// SPDX-License-Identifier: GPL-2.0-or-later

  /*
   *	SNAP data link layer. Derived from 802.2
   *

   *		Alan Cox <alan@lxorguk.ukuu.org.uk>,

   *		from the 802.2 layer by Greg Page.
   *		Merged in additions from Greg Page's psnap.c.

   */
  
  #include <linux/module.h>
  #include <linux/netdevice.h>
  #include <linux/skbuff.h>

  #include <linux/slab.h>

  #include <net/datalink.h>
  #include <net/llc.h>
  #include <net/psnap.h>
  #include <linux/mm.h>
  #include <linux/in.h>
  #include <linux/init.h>

  #include <linux/rculist.h>

  
  static LIST_HEAD(snap_list);
  static DEFINE_SPINLOCK(snap_lock);
  static struct llc_sap *snap_sap;
  
  /*
   *	Find a snap client by matching the 5 bytes.
   */

  static struct datalink_proto *find_snap_client(const unsigned char *desc)

  {

  	struct datalink_proto *proto = NULL, *p;

  	list_for_each_entry_rcu(p, &snap_list, node, lockdep_is_held(&snap_lock)) {

  		if (!memcmp(p->type, desc, 5)) {
  			proto = p;
  			break;
  		}
  	}
  	return proto;
  }
  
  /*
   *	A SNAP packet has arrived
   */
  static int snap_rcv(struct sk_buff *skb, struct net_device *dev,

  		    struct packet_type *pt, struct net_device *orig_dev)

  {
  	int rc = 1;
  	struct datalink_proto *proto;
  	static struct packet_type snap_packet_type = {

  		.type = cpu_to_be16(ETH_P_SNAP),

  	};

  	if (unlikely(!pskb_may_pull(skb, 5)))
  		goto drop;

  	rcu_read_lock();

  	proto = find_snap_client(skb_transport_header(skb));

  	if (proto) {
  		/* Pass the frame on. */

  		skb->transport_header += 5;

  		skb_pull_rcsum(skb, 5);

  		rc = proto->rcvfunc(skb, dev, &snap_packet_type, orig_dev);

  	}

  	rcu_read_unlock();

  
  	if (unlikely(!proto))
  		goto drop;
  
  out:

  	return rc;

  
  drop:
  	kfree_skb(skb);
  	goto out;

  }
  
  /*
   *	Put a SNAP header on a frame and pass to 802.2
   */
  static int snap_request(struct datalink_proto *dl,
  			struct sk_buff *skb, u8 *dest)
  {
  	memcpy(skb_push(skb, 5), dl->type, 5);
  	llc_build_and_send_ui_pkt(snap_sap, skb, dest, snap_sap->laddr.lsap);
  	return 0;
  }
  
  /*
   *	Set up the SNAP layer
   */
  EXPORT_SYMBOL(register_snap_client);
  EXPORT_SYMBOL(unregister_snap_client);

  static const char snap_err_msg[] __initconst =

  	KERN_CRIT "SNAP - unable to register with 802.2
  ";
  
  static int __init snap_init(void)
  {
  	snap_sap = llc_sap_open(0xAA, snap_rcv);

  	if (!snap_sap) {

  		printk(snap_err_msg);

  		return -EBUSY;
  	}

  
  	return 0;
  }
  
  module_init(snap_init);
  
  static void __exit snap_exit(void)
  {

  	llc_sap_put(snap_sap);

  }
  
  module_exit(snap_exit);
  
  
  /*
   *	Register SNAP clients. We don't yet use this for IP.
   */

  struct datalink_proto *register_snap_client(const unsigned char *desc,

  					    int (*rcvfunc)(struct sk_buff *,

  							   struct net_device *,

  							   struct packet_type *,
  							   struct net_device *))

  {
  	struct datalink_proto *proto = NULL;
  
  	spin_lock_bh(&snap_lock);
  
  	if (find_snap_client(desc))
  		goto out;
  
  	proto = kmalloc(sizeof(*proto), GFP_ATOMIC);
  	if (proto) {

  		memcpy(proto->type, desc, 5);

  		proto->rcvfunc		= rcvfunc;
  		proto->header_length	= 5 + 3; /* snap + 802.2 */
  		proto->request		= snap_request;
  		list_add_rcu(&proto->node, &snap_list);
  	}
  out:
  	spin_unlock_bh(&snap_lock);

  	return proto;
  }
  
  /*
   *	Unregister SNAP clients. Protocols no longer want to play with us ...
   */
  void unregister_snap_client(struct datalink_proto *proto)
  {
  	spin_lock_bh(&snap_lock);
  	list_del_rcu(&proto->node);
  	spin_unlock_bh(&snap_lock);
  
  	synchronize_net();
  
  	kfree(proto);
  }
  
  MODULE_LICENSE("GPL");