Merge branch 'v2.6.36-rc8' into for-2.6.37/barrier
[linux-3.10.git] / block / elevator.c
index 241c69c..282e830 100644 (file)
@@ -877,6 +877,7 @@ int elv_register_queue(struct request_queue *q)
                        }
                }
                kobject_uevent(&e->kobj, KOBJ_ADD);
+               e->registered = 1;
        }
        return error;
 }
@@ -886,6 +887,7 @@ static void __elv_unregister_queue(struct elevator_queue *e)
 {
        kobject_uevent(&e->kobj, KOBJ_REMOVE);
        kobject_del(&e->kobj);
+       e->registered = 0;
 }
 
 void elv_unregister_queue(struct request_queue *q)
@@ -948,18 +950,19 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 {
        struct elevator_queue *old_elevator, *e;
        void *data;
+       int err;
 
        /*
         * Allocate new elevator
         */
        e = elevator_alloc(q, new_e);
        if (!e)
-               return 0;
+               return -ENOMEM;
 
        data = elevator_init_queue(q, e);
        if (!data) {
                kobject_put(&e->kobj);
-               return 0;
+               return -ENOMEM;
        }
 
        /*
@@ -980,10 +983,13 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 
        spin_unlock_irq(q->queue_lock);
 
-       __elv_unregister_queue(old_elevator);
+       if (old_elevator->registered) {
+               __elv_unregister_queue(old_elevator);
 
-       if (elv_register_queue(q))
-               goto fail_register;
+               err = elv_register_queue(q);
+               if (err)
+                       goto fail_register;
+       }
 
        /*
         * finally exit old elevator and turn off BYPASS.
@@ -995,7 +1001,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 
        blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);
 
-       return 1;
+       return 0;
 
 fail_register:
        /*
@@ -1010,17 +1016,19 @@ fail_register:
        queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
        spin_unlock_irq(q->queue_lock);
 
-       return 0;
+       return err;
 }
 
-ssize_t elv_iosched_store(struct request_queue *q, const char *name,
-                         size_t count)
+/*
+ * Switch this queue to the given IO scheduler.
+ */
+int elevator_change(struct request_queue *q, const char *name)
 {
        char elevator_name[ELV_NAME_MAX];
        struct elevator_type *e;
 
        if (!q->elevator)
-               return count;
+               return -ENXIO;
 
        strlcpy(elevator_name, name, sizeof(elevator_name));
        e = elevator_get(strstrip(elevator_name));
@@ -1031,13 +1039,27 @@ ssize_t elv_iosched_store(struct request_queue *q, const char *name,
 
        if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
                elevator_put(e);
-               return count;
+               return 0;
        }
 
-       if (!elevator_switch(q, e))
-               printk(KERN_ERR "elevator: switch to %s failed\n",
-                                                       elevator_name);
-       return count;
+       return elevator_switch(q, e);
+}
+EXPORT_SYMBOL(elevator_change);
+
+ssize_t elv_iosched_store(struct request_queue *q, const char *name,
+                         size_t count)
+{
+       int ret;
+
+       if (!q->elevator)
+               return count;
+
+       ret = elevator_change(q, name);
+       if (!ret)
+               return count;
+
+       printk(KERN_ERR "elevator: switch to %s failed\n", name);
+       return ret;
 }
 
 ssize_t elv_iosched_show(struct request_queue *q, char *name)