Re: [Xen-devel] Re: userspace block backend / gntdev problems

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 26/1/08 08:41, "Markus Armbruster" <armbru@xxxxxxxxxx> wrote:

>> In my latest post on "Dynamic modes support for PV xenfb" I am using
>> grants to map an extended framebuffer. I have a single grant ref that
>> points to 10 other refs. The other refs contain MFNs. Same technique as
>> the current framebuffer pd array but avoids the 64bit long issue. Kind
>> of a hybrid approach. I am able to map a 22MB framebuffer when running a
>> 64 bit guest and 44MB when running a 32 bit guest. When the backend is
>> done with the mapping it sends a message to the frontend to free up the
>> refs.
> 
> Uhm, I fear I didn't get the advantage of your hybrid approach.  Could
> you explain?

Presumably it allows creation of huge framebuffers without using up lots of
grants, or slots in accounting tables that Xen maintains. Given that those
tables can dynamically grow, I'm not sure how useful the two-level grant
table would be.

 -- Keir



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