Re: [Xen-devel] Looking for information on xen bus

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> On Mon, 2007-12-17 at 14:25 -0800, Parag Chakraborty wrote:
> > I am trying to build something that needs a communication channel
> > between 2 domU partitions.
> > Does xen bus support communication between domUs or does it only
> > support communication between dom0 and domU?
>
> Well according to my copy of "The Definitive Guide to the Xen
> Hypervisor", xenbus is "an informal protocol built on top of the
> xenstore, which provides a way of enumerating the (virtual) devices
> available to a given domain, and connecting to them". So it's really for
> setup info, not inter-dom communication.
>
> You probably want your domUs to share pages. One of your domUs can
> advertise where the page it has shared is (grant ref#, domid) via xenbus
> and then the other domU can read xenbus to get the gref and domid, and
> map that page.

Earlier versions of Xen don't allow domUs to share pages directly using grant 
tables.  I think in more recent versions of Xen this is possible, although 
the initial support was buggy.  The code in xen-unstable / Xen 3.2 probably 
does this all right, I think.  I'm not sure off the top of my head what the 
status was for previous versions.

Parag: like Andy says, XenBus is basically just a mechanism for determining 
what virtual devices you have got and for doing the "handshaking" required to 
establish shared memory and event channels.  The bulk of the work of a PV 
virtual device is then done using this shared memory and event channels.

Xenbus is "control plane", and the shared memory and event channels are 
the "fast path" which handles the actual IO.

Cheers,
Mark

> > Are there any windows implementation for xenbus on the domU side?
>
> Yes, check out http://xenbits.xensource.com/ext/win-pvdrivers.hg . For
> the moment you'll have to compile it yourself.
>
> Regards -- Andy
>
>
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-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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