Re: [Xen-devel] Re: [Qemu-devel] [PATCH 1/7] xen: groundwork for xen support

["Daniel P. Berrange" <berrange@redhat.com>]

On Tue, Jul 29, 2008 at 08:32:11AM -0500, Anthony Liguori wrote:
> Daniel P. Berrange wrote:
> >On Mon, Jul 28, 2008 at 04:52:28PM +0200, Gerd Hoffmann wrote:
> >  
> >>>>+/* xen_machine.c */
> >>>>+extern QEMUMachine xenpv_machine;
> >>>>+extern QEMUMachine xenfv_machine;
> >>>>        
> >>>Why does xenfv need its own machine type?
> >>>      
> >>This is how xen's qemu-dm handles it at the moment and I've decided to
> >>do it the same way for simplicity.  I think qemu could also figure it
> >>using a hypercall.
> >>    
> >
> >This is something I originally added to QEMU in Xen's tree. The basic
> >idea is that the 'xenpv' macjine is a machine which /only/ provides the
> >paravirtualized Xen backends drivers. The 'xenfv' machine type is just
> >the same as the 'pc' machine type, but with the /addition/ of the Xen
> >paravirtualized backends. Perhaps the latter could be thought of as
> >more of a 'xenpc' (cf 'pc' and 'isapc') becasue its a variation on the
> >regular PC machine type. Annoying that all the acronyms I come up with
> >only differ by one letter :-)
> >  
> 
> Why wouldn't the Xen backends be added by appropriate -net or -drive 
> options?  For instance, qemu -drive file=foo.img,if=xen -net nic,model=xen

That would work for certain setup tasks, but not all. In Xen's branch
of QEMU, the machine init function has to set various hypervisor 
parameters which aren't directly associated with QEMU command line
args, and initialize things like the map-cache for > 4GB guest support.
In the Xennite work I had further stuff going on there too - more general
initialization of Xenstore parameters - eg stuffing the name & uuid from
QEMU's argv into right place in xenstore. 

Daniel
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