Making Changes Using Git

The Apache NuttX project uses the Git version control system to track changes, and the source code is hosted on GitHub.

If you want to make changes to NuttX, for your own personal use, or to submit them back to project to improve NuttX, that’s easy. For the purposes of this guide, you’ll need a GitHub account, since the Apache NuttX team uses GitHub. (You could also use git locally, or save your changes to other sites like GitLab or BitBucket, but that’s beyond the scope of this guide).

Here’s how to do it:

  1. Set your git user name and email

    $ cd nuttx/
$ git config --global user.name "Your Name"
$ git config --global user.email "yourname@somedomaincom"

  2. Sign in to GitHub

    If you don’t have a GitHub account, it’s free to sign up.

  3. Fork the Projects

    Visit both these links and hit the Fork button in the upper right of the page:

  4. Clone the Repositories

    On the GitHub web page for your forked nuttx project, copy the clone url – get it by hitting the green Clone or Download button in the upper right. Then do this:

    $ git clone <your forked nuttx project clone url> nuttx
$ cd nuttx
$ git remote add upstream https://github.com/apache/nuttx.git

    Do the same for your forked nuttx-apps project:

    $ cd ..
$ git clone <your forked nuttx-apps project clone url> apps
$ cd apps
$ git remote add upstream https://github.com/apache/nuttx-apps.git

  5. Create a Local Git Branch

    Now you can create local git branches and push them to GitHub:

    $ git checkout -b test/my-new-branch
$ git push

Git Workflow With an Upstream Repository

The main NuttX git repository is called an “upstream” repository - this is because it’s the main source of truth, and its changes flow downstream to people who’ve forked that repository, like us.

Working with an upstream repo is a bit more complex, but it’s worth it since you can submit fixes and features to the main NuttX repos. One of the things you need to do regularly is keep your local repo in sync with the upstream. I work with a local branch, make changes, pull new software from the upstream and merge it in, maybe doing that several times. Then when everything works, I get my branch ready to do a Pull Request. Here’s how:

  1. Fetch upstream changes and merge into my local master:

    $ git checkout master
$ git fetch upstream
$ git merge upstream/master
$ git push

  2. Merge my local master with my local branch:

    $ git checkout my-local-branch
$ git merge master
$ git push

  3. Make changes and push them to my fork

    $ vim my-file.c
$ git add my-file.c
$ git commit my-file.c
$ git push

  4. Repeat 1-3 as necessary

  5. Run the tools/checkpatch.sh script on your files

    When your code runs, then you’re almost ready to submit it. But first you need to check the code to ensure that it conforms to the NuttX C Coding Standard. The tools/checkpatch.sh script will do that. Here’s the usage info:

    $ ./tools/checkpatch.sh -h
USAGE: ./tools/checkpatch.sh [options] [list|-]

Options:
-h
-c spell check with codespell(install with: pip install codespell
-r range check only (used with -p and -g)
-p <patch list> (default)
-g <commit list>
-f <file list>
-  read standard input mainly used by git pre-commit hook as below:
   git diff --cached | ./tools/checkpatch.sh -

    Run it against your files and correct all the errors in the code you added, so that tools/checkpatch.sh reports no errors. Then commit the result. For example:

    $ ./tools/checkpatch.sh -f my-file.c
arch/arm/src/sama5/hardware/my-file.c:876:82: warning: Long line found
$ # fix errors
$ vim my-file.c
$ # run again
$ ./tools/checkpatch.sh -f my-file.c

    If you have made a lot of changes, you can also use this bash commandline to see the errors for all the changed C files in your branch (assumes you are currently on the branch that has the changed files):

    $ git diff --name-only master | egrep "\.c|\.h" | xargs echo | xargs ./tools/checkpatch.sh -f | less

    Note that there are some bugs in the nxstyle program that checkpatch.sh uses, so it may report a few errors that are not actually errors. The committers will help you find these. (Or view the nxstyle Issues.)

  6. Commit the fixed files

    $ git add my-file.c
$ git commit my-file.c
$ git push

Submitting Your Changes to NuttX

Pull requests let you tell others about changes you’ve pushed to a branch in a repository on GitHub. Once a pull request is opened, you can discuss and review the potential changes with collaborators and add follow-up commits before your changes are merged into the base branch.

(from GitHub’s About pull requests page)

Before you do a Pull Request, the NuttX team will usually want all the changes you made in your branch “squashed” into a single commit, so that when they review your changes, there’s a clean view of the history. If there are changes after Pull Request review feedback, they can be separate commits. Here’s the easiest way I found to do that initial squash before submitting the Pull Request:

  1. Check out my branch

    $ git checkout my-branch

  2. Fetch the upstream code

    $ git fetch upstream

  3. Rebase onto the upstream code

    $ git rebase upstream/master

  4. Push to your remote

    This needs to a force push with -f.

    $ git push -u my-branch -f

  5. Create a GitHub Pull Request

    A Pull Request is how you ask your upstream to review and merge your changes.

    Here’s GitHub’s instructions for creating a Pull Request.

    It is important to include an informative commit title and a commit message.

    In the commit title please include the subsystem/area related to your contribution, followed by a descriptive message. Some examples:

    Adding or fixing a platform

    arch/arm/stm32/: Add arch support for stm32 platform

This patch adds initial support for stm32 platform. Please read
the documentation included for more details how to wire the display.

Signed-off-by: Your Name <you@whoareyou.com>

    Adding or fixing a board

    arm/stm32f4discover: Add board initialization for SSD1306 OLED Display

This patch adds support to use the display SSD1306 on I2C1, please read
the documentation included for more details how to wire the display.

Signed-off-by: Your Name <you@whoareyou.com>

    Another example, submitting a commit to fix an issue in the fictional sensor xyz123:

    sensors/xyz123: Fix a pressure conversion resolution issue

I found an issue in the XYZ123 sensor when converting the
pressure. The raw value should be divided by 4.25 instead
of 4.52.

Signed-off-by: Your Name <you@whoareyou.com>

    You can search in the github commit history for more examples.

  6. Get Pull Request feedback and implement changes

    Get suggestions for improvements from reviewers, make changes, and push them to the branch. Once the reviewers are happy, they may suggest squashing and merging again to make a single commit. In this case you would repeat steps 1 through 6.

How to Include the Suggestions on Your Pull Request?

If you submitted your first PR (Pull Request) and received some feedbacks to modify your commit, then probably you already modified it and created a new commit with these modifications and submitted it.

Also probably you saw that this new commit appeared on your Pull Request at NuttX’s github page (at Commits tab).

So, someone will ask you some enigmatic thing: “Please rebase and squash these commits!”

Basically what they are saying is that you need to update your repository and fuse your commits in a single commit.

Let walk through the steps to do it!

Move to upstream branch and pull the new commits from there:

$ git checkout upstream
$ git pull

Return to your working branch and rebase it with upstream:

$ git checkout my-branch
$ git rebase upstream

If you run git log will see that your commits still there:

$ git log
commit xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx (HEAD -> firstpr, upstream/master, upstream)

Author: Me Myself
Date: Today few seconds ago

Fix suggestions from mainline

commit xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Author: Me Myself
Date: Today few minutes ago

Initial support for something fantastic

commit 6aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
Author: Xiang Xiao <xiaoxiang@xiaomi.com>
Date:   Sun Dec 18 00:00:00 2022 +0800

Some existing commit from mainline

See, you have two commits (Fix suggestions… and Initial support…), we can squash both in a single commit!

You can use the git rebase interactive command to squash both commits:

$ git rebase -i HEAD~2

Note: case you had 3 commits, then you should replace HEAD~2 with HEAD~3 and so on.

This command will open the nano editor with this screen:

pick 10ef3900b2 Initial support for something fantastic
pick 9431582586 Fix suggestions from mainline

# Rebase 9b0e1659ea..9431582586 onto 9b0e1659ea (2 commands)
#
# Commands:
# p, pick <commit> = use commit
...

Here you can control the actions that git will execute over your commits.

Because we want to squash the second commit with the first you need to replace the ‘pick’ of the second line with a ‘squash’ (or just a ‘s’) this way:

pick 10ef3900b2 Initial support for something fantastic
squash 9431582586 Fix suggestions from mainline

# Rebase 9b0e1659ea..9431582586 onto 9b0e1659ea (2 commands)
#
# Commands:
# p, pick <commit> = use commit
...

Now just press Ctrl + X to save this modification. In the next screen you can edit your git commit messages. After that press Ctrl + X again to save.

If you run git log again will see that now there is one a single commit:

$ git log
commit xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx (HEAD -> firstpr, upstream/master, upstream)
Author: Me Myself
Date: Right now baby, right now

Initial support for something fantastic

This commit includes the suggestions from mainline

commit 6aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
Author: Xiang Xiao <xiaoxiang@xiaomi.com>
Date:   Sun Dec 18 00:00:00 2022 +0800

Some existing commit from mainline

Just push forced this new commit to your repository:

$ git push -f

Now you can look at your PR at NuttX’s github to confirm that this squashed commit is there.

Git Resources