text: /*
   *	Things to sort out:
   *
   *	o	tbusy handling
   *	o	allow users to set the parameters
   *	o	sync/async switching ?
   *
   *	Note: This does _not_ implement CCITT X.25 asynchronous framing
   *	recommendations. Its primarily for testing purposes. If you wanted
   *	to do CCITT then in theory all you need is to nick the HDLC async
   *	checksum routines from ppp.c
   *      Changes:
   *
   *	2000-10-29	Henner Eisen	lapb_data_indication() return status.
   */
  
  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #include <linux/module.h>
  
  #include <linux/uaccess.h>
  #include <linux/bitops.h>
  #include <linux/string.h>
  #include <linux/mm.h>
  #include <linux/interrupt.h>
  #include <linux/in.h>
  #include <linux/tty.h>
  #include <linux/errno.h>
  #include <linux/netdevice.h>
  #include <linux/etherdevice.h>
  #include <linux/skbuff.h>
  #include <linux/if_arp.h>
  #include <linux/lapb.h>
  #include <linux/init.h>
  #include <linux/rtnetlink.h>
  #include <linux/compat.h>
  #include <linux/slab.h>
  #include <net/x25device.h>
  #include "x25_asy.h"
  
  static struct net_device **x25_asy_devs;
  static int x25_asy_maxdev = SL_NRUNIT;
  
  module_param(x25_asy_maxdev, int, 0);
  MODULE_LICENSE("GPL");
  
  static int x25_asy_esc(unsigned char *p, unsigned char *d, int len);
  static void x25_asy_unesc(struct x25_asy *sl, unsigned char c);
  static void x25_asy_setup(struct net_device *dev);
  
  /* Find a free X.25 channel, and link in this `tty' line. */
  static struct x25_asy *x25_asy_alloc(void)
  {
  	struct net_device *dev = NULL;
  	struct x25_asy *sl;
  	int i;
  
  	if (x25_asy_devs == NULL)
  		return NULL;	/* Master array missing ! */
  
  	for (i = 0; i < x25_asy_maxdev; i++) {
  		dev = x25_asy_devs[i];
  
  		/* Not allocated ? */
  		if (dev == NULL)
  			break;
  
  		sl = netdev_priv(dev);
  		/* Not in use ? */
  		if (!test_and_set_bit(SLF_INUSE, &sl->flags))
  			return sl;
  	}
  
  
  	/* Sorry, too many, all slots in use */
  	if (i >= x25_asy_maxdev)
  		return NULL;
  
  	/* If no channels are available, allocate one */
  	if (!dev) {
  		char name[IFNAMSIZ];
  		sprintf(name, "x25asy%d", i);
  
  		dev = alloc_netdev(sizeof(struct x25_asy),
  				   name, x25_asy_setup);
  		if (!dev)
  			return NULL;
  
  		/* Initialize channel control data */
  		sl = netdev_priv(dev);
  		dev->base_addr    = i;
  
  		/* register device so that it can be ifconfig'ed       */
  		if (register_netdev(dev) == 0) {
  			/* (Re-)Set the INUSE bit.   Very Important! */
  			set_bit(SLF_INUSE, &sl->flags);
  			x25_asy_devs[i] = dev;
  			return sl;
  		} else {
  			pr_warn("%s(): register_netdev() failure\n", __func__);
  			free_netdev(dev);
  		}
  	}
  	return NULL;
  }
  
  
  /* Free an X.25 channel. */
  static void x25_asy_free(struct x25_asy *sl)
  {
  	/* Free all X.25 frame buffers. */
  	kfree(sl->rbuff);
  	sl->rbuff = NULL;
  	kfree(sl->xbuff);
  	sl->xbuff = NULL;
  
  	if (!test_and_clear_bit(SLF_INUSE, &sl->flags))
  		netdev_err(sl->dev, "x25_asy_free for already free unit\n");
  }
  
  static int x25_asy_change_mtu(struct net_device *dev, int newmtu)
  {
  	struct x25_asy *sl = netdev_priv(dev);
  	unsigned char *xbuff, *rbuff;
  	int len = 2 * newmtu;
  
  	xbuff = kmalloc(len + 4, GFP_ATOMIC);
  	rbuff = kmalloc(len + 4, GFP_ATOMIC);
  
  	if (xbuff == NULL || rbuff == NULL) {
  		netdev_warn(dev, "unable to grow X.25 buffers, MTU change cancelled\n");
  		kfree(xbuff);
  		kfree(rbuff);
  		return -ENOMEM;
  	}
  
  	spin_lock_bh(&sl->lock);
  	xbuff    = xchg(&sl->xbuff, xbuff);
  	if (sl->xleft)  {
  		if (sl->xleft <= len)  {
  			memcpy(sl->xbuff, sl->xhead, sl->xleft);
  		} else  {
  			sl->xleft = 0;
  			dev->stats.tx_dropped++;
  		}
  	}
  	sl->xhead = sl->xbuff;
  
  	rbuff	 = xchg(&sl->rbuff, rbuff);
  	if (sl->rcount)  {
  		if (sl->rcount <= len) {
  			memcpy(sl->rbuff, rbuff, sl->rcount);
  		} else  {
  			sl->rcount = 0;
  			dev->stats.rx_over_errors++;
  			set_bit(SLF_ERROR, &sl->flags);
  		}
  	}
  
  	dev->mtu    = newmtu;
  	sl->buffsize = len;
  
  	spin_unlock_bh(&sl->lock);
  
  	kfree(xbuff);
  	kfree(rbuff);
  	return 0;
  }
  
  
  /* Set the "sending" flag.  This must be atomic, hence the ASM. */
  
  static inline void x25_asy_lock(struct x25_asy *sl)
  {
  	netif_stop_queue(sl->dev);
  }
  
  
  /* Clear the "sending" flag.  This must be atomic, hence the ASM. */
  
  static inline void x25_asy_unlock(struct x25_asy *sl)
  {
  	netif_wake_queue(sl->dev);
  }
  
  /* Send one completely decapsulated IP datagram to the IP layer. */
  
  static void x25_asy_bump(struct x25_asy *sl)
  {
  	struct net_device *dev = sl->dev;
  	struct sk_buff *skb;
  	int count;
  	int err;
  
  	count = sl->rcount;
  	dev->stats.rx_bytes += count;
  
  	skb = dev_alloc_skb(count+1);
  	if (skb == NULL) {
  		netdev_warn(sl->dev, "memory squeeze, dropping packet\n");
  		dev->stats.rx_dropped++;
  		return;
  	}
  	skb_push(skb, 1);	/* LAPB internal control */
  	memcpy(skb_put(skb, count), sl->rbuff, count);
  	skb->protocol = x25_type_trans(skb, sl->dev);
  	err = lapb_data_received(skb->dev, skb);
  	if (err != LAPB_OK) {
  		kfree_skb(skb);
  		printk(KERN_DEBUG "x25_asy: data received err - %d\n", err);
  	} else {
  		netif_rx(skb);
  		dev->stats.rx_packets++;
  	}
  }
  
  /* Encapsulate one IP datagram and stuff into a TTY queue. */
  static void x25_asy_encaps(struct x25_asy *sl, unsigned char *icp, int len)
  {
  	unsigned char *p;
  	int actual, count, mtu = sl->dev->mtu;
  
  	if (len > mtu) {
  		/* Sigh, shouldn't occur BUT ... */
  		len = mtu;
  		printk(KERN_DEBUG "%s: truncating oversized transmit packet!\n",
  					sl->dev->name);
  		sl->dev->stats.tx_dropped++;
  		x25_asy_unlock(sl);
  		return;
  	}
  
  	p = icp;
  	count = x25_asy_esc(p, sl->xbuff, len);
  
  	/* Order of next two lines is *very* important.
  	 * When we are sending a little amount of data,
  	 * the transfer may be completed inside driver.write()
  	 * routine, because it's running with interrupts enabled.
  	 * In this case we *never* got WRITE_WAKEUP event,
  	 * if we did not request it before write operation.
  	 *       14 Oct 1994  Dmitry Gorodchanin.
  	 */
  	set_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
  	actual = sl->tty->ops->write(sl->tty, sl->xbuff, count);
  	sl->xleft = count - actual;
  	sl->xhead = sl->xbuff + actual;
  	/* VSV */
  	clear_bit(SLF_OUTWAIT, &sl->flags);	/* reset outfill flag */
  }
  
  /*
   * Called by the driver when there's room for more data.  If we have
   * more packets to send, we send them here.
   */
  static void x25_asy_write_wakeup(struct tty_struct *tty)
  {
  	int actual;
  	struct x25_asy *sl = tty->disc_data;
  
  	/* First make sure we're connected. */
  	if (!sl || sl->magic != X25_ASY_MAGIC || !netif_running(sl->dev))
  		return;
  
  	if (sl->xleft <= 0) {
  		/* Now serial buffer is almost free & we can start
  		 * transmission of another packet */
  		sl->dev->stats.tx_packets++;
  		clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
  		x25_asy_unlock(sl);
  		return;
  	}
  
  	actual = tty->ops->write(tty, sl->xhead, sl->xleft);
  	sl->xleft -= actual;
  	sl->xhead += actual;
  }
  
  static void x25_asy_timeout(struct net_device *dev)
  {
  	struct x25_asy *sl = netdev_priv(dev);
  
  	spin_lock(&sl->lock);
  	if (netif_queue_stopped(dev)) {
  		/* May be we must check transmitter timeout here ?
  		 *      14 Oct 1994 Dmitry Gorodchanin.
  		 */
  		netdev_warn(dev, "transmit timed out, %s?\n",
  			    (tty_chars_in_buffer(sl->tty) || sl->xleft) ?
  			    "bad line quality" : "driver error");
  		sl->xleft = 0;
  		clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
  		x25_asy_unlock(sl);
  	}
  	spin_unlock(&sl->lock);
  }
  
  /* Encapsulate an IP datagram and kick it into a TTY queue. */
  
  static netdev_tx_t x25_asy_xmit(struct sk_buff *skb,
  				      struct net_device *dev)
  {
  	struct x25_asy *sl = netdev_priv(dev);
  	int err;
  
  	if (!netif_running(sl->dev)) {
  		netdev_err(dev, "xmit call when iface is down\n");
  		kfree_skb(skb);
  		return NETDEV_TX_OK;
  	}
  
  	switch (skb->data[0]) {
  	case X25_IFACE_DATA:
  		break;
  	case X25_IFACE_CONNECT: /* Connection request .. do nothing */
  		err = lapb_connect_request(dev);
  		if (err != LAPB_OK)
  			netdev_err(dev, "lapb_connect_request error: %d\n",
  				   err);
  		kfree_skb(skb);
  		return NETDEV_TX_OK;
  	case X25_IFACE_DISCONNECT: /* do nothing - hang up ?? */
  		err = lapb_disconnect_request(dev);
  		if (err != LAPB_OK)
  			netdev_err(dev, "lapb_disconnect_request error: %d\n",
  				   err);
  	default:
  		kfree_skb(skb);
  		return NETDEV_TX_OK;
  	}
  	skb_pull(skb, 1);	/* Remove control byte */
  	/*
  	 * If we are busy already- too bad.  We ought to be able
  	 * to queue things at this point, to allow for a little
  	 * frame buffer.  Oh well...
  	 * -----------------------------------------------------
  	 * I hate queues in X.25 driver. May be it's efficient,
  	 * but for me latency is more important. ;)
  	 * So, no queues !
  	 *        14 Oct 1994  Dmitry Gorodchanin.
  	 */
  
  	err = lapb_data_request(dev, skb);
  	if (err != LAPB_OK) {
  		netdev_err(dev, "lapb_data_request error: %d\n", err);
  		kfree_skb(skb);
  		return NETDEV_TX_OK;
  	}
  	return NETDEV_TX_OK;
  }
  
  
  /*
   *	LAPB interface boilerplate
   */
  
  /*
   *	Called when I frame data arrives. We did the work above - throw it
   *	at the net layer.
   */
  
  static int x25_asy_data_indication(struct net_device *dev, struct sk_buff *skb)
  {
  	return netif_rx(skb);
  }
  
  /*
   *	Data has emerged from the LAPB protocol machine. We don't handle
   *	busy cases too well. Its tricky to see how to do this nicely -
   *	perhaps lapb should allow us to bounce this ?
   */
  
  static void x25_asy_data_transmit(struct net_device *dev, struct sk_buff *skb)
  {
  	struct x25_asy *sl = netdev_priv(dev);
  
  	spin_lock(&sl->lock);
  	if (netif_queue_stopped(sl->dev) || sl->tty == NULL) {
  		spin_unlock(&sl->lock);
  		netdev_err(dev, "tbusy drop\n");
  		kfree_skb(skb);
  		return;
  	}
  	/* We were not busy, so we are now... :-) */
  	if (skb != NULL) {
  		x25_asy_lock(sl);
  		dev->stats.tx_bytes += skb->len;
  		x25_asy_encaps(sl, skb->data, skb->len);
  		dev_kfree_skb(skb);
  	}
  	spin_unlock(&sl->lock);
  }
  
  /*
   *	LAPB connection establish/down information.
   */
  
  static void x25_asy_connected(struct net_device *dev, int reason)
  {
  	struct x25_asy *sl = netdev_priv(dev);
  	struct sk_buff *skb;
  	unsigned char *ptr;
  
  	skb = dev_alloc_skb(1);
  	if (skb == NULL) {
  		netdev_err(dev, "out of memory\n");
  		return;
  	}
  
  	ptr  = skb_put(skb, 1);
  	*ptr = X25_IFACE_CONNECT;
  
  	skb->protocol = x25_type_trans(skb, sl->dev);
  	netif_rx(skb);
  }
  
  static void x25_asy_disconnected(struct net_device *dev, int reason)
  {
  	struct x25_asy *sl = netdev_priv(dev);
  	struct sk_buff *skb;
  	unsigned char *ptr;
  
  	skb = dev_alloc_skb(1);
  	if (skb == NULL) {
  		netdev_err(dev, "out of memory\n");
  		return;
  	}
  
  	ptr  = skb_put(skb, 1);
  	*ptr = X25_IFACE_DISCONNECT;
  
  	skb->protocol = x25_type_trans(skb, sl->dev);
  	netif_rx(skb);
  }
  
  static const struct lapb_register_struct x25_asy_callbacks = {
  	.connect_confirmation = x25_asy_connected,
  	.connect_indication = x25_asy_connected,
  	.disconnect_confirmation = x25_asy_disconnected,
  	.disconnect_indication = x25_asy_disconnected,
  	.data_indication = x25_asy_data_indication,
  	.data_transmit = x25_asy_data_transmit,
  };
  
  
  /* Open the low-level part of the X.25 channel. Easy! */
  static int x25_asy_open(struct net_device *dev)
  {
  	struct x25_asy *sl = netdev_priv(dev);
  	unsigned long len;
  	int err;
  
  	if (sl->tty == NULL)
  		return -ENODEV;
  
  	/*
  	 * Allocate the X.25 frame buffers:
  	 *
  	 * rbuff	Receive buffer.
  	 * xbuff	Transmit buffer.
  	 */
  
  	len = dev->mtu * 2;
  
  	sl->rbuff = kmalloc(len + 4, GFP_KERNEL);
  	if (sl->rbuff == NULL)
  		goto norbuff;
  	sl->xbuff = kmalloc(len + 4, GFP_KERNEL);
  	if (sl->xbuff == NULL)
  		goto noxbuff;
  
  	sl->buffsize = len;
  	sl->rcount   = 0;
  	sl->xleft    = 0;
  	sl->flags   &= (1 << SLF_INUSE);      /* Clear ESCAPE & ERROR flags */
  
  	netif_start_queue(dev);
  
  	/*
  	 *	Now attach LAPB
  	 */
  	err = lapb_register(dev, &x25_asy_callbacks);
  	if (err == LAPB_OK)
  		return 0;
  
  	/* Cleanup */
  	kfree(sl->xbuff);
  noxbuff:
  	kfree(sl->rbuff);
  norbuff:
  	return -ENOMEM;
  }
  
  
  /* Close the low-level part of the X.25 channel. Easy! */
  static int x25_asy_close(struct net_device *dev)
  {
  	struct x25_asy *sl = netdev_priv(dev);
  
  	spin_lock(&sl->lock);
  	if (sl->tty)
  		clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
  
  	netif_stop_queue(dev);
  	sl->rcount = 0;
  	sl->xleft  = 0;
  	spin_unlock(&sl->lock);
  	return 0;
  }
  
  /*
   * Handle the 'receiver data ready' interrupt.
   * This function is called by the 'tty_io' module in the kernel when
   * a block of X.25 data has been received, which can now be decapsulated
   * and sent on to some IP layer for further processing.
   */
  
  static void x25_asy_receive_buf(struct tty_struct *tty,
  				const unsigned char *cp, char *fp, int count)
  {
  	struct x25_asy *sl = tty->disc_data;
  
  	if (!sl || sl->magic != X25_ASY_MAGIC || !netif_running(sl->dev))
  		return;
  
  
  	/* Read the characters out of the buffer */
  	while (count--) {
  		if (fp && *fp++) {
  			if (!test_and_set_bit(SLF_ERROR, &sl->flags))
  				sl->dev->stats.rx_errors++;
  			cp++;
  			continue;
  		}
  		x25_asy_unesc(sl, *cp++);
  	}
  }
  
  /*
   * Open the high-level part of the X.25 channel.
   * This function is called by the TTY module when the
   * X.25 line discipline is called for.  Because we are
   * sure the tty line exists, we only have to link it to
   * a free X.25 channel...
   */
  
  static int x25_asy_open_tty(struct tty_struct *tty)
  {
  	struct x25_asy *sl = tty->disc_data;
  	int err;
  
  	if (tty->ops->write == NULL)
  		return -EOPNOTSUPP;
  
  	/* First make sure we're not already connected. */
  	if (sl && sl->magic == X25_ASY_MAGIC)
  		return -EEXIST;
  
  	/* OK.  Find a free X.25 channel to use. */
  	sl = x25_asy_alloc();
  	if (sl == NULL)
  		return -ENFILE;
  
  	sl->tty = tty;
  	tty->disc_data = sl;
  	tty->receive_room = 65536;
  	tty_driver_flush_buffer(tty);
  	tty_ldisc_flush(tty);
  
  	/* Restore default settings */
  	sl->dev->type = ARPHRD_X25;
  
  	/* Perform the low-level X.25 async init */
  	err = x25_asy_open(sl->dev);
  	if (err)
  		return err;
  	/* Done.  We have linked the TTY line to a channel. */
  	return 0;
  }
  
  
  /*
   * Close down an X.25 channel.
   * This means flushing out any pending queues, and then restoring the
   * TTY line discipline to what it was before it got hooked to X.25
   * (which usually is TTY again).
   */
  static void x25_asy_close_tty(struct tty_struct *tty)
  {
  	struct x25_asy *sl = tty->disc_data;
  	int err;
  
  	/* First make sure we're connected. */
  	if (!sl || sl->magic != X25_ASY_MAGIC)
  		return;
  
  	rtnl_lock();
  	if (sl->dev->flags & IFF_UP)
  		dev_close(sl->dev);
  	rtnl_unlock();
  
  	err = lapb_unregister(sl->dev);
  	if (err != LAPB_OK)
  		pr_err("x25_asy_close: lapb_unregister error: %d\n",
  		       err);
  
  	tty->disc_data = NULL;
  	sl->tty = NULL;
  	x25_asy_free(sl);
  }
  
   /************************************************************************
    *			STANDARD X.25 ENCAPSULATION		  	 *
    ************************************************************************/
  
  static int x25_asy_esc(unsigned char *s, unsigned char *d, int len)
  {
  	unsigned char *ptr = d;
  	unsigned char c;
  
  	/*
  	 * Send an initial END character to flush out any
  	 * data that may have accumulated in the receiver
  	 * due to line noise.
  	 */
  
  	*ptr++ = X25_END;	/* Send 10111110 bit seq */
  
  	/*
  	 * For each byte in the packet, send the appropriate
  	 * character sequence, according to the X.25 protocol.
  	 */
  
  	while (len-- > 0) {
  		switch (c = *s++) {
  		case X25_END:
  			*ptr++ = X25_ESC;
  			*ptr++ = X25_ESCAPE(X25_END);
  			break;
  		case X25_ESC:
  			*ptr++ = X25_ESC;
  			*ptr++ = X25_ESCAPE(X25_ESC);
  			break;
  		default:
  			*ptr++ = c;
  			break;
  		}
  	}
  	*ptr++ = X25_END;
  	return ptr - d;
  }
  
  static void x25_asy_unesc(struct x25_asy *sl, unsigned char s)
  {
  
  	switch (s) {
  	case X25_END:
  		if (!test_and_clear_bit(SLF_ERROR, &sl->flags) &&
  		    sl->rcount > 2)
  			x25_asy_bump(sl);
  		clear_bit(SLF_ESCAPE, &sl->flags);
  		sl->rcount = 0;
  		return;
  	case X25_ESC:
  		set_bit(SLF_ESCAPE, &sl->flags);
  		return;
  	case X25_ESCAPE(X25_ESC):
  	case X25_ESCAPE(X25_END):
  		if (test_and_clear_bit(SLF_ESCAPE, &sl->flags))
  			s = X25_UNESCAPE(s);
  		break;
  	}
  	if (!test_bit(SLF_ERROR, &sl->flags)) {
  		if (sl->rcount < sl->buffsize) {
  			sl->rbuff[sl->rcount++] = s;
  			return;
  		}
  		sl->dev->stats.rx_over_errors++;
  		set_bit(SLF_ERROR, &sl->flags);
  	}
  }
  
  
  /* Perform I/O control on an active X.25 channel. */
  static int x25_asy_ioctl(struct tty_struct *tty, struct file *file,
  			 unsigned int cmd,  unsigned long arg)
  {
  	struct x25_asy *sl = tty->disc_data;
  
  	/* First make sure we're connected. */
  	if (!sl || sl->magic != X25_ASY_MAGIC)
  		return -EINVAL;
  
  	switch (cmd) {
  	case SIOCGIFNAME:
  		if (copy_to_user((void __user *)arg, sl->dev->name,
  					strlen(sl->dev->name) + 1))
  			return -EFAULT;
  		return 0;
  	case SIOCSIFHWADDR:
  		return -EINVAL;
  	default:
  		return tty_mode_ioctl(tty, file, cmd, arg);
  	}
  }
  
  #ifdef CONFIG_COMPAT
  static long x25_asy_compat_ioctl(struct tty_struct *tty, struct file *file,
  			 unsigned int cmd,  unsigned long arg)
  {
  	switch (cmd) {
  	case SIOCGIFNAME:
  	case SIOCSIFHWADDR:
  		return x25_asy_ioctl(tty, file, cmd,
  				     (unsigned long)compat_ptr(arg));
  	}
  
  	return -ENOIOCTLCMD;
  }
  #endif
  
  static int x25_asy_open_dev(struct net_device *dev)
  {
  	struct x25_asy *sl = netdev_priv(dev);
  	if (sl->tty == NULL)
  		return -ENODEV;
  	return 0;
  }
  
  static const struct net_device_ops x25_asy_netdev_ops = {
  	.ndo_open	= x25_asy_open_dev,
  	.ndo_stop	= x25_asy_close,
  	.ndo_start_xmit	= x25_asy_xmit,
  	.ndo_tx_timeout	= x25_asy_timeout,
  	.ndo_change_mtu	= x25_asy_change_mtu,
  };
  
  /* Initialise the X.25 driver.  Called by the device init code */
  static void x25_asy_setup(struct net_device *dev)
  {
  	struct x25_asy *sl = netdev_priv(dev);
  
  	sl->magic  = X25_ASY_MAGIC;
  	sl->dev	   = dev;
  	spin_lock_init(&sl->lock);
  	set_bit(SLF_INUSE, &sl->flags);
  
  	/*
  	 *	Finish setting up the DEVICE info.
  	 */
  
  	dev->mtu		= SL_MTU;
  	dev->netdev_ops		= &x25_asy_netdev_ops;
  	dev->watchdog_timeo	= HZ*20;
  	dev->hard_header_len	= 0;
  	dev->addr_len		= 0;
  	dev->type		= ARPHRD_X25;
  	dev->tx_queue_len	= 10;
  
  	/* New-style flags. */
  	dev->flags		= IFF_NOARP;
  }
  
  static struct tty_ldisc_ops x25_ldisc = {
  	.owner		= THIS_MODULE,
  	.magic		= TTY_LDISC_MAGIC,
  	.name		= "X.25",
  	.open		= x25_asy_open_tty,
  	.close		= x25_asy_close_tty,
  	.ioctl		= x25_asy_ioctl,
  #ifdef CONFIG_COMPAT
  	.compat_ioctl	= x25_asy_compat_ioctl,
  #endif
  	.receive_buf	= x25_asy_receive_buf,
  	.write_wakeup	= x25_asy_write_wakeup,
  };
  
  static int __init init_x25_asy(void)
  {
  	if (x25_asy_maxdev < 4)
  		x25_asy_maxdev = 4; /* Sanity */
  
  	pr_info("X.25 async: version 0.00 ALPHA (dynamic channels, max=%d)\n",
  		x25_asy_maxdev);
  
  	x25_asy_devs = kcalloc(x25_asy_maxdev, sizeof(struct net_device *),
  				GFP_KERNEL);
  	if (!x25_asy_devs)
  		return -ENOMEM;
  
  	return tty_register_ldisc(N_X25, &x25_ldisc);
  }
  
  
  static void __exit exit_x25_asy(void)
  {
  	struct net_device *dev;
  	int i;
  
  	for (i = 0; i < x25_asy_maxdev; i++) {
  		dev = x25_asy_devs[i];
  		if (dev) {
  			struct x25_asy *sl = netdev_priv(dev);
  
  			spin_lock_bh(&sl->lock);
  			if (sl->tty)
  				tty_hangup(sl->tty);
  
  			spin_unlock_bh(&sl->lock);
  			/*
  			 * VSV = if dev->start==0, then device
  			 * unregistered while close proc.
  			 */
  			unregister_netdev(dev);
  			free_netdev(dev);
  		}
  	}
  
  	kfree(x25_asy_devs);
  	tty_unregister_ldisc(N_X25);
  }
  
  module_init(init_x25_asy);
  module_exit(exit_x25_asy);
  