linux/Documentation/ABI
Linus Torvalds 7f5b09c15a Merge git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb-2.6
* git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb-2.6: (220 commits)
  USB: backlight, appledisplay: fix incomplete registration failure handling
  USB: pl2303: remove unnecessary reset of usb_device in urbs
  USB: ftdi_sio: remove obsolete check in unthrottle
  USB: ftdi_sio: remove unused tx_bytes counter
  USB: qcaux: driver for auxiliary serial ports on Qualcomm devices
  USB: pl2303: initial TIOCGSERIAL support
  USB: option: add Longcheer/Longsung vendor ID
  USB: fix I2C API usage in ohci-pnx4008.
  USB: usbmon: mask seconds properly in text API
  USB: sisusbvga: no unnecessary GFP_ATOMIC
  USB: storage: onetouch: unnecessary GFP_ATOMIC
  USB: serial: ftdi: add CONTEC vendor and product id
  USB: remove references to port->port.count from the serial drivers
  USB: tty: Prune uses of tty_request_room in the USB layer
  USB: tty: Add a function to insert a string of characters with the same flag
  USB: don't read past config->interface[] if usb_control_msg() fails in usb_reset_configuration()
  USB: tty: kill request_room for USB ACM class
  USB: tty: sort out the request_room handling for whiteheat
  USB: storage: fix misplaced parenthesis
  USB: vstusb.c: removal of driver for Vernier Software & Technology, Inc., devices and spectrometers
  ...
2010-03-03 08:48:58 -08:00
..
obsolete ocfs2: Move /sys/o2cb to /sys/fs/o2cb 2008-04-18 08:56:10 -07:00
removed ieee1394: remove old isochronous ABI 2007-07-10 00:07:41 +02:00
stable [SCSI] qla2xxx: Add firmware-dump kobject uevent notification. 2009-12-04 12:00:10 -06:00
testing Merge git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb-2.6 2010-03-03 08:48:58 -08:00
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.