/*

   * 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/uio.h>

  #include <linux/iocontext.h>

  #include <linux/slab.h>
  #include <linux/init.h>
  #include <linux/kernel.h>

  #include <linux/export.h>

  #include <linux/mempool.h>
  #include <linux/workqueue.h>

  #include <linux/cgroup.h>

  #include <linux/blk-cgroup.h>

  #include <trace/events/block.h>

  #include "blk.h"

  #include "blk-rq-qos.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

  /*
   * 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, n) { .nr_vecs = x, .name = "biovec-"#n }

  static struct biovec_slab bvec_slabs[BVEC_POOL_NR] __read_mostly = {

  	BV(1, 1), BV(4, 4), BV(16, 16), BV(64, 64), BV(128, 128), BV(BIO_MAX_PAGES, max),

  };
  #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;

  EXPORT_SYMBOL(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, *new_bio_slabs;

  	unsigned int new_bio_slab_max;

  	unsigned int i, entry = -1;
  
  	mutex_lock(&bio_slab_lock);
  
  	i = 0;
  	while (i < bio_slab_nr) {

  		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) {

  		new_bio_slab_max = bio_slab_max << 1;

  		new_bio_slabs = krealloc(bio_slabs,

  					 new_bio_slab_max * sizeof(struct bio_slab),

  					 GFP_KERNEL);
  		if (!new_bio_slabs)

  			goto out_unlock;

  		bio_slab_max = new_bio_slab_max;

  		bio_slabs = new_bio_slabs;

  	}
  	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, ARCH_KMALLOC_MINALIGN,
  				 SLAB_HWCACHE_ALIGN, NULL);

  	if (!slab)
  		goto out_unlock;

  	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(mempool_t *pool, struct bio_vec *bv, unsigned int idx)

  {

  	if (!idx)
  		return;
  	idx--;
  
  	BIO_BUG_ON(idx >= BVEC_POOL_NR);

  	if (idx == BVEC_POOL_MAX) {

  		mempool_free(bv, pool);

  	} else {

  		struct biovec_slab *bvs = bvec_slabs + idx;
  
  		kmem_cache_free(bvs->slab, bv);
  	}
  }

  struct bio_vec *bvec_alloc(gfp_t gfp_mask, int nr, unsigned long *idx,
  			   mempool_t *pool)

  {
  	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 == BVEC_POOL_MAX) {

  fallback:

  		bvl = mempool_alloc(pool, gfp_mask);

  	} else {
  		struct biovec_slab *bvs = bvec_slabs + *idx;

  		gfp_t __gfp_mask = gfp_mask & ~(__GFP_DIRECT_RECLAIM | __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_DIRECT_RECLAIM

  		 * is set, retry with the 1-entry mempool

  		 */

  		bvl = kmem_cache_alloc(bvs->slab, __gfp_mask);

  		if (unlikely(!bvl && (gfp_mask & __GFP_DIRECT_RECLAIM))) {

  			*idx = BVEC_POOL_MAX;

  			goto fallback;
  		}
  	}

  	(*idx)++;

  	return bvl;
  }

  void bio_uninit(struct bio *bio)

  {

  	bio_disassociate_task(bio);

  }

  EXPORT_SYMBOL(bio_uninit);

  static void bio_free(struct bio *bio)
  {
  	struct bio_set *bs = bio->bi_pool;
  	void *p;

  	bio_uninit(bio);

  
  	if (bs) {

  		bvec_free(&bs->bvec_pool, bio->bi_io_vec, BVEC_POOL_IDX(bio));

  
  		/*
  		 * If we have front padding, adjust the bio pointer before freeing
  		 */
  		p = bio;

  		p -= bs->front_pad;

  		mempool_free(p, &bs->bio_pool);

  	} else {
  		/* Bio was allocated by bio_kmalloc() */
  		kfree(bio);
  	}

  }

  /*
   * Users of this function have their own bio allocation. Subsequently,
   * they must remember to pair any call to bio_init() with bio_uninit()
   * when IO has completed, or when the bio is released.
   */

  void bio_init(struct bio *bio, struct bio_vec *table,
  	      unsigned short max_vecs)

  {

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

  	atomic_set(&bio->__bi_remaining, 1);

  	atomic_set(&bio->__bi_cnt, 1);

  
  	bio->bi_io_vec = table;
  	bio->bi_max_vecs = max_vecs;

  }

  EXPORT_SYMBOL(bio_init);

  
  /**

   * bio_reset - reinitialize a bio
   * @bio:	bio to reset
   *
   * Description:
   *   After calling bio_reset(), @bio will be in the same state as a freshly
   *   allocated bio returned bio bio_alloc_bioset() - the only fields that are
   *   preserved are the ones that are initialized by bio_alloc_bioset(). See
   *   comment in struct bio.
   */
  void bio_reset(struct bio *bio)
  {
  	unsigned long flags = bio->bi_flags & (~0UL << BIO_RESET_BITS);

  	bio_uninit(bio);

  
  	memset(bio, 0, BIO_RESET_BYTES);

  	bio->bi_flags = flags;

  	atomic_set(&bio->__bi_remaining, 1);

  }
  EXPORT_SYMBOL(bio_reset);

  static struct bio *__bio_chain_endio(struct bio *bio)

  {

  	struct bio *parent = bio->bi_private;

  	if (!parent->bi_status)
  		parent->bi_status = bio->bi_status;

  	bio_put(bio);

  	return parent;
  }
  
  static void bio_chain_endio(struct bio *bio)
  {
  	bio_endio(__bio_chain_endio(bio));

  }
  
  /**
   * bio_chain - chain bio completions

   * @bio: the target bio
   * @parent: the @bio's parent bio

   *
   * The caller won't have a bi_end_io called when @bio completes - instead,
   * @parent's bi_end_io won't be called until both @parent and @bio have
   * completed; the chained bio will also be freed when it completes.
   *
   * The caller must not set bi_private or bi_end_io in @bio.
   */
  void bio_chain(struct bio *bio, struct bio *parent)
  {
  	BUG_ON(bio->bi_private || bio->bi_end_io);
  
  	bio->bi_private = parent;
  	bio->bi_end_io	= bio_chain_endio;

  	bio_inc_remaining(parent);

  }
  EXPORT_SYMBOL(bio_chain);

  static void bio_alloc_rescue(struct work_struct *work)
  {
  	struct bio_set *bs = container_of(work, struct bio_set, rescue_work);
  	struct bio *bio;
  
  	while (1) {
  		spin_lock(&bs->rescue_lock);
  		bio = bio_list_pop(&bs->rescue_list);
  		spin_unlock(&bs->rescue_lock);
  
  		if (!bio)
  			break;
  
  		generic_make_request(bio);
  	}
  }
  
  static void punt_bios_to_rescuer(struct bio_set *bs)
  {
  	struct bio_list punt, nopunt;
  	struct bio *bio;

  	if (WARN_ON_ONCE(!bs->rescue_workqueue))
  		return;

  	/*
  	 * In order to guarantee forward progress we must punt only bios that
  	 * were allocated from this bio_set; otherwise, if there was a bio on
  	 * there for a stacking driver higher up in the stack, processing it
  	 * could require allocating bios from this bio_set, and doing that from
  	 * our own rescuer would be bad.
  	 *
  	 * Since bio lists are singly linked, pop them all instead of trying to
  	 * remove from the middle of the list:
  	 */
  
  	bio_list_init(&punt);
  	bio_list_init(&nopunt);

  	while ((bio = bio_list_pop(&current->bio_list[0])))

  		bio_list_add(bio->bi_pool == bs ? &punt : &nopunt, bio);

  	current->bio_list[0] = nopunt;

  	bio_list_init(&nopunt);
  	while ((bio = bio_list_pop(&current->bio_list[1])))
  		bio_list_add(bio->bi_pool == bs ? &punt : &nopunt, bio);
  	current->bio_list[1] = nopunt;

  
  	spin_lock(&bs->rescue_lock);
  	bio_list_merge(&bs->rescue_list, &punt);
  	spin_unlock(&bs->rescue_lock);
  
  	queue_work(bs->rescue_workqueue, &bs->rescue_work);
  }

  /**

   * 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.

   *
   * Description:

   *   If @bs is NULL, uses kmalloc() to allocate the bio; else the allocation is
   *   backed by the @bs's mempool.
   *

   *   When @bs is not NULL, if %__GFP_DIRECT_RECLAIM 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 a time
   *   from this pool. Callers that need to allocate more than 1 bio must always
   *   submit the previously allocated bio for IO before attempting to allocate
   *   a new one. Failure to do so can cause deadlocks under memory pressure.

   *

   *   Note that when running under generic_make_request() (i.e. any block
   *   driver), bios are not submitted until after you return - see the code in
   *   generic_make_request() that converts recursion into iteration, to prevent
   *   stack overflows.
   *
   *   This would normally mean allocating multiple bios under
   *   generic_make_request() would be susceptible to deadlocks, but we have
   *   deadlock avoidance code that resubmits any blocked bios from a rescuer
   *   thread.
   *
   *   However, we do not guarantee forward progress for allocations from other
   *   mempools. Doing multiple allocations from the same mempool under
   *   generic_make_request() should be avoided - instead, use bio_set's front_pad
   *   for per bio allocations.
   *

   *   RETURNS:
   *   Pointer to new bio on success, NULL on failure.
   */

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

  {

  	gfp_t saved_gfp = gfp_mask;

  	unsigned front_pad;
  	unsigned inline_vecs;

  	struct bio_vec *bvl = NULL;

  	struct bio *bio;
  	void *p;

  	if (!bs) {
  		if (nr_iovecs > UIO_MAXIOV)
  			return NULL;
  
  		p = kmalloc(sizeof(struct bio) +
  			    nr_iovecs * sizeof(struct bio_vec),
  			    gfp_mask);
  		front_pad = 0;
  		inline_vecs = nr_iovecs;
  	} else {

  		/* should not use nobvec bioset for nr_iovecs > 0 */

  		if (WARN_ON_ONCE(!mempool_initialized(&bs->bvec_pool) &&
  				 nr_iovecs > 0))

  			return NULL;

  		/*
  		 * generic_make_request() converts recursion to iteration; this
  		 * means if we're running beneath it, any bios we allocate and
  		 * submit will not be submitted (and thus freed) until after we
  		 * return.
  		 *
  		 * This exposes us to a potential deadlock if we allocate
  		 * multiple bios from the same bio_set() while running
  		 * underneath generic_make_request(). If we were to allocate
  		 * multiple bios (say a stacking block driver that was splitting
  		 * bios), we would deadlock if we exhausted the mempool's
  		 * reserve.
  		 *
  		 * We solve this, and guarantee forward progress, with a rescuer
  		 * workqueue per bio_set. If we go to allocate and there are
  		 * bios on current->bio_list, we first try the allocation

  		 * without __GFP_DIRECT_RECLAIM; if that fails, we punt those
  		 * bios we would be blocking to the rescuer workqueue before
  		 * we retry with the original gfp_flags.

  		 */

  		if (current->bio_list &&
  		    (!bio_list_empty(&current->bio_list[0]) ||

  		     !bio_list_empty(&current->bio_list[1])) &&
  		    bs->rescue_workqueue)

  			gfp_mask &= ~__GFP_DIRECT_RECLAIM;

  		p = mempool_alloc(&bs->bio_pool, gfp_mask);

  		if (!p && gfp_mask != saved_gfp) {
  			punt_bios_to_rescuer(bs);
  			gfp_mask = saved_gfp;

  			p = mempool_alloc(&bs->bio_pool, gfp_mask);

  		}

  		front_pad = bs->front_pad;
  		inline_vecs = BIO_INLINE_VECS;
  	}

  	if (unlikely(!p))
  		return NULL;

  	bio = p + front_pad;

  	bio_init(bio, NULL, 0);

  	if (nr_iovecs > inline_vecs) {

  		unsigned long idx = 0;

  		bvl = bvec_alloc(gfp_mask, nr_iovecs, &idx, &bs->bvec_pool);

  		if (!bvl && gfp_mask != saved_gfp) {
  			punt_bios_to_rescuer(bs);
  			gfp_mask = saved_gfp;

  			bvl = bvec_alloc(gfp_mask, nr_iovecs, &idx, &bs->bvec_pool);

  		}

  		if (unlikely(!bvl))
  			goto err_free;

  		bio->bi_flags |= idx << BVEC_POOL_OFFSET;

  	} else if (nr_iovecs) {
  		bvl = bio->bi_inline_vecs;

  	}

  
  	bio->bi_pool = bs;

  	bio->bi_max_vecs = nr_iovecs;

  	bio->bi_io_vec = bvl;

  	return bio;

  
  err_free:

  	mempool_free(p, &bs->bio_pool);

  	return NULL;

  }

  EXPORT_SYMBOL(bio_alloc_bioset);

  void zero_fill_bio_iter(struct bio *bio, struct bvec_iter start)

  {
  	unsigned long flags;

  	struct bio_vec bv;
  	struct bvec_iter iter;

  	__bio_for_each_segment(bv, bio, iter, start) {

  		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_iter);

  
  /**
   * 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, bio_get or bio_clone_*. The last put of a bio will free it.

   **/
  void bio_put(struct bio *bio)
  {

  	if (!bio_flagged(bio, BIO_REFFED))

  		bio_free(bio);

  	else {
  		BIO_BUG_ON(!atomic_read(&bio->__bi_cnt));
  
  		/*
  		 * last put frees it
  		 */
  		if (atomic_dec_and_test(&bio->__bi_cnt))
  			bio_free(bio);
  	}

  }

  EXPORT_SYMBOL(bio_put);

  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;
  }

  EXPORT_SYMBOL(bio_phys_segments);

  /**

   * 	__bio_clone_fast - clone a bio that shares the original bio's biovec
   * 	@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.
   *
   * 	Caller must ensure that @bio_src is not freed before @bio.
   */
  void __bio_clone_fast(struct bio *bio, struct bio *bio_src)
  {

  	BUG_ON(bio->bi_pool && BVEC_POOL_IDX(bio));

  
  	/*

  	 * most users will be overriding ->bi_disk with a new target,

  	 * so we don't set nor calculate new physical/hw segment counts here
  	 */

  	bio->bi_disk = bio_src->bi_disk;

  	bio->bi_partno = bio_src->bi_partno;

  	bio_set_flag(bio, BIO_CLONED);

  	if (bio_flagged(bio_src, BIO_THROTTLED))
  		bio_set_flag(bio, BIO_THROTTLED);

  	bio->bi_opf = bio_src->bi_opf;

  	bio->bi_ioprio = bio_src->bi_ioprio;

  	bio->bi_write_hint = bio_src->bi_write_hint;

  	bio->bi_iter = bio_src->bi_iter;
  	bio->bi_io_vec = bio_src->bi_io_vec;

  
  	bio_clone_blkcg_association(bio, bio_src);

  }
  EXPORT_SYMBOL(__bio_clone_fast);
  
  /**
   *	bio_clone_fast - clone a bio that shares the original bio's biovec
   *	@bio: bio to clone
   *	@gfp_mask: allocation priority
   *	@bs: bio_set to allocate from
   *
   * 	Like __bio_clone_fast, only also allocates the returned bio
   */
  struct bio *bio_clone_fast(struct bio *bio, gfp_t gfp_mask, struct bio_set *bs)
  {
  	struct bio *b;
  
  	b = bio_alloc_bioset(gfp_mask, 0, bs);
  	if (!b)
  		return NULL;
  
  	__bio_clone_fast(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;
  }
  EXPORT_SYMBOL(bio_clone_fast);

  /**

   *	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 up to 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)

  {
  	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_iter.bi_size + len) >> 9) > queue_max_hw_sectors(q))

  		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;

  			bio->bi_iter.bi_size += len;

  			goto done;
  		}

  
  		/*
  		 * If the queue doesn't support SG gaps and adding this
  		 * offset would create a gap, disallow it.
  		 */

  		if (bvec_gap_to_prev(q, prev, offset))

  			return 0;

  	}

  	if (bio_full(bio))

  		return 0;
  
  	/*

  	 * 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;
  	bio->bi_vcnt++;
  	bio->bi_phys_segments++;
  	bio->bi_iter.bi_size += len;
  
  	/*
  	 * Perform a recount if the number of segments is greater
  	 * than queue_max_segments(q).

  	 */

  	while (bio->bi_phys_segments > queue_max_segments(q)) {

  
  		if (retried_segments)

  			goto failed;

  
  		retried_segments = 1;
  		blk_recount_segments(q, bio);
  	}

  	/* If we may be able to merge these biovecs, force a recount */

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

  		bio_clear_flag(bio, BIO_SEG_VALID);

   done:

  	return len;

  
   failed:
  	bvec->bv_page = NULL;
  	bvec->bv_len = 0;
  	bvec->bv_offset = 0;
  	bio->bi_vcnt--;
  	bio->bi_iter.bi_size -= len;
  	blk_recount_segments(q, bio);
  	return 0;

  }

  EXPORT_SYMBOL(bio_add_pc_page);

  
  /**

   * __bio_try_merge_page - try appending data to an existing bvec.
   * @bio: destination bio
   * @page: page to add
   * @len: length of the data to add
   * @off: offset of the data in @page

   *

   * Try to add the data at @page + @off to the last bvec of @bio.  This is a
   * a useful optimisation for file systems with a block size smaller than the
   * page size.
   *
   * Return %true on success or %false on failure.

   */

  bool __bio_try_merge_page(struct bio *bio, struct page *page,
  		unsigned int len, unsigned int off)

  {

  	if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))

  		return false;

  	if (bio->bi_vcnt > 0) {

  		struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];

  		if (page == bv->bv_page && off == bv->bv_offset + bv->bv_len) {

  			bv->bv_len += len;

  			bio->bi_iter.bi_size += len;
  			return true;

  		}
  	}

  	return false;
  }
  EXPORT_SYMBOL_GPL(__bio_try_merge_page);

  /**
   * __bio_add_page - add page to a bio in a new segment
   * @bio: destination bio
   * @page: page to add
   * @len: length of the data to add
   * @off: offset of the data in @page
   *
   * Add the data at @page + @off to @bio as a new bvec.  The caller must ensure
   * that @bio has space for another bvec.
   */
  void __bio_add_page(struct bio *bio, struct page *page,
  		unsigned int len, unsigned int off)
  {
  	struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt];

  	WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED));
  	WARN_ON_ONCE(bio_full(bio));
  
  	bv->bv_page = page;
  	bv->bv_offset = off;
  	bv->bv_len = len;

  	bio->bi_iter.bi_size += len;

  	bio->bi_vcnt++;
  }
  EXPORT_SYMBOL_GPL(__bio_add_page);
  
  /**
   *	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 will only fail
   *	if either bio->bi_vcnt == bio->bi_max_vecs or it's a cloned bio.
   */
  int bio_add_page(struct bio *bio, struct page *page,
  		 unsigned int len, unsigned int offset)
  {
  	if (!__bio_try_merge_page(bio, page, len, offset)) {
  		if (bio_full(bio))
  			return 0;
  		__bio_add_page(bio, page, len, offset);
  	}

  	return len;

  }

  EXPORT_SYMBOL(bio_add_page);

  /**

   * __bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio

   * @bio: bio to add pages to
   * @iter: iov iterator describing the region to be mapped
   *

   * Pins pages from *iter and appends them to @bio's bvec array. The

   * pages will have to be released using put_page() when done.

   * For multi-segment *iter, this function only adds pages from the
   * the next non-empty segment of the iov iterator.

   */

  static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)

  {

  	unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt, idx;

  	struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
  	struct page **pages = (struct page **)bv;

  	size_t offset;

  	ssize_t size;
  
  	size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
  	if (unlikely(size <= 0))
  		return size ? size : -EFAULT;

  	idx = nr_pages = (size + offset + PAGE_SIZE - 1) / PAGE_SIZE;

  
  	/*
  	 * Deep magic below:  We need to walk the pinned pages backwards
  	 * because we are abusing the space allocated for the bio_vecs
  	 * for the page array.  Because the bio_vecs are larger than the
  	 * page pointers by definition this will always work.  But it also
  	 * means we can't use bio_add_page, so any changes to it's semantics
  	 * need to be reflected here as well.
  	 */
  	bio->bi_iter.bi_size += size;
  	bio->bi_vcnt += nr_pages;

  	while (idx--) {
  		bv[idx].bv_page = pages[idx];
  		bv[idx].bv_len = PAGE_SIZE;
  		bv[idx].bv_offset = 0;

  	}
  
  	bv[0].bv_offset += offset;
  	bv[0].bv_len -= offset;

  	bv[nr_pages - 1].bv_len -= nr_pages * PAGE_SIZE - offset - size;

  
  	iov_iter_advance(iter, size);
  	return 0;
  }

  
  /**
   * bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio
   * @bio: bio to add pages to
   * @iter: iov iterator describing the region to be mapped
   *
   * Pins pages from *iter and appends them to @bio's bvec array. The
   * pages will have to be released using put_page() when done.
   * The function tries, but does not guarantee, to pin as many pages as
   * fit into the bio, or are requested in *iter, whatever is smaller.
   * If MM encounters an error pinning the requested pages, it stops.
   * Error is returned only if 0 pages could be pinned.
   */
  int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
  {
  	unsigned short orig_vcnt = bio->bi_vcnt;
  
  	do {
  		int ret = __bio_iov_iter_get_pages(bio, iter);
  
  		if (unlikely(ret))
  			return bio->bi_vcnt > orig_vcnt ? 0 : ret;
  
  	} while (iov_iter_count(iter) && !bio_full(bio));
  
  	return 0;
  }

  EXPORT_SYMBOL_GPL(bio_iov_iter_get_pages);

  static void submit_bio_wait_endio(struct bio *bio)

  {

  	complete(bio->bi_private);

  }
  
  /**
   * submit_bio_wait - submit a bio, and wait until it completes

   * @bio: The &struct bio which describes the I/O
   *
   * Simple wrapper around submit_bio(). Returns 0 on success, or the error from
   * bio_endio() on failure.

   *
   * WARNING: Unlike to how submit_bio() is usually used, this function does not
   * result in bio reference to be consumed. The caller must drop the reference
   * on his own.

   */

  int submit_bio_wait(struct bio *bio)

  {

  	DECLARE_COMPLETION_ONSTACK_MAP(done, bio->bi_disk->lockdep_map);

  	bio->bi_private = &done;

  	bio->bi_end_io = submit_bio_wait_endio;

  	bio->bi_opf |= REQ_SYNC;

  	submit_bio(bio);

  	wait_for_completion_io(&done);

  	return blk_status_to_errno(bio->bi_status);

  }
  EXPORT_SYMBOL(submit_bio_wait);

  /**
   * bio_advance - increment/complete a bio by some number of bytes
   * @bio:	bio to advance
   * @bytes:	number of bytes to complete
   *
   * This updates bi_sector, bi_size and bi_idx; if the number of bytes to
   * complete doesn't align with a bvec boundary, then bv_len and bv_offset will
   * be updated on the last bvec as well.
   *
   * @bio will then represent the remaining, uncompleted portion of the io.
   */
  void bio_advance(struct bio *bio, unsigned bytes)
  {
  	if (bio_integrity(bio))
  		bio_integrity_advance(bio, bytes);

  	bio_advance_iter(bio, &bio->bi_iter, bytes);

  }
  EXPORT_SYMBOL(bio_advance);

  void bio_copy_data_iter(struct bio *dst, struct bvec_iter *dst_iter,
  			struct bio *src, struct bvec_iter *src_iter)

  {

  	struct bio_vec src_bv, dst_bv;

  	void *src_p, *dst_p;

  	unsigned bytes;

  	while (src_iter->bi_size && dst_iter->bi_size) {
  		src_bv = bio_iter_iovec(src, *src_iter);
  		dst_bv = bio_iter_iovec(dst, *dst_iter);

  
  		bytes = min(src_bv.bv_len, dst_bv.bv_len);

  		src_p = kmap_atomic(src_bv.bv_page);
  		dst_p = kmap_atomic(dst_bv.bv_page);

  		memcpy(dst_p + dst_bv.bv_offset,
  		       src_p + src_bv.bv_offset,

  		       bytes);
  
  		kunmap_atomic(dst_p);
  		kunmap_atomic(src_p);

  		flush_dcache_page(dst_bv.bv_page);

  		bio_advance_iter(src, src_iter, bytes);
  		bio_advance_iter(dst, dst_iter, bytes);

  	}
  }

  EXPORT_SYMBOL(bio_copy_data_iter);
  
  /**

   * bio_copy_data - copy contents of data buffers from one bio to another
   * @src: source bio
   * @dst: destination bio

   *
   * Stops when it reaches the end of either @src or @dst - that is, copies
   * min(src->bi_size, dst->bi_size) bytes (or the equivalent for lists of bios).
   */
  void bio_copy_data(struct bio *dst, struct bio *src)
  {

  	struct bvec_iter src_iter = src->bi_iter;
  	struct bvec_iter dst_iter = dst->bi_iter;
  
  	bio_copy_data_iter(dst, &dst_iter, src, &src_iter);

  }

  EXPORT_SYMBOL(bio_copy_data);

  /**
   * bio_list_copy_data - copy contents of data buffers from one chain of bios to
   * another
   * @src: source bio list
   * @dst: destination bio list
   *
   * Stops when it reaches the end of either the @src list or @dst list - that is,
   * copies min(src->bi_size, dst->bi_size) bytes (or the equivalent for lists of
   * bios).
   */
  void bio_list_copy_data(struct bio *dst, struct bio *src)
  {
  	struct bvec_iter src_iter = src->bi_iter;
  	struct bvec_iter dst_iter = dst->bi_iter;
  
  	while (1) {
  		if (!src_iter.bi_size) {
  			src = src->bi_next;
  			if (!src)
  				break;
  
  			src_iter = src->bi_iter;
  		}
  
  		if (!dst_iter.bi_size) {
  			dst = dst->bi_next;
  			if (!dst)
  				break;
  
  			dst_iter = dst->bi_iter;
  		}
  
  		bio_copy_data_iter(dst, &dst_iter, src, &src_iter);
  	}
  }
  EXPORT_SYMBOL(bio_list_copy_data);

  struct bio_map_data {

  	int is_our_pages;

  	struct iov_iter iter;
  	struct iovec iov[];

  };

  static struct bio_map_data *bio_alloc_map_data(struct iov_iter *data,

  					       gfp_t gfp_mask)

  {

  	struct bio_map_data *bmd;
  	if (data->nr_segs > UIO_MAXIOV)

  		return NULL;

  	bmd = kmalloc(sizeof(struct bio_map_data) +
  		       sizeof(struct iovec) * data->nr_segs, gfp_mask);
  	if (!bmd)
  		return NULL;
  	memcpy(bmd->iov, data->iov, sizeof(struct iovec) * data->nr_segs);
  	bmd->iter = *data;
  	bmd->iter.iov = bmd->iov;
  	return bmd;

  }

  /**
   * bio_copy_from_iter - copy all pages from iov_iter to bio
   * @bio: The &struct bio which describes the I/O as destination
   * @iter: iov_iter as source
   *
   * Copy all pages from iov_iter to bio.
   * Returns 0 on success, or error on failure.
   */

  static int bio_copy_from_iter(struct bio *bio, struct iov_iter *iter)

  {

  	int i;

  	struct bio_vec *bvec;

  	bio_for_each_segment_all(bvec, bio, i) {

  		ssize_t ret;

  		ret = copy_page_from_iter(bvec->bv_page,
  					  bvec->bv_offset,
  					  bvec->bv_len,

  					  iter);

  		if (!iov_iter_count(iter))

  			break;
  
  		if (ret < bvec->bv_len)
  			return -EFAULT;

  	}

  	return 0;
  }
  
  /**
   * bio_copy_to_iter - copy all pages from bio to iov_iter
   * @bio: The &struct bio which describes the I/O as source
   * @iter: iov_iter as destination
   *
   * Copy all pages from bio to iov_iter.
   * Returns 0 on success, or error on failure.
   */
  static int bio_copy_to_iter(struct bio *bio, struct iov_iter iter)
  {
  	int i;
  	struct bio_vec *bvec;
  
  	bio_for_each_segment_all(bvec, bio, i) {
  		ssize_t ret;
  
  		ret = copy_page_to_iter(bvec->bv_page,
  					bvec->bv_offset,
  					bvec->bv_len,
  					&iter);
  
  		if (!iov_iter_count(&iter))
  			break;
  
  		if (ret < bvec->bv_len)
  			return -EFAULT;
  	}
  
  	return 0;

  }

  void bio_free_pages(struct bio *bio)

  {
  	struct bio_vec *bvec;
  	int i;
  
  	bio_for_each_segment_all(bvec, bio, i)
  		__free_page(bvec->bv_page);
  }

  EXPORT_SYMBOL(bio_free_pages);

  /**
   *	bio_uncopy_user	-	finish previously mapped bio
   *	@bio: bio being terminated
   *

   *	Free pages allocated from bio_copy_user_iov() 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)) {
  		/*
  		 * if we're in a workqueue, the request is orphaned, so

  		 * don't copy into a random user address space, just free
  		 * and return -EINTR so user space doesn't expect any data.

  		 */

  		if (!current->mm)
  			ret = -EINTR;
  		else if (bio_data_dir(bio) == READ)

  			ret = bio_copy_to_iter(bio, bmd->iter);

  		if (bmd->is_our_pages)
  			bio_free_pages(bio);

  	}

  	kfree(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)
   *	@iter:		iovec iterator
   *	@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 iov_iter *iter,

  			      gfp_t gfp_mask)

  {

  	struct bio_map_data *bmd;

  	struct page *page;
  	struct bio *bio;

  	int i = 0, ret;
  	int nr_pages;

  	unsigned int len = iter->count;

  	unsigned int offset = map_data ? offset_in_page(map_data->offset) : 0;

  	bmd = bio_alloc_map_data(iter, gfp_mask);

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

  	/*
  	 * We need to do a deep copy of the iov_iter including the iovecs.
  	 * The caller provided iov might point to an on-stack or otherwise
  	 * shortlived one.
  	 */
  	bmd->is_our_pages = map_data ? 0 : 1;

  	nr_pages = DIV_ROUND_UP(offset + len, PAGE_SIZE);
  	if (nr_pages > BIO_MAX_PAGES)
  		nr_pages = BIO_MAX_PAGES;

  	ret = -ENOMEM;

  	bio = bio_kmalloc(gfp_mask, nr_pages);

  	if (!bio)
  		goto out_bmd;

  	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) {
  			if (!map_data)
  				__free_page(page);

  			break;

  		}

  
  		len -= bytes;

  		offset = 0;

  	}
  
  	if (ret)
  		goto cleanup;

  	if (map_data)
  		map_data->offset += bio->bi_iter.bi_size;

  	/*
  	 * success
  	 */

  	if (((iter->type & WRITE) && (!map_data || !map_data->null_mapped)) ||

  	    (map_data && map_data->from_user)) {

  		ret = bio_copy_from_iter(bio, iter);

  		if (ret)
  			goto cleanup;

  	} else {

  		if (bmd->is_our_pages)
  			zero_fill_bio(bio);

  		iov_iter_advance(iter, bio->bi_iter.bi_size);

  	}

  	bio->bi_private = bmd;

  	if (map_data && map_data->null_mapped)
  		bio_set_flag(bio, BIO_NULL_MAPPED);

  	return bio;
  cleanup:

  	if (!map_data)

  		bio_free_pages(bio);

  	bio_put(bio);
  out_bmd:

  	kfree(bmd);

  	return ERR_PTR(ret);
  }

  /**
   *	bio_map_user_iov - map user iovec into bio
   *	@q:		the struct request_queue for the bio
   *	@iter:		iovec iterator
   *	@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 iov_iter *iter,

  			     gfp_t gfp_mask)

  {

  	int j;

  	struct bio *bio;

  	int ret;

  	struct bio_vec *bvec;

  	if (!iov_iter_count(iter))

  		return ERR_PTR(-EINVAL);

  	bio = bio_kmalloc(gfp_mask, iov_iter_npages(iter, BIO_MAX_PAGES));

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

  	while (iov_iter_count(iter)) {

  		struct page **pages;

  		ssize_t bytes;
  		size_t offs, added = 0;
  		int npages;

  		bytes = iov_iter_get_pages_alloc(iter, &pages, LONG_MAX, &offs);

  		if (unlikely(bytes <= 0)) {
  			ret = bytes ? bytes : -EFAULT;

  			goto out_unmap;

  		}

  		npages = DIV_ROUND_UP(offs + bytes, PAGE_SIZE);

  		if (unlikely(offs & queue_dma_alignment(q))) {
  			ret = -EINVAL;
  			j = 0;
  		} else {
  			for (j = 0; j < npages; j++) {
  				struct page *page = pages[j];
  				unsigned int n = PAGE_SIZE - offs;
  				unsigned short prev_bi_vcnt = bio->bi_vcnt;

  				if (n > bytes)
  					n = bytes;

  				if (!bio_add_pc_page(q, bio, page, n, offs))
  					break;

  				/*
  				 * check if vector was merged with previous
  				 * drop page reference if needed
  				 */
  				if (bio->bi_vcnt == prev_bi_vcnt)
  					put_page(page);
  
  				added += n;
  				bytes -= n;
  				offs = 0;
  			}

  			iov_iter_advance(iter, added);

  		}

  		/*

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

  		 */

  		while (j < npages)

  			put_page(pages[j++]);

  		kvfree(pages);

  		/* couldn't stuff something into bio? */
  		if (bytes)
  			break;

  	}

  	bio_set_flag(bio, BIO_USER_MAPPED);

  
  	/*

  	 * subtle -- if bio_map_user_iov() 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;

  
   out_unmap:

  	bio_for_each_segment_all(bvec, bio, j) {
  		put_page(bvec->bv_page);

  	}

  	bio_put(bio);
  	return ERR_PTR(ret);
  }

  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_all(bvec, bio, i) {

  		if (bio_data_dir(bio) == READ)
  			set_page_dirty_lock(bvec->bv_page);

  		put_page(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_iov(). Must be called from
   *	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)

  {

  	bio_put(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)

  {
  	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) {
  			/* we don't support partial mappings */
  			bio_put(bio);
  			return ERR_PTR(-EINVAL);
  		}

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

  	bio->bi_end_io = bio_map_kern_endio;

  	return bio;
  }

  EXPORT_SYMBOL(bio_map_kern);

  static void bio_copy_kern_endio(struct bio *bio)

  {

  	bio_free_pages(bio);
  	bio_put(bio);
  }

  static void bio_copy_kern_endio_read(struct bio *bio)

  {

  	char *p = bio->bi_private;

  	struct bio_vec *bvec;

  	int i;

  	bio_for_each_segment_all(bvec, bio, i) {

  		memcpy(p, page_address(bvec->bv_page), bvec->bv_len);

  		p += bvec->bv_len;

  	}

  	bio_copy_kern_endio(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)
  {

  	unsigned long kaddr = (unsigned long)data;
  	unsigned long end = (kaddr + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
  	unsigned long start = kaddr >> PAGE_SHIFT;

  	struct bio *bio;
  	void *p = data;

  	int nr_pages = 0;

  	/*
  	 * Overflow, abort
  	 */
  	if (end < start)
  		return ERR_PTR(-EINVAL);

  	nr_pages = end - start;
  	bio = bio_kmalloc(gfp_mask, nr_pages);
  	if (!bio)
  		return ERR_PTR(-ENOMEM);

  	while (len) {
  		struct page *page;
  		unsigned int bytes = PAGE_SIZE;

  		if (bytes > len)
  			bytes = len;
  
  		page = alloc_page(q->bounce_gfp | gfp_mask);
  		if (!page)
  			goto cleanup;
  
  		if (!reading)
  			memcpy(page_address(page), p, bytes);
  
  		if (bio_add_pc_page(q, bio, page, bytes, 0) < bytes)
  			break;
  
  		len -= bytes;
  		p += bytes;

  	}

  	if (reading) {
  		bio->bi_end_io = bio_copy_kern_endio_read;
  		bio->bi_private = data;
  	} else {
  		bio->bi_end_io = bio_copy_kern_endio;

  	}

  	return bio;

  
  cleanup:

  	bio_free_pages(bio);

  	bio_put(bio);
  	return ERR_PTR(-ENOMEM);

  }

  /*
   * 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, flusher threads) 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;

  	int i;

  	bio_for_each_segment_all(bvec, bio, i) {

  		if (!PageCompound(bvec->bv_page))
  			set_page_dirty_lock(bvec->bv_page);

  	}
  }

  EXPORT_SYMBOL_GPL(bio_set_pages_dirty);

  static void bio_release_pages(struct bio *bio)

  {

  	struct bio_vec *bvec;

  	int i;

  	bio_for_each_segment_all(bvec, bio, i)
  		put_page(bvec->bv_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 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 put_page() 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)

  {

  	struct bio *bio, *next;

  	spin_lock_irq(&bio_dirty_lock);
  	next = bio_dirty_list;

  	bio_dirty_list = NULL;

  	spin_unlock_irq(&bio_dirty_lock);

  	while ((bio = next) != NULL) {
  		next = bio->bi_private;

  
  		bio_set_pages_dirty(bio);
  		bio_release_pages(bio);
  		bio_put(bio);

  	}
  }
  
  void bio_check_pages_dirty(struct bio *bio)
  {

  	struct bio_vec *bvec;

  	unsigned long flags;

  	int i;

  	bio_for_each_segment_all(bvec, bio, i) {

  		if (!PageDirty(bvec->bv_page) && !PageCompound(bvec->bv_page))
  			goto defer;

  	}

  	bio_release_pages(bio);
  	bio_put(bio);
  	return;
  defer:
  	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);

  }

  EXPORT_SYMBOL_GPL(bio_check_pages_dirty);

  void generic_start_io_acct(struct request_queue *q, int op,

  			   unsigned long sectors, struct hd_struct *part)

  {

  	const int sgrp = op_stat_group(op);

  	int cpu = part_stat_lock();

  	part_round_stats(q, cpu, part);

  	part_stat_inc(cpu, part, ios[sgrp]);
  	part_stat_add(cpu, part, sectors[sgrp], sectors);
  	part_inc_in_flight(q, part, op_is_write(op));

  
  	part_stat_unlock();
  }
  EXPORT_SYMBOL(generic_start_io_acct);

  void generic_end_io_acct(struct request_queue *q, int req_op,

  			 struct hd_struct *part, unsigned long start_time)

  {
  	unsigned long duration = jiffies - start_time;

  	const int sgrp = op_stat_group(req_op);

  	int cpu = part_stat_lock();

  	part_stat_add(cpu, part, nsecs[sgrp], jiffies_to_nsecs(duration));

  	part_round_stats(q, cpu, part);

  	part_dec_in_flight(q, part, op_is_write(req_op));

  
  	part_stat_unlock();
  }
  EXPORT_SYMBOL(generic_end_io_acct);

  #if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
  void bio_flush_dcache_pages(struct bio *bi)
  {

  	struct bio_vec bvec;
  	struct bvec_iter iter;

  	bio_for_each_segment(bvec, bi, iter)
  		flush_dcache_page(bvec.bv_page);

  }
  EXPORT_SYMBOL(bio_flush_dcache_pages);
  #endif

  static inline bool bio_remaining_done(struct bio *bio)
  {
  	/*
  	 * If we're not chaining, then ->__bi_remaining is always 1 and
  	 * we always end io on the first invocation.
  	 */
  	if (!bio_flagged(bio, BIO_CHAIN))
  		return true;
  
  	BUG_ON(atomic_read(&bio->__bi_remaining) <= 0);

  	if (atomic_dec_and_test(&bio->__bi_remaining)) {

  		bio_clear_flag(bio, BIO_CHAIN);

  		return true;

  	}

  
  	return false;
  }

  /**
   * bio_endio - end I/O on a bio
   * @bio:	bio

   *
   * Description:

   *   bio_endio() will end I/O on the whole bio. bio_endio() is the preferred
   *   way to end I/O on a bio. No one should call bi_end_io() directly on a
   *   bio unless they own it and thus know that it has an end_io function.

   *
   *   bio_endio() can be called several times on a bio that has been chained
   *   using bio_chain().  The ->bi_end_io() function will only be called the
   *   last time.  At this point the BLK_TA_COMPLETE tracing event will be
   *   generated if BIO_TRACE_COMPLETION is set.

   **/

  void bio_endio(struct bio *bio)

  {

  again:

  	if (!bio_remaining_done(bio))

  		return;

  	if (!bio_integrity_endio(bio))
  		return;

  	if (bio->bi_disk)
  		rq_qos_done_bio(bio->bi_disk->queue, bio);

  	/*
  	 * Need to have a real endio function for chained bios, otherwise
  	 * various corner cases will break (like stacking block devices that
  	 * save/restore bi_end_io) - however, we want to avoid unbounded
  	 * recursion and blowing the stack. Tail call optimization would
  	 * handle this, but compiling with frame pointers also disables
  	 * gcc's sibling call optimization.
  	 */
  	if (bio->bi_end_io == bio_chain_endio) {
  		bio = __bio_chain_endio(bio);
  		goto again;

  	}

  	if (bio->bi_disk && bio_flagged(bio, BIO_TRACE_COMPLETION)) {
  		trace_block_bio_complete(bio->bi_disk->queue, bio,

  					 blk_status_to_errno(bio->bi_status));

  		bio_clear_flag(bio, BIO_TRACE_COMPLETION);
  	}

  	blk_throtl_bio_endio(bio);