[mirror_ubuntu-artful-kernel.git] / block / blk-barrier.c

/*
 * Functions related to barrier IO handling
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/gfp.h>

#include "blk.h"

/**
 * blk_queue_ordered - does this queue support ordered writes
 * @q:        the request queue
 * @ordered:  one of QUEUE_ORDERED_*
 *
 * Description:
 *   For journalled file systems, doing ordered writes on a commit
 *   block instead of explicitly doing wait_on_buffer (which is bad
 *   for performance) can be a big win. Block drivers supporting this
 *   feature should call this function and indicate so.
 *
 **/
int blk_queue_ordered(struct request_queue *q, unsigned ordered)
{
	if (ordered != QUEUE_ORDERED_NONE &&
	    ordered != QUEUE_ORDERED_DRAIN &&
	    ordered != QUEUE_ORDERED_DRAIN_FLUSH &&
	    ordered != QUEUE_ORDERED_DRAIN_FUA &&
	    ordered != QUEUE_ORDERED_TAG &&
	    ordered != QUEUE_ORDERED_TAG_FLUSH &&
	    ordered != QUEUE_ORDERED_TAG_FUA) {
		printk(KERN_ERR "blk_queue_ordered: bad value %d\n", ordered);
		return -EINVAL;
	}

	q->ordered = ordered;
	q->next_ordered = ordered;

	return 0;
}
EXPORT_SYMBOL(blk_queue_ordered);

/*
 * Cache flushing for ordered writes handling
 */
unsigned blk_ordered_cur_seq(struct request_queue *q)
{
	if (!q->ordseq)
		return 0;
	return 1 << ffz(q->ordseq);
}

unsigned blk_ordered_req_seq(struct request *rq)
{
	struct request_queue *q = rq->q;

	BUG_ON(q->ordseq == 0);

	if (rq == &q->pre_flush_rq)
		return QUEUE_ORDSEQ_PREFLUSH;
	if (rq == &q->bar_rq)
		return QUEUE_ORDSEQ_BAR;
	if (rq == &q->post_flush_rq)
		return QUEUE_ORDSEQ_POSTFLUSH;

	/*
	 * !fs requests don't need to follow barrier ordering.  Always
	 * put them at the front.  This fixes the following deadlock.
	 *
	 * http://thread.gmane.org/gmane.linux.kernel/537473
	 */
	if (rq->cmd_type != REQ_TYPE_FS)
		return QUEUE_ORDSEQ_DRAIN;

	if ((rq->cmd_flags & REQ_ORDERED_COLOR) ==
	    (q->orig_bar_rq->cmd_flags & REQ_ORDERED_COLOR))
		return QUEUE_ORDSEQ_DRAIN;
	else
		return QUEUE_ORDSEQ_DONE;
}

bool blk_ordered_complete_seq(struct request_queue *q, unsigned seq, int error)
{
	struct request *rq;

	if (error && !q->orderr)
		q->orderr = error;

	BUG_ON(q->ordseq & seq);
	q->ordseq |= seq;

	if (blk_ordered_cur_seq(q) != QUEUE_ORDSEQ_DONE)
		return false;

	/*
	 * Okay, sequence complete.
	 */
	q->ordseq = 0;
	rq = q->orig_bar_rq;
	__blk_end_request_all(rq, q->orderr);
	return true;
}

static void pre_flush_end_io(struct request *rq, int error)
{
	elv_completed_request(rq->q, rq);
	blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_PREFLUSH, error);
}

static void bar_end_io(struct request *rq, int error)
{
	elv_completed_request(rq->q, rq);
	blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_BAR, error);
}

static void post_flush_end_io(struct request *rq, int error)
{
	elv_completed_request(rq->q, rq);
	blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_POSTFLUSH, error);
}

static void queue_flush(struct request_queue *q, unsigned which)
{
	struct request *rq;
	rq_end_io_fn *end_io;

	if (which == QUEUE_ORDERED_DO_PREFLUSH) {
		rq = &q->pre_flush_rq;
		end_io = pre_flush_end_io;
	} else {
		rq = &q->post_flush_rq;
		end_io = post_flush_end_io;
	}

	blk_rq_init(q, rq);
	rq->cmd_flags = REQ_HARDBARRIER | REQ_FLUSH;
	rq->rq_disk = q->bar_rq.rq_disk;
	rq->end_io = end_io;

	elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
}

static inline bool start_ordered(struct request_queue *q, struct request **rqp)
{
	struct request *rq = *rqp;
	unsigned skip = 0;

	q->orderr = 0;
	q->ordered = q->next_ordered;
	q->ordseq |= QUEUE_ORDSEQ_STARTED;

	/*
	 * For an empty barrier, there's no actual BAR request, which
	 * in turn makes POSTFLUSH unnecessary.  Mask them off.
	 */
	if (!blk_rq_sectors(rq)) {
		q->ordered &= ~(QUEUE_ORDERED_DO_BAR |
				QUEUE_ORDERED_DO_POSTFLUSH);
		/*
		 * Empty barrier on a write-through device w/ ordered
		 * tag has no command to issue and without any command
		 * to issue, ordering by tag can't be used.  Drain
		 * instead.
		 */
		if ((q->ordered & QUEUE_ORDERED_BY_TAG) &&
		    !(q->ordered & QUEUE_ORDERED_DO_PREFLUSH)) {
			q->ordered &= ~QUEUE_ORDERED_BY_TAG;
			q->ordered |= QUEUE_ORDERED_BY_DRAIN;
		}
	}

	/* stash away the original request */
	blk_dequeue_request(rq);
	q->orig_bar_rq = rq;
	rq = NULL;

	/*
	 * Queue ordered sequence.  As we stack them at the head, we
	 * need to queue in reverse order.  Note that we rely on that
	 * no fs request uses ELEVATOR_INSERT_FRONT and thus no fs
	 * request gets inbetween ordered sequence.
	 */
	if (q->ordered & QUEUE_ORDERED_DO_POSTFLUSH) {
		queue_flush(q, QUEUE_ORDERED_DO_POSTFLUSH);
		rq = &q->post_flush_rq;
	} else
		skip |= QUEUE_ORDSEQ_POSTFLUSH;

	if (q->ordered & QUEUE_ORDERED_DO_BAR) {
		rq = &q->bar_rq;

		/* initialize proxy request and queue it */
		blk_rq_init(q, rq);
		if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
			rq->cmd_flags |= REQ_WRITE;
		if (q->ordered & QUEUE_ORDERED_DO_FUA)
			rq->cmd_flags |= REQ_FUA;
		init_request_from_bio(rq, q->orig_bar_rq->bio);
		rq->end_io = bar_end_io;

		elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
	} else
		skip |= QUEUE_ORDSEQ_BAR;

	if (q->ordered & QUEUE_ORDERED_DO_PREFLUSH) {
		queue_flush(q, QUEUE_ORDERED_DO_PREFLUSH);
		rq = &q->pre_flush_rq;
	} else
		skip |= QUEUE_ORDSEQ_PREFLUSH;

	if ((q->ordered & QUEUE_ORDERED_BY_DRAIN) && queue_in_flight(q))
		rq = NULL;
	else
		skip |= QUEUE_ORDSEQ_DRAIN;

	*rqp = rq;

	/*
	 * Complete skipped sequences.  If whole sequence is complete,
	 * return false to tell elevator that this request is gone.
	 */
	return !blk_ordered_complete_seq(q, skip, 0);
}

bool blk_do_ordered(struct request_queue *q, struct request **rqp)
{
	struct request *rq = *rqp;
	const int is_barrier = rq->cmd_type == REQ_TYPE_FS &&
				(rq->cmd_flags & REQ_HARDBARRIER);

	if (!q->ordseq) {
		if (!is_barrier)
			return true;

		if (q->next_ordered != QUEUE_ORDERED_NONE)
			return start_ordered(q, rqp);
		else {
			/*
			 * Queue ordering not supported.  Terminate
			 * with prejudice.
			 */
			blk_dequeue_request(rq);
			__blk_end_request_all(rq, -EOPNOTSUPP);
			*rqp = NULL;
			return false;
		}
	}

	/*
	 * Ordered sequence in progress
	 */

	/* Special requests are not subject to ordering rules. */
	if (rq->cmd_type != REQ_TYPE_FS &&
	    rq != &q->pre_flush_rq && rq != &q->post_flush_rq)
		return true;

	if (q->ordered & QUEUE_ORDERED_BY_TAG) {
		/* Ordered by tag.  Blocking the next barrier is enough. */
		if (is_barrier && rq != &q->bar_rq)
			*rqp = NULL;
	} else {
		/* Ordered by draining.  Wait for turn. */
		WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
		if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
			*rqp = NULL;
	}

	return true;
}

static void bio_end_empty_barrier(struct bio *bio, int err)
{
	if (err) {
		if (err == -EOPNOTSUPP)
			set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
		clear_bit(BIO_UPTODATE, &bio->bi_flags);
	}
	if (bio->bi_private)
		complete(bio->bi_private);
	bio_put(bio);
}

/**
 * blkdev_issue_flush - queue a flush
 * @bdev:	blockdev to issue flush for
 * @gfp_mask:	memory allocation flags (for bio_alloc)
 * @error_sector:	error sector
 * @flags:	BLKDEV_IFL_* flags to control behaviour
 *
 * Description:
 *    Issue a flush for the block device in question. Caller can supply
 *    room for storing the error offset in case of a flush error, if they
 *    wish to. If WAIT flag is not passed then caller may check only what
 *    request was pushed in some internal queue for later handling.
 */
int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
		sector_t *error_sector, unsigned long flags)
{
	DECLARE_COMPLETION_ONSTACK(wait);
	struct request_queue *q;
	struct bio *bio;
	int ret = 0;

	if (bdev->bd_disk == NULL)
		return -ENXIO;

	q = bdev_get_queue(bdev);
	if (!q)
		return -ENXIO;

	/*
	 * some block devices may not have their queue correctly set up here
	 * (e.g. loop device without a backing file) and so issuing a flush
	 * here will panic. Ensure there is a request function before issuing
	 * the barrier.
	 */
	if (!q->make_request_fn)
		return -ENXIO;

	bio = bio_alloc(gfp_mask, 0);
	bio->bi_end_io = bio_end_empty_barrier;
	bio->bi_bdev = bdev;
	if (test_bit(BLKDEV_WAIT, &flags))
		bio->bi_private = &wait;

	bio_get(bio);
	submit_bio(WRITE_BARRIER, bio);
	if (test_bit(BLKDEV_WAIT, &flags)) {
		wait_for_completion(&wait);
		/*
		 * The driver must store the error location in ->bi_sector, if
		 * it supports it. For non-stacked drivers, this should be
		 * copied from blk_rq_pos(rq).
		 */
		if (error_sector)
			*error_sector = bio->bi_sector;
	}

	if (bio_flagged(bio, BIO_EOPNOTSUPP))
		ret = -EOPNOTSUPP;
	else if (!bio_flagged(bio, BIO_UPTODATE))
		ret = -EIO;

	bio_put(bio);
	return ret;
}
EXPORT_SYMBOL(blkdev_issue_flush);
Commit	Line	Data
86db1e29 JA	1	/*
	2	* Functions related to barrier IO handling
	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/gfp.h>
86db1e29 JA	9
	10	#include "blk.h"
	11
	12	/**
	13	* blk_queue_ordered - does this queue support ordered writes
	14	* @q: the request queue
	15	* @ordered: one of QUEUE_ORDERED_*
86db1e29 JA	16	*
	17	* Description:
	18	* For journalled file systems, doing ordered writes on a commit
	19	* block instead of explicitly doing wait_on_buffer (which is bad
	20	* for performance) can be a big win. Block drivers supporting this
	21	* feature should call this function and indicate so.
	22	*
	23	**/
00fff265	24	int blk_queue_ordered(struct request_queue *q, unsigned ordered)
86db1e29	25	{
86db1e29 JA	26	if (ordered != QUEUE_ORDERED_NONE &&
	27	ordered != QUEUE_ORDERED_DRAIN &&
	28	ordered != QUEUE_ORDERED_DRAIN_FLUSH &&
	29	ordered != QUEUE_ORDERED_DRAIN_FUA &&
	30	ordered != QUEUE_ORDERED_TAG &&
	31	ordered != QUEUE_ORDERED_TAG_FLUSH &&
	32	ordered != QUEUE_ORDERED_TAG_FUA) {
	33	printk(KERN_ERR "blk_queue_ordered: bad value %d\n", ordered);
	34	return -EINVAL;
	35	}
	36
	37	q->ordered = ordered;
	38	q->next_ordered = ordered;
86db1e29 JA	39
	40	return 0;
	41	}
86db1e29 JA	42	EXPORT_SYMBOL(blk_queue_ordered);
	43
	44	/*
	45	* Cache flushing for ordered writes handling
	46	*/
6f6a036e	47	unsigned blk_ordered_cur_seq(struct request_queue *q)
86db1e29 JA	48	{
	49	if (!q->ordseq)
	50	return 0;
	51	return 1 << ffz(q->ordseq);
	52	}
	53
	54	unsigned blk_ordered_req_seq(struct request *rq)
	55	{
	56	struct request_queue *q = rq->q;
	57
	58	BUG_ON(q->ordseq == 0);
	59
	60	if (rq == &q->pre_flush_rq)
	61	return QUEUE_ORDSEQ_PREFLUSH;
	62	if (rq == &q->bar_rq)
	63	return QUEUE_ORDSEQ_BAR;
	64	if (rq == &q->post_flush_rq)
	65	return QUEUE_ORDSEQ_POSTFLUSH;
	66
	67	/*
	68	* !fs requests don't need to follow barrier ordering. Always
	69	* put them at the front. This fixes the following deadlock.
	70	*
	71	* http://thread.gmane.org/gmane.linux.kernel/537473
	72	*/
33659ebb	73	if (rq->cmd_type != REQ_TYPE_FS)
86db1e29 JA	74	return QUEUE_ORDSEQ_DRAIN;
	75
	76	if ((rq->cmd_flags & REQ_ORDERED_COLOR) ==
	77	(q->orig_bar_rq->cmd_flags & REQ_ORDERED_COLOR))
	78	return QUEUE_ORDSEQ_DRAIN;
	79	else
	80	return QUEUE_ORDSEQ_DONE;
	81	}
	82
8f11b3e9	83	bool blk_ordered_complete_seq(struct request_queue *q, unsigned seq, int error)
86db1e29 JA	84	{
	85	struct request *rq;
	86
	87	if (error && !q->orderr)
	88	q->orderr = error;
	89
	90	BUG_ON(q->ordseq & seq);
	91	q->ordseq \|= seq;
	92
	93	if (blk_ordered_cur_seq(q) != QUEUE_ORDSEQ_DONE)
8f11b3e9	94	return false;
86db1e29 JA	95
	96	/*
	97	* Okay, sequence complete.
	98	*/
	99	q->ordseq = 0;
	100	rq = q->orig_bar_rq;
40cbbb78	101	__blk_end_request_all(rq, q->orderr);
8f11b3e9	102	return true;
86db1e29 JA	103	}
	104
	105	static void pre_flush_end_io(struct request *rq, int error)
	106	{
	107	elv_completed_request(rq->q, rq);
	108	blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_PREFLUSH, error);
	109	}
	110
	111	static void bar_end_io(struct request *rq, int error)
	112	{
	113	elv_completed_request(rq->q, rq);
	114	blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_BAR, error);
	115	}
	116
	117	static void post_flush_end_io(struct request *rq, int error)
	118	{
	119	elv_completed_request(rq->q, rq);
	120	blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_POSTFLUSH, error);
	121	}
	122
	123	static void queue_flush(struct request_queue *q, unsigned which)
	124	{
	125	struct request *rq;
	126	rq_end_io_fn *end_io;
	127
313e4299	128	if (which == QUEUE_ORDERED_DO_PREFLUSH) {
86db1e29 JA	129	rq = &q->pre_flush_rq;
	130	end_io = pre_flush_end_io;
	131	} else {
	132	rq = &q->post_flush_rq;
	133	end_io = post_flush_end_io;
	134	}
	135
2a4aa30c	136	blk_rq_init(q, rq);
8749534f	137	rq->cmd_flags = REQ_HARDBARRIER \| REQ_FLUSH;
86db1e29 JA	138	rq->rq_disk = q->bar_rq.rq_disk;
86db1e29 JA	139	rq->end_io = end_io;
86db1e29 JA	140
	141	elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
	142	}
	143
8f11b3e9	144	static inline bool start_ordered(struct request_queue q, struct request *rqp)
86db1e29	145	{
8f11b3e9 TH	146	struct request rq = rqp;
	147	unsigned skip = 0;
	148
86db1e29 JA	149	q->orderr = 0;
	150	q->ordered = q->next_ordered;
	151	q->ordseq \|= QUEUE_ORDSEQ_STARTED;
	152
58eea927 TH	153	/*
	154	* For an empty barrier, there's no actual BAR request, which
	155	* in turn makes POSTFLUSH unnecessary. Mask them off.
	156	*/
5b93629b	157	if (!blk_rq_sectors(rq)) {
58eea927 TH	158	q->ordered &= ~(QUEUE_ORDERED_DO_BAR \|
58eea927 TH	159	QUEUE_ORDERED_DO_POSTFLUSH);
a185eb4b TH	160	/*
	161	* Empty barrier on a write-through device w/ ordered
	162	* tag has no command to issue and without any command
	163	* to issue, ordering by tag can't be used. Drain
	164	* instead.
	165	*/
	166	if ((q->ordered & QUEUE_ORDERED_BY_TAG) &&
	167	!(q->ordered & QUEUE_ORDERED_DO_PREFLUSH)) {
	168	q->ordered &= ~QUEUE_ORDERED_BY_TAG;
	169	q->ordered \|= QUEUE_ORDERED_BY_DRAIN;
	170	}
	171	}
58eea927	172
f671620e	173	/* stash away the original request */
9934c8c0	174	blk_dequeue_request(rq);
86db1e29	175	q->orig_bar_rq = rq;
f671620e	176	rq = NULL;
86db1e29 JA	177
	178	/*
	179	* Queue ordered sequence. As we stack them at the head, we
	180	* need to queue in reverse order. Note that we rely on that
	181	* no fs request uses ELEVATOR_INSERT_FRONT and thus no fs
58eea927	182	* request gets inbetween ordered sequence.
86db1e29	183	*/
58eea927	184	if (q->ordered & QUEUE_ORDERED_DO_POSTFLUSH) {
313e4299	185	queue_flush(q, QUEUE_ORDERED_DO_POSTFLUSH);
f671620e TH	186	rq = &q->post_flush_rq;
f671620e TH	187	} else
8f11b3e9	188	skip \|= QUEUE_ORDSEQ_POSTFLUSH;
86db1e29	189
f671620e TH	190	if (q->ordered & QUEUE_ORDERED_DO_BAR) {
	191	rq = &q->bar_rq;
	192
	193	/* initialize proxy request and queue it */
	194	blk_rq_init(q, rq);
	195	if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
7b6d91da	196	rq->cmd_flags \|= REQ_WRITE;
f671620e TH	197	if (q->ordered & QUEUE_ORDERED_DO_FUA)
	198	rq->cmd_flags \|= REQ_FUA;
	199	init_request_from_bio(rq, q->orig_bar_rq->bio);
	200	rq->end_io = bar_end_io;
	201
	202	elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
	203	} else
8f11b3e9	204	skip \|= QUEUE_ORDSEQ_BAR;
86db1e29	205
313e4299 TH	206	if (q->ordered & QUEUE_ORDERED_DO_PREFLUSH) {
313e4299 TH	207	queue_flush(q, QUEUE_ORDERED_DO_PREFLUSH);
86db1e29 JA	208	rq = &q->pre_flush_rq;
86db1e29 JA	209	} else
8f11b3e9	210	skip \|= QUEUE_ORDSEQ_PREFLUSH;
86db1e29	211
0a7ae2ff	212	if ((q->ordered & QUEUE_ORDERED_BY_DRAIN) && queue_in_flight(q))
86db1e29	213	rq = NULL;
f671620e	214	else
8f11b3e9	215	skip \|= QUEUE_ORDSEQ_DRAIN;
86db1e29	216
8f11b3e9 TH	217	*rqp = rq;
	218
	219	/*
	220	* Complete skipped sequences. If whole sequence is complete,
	221	* return false to tell elevator that this request is gone.
	222	*/
	223	return !blk_ordered_complete_seq(q, skip, 0);
86db1e29 JA	224	}
86db1e29 JA	225
8f11b3e9	226	bool blk_do_ordered(struct request_queue q, struct request *rqp)
86db1e29 JA	227	{
86db1e29 JA	228	struct request rq = rqp;
33659ebb CH	229	const int is_barrier = rq->cmd_type == REQ_TYPE_FS &&
33659ebb CH	230	(rq->cmd_flags & REQ_HARDBARRIER);
86db1e29 JA	231
	232	if (!q->ordseq) {
	233	if (!is_barrier)
8f11b3e9	234	return true;
86db1e29	235
8f11b3e9 TH	236	if (q->next_ordered != QUEUE_ORDERED_NONE)
	237	return start_ordered(q, rqp);
	238	else {
86db1e29	239	/*
a7384677 TH	240	* Queue ordering not supported. Terminate
a7384677 TH	241	* with prejudice.
86db1e29	242	*/
9934c8c0	243	blk_dequeue_request(rq);
40cbbb78	244	__blk_end_request_all(rq, -EOPNOTSUPP);
86db1e29	245	*rqp = NULL;
8f11b3e9	246	return false;
86db1e29 JA	247	}
	248	}
	249
	250	/*
	251	* Ordered sequence in progress
	252	*/
	253
	254	/* Special requests are not subject to ordering rules. */
33659ebb	255	if (rq->cmd_type != REQ_TYPE_FS &&
86db1e29	256	rq != &q->pre_flush_rq && rq != &q->post_flush_rq)
8f11b3e9	257	return true;
86db1e29	258
313e4299	259	if (q->ordered & QUEUE_ORDERED_BY_TAG) {
86db1e29 JA	260	/* Ordered by tag. Blocking the next barrier is enough. */
	261	if (is_barrier && rq != &q->bar_rq)
	262	*rqp = NULL;
	263	} else {
	264	/* Ordered by draining. Wait for turn. */
	265	WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
	266	if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
	267	*rqp = NULL;
	268	}
	269
8f11b3e9	270	return true;
86db1e29 JA	271	}
	272
	273	static void bio_end_empty_barrier(struct bio *bio, int err)
	274	{
cc66b451 JA	275	if (err) {
	276	if (err == -EOPNOTSUPP)
	277	set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
86db1e29	278	clear_bit(BIO_UPTODATE, &bio->bi_flags);
cc66b451	279	}
f17e232e DM	280	if (bio->bi_private)
	281	complete(bio->bi_private);
	282	bio_put(bio);
86db1e29 JA	283	}
	284
	285	/**
	286	* blkdev_issue_flush - queue a flush
	287	* @bdev: blockdev to issue flush for
fbd9b09a	288	* @gfp_mask: memory allocation flags (for bio_alloc)
86db1e29	289	* @error_sector: error sector
fbd9b09a	290	* @flags: BLKDEV_IFL_* flags to control behaviour
86db1e29 JA	291	*
	292	* Description:
	293	* Issue a flush for the block device in question. Caller can supply
	294	* room for storing the error offset in case of a flush error, if they
f17e232e DM	295	* wish to. If WAIT flag is not passed then caller may check only what
f17e232e DM	296	* request was pushed in some internal queue for later handling.
86db1e29	297	*/
fbd9b09a DM	298	int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
fbd9b09a DM	299	sector_t *error_sector, unsigned long flags)
86db1e29 JA	300	{
	301	DECLARE_COMPLETION_ONSTACK(wait);
	302	struct request_queue *q;
	303	struct bio *bio;
fbd9b09a	304	int ret = 0;
86db1e29 JA	305
	306	if (bdev->bd_disk == NULL)
	307	return -ENXIO;
	308
	309	q = bdev_get_queue(bdev);
	310	if (!q)
	311	return -ENXIO;
	312
f10d9f61 DC	313	/*
	314	* some block devices may not have their queue correctly set up here
	315	* (e.g. loop device without a backing file) and so issuing a flush
	316	* here will panic. Ensure there is a request function before issuing
	317	* the barrier.
	318	*/
	319	if (!q->make_request_fn)
	320	return -ENXIO;
	321
fbd9b09a	322	bio = bio_alloc(gfp_mask, 0);
86db1e29	323	bio->bi_end_io = bio_end_empty_barrier;
86db1e29	324	bio->bi_bdev = bdev;
f17e232e DM	325	if (test_bit(BLKDEV_WAIT, &flags))
f17e232e DM	326	bio->bi_private = &wait;
86db1e29	327
f17e232e DM	328	bio_get(bio);
	329	submit_bio(WRITE_BARRIER, bio);
	330	if (test_bit(BLKDEV_WAIT, &flags)) {
	331	wait_for_completion(&wait);
	332	/*
	333	* The driver must store the error location in ->bi_sector, if
	334	* it supports it. For non-stacked drivers, this should be
	335	* copied from blk_rq_pos(rq).
	336	*/
	337	if (error_sector)
	338	*error_sector = bio->bi_sector;
	339	}
86db1e29	340
cc66b451 JA	341	if (bio_flagged(bio, BIO_EOPNOTSUPP))
	342	ret = -EOPNOTSUPP;
	343	else if (!bio_flagged(bio, BIO_UPTODATE))
86db1e29 JA	344	ret = -EIO;
	345
	346	bio_put(bio);
	347	return ret;
	348	}
86db1e29	349	EXPORT_SYMBOL(blkdev_issue_flush);