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RE: [Xen-devel] is a pure usermode backend possible?

To: "Stefano Stabellini" <stefano.stabellini@xxxxxxxxxxxxx>
Subject: RE: [Xen-devel] is a pure usermode backend possible?
From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Date: Wed, 24 Nov 2010 23:44:56 +1100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Keir Fraser <keir@xxxxxxx>
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Thread-topic: [Xen-devel] is a pure usermode backend possible?
> 
> On Wed, 24 Nov 2010, James Harper wrote:
> > I looked through the patch set, and it appears that this integrates
> > fairly closely to qemu. I assume that the xenstore state management
is
> > handled somewhere inside qemu right?
> >
> 
> Yes, there is generic code in xen_backend.c to take care of it.
> 
> > Would it be possible to have a completely separate (from qemu)
userspace
> > backend or would that leave an unclean termination in the event of
the
> > userspace code crashing?
> >
> 
> Yes, it is possible. Of course if the backend crashes the guest would
be
> in trouble.
> 
> 
> > Is qemu modular in any way and could support a module build
completely
> > separately?
> 
> No, it does not.
> 
> However it is possible to start a qemu instance that only provides
> the disk backend and does nothing else and can be run in parallel to
any
> other qemu instance you need for that VM.
> You just need to start qemu with command line options to choose the
> xenpv machine and comment out all the other xen_be_register apart from
> "qdisk" in hw/xen_machine_pv.c
> 
> The fact that the backend is in qemu doesn't mean that has to be run
in
> the same qemu instance that provides device emulation.
> 

Looks like there are almost too many choices :)

Thanks

James


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