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[PATCH v3 3/3] docs: rSTify the "SubmitAPatch" wiki
[PATCH v3 3/3] docs: rSTify the "SubmitAPatch" wiki
Wed, 10 Nov 2021 15:49:02 +0100
- The original wiki is here. I copied the wiki source into a .wiki
file, and used `pandoc` to convert it to rST:
$> pandoc -f Mediawiki -t rst submitting-a-patch.wiki -o
- The only minor touch-ups I did was to fix URLs. But 99%, it is a 1-1
(An example of a "touch-up": under the section "Patch emails must
include a Signed-off-by: line", I updated the "see SubmittingPatches
1.12" to "1.12) Sign your work")
- I have also converted a couple other related wiki pages (included in
this patch series) that were hyperlinked within the SubmitAPatch page,
or a page that it refers to:
- SubmitAPullRequest: https://wiki.qemu.org/Contribute/SubmitAPullRequest
- TrivialPatches: https://wiki.qemu.org/Contribute/TrivialPatches
- Over time, many people contributed to this wiki page; you can find all
the authors in the wiki history.
Signed-off-by: Kashyap Chamarthy <firstname.lastname@example.org>
docs/devel/index.rst | 1 +
docs/devel/submitting-a-patch.rst | 456 ++++++++++++++++++++++++++++++
2 files changed, 457 insertions(+)
create mode 100644 docs/devel/submitting-a-patch.rst
diff --git a/docs/devel/index.rst b/docs/devel/index.rst
index 816eb7b7b0..c3cfa9e41f 100644
@@ -47,3 +47,4 @@ modifying QEMU's source code.
diff --git a/docs/devel/submitting-a-patch.rst
new file mode 100644
@@ -0,0 +1,456 @@
+Submitting a Patch
+QEMU welcomes contributions of code (either fixing bugs or adding new
+functionality). However, we get a lot of patches, and so we have some
+guidelines about submitting patches. If you follow these, you'll help
+make our task of code review easier and your patch is likely to be
+This page seems very long, so if you are only trying to post a quick
+one-shot fix, the bare minimum we ask is that:
+- You **must** provide a Signed-off-by: line (this is a hard
+ requirement because it's how you say "I'm legally okay to contribute
+ this and happy for it to go into QEMU", modeled after the `Linux
+ policy.) ``git commit -s`` or ``git format-patch -s`` will add one.
+- All contributions to QEMU must be **sent as patches** to the
+ qemu-devel `mailing list <MailingLists>`__. Patch contributions
+ should not be posted on the bug tracker, posted on forums, or
+ externally hosted and linked to. (We have other mailing lists too,
+ but all patches must go to qemu-devel, possibly with a Cc: to another
+ list.) ``git send-email`` works best for delivering the patch without
+ mangling it (`hints for setting it
+ but attachments can be used as a last resort on a first-time
+- You must read replies to your message, and be willing to act on them.
+ Note, however, that maintainers are often willing to manually fix up
+ first-time contributions, since there is a learning curve involved in
+ making an ideal patch submission.
+You do not have to subscribe to post (list policy is to reply-to-all to
+preserve CCs and keep non-subscribers in the loop on the threads they
+start), although you may find it easier as a subscriber to pick up good
+ideas from other posts. If you do subscribe, be prepared for a high
+volume of email, often over one thousand messages in a week. The list is
+moderated; first-time posts from an email address (whether or not you
+subscribed) may be subject to some delay while waiting for a moderator
+to whitelist your address.
+The larger your contribution is, or if you plan on becoming a long-term
+contributor, then the more important the rest of this page becomes.
+Reading the table of contents below should already give you an idea of
+the basic requirements. Use the table of contents as a reference, and
+read the parts that you have doubts about.
+Writing your Patches
+Use the QEMU coding style
+You can run run *scripts/checkpatch.pl <patchfile>* before submitting to
+check that you are in compliance with our coding standards. Be aware
+that ``checkpatch.pl`` is not infallible, though, especially where C
+preprocessor macros are involved; use some common sense too. See also:
+- `QEMU Coding Style
+- `Automate a checkpatch run on
+Base patches against current git master
+There's no point submitting a patch which is based on a released version
+of QEMU because development will have moved on from then and it probably
+won't even apply to master. We only apply selected bugfixes to release
+branches and then only as backports once the code has gone into master.
+Split up long patches
+Split up longer patches into a patch series of logical code changes.
+Each change should compile and execute successfully. For instance, don't
+add a file to the makefile in patch one and then add the file itself in
+patch two. (This rule is here so that people can later use tools like
+```git bisect`` <http://git-scm.com/docs/git-bisect>`__ without hitting
+points in the commit history where QEMU doesn't work for reasons
+unrelated to the bug they're chasing.) Put documentation first, not
+last, so that someone reading the series can do a clean-room evaluation
+of the documentation, then validate that the code matched the
+documentation. A commit message that mentions "Also, ..." is often a
+good candidate for splitting into multiple patches. For more thoughts on
+properly splitting patches and writing good commit messages, see `this
+Make code motion patches easy to review
+If a series requires large blocks of code motion, there are tricks for
+making the refactoring easier to review. Split up the series so that
+semantic changes (or even function renames) are done in a separate patch
+from the raw code motion. Use a one-time setup of
+``git config diff.renames true; git config diff.algorithm patience``
+(Refer to `git-config <http://git-scm.com/docs/git-config>`__.) The
+``diff.renames`` property ensures file rename patches will be given in a
+more compact representation that focuses only on the differences across
+the file rename, instead of showing the entire old file as a deletion
+and the new file as an insertion. Meanwhile, the 'diff.algorithm'
+property ensures that extracting a non-contiguous subset of one file
+into a new file, but where all extracted parts occur in the same order
+both before and after the patch, will reduce churn in trying to treat
+unrelated ``}`` lines in the original file as separating hunks of
+Ideally, a code motion patch can be reviewed by doing::
+ git format-patch --stdout -1 > patch;
+ diff -u <(sed -n 's/^-//p' patch) <(sed -n 's/^\+//p' patch)
+to focus on the few changes that weren't wholesale code motion.
+Don't include irrelevant changes
+In particular, don't include formatting, coding style or whitespace
+changes to bits of code that would otherwise not be touched by the
+patch. (It's OK to fix coding style issues in the immediate area (few
+lines) of the lines you're changing.) If you think a section of code
+really does need a reindent or other large-scale style fix, submit this
+as a separate patch which makes no semantic changes; don't put it in the
+same patch as your bug fix.
+For smaller patches in less frequently changed areas of QEMU, consider
+using the `trivial patches process
+Write a meaningful commit message
+Commit messages should be meaningful and should stand on their own as a
+historical record of why the changes you applied were necessary or
+QEMU follows the usual standard for git commit messages: the first line
+(which becomes the email subject line) is "subsystem: single line
+summary of change". Whether the "single line summary of change" starts
+with a capital is a matter of taste, but we prefer that the summary does
+not end in ".". Look at ``git shortlog -30`` for an idea of sample
+subject lines. Then there is a blank line and a more detailed
+description of the patch, another blank and your Signed-off-by: line.
+Please do not use lines that are longer than 76 characters in your
+commit message (so that the text still shows up nicely with "git show"
+in a 80-columns terminal window).
+The body of the commit message is a good place to document why your
+change is important. Don't include comments like "This is a suggestion
+for fixing this bug" (they can go below the "---" line in the email so
+they don't go into the final commit message). Make sure the body of the
+commit message can be read in isolation even if the reader's mailer
+displays the subject line some distance apart (that is, a body that
+starts with "... so that" as a continuation of the subject line is
+harder to follow).
+Submitting your Patches
+CC the relevant maintainer
+Send patches both to the mailing list and CC the maintainer(s) of the
+files you are modifying. look in the MAINTAINERS file to find out who
+that is. Also try using scripts/get_maintainer.pl from the repository
+for learning the most common committers for the files you touched.
+ ~/src/qemu/scripts/get_maintainer.pl -f hw/ide/core.c
+In fact, you can automate this, via a one-time setup of ``git config
+sendemail.cccmd 'scripts/get_maintainer.pl --nogit-fallback'`` (Refer to
+Do not send as an attachment
+Send patches inline so they are easy to reply to with review comments.
+Do not put patches in attachments.
+Use ``git format-patch``
+Use the right diff format.
+`git format-patch <http://git-scm.com/docs/git-format-patch>`__ will
+produce patch emails in the right format (check the documentation to
+find out how to drive it). You can then edit the cover letter before
+using ``git send-email`` to mail the files to the mailing list. (We
+recommend `git send-email <http://git-scm.com/docs/git-send-email>`__
+because mail clients often mangle patches by wrapping long lines or
+messing up whitespace. Some distributions do not include send-email in a
+default install of git; you may need to download additional packages,
+such as 'git-email' on Fedora-based systems.) Patch series need a cover
+letter, with shallow threading (all patches in the series are
+in-reply-to the cover letter, but not to each other); single unrelated
+patches do not need a cover letter (but if you do send a cover letter,
+use --numbered so the cover and the patch have distinct subject lines).
+Patches are easier to find if they start a new top-level thread, rather
+than being buried in-reply-to another existing thread.
+Patch emails must include a ``Signed-off-by:`` line
+For more information see `1.12) Sign your work
+This is vital or we will not be able to apply your patch! Please use
+your real name to sign a patch (not an alias or acronym).
+If you wrote the patch, make sure your "From:" and "Signed-off-by:"
+lines use the same spelling. It's okay if you subscribe or contribute to
+the list via more than one address, but using multiple addresses in one
+commit just confuses things. If someone else wrote the patch, git will
+include a "From:" line in the body of the email (different from your
+envelope From:) that will give credit to the correct author; but again,
+that author's Signed-off-by: line is mandatory, with the same spelling.
+Include a meaningful cover letter
+This usually applies only to a series that includes multiple patches;
+the cover letter explains the overall goal of such a series.
+When reviewers don't know your goal at the start of their review, they
+may object to early changes that don't make sense until the end of the
+series, because they do not have enough context yet at that point of
+their review. A series where the goal is unclear also risks a higher
+number of review-fix cycles because the reviewers haven't bought into
+the idea yet. If the cover letter can explain these points to the
+reviewer, the process will be smoother patches will get merged faster.
+Make sure your cover letter includes a diffstat of changes made over the
+entire series; potential reviewers know what files they are interested
+in, and they need an easy way determine if your series touches them.
+Use the RFC tag if needed
+For example, "[PATCH RFC v2]". ``git format-patch --subject-prefix=RFC``
+"RFC" means "Request For Comments" and is a statement that you don't
+intend for your patchset to be applied to master, but would like some
+review on it anyway. Reasons for doing this include:
+- the patch depends on some pending kernel changes which haven't yet
+ been accepted, so the QEMU patch series is blocked until that
+ dependency has been dealt with, but is worth reviewing anyway
+- the patch set is not finished yet (perhaps it doesn't cover all use
+ cases or work with all targets) but you want early review of a major
+ API change or design structure before continuing
+In general, since it's asking other people to do review work on a
+patchset that the submitter themselves is saying shouldn't be applied,
+it's best to:
+- use it sparingly
+- in the cover letter, be clear about why a patch is an RFC, what areas
+ of the patchset you're looking for review on, and why reviewers
+ should care
+Participating in Code Review
+All patches submitted to the QEMU project go through a code review
+process before they are accepted. Some areas of code that are well
+maintained may review patches quickly, lesser-loved areas of code may
+have a longer delay.
+Stay around to fix problems raised in code review
+Not many patches get into QEMU straight away -- it is quite common that
+developers will identify bugs, or suggest a cleaner approach, or even
+just point out code style issues or commit message typos. You'll need to
+respond to these, and then send a second version of your patches with
+the issues fixed. This takes a little time and effort on your part, but
+if you don't do it then your changes will never get into QEMU. It's also
+just polite -- it is quite disheartening for a developer to spend time
+reviewing your code and suggesting improvements, only to find that
+you're not going to do anything further and it was all wasted effort.
+When replying to comments on your patches **reply to all and not just
+the sender** -- keeping discussion on the mailing list means everybody
+can follow it.
+Pay attention to review comments
+Someone took their time to review your work, and it pays to respect that
+effort; repeatedly submitting a series without addressing all comments
+from the previous round tends to alienate reviewers and stall your
+patch. Reviewers aren't always perfect, so it is okay if you want to
+argue that your code was correct in the first place instead of blindly
+doing everything the reviewer asked. On the other hand, if someone
+pointed out a potential issue during review, then even if your code
+turns out to be correct, it's probably a sign that you should improve
+your commit message and/or comments in the code explaining why the code
+If you fix issues that are raised during review **resend the entire
+patch series** not just the one patch that was changed. This allows
+maintainers to easily apply the fixed series without having to manually
+identify which patches are relevant. Send the new version as a complete
+fresh email or series of emails -- don't try to make it a followup to
+version 1. (This helps automatic patch email handling tools distinguish
+between v1 and v2 emails.)
+When resending patches add a version tag
+All patches beyond the first version should include a version tag -- for
+example, "[PATCH v2]". This means people can easily identify whether
+they're looking at the most recent version. (The first version of a
+patch need not say "v1", just [PATCH] is sufficient.) For patch series,
+the version applies to the whole series -- even if you only change one
+patch, you resend the entire series and mark it as "v2". Don't try to
+track versions of different patches in the series separately. `git
+format-patch <http://git-scm.com/docs/git-format-patch>`__ and `git
+send-email <http://git-scm.com/docs/git-send-email>`__ both understand
+the ``-v2`` option to make this easier. Send each new revision as a new
+top-level thread, rather than burying it in-reply-to an earlier
+revision, as many reviewers are not looking inside deep threads for new
+Include version history in patchset revisions
+For later versions of patches, include a summary of changes from
+previous versions, but not in the commit message itself. In an email
+formatted as a git patch, the commit message is the part above the "---"
+line, and this will go into the git changelog when the patch is
+committed. This part should be a self-contained description of what this
+version of the patch does, written to make sense to anybody who comes
+back to look at this commit in git in six months' time. The part below
+the "---" line and above the patch proper (git format-patch puts the
+diffstat here) is a good place to put remarks for people reading the
+patch email, and this is where the "changes since previous version"
+summary belongs. The
+`git-publish <https://github.com/stefanha/git-publish>`__ script can
+help with tracking a good summary across versions. Also, the
+`git-backport-diff <https://github.com/codyprime/git-scripts>`__ script
+can help focus reviewers on what changed between revisions.
+Tips and Tricks
+Proper use of Reviewed-by: tags can aid review
+When reviewing a large series, a reviewer can reply to some of the
+patches with a Reviewed-by tag, stating that they are happy with that
+patch in isolation (sometimes conditional on minor cleanup, like fixing
+whitespace, that doesn't affect code content). You should then update
+those commit messages by hand to include the Reviewed-by tag, so that in
+the next revision, reviewers can spot which patches were already clean
+from the previous round. Conversely, if you significantly modify a patch
+that was previously reviewed, remove the reviewed-by tag out of the
+commit message, as well as listing the changes from the previous
+version, to make it easier to focus a reviewer's attention to your
+If your patch seems to have been ignored
+If your patchset has received no replies you should "ping" it after a
+week or two, by sending an email as a reply-to-all to the patch mail,
+including the word "ping" and ideally also a link to the page for the
+`patchwork <http://patchwork.ozlabs.org/project/qemu-devel/list/>`__ or
+GMANE. It's worth double-checking for reasons why your patch might have
+been ignored (forgot to CC the maintainer? annoyed people by failing to
+respond to review comments on an earlier version?), but often for
+less-maintained areas of QEMU patches do just slip through the cracks.
+If your ping is also ignored, ping again after another week or so. As
+the submitter, you are the person with the most motivation to get your
+patch applied, so you have to be persistent.
+Is my patch in?
+Once your patch has had enough review on list, the maintainer for that
+area of code will send notification to the list that they are including
+your patch in a particular staging branch. Periodically, the maintainer
+then sends a `pull request
+for aggregating topic branches into mainline qemu. Generally, you do not
+need to send a pull request unless you have contributed enough patches
+to become a maintainer over a particular section of code. Maintainers
+may further modify your commit, by resolving simple merge conflicts or
+fixing minor typos pointed out during review, but will always add a
+Signed-off-by line in addition to yours, indicating that it went through
+their tree. Occasionally, the maintainer's pull request may hit more
+difficult merge conflicts, where you may be requested to help rebase and
+resolve the problems. It may take a couple of weeks between when your
+patch first had a positive review to when it finally lands in qemu.git;
+release cycle freezes may extend that time even longer.
+Return the favor
+Peer review only works if everyone chips in a bit of review time. If
+everyone submitted more patches than they reviewed, we would have a
+patch backlog. A good goal is to try to review at least as many patches
+from others as what you submit. Don't worry if you don't know the code
+base as well as a maintainer; it's perfectly fine to admit when your
+review is weak because you are unfamiliar with the code.
Re: [PATCH v3 0/3] rSTify contribution-related wiki pages, Philippe Mathieu-Daudé, 2021/11/10