Documentation/process/howto.rst

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.. _process_howto:

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
to work with the Linux kernel development community.  It tries to not
contain anything related to the technical aspects of kernel programming,
but will help point you in the right direction for that.

If anything in this document becomes out of date, please send in patches
to the maintainer of this file, who is listed at the bottom of the
document.


Introduction
------------

So, you want to learn how to become a Linux kernel developer?  Or you
have been told by your manager, "Go write a Linux driver for this
device."  This document's goal is to teach you everything you need to
know to achieve this by describing the process you need to go through,
and hints on how to work with the community.  It will also try to
explain some of the reasons why the community works like it does.

The kernel is written mostly in C, with some architecture-dependent
parts written in assembly. A good understanding of C is required for
kernel development.  Assembly (any architecture) is not required unless
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]

The kernel is written using GNU C and the GNU toolchain.  While it
adheres to the ISO C11 standard, it uses a number of extensions that are
not featured in the standard.  The kernel is a freestanding C
environment, with no reliance on the standard C library, so some
portions of the C standard are not supported.  Arbitrary long long
divisions and floating point are not allowed.  It can sometimes be
difficult to understand the assumptions the kernel has on the toolchain
and the extensions that it uses, and unfortunately there is no
definitive reference for them.  Please check the gcc info pages (`info
gcc`) for some information on them.

Please remember that you are trying to learn how to work with the
existing development community.  It is a diverse group of people, with
high standards for coding, style and procedure.  These standards have
been created over time based on what they have found to work best for
such a large and geographically dispersed team.  Try to learn as much as
possible about these standards ahead of time, as they are well
documented; do not expect people to adapt to you or your company's way
of doing things.


Legal Issues
------------

The Linux kernel source code is released under the GPL.  Please see the file
COPYING in the main directory of the source tree. The Linux kernel licensing
rules and how to use `SPDX <https://spdx.org/>`_ identifiers in source code are
described in :ref:`Documentation/process/license-rules.rst <kernel_licensing>`.
If you have further questions about the license, please contact a lawyer, and do
not ask on the Linux kernel mailing list.  The people on the mailing lists are
not lawyers, and you should not rely on their statements on legal matters.

For common questions and answers about the GPL, please see:

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