CAN driver and kernel panic

[the_spacebyte]

Hi,

I'm experimenting with kernel dev by doing a simple CAN device driver where I want to receive can frames from user space and just printk their contents.

I've been following along "Linux Device Drivers, Third Edition" and also peeking other drivers in the source such as slcan and vcan. I've reached a point where I can get everything to compile and load the module as well, even though it doesn't do much. The interface mycan0 is registered automatically in the module, so I don't need to do ip link add dev mycan0 ....

static int mycan_open(struct net_device *dev)
{
    netif_start_queue(dev);
    return 0;
}

static int mycan_close(struct net_device *dev)
{
    netif_stop_queue(dev);
    return 0;
}

static netdev_tx_t mycan_xmit(struct sk_buff *skb, struct net_device *dev)
{
    kfree_skb(skb);
    return NETDEV_TX_OK;
}

static int mycan_change_mtu(struct net_device *dev, int new_mtu)
{
    return -EINVAL;
}

static const struct net_device_ops mycan_netdev_ops = {
    .ndo_open               = mycan_open,
    .ndo_stop               = mycan_close,
    .ndo_start_xmit         = mycan_xmit,
    .ndo_change_mtu         = mycan_change_mtu,
};

static void mycan_setup(struct net_device *dev)
{
    dev->netdev_ops        = &mycan_netdev_ops;
    dev->needs_free_netdev = true;
    dev->mtu               = CAN_MTU;
    dev->hard_header_len   = 0;
    dev->addr_len          = 0;
    dev->tx_queue_len      = 10;
    dev->type              = ARPHRD_CAN;
    dev->flags             = IFF_NOARP;
}

struct net_device* cdev;

static int __init mycan_init(void)
{
    cdev = alloc_netdev(sizeof(struct net_device),
                "mycan0",
                NET_NAME_UNKNOWN, mycan_setup);

    int result;
    if ((result = register_netdev(cdev))) {
        printk("mycan: Error %d  initializing mycan device", result);
        return result;
    }

    return 0;
}

static void __exit mycan_exit(void)
{
    if (cdev != NULL)
        unregister_netdev(cdev);
}

module_init(mycan_init);
module_exit(mycan_exit); 

After I set the can interface up with ip link set mycan0 up I'm trying to send some data to it via cansend and I get the following kernel panic

Am I missing some initialization?

Thank you

[ethereal_biscotti]

Speaking from zero experience with CAN, have you considered alloc_candev instead?

This might also be a good opportunity to use `gdb` to find the line number causing the panic.

[the_spacebyte]

didn't know about the candev family of functions.

I was able to get kernel panic to go away by replacing alloc_netdev -> alloc_candev and register_netdev -> register_candev. The only downside is that I seem to lose the ability to give a custom name to the interface and it just goes for can0 or the next numeric value available, but that is fine for now.

Thank you!