2 files changed, 98 insertions, 18 deletions

diff --git a/sound/Kconfig b/sound/Kconfig
index 1eceb85287c5..439e15c8faa3 100644
--- a/sound/Kconfig
+++ b/sound/Kconfig
@@ -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
diff --git a/sound/sound_core.c b/sound/sound_core.c
index 786067c49b01..bb4b88e606bb 100644
--- a/sound/sound_core.c
+++ b/sound/sound_core.c
@@ -128,6 +128,46 @@ 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
  */
@@ -219,8 +259,9 @@ static int sound_insert_unit(struct sound_unit **list, const struct file_operati
 
         if (!s)
                 return -ENOMEM;
-                
+
         spin_lock(&sound_loader_lock);
+retry:
         r = __sound_insert_unit(s, list, fops, index, low, top);
         spin_unlock(&sound_loader_lock);
         
@@ -231,11 +272,31 @@ 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:
+fail:
         kfree(s);
         return r;
 }
@@ -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;
         }