[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 <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
 *
 * 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>
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	/**
	30	* __blk_free_tags - release a given set of tag maintenance info
	31	* @bqt: the tag map to free
	32	*
710027a4	33	* Tries to free the specified @bqt. Returns true if it was
8324aa91 JA	34	* actually freed and false if there are still references using it
	35	*/
	36	static int __blk_free_tags(struct blk_queue_tag *bqt)
	37	{
	38	int retval;
	39
	40	retval = atomic_dec_and_test(&bqt->refcnt);
	41	if (retval) {
0e3eb45e MW	42	BUG_ON(find_first_bit(bqt->tag_map, bqt->max_depth) <
0e3eb45e MW	43	bqt->max_depth);
8324aa91 JA	44
	45	kfree(bqt->tag_index);
	46	bqt->tag_index = NULL;
	47
	48	kfree(bqt->tag_map);
	49	bqt->tag_map = NULL;
	50
	51	kfree(bqt);
	52	}
	53
	54	return retval;
	55	}
	56
	57	/**
	58	* __blk_queue_free_tags - release tag maintenance info
	59	* @q: the request queue for the device
	60	*
	61	* Notes:
	62	* blk_cleanup_queue() will take care of calling this function, if tagging
	63	* has been used. So there's no need to call this directly.
	64	**/
	65	void __blk_queue_free_tags(struct request_queue *q)
	66	{
	67	struct blk_queue_tag *bqt = q->queue_tags;
	68
	69	if (!bqt)
	70	return;
	71
	72	__blk_free_tags(bqt);
	73
	74	q->queue_tags = NULL;
aa94b537	75	queue_flag_clear_unlocked(QUEUE_FLAG_QUEUED, q);
8324aa91 JA	76	}
	77
	78	/**
	79	* blk_free_tags - release a given set of tag maintenance info
	80	* @bqt: the tag map to free
	81	*
710027a4	82	* For externally managed @bqt frees the map. Callers of this
8324aa91 JA	83	* function must guarantee to have released all the queues that
	84	* might have been using this tag map.
	85	*/
	86	void blk_free_tags(struct blk_queue_tag *bqt)
	87	{
	88	if (unlikely(!__blk_free_tags(bqt)))
	89	BUG();
	90	}
	91	EXPORT_SYMBOL(blk_free_tags);
	92
	93	/**
	94	* blk_queue_free_tags - release tag maintenance info
	95	* @q: the request queue for the device
	96	*
	97	* Notes:
710027a4	98	* This is used to disable tagged queuing to a device, yet leave
8324aa91 JA	99	* queue in function.
	100	**/
	101	void blk_queue_free_tags(struct request_queue *q)
	102	{
aa94b537	103	queue_flag_clear_unlocked(QUEUE_FLAG_QUEUED, q);
8324aa91	104	}
8324aa91 JA	105	EXPORT_SYMBOL(blk_queue_free_tags);
	106
	107	static int
	108	init_tag_map(struct request_queue q, struct blk_queue_tag tags, int depth)
	109	{
	110	struct request **tag_index;
	111	unsigned long *tag_map;
	112	int nr_ulongs;
	113
	114	if (q && depth > q->nr_requests * 2) {
	115	depth = q->nr_requests * 2;
	116	printk(KERN_ERR "%s: adjusted depth to %d\n",
24c03d47	117	__func__, depth);
8324aa91 JA	118	}
	119
	120	tag_index = kzalloc(depth * sizeof(struct request *), GFP_ATOMIC);
	121	if (!tag_index)
	122	goto fail;
	123
	124	nr_ulongs = ALIGN(depth, BITS_PER_LONG) / BITS_PER_LONG;
	125	tag_map = kzalloc(nr_ulongs * sizeof(unsigned long), GFP_ATOMIC);
	126	if (!tag_map)
	127	goto fail;
	128
	129	tags->real_max_depth = depth;
	130	tags->max_depth = depth;
	131	tags->tag_index = tag_index;
	132	tags->tag_map = tag_map;
	133
	134	return 0;
	135	fail:
	136	kfree(tag_index);
	137	return -ENOMEM;
	138	}
	139
	140	static struct blk_queue_tag __blk_queue_init_tags(struct request_queue q,
	141	int depth)
	142	{
	143	struct blk_queue_tag *tags;
	144
	145	tags = kmalloc(sizeof(struct blk_queue_tag), GFP_ATOMIC);
	146	if (!tags)
	147	goto fail;
	148
	149	if (init_tag_map(q, tags, depth))
	150	goto fail;
	151
8324aa91 JA	152	atomic_set(&tags->refcnt, 1);
	153	return tags;
	154	fail:
	155	kfree(tags);
	156	return NULL;
	157	}
	158
	159	/**
	160	* blk_init_tags - initialize the tag info for an external tag map
	161	* @depth: the maximum queue depth supported
8324aa91 JA	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:
710027a4	274	* Typically called when end_that_request_first() returns %0, meaning
8324aa91 JA	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);
8324aa91	316	}
8324aa91 JA	317	EXPORT_SYMBOL(blk_queue_end_tag);
	318
	319	/**
	320	* blk_queue_start_tag - find a free tag and assign it
	321	* @q: the request queue for the device
	322	* @rq: the block request that needs tagging
	323	*
	324	* Description:
	325	* This can either be used as a stand-alone helper, or possibly be
	326	* assigned as the queue &prep_rq_fn (in which case &struct request
	327	* automagically gets a tag assigned). Note that this function
	328	* assumes that any type of request can be queued! if this is not
	329	* true for your device, you must check the request type before
	330	* calling this function. The request will also be removed from
	331	* the request queue, so it's the drivers responsibility to readd
	332	* it if it should need to be restarted for some reason.
	333	*
	334	* Notes:
	335	* queue lock must be held.
	336	**/
	337	int blk_queue_start_tag(struct request_queue q, struct request rq)
	338	{
	339	struct blk_queue_tag *bqt = q->queue_tags;
0a7ae2ff	340	unsigned max_depth;
8324aa91 JA	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.
e3ba9ae5 JA	354	*
	355	* We reserve a few tags just for sync IO, since we don't want
	356	* to starve sync IO on behalf of flooding async IO.
8324aa91	357	*/
e3ba9ae5	358	max_depth = bqt->max_depth;
0a7ae2ff JA	359	if (!rq_is_sync(rq) && max_depth > 1) {
	360	max_depth -= 2;
	361	if (!max_depth)
	362	max_depth = 1;
1b59dd51	363	if (q->in_flight[BLK_RW_ASYNC] > max_depth)
0a7ae2ff JA	364	return 1;
0a7ae2ff JA	365	}
e3ba9ae5	366
8324aa91	367	do {
0a7ae2ff	368	tag = find_first_zero_bit(bqt->tag_map, max_depth);
e3ba9ae5	369	if (tag >= max_depth)
8324aa91 JA	370	return 1;
	371
	372	} while (test_and_set_bit_lock(tag, bqt->tag_map));
	373	/*
	374	* We need lock ordering semantics given by test_and_set_bit_lock.
	375	* See blk_queue_end_tag for details.
	376	*/
	377
	378	rq->cmd_flags \|= REQ_QUEUED;
	379	rq->tag = tag;
	380	bqt->tag_index[tag] = rq;
9934c8c0	381	blk_start_request(rq);
8324aa91	382	list_add(&rq->queuelist, &q->tag_busy_list);
8324aa91 JA	383	return 0;
8324aa91 JA	384	}
8324aa91 JA	385	EXPORT_SYMBOL(blk_queue_start_tag);
	386
	387	/**
	388	* blk_queue_invalidate_tags - invalidate all pending tags
	389	* @q: the request queue for the device
	390	*
	391	* Description:
	392	* Hardware conditions may dictate a need to stop all pending requests.
	393	* In this case, we will safely clear the block side of the tag queue and
	394	* readd all requests to the request queue in the right order.
	395	*
	396	* Notes:
	397	* queue lock must be held.
	398	**/
	399	void blk_queue_invalidate_tags(struct request_queue *q)
	400	{
	401	struct list_head tmp, n;
	402
	403	list_for_each_safe(tmp, n, &q->tag_busy_list)
	404	blk_requeue_request(q, list_entry_rq(tmp));
	405	}
8324aa91	406	EXPORT_SYMBOL(blk_queue_invalidate_tags);