Using Gerrit

Gerrit is a source code review system developed by Google for use with Android (though it can be applied to any type of project). You must use Gerrit to submit code changes, in case you find an error in the source code, you want to contribute with good new features or even if you believe you have a better way of implementing a certain feature.

Check out LineageOS’s review system - Gerrit.

There you can see what has been recently merged into the codebase. More interestingly, you can see what people have been submitting for review. If there’s something you want to try, you can actually test it by merging it into your code and building. It’s a simple matter.

Prepare your build environment

Go to the root of the source code:

cd ~/android/lineage

Setup build environment:

source build/envsetup.sh

The rest of this guide will rely on this being done. You can check the proper execution of the commands by typing:

croot

Your shell will then navigate to the root of the sources, ~/android/lineage or give an error.

Retrieving and building a patch submission already on Gerrit

Let’s say you’d like to try and catch’em all (just an example of a proposed commit that isn’t merged).

To add this patch to your local build source code:

Using repopick

repopick is a new command as of November, 2014 that makes adding proposed patches almost too easy.

If you type repopick -h you’ll get a list of supported commands, such as the ability to pick multiple patches or ranges of patches in a single command.

Start by noting down the URL of the proposed commit. In the above example, it’s https://review.lineageos.org/#/c/65062/. That number, 65062 will come in handy in a second.

The patch should be applied automatically after typing:

repopick 65062

Go ahead and build. When you’re done, you’ll hopefully have the feature you wanted. If it worked alright, go sign up for Gerrit and give a +1 vote to the proposed contribution.

Manually applying the commit

Alternately, you can do the commit “manually” (that is, the OLD way of doing it).

Look for the download dropdown menu on the change you want to apply. There will be some methods you can choose from, just highlight and copy (or simply click the little icon on the right). Referring to the same example, to use the cherry-pick method, copy git fetch https://review.lineageos.org/LineageOS/android_frameworks_base refs/changes/62/65062/5 && git cherry-pick FETCH_HEAD to clipboard. The example patch affects android_frameworks_base (as you can see at the top of the change description on Gerrit), so type:

cd frameworks/base

Now paste the command you copied from Gerrit. You’ve just added the proposed change to your copy of the source code. Go ahead and build. When you’re done, you’ll hopefully have the feature you wanted. If it worked alright, go sign up for Gerrit and give a +1 vote to the proposed contribution.

Submitting to Gerrit

If you haven’t yet successfully downloaded the source and generated a build of LineageOS, make sure you are familiar with those steps. Information on doing a build is available elsewhere on this wiki.

Setup an account on Gerrit and configure your Gerrit username in the Gerrit portal under Settings -> HTTP Password. Then, make sure your local git username matches with your Gerrit username::

git config --global review.review.lineageos.org.username "gerrit username"

If you already have SSH keys set up (e.g. for GitHub), skip the following steps.

Generate SSH keys,[1] and copy/paste to your Gerrit account under Settings -> SSH Public Keys:

ssh-keygen -t rsa -C "your@email.com"

Make sure your keys are added to your ssh agent:

eval `ssh-agent -s`
ssh-add ~/.ssh/id_rsa
ssh-add

Uploading your changes

First, you need to start a topic branch. This ‘branch’ holds the changes you make to the files on your computer that you will ultimately send to the LineageOS’s Gerrit instance for review. Create your topic branch:

repo start <branch name> <project path>

Change to the project (directory) that contains the file(s) you want to edit:

cd path/to/project

Do all the changes you need.

After you make your changes, you can commit them just as you normally would:

git add <file you edited>
git commit

Now you can upload your changes to Gerrit:

repo upload .

That’s it! Your change will be reviewed and may be accepted or rejected. See #Example_cases below for an example.

Submitting Patch Sets

It can happen that your submitted patch has issues or errors, which are noted in the code review, so you will want to resolve them. Sometimes it’s just tabs instead of spaces or typos in strings and variable names. To avoid some formal mistakes, make sure you’re familiar with the Android code style. For Eclipse users, just follow the instructions in development/ide/eclipse/README.importing-to-eclipse.txt.

Before you edit those files, make sure you are on the correct branch:

git branch

If you are not or in no branch at all, switch to the correct branch:

git checkout [branchname]

Now you can edit the files you want. After that, do the usual git status and notice that git diff will only show you the changes you just made. Make sure you add the files that you’ve modified by using git add. Once you’re satisfied, prepare the upload, by amending your commit:

git commit --amend

This will open an editor with your initial commit message. You can change the commit message if you want to, but make sure the last two lines stay as are as it contains the initial change ID and a blank line. With this id, Gerrit will detect your upload as a patch set and not as a new patch.

You can do git log and git status again. Notice how git handles your initial commit and the amended commit as one single patch. As for git show, it shows you all the changes made on that commit.

Finally, you can submit your patch set to your initial patch by typing:

repo upload .

Example cases

Edit InputDevice.java

Let’s say you want to make a change in InputDevice.java that resides in the frameworks/base project, and upload that to Gerrit for review. Start a local branch of that repo (directory) and call it mychanges:

cd frameworks/base
repo start mychanges .

Make the edits to that file. You can check those changes:

git add InputDevice.java -n

If the results are acceptable, stage the modified file:

git add InputDevice.java

Then commit it:

git commit -m 'Added feature xyz'

Issue the upload:

repo upload .

You should be asked a few questions and your commit should then be uploaded to Gerrit for review.

Add AWEXT Support

Start the new branch:

cd external/wpa_supplicant
repo start mychanges-wpa_supplicant .

Make changes, edit a few files, add new drivers.. etc.

git add *
git commit -am 'Added AWEXT drivers'
repo upload .

Common commands

See Git Immersion for more information.

repo

  • repo abandon <branch name> to abandon any changes (commits) that have not been uploaded.

  • repo start <branch> <project> to start repo listening for changes through git.

  • repo upload <project name> to upload committed changes to the remote review server.

git

  • git add <file name> to stage a file that has been changed or added.

  • git commit -m "comment" to commit a change.

  • git reset HEAD <file name> to unstage a file.

  • git revert HEAD to undo the last commit.

  • git status to see the status of a project.

Troubleshooting

[1] If you get a “Permission denied (publickey)” error and you’re sure that everything is right, try using a DSA key instead of RSA. ssh-keygen -t dsa -C "<email>@<server>.<domain>"

Getting your submission reviewed/merged

All submitted patches go through a code review process prior to merger. In addition to getting reviewed by your peers, selected project members have the capability to merge your code into LineageOS (to make sure they get informed, add one or more responsible reviewers to your change). To see a breakdown of who is responsible for the various areas, please see the list of LineageOS contributors.

Resources

Git Immersion

Using git and repo

Gerrit Documentation