Re: [PATCH 1/3] driver core: class: add class_pseudo_register

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Dec 04, 2024 at 06:04:32PM +0100, Heiner Kallweit wrote:
> On 04.12.2024 10:33, Greg Kroah-Hartman wrote:
> > On Tue, Dec 03, 2024 at 09:10:05PM +0100, Heiner Kallweit wrote:
> >> In preparation of removing class_compat support, add a helper for
> >> creating a pseudo class in sysfs. This way we can keep class_kset
> >> private to driver core. This helper will be used by vfio/mdev,
> >> replacing the call to class_compat_create().
> >>
> >> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
> >> ---
> >>  drivers/base/class.c         | 14 ++++++++++++++
> >>  include/linux/device/class.h |  1 +
> >>  2 files changed, 15 insertions(+)
> >>
> >> diff --git a/drivers/base/class.c b/drivers/base/class.c
> >> index 582b5a02a..f812236e2 100644
> >> --- a/drivers/base/class.c
> >> +++ b/drivers/base/class.c
> >> @@ -578,6 +578,20 @@ struct class_compat *class_compat_register(const char *name)
> >>  }
> >>  EXPORT_SYMBOL_GPL(class_compat_register);
> >>  
> >> +/**
> >> + * class_pseudo_register - create a pseudo class entry in sysfs
> >> + * @name: the name of the child
> >> + *
> >> + * Helper for creating a pseudo class in sysfs, keeps class_kset private
> >> + *
> >> + * Returns: the created kobject
> >> + */
> >> +struct kobject *class_pseudo_register(const char *name)
> >> +{
> >> +	return kobject_create_and_add(name, &class_kset->kobj);
> >> +}
> >> +EXPORT_SYMBOL_GPL(class_pseudo_register);
> > 
> > I see the goal here, but let's not continue on and create fake kobjects
> > in places where there should NOT be any kobjects.  Also, you might get
> > in trouble when removing this kobject as it thinks it is a 'struct
> > class' but yet it isn't, right?  Did you test that?
> > 
> 
> It's removed using kobject_put(), same as what class_compat_unregister() does.
> I only compile-tested the changes.

I would not be able to take these unless someone actually runs them as
the kobject removal here might be getting confused a bit.

thanks,

greg k-h