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![Jakub Wilk](/assets/img/avatar_default.png)
Signed-off-by: Jakub Wilk <jwilk@jwilk.net> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
821 lines
36 KiB
Text
821 lines
36 KiB
Text
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How to Get Your Change Into the Linux Kernel
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or
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Care And Operation Of Your Linus Torvalds
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For a person or company who wishes to submit a change to the Linux
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kernel, the process can sometimes be daunting if you're not familiar
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with "the system." This text is a collection of suggestions which
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can greatly increase the chances of your change being accepted.
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This document contains a large number of suggestions in a relatively terse
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format. For detailed information on how the kernel development process
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works, see Documentation/development-process. Also, read
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Documentation/SubmitChecklist for a list of items to check before
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submitting code. If you are submitting a driver, also read
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Documentation/SubmittingDrivers; for device tree binding patches, read
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Documentation/devicetree/bindings/submitting-patches.txt.
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Many of these steps describe the default behavior of the git version
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control system; if you use git to prepare your patches, you'll find much
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of the mechanical work done for you, though you'll still need to prepare
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and document a sensible set of patches. In general, use of git will make
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your life as a kernel developer easier.
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--------------------------------------------
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SECTION 1 - CREATING AND SENDING YOUR CHANGE
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--------------------------------------------
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0) Obtain a current source tree
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-------------------------------
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If you do not have a repository with the current kernel source handy, use
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git to obtain one. You'll want to start with the mainline repository,
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which can be grabbed with:
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git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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Note, however, that you may not want to develop against the mainline tree
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directly. Most subsystem maintainers run their own trees and want to see
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patches prepared against those trees. See the "T:" entry for the subsystem
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in the MAINTAINERS file to find that tree, or simply ask the maintainer if
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the tree is not listed there.
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It is still possible to download kernel releases via tarballs (as described
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in the next section), but that is the hard way to do kernel development.
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1) "diff -up"
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------------
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If you must generate your patches by hand, use "diff -up" or "diff -uprN"
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to create patches. Git generates patches in this form by default; if
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you're using git, you can skip this section entirely.
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All changes to the Linux kernel occur in the form of patches, as
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generated by diff(1). When creating your patch, make sure to create it
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in "unified diff" format, as supplied by the '-u' argument to diff(1).
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Also, please use the '-p' argument which shows which C function each
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change is in - that makes the resultant diff a lot easier to read.
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Patches should be based in the root kernel source directory,
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not in any lower subdirectory.
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To create a patch for a single file, it is often sufficient to do:
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SRCTREE= linux
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MYFILE= drivers/net/mydriver.c
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cd $SRCTREE
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cp $MYFILE $MYFILE.orig
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vi $MYFILE # make your change
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cd ..
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diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch
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To create a patch for multiple files, you should unpack a "vanilla",
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or unmodified kernel source tree, and generate a diff against your
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own source tree. For example:
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MYSRC= /devel/linux
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tar xvfz linux-3.19.tar.gz
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mv linux-3.19 linux-3.19-vanilla
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diff -uprN -X linux-3.19-vanilla/Documentation/dontdiff \
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linux-3.19-vanilla $MYSRC > /tmp/patch
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"dontdiff" is a list of files which are generated by the kernel during
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the build process, and should be ignored in any diff(1)-generated
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patch.
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Make sure your patch does not include any extra files which do not
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belong in a patch submission. Make sure to review your patch -after-
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generating it with diff(1), to ensure accuracy.
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If your changes produce a lot of deltas, you need to split them into
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individual patches which modify things in logical stages; see section
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#3. This will facilitate review by other kernel developers,
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very important if you want your patch accepted.
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If you're using git, "git rebase -i" can help you with this process. If
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you're not using git, quilt <http://savannah.nongnu.org/projects/quilt>
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is another popular alternative.
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2) Describe your changes.
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-------------------------
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Describe your problem. Whether your patch is a one-line bug fix or
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5000 lines of a new feature, there must be an underlying problem that
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motivated you to do this work. Convince the reviewer that there is a
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problem worth fixing and that it makes sense for them to read past the
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first paragraph.
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Describe user-visible impact. Straight up crashes and lockups are
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pretty convincing, but not all bugs are that blatant. Even if the
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problem was spotted during code review, describe the impact you think
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it can have on users. Keep in mind that the majority of Linux
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installations run kernels from secondary stable trees or
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vendor/product-specific trees that cherry-pick only specific patches
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from upstream, so include anything that could help route your change
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downstream: provoking circumstances, excerpts from dmesg, crash
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descriptions, performance regressions, latency spikes, lockups, etc.
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Quantify optimizations and trade-offs. If you claim improvements in
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performance, memory consumption, stack footprint, or binary size,
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include numbers that back them up. But also describe non-obvious
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costs. Optimizations usually aren't free but trade-offs between CPU,
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memory, and readability; or, when it comes to heuristics, between
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different workloads. Describe the expected downsides of your
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optimization so that the reviewer can weigh costs against benefits.
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Once the problem is established, describe what you are actually doing
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about it in technical detail. It's important to describe the change
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in plain English for the reviewer to verify that the code is behaving
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as you intend it to.
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The maintainer will thank you if you write your patch description in a
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form which can be easily pulled into Linux's source code management
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system, git, as a "commit log". See #15, below.
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Solve only one problem per patch. If your description starts to get
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long, that's a sign that you probably need to split up your patch.
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See #3, next.
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When you submit or resubmit a patch or patch series, include the
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complete patch description and justification for it. Don't just
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say that this is version N of the patch (series). Don't expect the
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subsystem maintainer to refer back to earlier patch versions or referenced
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URLs to find the patch description and put that into the patch.
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I.e., the patch (series) and its description should be self-contained.
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This benefits both the maintainers and reviewers. Some reviewers
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probably didn't even receive earlier versions of the patch.
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Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
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instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
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to do frotz", as if you are giving orders to the codebase to change
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its behaviour.
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If the patch fixes a logged bug entry, refer to that bug entry by
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number and URL. If the patch follows from a mailing list discussion,
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give a URL to the mailing list archive; use the https://lkml.kernel.org/
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redirector with a Message-Id, to ensure that the links cannot become
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stale.
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However, try to make your explanation understandable without external
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resources. In addition to giving a URL to a mailing list archive or
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bug, summarize the relevant points of the discussion that led to the
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patch as submitted.
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If you want to refer to a specific commit, don't just refer to the
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SHA-1 ID of the commit. Please also include the oneline summary of
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the commit, to make it easier for reviewers to know what it is about.
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Example:
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Commit e21d2170f36602ae2708 ("video: remove unnecessary
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platform_set_drvdata()") removed the unnecessary
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platform_set_drvdata(), but left the variable "dev" unused,
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delete it.
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You should also be sure to use at least the first twelve characters of the
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SHA-1 ID. The kernel repository holds a *lot* of objects, making
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collisions with shorter IDs a real possibility. Bear in mind that, even if
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there is no collision with your six-character ID now, that condition may
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change five years from now.
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If your patch fixes a bug in a specific commit, e.g. you found an issue using
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git-bisect, please use the 'Fixes:' tag with the first 12 characters of the
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SHA-1 ID, and the one line summary. For example:
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Fixes: e21d2170f366 ("video: remove unnecessary platform_set_drvdata()")
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The following git-config settings can be used to add a pretty format for
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outputting the above style in the git log or git show commands
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[core]
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abbrev = 12
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[pretty]
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fixes = Fixes: %h (\"%s\")
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3) Separate your changes.
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-------------------------
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Separate each _logical change_ into a separate patch.
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For example, if your changes include both bug fixes and performance
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enhancements for a single driver, separate those changes into two
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or more patches. If your changes include an API update, and a new
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driver which uses that new API, separate those into two patches.
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On the other hand, if you make a single change to numerous files,
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group those changes into a single patch. Thus a single logical change
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is contained within a single patch.
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The point to remember is that each patch should make an easily understood
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change that can be verified by reviewers. Each patch should be justifiable
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on its own merits.
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If one patch depends on another patch in order for a change to be
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complete, that is OK. Simply note "this patch depends on patch X"
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in your patch description.
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When dividing your change into a series of patches, take special care to
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ensure that the kernel builds and runs properly after each patch in the
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series. Developers using "git bisect" to track down a problem can end up
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splitting your patch series at any point; they will not thank you if you
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introduce bugs in the middle.
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If you cannot condense your patch set into a smaller set of patches,
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then only post say 15 or so at a time and wait for review and integration.
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4) Style-check your changes.
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----------------------------
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Check your patch for basic style violations, details of which can be
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found in Documentation/CodingStyle. Failure to do so simply wastes
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the reviewers time and will get your patch rejected, probably
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without even being read.
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One significant exception is when moving code from one file to
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another -- in this case you should not modify the moved code at all in
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the same patch which moves it. This clearly delineates the act of
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moving the code and your changes. This greatly aids review of the
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actual differences and allows tools to better track the history of
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the code itself.
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Check your patches with the patch style checker prior to submission
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(scripts/checkpatch.pl). Note, though, that the style checker should be
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viewed as a guide, not as a replacement for human judgment. If your code
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looks better with a violation then its probably best left alone.
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The checker reports at three levels:
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- ERROR: things that are very likely to be wrong
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- WARNING: things requiring careful review
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- CHECK: things requiring thought
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You should be able to justify all violations that remain in your
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patch.
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5) Select the recipients for your patch.
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----------------------------------------
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You should always copy the appropriate subsystem maintainer(s) on any patch
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to code that they maintain; look through the MAINTAINERS file and the
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source code revision history to see who those maintainers are. The
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script scripts/get_maintainer.pl can be very useful at this step. If you
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cannot find a maintainer for the subsystem you are working on, Andrew
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Morton (akpm@linux-foundation.org) serves as a maintainer of last resort.
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You should also normally choose at least one mailing list to receive a copy
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of your patch set. linux-kernel@vger.kernel.org functions as a list of
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last resort, but the volume on that list has caused a number of developers
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to tune it out. Look in the MAINTAINERS file for a subsystem-specific
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list; your patch will probably get more attention there. Please do not
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spam unrelated lists, though.
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Many kernel-related lists are hosted on vger.kernel.org; you can find a
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list of them at http://vger.kernel.org/vger-lists.html. There are
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kernel-related lists hosted elsewhere as well, though.
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Do not send more than 15 patches at once to the vger mailing lists!!!
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Linus Torvalds is the final arbiter of all changes accepted into the
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Linux kernel. His e-mail address is <torvalds@linux-foundation.org>.
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He gets a lot of e-mail, and, at this point, very few patches go through
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Linus directly, so typically you should do your best to -avoid-
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sending him e-mail.
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If you have a patch that fixes an exploitable security bug, send that patch
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to security@kernel.org. For severe bugs, a short embargo may be considered
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to allow distributors to get the patch out to users; in such cases,
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obviously, the patch should not be sent to any public lists.
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Patches that fix a severe bug in a released kernel should be directed
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toward the stable maintainers by putting a line like this:
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Cc: stable@vger.kernel.org
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into the sign-off area of your patch (note, NOT an email recipient). You
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should also read Documentation/stable_kernel_rules.txt in addition to this
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file.
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Note, however, that some subsystem maintainers want to come to their own
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conclusions on which patches should go to the stable trees. The networking
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maintainer, in particular, would rather not see individual developers
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adding lines like the above to their patches.
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If changes affect userland-kernel interfaces, please send the MAN-PAGES
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maintainer (as listed in the MAINTAINERS file) a man-pages patch, or at
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least a notification of the change, so that some information makes its way
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into the manual pages. User-space API changes should also be copied to
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linux-api@vger.kernel.org.
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For small patches you may want to CC the Trivial Patch Monkey
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trivial@kernel.org which collects "trivial" patches. Have a look
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into the MAINTAINERS file for its current manager.
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Trivial patches must qualify for one of the following rules:
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Spelling fixes in documentation
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Spelling fixes for errors which could break grep(1)
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Warning fixes (cluttering with useless warnings is bad)
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Compilation fixes (only if they are actually correct)
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Runtime fixes (only if they actually fix things)
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Removing use of deprecated functions/macros
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Contact detail and documentation fixes
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Non-portable code replaced by portable code (even in arch-specific,
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since people copy, as long as it's trivial)
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Any fix by the author/maintainer of the file (ie. patch monkey
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in re-transmission mode)
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6) No MIME, no links, no compression, no attachments. Just plain text.
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-----------------------------------------------------------------------
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Linus and other kernel developers need to be able to read and comment
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on the changes you are submitting. It is important for a kernel
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developer to be able to "quote" your changes, using standard e-mail
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tools, so that they may comment on specific portions of your code.
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For this reason, all patches should be submitted by e-mail "inline".
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WARNING: Be wary of your editor's word-wrap corrupting your patch,
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if you choose to cut-n-paste your patch.
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Do not attach the patch as a MIME attachment, compressed or not.
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Many popular e-mail applications will not always transmit a MIME
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attachment as plain text, making it impossible to comment on your
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code. A MIME attachment also takes Linus a bit more time to process,
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decreasing the likelihood of your MIME-attached change being accepted.
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Exception: If your mailer is mangling patches then someone may ask
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you to re-send them using MIME.
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See Documentation/email-clients.txt for hints about configuring
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your e-mail client so that it sends your patches untouched.
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7) E-mail size.
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---------------
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Large changes are not appropriate for mailing lists, and some
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maintainers. If your patch, uncompressed, exceeds 300 kB in size,
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it is preferred that you store your patch on an Internet-accessible
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server, and provide instead a URL (link) pointing to your patch. But note
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that if your patch exceeds 300 kB, it almost certainly needs to be broken up
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anyway.
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8) Respond to review comments.
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------------------------------
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Your patch will almost certainly get comments from reviewers on ways in
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which the patch can be improved. You must respond to those comments;
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ignoring reviewers is a good way to get ignored in return. Review comments
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or questions that do not lead to a code change should almost certainly
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bring about a comment or changelog entry so that the next reviewer better
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understands what is going on.
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Be sure to tell the reviewers what changes you are making and to thank them
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for their time. Code review is a tiring and time-consuming process, and
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reviewers sometimes get grumpy. Even in that case, though, respond
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politely and address the problems they have pointed out.
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9) Don't get discouraged - or impatient.
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----------------------------------------
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After you have submitted your change, be patient and wait. Reviewers are
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busy people and may not get to your patch right away.
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Once upon a time, patches used to disappear into the void without comment,
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but the development process works more smoothly than that now. You should
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receive comments within a week or so; if that does not happen, make sure
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that you have sent your patches to the right place. Wait for a minimum of
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one week before resubmitting or pinging reviewers - possibly longer during
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busy times like merge windows.
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10) Include PATCH in the subject
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--------------------------------
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Due to high e-mail traffic to Linus, and to linux-kernel, it is common
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convention to prefix your subject line with [PATCH]. This lets Linus
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and other kernel developers more easily distinguish patches from other
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e-mail discussions.
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11) Sign your work
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------------------
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To improve tracking of who did what, especially with patches that can
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percolate to their final resting place in the kernel through several
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layers of maintainers, we've introduced a "sign-off" procedure on
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patches that are being emailed around.
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The sign-off is a simple line at the end of the explanation for the
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patch, which certifies that you wrote it or otherwise have the right to
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pass it on as an open-source patch. The rules are pretty simple: if you
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can certify the below:
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Developer's Certificate of Origin 1.1
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By making a contribution to this project, I certify that:
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(a) The contribution was created in whole or in part by me and I
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have the right to submit it under the open source license
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indicated in the file; or
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(b) The contribution is based upon previous work that, to the best
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of my knowledge, is covered under an appropriate open source
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license and I have the right under that license to submit that
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work with modifications, whether created in whole or in part
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by me, under the same open source license (unless I am
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permitted to submit under a different license), as indicated
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in the file; or
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(c) The contribution was provided directly to me by some other
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person who certified (a), (b) or (c) and I have not modified
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it.
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(d) I understand and agree that this project and the contribution
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are public and that a record of the contribution (including all
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personal information I submit with it, including my sign-off) is
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maintained indefinitely and may be redistributed consistent with
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this project or the open source license(s) involved.
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then you just add a line saying
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Signed-off-by: Random J Developer <random@developer.example.org>
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using your real name (sorry, no pseudonyms or anonymous contributions.)
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Some people also put extra tags at the end. They'll just be ignored for
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now, but you can do this to mark internal company procedures or just
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point out some special detail about the sign-off.
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If you are a subsystem or branch maintainer, sometimes you need to slightly
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modify patches you receive in order to merge them, because the code is not
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exactly the same in your tree and the submitters'. If you stick strictly to
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rule (c), you should ask the submitter to rediff, but this is a totally
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counter-productive waste of time and energy. Rule (b) allows you to adjust
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the code, but then it is very impolite to change one submitter's code and
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make him endorse your bugs. To solve this problem, it is recommended that
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you add a line between the last Signed-off-by header and yours, indicating
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the nature of your changes. While there is nothing mandatory about this, it
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seems like prepending the description with your mail and/or name, all
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enclosed in square brackets, is noticeable enough to make it obvious that
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you are responsible for last-minute changes. Example :
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Signed-off-by: Random J Developer <random@developer.example.org>
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[lucky@maintainer.example.org: struct foo moved from foo.c to foo.h]
|
|
Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org>
|
|
|
|
This practice 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 practice
|
|
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 a 3.x-stable release:
|
|
|
|
Date: Tue Oct 7 07:26:38 2014 -0400
|
|
|
|
libata: Un-break ATA blacklist
|
|
|
|
commit 1c40279960bcd7d52dbdf1d466b20d24b99176c8 upstream.
|
|
|
|
And here's what might appear in an older kernel once a patch is backported:
|
|
|
|
Date: Tue May 13 22:12:27 2008 +0200
|
|
|
|
wireless, airo: waitbusy() won't delay
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|
|
|
[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 troubleshoot bugs in your
|
|
tree.
|
|
|
|
|
|
12) 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
|
|
ask 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: (but note that it is usually better to ask for an
|
|
explicit ack).
|
|
|
|
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 - but it should indicate that this person was copied on the
|
|
patch. This tag documents that potentially interested parties
|
|
have been included in the discussion.
|
|
|
|
|
|
13) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
|
|
--------------------------------------------------------------------------
|
|
|
|
The Reported-by tag gives credit to people who find bugs and report them and it
|
|
hopefully inspires them to help us again in the future. Please note that if
|
|
the bug was reported in private, then ask for permission first before using the
|
|
Reported-by tag.
|
|
|
|
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
|
|
the mainline kernel.
|
|
|
|
(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 the kernel, 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 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.
|
|
|
|
A Suggested-by: tag indicates that the patch idea is suggested by the person
|
|
named and ensures credit to the person for the idea. Please note that this
|
|
tag should not be added without the reporter's permission, especially if the
|
|
idea was not posted in a public forum. That said, if we diligently credit our
|
|
idea reporters, they will, hopefully, be inspired to help us again in the
|
|
future.
|
|
|
|
A Fixes: tag indicates that the patch fixes an issue in a previous commit. It
|
|
is used to make it easy to determine where a bug originated, which can help
|
|
review a bug fix. This tag also assists the stable kernel team in determining
|
|
which stable kernel versions should receive your fix. This is the preferred
|
|
method for indicating a bug fixed by the patch. See #2 above for more details.
|
|
|
|
|
|
14) The canonical patch format
|
|
------------------------------
|
|
|
|
This section describes how the patch itself should be formatted. Note
|
|
that, if you have your patches stored in a git repository, proper patch
|
|
formatting can be had with "git format-patch". The tools cannot create
|
|
the necessary text, though, so read the instructions below anyway.
|
|
|
|
The canonical patch subject line is:
|
|
|
|
Subject: [PATCH 001/123] subsystem: summary phrase
|
|
|
|
The canonical patch message body contains the following:
|
|
|
|
- A "from" line specifying the patch author (only needed if the person
|
|
sending the patch is not the author).
|
|
|
|
- An empty line.
|
|
|
|
- The body of the explanation, line wrapped at 75 columns, 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 "subsystem" in the email's Subject should identify which
|
|
area or subsystem of the kernel is being patched.
|
|
|
|
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 git 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 tools such as "gitk" or "git log
|
|
--oneline".
|
|
|
|
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.
|
|
|
|
A couple of example Subjects:
|
|
|
|
Subject: [PATCH 2/5] ext2: improve scalability of bitmap searching
|
|
Subject: [PATCH v2 01/27] x86: fix eflags tracking
|
|
|
|
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.
|
|
|
|
If you are going to include a diffstat after the "---" marker, please
|
|
use diffstat options "-p 1 -w 70" so that filenames are listed from
|
|
the top of the kernel source tree and don't use too much horizontal
|
|
space (easily fit in 80 columns, maybe with some indentation). (git
|
|
generates appropriate diffstats by default.)
|
|
|
|
See more details on the proper patch format in the following
|
|
references.
|
|
|
|
15) Explicit In-Reply-To headers
|
|
--------------------------------
|
|
|
|
It can be helpful to manually add In-Reply-To: headers to a patch
|
|
(e.g., when using "git send-email") to associate the patch with
|
|
previous relevant discussion, e.g. to link a bug fix to the email with
|
|
the bug report. However, for a multi-patch series, it is generally
|
|
best to avoid using In-Reply-To: to link to older versions of the
|
|
series. This way multiple versions of the patch don't become an
|
|
unmanageable forest of references in email clients. If a link is
|
|
helpful, you can use the https://lkml.kernel.org/ redirector (e.g., in
|
|
the cover email text) to link to an earlier version of the patch series.
|
|
|
|
|
|
16) Sending "git pull" requests
|
|
-------------------------------
|
|
|
|
If you have a series of patches, it may be most convenient to have the
|
|
maintainer pull them directly into the subsystem repository with a
|
|
"git pull" operation. Note, however, that pulling patches from a developer
|
|
requires a higher degree of trust than taking patches from a mailing list.
|
|
As a result, many subsystem maintainers are reluctant to take pull
|
|
requests, especially from new, unknown developers. If in doubt you can use
|
|
the pull request as the cover letter for a normal posting of the patch
|
|
series, giving the maintainer the option of using either.
|
|
|
|
A pull request should have [GIT] or [PULL] in the subject line. The
|
|
request itself should include the repository name and the branch of
|
|
interest on a single line; it should look something like:
|
|
|
|
Please pull from
|
|
|
|
git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
|
|
|
|
to get these changes:
|
|
|
|
A pull request should also include an overall message saying what will be
|
|
included in the request, a "git shortlog" listing of the patches
|
|
themselves, and a diffstat showing the overall effect of the patch series.
|
|
The easiest way to get all this information together is, of course, to let
|
|
git do it for you with the "git request-pull" command.
|
|
|
|
Some maintainers (including Linus) want to see pull requests from signed
|
|
commits; that increases their confidence that the request actually came
|
|
from you. Linus, in particular, will not pull from public hosting sites
|
|
like GitHub in the absence of a signed tag.
|
|
|
|
The first step toward creating such tags is to make a GNUPG key and get it
|
|
signed by one or more core kernel developers. This step can be hard for
|
|
new developers, but there is no way around it. Attending conferences can
|
|
be a good way to find developers who can sign your key.
|
|
|
|
Once you have prepared a patch series in git that you wish to have somebody
|
|
pull, create a signed tag with "git tag -s". This will create a new tag
|
|
identifying the last commit in the series and containing a signature
|
|
created with your private key. You will also have the opportunity to add a
|
|
changelog-style message to the tag; this is an ideal place to describe the
|
|
effects of the pull request as a whole.
|
|
|
|
If the tree the maintainer will be pulling from is not the repository you
|
|
are working from, don't forget to push the signed tag explicitly to the
|
|
public tree.
|
|
|
|
When generating your pull request, use the signed tag as the target. A
|
|
command like this will do the trick:
|
|
|
|
git request-pull master git://my.public.tree/linux.git my-signed-tag
|
|
|
|
|
|
----------------------
|
|
SECTION 2 - REFERENCES
|
|
----------------------
|
|
|
|
Andrew Morton, "The perfect patch" (tpp).
|
|
<http://www.ozlabs.org/~akpm/stuff/tpp.txt>
|
|
|
|
Jeff Garzik, "Linux kernel patch submission format".
|
|
<http://linux.yyz.us/patch-format.html>
|
|
|
|
Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
|
|
<http://www.kroah.com/log/linux/maintainer.html>
|
|
<http://www.kroah.com/log/linux/maintainer-02.html>
|
|
<http://www.kroah.com/log/linux/maintainer-03.html>
|
|
<http://www.kroah.com/log/linux/maintainer-04.html>
|
|
<http://www.kroah.com/log/linux/maintainer-05.html>
|
|
<http://www.kroah.com/log/linux/maintainer-06.html>
|
|
|
|
NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
|
|
<https://lkml.org/lkml/2005/7/11/336>
|
|
|
|
Kernel Documentation/CodingStyle:
|
|
<Documentation/CodingStyle>
|
|
|
|
Linus Torvalds's mail on the canonical patch format:
|
|
<http://lkml.org/lkml/2005/4/7/183>
|
|
|
|
Andi Kleen, "On submitting kernel patches"
|
|
Some strategies to get difficult or controversial changes in.
|
|
http://halobates.de/on-submitting-patches.pdf
|
|
|
|
--
|