Merge tag 'hwspinlock-3.17' of git://git.kernel.org/pub/scm/linux/kernel/git/ohad...

[mirror_ubuntu-zesty-kernel.git] / block / bio.c

/*
 * 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 <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

/*
 * 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) }
static 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;
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!\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(mempool_t *pool, struct bio_vec *bv, unsigned int idx)
{
        BIO_BUG_ON(idx >= BIOVEC_NR_POOLS);

        if (idx == BIOVEC_MAX_IDX)
                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 == BIOVEC_MAX_IDX) {
fallback:
                bvl = mempool_alloc(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;
}

static void __bio_free(struct bio *bio)
{
        bio_disassociate_task(bio);

        if (bio_integrity(bio))
                bio_integrity_free(bio);
}

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

        __bio_free(bio);

        if (bs) {
                if (bio_flagged(bio, BIO_OWNS_VEC))
                        bvec_free(bs->bvec_pool, bio->bi_io_vec, BIO_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);
        }
}

void bio_init(struct bio *bio)
{
        memset(bio, 0, sizeof(*bio));
        bio->bi_flags = 1 << BIO_UPTODATE;
        atomic_set(&bio->bi_remaining, 1);
        atomic_set(&bio->bi_cnt, 1);
}
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_free(bio);

        memset(bio, 0, BIO_RESET_BYTES);
        bio->bi_flags = flags|(1 << BIO_UPTODATE);
        atomic_set(&bio->bi_remaining, 1);
}
EXPORT_SYMBOL(bio_reset);

static void bio_chain_endio(struct bio *bio, int error)
{
        bio_endio(bio->bi_private, error);
        bio_put(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;
        atomic_inc(&parent->bi_remaining);
}
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;

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

        *current->bio_list = 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_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 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, int nr_iovecs, struct bio_set *bs)
{
        gfp_t saved_gfp = gfp_mask;
        unsigned front_pad;
        unsigned inline_vecs;
        unsigned long idx = BIO_POOL_NONE;
        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 {
                /*
                 * 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_WAIT; 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))
                        gfp_mask &= ~__GFP_WAIT;

                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);

        if (nr_iovecs > inline_vecs) {
                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 |= 1 << BIO_OWNS_VEC;
        } else if (nr_iovecs) {
                bvl = bio->bi_inline_vecs;
        }

        bio->bi_pool = bs;
        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);

void zero_fill_bio(struct bio *bio)
{
        unsigned long flags;
        struct bio_vec bv;
        struct bvec_iter iter;

        bio_for_each_segment(bv, bio, iter) {
                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_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 && BIO_POOL_IDX(bio) != BIO_POOL_NONE);

        /*
         * 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_bdev = bio_src->bi_bdev;
        bio->bi_flags |= 1 << BIO_CLONED;
        bio->bi_rw = bio_src->bi_rw;
        bio->bi_iter = bio_src->bi_iter;
        bio->bi_io_vec = bio_src->bi_io_vec;
}
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_clone_bioset - clone a bio
 *      @bio_src: bio to clone
 *      @gfp_mask: allocation priority
 *      @bs: bio_set to allocate from
 *
 *      Clone bio. Caller will own the returned bio, but not the actual data it
 *      points to. Reference count of returned bio will be one.
 */
struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
                             struct bio_set *bs)
{
        struct bvec_iter iter;
        struct bio_vec bv;
        struct bio *bio;

        /*
         * Pre immutable biovecs, __bio_clone() used to just do a memcpy from
         * bio_src->bi_io_vec to bio->bi_io_vec.
         *
         * We can't do that anymore, because:
         *
         *  - The point of cloning the biovec is to produce a bio with a biovec
         *    the caller can modify: bi_idx and bi_bvec_done should be 0.
         *
         *  - The original bio could've had more than BIO_MAX_PAGES biovecs; if
         *    we tried to clone the whole thing bio_alloc_bioset() would fail.
         *    But the clone should succeed as long as the number of biovecs we
         *    actually need to allocate is fewer than BIO_MAX_PAGES.
         *
         *  - Lastly, bi_vcnt should not be looked at or relied upon by code
         *    that does not own the bio - reason being drivers don't use it for
         *    iterating over the biovec anymore, so expecting it to be kept up
         *    to date (i.e. for clones that share the parent biovec) is just
         *    asking for trouble and would force extra work on
         *    __bio_clone_fast() anyways.
         */

        bio = bio_alloc_bioset(gfp_mask, bio_segments(bio_src), bs);
        if (!bio)
                return NULL;

        bio->bi_bdev            = bio_src->bi_bdev;
        bio->bi_rw              = bio_src->bi_rw;
        bio->bi_iter.bi_sector  = bio_src->bi_iter.bi_sector;
        bio->bi_iter.bi_size    = bio_src->bi_iter.bi_size;

        if (bio->bi_rw & REQ_DISCARD)
                goto integrity_clone;

        if (bio->bi_rw & REQ_WRITE_SAME) {
                bio->bi_io_vec[bio->bi_vcnt++] = bio_src->bi_io_vec[0];
                goto integrity_clone;
        }

        bio_for_each_segment(bv, bio_src, iter)
                bio->bi_io_vec[bio->bi_vcnt++] = bv;

integrity_clone:
        if (bio_integrity(bio_src)) {
                int ret;

                ret = bio_integrity_clone(bio, bio_src, gfp_mask);
                if (ret < 0) {
                        bio_put(bio);
                        return NULL;
                }
        }

        return bio;
}
EXPORT_SYMBOL(bio_clone_bioset);

/**
 *      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 = min_t(unsigned,
                     queue_max_segments(q),
                     queue_max_sectors(q) / (PAGE_SIZE >> 9) + 1);

        return min_t(unsigned, nr_pages, BIO_MAX_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 int 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_iter.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) {
                        unsigned int prev_bv_len = prev->bv_len;
                        prev->bv_len += len;

                        if (q->merge_bvec_fn) {
                                struct bvec_merge_data bvm = {
                                        /* prev_bvec is already charged in
                                           bi_size, discharge it in order to
                                           simulate merging updated prev_bvec
                                           as new bvec. */
                                        .bi_bdev = bio->bi_bdev,
                                        .bi_sector = bio->bi_iter.bi_sector,
                                        .bi_size = bio->bi_iter.bi_size -
                                                prev_bv_len,
                                        .bi_rw = bio->bi_rw,
                                };

                                if (q->merge_bvec_fn(q, &bvm, prev) < prev->bv_len) {
                                        prev->bv_len -= len;
                                        return 0;
                                }
                        }

                        goto done;
                }

                /*
                 * If the queue doesn't support SG gaps and adding this
                 * offset would create a gap, disallow it.
                 */
                if (q->queue_flags & (1 << QUEUE_FLAG_SG_GAPS) &&
                    bvec_gap_to_prev(prev, offset))
                        return 0;
        }

        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_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_iter.bi_sector,
                        .bi_size = bio->bi_iter.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) < bvec->bv_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_iter.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 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)
{
        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 up to 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);
        unsigned int max_sectors;

        max_sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
        if ((max_sectors < (len >> 9)) && !bio->bi_iter.bi_size)
                max_sectors = len >> 9;

        return __bio_add_page(q, bio, page, len, offset, max_sectors);
}
EXPORT_SYMBOL(bio_add_page);

struct submit_bio_ret {
        struct completion event;
        int error;
};

static void submit_bio_wait_endio(struct bio *bio, int error)
{
        struct submit_bio_ret *ret = bio->bi_private;

        ret->error = error;
        complete(&ret->event);
}

/**
 * submit_bio_wait - submit a bio, and wait until it completes
 * @rw: whether to %READ or %WRITE, or maybe to %READA (read ahead)
 * @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.
 */
int submit_bio_wait(int rw, struct bio *bio)
{
        struct submit_bio_ret ret;

        rw |= REQ_SYNC;
        init_completion(&ret.event);
        bio->bi_private = &ret;
        bio->bi_end_io = submit_bio_wait_endio;
        submit_bio(rw, bio);
        wait_for_completion(&ret.event);

        return ret.error;
}
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);

/**
 * bio_alloc_pages - allocates a single page for each bvec in a bio
 * @bio: bio to allocate pages for
 * @gfp_mask: flags for allocation
 *
 * Allocates pages up to @bio->bi_vcnt.
 *
 * Returns 0 on success, -ENOMEM on failure. On failure, any allocated pages are
 * freed.
 */
int bio_alloc_pages(struct bio *bio, gfp_t gfp_mask)
{
        int i;
        struct bio_vec *bv;

        bio_for_each_segment_all(bv, bio, i) {
                bv->bv_page = alloc_page(gfp_mask);
                if (!bv->bv_page) {
                        while (--bv >= bio->bi_io_vec)
                                __free_page(bv->bv_page);
                        return -ENOMEM;
                }
        }

        return 0;
}
EXPORT_SYMBOL(bio_alloc_pages);

/**
 * bio_copy_data - copy contents of data buffers from one chain of bios to
 * another
 * @src: source bio list
 * @dst: destination bio list
 *
 * If @src and @dst are single bios, bi_next must be NULL - otherwise, treats
 * @src and @dst as linked lists of bios.
 *
 * 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, dst_iter;
        struct bio_vec src_bv, dst_bv;
        void *src_p, *dst_p;
        unsigned bytes;

        src_iter = src->bi_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;
                }

                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);

                bio_advance_iter(src, &src_iter, bytes);
                bio_advance_iter(dst, &dst_iter, bytes);
        }
}
EXPORT_SYMBOL(bio_copy_data);

struct bio_map_data {
        int nr_sgvecs;
        int is_our_pages;
        struct sg_iovec sgvecs[];
};

static void bio_set_map_data(struct bio_map_data *bmd, struct bio *bio,
                             const struct sg_iovec *iov, int iov_count,
                             int is_our_pages)
{
        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 struct bio_map_data *bio_alloc_map_data(unsigned int iov_count,
                                               gfp_t gfp_mask)
{
        if (iov_count > UIO_MAXIOV)
                return NULL;

        return kmalloc(sizeof(struct bio_map_data) +
                       sizeof(struct sg_iovec) * iov_count, gfp_mask);
}

static int __bio_copy_iov(struct bio *bio, const 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_all(bvec, bio, i) {
                char *bv_addr = page_address(bvec->bv_page);
                unsigned int bv_len = bvec->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;
        struct bio_vec *bvec;
        int ret = 0, i;

        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.
                 */
                if (current->mm)
                        ret = __bio_copy_iov(bio, bmd->sgvecs, bmd->nr_sgvecs,
                                             bio_data_dir(bio) == READ,
                                             0, bmd->is_our_pages);
                else if (bmd->is_our_pages)
                        bio_for_each_segment_all(bvec, bio, i)
                                __free_page(bvec->bv_page);
        }
        kfree(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,
                              const 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;

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

                nr_pages += end - start;
                len += iov[i].iov_len;
        }

        if (offset)
                nr_pages++;

        bmd = bio_alloc_map_data(iov_count, gfp_mask);
        if (!bmd)
                return ERR_PTR(-ENOMEM);

        ret = -ENOMEM;
        bio = bio_kmalloc(gfp_mask, nr_pages);
        if (!bio)
                goto out_bmd;

        if (!write_to_vm)
                bio->bi_rw |= REQ_WRITE;

        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, 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_all(bvec, bio, i)
                        __free_page(bvec->bv_page);

        bio_put(bio);
out_bmd:
        kfree(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,
                                      const 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;

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

                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 |= REQ_WRITE;

        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,
                             const 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_all(bvec, bio, i) {
                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_iter.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_all(bvec, bio, i) {
                char *addr = page_address(bvec->bv_page);

                if (read)
                        memcpy(p, addr, bvec->bv_len);

                __free_page(bvec->bv_page);
                p += bvec->bv_len;
        }

        kfree(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_all(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, 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) {
                struct page *page = bvec->bv_page;

                if (page && !PageCompound(page))
                        set_page_dirty_lock(page);
        }
}

static void bio_release_pages(struct bio *bio)
{
        struct bio_vec *bvec;
        int i;

        bio_for_each_segment_all(bvec, bio, i) {
                struct page *page = bvec->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;
        int nr_clean_pages = 0;
        int i;

        bio_for_each_segment_all(bvec, bio, i) {
                struct page *page = bvec->bv_page;

                if (PageDirty(page) || PageCompound(page)) {
                        page_cache_release(page);
                        bvec->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);
        }
}

#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

/**
 * 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. 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.
 **/
void bio_endio(struct bio *bio, int error)
{
        while (bio) {
                BUG_ON(atomic_read(&bio->bi_remaining) <= 0);

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

                if (!atomic_dec_and_test(&bio->bi_remaining))
                        return;

                /*
                 * 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) {
                        struct bio *parent = bio->bi_private;
                        bio_put(bio);
                        bio = parent;
                } else {
                        if (bio->bi_end_io)
                                bio->bi_end_io(bio, error);
                        bio = NULL;
                }
        }
}
EXPORT_SYMBOL(bio_endio);

/**
 * bio_endio_nodec - end I/O on a bio, without decrementing bi_remaining
 * @bio:        bio
 * @error:      error, if any
 *
 * For code that has saved and restored bi_end_io; thing hard before using this
 * function, probably you should've cloned the entire bio.
 **/
void bio_endio_nodec(struct bio *bio, int error)
{
        atomic_inc(&bio->bi_remaining);
        bio_endio(bio, error);
}
EXPORT_SYMBOL(bio_endio_nodec);

/**
 * bio_split - split a bio
 * @bio:        bio to split
 * @sectors:    number of sectors to split from the front of @bio
 * @gfp:        gfp mask
 * @bs:         bio set to allocate from
 *
 * Allocates and returns a new bio which represents @sectors from the start of
 * @bio, and updates @bio to represent the remaining sectors.
 *
 * The newly allocated bio will point to @bio's bi_io_vec; it is the caller's
 * responsibility to ensure that @bio is not freed before the split.
 */
struct bio *bio_split(struct bio *bio, int sectors,
                      gfp_t gfp, struct bio_set *bs)
{
        struct bio *split = NULL;

        BUG_ON(sectors <= 0);
        BUG_ON(sectors >= bio_sectors(bio));

        split = bio_clone_fast(bio, gfp, bs);
        if (!split)
                return NULL;

        split->bi_iter.bi_size = sectors << 9;

        if (bio_integrity(split))
                bio_integrity_trim(split, 0, sectors);

        bio_advance(bio, split->bi_iter.bi_size);

        return split;
}
EXPORT_SYMBOL(bio_split);

/**
 * bio_trim - trim a bio
 * @bio:        bio to trim
 * @offset:     number of sectors to trim from the front of @bio
 * @size:       size we want to trim @bio to, in sectors
 */
void bio_trim(struct bio *bio, int offset, int size)
{
        /* 'bio' is a cloned bio which we need to trim to match
         * the given offset and size.
         */

        size <<= 9;
        if (offset == 0 && size == bio->bi_iter.bi_size)
                return;

        clear_bit(BIO_SEG_VALID, &bio->bi_flags);

        bio_advance(bio, offset << 9);

        bio->bi_iter.bi_size = size;
}
EXPORT_SYMBOL_GPL(bio_trim);

/*
 * create memory pools for biovec's in a bio_set.
 * use the global biovec slabs created for general use.
 */
mempool_t *biovec_create_pool(int pool_entries)
{
        struct biovec_slab *bp = bvec_slabs + BIOVEC_MAX_IDX;

        return mempool_create_slab_pool(pool_entries, bp->slab);
}

void bioset_free(struct bio_set *bs)
{
        if (bs->rescue_workqueue)
                destroy_workqueue(bs->rescue_workqueue);

        if (bs->bio_pool)
                mempool_destroy(bs->bio_pool);

        if (bs->bvec_pool)
                mempool_destroy(bs->bvec_pool);

        bioset_integrity_free(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;

        spin_lock_init(&bs->rescue_lock);
        bio_list_init(&bs->rescue_list);
        INIT_WORK(&bs->rescue_work, bio_alloc_rescue);

        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;

        bs->bvec_pool = biovec_create_pool(pool_size);
        if (!bs->bvec_pool)
                goto bad;

        bs->rescue_workqueue = alloc_workqueue("bioset", WQ_MEM_RECLAIM, 0);
        if (!bs->rescue_workqueue)
                goto bad;

        return bs;
bad:
        bioset_free(bs);
        return NULL;
}
EXPORT_SYMBOL(bioset_create);

#ifdef CONFIG_BLK_CGROUP
/**
 * bio_associate_current - associate a bio with %current
 * @bio: target bio
 *
 * Associate @bio with %current if it hasn't been associated yet.  Block
 * layer will treat @bio as if it were issued by %current no matter which
 * task actually issues it.
 *
 * This function takes an extra reference of @task's io_context and blkcg
 * which will be put when @bio is released.  The caller must own @bio,
 * ensure %current->io_context exists, and is responsible for synchronizing
 * calls to this function.
 */
int bio_associate_current(struct bio *bio)
{
        struct io_context *ioc;
        struct cgroup_subsys_state *css;

        if (bio->bi_ioc)
                return -EBUSY;

        ioc = current->io_context;
        if (!ioc)
                return -ENOENT;

        /* acquire active ref on @ioc and associate */
        get_io_context_active(ioc);
        bio->bi_ioc = ioc;

        /* associate blkcg if exists */
        rcu_read_lock();
        css = task_css(current, blkio_cgrp_id);
        if (css && css_tryget_online(css))
                bio->bi_css = css;
        rcu_read_unlock();

        return 0;
}

/**
 * bio_disassociate_task - undo bio_associate_current()
 * @bio: target bio
 */
void bio_disassociate_task(struct bio *bio)
{
        if (bio->bi_ioc) {
                put_io_context(bio->bi_ioc);
                bio->bi_ioc = NULL;
        }
        if (bio->bi_css) {
                css_put(bio->bi_css);
                bio->bi_css = NULL;
        }
}

#endif /* CONFIG_BLK_CGROUP */

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;

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

                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");

        if (bioset_integrity_create(fs_bio_set, BIO_POOL_SIZE))
                panic("bio: can't create integrity pool\n");

        return 0;
}
subsys_initcall(init_bio);