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_!
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