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.. _submittingpatches: |
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Submitting patches: the essential guide to getting your code into the kernel |
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============================================================================ |
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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/process/development-process.rst. Also, read |
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Documentation/process/submit-checklist.rst |
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for a list of items to check before submitting code. If you are submitting |
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a driver, also read Documentation/process/submitting-drivers.rst; for device |
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tree binding patches, read Documentation/process/submitting-patches.rst. |
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This documentation assumes that you're using ``git`` to prepare your patches. |
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If you're unfamiliar with ``git``, you would be well-advised to learn how to |
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use it, it will make your life as a kernel developer and in general much |
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easier. |
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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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.. _describe_changes: |
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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 :ref:`explicit_in_reply_to`. |
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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 :ref:`split_changes`. |
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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 |
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the SHA-1 ID, and the one line summary. Do not split the tag across multiple |
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lines, tags are exempt from the "wrap at 75 columns" rule in order to simplify |
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parsing scripts. For example:: |
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Fixes: 54a4f0239f2e ("KVM: MMU: make kvm_mmu_zap_page() return the number of pages it actually freed") |
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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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An example call:: |
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$ git log -1 --pretty=fixes 54a4f0239f2e |
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Fixes: 54a4f0239f2e ("KVM: MMU: make kvm_mmu_zap_page() return the number of pages it actually freed") |
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.. _split_changes: |
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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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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/process/coding-style.rst. |
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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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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 ([email protected]) 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. [email protected] should be used by default |
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for all patches, but the volume on that list has caused a number of |
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developers to tune it out. Look in the MAINTAINERS file for a |
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subsystem-specific list; your patch will probably get more attention there. |
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Please do not 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 <[email protected]>. |
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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 [email protected]. 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. See also |
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Documentation/admin-guide/security-bugs.rst. |
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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: [email protected] |
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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/process/stable-kernel-rules.rst |
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in addition to this document. |
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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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[email protected]. |
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For small patches you may want to CC the Trivial Patch Monkey |
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[email protected] 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 :manpage:`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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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". The |
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easiest way to do this is with ``git send-email``, which is strongly |
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recommended. An interactive tutorial for ``git send-email`` is available at |
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https://git-send-email.io. |
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If you choose not to use ``git send-email``: |
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.. warning:: |
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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/process/email-clients.rst for hints about configuring |
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your e-mail client so that it sends your patches untouched. |
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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, in the form of a reply to your email. You must |
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respond to those comments; ignoring reviewers is a good way to get ignored in |
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return. You can simply reply to their emails to answer their comments. Review |
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comments 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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See Documentation/process/email-clients.rst for recommendations on email |
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clients and mailing list etiquette. |
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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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It's also ok to resend the patch or the patch series after a couple of |
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weeks with the word "RESEND" added to the subject line:: |
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[PATCH Vx RESEND] sub/sys: Condensed patch summary |
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Don't add "RESEND" when you are submitting a modified version of your |
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patch or patch series - "RESEND" only applies to resubmission of a |
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patch or patch series which have not been modified in any way from the |
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previous submission. |
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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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``git send-email`` will do this for you automatically. |
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Sign your work - the Developer's Certificate of Origin |
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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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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
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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 <[email protected]> |
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using your real name (sorry, no pseudonyms or anonymous contributions.) |
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This will be done for you automatically if you use ``git commit -s``. |
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Reverts should also include "Signed-off-by". ``git revert -s`` does that |
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for you. |
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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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Any further SoBs (Signed-off-by:'s) following the author's SoB are from |
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people handling and transporting the patch, but were not involved in its |
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development. SoB chains should reflect the **real** route a patch took |
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as it was propagated to the maintainers and ultimately to Linus, with |
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the first SoB entry signalling primary authorship of a single author. |
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When to use Acked-by:, Cc:, and Co-developed-by: |
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------------------------------------------------ |
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The Signed-off-by: tag indicates that the signer was involved in the |
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development of the patch, or that he/she was in the patch's delivery path. |
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If a person was not directly involved in the preparation or handling of a |
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patch but wishes to signify and record their approval of it then they can |
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ask to have an Acked-by: line added to the patch's changelog. |
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Acked-by: is often used by the maintainer of the affected code when that |
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maintainer neither contributed to nor forwarded the patch. |
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Acked-by: is not as formal as Signed-off-by:. It is a record that the acker |
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has at least reviewed the patch and has indicated acceptance. Hence patch |
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mergers will sometimes manually convert an acker's "yep, looks good to me" |
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into an Acked-by: (but note that it is usually better to ask for an |
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explicit ack). |
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Acked-by: does not necessarily indicate acknowledgement of the entire patch. |
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For example, if a patch affects multiple subsystems and has an Acked-by: from |
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one subsystem maintainer then this usually indicates acknowledgement of just |
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the part which affects that maintainer's code. Judgement should be used here. |
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When in doubt people should refer to the original discussion in the mailing |
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list archives. |
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If a person has had the opportunity to comment on a patch, but has not |
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provided such comments, you may optionally add a ``Cc:`` tag to the patch. |
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This is the only tag which might be added without an explicit action by the |
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person it names - but it should indicate that this person was copied on the |
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patch. This tag documents that potentially interested parties |
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have been included in the discussion. |
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Co-developed-by: states that the patch was co-created by multiple developers; |
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it is used to give attribution to co-authors (in addition to the author |
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attributed by the From: tag) when several people work on a single patch. Since |
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Co-developed-by: denotes authorship, every Co-developed-by: must be immediately |
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followed by a Signed-off-by: of the associated co-author. Standard sign-off |
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procedure applies, i.e. the ordering of Signed-off-by: tags should reflect the |
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chronological history of the patch insofar as possible, regardless of whether |
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the author is attributed via From: or Co-developed-by:. Notably, the last |
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Signed-off-by: must always be that of the developer submitting the patch. |
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Note, the From: tag is optional when the From: author is also the person (and |
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email) listed in the From: line of the email header. |
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Example of a patch submitted by the From: author:: |
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<changelog> |
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Co-developed-by: First Co-Author <[email protected]> |
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Signed-off-by: First Co-Author <[email protected]> |
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Co-developed-by: Second Co-Author <[email protected]> |
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Signed-off-by: Second Co-Author <[email protected]> |
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Signed-off-by: From Author <[email protected]> |
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Example of a patch submitted by a Co-developed-by: author:: |
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From: From Author <[email protected]> |
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<changelog> |
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Co-developed-by: Random Co-Author <[email protected]> |
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Signed-off-by: Random Co-Author <[email protected]> |
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Signed-off-by: From Author <[email protected]> |
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Co-developed-by: Submitting Co-Author <[email protected]> |
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Signed-off-by: Submitting Co-Author <[email protected]> |
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Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes: |
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---------------------------------------------------------------------- |
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The Reported-by tag gives credit to people who find bugs and report them and it |
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hopefully inspires them to help us again in the future. Please note that if |
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the bug was reported in private, then ask for permission first before using the |
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Reported-by tag. |
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A Tested-by: tag indicates that the patch has been successfully tested (in |
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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. |
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Reviewed-by:, instead, indicates that the patch has been reviewed and found |
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acceptable according to the Reviewer's Statement: |
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Reviewer's statement of oversight |
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
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By offering my Reviewed-by: tag, I state that: |
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(a) I have carried out a technical review of this patch to |
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evaluate its appropriateness and readiness for inclusion into |
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the mainline kernel. |
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(b) Any problems, concerns, or questions relating to the patch |
|
have been communicated back to the submitter. I am satisfied |
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with the submitter's response to my comments. |
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(c) While there may be things that could be improved with this |
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submission, I believe that it is, at this time, (1) a |
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worthwhile modification to the kernel, and (2) free of known |
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issues which would argue against its inclusion. |
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(d) While I have reviewed the patch and believe it to be sound, I |
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do not (unless explicitly stated elsewhere) make any |
|
warranties or guarantees that it will achieve its stated |
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purpose or function properly in any given situation. |
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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 |
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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. |
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Both Tested-by and Reviewed-by tags, once received on mailing list from tester |
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or reviewer, should be added by author to the applicable patches when sending |
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next versions. However if the patch has changed substantially in following |
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version, these tags might not be applicable anymore and thus should be removed. |
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Usually removal of someone's Tested-by or Reviewed-by tags should be mentioned |
|
in the patch changelog (after the '---' separator). |
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A Suggested-by: tag indicates that the patch idea is suggested by the person |
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named and ensures credit to the person for the idea. Please note that this |
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tag should not be added without the reporter's permission, especially if the |
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idea was not posted in a public forum. That said, if we diligently credit our |
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idea reporters, they will, hopefully, be inspired to help us again in the |
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future. |
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A Fixes: tag indicates that the patch fixes an issue in a previous commit. It |
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is used to make it easy to determine where a bug originated, which can help |
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review a bug fix. This tag also assists the stable kernel team in determining |
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which stable kernel versions should receive your fix. This is the preferred |
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method for indicating a bug fixed by the patch. See :ref:`describe_changes` |
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for more details. |
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Note: Attaching a Fixes: tag does not subvert the stable kernel rules |
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process nor the requirement to Cc: [email protected] on all stable |
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patch candidates. For more information, please read |
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Documentation/process/stable-kernel-rules.rst. |
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.. _the_canonical_patch_format: |
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The canonical patch format |
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-------------------------- |
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This section describes how the patch itself should be formatted. Note |
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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 |
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the necessary text, though, so read the instructions below anyway. |
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The canonical patch subject line is:: |
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Subject: [PATCH 001/123] subsystem: summary phrase |
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The canonical patch message body contains the following: |
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- A ``from`` line specifying the patch author, followed by an empty |
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line (only needed if the person sending the patch is not the author). |
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- The body of the explanation, line wrapped at 75 columns, which will |
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be copied to the permanent changelog to describe this patch. |
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- An empty line. |
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- The ``Signed-off-by:`` lines, described above, which will |
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also go in the changelog. |
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- A marker line containing simply ``---``. |
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- Any additional comments not suitable for the changelog. |
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- The actual patch (``diff`` output). |
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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, |
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the numerical and alphabetic sort is the same. |
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The ``subsystem`` in the email's Subject should identify which |
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area or subsystem of the kernel is being patched. |
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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). |
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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``. |
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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. |
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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. |
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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. |
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Here are some good example Subjects:: |
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Subject: [PATCH 2/5] ext2: improve scalability of bitmap searching |
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Subject: [PATCH v2 01/27] x86: fix eflags tracking |
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Subject: [PATCH v2] sub/sys: Condensed patch summary |
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Subject: [PATCH v2 M/N] sub/sys: Condensed patch summary |
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The ``from`` line must be the very first line in the message body, |
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and has the form: |
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From: Patch Author <[email protected]> |
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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. |
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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.) are especially useful for |
|
people who might be searching the commit logs looking for the applicable |
|
patch. The text should be written in such detail so that when read |
|
weeks, months or even years later, it can give the reader the needed |
|
details to grasp the reasoning for **why** the patch was created. |
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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. |
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The ``---`` marker line serves the essential purpose of marking for |
|
patch handling tools where the changelog message ends. |
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|
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. 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.) |
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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. |
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Please put this information **after** the ``---`` line which separates |
|
the changelog from the rest of the patch. The version information is |
|
not part of the changelog which gets committed to the git tree. It is |
|
additional information for the reviewers. If it's placed above the |
|
commit tags, it needs manual interaction to remove it. If it is below |
|
the separator line, it gets automatically stripped off when applying the |
|
patch:: |
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<commit message> |
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... |
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Signed-off-by: Author <author@mail> |
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--- |
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V2 -> V3: Removed redundant helper function |
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V1 -> V2: Cleaned up coding style and addressed review comments |
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path/to/file | 5+++-- |
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... |
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See more details on the proper patch format in the following |
|
references. |
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Backtraces in commit mesages |
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
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|
Backtraces help document the call chain leading to a problem. However, |
|
not all backtraces are helpful. For example, early boot call chains are |
|
unique and obvious. Copying the full dmesg output verbatim, however, |
|
adds distracting information like timestamps, module lists, register and |
|
stack dumps. |
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Therefore, the most useful backtraces should distill the relevant |
|
information from the dump, which makes it easier to focus on the real |
|
issue. Here is an example of a well-trimmed backtrace:: |
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unchecked MSR access error: WRMSR to 0xd51 (tried to write 0x0000000000000064) |
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at rIP: 0xffffffffae059994 (native_write_msr+0x4/0x20) |
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Call Trace: |
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mba_wrmsr |
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update_domains |
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rdtgroup_mkdir |
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.. _explicit_in_reply_to: |
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|
|
Explicit In-Reply-To headers |
|
---------------------------- |
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|
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. |
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Providing base tree information |
|
------------------------------- |
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|
When other developers receive your patches and start the review process, |
|
it is often useful for them to know where in the tree history they |
|
should place your work. This is particularly useful for automated CI |
|
processes that attempt to run a series of tests in order to establish |
|
the quality of your submission before the maintainer starts the review. |
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|
|
If you are using ``git format-patch`` to generate your patches, you can |
|
automatically include the base tree information in your submission by |
|
using the ``--base`` flag. The easiest and most convenient way to use |
|
this option is with topical branches:: |
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|
$ git checkout -t -b my-topical-branch master |
|
Branch 'my-topical-branch' set up to track local branch 'master'. |
|
Switched to a new branch 'my-topical-branch' |
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|
|
[perform your edits and commits] |
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|
$ git format-patch --base=auto --cover-letter -o outgoing/ master |
|
outgoing/0000-cover-letter.patch |
|
outgoing/0001-First-Commit.patch |
|
outgoing/... |
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|
|
When you open ``outgoing/0000-cover-letter.patch`` for editing, you will |
|
notice that it will have the ``base-commit:`` trailer at the very |
|
bottom, which provides the reviewer and the CI tools enough information |
|
to properly perform ``git am`` without worrying about conflicts:: |
|
|
|
$ git checkout -b patch-review [base-commit-id] |
|
Switched to a new branch 'patch-review' |
|
$ git am patches.mbox |
|
Applying: First Commit |
|
Applying: ... |
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|
Please see ``man git-format-patch`` for more information about this |
|
option. |
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|
|
.. note:: |
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|
|
The ``--base`` feature was introduced in git version 2.9.0. |
|
|
|
If you are not using git to format your patches, you can still include |
|
the same ``base-commit`` trailer to indicate the commit hash of the tree |
|
on which your work is based. You should add it either in the cover |
|
letter or in the first patch of the series and it should be placed |
|
either below the ``---`` line or at the very bottom of all other |
|
content, right before your email signature. |
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|
|
|
|
References |
|
---------- |
|
|
|
Andrew Morton, "The perfect patch" (tpp). |
|
<https://www.ozlabs.org/~akpm/stuff/tpp.txt> |
|
|
|
Jeff Garzik, "Linux kernel patch submission format". |
|
<https://web.archive.org/web/20180829112450/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> |
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|
|
<http://www.kroah.com/log/linux/maintainer-02.html> |
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|
|
<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> |
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|
|
<http://www.kroah.com/log/linux/maintainer-06.html> |
|
|
|
NO!!!! No more huge patch bombs to [email protected] people! |
|
<https://lore.kernel.org/r/[email protected]> |
|
|
|
Kernel Documentation/process/coding-style.rst |
|
|
|
Linus Torvalds's mail on the canonical patch format: |
|
<https://lore.kernel.org/r/[email protected]> |
|
|
|
Andi Kleen, "On submitting kernel patches" |
|
Some strategies to get difficult or controversial changes in. |
|
|
|
http://halobates.de/on-submitting-patches.pdf
|
|
|