Want to contribute? Great! First, read this page.

### Before you contribute

Before we can use your code, you must sign the
[Google Individual Contributor License Agreement][gcla] (CLA), which you can do
online. The CLA is necessary mainly because you own the copyright to your
changes, even after your contribution becomes part of our codebase, so we need
your permission to use and distribute your code. We also need to be sure of
various other things—for instance that you'll tell us if you know that your code
infringes on other people's patents. You don't have to sign the CLA until after
you've submitted your code for review and a member has approved it, but you must
do it before we can put your code into our codebase. Before you start working on
a larger contribution, you should get in touch with us first through the issue
tracker with your idea so that we can help out and possibly guide you.
Coordinating up front makes it much easier to avoid frustration later on.

### Coding Guidelines

All code should conform to the [Go style guidelines][gostyle].

As a secure runtime, we need to maintain the safety of all of code included in
gVisor. The following rules help mitigate issues.

Definitions for the rules below:

`core`:

*   `//pkg/sentry/...`
*   Transitive dependencies in `//pkg/...`

`runsc`:

*   `//runsc/...`

Rules:

*   No cgo in `core` or `runsc`. The final binary must be a statically-linked
    pure Go binary.

*   Any files importing "unsafe" must have a name ending in `_unsafe.go`.

*   `core` may only depend on the following packages:

    *   Itself.
    *   Go standard library.
        *   Except (transitively) package "net" (this will result in a non-cgo
            binary). Use `//pkg/unet` instead.
    *   `@org_golang_x_sys//unix:go_default_library` (Go import
        `golang.org/x/sys/unix`).
    *   Generated Go protobuf packages.
    *   `@com_github_golang_protobuf//proto:go_default_library` (Go import
        `github.com/golang/protobuf/proto`).
    *   `@com_github_golang_protobuf//ptypes:go_default_library` (Go import
        `github.com/golang/protobuf/ptypes`).

*   `runsc` may only depend on the following packages:

    *   All packages allowed for `core`.
    *   `@com_github_google_subcommands//:go_default_library` (Go import
        `github.com/google/subcommands`).
    *   `@com_github_opencontainers_runtime_spec//specs_go:go_default_library`
        (Go import `github.com/opencontainers/runtime-spec/specs_go`).

### Code reviews

All changes must be submitted via [Gerrit][gerrit].

All submissions, including submissions by project members, require review.

To submit a patch, first clone the canonical repository.

```
git clone https://gvisor.googlesource.com/gvisor
```

From within the cloned directory, install the commit hooks (optional, but if you
don't you will need to generate Change-Ids manually in your commits).

```
curl -Lo `git rev-parse --git-dir`/hooks/commit-msg https://gerrit-review.googlesource.com/tools/hooks/commit-msg
chmod +x `git rev-parse --git-dir`/hooks/commit-msg
```

Edit the source and generate commits as you normally would. While making
changes, remember to organize commits logically. Changes are not reviewed per
branch (as with a pull request), they are reviewed per commit.

Before posting a new patch, you will need to generate an appropriate
authentication cookie. Visit the [repository][repo] and click the "Generate
Password" link at the top of the page for instructions.

To post a patch for review, push to a special "for" reference.

```
git push origin HEAD:refs/for/master
```

A change link will be generated for the commit, and a team member will review
your change request, provide feedback (and submit when appropriate). To address
feedback, you may be required to amend your commit and repush (don't change the
Commit-Id in the commit message). This will generate a new version of the
change.

When approved, the change will be submitted by a team member and automatically
merged into the repository.

### The small print

Contributions made by corporations are covered by a different agreement than the
one above, the
[Software Grant and Corporate Contributor License Agreement][gccla].

[gcla]: https://cla.developers.google.com/about/google-individual
[gccla]: https://cla.developers.google.com/about/google-corporate
[gerrit]: https://gvisor-review.googlesource.com
[gostyle]: https://github.com/golang/go/wiki/CodeReviewComments
[repo]: https://gvisor.googlesource.com