Re: cdev documentation (was Drop second arg of unregister_chrdev())

[corbet@lwn.net (Jonathan Corbet)]

Rolf Eike Beer <eike-kernel@sf-tec.de> wrote:

> Nevertheless, I ported my driver to the new interface. I see it cdev_add() 
> succeeding, but the device never shows up in sysfs. Do I have to do any more 
> tricks with class devices and stuff?

Yes, cdevs do not, themselves, show up in sysfs.  A simple class is what
you want for that part of the job.

> While I was sneaking around in the code I found this drivers/char/tty_io:3093
> 
>         cdev_init(&driver->cdev, &tty_fops);
>         driver->cdev.owner = driver->owner;
>         error = cdev_add(&driver->cdev, dev, driver->num);
>         if (error) {
>                 cdev_del(&driver->cdev);
> 
> Isn't the call to cdev_del() just wrong here?

It is correct, in that it returns the reference you hold to the cdev's
internal kobject.  If you got the cdev with cdev_alloc(), that's the
only way it will get returned to the system.  For a cdev allocated
elsewhere (as is the case here) it probably doesn't make any difference.

jon