	#include <asm/uaccess.h>
1da177e4 LT	49
	50	#define PPP_VERSION "2.4.2"
	51
	52	/* Structure for storing local state. */
	53	struct syncppp {
	54	struct tty_struct *tty;
	55	unsigned int flags;
	56	unsigned int rbits;
	57	int mru;
	58	spinlock_t xmit_lock;
	59	spinlock_t recv_lock;
	60	unsigned long xmit_flags;
	61	u32 xaccm[8];
	62	u32 raccm;
	63	unsigned int bytes_sent;
	64	unsigned int bytes_rcvd;
	65
	66	struct sk_buff *tpkt;
	67	unsigned long last_xmit;
	68
	69	struct sk_buff_head rqueue;
	70
	71	struct tasklet_struct tsk;
	72
	73	atomic_t refcnt;
5e41fb83	74	struct completion dead_cmp;
1da177e4 LT	75	struct ppp_channel chan; /* interface to generic ppp layer */
	76	};
	77
	78	/* Bit numbers in xmit_flags */
	79	#define XMIT_WAKEUP 0
	80	#define XMIT_FULL 1
	81
	82	/* Bits in rbits */
	83	#define SC_RCV_BITS (SC_RCV_B7_1\|SC_RCV_B7_0\|SC_RCV_ODDP\|SC_RCV_EVNP)
	84
	85	#define PPPSYNC_MAX_RQLEN 32 /* arbitrary */
	86
	87	/*
	88	* Prototypes.
	89	*/
	90	static struct sk_buff* ppp_sync_txmunge(struct syncppp ap, struct sk_buff );
	91	static int ppp_sync_send(struct ppp_channel chan, struct sk_buff skb);
	92	static int ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd,
	93	unsigned long arg);
	94	static void ppp_sync_process(unsigned long arg);
	95	static int ppp_sync_push(struct syncppp *ap);
	96	static void ppp_sync_flush_output(struct syncppp *ap);
	97	static void ppp_sync_input(struct syncppp ap, const unsigned char buf,
	98	char *flags, int count);
	99
d7100da0	100	static const struct ppp_channel_ops sync_ops = {
	101	.start_xmit = ppp_sync_send,
	102	.ioctl = ppp_sync_ioctl,
1da177e4 LT	103	};
	104
	105	/*
	106	* Utility procedures to print a buffer in hex/ascii
	107	*/
	108	static void
	109	ppp_print_hex (register __u8 * out, const __u8 * in, int count)
	110	{
	111	register __u8 next_ch;
f71e1309	112	static const char hex[] = "0123456789ABCDEF";
1da177e4 LT	113
	114	while (count-- > 0) {
	115	next_ch = *in++;
	116	*out++ = hex[(next_ch >> 4) & 0x0F];
	117	*out++ = hex[next_ch & 0x0F];
	118	++out;
	119	}
	120	}
	121
	122	static void
	123	ppp_print_char (register __u8 * out, const __u8 * in, int count)
	124	{
	125	register __u8 next_ch;
	126
	127	while (count-- > 0) {
	128	next_ch = *in++;
	129
	130	if (next_ch < 0x20 \|\| next_ch > 0x7e)
	131	*out++ = '.';
	132	else {
	133	*out++ = next_ch;
	134	if (next_ch == '%') /* printk/syslogd has a bug !! */
	135	*out++ = '%';
	136	}
	137	}
	138	*out = '\0';
	139	}
	140
	141	static void
	142	ppp_print_buffer (const char name, const __u8 buf, int count)
	143	{
	144	__u8 line[44];
	145
	146	if (name != NULL)
	147	printk(KERN_DEBUG "ppp_synctty: %s, count = %d\n", name, count);
	148
	149	while (count > 8) {
	150	memset (line, 32, 44);
	151	ppp_print_hex (line, buf, 8);
	152	ppp_print_char (&line[8 * 3], buf, 8);
	153	printk(KERN_DEBUG "%s\n", line);
	154	count -= 8;
	155	buf += 8;
	156	}
	157
	158	if (count > 0) {
	159	memset (line, 32, 44);
	160	ppp_print_hex (line, buf, count);
	161	ppp_print_char (&line[8 * 3], buf, count);
	162	printk(KERN_DEBUG "%s\n", line);
	163	}
	164	}
	165
	166
	167	/*
	168	* Routines implementing the synchronous PPP line discipline.
	169	*/
	170
	171	/*
	172	* We have a potential race on dereferencing tty->disc_data,
	173	* because the tty layer provides no locking at all - thus one
	174	* cpu could be running ppp_synctty_receive while another
	175	* calls ppp_synctty_close, which zeroes tty->disc_data and
	176	* frees the memory that ppp_synctty_receive is using. The best
177	* way to fix this is to use a rwlock in the tty struct, but for now
178	* we use a single global rwlock for all ttys in ppp line discipline.
179	*
180	* FIXME: Fixed in tty_io nowdays.
181	*/
182	static DEFINE_RWLOCK(disc_data_lock);
183
184	static struct syncppp sp_get(struct tty_struct tty)
185	{
186	struct syncppp *ap;
187
188	read_lock(&disc_data_lock);
189	ap = tty->disc_data;
190	if (ap != NULL)
191	atomic_inc(&ap->refcnt);
192	read_unlock(&disc_data_lock);
193	return ap;
194	}
195
196	static void sp_put(struct syncppp *ap)
197	{
198	if (atomic_dec_and_test(&ap->refcnt))
5e41fb83	199	complete(&ap->dead_cmp);
1da177e4 LT	200	}
	201
	202	/*
	203	* Called when a tty is put into sync-PPP line discipline.
	204	*/
	205	static int
	206	ppp_sync_open(struct tty_struct *tty)
	207	{
	208	struct syncppp *ap;
	209	int err;
9c705260	210	int speed;
1da177e4	211
f34d7a5b AC	212	if (tty->ops->write == NULL)
	213	return -EOPNOTSUPP;
	214
dd00cc48	215	ap = kzalloc(sizeof(*ap), GFP_KERNEL);
1da177e4	216	err = -ENOMEM;
cd228d54	217	if (!ap)
1da177e4 LT	218	goto out;
	219
	220	/* initialize the syncppp structure */
1da177e4 LT	221	ap->tty = tty;
	222	ap->mru = PPP_MRU;
	223	spin_lock_init(&ap->xmit_lock);
	224	spin_lock_init(&ap->recv_lock);
	225	ap->xaccm[0] = ~0U;
	226	ap->xaccm[3] = 0x60000000U;
	227	ap->raccm = ~0U;
	228
	229	skb_queue_head_init(&ap->rqueue);
	230	tasklet_init(&ap->tsk, ppp_sync_process, (unsigned long) ap);
	231
	232	atomic_set(&ap->refcnt, 1);
5e41fb83	233	init_completion(&ap->dead_cmp);
1da177e4 LT	234
	235	ap->chan.private = ap;
	236	ap->chan.ops = &sync_ops;
	237	ap->chan.mtu = PPP_MRU;
	238	ap->chan.hdrlen = 2; /* for A/C bytes */
9c705260 GP	239	speed = tty_get_baud_rate(tty);
9c705260 GP	240	ap->chan.speed = speed;
1da177e4 LT	241	err = ppp_register_channel(&ap->chan);
	242	if (err)
	243	goto out_free;
	244
	245	tty->disc_data = ap;
33f0f88f	246	tty->receive_room = 65536;
1da177e4 LT	247	return 0;
	248
	249	out_free:
	250	kfree(ap);
	251	out:
	252	return err;
	253	}
	254
	255	/*
	256	* Called when the tty is put into another line discipline
	257	* or it hangs up. We have to wait for any cpu currently
	258	* executing in any of the other ppp_synctty_* routines to
	259	* finish before we can call ppp_unregister_channel and free
	260	* the syncppp struct. This routine must be called from
	261	* process context, not interrupt or softirq context.
	262	*/
	263	static void
	264	ppp_sync_close(struct tty_struct *tty)
	265	{
	266	struct syncppp *ap;
	267
	268	write_lock_irq(&disc_data_lock);
	269	ap = tty->disc_data;
	270	tty->disc_data = NULL;
	271	write_unlock_irq(&disc_data_lock);
cd228d54	272	if (!ap)
1da177e4 LT	273	return;
	274
	275	/*
	276	* We have now ensured that nobody can start using ap from now
	277	* on, but we have to wait for all existing users to finish.
	278	* Note that ppp_unregister_channel ensures that no calls to
	279	* our channel ops (i.e. ppp_sync_send/ioctl) are in progress
	280	* by the time it returns.
	281	*/
	282	if (!atomic_dec_and_test(&ap->refcnt))
5e41fb83	283	wait_for_completion(&ap->dead_cmp);
1da177e4 LT	284	tasklet_kill(&ap->tsk);
	285
	286	ppp_unregister_channel(&ap->chan);
	287	skb_queue_purge(&ap->rqueue);
1d2f8c95	288	kfree_skb(ap->tpkt);
1da177e4 LT	289	kfree(ap);
	290	}
	291
	292	/*
	293	* Called on tty hangup in process context.
	294	*
	295	* Wait for I/O to driver to complete and unregister PPP channel.
	296	* This is already done by the close routine, so just call that.
	297	*/
	298	static int ppp_sync_hangup(struct tty_struct *tty)
	299	{
	300	ppp_sync_close(tty);
	301	return 0;
	302	}
	303
	304	/*
	305	* Read does nothing - no data is ever available this way.
	306	* Pppd reads and writes packets via /dev/ppp instead.
	307	*/
	308	static ssize_t
	309	ppp_sync_read(struct tty_struct tty, struct file file,
	310	unsigned char __user *buf, size_t count)
	311	{
	312	return -EAGAIN;
	313	}
	314
	315	/*
	316	* Write on the tty does nothing, the packets all come in
	317	* from the ppp generic stuff.
	318	*/
	319	static ssize_t
	320	ppp_sync_write(struct tty_struct tty, struct file file,
	321	const unsigned char *buf, size_t count)
	322	{
	323	return -EAGAIN;
	324	}
	325
	326	static int
	327	ppp_synctty_ioctl(struct tty_struct tty, struct file file,
	328	unsigned int cmd, unsigned long arg)
	329	{
	330	struct syncppp *ap = sp_get(tty);
	331	int __user p = (int __user )arg;
	332	int err, val;
	333
cd228d54	334	if (!ap)
1da177e4 LT	335	return -ENXIO;
	336	err = -EFAULT;
	337	switch (cmd) {
	338	case PPPIOCGCHAN:
1da177e4 LT	339	err = -EFAULT;
	340	if (put_user(ppp_channel_index(&ap->chan), p))
	341	break;
	342	err = 0;
	343	break;
	344
	345	case PPPIOCGUNIT:
1da177e4 LT	346	err = -EFAULT;
	347	if (put_user(ppp_unit_number(&ap->chan), p))
	348	break;
	349	err = 0;
	350	break;
	351
1da177e4 LT	352	case TCFLSH:
	353	/* flush our buffers and the serial port's buffer */
	354	if (arg == TCIOFLUSH \|\| arg == TCOFLUSH)
	355	ppp_sync_flush_output(ap);
d0127539	356	err = tty_perform_flush(tty, arg);
1da177e4 LT	357	break;
	358
	359	case FIONREAD:
	360	val = 0;
	361	if (put_user(val, p))
	362	break;
	363	err = 0;
	364	break;
	365
	366	default:
d0127539 AC	367	err = tty_mode_ioctl(tty, file, cmd, arg);
d0127539 AC	368	break;
1da177e4 LT	369	}
	370
	371	sp_put(ap);
	372	return err;
	373	}
	374
	375	/* No kernel lock - fine */
	376	static unsigned int
	377	ppp_sync_poll(struct tty_struct tty, struct file file, poll_table *wait)
	378	{
	379	return 0;
	380	}
	381
92d326f6	382	/* May sleep, don't call from interrupt level or with interrupts disabled */
1da177e4 LT	383	static void
	384	ppp_sync_receive(struct tty_struct tty, const unsigned char buf,
	385	char *cflags, int count)
	386	{
	387	struct syncppp *ap = sp_get(tty);
	388	unsigned long flags;
	389
cd228d54	390	if (!ap)
1da177e4 LT	391	return;
	392	spin_lock_irqsave(&ap->recv_lock, flags);
	393	ppp_sync_input(ap, buf, cflags, count);
	394	spin_unlock_irqrestore(&ap->recv_lock, flags);
b03efcfb	395	if (!skb_queue_empty(&ap->rqueue))
1da177e4 LT	396	tasklet_schedule(&ap->tsk);
1da177e4 LT	397	sp_put(ap);
4a21b8cb	398	tty_unthrottle(tty);
1da177e4 LT	399	}
	400
	401	static void
	402	ppp_sync_wakeup(struct tty_struct *tty)
	403	{
	404	struct syncppp *ap = sp_get(tty);
	405
	406	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
cd228d54	407	if (!ap)
1da177e4 LT	408	return;
	409	set_bit(XMIT_WAKEUP, &ap->xmit_flags);
	410	tasklet_schedule(&ap->tsk);
	411	sp_put(ap);
	412	}
	413
	414
a352def2	415	static struct tty_ldisc_ops ppp_sync_ldisc = {
1da177e4 LT	416	.owner = THIS_MODULE,
	417	.magic = TTY_LDISC_MAGIC,
	418	.name = "pppsync",
	419	.open = ppp_sync_open,
	420	.close = ppp_sync_close,
	421	.hangup = ppp_sync_hangup,
	422	.read = ppp_sync_read,
	423	.write = ppp_sync_write,
	424	.ioctl = ppp_synctty_ioctl,
	425	.poll = ppp_sync_poll,
1da177e4 LT	426	.receive_buf = ppp_sync_receive,
	427	.write_wakeup = ppp_sync_wakeup,
	428	};
	429
	430	static int __init
	431	ppp_sync_init(void)
	432	{
	433	int err;
	434
	435	err = tty_register_ldisc(N_SYNC_PPP, &ppp_sync_ldisc);
	436	if (err != 0)
	437	printk(KERN_ERR "PPP_sync: error %d registering line disc.\n",
	438	err);
	439	return err;
	440	}
	441
	442	/*
	443	* The following routines provide the PPP channel interface.
	444	*/
	445	static int
	446	ppp_sync_ioctl(struct ppp_channel *chan, unsigned int cmd, unsigned long arg)
	447	{
	448	struct syncppp *ap = chan->private;
	449	int err, val;
	450	u32 accm[8];
	451	void __user argp = (void __user )arg;
	452	u32 __user *p = argp;
	453
	454	err = -EFAULT;
	455	switch (cmd) {
	456	case PPPIOCGFLAGS:
	457	val = ap->flags \| ap->rbits;
	458	if (put_user(val, (int __user *) argp))
	459	break;
	460	err = 0;
	461	break;
	462	case PPPIOCSFLAGS:
	463	if (get_user(val, (int __user *) argp))
	464	break;
	465	ap->flags = val & ~SC_RCV_BITS;
	466	spin_lock_irq(&ap->recv_lock);
	467	ap->rbits = val & SC_RCV_BITS;
	468	spin_unlock_irq(&ap->recv_lock);
	469	err = 0;
	470	break;
	471
	472	case PPPIOCGASYNCMAP:
	473	if (put_user(ap->xaccm[0], p))
	474	break;
	475	err = 0;
	476	break;
	477	case PPPIOCSASYNCMAP:
	478	if (get_user(ap->xaccm[0], p))
	479	break;
	480	err = 0;
	481	break;
	482
	483	case PPPIOCGRASYNCMAP:
	484	if (put_user(ap->raccm, p))
	485	break;
	486	err = 0;
	487	break;
	488	case PPPIOCSRASYNCMAP:
	489	if (get_user(ap->raccm, p))
490	break;
491	err = 0;
492	break;
493
494	case PPPIOCGXASYNCMAP:
495	if (copy_to_user(argp, ap->xaccm, sizeof(ap->xaccm)))
496	break;
497	err = 0;
498	break;
499	case PPPIOCSXASYNCMAP:
500	if (copy_from_user(accm, argp, sizeof(accm)))
501	break;
502	accm[2] &= ~0x40000000U; /* can't escape 0x5e */
503	accm[3] \|= 0x60000000U; /* must escape 0x7d, 0x7e */
504	memcpy(ap->xaccm, accm, sizeof(ap->xaccm));
505	err = 0;
506	break;
507
508	case PPPIOCGMRU:
509	if (put_user(ap->mru, (int __user *) argp))
510	break;
511	err = 0;
512	break;
513	case PPPIOCSMRU:
514	if (get_user(val, (int __user *) argp))
515	break;
516	if (val < PPP_MRU)
517	val = PPP_MRU;
518	ap->mru = val;
519	err = 0;
520	break;
521
522	default:
523	err = -ENOTTY;
524	}
525	return err;
526	}
527
528	/*
529	* This is called at softirq level to deliver received packets
530	* to the ppp_generic code, and to tell the ppp_generic code
531	* if we can accept more output now.
532	*/
533	static void ppp_sync_process(unsigned long arg)
534	{
535	struct syncppp ap = (struct syncppp ) arg;
536	struct sk_buff *skb;
537
538	/* process received packets */
539	while ((skb = skb_dequeue(&ap->rqueue)) != NULL) {
540	if (skb->len == 0) {
541	/* zero length buffers indicate error */
542	ppp_input_error(&ap->chan, 0);
543	kfree_skb(skb);
544	}
545	else
546	ppp_input(&ap->chan, skb);
547	}
548
549	/* try to push more stuff out */
550	if (test_bit(XMIT_WAKEUP, &ap->xmit_flags) && ppp_sync_push(ap))
551	ppp_output_wakeup(&ap->chan);
552	}
553
554	/*
555	* Procedures for encapsulation and framing.
556	*/
557
3c582b30	558	static struct sk_buff*
1da177e4 LT	559	ppp_sync_txmunge(struct syncppp ap, struct sk_buff skb)
	560	{
	561	int proto;
	562	unsigned char *data;
	563	int islcp;
	564
	565	data = skb->data;
	566	proto = (data[0] << 8) + data[1];
	567
	568	/* LCP packets with codes between 1 (configure-request)
	569	* and 7 (code-reject) must be sent as though no options
	570	* have been negotiated.
	571	*/
	572	islcp = proto == PPP_LCP && 1 <= data[2] && data[2] <= 7;
	573
	574	/* compress protocol field if option enabled */
	575	if (data[0] == 0 && (ap->flags & SC_COMP_PROT) && !islcp)
	576	skb_pull(skb,1);
	577
	578	/* prepend address/control fields if necessary */
	579	if ((ap->flags & SC_COMP_AC) == 0 \|\| islcp) {
	580	if (skb_headroom(skb) < 2) {
	581	struct sk_buff *npkt = dev_alloc_skb(skb->len + 2);
	582	if (npkt == NULL) {
	583	kfree_skb(skb);
	584	return NULL;
	585	}
	586	skb_reserve(npkt,2);
d626f62b ACM	587	skb_copy_from_linear_data(skb,
d626f62b ACM	588	skb_put(npkt, skb->len), skb->len);
1da177e4 LT	589	kfree_skb(skb);
	590	skb = npkt;
	591	}
	592	skb_push(skb,2);
	593	skb->data[0] = PPP_ALLSTATIONS;
	594	skb->data[1] = PPP_UI;
	595	}
	596
	597	ap->last_xmit = jiffies;
	598
	599	if (skb && ap->flags & SC_LOG_OUTPKT)
	600	ppp_print_buffer ("send buffer", skb->data, skb->len);
	601
	602	return skb;
	603	}
	604
	605	/*
	606	* Transmit-side routines.
	607	*/
	608
	609	/*
	610	* Send a packet to the peer over an sync tty line.
	611	* Returns 1 iff the packet was accepted.
	612	* If the packet was not accepted, we will call ppp_output_wakeup
	613	* at some later time.
	614	*/
	615	static int
	616	ppp_sync_send(struct ppp_channel chan, struct sk_buff skb)
	617	{
	618	struct syncppp *ap = chan->private;
	619
	620	ppp_sync_push(ap);
	621
	622	if (test_and_set_bit(XMIT_FULL, &ap->xmit_flags))
	623	return 0; /* already full */
	624	skb = ppp_sync_txmunge(ap, skb);
	625	if (skb != NULL)
	626	ap->tpkt = skb;
	627	else
	628	clear_bit(XMIT_FULL, &ap->xmit_flags);
	629
	630	ppp_sync_push(ap);
	631	return 1;
	632	}
	633
	634	/*
	635	* Push as much data as possible out to the tty.
	636	*/
	637	static int
	638	ppp_sync_push(struct syncppp *ap)
	639	{
	640	int sent, done = 0;
	641	struct tty_struct *tty = ap->tty;
	642	int tty_stuffed = 0;
	643
	644	if (!spin_trylock_bh(&ap->xmit_lock))
	645	return 0;
	646	for (;;) {
	647	if (test_and_clear_bit(XMIT_WAKEUP, &ap->xmit_flags))
	648	tty_stuffed = 0;
cd228d54	649	if (!tty_stuffed && ap->tpkt) {
1da177e4	650	set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
f34d7a5b	651	sent = tty->ops->write(tty, ap->tpkt->data, ap->tpkt->len);
1da177e4 LT	652	if (sent < 0)
	653	goto flush; /* error, e.g. loss of CD */
	654	if (sent < ap->tpkt->len) {
	655	tty_stuffed = 1;
	656	} else {
	657	kfree_skb(ap->tpkt);
	658	ap->tpkt = NULL;
	659	clear_bit(XMIT_FULL, &ap->xmit_flags);
	660	done = 1;
	661	}
	662	continue;
	663	}
	664	/* haven't made any progress */
	665	spin_unlock_bh(&ap->xmit_lock);
8e95a202 JP	666	if (!(test_bit(XMIT_WAKEUP, &ap->xmit_flags) \|\|
8e95a202 JP	667	(!tty_stuffed && ap->tpkt)))
1da177e4 LT	668	break;
	669	if (!spin_trylock_bh(&ap->xmit_lock))
	670	break;
	671	}
	672	return done;
	673
	674	flush:
cd228d54	675	if (ap->tpkt) {
1da177e4 LT	676	kfree_skb(ap->tpkt);
	677	ap->tpkt = NULL;
	678	clear_bit(XMIT_FULL, &ap->xmit_flags);
	679	done = 1;
	680	}
	681	spin_unlock_bh(&ap->xmit_lock);
	682	return done;
	683	}
	684
	685	/*
	686	* Flush output from our internal buffers.
	687	* Called for the TCFLSH ioctl.
	688	*/
	689	static void
	690	ppp_sync_flush_output(struct syncppp *ap)
	691	{
	692	int done = 0;
	693
	694	spin_lock_bh(&ap->xmit_lock);
	695	if (ap->tpkt != NULL) {
	696	kfree_skb(ap->tpkt);
	697	ap->tpkt = NULL;
	698	clear_bit(XMIT_FULL, &ap->xmit_flags);
	699	done = 1;
	700	}
	701	spin_unlock_bh(&ap->xmit_lock);
	702	if (done)
	703	ppp_output_wakeup(&ap->chan);
	704	}
	705
	706	/*
	707	* Receive-side routines.
	708	*/
	709
	710	/* called when the tty driver has data for us.
	711	*
	712	* Data is frame oriented: each call to ppp_sync_input is considered
	713	* a whole frame. If the 1st flag byte is non-zero then the whole
	714	* frame is considered to be in error and is tossed.
	715	*/
	716	static void
	717	ppp_sync_input(struct syncppp ap, const unsigned char buf,
	718	char *flags, int count)
	719	{
	720	struct sk_buff *skb;
	721	unsigned char *p;
	722
	723	if (count == 0)
	724	return;
	725
	726	if (ap->flags & SC_LOG_INPKT)
	727	ppp_print_buffer ("receive buffer", buf, count);
	728
	729	/* stuff the chars in the skb */
cd228d54 JP	730	skb = dev_alloc_skb(ap->mru + PPP_HDRLEN + 2);
cd228d54 JP	731	if (!skb) {
1da177e4 LT	732	printk(KERN_ERR "PPPsync: no memory (input pkt)\n");
	733	goto err;
	734	}
	735	/* Try to get the payload 4-byte aligned */
	736	if (buf[0] != PPP_ALLSTATIONS)
	737	skb_reserve(skb, 2 + (buf[0] & 1));
	738
cd228d54	739	if (flags && *flags) {
1da177e4 LT	740	/* error flag set, ignore frame */
	741	goto err;
	742	} else if (count > skb_tailroom(skb)) {
	743	/* packet overflowed MRU */
	744	goto err;
	745	}
	746
	747	p = skb_put(skb, count);
	748	memcpy(p, buf, count);
	749
	750	/* strip address/control field if present */
	751	p = skb->data;
	752	if (p[0] == PPP_ALLSTATIONS && p[1] == PPP_UI) {
	753	/* chop off address/control */
	754	if (skb->len < 3)
	755	goto err;
	756	p = skb_pull(skb, 2);
	757	}
	758
	759	/* decompress protocol field if compressed */
	760	if (p[0] & 1) {
	761	/* protocol is compressed */
	762	skb_push(skb, 1)[0] = 0;
	763	} else if (skb->len < 2)
	764	goto err;
	765
	766	/* queue the frame to be processed */
	767	skb_queue_tail(&ap->rqueue, skb);
	768	return;
	769
	770	err:
	771	/* queue zero length packet as error indication */
	772	if (skb \|\| (skb = dev_alloc_skb(0))) {
	773	skb_trim(skb, 0);
	774	skb_queue_tail(&ap->rqueue, skb);
	775	}
	776	}
	777
	778	static void __exit
	779	ppp_sync_cleanup(void)
	780	{
64ccd715	781	if (tty_unregister_ldisc(N_SYNC_PPP) != 0)
1da177e4 LT	782	printk(KERN_ERR "failed to unregister Sync PPP line discipline\n");
	783	}
	784
	785	module_init(ppp_sync_init);
	786	module_exit(ppp_sync_cleanup);
	787	MODULE_LICENSE("GPL");
	788	MODULE_ALIAS_LDISC(N_SYNC_PPP);