HOWTO do Linux kernel development
----------------------------------
+=================================
This is the be-all, end-all document on this topic. It contains
instructions on how to become a Linux kernel developer and how to learn
you plan to do low-level development for that architecture. Though they
are not a good substitute for a solid C education and/or years of
experience, the following books are good for, if anything, reference:
+
- "The C Programming Language" by Kernighan and Ritchie [Prentice Hall]
- "Practical C Programming" by Steve Oualline [O'Reilly]
- "C: A Reference Manual" by Harbison and Steele [Prentice Hall]
their statements on legal matters.
For common questions and answers about the GPL, please see:
- http://www.gnu.org/licenses/gpl-faq.html
+
+ https://www.gnu.org/licenses/gpl-faq.html
Documentation
Here is a list of files that are in the kernel source tree that are
required reading:
+
README
This file gives a short background on the Linux kernel and describes
what is necessary to do to configure and build the kernel. People
who are new to the kernel should start here.
- Documentation/Changes
+ :ref:`Documentation/Changes <changes>`
This file gives a list of the minimum levels of various software
packages that are necessary to build and run the kernel
successfully.
- Documentation/CodingStyle
+ :ref:`Documentation/CodingStyle <codingstyle>`
This describes the Linux kernel coding style, and some of the
rationale behind it. All new code is expected to follow the
guidelines in this document. Most maintainers will only accept
patches if these rules are followed, and many people will only
review code if it is in the proper style.
- Documentation/SubmittingPatches
- Documentation/SubmittingDrivers
+ :ref:`Documentation/SubmittingPatches <submittingpatches>` and :ref:`Documentation/SubmittingDrivers <submittingdrivers>`
These files describe in explicit detail how to successfully create
and send a patch, including (but not limited to):
+
- Email contents
- Email format
- Who to send it to
+
Following these rules will not guarantee success (as all patches are
subject to scrutiny for content and style), but not following them
will almost always prevent it.
Other excellent descriptions of how to create patches properly are:
+
"The Perfect Patch"
- http://www.ozlabs.org/~akpm/stuff/tpp.txt
+ https://www.ozlabs.org/~akpm/stuff/tpp.txt
+
"Linux kernel patch submission format"
http://linux.yyz.us/patch-format.html
- Documentation/stable_api_nonsense.txt
+ :ref:`Documentation/stable_api_nonsense.txt <stable_api_nonsense>`
This file describes the rationale behind the conscious decision to
not have a stable API within the kernel, including things like:
+
- Subsystem shim-layers (for compatibility?)
- Driver portability between Operating Systems.
- Mitigating rapid change within the kernel source tree (or
preventing rapid change)
+
This document is crucial for understanding the Linux development
philosophy and is very important for people moving to Linux from
development on other Operating Systems.
- Documentation/SecurityBugs
+ :ref:`Documentation/SecurityBugs <securitybugs>`
If you feel you have found a security problem in the Linux kernel,
please follow the steps in this document to help notify the kernel
developers, and help solve the issue.
- Documentation/ManagementStyle
+ :ref:`Documentation/ManagementStyle <managementstyle>`
This document describes how Linux kernel maintainers operate and the
shared ethos behind their methodologies. This is important reading
for anyone new to kernel development (or anyone simply curious about
it), as it resolves a lot of common misconceptions and confusion
about the unique behavior of kernel maintainers.
- Documentation/stable_kernel_rules.txt
+ :ref:`Documentation/stable_kernel_rules.txt <stable_kernel_rules>`
This file describes the rules on how the stable kernel releases
happen, and what to do if you want to get a change into one of these
releases.
- Documentation/kernel-docs.txt
+ :ref:`Documentation/kernel-docs.txt <kernel_docs>`
A list of external documentation that pertains to kernel
development. Please consult this list if you do not find what you
are looking for within the in-kernel documentation.
- Documentation/applying-patches.txt
+ :ref:`Documentation/applying-patches.txt <applying_patches>`
A good introduction describing exactly what a patch is and how to
apply it to the different development branches of the kernel.
The kernel also has a large number of documents that can be
-automatically generated from the source code itself. This includes a
+automatically generated from the source code itself or from
+ReStructuredText markups (ReST), like this one. This includes a
full description of the in-kernel API, and rules on how to handle
-locking properly. The documents will be created in the
-Documentation/DocBook/ directory and can be generated as PDF,
-Postscript, HTML, and man pages by running:
+locking properly.
+
+All such documents can be generated as PDF or HTML by running::
+
make pdfdocs
- make psdocs
make htmldocs
- make mandocs
+
respectively from the main kernel source directory.
+The documents that uses ReST markup will be generated at Documentation/output.
+They can also be generated on LaTeX and ePub formats with::
+
+ make latexdocs
+ make epubdocs
+
+Currently, there are some documents written on DocBook that are in
+the process of conversion to ReST. Such documents will be created in the
+Documentation/DocBook/ directory and can be generated also as
+Postscript or man pages by running::
+
+ make psdocs
+ make mandocs
Becoming A Kernel Developer
---------------------------
If you do not know anything about Linux kernel development, you should
look at the Linux KernelNewbies project:
- http://kernelnewbies.org
+
+ https://kernelnewbies.org
+
It consists of a helpful mailing list where you can ask almost any type
of basic kernel development question (make sure to search the archives
first, before asking something that has already been answered in the
If you do not know where you want to start, but you want to look for
some task to start doing to join into the kernel development community,
go to the Linux Kernel Janitor's project:
- http://kernelnewbies.org/KernelJanitors
+
+ https://kernelnewbies.org/KernelJanitors
+
It is a great place to start. It describes a list of relatively simple
problems that need to be cleaned up and fixed within the Linux kernel
source tree. Working with the developers in charge of this project, you
tree, but need some help getting it in the proper form, the
kernel-mentors project was created to help you out with this. It is a
mailing list, and can be found at:
- http://selenic.com/mailman/listinfo/kernel-mentors
+
+ https://selenic.com/mailman/listinfo/kernel-mentors
Before making any actual modifications to the Linux kernel code, it is
imperative to understand how the code in question works. For this
Cross-Reference project, which is able to present source code in a
self-referential, indexed webpage format. An excellent up-to-date
repository of the kernel code may be found at:
+
http://lxr.free-electrons.com/
Linux kernel development process currently consists of a few different
main kernel "branches" and lots of different subsystem-specific kernel
branches. These different branches are:
+
- main 4.x kernel tree
- 4.x.y -stable kernel tree
- 4.x -git kernel patches
4.x kernel tree
-----------------
4.x kernels are maintained by Linus Torvalds, and can be found on
-kernel.org in the pub/linux/kernel/v4.x/ directory. Its development
+https://kernel.org in the pub/linux/kernel/v4.x/ directory. Its development
process is as follows:
+
- As soon as a new kernel is released a two weeks window is open,
during this period of time maintainers can submit big diffs to
Linus, usually the patches that have already been included in the
-next kernel for a few weeks. The preferred way to submit big changes
is using git (the kernel's source management tool, more information
- can be found at http://git-scm.com/) but plain patches are also just
+ can be found at https://git-scm.com/) but plain patches are also just
fine.
- After two weeks a -rc1 kernel is released it is now possible to push
only patches that do not include new features that could affect the
It is worth mentioning what Andrew Morton wrote on the linux-kernel
mailing list about kernel releases:
- "Nobody knows when a kernel will be released, because it's
+
+ *"Nobody knows when a kernel will be released, because it's
released according to perceived bug status, not according to a
- preconceived timeline."
+ preconceived timeline."*
4.x.y -stable kernel tree
-------------------------
Most of these repositories are git trees, but there are also other SCMs
in use, or patch queues being published as quilt series. Addresses of
these subsystem repositories are listed in the MAINTAINERS file. Many
-of them can be browsed at http://git.kernel.org/.
+of them can be browsed at https://git.kernel.org/.
Before a proposed patch is committed to such a subsystem tree, it is
subject to review which primarily happens on mailing lists (see the
interface which shows patch postings, any comments on a patch or
revisions to it, and maintainers can mark patches as under review,
accepted, or rejected. Most of these patchwork sites are listed at
-http://patchwork.kernel.org/.
+https://patchwork.kernel.org/.
4.x -next kernel tree for integration tests
-------------------------------------------
tree, they need to be integration-tested. For this purpose, a special
testing repository exists into which virtually all subsystem trees are
pulled on an almost daily basis:
- http://git.kernel.org/?p=linux/kernel/git/next/linux-next.git
+
+ https://git.kernel.org/?p=linux/kernel/git/next/linux-next.git
This way, the -next kernel gives a summary outlook onto what will be
expected to go into the mainline kernel at the next merge period.
Bug Reporting
-------------
-bugzilla.kernel.org is where the Linux kernel developers track kernel
+https://bugzilla.kernel.org is where the Linux kernel developers track kernel
bugs. Users are encouraged to report all bugs that they find in this
tool. For details on how to use the kernel bugzilla, please see:
- http://bugzilla.kernel.org/page.cgi?id=faq.html
+
+ https://bugzilla.kernel.org/page.cgi?id=faq.html
The file REPORTING-BUGS in the main kernel source directory has a good
template for how to report a possible kernel bug, and details what kind
bugs is one of the best ways to get merits among other developers, because
not many people like wasting time fixing other people's bugs.
-To work in the already reported bug reports, go to http://bugzilla.kernel.org.
+To work in the already reported bug reports, go to https://bugzilla.kernel.org.
If you want to be advised of the future bug reports, you can subscribe to the
bugme-new mailing list (only new bug reports are mailed here) or to the
bugme-janitor mailing list (every change in the bugzilla is mailed here)
- http://lists.linux-foundation.org/mailman/listinfo/bugme-new
- http://lists.linux-foundation.org/mailman/listinfo/bugme-janitors
+ https://lists.linux-foundation.org/mailman/listinfo/bugme-new
+
+ https://lists.linux-foundation.org/mailman/listinfo/bugme-janitors
As some of the above documents describe, the majority of the core kernel
developers participate on the Linux Kernel Mailing list. Details on how
to subscribe and unsubscribe from the list can be found at:
+
http://vger.kernel.org/vger-lists.html#linux-kernel
+
There are archives of the mailing list on the web in many different
places. Use a search engine to find these archives. For example:
+
http://dir.gmane.org/gmane.linux.kernel
+
It is highly recommended that you search the archives about the topic
you want to bring up, before you post it to the list. A lot of things
already discussed in detail are only recorded at the mailing list
Many of the lists are hosted on kernel.org. Information on them can be
found at:
+
http://vger.kernel.org/vger-lists.html
Please remember to follow good behavioral habits when using the lists.
Though a bit cheesy, the following URL has some simple guidelines for
interacting with the list (or any list):
+
http://www.albion.com/netiquette/
If multiple people respond to your mail, the CC: list of recipients may
writing at the top of the mail.
If you add patches to your mail, make sure they are plain readable text
-as stated in Documentation/SubmittingPatches. Kernel developers don't
-want to deal with attachments or compressed patches; they may want
-to comment on individual lines of your patch, which works only that way.
-Make sure you use a mail program that does not mangle spaces and tab
-characters. A good first test is to send the mail to yourself and try
-to apply your own patch by yourself. If that doesn't work, get your
-mail program fixed or change it until it works.
+as stated in Documentation/SubmittingPatches.
+Kernel developers don't want to deal with
+attachments or compressed patches; they may want to comment on
+individual lines of your patch, which works only that way. Make sure you
+use a mail program that does not mangle spaces and tab characters. A
+good first test is to send the mail to yourself and try to apply your
+own patch by yourself. If that doesn't work, get your mail program fixed
+or change it until it works.
Above all, please remember to show respect to other subscribers.
there is. When you submit a patch for acceptance, it will be reviewed
on its technical merits and those alone. So, what should you be
expecting?
+
- criticism
- comments
- requests for change
again, sometimes things get lost in the huge volume.
What should you not do?
+
- expect your patch to be accepted without question
- become defensive
- ignore comments
toward a solution that is right.
It is normal that the answers to your first patch might simply be a list
-of a dozen things you should correct. This does _not_ imply that your
-patch will not be accepted, and it is _not_ meant against you
+of a dozen things you should correct. This does **not** imply that your
+patch will not be accepted, and it is **not** meant against you
personally. Simply correct all issues raised against your patch and
resend it.
The kernel community works differently than most traditional corporate
development environments. Here are a list of things that you can try to
do to avoid problems:
+
Good things to say regarding your proposed changes:
+
- "This solves multiple problems."
- "This deletes 2000 lines of code."
- "Here is a patch that explains what I am trying to describe."
- "This increases performance on typical machines..."
Bad things you should avoid saying:
+
- "We did it this way in AIX/ptx/Solaris, so therefore it must be
good..."
- "I've being doing this for 20 years, so..."
and simplify (or simply re-order) patches before submitting them.
Here is an analogy from kernel developer Al Viro:
- "Think of a teacher grading homework from a math student. The
+
+ *"Think of a teacher grading homework from a math student. The
teacher does not want to see the student's trials and errors
before they came up with the solution. They want to see the
cleanest, most elegant answer. A good student knows this, and
would never submit her intermediate work before the final
- solution."
+ solution.*
- The same is true of kernel development. The maintainers and
+ *The same is true of kernel development. The maintainers and
reviewers do not want to see the thought process behind the
solution to the problem one is solving. They want to see a
- simple and elegant solution."
+ simple and elegant solution."*
It may be challenging to keep the balance between presenting an elegant
solution and working together with the community and discussing your
the text in your email. This information will become the ChangeLog
information for the patch, and will be preserved for everyone to see for
all time. It should describe the patch completely, containing:
+
- why the change is necessary
- the overall design approach in the patch
- implementation details
For more details on what this should all look like, please see the
ChangeLog section of the document:
+
"The Perfect Patch"
http://www.ozlabs.org/~akpm/stuff/tpp.txt
-
-
All of these things are sometimes very hard to do. It can take years to
perfect these practices (if at all). It's a continuous process of
improvement that requires a lot of patience and determination. But
----------
+
Thanks to Paolo Ciarrocchi who allowed the "Development Process"
-(http://lwn.net/Articles/94386/) section
+(https://lwn.net/Articles/94386/) section
to be based on text he had written, and to Randy Dunlap and Gerrit
Huizenga for some of the list of things you should and should not say.
Also thanks to Pat Mochel, Hanna Linder, Randy Dunlap, Kay Sievers,
projects / cascardo / linux.git / blobdiff