Re: [Intel-gfx] [PATCH v5 16/19] vfio: Add VFIO_DEVICE_BIND_IOMMUFD

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, Mar 07, 2023 at 06:38:59AM +0000, Tian, Kevin wrote:
> > From: Liu, Yi L <yi.l.liu@intel.com>
> > Sent: Friday, March 3, 2023 2:58 PM
> > 
> > > What should we return here anyhow if an access was created?
> > 
> > iommufd_access->obj.id. should be fine. Is it?
> 
> Thinking more I'm not sure whether it's a good idea to fill the
> dev_id field with an access object id and then later confuse
> the user to get an -ENOENT error when trying to allocate a
> hwpt with an access object id.
> 
> How can user differentiate it from the real error case where
> invalid iommufd object is used?
> 
> It sounds clearer to return dev_id only when there is a true
> device object being created by the bind_iommufd cmd. Then
> the user can use it to decide whether  to further attempt
> dev_id related cmds.

It means we can never return an access_id

I don't think this is a problem, the first thing userspace should do
is a get info to the dev_id which is needed to learn which iommu
driver is running it, if that returns EOPNOTSUPP then it isn't a
physical iommu device.

Jason