These are the basics steps you need to follow to contribute to libvirt software development.
The official upstream repository is kept in git (https://gitlab.com/libvirt/libvirt) and is browsable along with other libvirt-related repositories (e.g. libvirt-python) online.
Patches to translations are maintained via the Fedora Weblate service. If you want to contribute to translations of libvirt, join the appropriate language team in Weblate. Translation updates to libvirt will be merged during the feature freeze window.
In general you should base your work upon the git master branch.
The "Git checkout" section of the libvirt installation instructions give an overview of the compilation process.
Optionally, Clangd with libvirt can be used to navigate the code base etc. within most code editors (and IDEs).
Make sure your patches apply against the libvirt git master branch. The backporting of changes to existing releases is typically carried out by downstream users at their discretion after code is merged into the upstream git.
Run the automated tests on your code before submitting any changes. That is:
$ ninja test
These tests help making sure that your changes don't introduce regressions in libvirt, as well as validating that any new code follows the project's coding style.
If you're going to submit multiple patches, the automated tests must pass after each patch, not just after the last one.
Update tests and/or documentation, particularly if you are adding a new feature or changing the output of a program, and don't forget to update the release notes if your changes are significant and user-visible.
To test across a variety of build platforms prior to submitting your changes, you may create your own fork of the project on gitlab. This will give you access to (a subset of) libvirt's continuous integration test suite.
Please note that you should still follow the instructions below, rather than following gitlab's prompts to open a "merge request".
Libvirt uses a mailing list based development workflow.
While preparing your patches for submissions, make sure you follow the best practices and, once you're satisfied with the result, go ahead and submit your patches.
Contributors to libvirt projects must assert that they are in compliance with the Developer Certificate of Origin 1.1. This is achieved by adding a "Signed-off-by" line containing the contributor's name and e-mail to every commit message. The presence of this line attests that the contributor has read the above lined DCO and agrees with its statements.
This page only covers the very basics, so it's recommended that you also take a look at the following documents: