Linux Device Driver open error - linux

Question

I am new with Linux.
I have made a USB skeleton driver and one application program which open and close skeleton.
But it gives error can't open device.
Can anyone tell me the possible reason why this may happen?
This simple driver programs needs any device attached with usb port ?
Here is my application programs
int main()
/* no memory-swapping for this programm */
ret = mlockall(MCL_CURRENT | MCL_FUTURE);
if (ret) {
perror("ERROR : mlockall has failled");
exit(1);
}
/*
* Turn the NRTcurrent task into a RT-task.
* */
ret = rt_task_shadow(&rt_task_desc, NULL, 1, 0);
if (ret)
{
fprintf(stderr, "ERROR : rt_task_shadow: %s\n",
strerror(-ret));
exit(1);
}
/* open the device */
device = rt_dev_open(DEVICE_NAME, 0);
if (device < 0) {
printf("ERROR : can't open device %s (%s)\n",
DEVICE_NAME, strerror(-device));
exit(1);
}
/*
* If an argument was given on the command line, write it to the device,
* otherwise, read from the device.
*/
/* close the device */
ret = rt_dev_close(device);
if (ret < 0) {
printf("ERROR : can't close device %s (%s)\n",
DEVICE_NAME, strerror(-ret));
exit(1);
}
return 0;
}
Here is a my driver open function
static int skel_open(struct inode *inode, struct file *file)
{
struct usb_skel *dev;
struct usb_interface *interface;
int subminor;
int retval = 0;
subminor = iminor(inode);
interface = usb_find_interface(&skel_driver, subminor);
if (!interface) {
pr_err("%s - error, can't find device for minor %d\n",
__func__, subminor);
retval = -ENODEV;
goto exit;
}
dev = usb_get_intfdata(interface);
if (!dev) {
retval = -ENODEV;
goto exit;
}
/* increment our usage count for the device */
kref_get(&dev->kref);
/* lock the device to allow correctly handling errors
* in resumption */
mutex_lock(&dev->io_mutex);
retval = usb_autopm_get_interface(interface);
if (retval)
goto out_err;
/* save our object in the file's private structure */
file->private_data = dev;
mutex_unlock(&dev->io_mutex);
exit:
return retval;
}