sound: make OSS device number claiming optional and schedule its removal

If any OSS support is enabled, regardless of built-in or module,
sound_core claims full OSS major number (that is, the old 0-255
region) to trap open attempts and request sound modules using custom
module aliases.  This feature is redundant as chrdev already has such
mechanism.  This preemptive claiming prevents alternative OSS
implementation.

The custom module aliases are scheduled to be removed and the previous
patch made soundcore emit the standard chrdev aliases too to help
transition.

This patch schedule the feature for removal in a year and makes it
optional so that developers and distros can try new things in the
meantime without rebuilding the kernel.  The pre-claiming can be
turned off by using SOUND_OSS_CORE_PRECLAIM and/or kernel parameter
soundcore.preclaim_oss.

As this allows sound minors to be individually grabbed by other users,
this patch updates sound_insert_unit() such that if registering
individual device region fails, it tries the next available slot.

For details on removal plan, please read the entry added by this patch
in feature-removal-schedule.txt .

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 24 insertions, 0 deletions

diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
index 09e031c55887..f0690bbbd73c 100644
--- a/Documentation/feature-removal-schedule.txt
+++ b/Documentation/feature-removal-schedule.txt
@@ -468,3 +468,27 @@ Why:	cpu_policy_rwsem has a new cleaner definition making it local to
 	cpufreq core and contained inside cpufreq.c. Other dependent
 	drivers should not use it in order to safely avoid lockdep issues.
 Who:	Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
+
+----------------------------
+
+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>