Re: [Qemu-devel] [PATCH v3 12/15] monitor: use qmp_dispatch()

[Markus Armbruster <armbru@redhat.com>]

Marc-André Lureau <mlureau@redhat.com> writes:

> Hi
>
> ----- Original Message -----
>> marcandre.lureau@redhat.com writes:
>> 
>> > From: Marc-André Lureau <marcandre.lureau@redhat.com>
>> >
>> > Replace the old manual dispatch and validation code by the generic one
>> > provided by qapi common code.
>> >
>> > Note that it is now possible to call the following commands that used to
>> > be disabled by compile-time conditionals:
>> > - dump-skeys
>> > - query-spice
>> > - rtc-reset-reinjection
>> > - query-gic-capabilities
>> >
>> > Their fallback functions return an appropriate "feature disabled" error.
>> >
>> > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
>> 
>> Means query-qmp-schema no longer shows whether these commands are
>> supported, doesn't it?
>> 
>> Eric, could this create difficulties for libvirt or other introspection
>> users?
>
> Thinking a bit about this, I guess it would be fairly straightforward
> to have a new key "c-conditional" : "#ifdef CONFIG_SPICE" that would
> prepend it in C generated files, with a corresponding "#endif". Would
> that be acceptable?

Not exactly pretty, but the only alternative I can think of right now
would be conditional qapi generation, i.e. something like

{ 'if': 'CONFIG_SPICE'
  'then': { 'command': 'query-spice', 'returns': 'SpiceInfo' } }

More general, but *much* more work.  Let's not go there now.

The value of key 'c-conditional' must be a preprocessing directive that
pairs with #endif.  Hmm.

Could make it an expression instead, and call the key just
'conditional'.  If given, wrap the code generated for the QAPI
definition in

    #if <value of conditional>
    ...
    #endif

Feels cleaner, but to avoid -Wundef warnings, we'd have to say
'defined(CONFIG_SPICE)'.

Thoughts?