path: root/Documentation/feature-removal-schedule.txt

The following is a list of files and features that are going to be
removed in the kernel source tree.  Every entry should contain what
exactly is going away, why it is happening, and who is going to be doing
the work.  When the feature is removed from the kernel, it should also
be removed from this file.

---------------------------

What:	PRISM54
When:	2.6.34

Why:	prism54 FullMAC PCI / Cardbus devices used to be supported only by the
	prism54 wireless driver. After Intersil stopped selling these
	devices in preference for the newer more flexible SoftMAC devices
	a SoftMAC device driver was required and prism54 did not support
	them. The p54pci driver now exists and has been present in the kernel for
	a while. This driver supports both SoftMAC devices and FullMAC devices.
	The main difference between these devices was the amount of memory which
	could be used for the firmware. The SoftMAC devices support a smaller
	amount of memory. Because of this the SoftMAC firmware fits into FullMAC
	devices's memory. p54pci supports not only PCI / Cardbus but also USB
	and SPI. Since p54pci supports all devices prism54 supports
	you will have a conflict. I'm not quite sure how distributions are
	handling this conflict right now. prism54 was kept around due to
	claims users may experience issues when using the SoftMAC driver.
	Time has passed users have not reported issues. If you use prism54
	and for whatever reason you cannot use p54pci please let us know!
	E-mail us at: linux-wireless@vger.kernel.org

	For more information see the p54 wiki page:

	http://wireless.kernel.org/en/users/Drivers/p54

Who:	Luis R. Rodriguez <lrodriguez@atheros.com>

---------------------------

What:	IRQF_SAMPLE_RANDOM
Check:	IRQF_SAMPLE_RANDOM
When:	July 2009

Why:	Many of IRQF_SAMPLE_RANDOM users are technically bogus as entropy
	sources in the kernel's current entropy model. To resolve this, every
	input point to the kernel's entropy pool needs to better document the
	type of entropy source it actually is. This will be replaced with
	additional add_*_randomness functions in drivers/char/random.c

Who:	Robin Getz <rgetz@blackfin.uclinux.org> & Matt Mackall <mpm@selenic.com>

---------------------------

What:	Deprecated snapshot ioctls
When:	2.6.36

Why:	The ioctls in kernel/power/user.c were marked as deprecated long time
	ago. Now they notify users about that so that they need to replace
	their userspace. After some more time, remove them completely.

Who:	Jiri Slaby <jirislaby@gmail.com>

---------------------------

What:	The ieee80211_regdom module parameter
When:	March 2010 / desktop catchup

Why:	This was inherited by the CONFIG_WIRELESS_OLD_REGULATORY code,
	and currently serves as an option for users to define an
	ISO / IEC 3166 alpha2 code for the country they are currently
	present in. Although there are userspace API replacements for this
	through nl80211 distributions haven't yet caught up with implementing
	decent alternatives through standard GUIs. Although available as an
	option through iw or wpa_supplicant its just a matter of time before
	distributions pick up good GUI options for this. The ideal solution
	would actually consist of intelligent designs which would do this for
	the user automatically even when travelling through different countries.
	Until then we leave this module parameter as a compromise.

	When userspace improves with reasonable widely-available alternatives for
	this we will no longer need this module parameter. This entry hopes that
	by the super-futuristically looking date of "March 2010" we will have
	such replacements widely available.

Who:	Luis R. Rodriguez <lrodriguez@atheros.com>

---------------------------

What:	dev->power.power_state
When:	July 2007
Why:	Broken design for runtime control over driver power states, confusing
	driver-internal runtime power management with:  mechanisms to support
	system-wide sleep state transitions; event codes that distinguish
	different phases of swsusp "sleep" transitions; and userspace policy
	inputs.  This framework was never widely used, and most attempts to
	use it were broken.  Drivers should instead be exposing domain-specific
	interfaces either to kernel or to userspace.
Who:	Pavel Machek <pavel@ucw.cz>

---------------------------

What:	Video4Linux API 1 ioctls and from Video devices.
When:	July 2009
Files:	include/linux/videodev.h
Check:	include/linux/videodev.h
Why:	V4L1 AP1 was replaced by V4L2 API during migration from 2.4 to 2.6
	series. The old API have lots of drawbacks and don't provide enough
	means to work with all video and audio standards. The newer API is
	already available on the main drivers and should be used instead.
	Newer drivers should use v4l_compat_translate_ioctl function to handle
	old calls, replacing to newer ones.
	Decoder iocts are using internally to allow video drivers to
	communicate with video decoders. This should also be improved to allow
	V4L2 calls being translated into compatible internal ioctls.
	Compatibility ioctls will be provided, for a while, via 
	v4l1-compat module. 
Who:	Mauro Carvalho Chehab <mchehab@infradead.org>

---------------------------

What:	sys_sysctl
When:	September 2010
Option: CONFIG_SYSCTL_SYSCALL
Why:	The same information is available in a more convenient from
	/proc/sys, and none of the sysctl variables appear to be
	important performance wise.

	Binary sysctls are a long standing source of subtle kernel
	bugs and security issues.

	When I looked several months ago all I could find after
	searching several distributions were 5 user space programs and
	glibc (which falls back to /proc/sys) using this syscall.

	The man page for sysctl(2) documents it as unusable for user
	space programs.

	sysctl(2) is not generally ABI compatible to a 32bit user
	space application on a 64bit and a 32bit kernel.

	For the last several months the policy has been no new binary
	sysctls and no one has put forward an argument to use them.

	Binary sysctls issues seem to keep happening appearing so
	properly deprecating them (with a warning to user space) and a
	2 year grace warning period will mean eventually we can kill
	them and end the pain.

	In the mean time individual binary sysctls can be dealt with
	in a piecewise fashion.

Who:	Eric Biederman <ebiederm@xmission.com>

---------------------------

What:	/proc/<pid>/oom_adj
When:	August 2012
Why:	/proc/<pid>/oom_adj allows userspace to influence the oom killer's
	badness heuristic used to determine which task to kill when the kernel
	is out of memory.

	The badness heuristic has since been rewritten since the introduction of
	this tunable such that its meaning is deprecated.  The value was
	implemented as a bitshift on a score generated by the badness()
	function that did not have any precise units of measure.  With the
	rewrite, the score is given as a proportion of available memory to the
	task allocating pages, so using a bitshift which grows the score
	exponentially is, thus, impossible to tune with fine granularity.

	A much more powerful interface, /proc/<pid>/oom_score_adj, was
	introduced with the oom killer rewrite that allows users to increase or
	decrease the badness() score linearly.  This interface will replace
	/proc/<pid>/oom_adj.

	A warning will be emitted to the kernel log if an application uses this
	deprecated interface.  After it is printed once, future warnings will be
	suppressed until the kernel is rebooted.

---------------------------

What:	remove EXPORT_SYMBOL(kernel_thread)
When:	August 2006
Files:	arch/*/kernel/*_ksyms.c
Check:	kernel_thread
Why:	kernel_thread is a low-level implementation detail.  Drivers should
        use the <linux/kthread.h> API instead which shields them from
	implementation details and provides a higherlevel interface that
	prevents bugs and code duplication
Who:	Christoph Hellwig <hch@lst.de>

---------------------------

What:	Unused EXPORT_SYMBOL/EXPORT_SYMBOL_GPL exports
	(temporary transition config option provided until then)
	The transition config option will also be removed at the same time.
When:	before 2.6.19
Why:	Unused symbols are both increasing the size of the kernel binary
	and are often a sign of "wrong API"
Who:	Arjan van de Ven <arjan@linux.intel.com>

---------------------------

What:	PHYSDEVPATH, PHYSDEVBUS, PHYSDEVDRIVER in the uevent environment
When:	October 2008
Why:	The stacking of class devices makes these values misleading and
	inconsistent.
	Class devices should not carry any of these properties, and bus
	devices have SUBSYTEM and DRIVER as a replacement.
Who:	Kay Sievers <kay.sievers@suse.de>

---------------------------

What:	ACPI procfs interface
When:	July 2008
Why:	ACPI sysfs conversion should be finished by January 2008.
	ACPI procfs interface will be removed in July 2008 so that
	there is enough time for the user space to catch up.
Who:	Zhang Rui <rui.zhang@intel.com>

---------------------------

What:	/proc/acpi/button
When:	August 2007
Why:	/proc/acpi/button has been replaced by events to the input layer
	since 2.6.20.
Who:	Len Brown <len.brown@intel.com>

---------------------------

What:	/proc/acpi/event
When:	February 2008
Why:	/proc/acpi/event has been replaced by events via the input layer
	and netlink since 2.6.23.
Who:	Len Brown <len.brown@intel.com>

---------------------------

What:	i386/x86_64 bzImage symlinks
When:	April 2010

Why:	The i386/x86_64 merge provides a symlink to the old bzImage
	location so not yet updated user space tools, e.g. package
	scripts, do not break.
Who:	Thomas Gleixner <tglx@linutronix.de>

---------------------------

What:	GPIO autorequest on gpio_direction_{input,output}() in gpiolib
When:	February 2010
Why:	All callers should use explicit gpio_request()/gpio_free().
	The autorequest mechanism in gpiolib was provided mostly as a
	migration aid for legacy GPIO interfaces (for SOC based GPIOs).
	Those users have now largely migrated.  Platforms implementing
	the GPIO interfaces without using gpiolib will see no changes.
Who:	David Brownell <dbrownell@users.sourceforge.net>
---------------------------

What:	b43 support for firmware revision < 410
When:	The schedule was July 2008, but it was decided that we are going to keep the
        code as long as there are no major maintanance headaches.
	So it _could_ be removed _any_ time now, if it conflicts with something new.
Why:	The support code for the old firmware hurts code readability/maintainability
	and slightly hurts runtime performance. Bugfixes for the old firmware
	are not provided by Broadcom anymore.
Who:	Michael Buesch <mb@bu3sch.de>

---------------------------

What:	/sys/o2cb symlink
When:	January 2010
Why:	/sys/fs/o2cb is the proper location for this information - /sys/o2cb
	exists as a symlink for backwards compatibility for old versions of
	ocfs2-tools. 2 years should be sufficient time to phase in new versions
	which know to look in /sys/fs/o2cb.
Who:	ocfs2-devel@oss.oracle.com

---------------------------

What:	Ability for non root users to shm_get hugetlb pages based on mlock
	resource limits
When:	2.6.31
Why:	Non root users need to be part of /proc/sys/vm/hugetlb_shm_group or
	have CAP_IPC_LOCK to be able to allocate shm segments backed by
	huge pages.  The mlock based rlimit check to allow shm hugetlb is
	inconsistent with mmap based allocations.  Hence it is being
	deprecated.
Who:	Ravikiran Thirumalai <kiran@scalex86.org>

---------------------------

What:	CONFIG_THERMAL_HWMON
When:	January 2009
Why:	This option was introduced just to allow older lm-sensors userspace
	to keep working over the upgrade to 2.6.26. At the scheduled time of
	removal fixed lm-sensors (2.x or 3.x) should be readily available.
Who:	Rene Herman <rene.herman@gmail.com>

---------------------------

What:	Code that is now under CONFIG_WIRELESS_EXT_SYSFS
	(in net/core/net-sysfs.c)
When:	After the only user (hal) has seen a release with the patches
	for enough time, probably some time in 2010.
Why:	Over 1K .text/.data size reduction, data is available in other
	ways (ioctls)
Who:	Johannes Berg <johannes@sipsolutions.net>

---------------------------

What:	sysfs ui for changing p4-clockmod parameters
When:	September 2009
Why:	See commits 129f8ae9b1b5be94517da76009ea956e89104ce8 and
	e088e4c9cdb618675874becb91b2fd581ee707e6.
	Removal is subject to fixing any remaining bugs in ACPI which may
	cause the thermal throttling not to happen at the right time.
Who:	Dave Jones <davej@redhat.com>, Matthew Garrett <mjg@redhat.com>

-----------------------------

What:	__do_IRQ all in one fits nothing interrupt handler
When:	2.6.32
Why:	__do_IRQ was kept for easy migration to the type flow handlers.
	More than two years of migration time is enough.
Who:	Thomas Gleixner <tglx@linutronix.de>

-----------------------------

What:	fakephp and associated sysfs files in /sys/bus/pci/slots/
When:	2011
Why:	In 2.6.27, the semantics of /sys/bus/pci/slots was redefined to
	represent a machine's physical PCI slots. The change in semantics
	had userspace implications, as the hotplug core no longer allowed
	drivers to create multiple sysfs files per physical slot (required
	for multi-function devices, e.g.). fakephp was seen as a developer's
	tool only, and its interface changed. Too late, we learned that
	there were some users of the fakephp interface.

	In 2.6.30, the original fakephp interface was restored. At the same
	time, the PCI core gained the ability that fakephp provided, namely
	function-level hot-remove and hot-add.

	Since the PCI core now provides the same functionality, exposed in:

		/sys/bus/pci/rescan
		/sys/bus/pci/devices/.../remove
		/sys/bus/pci/devices/.../rescan

	there is no functional reason to maintain fakephp as well.

	We will keep the existing module so that 'modprobe fakephp' will
	present the old /sys/bus/pci/slots/... interface for compatibility,
	but users are urged to migrate their applications to the API above.

	After a reasonable transition period, we will remove the legacy
	fakephp interface.
Who:	Alex Chiang <achiang@hp.com>

---------------------------

What:	CONFIG_RFKILL_INPUT
When:	2.6.33
Why:	Should be implemented in userspace, policy daemon.
Who:	Johannes Berg <johannes@sipsolutions.net>

----------------------------

What:	sound-slot/service-* module aliases and related clutters in
	sound/sound_core.c
When:	August 2010
Why:	OSS sound_core grabs all legacy minors (0-255) of SOUND_MAJOR
	(14) and requests modules using custom sound-slot/service-*
	module aliases.  The only benefit of doing this is allowing
	use of custom module aliases which might as well be considered
	a bug at this point.  This preemptive claiming prevents
	alternative OSS implementations.

	Till the feature is removed, the kernel will be requesting
	both sound-slot/service-* and the standard char-major-* module
	aliases and allow turning off the pre-claiming selectively via
	CONFIG_SOUND_OSS_CORE_PRECLAIM and soundcore.preclaim_oss
	kernel parameter.

	After the transition phase is complete, both the custom module
	aliases and switches to disable it will go away.  This removal
	will also allow making ALSA OSS emulation independent of
	sound_core.  The dependency will be broken then too.
Who:	Tejun Heo <tj@kernel.org>

----------------------------

What:	Support for VMware's guest paravirtuliazation technique [VMI] will be
	dropped.
When:	2.6.37 or earlier.
Why:	With the recent innovations in CPU hardware acceleration technologies
	from Intel and AMD, VMware ran a few experiments to compare these
	techniques to guest paravirtualization technique on VMware's platform.
	These hardware assisted virtualization techniques have outperformed the
	performance benefits provided by VMI in most of the workloads. VMware
	expects that these hardware features will be ubiquitous in a couple of
	years, as a result, VMware has started a phased retirement of this
	feature from the hypervisor. We will be removing this feature from the
	Kernel too. Right now we are targeting 2.6.37 but can retire earlier if
	technical reasons (read opportunity to remove major chunk of pvops)
	arise.

	Please note that VMI has always been an optimization and non-VMI kernels
	still work fine on VMware's platform.
	Latest versions of VMware's product which support VMI are,
	Workstation 7.0 and VSphere 4.0 on ESX side, future maintainence
	releases for these products will continue supporting VMI.

	For more details about VMI retirement take a look at this,
	http://blogs.vmware.com/guestosguide/2009/09/vmi-retirement.html

Who:	Alok N Kataria <akataria@vmware.com>

----------------------------

What:	Support for lcd_switch and display_get in asus-laptop driver
When:	March 2010
Why:	These two features use non-standard interfaces. There are the
	only features that really need multiple path to guess what's
	the right method name on a specific laptop.

	Removing them will allow to remove a lot of code an significantly
	clean the drivers.

	This will affect the backlight code which won't be able to know
	if the backlight is on or off. The platform display file will also be
	write only (like the one in eeepc-laptop).

	This should'nt affect a lot of user because they usually know
	when their display is on or off.

Who:	Corentin Chary <corentin.chary@gmail.com>

----------------------------

What:	sysfs-class-rfkill state file
When:	Feb 2014
Files:	net/rfkill/core.c
Why: 	Documented as obsolete since Feb 2010. This file is limited to 3
	states while the rfkill drivers can have 4 states.
Who: 	anybody or Florian Mickler <florian@mickler.org>

----------------------------

What: 	sysfs-class-rfkill claim file
When:	Feb 2012
Files:	net/rfkill/core.c
Why:	It is not possible to claim an rfkill driver since 2007. This is
	Documented as obsolete since Feb 2010.
Who: 	anybody or Florian Mickler <florian@mickler.org>

----------------------------

What:	capifs
When:	February 2011
Files:	drivers/isdn/capi/capifs.*
Why:	udev fully replaces this special file system that only contains CAPI
	NCCI TTY device nodes. User space (pppdcapiplugin) works without
	noticing the difference.
Who:	Jan Kiszka <jan.kiszka@web.de>

----------------------------

What:	KVM paravirt mmu host support
When:	January 2011
Why:	The paravirt mmu host support is slower than non-paravirt mmu, both
	on newer and older hardware.  It is already not exposed to the guest,
	and kept only for live migration purposes.
Who:	Avi Kivity <avi@redhat.com>

----------------------------

What:	iwlwifi 50XX module parameters
When:	2.6.40
Why:	The "..50" modules parameters were used to configure 5000 series and
	up devices; different set of module parameters also available for 4965
	with same functionalities. Consolidate both set into single place
	in drivers/net/wireless/iwlwifi/iwl-agn.c

Who:	Wey-Yi Guy <wey-yi.w.guy@intel.com>

----------------------------

What:	iwl4965 alias support
When:	2.6.40
Why:	Internal alias support has been present in module-init-tools for some
	time, the MODULE_ALIAS("iwl4965") boilerplate aliases can be removed
	with no impact.

Who:	Wey-Yi Guy <wey-yi.w.guy@intel.com>

---------------------------

What:	xt_NOTRACK
Files:	net/netfilter/xt_NOTRACK.c
When:	April 2011
Why:	Superseded by xt_CT
Who:	Netfilter developer team <netfilter-devel@vger.kernel.org>

---------------------------

What:	video4linux /dev/vtx teletext API support
When:	2.6.35
Files:	drivers/media/video/saa5246a.c drivers/media/video/saa5249.c
	include/linux/videotext.h
Why:	The vtx device nodes have been superseded by vbi device nodes
	for many years. No applications exist that use the vtx support.
	Of the two i2c drivers that actually support this API the saa5249
	has been impossible to use for a year now and no known hardware
	that supports this device exists. The saa5246a is theoretically
	supported by the old mxb boards, but it never actually worked.

	In summary: there is no hardware that can use this API and there
	are no applications actually implementing this API.

	The vtx support still reserves minors 192-223 and we would really
	like to reuse those for upcoming new functionality. In the unlikely
	event that new hardware appears that wants to use the functionality
	provided by the vtx API, then that functionality should be build
	around the sliced VBI API instead.
Who:	Hans Verkuil <hverkuil@xs4all.nl>

----------------------------

What:	IRQF_DISABLED
When:	2.6.36
Why:	The flag is a NOOP as we run interrupt handlers with interrupts disabled
Who:	Thomas Gleixner <tglx@linutronix.de>

----------------------------

What:	old ieee1394 subsystem (CONFIG_IEEE1394)
When:	2.6.37
Files:	drivers/ieee1394/ except init_ohci1394_dma.c
Why:	superseded by drivers/firewire/ (CONFIG_FIREWIRE) which offers more
	features, better performance, and better security, all with smaller
	and more modern code base
Who:	Stefan Richter <stefanr@s5r6.in-berlin.de>

----------------------------

What:	The acpi_sleep=s4_nonvs command line option
When:	2.6.37
Files:	arch/x86/kernel/acpi/sleep.c
Why:	superseded by acpi_sleep=nonvs
Who:	Rafael J. Wysocki <rjw@sisk.pl>

----------------------------

What: 	PCI DMA unmap state API
When:	August 2012
Why:	PCI DMA unmap state API (include/linux/pci-dma.h) was replaced
	with DMA unmap state API (DMA unmap state API can be used for
	any bus).
Who:	FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

----------------------------

What: 	DMA_xxBIT_MASK macros
When:	Jun 2011
Why:	DMA_xxBIT_MASK macros were replaced with DMA_BIT_MASK() macros.
Who:	FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

----------------------------