C Linux USB Driver | Error received with usb_control_msg()

Question

I'm new to Linux driver development, and I love it so far! However, I've come across an issue, and I cannot resolve it. I'm trying to send a GET_STATUS RequestType control message to my device, and read the response back in the data variable, then print it out, but when I add the usb_control_msg code to my probe function, my Ubuntu VM freezes. When I add the usb_control_msg code to my open function below, I get an error ("Message too long") when I open the device file. I just want to get the status of my device, but the open function appears to be the only place I can insert the usb_control_msg code, without my Ubuntu VM freezing. Have I misunderstood how the usb_control_msg function works?

Thanks so much for your help!

Code:

static int xb1_open(struct inode *inode, struct file *file) {

    printk(KERN_INFO "open function called..");

    struct xb1_controller *dev;
    struct usb_interface *interface;
    int subminor;
    int retval = 0;

    subminor = iminor(inode);

    interface = usb_find_interface(&xb1_driver, subminor);
    if(!interface) {
        printk(KERN_INFO "Unable to locate interface in open   
               function");
        retval = -ENODEV;
        goto exit;
    }

    dev = usb_get_intfdata(interface);
        if(!dev) {
            printk(KERN_INFO "Unable to locate dev structure in open   
                   function");
            retval = -ENODEV;
            goto exit;
        }

    usb_fill_int_urb(dev->int_in_urb, dev->udev, usb_rcvintpipe(dev- 
                 >udev, dev->int_in_endpoint->bEndpointAddress),
                 dev->int_in_buffer, dev->int_in_endpoint- 
                 >wMaxPacketSize, xb1_int_in_callback,
                 dev, dev->int_in_endpoint->bInterval);

    dev->int_in_running = 1;

    retval = usb_submit_urb(dev->int_in_urb, GFP_KERNEL);
    if(retval) {
        printk(KERN_INFO "Unable to submit int_in_urb in open 
               function");
        dev->int_in_running = 0;
        goto exit;
    }

    file->private_data = dev;

    u8 data[8];

    retval = usb_control_msg(dev, usb_rcvctrlpipe(dev->udev, 0), 0x00,   
                             0xa3, 0x0000, 0x0, &data, sizeof(data),  
                             5);
    if(retval < 0) {
        printk(KERN_INFO "usb_control_msg failed | Retval = %d", 
               retval);
    }
    else {
        printk(KERN_INFO "data: %phC", data);
    }

exit:
    return retval;
}

Answer 1

You are using both usb_submit_urb and usb_control_msg, which is wrong. You need to use any one, depending on the context.