Re: How to get /dev entry created automaticly for dynamic major number?

Greg KH
2007-01-25T15:52:36Z

On Thu, Jan 25, 2007 at 03:11:15PM +0200, Markku Savela wrote:
> Solution found!
>
> > On Thu, Jan 25, 2007 at 09:35:07AM +0200, Markku Savela wrote:
> > > If want to write a loadable module which "implements" a char device
> > > ("virtual", no real device present). How do I get the correct
> > > "/dev/foo" to appear automaticly?
>
> > From: Greg KH <greg@kroah.com>
>
> > If you look in the book, Linux Device Drivers, third edition, free
> > online, there's a section on what is needed for udev to work properly.
> >
> > The ideas are still the same, but the way to do it has changed since the
> > book was written. Just use a struct device and a class, and you will be
> > fine. Look at the misc device core or the mem code in
> > drivers/char/mem.c for examples of what you need to do.
>
> Thanks! The solution seems to work. The final *obstacle* was, that
> class_* symbols were not available until I added the
> LICENSE("GPL"). Here is the resulting template, maybe useful for
> someone, and just for verification, that I got it right.

Your code _is_ licensed under the GPL, right?

> ...
> static int foo_major = 0;
> static struct class *foo_class;
> static struct class_device *foo_device;
> ...
>
> static int __init foo_init(void)
> {
> foo_major = 0;
> foo_class = NULL;
> foo_device = NULL;
>
> foo_major = register_chrdev(foo_major, "foo", &foo_fops);
> if (foo_major <= 0)
> return -EIO;
> foo_class = class_create(THIS_MODULE, "foo");
> if (IS_ERR(foo_class))
> {
> return PTR_ERR(foo_class);
> }
> foo_device = class_device_create(foo_class, NULL, MKDEV(foo_major, 0), NULL, "foo0");
> if (IS_ERR(foo_device))
> {
> return PTR_ERR(foo_device);
> }
> return 0;
> }
>
> static void __exit foo_exit(void)
> {
> if (foo_device && !IS_ERR(foo_device))
> class_device_del(foo_device);
> if (foo_class && !IS_ERR(foo_class))
> class_destroy(foo_class);
> if (foo_major > 0)
> unregister_chrdev(foo_major, "foo");
> }

Yes, this should work just fine. But as others said, try just using
'device_create' instead, so I don't have to go changing your code in the
next few months when 'struct class_device' finally goes away (it is
being replaced.)

thanks,

greg k-h