[mirror_ubuntu-zesty-kernel.git] / block / blk-tag.c

/*
 * Functions related to tagged command queuing
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/slab.h>

#include "blk.h"

/**
 * blk_queue_find_tag - find a request by its tag and queue
 * @q:	 The request queue for the device
 * @tag: The tag of the request
 *
 * Notes:
 *    Should be used when a device returns a tag and you want to match
 *    it with a request.
 *
 *    no locks need be held.
 **/
struct request *blk_queue_find_tag(struct request_queue *q, int tag)
{
	return blk_map_queue_find_tag(q->queue_tags, tag);
}
EXPORT_SYMBOL(blk_queue_find_tag);

/**
 * blk_free_tags - release a given set of tag maintenance info
 * @bqt:	the tag map to free
 *
 * Drop the reference count on @bqt and frees it when the last reference
 * is dropped.
 */
void blk_free_tags(struct blk_queue_tag *bqt)
{
	if (atomic_dec_and_test(&bqt->refcnt)) {
		BUG_ON(find_first_bit(bqt->tag_map, bqt->max_depth) <
							bqt->max_depth);

		kfree(bqt->tag_index);
		bqt->tag_index = NULL;

		kfree(bqt->tag_map);
		bqt->tag_map = NULL;

		kfree(bqt);
	}
}
EXPORT_SYMBOL(blk_free_tags);

/**
 * __blk_queue_free_tags - release tag maintenance info
 * @q:  the request queue for the device
 *
 *  Notes:
 *    blk_cleanup_queue() will take care of calling this function, if tagging
 *    has been used. So there's no need to call this directly.
 **/
void __blk_queue_free_tags(struct request_queue *q)
{
	struct blk_queue_tag *bqt = q->queue_tags;

	if (!bqt)
		return;

	blk_free_tags(bqt);

	q->queue_tags = NULL;
	queue_flag_clear_unlocked(QUEUE_FLAG_QUEUED, q);
}

/**
 * blk_queue_free_tags - release tag maintenance info
 * @q:  the request queue for the device
 *
 *  Notes:
 *	This is used to disable tagged queuing to a device, yet leave
 *	queue in function.
 **/
void blk_queue_free_tags(struct request_queue *q)
{
	queue_flag_clear_unlocked(QUEUE_FLAG_QUEUED, q);
}
EXPORT_SYMBOL(blk_queue_free_tags);

static int
init_tag_map(struct request_queue *q, struct blk_queue_tag *tags, int depth)
{
	struct request **tag_index;
	unsigned long *tag_map;
	int nr_ulongs;

	if (q && depth > q->nr_requests * 2) {
		depth = q->nr_requests * 2;
		printk(KERN_ERR "%s: adjusted depth to %d\n",
		       __func__, depth);
	}

	tag_index = kzalloc(depth * sizeof(struct request *), GFP_ATOMIC);
	if (!tag_index)
		goto fail;

	nr_ulongs = ALIGN(depth, BITS_PER_LONG) / BITS_PER_LONG;
	tag_map = kzalloc(nr_ulongs * sizeof(unsigned long), GFP_ATOMIC);
	if (!tag_map)
		goto fail;

	tags->real_max_depth = depth;
	tags->max_depth = depth;
	tags->tag_index = tag_index;
	tags->tag_map = tag_map;

	return 0;
fail:
	kfree(tag_index);
	return -ENOMEM;
}

static struct blk_queue_tag *__blk_queue_init_tags(struct request_queue *q,
						int depth, int alloc_policy)
{
	struct blk_queue_tag *tags;

	tags = kmalloc(sizeof(struct blk_queue_tag), GFP_ATOMIC);
	if (!tags)
		goto fail;

	if (init_tag_map(q, tags, depth))
		goto fail;

	atomic_set(&tags->refcnt, 1);
	tags->alloc_policy = alloc_policy;
	tags->next_tag = 0;
	return tags;
fail:
	kfree(tags);
	return NULL;
}

/**
 * blk_init_tags - initialize the tag info for an external tag map
 * @depth:	the maximum queue depth supported
 * @alloc_policy: tag allocation policy
 **/
struct blk_queue_tag *blk_init_tags(int depth, int alloc_policy)
{
	return __blk_queue_init_tags(NULL, depth, alloc_policy);
}
EXPORT_SYMBOL(blk_init_tags);

/**
 * blk_queue_init_tags - initialize the queue tag info
 * @q:  the request queue for the device
 * @depth:  the maximum queue depth supported
 * @tags: the tag to use
 * @alloc_policy: tag allocation policy
 *
 * Queue lock must be held here if the function is called to resize an
 * existing map.
 **/
int blk_queue_init_tags(struct request_queue *q, int depth,
			struct blk_queue_tag *tags, int alloc_policy)
{
	int rc;

	BUG_ON(tags && q->queue_tags && tags != q->queue_tags);

	if (!tags && !q->queue_tags) {
		tags = __blk_queue_init_tags(q, depth, alloc_policy);

		if (!tags)
			return -ENOMEM;

	} else if (q->queue_tags) {
		rc = blk_queue_resize_tags(q, depth);
		if (rc)
			return rc;
		queue_flag_set(QUEUE_FLAG_QUEUED, q);
		return 0;
	} else
		atomic_inc(&tags->refcnt);

	/*
	 * assign it, all done
	 */
	q->queue_tags = tags;
	queue_flag_set_unlocked(QUEUE_FLAG_QUEUED, q);
	INIT_LIST_HEAD(&q->tag_busy_list);
	return 0;
}
EXPORT_SYMBOL(blk_queue_init_tags);

/**
 * blk_queue_resize_tags - change the queueing depth
 * @q:  the request queue for the device
 * @new_depth: the new max command queueing depth
 *
 *  Notes:
 *    Must be called with the queue lock held.
 **/
int blk_queue_resize_tags(struct request_queue *q, int new_depth)
{
	struct blk_queue_tag *bqt = q->queue_tags;
	struct request **tag_index;
	unsigned long *tag_map;
	int max_depth, nr_ulongs;

	if (!bqt)
		return -ENXIO;

	/*
	 * if we already have large enough real_max_depth.  just
	 * adjust max_depth.  *NOTE* as requests with tag value
	 * between new_depth and real_max_depth can be in-flight, tag
	 * map can not be shrunk blindly here.
	 */
	if (new_depth <= bqt->real_max_depth) {
		bqt->max_depth = new_depth;
		return 0;
	}

	/*
	 * Currently cannot replace a shared tag map with a new
	 * one, so error out if this is the case
	 */
	if (atomic_read(&bqt->refcnt) != 1)
		return -EBUSY;

	/*
	 * save the old state info, so we can copy it back
	 */
	tag_index = bqt->tag_index;
	tag_map = bqt->tag_map;
	max_depth = bqt->real_max_depth;

	if (init_tag_map(q, bqt, new_depth))
		return -ENOMEM;

	memcpy(bqt->tag_index, tag_index, max_depth * sizeof(struct request *));
	nr_ulongs = ALIGN(max_depth, BITS_PER_LONG) / BITS_PER_LONG;
	memcpy(bqt->tag_map, tag_map, nr_ulongs * sizeof(unsigned long));

	kfree(tag_index);
	kfree(tag_map);
	return 0;
}
EXPORT_SYMBOL(blk_queue_resize_tags);

/**
 * blk_queue_end_tag - end tag operations for a request
 * @q:  the request queue for the device
 * @rq: the request that has completed
 *
 *  Description:
 *    Typically called when end_that_request_first() returns %0, meaning
 *    all transfers have been done for a request. It's important to call
 *    this function before end_that_request_last(), as that will put the
 *    request back on the free list thus corrupting the internal tag list.
 *
 *  Notes:
 *   queue lock must be held.
 **/
void blk_queue_end_tag(struct request_queue *q, struct request *rq)
{
	struct blk_queue_tag *bqt = q->queue_tags;
	unsigned tag = rq->tag; /* negative tags invalid */

	BUG_ON(tag >= bqt->real_max_depth);

	list_del_init(&rq->queuelist);
	rq->rq_flags &= ~RQF_QUEUED;
	rq->tag = -1;

	if (unlikely(bqt->tag_index[tag] == NULL))
		printk(KERN_ERR "%s: tag %d is missing\n",
		       __func__, tag);

	bqt->tag_index[tag] = NULL;

	if (unlikely(!test_bit(tag, bqt->tag_map))) {
		printk(KERN_ERR "%s: attempt to clear non-busy tag (%d)\n",
		       __func__, tag);
		return;
	}
	/*
	 * The tag_map bit acts as a lock for tag_index[bit], so we need
	 * unlock memory barrier semantics.
	 */
	clear_bit_unlock(tag, bqt->tag_map);
}
EXPORT_SYMBOL(blk_queue_end_tag);

/**
 * blk_queue_start_tag - find a free tag and assign it
 * @q:  the request queue for the device
 * @rq:  the block request that needs tagging
 *
 *  Description:
 *    This can either be used as a stand-alone helper, or possibly be
 *    assigned as the queue &prep_rq_fn (in which case &struct request
 *    automagically gets a tag assigned). Note that this function
 *    assumes that any type of request can be queued! if this is not
 *    true for your device, you must check the request type before
 *    calling this function.  The request will also be removed from
 *    the request queue, so it's the drivers responsibility to readd
 *    it if it should need to be restarted for some reason.
 *
 *  Notes:
 *   queue lock must be held.
 **/
int blk_queue_start_tag(struct request_queue *q, struct request *rq)
{
	struct blk_queue_tag *bqt = q->queue_tags;
	unsigned max_depth;
	int tag;

	if (unlikely((rq->rq_flags & RQF_QUEUED))) {
		printk(KERN_ERR
		       "%s: request %p for device [%s] already tagged %d",
		       __func__, rq,
		       rq->rq_disk ? rq->rq_disk->disk_name : "?", rq->tag);
		BUG();
	}

	/*
	 * Protect against shared tag maps, as we may not have exclusive
	 * access to the tag map.
	 *
	 * We reserve a few tags just for sync IO, since we don't want
	 * to starve sync IO on behalf of flooding async IO.
	 */
	max_depth = bqt->max_depth;
	if (!rq_is_sync(rq) && max_depth > 1) {
		switch (max_depth) {
		case 2:
			max_depth = 1;
			break;
		case 3:
			max_depth = 2;
			break;
		default:
			max_depth -= 2;
		}
		if (q->in_flight[BLK_RW_ASYNC] > max_depth)
			return 1;
	}

	do {
		if (bqt->alloc_policy == BLK_TAG_ALLOC_FIFO) {
			tag = find_first_zero_bit(bqt->tag_map, max_depth);
			if (tag >= max_depth)
				return 1;
		} else {
			int start = bqt->next_tag;
			int size = min_t(int, bqt->max_depth, max_depth + start);
			tag = find_next_zero_bit(bqt->tag_map, size, start);
			if (tag >= size && start + size > bqt->max_depth) {
				size = start + size - bqt->max_depth;
				tag = find_first_zero_bit(bqt->tag_map, size);
			}
			if (tag >= size)
				return 1;
		}

	} while (test_and_set_bit_lock(tag, bqt->tag_map));
	/*
	 * We need lock ordering semantics given by test_and_set_bit_lock.
	 * See blk_queue_end_tag for details.
	 */

	bqt->next_tag = (tag + 1) % bqt->max_depth;
	rq->rq_flags |= RQF_QUEUED;
	rq->tag = tag;
	bqt->tag_index[tag] = rq;
	blk_start_request(rq);
	list_add(&rq->queuelist, &q->tag_busy_list);
	return 0;
}
EXPORT_SYMBOL(blk_queue_start_tag);

/**
 * blk_queue_invalidate_tags - invalidate all pending tags
 * @q:  the request queue for the device
 *
 *  Description:
 *   Hardware conditions may dictate a need to stop all pending requests.
 *   In this case, we will safely clear the block side of the tag queue and
 *   readd all requests to the request queue in the right order.
 *
 *  Notes:
 *   queue lock must be held.
 **/
void blk_queue_invalidate_tags(struct request_queue *q)
{
	struct list_head *tmp, *n;

	list_for_each_safe(tmp, n, &q->tag_busy_list)
		blk_requeue_request(q, list_entry_rq(tmp));
}
EXPORT_SYMBOL(blk_queue_invalidate_tags);
Commit	Line	Data
8324aa91 JA	1	/*
	2	* Functions related to tagged command queuing
	3	*/
	4	#include <linux/kernel.h>
	5	#include <linux/module.h>
	6	#include <linux/bio.h>
	7	#include <linux/blkdev.h>
5a0e3ad6	8	#include <linux/slab.h>
8324aa91	9
278caf01 AB	10	#include "blk.h"
278caf01 AB	11
8324aa91 JA	12	/**
	13	* blk_queue_find_tag - find a request by its tag and queue
	14	* @q: The request queue for the device
	15	* @tag: The tag of the request
	16	*
	17	* Notes:
	18	* Should be used when a device returns a tag and you want to match
	19	* it with a request.
	20	*
	21	* no locks need be held.
	22	**/
	23	struct request blk_queue_find_tag(struct request_queue q, int tag)
	24	{
	25	return blk_map_queue_find_tag(q->queue_tags, tag);
	26	}
8324aa91 JA	27	EXPORT_SYMBOL(blk_queue_find_tag);
	28
	29	/**
d45b3279	30	* blk_free_tags - release a given set of tag maintenance info
8324aa91 JA	31	* @bqt: the tag map to free
8324aa91 JA	32	*
d45b3279 CH	33	* Drop the reference count on @bqt and frees it when the last reference
d45b3279 CH	34	* is dropped.
8324aa91	35	*/
d45b3279	36	void blk_free_tags(struct blk_queue_tag *bqt)
8324aa91	37	{
d45b3279	38	if (atomic_dec_and_test(&bqt->refcnt)) {
0e3eb45e MW	39	BUG_ON(find_first_bit(bqt->tag_map, bqt->max_depth) <
0e3eb45e MW	40	bqt->max_depth);
8324aa91 JA	41
	42	kfree(bqt->tag_index);
	43	bqt->tag_index = NULL;
	44
	45	kfree(bqt->tag_map);
	46	bqt->tag_map = NULL;
	47
	48	kfree(bqt);
	49	}
8324aa91	50	}
d45b3279	51	EXPORT_SYMBOL(blk_free_tags);
8324aa91 JA	52
	53	/**
	54	* __blk_queue_free_tags - release tag maintenance info
	55	* @q: the request queue for the device
	56	*
	57	* Notes:
	58	* blk_cleanup_queue() will take care of calling this function, if tagging
	59	* has been used. So there's no need to call this directly.
	60	**/
	61	void __blk_queue_free_tags(struct request_queue *q)
	62	{
	63	struct blk_queue_tag *bqt = q->queue_tags;
	64
	65	if (!bqt)
	66	return;
	67
d45b3279	68	blk_free_tags(bqt);
8324aa91 JA	69
8324aa91 JA	70	q->queue_tags = NULL;
aa94b537	71	queue_flag_clear_unlocked(QUEUE_FLAG_QUEUED, q);
8324aa91 JA	72	}
8324aa91 JA	73
8324aa91 JA	74	/**
	75	* blk_queue_free_tags - release tag maintenance info
	76	* @q: the request queue for the device
	77	*
	78	* Notes:
710027a4	79	* This is used to disable tagged queuing to a device, yet leave
8324aa91 JA	80	* queue in function.
	81	**/
	82	void blk_queue_free_tags(struct request_queue *q)
	83	{
aa94b537	84	queue_flag_clear_unlocked(QUEUE_FLAG_QUEUED, q);
8324aa91	85	}
8324aa91 JA	86	EXPORT_SYMBOL(blk_queue_free_tags);
	87
	88	static int
	89	init_tag_map(struct request_queue q, struct blk_queue_tag tags, int depth)
	90	{
	91	struct request **tag_index;
	92	unsigned long *tag_map;
	93	int nr_ulongs;
	94
	95	if (q && depth > q->nr_requests * 2) {
	96	depth = q->nr_requests * 2;
	97	printk(KERN_ERR "%s: adjusted depth to %d\n",
24c03d47	98	__func__, depth);
8324aa91 JA	99	}
	100
	101	tag_index = kzalloc(depth * sizeof(struct request *), GFP_ATOMIC);
	102	if (!tag_index)
	103	goto fail;
	104
	105	nr_ulongs = ALIGN(depth, BITS_PER_LONG) / BITS_PER_LONG;
	106	tag_map = kzalloc(nr_ulongs * sizeof(unsigned long), GFP_ATOMIC);
	107	if (!tag_map)
	108	goto fail;
	109
	110	tags->real_max_depth = depth;
	111	tags->max_depth = depth;
	112	tags->tag_index = tag_index;
	113	tags->tag_map = tag_map;
	114
	115	return 0;
	116	fail:
	117	kfree(tag_index);
	118	return -ENOMEM;
	119	}
	120
	121	static struct blk_queue_tag __blk_queue_init_tags(struct request_queue q,
ee1b6f7a	122	int depth, int alloc_policy)
8324aa91 JA	123	{
	124	struct blk_queue_tag *tags;
	125
	126	tags = kmalloc(sizeof(struct blk_queue_tag), GFP_ATOMIC);
	127	if (!tags)
	128	goto fail;
	129
	130	if (init_tag_map(q, tags, depth))
	131	goto fail;
	132
8324aa91	133	atomic_set(&tags->refcnt, 1);
ee1b6f7a SL	134	tags->alloc_policy = alloc_policy;
ee1b6f7a SL	135	tags->next_tag = 0;
8324aa91 JA	136	return tags;
	137	fail:
	138	kfree(tags);
	139	return NULL;
	140	}
	141
	142	/**
	143	* blk_init_tags - initialize the tag info for an external tag map
	144	* @depth: the maximum queue depth supported
ee1b6f7a	145	* @alloc_policy: tag allocation policy
8324aa91	146	**/
ee1b6f7a	147	struct blk_queue_tag *blk_init_tags(int depth, int alloc_policy)
8324aa91	148	{
ee1b6f7a	149	return __blk_queue_init_tags(NULL, depth, alloc_policy);
8324aa91 JA	150	}
	151	EXPORT_SYMBOL(blk_init_tags);
	152
	153	/**
	154	* blk_queue_init_tags - initialize the queue tag info
	155	* @q: the request queue for the device
	156	* @depth: the maximum queue depth supported
	157	* @tags: the tag to use
ee1b6f7a	158	* @alloc_policy: tag allocation policy
aa94b537 JA	159	*
	160	* Queue lock must be held here if the function is called to resize an
	161	* existing map.
8324aa91 JA	162	**/
8324aa91 JA	163	int blk_queue_init_tags(struct request_queue *q, int depth,
ee1b6f7a	164	struct blk_queue_tag *tags, int alloc_policy)
8324aa91 JA	165	{
	166	int rc;
	167
	168	BUG_ON(tags && q->queue_tags && tags != q->queue_tags);
	169
	170	if (!tags && !q->queue_tags) {
ee1b6f7a	171	tags = __blk_queue_init_tags(q, depth, alloc_policy);
8324aa91 JA	172
8324aa91 JA	173	if (!tags)
d41570b7 PST	174	return -ENOMEM;
d41570b7 PST	175
8324aa91	176	} else if (q->queue_tags) {
6728cb0e JA	177	rc = blk_queue_resize_tags(q, depth);
6728cb0e JA	178	if (rc)
8324aa91	179	return rc;
75ad23bc	180	queue_flag_set(QUEUE_FLAG_QUEUED, q);
8324aa91 JA	181	return 0;
	182	} else
	183	atomic_inc(&tags->refcnt);
	184
	185	/*
	186	* assign it, all done
	187	*/
	188	q->queue_tags = tags;
aa94b537	189	queue_flag_set_unlocked(QUEUE_FLAG_QUEUED, q);
8324aa91 JA	190	INIT_LIST_HEAD(&q->tag_busy_list);
8324aa91 JA	191	return 0;
8324aa91	192	}
8324aa91 JA	193	EXPORT_SYMBOL(blk_queue_init_tags);
	194
	195	/**
	196	* blk_queue_resize_tags - change the queueing depth
	197	* @q: the request queue for the device
	198	* @new_depth: the new max command queueing depth
	199	*
	200	* Notes:
	201	* Must be called with the queue lock held.
	202	**/
	203	int blk_queue_resize_tags(struct request_queue *q, int new_depth)
	204	{
	205	struct blk_queue_tag *bqt = q->queue_tags;
	206	struct request **tag_index;
	207	unsigned long *tag_map;
	208	int max_depth, nr_ulongs;
	209
	210	if (!bqt)
	211	return -ENXIO;
	212
	213	/*
	214	* if we already have large enough real_max_depth. just
	215	* adjust max_depth. NOTE as requests with tag value
	216	* between new_depth and real_max_depth can be in-flight, tag
	217	* map can not be shrunk blindly here.
	218	*/
	219	if (new_depth <= bqt->real_max_depth) {
	220	bqt->max_depth = new_depth;
	221	return 0;
	222	}
	223
	224	/*
	225	* Currently cannot replace a shared tag map with a new
	226	* one, so error out if this is the case
	227	*/
	228	if (atomic_read(&bqt->refcnt) != 1)
	229	return -EBUSY;
	230
	231	/*
	232	* save the old state info, so we can copy it back
	233	*/
	234	tag_index = bqt->tag_index;
	235	tag_map = bqt->tag_map;
	236	max_depth = bqt->real_max_depth;
	237
	238	if (init_tag_map(q, bqt, new_depth))
	239	return -ENOMEM;
	240
	241	memcpy(bqt->tag_index, tag_index, max_depth * sizeof(struct request *));
	242	nr_ulongs = ALIGN(max_depth, BITS_PER_LONG) / BITS_PER_LONG;
	243	memcpy(bqt->tag_map, tag_map, nr_ulongs * sizeof(unsigned long));
	244
	245	kfree(tag_index);
	246	kfree(tag_map);
	247	return 0;
	248	}
8324aa91 JA	249	EXPORT_SYMBOL(blk_queue_resize_tags);
	250
	251	/**
	252	* blk_queue_end_tag - end tag operations for a request
	253	* @q: the request queue for the device
	254	* @rq: the request that has completed
	255	*
	256	* Description:
710027a4	257	* Typically called when end_that_request_first() returns %0, meaning
8324aa91 JA	258	* all transfers have been done for a request. It's important to call
	259	* this function before end_that_request_last(), as that will put the
	260	* request back on the free list thus corrupting the internal tag list.
	261	*
	262	* Notes:
	263	* queue lock must be held.
	264	**/
	265	void blk_queue_end_tag(struct request_queue q, struct request rq)
	266	{
	267	struct blk_queue_tag *bqt = q->queue_tags;
f2b20d43	268	unsigned tag = rq->tag; /* negative tags invalid */
8324aa91	269
f2b20d43	270	BUG_ON(tag >= bqt->real_max_depth);
8324aa91 JA	271
8324aa91 JA	272	list_del_init(&rq->queuelist);
e8064021	273	rq->rq_flags &= ~RQF_QUEUED;
8324aa91 JA	274	rq->tag = -1;
	275
	276	if (unlikely(bqt->tag_index[tag] == NULL))
	277	printk(KERN_ERR "%s: tag %d is missing\n",
24c03d47	278	__func__, tag);
8324aa91 JA	279
	280	bqt->tag_index[tag] = NULL;
	281
	282	if (unlikely(!test_bit(tag, bqt->tag_map))) {
	283	printk(KERN_ERR "%s: attempt to clear non-busy tag (%d)\n",
24c03d47	284	__func__, tag);
8324aa91 JA	285	return;
	286	}
	287	/*
	288	* The tag_map bit acts as a lock for tag_index[bit], so we need
	289	* unlock memory barrier semantics.
	290	*/
	291	clear_bit_unlock(tag, bqt->tag_map);
8324aa91	292	}
8324aa91 JA	293	EXPORT_SYMBOL(blk_queue_end_tag);
	294
	295	/**
	296	* blk_queue_start_tag - find a free tag and assign it
	297	* @q: the request queue for the device
	298	* @rq: the block request that needs tagging
	299	*
	300	* Description:
	301	* This can either be used as a stand-alone helper, or possibly be
	302	* assigned as the queue &prep_rq_fn (in which case &struct request
	303	* automagically gets a tag assigned). Note that this function
	304	* assumes that any type of request can be queued! if this is not
	305	* true for your device, you must check the request type before
	306	* calling this function. The request will also be removed from
	307	* the request queue, so it's the drivers responsibility to readd
	308	* it if it should need to be restarted for some reason.
	309	*
	310	* Notes:
	311	* queue lock must be held.
	312	**/
	313	int blk_queue_start_tag(struct request_queue q, struct request rq)
	314	{
	315	struct blk_queue_tag *bqt = q->queue_tags;
0a7ae2ff	316	unsigned max_depth;
8324aa91 JA	317	int tag;
8324aa91 JA	318
e8064021	319	if (unlikely((rq->rq_flags & RQF_QUEUED))) {
6728cb0e	320	printk(KERN_ERR
8324aa91	321	"%s: request %p for device [%s] already tagged %d",
24c03d47	322	__func__, rq,
8324aa91 JA	323	rq->rq_disk ? rq->rq_disk->disk_name : "?", rq->tag);
	324	BUG();
	325	}
	326
	327	/*
	328	* Protect against shared tag maps, as we may not have exclusive
	329	* access to the tag map.
e3ba9ae5 JA	330	*
	331	* We reserve a few tags just for sync IO, since we don't want
	332	* to starve sync IO on behalf of flooding async IO.
8324aa91	333	*/
e3ba9ae5	334	max_depth = bqt->max_depth;
0a7ae2ff	335	if (!rq_is_sync(rq) && max_depth > 1) {
a6b3f761 JK	336	switch (max_depth) {
a6b3f761 JK	337	case 2:
0a7ae2ff	338	max_depth = 1;
a6b3f761 JK	339	break;
	340	case 3:
	341	max_depth = 2;
	342	break;
	343	default:
	344	max_depth -= 2;
	345	}
1b59dd51	346	if (q->in_flight[BLK_RW_ASYNC] > max_depth)
0a7ae2ff JA	347	return 1;
0a7ae2ff JA	348	}
e3ba9ae5	349
8324aa91	350	do {
ee1b6f7a SL	351	if (bqt->alloc_policy == BLK_TAG_ALLOC_FIFO) {
	352	tag = find_first_zero_bit(bqt->tag_map, max_depth);
	353	if (tag >= max_depth)
	354	return 1;
	355	} else {
	356	int start = bqt->next_tag;
	357	int size = min_t(int, bqt->max_depth, max_depth + start);
	358	tag = find_next_zero_bit(bqt->tag_map, size, start);
	359	if (tag >= size && start + size > bqt->max_depth) {
	360	size = start + size - bqt->max_depth;
	361	tag = find_first_zero_bit(bqt->tag_map, size);
	362	}
	363	if (tag >= size)
	364	return 1;
	365	}
8324aa91 JA	366
	367	} while (test_and_set_bit_lock(tag, bqt->tag_map));
	368	/*
	369	* We need lock ordering semantics given by test_and_set_bit_lock.
	370	* See blk_queue_end_tag for details.
	371	*/
	372
ee1b6f7a	373	bqt->next_tag = (tag + 1) % bqt->max_depth;
e8064021	374	rq->rq_flags \|= RQF_QUEUED;
8324aa91 JA	375	rq->tag = tag;
8324aa91 JA	376	bqt->tag_index[tag] = rq;
9934c8c0	377	blk_start_request(rq);
8324aa91	378	list_add(&rq->queuelist, &q->tag_busy_list);
8324aa91 JA	379	return 0;
8324aa91 JA	380	}
8324aa91 JA	381	EXPORT_SYMBOL(blk_queue_start_tag);
	382
	383	/**
	384	* blk_queue_invalidate_tags - invalidate all pending tags
	385	* @q: the request queue for the device
	386	*
	387	* Description:
	388	* Hardware conditions may dictate a need to stop all pending requests.
	389	* In this case, we will safely clear the block side of the tag queue and
	390	* readd all requests to the request queue in the right order.
	391	*
	392	* Notes:
	393	* queue lock must be held.
	394	**/
	395	void blk_queue_invalidate_tags(struct request_queue *q)
	396	{
	397	struct list_head tmp, n;
	398
	399	list_for_each_safe(tmp, n, &q->tag_busy_list)
	400	blk_requeue_request(q, list_entry_rq(tmp));
	401	}
8324aa91	402	EXPORT_SYMBOL(blk_queue_invalidate_tags);