Paolo Bonzini <pbonz...@redhat.com> writes: > Historically, the critical dependency for both building and running > QEMU has been the distro packages. Because QEMU is written in C and C's > package management has been tied to distros (at least if you do not want > to bundle libraries with the binary, otherwise I suppose you could use > something like conda or wrapdb), C dependencies of QEMU would target the > version that is shipped in relatively old but still commonly used distros. > > For non-C libraries, however, the situation is different, as these > languages have their own package management tool (cpan, pip, gem, npm, > and so on). For some of these languages, the amount of dependencies > for even a simple program can easily balloon to the point that many > distros have given up on packaging non-C code. For this reason, it has > become increasingly normal for developers to download dependencies into > a self-contained local environment, instead of relying on distro packages. > > Fortunately, this affects QEMU only at build time, as qemu.git does > not package non-C artifacts such as the qemu.qmp package; but still, > as we make more use of Python, we experience a clash between a support > policy that is written for the C world, and dependencies (both direct > and indirect) that increasingly do not care for the distro versions > and are quick at moving past Python runtime versions that are declared > end-of-life. > > For example, Python 3.6 has been EOL'd since December 2021 and Meson 0.62 > (released the following March) already dropped support for it. Yet, > Python 3.6 is the default version of the Python runtime for RHEL/CentOS > 8 and SLE 15, respectively the penultimate and the most recent version > of two distros that QEMU would like to support. (It is also the version > used by Ubuntu 18.04, but QEMU stopped supporting it in April 2022). > > Fortunately, these long-term support distros do include newer versions of > the Python runtime. However, these more recent runtimes only come with > a very small subset of the Python packages that the distro includes. > Because most dependencies are optional tests (avocado, mypy, flake8) > and Meson is bundled with QEMU, the most noticeably missing package is > Sphinx (and the readthedocs theme). > > Assuming QEMU would like to move forward with the deprecation of > Python 3.6 (for which there are some good reasons: completing the > configure->meson switch, which requires Meson 0.63, or making qapidoc
I think you mean "the QAPI generator". > fully typed which requires newer versions of mypy and also Python due > to PEP563), there are four possibilities: > > * we change the support policy and stop supporting CentOS 8 and SLE 15; > not a good idea since CentOS 8 is not an unreasonable distro for us to > want to continue to support > > * we keep supporting Python 3.6 until CentOS 8 and SLE 15 stop being > supported. This is a possibility---but we may want to revise the support > policy anyway because SLE 16 has not even been released, so this would > mean delaying those desirable reasons for perhaps three years; > > * we support Python 3.6 just for building documentation, i.e. we are > careful not to use Python 3.7+ features in our Sphinx extensions but are > free to use them elsewhere. Besides being more complicated to understand > for developers, this is difficult to apply because qapidoc runs at Suggest "some QAPI generator code runs". > sphinx-build time, and it is one of the areas which would benefit from > a newer version of the runtime; > > * we only support Python 3.7+, which means CentOS 8 CI and users > have to either install Sphinx from pip or disable documentation. > > This proposed update to the support policy chooses the last of these > possibilities. It does by modifying two aspects of the support policy: > > * it introduces different support periods for *native* vs. *non-native* > dependencies. Non-native dependencies are currently Python ones only, > and for simplicity the policy only mentions Python; however, the concept > generalizes to other languages with a well-known upstream package > manager, that users of older distributions can fetch dependencies from; > > * it limits the support period for non-native dependencies to a fixed > amount of 4 years. This is intended to be close to the Python 5-year > lifecycle while accounting for the time between a distro's feature freeze > and the day it's released. This limit applies to all distro versions, > not just the previous one, in order to cater for the delay of SLE 16. > > The 4 year cutoff in practice means that QEMU will be able to drop Python > 3.6 support for QEMU 7.1 (RHEL8 becomes 4 year old next May, while SLE We released 7.1 last August, do you mean 8.0 or 8.1? > is already over the threshold). > > Note that all "non-native" packages are currently build dependencies. > If in the future some non-native packages became runtime dependencies for > parts of QEMU, it would still be possible to choose any of the first > three possibilities for them. > > Another possible future change is to the way that these dependencies > have to be obtained by the person building QEMU. Right now they have to > run pip before the build; it may be desirable for configure to set up a > virtual environment and download them in the same way that it populates > git submodules. Just like with submodules, this would make things > easier for people that can afford accessing the network in their build > environment; the option to populate the build environment manually with > pip would remain for people whose build machines lack network access. > The change to the support policy neither requires nor forbids this change. > > [Thanks to Daniel P. Berrangé, Peter Maydell and others for discussions > that were copied or summarized in the above commit message] > > Cc: Markus Armbruster <arm...@redhat.com> > Cc: Daniel P. Berrangé <berra...@redhat.com> > Cc: Peter Maydell <peter.mayd...@linaro.org> > Cc: John Snow <js...@redhat.com> > Cc: Kevin Wolf <kw...@redhat.com> > Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> > --- > docs/about/build-platforms.rst | 19 +++++++++++++++++++ > 1 file changed, 19 insertions(+) > > diff --git a/docs/about/build-platforms.rst b/docs/about/build-platforms.rst > index 1c1e7b9e11c3..e1ea09789107 100644 > --- a/docs/about/build-platforms.rst > +++ b/docs/about/build-platforms.rst > @@ -86,6 +86,25 @@ respective ports repository, while NetBSD will use the > pkgsrc repository. > For macOS, `Homebrew`_ will be used, although `MacPorts`_ is expected to > carry > similar versions. > > +Python build dependencies > +~~~~~~~~~~~~~~~~~~~~~~~~~ > + > +The minimum supported version of Python is currently 3.6. > + > +Distributions with long-term support often provide multiple > +versions of the Python runtime. QEMU aims to support the default > +Python runtime for 4 years after the initial release of a new version. Just to be crystal clear: new version of what? > +Afterwards, you may have to point QEMU to a newer version of the Python > +runtime using the ``--python`` command line option of the ``configure`` > +script. > + > +Some of QEMU's build dependencies are written in Python and available > +through the Python Package Index (PyPI). QEMU aims to be compatible > +with the versions packaged by common Linux distributions for the first > +4 years after the major release of the distribution. After 4 years, > +you may have to use ``pip`` to install some of these build dependencies. > + > + > Windows > -------
