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Date:   Thu, 30 Sep 2021 13:10:29 +1000
From:   David Gibson <david@gibson.dropbear.id.au>
To:     Jason Gunthorpe <jgg@nvidia.com>
Cc:     Liu Yi L <yi.l.liu@intel.com>, alex.williamson@redhat.com,
        hch@lst.de, jasowang@redhat.com, joro@8bytes.org,
        jean-philippe@linaro.org, kevin.tian@intel.com, parav@mellanox.com,
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        kwankhede@nvidia.com, robin.murphy@arm.com, kvm@vger.kernel.org,
        iommu@lists.linux-foundation.org, dwmw2@infradead.org,
        linux-kernel@vger.kernel.org, baolu.lu@linux.intel.com,
        nicolinc@nvidia.com
Subject: Re: [RFC 07/20] iommu/iommufd: Add iommufd_[un]bind_device()
Message-ID: <YVUqpff7DUtTLYKx@yekko>
References: <20210919063848.1476776-1-yi.l.liu@intel.com>
 <20210919063848.1476776-8-yi.l.liu@intel.com>
 <YVP44v4FVYJBSEEF@yekko>
 <20210929122457.GP964074@nvidia.com>
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On Wed, Sep 29, 2021 at 09:24:57AM -0300, Jason Gunthorpe wrote:
65;6402;1c> On Wed, Sep 29, 2021 at 03:25:54PM +1000, David Gibson wrote:
>=20
> > > +struct iommufd_device {
> > > +	unsigned int id;
> > > +	struct iommufd_ctx *ictx;
> > > +	struct device *dev; /* always be the physical device */
> > > +	u64 dev_cookie;
> >=20
> > Why do you need both an 'id' and a 'dev_cookie'?  Since they're both
> > unique, couldn't you just use the cookie directly as the index into
> > the xarray?
>=20
> ID is the kernel value in the xarray - xarray is much more efficient &
> safe with small kernel controlled values.
>=20
> dev_cookie is a user assigned value that may not be unique. It's
> purpose is to allow userspace to receive and event and go back to its
> structure. Most likely userspace will store a pointer here, but it is
> also possible userspace could not use it.
>=20
> It is a pretty normal pattern

Hm, ok.  Could you point me at an example?

--=20
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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