wiki:SubmittingPatches

How to Get Your Change Into OpenWrt

(based on Linux Kernel patch submission guidelines)

OpenWrt is constantly being improved. We'd like as many people to contribute to this as we can get. If you find a change useful, by all means try to get it incorporated into the project. This should improve OpenWrt and it should help carry your changes forward into future versions

For a person or company who wishes to submit a change to OpenWrt, the process can sometimes be daunting if you're not familiar with "the system." This text is a collection of suggestions which can greatly increase the chances of your change being accepted.

This document tries to lay out a procedure to enable people to submit patches in a way that is most effective for all concerned.

It is important to do all these steps repeatedly:

  • listen to what other people think
  • talk explaining what problem you are addressing and your proposed solution
  • do write useful patches including documentation
  • test test test

where to listen and talk

Documentation

It is often best to document what you are doing before you do it. The process of documentation often exposes possible improvements. Keep your documentation up to date.

Creating and Sending your change

Read SubmitChecklist for a list of items to check before submitting code.

For patches against external package sources, refer to the quilt howto at http://wiki.openwrt.org/doc/devel/patches

Please read http://kerneltrap.org/Linux/Email_Clients_and_Patches to find out how to make sure your email client doesn't destroy your patch.

1. Creating a patch

All changes to OpenWrt occur in the form of patches.

Patches should be based in the root trunk not in any lower subdirectory.

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, 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 OpenWrt developers, very important if you want your patch accepted.

The tools you can use to create a patch, in order of preference, are:

2. Describe your changes

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

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

The maintainer will thank you if you write your patch description in a form which can be used unmodified as a commit message for OpenWrt source code management system. See par.13, below.

If your description starts to get long, that's a sign that you probably need to split up your patch. See par.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 trac entry, refer to that bug entry by number.

3. Separate your changes.

Separate logical changes into a single patch file.

For example, if your changes include both bug fixes and enhancements for a single package, separate those changes into two or more 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.

4. Style check your changes

Check your patch for basic style violations. Failure to do so simply wastes the reviewers time and will get your patch rejected, probably without even being read.

5. Select e-mail destination.

Look in the Makefile if a MAINTAINER macro exists. If so, e-mail that person. Unless you have a reason NOT to do so, always CC openwrt-devel <at> lists.openwrt.org. If no maintainer is listed, send your patch to the primary OpenWrt developer's mailing list. Most OpenWrt developers monitor this e-mail list, and can comment on your changes.

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

OpenWrt developers need to be able to read and comment on the changes you are submitting. It is important for an OpenWrt 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.

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

7. E-mail size

Large changes are not appropriate for mailing lists, and some maintainers. If your patch, uncompressed, exceeds 300 kB in size, it is preferred that you store your patch on an Internet-accessible server, and provide instead a URL (link) pointing to your patch.

8. Don't get discouraged. Re-submit

After you have submitted your change, be patient and wait. If developers like your change and apply it, it will appear as new revision in the source code management system.

However, if your change doesn't appear in the source code management system, there could be any number of reasons. It's YOUR job to narrow down those reasons, correct what was wrong, and submit your updated change.

Sometimes, developers may "drop" your patch with or without comment. That's the nature of the system. If your patch is dropped, it could be due to:

  • Your patch did not apply cleanly to the latest OpenWrt revision.
  • Your patch was not sufficiently discussed on openwrt-devel.
  • A style issue.
  • An e-mail formatting issue (re-read this section).
  • A technical problem with your change.
  • They get tons of e-mail, and yours got lost in the shuffle.
  • You are being annoying.

When in doubt, solicit comments on openwrt-devel mailing list.

9. Include PATCH in the subject

Due to high e-mail traffic to openwrt-devel, it is common convention to prefix your subject line with [PATCH]. This lets OpenWrt developers more easily distinguish patches from other e-mail discussions.

10. Sign your work

To improve tracking of who did what, especially with patches that can percolate to their final resting place in OpenWrt through several layers of developers, we use 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 an 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:
  
(a) 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
  
(b) 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
  
(c) The contribution was provided directly to me by some other
    person who certified (a), (b) or (c) and I have not modified
    it.
  
(d) 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 package or target 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 him 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:

Date:   Wed Jul 25 15:14:50 2012 +0300

    [generic] add missing symbols

    [backport r12345]

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.

11. 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 packages and has an Acked-by: from one package maintainer then this usually indicates acknowledgement of just the part which affects that maintainer's code. Judgement should be used here.

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

12. 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:

(a) I have carried out a technical review of this patch to
    evaluate its appropriateness and readiness for inclusion into
    OpenWrt.

(b) 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.

(c) 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 OpenWrt, and (2) free of known
    issues which would argue against its inclusion.

(d) 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 OpenWrt 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 OpenWrt.

13. The canonical patch format

The canonical patch subject line is:

Subject: [PATCH 001/123] [section] summary phrase

The canonical patch message body contains the following:

  • A "from" line specifying the patch author.
  • An empty line.
  • The body of the explanation, which will be copied to the permanent changelog to describe this patch.
  • The "Signed-off-by:" lines, described above, which will also go in the changelog.
  • A marker line containing simply "---".
  • Any additional comments not suitable for the changelog.
  • The actual patch (diff output).

The Subject line format makes it very easy to sort the emails alphabetically by subject line - pretty much any email reader will support that - since because the sequence number is zero-padded, the numerical and alphabetic sort is the same.

The "section" in the email's Subject should identify which section of OpenWrt is being patched. Some example sections are:

  • [include]
  • [(kernel|generic)]
  • [packages]
  • [package]
  • [scripts]
  • [tools]

The "summary phrase" in the email's Subject should concisely describe the patch which that email contains. The "summary phrase" should not be a filename. Do not use the same "summary phrase" for every patch in a whole patch series (where a "patch series" is an ordered sequence of multiple, related patches).

Bear in mind that the "summary phrase" of your email becomes a globally-unique identifier for that patch. It propagates all the way into the source code management system changelog. The "summary phrase" may later be used in developer discussions which refer to the patch. People will want to google for the "summary phrase" to read discussion regarding that patch. It will also be the only thing that people may quickly see when, two or three months later, they are going through perhaps thousands of patches using source code management browsing tools.

For these reasons, the "summary" must be no more than 70-75 characters, and it must describe both what the patch changes, as well as why the patch might be necessary. It is challenging to be both succinct and descriptive, but that is what a well-written summary should do.

The "summary phrase" may be prefixed by tags enclosed in square brackets: "Subject: [PATCH tag] <summary phrase>". The tags are not considered part of the summary phrase, but describe how the patch should be treated. Common tags might include a version descriptor if the multiple versions of the patch have been sent out in response to comments (i.e., "v1, v2, v3"), or "RFC" to indicate a request for comments. If there are four patches in a patch series the individual patches may be numbered like this: 1/4, 2/4, 3/4, 4/4. This assures that developers understand the order in which the patches should be applied and that they have reviewed or applied all of the patches in the patch series.

Some example Subjects:

    Subject: [PATCH] [packages] e2fsprogs: Bump to 1.41.3
    Subject: [PATCH] [x86] generic: switch to 3.3
    Subject: [PATCHv2 001/207] [ar71xx] enable sysupgrade on the WRT160Nl

The "from" line must be the very first line in the message body, and has the form:

        From: Original Author <author@example.com>

The "from" line specifies who will be credited as the author of the patch in the permanent changelog. If the "from" line is missing, then the "From:" line from the email header will be used to determine the patch author in the changelog.

The explanation body will be committed to the permanent source changelog, so should make sense to a competent reader who has long since forgotten the immediate details of the discussion that might have led to this patch. Including symptoms of the failure which the patch addresses (kernel log messages, oops messages, etc.) is especially useful for people who might be searching the commit logs looking for the applicable patch. If a patch fixes a compile failure, it may not be necessary to include _all_ of the compile failures; just enough that it is likely that someone searching for the patch can find it. As in the "summary phrase", it is important to be both succinct as well as descriptive.

The "---" marker line serves the essential purpose of marking for patch handling tools where the changelog message ends.

One good use for the additional comments after the "---" marker is for a diffstat, to show what files have changed, and the number of inserted and deleted lines per file. A diffstat is especially useful on bigger patches. Other comments relevant only to the moment or the maintainer, not suitable for the permanent changelog, should also go here. A good example of such comments might be "patch changelogs" which describe what has changed between the v1 and v2 version of the patch.

See more details on the proper patch format in the following References.

Monitoring Patches

Patches sent to the Development mailing list can be followed on Patchwork at https://patchwork.ozlabs.org/project/openwrt/list/.

References

Last modified 15 months ago Last modified on 2015-03-01T21:55:20+01:00