Re: [Qemu-devel] Spice project is now open

[Izik Eidus <ieidus@redhat.com>]

On Fri, 11 Dec 2009 09:57:48 -0600
Anthony Liguori <anthony@codemonkey.ws> wrote:

> Yaniv Kamay wrote:
> > Hi,
> >
> > Spice project is now open, for more information visit
> > http://spice-space.org, due to a server relocation the site will be
> > down during this weekend.
> >
> > Spice ship patched QEMU based on fairly old KVM snapshot as a
> > reference implementation. The Spice team plane to push all the
> > relevant bits into QEMU upstream.
> >   
> 
> Historically, we have not supported multiple display mechanisms
> favoring making one mechanism as good as it can be.
> 
> Supporting both Spice and VNC would go against this policy.  It's not 
> outside the realm of possibility, but there has to be a good 
> justification for it.
> 
> We need to separate the advantages of having a paravirtual display 
> driver from the advantages of a remote display protocol.  For
> instance, VNC is capable of doing ARGB cursor offloading to the
> client.  We do not support it in QEMU because the VGA drivers we
> emulate do not support this functionality.  Likewise, VNC can support
> sound tunneling and QEMU does implement this (although virt-manager
> does not yet).
> 
> So from a protocol perspective, what are the advantages of Spice over
> VNC?


Spice desgien is highly diffrence than VNC
The first thing about spice is that it isnt just a framebuffer drawing
and not a bitmaps protocol.

Spice protocl support multiple graphics commands, multiple surfaces
drawings, Spice is desgined to render as less as it can on the server
and instead to render on the client side much of the work,
To achive this spice use all kind of techniques such as depth viewing
tree.

We already have patchs that support offscreen surfaces -> the
architacture for high end 3d, this make things even more complicated.

Spice is a library, it is library for remote display, it handle by
itself all the connection between the spice client to the host that run
the guest, it include:
sound, display, keyboard, usb, network tunneling (for printers) and so
on...

The patchs that we wanted to push into qemu were what is called VDI
interfaces, it allow to qemu work with what ever interface it want,
what so bad about that?

I think we should allow freedom of choice to the users to decide what
protcol they want to use, Spice and VNC are all diffrent and were born
to meet diffrent goals.

I would happy to answer more questions if anyone have

Thanks.


> 
> Obviously, the disadvantages are that for all practical purposes,
> it's a closed protocol.  While there is now a specification, there is
> not a clear mechanism for extending it by third parties.  VNC has a
> published protocol and there's a documented process for extending by
> third parties.  There are a large number of existing VNC clients so
> from an interoperability perspective, VNC clearly wins.
> 
> Since VNC is extensible (and we've extended it many times for QEMU),
> if Spice possesses unique encoding mechanisms that are advantageous,
> why wouldn't we just add those mechanisms to VNC as an extension?
> 
> Regards,
> 
> Anthony Liguori
> 
>