Messages in this thread | | | Date | Wed, 29 Sep 2021 09:24:57 -0300 | From | Jason Gunthorpe <> | Subject | Re: [RFC 07/20] iommu/iommufd: Add iommufd_[un]bind_device() |
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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
Jason
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