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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

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.

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