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Diffstat (limited to 'Documentation/maintainer')
| -rw-r--r-- | Documentation/maintainer/configure-git.rst | 64 | ||||
| -rw-r--r-- | Documentation/maintainer/index.rst | 17 | ||||
| -rw-r--r-- | Documentation/maintainer/maintainer-entry-profile.rst | 104 | ||||
| -rw-r--r-- | Documentation/maintainer/modifying-patches.rst | 50 | ||||
| -rw-r--r-- | Documentation/maintainer/pull-requests.rst | 178 | ||||
| -rw-r--r-- | Documentation/maintainer/rebasing-and-merging.rst | 226 |
6 files changed, 639 insertions, 0 deletions
diff --git a/Documentation/maintainer/configure-git.rst b/Documentation/maintainer/configure-git.rst new file mode 100644 index 000000000..80ae5030a --- /dev/null +++ b/Documentation/maintainer/configure-git.rst @@ -0,0 +1,64 @@ +.. _configuregit: + +Configure Git +============= + +This chapter describes maintainer level git configuration. + +Tagged branches used in :ref:`Documentation/maintainer/pull-requests.rst +<pullrequests>` should be signed with the developers public GPG key. Signed +tags can be created by passing the ``-u`` flag to ``git tag``. However, +since you would *usually* use the same key for the same project, you can +set it once with +:: + + git config user.signingkey "keyname" + +Alternatively, edit your ``.git/config`` or ``~/.gitconfig`` file by hand: +:: + + [user] + name = Jane Developer + email = jd@domain.org + signingkey = jd@domain.org + +You may need to tell ``git`` to use ``gpg2`` +:: + + [gpg] + program = /path/to/gpg2 + +You may also like to tell ``gpg`` which ``tty`` to use (add to your shell rc file) +:: + + export GPG_TTY=$(tty) + + +Creating commit links to lore.kernel.org +---------------------------------------- + +The web site http://lore.kernel.org is meant as a grand archive of all mail +list traffic concerning or influencing the kernel development. Storing archives +of patches here is a recommended practice, and when a maintainer applies a +patch to a subsystem tree, it is a good idea to provide a Link: tag with a +reference back to the lore archive so that people that browse the commit +history can find related discussions and rationale behind a certain change. +The link tag will look like this: + + Link: https://lore.kernel.org/r/<message-id> + +This can be configured to happen automatically any time you issue ``git am`` +by adding the following hook into your git: + +.. code-block:: none + + $ git config am.messageid true + $ cat >.git/hooks/applypatch-msg <<'EOF' + #!/bin/sh + . git-sh-setup + perl -pi -e 's|^Message-Id:\s*<?([^>]+)>?$|Link: https://lore.kernel.org/r/$1|g;' "$1" + test -x "$GIT_DIR/hooks/commit-msg" && + exec "$GIT_DIR/hooks/commit-msg" ${1+"$@"} + : + EOF + $ chmod a+x .git/hooks/applypatch-msg diff --git a/Documentation/maintainer/index.rst b/Documentation/maintainer/index.rst new file mode 100644 index 000000000..f0a60435b --- /dev/null +++ b/Documentation/maintainer/index.rst @@ -0,0 +1,17 @@ +========================== +Kernel Maintainer Handbook +========================== + +This document is the humble beginning of a manual for kernel maintainers. +There is a lot yet to go here! Please feel free to propose (and write) +additions to this manual. + +.. toctree:: + :maxdepth: 2 + + configure-git + rebasing-and-merging + pull-requests + maintainer-entry-profile + modifying-patches + diff --git a/Documentation/maintainer/maintainer-entry-profile.rst b/Documentation/maintainer/maintainer-entry-profile.rst new file mode 100644 index 000000000..b7a627d6c --- /dev/null +++ b/Documentation/maintainer/maintainer-entry-profile.rst @@ -0,0 +1,104 @@ +.. _maintainerentryprofile: + +Maintainer Entry Profile +======================== + +The Maintainer Entry Profile supplements the top-level process documents +(submitting-patches, submitting drivers...) with +subsystem/device-driver-local customs as well as details about the patch +submission life-cycle. A contributor uses this document to level set +their expectations and avoid common mistakes; maintainers may use these +profiles to look across subsystems for opportunities to converge on +common practices. + + +Overview +-------- +Provide an introduction to how the subsystem operates. While MAINTAINERS +tells the contributor where to send patches for which files, it does not +convey other subsystem-local infrastructure and mechanisms that aid +development. + +Example questions to consider: + +- Are there notifications when patches are applied to the local tree, or + merged upstream? +- Does the subsystem have a patchwork instance? Are patchwork state + changes notified? +- Any bots or CI infrastructure that watches the list, or automated + testing feedback that the subsystem uses to gate acceptance? +- Git branches that are pulled into -next? +- What branch should contributors submit against? +- Links to any other Maintainer Entry Profiles? For example a + device-driver may point to an entry for its parent subsystem. This makes + the contributor aware of obligations a maintainer may have for + other maintainers in the submission chain. + + +Submit Checklist Addendum +------------------------- +List mandatory and advisory criteria, beyond the common "submit-checklist", +for a patch to be considered healthy enough for maintainer attention. +For example: "pass checkpatch.pl with no errors, or warning. Pass the +unit test detailed at $URI". + +The Submit Checklist Addendum can also include details about the status +of related hardware specifications. For example, does the subsystem +require published specifications at a certain revision before patches +will be considered. + + +Key Cycle Dates +--------------- +One of the common misunderstandings of submitters is that patches can be +sent at any time before the merge window closes and can still be +considered for the next -rc1. The reality is that most patches need to +be settled in soaking in linux-next in advance of the merge window +opening. Clarify for the submitter the key dates (in terms of -rc release +week) that patches might be considered for merging and when patches need to +wait for the next -rc. At a minimum: + +- Last -rc for new feature submissions: + New feature submissions targeting the next merge window should have + their first posting for consideration before this point. Patches that + are submitted after this point should be clear that they are targeting + the NEXT+1 merge window, or should come with sufficient justification + why they should be considered on an expedited schedule. A general + guideline is to set expectation with contributors that new feature + submissions should appear before -rc5. + +- Last -rc to merge features: Deadline for merge decisions + Indicate to contributors the point at which an as yet un-applied patch + set will need to wait for the NEXT+1 merge window. Of course there is no + obligation to ever accept any given patchset, but if the review has not + concluded by this point the expectation is the contributor should wait and + resubmit for the following merge window. + +Optional: + +- First -rc at which the development baseline branch, listed in the + overview section, should be considered ready for new submissions. + + +Review Cadence +-------------- +One of the largest sources of contributor angst is how soon to ping +after a patchset has been posted without receiving any feedback. In +addition to specifying how long to wait before a resubmission this +section can also indicate a preferred style of update like, resend the +full series, or privately send a reminder email. This section might also +list how review works for this code area and methods to get feedback +that are not directly from the maintainer. + +Existing profiles +----------------- + +For now, existing maintainer profiles are listed here; we will likely want +to do something different in the near future. + +.. toctree:: + :maxdepth: 1 + + ../doc-guide/maintainer-profile + ../nvdimm/maintainer-entry-profile + ../riscv/patch-acceptance diff --git a/Documentation/maintainer/modifying-patches.rst b/Documentation/maintainer/modifying-patches.rst new file mode 100644 index 000000000..58385d2e8 --- /dev/null +++ b/Documentation/maintainer/modifying-patches.rst @@ -0,0 +1,50 @@ +.. _modifyingpatches: + +Modifying Patches +================= + +If you are a subsystem or branch maintainer, sometimes you need to slightly +modify patches you receive in order to merge them, because the code is not +exactly the same in your tree and the submitters'. If you stick strictly to +rule (c) of the developers certificate of origin, you should ask the submitter +to rediff, but this is a totally counter-productive waste of time and energy. +Rule (b) allows you to adjust the code, but then it is very impolite to change +one submitters code and make him endorse your bugs. To solve this problem, it +is recommended that you add a line between the last Signed-off-by header and +yours, indicating the nature of your changes. While there is nothing mandatory +about this, it seems like prepending the description with your mail and/or +name, all enclosed in square brackets, is noticeable enough to make it obvious +that you are responsible for last-minute changes. Example:: + + Signed-off-by: Random J Developer <random@developer.example.org> + [lucky@maintainer.example.org: struct foo moved from foo.c to foo.h] + Signed-off-by: Lucky K Maintainer <lucky@maintainer.example.org> + +This 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 + + [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. diff --git a/Documentation/maintainer/pull-requests.rst b/Documentation/maintainer/pull-requests.rst new file mode 100644 index 000000000..1a2f99b67 --- /dev/null +++ b/Documentation/maintainer/pull-requests.rst @@ -0,0 +1,178 @@ +.. _pullrequests: + +Creating Pull Requests +====================== + +This chapter describes how maintainers can create and submit pull requests +to other maintainers. This is useful for transferring changes from one +maintainers tree to another maintainers tree. + +This document was written by Tobin C. Harding (who at that time, was not an +experienced maintainer) primarily from comments made by Greg Kroah-Hartman +and Linus Torvalds on LKML. Suggestions and fixes by Jonathan Corbet and +Mauro Carvalho Chehab. Misrepresentation was unintentional but inevitable, +please direct abuse to Tobin C. Harding <me@tobin.cc>. + +Original email thread:: + + http://lkml.kernel.org/r/20171114110500.GA21175@kroah.com + + +Create Branch +------------- + +To start with you will need to have all the changes you wish to include in +the pull request on a separate branch. Typically you will base this branch +off of a branch in the developers tree whom you intend to send the pull +request to. + +In order to create the pull request you must first tag the branch that you +have just created. It is recommended that you choose a meaningful tag name, +in a way that you and others can understand, even after some time. A good +practice is to include in the name an indicator of the subsystem of origin +and the target kernel version. + +Greg offers the following. A pull request with miscellaneous stuff for +drivers/char, to be applied at the Kernel version 4.15-rc1 could be named +as ``char-misc-4.15-rc1``. If such tag would be produced from a branch +named ``char-misc-next``, you would be using the following command:: + + git tag -s char-misc-4.15-rc1 char-misc-next + +that will create a signed tag called ``char-misc-4.15-rc1`` based on the +last commit in the ``char-misc-next`` branch, and sign it with your gpg key +(see :ref:`Documentation/maintainer/configure-git.rst <configuregit>`). + +Linus will only accept pull requests based on a signed tag. Other +maintainers may differ. + +When you run the above command ``git`` will drop you into an editor and ask +you to describe the tag. In this case, you are describing a pull request, +so outline what is contained here, why it should be merged, and what, if +any, testing has been done. All of this information will end up in the tag +itself, and then in the merge commit that the maintainer makes if/when they +merge the pull request. So write it up well, as it will be in the kernel +tree for forever. + +As said by Linus:: + + Anyway, at least to me, the important part is the *message*. I want + to understand what I'm pulling, and why I should pull it. I also + want to use that message as the message for the merge, so it should + not just make sense to me, but make sense as a historical record + too. + + Note that if there is something odd about the pull request, that + should very much be in the explanation. If you're touching files + that you don't maintain, explain _why_. I will see it in the + diffstat anyway, and if you didn't mention it, I'll just be extra + suspicious. And when you send me new stuff after the merge window + (or even bug-fixes, but ones that look scary), explain not just + what they do and why they do it, but explain the _timing_. What + happened that this didn't go through the merge window.. + + I will take both what you write in the email pull request _and_ in + the signed tag, so depending on your workflow, you can either + describe your work in the signed tag (which will also automatically + make it into the pull request email), or you can make the signed + tag just a placeholder with nothing interesting in it, and describe + the work later when you actually send me the pull request. + + And yes, I will edit the message. Partly because I tend to do just + trivial formatting (the whole indentation and quoting etc), but + partly because part of the message may make sense for me at pull + time (describing the conflicts and your personal issues for sending + it right now), but may not make sense in the context of a merge + commit message, so I will try to make it all make sense. I will + also fix any speeling mistaeks and bad grammar I notice, + particularly for non-native speakers (but also for native ones + ;^). But I may miss some, or even add some. + + Linus + +Greg gives, as an example pull request:: + + Char/Misc patches for 4.15-rc1 + + Here is the big char/misc patch set for the 4.15-rc1 merge window. + Contained in here is the normal set of new functions added to all + of these crazy drivers, as well as the following brand new + subsystems: + - time_travel_controller: Finally a set of drivers for the + latest time travel bus architecture that provides i/o to + the CPU before it asked for it, allowing uninterrupted + processing + - relativity_shifters: due to the affect that the + time_travel_controllers have on the overall system, there + was a need for a new set of relativity shifter drivers to + accommodate the newly formed black holes that would + threaten to suck CPUs into them. This subsystem handles + this in a way to successfully neutralize the problems. + There is a Kconfig option to force these to be enabled + when needed, so problems should not occur. + + All of these patches have been successfully tested in the latest + linux-next releases, and the original problems that it found have + all been resolved (apologies to anyone living near Canberra for the + lack of the Kconfig options in the earlier versions of the + linux-next tree creations.) + + Signed-off-by: Your-name-here <your_email@domain> + + +The tag message format is just like a git commit id. One line at the top +for a "summary subject" and be sure to sign-off at the bottom. + +Now that you have a local signed tag, you need to push it up to where it +can be retrieved:: + + git push origin char-misc-4.15-rc1 + + +Create Pull Request +------------------- + +The last thing to do is create the pull request message. ``git`` handily +will do this for you with the ``git request-pull`` command, but it needs a +bit of help determining what you want to pull, and on what to base the pull +against (to show the correct changes to be pulled and the diffstat). The +following command(s) will generate a pull request:: + + git request-pull master git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git/ char-misc-4.15-rc1 + +Quoting Greg:: + + This is asking git to compare the difference from the + 'char-misc-4.15-rc1' tag location, to the head of the 'master' + branch (which in my case points to the last location in Linus's + tree that I diverged from, usually a -rc release) and to use the + git:// protocol to pull from. If you wish to use https://, that + can be used here instead as well (but note that some people behind + firewalls will have problems with https git pulls). + + If the char-misc-4.15-rc1 tag is not present in the repo that I am + asking to be pulled from, git will complain saying it is not there, + a handy way to remember to actually push it to a public location. + + The output of 'git request-pull' will contain the location of the + git tree and specific tag to pull from, and the full text + description of that tag (which is why you need to provide good + information in that tag). It will also create a diffstat of the + pull request, and a shortlog of the individual commits that the + pull request will provide. + +Linus responded that he tends to prefer the ``git://`` protocol. Other +maintainers may have different preferences. Also, note that if you are +creating pull requests without a signed tag then ``https://`` may be a +better choice. Please see the original thread for the full discussion. + + +Submit Pull Request +------------------- + +A pull request is submitted in the same way as an ordinary patch. Send as +inline email to the maintainer and CC LKML and any sub-system specific +lists if required. Pull requests to Linus typically have a subject line +something like:: + + [GIT PULL] <subsystem> changes for v4.15-rc1 diff --git a/Documentation/maintainer/rebasing-and-merging.rst b/Documentation/maintainer/rebasing-and-merging.rst new file mode 100644 index 000000000..09f988e7f --- /dev/null +++ b/Documentation/maintainer/rebasing-and-merging.rst @@ -0,0 +1,226 @@ +.. SPDX-License-Identifier: GPL-2.0 + +==================== +Rebasing and merging +==================== + +Maintaining a subsystem, as a general rule, requires a familiarity with the +Git source-code management system. Git is a powerful tool with a lot of +features; as is often the case with such tools, there are right and wrong +ways to use those features. This document looks in particular at the use +of rebasing and merging. Maintainers often get in trouble when they use +those tools incorrectly, but avoiding problems is not actually all that +hard. + +One thing to be aware of in general is that, unlike many other projects, +the kernel community is not scared by seeing merge commits in its +development history. Indeed, given the scale of the project, avoiding +merges would be nearly impossible. Some problems encountered by +maintainers result from a desire to avoid merges, while others come from +merging a little too often. + +Rebasing +======== + +"Rebasing" is the process of changing the history of a series of commits +within a repository. There are two different types of operations that are +referred to as rebasing since both are done with the ``git rebase`` +command, but there are significant differences between them: + + - Changing the parent (starting) commit upon which a series of patches is + built. For example, a rebase operation could take a patch set built on + the previous kernel release and base it, instead, on the current + release. We'll call this operation "reparenting" in the discussion + below. + + - Changing the history of a set of patches by fixing (or deleting) broken + commits, adding patches, adding tags to commit changelogs, or changing + the order in which commits are applied. In the following text, this + type of operation will be referred to as "history modification" + +The term "rebasing" will be used to refer to both of the above operations. +Used properly, rebasing can yield a cleaner and clearer development +history; used improperly, it can obscure that history and introduce bugs. + +There are a few rules of thumb that can help developers to avoid the worst +perils of rebasing: + + - History that has been exposed to the world beyond your private system + should usually not be changed. Others may have pulled a copy of your + tree and built on it; modifying your tree will create pain for them. If + work is in need of rebasing, that is usually a sign that it is not yet + ready to be committed to a public repository. + + That said, there are always exceptions. Some trees (linux-next being + a significant example) are frequently rebased by their nature, and + developers know not to base work on them. Developers will sometimes + expose an unstable branch for others to test with or for automated + testing services. If you do expose a branch that may be unstable in + this way, be sure that prospective users know not to base work on it. + + - Do not rebase a branch that contains history created by others. If you + have pulled changes from another developer's repository, you are now a + custodian of their history. You should not change it. With few + exceptions, for example, a broken commit in a tree like this should be + explicitly reverted rather than disappeared via history modification. + + - Do not reparent a tree without a good reason to do so. Just being on a + newer base or avoiding a merge with an upstream repository is not + generally a good reason. + + - If you must reparent a repository, do not pick some random kernel commit + as the new base. The kernel is often in a relatively unstable state + between release points; basing development on one of those points + increases the chances of running into surprising bugs. When a patch + series must move to a new base, pick a stable point (such as one of + the -rc releases) to move to. + + - Realize that reparenting a patch series (or making significant history + modifications) changes the environment in which it was developed and, + likely, invalidates much of the testing that was done. A reparented + patch series should, as a general rule, be treated like new code and + retested from the beginning. + +A frequent cause of merge-window trouble is when Linus is presented with a +patch series that has clearly been reparented, often to a random commit, +shortly before the pull request was sent. The chances of such a series +having been adequately tested are relatively low - as are the chances of +the pull request being acted upon. + +If, instead, rebasing is limited to private trees, commits are based on a +well-known starting point, and they are well tested, the potential for +trouble is low. + +Merging +======= + +Merging is a common operation in the kernel development process; the 5.1 +development cycle included 1,126 merge commits - nearly 9% of the total. +Kernel work is accumulated in over 100 different subsystem trees, each of +which may contain multiple topic branches; each branch is usually developed +independently of the others. So naturally, at least one merge will be +required before any given branch finds its way into an upstream repository. + +Many projects require that branches in pull requests be based on the +current trunk so that no merge commits appear in the history. The kernel +is not such a project; any rebasing of branches to avoid merges will, most +likely, lead to trouble. + +Subsystem maintainers find themselves having to do two types of merges: +from lower-level subsystem trees and from others, either sibling trees or +the mainline. The best practices to follow differ in those two situations. + +Merging from lower-level trees +------------------------------ + +Larger subsystems tend to have multiple levels of maintainers, with the +lower-level maintainers sending pull requests to the higher levels. Acting +on such a pull request will almost certainly generate a merge commit; that +is as it should be. In fact, subsystem maintainers may want to use +the --no-ff flag to force the addition of a merge commit in the rare cases +where one would not normally be created so that the reasons for the merge +can be recorded. The changelog for the merge should, for any kind of +merge, say *why* the merge is being done. For a lower-level tree, "why" is +usually a summary of the changes that will come with that pull. + +Maintainers at all levels should be using signed tags on their pull +requests, and upstream maintainers should verify the tags when pulling +branches. Failure to do so threatens the security of the development +process as a whole. + +As per the rules outlined above, once you have merged somebody else's +history into your tree, you cannot rebase that branch, even if you +otherwise would be able to. + +Merging from sibling or upstream trees +-------------------------------------- + +While merges from downstream are common and unremarkable, merges from other +trees tend to be a red flag when it comes time to push a branch upstream. +Such merges need to be carefully thought about and well justified, or +there's a good chance that a subsequent pull request will be rejected. + +It is natural to want to merge the master branch into a repository; this +type of merge is often called a "back merge". Back merges can help to make +sure that there are no conflicts with parallel development and generally +gives a warm, fuzzy feeling of being up-to-date. But this temptation +should be avoided almost all of the time. + +Why is that? Back merges will muddy the development history of your own +branch. They will significantly increase your chances of encountering bugs +from elsewhere in the community and make it hard to ensure that the work +you are managing is stable and ready for upstream. Frequent merges can +also obscure problems with the development process in your tree; they can +hide interactions with other trees that should not be happening (often) in +a well-managed branch. + +That said, back merges are occasionally required; when that happens, be +sure to document *why* it was required in the commit message. As always, +merge to a well-known stable point, rather than to some random commit. +Even then, you should not back merge a tree above your immediate upstream +tree; if a higher-level back merge is really required, the upstream tree +should do it first. + +One of the most frequent causes of merge-related trouble is when a +maintainer merges with the upstream in order to resolve merge conflicts +before sending a pull request. Again, this temptation is easy enough to +understand, but it should absolutely be avoided. This is especially true +for the final pull request: Linus is adamant that he would much rather see +merge conflicts than unnecessary back merges. Seeing the conflicts lets +him know where potential problem areas are. He does a lot of merges (382 +in the 5.1 development cycle) and has gotten quite good at conflict +resolution - often better than the developers involved. + +So what should a maintainer do when there is a conflict between their +subsystem branch and the mainline? The most important step is to warn +Linus in the pull request that the conflict will happen; if nothing else, +that demonstrates an awareness of how your branch fits into the whole. For +especially difficult conflicts, create and push a *separate* branch to show +how you would resolve things. Mention that branch in your pull request, +but the pull request itself should be for the unmerged branch. + +Even in the absence of known conflicts, doing a test merge before sending a +pull request is a good idea. It may alert you to problems that you somehow +didn't see from linux-next and helps to understand exactly what you are +asking upstream to do. + +Another reason for doing merges of upstream or another subsystem tree is to +resolve dependencies. These dependency issues do happen at times, and +sometimes a cross-merge with another tree is the best way to resolve them; +as always, in such situations, the merge commit should explain why the +merge has been done. Take a moment to do it right; people will read those +changelogs. + +Often, though, dependency issues indicate that a change of approach is +needed. Merging another subsystem tree to resolve a dependency risks +bringing in other bugs and should almost never be done. If that subsystem +tree fails to be pulled upstream, whatever problems it had will block the +merging of your tree as well. Preferable alternatives include agreeing +with the maintainer to carry both sets of changes in one of the trees or +creating a topic branch dedicated to the prerequisite commits that can be +merged into both trees. If the dependency is related to major +infrastructural changes, the right solution might be to hold the dependent +commits for one development cycle so that those changes have time to +stabilize in the mainline. + +Finally +======= + +It is relatively common to merge with the mainline toward the beginning of +the development cycle in order to pick up changes and fixes done elsewhere +in the tree. As always, such a merge should pick a well-known release +point rather than some random spot. If your upstream-bound branch has +emptied entirely into the mainline during the merge window, you can pull it +forward with a command like:: + + git merge v5.2-rc1^0 + +The "^0" will cause Git to do a fast-forward merge (which should be +possible in this situation), thus avoiding the addition of a spurious merge +commit. + +The guidelines laid out above are just that: guidelines. There will always +be situations that call out for a different solution, and these guidelines +should not prevent developers from doing the right thing when the need +arises. But one should always think about whether the need has truly +arisen and be prepared to explain why something abnormal needs to be done. |