sound: make OSS device number claiming optional and schedule its removal (93fe4483) · Commits · 戴 / test

Documentation/feature-removal-schedule.txt

+24 −0

Original line number	Diff line number	Diff line
		@@ -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>

sound/Kconfig

+28 −0

Original line number	Diff line number	Diff line
		@@ -32,6 +32,34 @@ config SOUND_OSS_CORE
		bool
		default n

		config SOUND_OSS_CORE_PRECLAIM
		bool "Preclaim OSS device numbers"
		depends on SOUND_OSS_CORE
		default y
		help
		With this option enabled, the kernel will claim all OSS device
		numbers if any OSS support (native or emulation) is enabled
		whether the respective module is loaded or not and try to load the
		appropriate module using sound-slot/service-* and char-major-*
		module aliases when one of the device numbers is opened. With
		this option disabled, kernel will only claim actually in-use
		device numbers and opening a missing device will generate only the
		standard char-major-* aliases.

		The only visible difference is use of additional module aliases
		and whether OSS sound devices appear multiple times in
		/proc/devices. sound-slot/service-* module aliases are scheduled
		to be removed (ie. PRECLAIM won't be available) and this option is
		to make the transition easier. This option can be overridden
		during boot using the kernel parameter soundcore.preclaim_oss.

		Disabling this allows alternative OSS implementations.

		Please read Documentation/feature-removal-schedule.txt for
		details.

		If unusre, say Y.

		source "sound/oss/dmasound/Kconfig"

		if !M68K

sound/sound_core.c

+70 −18

Original line number	Diff line number	Diff line
		@@ -127,6 +127,46 @@ extern int msnd_classic_init(void);
		extern int msnd_pinnacle_init(void);
		#endif

		/*
		* By default, OSS sound_core claims full legacy minor range (0-255)
		* of SOUND_MAJOR to trap open attempts to any sound minor and
		* requests modules using custom sound-slot/service-* module aliases.
		* The only benefit of doing this is allowing use of custom module
		* aliases instead of the standard char-major-* ones. This behavior
		* prevents alternative OSS implementation and is scheduled to be
		* removed.
		*
		* CONFIG_SOUND_OSS_CORE_PRECLAIM and soundcore.preclaim_oss kernel
		* parameter are added to allow distros and developers to try and
		* switch to alternative implementations without needing to rebuild
		* the kernel in the meantime. If preclaim_oss is non-zero, the
		* kernel will behave the same as before. All SOUND_MAJOR minors are
		* preclaimed and the custom module aliases along with standard chrdev
		* ones are emitted if a missing device is opened. If preclaim_oss is
		* zero, sound_core only grabs what's actually in use and for missing
		* devices only the standard chrdev aliases are requested.
		*
		* All these clutters are scheduled to be removed along with
		* sound-slot/service-* module aliases. Please take a look at
		* feature-removal-schedule.txt for details.
		*/
		#ifdef CONFIG_SOUND_OSS_CORE_PRECLAIM
		static int preclaim_oss = 1;
		#else
		static int preclaim_oss = 0;
		#endif

		module_param(preclaim_oss, int, 0444);

		static int soundcore_open(struct inode , struct file );

		static const struct file_operations soundcore_fops =
		{
		/* We must have an owner or the module locking fails */
		.owner = THIS_MODULE,
		.open = soundcore_open,
		};

		/*
		* Low level list operator. Scan the ordered list, find a hole and
		* join into it. Called with the lock asserted
		@@ -221,6 +261,7 @@ static int sound_insert_unit(struct sound_unit **list, const struct file_operati
		return -ENOMEM;

		spin_lock(&sound_loader_lock);
		retry:
		r = __sound_insert_unit(s, list, fops, index, low, top);
		spin_unlock(&sound_loader_lock);

		@@ -231,9 +272,29 @@ static int sound_insert_unit(struct sound_unit **list, const struct file_operati
		else
		sprintf(s->name, "sound/%s%d", name, r / SOUND_STEP);

		if (!preclaim_oss) {
		/*
		* Something else might have grabbed the minor. If
		* first free slot is requested, rescan with @low set
		* to the next unit; otherwise, -EBUSY.
		*/
		r = __register_chrdev(SOUND_MAJOR, s->unit_minor, 1, s->name,
		&soundcore_fops);
		if (r < 0) {
		spin_lock(&sound_loader_lock);
		__sound_remove_unit(list, s->unit_minor);
		if (index < 0) {
		low = s->unit_minor + SOUND_STEP;
		goto retry;
		}
		spin_unlock(&sound_loader_lock);
		return -EBUSY;
		}
		}

		device_create(sound_class, dev, MKDEV(SOUND_MAJOR, s->unit_minor),
		NULL, s->name+6);
		return r;
		return s->unit_minor;

		fail:
		kfree(s);
		@@ -254,6 +315,9 @@ static void sound_remove_unit(struct sound_unit **list, int unit)
		p = __sound_remove_unit(list, unit);
		spin_unlock(&sound_loader_lock);
		if (p) {
		if (!preclaim_oss)
		__unregister_chrdev(SOUND_MAJOR, p->unit_minor, 1,
		p->name);
		device_destroy(sound_class, MKDEV(SOUND_MAJOR, p->unit_minor));
		kfree(p);
		}
		@@ -491,19 +555,6 @@ void unregister_sound_dsp(int unit)

		EXPORT_SYMBOL(unregister_sound_dsp);

		/*
		* Now our file operations
		*/

		static int soundcore_open(struct inode , struct file );

		static const struct file_operations soundcore_fops=
		{
		/* We must have an owner or the module locking fails */
		.owner = THIS_MODULE,
		.open = soundcore_open,
		};

		static struct sound_unit *__look_for_unit(int chain, int unit)
		{
		struct sound_unit *s;
		@@ -539,7 +590,7 @@ static int soundcore_open(struct inode inode, struct file file)
		s = __look_for_unit(chain, unit);
		if (s)
		new_fops = fops_get(s->unit_fops);
		if (!new_fops) {
		if (preclaim_oss && !new_fops) {
		spin_unlock(&sound_loader_lock);

		/*
		@@ -605,7 +656,8 @@ static void cleanup_oss_soundcore(void)

		static int __init init_oss_soundcore(void)
		{
		if (register_chrdev(SOUND_MAJOR, "sound", &soundcore_fops)==-1) {
		if (preclaim_oss &&
		register_chrdev(SOUND_MAJOR, "sound", &soundcore_fops) == -1) {
		printk(KERN_ERR "soundcore: sound device already in use.\n");
		return -EBUSY;
		}

Admin message