[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 (file)
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -139,35 +139,16 @@ static int elevator_attach(request_queue_t *q, struct elevator_type *e,
 
 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 @@ int elevator_init(request_queue_t *q, char *name)
        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 @@ int elv_register(struct elevator_type *e)
        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;
 }