Contributing to LinuxCNC

The official LinuxCNC git repo is at https://github.com/linuxcnc/linuxcnc/

Anyone can get a read-only copy of the LinuxCNC source tree via git:

If you are a developer with push access, then follow github’s instructions for setting up a repository that you can push from.

Note that the clone command put the local LinuxCNC repo in a directory called linuxcnc-dev, instead of the default linuxcnc. This is because the LinuxCNC software by default expects configs and G-code programs in a directory called $HOME/linuxcnc, and having the git repo there too is confusing.

Issues and pull requests (abbreviated PRs) are welcome on GitHub: https://github.com/LinuxCNC/linuxcnc/issues https://github.com/LinuxCNC/linuxcnc/pulls

We use the "merging upwards" and "topic branches" git workflows described here:

https://www.kernel.org/pub/software/scm/git/docs/gitworkflows.html

We have a development branch called master, and one or more stable branches with names like 2.6 and 2.7 indicating the version number of the releases we make from it.

Bugfixes go in the oldest applicable stable branch, and that branch gets merged into the next newer stable branch, and so on up to master. The committer of the bugfix may do the merges themselves, or they may leave the merges for someone else.

New features generally go in the master branch, but some kinds of features (specifically well isolated device drivers and documentation) may (at the discretion of the stable branch release managers) go into a stable branch and get merged up just like bugfixes do.

There are many excellent, free git tutorials on the internet.

The first place to look is probably the "gittutorial" manpage. This manpage is accessible by running "man gittutorial" in a terminal (if you have the git manpages installed). The gittutorial and its follow-on documentation are also available online here:

For a more thorough documentation of git see the "Pro Git" book: https://git-scm.com/book

Another online tutorial that has been recommended is "Git for the Lazy": https://wiki.spheredev.org/index.php/Git_for_the_lazy

Keep your commits small and to the point. Each commit should accomplish one logical change to the repo.

Keep commit messages around 72 columns wide (so that in a default-size terminal window, they don’t wrap when shown by git log).

Use the first line as a summary of the intent of the change (almost like the subject line of an e-mail). Follow it with a blank line, then a longer message explaining the change. Example:

Bugfixes should go on the oldest applicable branch. New features should go in the master branch. If you’re not sure where a change belongs, ask on irc or on the mailing list.

When appropriate, organize your changes into a branch (a series of commits) where each commit is a logical step towards your ultimate goal. For example, first factor out some complex code into a new function. Then, in a second commit, fix an underlying bug. Then, in the third commit, add a new feature which is made easier by the refactoring and which would not have worked without fixing that bug.

This is helpful to reviewers, because it is easier to see that the "factor out code into new function" step was right when there aren’t other edits mixed in; it’s easier to see that the bug is fixed when the change that fixes it is separate from the new feature; and so on.

Make an effort to follow the prevailing indentation style of surrounding code. In particular, changes to whitespace make it harder for other developers to track changes over time. When reformatting code must be done, do it as a commit separate from any semantic changes.

The test "retval < 0" should feel familiar; it’s the same kind of test you use in userspace (returns -1 for error) and in kernel space (returns -ERRNO for error).

With git, it’s possible to record every edit and false start as a separate commit. This is very convenient as a way to create checkpoints during development, but often you don’t want to share these false starts with others.

Git provides two main ways to clean history, both of which can be done freely before you share the change:

git commit --amend lets you make additional changes to the last thing you committed, optionally modifying the commit message as well. Use this if you realized right away that you left something out of the commit, or if you typo’d the commit message.

git rebase --interactive upstream-branch lets you go back through each commit made since you forked your feature branch from the upstream branch, possibly editing commits, dropping commits, or squashing (combining) commits with others. Rebase can also be used to split individual commits into multiple new commits.

If your change consists of several patches, git rebase -i may be used to reorder these patches into a sequence of commits which more clearly lays out the steps of your work. A potential consequence of reordering patches is that one might get dependencies wrong - for instance, introducing a use of a variable, and the declaration of that variable only follows in a later patch.

While the branch HEAD will build, not every commit might build in such a case. That breaks git bisect - something somebody else might use later on to find the commit which introduced a bug. So beyond making sure your branch builds, it is important to assure every single commit builds as well.

There’s an automatic way to check a branch for each commit being buildable - see https://dustin.sallings.org/2010/03/28/git-test-sequence.html and the code at https://github.com/dustin/bindir/blob/master/git-test-sequence. Use as follows (in this case testing every commit from origin/master to HEAD, including running regression tests):

This will either report All is well or Broke on <commit>

Please use the ability to rename files very cautiously. Like running indent on single files, renames still make it more difficult to follow changes over time. At a minimum, you should seek consensus on irc or the mailing list that the rename is an improvement.

Use git pull --rebase instead of bare git pull in order to keep a nice linear history. When you rebase, you always retain your work as revisions that are ahead of origin/master, so you can do things like git format-patch them to share with others without pushing to the central repository.