[BLOCK] elevator: default choice selection
My previous default iosched patch did a poor job dealing with the
'elevator=' boot-time option. The old behavior falls back to the
compiled-in default if the requested one is not registered at boot
time. This patch dynamically evaluates which default
to use, and emits a suitable error message when the requested scheduler
is not available. It also does the 'as' -> 'anticipatory' conversion
before elevator registration, which along with a modified registration
function, allows it to correctly indicate which default scheduler is
in use.
Tested for a range of boot options on 2.6.16-rc1-mm2.
Signed-off-by: Nate Diller <nate.diller@gmail.com>
Signed-off-by: Jens Axboe <axboe@suse.de>
diff --git a/block/elevator.c b/block/elevator.c
index c9f424d..dbbea73 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -139,35 +139,16 @@
static char chosen_elevator[16];
-static void elevator_setup_default(void)
+static int __init elevator_setup(char *str)
{
- struct elevator_type *e;
-
- /*
- * If default has not been set, use the compiled-in selection.
- */
- if (!chosen_elevator[0])
- strcpy(chosen_elevator, CONFIG_DEFAULT_IOSCHED);
-
/*
* Be backwards-compatible with previous kernels, so users
* won't get the wrong elevator.
*/
- if (!strcmp(chosen_elevator, "as"))
+ if (!strcmp(str, "as"))
strcpy(chosen_elevator, "anticipatory");
-
- /*
- * If the given scheduler is not available, fall back to the default
- */
- if ((e = elevator_find(chosen_elevator)))
- elevator_put(e);
else
- strcpy(chosen_elevator, CONFIG_DEFAULT_IOSCHED);
-}
-
-static int __init elevator_setup(char *str)
-{
- strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
+ strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
return 0;
}
@@ -184,15 +165,15 @@
q->end_sector = 0;
q->boundary_rq = NULL;
- elevator_setup_default();
-
- if (!name)
- name = chosen_elevator;
-
- e = elevator_get(name);
- if (!e)
+ if (name && !(e = elevator_get(name)))
return -EINVAL;
+ if (!e && !(e = elevator_get(chosen_elevator))) {
+ e = elevator_get(CONFIG_DEFAULT_IOSCHED);
+ if (*chosen_elevator)
+ printk("I/O scheduler %s not found\n", chosen_elevator);
+ }
+
eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);
if (!eq) {
elevator_put(e);
@@ -669,8 +650,10 @@
spin_unlock_irq(&elv_list_lock);
printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
- if (!strcmp(e->elevator_name, chosen_elevator))
- printk(" (default)");
+ if (!strcmp(e->elevator_name, chosen_elevator) ||
+ (!*chosen_elevator &&
+ !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
+ printk(" (default)");
printk("\n");
return 0;
}