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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). There are good reasons to move forward with the deprecation of Python 3.6 in QEMU as well: completing the configure->meson switch (which requires Meson 0.63), and making the QAPI generator fully typed (which requires newer versions of not just mypy but also Python, due to PEP563). 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). 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 can be quite limiting; parts of the QAPI generator run at sphinx-build time, which would exclude 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 three 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 opens up the possibility of taking non-native dependencies from their own package index instead of using the version in the distribution. The wording right now is specific to dependencies that are only required at build time. In the future we may have to refine it if, for example, parts of QEMU will be written in Rust; in that case, crates would be handled in a similar way to submodules and vendored in the release tarballs. * it mentions specifically that optional build dependencies are excluded from the platform policy. Tools such as mypy don't affect the ability to build QEMU and move fast enough that distros cannot standardize on a single version of them (for example RHEL9 does not package them at all, nor does it run them at rpmbuild time). In other cases, such as cross compilers, we have alternatives. Right now, non-native dependencies have to be download manually by running "pip" before "configure". In the future, it will be desirable for configure to set up a virtual environment and download them in the same way that it populates git submodules (but, in this case, without vendoring them in the release tarballs). 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 would remain for people whose build machines lack network access. The change to the support policy neither requires nor forbids this future 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 <armbru@redhat.com> Cc: Peter Maydell <peter.maydell@linaro.org> Cc: John Snow <jsnow@redhat.com> Cc: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
=========== QEMU README =========== QEMU is a generic and open source machine & userspace emulator and virtualizer. QEMU is capable of emulating a complete machine in software without any need for hardware virtualization support. By using dynamic translation, it achieves very good performance. QEMU can also integrate with the Xen and KVM hypervisors to provide emulated hardware while allowing the hypervisor to manage the CPU. With hypervisor support, QEMU can achieve near native performance for CPUs. When QEMU emulates CPUs directly it is capable of running operating systems made for one machine (e.g. an ARMv7 board) on a different machine (e.g. an x86_64 PC board). QEMU is also capable of providing userspace API virtualization for Linux and BSD kernel interfaces. This allows binaries compiled against one architecture ABI (e.g. the Linux PPC64 ABI) to be run on a host using a different architecture ABI (e.g. the Linux x86_64 ABI). This does not involve any hardware emulation, simply CPU and syscall emulation. QEMU aims to fit into a variety of use cases. It can be invoked directly by users wishing to have full control over its behaviour and settings. It also aims to facilitate integration into higher level management layers, by providing a stable command line interface and monitor API. It is commonly invoked indirectly via the libvirt library when using open source applications such as oVirt, OpenStack and virt-manager. QEMU as a whole is released under the GNU General Public License, version 2. For full licensing details, consult the LICENSE file. Documentation ============= Documentation can be found hosted online at `<https://www.qemu.org/documentation/>`_. The documentation for the current development version that is available at `<https://www.qemu.org/docs/master/>`_ is generated from the ``docs/`` folder in the source tree, and is built by `Sphinx <https://www.sphinx-doc.org/en/master/>`_. Building ======== QEMU is multi-platform software intended to be buildable on all modern Linux platforms, OS-X, Win32 (via the Mingw64 toolchain) and a variety of other UNIX targets. The simple steps to build QEMU are: .. code-block:: shell mkdir build cd build ../configure make Additional information can also be found online via the QEMU website: * `<https://wiki.qemu.org/Hosts/Linux>`_ * `<https://wiki.qemu.org/Hosts/Mac>`_ * `<https://wiki.qemu.org/Hosts/W32>`_ Submitting patches ================== The QEMU source code is maintained under the GIT version control system. .. code-block:: shell git clone https://gitlab.com/qemu-project/qemu.git When submitting patches, one common approach is to use 'git format-patch' and/or 'git send-email' to format & send the mail to the qemu-devel@nongnu.org mailing list. All patches submitted must contain a 'Signed-off-by' line from the author. Patches should follow the guidelines set out in the `style section <https://www.qemu.org/docs/master/devel/style.html>`_ of the Developers Guide. Additional information on submitting patches can be found online via the QEMU website * `<https://wiki.qemu.org/Contribute/SubmitAPatch>`_ * `<https://wiki.qemu.org/Contribute/TrivialPatches>`_ The QEMU website is also maintained under source control. .. code-block:: shell git clone https://gitlab.com/qemu-project/qemu-web.git * `<https://www.qemu.org/2017/02/04/the-new-qemu-website-is-up/>`_ A 'git-publish' utility was created to make above process less cumbersome, and is highly recommended for making regular contributions, or even just for sending consecutive patch series revisions. It also requires a working 'git send-email' setup, and by default doesn't automate everything, so you may want to go through the above steps manually for once. For installation instructions, please go to * `<https://github.com/stefanha/git-publish>`_ The workflow with 'git-publish' is: .. code-block:: shell $ git checkout master -b my-feature $ # work on new commits, add your 'Signed-off-by' lines to each $ git publish Your patch series will be sent and tagged as my-feature-v1 if you need to refer back to it in the future. Sending v2: .. code-block:: shell $ git checkout my-feature # same topic branch $ # making changes to the commits (using 'git rebase', for example) $ git publish Your patch series will be sent with 'v2' tag in the subject and the git tip will be tagged as my-feature-v2. Bug reporting ============= The QEMU project uses GitLab issues to track bugs. Bugs found when running code built from QEMU git or upstream released sources should be reported via: * `<https://gitlab.com/qemu-project/qemu/-/issues>`_ If using QEMU via an operating system vendor pre-built binary package, it is preferable to report bugs to the vendor's own bug tracker first. If the bug is also known to affect latest upstream code, it can also be reported via GitLab. For additional information on bug reporting consult: * `<https://wiki.qemu.org/Contribute/ReportABug>`_ ChangeLog ========= For version history and release notes, please visit `<https://wiki.qemu.org/ChangeLog/>`_ or look at the git history for more detailed information. Contact ======= The QEMU community can be contacted in a number of ways, with the two main methods being email and IRC * `<mailto:qemu-devel@nongnu.org>`_ * `<https://lists.nongnu.org/mailman/listinfo/qemu-devel>`_ * #qemu on irc.oftc.net Information on additional methods of contacting the community can be found online via the QEMU website: * `<https://wiki.qemu.org/Contribute/StartHere>`_