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-5: POSTING PATCHES
-
-Sooner or later, the time comes when your work is ready to be presented to
-the community for review and, eventually, inclusion into the mainline
-kernel. Unsurprisingly, the kernel development community has evolved a set
-of conventions and procedures which are used in the posting of patches;
-following them will make life much easier for everybody involved. This
-document will attempt to cover these expectations in reasonable detail;
-more information can also be found in the files SubmittingPatches,
-SubmittingDrivers, and SubmitChecklist in the kernel documentation
-directory.
-
-
-5.1: WHEN TO POST
-
-There is a constant temptation to avoid posting patches before they are
-completely "ready." For simple patches, that is not a problem. If the
-work being done is complex, though, there is a lot to be gained by getting
-feedback from the community before the work is complete. So you should
-consider posting in-progress work, or even making a git tree available so
-that interested developers can catch up with your work at any time.
-
-When posting code which is not yet considered ready for inclusion, it is a
-good idea to say so in the posting itself. Also mention any major work
-which remains to be done and any known problems. Fewer people will look at
-patches which are known to be half-baked, but those who do will come in
-with the idea that they can help you drive the work in the right direction.
-
-
-5.2: BEFORE CREATING PATCHES
-
-There are a number of things which should be done before you consider
-sending patches to the development community. These include:
-
- - Test the code to the extent that you can. Make use of the kernel's
- debugging tools, ensure that the kernel will build with all reasonable
- combinations of configuration options, use cross-compilers to build for
- different architectures, etc.
-
- - Make sure your code is compliant with the kernel coding style
- guidelines.
-
- - Does your change have performance implications? If so, you should run
- benchmarks showing what the impact (or benefit) of your change is; a
- summary of the results should be included with the patch.
-
- - Be sure that you have the right to post the code. If this work was done
- for an employer, the employer likely has a right to the work and must be
- agreeable with its release under the GPL.
-
-As a general rule, putting in some extra thought before posting code almost
-always pays back the effort in short order.
-
-
-5.3: PATCH PREPARATION
-
-The preparation of patches for posting can be a surprising amount of work,
-but, once again, attempting to save time here is not generally advisable
-even in the short term.
-
-Patches must be prepared against a specific version of the kernel. As a
-general rule, a patch should be based on the current mainline as found in
-Linus's git tree. When basing on mainline, start with a well-known release
-point - a stable or -rc release - rather than branching off the mainline at
-an arbitrary spot.
-
-It may become necessary to make versions against -mm, linux-next, or a
-subsystem tree, though, to facilitate wider testing and review. Depending
-on the area of your patch and what is going on elsewhere, basing a patch
-against these other trees can require a significant amount of work
-resolving conflicts and dealing with API changes.
-
-Only the most simple changes should be formatted as a single patch;
-everything else should be made as a logical series of changes. Splitting
-up patches is a bit of an art; some developers spend a long time figuring
-out how to do it in the way that the community expects. There are a few
-rules of thumb, however, which can help considerably:
-
- - The patch series you post will almost certainly not be the series of
- changes found in your working revision control system. Instead, the
- changes you have made need to be considered in their final form, then
- split apart in ways which make sense. The developers are interested in
- discrete, self-contained changes, not the path you took to get to those
- changes.
-
- - Each logically independent change should be formatted as a separate
- patch. These changes can be small ("add a field to this structure") or
- large (adding a significant new driver, for example), but they should be
- conceptually small and amenable to a one-line description. Each patch
- should make a specific change which can be reviewed on its own and
- verified to do what it says it does.
-
- - As a way of restating the guideline above: do not mix different types of
- changes in the same patch. If a single patch fixes a critical security
- bug, rearranges a few structures, and reformats the code, there is a
- good chance that it will be passed over and the important fix will be
- lost.
-
- - Each patch should yield a kernel which builds and runs properly; if your
- patch series is interrupted in the middle, the result should still be a
- working kernel. Partial application of a patch series is a common
- scenario when the "git bisect" tool is used to find regressions; if the
- result is a broken kernel, you will make life harder for developers and
- users who are engaging in the noble work of tracking down problems.
-
- - Do not overdo it, though. One developer once posted a set of edits
- to a single file as 500 separate patches - an act which did not make him
- the most popular person on the kernel mailing list. A single patch can
- be reasonably large as long as it still contains a single *logical*
- change.
-
- - It can be tempting to add a whole new infrastructure with a series of
- patches, but to leave that infrastructure unused until the final patch
- in the series enables the whole thing. This temptation should be
- avoided if possible; if that series adds regressions, bisection will
- finger the last patch as the one which caused the problem, even though
- the real bug is elsewhere. Whenever possible, a patch which adds new
- code should make that code active immediately.
-
-Working to create the perfect patch series can be a frustrating process
-which takes quite a bit of time and thought after the "real work" has been
-done. When done properly, though, it is time well spent.
-
-
-5.4: PATCH FORMATTING AND CHANGELOGS
-
-So now you have a perfect series of patches for posting, but the work is
-not done quite yet. Each patch needs to be formatted into a message which
-quickly and clearly communicates its purpose to the rest of the world. To
-that end, each patch will be composed of the following:
-
- - An optional "From" line naming the author of the patch. This line is
- only necessary if you are passing on somebody else's patch via email,
- but it never hurts to add it when in doubt.
-
- - A one-line description of what the patch does. This message should be
- enough for a reader who sees it with no other context to figure out the
- scope of the patch; it is the line that will show up in the "short form"
- changelogs. This message is usually formatted with the relevant
- subsystem name first, followed by the purpose of the patch. For
- example:
-
- gpio: fix build on CONFIG_GPIO_SYSFS=n
-
- - A blank line followed by a detailed description of the contents of the
- patch. This description can be as long as is required; it should say
- what the patch does and why it should be applied to the kernel.
-
- - One or more tag lines, with, at a minimum, one Signed-off-by: line from
- the author of the patch. Tags will be described in more detail below.
-
-The items above, together, form the changelog for the patch. Writing good
-changelogs is a crucial but often-neglected art; it's worth spending
-another moment discussing this issue. When writing a changelog, you should
-bear in mind that a number of different people will be reading your words.
-These include subsystem maintainers and reviewers who need to decide
-whether the patch should be included, distributors and other maintainers
-trying to decide whether a patch should be backported to other kernels, bug
-hunters wondering whether the patch is responsible for a problem they are
-chasing, users who want to know how the kernel has changed, and more. A
-good changelog conveys the needed information to all of these people in the
-most direct and concise way possible.
-
-To that end, the summary line should describe the effects of and motivation
-for the change as well as possible given the one-line constraint. The
-detailed description can then amplify on those topics and provide any
-needed additional information. If the patch fixes a bug, cite the commit
-which introduced the bug if possible (and please provide both the commit ID
-and the title when citing commits). If a problem is associated with
-specific log or compiler output, include that output to help others
-searching for a solution to the same problem. If the change is meant to
-support other changes coming in later patch, say so. If internal APIs are
-changed, detail those changes and how other developers should respond. In
-general, the more you can put yourself into the shoes of everybody who will
-be reading your changelog, the better that changelog (and the kernel as a
-whole) will be.
-
-Needless to say, the changelog should be the text used when committing the
-change to a revision control system. It will be followed by:
-
- - The patch itself, in the unified ("-u") patch format. Using the "-p"
- option to diff will associate function names with changes, making the
- resulting patch easier for others to read.
-
-You should avoid including changes to irrelevant files (those generated by
-the build process, for example, or editor backup files) in the patch. The
-file "dontdiff" in the Documentation directory can help in this regard;
-pass it to diff with the "-X" option.
-
-The tags mentioned above are used to describe how various developers have
-been associated with the development of this patch. They are described in
-detail in the SubmittingPatches document; what follows here is a brief
-summary. Each of these lines has the format:
-
- tag: Full Name <email address> optional-other-stuff
-
-The tags in common use are:
-
- - Signed-off-by: this is a developer's certification that he or she has
- the right to submit the patch for inclusion into the kernel. It is an
- agreement to the Developer's Certificate of Origin, the full text of
- which can be found in Documentation/SubmittingPatches. Code without a
- proper signoff cannot be merged into the mainline.
-
- - Acked-by: indicates an agreement by another developer (often a
- maintainer of the relevant code) that the patch is appropriate for
- inclusion into the kernel.
-
- - Tested-by: states that the named person has tested the patch and found
- it to work.
-
- - Reviewed-by: the named developer has reviewed the patch for correctness;
- see the reviewer's statement in Documentation/SubmittingPatches for more
- detail.
-
- - Reported-by: names a user who reported a problem which is fixed by this
- patch; this tag is used to give credit to the (often underappreciated)
- people who test our code and let us know when things do not work
- correctly.
-
- - Cc: the named person received a copy of the patch and had the
- opportunity to comment on it.
-
-Be careful in the addition of tags to your patches: only Cc: is appropriate
-for addition without the explicit permission of the person named.
-
-
-5.5: SENDING THE PATCH
-
-Before you mail your patches, there are a couple of other things you should
-take care of:
-
- - Are you sure that your mailer will not corrupt the patches? Patches
- which have had gratuitous white-space changes or line wrapping performed
- by the mail client will not apply at the other end, and often will not
- be examined in any detail. If there is any doubt at all, mail the patch
- to yourself and convince yourself that it shows up intact.
-
- Documentation/email-clients.txt has some helpful hints on making
- specific mail clients work for sending patches.
-
- - Are you sure your patch is free of silly mistakes? You should always
- run patches through scripts/checkpatch.pl and address the complaints it
- comes up with. Please bear in mind that checkpatch.pl, while being the
- embodiment of a fair amount of thought about what kernel patches should
- look like, is not smarter than you. If fixing a checkpatch.pl complaint
- would make the code worse, don't do it.
-
-Patches should always be sent as plain text. Please do not send them as
-attachments; that makes it much harder for reviewers to quote sections of
-the patch in their replies. Instead, just put the patch directly into your
-message.
-
-When mailing patches, it is important to send copies to anybody who might
-be interested in it. Unlike some other projects, the kernel encourages
-people to err on the side of sending too many copies; don't assume that the
-relevant people will see your posting on the mailing lists. In particular,
-copies should go to:
-
- - The maintainer(s) of the affected subsystem(s). As described earlier,
- the MAINTAINERS file is the first place to look for these people.
-
- - Other developers who have been working in the same area - especially
- those who might be working there now. Using git to see who else has
- modified the files you are working on can be helpful.
-
- - If you are responding to a bug report or a feature request, copy the
- original poster as well.
-
- - Send a copy to the relevant mailing list, or, if nothing else applies,
- the linux-kernel list.
-
- - If you are fixing a bug, think about whether the fix should go into the
- next stable update. If so, stable@vger.kernel.org should get a copy of
- the patch. Also add a "Cc: stable@vger.kernel.org" to the tags within
- the patch itself; that will cause the stable team to get a notification
- when your fix goes into the mainline.
-
-When selecting recipients for a patch, it is good to have an idea of who
-you think will eventually accept the patch and get it merged. While it
-is possible to send patches directly to Linus Torvalds and have him merge
-them, things are not normally done that way. Linus is busy, and there are
-subsystem maintainers who watch over specific parts of the kernel. Usually
-you will be wanting that maintainer to merge your patches. If there is no
-obvious maintainer, Andrew Morton is often the patch target of last resort.
-
-Patches need good subject lines. The canonical format for a patch line is
-something like:
-
- [PATCH nn/mm] subsys: one-line description of the patch
-
-where "nn" is the ordinal number of the patch, "mm" is the total number of
-patches in the series, and "subsys" is the name of the affected subsystem.
-Clearly, nn/mm can be omitted for a single, standalone patch.
-
-If you have a significant series of patches, it is customary to send an
-introductory description as part zero. This convention is not universally
-followed though; if you use it, remember that information in the
-introduction does not make it into the kernel changelogs. So please ensure
-that the patches, themselves, have complete changelog information.
-
-In general, the second and following parts of a multi-part patch should be
-sent as a reply to the first part so that they all thread together at the
-receiving end. Tools like git and quilt have commands to mail out a set of
-patches with the proper threading. If you have a long series, though, and
-are using git, please stay away from the --chain-reply-to option to avoid
-creating exceptionally deep nesting.