block: add function call to switch the IO scheduler from a driver
Currently drivers must do an elevator_exit() + elevator_init()
to switch IO schedulers. There are a few problems with this:
- Since commit 1abec4fdbb142e3ccb6ce99832fae42129134a96,
elevator_init() requires a zeroed out q->elevator
pointer. The two existing in-kernel users don't do that.
- It will only work at initialization time, since using the
above two-staged construct does not properly quisce the queue.
So add elevator_change() which takes care of this, and convert
the elv_iosched_store() sysfs interface to use this helper as well.
Reported-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Reported-by: Kevin Vigor <kevin@vigor.nu>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/block/elevator.c b/block/elevator.c
index ec585c9..205b09a 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -1009,18 +1009,19 @@
{
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;
}
/*
@@ -1043,7 +1044,8 @@
__elv_unregister_queue(old_elevator);
- if (elv_register_queue(q))
+ err = elv_register_queue(q);
+ if (err)
goto fail_register;
/*
@@ -1056,7 +1058,7 @@
blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);
- return 1;
+ return 0;
fail_register:
/*
@@ -1071,17 +1073,19 @@
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));
@@ -1092,13 +1096,27 @@
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)
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index 2c958f4..926b503 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -136,6 +136,7 @@
extern int elevator_init(struct request_queue *, char *);
extern void elevator_exit(struct elevator_queue *);
+extern int elevator_change(struct request_queue *, const char *);
extern int elv_rq_merge_ok(struct request *, struct bio *);
/*