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/*
* linux/drivers/block/elevator.c
*
* Block device elevator/IO-scheduler.
*
* Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
*
* 30042000 Jens Axboe <axboe@suse.de> :
*
* 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
*
*/
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/blk.h>
#include <asm/uaccess.h>
/*
* Order ascending, but only allow a request to be skipped a certain
* number of times
*/
void elevator_linus(struct request *req, elevator_t *elevator,
struct list_head *real_head,
struct list_head *head, int orig_latency)
{
struct list_head *entry = real_head;
struct request *tmp;
req->elevator_sequence = orig_latency;
while ((entry = entry->prev) != head) {
tmp = blkdev_entry_to_request(entry);
if (IN_ORDER(tmp, req))
break;
if (!tmp->elevator_sequence)
break;
tmp->elevator_sequence--;
}
list_add(&req->queue, entry);
}
int elevator_linus_merge(request_queue_t *q, struct request **req,
struct buffer_head *bh, int rw,
int *max_sectors, int *max_segments)
{
struct list_head *entry, *head = &q->queue_head;
unsigned int count = bh->b_size >> 9, ret = ELEVATOR_NO_MERGE;
entry = head;
if (q->head_active && !q->plugged)
head = head->next;
while ((entry = entry->prev) != head) {
struct request *__rq = *req = blkdev_entry_to_request(entry);
if (__rq->sem)
continue;
if (__rq->cmd != rw)
continue;
if (__rq->nr_sectors + count > *max_sectors)
continue;
if (__rq->rq_dev != bh->b_rdev)
continue;
if (__rq->sector + __rq->nr_sectors == bh->b_rsector) {
ret = ELEVATOR_BACK_MERGE;
break;
}
if (!__rq->elevator_sequence)
break;
if (__rq->sector - count == bh->b_rsector) {
__rq->elevator_sequence--;
ret = ELEVATOR_FRONT_MERGE;
break;
}
}
/*
* second pass scan of requests that got passed over, if any
*/
if (ret != ELEVATOR_NO_MERGE && *req) {
while ((entry = entry->next) != &q->queue_head) {
struct request *tmp = blkdev_entry_to_request(entry);
tmp->elevator_sequence--;
}
}
return ret;
}
/*
* No request sorting, just add it to the back of the list
*/
void elevator_noop(struct request *req, elevator_t *elevator,
struct list_head *real_head, struct list_head *head,
int orig_latency)
{
list_add_tail(&req->queue, real_head);
}
/*
* See if we can find a request that is buffer can be coalesced with.
*/
int elevator_noop_merge(request_queue_t *q, struct request **req,
struct buffer_head *bh, int rw,
int *max_sectors, int *max_segments)
{
struct list_head *entry, *head = &q->queue_head;
unsigned int count = bh->b_size >> 9;
if (q->head_active && !q->plugged)
head = head->next;
entry = head;
while ((entry = entry->prev) != head) {
struct request *__rq = *req = blkdev_entry_to_request(entry);
if (__rq->sem)
continue;
if (__rq->cmd != rw)
continue;
if (__rq->nr_sectors + count > *max_sectors)
continue;
if (__rq->rq_dev != bh->b_rdev)
continue;
if (__rq->sector + __rq->nr_sectors == bh->b_rsector)
return ELEVATOR_BACK_MERGE;
if (__rq->sector - count == bh->b_rsector)
return ELEVATOR_FRONT_MERGE;
}
return ELEVATOR_NO_MERGE;
}
/*
* The noop "elevator" does not do any accounting
*/
void elevator_noop_dequeue(struct request *req) {}
int blkelvget_ioctl(elevator_t * elevator, blkelv_ioctl_arg_t * arg)
{
blkelv_ioctl_arg_t output;
output.queue_ID = elevator->queue_ID;
output.read_latency = elevator->read_latency;
output.write_latency = elevator->write_latency;
output.max_bomb_segments = elevator->max_bomb_segments;
if (copy_to_user(arg, &output, sizeof(blkelv_ioctl_arg_t)))
return -EFAULT;
return 0;
}
int blkelvset_ioctl(elevator_t * elevator, const blkelv_ioctl_arg_t * arg)
{
blkelv_ioctl_arg_t input;
if (copy_from_user(&input, arg, sizeof(blkelv_ioctl_arg_t)))
return -EFAULT;
if (input.read_latency < 0)
return -EINVAL;
if (input.write_latency < 0)
return -EINVAL;
if (input.max_bomb_segments <= 0)
return -EINVAL;
elevator->read_latency = input.read_latency;
elevator->write_latency = input.write_latency;
elevator->max_bomb_segments = input.max_bomb_segments;
return 0;
}
void elevator_init(elevator_t * elevator, elevator_t type)
{
static unsigned int queue_ID;
*elevator = type;
elevator->queue_ID = queue_ID++;
}
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