Re: [PATCH v4 0/4] Python: Improvements for iotest 040,041

[John Snow]

On Tue, Feb 1, 2022 at 8:28 AM Kevin Wolf <kwolf@redhat.com> wrote:
>
> Am 01.02.2022 um 05:11 hat John Snow geschrieben:
> > GitLab: https://gitlab.com/jsnow/qemu/-/commits/python-aqmp-fixes
> > CI: https://gitlab.com/jsnow/qemu/-/pipelines/455146881
> >
> > Fixes and improvements all relating to "iotest 040,041, intermittent
> > failure in netbsd VM"
> > https://lists.gnu.org/archive/html/qemu-devel/2022-01/msg01975.html
> >
> > See each patch for details.
>
> Thanks, the new output when QEMU fails to start looks really useful!
>
> The only thing we could probably still improve is detecting that the
> QEMU process has exited instead of waiting for the socket connection to
> time out. But since it only happens in case of failure, the additional
> seconds of waiting are probably only a bit annoying for debugging, but
> not a big problem.

That's absolutely on my radar, I assure you!

It's something that is easy to solve with asyncio:

async def launch(self, ...):
    task1 = asyncio.create_task(self.qmp.accept(...))
    task2 = asyncio.create_subprocess_exec(...)
    ret = asyncio.wait_for((task1, task2))
    ...

If either task raises, then the wait_for will also end prematurely
(and cancel the other task). I'm sure it won't actually be this easy,
but that's the general idea.

Though, that's a pretty big upheaval to the Python code again, so it's
not something I can jam in quickly. I have some light sketches that
examine a "what-if" for an asyncio-native machine.py using the asyncio
QMP code, but there are some design concerns there -- if I go through
the effort of doing this, I will want to publish that python package
upstream as well, and if I do that, it needs to be carefully thought
through in terms of a supportable interface.

Well, I'm thinking about it, anyway. For right now I am interested in
getting the qemu.qmp project out the door and onto PyPI.org, and then
I'll worry about machine improvements. If in the meantime you have a
good idea for how to fix up the machine.py code we already have, I'm
happy to take patches. Otherwise, I'll try to get to it "soon".

>
> Reviewed-by: Kevin Wolf <kwolf@redhat.com>
>

Thanks!