path: root/block/elevator.c

/*
 *  Block device elevator/IO-scheduler.
 *
 *  Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
 *
 * 30042000 Jens Axboe <axboe@kernel.dk> :
 *
 * Split the elevator a bit so that it is possible to choose a different
 * one or even write a new "plug in". There are three pieces:
 * - elevator_fn, inserts a new request in the queue list
 * - elevator_merge_fn, decides whether a new buffer can be merged with
 *   an existing request
 * - elevator_dequeue_fn, called when a request is taken off the active list
 *
 * 20082000 Dave Jones <davej@suse.de> :
 * Removed tests for max-bomb-segments, which was breaking elvtune
 *  when run without -bN
 *
 * Jens:
 * - Rework again to work with bio instead of buffer_heads
 * - loose bi_dev comparisons, partition handling is right now
 * - completely modularize elevator setup and teardown
 *
 */
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/bio.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/compiler.h>
#include <linux/blktrace_api.h>
#include <linux/hash.h>
#include <linux/uaccess.h>

#include <trace/events/block.h>

#include "blk.h"

static DEFINE_SPINLOCK(elv_list_lock);
static LIST_HEAD(elv_list);

/*
 * Merge hash stuff.
 */
static const int elv_hash_shift = 6;
#define ELV_HASH_BLOCK(sec)	((sec) >> 3)
#define ELV_HASH_FN(sec)	\
		(hash_long(ELV_HASH_BLOCK((sec)), elv_hash_shift))
#define ELV_HASH_ENTRIES	(1 << elv_hash_shift)
#define rq_hash_key(rq)		(blk_rq_pos(rq) + blk_rq_sectors(rq))

/*
 * Query io scheduler to see if the current process issuing bio may be
 * merged with rq.
 */
static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
{
	struct request_queue *q = rq->q;
	struct elevator_queue *e = q->elevator;

	if (e->type->ops.elevator_allow_merge_fn)
		return e->type->ops.elevator_allow_merge_fn(q, rq, bio);

	return 1;
}

/*
 * can we safely merge with this request?
 */
bool elv_rq_merge_ok(struct request *rq, struct bio *bio)
{
	if (!blk_rq_merge_ok(rq, bio))
		return 0;

	if (!elv_iosched_allow_merge(rq, bio))
		return 0;

	return 1;
}
EXPORT_SYMBOL(elv_rq_merge_ok);

static struct elevator_type *elevator_find(const char *name)
{
	struct elevator_type *e;

	list_for_each_entry(e, &elv_list, list) {
		if (!strcmp(e->elevator_name, name))
			return e;
	}

	return NULL;
}

static void elevator_put(struct elevator_type *e)
{
	module_put(e->elevator_owner);
}

static struct elevator_type *elevator_get(const char *name)
{
	struct elevator_type *e;

	spin_lock(&elv_list_lock);

	e = elevator_find(name);
	if (!e) {
		spin_unlock(&elv_list_lock);
		request_module("%s-iosched", name);
		spin_lock(&elv_list_lock);
		e = elevator_find(name);
	}

	if (e && !try_module_get(e->elevator_owner))
		e = NULL;

	spin_unlock(&elv_list_lock);

	return e;
}

static int elevator_init_queue(struct request_queue *q,
			       struct elevator_queue *eq)
{
	eq->elevator_data = eq->type->ops.elevator_init_fn(q);
	if (eq->elevator_data)
		return 0;
	return -ENOMEM;
}

static char chosen_elevator[ELV_NAME_MAX];

static int __init elevator_setup(char *str)
{
	/*
	 * Be backwards-compatible with previous kernels, so users
	 * won't get the wrong elevator.
	 */
	strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
	return 1;
}

__setup("elevator=", elevator_setup);

static struct kobj_type elv_ktype;

static struct elevator_queue *elevator_alloc(struct request_queue *q,
				  struct elevator_type *e)
{
	struct elevator_queue *eq;
	int i;

	eq = kmalloc_node(sizeof(*eq), GFP_KERNEL | __GFP_ZERO, q->node);
	if (unlikely(!eq))
		goto err;

	eq->type = e;
	kobject_init(&eq->kobj, &elv_ktype);
	mutex_init(&eq->sysfs_lock);

	eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
					GFP_KERNEL, q->node);
	if (!eq->hash)
		goto err;

	for (i = 0; i < ELV_HASH_ENTRIES;