RE: [PATCH v2 01/11] iommu: Add new iommu op to create domains owned by userspace

[Tian, Kevin]

> From: Nicolin Chen <nicolinc@xxxxxxxxxx>
> Sent: Saturday, May 20, 2023 2:45 AM
> 
> On Fri, May 19, 2023 at 08:47:45AM +0000, Tian, Kevin wrote:
> > > From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> > > Sent: Thursday, May 11, 2023 10:39 PM
> > > @@ -229,6 +238,15 @@ struct iommu_iotlb_gather {
> > >   *           after use. Return the data buffer if success, or ERR_PTR on
> > >   *           failure.
> > >   * @domain_alloc: allocate iommu domain
> > > + * @domain_alloc_user: allocate user iommu domain
> > > + * @domain_alloc_user_data_len: return the required length of the user
> > > data
> > > + *                              to allocate a specific type user iommu domain.
> > > + *                              @hwpt_type is defined as enum iommu_hwpt_type
> > > + *                              in include/uapi/linux/iommufd.h. The returned
> > > + *                              length is the corresponding sizeof driver data
> > > + *                              structures in include/uapi/linux/iommufd.h.
> > > + *                              -EOPNOTSUPP would be returned if the input
> > > + *                              @hwpt_type is not supported by the driver.
> >
> > Can this be merged with earlier @hw_info callback? That will already
> > report a list of supported hwpt types. is there a problem to further
> > describe the data length for each type in that interface?
> 
> Yi and I had a last minute talk before he sent this version
> actually... This version of hw_info no longer reports a list
> of supported hwpt types. We previously did that in a bitmap,
> but we found that a bitmap will not be sufficient eventually
> if there are more than 64 hwpt_types.
> 
> And this domain_alloc_user_data_len might not be necessary,
> because in this version the IOMMUFD core doesn't really care
> about the actual data_len since it copies the data into the
> ucmd_buffer, i.e. we would probably only need a bool op like
> "hwpt_type_is_supported".
> 

Or just pass to the @domain_alloc_user ops which should fail
if the type is not supported?