Re: [Xen-devel] Grant tables

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

>  >> it's fine, except that I don't understand how to obtain the gref.
>
> IOW how can I build a grant reference from a domain?

The idea is that the domain you're mapping memory from will create a grant 
reference, then (somehow) tell your mapping code what that reference is.

For the split front/back drivers, the frontend picks a page to be used for the 
communications ring, grants it to the backend domain, and puts the grant 
reference into XenStore so the backend can map that page.

During IO, grant references can then be passed through the shared memory ring 
already established, which is more efficient.  This is how most of the driver 
code does things under Xen.

>  > To my knowledge, there is no user interface for that yet, you need to do
>  > it from the Linux kernel.
>
> I agree, can you provide some examples about that?

Take a look in the Xen Linux tree at the drivers/xen/blkfront/ for some 
creation of grant references.  As Samuel says, searching for grant table 
functions under drivers/xen/ is going to find you some interesting examples 
in various places.

hope that helps,
Cheers,
Mark


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