Ostro™ OS Pull Request Guidelines🔗

The Ostro™ OS Contributor Guide explains how to submit changes as pull requests (PRs) and how they will get merged.

This document complements those instructions with more hands-on guidelines about what information will be needed during a review, what kind of mistakes to watch out for during review, and how to deal with PRs.

The goal is to make the review process more consistent and help less experienced reviewers in catching potential mistakes that otherwise might get overlooked. A submitter can use this to avoid these mistakes before even submitting the pull request.


PRs are typically checked in this order:

  1. pull request message
  2. commit messages
  3. actual diff

Reviewers should be aware of that context before looking at the diff and, when in doubt, also look at the entire file that gets modified to ensure that the change is consistent with the rest.

If reviewers find issues with the PR, a review of all changes may be abandoned early with a request to the submitter to fix those things first before the review continues.

Pull Request Message🔗

The main pull request message summarizes the change. Relevant information is how important the PR is, whether there are dependencies on other PRs, and who should, might, or needs to review it.

Submitters should mention specific reviewers (if known) by using their Github handle with the at symbol to alert them of the PR, as in @johndoe please review or @joandoe needs to review this.

Commit Messages🔗

Your commit messages should follow the format explained in Ostro™ OS Contributor Guide, for the sake of consistency and completeness.

The commit message will be used in different ways and with different goals:

  • Listing commits (for example, git log --oneline, Jenkins PR overview pages, gitk): the first line should be informative and ideally unique.
  • Reviewing the change: what is the motivation for the change, why was it solved this way?
  • Distro maintenance at a later point in time: is the change still relevant? What breaks if the change has to removed or modified? This might also get answered in the actual code, but sometimes there is additional information like verbatim copies of error messages that are too large for the code itself. Storing them in the commit message preserves that additional information (see next point).
  • Searching for problems and how they were solved: git log --grep can be useful to find commits again.
  • Commit author: when including something written by others (like patches or complete files), try to submit that in a separate commit with the original author set as author of the commit. This is important for tracking the origin of code in Ostro OS, which is assisted by automated tooling. When multiple people authored the change, use the upstream project’s mailing list as author. Alternatively, using git am format for patches can also be used to document the author of a code patch (see next section).

Content of a Pull Request🔗

When a change affects user-visible behavior, make sure that relevant user documentation gets updated, ideally in the same commit (only works when submitting to meta-ostro, which is where the doc directory is maintained). If that is not possible or not desirable at the time, include enough information in the change or commit message for a technical writer to update the Ostro OS user documentation later.

Avoid unnecessary changes, like arbitrarily reformatting unrelated code.

Avoid mixing unrelated changes in the same commit. Changes that are not mentioned in the commit message are questionable because they may have been included accidentally. Split large changes into smaller, individual commits because they are easier to review. They also support bisecting better when there are problems.

When adding patches inside a PR:

  • It is really necessary? Can the problem be fixed upstream first? Are there other solutions that are easier to maintain?
  • Document the patch status by adding a Upstream-Status line in the patch header. “Pending” patches are discouraged because they contribute to the technical debt in Ostro OS.
  • The author of the patch must be clear, either by using git am format with an Author: line, adding such a line manually to the patch header, or by committing the entire file with the author of the commit set to the author of the patch.

Adding or removing layers needs to be done in two separate PRs:

  • In the ostro-os repo, update combo-layer.conf and combo-layer-local-sample.conf, then include the initial import of the new component in the PR.
  • In the meta-ostro repo, update:
    • .gitignore - imported files must not be ignored
    • README.rst - the list of layers
    • meta-ostro/conf/bblayers.conf.sample - add the layer and increase LCONF_VERSION by one
    • meta-ostro/conf/layer.conf - increase LAYER_CONF_VERSION by one. It must match LCONF_VERSION.

The layer config file versioning ensures that developers who update to a new revision of ostro-os where the new layer was added are told to update their local bblayers.conf when invoking bitbake in older build directories

Similarly, when making changes to local.conf.sample, increase both LOCALCONF_VERSION in meta-ostro/conf/layer.conf and CONF_VERSION in meta-ostro/conf/local.conf.sample.

Dos and Don’ts🔗

  • When providing feedback, be clear whether you consider highlighted issues as critical enough that they need to be fixed before merging.
  • Try to write correct English. Use a spell checker when unsure. Pointing out language mistakes is acceptable during a review, but typically is considered a minor issue that the submitter may or may not want to fix. Review comments about spelling, grammar, and clarity in documentation should be addressed.
  • A code review typically is done by just looking at a change. Review comments such as Looks good to me = LGTM, +1 or adding a positive reaction via the Github button typically just means that the reviewer has agreed to merge the pull request based on such a visual inspection.
  • The submitter is expected to have tested the change, i.e. it is expected to work at a functional level. However, exhaustive testing often is not possible. So when there is additional need for testing, describe that.
  • If a reviewer actually tries out a change, that should be mentioned in a review comment because it provides additional assurance that a pull request is really okay.
  • Ostro™ OS Contributor Guide explains when a PR is considered ready for merging (enough time to provide feedback, no objections, etc.).
  • The Ostro project uses Github’s non-fast-forward merges (aka the “merge” button in the Gitub web interface). The reason is that this style of merging records when commits were merged and by whom. The merge commit message can be used to add additional information about the merge (but in practice, that is not done often). Automatic testing happens only for the full set of commits that are getting merged, so when bisecting history, the merge commits are good candidates for testing because they are more likely to build correctly.
  • Never add backdoors (i.e., something that enables unexpected and unauthorized access to the system or some of its features) or debug features to the default configuration. Such capabilities may be enabled only in explicit debug configurations of the OS images.