/*
   * 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"

  struct bio_batch {
  	atomic_t		done;
  	unsigned long		flags;
  	struct completion	*wait;
  };
  
  static void bio_batch_end_io(struct bio *bio, int err)

  {

  	struct bio_batch *bb = bio->bi_private;

  	if (err && (err != -EOPNOTSUPP))

  		clear_bit(BIO_UPTODATE, &bb->flags);

  	if (atomic_dec_and_test(&bb->done))
  		complete(bb->wait);

  	bio_put(bio);
  }
  
  /**
   * 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)
  {
  	DECLARE_COMPLETION_ONSTACK(wait);
  	struct request_queue *q = bdev_get_queue(bdev);

  	int type = REQ_WRITE | REQ_DISCARD;

  	unsigned int max_discard_sectors, granularity;
  	int alignment;

  	struct bio_batch bb;

  	struct bio *bio;

  	int ret = 0;

  	struct blk_plug plug;

  
  	if (!q)
  		return -ENXIO;
  
  	if (!blk_queue_discard(q))
  		return -EOPNOTSUPP;

  	/* 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;

  	/*
  	 * Ensure that max_discard_sectors is of the proper

  	 * granularity, so that requests stay aligned after a split.

  	 */
  	max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);

  	max_discard_sectors -= max_discard_sectors % granularity;

  	if (unlikely(!max_discard_sectors)) {

  		/* Avoid infinite loop below. Being cautious never hurts. */
  		return -EOPNOTSUPP;

  	}

  	if (flags & BLKDEV_DISCARD_SECURE) {

  		if (!blk_queue_secdiscard(q))
  			return -EOPNOTSUPP;

  		type |= REQ_SECURE;

  	}

  	atomic_set(&bb.done, 1);
  	bb.flags = 1 << BIO_UPTODATE;
  	bb.wait = &wait;

  	blk_start_plug(&plug);

  	while (nr_sects) {

  		unsigned int req_sects;

  		sector_t end_sect, tmp;

  		bio = bio_alloc(gfp_mask, 1);

  		if (!bio) {
  			ret = -ENOMEM;
  			break;
  		}

  		req_sects = min_t(sector_t, nr_sects, max_discard_sectors);
  
  		/*
  		 * 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->bi_iter.bi_sector = sector;

  		bio->bi_end_io = bio_batch_end_io;

  		bio->bi_bdev = bdev;

  		bio->bi_private = &bb;

  		bio->bi_iter.bi_size = req_sects << 9;

  		nr_sects -= req_sects;
  		sector = end_sect;

  		atomic_inc(&bb.done);

  		submit_bio(type, bio);

  
  		/*
  		 * 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();

  	}

  	blk_finish_plug(&plug);

  	/* Wait for bios in-flight */
  	if (!atomic_dec_and_test(&bb.done))

  		wait_for_completion_io(&wait);

  	if (!test_bit(BIO_UPTODATE, &bb.flags))

  		ret = -EIO;

  	return ret;

  }
  EXPORT_SYMBOL(blkdev_issue_discard);

  /**

   * 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 to write
   *
   * 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)
  {
  	DECLARE_COMPLETION_ONSTACK(wait);
  	struct request_queue *q = bdev_get_queue(bdev);
  	unsigned int max_write_same_sectors;
  	struct bio_batch bb;
  	struct bio *bio;
  	int ret = 0;
  
  	if (!q)
  		return -ENXIO;
  
  	max_write_same_sectors = q->limits.max_write_same_sectors;
  
  	if (max_write_same_sectors == 0)
  		return -EOPNOTSUPP;
  
  	atomic_set(&bb.done, 1);
  	bb.flags = 1 << BIO_UPTODATE;
  	bb.wait = &wait;
  
  	while (nr_sects) {
  		bio = bio_alloc(gfp_mask, 1);
  		if (!bio) {
  			ret = -ENOMEM;
  			break;
  		}

  		bio->bi_iter.bi_sector = sector;

  		bio->bi_end_io = bio_batch_end_io;
  		bio->bi_bdev = bdev;
  		bio->bi_private = &bb;
  		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);
  
  		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;
  		}
  
  		atomic_inc(&bb.done);
  		submit_bio(REQ_WRITE | REQ_WRITE_SAME, bio);
  	}
  
  	/* Wait for bios in-flight */
  	if (!atomic_dec_and_test(&bb.done))

  		wait_for_completion_io(&wait);

  
  	if (!test_bit(BIO_UPTODATE, &bb.flags))
  		ret = -ENOTSUPP;
  
  	return ret;
  }
  EXPORT_SYMBOL(blkdev_issue_write_same);
  
  /**

   * 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)

   *
   * Description:
   *  Generate and issue number of bios with zerofiled pages.

   */

  static int __blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
  				  sector_t nr_sects, gfp_t gfp_mask)

  {

  	int ret;

  	struct bio *bio;
  	struct bio_batch bb;

  	unsigned int sz;

  	DECLARE_COMPLETION_ONSTACK(wait);

  	atomic_set(&bb.done, 1);

  	bb.flags = 1 << BIO_UPTODATE;
  	bb.wait = &wait;

  	ret = 0;

  	while (nr_sects != 0) {
  		bio = bio_alloc(gfp_mask,
  				min(nr_sects, (sector_t)BIO_MAX_PAGES));

  		if (!bio) {
  			ret = -ENOMEM;

  			break;

  		}

  		bio->bi_iter.bi_sector = sector;

  		bio->bi_bdev   = bdev;
  		bio->bi_end_io = bio_batch_end_io;

  		bio->bi_private = &bb;

  		while (nr_sects != 0) {
  			sz = min((sector_t) PAGE_SIZE >> 9 , nr_sects);

  			ret = bio_add_page(bio, ZERO_PAGE(0), sz << 9, 0);
  			nr_sects -= ret >> 9;
  			sector += ret >> 9;
  			if (ret < (sz << 9))
  				break;
  		}

  		ret = 0;

  		atomic_inc(&bb.done);

  		submit_bio(WRITE, bio);
  	}

  	/* Wait for bios in-flight */

  	if (!atomic_dec_and_test(&bb.done))

  		wait_for_completion_io(&wait);

  
  	if (!test_bit(BIO_UPTODATE, &bb.flags))
  		/* One of bios in the batch was completed with error.*/
  		ret = -EIO;

  	return ret;
  }

  
  /**
   * 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)
   *
   * 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)
  {
  	if (bdev_write_same(bdev)) {
  		unsigned char bdn[BDEVNAME_SIZE];
  
  		if (!blkdev_issue_write_same(bdev, sector, nr_sects, gfp_mask,
  					     ZERO_PAGE(0)))
  			return 0;
  
  		bdevname(bdev, bdn);
  		pr_err("%s: WRITE SAME failed. Manually zeroing.
  ", bdn);
  	}
  
  	return __blkdev_issue_zeroout(bdev, sector, nr_sects, gfp_mask);
  }

  EXPORT_SYMBOL(blkdev_issue_zeroout);