Re: [Qemu-devel] [RFC PATCH 1/6] utils/python_api: add scripting interface for Qemu with python lib

[Philippe Mathieu-Daudé]

On 8/8/19 12:49 PM, Daniel P. Berrangé wrote:
> On Wed, Aug 07, 2019 at 12:44:40PM +0530, Balamuruhan S wrote:
>> Adds scripting interface with python library to call functions in
>> python modules from Qemu that can be used to feed input externally
>> and without recompiling Qemu that can be used for early development,
>> testing and can be extended to abstract some of Qemu code out to a
>> python script to ease maintenance.
> 
> I admit the use case is interesting, but this is opening a can of
> worms...
> 
> Historically the project has held the view that we do not wish
> to have an mechanism to support loading out of tree code into the
> QEMU process. Much previously talk was around dlopen'd C plugins,
> but dynanically loaded Python plugins are doing the same thing
> at a conceptual level.
> 
> We didn't wish to expose internals of QEMU in a plugin API to
> avoid having any kind of API promise across releases.
> 
> There was also the question of licensing with plugins opening
> the door for people to extend QEMU with non-free/closed source
> functionality.
> 
> While this series only uses the plugin for one fairly obscure
> device, once a python plugin feature is intergrated in QEMU
> there will inevitably be requests to use it in further areas
> of QEMU.
> 
> IOW, acceptance of this patch is a significant question for
> the project, and a broader discussion point, than just this
> PPC feature patch series.

Since performance is not an issue, we can use a QMP-PyMMIO bridge.
Most of the functions required are already exposed, Damien completed the
missing ones in his 'FAULT INJECTION FRAMEWORK' series:
https://lists.gnu.org/archive/html/qemu-devel/2019-06/msg06230.html

Maybe we simply need a clearer (better documented) QMP 'MMIO' API?