Development/Gerrit

From KDE TechBase

Getting Started

Gerrit is a tool for web-based code review -- similar to ReviewBoard, but it has some neat features. For instance, it has built-in CI bot (Code Integration) support and general workflow is much straight-forward. Some KDE projects, like Trojita are experimenting with its functionality now.

The first step is to activate your account at Gerrit. Use your KDE Identity account to log in. Go into Settings -> SSH Keys and upload your public SSH key in there. If you don't have these so far, you would need to get one. For starters, there is a Git QuickStart Guide that will help you to create SSH keys and clone KDE repository you are interested in.

Patches can be uploaded for review by any KDE user with legit Identity account, so you are not obligated to have a KDE Developer account at all. Here is a little hint to get started. We will assume that your repository is already cloned from KDE servers. Take a note that you obviously need to do this once per repo. 

 # At first, let's add a new git remote
 git remote add gerrit ssh://YourKdeIdentityUsername@gerrit.vesnicky.cesnet.cz:29418/RepositoryName
 # Gerrit needs a client-side hook for putting the Change-Id tags into commit messages
 scp -p -P 29418 YourKdeIdentityUsername@gerrit.vesnicky.cesnet.cz:hooks/commit-msg .git/hooks/

Submitting Changes to Gerrit

So you've got some code changes now and you want to submit these into a Change. Good practice is to use "topic branch here" and do everything in it, so you don't affect any remote branches. Simply make commits (one per change) and when you're done, push them to a "magic ref". Instead of doing stuff like git push gerrit master, you do: 

 git push gerrit HEAD:refs/for/master

The above will open a review request(s) on top of master, one for each commit that you made.

The key point is the refs/for/ prefix. This is a magic ref, or a magic branch. It does not really exist on-disk, but whenever you push there, Gerrit notices that you want to update or create a new patch/change/request/... and do the right thing.

Gerrit will tell you what has happened -- either everything went well and then you got a link to a change request on the web, or something broke and then you should get an error message about what was it. There are also advanced possibilities, see further down in this page for them.

Advanced: Using gpush

Gerrit works well out-of-the-box with regular git functionality, but for some advanced usage, you might want to use script by Qt's developers -- gpush. It provides smart interface to some Gerrit features. You can get it along with qtrepotools from official Qt repository. Just make sure that its bin directory is in $PATH. Here are some examples of its usage: 

 # Pushes HEAD:refs/for/branch to 'gerrit' without any reviewers
 git gpush
 # Pushes HEAD:refs/for/$TRB to 'gerrit', adding mariuso as a reviewer
 # and sends thiago a CC mail
 git gpush +mariuso =thiago
 # Pushes HEAD:refs/for/buildsystem to 'gerrit', no reviewers
 git gpush :refs/for/buildsystem

But we still recommend you to read and understand how does the whole thing work in the next section.

Reviewing Changes

Since many users, who mess up with not trivial Gerrit UI, you should see the documentation on how to work with the web UI, or an older basic tutorial if you want to deal with everything UI-related.

Any registered user can give you +1 .. -1 points for Code Review. KDE developers can give you +2 .. -2 points for any review request. Your change becomes submittable when it has at least single +2 grade and there are no -2 "veto" reviews.

Modifying Changes

Just amend/rebase/modify-in-any-other-way your commit and push to refs/for/targetBranchName. Here is a way to do this with amend: 

 # Make some changes over existing commit
 git add -u
 git commit --amend
 git push gerrit HEAD:/refs/for/targetBranchName

As long as the Change-Id line in the commit is preserved, Gerrit will do the right thing and notice that it's an updated version of an existing change.

Receiving Notifications

Go to settings, add a project, and then make sure all checkboxes are ticked. The default operation adds a project to your watchlist, but no events would be delivered to you.

Please note that this is a pretty recent version of Gerrit which differs in a few ways from the version used by e.g. the Qt project. Most of the changes are in the UI, e.g. to apply stuff locally, use the Download menu at the top-right corner of the change view.

Nice Tweaks

Getting Information About Review through Git

Once a change is approved and submitted to git, Gerrit automatically inserts a proper note about that into git. Here's how to enable showing of them. At first, configure git so that it gets fetched automatically (assuming origin is your KDE remote, and that at least one change has been already merged: 

 git config --add remote.origin.fetch refs/notes/review:refs/notes/review
 git fetch origin

To show this information, add a fancy argument to e.g. git log: 

 $ git log --notes=review
 commit 39f98861cec1cba192171b6ad998328b16106c46
 Author: Jan Kundrát <[email protected]>
 Date:   Sat Sep 6 17:30:57 2014 +0200
 
 tests: Improve debugging for extra unexpected child tasks
   
 I can as well just leave this in instead of removing it every time I hit a
 failure in the subsequent QVERIFY.
   
 Change-Id: Ia4a7c72d0193827e013bfe3d47a0bd7a99567058
 
 Notes (review):
   Code-Review+2: Jan Kundrát <[email protected]>
   Submitted-by: Jan Kundrát <[email protected]>
   Submitted-at: Mon, 08 Sep 2014 09:19:44 +0200
   Reviewed-on: https://gerrit.vesnicky.cesnet.cz/r/11
   Project: trojita
   Branch: refs/heads/master

Doing Pushes the Fancy Way

If you dislike the refs/for/ prefix, you can set up gerrit so that you can push "directly to branch", yet git will do the right thing for you: 

 git config remote.gerrit.push refs/heads/*:refs/for/*
 git push gerrit

Anything Else?

As Gerrit is based on git, there is a ton of possible workflows. Maybe we should settle on one and thoroughly document it?

What tricks do you find neat?

Sysadmin Stuff

Adding Projects

The name of the project repository at KDE's git and in gerrit have to match. One can only add regular project repositories, not personal clones or scratch repos.

At first, setup the project in Gerrit: 

 ssh -p 29418 gerrit.vesnicky.cesnet.cz gerrit create-project --parent sysadmin/gerrit-kde-traditional-projects NameOfGitRepo

Now set up KDE's infrastructure so that any pushes propagate to Gerrit: 

 cd kde/repo-management
 # do an equivalent of commit 6bd604f73902d9a14c05a2abb88da5e1838ce2ea
 echo ssh://[email protected]:29418/YourRepoName > repo-configs/remote-update/YourRepoName.git
 git commit -a
 git push

At this point, you can either wait for any push to KDE's git, or push the data yourself. The manual options needs special access, though. Do not push to refs/for/*, do something like git push gerrit master:refs/heads/master and git push gerrit --tags.

How Stuff Works

Everything was deployed to CESNET's cluster within the XIFI project. The VM runs within OpenStack, and everything is deployed by Puppet. Ask jkt for details, full release is pending.

TODO list

  • Documentation: Write a howto for users/developers (this page)
  • Define how to get support
    • through IRC at #kde-sysadmin on freenode (ping jkt)
    • sysadmin's tickets?
      • gerrit admins have to be able to read these
    • Anything which needs hard-core stuff like recreating the whole VM: a sysadmin should file a ticket at CESNET's XIFI support. Any user who does that will be shot.
  • give access to additional admins
    • Frederik Gladhorn -- done
    • Ben Cooksley -- done
    • vblazquez -- done
    • tosky?
    • Who else? Register at Gerrit, send a mail to jkt and I'll make it happen.
  • Implement the CI
    • Jenkins, its job builder, zuul,...
    • Tool idea: run krazy over submitted patches before committing and inform committer about possible changes
  • Get SSH keys from LDAP (bugreport)
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