block/blk-lib.c - kernel/msm-4.19 - Gitiles

 /*
  * Functions related to generic helpers functions
  */
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/bio.h>
 #include <linux/blkdev.h>
 #include <linux/scatterlist.h>

 #include "blk.h"

 static struct bio *next_bio(struct bio *bio, unsigned int nr_pages,
 		gfp_t gfp)
 {
 	struct bio *new = bio_alloc(gfp, nr_pages);

 	if (bio) {
 		bio_chain(bio, new);
 		submit_bio(bio);
 	}

 	return new;
 }

 int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
 		sector_t nr_sects, gfp_t gfp_mask, int flags,
 		struct bio **biop)
 {
 	struct request_queue *q = bdev_get_queue(bdev);
 	struct bio *bio = *biop;
 	unsigned int granularity;
 	unsigned int op;
 	int alignment;
 	sector_t bs_mask;

 	if (!q)
 		return -ENXIO;

 	if (flags & BLKDEV_DISCARD_SECURE) {
 		if (flags & BLKDEV_DISCARD_ZERO)
 			return -EOPNOTSUPP;
 		if (!blk_queue_secure_erase(q))
 			return -EOPNOTSUPP;
 		op = REQ_OP_SECURE_ERASE;
 	} else {
 		if (!blk_queue_discard(q))
 			return -EOPNOTSUPP;
 		if ((flags & BLKDEV_DISCARD_ZERO) &&
 		    !q->limits.discard_zeroes_data)
 			return -EOPNOTSUPP;
 		op = REQ_OP_DISCARD;
 	}

 	bs_mask = (bdev_logical_block_size(bdev) >> 9) - 1;
 	if ((sector | nr_sects) & bs_mask)
 		return -EINVAL;

 	/* Zero-sector (unknown) and one-sector granularities are the same.  */
 	granularity = max(q->limits.discard_granularity >> 9, 1U);
 	alignment = (bdev_discard_alignment(bdev) >> 9) % granularity;

 	while (nr_sects) {
 		unsigned int req_sects;
 		sector_t end_sect, tmp;

 		/* Make sure bi_size doesn't overflow */
 		req_sects = min_t(sector_t, nr_sects, UINT_MAX >> 9);

 		/**
 		 * If splitting a request, and the next starting sector would be
 		 * misaligned, stop the discard at the previous aligned sector.
 		 */
 		end_sect = sector + req_sects;
 		tmp = end_sect;
 		if (req_sects < nr_sects &&
 		    sector_div(tmp, granularity) != alignment) {
 			end_sect = end_sect - alignment;
 			sector_div(end_sect, granularity);
 			end_sect = end_sect * granularity + alignment;
 			req_sects = end_sect - sector;
 		}

 		bio = next_bio(bio, 0, gfp_mask);
 		bio->bi_iter.bi_sector = sector;
 		bio->bi_bdev = bdev;
 		bio_set_op_attrs(bio, op, 0);

 		bio->bi_iter.bi_size = req_sects << 9;
 		nr_sects -= req_sects;
 		sector = end_sect;

 		/*
 		 * We can loop for a long time in here, if someone does
 		 * full device discards (like mkfs). Be nice and allow
 		 * us to schedule out to avoid softlocking if preempt
 		 * is disabled.
 		 */
 		cond_resched();
 	}

 	*biop = bio;
 	return 0;
 }
 EXPORT_SYMBOL(__blkdev_issue_discard);

 /**
  * blkdev_issue_discard - queue a discard
  * @bdev:	blockdev to issue discard for
  * @sector:	start sector
  * @nr_sects:	number of sectors to discard
  * @gfp_mask:	memory allocation flags (for bio_alloc)
  * @flags:	BLKDEV_IFL_* flags to control behaviour
  *
  * Description:
  *    Issue a discard request for the sectors in question.
  */
 int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
 		sector_t nr_sects, gfp_t gfp_mask, unsigned long flags)
 {
 	struct bio *bio = NULL;
 	struct blk_plug plug;
 	int ret;

 	blk_start_plug(&plug);
 	ret = __blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask, flags,
 			&bio);
 	if (!ret && bio) {
 		ret = submit_bio_wait(bio);
 		if (ret == -EOPNOTSUPP && !(flags & BLKDEV_DISCARD_ZERO))
 			ret = 0;
 		bio_put(bio);
 	}
 	blk_finish_plug(&plug);

 	return ret;
 }
 EXPORT_SYMBOL(blkdev_issue_discard);

 /**
  * __blkdev_issue_write_same - generate number of bios with same page
  * @bdev:	target blockdev
  * @sector:	start sector
  * @nr_sects:	number of sectors to write
  * @gfp_mask:	memory allocation flags (for bio_alloc)
  * @page:	page containing data to write
  * @biop:	pointer to anchor bio
  *
  * Description:
  *  Generate and issue number of bios(REQ_OP_WRITE_SAME) with same page.
  */
 static int __blkdev_issue_write_same(struct block_device *bdev, sector_t sector,
 		sector_t nr_sects, gfp_t gfp_mask, struct page *page,
 		struct bio **biop)
 {
 	struct request_queue *q = bdev_get_queue(bdev);
 	unsigned int max_write_same_sectors;
 	struct bio *bio = *biop;
 	sector_t bs_mask;

 	if (!q)
 		return -ENXIO;

 	bs_mask = (bdev_logical_block_size(bdev) >> 9) - 1;
 	if ((sector | nr_sects) & bs_mask)
 		return -EINVAL;

 	if (!bdev_write_same(bdev))
 		return -EOPNOTSUPP;

 	/* Ensure that max_write_same_sectors doesn't overflow bi_size */
 	max_write_same_sectors = UINT_MAX >> 9;

 	while (nr_sects) {
 		bio = next_bio(bio, 1, gfp_mask);
 		bio->bi_iter.bi_sector = sector;
 		bio->bi_bdev = bdev;
 		bio->bi_vcnt = 1;
 		bio->bi_io_vec->bv_page = page;
 		bio->bi_io_vec->bv_offset = 0;
 		bio->bi_io_vec->bv_len = bdev_logical_block_size(bdev);
 		bio_set_op_attrs(bio, REQ_OP_WRITE_SAME, 0);

 		if (nr_sects > max_write_same_sectors) {
 			bio->bi_iter.bi_size = max_write_same_sectors << 9;
 			nr_sects -= max_write_same_sectors;
 			sector += max_write_same_sectors;
 		} else {
 			bio->bi_iter.bi_size = nr_sects << 9;
 			nr_sects = 0;
 		}
 		cond_resched();
 	}

 	*biop = bio;
 	return 0;
 }

 /**
  * blkdev_issue_write_same - queue a write same operation
  * @bdev:	target blockdev
  * @sector:	start sector
  * @nr_sects:	number of sectors to write
  * @gfp_mask:	memory allocation flags (for bio_alloc)
  * @page:	page containing data
  *
  * Description:
  *    Issue a write same request for the sectors in question.
  */
 int blkdev_issue_write_same(struct block_device *bdev, sector_t sector,
 				sector_t nr_sects, gfp_t gfp_mask,
 				struct page *page)
 {
 	struct bio *bio = NULL;
 	struct blk_plug plug;
 	int ret;

 	blk_start_plug(&plug);
 	ret = __blkdev_issue_write_same(bdev, sector, nr_sects, gfp_mask, page,
 			&bio);
 	if (ret == 0 && bio) {
 		ret = submit_bio_wait(bio);
 		bio_put(bio);
 	}
 	blk_finish_plug(&plug);
 	return ret;
 }
 EXPORT_SYMBOL(blkdev_issue_write_same);

 /**
  * __blkdev_issue_write_zeroes - generate number of bios with WRITE ZEROES
  * @bdev:	blockdev to issue
  * @sector:	start sector
  * @nr_sects:	number of sectors to write
  * @gfp_mask:	memory allocation flags (for bio_alloc)
  * @biop:	pointer to anchor bio
  *
  * Description:
  *  Generate and issue number of bios(REQ_OP_WRITE_ZEROES) with zerofiled pages.
  */
 static int __blkdev_issue_write_zeroes(struct block_device *bdev,
 		sector_t sector, sector_t nr_sects, gfp_t gfp_mask,
 		struct bio **biop)
 {
 	struct bio *bio = *biop;
 	unsigned int max_write_zeroes_sectors;
 	struct request_queue *q = bdev_get_queue(bdev);

 	if (!q)
 		return -ENXIO;

 	/* Ensure that max_write_zeroes_sectors doesn't overflow bi_size */
 	max_write_zeroes_sectors = bdev_write_zeroes_sectors(bdev);

 	if (max_write_zeroes_sectors == 0)
 		return -EOPNOTSUPP;

 	while (nr_sects) {
 		bio = next_bio(bio, 0, gfp_mask);
 		bio->bi_iter.bi_sector = sector;
 		bio->bi_bdev = bdev;
 		bio_set_op_attrs(bio, REQ_OP_WRITE_ZEROES, 0);

 		if (nr_sects > max_write_zeroes_sectors) {
 			bio->bi_iter.bi_size = max_write_zeroes_sectors << 9;
 			nr_sects -= max_write_zeroes_sectors;
 			sector += max_write_zeroes_sectors;
 		} else {
 			bio->bi_iter.bi_size = nr_sects << 9;
 			nr_sects = 0;
 		}
 		cond_resched();
 	}

 	*biop = bio;
 	return 0;
 }

 /**
  * __blkdev_issue_zeroout - generate number of zero filed write bios
  * @bdev:	blockdev to issue
  * @sector:	start sector
  * @nr_sects:	number of sectors to write
  * @gfp_mask:	memory allocation flags (for bio_alloc)
  * @biop:	pointer to anchor bio
  * @discard:	discard flag
  *
  * Description:
  *  Generate and issue number of bios with zerofiled pages.
  */
 int __blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
 		sector_t nr_sects, gfp_t gfp_mask, struct bio **biop,
 		bool discard)
 {
 	int ret;
 	int bi_size = 0;
 	struct bio *bio = *biop;
 	unsigned int sz;
 	sector_t bs_mask;

 	bs_mask = (bdev_logical_block_size(bdev) >> 9) - 1;
 	if ((sector | nr_sects) & bs_mask)
 		return -EINVAL;

 	ret = __blkdev_issue_write_zeroes(bdev, sector, nr_sects, gfp_mask,
 			biop);
 	if (ret == 0 || (ret && ret != -EOPNOTSUPP))
 		goto out;

 	ret = __blkdev_issue_write_same(bdev, sector, nr_sects, gfp_mask,
 			ZERO_PAGE(0), biop);
 	if (ret == 0 || (ret && ret != -EOPNOTSUPP))
 		goto out;

 	ret = 0;
 	while (nr_sects != 0) {
 		bio = next_bio(bio, min(nr_sects, (sector_t)BIO_MAX_PAGES),
 				gfp_mask);
 		bio->bi_iter.bi_sector = sector;
 		bio->bi_bdev   = bdev;
 		bio_set_op_attrs(bio, REQ_OP_WRITE, 0);

 		while (nr_sects != 0) {
 			sz = min((sector_t) PAGE_SIZE >> 9 , nr_sects);
 			bi_size = bio_add_page(bio, ZERO_PAGE(0), sz << 9, 0);
 			nr_sects -= bi_size >> 9;
 			sector += bi_size >> 9;
 			if (bi_size < (sz << 9))
 				break;
 		}
 		cond_resched();
 	}

 	*biop = bio;
 out:
 	return ret;
 }
 EXPORT_SYMBOL(__blkdev_issue_zeroout);

 /**
  * blkdev_issue_zeroout - zero-fill a block range
  * @bdev:	blockdev to write
  * @sector:	start sector
  * @nr_sects:	number of sectors to write
  * @gfp_mask:	memory allocation flags (for bio_alloc)
  * @discard:	whether to discard the block range
  *
  * Description:
  *  Zero-fill a block range.  If the discard flag is set and the block
  *  device guarantees that subsequent READ operations to the block range
  *  in question will return zeroes, the blocks will be discarded. Should
  *  the discard request fail, if the discard flag is not set, or if
  *  discard_zeroes_data is not supported, this function will resort to
  *  zeroing the blocks manually, thus provisioning (allocating,
  *  anchoring) them. If the block device supports WRITE ZEROES or WRITE SAME
  *  command(s), blkdev_issue_zeroout() will use it to optimize the process of
  *  clearing the block range. Otherwise the zeroing will be performed
  *  using regular WRITE calls.
  */
 int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
 			 sector_t nr_sects, gfp_t gfp_mask, bool discard)
 {
 	int ret;
 	struct bio *bio = NULL;
 	struct blk_plug plug;

 	if (discard) {
 		if (!blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask,
 				BLKDEV_DISCARD_ZERO))
 			return 0;
 	}

 	blk_start_plug(&plug);
 	ret = __blkdev_issue_zeroout(bdev, sector, nr_sects, gfp_mask,
 			&bio, discard);
 	if (ret == 0 && bio) {
 		ret = submit_bio_wait(bio);
 		bio_put(bio);
 	}
 	blk_finish_plug(&plug);

 	return ret;
 }
 EXPORT_SYMBOL(blkdev_issue_zeroout);
	/*
	* Functions related to generic helpers functions
	*/
	#include <linux/kernel.h>
	#include <linux/module.h>
	#include <linux/bio.h>
	#include <linux/blkdev.h>
	#include <linux/scatterlist.h>

	#include "blk.h"

	static struct bio next_bio(struct bio bio, unsigned int nr_pages,
	gfp_t gfp)
	{
	struct bio *new = bio_alloc(gfp, nr_pages);

	if (bio) {
	bio_chain(bio, new);
	submit_bio(bio);
	}

	return new;
	}

	int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
	sector_t nr_sects, gfp_t gfp_mask, int flags,
	struct bio **biop)
	{
	struct request_queue *q = bdev_get_queue(bdev);
	struct bio bio = biop;
	unsigned int granularity;
	unsigned int op;
	int alignment;
	sector_t bs_mask;

	if (!q)
	return -ENXIO;

	if (flags & BLKDEV_DISCARD_SECURE) {
	if (flags & BLKDEV_DISCARD_ZERO)
	return -EOPNOTSUPP;
	if (!blk_queue_secure_erase(q))
	return -EOPNOTSUPP;
	op = REQ_OP_SECURE_ERASE;
	} else {
	if (!blk_queue_discard(q))
	return -EOPNOTSUPP;
	if ((flags & BLKDEV_DISCARD_ZERO) &&
	!q->limits.discard_zeroes_data)
	return -EOPNOTSUPP;
	op = REQ_OP_DISCARD;
	}

	bs_mask = (bdev_logical_block_size(bdev) >> 9) - 1;
	if ((sector \| nr_sects) & bs_mask)
	return -EINVAL;

	/* Zero-sector (unknown) and one-sector granularities are the same. */
	granularity = max(q->limits.discard_granularity >> 9, 1U);
	alignment = (bdev_discard_alignment(bdev) >> 9) % granularity;

	while (nr_sects) {
	unsigned int req_sects;
	sector_t end_sect, tmp;

	/* Make sure bi_size doesn't overflow */
	req_sects = min_t(sector_t, nr_sects, UINT_MAX >> 9);

	/**
	* If splitting a request, and the next starting sector would be
	* misaligned, stop the discard at the previous aligned sector.
	*/
	end_sect = sector + req_sects;
	tmp = end_sect;
	if (req_sects < nr_sects &&
	sector_div(tmp, granularity) != alignment) {
	end_sect = end_sect - alignment;
	sector_div(end_sect, granularity);
	end_sect = end_sect * granularity + alignment;
	req_sects = end_sect - sector;
	}

	bio = next_bio(bio, 0, gfp_mask);
	bio->bi_iter.bi_sector = sector;
	bio->bi_bdev = bdev;
	bio_set_op_attrs(bio, op, 0);

	bio->bi_iter.bi_size = req_sects << 9;
	nr_sects -= req_sects;
	sector = end_sect;

	/*
	* We can loop for a long time in here, if someone does
	* full device discards (like mkfs). Be nice and allow
	* us to schedule out to avoid softlocking if preempt
	* is disabled.
	*/
	cond_resched();
	}

	*biop = bio;
	return 0;
	}
	EXPORT_SYMBOL(__blkdev_issue_discard);

	/**
	* blkdev_issue_discard - queue a discard
	* @bdev: blockdev to issue discard for
	* @sector: start sector
	* @nr_sects: number of sectors to discard
	* @gfp_mask: memory allocation flags (for bio_alloc)
	* @flags: BLKDEV_IFL_* flags to control behaviour
	*
	* Description:
	* Issue a discard request for the sectors in question.
	*/
	int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
	sector_t nr_sects, gfp_t gfp_mask, unsigned long flags)
	{
	struct bio *bio = NULL;
	struct blk_plug plug;
	int ret;

	blk_start_plug(&plug);
	ret = __blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask, flags,
	&bio);
	if (!ret && bio) {
	ret = submit_bio_wait(bio);
	if (ret == -EOPNOTSUPP && !(flags & BLKDEV_DISCARD_ZERO))
	ret = 0;
	bio_put(bio);
	}
	blk_finish_plug(&plug);

	return ret;
	}
	EXPORT_SYMBOL(blkdev_issue_discard);

	/**
	* __blkdev_issue_write_same - generate number of bios with same page
	* @bdev: target blockdev
	* @sector: start sector
	* @nr_sects: number of sectors to write
	* @gfp_mask: memory allocation flags (for bio_alloc)
	* @page: page containing data to write
	* @biop: pointer to anchor bio
	*
	* Description:
	* Generate and issue number of bios(REQ_OP_WRITE_SAME) with same page.
	*/
	static int __blkdev_issue_write_same(struct block_device *bdev, sector_t sector,
	sector_t nr_sects, gfp_t gfp_mask, struct page *page,
	struct bio **biop)
	{
	struct request_queue *q = bdev_get_queue(bdev);
	unsigned int max_write_same_sectors;
	struct bio bio = biop;
	sector_t bs_mask;

	if (!q)
	return -ENXIO;

	bs_mask = (bdev_logical_block_size(bdev) >> 9) - 1;
	if ((sector \| nr_sects) & bs_mask)
	return -EINVAL;

	if (!bdev_write_same(bdev))
	return -EOPNOTSUPP;

	/* Ensure that max_write_same_sectors doesn't overflow bi_size */
	max_write_same_sectors = UINT_MAX >> 9;

	while (nr_sects) {
	bio = next_bio(bio, 1, gfp_mask);
	bio->bi_iter.bi_sector = sector;
	bio->bi_bdev = bdev;
	bio->bi_vcnt = 1;
	bio->bi_io_vec->bv_page = page;
	bio->bi_io_vec->bv_offset = 0;
	bio->bi_io_vec->bv_len = bdev_logical_block_size(bdev);
	bio_set_op_attrs(bio, REQ_OP_WRITE_SAME, 0);

	if (nr_sects > max_write_same_sectors) {
	bio->bi_iter.bi_size = max_write_same_sectors << 9;
	nr_sects -= max_write_same_sectors;
	sector += max_write_same_sectors;
	} else {
	bio->bi_iter.bi_size = nr_sects << 9;
	nr_sects = 0;
	}
	cond_resched();
	}

	*biop = bio;
	return 0;
	}

	/**
	* blkdev_issue_write_same - queue a write same operation
	* @bdev: target blockdev
	* @sector: start sector
	* @nr_sects: number of sectors to write
	* @gfp_mask: memory allocation flags (for bio_alloc)
	* @page: page containing data
	*
	* Description:
	* Issue a write same request for the sectors in question.
	*/
	int blkdev_issue_write_same(struct block_device *bdev, sector_t sector,
	sector_t nr_sects, gfp_t gfp_mask,
	struct page *page)
	{
	struct bio *bio = NULL;
	struct blk_plug plug;
	int ret;

	blk_start_plug(&plug);
	ret = __blkdev_issue_write_same(bdev, sector, nr_sects, gfp_mask, page,
	&bio);
	if (ret == 0 && bio) {
	ret = submit_bio_wait(bio);
	bio_put(bio);
	}
	blk_finish_plug(&plug);
	return ret;
	}
	EXPORT_SYMBOL(blkdev_issue_write_same);

	/**
	* __blkdev_issue_write_zeroes - generate number of bios with WRITE ZEROES
	* @bdev: blockdev to issue
	* @sector: start sector
	* @nr_sects: number of sectors to write
	* @gfp_mask: memory allocation flags (for bio_alloc)
	* @biop: pointer to anchor bio
	*
	* Description:
	* Generate and issue number of bios(REQ_OP_WRITE_ZEROES) with zerofiled pages.
	*/
	static int __blkdev_issue_write_zeroes(struct block_device *bdev,
	sector_t sector, sector_t nr_sects, gfp_t gfp_mask,
	struct bio **biop)
	{
	struct bio bio = biop;
	unsigned int max_write_zeroes_sectors;
	struct request_queue *q = bdev_get_queue(bdev);

	if (!q)
	return -ENXIO;

	/* Ensure that max_write_zeroes_sectors doesn't overflow bi_size */
	max_write_zeroes_sectors = bdev_write_zeroes_sectors(bdev);

	if (max_write_zeroes_sectors == 0)
	return -EOPNOTSUPP;

	while (nr_sects) {
	bio = next_bio(bio, 0, gfp_mask);
	bio->bi_iter.bi_sector = sector;
	bio->bi_bdev = bdev;
	bio_set_op_attrs(bio, REQ_OP_WRITE_ZEROES, 0);

	if (nr_sects > max_write_zeroes_sectors) {
	bio->bi_iter.bi_size = max_write_zeroes_sectors << 9;
	nr_sects -= max_write_zeroes_sectors;
	sector += max_write_zeroes_sectors;
	} else {
	bio->bi_iter.bi_size = nr_sects << 9;
	nr_sects = 0;
	}
	cond_resched();
	}

	*biop = bio;
	return 0;
	}

	/**
	* __blkdev_issue_zeroout - generate number of zero filed write bios
	* @bdev: blockdev to issue
	* @sector: start sector
	* @nr_sects: number of sectors to write
	* @gfp_mask: memory allocation flags (for bio_alloc)
	* @biop: pointer to anchor bio
	* @discard: discard flag
	*
	* Description:
	* Generate and issue number of bios with zerofiled pages.
	*/
	int __blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
	sector_t nr_sects, gfp_t gfp_mask, struct bio **biop,
	bool discard)
	{
	int ret;
	int bi_size = 0;
	struct bio bio = biop;
	unsigned int sz;
	sector_t bs_mask;

	bs_mask = (bdev_logical_block_size(bdev) >> 9) - 1;
	if ((sector \| nr_sects) & bs_mask)
	return -EINVAL;

	ret = __blkdev_issue_write_zeroes(bdev, sector, nr_sects, gfp_mask,
	biop);
	if (ret == 0 \|\| (ret && ret != -EOPNOTSUPP))
	goto out;

	ret = __blkdev_issue_write_same(bdev, sector, nr_sects, gfp_mask,
	ZERO_PAGE(0), biop);
	if (ret == 0 \|\| (ret && ret != -EOPNOTSUPP))
	goto out;

	ret = 0;
	while (nr_sects != 0) {
	bio = next_bio(bio, min(nr_sects, (sector_t)BIO_MAX_PAGES),
	gfp_mask);
	bio->bi_iter.bi_sector = sector;
	bio->bi_bdev = bdev;
	bio_set_op_attrs(bio, REQ_OP_WRITE, 0);

	while (nr_sects != 0) {
	sz = min((sector_t) PAGE_SIZE >> 9 , nr_sects);
	bi_size = bio_add_page(bio, ZERO_PAGE(0), sz << 9, 0);
	nr_sects -= bi_size >> 9;
	sector += bi_size >> 9;
	if (bi_size < (sz << 9))
	break;
	}
	cond_resched();
	}

	*biop = bio;
	out:
	return ret;
	}
	EXPORT_SYMBOL(__blkdev_issue_zeroout);

	/**
	* blkdev_issue_zeroout - zero-fill a block range
	* @bdev: blockdev to write
	* @sector: start sector
	* @nr_sects: number of sectors to write
	* @gfp_mask: memory allocation flags (for bio_alloc)
	* @discard: whether to discard the block range
	*
	* Description:
	* Zero-fill a block range. If the discard flag is set and the block
	* device guarantees that subsequent READ operations to the block range
	* in question will return zeroes, the blocks will be discarded. Should
	* the discard request fail, if the discard flag is not set, or if
	* discard_zeroes_data is not supported, this function will resort to
	* zeroing the blocks manually, thus provisioning (allocating,
	* anchoring) them. If the block device supports WRITE ZEROES or WRITE SAME
	* command(s), blkdev_issue_zeroout() will use it to optimize the process of
	* clearing the block range. Otherwise the zeroing will be performed
	* using regular WRITE calls.
	*/
	int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
	sector_t nr_sects, gfp_t gfp_mask, bool discard)
	{
	int ret;
	struct bio *bio = NULL;
	struct blk_plug plug;

	if (discard) {
	if (!blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask,
	BLKDEV_DISCARD_ZERO))
	return 0;
	}

	blk_start_plug(&plug);
	ret = __blkdev_issue_zeroout(bdev, sector, nr_sects, gfp_mask,
	&bio, discard);
	if (ret == 0 && bio) {
	ret = submit_bio_wait(bio);
	bio_put(bio);
	}
	blk_finish_plug(&plug);

	return ret;
	}
	EXPORT_SYMBOL(blkdev_issue_zeroout);