Contribution Guidelines

As an open-source project, we welcome and encourage the community to submit patches directly to project ACRN. 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 and track bugs and enhancement requests, and submit patches to the project so that your patch will be accepted quickly into the codebase.

Here’s a quick summary:

  • ACRN uses the permissive open source BSD 3-Clause license that allows you to freely use, modify, distribute and sell your own products that include such licensed software.

  • There are some imported or reused components of the ACRN project that use other licensing and are clearly identified.

  • The Developer Certificate of Origin (DCO) process is followed to ensure developers are following licensing criteria for their contributions, and documented with a Signed-off-by line in commits.

  • ACRN development workflow is supported on Linux.

  • Source code for the project is maintained in the GitHub repo:

  • Issue and feature tracking is done using GitHub issues in this repo.

  • A Continuous Integration (CI) system runs on every Pull Request (PR) to verify several aspects of the PR including Git commit formatting, coding style, sanity-check builds, and documentation builds.

  • The ACRN user mailing list is a great place to engage with the community, ask questions, discuss issues, and help each other.

Technical Steering Committee (TSC)

The Technical Steering Committee (TSC) is responsible for technical oversight of the open source ACRN project. The role and rules governing the operations of the TSC and its membership, are described in the project’s technical-charter.

These are the current TSC voting members and chair person:


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

Project ACRN uses a BSD-3-Clause license, as found in the LICENSE in the project’s GitHub repo.

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.

Developer Certification of Origin (DCO)

To make a good faith effort to ensure that licensing criteria are met, project ACRN 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

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

(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)

DCO Sign-Off Methods

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

Signed-off-by: Acrnus Jones <>

You can either manually add the DCO text to your commit body or you can add -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.


The name and email address of the account you use to submit your PR must match the name and email address on the Signed-off-by line in your commit message.


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

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

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

Repository Layout

To clone the ACRN hypervisor repository (including the hypervisor, devicemodel, and doc folders), use:

$ git clone

In addition to the ACRN hypervisor and Device Model itself, you’ll also find the sources for technical documentation available from the ACRN documentation site. All of these are available for developers to contribute to and enhance.

Submitting Issues

Issue tracking for project ACRN bugs or enhancement requests is done using GitHub issues in the ACRN hypervisor issues list. Before submitting a bug or enhancement request, first check to see what’s already been reported, and add to that discussion if you have additional information. (Be sure to check both the “open” and “closed” issues.) You should also read through discussions in the ACRN-users mailing list (and the ACRN-dev mailing list) to see what’s been reported on or discussed. You may find others that have encountered the issue you’re finding, or that have similar ideas for changes or additions.

If you don’t find an existing issue listed in the ACRN hypervisor issues list, then click the “New Issue” button and provide a summary title and a more-detailed description of your bug or enhancement request.

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. Use the ACRN hypervisor issues list to track the status of your submitted issues as well, or to add additional comments.

Contribution Tools and Git Setup


If you’ll be submitting code patches, you may need to install the git-email package for easier patch submission. On Ubuntu, for example, use:

$ sudo apt install git-email

and then configure Git with your SMTP server information as described in the Git send-email documentation.


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

$ git config --global "David Developer"
$ git config --global ""


All commits must be mapped to a GitHub issue for a feature or bug. Add a Tracked-On: #issue-number line to your commit message together with the issue number. For example:

Tracked-On: #1420

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 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 line limit is 120 columns instead of 80 columns. Note that tabs are 8-column wide.

You can use checkpatch from the Linux kernel to check the compliance. ACRN maintains a .checkpatch.conf file that customizes the script to stop warnings on the exceptions above. Invoke checkpatch with the root of the acrn-hypervisor repository as the current working directory to make the configurations effective.

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 project ACRN, it is also important that you provide as much information as you can about your change, update appropriate documentation, and test your changes thoroughly before submitting.

Documentation changes should also be checked for technical accuracy, spelling, grammar, and clarity and that the Documentation Guidelines are being followed. It’s also good practice to do a local documentation build to verify that the changes don’t cause the build to fail. See ACRN Documentation Generation for details.

The general GitHub workflow used by project ACRN 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 for the acrn-hypervisor repo, which includes the source files for the hypervisor, devicemodel, and documentation.


Both code and documentation changes follow the same steps shown here, with one exception: before submitting a GitHub pull request (PR) with your changes, all code changes are first sent to the ACRN developer mailing list for discussion and review. After obtaining the proper Reviewed-by: and Acked-by: approvals, code patches may then be submitted as a GitHub PR. Documentation changes should be submitted separately from code changes, and are reviewed via GitHub comments to the PR.

  1. Create a Fork of acrn-hypervisor to your personal account on GitHub. (Click on the fork button in the top right corner of the project acrn-hypervisor repo page in GitHub.) When you want to submit a pull request with your changes, you’ll first submit them to your personal branch, and then to the project’s main branch for review and merging by the ACRN maintainers.

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

    $ git clone<your github id>/acrn-hypervisor

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

    $ git remote add upstream

    and verify the remote repos:

    $ git remote -v
  3. Create a topic branch (off of the main branch) 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

    Give your branch a short descriptive name.

  4. Make changes, test locally, change, test, test again, …

  5. When things look good, start the pull request process by checking which files have not been staged:

    $ git status

    Then add the changed files:

    $ git add [file(s) that changed]

    (or to have all changed files staged, use):

    $ git add -A
  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 below for specific guidelines for writing your commit messages.

    All commits must be mapped to a GitHub issue for a feature or bug. Add a Tracked-On: #issue-number line to your commit message together with the issue number. For example:

    Tracked-On: #1420

    If only documentation changes are made, you can submit your PR without a review on the ACRN developer mailing list, so you can skip directly to step 9.

  1. As mentioned earlier, all code changes must first be reviewed and approved via the developer mailing list. You start this review process by sending a patch file for each commit, as created by the git format-patch command. For example, if your change is contained in one commit, create a patch file (in /tmp, or some other location) with the command:

    $ git format-patch -o /tmp/ -1

    Then email the generated .patch file(s) to the ACRN developer mailing list, using the git send-email command. (See the Git send-email documentation for details. For example:

    $ git send-email /tmp/000*.patch --to

    You can see examples of change requests and discussions in the ACRN developer mailing list archive.

    After all review issues have been resolved, amend your commit with necessary changes, and also update the commit message with approvals given in the mailing list discussion by adding Reviewed-by: and Acked-by: tags.

    You can then proceed to the next step and submit a Git pull request to the repo.

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

    $ git push origin fix_comment_typo
  3. In your web browser, go to your personal forked repo and click the Compare & pull request button for the branch you just worked on and want to submit to the upstream ACRN repo.

  4. 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.

  5. 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. If no reviewers are selected, the ACRN triage team will assign reviewers as appropriate.

  6. Click the submit button. Your pull request is sent and awaits review. For code changes, this review should be cursory since any issues were handled via the mailing list review. Email will be sent as review comments are made, or you can check on your pull request at

  7. 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 the main branch and not the previous branch):

    $ git checkout master
    $ git checkout -b fix_another_issue

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

  8. If reviewers request changes to your patch, you can interactively rebase one or more commits to fix review issues. In your development repo, make the needed changes on the branch that you initially submitted:

    $ git checkout fix-comment-typo

    Make the requested changes, and then:

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

    This is an important step to make sure that your changes are properly merged with changes from other developers that may have occurred while you were working on your changes.

    The --ignore-whitespace option stops git apply (called by rebase) from changing any whitespace characters (such as spaces, tabs, and newlines). If any merging issues are detected you can address them with:

    $ 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 then continue:

    $ git push --force origin fix_comment_typo

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

    You can follow the same workflow for contributing to the acrn-devicemodel or acrn-documentation repos.

Commit Guidelines

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

  • A short and descriptive subject line that is fewer 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 commit guidelines instructions. (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

  • For traceability, all changes must include reference to a GitHub issue. Include a line of the form:

    Tracked-On: #issue-number

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

Commit Message Body

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


An empty change summary body is not permitted. Even for trivial changes, include a summary body in the commit 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 acrn-hypervisor GitHub changelog.

Other Commit Expectations

  • Commits must build cleanly when applied on top of each other, thus avoiding breaking bisectability.

  • 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 or progress snapshots of your work, or to get early feedback on features or changes that will affect multiple areas in the code base.

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 acrn-hypervisor, 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 must 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 whether the file will be maintained by the acrn-hypervisor project (whether project ACRN will contain a localized branch or whether it is a downstream copy).

For example, a copy of a locally maintained import:

Origin: Contiki OS
License: BSD 3-Clause
commit: 853207acfdc6549b10eb3e44504b1a75ae1ad63a
Purpose: Introduction of networking stack.
Maintained-by: acrn-hypervisor

For example, a copy of an externally maintained import:

Origin: Tiny Crypt
License: BSD 3-Clause
commit: 08ded7f21529c39e5133688ffb93a9d0c94e5c6e
Purpose: Introduction of TinyCrypt
Maintained-by: External