Workflow: Questions and Answers

You are encouraged to add your own questions (and answers) here!

Q: Is there a standard Git workflow for Fuchsia?

A: No. Instead, the Git tool offers infinite control and variety for defining your own workflow. Carve out the workflow you need.


Update all projects simultaneously, and rebase your work branch on JIRI_HEAD:

$ jiri update -gc -rebase-untracked
$ cd garnet  # go into a petal
$ git checkout <my_branch>
$ git rebase JIRI_HEAD

The git rebase to JIRI_HEAD should be done in each repo where you have ongoing work. It‘s not needed for repos you haven’t touched.

Uploading a new patch set (snapshot) of a change

You'll need to upload a patch set to Gerrit to have it reviewed by others. We do this with jiri upload.

Gerrit uses an auto-generated metadata marker in the CL description to figure out which Gerrit review thread to upload a patch to, such as: Change-Id: I681125d950205fa7654e4a8ac0b3fee7985f5a4f

This is different from a git commit's SHA hash, and can be considered stable during review, as you make edits to your changes and commits. Use the same Change-Id for a given review (in case you are squashing multiple commits).

If you've made changes and want to upload a new patch set, then (assuming that this is the latest change in your branch; use git log to find out) you can do something like:

$ git commit -a --amend
# -a for all uncommitted files, --amend to amend latest commit
$ jiri upload

Resolving merge conflicts

Attempt a rebase:

$ git fetch origin && git rebase origin/master
# Resolve conflicts as needed...
$ jiri upload

But read below about how a git rebase can negatively interact with jiri update.


You can save all uncommitted changes aside, and re-apply them at a later time. This is often useful when you're starting out with Git.

$ git stash # uncommitted changes will go away
# do stuff
$ git stash pop # uncommitted changes will come back

Q: I use fx and jiri a lot. How are they related?

A: jiri is source management for multiple repositories. fx is a convenience wrapper for configuring and running the build system (Make for Zircon, GN and Ninja for everything else), as well as facilities to help with day-to-day engineering (fx boot, fx log, etc).

Q: Will a git rebase to origin/master mess up my jiri-updated (i.e. synchronized) view of the repository?

A: No, if jiri is managing up to the same petal as your repository.

When working at petal X (accomplished with fx set-petal X), jiri update will rebase the local branches in repo X onto HEAD of origin/master. But other petals' repos will be synced to specific revisions that may be behind HEAD of their origin/master.

Our continuous integration system (specifically rollers) makes a new revision of a petal available to other petals only after testing that the new revision doesn't break other petals. jiri update will always leave other petals synced to these successfully-tested revisions. But a git rebase to origin/master for a petal may advance that repo beyond the tested revision, which has the potential to introduce breaking changes. The result may be that you can build for a certain petal, but not for other petals (e.g., correctly build garnet, but not be able to build topaz).

If you have a particular commit that you want jiri to honor, download its jiri.update file and feed it to jiri update.

Q: What if I need an atomic commit across git repositories?

A: Can't, sorry. Try to arrange your CLs to not break each petal during a transition (i.e., do a soft transition). But sometimes you will necessarily break things; aim to minimize the duration of breakage (i.e., a hard transition).

Example scenario: I have an interface defined in stem, and it is implemented in another petal. If I change the interface, am I doomed to break other petals?

Yes. But you can “babysit” the rollers so that the breakage range is minimized. The gotcha with babysitting is that others may also be babysitting a breakage, and you may end up babysitting for longer than you had intended.

Alternatively, you could do something as follows:

  1. Introduce a new interface in lower that is a copy of the original interface.
  2. Wait for lower-roller to roll into upper, or roll yourself by updating the file upper/manifest.
  3. Change upper to use the new clone interface that maintains the old contract.
  4. Change lower such that the original interface’s contract is modified to the new, desired form.
  5. Wait for lower-roller, or roll yourself.
  6. Change upper to use the original interface name, now with its new contract. Make any changes required.
  7. Delete the clone interface in lower.

Q: How do I do parallel builds from a single set of sources?

A: Currently, this is not possible. The vanilla GN + Ninja workflow should allow this, but fx maintains additional global state.

Another slight limitation is that GN files for Zircon are currently generated at build-time, and running multiple parallel builds which both try to generate GN files may confuse Ninja. It's unclear whether this is a real issue or not.

Q: What if I want to build at a previous snapshot across the repos?

A: You'll need to jiri update against a jiri snapshot file, an XML file that captures the state of each repo tracked by jiri.

Q: I'm building on Mac, how to do I stop getting spammed with ‘incoming network connection’ notifications?

A: You'll want to run fx setup-macos, which registers all the relevant Fuchsia tools with the MacOS Application Firewall.

Q: When/how do I make a soft vs hard transition when changing APIs?

See this section about hard and soft transitions.

Q: How do I update a FIDL protocol?

A: The preferred method for updating a FIDL protocol is to use a soft transition. In order for a soft transition to work, you need to create an intermediate state that supports both the old and new versions of the protocol.

Use the following steps to execute a soft transition:

  1. Modify the FIDL definition in the Stem repository to support both the old and new protocol elements. Before landing the change, trigger the global integration tryjobs to validate that step 2 will succeed.

  2. Publish the Stem repository, either by waiting for the daily automatic publication or by manually publishing the repository.

  3. Update all the clients to use the new protocol elements.

  4. Publish all the clients.

  5. Remove the old protocol elements from the FIDL definition in the Stem repository.

  6. Publish the Stem repository, typically by waiting for the daily automatic publication.

Q: How do I coordinate changes across multiple Petals?

A: Coordinating an atomic change across multiple Petals (or between the Stem repository and one or more Petals) requires performing a hard transition.

Use the following steps to execute a hard transition:

  1. Prepare changes to all affected repositories. If all of these repositories are part of the Fuchsia source tree:

    1. Upload CLs containing the changes to
    2. Upload another CL that modifies the global integration repository to reference the git revisions from your CLs. Perform a “dry run” of the commit queue for this CL.
  2. Notify the team stating your intention to execute a hard transition.

  3. Land all the changes in the affected repositories. This step will break local integration in these repositories but will not break global integration because the changes have not been published yet.

  4. Land a change in the global integration repository that references the new versions of the affected repositories. This change will publish the new version of all the affected repositories and should not break global integration. This change should unbreak local integration in the affected repositories.

Q: How do I bisect history to track down when something changed?

A: To bisect history, perform the following steps:

  1. Bisect the history in the configuration repository, which contains the revision history of global integration, before and after the observable change. The result of this bisect will be a single change to configuration repository, presumably that includes the publication of one or more repositories or prebuilt packages.

  2. If the change to the configuration repository is a publication of a single repository, bisect the history of that repository before and after the publication of global integration. The result of this bisect should be the revision at which the behavior changed.

  3. If the change to the configuration repository is a publication of prebuilt packages, switch to the source tree from which the prebuilt packages were created. Consult the documentation for that repository regarding how to bisect changes in that repository.

  4. If the change to the configuration repository is a publication of multiple repositories, bisecting history becomes complicated because the two repositories have likely been changed in concert and you will need to traverse their history in concert. Consider studying the history of the repositories to understand why they were published together.