Re: [PATCH 3/8] vfio/mdev: simplify mdev_type handling

[Christoph Hellwig <hch@lst.de>]

On Tue, Jun 07, 2022 at 12:52:49AM +0530, Kirti Wankhede wrote:
>>   	void (*remove)(struct mdev_device *dev);
>> -	struct attribute_group **supported_type_groups;
>>   	struct device_driver driver;
>>   };
>
> mdev_type should be part of mdev_parent, separating it from mdev_parent 
> could result in more errors while using mdev framework.

Why?

> Similarly it should 
> be added as part of mdev_register_device. Below adding types is separated 
> from mdev_register_device which is more error prone.

How so?

> What if driver 
> registering to mdev doesn't add mdev_types? - mdev framework is un-usable 
> in that case.

Yes, so it is if you don't add it to the supported_type_groups field
in the current kernel.  Basic programmer error, and trivially caught.

> We had kept it together with mdev registration so that 
> mdev_types should be mandatory to be defined by driver during registration. 
> How would you mandate mdev_type by such separation?

I would not.  Registering a parent without types is perfectly valid from
the code correctness perspective.  It just isn't very useful.  Just
like say creating a kobject without attributes in the device model.