Re: [Qemu-devel] [PULL 0/8] Python queue, 2019-06-07

[Eduardo Habkost <ehabkost@redhat.com>]

On Tue, Sep 17, 2019 at 07:10:13PM -0400, John Snow wrote:
> On 9/17/19 5:48 PM, Eduardo Habkost wrote:
> > On Tue, Sep 17, 2019 at 03:57:26PM +0200, Kevin Wolf wrote:
> >> Am 11.06.2019 um 19:12 hat Eduardo Habkost geschrieben:
> >>> On Tue, Jun 11, 2019 at 05:07:55PM +0100, Peter Maydell wrote:
> >>>> On Tue, 11 Jun 2019 at 17:03, Eduardo Habkost <ehabkost@redhat.com> wrote:
> >>>>>
> >>>>> On Tue, Jun 11, 2019 at 04:50:34PM +0100, Peter Maydell wrote:
> >>>>>> On Mon, 10 Jun 2019 at 13:58, Peter Maydell <peter.maydell@linaro.org> wrote:
> >>>>>>> Hi. This fails to build on one of my buildtest machines:
> >>>>>>>
> >>>>>>> ERROR: Cannot use 'python3', Python 2 >= 2.7 or Python 3 >= 3.5 is required.
> >>>>>>>        Use --python=/path/to/python to specify a supported Python.
> >>>>>>>
> >>>>>>> The machine has python 2.7.6 and 3.4.3. (It's an Ubuntu trusty
> >>>>>>> box; it's one of the gcc compile farm machines so upgrades to its
> >>>>>>> OS are not really under my control.)
> >>>>>>
> >>>>>> Rereading this, I realise that either the check or the error
> >>>>>> message is wrong here. The machine has 2.7.6, which satisfies
> >>>>>> "python 2 >= 2.7", so we should be OK to build. The bug
> >>>>>> seems to be that we say "prefer python3 over plain python
> >>>>>> on python2" early, but don't revisit that decision if the
> >>>>>> python3 we found isn't actually good enough for us.
> >>>>>
> >>>>> Right.  The error message is technically correct, but misleading.
> >>>>> python3 is too old, but python2 would work.
> >>>>>
> >>>>> We can make configure not use python3 by default if it's too old,
> >>>>> and fall back to python2 in this case.
> >>>>
> >>>> Sounds good. Since I have now managed to get my alternate
> >>>> aarch64 box set up, how about I apply this pullreq and you
> >>>> send a followup patch which does the fallback to python/python2 ?
> >>>
> >>> I will remove the python2/python3 patches and send a new pull
> >>> request.
> >>
> >> What is the plan forward with this? Are the patches dropped for good?
> >>
> >> I think the plan was to drop Python 2 after QEMU 4.2, and then it
> >> becomes really relevant what our minimum Python 3 version is. We've just
> >> had another Python version discussion in the context of iotests (John
> >> suggested using function annotations, but these are >= 3.5 only).
> >>
> >> Also, the fallback to Python 2 obviously makes no sense any more then,
> >> so maybe it's not that important to add for a single QEMU release?
> >>
> >> As Peter seems to have indicated above that he found a replacement for
> >> the test machine with an OS that isn't out of support, can we just
> >> revive this patch as it is?
> > 
> > My plan is to remove Python 2 support in QEMU 4.2 (making the
> > fallback to Python 2 a non-issue), and require Python >= 3.5.
> > 
> > Now, even if my plan is rejected and we keep supporting Python 2
> > when building QEMU 4.2, my suggestion for the iotest maintainers
> > is to make it require Python 3.5+ immediately, just like we do
> > for tests/acceptance.  I don't see why we should keep wasting our
> > energy supporting ancient Python versions in a test suite that is
> > not a requirement for building QEMU.
> > 
> 
> It's unfortunately now part of the 'make check' target which we use in
> the vm tests as a default target ... but I think we can make the push to
> change the build requires to 3.5+.

In the worst case, we can make "make check" skip iotests if
Python 2 is detected (after printing a warning).  But requiring
3.5+ for the build would really be the best option.

I've just restarted the thread about Python 2 in tests/vm:
https://lore.kernel.org/qemu-devel/20190917233140.GK4082@habkost.net/

-- 
Eduardo