Re: [RFC 07/20] iommu/iommufd: Add iommufd_[un]bind_device()

David Gibson
2021-09-30T04:19:49Z

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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:
>
> > > +struct iommufd_device {
> > > + unsigned int id;
> > > + struct iommufd_ctx *ictx;
> > > + struct device *dev; /* always be the physical device */
> > > + u64 dev_cookie;
> >
> > 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?
>
> ID is the kernel value in the xarray - xarray is much more efficient &
> safe with small kernel controlled values.
>
> 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.
>
> It is a pretty normal pattern

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

--
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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