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LTTng-tools contributor's guide

Being an open source project, the LTTng-tools project welcomes contributions from anyone. This guide walks you through the process of contributing a patch to LTTng-tools.

Getting the source code

The LTTng-tools project uses Git for version control. The upstream Git repository URL is:

git://git.lttng.org/lttng-tools.git

Coding standard

LTTng-tools uses the Linux kernel coding style with one addition: single-line if/for/while statements must be wrapped in braces.

Example:

/* not good */
if (this == that)
    goto fail;

/* good */
if (this == that) {
    goto fail;
}

Although the LTTng-tools code base is primarily written in C, it does contain shell, Perl, and Python code as well. There is no official coding standard for these languages. However, using a style consistent with the rest of the code written in that language is strongly encouraged.

Creating and sending a patch

LTTng-tools's development flow is primarily email-based, although we also accept pull requests on our GitHub mirror. If you're going to create GitHub pull requests, make sure you still follow the guidelines below.

Like a lot of open source projects, patches are submitted and reviewed on its development mailing list, lttng-dev ([email protected]). The mailing list is also used to share and comment on RFCs and answer user questions.

Once your changes have been committed to your local branch, you may use Git's format-patch command to generate a patch file. The following command line generates a patch from the latest commit:

git format-patch -N1 -s --subject-prefix="PATCH lttng-tools"

The custom PATCH lttng-tools subject prefix is mandatory when submitting patches that apply to the LTTng-tools project.

The patch's subject (the commit message's first line) should:

  • begin with an uppercase letter
  • be written in the present tense
  • not exceed 72 characters in length
  • not end with a period
  • be prefixed with Fix: if the commit fixes a bug

The commit message's body should be as detailed as possible and explain the reasons behind the proposed change. Any related bug report(s) should be mentioned at the end of the message using the #123 format, where 123 is the bug number:

  • Use Refs: #123 if the patch is related to bug 123, but does not fix it yet.
  • Use Fixes: #123 to signify that this patch fixes the bug.

Make sure to sign-off your submitted patches (the -s argument to Git's commit and format-patch commands).

Here's a complete example:

Fix: use this instead of that in some context

Ball tip jowl beef ribs shankle, leberkas venison turducken tail pork
chop t-bone meatball tri-tip. Tongue beef ribs corned beef ball tip
kevin ground round sausage rump meatloaf pig meatball prosciutto
landjaeger strip steak. Pork pork belly beef.

Biltong turkey porchetta filet mignon corned beef. T-bone bresaola
shoulder meatloaf tongue kielbasa.

Fixes: #321
Refs: #456
Refs: #1987

Signed-off-by: Jeanne Mance <[email protected]>

Please note that patches should be as focused as possible. Do not, for instance, fix a bug and correct the indentation of an unrelated block of code as part of the same patch.

The project contains a script, extras/checkpatch.pl, that performs a number of checks on a patch to ensure it is ready for submission. Run this script on your patch and correct any reported errors before posting it to the mailing list:

extras/checkpatch.pl --no-tree 0001-Fix...patch

Once you are confident your patch meets the required guidelines, you may use Git's send-email command to send your patch to the mailing list:

git send-email --suppress-cc=self --to [email protected] *.patch

Make sure you are subscribed to the mailing list to follow and take part in discussions about your changes. You may join the file to an email as an attachment if you can't send the patch directly using git send‑email.

Reviews

Once your patch has been posted to the mailing list or as a GitHub pull request, other contributors may propose modifications. This is completely normal. This collaborative code review is an integral part of the open source development process in general and LTTng-tools makes no exception.

Keep in mind that reviewing patches is a time-consuming process and, as such, may not be done right away. The delays may be affected by the current release cycle phase and the complexity of the proposed changes. If you think your patch might have been forgotten, please mention it on the #lttng IRC channel rather than resubmitting.

Release cycle

The LTTng-tools project follows a release cycle that alternates between development and release candidate (RC) phases. The master branch is feature-frozen during RC phases: only bug fixes are accepted during this period. However, patches adding new functionality may still be submitted and reviewed during the RC. The upcoming features and release dates are posted in a monthly digest on the mailing list.