Skip to content
Snippets Groups Projects
Select Git revision
  • 51bb296b09a83ee1aae025778db38f9d2cc7bb1a
  • vme-testing default
  • ci-test
  • master
  • remoteproc
  • am625-sk-ov5640
  • pcal6534-upstreaming
  • lps22df-upstreaming
  • msc-upstreaming
  • imx8mp
  • iio/noa1305
  • vme-next
  • vme-next-4.14-rc4
  • v4.14-rc4
  • v4.14-rc3
  • v4.14-rc2
  • v4.14-rc1
  • v4.13
  • vme-next-4.13-rc7
  • v4.13-rc7
  • v4.13-rc6
  • v4.13-rc5
  • v4.13-rc4
  • v4.13-rc3
  • v4.13-rc2
  • v4.13-rc1
  • v4.12
  • v4.12-rc7
  • v4.12-rc6
  • v4.12-rc5
  • v4.12-rc4
  • v4.12-rc3
32 results

bio.c

Blame
  • bio.c 39.09 KiB
    /*
     * 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 <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\n", 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!\n"))
    		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, bs);
    
    	/*
    	 * 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);
    }
    EXPORT_SYMBOL(bio_free);
    
    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);
    }
    EXPORT_SYMBOL(bio_init);
    
    /**
     * 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;
    }
    EXPORT_SYMBOL(bio_alloc_bioset);
    
    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
     *
     *	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 and @bio_kmalloc.
     *
     *	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 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 livelocks under memory pressure.
     *
     *	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;
    }
    EXPORT_SYMBOL(bio_alloc);
    
    static void bio_kmalloc_destructor(struct bio *bio)
    {
    	if (bio_integrity(bio))
    		bio_integrity_free(bio, fs_bio_set);
    	kfree(bio);
    }
    
    /**
     * bio_kmalloc - allocate a bio for I/O using kmalloc()
     * @gfp_mask:   the GFP_ mask given to the slab allocator
     * @nr_iovecs:	number of iovecs to pre-allocate
     *
     * Description:
     *   Allocate a new bio with @nr_iovecs bvecs.  If @gfp_mask contains
     *   %__GFP_WAIT, the allocation is guaranteed to succeed.
     *
     **/
    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;
    }
    EXPORT_SYMBOL(bio_kmalloc);
    
    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, bio_get or bio_clone. 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);
    	}
    }
    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	-	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;
    }
    EXPORT_SYMBOL(__bio_clone);
    
    /**
     *	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, fs_bio_set);
    
    		if (ret < 0) {
    			bio_put(b);
    			return NULL;
    		}
    	}
    
    	return b;
    }
    EXPORT_SYMBOL(bio_clone);
    
    /**
     *	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;
    }
    EXPORT_SYMBOL(bio_get_nr_vecs);
    
    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));
    }
    EXPORT_SYMBOL(bio_add_pc_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 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));
    }
    EXPORT_SYMBOL(bio_add_page);
    
    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 to_user, int from_user, int do_free_page)
    {
    	int ret = 0, i;
    	struct bio_vec *bvec;
    	int iov_idx = 0;
    	unsigned int iov_off = 0;
    
    	__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 (to_user)
    					ret = copy_to_user(iov_addr, bv_addr,
    							   bytes);
    
    				if (from_user)
    					ret = copy_from_user(bv_addr, iov_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, bio_data_dir(bio) == READ,
    				     0, bmd->is_our_pages);
    	bio_free_map_data(bmd);
    	bio_put(bio);
    	return ret;
    }
    EXPORT_SYMBOL(bio_uncopy_user);
    
    /**
     *	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)) ||
    	    (map_data && map_data->from_user)) {
    		ret = __bio_copy_iov(bio, bio->bi_io_vec, iov, iov_count, 0, 1, 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);
    }
    EXPORT_SYMBOL(bio_copy_user);
    
    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);
    }
    EXPORT_SYMBOL(bio_map_user);
    
    /**
     *	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);
    }
    EXPORT_SYMBOL(bio_unmap_user);
    
    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);
    }
    EXPORT_SYMBOL(bio_map_kern);
    
    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;
    }
    EXPORT_SYMBOL(bio_copy_kern);
    
    /*
     * 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);
    }
    EXPORT_SYMBOL(bio_endio);
    
    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);
    	}
    }
    EXPORT_SYMBOL(bio_pair_release);
    
    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;
    }
    EXPORT_SYMBOL(bio_split);
    
    /**
     *      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);
    
    	bioset_integrity_free(bs);
    	biovec_free_pools(bs);
    	bio_put_slab(bs);
    
    	kfree(bs);
    }
    EXPORT_SYMBOL(bioset_free);
    
    /**
     * 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 (bioset_integrity_create(bs, pool_size))
    		goto bad;
    
    	if (!biovec_create_pools(bs, pool_size))
    		return bs;
    
    bad:
    	bioset_free(bs);
    	return NULL;
    }
    EXPORT_SYMBOL(bioset_create);
    
    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\n");
    
    	bio_integrity_init();
    	biovec_init_slabs();
    
    	fs_bio_set = bioset_create(BIO_POOL_SIZE, 0);
    	if (!fs_bio_set)
    		panic("bio: can't allocate bios\n");
    
    	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\n");
    
    	return 0;
    }
    subsys_initcall(init_bio);