libvirt/docs/hacking.rst

Contributor guidelines

General tips for contributing patches

1. Discuss any large changes on the mailing list first. Post patches early and listen to feedback.

2. Official upstream repository is kept in git (https://libvirt.org/git/libvirt.git) and is browsable along with other libvirt-related repositories (e.g. libvirt-python) online.

3. Patches to translations are maintained via the zanata project. If you want to fix a translation in a .po file, join the appropriate language team. The libvirt release process automatically pulls the latest version of each translation file from zanata.

4. The simplest way to send patches is to use the git-publish tool. All libvirt-related repositories contain a config file that tells git-publish to use the correct mailing list and subject prefix.

   Alternatively, you may send patches using git send-email.

   Also, for code motion patches, you may find that git diff --patience provides an easier-to-read patch. However, the usual workflow of libvirt developer is:

   git checkout master
   git pull
   git checkout -t origin -b workbranch
   Hack, committing any changes along the way

   More hints on compiling can be found here. When you want to post your patches:

   git pull --rebase
   (fix any conflicts)
   git send-email --cover-letter --no-chain-reply-to --annotate \
                  --confirm=always --to=libvir-list@redhat.com master

   For a single patch you can omit --cover-letter, but a series of two or more patches needs a cover letter.

   Note that the git send-email subcommand may not be in the main git package and using it may require installation of a separate package, for example the "git-email" package in Fedora and Debian. If this is your first time using git send-email, you might need to configure it to point it to your SMTP server with something like:

   git config --global sendemail.smtpServer stmp.youremailprovider.net

   If you get tired of typing --to=libvir-list@redhat.com all the time, you can configure that to be automatically handled as well:

   git config sendemail.to libvir-list@redhat.com

   As a rule, patches should be sent to the mailing list only: all developers are subscribed to libvir-list and read it regularly, so please don't CC individual developers unless they've explicitly asked you to.

   Avoid using mail clients for sending patches, as most of them will mangle the messages in some way, making them unusable for our purposes. Gmail and other Web-based mail clients are particularly bad at this.

   If everything went well, your patch should show up on the libvir-list archives in a matter of minutes; if you still can't find it on there after an hour or so, you should double-check your setup. Note that, if you are not already a subscriber, your very first post to the mailing list will be subject to moderation, and it's not uncommon for that to take around a day.

   Please follow this as close as you can, especially the rebase and git send-email part, as it makes life easier for other developers to review your patch set.

   One should avoid sending patches as attachments, but rather send them in email body along with commit message. If a developer is sending another version of the patch (e.g. to address review comments), they are advised to note differences to previous versions after the --- line in the patch so that it helps reviewers but doesn't become part of git history. Moreover, such patch needs to be prefixed correctly with --subject-prefix=PATCHv2 appended to git send-email (substitute v2 with the correct version if needed though).

5. In your commit message, make the summary line reasonably short (60 characters is typical), followed by a blank line, followed by any longer description of why your patch makes sense. If the patch fixes a regression, and you know what commit introduced the problem, mentioning that is useful. If the patch resolves a bugzilla report, mentioning the URL of the bug number is useful; but also summarize the issue rather than making all readers follow the link. You can use 'git shortlog -30' to get an idea of typical summary lines.

6. 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.

7. Split large changes into a series of smaller patches, self-contained if possible, with an explanation of each patch and an explanation of how the sequence of patches fits together. Moreover, please keep in mind that it's required to be able to compile cleanly (including make check and make syntax-check) after each patch. A feature does not have to work until the end of a series, but intermediate patches must compile and not cause test-suite failures (this is to preserve the usefulness of git bisect, among other things).

8. Make sure your patches apply against libvirt GIT. Developers only follow GIT and don't care much about released versions.

9. Run the automated tests on your code before submitting any changes. That is:

   make check
   make syntax-check

10. Update tests and/or documentation, particularly if you are adding a new feature or changing the output of a program.

11. Don't forget to update the release notes by changing docs/news.xml if your changes are significant. All user-visible changes, such as adding new XML elements or fixing all but the most obscure bugs, must be (briefly) described in a release notes entry; changes that are only relevant to other libvirt developers, such as code refactoring, don't belong in the release notes. Note that docs/news.xml should be updated in its own commit not to get in the way of backports.

There is more on this subject, including lots of links to background reading on the subject, on Richard Jones' guide to working with open source projects.