/*

   * Copyright (C) 2001 Jens Axboe <axboe@kernel.dk>

   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License version 2 as
   * published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public Licens
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-
   *
   */
  #include <linux/mm.h>
  #include <linux/swap.h>
  #include <linux/bio.h>
  #include <linux/blkdev.h>
  #include <linux/slab.h>
  #include <linux/init.h>
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/mempool.h>
  #include <linux/workqueue.h>

  #include <linux/blktrace_api.h>

  #include <scsi/sg.h>		/* for struct sg_iovec */

  #include <trace/events/block.h>

  /*
   * Test patch to inline a certain number of bi_io_vec's inside the bio
   * itself, to shrink a bio data allocation from two mempool calls to one
   */
  #define BIO_INLINE_VECS		4

  static mempool_t *bio_split_pool __read_mostly;

  /*
   * if you change this list, also change bvec_alloc or things will
   * break badly! cannot be bigger than what you can fit into an
   * unsigned short
   */

  #define BV(x) { .nr_vecs = x, .name = "biovec-"__stringify(x) }

  struct biovec_slab bvec_slabs[BIOVEC_NR_POOLS] __read_mostly = {

  	BV(1), BV(4), BV(16), BV(64), BV(128), BV(BIO_MAX_PAGES),
  };
  #undef BV
  
  /*

   * fs_bio_set is the bio_set containing bio and iovec memory pools used by
   * IO code that does not need private memory pools.
   */

  struct bio_set *fs_bio_set;

  /*
   * Our slab pool management
   */
  struct bio_slab {
  	struct kmem_cache *slab;
  	unsigned int slab_ref;
  	unsigned int slab_size;
  	char name[8];
  };
  static DEFINE_MUTEX(bio_slab_lock);
  static struct bio_slab *bio_slabs;
  static unsigned int bio_slab_nr, bio_slab_max;
  
  static struct kmem_cache *bio_find_or_create_slab(unsigned int extra_size)
  {
  	unsigned int sz = sizeof(struct bio) + extra_size;
  	struct kmem_cache *slab = NULL;
  	struct bio_slab *bslab;
  	unsigned int i, entry = -1;
  
  	mutex_lock(&bio_slab_lock);
  
  	i = 0;
  	while (i < bio_slab_nr) {
  		struct bio_slab *bslab = &bio_slabs[i];
  
  		if (!bslab->slab && entry == -1)
  			entry = i;
  		else if (bslab->slab_size == sz) {
  			slab = bslab->slab;
  			bslab->slab_ref++;
  			break;
  		}
  		i++;
  	}
  
  	if (slab)
  		goto out_unlock;
  
  	if (bio_slab_nr == bio_slab_max && entry == -1) {
  		bio_slab_max <<= 1;
  		bio_slabs = krealloc(bio_slabs,
  				     bio_slab_max * sizeof(struct bio_slab),
  				     GFP_KERNEL);
  		if (!bio_slabs)
  			goto out_unlock;
  	}
  	if (entry == -1)
  		entry = bio_slab_nr++;
  
  	bslab = &bio_slabs[entry];
  
  	snprintf(bslab->name, sizeof(bslab->name), "bio-%d", entry);
  	slab = kmem_cache_create(bslab->name, sz, 0, SLAB_HWCACHE_ALIGN, NULL);
  	if (!slab)
  		goto out_unlock;
  
  	printk("bio: create slab <%s> at %d
  ", bslab->name, entry);
  	bslab->slab = slab;
  	bslab->slab_ref = 1;
  	bslab->slab_size = sz;
  out_unlock:
  	mutex_unlock(&bio_slab_lock);
  	return slab;
  }
  
  static void bio_put_slab(struct bio_set *bs)
  {
  	struct bio_slab *bslab = NULL;
  	unsigned int i;
  
  	mutex_lock(&bio_slab_lock);
  
  	for (i = 0; i < bio_slab_nr; i++) {
  		if (bs->bio_slab == bio_slabs[i].slab) {
  			bslab = &bio_slabs[i];
  			break;
  		}
  	}
  
  	if (WARN(!bslab, KERN_ERR "bio: unable to find slab!
  "))
  		goto out;
  
  	WARN_ON(!bslab->slab_ref);
  
  	if (--bslab->slab_ref)
  		goto out;
  
  	kmem_cache_destroy(bslab->slab);
  	bslab->slab = NULL;
  
  out:
  	mutex_unlock(&bio_slab_lock);
  }

  unsigned int bvec_nr_vecs(unsigned short idx)
  {
  	return bvec_slabs[idx].nr_vecs;
  }

  void bvec_free_bs(struct bio_set *bs, struct bio_vec *bv, unsigned int idx)
  {
  	BIO_BUG_ON(idx >= BIOVEC_NR_POOLS);
  
  	if (idx == BIOVEC_MAX_IDX)
  		mempool_free(bv, bs->bvec_pool);
  	else {
  		struct biovec_slab *bvs = bvec_slabs + idx;
  
  		kmem_cache_free(bvs->slab, bv);
  	}
  }

  struct bio_vec *bvec_alloc_bs(gfp_t gfp_mask, int nr, unsigned long *idx,
  			      struct bio_set *bs)

  {
  	struct bio_vec *bvl;

  
  	/*

  	 * see comment near bvec_array define!
  	 */
  	switch (nr) {
  	case 1:
  		*idx = 0;
  		break;
  	case 2 ... 4:
  		*idx = 1;
  		break;
  	case 5 ... 16:
  		*idx = 2;
  		break;
  	case 17 ... 64:
  		*idx = 3;
  		break;
  	case 65 ... 128:
  		*idx = 4;
  		break;
  	case 129 ... BIO_MAX_PAGES:
  		*idx = 5;
  		break;
  	default:
  		return NULL;
  	}
  
  	/*
  	 * idx now points to the pool we want to allocate from. only the
  	 * 1-vec entry pool is mempool backed.
  	 */
  	if (*idx == BIOVEC_MAX_IDX) {
  fallback:
  		bvl = mempool_alloc(bs->bvec_pool, gfp_mask);
  	} else {
  		struct biovec_slab *bvs = bvec_slabs + *idx;
  		gfp_t __gfp_mask = gfp_mask & ~(__GFP_WAIT | __GFP_IO);

  		/*

  		 * Make this allocation restricted and don't dump info on
  		 * allocation failures, since we'll fallback to the mempool
  		 * in case of failure.

  		 */

  		__gfp_mask |= __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN;

  		/*

  		 * Try a slab allocation. If this fails and __GFP_WAIT
  		 * is set, retry with the 1-entry mempool

  		 */

  		bvl = kmem_cache_alloc(bvs->slab, __gfp_mask);
  		if (unlikely(!bvl && (gfp_mask & __GFP_WAIT))) {
  			*idx = BIOVEC_MAX_IDX;
  			goto fallback;
  		}
  	}

  	return bvl;
  }

  void bio_free(struct bio *bio, struct bio_set *bs)

  {

  	void *p;

  	if (bio_has_allocated_vec(bio))

  		bvec_free_bs(bs, bio->bi_io_vec, BIO_POOL_IDX(bio));

  	if (bio_integrity(bio))

  		bio_integrity_free(bio);

  	/*
  	 * If we have front padding, adjust the bio pointer before freeing
  	 */
  	p = bio;
  	if (bs->front_pad)
  		p -= bs->front_pad;
  
  	mempool_free(p, bs->bio_pool);

  }

  void bio_init(struct bio *bio)

  {

  	memset(bio, 0, sizeof(*bio));

  	bio->bi_flags = 1 << BIO_UPTODATE;

  	bio->bi_comp_cpu = -1;

  	atomic_set(&bio->bi_cnt, 1);

  }
  
  /**
   * bio_alloc_bioset - allocate a bio for I/O
   * @gfp_mask:   the GFP_ mask given to the slab allocator
   * @nr_iovecs:	number of iovecs to pre-allocate

   * @bs:		the bio_set to allocate from. If %NULL, just use kmalloc

   *
   * Description:

   *   bio_alloc_bioset will first try its own mempool to satisfy the allocation.

   *   If %__GFP_WAIT is set then we will block on the internal pool waiting

   *   for a &struct bio to become free. If a %NULL @bs is passed in, we will
   *   fall back to just using @kmalloc to allocate the required memory.

   *

   *   Note that the caller must set ->bi_destructor on succesful return
   *   of a bio, to do the appropriate freeing of the bio once the reference
   *   count drops to zero.

   **/

  struct bio *bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set *bs)

  {

  	unsigned long idx = BIO_POOL_NONE;

  	struct bio_vec *bvl = NULL;

  	struct bio *bio;
  	void *p;
  
  	p = mempool_alloc(bs->bio_pool, gfp_mask);
  	if (unlikely(!p))
  		return NULL;
  	bio = p + bs->front_pad;

  	bio_init(bio);
  
  	if (unlikely(!nr_iovecs))
  		goto out_set;
  
  	if (nr_iovecs <= BIO_INLINE_VECS) {
  		bvl = bio->bi_inline_vecs;
  		nr_iovecs = BIO_INLINE_VECS;
  	} else {
  		bvl = bvec_alloc_bs(gfp_mask, nr_iovecs, &idx, bs);
  		if (unlikely(!bvl))
  			goto err_free;
  
  		nr_iovecs = bvec_nr_vecs(idx);

  	}

  out_set:

  	bio->bi_flags |= idx << BIO_POOL_OFFSET;
  	bio->bi_max_vecs = nr_iovecs;

  	bio->bi_io_vec = bvl;

  	return bio;

  
  err_free:

  	mempool_free(p, bs->bio_pool);

  	return NULL;

  }

  static void bio_fs_destructor(struct bio *bio)
  {
  	bio_free(bio, fs_bio_set);
  }
  
  /**
   *	bio_alloc - allocate a new bio, memory pool backed
   *	@gfp_mask: allocation mask to use
   *	@nr_iovecs: number of iovecs
   *
   *	Allocate a new bio with @nr_iovecs bvecs.  If @gfp_mask
   *	contains __GFP_WAIT, the allocation is guaranteed to succeed.
   *
   *	RETURNS:
   *	Pointer to new bio on success, NULL on failure.
   */
  struct bio *bio_alloc(gfp_t gfp_mask, int nr_iovecs)
  {
  	struct bio *bio = bio_alloc_bioset(gfp_mask, nr_iovecs, fs_bio_set);
  
  	if (bio)
  		bio->bi_destructor = bio_fs_destructor;
  
  	return bio;
  }
  
  static void bio_kmalloc_destructor(struct bio *bio)
  {
  	if (bio_integrity(bio))
  		bio_integrity_free(bio);
  	kfree(bio);
  }

  /**
   * bio_alloc - allocate a bio for I/O
   * @gfp_mask:   the GFP_ mask given to the slab allocator
   * @nr_iovecs:	number of iovecs to pre-allocate
   *
   * Description:
   *   bio_alloc will allocate a bio and associated bio_vec array that can hold
   *   at least @nr_iovecs entries. Allocations will be done from the
   *   fs_bio_set. Also see @bio_alloc_bioset.
   *
   *   If %__GFP_WAIT is set, then bio_alloc will always be able to allocate
   *   a bio. This is due to the mempool guarantees. To make this work, callers
   *   must never allocate more than 1 bio at the time from this pool. Callers
   *   that need to allocate more than 1 bio must always submit the previously
   *   allocate bio for IO before attempting to allocate a new one. Failure to
   *   do so can cause livelocks under memory pressure.
   *
   **/

  struct bio *bio_kmalloc(gfp_t gfp_mask, int nr_iovecs)
  {

  	struct bio *bio;

  	bio = kmalloc(sizeof(struct bio) + nr_iovecs * sizeof(struct bio_vec),
  		      gfp_mask);
  	if (unlikely(!bio))
  		return NULL;
  
  	bio_init(bio);
  	bio->bi_flags |= BIO_POOL_NONE << BIO_POOL_OFFSET;
  	bio->bi_max_vecs = nr_iovecs;
  	bio->bi_io_vec = bio->bi_inline_vecs;
  	bio->bi_destructor = bio_kmalloc_destructor;

  
  	return bio;
  }

  void zero_fill_bio(struct bio *bio)
  {
  	unsigned long flags;
  	struct bio_vec *bv;
  	int i;
  
  	bio_for_each_segment(bv, bio, i) {
  		char *data = bvec_kmap_irq(bv, &flags);
  		memset(data, 0, bv->bv_len);
  		flush_dcache_page(bv->bv_page);
  		bvec_kunmap_irq(data, &flags);
  	}
  }
  EXPORT_SYMBOL(zero_fill_bio);
  
  /**
   * bio_put - release a reference to a bio
   * @bio:   bio to release reference to
   *
   * Description:
   *   Put a reference to a &struct bio, either one you have gotten with
   *   bio_alloc or bio_get. The last put of a bio will free it.
   **/
  void bio_put(struct bio *bio)
  {
  	BIO_BUG_ON(!atomic_read(&bio->bi_cnt));
  
  	/*
  	 * last put frees it
  	 */
  	if (atomic_dec_and_test(&bio->bi_cnt)) {
  		bio->bi_next = NULL;
  		bio->bi_destructor(bio);
  	}
  }

  inline int bio_phys_segments(struct request_queue *q, struct bio *bio)

  {
  	if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
  		blk_recount_segments(q, bio);
  
  	return bio->bi_phys_segments;
  }

  /**
   * 	__bio_clone	-	clone a bio
   * 	@bio: destination bio
   * 	@bio_src: bio to clone
   *
   *	Clone a &bio. Caller will own the returned bio, but not
   *	the actual data it points to. Reference count of returned
   * 	bio will be one.
   */

  void __bio_clone(struct bio *bio, struct bio *bio_src)

  {

  	memcpy(bio->bi_io_vec, bio_src->bi_io_vec,
  		bio_src->bi_max_vecs * sizeof(struct bio_vec));

  	/*
  	 * most users will be overriding ->bi_bdev with a new target,
  	 * so we don't set nor calculate new physical/hw segment counts here
  	 */

  	bio->bi_sector = bio_src->bi_sector;
  	bio->bi_bdev = bio_src->bi_bdev;
  	bio->bi_flags |= 1 << BIO_CLONED;
  	bio->bi_rw = bio_src->bi_rw;

  	bio->bi_vcnt = bio_src->bi_vcnt;
  	bio->bi_size = bio_src->bi_size;

  	bio->bi_idx = bio_src->bi_idx;

  }
  
  /**
   *	bio_clone	-	clone a bio
   *	@bio: bio to clone
   *	@gfp_mask: allocation priority
   *
   * 	Like __bio_clone, only also allocates the returned bio
   */

  struct bio *bio_clone(struct bio *bio, gfp_t gfp_mask)

  {
  	struct bio *b = bio_alloc_bioset(gfp_mask, bio->bi_max_vecs, fs_bio_set);

  	if (!b)
  		return NULL;
  
  	b->bi_destructor = bio_fs_destructor;
  	__bio_clone(b, bio);
  
  	if (bio_integrity(bio)) {
  		int ret;

  		ret = bio_integrity_clone(b, bio, gfp_mask);

  		if (ret < 0) {
  			bio_put(b);

  			return NULL;

  		}

  	}

  
  	return b;
  }
  
  /**
   *	bio_get_nr_vecs		- return approx number of vecs
   *	@bdev:  I/O target
   *
   *	Return the approximate number of pages we can send to this target.
   *	There's no guarantee that you will be able to fit this number of pages
   *	into a bio, it does not account for dynamic restrictions that vary
   *	on offset.
   */
  int bio_get_nr_vecs(struct block_device *bdev)
  {

  	struct request_queue *q = bdev_get_queue(bdev);

  	int nr_pages;

  	nr_pages = ((queue_max_sectors(q) << 9) + PAGE_SIZE - 1) >> PAGE_SHIFT;
  	if (nr_pages > queue_max_phys_segments(q))
  		nr_pages = queue_max_phys_segments(q);
  	if (nr_pages > queue_max_hw_segments(q))
  		nr_pages = queue_max_hw_segments(q);

  
  	return nr_pages;
  }

  static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page

  			  *page, unsigned int len, unsigned int offset,
  			  unsigned short max_sectors)

  {
  	int retried_segments = 0;
  	struct bio_vec *bvec;
  
  	/*
  	 * cloned bio must not modify vec list
  	 */
  	if (unlikely(bio_flagged(bio, BIO_CLONED)))
  		return 0;

  	if (((bio->bi_size + len) >> 9) > max_sectors)

  		return 0;

  	/*
  	 * For filesystems with a blocksize smaller than the pagesize
  	 * we will often be called with the same page as last time and
  	 * a consecutive offset.  Optimize this special case.
  	 */
  	if (bio->bi_vcnt > 0) {
  		struct bio_vec *prev = &bio->bi_io_vec[bio->bi_vcnt - 1];
  
  		if (page == prev->bv_page &&
  		    offset == prev->bv_offset + prev->bv_len) {
  			prev->bv_len += len;

  
  			if (q->merge_bvec_fn) {
  				struct bvec_merge_data bvm = {
  					.bi_bdev = bio->bi_bdev,
  					.bi_sector = bio->bi_sector,
  					.bi_size = bio->bi_size,
  					.bi_rw = bio->bi_rw,
  				};
  
  				if (q->merge_bvec_fn(q, &bvm, prev) < len) {
  					prev->bv_len -= len;
  					return 0;
  				}

  			}
  
  			goto done;
  		}
  	}
  
  	if (bio->bi_vcnt >= bio->bi_max_vecs)

  		return 0;
  
  	/*
  	 * we might lose a segment or two here, but rather that than
  	 * make this too complex.
  	 */

  	while (bio->bi_phys_segments >= queue_max_phys_segments(q)
  	       || bio->bi_phys_segments >= queue_max_hw_segments(q)) {

  
  		if (retried_segments)
  			return 0;
  
  		retried_segments = 1;
  		blk_recount_segments(q, bio);
  	}
  
  	/*
  	 * setup the new entry, we might clear it again later if we
  	 * cannot add the page
  	 */
  	bvec = &bio->bi_io_vec[bio->bi_vcnt];
  	bvec->bv_page = page;
  	bvec->bv_len = len;
  	bvec->bv_offset = offset;
  
  	/*
  	 * if queue has other restrictions (eg varying max sector size
  	 * depending on offset), it can specify a merge_bvec_fn in the
  	 * queue to get further control
  	 */
  	if (q->merge_bvec_fn) {

  		struct bvec_merge_data bvm = {
  			.bi_bdev = bio->bi_bdev,
  			.bi_sector = bio->bi_sector,
  			.bi_size = bio->bi_size,
  			.bi_rw = bio->bi_rw,
  		};

  		/*
  		 * merge_bvec_fn() returns number of bytes it can accept
  		 * at this offset
  		 */

  		if (q->merge_bvec_fn(q, &bvm, bvec) < len) {

  			bvec->bv_page = NULL;
  			bvec->bv_len = 0;
  			bvec->bv_offset = 0;
  			return 0;
  		}
  	}
  
  	/* If we may be able to merge these biovecs, force a recount */

  	if (bio->bi_vcnt && (BIOVEC_PHYS_MERGEABLE(bvec-1, bvec)))

  		bio->bi_flags &= ~(1 << BIO_SEG_VALID);
  
  	bio->bi_vcnt++;
  	bio->bi_phys_segments++;

   done:

  	bio->bi_size += len;
  	return len;
  }
  
  /**

   *	bio_add_pc_page	-	attempt to add page to bio

   *	@q: the target queue

   *	@bio: destination bio
   *	@page: page to add
   *	@len: vec entry length
   *	@offset: vec entry offset
   *
   *	Attempt to add a page to the bio_vec maplist. This can fail for a
   *	number of reasons, such as the bio being full or target block
   *	device limitations. The target block device must allow bio's
   *      smaller than PAGE_SIZE, so it is always possible to add a single
   *      page to an empty bio. This should only be used by REQ_PC bios.
   */

  int bio_add_pc_page(struct request_queue *q, struct bio *bio, struct page *page,

  		    unsigned int len, unsigned int offset)
  {

  	return __bio_add_page(q, bio, page, len, offset,
  			      queue_max_hw_sectors(q));

  }
  
  /**

   *	bio_add_page	-	attempt to add page to bio
   *	@bio: destination bio
   *	@page: page to add
   *	@len: vec entry length
   *	@offset: vec entry offset
   *
   *	Attempt to add a page to the bio_vec maplist. This can fail for a
   *	number of reasons, such as the bio being full or target block
   *	device limitations. The target block device must allow bio's
   *      smaller than PAGE_SIZE, so it is always possible to add a single
   *      page to an empty bio.
   */
  int bio_add_page(struct bio *bio, struct page *page, unsigned int len,
  		 unsigned int offset)
  {

  	struct request_queue *q = bdev_get_queue(bio->bi_bdev);

  	return __bio_add_page(q, bio, page, len, offset, queue_max_sectors(q));

  }
  
  struct bio_map_data {
  	struct bio_vec *iovecs;

  	struct sg_iovec *sgvecs;

  	int nr_sgvecs;
  	int is_our_pages;

  };

  static void bio_set_map_data(struct bio_map_data *bmd, struct bio *bio,

  			     struct sg_iovec *iov, int iov_count,
  			     int is_our_pages)

  {
  	memcpy(bmd->iovecs, bio->bi_io_vec, sizeof(struct bio_vec) * bio->bi_vcnt);

  	memcpy(bmd->sgvecs, iov, sizeof(struct sg_iovec) * iov_count);
  	bmd->nr_sgvecs = iov_count;

  	bmd->is_our_pages = is_our_pages;

  	bio->bi_private = bmd;
  }
  
  static void bio_free_map_data(struct bio_map_data *bmd)
  {
  	kfree(bmd->iovecs);

  	kfree(bmd->sgvecs);

  	kfree(bmd);
  }

  static struct bio_map_data *bio_alloc_map_data(int nr_segs, int iov_count,
  					       gfp_t gfp_mask)

  {

  	struct bio_map_data *bmd = kmalloc(sizeof(*bmd), gfp_mask);

  
  	if (!bmd)
  		return NULL;

  	bmd->iovecs = kmalloc(sizeof(struct bio_vec) * nr_segs, gfp_mask);

  	if (!bmd->iovecs) {
  		kfree(bmd);
  		return NULL;
  	}

  	bmd->sgvecs = kmalloc(sizeof(struct sg_iovec) * iov_count, gfp_mask);

  	if (bmd->sgvecs)

  		return bmd;

  	kfree(bmd->iovecs);

  	kfree(bmd);
  	return NULL;
  }

  static int __bio_copy_iov(struct bio *bio, struct bio_vec *iovecs,

  			  struct sg_iovec *iov, int iov_count, int uncopy,
  			  int do_free_page)

  {
  	int ret = 0, i;
  	struct bio_vec *bvec;
  	int iov_idx = 0;
  	unsigned int iov_off = 0;
  	int read = bio_data_dir(bio) == READ;
  
  	__bio_for_each_segment(bvec, bio, i, 0) {
  		char *bv_addr = page_address(bvec->bv_page);

  		unsigned int bv_len = iovecs[i].bv_len;

  
  		while (bv_len && iov_idx < iov_count) {
  			unsigned int bytes;

  			char __user *iov_addr;

  
  			bytes = min_t(unsigned int,
  				      iov[iov_idx].iov_len - iov_off, bv_len);
  			iov_addr = iov[iov_idx].iov_base + iov_off;
  
  			if (!ret) {
  				if (!read && !uncopy)
  					ret = copy_from_user(bv_addr, iov_addr,
  							     bytes);
  				if (read && uncopy)
  					ret = copy_to_user(iov_addr, bv_addr,
  							   bytes);
  
  				if (ret)
  					ret = -EFAULT;
  			}
  
  			bv_len -= bytes;
  			bv_addr += bytes;
  			iov_addr += bytes;
  			iov_off += bytes;
  
  			if (iov[iov_idx].iov_len == iov_off) {
  				iov_idx++;
  				iov_off = 0;
  			}
  		}

  		if (do_free_page)

  			__free_page(bvec->bv_page);
  	}
  
  	return ret;
  }

  /**
   *	bio_uncopy_user	-	finish previously mapped bio
   *	@bio: bio being terminated
   *
   *	Free pages allocated from bio_copy_user() and write back data
   *	to user space in case of a read.
   */
  int bio_uncopy_user(struct bio *bio)
  {
  	struct bio_map_data *bmd = bio->bi_private;

  	int ret = 0;

  	if (!bio_flagged(bio, BIO_NULL_MAPPED))
  		ret = __bio_copy_iov(bio, bmd->iovecs, bmd->sgvecs,
  				     bmd->nr_sgvecs, 1, bmd->is_our_pages);

  	bio_free_map_data(bmd);
  	bio_put(bio);
  	return ret;
  }
  
  /**

   *	bio_copy_user_iov	-	copy user data to bio

   *	@q: destination block queue

   *	@map_data: pointer to the rq_map_data holding pages (if necessary)

   *	@iov:	the iovec.
   *	@iov_count: number of elements in the iovec

   *	@write_to_vm: bool indicating writing to pages or not

   *	@gfp_mask: memory allocation flags

   *
   *	Prepares and returns a bio for indirect user io, bouncing data
   *	to/from kernel pages as necessary. Must be paired with
   *	call bio_uncopy_user() on io completion.
   */

  struct bio *bio_copy_user_iov(struct request_queue *q,
  			      struct rq_map_data *map_data,
  			      struct sg_iovec *iov, int iov_count,
  			      int write_to_vm, gfp_t gfp_mask)

  {

  	struct bio_map_data *bmd;
  	struct bio_vec *bvec;
  	struct page *page;
  	struct bio *bio;
  	int i, ret;

  	int nr_pages = 0;
  	unsigned int len = 0;

  	unsigned int offset = map_data ? map_data->offset & ~PAGE_MASK : 0;

  	for (i = 0; i < iov_count; i++) {
  		unsigned long uaddr;
  		unsigned long end;
  		unsigned long start;
  
  		uaddr = (unsigned long)iov[i].iov_base;
  		end = (uaddr + iov[i].iov_len + PAGE_SIZE - 1) >> PAGE_SHIFT;
  		start = uaddr >> PAGE_SHIFT;
  
  		nr_pages += end - start;
  		len += iov[i].iov_len;
  	}

  	if (offset)
  		nr_pages++;

  	bmd = bio_alloc_map_data(nr_pages, iov_count, gfp_mask);

  	if (!bmd)
  		return ERR_PTR(-ENOMEM);

  	ret = -ENOMEM;

  	bio = bio_kmalloc(gfp_mask, nr_pages);

  	if (!bio)
  		goto out_bmd;
  
  	bio->bi_rw |= (!write_to_vm << BIO_RW);
  
  	ret = 0;

  
  	if (map_data) {

  		nr_pages = 1 << map_data->page_order;

  		i = map_data->offset / PAGE_SIZE;
  	}

  	while (len) {

  		unsigned int bytes = PAGE_SIZE;

  		bytes -= offset;

  		if (bytes > len)
  			bytes = len;

  		if (map_data) {

  			if (i == map_data->nr_entries * nr_pages) {

  				ret = -ENOMEM;
  				break;
  			}

  
  			page = map_data->pages[i / nr_pages];
  			page += (i % nr_pages);
  
  			i++;
  		} else {

  			page = alloc_page(q->bounce_gfp | gfp_mask);

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

  		}

  		if (bio_add_pc_page(q, bio, page, bytes, offset) < bytes)

  			break;

  
  		len -= bytes;

  		offset = 0;

  	}
  
  	if (ret)
  		goto cleanup;
  
  	/*
  	 * success
  	 */

  	if (!write_to_vm && (!map_data || !map_data->null_mapped)) {

  		ret = __bio_copy_iov(bio, bio->bi_io_vec, iov, iov_count, 0, 0);

  		if (ret)
  			goto cleanup;

  	}

  	bio_set_map_data(bmd, bio, iov, iov_count, map_data ? 0 : 1);

  	return bio;
  cleanup:

  	if (!map_data)
  		bio_for_each_segment(bvec, bio, i)
  			__free_page(bvec->bv_page);

  
  	bio_put(bio);
  out_bmd:
  	bio_free_map_data(bmd);
  	return ERR_PTR(ret);
  }

  /**
   *	bio_copy_user	-	copy user data to bio
   *	@q: destination block queue

   *	@map_data: pointer to the rq_map_data holding pages (if necessary)

   *	@uaddr: start of user address
   *	@len: length in bytes
   *	@write_to_vm: bool indicating writing to pages or not

   *	@gfp_mask: memory allocation flags

   *
   *	Prepares and returns a bio for indirect user io, bouncing data
   *	to/from kernel pages as necessary. Must be paired with
   *	call bio_uncopy_user() on io completion.
   */

  struct bio *bio_copy_user(struct request_queue *q, struct rq_map_data *map_data,
  			  unsigned long uaddr, unsigned int len,
  			  int write_to_vm, gfp_t gfp_mask)

  {
  	struct sg_iovec iov;
  
  	iov.iov_base = (void __user *)uaddr;
  	iov.iov_len = len;

  	return bio_copy_user_iov(q, map_data, &iov, 1, write_to_vm, gfp_mask);

  }

  static struct bio *__bio_map_user_iov(struct request_queue *q,

  				      struct block_device *bdev,
  				      struct sg_iovec *iov, int iov_count,

  				      int write_to_vm, gfp_t gfp_mask)

  {

  	int i, j;
  	int nr_pages = 0;

  	struct page **pages;
  	struct bio *bio;

  	int cur_page = 0;
  	int ret, offset;

  	for (i = 0; i < iov_count; i++) {
  		unsigned long uaddr = (unsigned long)iov[i].iov_base;
  		unsigned long len = iov[i].iov_len;
  		unsigned long end = (uaddr + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
  		unsigned long start = uaddr >> PAGE_SHIFT;
  
  		nr_pages += end - start;
  		/*

  		 * buffer must be aligned to at least hardsector size for now

  		 */

  		if (uaddr & queue_dma_alignment(q))

  			return ERR_PTR(-EINVAL);
  	}
  
  	if (!nr_pages)

  		return ERR_PTR(-EINVAL);

  	bio = bio_kmalloc(gfp_mask, nr_pages);

  	if (!bio)
  		return ERR_PTR(-ENOMEM);
  
  	ret = -ENOMEM;

  	pages = kcalloc(nr_pages, sizeof(struct page *), gfp_mask);

  	if (!pages)
  		goto out;

  	for (i = 0; i < iov_count; i++) {
  		unsigned long uaddr = (unsigned long)iov[i].iov_base;
  		unsigned long len = iov[i].iov_len;
  		unsigned long end = (uaddr + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
  		unsigned long start = uaddr >> PAGE_SHIFT;
  		const int local_nr_pages = end - start;
  		const int page_limit = cur_page + local_nr_pages;
  		

  		ret = get_user_pages_fast(uaddr, local_nr_pages,
  				write_to_vm, &pages[cur_page]);

  		if (ret < local_nr_pages) {
  			ret = -EFAULT;

  			goto out_unmap;

  		}

  
  		offset = uaddr & ~PAGE_MASK;
  		for (j = cur_page; j < page_limit; j++) {
  			unsigned int bytes = PAGE_SIZE - offset;
  
  			if (len <= 0)
  				break;
  			
  			if (bytes > len)
  				bytes = len;
  
  			/*
  			 * sorry...
  			 */

  			if (bio_add_pc_page(q, bio, pages[j], bytes, offset) <
  					    bytes)

  				break;
  
  			len -= bytes;
  			offset = 0;
  		}

  		cur_page = j;

  		/*

  		 * release the pages we didn't map into the bio, if any

  		 */

  		while (j < page_limit)
  			page_cache_release(pages[j++]);

  	}

  	kfree(pages);
  
  	/*
  	 * set data direction, and check if mapped pages need bouncing
  	 */
  	if (!write_to_vm)
  		bio->bi_rw |= (1 << BIO_RW);

  	bio->bi_bdev = bdev;

  	bio->bi_flags |= (1 << BIO_USER_MAPPED);
  	return bio;

  
   out_unmap:
  	for (i = 0; i < nr_pages; i++) {
  		if(!pages[i])
  			break;
  		page_cache_release(pages[i]);
  	}
   out:

  	kfree(pages);
  	bio_put(bio);
  	return ERR_PTR(ret);
  }
  
  /**
   *	bio_map_user	-	map user address into bio

   *	@q: the struct request_queue for the bio

   *	@bdev: destination block device
   *	@uaddr: start of user address
   *	@len: length in bytes
   *	@write_to_vm: bool indicating writing to pages or not

   *	@gfp_mask: memory allocation flags

   *
   *	Map the user space address into a bio suitable for io to a block
   *	device. Returns an error pointer in case of error.
   */

  struct bio *bio_map_user(struct request_queue *q, struct block_device *bdev,

  			 unsigned long uaddr, unsigned int len, int write_to_vm,
  			 gfp_t gfp_mask)

  {

  	struct sg_iovec iov;

  	iov.iov_base = (void __user *)uaddr;

  	iov.iov_len = len;

  	return bio_map_user_iov(q, bdev, &iov, 1, write_to_vm, gfp_mask);

  }
  
  /**
   *	bio_map_user_iov - map user sg_iovec table into bio

   *	@q: the struct request_queue for the bio

   *	@bdev: destination block device
   *	@iov:	the iovec.
   *	@iov_count: number of elements in the iovec
   *	@write_to_vm: bool indicating writing to pages or not

   *	@gfp_mask: memory allocation flags

   *
   *	Map the user space address into a bio suitable for io to a block
   *	device. Returns an error pointer in case of error.
   */

  struct bio *bio_map_user_iov(struct request_queue *q, struct block_device *bdev,

  			     struct sg_iovec *iov, int iov_count,

  			     int write_to_vm, gfp_t gfp_mask)

  {

  	struct bio *bio;

  	bio = __bio_map_user_iov(q, bdev, iov, iov_count, write_to_vm,
  				 gfp_mask);

  	if (IS_ERR(bio))
  		return bio;
  
  	/*
  	 * subtle -- if __bio_map_user() ended up bouncing a bio,
  	 * it would normally disappear when its bi_end_io is run.
  	 * however, we need it for the unmap, so grab an extra
  	 * reference to it
  	 */
  	bio_get(bio);

  	return bio;

  }
  
  static void __bio_unmap_user(struct bio *bio)
  {
  	struct bio_vec *bvec;
  	int i;
  
  	/*
  	 * make sure we dirty pages we wrote to
  	 */
  	__bio_for_each_segment(bvec, bio, i, 0) {
  		if (bio_data_dir(bio) == READ)
  			set_page_dirty_lock(bvec->bv_page);
  
  		page_cache_release(bvec->bv_page);
  	}
  
  	bio_put(bio);
  }
  
  /**
   *	bio_unmap_user	-	unmap a bio
   *	@bio:		the bio being unmapped
   *
   *	Unmap a bio previously mapped by bio_map_user(). Must be called with
   *	a process context.
   *
   *	bio_unmap_user() may sleep.
   */
  void bio_unmap_user(struct bio *bio)
  {
  	__bio_unmap_user(bio);
  	bio_put(bio);
  }

  static void bio_map_kern_endio(struct bio *bio, int err)

  {

  	bio_put(bio);

  }

  static struct bio *__bio_map_kern(struct request_queue *q, void *data,

  				  unsigned int len, gfp_t gfp_mask)

  {
  	unsigned long kaddr = (unsigned long)data;
  	unsigned long end = (kaddr + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
  	unsigned long start = kaddr >> PAGE_SHIFT;
  	const int nr_pages = end - start;
  	int offset, i;
  	struct bio *bio;

  	bio = bio_kmalloc(gfp_mask, nr_pages);

  	if (!bio)
  		return ERR_PTR(-ENOMEM);
  
  	offset = offset_in_page(kaddr);
  	for (i = 0; i < nr_pages; i++) {
  		unsigned int bytes = PAGE_SIZE - offset;
  
  		if (len <= 0)
  			break;
  
  		if (bytes > len)
  			bytes = len;

  		if (bio_add_pc_page(q, bio, virt_to_page(data), bytes,
  				    offset) < bytes)

  			break;
  
  		data += bytes;
  		len -= bytes;
  		offset = 0;
  	}

  	bio->bi_end_io = bio_map_kern_endio;

  	return bio;
  }
  
  /**
   *	bio_map_kern	-	map kernel address into bio

   *	@q: the struct request_queue for the bio

   *	@data: pointer to buffer to map
   *	@len: length in bytes
   *	@gfp_mask: allocation flags for bio allocation
   *
   *	Map the kernel address into a bio suitable for io to a block
   *	device. Returns an error pointer in case of error.
   */

  struct bio *bio_map_kern(struct request_queue *q, void *data, unsigned int len,

  			 gfp_t gfp_mask)

  {
  	struct bio *bio;
  
  	bio = __bio_map_kern(q, data, len, gfp_mask);
  	if (IS_ERR(bio))
  		return bio;
  
  	if (bio->bi_size == len)
  		return bio;
  
  	/*
  	 * Don't support partial mappings.
  	 */
  	bio_put(bio);
  	return ERR_PTR(-EINVAL);
  }

  static void bio_copy_kern_endio(struct bio *bio, int err)
  {
  	struct bio_vec *bvec;
  	const int read = bio_data_dir(bio) == READ;

  	struct bio_map_data *bmd = bio->bi_private;

  	int i;

  	char *p = bmd->sgvecs[0].iov_base;

  
  	__bio_for_each_segment(bvec, bio, i, 0) {
  		char *addr = page_address(bvec->bv_page);

  		int len = bmd->iovecs[i].bv_len;

  		if (read)

  			memcpy(p, addr, len);

  
  		__free_page(bvec->bv_page);

  		p += len;

  	}

  	bio_free_map_data(bmd);

  	bio_put(bio);
  }
  
  /**
   *	bio_copy_kern	-	copy kernel address into bio
   *	@q: the struct request_queue for the bio
   *	@data: pointer to buffer to copy
   *	@len: length in bytes
   *	@gfp_mask: allocation flags for bio and page allocation

   *	@reading: data direction is READ

   *
   *	copy the kernel address into a bio suitable for io to a block
   *	device. Returns an error pointer in case of error.
   */
  struct bio *bio_copy_kern(struct request_queue *q, void *data, unsigned int len,
  			  gfp_t gfp_mask, int reading)
  {

  	struct bio *bio;
  	struct bio_vec *bvec;

  	int i;

  	bio = bio_copy_user(q, NULL, (unsigned long)data, len, 1, gfp_mask);
  	if (IS_ERR(bio))
  		return bio;

  
  	if (!reading) {
  		void *p = data;
  
  		bio_for_each_segment(bvec, bio, i) {
  			char *addr = page_address(bvec->bv_page);
  
  			memcpy(addr, p, bvec->bv_len);
  			p += bvec->bv_len;
  		}
  	}

  	bio->bi_end_io = bio_copy_kern_endio;

  	return bio;

  }

  /*
   * bio_set_pages_dirty() and bio_check_pages_dirty() are support functions
   * for performing direct-IO in BIOs.
   *
   * The problem is that we cannot run set_page_dirty() from interrupt context
   * because the required locks are not interrupt-safe.  So what we can do is to
   * mark the pages dirty _before_ performing IO.  And in interrupt context,
   * check that the pages are still dirty.   If so, fine.  If not, redirty them
   * in process context.
   *
   * We special-case compound pages here: normally this means reads into hugetlb
   * pages.  The logic in here doesn't really work right for compound pages
   * because the VM does not uniformly chase down the head page in all cases.
   * But dirtiness of compound pages is pretty meaningless anyway: the VM doesn't
   * handle them at all.  So we skip compound pages here at an early stage.
   *
   * Note that this code is very hard to test under normal circumstances because
   * direct-io pins the pages with get_user_pages().  This makes
   * is_page_cache_freeable return false, and the VM will not clean the pages.
   * But other code (eg, pdflush) could clean the pages if they are mapped
   * pagecache.
   *
   * Simply disabling the call to bio_set_pages_dirty() is a good way to test the
   * deferred bio dirtying paths.
   */
  
  /*
   * bio_set_pages_dirty() will mark all the bio's pages as dirty.
   */
  void bio_set_pages_dirty(struct bio *bio)
  {
  	struct bio_vec *bvec = bio->bi_io_vec;
  	int i;
  
  	for (i = 0; i < bio->bi_vcnt; i++) {
  		struct page *page = bvec[i].bv_page;
  
  		if (page && !PageCompound(page))
  			set_page_dirty_lock(page);
  	}
  }

  static void bio_release_pages(struct bio *bio)

  {
  	struct bio_vec *bvec = bio->bi_io_vec;
  	int i;
  
  	for (i = 0; i < bio->bi_vcnt; i++) {
  		struct page *page = bvec[i].bv_page;
  
  		if (page)
  			put_page(page);
  	}
  }
  
  /*
   * bio_check_pages_dirty() will check that all the BIO's pages are still dirty.
   * If they are, then fine.  If, however, some pages are clean then they must
   * have been written out during the direct-IO read.  So we take another ref on
   * the BIO and the offending pages and re-dirty the pages in process context.
   *
   * It is expected that bio_check_pages_dirty() will wholly own the BIO from
   * here on.  It will run one page_cache_release() against each page and will
   * run one bio_put() against the BIO.
   */

  static void bio_dirty_fn(struct work_struct *work);

  static DECLARE_WORK(bio_dirty_work, bio_dirty_fn);

  static DEFINE_SPINLOCK(bio_dirty_lock);
  static struct bio *bio_dirty_list;
  
  /*
   * This runs in process context
   */

  static void bio_dirty_fn(struct work_struct *work)

  {
  	unsigned long flags;
  	struct bio *bio;
  
  	spin_lock_irqsave(&bio_dirty_lock, flags);
  	bio = bio_dirty_list;
  	bio_dirty_list = NULL;
  	spin_unlock_irqrestore(&bio_dirty_lock, flags);
  
  	while (bio) {
  		struct bio *next = bio->bi_private;
  
  		bio_set_pages_dirty(bio);
  		bio_release_pages(bio);
  		bio_put(bio);
  		bio = next;
  	}
  }
  
  void bio_check_pages_dirty(struct bio *bio)
  {
  	struct bio_vec *bvec = bio->bi_io_vec;
  	int nr_clean_pages = 0;
  	int i;
  
  	for (i = 0; i < bio->bi_vcnt; i++) {
  		struct page *page = bvec[i].bv_page;
  
  		if (PageDirty(page) || PageCompound(page)) {
  			page_cache_release(page);
  			bvec[i].bv_page = NULL;
  		} else {
  			nr_clean_pages++;
  		}
  	}
  
  	if (nr_clean_pages) {
  		unsigned long flags;
  
  		spin_lock_irqsave(&bio_dirty_lock, flags);
  		bio->bi_private = bio_dirty_list;
  		bio_dirty_list = bio;
  		spin_unlock_irqrestore(&bio_dirty_lock, flags);
  		schedule_work(&bio_dirty_work);
  	} else {
  		bio_put(bio);
  	}
  }
  
  /**
   * bio_endio - end I/O on a bio
   * @bio:	bio

   * @error:	error, if any
   *
   * Description:

   *   bio_endio() will end I/O on the whole bio. bio_endio() is the

   *   preferred way to end I/O on a bio, it takes care of clearing
   *   BIO_UPTODATE on error. @error is 0 on success, and and one of the
   *   established -Exxxx (-EIO, for instance) error values in case
   *   something went wrong. Noone should call bi_end_io() directly on a
   *   bio unless they own it and thus know that it has an end_io
   *   function.

   **/

  void bio_endio(struct bio *bio, int error)

  {
  	if (error)
  		clear_bit(BIO_UPTODATE, &bio->bi_flags);

  	else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
  		error = -EIO;

  	if (bio->bi_end_io)

  		bio->bi_end_io(bio, error);

  }
  
  void bio_pair_release(struct bio_pair *bp)
  {
  	if (atomic_dec_and_test(&bp->cnt)) {
  		struct bio *master = bp->bio1.bi_private;

  		bio_endio(master, bp->error);

  		mempool_free(bp, bp->bio2.bi_private);
  	}
  }

  static void bio_pair_end_1(struct bio *bi, int err)

  {
  	struct bio_pair *bp = container_of(bi, struct bio_pair, bio1);
  
  	if (err)
  		bp->error = err;

  	bio_pair_release(bp);

  }

  static void bio_pair_end_2(struct bio *bi, int err)

  {
  	struct bio_pair *bp = container_of(bi, struct bio_pair, bio2);
  
  	if (err)
  		bp->error = err;

  	bio_pair_release(bp);

  }
  
  /*

   * split a bio - only worry about a bio with a single page in its iovec

   */

  struct bio_pair *bio_split(struct bio *bi, int first_sectors)

  {

  	struct bio_pair *bp = mempool_alloc(bio_split_pool, GFP_NOIO);

  
  	if (!bp)
  		return bp;

  	trace_block_split(bdev_get_queue(bi->bi_bdev), bi,

  				bi->bi_sector + first_sectors);

  	BUG_ON(bi->bi_vcnt != 1);
  	BUG_ON(bi->bi_idx != 0);
  	atomic_set(&bp->cnt, 3);
  	bp->error = 0;
  	bp->bio1 = *bi;
  	bp->bio2 = *bi;
  	bp->bio2.bi_sector += first_sectors;
  	bp->bio2.bi_size -= first_sectors << 9;
  	bp->bio1.bi_size = first_sectors << 9;
  
  	bp->bv1 = bi->bi_io_vec[0];
  	bp->bv2 = bi->bi_io_vec[0];
  	bp->bv2.bv_offset += first_sectors << 9;
  	bp->bv2.bv_len -= first_sectors << 9;
  	bp->bv1.bv_len = first_sectors << 9;
  
  	bp->bio1.bi_io_vec = &bp->bv1;
  	bp->bio2.bi_io_vec = &bp->bv2;

  	bp->bio1.bi_max_vecs = 1;
  	bp->bio2.bi_max_vecs = 1;

  	bp->bio1.bi_end_io = bio_pair_end_1;
  	bp->bio2.bi_end_io = bio_pair_end_2;
  
  	bp->bio1.bi_private = bi;

  	bp->bio2.bi_private = bio_split_pool;

  	if (bio_integrity(bi))
  		bio_integrity_split(bi, bp, first_sectors);

  	return bp;
  }

  /**
   *      bio_sector_offset - Find hardware sector offset in bio
   *      @bio:           bio to inspect
   *      @index:         bio_vec index
   *      @offset:        offset in bv_page
   *
   *      Return the number of hardware sectors between beginning of bio
   *      and an end point indicated by a bio_vec index and an offset
   *      within that vector's page.
   */
  sector_t bio_sector_offset(struct bio *bio, unsigned short index,
  			   unsigned int offset)
  {

  	unsigned int sector_sz;

  	struct bio_vec *bv;
  	sector_t sectors;
  	int i;

  	sector_sz = queue_logical_block_size(bio->bi_bdev->bd_disk->queue);

  	sectors = 0;
  
  	if (index >= bio->bi_idx)
  		index = bio->bi_vcnt - 1;
  
  	__bio_for_each_segment(bv, bio, i, 0) {
  		if (i == index) {
  			if (offset > bv->bv_offset)
  				sectors += (offset - bv->bv_offset) / sector_sz;
  			break;
  		}
  
  		sectors += bv->bv_len / sector_sz;
  	}
  
  	return sectors;
  }
  EXPORT_SYMBOL(bio_sector_offset);

  
  /*
   * create memory pools for biovec's in a bio_set.
   * use the global biovec slabs created for general use.
   */

  static int biovec_create_pools(struct bio_set *bs, int pool_entries)

  {

  	struct biovec_slab *bp = bvec_slabs + BIOVEC_MAX_IDX;

  	bs->bvec_pool = mempool_create_slab_pool(pool_entries, bp->slab);
  	if (!bs->bvec_pool)
  		return -ENOMEM;

  	return 0;
  }
  
  static void biovec_free_pools(struct bio_set *bs)
  {

  	mempool_destroy(bs->bvec_pool);

  }
  
  void bioset_free(struct bio_set *bs)
  {
  	if (bs->bio_pool)
  		mempool_destroy(bs->bio_pool);
  
  	biovec_free_pools(bs);

  	bio_put_slab(bs);

  
  	kfree(bs);
  }

  /**
   * bioset_create  - Create a bio_set
   * @pool_size:	Number of bio and bio_vecs to cache in the mempool
   * @front_pad:	Number of bytes to allocate in front of the returned bio
   *
   * Description:
   *    Set up a bio_set to be used with @bio_alloc_bioset. Allows the caller
   *    to ask for a number of bytes to be allocated in front of the bio.
   *    Front pad allocation is useful for embedding the bio inside
   *    another structure, to avoid allocating extra data to go with the bio.
   *    Note that the bio must be embedded at the END of that structure always,
   *    or things will break badly.
   */
  struct bio_set *bioset_create(unsigned int pool_size, unsigned int front_pad)

  {

  	unsigned int back_pad = BIO_INLINE_VECS * sizeof(struct bio_vec);

  	struct bio_set *bs;

  	bs = kzalloc(sizeof(*bs), GFP_KERNEL);

  	if (!bs)
  		return NULL;

  	bs->front_pad = front_pad;

  	bs->bio_slab = bio_find_or_create_slab(front_pad + back_pad);

  	if (!bs->bio_slab) {
  		kfree(bs);
  		return NULL;
  	}
  
  	bs->bio_pool = mempool_create_slab_pool(pool_size, bs->bio_slab);

  	if (!bs->bio_pool)
  		goto bad;

  	if (!biovec_create_pools(bs, pool_size))

  		return bs;
  
  bad:
  	bioset_free(bs);
  	return NULL;
  }
  
  static void __init biovec_init_slabs(void)
  {
  	int i;
  
  	for (i = 0; i < BIOVEC_NR_POOLS; i++) {
  		int size;
  		struct biovec_slab *bvs = bvec_slabs + i;

  #ifndef CONFIG_BLK_DEV_INTEGRITY
  		if (bvs->nr_vecs <= BIO_INLINE_VECS) {
  			bvs->slab = NULL;
  			continue;
  		}
  #endif

  		size = bvs->nr_vecs * sizeof(struct bio_vec);
  		bvs->slab = kmem_cache_create(bvs->name, size, 0,

                                  SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);

  	}
  }
  
  static int __init init_bio(void)
  {

  	bio_slab_max = 2;
  	bio_slab_nr = 0;
  	bio_slabs = kzalloc(bio_slab_max * sizeof(struct bio_slab), GFP_KERNEL);
  	if (!bio_slabs)
  		panic("bio: can't allocate bios
  ");

  
  	biovec_init_slabs();

  	fs_bio_set = bioset_create(BIO_POOL_SIZE, 0);

  	if (!fs_bio_set)
  		panic("bio: can't allocate bios
  ");

  	bio_split_pool = mempool_create_kmalloc_pool(BIO_SPLIT_ENTRIES,
  						     sizeof(struct bio_pair));

  	if (!bio_split_pool)
  		panic("bio: can't create split pool
  ");
  
  	return 0;
  }
  
  subsys_initcall(init_bio);
  
  EXPORT_SYMBOL(bio_alloc);

  EXPORT_SYMBOL(bio_kmalloc);

  EXPORT_SYMBOL(bio_put);

  EXPORT_SYMBOL(bio_free);

  EXPORT_SYMBOL(bio_endio);
  EXPORT_SYMBOL(bio_init);
  EXPORT_SYMBOL(__bio_clone);
  EXPORT_SYMBOL(bio_clone);
  EXPORT_SYMBOL(bio_phys_segments);

  EXPORT_SYMBOL(bio_add_page);

  EXPORT_SYMBOL(bio_add_pc_page);

  EXPORT_SYMBOL(bio_get_nr_vecs);

  EXPORT_SYMBOL(bio_map_user);
  EXPORT_SYMBOL(bio_unmap_user);

  EXPORT_SYMBOL(bio_map_kern);

  EXPORT_SYMBOL(bio_copy_kern);

  EXPORT_SYMBOL(bio_pair_release);
  EXPORT_SYMBOL(bio_split);

  EXPORT_SYMBOL(bio_copy_user);
  EXPORT_SYMBOL(bio_uncopy_user);
  EXPORT_SYMBOL(bioset_create);
  EXPORT_SYMBOL(bioset_free);
  EXPORT_SYMBOL(bio_alloc_bioset);