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Bring in the big SubmittingPatches thrashup.

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	Documentation/SubmittingPatches
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Jonathan Corbet 2015-01-29 13:08:28 -07:00
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@ -10,27 +10,49 @@ kernel, the process can sometimes be daunting if you're not familiar
with "the system." This text is a collection of suggestions which
can greatly increase the chances of your change being accepted.
Read Documentation/SubmitChecklist for a list of items to check
before submitting code. If you are submitting a driver, also read
Documentation/SubmittingDrivers.
This document contains a large number of suggestions in a relatively terse
format. For detailed information on how the kernel development process
works, see Documentation/development-process. Also, read
Documentation/SubmitChecklist for a list of items to check before
submitting code. If you are submitting a driver, also read
Documentation/SubmittingDrivers; for device tree binding patches, read
Documentation/devicetree/bindings/submitting-patches.txt.
Many of these steps describe the default behavior of the git version
control system; if you use git to prepare your patches, you'll find much
of the mechanical work done for you, though you'll still need to prepare
and document a sensible set of patches.
and document a sensible set of patches. In general, use of git will make
your life as a kernel developer easier.
--------------------------------------------
SECTION 1 - CREATING AND SENDING YOUR CHANGE
--------------------------------------------
0) Obtain a current source tree
-------------------------------
If you do not have a repository with the current kernel source handy, use
git to obtain one. You'll want to start with the mainline repository,
which can be grabbed with:
git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Note, however, that you may not want to develop against the mainline tree
directly. Most subsystem maintainers run their own trees and want to see
patches prepared against those trees. See the "T:" entry for the subsystem
in the MAINTAINERS file to find that tree, or simply ask the maintainer if
the tree is not listed there.
It is still possible to download kernel releases via tarballs (as described
in the next section), but that is the hard way to do kernel development.
1) "diff -up"
------------
Use "diff -up" or "diff -uprN" to create patches. git generates patches
in this form by default; if you're using git, you can skip this section
entirely.
If you must generate your patches by hand, use "diff -up" or "diff -uprN"
to create patches. Git generates patches in this form by default; if
you're using git, you can skip this section entirely.
All changes to the Linux kernel occur in the form of patches, as
generated by diff(1). When creating your patch, make sure to create it
@ -42,7 +64,7 @@ not in any lower subdirectory.
To create a patch for a single file, it is often sufficient to do:
SRCTREE= linux-2.6
SRCTREE= linux
MYFILE= drivers/net/mydriver.c
cd $SRCTREE
@ -55,17 +77,16 @@ To create a patch for multiple files, you should unpack a "vanilla",
or unmodified kernel source tree, and generate a diff against your
own source tree. For example:
MYSRC= /devel/linux-2.6
MYSRC= /devel/linux
tar xvfz linux-2.6.12.tar.gz
mv linux-2.6.12 linux-2.6.12-vanilla
diff -uprN -X linux-2.6.12-vanilla/Documentation/dontdiff \
linux-2.6.12-vanilla $MYSRC > /tmp/patch
tar xvfz linux-3.19.tar.gz
mv linux-3.19 linux-3.19-vanilla
diff -uprN -X linux-3.19-vanilla/Documentation/dontdiff \
linux-3.19-vanilla $MYSRC > /tmp/patch
"dontdiff" is a list of files which are generated by the kernel during
the build process, and should be ignored in any diff(1)-generated
patch. The "dontdiff" file is included in the kernel tree in
2.6.12 and later.
patch.
Make sure your patch does not include any extra files which do not
belong in a patch submission. Make sure to review your patch -after-
@ -83,6 +104,7 @@ is another popular alternative.
2) Describe your changes.
-------------------------
Describe your problem. Whether your patch is a one-line bug fix or
5000 lines of a new feature, there must be an underlying problem that
@ -124,10 +146,10 @@ See #3, next.
When you submit or resubmit a patch or patch series, include the
complete patch description and justification for it. Don't just
say that this is version N of the patch (series). Don't expect the
patch merger to refer back to earlier patch versions or referenced
subsystem maintainer to refer back to earlier patch versions or referenced
URLs to find the patch description and put that into the patch.
I.e., the patch (series) and its description should be self-contained.
This benefits both the patch merger(s) and reviewers. Some reviewers
This benefits both the maintainers and reviewers. Some reviewers
probably didn't even receive earlier versions of the patch.
Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
@ -156,10 +178,15 @@ Example:
platform_set_drvdata(), but left the variable "dev" unused,
delete it.
You should also be sure to use at least the first twelve characters of the
SHA-1 ID. The kernel repository holds a *lot* of objects, making
collisions with shorter IDs a real possibility. Bear in mind that, even if
there is no collision with your six-character ID now, that condition may
change five years from now.
If your patch fixes a bug in a specific commit, e.g. you found an issue using
git-bisect, please use the 'Fixes:' tag with the first 12 characters of the
SHA-1 ID, and the one line summary.
Example:
SHA-1 ID, and the one line summary. For example:
Fixes: e21d2170f366 ("video: remove unnecessary platform_set_drvdata()")
@ -172,8 +199,9 @@ outputting the above style in the git log or git show commands
fixes = Fixes: %h (\"%s\")
3) Separate your changes.
-------------------------
Separate _logical changes_ into a single patch file.
Separate each _logical change_ into a separate patch.
For example, if your changes include both bug fixes and performance
enhancements for a single driver, separate those changes into two
@ -184,90 +212,116 @@ On the other hand, if you make a single change to numerous files,
group those changes into a single patch. Thus a single logical change
is contained within a single patch.
The point to remember is that each patch should make an easily understood
change that can be verified by reviewers. Each patch should be justifiable
on its own merits.
If one patch depends on another patch in order for a change to be
complete, that is OK. Simply note "this patch depends on patch X"
in your patch description.
When dividing your change into a series of patches, take special care to
ensure that the kernel builds and runs properly after each patch in the
series. Developers using "git bisect" to track down a problem can end up
splitting your patch series at any point; they will not thank you if you
introduce bugs in the middle.
If you cannot condense your patch set into a smaller set of patches,
then only post say 15 or so at a time and wait for review and integration.
4) Style check your changes.
4) Style-check your changes.
----------------------------
Check your patch for basic style violations, details of which can be
found in Documentation/CodingStyle. Failure to do so simply wastes
the reviewers time and will get your patch rejected, probably
without even being read.
At a minimum you should check your patches with the patch style
checker prior to submission (scripts/checkpatch.pl). You should
be able to justify all violations that remain in your patch.
One significant exception is when moving code from one file to
another -- in this case you should not modify the moved code at all in
the same patch which moves it. This clearly delineates the act of
moving the code and your changes. This greatly aids review of the
actual differences and allows tools to better track the history of
the code itself.
Check your patches with the patch style checker prior to submission
(scripts/checkpatch.pl). Note, though, that the style checker should be
viewed as a guide, not as a replacement for human judgment. If your code
looks better with a violation then its probably best left alone.
The checker reports at three levels:
- ERROR: things that are very likely to be wrong
- WARNING: things requiring careful review
- CHECK: things requiring thought
You should be able to justify all violations that remain in your
patch.
5) Select the recipients for your patch.
----------------------------------------
5) Select e-mail destination.
You should always copy the appropriate subsystem maintainer(s) on any patch
to code that they maintain; look through the MAINTAINERS file and the
source code revision history to see who those maintainers are. The
script scripts/get_maintainer.pl can be very useful at this step. If you
cannot find a maintainer for the subsystem your are working on, Andrew
Morton (akpm@linux-foundation.org) serves as a maintainer of last resort.
Look through the MAINTAINERS file and the source code, and determine
if your change applies to a specific subsystem of the kernel, with
an assigned maintainer. If so, e-mail that person. The script
scripts/get_maintainer.pl can be very useful at this step.
If no maintainer is listed, or the maintainer does not respond, send
your patch to the primary Linux kernel developer's mailing list,
linux-kernel@vger.kernel.org. Most kernel developers monitor this
e-mail list, and can comment on your changes.
You should also normally choose at least one mailing list to receive a copy
of your patch set. linux-kernel@vger.kernel.org functions as a list of
last resort, but the volume on that list has caused a number of developers
to tune it out. Look in the MAINTAINERS file for a subsystem-specific
list; your patch will probably get more attention there. Please do not
spam unrelated lists, though.
Many kernel-related lists are hosted on vger.kernel.org; you can find a
list of them at http://vger.kernel.org/vger-lists.html. There are
kernel-related lists hosted elsewhere as well, though.
Do not send more than 15 patches at once to the vger mailing lists!!!
Linus Torvalds is the final arbiter of all changes accepted into the
Linux kernel. His e-mail address is <torvalds@linux-foundation.org>.
He gets a lot of e-mail, so typically you should do your best to -avoid-
He gets a lot of e-mail, and, at this point, very few patches go through
Linus directly, so typically you should do your best to -avoid-
sending him e-mail.
Patches which are bug fixes, are "obvious" changes, or similarly
require little discussion should be sent or CC'd to Linus. Patches
which require discussion or do not have a clear advantage should
usually be sent first to linux-kernel. Only after the patch is
discussed should the patch then be submitted to Linus.
If you have a patch that fixes an exploitable security bug, send that patch
to security@kernel.org. For severe bugs, a short embargo may be considered
to allow distrbutors to get the patch out to users; in such cases,
obviously, the patch should not be sent to any public lists.
Patches that fix a severe bug in a released kernel should be directed
toward the stable maintainers by putting a line like this:
Cc: stable@vger.kernel.org
6) Select your CC (e-mail carbon copy) list.
into your patch.
Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
Note, however, that some subsystem maintainers want to come to their own
conclusions on which patches should go to the stable trees. The networking
maintainer, in particular, would rather not see individual developers
adding lines like the above to their patches.
Other kernel developers besides Linus need to be aware of your change,
so that they may comment on it and offer code review and suggestions.
linux-kernel is the primary Linux kernel developer mailing list.
Other mailing lists are available for specific subsystems, such as
USB, framebuffer devices, the VFS, the SCSI subsystem, etc. See the
MAINTAINERS file for a mailing list that relates specifically to
your change.
Majordomo lists of VGER.KERNEL.ORG at:
<http://vger.kernel.org/vger-lists.html>
If changes affect userland-kernel interfaces, please send
the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
a man-pages patch, or at least a notification of the change,
so that some information makes its way into the manual pages.
Even if the maintainer did not respond in step #5, make sure to ALWAYS
copy the maintainer when you change their code.
If changes affect userland-kernel interfaces, please send the MAN-PAGES
maintainer (as listed in the MAINTAINERS file) a man-pages patch, or at
least a notification of the change, so that some information makes its way
into the manual pages. User-space API changes should also be copied to
linux-api@vger.kernel.org.
For small patches you may want to CC the Trivial Patch Monkey
trivial@kernel.org which collects "trivial" patches. Have a look
into the MAINTAINERS file for its current manager.
Trivial patches must qualify for one of the following rules:
Spelling fixes in documentation
Spelling fixes which could break grep(1)
Spelling fixes for errors which could break grep(1)
Warning fixes (cluttering with useless warnings is bad)
Compilation fixes (only if they are actually correct)
Runtime fixes (only if they actually fix things)
Removing use of deprecated functions/macros (eg. check_region)
Removing use of deprecated functions/macros
Contact detail and documentation fixes
Non-portable code replaced by portable code (even in arch-specific,
since people copy, as long as it's trivial)
@ -276,7 +330,8 @@ Trivial patches must qualify for one of the following rules:
7) No MIME, no links, no compression, no attachments. Just plain text.
6) No MIME, no links, no compression, no attachments. Just plain text.
-----------------------------------------------------------------------
Linus and other kernel developers need to be able to read and comment
on the changes you are submitting. It is important for a kernel
@ -299,54 +354,48 @@ you to re-send them using MIME.
See Documentation/email-clients.txt for hints about configuring
your e-mail client so that it sends your patches untouched.
8) E-mail size.
When sending patches to Linus, always follow step #7.
7) E-mail size.
---------------
Large changes are not appropriate for mailing lists, and some
maintainers. If your patch, uncompressed, exceeds 300 kB in size,
it is preferred that you store your patch on an Internet-accessible
server, and provide instead a URL (link) pointing to your patch.
server, and provide instead a URL (link) pointing to your patch. But note
that if your patch exceeds 300 kB, it almost certainly needs to be broken up
anyway.
8) Respond to review comments.
------------------------------
Your patch will almost certainly get comments from reviewers on ways in
which the patch can be improved. You must respond to those comments;
ignoring reviewers is a good way to get ignored in return. Review comments
or questions that do not lead to a code change should almost certainly
bring about a comment or changelog entry so that the next reviewer better
understands what is going on.
Be sure to tell the reviewers what changes you are making and to thank them
for their time. Code review is a tiring and time-consuming process, and
reviewers sometimes get grumpy. Even in that case, though, respond
politely and address the problems they have pointed out.
9) Don't get discouraged - or impatient.
----------------------------------------
9) Name your kernel version.
After you have submitted your change, be patient and wait. Reviewers are
busy people and may not get to your patch right away.
It is important to note, either in the subject line or in the patch
description, the kernel version to which this patch applies.
If the patch does not apply cleanly to the latest kernel version,
Linus will not apply it.
Once upon a time, patches used to disappear into the void without comment,
but the development process works more smoothly than that now. You should
receive comments within a week or so; if that does not happen, make sure
that you have sent your patches to the right place. Wait for a minimum of
one week before resubmitting or pinging reviewers - possibly longer during
busy times like merge windows.
10) Don't get discouraged. Re-submit.
After you have submitted your change, be patient and wait. If Linus
likes your change and applies it, it will appear in the next version
of the kernel that he releases.
However, if your change doesn't appear in the next version of the
kernel, there could be any number of reasons. It's YOUR job to
narrow down those reasons, correct what was wrong, and submit your
updated change.
It is quite common for Linus to "drop" your patch without comment.
That's the nature of the system. If he drops your patch, it could be
due to
* Your patch did not apply cleanly to the latest kernel version.
* Your patch was not sufficiently discussed on linux-kernel.
* A style issue (see section 2).
* An e-mail formatting issue (re-read this section).
* A technical problem with your change.
* He gets tons of e-mail, and yours got lost in the shuffle.
* You are being annoying.
When in doubt, solicit comments on linux-kernel mailing list.
11) Include PATCH in the subject
10) Include PATCH in the subject
--------------------------------
Due to high e-mail traffic to Linus, and to linux-kernel, it is common
convention to prefix your subject line with [PATCH]. This lets Linus
@ -355,7 +404,8 @@ e-mail discussions.
12) Sign your work
11) Sign your work
------------------
To improve tracking of who did what, especially with patches that can
percolate to their final resting place in the kernel through several
@ -429,15 +479,15 @@ 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 2.6-stable :
here's what we see in a 3.x-stable release:
Date: Tue May 13 19:10:30 2008 +0000
Date: Tue Oct 7 07:26:38 2014 -0400
SCSI: libiscsi regression in 2.6.25: fix nop timer handling
libata: Un-break ATA blacklist
commit 4cf1043593db6a337f10e006c23c69e5fc93e722 upstream
commit 1c40279960bcd7d52dbdf1d466b20d24b99176c8 upstream.
And here's what appears in 2.4 :
And here's what might appear in an older kernel once a patch is backported:
Date: Tue May 13 22:12:27 2008 +0200
@ -446,18 +496,19 @@ And here's what appears in 2.4 :
[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 trouble-shoot bugs in your
tracking your trees, and to people trying to troubleshoot bugs in your
tree.
13) When to use Acked-by: and Cc:
12) When to use Acked-by: and Cc:
---------------------------------
The Signed-off-by: tag indicates that the signer was involved in the
development of the patch, or that he/she was in the patch's delivery path.
If a person was not directly involved in the preparation or handling of a
patch but wishes to signify and record their approval of it then they can
arrange to have an Acked-by: line added to the patch's changelog.
ask to have an Acked-by: line added to the patch's changelog.
Acked-by: is often used by the maintainer of the affected code when that
maintainer neither contributed to nor forwarded the patch.
@ -465,7 +516,8 @@ maintainer neither contributed to nor forwarded the patch.
Acked-by: is not as formal as Signed-off-by:. It is a record that the acker
has at least reviewed the patch and has indicated acceptance. Hence patch
mergers will sometimes manually convert an acker's "yep, looks good to me"
into an Acked-by:.
into an Acked-by: (but note that it is usually better to ask for an
explicit ack).
Acked-by: does not necessarily indicate acknowledgement of the entire patch.
For example, if a patch affects multiple subsystems and has an Acked-by: from
@ -477,11 +529,13 @@ list archives.
If a person has had the opportunity to comment on a patch, but has not
provided such comments, you may optionally add a "Cc:" tag to the patch.
This is the only tag which might be added without an explicit action by the
person it names. This tag documents that potentially interested parties
have been included in the discussion
person it names - but it should indicate that this person was copied on the
patch. This tag documents that potentially interested parties
have been included in the discussion.
14) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
13) Using Reported-by:, Tested-by:, Reviewed-by:, Suggested-by: and Fixes:
--------------------------------------------------------------------------
The Reported-by tag gives credit to people who find bugs and report them and it
hopefully inspires them to help us again in the future. Please note that if
@ -541,7 +595,13 @@ which stable kernel versions should receive your fix. This is the preferred
method for indicating a bug fixed by the patch. See #2 above for more details.
15) The canonical patch format
14) The canonical patch format
------------------------------
This section describes how the patch itself should be formatted. Note
that, if you have your patches stored in a git repository, proper patch
formatting can be had with "git format-patch". The tools cannot create
the necessary text, though, so read the instructions below anyway.
The canonical patch subject line is:
@ -549,7 +609,8 @@ The canonical patch subject line is:
The canonical patch message body contains the following:
- A "from" line specifying the patch author.
- A "from" line specifying the patch author (only needed if the person
sending the patch is not the author).
- An empty line.
@ -656,128 +717,63 @@ See more details on the proper patch format in the following
references.
16) Sending "git pull" requests (from Linus emails)
15) Sending "git pull" requests
-------------------------------
Please write the git repo address and branch name alone on the same line
so that I can't even by mistake pull from the wrong branch, and so
that a triple-click just selects the whole thing.
If you have a series of patches, it may be most convenient to have the
maintainer pull them directly into the subsystem repository with a
"git pull" operation. Note, however, that pulling patches from a developer
requires a higher degree of trust than taking patches from a mailing list.
As a result, many subsystem maintainers are reluctant to take pull
requests, especially from new, unknown developers. If in doubt you can use
the pull request as the cover letter for a normal posting of the patch
series, giving the maintainer the option of using either.
So the proper format is something along the lines of:
A pull request should have [GIT] or [PULL] in the subject line. The
request itself should include the repository name and the branch of
interest on a single line; it should look something like:
"Please pull from
Please pull from
git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
git://jdelvare.pck.nerim.net/jdelvare-2.6 i2c-for-linus
to get these changes:"
to get these changes:"
so that I don't have to hunt-and-peck for the address and inevitably
get it wrong (actually, I've only gotten it wrong a few times, and
checking against the diffstat tells me when I get it wrong, but I'm
just a lot more comfortable when I don't have to "look for" the right
thing to pull, and double-check that I have the right branch-name).
A pull request should also include an overall message saying what will be
included in the request, a "git shortlog" listing of the patches
themselves, and a diffstat showing the overall effect of the patch series.
The easiest way to get all this information together is, of course, to let
git do it for you with the "git request-pull" command.
Some maintainers (including Linus) want to see pull requests from signed
commits; that increases their confidence that the request actually came
from you. Linus, in particular, will not pull from public hosting sites
like GitHub in the absence of a signed tag.
Please use "git diff -M --stat --summary" to generate the diffstat:
the -M enables rename detection, and the summary enables a summary of
new/deleted or renamed files.
The first step toward creating such tags is to make a GNUPG key and get it
signed by one or more core kernel developers. This step can be hard for
new developers, but there is no way around it. Attending conferences can
be a good way to find developers who can sign your key.
With rename detection, the statistics are rather different [...]
because git will notice that a fair number of the changes are renames.
Once you have prepared a patch series in git that you wish to have somebody
pull, create a signed tag with "git tag -s". This will create a new tag
identifying the last commit in the series and containing a signature
created with your private key. You will also have the opportunity to add a
changelog-style message to the tag; this is an ideal place to describe the
effects of the pull request as a whole.
-----------------------------------
SECTION 2 - HINTS, TIPS, AND TRICKS
-----------------------------------
If the tree the maintainer will be pulling from is not the repository you
are working from, don't forget to push the signed tag explicitly to the
public tree.
This section lists many of the common "rules" associated with code
submitted to the kernel. There are always exceptions... but you must
have a really good reason for doing so. You could probably call this
section Linus Computer Science 101.
1) Read Documentation/CodingStyle
Nuff said. If your code deviates too much from this, it is likely
to be rejected without further review, and without comment.
One significant exception is when moving code from one file to
another -- in this case you should not modify the moved code at all in
the same patch which moves it. This clearly delineates the act of
moving the code and your changes. This greatly aids review of the
actual differences and allows tools to better track the history of
the code itself.
Check your patches with the patch style checker prior to submission
(scripts/checkpatch.pl). The style checker should be viewed as
a guide not as the final word. If your code looks better with
a violation then its probably best left alone.
The checker reports at three levels:
- ERROR: things that are very likely to be wrong
- WARNING: things requiring careful review
- CHECK: things requiring thought
You should be able to justify all violations that remain in your
patch.
2) #ifdefs are ugly
Code cluttered with ifdefs is difficult to read and maintain. Don't do
it. Instead, put your ifdefs in a header, and conditionally define
'static inline' functions, or macros, which are used in the code.
Let the compiler optimize away the "no-op" case.
Simple example, of poor code:
dev = alloc_etherdev (sizeof(struct funky_private));
if (!dev)
return -ENODEV;
#ifdef CONFIG_NET_FUNKINESS
init_funky_net(dev);
#endif
Cleaned-up example:
(in header)
#ifndef CONFIG_NET_FUNKINESS
static inline void init_funky_net (struct net_device *d) {}
#endif
(in the code itself)
dev = alloc_etherdev (sizeof(struct funky_private));
if (!dev)
return -ENODEV;
init_funky_net(dev);
3) 'static inline' is better than a macro
Static inline functions are greatly preferred over macros.
They provide type safety, have no length limitations, no formatting
limitations, and under gcc they are as cheap as macros.
Macros should only be used for cases where a static inline is clearly
suboptimal [there are a few, isolated cases of this in fast paths],
or where it is impossible to use a static inline function [such as
string-izing].
'static inline' is preferred over 'static __inline__', 'extern inline',
and 'extern __inline__'.
4) Don't over-design.
Don't try to anticipate nebulous future cases which may or may not
be useful: "Make it as simple as you can, and no simpler."
When generating your pull request, use the signed tag as the target. A
command like this will do the trick:
git request-pull master git://my.public.tree/linux.git my-signed-tag
----------------------
SECTION 3 - REFERENCES
SECTION 2 - REFERENCES
----------------------
Andrew Morton, "The perfect patch" (tpp).