Re: [Qemu-devel] [PATCH 19/24] console: add and use qemu_display_find_default

[Darren Kenny]

On Fri, Nov 17, 2017 at 04:03:28PM +0100, Gerd Hoffmann wrote:
>  Hi,
>
> > OK, so the odd thing then is the check for !remote_display earlier
> > on in the function (missing from the quote above) which seems to end
> > up initializing VNC (albeit with localhost) when CONFIG_VNC is
> > defined, but no other local display type has been selected.
>
> remote_display is set in case either -vnc or -spice was given on the
> command line, and qemu will not start a local user display in that case
> (unless you explicitly ask for it via -display).

Makes sense.

> > OK, so neither SPICE or VNC really fit into this patchset because
> > they are seen as additional to the display type, not the actual
> > display type - SPICE is even more special too given the dependency
> > on a guest VM driver to really function correctly.
>
> Hmm?  spice works just fine with any display.

Sorry, mixed that up with EGL I think.

> > I wonder should there be a, similar, qemu_display_find_remote_default()
> > which would be used when no local display is defined. And that would
> > use a similar mechanism to permit selecting VNC or SPICE via
> > registration mechanisms over rather than the #ifdef style for remote
> > displays that will remain ever after this patchset (certainly could
> > be another patchset beyond this one).
>
> Well, historically qemu tried to do alot of stuff (like picking a
> display to use) automatically for the user.  And we did stick to that
> for backward compatibility reasons.  But this automagic causes quite
> some headache now and then, when changing things and the autmagic logic
> gets into the way.  So I don't feel like adding more of this.  Also vnc

Agree, there are times when automagic works - but unfortunately for
more consistent usage, you are better being explicit.

> is in pretty much any qemu build, because it is enabled by default and
> doesn't need any external dependencies, so falling back to spice would
> be quite rare ...

Understood - definitely VNC is a pretty good fall-back for most
people.

Thanks for outlining your thoughts on this, very helpful in
understanding the UI code and why somethings are how they are.

Thanks,

Darren.