[linux-2.6-block.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(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);
	}

	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 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)
{
	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);
	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
 **/
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);
}
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->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.
	 *
	 * 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) {
		max_depth -= 2;
		if (!max_depth)
			max_depth = 1;
		if (q->in_flight[BLK_RW_ASYNC] > max_depth)
			return 1;
	}

	do {
		tag = find_first_zero_bit(bqt->tag_map, max_depth);
		if (tag >= 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;
	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>
	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	*
710027a4	32	* Tries to free the specified @bqt. Returns true if it was
8324aa91 JA	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) {
0e3eb45e MW	41	BUG_ON(find_first_bit(bqt->tag_map, bqt->max_depth) <
0e3eb45e MW	42	bqt->max_depth);
8324aa91 JA	43
	44	kfree(bqt->tag_index);
	45	bqt->tag_index = NULL;
	46
	47	kfree(bqt->tag_map);
	48	bqt->tag_map = NULL;
	49
	50	kfree(bqt);
	51	}
	52
	53	return retval;
	54	}
	55
	56	/**
	57	* __blk_queue_free_tags - release tag maintenance info
	58	* @q: the request queue for the device
	59	*
	60	* Notes:
	61	* blk_cleanup_queue() will take care of calling this function, if tagging
	62	* has been used. So there's no need to call this directly.
	63	**/
	64	void __blk_queue_free_tags(struct request_queue *q)
	65	{
	66	struct blk_queue_tag *bqt = q->queue_tags;
	67
	68	if (!bqt)
	69	return;
	70
	71	__blk_free_tags(bqt);
	72
	73	q->queue_tags = NULL;
aa94b537	74	queue_flag_clear_unlocked(QUEUE_FLAG_QUEUED, q);
8324aa91 JA	75	}
	76
	77	/**
	78	* blk_free_tags - release a given set of tag maintenance info
	79	* @bqt: the tag map to free
	80	*
710027a4	81	* For externally managed @bqt frees the map. Callers of this
8324aa91 JA	82	* function must guarantee to have released all the queues that
	83	* might have been using this tag map.
	84	*/
	85	void blk_free_tags(struct blk_queue_tag *bqt)
	86	{
	87	if (unlikely(!__blk_free_tags(bqt)))
	88	BUG();
	89	}
	90	EXPORT_SYMBOL(blk_free_tags);
	91
	92	/**
	93	* blk_queue_free_tags - release tag maintenance info
	94	* @q: the request queue for the device
	95	*
	96	* Notes:
710027a4	97	* This is used to disable tagged queuing to a device, yet leave
8324aa91 JA	98	* queue in function.
	99	**/
	100	void blk_queue_free_tags(struct request_queue *q)
	101	{
aa94b537	102	queue_flag_clear_unlocked(QUEUE_FLAG_QUEUED, q);
8324aa91	103	}
8324aa91 JA	104	EXPORT_SYMBOL(blk_queue_free_tags);
	105
	106	static int
	107	init_tag_map(struct request_queue q, struct blk_queue_tag tags, int depth)
	108	{
	109	struct request **tag_index;
	110	unsigned long *tag_map;
	111	int nr_ulongs;
	112
	113	if (q && depth > q->nr_requests * 2) {
	114	depth = q->nr_requests * 2;
	115	printk(KERN_ERR "%s: adjusted depth to %d\n",
24c03d47	116	__func__, depth);
8324aa91 JA	117	}
	118
	119	tag_index = kzalloc(depth * sizeof(struct request *), GFP_ATOMIC);
	120	if (!tag_index)
	121	goto fail;
	122
	123	nr_ulongs = ALIGN(depth, BITS_PER_LONG) / BITS_PER_LONG;
	124	tag_map = kzalloc(nr_ulongs * sizeof(unsigned long), GFP_ATOMIC);
	125	if (!tag_map)
	126	goto fail;
	127
	128	tags->real_max_depth = depth;
	129	tags->max_depth = depth;
	130	tags->tag_index = tag_index;
	131	tags->tag_map = tag_map;
	132
	133	return 0;
	134	fail:
	135	kfree(tag_index);
	136	return -ENOMEM;
	137	}
	138
	139	static struct blk_queue_tag __blk_queue_init_tags(struct request_queue q,
	140	int depth)
	141	{
	142	struct blk_queue_tag *tags;
	143
	144	tags = kmalloc(sizeof(struct blk_queue_tag), GFP_ATOMIC);
	145	if (!tags)
	146	goto fail;
	147
	148	if (init_tag_map(q, tags, depth))
	149	goto fail;
	150
8324aa91 JA	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
8324aa91 JA	161	**/
	162	struct blk_queue_tag *blk_init_tags(int depth)
	163	{
	164	return __blk_queue_init_tags(NULL, depth);
	165	}
	166	EXPORT_SYMBOL(blk_init_tags);
	167
	168	/**
	169	* blk_queue_init_tags - initialize the queue tag info
	170	* @q: the request queue for the device
	171	* @depth: the maximum queue depth supported
	172	* @tags: the tag to use
aa94b537 JA	173	*
	174	* Queue lock must be held here if the function is called to resize an
	175	* existing map.
8324aa91 JA	176	**/
	177	int blk_queue_init_tags(struct request_queue *q, int depth,
	178	struct blk_queue_tag *tags)
	179	{
	180	int rc;
	181
	182	BUG_ON(tags && q->queue_tags && tags != q->queue_tags);
	183
	184	if (!tags && !q->queue_tags) {
	185	tags = __blk_queue_init_tags(q, depth);
	186
	187	if (!tags)
	188	goto fail;
	189	} else if (q->queue_tags) {
6728cb0e JA	190	rc = blk_queue_resize_tags(q, depth);
6728cb0e JA	191	if (rc)
8324aa91	192	return rc;
75ad23bc	193	queue_flag_set(QUEUE_FLAG_QUEUED, q);
8324aa91 JA	194	return 0;
	195	} else
	196	atomic_inc(&tags->refcnt);
	197
	198	/*
	199	* assign it, all done
	200	*/
	201	q->queue_tags = tags;
aa94b537	202	queue_flag_set_unlocked(QUEUE_FLAG_QUEUED, q);
8324aa91 JA	203	INIT_LIST_HEAD(&q->tag_busy_list);
	204	return 0;
	205	fail:
	206	kfree(tags);
	207	return -ENOMEM;
	208	}
8324aa91 JA	209	EXPORT_SYMBOL(blk_queue_init_tags);
	210
	211	/**
	212	* blk_queue_resize_tags - change the queueing depth
	213	* @q: the request queue for the device
	214	* @new_depth: the new max command queueing depth
	215	*
	216	* Notes:
	217	* Must be called with the queue lock held.
	218	**/
	219	int blk_queue_resize_tags(struct request_queue *q, int new_depth)
	220	{
	221	struct blk_queue_tag *bqt = q->queue_tags;
	222	struct request **tag_index;
	223	unsigned long *tag_map;
	224	int max_depth, nr_ulongs;
	225
	226	if (!bqt)
	227	return -ENXIO;
	228
	229	/*
	230	* if we already have large enough real_max_depth. just
	231	* adjust max_depth. NOTE as requests with tag value
	232	* between new_depth and real_max_depth can be in-flight, tag
	233	* map can not be shrunk blindly here.
	234	*/
	235	if (new_depth <= bqt->real_max_depth) {
	236	bqt->max_depth = new_depth;
	237	return 0;
	238	}
	239
	240	/*
	241	* Currently cannot replace a shared tag map with a new
	242	* one, so error out if this is the case
	243	*/
	244	if (atomic_read(&bqt->refcnt) != 1)
	245	return -EBUSY;
	246
	247	/*
	248	* save the old state info, so we can copy it back
	249	*/
	250	tag_index = bqt->tag_index;
	251	tag_map = bqt->tag_map;
	252	max_depth = bqt->real_max_depth;
	253
	254	if (init_tag_map(q, bqt, new_depth))
	255	return -ENOMEM;
	256
	257	memcpy(bqt->tag_index, tag_index, max_depth * sizeof(struct request *));
	258	nr_ulongs = ALIGN(max_depth, BITS_PER_LONG) / BITS_PER_LONG;
	259	memcpy(bqt->tag_map, tag_map, nr_ulongs * sizeof(unsigned long));
	260
	261	kfree(tag_index);
	262	kfree(tag_map);
	263	return 0;
	264	}
8324aa91 JA	265	EXPORT_SYMBOL(blk_queue_resize_tags);
	266
	267	/**
	268	* blk_queue_end_tag - end tag operations for a request
	269	* @q: the request queue for the device
	270	* @rq: the request that has completed
	271	*
	272	* Description:
710027a4	273	* Typically called when end_that_request_first() returns %0, meaning
8324aa91 JA	274	* all transfers have been done for a request. It's important to call
	275	* this function before end_that_request_last(), as that will put the
	276	* request back on the free list thus corrupting the internal tag list.
	277	*
	278	* Notes:
	279	* queue lock must be held.
	280	**/
	281	void blk_queue_end_tag(struct request_queue q, struct request rq)
	282	{
	283	struct blk_queue_tag *bqt = q->queue_tags;
	284	int tag = rq->tag;
	285
	286	BUG_ON(tag == -1);
	287
	288	if (unlikely(tag >= bqt->real_max_depth))
	289	/*
	290	* This can happen after tag depth has been reduced.
	291	* FIXME: how about a warning or info message here?
	292	*/
	293	return;
	294
	295	list_del_init(&rq->queuelist);
	296	rq->cmd_flags &= ~REQ_QUEUED;
	297	rq->tag = -1;
	298
	299	if (unlikely(bqt->tag_index[tag] == NULL))
	300	printk(KERN_ERR "%s: tag %d is missing\n",
24c03d47	301	__func__, tag);
8324aa91 JA	302
	303	bqt->tag_index[tag] = NULL;
	304
	305	if (unlikely(!test_bit(tag, bqt->tag_map))) {
	306	printk(KERN_ERR "%s: attempt to clear non-busy tag (%d)\n",
24c03d47	307	__func__, tag);
8324aa91 JA	308	return;
	309	}
	310	/*
	311	* The tag_map bit acts as a lock for tag_index[bit], so we need
	312	* unlock memory barrier semantics.
	313	*/
	314	clear_bit_unlock(tag, bqt->tag_map);
8324aa91	315	}
8324aa91 JA	316	EXPORT_SYMBOL(blk_queue_end_tag);
	317
	318	/**
	319	* blk_queue_start_tag - find a free tag and assign it
	320	* @q: the request queue for the device
	321	* @rq: the block request that needs tagging
	322	*
	323	* Description:
	324	* This can either be used as a stand-alone helper, or possibly be
	325	* assigned as the queue &prep_rq_fn (in which case &struct request
	326	* automagically gets a tag assigned). Note that this function
	327	* assumes that any type of request can be queued! if this is not
	328	* true for your device, you must check the request type before
	329	* calling this function. The request will also be removed from
	330	* the request queue, so it's the drivers responsibility to readd
	331	* it if it should need to be restarted for some reason.
	332	*
	333	* Notes:
	334	* queue lock must be held.
	335	**/
	336	int blk_queue_start_tag(struct request_queue q, struct request rq)
	337	{
	338	struct blk_queue_tag *bqt = q->queue_tags;
0a7ae2ff	339	unsigned max_depth;
8324aa91 JA	340	int tag;
	341
	342	if (unlikely((rq->cmd_flags & REQ_QUEUED))) {
6728cb0e	343	printk(KERN_ERR
8324aa91	344	"%s: request %p for device [%s] already tagged %d",
24c03d47	345	__func__, rq,
8324aa91 JA	346	rq->rq_disk ? rq->rq_disk->disk_name : "?", rq->tag);
	347	BUG();
	348	}
	349
	350	/*
	351	* Protect against shared tag maps, as we may not have exclusive
	352	* access to the tag map.
e3ba9ae5 JA	353	*
	354	* We reserve a few tags just for sync IO, since we don't want
	355	* to starve sync IO on behalf of flooding async IO.
8324aa91	356	*/
e3ba9ae5	357	max_depth = bqt->max_depth;
0a7ae2ff JA	358	if (!rq_is_sync(rq) && max_depth > 1) {
	359	max_depth -= 2;
	360	if (!max_depth)
	361	max_depth = 1;
1b59dd51	362	if (q->in_flight[BLK_RW_ASYNC] > max_depth)
0a7ae2ff JA	363	return 1;
0a7ae2ff JA	364	}
e3ba9ae5	365
8324aa91	366	do {
0a7ae2ff	367	tag = find_first_zero_bit(bqt->tag_map, max_depth);
e3ba9ae5	368	if (tag >= max_depth)
8324aa91 JA	369	return 1;
	370
	371	} while (test_and_set_bit_lock(tag, bqt->tag_map));
	372	/*
	373	* We need lock ordering semantics given by test_and_set_bit_lock.
	374	* See blk_queue_end_tag for details.
	375	*/
	376
	377	rq->cmd_flags \|= REQ_QUEUED;
	378	rq->tag = tag;
	379	bqt->tag_index[tag] = rq;
9934c8c0	380	blk_start_request(rq);
8324aa91	381	list_add(&rq->queuelist, &q->tag_busy_list);
8324aa91 JA	382	return 0;
8324aa91 JA	383	}
8324aa91 JA	384	EXPORT_SYMBOL(blk_queue_start_tag);
	385
	386	/**
	387	* blk_queue_invalidate_tags - invalidate all pending tags
	388	* @q: the request queue for the device
	389	*
	390	* Description:
	391	* Hardware conditions may dictate a need to stop all pending requests.
	392	* In this case, we will safely clear the block side of the tag queue and
	393	* readd all requests to the request queue in the right order.
	394	*
	395	* Notes:
	396	* queue lock must be held.
	397	**/
	398	void blk_queue_invalidate_tags(struct request_queue *q)
	399	{
	400	struct list_head tmp, n;
	401
	402	list_for_each_safe(tmp, n, &q->tag_busy_list)
	403	blk_requeue_request(q, list_entry_rq(tmp));
	404	}
8324aa91	405	EXPORT_SYMBOL(blk_queue_invalidate_tags);