On 5/7/25 12:55 AM, Markus Armbruster wrote:
[...]
- First, it's already broken because we rely on ifdef that won't be
there in Rust or Go.
I don't think it's broken. QAPI 'if' translates straightforwardly to C
#if, but that doesn't mean it cannot be translated to conditional
compilation / metaprogramming in other languages.
In fact, the value of 'if' used to be C constant expressions suitable
for use with #if, and we changed it to its current form specifically to
enable Rust work, in merge commit c83fcfaf8a5. Marc-André's was trying
to develop Rust bindings back then, and if I remember correctly this
change was enough to let him implement 'if' with Rust.
Sure, I didn't mean "this approach is doomed", simply that it needs
changes, the same way code doing a runtime check would need changes as well.
- Second, it's code, we can just change it later if needed.
True!
- Third, those json are consumed only by QEMU (right?), so we are free
to write/modify them as we want.
Also true.
The only thing that must stay the same is what we expose to the consumer
in the schema, and which commands we expose in qemu.
We may evolve the external interface as long as we honor our
compatibility promise.
You're aiming for "no change at all" there. I understand why that's
desirable. But if it should turn out that a bit of compatible change
simplifies the job, we can take the simpler route.
I have a local prototype doing what was described: introduce a
runtime_if, additional to if (no worries, the name can be changed
later), exposing schema parts conditionnally, and same for visiting
types and registering commands.
It's not too ugly, and easy to combine compilation if and runtime if
together.
I should be able to post it next week.
[...]
Regards,
Pierrick.
