[ALSA] Improve the slots option handling

Fix and improve the slots option handling.  The sound core tries to
find the slot with the given module name first and assign if it's
still available.  If all pre-given slots are unavailable, then try
to find another free slot.

Also, when a module name begins with '!', it means the negative match:
the slot will be given for any modules but that one.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Documentation/sound/alsa/ALSA-Configuration.txt

@@ -2271,6 +2271,10 @@ case above again, the first two slots are already reserved.  If any
 other driver (e.g. snd-usb-audio) is loaded before snd-interwave or
 snd-ens1371, it will be assigned to the third or later slot.
 
+When a module name is given with '!', the slot will be given for any
+modules but that name.  For example, "slots=!snd-pcsp" will reserve
+the first slot for any modules but snd-pcsp. 
+
 
 ALSA PCM devices to OSS devices mapping
 =======================================

sound/core/init.c

@@ -46,17 +46,24 @@ static char *slots[SNDRV_CARDS];
 module_param_array(slots, charp, NULL, 0444);
 MODULE_PARM_DESC(slots, "Module names assigned to the slots.");
 
-/* return non-zero if the given index is already reserved for another
+/* return non-zero if the given index is reserved for the given
  * module via slots option
  */
-static int module_slot_mismatch(struct module *module, int idx)
+static int module_slot_match(struct module *module, int idx)
 {
+	int match = 1;
 #ifdef MODULE
-	char *s1, *s2;
+	const char *s1, *s2;
+
 	if (!module || !module->name || !slots[idx])
 		return 0;
-	s1 = slots[idx];
-	s2 = module->name;
+
+	s1 = module->name;
+	s2 = slots[idx];
+	if (*s2 == '!') {
+		match = 0; /* negative match */
+		s2++;
+	}
 	/* compare module name strings
 	 * hyphens are handled as equivalent with underscore
 	 */
@@ -68,12 +75,12 @@ static int module_slot_mismatch(struct module *module, int idx)
 		if (c2 == '-')
 			c2 = '_';
 		if (c1 != c2)
-			return 1;
+			return !match;
 		if (!c1)
 			break;
 	}
-#endif
-	return 0;
+#endif /* MODULE */
+	return match;
 }
 
 #if defined(CONFIG_SND_MIXER_OSS) || defined(CONFIG_SND_MIXER_OSS_MODULE)
@@ -129,7 +136,7 @@ struct snd_card *snd_card_new(int idx, const char *xid,
 			 struct module *module, int extra_size)
 {
 	struct snd_card *card;
-	int err;
+	int err, idx2;
 
 	if (extra_size < 0)
 		extra_size = 0;
@@ -144,35 +151,41 @@ struct snd_card *snd_card_new(int idx, const char *xid,
 	err = 0;
 	mutex_lock(&snd_card_mutex);
 	if (idx < 0) {
-		int idx2;
 		for (idx2 = 0; idx2 < SNDRV_CARDS; idx2++)
 			/* idx == -1 == 0xffff means: take any free slot */
 			if (~snd_cards_lock & idx & 1<<idx2) {
-				if (module_slot_mismatch(module, idx2))
-					continue;
+				if (module_slot_match(module, idx2)) {
 					idx = idx2;
-				if (idx >= snd_ecards_limit)
-					snd_ecards_limit = idx + 1;
 					break;
 				}
-	} else {
-		 if (idx < snd_ecards_limit) {
+			}
+	}
+	if (idx < 0) {
+		for (idx2 = 0; idx2 < SNDRV_CARDS; idx2++)
+			/* idx == -1 == 0xffff means: take any free slot */
+			if (~snd_cards_lock & idx & 1<<idx2) {
+				if (!slots[idx2] || !*slots[idx2]) {
+					idx = idx2;
+					break;
+				}
+			}
+	}
+	if (idx < 0)
+		err = -ENODEV;
+	else if (idx < snd_ecards_limit) {
 		if (snd_cards_lock & (1 << idx))
 			err = -EBUSY;	/* invalid */
-		} else {
-			if (idx < SNDRV_CARDS)
-				snd_ecards_limit = idx + 1; /* increase the limit */
-			else
+	} else if (idx >= SNDRV_CARDS)
 		err = -ENODEV;
-		}
-	}
-	if (idx < 0 || err < 0) {
+	if (err < 0) {
 		mutex_unlock(&snd_card_mutex);
 		snd_printk(KERN_ERR "cannot find the slot for index %d (range 0-%i), error: %d\n",
 			 idx, snd_ecards_limit - 1, err);
 		goto __error;
 	}
 	snd_cards_lock |= 1 << idx;		/* lock it */
+	if (idx >= snd_ecards_limit)
+		snd_ecards_limit = idx + 1; /* increase the limit */
 	mutex_unlock(&snd_card_mutex);
 	card->number = idx;
 	card->module = module;