Submitting Patches to Ceph - Kernel Components

Submission of patches to the Ceph kernel code is subject to the same rules and guidelines as any other patches to the Linux Kernel. These are set out in Documentation/process/submitting-patches.rst in the kernel source tree.

What follows is a condensed version of those rules and guidelines, updated based on the Ceph project's best practices.

Signing contributions

In order to keep the record of code attribution clean within the source repository, 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 <random@developer.example.org>

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 <random@developer.example.org>
[lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>

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. 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

For the kernel client, patches are expected to be emailed directly to the email list ceph-devel@vger.kernel.org (note: not dev@ceph.io) and reviewed in the email list.

The best way to generate a patch for manual submission is to work from a Git checkout of the Ceph kernel client (kernel modules) repository located at https://github.com/ceph/ceph-client. 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 necessarily 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 ceph-devel@vger.kernel.org my.patch

for a single patch, or

$ git send-email --to ceph-devel@vger.kernel.org mything

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

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.

Style Guide

The Linux Kernel has coding style conventions, which are set forth in Documentation/process/coding-style.rst. Please adhere to these conventions.