Re: [Xen-devel] [PATCH v4] libxl: add basic spice support for pv domUs

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-05-13 at 10:00 +0200, Fabio Fantoni wrote:
> > But: Does spice already require a VFB? In which case the existing
> > handing of that will suffice.
> >
> > I think I'm probably confused about something: Does this patch
> > enable/expose SPICE to the guest? Or does it simply enable the existing
> > PVFB's output to be exposed from the qemu process to a spice client? I
> > had been thinking this was a parallel feature to PVFB, but I'm starting
> > to suspect this might actually be an additional feature *of* PVFB, which
> > is correct? (I'm afraid that depending on which it is I might have to
> > check back over my review to make sure I haven't suggested anything
> > stupid)
> >
> > Does QXL change that answer?
> 
> QXL and other emulated vga is now not supported on pv domUs because 
> require an emulated pci bus and MMIO not supported on pv domUs FWIK.

Right, but what about the previous paragraph? That was the important bit
for me to understand, since it impacts the entire configuration model
and libxl API.

> During my first test, I was enabled spice in pv domus but the guest wont 
> show nothing while connecting to it.
> On my second shot, I've added -vga xenfb but it is deprecated. This way 
> I've got at least video out but no mouse nor keyboard.
> Following the suggestions from Stefano Stabellini I've then activated 
> vfb the same way as for vnc and i got it all working but mouse, which is 
> only visible in some circumstances (such grafical debian installer) but 
> always working (even if not visible).
> The last one is the actual patch.
> Probably the vfb part is not complete or at least improvable.
> Perhaps it is even not necessary if pvfb will became modified to works 
> with spice, so domUs use this through its modules.

Is SPICE a mechanism for exposing the PVFB or is it something entirely
separate? That is the crux of my question above.

> I feel I'm not perfectly undrestanding pvfb. Please would you like 
> better describe me this component?

I need to understand what it is this patch is actually doing. I'm
starting to worry that perhaps you don't understand either.

> Another thing: i noticed that vnc has all its parameters duplicated in 
> vfb too. For the moment I omissed them since i feel they are not 
> necessary - aren't they

It really depends on the answer to my questions above.

If SPICE is nothing to do with PVFB then it obviously makes no sense for
it to be separate.

If SPICE is just a backend for PVFB then it actually makes *more* sense
to expose spice as a PVFB configuration parameter than as a set of top
level options. The fact that VNC is exposed as a top level thing too is
somewhat anomalous but was done for xend compatibility (nb: it is the
top level duplicating the vfb VNC settings, not vice versa IMHO).

Ian.


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