Submitting Patches to Ceph

Patches to Ceph can be divided into three categories:

1. patches targeting Ceph kernel code
2. patches targeting the "master" branch
3. patches targeting stable branches (e.g.: "nautilus")

Some parts of Ceph - notably the RBD and CephFS kernel clients - are maintained within the Linux Kernel. For patches targeting this code, please refer to the file SubmittingPatches-kernel.rst.

The rest of this document assumes that your patch relates to Ceph code that is maintained in the GitHub repository https://github.com/ceph/ceph

If you have a patch that fixes an issue, feel free to open a GitHub pull request ("PR") targeting the "master" branch, but do read this document first, as it contains important information for ensuring that your PR passes code review smoothly.

For patches targeting stable branches (e.g. "nautilus"), please also see the file SubmittingPatches-backports.rst.

Sign your work

The sign-off is a simple line at the end of the explanation for the commit, which certifies that you wrote it or otherwise have the right to pass it on as a open-source patch. The rules are pretty simple: if you can certify the below:

Developer's Certificate of Origin 1.1

By making a contribution to this project, I certify that:

1. The contribution was created in whole or in part by me and I have the right to submit it under the open source license indicated in the file; or
2. The contribution is based upon previous work that, to the best of my knowledge, is covered under an appropriate open source license and I have the right under that license to submit that work with modifications, whether created in whole or in part by me, under the same open source license (unless I am permitted to submit under a different license), as indicated in the file; or
3. The contribution was provided directly to me by some other person who certified (a), (b) or (c) and I have not modified it.
4. I understand and agree that this project and the contribution are public and that a record of the contribution (including all personal information I submit with it, including my sign-off) is maintained indefinitely and may be redistributed consistent with this project or the open source license(s) involved.

then you just add a line saying

Signed-off-by: Random J Developer <random@developer.example.org>

using your real name (sorry, no pseudonyms or anonymous contributions).

Git can sign off on your behalf

Please note that git makes it trivially easy to sign commits. First, set the following config options:

$ git config --list | grep user
user.email=my_real_email_address@example.com
user.name=My Real Name

Then just remember to use git commit -s. Git will add the Signed-off-by line automatically.

Separate your changes

Group logical changes into individual commits.

If you have a series of bulleted modifications, consider separating each of those into its own commit.

For example, if your changes include both bug fixes and performance enhancements for a single component, separate those changes into two or more commits. If your changes include an API update, and a new feature which uses that new API, separate those into two patches.

On the other hand, if you make a single change that affects numerous files, group those changes into a single commit. Thus a single logical change is contained within a single patch. (If the change needs to be backported, that might change the calculus, because smaller commits are easier to backport.)

Describe your changes

Each commit has an associated commit message that is stored in git. The first line of the commit message is the commit title. The second line should be left blank. The lines that follow constitute the commit message.

A commit and its message should be focused around a particular change.

Commit title

The text up to the first empty line in a commit message is the commit title. It should be a single short line of at most 72 characters, summarizing the change, and prefixed with the subsystem or module you are changing. Also, it is conventional to use the imperative mood in the commit title. Positive examples include:

mds: add perf counter for finisher of MDSRank
osd: make the ClassHandler::mutex private

If the change only touches the files under doc directory, the title should start with "doc". For instance, a commit fixing a typo in doc/mgr/dashboard.rst could have a title like:

doc/mgr/dashboard: fix a typo

More positive examples can be obtained from the git history of the master branch:

git log

Some negative examples (how not to title a commit message):

update driver X
bug fix for driver X
fix issue 99999

Further to the last negative example ("fix issue 99999"), see Fixes line(s).

Commit message

(This section is about the body of the commit message. Please also see the preceding section, Commit title, for advice on titling commit messages.)

In the body of your commit message, be as specific as possible. If the commit message title was too short to fully state what the commit is doing, use the body to explain not just the "what", but also the "why".

For positive examples, peruse git log in the master branch. A negative example would be a commit message that merely states the obvious. For example: "this patch includes updates for subsystem X. Please apply."

Fixes line(s)

If the commit fixes one or more issues tracked by http://tracker.ceph.com, add a Fixes: line (or lines) to the commit message, to connect this change to addressed issue(s) - for example:

Fixes: http://tracker.ceph.com/issues/12345

This line should be added just before the Signed-off-by: line (see Sign your work).

It helps reviewers to get more context of this bug and facilitates updating of the bug tracker. Also, anyone perusing the git history will see this line and be able to refer to the bug tracker easily.

Here is an example showing a properly-formed commit message:

doc: add "--foo" option to bar

This commit updates the man page for bar with the newly added "--foo"
option.

Fixes: http://tracker.ceph.com/issues/12345
Signed-off-by: Random J Developer <random@developer.example.org>

If a commit fixes a regression introduced by a different commit, please also (in addition to the above) add a line referencing the SHA1 of the commit that introduced the regression. For example:

Fixes: 9dbe7a003989f8bb45fe14aaa587e9d60a392727

PR best practices

PRs should be opened on branches contained in your fork of https://github.com/ceph/ceph.git - do not push branches directly to ceph/ceph.git.

PRs should target "master". If you need to add a patch to a stable branch, such as "nautilus", see the file SubmittingPatches-backports.rst.

In addition to a base, or "target" branch, PRs have several other components: the PR title, the PR description, labels, comments, etc. Of these, the PR title and description are relevant for new contributors.

PR title

If your PR has only one commit, the PR title can be the same as the commit title (and GitHub will suggest this). If the PR has multiple commits, do not accept the title GitHub suggests. Either use the title of the most relevant commit, or write your own title. In the latter case, use the same "subsystem: short description" convention described in Commit title for the PR title, with the following difference: the PR title describes the entire set of changes, while the Commit title describes only the changes in a particular commit.

If GitHub suggests a PR title based on a very long commit message it will split the result with an elipsis (...) and fold the remainder into the PR description. In such a case, please edit the title to be more concise and the description to remove the elipsis.

Keep in mind that the PR titles feed directly into the script that generates release notes and it is tedious to clean up non-conformant PR titles at release time. This document places no limit on the length of PR titles, but be aware that they are subject to editing as part of the release process.

PR description

In addition to a title, the PR also has a description field, or "body".

The PR description is a place for summarizing the PR as a whole. It need not duplicate information that is already in the commit messages. It can contain notices to maintainers, links to tracker issues and other related information, to-do lists, etc. The PR title and description should give readers a high-level notion of what the PR is about, quickly enabling them to decide whether they should take a closer look.

Flag your changes for backport

If you believe your changes should be backported to stable branches after the PR is merged, open a tracker issue at https://tracker.ceph.com explaining:

1. what bug is fixed
2. why does the bug need to be fixed in <release>

and fill out the Backport field in the tracker issue. For example:

Backport: mimic, nautilus

For information on how backports are done in the Ceph project, refer to the document SubmittingPatches-backports.rst.

Test your changes

Before opening your PR, it's a good idea to run tests on your patchset. Doing that is simple, though the process can take a long time to complete, especially on older machines with less memory and spinning disks.

The most simple test is to verify that your patchset builds, at least in your own development environment. The commands for this are:

./install-deps.sh
./do_cmake.sh
make

Ceph comes with a battery of tests that can be run on a single machine. These are collectively referred to as "make check", and can be run by executing the following command:

./run-make-check.sh

If your patchset does not build, or if one or more of the "make check" tests fails, but the error shown is not obviously related to your patchset, don't let that dissuade you from opening a PR. The Ceph project has a Jenkins instance which will build your PR branch and run "make check" on it in a controlled environment.

Once your patchset builds and passes "make check", you can run even more tests on it by issuing the following commands:

cd build
../qa/run-standalone.sh

Like "make check", the standalone tests take a long time to run. They also produce voluminous output. If one or more of the standalone tests fails, it's likely the relevant part of the output will have scrolled off your screen or gotten swapped out of your buffer. Therefore, it makes sense to capture the output in a file for later analysis.

Document your changes

If you have added or modified any user-facing functionality, such as CLI commands or their output, then the pull request must include appropriate updates to documentation.

It is the submitter's responsibility to make the changes, and the reviewer's responsibility to make sure they are not merging changes that do not have the needed updates to documentation.

Where there are areas that have absent documentation, or there is no clear place to note the change that is being made, the reviewer should contact the component lead, who should arrange for the missing section to be created with sufficient detail for the PR submitter to document their changes.

When writing and/or editing documentation, follow the Google Developer Documentation Style Guide: https://developers.google.com/style/