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