Contribution Guidelines

As an open-source project, we welcome and encourage the community to submit patches directly to the project. In our collaborative open source environment, standards and methods for submitting changes help reduce the chaos that can result from an active development community.

This document explains how to participate in project conversations, log bugs and enhancement requests, and submit patches to the project so your patch will be accepted quickly in the codebase.

Licensing

Licensing is very important to open source projects. It helps ensure the software continues to be available under the terms that the author desired.

Zephyr uses the Apache 2.0 license (as found in the LICENSE file in the project’s GitHub repo) to strike a balance between open contribution and allowing you to use the software however you would like to. The Apache 2.0 license is a permissive open source license that allows you to freely use, modify, distribute and sell your own products that include Apache 2.0 licensed software. (For more information about this, check out articles such as Why choose Apache 2.0 licensing and Top 10 Apache License Questions Answered).

A license tells you what rights you have as a developer, as provided by the copyright holder. It is important that the contributor fully understands the licensing rights and agrees to them. Sometimes the copyright holder isn’t the contributor, such as when the contributor is doing work on behalf of a company.

Components using other Licenses

There are some imported or reused components of the Zephyr project that use other licensing, as described in Licensing of Zephyr Project components.

Importing code into the Zephyr OS from other projects that use a license other than the Apache 2.0 license needs to be fully understood in context and approved by the Zephyr governing board.

By carefully reviewing potential contributions and also enforcing a Developer Certification of Origin (DCO) for contributed code, we can ensure that the Zephyr community can develop products with the Zephyr Project without concerns over patent or copyright issues.

See Contributing non-Apache 2.0 licensed components for more information about this contributing and review process for imported components.

Developer Certification of Origin (DCO)

To make a good faith effort to ensure licensing criteria are met, the Zephyr project requires the Developer Certificate of Origin (DCO) process to be followed.

The DCO is an attestation attached to every contribution made by every developer. In the commit message of the contribution, (described more fully later in this document), the developer simply adds a Signed-off-by statement and thereby agrees to the DCO.

When a developer submits a patch, it is a commitment that the contributor has the right to submit the patch per the license. The DCO agreement is shown below and at http://developercertificate.org/.

Developer's Certificate of Origin 1.1

By making a contribution to this project, I certify that:

(a) The contribution was created in whole or in part by me and I
    have the right to submit it under the open source license
    indicated in the file; or

(b) The contribution is based upon previous work that, to the
    best of my knowledge, is covered under an appropriate open
    source license and I have the right under that license to
    submit that work with modifications, whether created in whole
    or in part by me, under the same open source license (unless
    I am permitted to submit under a different license), as
    Indicated in the file; or

(c) The contribution was provided directly to me by some other
    person who certified (a), (b) or (c) and I have not modified
    it.

(d) I understand and agree that this project and the contribution
    are public and that a record of the contribution (including
    all personal information I submit with it, including my
    sign-off) is maintained indefinitely and may be redistributed
    consistent with this project or the open source license(s)
    involved.

DCO Sign-Off Methods

The DCO requires a sign-off message in the following format appear on each commit in the pull request:

Signed-off-by: Zephyrus Zephyr <zephyrus@zephyrproject.org>

The DCO text can either be manually added to your commit body, or you can add either -s or --signoff to your usual Git commit commands. If you forget to add the sign-off you can also amend a previous commit with the sign-off by running git commit --amend -s. If you’ve pushed your changes to GitHub already you’ll need to force push your branch after this with git push -f.

Prerequisites

As a contributor, you’ll want to be familiar with the Zephyr project, how to configure, install, and use it as explained in the Zephyr Project website and how to set up your development environment as introduced in the Zephyr Getting Started Guide.

You should be familiar with common developer tools such as Git and CMake, and platforms such as GitHub.

If you haven’t already done so, you’ll need to create a (free) GitHub account on https://github.com and have Git tools available on your development system.

Note

The Zephyr development workflow supports all 3 major operating systems (Linux, macOS, and Windows) but some of the tools used in the sections below are only available on Linux and macOS. On Windows, instead of running these tools yourself, you will need to rely on the Continuous Integration (CI) service shippable, which runs automatically on GitHub when you submit your Pull Request (PR). You can see any failure results in the Shippable details link near the end of the PR conversation list. See Continuous Integration for more information

Repository layout

To clone the main Zephyr Project repository use:

git clone https://github.com/zephyrproject-rtos/zephyr

The Zephyr project directory structure is described in Source Tree Structure documentation. In addition to the Zephyr kernel itself, you’ll also find the sources for technical documentation, sample code, supported board configurations, and a collection of subsystem tests. All of these are available for developers to contribute to and enhance.

Pull Requests and Issues

Before starting on a patch, first check in our issues Zephyr Project Issues system to see what’s been reported on the issue you’d like to address. Have a conversation on the Zephyr devel mailing list (or the #zephyrproject IRC channel on freenode.net) to see what others think of your issue (and proposed solution). You may find others that have encountered the issue you’re finding, or that have similar ideas for changes or additions. Send a message to the Zephyr devel mailing list to introduce and discuss your idea with the development community.

Please note that it’s common practice on IRC to be away from the channel, but still have a client logged in to receive traffic. If you ask a question to a particular person and they don’t answer, try to stay signed in to the channel if you can, so they have time to respond to you. This is especially important given the many different timezones Zephyr developers live in. If you don’t get a timely response on IRC, try sending a message to the mailing list instead.

It’s always a good practice to search for existing or related issues before submitting your own. When you submit an issue (bug or feature request), the triage team will review and comment on the submission, typically within a few business days.

You can find all open pull requests on GitHub and open Zephyr Project Issues in Github issues.

Continuous Integration (CI)

The Zephyr Project operates a Continuous Integration (CI) system that runs on every Pull Request (PR) in order to verify several aspects of the PR:

  • Git commit formatting
  • Coding Style
  • Sanity Check builds for multiple architectures and boards
  • Documentation build to verify any doc changes

CI is run on the shippable cloud service and it uses the same tools described in the Contribution Tools section. The CI results must be green indicating “All checks have passed” before the Pull Request can be merged. CI is run when the PR is created, and again every time the PR is modified with a commit.

Note

You can also force the CI system to recheck a PR by adding a comment to the PR saying simply recheck in the message (helpful if the CI system fails unexpectedly).

The current status of the CI run can always be found at the bottom of the GitHub PR page, below the review status. Depending on the success or failure of the run you will see:

  • “All checks have passed”
  • “All checks have failed”

In case of failure you can click on the “Details” link presented below the failure message in order to navigate to shippable and inspect the results. Once you click on the link you will be taken to the shippable summary results page where a table with all the different builds will be shown. To see what build or test failed click on the row that contains the failed (i.e. non-green) build and then click on the “Tests” tab to see the console output messages indicating the failure.

Contribution Tools and Git Setup

Signed-off-by

The name in the commit message Signed-off-by: line and your email must match the change authorship information. Make sure your .gitconfig is set up correctly:

git config --global user.name "David Developer"
git config --global user.email "david.developer@company.com"

gitlint

When you submit a pull request to the project, a series of checks are performed to verify your commit messages meet the requirements. The same step done during the CI process can be performed locally using the the gitlint command.

Run gitlint locally in your tree and branch where your patches have been committed:

gitlint

Note, gitlint only checks HEAD (the most recent commit), so you should run it after each commit, or use the --commits option to specify a commit range covering all the development patches to be submitted.

sanitycheck

Note

sanitycheck does not currently run on Windows.

To verify that your changes did not break any tests or samples, please run the sanitycheck script locally before submitting your pull request to GitHub. To run the same tests the CI system runs, follow these steps from within your local Zephyr source working directory:

source zephyr-env.sh
./scripts/sanitycheck

The above will execute the basic sanitycheck script, which will run various kernel tests using the QEMU emulator. It will also do some build tests on various samples with advanced features that can’t run in QEMU.

We highly recommend you run these tests locally to avoid any CI failures.

uncrustify

The uncrustify tool can be helpful to quickly reformat your source code to our Coding Style standards together with a configuration file we’ve provided:

# On Linux/macOS
uncrustify --replace --no-backup -l C -c $ZEPHYR_BASE/.uncrustify.cfg my_source_file.c
# On Windows
uncrustify --replace --no-backup -l C -c %ZEPHYR_BASE%\.uncrustify.cfg my_source_file.c

On Linux systems, you can install uncrustify with

sudo apt install uncrustify

For Windows installation instructions see the sourceforge listing for uncrustify.

Coding Style

Use these coding guidelines to ensure that your development complies with the project’s style and naming conventions.

In general, follow the Linux kernel coding style, with the following exceptions:

  • Add braces to every if and else body, even for single-line code blocks. Use the --ignore BRACES flag to make checkpatch stop complaining.
  • Use spaces instead of tabs to align comments after declarations, as needed.
  • Use C89-style single line comments, /*  */. The C99-style single line comment, //, is not allowed.
  • Use /**  */ for doxygen comments that need to appear in the documentation.

The Linux kernel GPL-licensed tool checkpatch is used to check coding style conformity.

Note

checkpatch does not currently run on Windows.

Checkpatch is available in the scripts directory. To invoke it when committing code, make the file $ZEPHYR_BASE/.git/hooks/pre-commit executable and edit it to contain:

#!/bin/sh
set -e exec
exec git diff --cached | ${ZEPHYR_BASE}/scripts/checkpatch.pl -

Contribution Workflow

One general practice we encourage, is to make small, controlled changes. This practice simplifies review, makes merging and rebasing easier, and keeps the change history clear and clean.

When contributing to the Zephyr Project, it is also important you provide as much information as you can about your change, update appropriate documentation, and test your changes thoroughly before submitting.

The general GitHub workflow used by Zephyr developers uses a combination of command line Git commands and browser interaction with GitHub. As it is with Git, there are multiple ways of getting a task done. We’ll describe a typical workflow here:

  1. Create a Fork of Zephyr to your personal account on GitHub. (Click on the fork button in the top right corner of the Zephyr project repo page in GitHub.)

  2. On your development computer, clone the fork you just made:

    git clone https://github.com/<your github id>/zephyr
    

    This would be a good time to let Git know about the upstream repo too:

    git remote add upstream https://github.com/zephyrproject-rtos/zephyr.git
    

    and verify the remote repos:

    git remote -v
    
  3. Create a topic branch (off of master) for your work (if you’re addressing an issue, we suggest including the issue number in the branch name):

    git checkout master
    git checkout -b fix_comment_typo
    

    Some Zephyr subsystems do development work on a separate branch from master so you may need to indicate this in your checkout:

    git checkout -b fix_out_of_date_patch origin/net
    
  4. Make changes, test locally, change, test, test again, … (Check out the prior chapter on sanitycheck as well).

  5. When things look good, start the pull request process by adding your changed files:

    git add [file(s) that changed, add -p if you want to be more specific]
    

    You can see files that are not yet staged using:

    git status
    
  6. Verify changes to be committed look as you expected:

    git diff --cached
    
  7. Commit your changes to your local repo:

    git commit -s
    

    The -s option automatically adds your Signed-off-by: to your commit message. Your commit will be rejected without this line that indicates your agreement with the DCO. See the Commit Guidelines section for specific guidelines for writing your commit messages.

  8. Push your topic branch with your changes to your fork in your personal GitHub account:

    git push origin fix_comment_typo
    
  9. In your web browser, go to your forked repo and click on the Compare & pull request button for the branch you just worked on and you want to open a pull request with.

  10. Review the pull request changes, and verify that you are opening a pull request for the appropriate branch. The title and message from your commit message should appear as well.

  11. If you’re working on a subsystem branch that’s not master, you may need to change the intended branch for the pull request here, for example, by changing the base branch from master to net.

  12. GitHub will assign one or more suggested reviewers (based on the CODEOWNERS file in the repo). If you are a project member, you can select additional reviewers now too.

  13. Click on the submit button and your pull request is sent and awaits review. Email will be sent as review comments are made, or you can check on your pull request at https://github.com/zephyrproject-rtos/zephyr/pulls.

  14. While you’re waiting for your pull request to be accepted and merged, you can create another branch to work on another issue. (Be sure to make your new branch off of master and not the previous branch.):

    git checkout master
    git checkout -b fix_another_issue
    

    and use the same process described above to work on this new topic branch.

  15. If reviewers do request changes to your patch, you can interactively rebase commit(s) to fix review issues. In your development repo:

    git fetch --all
    git rebase --ignore-whitespace upstream/master
    

    The --ignore-whitespace option stops git apply (called by rebase) from changing any whitespace. Continuing:

    git rebase -i <offending-commit-id>^
    

    In the interactive rebase editor, replace pick with edit to select a specific commit (if there’s more than one in your pull request), or remove the line to delete a commit entirely. Then edit files to fix the issues in the review.

    As before, inspect and test your changes. When ready, continue the patch submission:

    git add [file(s)]
    git rebase --continue
    

    Update commit comment if needed, and continue:

    git push --force origin fix_comment_typo
    

    By force pushing your update, your original pull request will be updated with your changes so you won’t need to resubmit the pull request.

  16. If the CI run fails, you will need to make changes to your code in order to fix the issues and amend your commits by rebasing as described above. Additional information about the CI system can be found in Continuous Integration.

Commit Guidelines

Changes are submitted as Git commits. Each commit message must contain:

  • A short and descriptive subject line that is less than 72 characters, followed by a blank line. The subject line must include a prefix that identifies the subsystem being changed, followed by a colon, and a short title, for example: doc: update wiki references to new site. (If you’re updating an existing file, you can use git log <filename> to see what developers used as the prefix for previous patches of this file.)

  • A change description with your logic or reasoning for the changes, followed by a blank line.

  • A Signed-off-by line, Signed-off-by: <name> <email> typically added automatically by using git commit -s

  • If the change addresses an issue, include a line of the form:

    Fixes #<issue number>.
    

All changes and topics sent to GitHub must be well-formed, as described above.

Commit Message Body

When editing the commit message, please briefly explain what your change does and why it’s needed. A change summary of "Fixes stuff" will be rejected.

Warning

An empty change summary body is not permitted. Even for trivial changes, please include a summary body in the commmit message.

The description body of the commit message must include:

  • what the change does,
  • why you chose that approach,
  • what assumptions were made, and
  • how you know it works – for example, which tests you ran.

For examples of accepted commit messages, you can refer to the Zephyr GitHub changelog.

Other Commit Expectations

  • Commits must build cleanly when applied on top of each other, thus avoiding breaking bisectability.
  • Commits must pass all CI checks (see Continuous Integration for more information)
  • Each commit must address a single identifiable issue and must be logically self-contained. Unrelated changes should be submitted as separate commits.
  • You may submit pull request RFCs (requests for comments) to send work proposals, progress snapshots of your work, or to get early feedback on features or changes that will affect multiple areas in the code base.
  • When major new functionality is added, tests for the new functionality MUST be added to the automated test suite. All new APIs MUST be documented and tested and tests MUST cover at least 80% of the added functionality using the code coverage tool and reporting provided by the project.

Submitting Proposals

You can request a new feature or submit a proposal by submitting an issue to our GitHub Repository. If you would like to implement a new feature, please submit an issue with a proposal (RFC) for your work first, to be sure that we can use it. Please consider what kind of change it is:

  • For a Major Feature, first open an issue and outline your proposal so that it can be discussed. This will also allow us to better coordinate our efforts, prevent duplication of work, and help you to craft the change so that it is successfully accepted into the project. Providing the following information will increase the chances of your issue being dealt with quickly:
    • Overview of the Proposal
    • Motivation for or Use Case
    • Design Details
    • Alternatives
    • Test Strategy
  • Small Features can be crafted and directly submitted as a Pull Request.

Identifying Contribution Origin

When adding a new file to the tree, it is important to detail the source of origin on the file, provide attributions, and detail the intended usage. In cases where the file is an original to Zephyr, the commit message should include the following (“Original” is the assumption if no Origin tag is present):

Origin: Original

In cases where the file is imported from an external project, the commit message shall contain details regarding the original project, the location of the project, the SHA-id of the origin commit for the file, the intended purpose, and if the file will be maintained by the Zephyr project, (whether or not the Zephyr project will contain a localized branch or if it is a downstream copy).

For example, a copy of a locally maintained import:

Origin: Contiki OS
License: BSD 3-Clause
URL: http://www.contiki-os.org/
commit: 853207acfdc6549b10eb3e44504b1a75ae1ad63a
Purpose: Introduction of networking stack.
Maintained-by: Zephyr

For example, a copy of an externally maintained import:

Origin: Tiny Crypt
License: BSD 3-Clause
URL: https://github.com/01org/tinycrypt
commit: 08ded7f21529c39e5133688ffb93a9d0c94e5c6e
Purpose: Introduction of TinyCrypt
Maintained-by: External

Contributing non-Apache 2.0 licensed components

Importing code into the Zephyr OS from other projects that use a license other than the Apache 2.0 license needs to be fully understood in context and approved by the Zephyr governing board.

By carefully reviewing potential contributions and also enforcing a Developer Certification of Origin (DCO) for contributed code, we ensure that the Zephyr community can develop products with the Zephyr Project without concerns over patent or copyright issues.

Submission and review process

All contributions to the Zephyr project are submitted through GitHub pull requests (PR) following the Zephyr Project’s Contribution Workflow.

Before you begin working on including a new component to the Zephyr Project (Apache-2.0 licensed or not), you should start up a conversation on the developer mailing list to see what the Zephyr community thinks about the idea. Maybe there’s someone else working on something similar you can collaborate with, or a different approach may make the new component unnecessary.

If the conclusion is that including a new component is the best solution, and this new component uses a license other than Apache-2.0, these additional steps must be followed:

  1. Complete a README for your code component and add it to your source code pull request (PR). A recommended README template can be found in doc/contribute/code_component_README (and included below for reference)
  2. The Zephyr Technical Steering Committee (TSC) will evaluate the code component README as part of the PR commit and vote on accepting it using the GitHub PR review tools.
    • If rejected by the TSC, a TSC member will communicate this to the contributor and the PR will be closed.
    • If approved by the TSC, the TSC chair will forward the README to the Zephyr governing board for further review.
  3. The Zephyr governing board has two weeks to review and ask questions:
    • If there are no objections, the matter is closed. Approval can be accelerated by unanimous approval of the board before the two weeks are up.
    • If a governing board member raises an objection that cannot be resolved via email, the board will meet to discuss whether to override the TSC approval or identify other approaches that can resolve the objections.
  4. On approval of the Zephyr TSC and governing board, final review of the PR may be made to ensure its proper placement in the Zephyr Project Source Tree Structure, (in the ext folder), and inclusion in the Licensing of Zephyr Project components document.

Note

External components not under the Apache-2.0 license cannot be included in a Zephyr OS release without approval of both the Zephyr TSC and the Zephyr governing board.

Code component README template

[Code Component Name]
#####################

Origin:
   [Name of project hosting the original open source code]
   [Provide a link to the source]

Status:
   [Current version of this component, supported by Zephyr]

Purpose:
   [Brief description of what this software does]

Description:
   [Long description that will help reviewers discuss suitability of the
   package to solve the problem at hand (there may be a better package
   available.)

   What is its primary functionality (e.g., SQLLite is a lightweight
   database)?

   What problem are you trying to solve? (e.g., a state store is
   required to maintain ...)

   Why is this the right package to solve it (e.g., SQLite is small,
   easy to use, and has a very liberal license.)]

Dependencies:
   [What other components does this package depend on? Does the software
   include any dynamic or static linking, or automatic downloading of any
   code?

   Will the Zephyr project have a direct dependency on the component, or
   will it be included via an abstraction layer with this component as a
   replacable implementation?]

URL:
   [location to the project's home, e.g., a github repo]

commit:
   [08ded7f21529c39e5133688ffb9a9d0c94e5c6e]

Maintained-by:
   [External]

License:
   [use SPDX identifier (https://spdx.org/licenses/), such as BSD-3-Clause]

License Link:
   [link to the project's LICENSE file, e.g., https://github.com/xyz/LICENSE]