[RFC QEMU PATCH] ui: Make the DisplayType enum entries conditional

[Thomas Huth]

On 09/06/2021 15.16, Markus Armbruster wrote:
> Thomas Huth <thuth at redhat.com> writes:
> 
>> Libvirt's "domcapabilities" command has a way to state whether
>> certain graphic frontends are available in QEMU or not. Originally,
>> libvirt looked at the "--help" output of the QEMU binary to determine
>> whether SDL was available or not (by looking for the "-sdl" parameter
>> in the help text), but since libvirt stopped doing this analysis of
>> the help text, the detection of SDL is currently broken, see:
>>
>>   https://bugzilla.redhat.com/show_bug.cgi?id=1790902
>>
>> QEMU should provide a way via the QMP interface instead. The simplest
>> way, without introducing additional commands, is to make the DisplayType
>> enum entries conditional, so that the enum only contains the entries if
>> the corresponding CONFIG_xxx switches have been set. Unfortunately, this
>> only works for sdl, cocoa and spice, since gtk, egl-headless and curses
>> are hard-wired in the "data" section of the DisplayOptions, and thus
>> unfortunately always have to be defined.
> 
> Here:
> 
>      { 'union'   : 'DisplayOptions',
>        'base'    : { 'type'           : 'DisplayType',
>                      '*full-screen'   : 'bool',
>                      '*window-close'  : 'bool',
>                      '*show-cursor'   : 'bool',
>                      '*gl'            : 'DisplayGLMode' },
>        'discriminator' : 'type',
>        'data'    : { 'gtk'            : 'DisplayGTK',
>                      'curses'         : 'DisplayCurses',
>                      'egl-headless'   : 'DisplayEGLHeadless'} }
> 
> Flat union branches can be made conditional like so:
> 
>        'data'    : { 'gtk'            : { 'type': 'DisplayGTK',
>                                           'if': 'defined(CONFIG_GTK)' },
> 
> Then you should be able to make the corresponding enum value
> conditional, too.

Thanks for the hint, I'll give it a try!

  Thomas