RE: [RFC 03/20] vfio: Add vfio_[un]register_device()

[Tian, Kevin]

> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Wednesday, September 22, 2021 12:01 AM
> 
> On Sun, Sep 19, 2021 at 02:38:31PM +0800, Liu Yi L wrote:
> > With /dev/vfio/devices introduced, now a vfio device driver has three
> > options to expose its device to userspace:
> >
> > a)  only legacy group interface, for devices which haven't been moved to
> >     iommufd (e.g. platform devices, sw mdev, etc.);
> >
> > b)  both legacy group interface and new device-centric interface, for
> >     devices which supports iommufd but also wants to keep backward
> >     compatibility (e.g. pci devices in this RFC);
> >
> > c)  only new device-centric interface, for new devices which don't carry
> >     backward compatibility burden (e.g. hw mdev/subdev with pasid);
> 
> We shouldn't have 'b'? Where does it come from?

a vfio-pci device can be opened via the existing group interface. if no b) it 
means legacy vfio userspace can never use vfio-pci device any more
once the latter is moved to iommufd.

Thanks
Kevin