[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>

1 files changed, 14 insertions, 31 deletions

diff --git a/block/elevator.c b/block/elevator.c
index c9f424d5399c..dbbea73a8b10 100644
--- 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;
 }