[PATCH 2/3] block cleanups: Add kconfig default iosched submenu

[Nate Diller <nate@namesys.com>]

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.

I saw a patch recently to add this option, and I don't think it got picked up.  This version is 
cleaner, since it eliminates all the #ifdef's in the code itself.

Thanks

NATE

Signed-off-by: Nate Diller <nate@namesys.com>

---

  Kconfig.iosched |   28 ++++++++++++++++++++++++++++
  elevator.c      |   24 +++++++++---------------
  2 files changed, 37 insertions(+), 15 deletions(-)

diff -urpN a/drivers/block/elevator.c b/drivers/block/elevator.c
--- a/drivers/block/elevator.c	2005-09-26 19:17:59.000000000 -0700
+++ b/drivers/block/elevator.c	2005-09-27 11:05:15.000000000 -0700
@@ -153,23 +153,17 @@ static char chosen_elevator[16];

  static void elevator_setup_default(void)
  {
-	/*
-	 * check if default is set and exists
+	/*
+	 * If default has not been set, use the compiled-in selection.
  	 */
-	if (chosen_elevator[0] && elevator_find(chosen_elevator))
-		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)
-	strcpy(chosen_elevator, "noop");
-#else
-#error "You must build at least 1 IO scheduler into the kernel"
-#endif
+	/*
+	 * If the given scheduler is not available, fall back to no-op.
+	 */
+	if (!elevator_find(chosen_elevator))
+		strcpy(chosen_elevator, "noop");
  }

  static int __init elevator_setup(char *str)
diff -urpN a/drivers/block/Kconfig.iosched b/drivers/block/Kconfig.iosched
--- a/drivers/block/Kconfig.iosched	2005-08-28 16:41:01.000000000 -0700
+++ b/drivers/block/Kconfig.iosched	2005-09-26 20:14:06.000000000 -0700
@@ -38,4 +28,32 @@ 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