[BLOCK] elevator: allow default scheduler to potentially be modular
Jens has decided that allowing the default scheduler to be a module is
a bug, and should not be allowed under kconfig. However, I find that
scenario useful for debugging, and wish for the kernel to be able to
handle this situation without OOPSing, if I enable such an option in
the .config directly. This patch dynamically checks for the presence
of the compiled-in default, and falls back to no-op, emitting a
suitable error message, when the default is not available
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 dbbea73..96a61e0 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -168,10 +168,12 @@
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);
+ if (!e && *chosen_elevator && !(e = elevator_get(chosen_elevator)))
+ printk("I/O scheduler %s not found\n", chosen_elevator);
+
+ if (!e && !(e = elevator_get(CONFIG_DEFAULT_IOSCHED))) {
+ printk("Default I/O scheduler not found, using no-op\n");
+ e = elevator_get("noop");
}
eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);