Re: [PATCH v2 02/10] iommu: Introduce a new iommu_group_replace_domain() API

[Jason Gunthorpe]

On Thu, Feb 09, 2023 at 02:55:24AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@xxxxxxxxxx>
> > Sent: Wednesday, February 8, 2023 5:18 AM
> > 
> > +int iommu_group_replace_domain(struct iommu_group *group,
> > +			       struct iommu_domain *new_domain)
> > +{
> > +	int ret;
> > +
> > +	if (!new_domain)
> > +		return -EINVAL;
> 
> Is there value of allowing NULL new domain so this plays like
> iommu_detach_group() then iommufd only needs call one
> function in both attach/detach path?

We've used NULL to mean the 'platform domain' in the iommu core code
in a few places, I'd prefer to avoid overloading NULL.

IMHO it doesn't help iommufd to substitute detach with replace.

Jason