elevator: make elevator_get() attempt to load the appropriate module

Currently we fail if someone requests a valid io scheduler, but it's
modular and not currently loaded. That can happen from a driver init
asking for a different scheduler, or online switching through sysfs
as requested by a user.

This patch makes elevator_get() request_module() to attempt to load
the appropriate module, instead of requiring that done manually.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/block/elevator.c b/block/elevator.c
index bafbae0344d3..88318c383608 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -134,6 +134,21 @@ static struct elevator_type *elevator_get(const char *name)
         spin_lock(&elv_list_lock);
 
         e = elevator_find(name);
+        if (!e) {
+                char elv[ELV_NAME_MAX + strlen("-iosched")];
+
+                spin_unlock(&elv_list_lock);
+
+                if (!strcmp(name, "anticipatory"))
+                        sprintf(elv, "as-iosched");
+                else
+                        sprintf(elv, "%s-iosched", name);
+
+                request_module(elv);
+                spin_lock(&elv_list_lock);
+                e = elevator_find(name);
+        }
+
         if (e && !try_module_get(e->elevator_owner))
                 e = NULL;