[Xen-devel] Re: [Qemu-devel] [RfC / Patch] xenner: event channel implementation.

[Gerd Hoffmann <kraxel@xxxxxxxxxx>]

On 04/22/09 18:23, Avi Kivity wrote:
> Gerd Hoffmann wrote:
> > The function calls in the source code (xen backend drivers) are not
> > changed directly, but using a include file with a bunch of #defines.
> > That way I don't have to change s/xc_evtchn_/xc_evtchn./ all over the
> > place. Also xenner can easily be disabled at compile time and the
> > indirect function pointer calls simply go away then.
> I don't think the last bit is worthwhile. Function pointers these days
> are pretty fast, their cost will be dwarfed by the syscall and hypercall
> overhead.
>
> > - --disable-xen) xen="no"
> > + --disable-xen) xen="no"; xenner="no"
> It would be nice to be able to build without the original Xen libraries.
Hmm.  I'll at least need the xen header files (at build time) anyway. 
Making xen and xenner independent config options and don't link the xen 
libraries for the !xen case should work without too much hassle (have to 
make the function pointers mandatory then though).
> > +
> > +static struct domain *get_domain(int domid)
> > +{
> > + struct domain *domain;
> Curious, can there be any domain other than the guest and the fake dom0
> you're emulating?
No.  It is the case for the current xenner implementation.  The event 
channels are handled by a daemon then and the guests can talk to each 
other.  This code is derived from the daemon.  When moving xenner into 
qemu the event channels allow only host <=> guest communication, so that 
can probably simplified a bit.  Not sure that would save that much code 
though.  I'll have a look.
cheers,
  Gerd

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