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/*

 *      SNAP data link layer. Derived from 802.2

 *

 *              Alan Cox <Alan.Cox@linux.org>,

 *              from the 802.2 layer by Greg Page.

 *              Merged in additions from Greg Page's psnap.c.

 *

 *              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.

 */

#include <linux/module.h>

#include <linux/netdevice.h>

#include <linux/skbuff.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>

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(unsigned char *desc)

{

        struct list_head *entry;

        struct datalink_proto *proto = NULL, *p;

        list_for_each_rcu(entry, &snap_list) {

                p = list_entry(entry, struct datalink_proto, node);

                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 = __constant_htons(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 char snap_err_msg[] __initdata =

        KERN_CRIT "SNAP - unable to register with 802.2\n";

static int __init snap_init(void)

{

        snap_sap = llc_sap_open(0xAA, snap_rcv);

        if (!snap_sap)

                printk(snap_err_msg);

        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(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);

        synchronize_net();

        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");