linux/Documentation/ABI
Linus Torvalds 91e67a996c Merge branch 'for_linus' of git://cavan.codon.org.uk/platform-drivers-x86
* 'for_linus' of git://cavan.codon.org.uk/platform-drivers-x86: (45 commits)
  acer-wmi: replaced the hard coded bitmap by the communication devices bitmap from SMBIOS
  acer-wmi: check the existence of internal wireless device when set capability
  acer-wmi: add ACER_WMID_v2 interface flag to represent new notebooks
  sony-laptop:irq: Remove IRQF_DISABLED
  asus-laptop: Add rfkill support for Pegatron Lucid tablet
  asus-laptop: pega_accel - Report accelerometer orientation change through udev
  asus-laptop: fix module description
  asus-laptop: hide leds on Pegatron Lucid
  asus-laptop: Pegatron Lucid accelerometer
  asus-laptop: allow boot time control of Pegatron ALS sensor
  Platform: samsung_laptop: add support for X520 machines.
  platform: samsung_laptop: add dmi information for Samsung R700 laptops
  hp_accel: Add axis-mapping for HP ProBook / EliteBook
  hp_accel: Add a new PNP id
  WMI: properly cleanup devices to avoid crashes
  ideapad: remove sysfs node for cfg
  ideapad: add debugfs support
  ideapad: add event for Novo key
  ideapad: change parameter of ideapad_sync_rfk_state
  ideapad: define vpc commands
  ...
2011-10-31 16:10:33 -07:00
..
obsolete oom: remove references to old badness() function 2011-07-25 20:57:09 -07:00
removed doc: raw1394: Trivial typo fix 2011-09-27 18:08:05 +02:00
stable Merge branch 'x86-vdso-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2011-07-22 17:05:15 -07:00
testing Merge branch 'for_linus' of git://cavan.codon.org.uk/platform-drivers-x86 2011-10-31 16:10:33 -07:00
README [PATCH] Add kernel<->userspace ABI stability documentation 2006-06-21 12:40:47 -07:00

README

This directory attempts to document the ABI between the Linux kernel and
userspace, and the relative stability of these interfaces.  Due to the
everchanging nature of Linux, and the differing maturity levels, these
interfaces should be used by userspace programs in different ways.

We have four different levels of ABI stability, as shown by the four
different subdirectories in this location.  Interfaces may change levels
of stability according to the rules described below.

The different levels of stability are:

  stable/
	This directory documents the interfaces that the developer has
	defined to be stable.  Userspace programs are free to use these
	interfaces with no restrictions, and backward compatibility for
	them will be guaranteed for at least 2 years.  Most interfaces
	(like syscalls) are expected to never change and always be
	available.

  testing/
	This directory documents interfaces that are felt to be stable,
	as the main development of this interface has been completed.
	The interface can be changed to add new features, but the
	current interface will not break by doing this, unless grave
	errors or security problems are found in them.  Userspace
	programs can start to rely on these interfaces, but they must be
	aware of changes that can occur before these interfaces move to
	be marked stable.  Programs that use these interfaces are
	strongly encouraged to add their name to the description of
	these interfaces, so that the kernel developers can easily
	notify them if any changes occur (see the description of the
	layout of the files below for details on how to do this.)

  obsolete/
  	This directory documents interfaces that are still remaining in
	the kernel, but are marked to be removed at some later point in
	time.  The description of the interface will document the reason
	why it is obsolete and when it can be expected to be removed.
	The file Documentation/feature-removal-schedule.txt may describe
	some of these interfaces, giving a schedule for when they will
	be removed.

  removed/
	This directory contains a list of the old interfaces that have
	been removed from the kernel.

Every file in these directories will contain the following information:

What:		Short description of the interface
Date:		Date created
KernelVersion:	Kernel version this feature first showed up in.
Contact:	Primary contact for this interface (may be a mailing list)
Description:	Long description of the interface and how to use it.
Users:		All users of this interface who wish to be notified when
		it changes.  This is very important for interfaces in
		the "testing" stage, so that kernel developers can work
		with userspace developers to ensure that things do not
		break in ways that are unacceptable.  It is also
		important to get feedback for these interfaces to make
		sure they are working in a proper way and do not need to
		be changed further.


How things move between levels:

Interfaces in stable may move to obsolete, as long as the proper
notification is given.

Interfaces may be removed from obsolete and the kernel as long as the
documented amount of time has gone by.

Interfaces in the testing state can move to the stable state when the
developers feel they are finished.  They cannot be removed from the
kernel tree without going through the obsolete state first.

It's up to the developer to place their interfaces in the category they
wish for it to start out in.