RE: [RFC v1 0/1] ui: Add a Wayland backend for Qemu UI

[Kasireddy, Vivek]

Hi Gerd,

> > Why does Qemu need a new Wayland UI backend?
> > The main reason why there needs to be a plain and simple Wayland backend
> > for Qemu UI is to eliminate the Blit (aka GPU copy) that happens if using
> > a toolkit like GTK or SDL (because they use EGL). The Blit can be eliminated
> > by sharing the dmabuf fd -- associated with the Guest scanout buffer --
> > directly with the Host compositor via the linux-dmabuf (unstable) protocol.
> 
> Hmm, that probably means no window decorations (and other UI elements),
[Kasireddy, Vivek] Right, unfortunately, no decorations or other UI elements. 
For
that we can use GTK. 
> right?  Also the code seems to not (yet?) handle mouse and kbd input.
[Kasireddy, Vivek] Yes, kbd and mouse support not added yet and that is why I
tagged it as WIP. But it should not be too hard to add that.

> 
> > The patch(es) are still WIP and the only reason why I am sending them now
> > is to get feedback and see if anyone thinks this work is interesting. And,
> > even after this work is complete, it is not meant to be merged and can be
> > used for performance testing purposes. Given Qemu UI's new direction, the
> > proper way to add new backends is to create a separate UI/display module
> > that is part of the dbus/pipewire infrastructure that Marc-Andre is
> > working on:
> > https://lists.nongnu.org/archive/html/qemu-devel/2021-03/msg04331.html
> 
> Separating emulation and UI has the big advantage that the guest
> lifecycle is decoupled from the desktop session lifecycle, i.e.
> the guest can continue to run when the desktop session ends.
> 
> Works today with spice (when using unix socket to connect it can pass
> dma-buf handles from qemu to spice client).
> 
> Using dbus instead certainly makes sense.  Whenever we'll just go send
> dma-buf handles over dbus or integrate with pipewire for display/sound
> not clear yet.  Marc-André thinks using pipewire doesn't bring benefits
> and I havn't found the time yet to learn more about pipewire ...
[Kasireddy, Vivek] On our side, we'll also try to learn how dbus and pipewire
fit in and work. Having said that, can Marc-Andre's work be merged in 
stages -- first only dbus and no pipewire?

Thanks,
Vivek
> 
> take care,
>   Gerd