[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: Nate Diller <nate@namesys.com>
Acked-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 38 insertions, 17 deletions

diff --git a/drivers/block/Kconfig.iosched b/drivers/block/Kconfig.iosched
index 6070a480600b..5b90d2fa63b8 100644
--- a/drivers/block/Kconfig.iosched
+++ b/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
diff --git a/drivers/block/elevator.c b/drivers/block/elevator.c
index 58e881bfd189..3b652eba2d20 100644
--- a/drivers/block/elevator.c
+++ b/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 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 (!chosen_elevator[0])
+                strcpy(chosen_elevator, CONFIG_DEFAULT_IOSCHED);
+
+        /*
+         * If the given scheduler is not available, fall back to no-op.
+         */
+        if (!(e = elevator_find(chosen_elevator)))
+                strcpy(chosen_elevator, "noop");
+        elevator_put(e);
 }
 
 static int __init elevator_setup(char *str)