patch-2.3.13 linux/drivers/net/ppp_async.c

• Lines: 958
• Date: Fri Aug 6 10:44:11 1999
• Orig file: v2.3.12/linux/drivers/net/ppp_async.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.3.12/linux/drivers/net/ppp_async.c linux/drivers/net/ppp_async.c
@@ -0,0 +1,957 @@
+/*
+ * 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.
+ *
+ * ==FILEVERSION 990806==
+ */
+
+/* $Id$ */
+
+#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 <asm/uaccess.h>
+
+#define PPP_VERSION	"2.4.0"
+
+#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;
+	unsigned long	busy;
+	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;
+	struct sk_buff_head xq;
+	unsigned long	last_xmit;
+
+	struct sk_buff	*rpkt;
+	struct sk_buff_head rq;
+	wait_queue_head_t rwait;
+
+	struct ppp_channel chan;	/* interface to generic ppp layer */
+	int		connected;
+	unsigned char	obuf[OBUFSIZE];
+};
+
+/* Bit numbers in busy */
+#define XMIT_BUSY	0
+#define RECV_BUSY	1
+#define XMIT_WAKEUP	2
+#define XMIT_FULL	3
+
+/* State bits */
+#define SC_TOSS		0x20000000
+#define SC_ESCAPE	0x40000000
+
+/* Bits in rbits */
+#define SC_RCV_BITS	(SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)
+
+#define PPPASYNC_MAX_RQLEN	32	/* arbitrary */
+
+static int flag_time = HZ;
+MODULE_PARM(flag_time, "i");
+
+/*
+ * 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);
+
+struct ppp_channel_ops async_ops = {
+	ppp_async_send
+};
+
+/*
+ * Routines for locking and unlocking the transmit and receive paths.
+ */
+static inline void
+lock_path(struct asyncppp *ap, int bit)
+{
+	do {
+		while (test_bit(bit, &ap->busy))
+		       mb();
+	} while (test_and_set_bit(bit, &ap->busy));
+	mb();
+}
+
+static inline int
+trylock_path(struct asyncppp *ap, int bit)
+{
+	if (test_and_set_bit(bit, &ap->busy))
+		return 0;
+	mb();
+	return 1;
+}
+
+static inline void
+unlock_path(struct asyncppp *ap, int bit)
+{
+	mb();
+	clear_bit(bit, &ap->busy);
+}
+
+#define lock_xmit_path(ap)	lock_path(ap, XMIT_BUSY)
+#define trylock_xmit_path(ap)	trylock_path(ap, XMIT_BUSY)
+#define unlock_xmit_path(ap)	unlock_path(ap, XMIT_BUSY)
+#define lock_recv_path(ap)	lock_path(ap, RECV_BUSY)
+#define trylock_recv_path(ap)	trylock_path(ap, RECV_BUSY)
+#define unlock_recv_path(ap)	unlock_path(ap, RECV_BUSY)
+
+static inline void
+flush_skb_queue(struct sk_buff_head *q)
+{
+	struct sk_buff *skb;
+
+	while ((skb = skb_dequeue(q)) != 0)
+		kfree_skb(skb);
+}
+
+/*
+ * Routines implementing the PPP line discipline.
+ */
+
+/*
+ * Called when a tty is put into PPP line discipline.
+ */
+static int
+ppp_async_open(struct tty_struct *tty)
+{
+	struct asyncppp *ap;
+
+	ap = kmalloc(sizeof(*ap), GFP_KERNEL);
+	if (ap == 0)
+		return -ENOMEM;
+
+	MOD_INC_USE_COUNT;
+
+	/* initialize the asyncppp structure */
+	memset(ap, 0, sizeof(*ap));
+	ap->tty = tty;
+	ap->mru = PPP_MRU;
+	ap->xaccm[0] = ~0U;
+	ap->xaccm[3] = 0x60000000U;
+	ap->raccm = ~0U;
+	ap->optr = ap->obuf;
+	ap->olim = ap->obuf;
+	skb_queue_head_init(&ap->xq);
+	skb_queue_head_init(&ap->rq);
+	init_waitqueue_head(&ap->rwait);
+
+	tty->disc_data = ap;
+
+	return 0;
+}
+
+/*
+ * Called when the tty is put into another line discipline
+ * (or it hangs up).
+ */
+static void
+ppp_async_close(struct tty_struct *tty)
+{
+	struct asyncppp *ap = tty->disc_data;
+
+	if (ap == 0)
+		return;
+	tty->disc_data = 0;
+	lock_xmit_path(ap);
+	lock_recv_path(ap);
+	if (ap->rpkt != 0)
+		kfree_skb(ap->rpkt);
+	flush_skb_queue(&ap->rq);
+	if (ap->tpkt != 0)
+		kfree_skb(ap->tpkt);
+	flush_skb_queue(&ap->xq);
+	if (ap->connected)
+		ppp_unregister_channel(&ap->chan);
+	kfree(ap);
+	MOD_DEC_USE_COUNT;
+}
+
+/*
+ * Read a PPP frame.  pppd can use this to negotiate over the
+ * channel before it joins it to a bundle.
+ */
+static ssize_t
+ppp_async_read(struct tty_struct *tty, struct file *file,
+	       unsigned char *buf, size_t count)
+{
+	struct asyncppp *ap = tty->disc_data;
+	DECLARE_WAITQUEUE(wait, current);
+	ssize_t ret;
+	struct sk_buff *skb = 0;
+
+	ret = -ENXIO;
+	if (ap == 0)
+		goto out;		/* should never happen */
+
+	add_wait_queue(&ap->rwait, &wait);
+	current->state = TASK_INTERRUPTIBLE;
+	for (;;) {
+		ret = -EAGAIN;
+		skb = skb_dequeue(&ap->rq);
+		if (skb)
+			break;
+		if (file->f_flags & O_NONBLOCK)
+			break;
+		ret = -ERESTARTSYS;
+		if (signal_pending(current))
+			break;
+		schedule();
+	}
+	current->state = TASK_RUNNING;
+	remove_wait_queue(&ap->rwait, &wait);
+
+	if (skb == 0)
+		goto out;
+
+	ret = -EOVERFLOW;
+	if (skb->len > count)
+		goto outf;
+	ret = -EFAULT;
+	if (copy_to_user(buf, skb->data, skb->len))
+		goto outf;
+	ret = skb->len;
+
+ outf:
+	kfree_skb(skb);
+ out:
+	return ret;
+}
+
+/*
+ * Write a ppp frame.  pppd can use this to send frames over
+ * this particular channel.
+ */
+static ssize_t
+ppp_async_write(struct tty_struct *tty, struct file *file,
+		const unsigned char *buf, size_t count)
+{
+	struct asyncppp *ap = tty->disc_data;
+	struct sk_buff *skb;
+	ssize_t ret;
+
+	ret = -ENXIO;
+	if (ap == 0)
+		goto out;	/* should never happen */
+
+	ret = -ENOMEM;
+	skb = alloc_skb(count + 2, GFP_KERNEL);
+	if (skb == 0)
+		goto out;
+	skb_reserve(skb, 2);
+	ret = -EFAULT;
+	if (copy_from_user(skb_put(skb, count), buf, count)) {
+		kfree_skb(skb);
+		goto out;
+	}
+
+	skb_queue_tail(&ap->xq, skb);
+	ppp_async_push(ap);
+
+	ret = count;
+
+ out:
+	return ret;
+}
+
+static int
+ppp_async_ioctl(struct tty_struct *tty, struct file *file,
+		unsigned int cmd, unsigned long arg)
+{
+	struct asyncppp *ap = tty->disc_data;
+	int err, val;
+	u32 accm[8];
+	struct sk_buff *skb;
+
+	err = -ENXIO;
+	if (ap == 0)
+		goto out;	/* should never happen */
+	err = -EPERM;
+	if (!capable(CAP_NET_ADMIN))
+		goto out;
+
+	err = -EFAULT;
+	switch (cmd) {
+	case PPPIOCGFLAGS:
+		val = ap->flags | ap->rbits;
+		if (put_user(ap->flags, (int *) arg))
+			break;
+		err = 0;
+		break;
+	case PPPIOCSFLAGS:
+		if (get_user(val, (int *) arg))
+			break;
+		ap->flags = val & ~SC_RCV_BITS;
+		ap->rbits = val & SC_RCV_BITS;
+		err = 0;
+		break;
+
+	case PPPIOCGASYNCMAP:
+		if (put_user(ap->xaccm[0], (u32 *) arg))
+			break;
+		err = 0;
+		break;
+	case PPPIOCSASYNCMAP:
+		if (get_user(ap->xaccm[0], (u32 *) arg))
+			break;
+		err = 0;
+		break;
+
+	case PPPIOCGRASYNCMAP:
+		if (put_user(ap->raccm, (u32 *) arg))
+			break;
+		err = 0;
+		break;
+	case PPPIOCSRASYNCMAP:
+		if (get_user(ap->raccm, (u32 *) arg))
+			break;
+		err = 0;
+		break;
+
+	case PPPIOCGXASYNCMAP:
+		if (copy_to_user((void *) arg, ap->xaccm, sizeof(ap->xaccm)))
+			break;
+		err = 0;
+		break;
+	case PPPIOCSXASYNCMAP:
+		if (copy_from_user(accm, (void *) arg, 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 *) arg))
+			break;
+		err = 0;
+		break;
+	case PPPIOCSMRU:
+		if (get_user(val, (int *) arg))
+			break;
+		if (val < PPP_MRU)
+			val = PPP_MRU;
+		ap->mru = val;
+		err = 0;
+		break;
+
+	case PPPIOCATTACH:
+		if (get_user(val, (int *) arg))
+			break;
+		err = -EALREADY;
+		if (ap->connected)
+			break;
+		ap->chan.private = ap;
+		ap->chan.ops = &async_ops;
+		err = ppp_register_channel(&ap->chan, val);
+		if (err != 0)
+			break;
+		ap->connected = 1;
+		break;
+	case PPPIOCDETACH:
+		err = -ENXIO;
+		if (!ap->connected)
+			break;
+		ppp_unregister_channel(&ap->chan);
+		ap->connected = 0;
+		err = 0;
+		break;
+
+	case TCGETS:
+	case TCGETA:
+		err = n_tty_ioctl(tty, file, cmd, arg);
+		break;
+
+	case TCFLSH:
+		/* flush our buffers and the serial port's buffer */
+		if (arg == TCIFLUSH || arg == TCIOFLUSH)
+			flush_skb_queue(&ap->rq);
+		if (arg == TCIOFLUSH || arg == TCOFLUSH)
+			ppp_async_flush_output(ap);
+		err = n_tty_ioctl(tty, file, cmd, arg);
+		break;
+
+	case FIONREAD:
+		val = 0;
+		if ((skb = skb_peek(&ap->rq)) != 0)
+			val = skb->len;
+		if (put_user(val, (int *) arg))
+			break;
+		err = 0;
+		break;
+
+	default:
+		err = -ENOIOCTLCMD;
+	}
+ out:
+	return err;
+}
+
+static unsigned int
+ppp_async_poll(struct tty_struct *tty, struct file *file, poll_table *wait)
+{
+	struct asyncppp *ap = tty->disc_data;
+	unsigned int mask;
+
+	if (ap == 0)
+		return 0;	/* should never happen */
+	poll_wait(file, &ap->rwait, wait);
+	mask = POLLOUT | POLLWRNORM;
+	if (skb_peek(&ap->rq))
+		mask |= POLLIN | POLLRDNORM;
+	if (test_bit(TTY_OTHER_CLOSED, &tty->flags) || tty_hung_up_p(file))
+		mask |= POLLHUP;
+	return mask;
+}
+
+static int
+ppp_async_room(struct tty_struct *tty)
+{
+	return 65535;
+}
+
+static void
+ppp_async_receive(struct tty_struct *tty, const unsigned char *buf,
+		  char *flags, int count)
+{
+	struct asyncppp *ap = tty->disc_data;
+
+	if (ap == 0)
+		return;
+	trylock_recv_path(ap);
+	ppp_async_input(ap, buf, flags, count);
+	unlock_recv_path(ap);
+	if (test_and_clear_bit(TTY_THROTTLED, &tty->flags)
+	    && tty->driver.unthrottle)
+		tty->driver.unthrottle(tty);
+}
+
+static void
+ppp_async_wakeup(struct tty_struct *tty)
+{
+	struct asyncppp *ap = tty->disc_data;
+
+	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
+	if (ap == 0)
+		return;
+	if (ppp_async_push(ap) && ap->connected)
+		ppp_output_wakeup(&ap->chan);
+}
+
+
+static struct tty_ldisc ppp_ldisc = {
+	magic:	TTY_LDISC_MAGIC,
+	name:	"ppp",
+	open:	ppp_async_open,
+	close:	ppp_async_close,
+	read:	ppp_async_read,
+	write:	ppp_async_write,
+	ioctl:	ppp_async_ioctl,
+	poll:	ppp_async_poll,
+	receive_room: ppp_async_room,
+	receive_buf: ppp_async_receive,
+	write_wakeup: ppp_async_wakeup,
+};
+
+int
+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;
+}
+
+/*
+ * Procedures for encapsulation and framing.
+ */
+
+u16 ppp_crc16_table[256] = {
+	0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
+	0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
+	0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
+	0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
+	0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
+	0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
+	0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
+	0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
+	0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
+	0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
+	0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
+	0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
+	0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
+	0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
+	0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
+	0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
+	0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
+	0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
+	0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
+	0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
+	0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
+	0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
+	0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,
+	0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
+	0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,
+	0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
+	0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
+	0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
+	0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
+	0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
+	0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
+	0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
+};
+EXPORT_SYMBOL(ppp_crc16_table);
+#define fcstab	ppp_crc16_table		/* for PPP_FCS macro */
+
+/*
+ * 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) {
+		/*
+		 * Start of a new packet - insert the leading FLAG
+		 * character if necessary.
+		 */
+		if (islcp || flag_time == 0
+		    || 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 = 0;
+	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->busy))
+		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;
+
+	if (!trylock_xmit_path(ap)) {
+		set_bit(XMIT_WAKEUP, &ap->busy);
+		return 0;
+	}
+	for (;;) {
+		if (test_and_clear_bit(XMIT_WAKEUP, &ap->busy))
+			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, 0, 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 != 0) {
+			if (ppp_async_encode(ap)) {
+				/* finished processing ap->tpkt */
+				struct sk_buff *skb = skb_dequeue(&ap->xq);
+				if (skb != 0) {
+					ap->tpkt = skb;
+				} else {
+					clear_bit(XMIT_FULL, &ap->busy);
+					done = 1;
+				}
+			}
+			continue;
+		}
+		/* haven't made any progress */
+		unlock_xmit_path(ap);
+		if (!(test_bit(XMIT_WAKEUP, &ap->busy)
+		      || (!tty_stuffed && ap->tpkt != 0)))
+			break;
+		if (!trylock_xmit_path(ap))
+			break;
+	}
+	return done;
+
+flush:
+	if (ap->tpkt != 0) {
+		kfree_skb(ap->tpkt);
+		ap->tpkt = 0;
+		clear_bit(XMIT_FULL, &ap->busy);
+		done = 1;
+	}
+	ap->optr = ap->olim;
+	unlock_xmit_path(ap);
+	return done;
+}
+
+/*
+ * Flush output from our internal buffers.
+ * Called for the TCFLSH ioctl.
+ */
+static void
+ppp_async_flush_output(struct asyncppp *ap)
+{
+	int done = 0;
+
+	flush_skb_queue(&ap->xq);
+	lock_xmit_path(ap);
+	ap->optr = ap->olim;
+	if (ap->tpkt != NULL) {
+		kfree_skb(ap->tpkt);
+		ap->tpkt = 0;
+		clear_bit(XMIT_FULL, &ap->busy);
+		done = 1;
+	}
+	unlock_xmit_path(ap);
+	if (done && ap->connected)
+		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 inline void
+process_input_packet(struct asyncppp *ap)
+{
+	struct sk_buff *skb;
+	unsigned char *p;
+	unsigned int len, fcs;
+	int code = 0;
+
+	skb = ap->rpkt;
+	ap->rpkt = 0;
+	if ((ap->state & (SC_TOSS | SC_ESCAPE)) || skb == 0) {
+		ap->state &= ~(SC_TOSS | SC_ESCAPE);
+		if (skb != 0)
+			kfree_skb(skb);
+		return;
+	}
+
+	/* 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 && p[1] == PPP_UI) {
+		/* chop off address/control */
+		if (skb->len < 3)
+			goto err;
+		p = skb_pull(skb, 2);
+	}
+	if (p[0] & 1) {
+		/* protocol is compressed */
+		skb_push(skb, 1)[0] = 0;
+	} else if (skb->len < 2)
+		goto err;
+
+	/* all OK, give it to the generic layer or queue it */
+	if (ap->connected) {
+		ppp_input(&ap->chan, skb);
+	} else {
+		skb_queue_tail(&ap->rq, skb);
+		/* drop old frames if queue too long */
+		while (ap->rq.qlen > PPPASYNC_MAX_RQLEN
+		       && (skb = skb_dequeue(&ap->rq)) != 0)
+			kfree(skb);
+		wake_up_interruptible(&ap->rwait);
+	}
+	return;
+
+ err:
+	kfree_skb(skb);
+	if (ap->connected)
+		ppp_input_error(&ap->chan, code);
+}
+
+static inline void
+input_error(struct asyncppp *ap, int code)
+{
+	ap->state |= SC_TOSS;
+	if (ap->connected)
+		ppp_input_error(&ap->chan, code);
+}
+
+/* called when the tty driver has data for us. */
+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 != 0 && 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 != 0 && (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 */
+			input_error(ap, f);
+
+		} else if (n > 0 && (ap->state & SC_TOSS) == 0) {
+			/* stuff the chars in the skb */
+			skb = ap->rpkt;
+			if (skb == 0) {
+				skb = alloc_skb(ap->mru + PPP_HDRLEN + 2,
+						GFP_ATOMIC);
+				if (skb == 0)
+					goto nomem;
+				/* Try to get the payload 4-byte aligned */
+				if (buf[0] != PPP_ALLSTATIONS)
+					skb_reserve(skb, 2 + (buf[0] & 1));
+				ap->rpkt = skb;
+			}
+			if (n > skb_tailroom(skb)) {
+				/* packet overflowed MRU */
+				input_error(ap, 1);
+			} 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 (c == PPP_FLAG) {
+			process_input_packet(ap);
+		} else if (c == PPP_ESCAPE) {
+			ap->state |= SC_ESCAPE;
+		}
+		/* otherwise it's a char in the recv ACCM */
+		++n;
+
+		buf += n;
+		if (flags != 0)
+			flags += n;
+		count -= n;
+	}
+	return;
+
+ nomem:
+	printk(KERN_ERR "PPPasync: no memory (input pkt)\n");
+	input_error(ap, 0);
+}
+
+#ifdef MODULE
+int
+init_module(void)
+{
+	return ppp_async_init();
+}
+
+void
+cleanup_module(void)
+{
+	if (tty_register_ldisc(N_PPP, NULL) != 0)
+		printk(KERN_ERR "failed to unregister PPP line discipline\n");
+}
+#endif /* MODULE */