linux/Documentation/ABI
Linus Torvalds 6d8ef53e8b for-f2fs-4.14
In this round, we've mostly tuned f2fs to provide better user experience
 for Android. Especially, we've worked on atomic write feature again with
 SQLite community in order to support it officially. And we added or modified
 several facilities to analyze and enhance IO behaviors.
 
 Major changes include:
 - add app/fs io stat
 - add inode checksum feature
 - support project/journalled quota
 - enhance atomic write with new ioctl() which exposes feature set
 - enhance background gc/discard/fstrim flows with new gc_urgent mode
 - add F2FS_IOC_FS{GET,SET}XATTR
 - fix some quota flows
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Merge tag 'f2fs-for-4.14' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs

Pull f2fs updates from Jaegeuk Kim:
 "In this round, we've mostly tuned f2fs to provide better user
  experience for Android. Especially, we've worked on atomic write
  feature again with SQLite community in order to support it officially.
  And we added or modified several facilities to analyze and enhance IO
  behaviors.

  Major changes include:
   - add app/fs io stat
   - add inode checksum feature
   - support project/journalled quota
   - enhance atomic write with new ioctl() which exposes feature set
   - enhance background gc/discard/fstrim flows with new gc_urgent mode
   - add F2FS_IOC_FS{GET,SET}XATTR
   - fix some quota flows"

* tag 'f2fs-for-4.14' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs: (63 commits)
  f2fs: hurry up to issue discard after io interruption
  f2fs: fix to show correct discard_granularity in sysfs
  f2fs: detect dirty inode in evict_inode
  f2fs: clear radix tree dirty tag of pages whose dirty flag is cleared
  f2fs: speed up gc_urgent mode with SSR
  f2fs: better to wait for fstrim completion
  f2fs: avoid race in between read xattr & write xattr
  f2fs: make get_lock_data_page to handle encrypted inode
  f2fs: use generic terms used for encrypted block management
  f2fs: introduce f2fs_encrypted_file for clean-up
  Revert "f2fs: add a new function get_ssr_cost"
  f2fs: constify super_operations
  f2fs: fix to wake up all sleeping flusher
  f2fs: avoid race in between atomic_read & atomic_inc
  f2fs: remove unneeded parameter of change_curseg
  f2fs: update i_flags correctly
  f2fs: don't check inode's checksum if it was dirtied or writebacked
  f2fs: don't need to update inode checksum for recovery
  f2fs: trigger fdatasync for non-atomic_write file
  f2fs: fix to avoid race in between aio and gc
  ...
2017-09-12 20:05:58 -07:00
..
obsolete ACPI / scan: Drop support for force_remove 2017-04-13 03:51:47 +02:00
removed rfkill: Remove obsolete "claim" sysfs interface 2016-02-24 09:04:24 +01:00
stable dmaengine updates for 4.14-rc1 2017-09-07 14:03:05 -07:00
testing for-f2fs-4.14 2017-09-12 20:05:58 -07:00
README docs: fix locations of several documents that got moved 2016-10-24 08:12:35 -02:00

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.

  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.


Notable bits of non-ABI, which should not under any circumstances be considered
stable:

- Kconfig.  Userspace should not rely on the presence or absence of any
  particular Kconfig symbol, in /proc/config.gz, in the copy of .config
  commonly installed to /boot, or in any invocation of the kernel build
  process.

- Kernel-internal symbols.  Do not rely on the presence, absence, location, or
  type of any kernel symbol, either in System.map files or the kernel binary
  itself.  See Documentation/process/stable-api-nonsense.rst.