llc_input.c revision f2ccd8fa06c8e302116e71df372f5c1f83432e03 
1/*
2 * llc_input.c - Minimal input path for LLC
3 *
4 * Copyright (c) 1997 by Procom Technology, Inc.
5 * 		 2001-2003 by Arnaldo Carvalho de Melo <acme@conectiva.com.br>
6 *
7 * This program can be redistributed or modified under the terms of the
8 * GNU General Public License as published by the Free Software Foundation.
9 * This program is distributed without any warranty or implied warranty
10 * of merchantability or fitness for a particular purpose.
11 *
12 * See the GNU General Public License for more details.
13 */
14#include <linux/netdevice.h>
15#include <net/llc.h>
16#include <net/llc_pdu.h>
17#include <net/llc_sap.h>
18
19#if 0
20#define dprintk(args...) printk(KERN_DEBUG args)
21#else
22#define dprintk(args...)
23#endif
24
25/*
26 * Packet handler for the station, registerable because in the minimal
27 * LLC core that is taking shape only the very minimal subset of LLC that
28 * is needed for things like IPX, Appletalk, etc will stay, with all the
29 * rest in the llc1 and llc2 modules.
30 */
31static void (*llc_station_handler)(struct sk_buff *skb);
32
33/*
34 * Packet handlers for LLC_DEST_SAP and LLC_DEST_CONN.
35 */
36static void (*llc_type_handlers[2])(struct llc_sap *sap,
37				    struct sk_buff *skb);
38
39void llc_add_pack(int type, void (*handler)(struct llc_sap *sap,
40					    struct sk_buff *skb))
41{
42	if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
43		llc_type_handlers[type - 1] = handler;
44}
45
46void llc_remove_pack(int type)
47{
48	if (type == LLC_DEST_SAP || type == LLC_DEST_CONN)
49		llc_type_handlers[type - 1] = NULL;
50}
51
52void llc_set_station_handler(void (*handler)(struct sk_buff *skb))
53{
54	llc_station_handler = handler;
55}
56
57/**
58 *	llc_pdu_type - returns which LLC component must handle for PDU
59 *	@skb: input skb
60 *
61 *	This function returns which LLC component must handle this PDU.
62 */
63static __inline__ int llc_pdu_type(struct sk_buff *skb)
64{
65	int type = LLC_DEST_CONN; /* I-PDU or S-PDU type */
66	struct llc_pdu_sn *pdu = llc_pdu_sn_hdr(skb);
67
68	if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) != LLC_PDU_TYPE_U)
69		goto out;
70	switch (LLC_U_PDU_CMD(pdu)) {
71	case LLC_1_PDU_CMD_XID:
72	case LLC_1_PDU_CMD_UI:
73	case LLC_1_PDU_CMD_TEST:
74		type = LLC_DEST_SAP;
75		break;
76	case LLC_2_PDU_CMD_SABME:
77	case LLC_2_PDU_CMD_DISC:
78	case LLC_2_PDU_RSP_UA:
79	case LLC_2_PDU_RSP_DM:
80	case LLC_2_PDU_RSP_FRMR:
81		break;
82	default:
83		type = LLC_DEST_INVALID;
84		break;
85	}
86out:
87	return type;
88}
89
90/**
91 *	llc_fixup_skb - initializes skb pointers
92 *	@skb: This argument points to incoming skb
93 *
94 *	Initializes internal skb pointer to start of network layer by deriving
95 *	length of LLC header; finds length of LLC control field in LLC header
96 *	by looking at the two lowest-order bits of the first control field
97 *	byte; field is either 3 or 4 bytes long.
98 */
99static inline int llc_fixup_skb(struct sk_buff *skb)
100{
101	u8 llc_len = 2;
102	struct llc_pdu_sn *pdu;
103
104	if (!pskb_may_pull(skb, sizeof(*pdu)))
105		return 0;
106
107	pdu = (struct llc_pdu_sn *)skb->data;
108	if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) == LLC_PDU_TYPE_U)
109		llc_len = 1;
110	llc_len += 2;
111	skb->h.raw += llc_len;
112	skb_pull(skb, llc_len);
113	if (skb->protocol == htons(ETH_P_802_2)) {
114		u16 pdulen = eth_hdr(skb)->h_proto,
115		    data_size = ntohs(pdulen) - llc_len;
116
117		skb_trim(skb, data_size);
118	}
119	return 1;
120}
121
122/**
123 *	llc_rcv - 802.2 entry point from net lower layers
124 *	@skb: received pdu
125 *	@dev: device that receive pdu
126 *	@pt: packet type
127 *
128 *	When the system receives a 802.2 frame this function is called. It
129 *	checks SAP and connection of received pdu and passes frame to
130 *	llc_{station,sap,conn}_rcv for sending to proper state machine. If
131 *	the frame is related to a busy connection (a connection is sending
132 *	data now), it queues this frame in the connection's backlog.
133 */
134int llc_rcv(struct sk_buff *skb, struct net_device *dev,
135	    struct packet_type *pt, struct net_device *orig_dev)
136{
137	struct llc_sap *sap;
138	struct llc_pdu_sn *pdu;
139	int dest;
140
141	/*
142	 * When the interface is in promisc. mode, drop all the crap that it
143	 * receives, do not try to analyse it.
144	 */
145	if (unlikely(skb->pkt_type == PACKET_OTHERHOST)) {
146		dprintk("%s: PACKET_OTHERHOST\n", __FUNCTION__);
147		goto drop;
148	}
149	skb = skb_share_check(skb, GFP_ATOMIC);
150	if (unlikely(!skb))
151		goto out;
152	if (unlikely(!llc_fixup_skb(skb)))
153		goto drop;
154	pdu = llc_pdu_sn_hdr(skb);
155	if (unlikely(!pdu->dsap)) /* NULL DSAP, refer to station */
156	       goto handle_station;
157	sap = llc_sap_find(pdu->dsap);
158	if (unlikely(!sap)) {/* unknown SAP */
159		dprintk("%s: llc_sap_find(%02X) failed!\n", __FUNCTION__,
160		        pdu->dsap);
161		goto drop;
162	}
163	/*
164	 * First the upper layer protocols that don't need the full
165	 * LLC functionality
166	 */
167	if (sap->rcv_func) {
168		sap->rcv_func(skb, dev, pt, orig_dev);
169		goto out;
170	}
171	dest = llc_pdu_type(skb);
172	if (unlikely(!dest || !llc_type_handlers[dest - 1]))
173		goto drop;
174	llc_type_handlers[dest - 1](sap, skb);
175out:
176	return 0;
177drop:
178	kfree_skb(skb);
179	goto out;
180handle_station:
181	if (!llc_station_handler)
182		goto drop;
183	llc_station_handler(skb);
184	goto out;
185}
186
187EXPORT_SYMBOL(llc_add_pack);
188EXPORT_SYMBOL(llc_remove_pack);
189EXPORT_SYMBOL(llc_set_station_handler);
190