/* *  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 * * 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/config.h>#include <linux/module.h>#include <linux/slab.h>#include <linux/init.h>#include <linux/compiler.h> #include <asm/uaccess.h> static DEFINE_SPINLOCK(elv_list_lock);static LIST_HEAD(elv_list); /* * can we safely merge with this request? */inline int elv_rq_merge_ok(struct request *rq, struct bio *bio){	if (!rq_mergeable(rq))		return 0; 	/*	 * different data direction or already started, don't merge	 */	if (bio_data_dir(bio) != rq_data_dir(rq))		return 0; 	/*	 * same device and no special stuff set, merge is ok	 */	if (rq->rq_disk == bio->bi_bdev->bd_disk &&	    !rq->waiting && !rq->special)		return 1; 	return 0;}EXPORT_SYMBOL(elv_rq_merge_ok); inline int elv_try_merge(struct request *__rq, struct bio *bio){	int ret = ELEVATOR_NO_MERGE; 	/*	 * we can merge and sequence is ok, check if it's possible	 */	if (elv_rq_merge_ok(__rq, bio)) {		if (__rq->sector + __rq->nr_sectors == bio->bi_sector)			ret = ELEVATOR_BACK_MERGE;		else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)			ret = ELEVATOR_FRONT_MERGE;	} 	return ret;}EXPORT_SYMBOL(elv_try_merge); inline int elv_try_last_merge(request_queue_t *q, struct bio *bio){	if (q->last_merge)		return elv_try_merge(q->last_merge, bio); 	return ELEVATOR_NO_MERGE;}EXPORT_SYMBOL(elv_try_last_merge); static struct elevator_type *elevator_find(const char *name){	struct elevator_type *e = NULL;	struct list_head *entry; 	spin_lock_irq(&elv_list_lock);	list_for_each(entry, &elv_list) {		struct elevator_type *__e; 		__e = list_entry(entry, struct elevator_type, list); 		if (!strcmp(__e->elevator_name, name)) {			e = __e;			break;		}	}	spin_unlock_irq(&elv_list_lock); 	return e;} 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 = elevator_find(name); 	if (!e)		return NULL;	if (!try_module_get(e->elevator_owner))		return NULL; 	return e;} static int elevator_attach(request_queue_t *q, struct elevator_type *e,			   struct elevator_queue *eq){	int ret = 0; 	memset(eq, 0, sizeof(*eq));	eq->ops = &e->ops;	eq->elevator_type = e; 	INIT_LIST_HEAD(&q->queue_head);	q->last_merge = NULL;	q->elevator = eq; 	if (eq->ops->elevator_init_fn)		ret = eq->ops->elevator_init_fn(q, eq); 	return ret;} static char chosen_elevator[16]; static void elevator_setup_default(void){	/*	 * check if default is set and exists	 */	if (chosen_elevator[0] && elevator_find(chosen_elevator))		return; #if defined(CONFIG_IOSCHED_AS)	strcpy(chosen_elevator, "anticipatory");#elif defined(CONFIG_IOSCHED_DEADLINE)	strcpy(chosen_elevator, "deadline");#elif defined(CONFIG_IOSCHED_CFQ)	strcpy(chosen_elevator, "cfq");#elif defined(CONFIG_IOSCHED_NOOP)	strcpy(chosen_elevator, "noop");#else#error "You must build at least 1 IO scheduler into the kernel"#endif} static int __init elevator_setup(char *str){	strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);	return 0;} __setup("elevator=", elevator_setup); int elevator_init(request_queue_t *q, char *name){	struct elevator_type *e = NULL;	struct elevator_queue *eq;	int ret = 0; 	elevator_setup_default(); 	if (!name)		name = chosen_elevator; 	e = elevator_get(name);	if (!e)		return -EINVAL; 	eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);	if (!eq) {		elevator_put(e->elevator_type);		return -ENOMEM;	} 	ret = elevator_attach(q, e, eq);	if (ret) {		kfree(eq);		elevator_put(e->elevator_type);	} 	return ret;} void elevator_exit(elevator_t *e){	if (e->ops->elevator_exit_fn)		e->ops->elevator_exit_fn(e); 	elevator_put(e->elevator_type);	e->elevator_type = NULL;	kfree(e);} int elv_merge(request_queue_t *q, struct request **req, struct bio *bio){	elevator_t *e = q->elevator; 	if (e->ops->elevator_merge_fn)		return e->ops->elevator_merge_fn(q, req, bio); 	return ELEVATOR_NO_MERGE;} void elv_merged_request(request_queue_t *q, struct request *rq){	elevator_t *e = q->elevator; 	if (e->ops->elevator_merged_fn)		e->ops->elevator_merged_fn(q, rq);} void elv_merge_requests(request_queue_t *q, struct request *rq,			     struct request *next){	elevator_t *e = q->elevator; 	if (q->last_merge == next)		q->last_merge = NULL; 	if (e->ops->elevator_merge_req_fn)		e->ops->elevator_merge_req_fn(q, rq, next);} /* * For careful internal use by the block layer. Essentially the same as * a requeue in that it tells the io scheduler that this request is not * active in the driver or hardware anymore, but we don't want the request * added back to the scheduler. Function is not exported. */void elv_deactivate_request(request_queue_t *q, struct request *rq){	elevator_t *e = q->elevator; 	/*	 * it already went through dequeue, we need to decrement the	 * in_flight count again	 */	if (blk_account_rq(rq))		q->in_flight--; 	rq->flags &= ~REQ_STARTED; 	if (e->ops->elevator_deactivate_req_fn)		e->ops->elevator_deactivate_req_fn(q, rq);} void elv_requeue_request(request_queue_t *q, struct request *rq){	elv_deactivate_request(q, rq); 	/*	 * if this is the flush, requeue the original instead and drop the flush	 */	if (rq->flags & REQ_BAR_FLUSH) {		clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);		rq = rq->end_io_data;	} 	/*	 * the request is prepped and may have some resources allocated.	 * allowing unprepped requests to pass this one may cause resource	 * deadlock.  turn on softbarrier.	 */	rq->flags |= REQ_SOFTBARRIER; 	/*	 * if iosched has an explicit requeue hook, then use that. otherwise	 * just put the request at the front of the queue	 */	if (q->elevator->ops->elevator_requeue_req_fn)		q->elevator->ops->elevator_requeue_req_fn(q, rq);	else		__elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);} void __elv_add_request(request_queue_t *q, struct request *rq, int where,		       int plug){	/*	 * barriers implicitly indicate back insertion	 */	if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER) &&	    where == ELEVATOR_INSERT_SORT)		where = ELEVATOR_INSERT_BACK; 	if (plug)		blk_plug_device(q); 	rq->q = q; 	if (!test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags)) {		q->elevator->ops->elevator_add_req_fn(q, rq, where); 		if (blk_queue_plugged(q)) {			int nrq = q->rq.count[READ] + q->rq.count[WRITE]				  - q->in_flight; 			if (nrq >= q->unplug_thresh)				__generic_unplug_device(q);		}	} else		/*		 * if drain is set, store the request "locally". when the drain		 * is finished, the requests will be handed ordered to the io		 * scheduler		 */		list_add_tail(&rq->queuelist, &q->drain_list);} void elv_add_request(request_queue_t *q, struct request *rq, int where,		     int plug){	unsigned long flags; 	spin_lock_irqsave(q->queue_lock, flags);	__elv_add_request(q, rq, where, plug);	spin_unlock_irqrestore(q->queue_lock, flags);} static inline struct request *__elv_next_request(request_queue_t *q){	struct request *rq = q->elevator->ops->elevator_next_req_fn(q); 	/*	 * if this is a barrier write and the device has to issue a	 * flush sequence to support it, check how far we are	 */	if (rq && blk_fs_request(rq) && blk_barrier_rq(rq)) {		BUG_ON(q->ordered == QUEUE_ORDERED_NONE); 		if (q->ordered == QUEUE_ORDERED_FLUSH &&		    !blk_barrier_preflush(rq))			rq = blk_start_pre_flush(q, rq);	} 	return rq;} struct request *elv_next_request(request_queue_t *q){	struct request *rq;	int ret; 	while ((rq = __elv_next_request(q)) != NULL) {		/*		 * just mark as started even if we don't start it, a request		 * that has been delayed should not be passed by new incoming		 * requests		 */		rq->flags |= REQ_STARTED; 		if (rq == q->last_merge)			q->last_merge = NULL; 		if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)			break; 		ret = q->prep_rq_fn(q, rq);		if (ret == BLKPREP_OK) {			break;		} else if (ret == BLKPREP_DEFER) {			/*			 * the request may have been (partially) prepped.			 * we need to keep this request in the front to			 * avoid resource deadlock.  turn on softbarrier.			 */			rq->flags |= REQ_SOFTBARRIER;			rq = NULL;			break;		} else if (ret == BLKPREP_KILL) {			int nr_bytes = rq->hard_nr_sectors << 9; 			if (!nr_bytes)				nr_bytes = rq->data_len; 			blkdev_dequeue_request(rq);			rq->flags |= REQ_QUIET;			end_that_request_chunk(rq, 0, nr_bytes);			end_that_request_last(rq);		} else {			printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,								ret);			break;		}	} 	return rq;} void elv_remove_request(request_queue_t *q, struct request *rq){	elevator_t *e = q->elevator; 	/*	 * the time frame between a request being removed from the lists	 * and to it is freed is accounted as io that is in progress at	 * the driver side. note that we only account requests that the	 * driver has seen (REQ_STARTED set), to avoid false accounting	 * for request-request merges	 */	if (blk_account_rq(rq))		q->in_flight++; 	/*	 * the main clearing point for q->last_merge is on retrieval of	 * request by driver (it calls elv_next_request()), but it _can_	 * also happen here if a request is added to the queue but later	 * deleted without ever being given to driver (merged with another	 * request).	 */	if (rq == q->last_merge)		q->last_merge = NULL; 	if (e->ops->elevator_remove_req_fn)		e->ops->elevator_remove_req_fn(q, rq);} int elv_queue_empty(request_queue_t *q){	elevator_t *e = q->elevator; 	if (e->ops->elevator_queue_empty_fn)		return e->ops->elevator_queue_empty_fn(q); 	return list_empty(&q->queue_head);} struct request *elv_latter_request(request_queue_t *q, struct request *rq){	struct list_head *next; 	elevator_t *e = q->elevator; 	if (e->ops->elevator_latter_req_fn)		return e->ops->elevator_latter_req_fn(q, rq); 	next = rq->queuelist.next;	if (next != &q->queue_head && next != &rq->queuelist)		return list_entry_rq(next); 	return NULL;} struct request *elv_former_request(request_queue_t *q, struct request *rq){	struct list_head *prev; 	elevator_t *e = q->elevator; 	if (e->ops->elevator_former_req_fn)		return e->ops->elevator_former_req_fn(q, rq); 	prev = rq->queuelist.prev;	if (prev != &q->queue_head && prev != &rq->queuelist)		return list_entry_rq(prev); 	return NULL;} int elv_set_request(request_queue_t *q, struct request *rq, struct bio *bio,		    int gfp_mask){	elevator_t *e = q->elevator; 	if (e->ops->elevator_set_req_fn)		return e->ops->elevator_set_req_fn(q, rq, bio, gfp_mask); 	rq->elevator_private = NULL;	return 0;} 

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