linux-sg2042/Documentation/ABI
Linus Torvalds d0195c7d7a f2fs-for-5.13-rc1
In this round, we added a new mount option, "checkpoint_merge", which introduces
 a kernel thread dealing with the f2fs checkpoints. Once we start to manage the
 IO priority along with blk-cgroup, the checkpoint operation can be processed in
 a lower priority under the process context. Since the checkpoint holds all the
 filesystem operations, we give a higher priority to the checkpoint thread all
 the time.
 
 Enhancement:
 - introduce gc_merge mount option to introduce a checkpoint thread
 - improve to run discard thread efficiently
 - allow modular compression algorithms
 - expose # of overprivision segments to sysfs
 - expose runtime compression stat to sysfs
 
 Bug fix:
 - fix OOB memory access by the node id lookup
 - avoid touching checkpointed data in the checkpoint-disabled mode
 - fix the resizing flow to avoid kernel panic and race conditions
 - fix block allocation issues on pinned files
 - address some swapfile issues
 - fix hugtask problem and kernel panic during atomic write operations
 - don't start checkpoint thread in RO
 
 And, we've cleaned up some kernel coding style and build warnings. In addition,
 we fixed some minor race conditions and error handling routines.
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Merge tag 'f2fs-for-5.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs

Pull f2fs updates from Jaegeuk Kim:
 "In this round, we added a new mount option, "checkpoint_merge", which
  introduces a kernel thread dealing with the f2fs checkpoints. Once we
  start to manage the IO priority along with blk-cgroup, the checkpoint
  operation can be processed in a lower priority under the process
  context. Since the checkpoint holds all the filesystem operations, we
  give a higher priority to the checkpoint thread all the time.

  Enhancements:
   - introduce gc_merge mount option to introduce a checkpoint thread
   - improve to run discard thread efficiently
   - allow modular compression algorithms
   - expose # of overprivision segments to sysfs
   - expose runtime compression stat to sysfs

  Bug fixes:
   - fix OOB memory access by the node id lookup
   - avoid touching checkpointed data in the checkpoint-disabled mode
   - fix the resizing flow to avoid kernel panic and race conditions
   - fix block allocation issues on pinned files
   - address some swapfile issues
   - fix hugtask problem and kernel panic during atomic write operations
   - don't start checkpoint thread in RO

  And, we've cleaned up some kernel coding style and build warnings. In
  addition, we fixed some minor race conditions and error handling
  routines"

* tag 'f2fs-for-5.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs: (48 commits)
  f2fs: drop inplace IO if fs status is abnormal
  f2fs: compress: remove unneed check condition
  f2fs: clean up left deprecated IO trace codes
  f2fs: avoid using native allocate_segment_by_default()
  f2fs: remove unnecessary struct declaration
  f2fs: fix to avoid NULL pointer dereference
  f2fs: avoid duplicated codes for cleanup
  f2fs: document: add description about compressed space handling
  f2fs: clean up build warnings
  f2fs: fix the periodic wakeups of discard thread
  f2fs: fix to avoid accessing invalid fio in f2fs_allocate_data_block()
  f2fs: fix to avoid GC/mmap race with f2fs_truncate()
  f2fs: set checkpoint_merge by default
  f2fs: Fix a hungtask problem in atomic write
  f2fs: fix to restrict mount condition on readonly block device
  f2fs: introduce gc_merge mount option
  f2fs: fix to cover __allocate_new_section() with curseg_lock
  f2fs: fix wrong alloc_type in f2fs_do_replace_block
  f2fs: delete empty compress.h
  f2fs: fix a typo in inode.c
  ...
2021-05-04 18:03:38 -07:00
..
obsolete batman-adv: Drop deprecated sysfs support 2020-12-04 08:40:52 +01:00
removed docs: ABI: cleanup several ABI documents 2020-10-30 13:14:29 +01:00
stable audit: drop /proc/PID/loginuid documentation Format field 2021-04-01 18:32:24 -04:00
testing f2fs-for-5.13-rc1 2021-05-04 18:03:38 -07:00
README docs: ABI: README: specify that files should be ReST compatible 2020-10-30 13:07:01 +01:00

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.

  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.


Note:
   The fields should be use a simple notation, compatible with ReST markup.
   Also, the file **should not** have a top-level index, like::

	===
	foo
	===

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.