Re: [Qemu-devel] [RFC PATCH 0/6] Enhancing Qemu MMIO emulation with scripting interface

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Wed, Aug 07, 2019 at 12:44:39PM +0530, Balamuruhan S wrote:
> This is a proposal to extend mmio callbacks in Qemu with scripting interface
> that is prototyped with python in this implementation. It gives ability to
> feed runtime data through callbacks without recompiling Qemu in generic way.
> This patchset adds library that provides APIs for Qemu to talk with python
> scripts placed in path -module-path and how existing xscom can be extended
> with python interface infrastructure.
> 
> We have also added an hacky emulation for memory region (OCC common area and HOMER)
> which is shared between core and un-core engine (ideally this should be via
> sram device) to showcase the effectiveness of having the scripting interface
> (uncore engine taken for discussion here is powerpc specificed called OCC).
> Having scripting interface helps to emulate/test different uncore-core
> interactions including uncore engine failure or hang. It also helps in feeding
> randomized data at byte level access. This patchset is primarily to extend mmio
> callbacks with scripting interface and to demonstrate effectiveness it.
> 
> Some changes are required in PowerPC skiboot tree to test these changes since
> the memory region is disabled currently for Qemu emulated PowerNV host,
> https://github.com/balamuruhans/skiboot/commit/a655514d2a730e0372a2faee277d1cf01f71a524

Although writing Python is quick and easy, carefully wiring up the
Python C API for it is not.  In practice you lose much of the benefit of
Python if you need to study the Python C API every time you wish to do
some quick scripting :(.

It must be possible to compile out the Python integration code.  If the
Python integration code remains in the device model then the QEMU binary
has a dependency on libpython, which is undesirable when this feature is
not in use.

Assuming this feature can be compiled out, I think it should have a
chance to prove its usefulness and gain users.  Documentation and an
active maintainer are essential.

Stefan

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