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+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
+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.
+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.
+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.
+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.
+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
+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.