.. _contribute_guidelines:

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 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.

Project ACRN uses a BSD-3-Clause license, as found in the
`LICENSE <https://github.com/projectacrn/acrn-hypervisor/blob/master/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.

.. _DCO:

Developer Certification of Origin (DCO)
***************************************

To make a good faith effort to ensure 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 http://developercertificate.org/.

.. code-block:: none

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

   Signed-off-by: Acrnus Jones <acrnusj@gmail.com>

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``.

.. note::
   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.

Prerequisites
*************

.. _project ACRN website: https://projectacrn.org

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`_.

.. _Getting Started Guide:
   https://projectacrn.github.io/getting_started/

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

Repository layout
*****************

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

    git clone https://github.com/projectacrn/acrn-hypervisor

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.

.. _ACRN documentation site:
   https://projectacrn.github.io/

Submitting Issues
******************

.. _ACRN-dev mailing list:
   https://lists.projectacrn.org/g/acrn-dev

.. _ACRN hypervisor issues:
   https://github.com/projectacrn/acrn-hypervisor/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-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 on the "New Issue" button and provide a summary title
and 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:

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 :file:`.gitconfig`
is set up correctly by using:

.. code-block:: none

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

Tracked-On
==========

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.

.. _Linux kernel coding style:
   https://kernel.org/doc/html/latest/process/coding-style.html

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 Linux kernel to check the compliance. ACRN
maintains a `checkpatch conf`_ which customizes the script to stop warning on
the exceptions above. Invoke *checkpatch* with the root of ``acrn-hypervisor``
repository as the current working directory to make the configurations
effective.

.. _checkpatch conf:
   https://github.com/projectacrn/acrn-hypervisor/blob/master/.checkpatch.conf

.. _Contribution workflow:

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 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 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:

.. _Create a Fork of acrn-hypervisor:
   https://github.com/projectacrn/acrn-hypervisor#fork-destination-box

#. `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
   master branch for review and merging by the ACRN maintainers.

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

     git clone https://github.com/<your github id>/acrn-hypervisor

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

     git remote add upstream https://github.com/projectacrn/acrn-hypervisor.git

   and verify the remote repos::

     git remote -v

#. 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

   Give your branch a short descriptive name.

#. Make changes, test locally, change, test, test again, ...

#. 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

#. Verify changes to be committed look as you expected::

     git diff --cached

#. 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

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

     git push origin fix_comment_typo

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

#. 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.

#. 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.

#. 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/projectacrn/acrn-hypervisor/pulls.

#. 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.

#. If reviewers request changes to your patch, you can interactively rebase
   commit(s) to fix review issues. In your development repo, make the
   needed changes on the branch you made the initial submission::

     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 your changes are properly
   merged with changes from other developers that may have happened while you
   were working on your changes.
   The ``--ignore-whitespace`` option
   stops ``git apply`` (called by rebase) from changing
   any whitespace. 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 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.

   You can follow the same workflow for contributing to 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 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 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, 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 acrn-hypervisor GitHub
`changelog <https://github.com/projectacrn/acrn-hypervisor/commits/master>`__.

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, 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 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 acrn-hypervisor project,
(whether or not project ACRN 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: acrn-hypervisor

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
