From:   "Tian, Kevin" <kevin.tian@intel.com>
To:     Jason Gunthorpe <jgg@nvidia.com>
CC:     Nicolin Chen <nicolinc@nvidia.com>,
        "joro@8bytes.org" <joro@8bytes.org>,
        "will@kernel.org" <will@kernel.org>,
        "robin.murphy@arm.com" <robin.murphy@arm.com>,
        "alex.williamson@redhat.com" <alex.williamson@redhat.com>,
        "shuah@kernel.org" <shuah@kernel.org>,
        "Liu, Yi L" <yi.l.liu@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "iommu@lists.linux.dev" <iommu@lists.linux.dev>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-kselftest@vger.kernel.org" <linux-kselftest@vger.kernel.org>,
        "baolu.lu@linux.intel.com" <baolu.lu@linux.intel.com>
Subject: RE: [PATCH v2 02/10] iommu: Introduce a new
 iommu_group_replace_domain() API
Thread-Topic: [PATCH v2 02/10] iommu: Introduce a new
 iommu_group_replace_domain() API
Thread-Index: AQHZOzoL2+M6IjP2sU+QmVuzFLJejK7F7DaQgACwnICAAMxeQA==
Date:   Fri, 10 Feb 2023 01:34:43 +0000
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> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Thursday, February 9, 2023 9:23 PM
>=20
> On Thu, Feb 09, 2023 at 02:55:24AM +0000, Tian, Kevin wrote:
> > > From: Nicolin Chen <nicolinc@nvidia.com>
> > > 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?
>=20
> 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.
>=20
> IMHO it doesn't help iommufd to substitute detach with replace.
>=20

OK