# How to Contribute to crosvm

## How to report bugs

We use Google issue tracker. Please use
[the public crosvm component](https://issuetracker.google.com/issues?q=status:open%20componentid:1161302).

**For Googlers**: See [go/crosvm#filing-bugs](https://goto.google.com/crosvm#filing-bugs).

## Contributing code

### Gerrit Account

You need to set up a user account with [gerrit](https://chromium-review.googlesource.com/). Once
logged in, you can obtain
[HTTP Credentials](https://chromium-review.googlesource.com/settings/#HTTPCredentials) to set up git
to upload changes.

Once set up, run `./tools/cl` to install the gerrit commit message hook. This will insert a unique
"Change-Id" into all commit messages so gerrit can identify changes. Even warning messages appear,
the message hook will be installed.

### Contributor License Agreement

Contributions to this project must be accompanied by a Contributor License Agreement (CLA). You (or
your employer) retain the copyright to your contribution; this simply gives us permission to use and
redistribute your contributions as part of the project. Head over to
<https://cla.developers.google.com/> to see your current agreements on file or to sign a new one.

You generally only need to submit a CLA once, so if you've already submitted one (even if it was for
a different project), you probably don't need to do it again.

### Commit Messages

As for commit messages, we follow
[ChromeOS's guideline](https://chromium.googlesource.com/chromiumos/docs/+/HEAD/contributing.md#commit-messages)
in general.

Here is an example of a good commit message:

```
devices: vhost: user: vmm: Add Connection type

This abstracts away the cross-platform differences: cfg(unix) uses a
Unix domain stream socket to connect to the vhost-user backend, and
cfg(windows) uses a Tube.

BUG=b:249361790
TEST=tools/presubmit --all

Change-Id: I47651060c2ce3a7e9f850b7ed9af8bd035f82de6
```

- The first line is a subject that starts with a tag that represents which components your commit
  relates to. Tags are usually the name of the crate you modified such as `devices:` or `base:`. If
  you only modified a specific component in a crate, you can specify the path to the component as a
  tag like `devices: vhost: user:`. If your commit modified multiple crates, specify the crate where
  your main change exists. The subject should be no more than 50 characters, including any tags.
- The body should consist of a motivation followed by an impact/action. The body text should be
  wrapped to 72 characters.
- `BUG` lines are used to specify an associated issue number. If the issue is filed at
  [Google's issue tracker](https://issuetracker.google.com/), write `BUG=b:<bug number>`. If no
  issue is associated, write `BUG=None`. You can have multiple `BUG` lines.
- `TEST` lines are used to describe how you tested your commit in a free form. You can have multiple
  `TEST` lines.
- `Change-Id` is used to identify your change on Gerrit. It's inserted by the gerrit commit message
  hook as explained in
  [the previous section](https://crosvm.dev/book/contributing/index.html#gerrit-account). If a new
  commit is uploaded with the same `Change-Id` as an existing CL's `Change-Id`, gerrit will
  recognize the new commit as a new patchset of the existing CL.

### Uploading changes

To make changes to crosvm, start your work on a new branch tracking `origin/main`.

```bash
git checkout --branch myfeature --track origin/main
```

After making the necessary changes, and testing them via
[Presubmit Checks](https://crosvm.dev/book/building_crosvm.html#presubmit-checks), you can commit
and upload them:

```bash
git commit
./tools/cl upload
```

If you need to revise your change, you can amend the existing commit and upload again:

```bash
git commit --amend
./tools/cl upload
```

This will create a new version of the same change in gerrit.

> Note: We don't accept any pull requests on the [GitHub mirror].

### Getting Reviews

All submissions needs to be reviewed by one of the [crosvm owners]. Use the gerrit UI to request a
review. If you are uncertain about the correct person to review, reach out to the team via
[chat](https://matrix.to/#/#crosvm:matrix.org) or
[email list](https://groups.google.com/a/chromium.org/g/crosvm-dev).

### Submitting code

Crosvm uses a Commit Queue, which will run pre-submit testing on all changes before merging them
into crosvm.

Once one of the [crosvm owners] has voted "Code-Review+2" on your change, you can use the "Submit to
CQ" button, which will trigger the test process.

Gerrit will show any test failures. Refer to
[Building Crosvm](https://crosvm.dev/book/building_crosvm.html) for information on how to run the
same tests locally.

When all tests pass, your change is merged into `origin/main`.

## Contributing to the documentation

[The book of crosvm] is built with [mdBook]. Each markdown file must follow
[Google Markdown style guide].

To render the book locally, you need to install mdbook and [mdbook-mermaid], which should be
installed when you run `./tools/install-deps` script. Or you can use the `tools/dev_container`
environment.

```sh
cd docs/book/
mdbook build
```

Output is found at `docs/book/book/html/`.

[crosvm owners]: https://chromium.googlesource.com/crosvm/crosvm/+/HEAD/OWNERS
[github mirror]: https://github.com/google/crosvm
[google markdown style guide]: https://github.com/google/styleguide/blob/gh-pages/docguide/style.md
[mdbook]: https://rust-lang.github.io/mdBook/
[mdbook-mermaid]: https://github.com/badboy/mdbook-mermaid
[the book of crosvm]: https://crosvm.dev/book/