linux/net/802/psnap.c
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   1/*
   2 *      SNAP data link layer. Derived from 802.2
   3 *
   4 *              Alan Cox <alan@lxorguk.ukuu.org.uk>,
   5 *              from the 802.2 layer by Greg Page.
   6 *              Merged in additions from Greg Page's psnap.c.
   7 *
   8 *              This program is free software; you can redistribute it and/or
   9 *              modify it under the terms of the GNU General Public License
  10 *              as published by the Free Software Foundation; either version
  11 *              2 of the License, or (at your option) any later version.
  12 */
  13
  14#include <linux/module.h>
  15#include <linux/netdevice.h>
  16#include <linux/skbuff.h>
  17#include <linux/slab.h>
  18#include <net/datalink.h>
  19#include <net/llc.h>
  20#include <net/psnap.h>
  21#include <linux/mm.h>
  22#include <linux/in.h>
  23#include <linux/init.h>
  24#include <linux/rculist.h>
  25
  26static LIST_HEAD(snap_list);
  27static DEFINE_SPINLOCK(snap_lock);
  28static struct llc_sap *snap_sap;
  29
  30/*
  31 *      Find a snap client by matching the 5 bytes.
  32 */
  33static struct datalink_proto *find_snap_client(const unsigned char *desc)
  34{
  35        struct datalink_proto *proto = NULL, *p;
  36
  37        list_for_each_entry_rcu(p, &snap_list, node) {
  38                if (!memcmp(p->type, desc, 5)) {
  39                        proto = p;
  40                        break;
  41                }
  42        }
  43        return proto;
  44}
  45
  46/*
  47 *      A SNAP packet has arrived
  48 */
  49static int snap_rcv(struct sk_buff *skb, struct net_device *dev,
  50                    struct packet_type *pt, struct net_device *orig_dev)
  51{
  52        int rc = 1;
  53        struct datalink_proto *proto;
  54        static struct packet_type snap_packet_type = {
  55                .type = cpu_to_be16(ETH_P_SNAP),
  56        };
  57
  58        if (unlikely(!pskb_may_pull(skb, 5)))
  59                goto drop;
  60
  61        rcu_read_lock();
  62        proto = find_snap_client(skb_transport_header(skb));
  63        if (proto) {
  64                /* Pass the frame on. */
  65                skb->transport_header += 5;
  66                skb_pull_rcsum(skb, 5);
  67                rc = proto->rcvfunc(skb, dev, &snap_packet_type, orig_dev);
  68        }
  69        rcu_read_unlock();
  70
  71        if (unlikely(!proto))
  72                goto drop;
  73
  74out:
  75        return rc;
  76
  77drop:
  78        kfree_skb(skb);
  79        goto out;
  80}
  81
  82/*
  83 *      Put a SNAP header on a frame and pass to 802.2
  84 */
  85static int snap_request(struct datalink_proto *dl,
  86                        struct sk_buff *skb, u8 *dest)
  87{
  88        memcpy(skb_push(skb, 5), dl->type, 5);
  89        llc_build_and_send_ui_pkt(snap_sap, skb, dest, snap_sap->laddr.lsap);
  90        return 0;
  91}
  92
  93/*
  94 *      Set up the SNAP layer
  95 */
  96EXPORT_SYMBOL(register_snap_client);
  97EXPORT_SYMBOL(unregister_snap_client);
  98
  99static const char snap_err_msg[] __initconst =
 100        KERN_CRIT "SNAP - unable to register with 802.2\n";
 101
 102static int __init snap_init(void)
 103{
 104        snap_sap = llc_sap_open(0xAA, snap_rcv);
 105        if (!snap_sap) {
 106                printk(snap_err_msg);
 107                return -EBUSY;
 108        }
 109
 110        return 0;
 111}
 112
 113module_init(snap_init);
 114
 115static void __exit snap_exit(void)
 116{
 117        llc_sap_put(snap_sap);
 118}
 119
 120module_exit(snap_exit);
 121
 122
 123/*
 124 *      Register SNAP clients. We don't yet use this for IP.
 125 */
 126struct datalink_proto *register_snap_client(const unsigned char *desc,
 127                                            int (*rcvfunc)(struct sk_buff *,
 128                                                           struct net_device *,
 129                                                           struct packet_type *,
 130                                                           struct net_device *))
 131{
 132        struct datalink_proto *proto = NULL;
 133
 134        spin_lock_bh(&snap_lock);
 135
 136        if (find_snap_client(desc))
 137                goto out;
 138
 139        proto = kmalloc(sizeof(*proto), GFP_ATOMIC);
 140        if (proto) {
 141                memcpy(proto->type, desc, 5);
 142                proto->rcvfunc          = rcvfunc;
 143                proto->header_length    = 5 + 3; /* snap + 802.2 */
 144                proto->request          = snap_request;
 145                list_add_rcu(&proto->node, &snap_list);
 146        }
 147out:
 148        spin_unlock_bh(&snap_lock);
 149
 150        return proto;
 151}
 152
 153/*
 154 *      Unregister SNAP clients. Protocols no longer want to play with us ...
 155 */
 156void unregister_snap_client(struct datalink_proto *proto)
 157{
 158        spin_lock_bh(&snap_lock);
 159        list_del_rcu(&proto->node);
 160        spin_unlock_bh(&snap_lock);
 161
 162        synchronize_net();
 163
 164        kfree(proto);
 165}
 166
 167MODULE_LICENSE("GPL");
 168
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