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charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" 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 _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu