psnap.c

Go to the documentation of this file.

/*
 *  SNAP data link layer. Derived from 802.2
 *
 *      Alan Cox <[email protected]>,
 *      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 <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) {
        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\n";

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");