Commit 5dd531a0 authored by Jens Axboe's avatar Jens Axboe
Browse files

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 1abec4fd,
  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: default avatarPeter Oberparleiter <oberpar@linux.vnet.ibm.com>
Reported-by: default avatarKevin Vigor <kevin@vigor.nu>
Signed-off-by: default avatarJens Axboe <jaxboe@fusionio.com>
parent 220eb7fd

block/elevator.c

+31 −13
Original line number Diff line number Diff line
@@ -1009,18 +1009,19 @@ 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;

	}



	/*
@@ -1043,7 +1044,8 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e) 


	__elv_unregister_queue(old_elevator);



	if (elv_register_queue(q))

	err = elv_register_queue(q);

	if (err)

		goto fail_register;



	/*
@@ -1056,7 +1058,7 @@ 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:

	/*
@@ -1071,17 +1073,19 @@ 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));
@@ -1092,13 +1096,27 @@ 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;

	}



	return elevator_switch(q, e);

}

EXPORT_SYMBOL(elevator_change);



	if (!elevator_switch(q, e))

		printk(KERN_ERR "elevator: switch to %s failed\n",

							elevator_name);

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)

include/linux/elevator.h

+1 −0
Original line number Diff line number Diff line
@@ -136,6 +136,7 @@ extern ssize_t elv_iosched_store(struct request_queue *, const char *, size_t); 


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 *);



/*

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