Re: [PATCH v6 2/6] iommufd: Add IOMMU_HWPT_INVALIDATE

[Nicolin Chen <nicolinc@nvidia.com>]

On Mon, Nov 20, 2023 at 08:34:58AM +0000, Tian, Kevin wrote:
> > From: Liu, Yi L <yi.l.liu@intel.com>
> > Sent: Monday, November 20, 2023 4:30 PM
> >
> > On 2023/11/20 16:09, Tian, Kevin wrote:
> > >> From: Liu, Yi L <yi.l.liu@intel.com>
> > >> Sent: Friday, November 17, 2023 9:07 PM
> > >> + * @req_len: Length (in bytes) of a request entry in the request array
> > >> + * @req_num: Input the number of cache invalidation requests in the
> > array.
> > >> + *           Output the number of requests successfully handled by kernel.
> > >> + * @out_driver_error_code: Report a driver speicifc error code upon
> > failure.
> > >> + *                         It's optional, driver has a choice to fill it or
> > >> + *                         not.
> > >
> > > Being optional how does the user tell whether the code is filled or not?

Well, naming it "error_code" indicates zero means no error while
non-zero means something? An error return from this ioctl could
also tell the user space to look up for this driver error code,
if it ever cares.

> > seems like we need a flag for it. otherwise, a reserved special value is
> > required. or is it enough to just document it that this field is available
> > or not per the iommu_hw_info_type?
> >
> 
> No guarantee that a reserved special value applies to all vendors.
> 
> I'll just remove the optional part. the viommu driver knows what a valid
> code is, if the driver fills it.

Hmm, remove out_driver_error_code? Do you mean by reusing ioctl
error code to tell the user space what driver error code it gets?

Nicolin