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Submitting Patches to Ceph

This is based on Documentation/SubmittingPatches from the Linux kernel, but has pared down significantly and updated based on the Ceph project's best practices.

The patch signing procedures and definitions are unmodified.

SIGNING CONTRIBUTIONS

In order to keep the record of code attribution clean within the source repository, please follow these guidelines for signing patches submitted to the project. These definitions are taken from those used by the Linux kernel and many other open source projects.

  1. Sign your work

    To improve tracking of who did what, especially with patches that can percolate to their final resting place in the kernel through several layers of maintainers, we've introduced a "sign-off" procedure on patches that are being emailed around.

    The sign-off is a simple line at the end of the explanation for the patch, 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 <[email protected]>

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

    Some people also put extra tags at the end. They'll just be ignored for now, but you can do this to mark internal company procedures or just point out some special detail about the sign-off.

    If you are a subsystem or branch maintainer, sometimes you need to slightly modify patches you receive in order to merge them, because the code is not exactly the same in your tree and the submitters'. If you stick strictly to rule (c), you should ask the submitter to rediff, but this is a totally counter-productive waste of time and energy. Rule (b) allows you to adjust the code, but then it is very impolite to change one submitter's code and make them endorse your bugs. To solve this problem, it is recommended that you add a line between the last Signed-off-by header and yours, indicating the nature of your changes. While there is nothing mandatory about this, it seems like prepending the description with your mail and/or name, all enclosed in square brackets, is noticeable enough to make it obvious that you are responsible for last-minute changes. Example

    Signed-off-by: Random J Developer <[email protected]>
[[email protected]: struct foo moved from foo.c to foo.h]
Signed-off-by: Lucky K Maintainer <[email protected]>

    This practise is particularly helpful if you maintain a stable branch and want at the same time to credit the author, track changes, merge the fix, and protect the submitter from complaints. Note that under no circumstances can you change the author's identity (the From header), as it is the one which appears in the changelog.

    Special note to back-porters: It seems to be a common and useful practise to insert an indication of the origin of a patch at the top of the commit message (just after the subject line) to facilitate tracking. For instance, here's what we see in 2.6-stable

    Date:   Tue May 13 19:10:30 2008 +0000

SCSI: libiscsi regression in 2.6.25: fix nop timer handling

commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream

    And here's what appears in 2.4

    Date:   Tue May 13 22:12:27 2008 +0200

wireless, airo: waitbusy() won't delay

[backport of 2.6 commit b7acbdfbd1f277c1eb23f344f899cfa4cd0bf36a]

    Whatever the format, this information provides a valuable help to people tracking your trees, and to people trying to trouble-shoot bugs in your tree.

  2. When to use Acked-by: and Cc:

    The Signed-off-by: tag indicates that the signer was involved in the development of the patch, or that he/she was in the patch's delivery path.

    If a person was not directly involved in the preparation or handling of a patch but wishes to signify and record their approval of it then they can arrange to have an Acked-by: line added to the patch's changelog.

    Acked-by: is often used by the maintainer of the affected code when that maintainer neither contributed to nor forwarded the patch.

    Acked-by: is not as formal as Signed-off-by:. It is a record that the acker has at least reviewed the patch and has indicated acceptance. Hence patch mergers will sometimes manually convert an acker's "yep, looks good to me" into an Acked-by:.

    Acked-by: does not necessarily indicate acknowledgement of the entire patch. For example, if a patch affects multiple subsystems and has an Acked-by: from one subsystem maintainer then this usually indicates acknowledgement of just the part which affects that maintainer's code. Judgement should be used here. When in doubt people should refer to the original discussion in the mailing list archives.

    If a person has had the opportunity to comment on a patch, but has not provided such comments, you may optionally add a "Cc:" tag to the patch. This is the only tag which might be added without an explicit action by the person it names. This tag documents that potentially interested parties have been included in the discussion

  3. Using Reported-by:, Tested-by: and Reviewed-by:

    If this patch fixes a problem reported by somebody else, consider adding a Reported-by: tag to credit the reporter for their contribution. Please note that this tag should not be added without the reporter's permission, especially if the problem was not reported in a public forum. That said, if we diligently credit our bug reporters, they will, hopefully, be inspired to help us again in the future.

    A Tested-by: tag indicates that the patch has been successfully tested (in some environment) by the person named. This tag informs maintainers that some testing has been performed, provides a means to locate testers for future patches, and ensures credit for the testers.

    Reviewed-by:, instead, indicates that the patch has been reviewed and found acceptable according to the Reviewer's Statement:

    Reviewer's statement of oversight

    By offering my Reviewed-by: tag, I state that:

    1. I have carried out a technical review of this patch to evaluate its appropriateness and readiness for inclusion into the mainline kernel.
    2. Any problems, concerns, or questions relating to the patch have been communicated back to the submitter. I am satisfied with the submitter's response to my comments.
    3. While there may be things that could be improved with this submission, I believe that it is, at this time, (1) a worthwhile modification to the kernel, and (2) free of known issues which would argue against its inclusion.
    4. While I have reviewed the patch and believe it to be sound, I do not (unless explicitly stated elsewhere) make any warranties or guarantees that it will achieve its stated purpose or function properly in any given situation.

    A Reviewed-by tag is a statement of opinion that the patch is an appropriate modification of the kernel without any remaining serious technical issues. Any interested reviewer (who has done the work) can offer a Reviewed-by tag for a patch. This tag serves to give credit to reviewers and to inform maintainers of the degree of review which has been done on the patch. Reviewed-by: tags, when supplied by reviewers known to understand the subject area and to perform thorough reviews, will normally increase the likelihood of your patch getting into the kernel.

PREPARING AND SENDING PATCHES

The upstream repository is managed by Git. You will find that it is easiest to work on the project and submit changes by using the git tools, both for managing your own code and for preparing and sending patches.

The project will generally accept code either by pulling code directly from a published git tree (usually on github), or via patches emailed directly to the email list ([email protected]). For the kernel client, patches are expected to be reviewed in the email list. And for everything else, github is preferred due to the convenience of the 'pull request' feature.

  1. Github pull request

    The preferred way to submit code is by publishing your patches in a branch in your github fork of the ceph repository and then submitting a github pull request.

    For example, prepare your changes

    # ...code furiously...
$ git commit     # git gui is also quite convenient
$ git push origin mything

    Then submit a pull request at

    https://github.com/ceph/ceph/pulls

    and click 'New pull request'. The 'hub' command-line tool, available from

    https://github.com/github/hub

    allows you to submit pull requests directly from the command line

    $ hub pull-request -b ceph:master -h you:mything

    Pull requests appear in the review queue at

    https://github.com/organizations/ceph/dashboard/pulls

    You may want to ping a developer in #ceph-devel on irc.oftc.net or on the email list to ensure your submission is noticed.

    When addressing review comments, can should either add additional patches to your branch or (better yet) squash those changes into the relevant commits so that the sequence of changes is "clean" and gets things right the first time. The 'git rebase -i' command is very helpful in this process. Once you have updated your local branch, you can simply force-push to the existing branch in your public repository that is referenced by the pull request with

    $ git push -f origin mything

    and your changes will be visible from the existing pull-request. You may want to ping the reviewer again or comment on the pull request to ensure the updates are noticed.

    Sometimes your change could be based on an outdated parent commit and has conflicts with the latest target branch, then you need to fetch the updates from the remote branch, rebase your change onto it, and resolve the conflicts before doing the force-push

    $ git pull --rebase origin target-branch

    So that the pull request does not contain any "merge" commit. Instead of "merging" the target branch, we expect a linear history in a pull request where you commit on top of the remote branch.

    Q: Which branch should I target in my pull request?

    A: The target branch depends on the nature of your change:

    If you are adding a feature, target the "master" branch in your pull request.

    If you are fixing a bug, target the named branch corresponding to the major version that is currently in development. For example, if Infernalis is the latest stable release and Jewel is development, target the "jewel" branch for bugfixes. The Ceph core developers will periodically merge this named branch into "master". When this happens, the master branch will contain your fix as well.

    If you are fixing a bug (see above) and the bug exists in older stable branches (for example, the "hammer" or "infernalis" branches), then you should file a Redmine ticket describing your issue and fill out the "Backport: <branchname>" form field. This will notify other developers that your commit should be cherry-picked to these stable branches. For example, you should set "Backport: hammer" in your Redmine ticket to indicate that you are fixing a bug that exists on the "hammer" branch and that you desire that your change be cherry-picked to that branch.

    Q: How to include Reviewed-by: tag(s) in my pull request?

    You don't. If someone reviews your pull request, they should indicate they have done so by commenting on it with "+1", "looks good to me", "LGTM", and/or the entire "Reviewed-by: ..." line with their name and email address.

    The developer merging the pull request should note positive reviews and include the appropriate Reviewed-by: lines in the merge commit.

  2. Patch submission via [email protected]

    The best way to generate a patch for manual submission is to work from a Git checkout of the Ceph source code. You can then generate patches with the 'git format-patch' command. For example,

    $ git format-patch HEAD^^ -o mything

    will take the last two commits and generate patches in the mything/ directory. The commit you specify on the command line is the 'upstream' commit that you are diffing against. Note that it does not necesarily have to be an ancestor of your current commit. You can do something like

    $ git checkout -b mything
# ... do lots of stuff ...
$ git fetch
# ...find out that origin/unstable has also moved forward...
$ git format-patch origin/unstable -o mything

    and the patches will be against origin/unstable.

    The -o dir is optional; if left off, the patch(es) will appear in the current directory. This can quickly get messy.

    You can also add --cover-letter and get a '0000' patch in the mything/ directory. That can be updated to include any overview stuff for a multipart patch series. If it's a single patch, don't bother.

    Make sure your patch does not include any extra files which do not belong in a patch submission. Make sure to review your patch -after- generated it with diff(1), to ensure accuracy.

    If your changes produce a lot of deltas, you may want to look into splitting them into individual patches which modify things in logical stages. This will facilitate easier reviewing by other kernel developers, very important if you want your patch accepted. There are a number of scripts which can aid in this.

    The git send-email command make it super easy to send patches (particularly those prepared with git format patch). It is careful to format the emails correctly so that you don't have to worry about your email client mangling whitespace or otherwise screwing things up. It works like so:

    $ git send-email --to [email protected] my.patch

    for a single patch, or

    $ git send-email --to [email protected] mything

    to send a whole patch series (prepared with, say, git format-patch).

  3. Describe your changes.

    Describe the technical detail of the change(s) your patch includes.

    The text up to the first empty line in a commit message is the commit title. Ideally it is a single short line less than 50 characters, summarizing the change. It is required to prefix it with the subsystem or module you are changing. For instance, the prefix could be "doc:", "osd:", or "common:". One can use:

    git log

    for more examples.

    Be as specific as possible. The WORST descriptions possible include things like "update driver X", "bug fix for driver X", or "this patch includes updates for subsystem X. Please apply."

    The maintainer will thank you if you write your patch description in a form which can be easily pulled into Linux's source code management system, git, as a "commit log". See #15, below.

    If your description starts to get long, that's a sign that you probably need to split up your patch. See #3, next.

    When you submit or resubmit a patch or patch series, include the complete patch description and justification for it. Don't just say that this is version N of the patch (series). Don't expect the patch merger to refer back to earlier patch versions or referenced URLs to find the patch description and put that into the patch. I.e., the patch (series) and its description should be self-contained. This benefits both the patch merger(s) and reviewers. Some reviewers probably didn't even receive earlier versions of the patch.

    If the patch fixes a logged bug entry, refer to that bug entry by number and URL. In particular, if this patch fixes one or more issues tracked by http://tracker.ceph.com, consider adding a Fixes: tag to connect this change to addressed issue(s). So a line saying

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

    is added before the Signed-off-by: line stating that this commit addresses http://tracker.ceph.com/issues/12345. It helps the reviewer to get more context of this bug, so she/he can hence update the issue on the bug tracker accordingly.

    So a typical commit message for revising the document could look like:

    doc: add "--foo" option to bar

* update the man page for bar with the newly added "--foo" option.
* fix a typo

Fixes: http://tracker.ceph.com/issues/12345
Signed-off-by: Random J Developer <[email protected]>

  4. Separate your changes.

    Separate logical changes into a single patch file.

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

    On the other hand, if you make a single change to numerous files, group those changes into a single patch. Thus a single logical change is contained within a single patch.

    If one patch depends on another patch in order for a change to be complete, that is OK. Simply note "this patch depends on patch X" in your patch description.

    If you cannot condense your patch set into a smaller set of patches, then only post say 15 or so at a time and wait for review and integration.

  5. Style check your changes.

    Check your patch for basic style violations, details of which can be found in CodingStyle.

  6. No MIME, no links, no compression, no attachments. Just plain text.

    Developers need to be able to read and comment on the changes you are submitting. It is important for a kernel developer to be able to "quote" your changes, using standard e-mail tools, so that they may comment on specific portions of your code.

    For this reason, all patches should be submitting e-mail "inline". WARNING: Be wary of your editor's word-wrap corrupting your patch, if you choose to cut-n-paste your patch.

    Do not attach the patch as a MIME attachment, compressed or not. Many popular e-mail applications will not always transmit a MIME attachment as plain text, making it impossible to comment on your code. A MIME attachment also takes Linus a bit more time to process, decreasing the likelihood of your MIME-attached change being accepted.

    Exception: If your mailer is mangling patches then someone may ask you to re-send them using MIME.