drivers/net/wan/lapbether.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  *	"LAPB via ethernet" driver release 001
  *
  *	This code REQUIRES 2.1.15 or higher/ NET3.038
  *
  *	This is a "pseudo" network driver to allow LAPB over Ethernet.
  *
  *	This driver can use any ethernet destination address, and can be
  *	limited to accept frames from one dedicated ethernet card only.
  *
  *	History
  *	LAPBETH 001	Jonathan Naylor		Cloned from bpqether.c
  *	2000-10-29	Henner Eisen	lapb_data_indication() return status.
  *	2000-11-14	Henner Eisen	dev_hold/put, NETDEV_GOING_DOWN support
  */

 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

 #include <linux/errno.h>
 #include <linux/types.h>
 #include <linux/socket.h>
 #include <linux/in.h>
 #include <linux/slab.h>
 #include <linux/kernel.h>
 #include <linux/string.h>
 #include <linux/net.h>
 #include <linux/inet.h>
 #include <linux/netdevice.h>
 #include <linux/if_arp.h>
 #include <linux/skbuff.h>
 #include <net/sock.h>
 #include <linux/uaccess.h>
 #include <linux/mm.h>
 #include <linux/interrupt.h>
 #include <linux/notifier.h>
 #include <linux/stat.h>
 #include <linux/module.h>
 #include <linux/lapb.h>
 #include <linux/init.h>

 #include <net/x25device.h>

 static const u8 bcast_addr[6] = { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF };

 /* If this number is made larger, check that the temporary string buffer
  * in lapbeth_new_device is large enough to store the probe device name.*/
 #define MAXLAPBDEV 100

 struct lapbethdev {
 	struct list_head	node;
 	struct net_device	*ethdev;	/* link to ethernet device */
 	struct net_device	*axdev;		/* lapbeth device (lapb#) */
 	bool			up;
 	spinlock_t		up_lock;	/* Protects "up" */
 };

 static LIST_HEAD(lapbeth_devices);

 /* ------------------------------------------------------------------------ */

 /*
  *	Get the LAPB device for the ethernet device
  */
 static struct lapbethdev *lapbeth_get_x25_dev(struct net_device *dev)
 {
 	struct lapbethdev *lapbeth;

 	list_for_each_entry_rcu(lapbeth, &lapbeth_devices, node, lockdep_rtnl_is_held()) {
 		if (lapbeth->ethdev == dev)
 			return lapbeth;
 	}
 	return NULL;
 }

 static __inline__ int dev_is_ethdev(struct net_device *dev)
 {
 	return dev->type == ARPHRD_ETHER && strncmp(dev->name, "dummy", 5);
 }

 /* ------------------------------------------------------------------------ */

 /*
  *	Receive a LAPB frame via an ethernet interface.
  */
 static int lapbeth_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *ptype, struct net_device *orig_dev)
 {
 	int len, err;
 	struct lapbethdev *lapbeth;

 	if (dev_net(dev) != &init_net)
 		goto drop;

 	if ((skb = skb_share_check(skb, GFP_ATOMIC)) == NULL)
 		return NET_RX_DROP;

 	if (!pskb_may_pull(skb, 2))
 		goto drop;

 	rcu_read_lock();
 	lapbeth = lapbeth_get_x25_dev(dev);
 	if (!lapbeth)
 		goto drop_unlock_rcu;
 	spin_lock_bh(&lapbeth->up_lock);
 	if (!lapbeth->up)
 		goto drop_unlock;

 	len = skb->data[0] + skb->data[1] * 256;
 	dev->stats.rx_packets++;
 	dev->stats.rx_bytes += len;

 	skb_pull(skb, 2);	/* Remove the length bytes */
 	skb_trim(skb, len);	/* Set the length of the data */

 	if ((err = lapb_data_received(lapbeth->axdev, skb)) != LAPB_OK) {
 		printk(KERN_DEBUG "lapbether: lapb_data_received err - %d\n", err);
 		goto drop_unlock;
 	}
 out:
 	spin_unlock_bh(&lapbeth->up_lock);
 	rcu_read_unlock();
 	return 0;
 drop_unlock:
 	kfree_skb(skb);
 	goto out;
 drop_unlock_rcu:
 	rcu_read_unlock();
 drop:
 	kfree_skb(skb);
 	return 0;
 }

 static int lapbeth_data_indication(struct net_device *dev, struct sk_buff *skb)
 {
 	unsigned char *ptr;

 	if (skb_cow(skb, 1)) {
 		kfree_skb(skb);
 		return NET_RX_DROP;
 	}

 	skb_push(skb, 1);

 	ptr  = skb->data;
 	*ptr = X25_IFACE_DATA;

 	skb->protocol = x25_type_trans(skb, dev);
 	return netif_rx(skb);
 }

 /*
  *	Send a LAPB frame via an ethernet interface
  */
 static netdev_tx_t lapbeth_xmit(struct sk_buff *skb,
 				      struct net_device *dev)
 {
 	struct lapbethdev *lapbeth = netdev_priv(dev);
 	int err;

 	spin_lock_bh(&lapbeth->up_lock);
 	if (!lapbeth->up)
 		goto drop;

 	/* There should be a pseudo header of 1 byte added by upper layers.
 	 * Check to make sure it is there before reading it.
 	 */
 	if (skb->len < 1)
 		goto drop;

 	switch (skb->data[0]) {
 	case X25_IFACE_DATA:
 		break;
 	case X25_IFACE_CONNECT:
 		if ((err = lapb_connect_request(dev)) != LAPB_OK)
 			pr_err("lapb_connect_request error: %d\n", err);
 		goto drop;
 	case X25_IFACE_DISCONNECT:
 		if ((err = lapb_disconnect_request(dev)) != LAPB_OK)
 			pr_err("lapb_disconnect_request err: %d\n", err);
 		fallthrough;
 	default:
 		goto drop;
 	}

 	skb_pull(skb, 1);

 	if ((err = lapb_data_request(dev, skb)) != LAPB_OK) {
 		pr_err("lapb_data_request error - %d\n", err);
 		goto drop;
 	}
 out:
 	spin_unlock_bh(&lapbeth->up_lock);
 	return NETDEV_TX_OK;
 drop:
 	kfree_skb(skb);
 	goto out;
 }

 static void lapbeth_data_transmit(struct net_device *ndev, struct sk_buff *skb)
 {
 	struct lapbethdev *lapbeth = netdev_priv(ndev);
 	unsigned char *ptr;
 	struct net_device *dev;
 	int size = skb->len;

 	ptr = skb_push(skb, 2);

 	*ptr++ = size % 256;
 	*ptr++ = size / 256;

 	ndev->stats.tx_packets++;
 	ndev->stats.tx_bytes += size;

 	skb->dev = dev = lapbeth->ethdev;

 	skb->protocol = htons(ETH_P_DEC);

 	skb_reset_network_header(skb);

 	dev_hard_header(skb, dev, ETH_P_DEC, bcast_addr, NULL, 0);

 	dev_queue_xmit(skb);
 }

 static void lapbeth_connected(struct net_device *dev, int reason)
 {
 	unsigned char *ptr;
 	struct sk_buff *skb = dev_alloc_skb(1);

 	if (!skb) {
 		pr_err("out of memory\n");
 		return;
 	}

 	ptr  = skb_put(skb, 1);
 	*ptr = X25_IFACE_CONNECT;

 	skb->protocol = x25_type_trans(skb, dev);
 	netif_rx(skb);
 }

 static void lapbeth_disconnected(struct net_device *dev, int reason)
 {
 	unsigned char *ptr;
 	struct sk_buff *skb = dev_alloc_skb(1);

 	if (!skb) {
 		pr_err("out of memory\n");
 		return;
 	}

 	ptr  = skb_put(skb, 1);
 	*ptr = X25_IFACE_DISCONNECT;

 	skb->protocol = x25_type_trans(skb, dev);
 	netif_rx(skb);
 }

 /*
  *	Set AX.25 callsign
  */
 static int lapbeth_set_mac_address(struct net_device *dev, void *addr)
 {
 	struct sockaddr *sa = addr;
 	memcpy(dev->dev_addr, sa->sa_data, dev->addr_len);
 	return 0;
 }


 static const struct lapb_register_struct lapbeth_callbacks = {
 	.connect_confirmation    = lapbeth_connected,
 	.connect_indication      = lapbeth_connected,
 	.disconnect_confirmation = lapbeth_disconnected,
 	.disconnect_indication   = lapbeth_disconnected,
 	.data_indication         = lapbeth_data_indication,
 	.data_transmit           = lapbeth_data_transmit,
 };

 /*
  * open/close a device
  */
 static int lapbeth_open(struct net_device *dev)
 {
 	struct lapbethdev *lapbeth = netdev_priv(dev);
 	int err;

 	if ((err = lapb_register(dev, &lapbeth_callbacks)) != LAPB_OK) {
 		pr_err("lapb_register error: %d\n", err);
 		return -ENODEV;
 	}

 	spin_lock_bh(&lapbeth->up_lock);
 	lapbeth->up = true;
 	spin_unlock_bh(&lapbeth->up_lock);

 	return 0;
 }

 static int lapbeth_close(struct net_device *dev)
 {
 	struct lapbethdev *lapbeth = netdev_priv(dev);
 	int err;

 	spin_lock_bh(&lapbeth->up_lock);
 	lapbeth->up = false;
 	spin_unlock_bh(&lapbeth->up_lock);

 	if ((err = lapb_unregister(dev)) != LAPB_OK)
 		pr_err("lapb_unregister error: %d\n", err);

 	return 0;
 }

 /* ------------------------------------------------------------------------ */

 static const struct net_device_ops lapbeth_netdev_ops = {
 	.ndo_open	     = lapbeth_open,
 	.ndo_stop	     = lapbeth_close,
 	.ndo_start_xmit	     = lapbeth_xmit,
 	.ndo_set_mac_address = lapbeth_set_mac_address,
 };

 static void lapbeth_setup(struct net_device *dev)
 {
 	dev->netdev_ops	     = &lapbeth_netdev_ops;
 	dev->needs_free_netdev = true;
 	dev->type            = ARPHRD_X25;
 	dev->hard_header_len = 0;
 	dev->mtu             = 1000;
 	dev->addr_len        = 0;
 }

 /*
  *	Setup a new device.
  */
 static int lapbeth_new_device(struct net_device *dev)
 {
 	struct net_device *ndev;
 	struct lapbethdev *lapbeth;
 	int rc = -ENOMEM;

 	ASSERT_RTNL();

 	ndev = alloc_netdev(sizeof(*lapbeth), "lapb%d", NET_NAME_UNKNOWN,
 			    lapbeth_setup);
 	if (!ndev)
 		goto out;

 	/* When transmitting data:
 	 * first this driver removes a pseudo header of 1 byte,
 	 * then the lapb module prepends an LAPB header of at most 3 bytes,
 	 * then this driver prepends a length field of 2 bytes,
 	 * then the underlying Ethernet device prepends its own header.
 	 */
 	ndev->needed_headroom = -1 + 3 + 2 + dev->hard_header_len
 					   + dev->needed_headroom;
 	ndev->needed_tailroom = dev->needed_tailroom;

 	lapbeth = netdev_priv(ndev);
 	lapbeth->axdev = ndev;

 	dev_hold(dev);
 	lapbeth->ethdev = dev;

 	lapbeth->up = false;
 	spin_lock_init(&lapbeth->up_lock);

 	rc = -EIO;
 	if (register_netdevice(ndev))
 		goto fail;

 	list_add_rcu(&lapbeth->node, &lapbeth_devices);
 	rc = 0;
 out:
 	return rc;
 fail:
 	dev_put(dev);
 	free_netdev(ndev);
 	goto out;
 }

 /*
  *	Free a lapb network device.
  */
 static void lapbeth_free_device(struct lapbethdev *lapbeth)
 {
 	dev_put(lapbeth->ethdev);
 	list_del_rcu(&lapbeth->node);
 	unregister_netdevice(lapbeth->axdev);
 }

 /*
  *	Handle device status changes.
  *
  * Called from notifier with RTNL held.
  */
 static int lapbeth_device_event(struct notifier_block *this,
 				unsigned long event, void *ptr)
 {
 	struct lapbethdev *lapbeth;
 	struct net_device *dev = netdev_notifier_info_to_dev(ptr);

 	if (dev_net(dev) != &init_net)
 		return NOTIFY_DONE;

 	if (!dev_is_ethdev(dev))
 		return NOTIFY_DONE;

 	switch (event) {
 	case NETDEV_UP:
 		/* New ethernet device -> new LAPB interface	 */
 		if (lapbeth_get_x25_dev(dev) == NULL)
 			lapbeth_new_device(dev);
 		break;
 	case NETDEV_DOWN:
 		/* ethernet device closed -> close LAPB interface */
 		lapbeth = lapbeth_get_x25_dev(dev);
 		if (lapbeth)
 			dev_close(lapbeth->axdev);
 		break;
 	case NETDEV_UNREGISTER:
 		/* ethernet device disappears -> remove LAPB interface */
 		lapbeth = lapbeth_get_x25_dev(dev);
 		if (lapbeth)
 			lapbeth_free_device(lapbeth);
 		break;
 	}

 	return NOTIFY_DONE;
 }

 /* ------------------------------------------------------------------------ */

 static struct packet_type lapbeth_packet_type __read_mostly = {
 	.type = cpu_to_be16(ETH_P_DEC),
 	.func = lapbeth_rcv,
 };

 static struct notifier_block lapbeth_dev_notifier = {
 	.notifier_call = lapbeth_device_event,
 };

 static const char banner[] __initconst =
 	KERN_INFO "LAPB Ethernet driver version 0.02\n";

 static int __init lapbeth_init_driver(void)
 {
 	dev_add_pack(&lapbeth_packet_type);

 	register_netdevice_notifier(&lapbeth_dev_notifier);

 	printk(banner);

 	return 0;
 }
 module_init(lapbeth_init_driver);

 static void __exit lapbeth_cleanup_driver(void)
 {
 	struct lapbethdev *lapbeth;
 	struct list_head *entry, *tmp;

 	dev_remove_pack(&lapbeth_packet_type);
 	unregister_netdevice_notifier(&lapbeth_dev_notifier);

 	rtnl_lock();
 	list_for_each_safe(entry, tmp, &lapbeth_devices) {
 		lapbeth = list_entry(entry, struct lapbethdev, node);

 		dev_put(lapbeth->ethdev);
 		unregister_netdevice(lapbeth->axdev);
 	}
 	rtnl_unlock();
 }
 module_exit(lapbeth_cleanup_driver);

 MODULE_AUTHOR("Jonathan Naylor <g4klx@g4klx.demon.co.uk>");
 MODULE_DESCRIPTION("The unofficial LAPB over Ethernet driver");
 MODULE_LICENSE("GPL");
	// SPDX-License-Identifier: GPL-2.0-or-later
	/*
	* "LAPB via ethernet" driver release 001
	*
	* This code REQUIRES 2.1.15 or higher/ NET3.038
	*
	* This is a "pseudo" network driver to allow LAPB over Ethernet.
	*
	* This driver can use any ethernet destination address, and can be
	* limited to accept frames from one dedicated ethernet card only.
	*
	* History
	* LAPBETH 001 Jonathan Naylor Cloned from bpqether.c
	* 2000-10-29 Henner Eisen lapb_data_indication() return status.
	* 2000-11-14 Henner Eisen dev_hold/put, NETDEV_GOING_DOWN support
	*/

	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

	#include <linux/errno.h>
	#include <linux/types.h>
	#include <linux/socket.h>
	#include <linux/in.h>
	#include <linux/slab.h>
	#include <linux/kernel.h>
	#include <linux/string.h>
	#include <linux/net.h>
	#include <linux/inet.h>
	#include <linux/netdevice.h>
	#include <linux/if_arp.h>
	#include <linux/skbuff.h>
	#include <net/sock.h>
	#include <linux/uaccess.h>
	#include <linux/mm.h>
	#include <linux/interrupt.h>
	#include <linux/notifier.h>
	#include <linux/stat.h>
	#include <linux/module.h>
	#include <linux/lapb.h>
	#include <linux/init.h>

	#include <net/x25device.h>

	static const u8 bcast_addr[6] = { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF };

	/* If this number is made larger, check that the temporary string buffer
	* in lapbeth_new_device is large enough to store the probe device name.*/
	#define MAXLAPBDEV 100

	struct lapbethdev {
	struct list_head node;
	struct net_device ethdev; / link to ethernet device */
	struct net_device axdev; / lapbeth device (lapb#) */
	bool up;
	spinlock_t up_lock; /* Protects "up" */
	};

	static LIST_HEAD(lapbeth_devices);

	/* ------------------------------------------------------------------------ */

	/*
	* Get the LAPB device for the ethernet device
	*/
	static struct lapbethdev lapbeth_get_x25_dev(struct net_device dev)
	{
	struct lapbethdev *lapbeth;

	list_for_each_entry_rcu(lapbeth, &lapbeth_devices, node, lockdep_rtnl_is_held()) {
	if (lapbeth->ethdev == dev)
	return lapbeth;
	}
	return NULL;
	}

	static __inline__ int dev_is_ethdev(struct net_device *dev)
	{
	return dev->type == ARPHRD_ETHER && strncmp(dev->name, "dummy", 5);
	}

	/* ------------------------------------------------------------------------ */

	/*
	* Receive a LAPB frame via an ethernet interface.
	*/
	static int lapbeth_rcv(struct sk_buff skb, struct net_device dev, struct packet_type ptype, struct net_device orig_dev)
	{
	int len, err;
	struct lapbethdev *lapbeth;

	if (dev_net(dev) != &init_net)
	goto drop;

	if ((skb = skb_share_check(skb, GFP_ATOMIC)) == NULL)
	return NET_RX_DROP;

	if (!pskb_may_pull(skb, 2))
	goto drop;

	rcu_read_lock();
	lapbeth = lapbeth_get_x25_dev(dev);
	if (!lapbeth)
	goto drop_unlock_rcu;
	spin_lock_bh(&lapbeth->up_lock);
	if (!lapbeth->up)
	goto drop_unlock;

	len = skb->data[0] + skb->data[1] * 256;
	dev->stats.rx_packets++;
	dev->stats.rx_bytes += len;

	skb_pull(skb, 2); /* Remove the length bytes */
	skb_trim(skb, len); /* Set the length of the data */

	if ((err = lapb_data_received(lapbeth->axdev, skb)) != LAPB_OK) {
	printk(KERN_DEBUG "lapbether: lapb_data_received err - %d\n", err);
	goto drop_unlock;
	}
	out:
	spin_unlock_bh(&lapbeth->up_lock);
	rcu_read_unlock();
	return 0;
	drop_unlock:
	kfree_skb(skb);
	goto out;
	drop_unlock_rcu:
	rcu_read_unlock();
	drop:
	kfree_skb(skb);
	return 0;
	}

	static int lapbeth_data_indication(struct net_device dev, struct sk_buff skb)
	{
	unsigned char *ptr;

	if (skb_cow(skb, 1)) {
	kfree_skb(skb);
	return NET_RX_DROP;
	}

	skb_push(skb, 1);

	ptr = skb->data;
	*ptr = X25_IFACE_DATA;

	skb->protocol = x25_type_trans(skb, dev);
	return netif_rx(skb);
	}

	/*
	* Send a LAPB frame via an ethernet interface
	*/
	static netdev_tx_t lapbeth_xmit(struct sk_buff *skb,
	struct net_device *dev)
	{
	struct lapbethdev *lapbeth = netdev_priv(dev);
	int err;

	spin_lock_bh(&lapbeth->up_lock);
	if (!lapbeth->up)
	goto drop;

	/* There should be a pseudo header of 1 byte added by upper layers.
	* Check to make sure it is there before reading it.
	*/
	if (skb->len < 1)
	goto drop;

	switch (skb->data[0]) {
	case X25_IFACE_DATA:
	break;
	case X25_IFACE_CONNECT:
	if ((err = lapb_connect_request(dev)) != LAPB_OK)
	pr_err("lapb_connect_request error: %d\n", err);
	goto drop;
	case X25_IFACE_DISCONNECT:
	if ((err = lapb_disconnect_request(dev)) != LAPB_OK)
	pr_err("lapb_disconnect_request err: %d\n", err);
	fallthrough;
	default:
	goto drop;
	}

	skb_pull(skb, 1);

	if ((err = lapb_data_request(dev, skb)) != LAPB_OK) {
	pr_err("lapb_data_request error - %d\n", err);
	goto drop;
	}
	out:
	spin_unlock_bh(&lapbeth->up_lock);
	return NETDEV_TX_OK;
	drop:
	kfree_skb(skb);
	goto out;
	}

	static void lapbeth_data_transmit(struct net_device ndev, struct sk_buff skb)
	{
	struct lapbethdev *lapbeth = netdev_priv(ndev);
	unsigned char *ptr;
	struct net_device *dev;
	int size = skb->len;

	ptr = skb_push(skb, 2);

	*ptr++ = size % 256;
	*ptr++ = size / 256;

	ndev->stats.tx_packets++;
	ndev->stats.tx_bytes += size;

	skb->dev = dev = lapbeth->ethdev;

	skb->protocol = htons(ETH_P_DEC);

	skb_reset_network_header(skb);

	dev_hard_header(skb, dev, ETH_P_DEC, bcast_addr, NULL, 0);

	dev_queue_xmit(skb);
	}

	static void lapbeth_connected(struct net_device *dev, int reason)
	{
	unsigned char *ptr;
	struct sk_buff *skb = dev_alloc_skb(1);

	if (!skb) {
	pr_err("out of memory\n");
	return;
	}

	ptr = skb_put(skb, 1);
	*ptr = X25_IFACE_CONNECT;

	skb->protocol = x25_type_trans(skb, dev);
	netif_rx(skb);
	}

	static void lapbeth_disconnected(struct net_device *dev, int reason)
	{
	unsigned char *ptr;
	struct sk_buff *skb = dev_alloc_skb(1);

	if (!skb) {
	pr_err("out of memory\n");
	return;
	}

	ptr = skb_put(skb, 1);
	*ptr = X25_IFACE_DISCONNECT;

	skb->protocol = x25_type_trans(skb, dev);
	netif_rx(skb);
	}

	/*
	* Set AX.25 callsign
	*/
	static int lapbeth_set_mac_address(struct net_device dev, void addr)
	{
	struct sockaddr *sa = addr;
	memcpy(dev->dev_addr, sa->sa_data, dev->addr_len);
	return 0;
	}


	static const struct lapb_register_struct lapbeth_callbacks = {
	.connect_confirmation = lapbeth_connected,
	.connect_indication = lapbeth_connected,
	.disconnect_confirmation = lapbeth_disconnected,
	.disconnect_indication = lapbeth_disconnected,
	.data_indication = lapbeth_data_indication,
	.data_transmit = lapbeth_data_transmit,
	};

	/*
	* open/close a device
	*/
	static int lapbeth_open(struct net_device *dev)
	{
	struct lapbethdev *lapbeth = netdev_priv(dev);
	int err;

	if ((err = lapb_register(dev, &lapbeth_callbacks)) != LAPB_OK) {
	pr_err("lapb_register error: %d\n", err);
	return -ENODEV;
	}

	spin_lock_bh(&lapbeth->up_lock);
	lapbeth->up = true;
	spin_unlock_bh(&lapbeth->up_lock);

	return 0;
	}

	static int lapbeth_close(struct net_device *dev)
	{
	struct lapbethdev *lapbeth = netdev_priv(dev);
	int err;

	spin_lock_bh(&lapbeth->up_lock);
	lapbeth->up = false;
	spin_unlock_bh(&lapbeth->up_lock);

	if ((err = lapb_unregister(dev)) != LAPB_OK)
	pr_err("lapb_unregister error: %d\n", err);

	return 0;
	}

	/* ------------------------------------------------------------------------ */

	static const struct net_device_ops lapbeth_netdev_ops = {
	.ndo_open = lapbeth_open,
	.ndo_stop = lapbeth_close,
	.ndo_start_xmit = lapbeth_xmit,
	.ndo_set_mac_address = lapbeth_set_mac_address,
	};

	static void lapbeth_setup(struct net_device *dev)
	{
	dev->netdev_ops = &lapbeth_netdev_ops;
	dev->needs_free_netdev = true;
	dev->type = ARPHRD_X25;
	dev->hard_header_len = 0;
	dev->mtu = 1000;
	dev->addr_len = 0;
	}

	/*
	* Setup a new device.
	*/
	static int lapbeth_new_device(struct net_device *dev)
	{
	struct net_device *ndev;
	struct lapbethdev *lapbeth;
	int rc = -ENOMEM;

	ASSERT_RTNL();

	ndev = alloc_netdev(sizeof(*lapbeth), "lapb%d", NET_NAME_UNKNOWN,
	lapbeth_setup);
	if (!ndev)
	goto out;

	/* When transmitting data:
	* first this driver removes a pseudo header of 1 byte,
	* then the lapb module prepends an LAPB header of at most 3 bytes,
	* then this driver prepends a length field of 2 bytes,
	* then the underlying Ethernet device prepends its own header.
	*/
	ndev->needed_headroom = -1 + 3 + 2 + dev->hard_header_len
	+ dev->needed_headroom;
	ndev->needed_tailroom = dev->needed_tailroom;

	lapbeth = netdev_priv(ndev);
	lapbeth->axdev = ndev;

	dev_hold(dev);
	lapbeth->ethdev = dev;

	lapbeth->up = false;
	spin_lock_init(&lapbeth->up_lock);

	rc = -EIO;
	if (register_netdevice(ndev))
	goto fail;

	list_add_rcu(&lapbeth->node, &lapbeth_devices);
	rc = 0;
	out:
	return rc;
	fail:
	dev_put(dev);
	free_netdev(ndev);
	goto out;
	}

	/*
	* Free a lapb network device.
	*/
	static void lapbeth_free_device(struct lapbethdev *lapbeth)
	{
	dev_put(lapbeth->ethdev);
	list_del_rcu(&lapbeth->node);
	unregister_netdevice(lapbeth->axdev);
	}

	/*
	* Handle device status changes.
	*
	* Called from notifier with RTNL held.
	*/
	static int lapbeth_device_event(struct notifier_block *this,
	unsigned long event, void *ptr)
	{
	struct lapbethdev *lapbeth;
	struct net_device *dev = netdev_notifier_info_to_dev(ptr);

	if (dev_net(dev) != &init_net)
	return NOTIFY_DONE;

	if (!dev_is_ethdev(dev))
	return NOTIFY_DONE;

	switch (event) {
	case NETDEV_UP:
	/* New ethernet device -> new LAPB interface */
	if (lapbeth_get_x25_dev(dev) == NULL)
	lapbeth_new_device(dev);
	break;
	case NETDEV_DOWN:
	/* ethernet device closed -> close LAPB interface */
	lapbeth = lapbeth_get_x25_dev(dev);
	if (lapbeth)
	dev_close(lapbeth->axdev);
	break;
	case NETDEV_UNREGISTER:
	/* ethernet device disappears -> remove LAPB interface */
	lapbeth = lapbeth_get_x25_dev(dev);
	if (lapbeth)
	lapbeth_free_device(lapbeth);
	break;
	}

	return NOTIFY_DONE;
	}

	/* ------------------------------------------------------------------------ */

	static struct packet_type lapbeth_packet_type __read_mostly = {
	.type = cpu_to_be16(ETH_P_DEC),
	.func = lapbeth_rcv,
	};

	static struct notifier_block lapbeth_dev_notifier = {
	.notifier_call = lapbeth_device_event,
	};

	static const char banner[] __initconst =
	KERN_INFO "LAPB Ethernet driver version 0.02\n";

	static int __init lapbeth_init_driver(void)
	{
	dev_add_pack(&lapbeth_packet_type);

	register_netdevice_notifier(&lapbeth_dev_notifier);

	printk(banner);

	return 0;
	}
	module_init(lapbeth_init_driver);

	static void __exit lapbeth_cleanup_driver(void)
	{
	struct lapbethdev *lapbeth;
	struct list_head entry, tmp;

	dev_remove_pack(&lapbeth_packet_type);
	unregister_netdevice_notifier(&lapbeth_dev_notifier);

	rtnl_lock();
	list_for_each_safe(entry, tmp, &lapbeth_devices) {
	lapbeth = list_entry(entry, struct lapbethdev, node);

	dev_put(lapbeth->ethdev);
	unregister_netdevice(lapbeth->axdev);
	}
	rtnl_unlock();
	}
	module_exit(lapbeth_cleanup_driver);

	MODULE_AUTHOR("Jonathan Naylor <g4klx@g4klx.demon.co.uk>");
	MODULE_DESCRIPTION("The unofficial LAPB over Ethernet driver");
	MODULE_LICENSE("GPL");