It's important to realize that we must free any buffers we have allocated. Here, however, as we performed a managed allocation in the init code (devm_kzalloc()), we have the benefit of not needing to worry about cleanup; the kernel handles it. Of course, in the driver's cleanup code path (invoked upon rmmod(8)), we deregister the misc driver with the kernel:
static void __exit miscdrv_rdwr_exit(void)
{
misc_deregister(&llkd_miscdev);
pr_info("LLKD misc (rdwr) driver deregistered, bye\n");
}
You will notice that we also, seemingly uselessly, use two global integers, ga and gb, in places in this version of the driver. Indeed, they have no real meaning here; the reason we have them at all becomes clear only in the last two chapters of this book, on kernel synchronization. Please ignore them for now.
On this note, you'll perhaps realize that the way we have arbitrarily accessed global data in this driver can cause concurrency issue (data races!); yes indeed; we shall set aside the deep and crucial coverage of kernel concurrency and synchronization to the book's last two chapters.
