[PATCH] block cleanups: Add kconfig default iosched submenu

Add a kconfig submenu to select the default I/O scheduler, in case
anticipatory is not compiled in or another default is preferred.  Also,
since no-op is always available, we should use it whenever the selected
default is not.
Signed-off-by: NNate Diller <nate@namesys.com>
Acked-by: NJens Axboe <axboe@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

drivers/block/Kconfig.iosched

@@ -38,4 +38,32 @@ config IOSCHED_CFQ
 	  among all processes in the system. It should provide a fair
 	  working environment, suitable for desktop systems.
 
+choice
+	prompt "Default I/O scheduler"
+	default DEFAULT_AS
+	help
+	  Select the I/O scheduler which will be used by default for all
+	  block devices.
+
+	config DEFAULT_AS
+		bool "Anticipatory" if IOSCHED_AS
+
+	config DEFAULT_DEADLINE
+		bool "Deadline" if IOSCHED_DEADLINE
+
+	config DEFAULT_CFQ
+		bool "CFQ" if IOSCHED_CFQ
+
+	config DEFAULT_NOOP
+		bool "No-op"
+
+endchoice
+
+config DEFAULT_IOSCHED
+	string
+	default "anticipatory" if DEFAULT_AS
+	default "deadline" if DEFAULT_DEADLINE
+	default "cfq" if DEFAULT_CFQ
+	default "noop" if DEFAULT_NOOP
+
 endmenu

drivers/block/elevator.c

@@ -147,24 +147,17 @@ static void elevator_setup_default(void)
 	struct elevator_type *e;
 
 	/*
-	 * check if default is set and exists
+	 * If default has not been set, use the compiled-in selection.
 	 */
-	if (chosen_elevator[0] && (e = elevator_get(chosen_elevator))) {
-		elevator_put(e);
-		return;
-	}
+	if (!chosen_elevator[0])
+		strcpy(chosen_elevator, CONFIG_DEFAULT_IOSCHED);
 
-#if defined(CONFIG_IOSCHED_AS)
-	strcpy(chosen_elevator, "anticipatory");
-#elif defined(CONFIG_IOSCHED_DEADLINE)
-	strcpy(chosen_elevator, "deadline");
-#elif defined(CONFIG_IOSCHED_CFQ)
-	strcpy(chosen_elevator, "cfq");
-#elif defined(CONFIG_IOSCHED_NOOP)
+ 	/*
+ 	 * If the given scheduler is not available, fall back to no-op.
+ 	 */
+ 	if (!(e = elevator_find(chosen_elevator)))
  		strcpy(chosen_elevator, "noop");
-#else
-#error "You must build at least 1 IO scheduler into the kernel"
-#endif
+	elevator_put(e);
 }
 
 static int __init elevator_setup(char *str)