[linux.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 "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
 *
 * Tries to free the specified @bqt@.  Returns true if it was
 * actually freed and false if there are still references using it
 */
static int __blk_free_tags(struct blk_queue_tag *bqt)
{
	int retval;

	retval = atomic_dec_and_test(&bqt->refcnt);
	if (retval) {
		BUG_ON(bqt->busy);

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

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

		kfree(bqt);
	}

	return retval;
}

/**
 * __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_free_tags - release a given set of tag maintenance info
 * @bqt:	the tag map to free
 *
 * For externally managed @bqt@ frees the map.  Callers of this
 * function must guarantee to have released all the queues that
 * might have been using this tag map.
 */
void blk_free_tags(struct blk_queue_tag *bqt)
{
	if (unlikely(!__blk_free_tags(bqt)))
		BUG();
}
EXPORT_SYMBOL(blk_free_tags);

/**
 * blk_queue_free_tags - release tag maintenance info
 * @q:  the request queue for the device
 *
 *  Notes:
 *	This is used to disabled 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)
{
	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;

	tags->busy = 0;
	atomic_set(&tags->refcnt, 1);
	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
 * @tags: the tag to use
 **/
struct blk_queue_tag *blk_init_tags(int depth)
{
	return __blk_queue_init_tags(NULL, depth);
}
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
 *
 * 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 rc;

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

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

		if (!tags)
			goto fail;
	} 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;
fail:
	kfree(tags);
	return -ENOMEM;
}
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;
	int tag = rq->tag;

	BUG_ON(tag == -1);

	if (unlikely(tag >= bqt->real_max_depth))
		/*
		 * This can happen after tag depth has been reduced.
		 * FIXME: how about a warning or info message here?
		 */
		return;

	list_del_init(&rq->queuelist);
	rq->cmd_flags &= ~REQ_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);
	bqt->busy--;
}
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;
	int tag;

	if (unlikely((rq->cmd_flags & REQ_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.
	 */
	do {
		tag = find_first_zero_bit(bqt->tag_map, bqt->max_depth);
		if (tag >= bqt->max_depth)
			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.
	 */

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