list debugging: use WARN() instead of BUG()

[linux-2.6/mini2440.git] / fs / 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/slab.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/mempool.h>
#include <linux/workqueue.h>
#include <linux/blktrace_api.h>
#include <scsi/sg.h>            /* for struct sg_iovec */

static struct kmem_cache *bio_slab __read_mostly;

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) }
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;

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

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
         */

        bvl = mempool_alloc(bs->bvec_pools[*idx], gfp_mask);
        if (bvl) {
                struct biovec_slab *bp = bvec_slabs + *idx;

                memset(bvl, 0, bp->nr_vecs * sizeof(struct bio_vec));
        }

        return bvl;
}

void bio_free(struct bio *bio, struct bio_set *bio_set)
{
        if (bio->bi_io_vec) {
                const int pool_idx = BIO_POOL_IDX(bio);

                BIO_BUG_ON(pool_idx >= BIOVEC_NR_POOLS);

                mempool_free(bio->bi_io_vec, bio_set->bvec_pools[pool_idx]);
        }

        if (bio_integrity(bio))
                bio_integrity_free(bio, bio_set);

        mempool_free(bio, bio_set->bio_pool);
}

/*
 * default destructor for a bio allocated with bio_alloc_bioset()
 */
static void bio_fs_destructor(struct bio *bio)
{
        bio_free(bio, fs_bio_set);
}

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

/**
 * bio_alloc_bioset - allocate a bio for I/O
 * @gfp_mask:   the GFP_ mask given to the slab allocator
 * @nr_iovecs:  number of iovecs to pre-allocate
 * @bs:         the bio_set to allocate from
 *
 * Description:
 *   bio_alloc_bioset will first try it's on 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.
 *
 *   allocate bio and iovecs from the memory pools specified by the
 *   bio_set structure.
 **/
struct bio *bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set *bs)
{
        struct bio *bio = mempool_alloc(bs->bio_pool, gfp_mask);

        if (likely(bio)) {
                struct bio_vec *bvl = NULL;

                bio_init(bio);
                if (likely(nr_iovecs)) {
                        unsigned long uninitialized_var(idx);

                        bvl = bvec_alloc_bs(gfp_mask, nr_iovecs, &idx, bs);
                        if (unlikely(!bvl)) {
                                mempool_free(bio, bs->bio_pool);
                                bio = NULL;
                                goto out;
                        }
                        bio->bi_flags |= idx << BIO_POOL_OFFSET;
                        bio->bi_max_vecs = bvec_slabs[idx].nr_vecs;
                }
                bio->bi_io_vec = bvl;
        }
out:
        return bio;
}

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;
}

void zero_fill_bio(struct bio *bio)
{
        unsigned long flags;
        struct bio_vec *bv;
        int i;

        bio_for_each_segment(bv, bio, i) {
                char *data = bvec_kmap_irq(bv, &flags);
                memset(data, 0, bv->bv_len);
                flush_dcache_page(bv->bv_page);
                bvec_kunmap_irq(data, &flags);
        }
}
EXPORT_SYMBOL(zero_fill_bio);

/**
 * bio_put - release a reference to a bio
 * @bio:   bio to release reference to
 *
 * Description:
 *   Put a reference to a &struct bio, either one you have gotten with
 *   bio_alloc or bio_get. The last put of a bio will free it.
 **/
void bio_put(struct bio *bio)
{
        BIO_BUG_ON(!atomic_read(&bio->bi_cnt));

        /*
         * last put frees it
         */
        if (atomic_dec_and_test(&bio->bi_cnt)) {
                bio->bi_next = NULL;
                bio->bi_destructor(bio);
        }
}

inline int bio_phys_segments(struct request_queue *q, struct bio *bio)
{
        if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
                blk_recount_segments(q, bio);

        return bio->bi_phys_segments;
}

inline int bio_hw_segments(struct request_queue *q, struct bio *bio)
{
        if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
                blk_recount_segments(q, bio);

        return bio->bi_hw_segments;
}

/**
 *      __bio_clone     -       clone a bio
 *      @bio: destination bio
 *      @bio_src: bio to clone
 *
 *      Clone a &bio. Caller will own the returned bio, but not
 *      the actual data it points to. Reference count of returned
 *      bio will be one.
 */
void __bio_clone(struct bio *bio, struct bio *bio_src)
{
        memcpy(bio->bi_io_vec, bio_src->bi_io_vec,
                bio_src->bi_max_vecs * sizeof(struct bio_vec));

        /*
         * most users will be overriding ->bi_bdev with a new target,
         * so we don't set nor calculate new physical/hw segment counts here
         */
        bio->bi_sector = bio_src->bi_sector;
        bio->bi_bdev = bio_src->bi_bdev;
        bio->bi_flags |= 1 << BIO_CLONED;
        bio->bi_rw = bio_src->bi_rw;
        bio->bi_vcnt = bio_src->bi_vcnt;
        bio->bi_size = bio_src->bi_size;
        bio->bi_idx = bio_src->bi_idx;
}

/**
 *      bio_clone       -       clone a bio
 *      @bio: bio to clone
 *      @gfp_mask: allocation priority
 *
 *      Like __bio_clone, only also allocates the returned bio
 */
struct bio *bio_clone(struct bio *bio, gfp_t gfp_mask)
{
        struct bio *b = bio_alloc_bioset(gfp_mask, bio->bi_max_vecs, fs_bio_set);

        if (!b)
                return NULL;

        b->bi_destructor = bio_fs_destructor;
        __bio_clone(b, bio);

        if (bio_integrity(bio)) {
                int ret;

                ret = bio_integrity_clone(b, bio, fs_bio_set);

                if (ret < 0)
                        return NULL;
        }

        return b;
}

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

        nr_pages = ((q->max_sectors << 9) + PAGE_SIZE - 1) >> PAGE_SHIFT;
        if (nr_pages > q->max_phys_segments)
                nr_pages = q->max_phys_segments;
        if (nr_pages > q->max_hw_segments)
                nr_pages = q->max_hw_segments;

        return nr_pages;
}

static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page
                          *page, unsigned int len, unsigned int offset,
                          unsigned short max_sectors)
{
        int retried_segments = 0;
        struct bio_vec *bvec;

        /*
         * cloned bio must not modify vec list
         */
        if (unlikely(bio_flagged(bio, BIO_CLONED)))
                return 0;

        if (((bio->bi_size + len) >> 9) > max_sectors)
                return 0;

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

                if (page == prev->bv_page &&
                    offset == prev->bv_offset + prev->bv_len) {
                        prev->bv_len += len;

                        if (q->merge_bvec_fn) {
                                struct bvec_merge_data bvm = {
                                        .bi_bdev = bio->bi_bdev,
                                        .bi_sector = bio->bi_sector,
                                        .bi_size = bio->bi_size,
                                        .bi_rw = bio->bi_rw,
                                };

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

                        goto done;
                }
        }

        if (bio->bi_vcnt >= bio->bi_max_vecs)
                return 0;

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

        while (bio->bi_phys_segments >= q->max_phys_segments
               || bio->bi_hw_segments >= q->max_hw_segments
               || BIOVEC_VIRT_OVERSIZE(bio->bi_size)) {

                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) ||
            BIOVEC_VIRT_MERGEABLE(bvec-1, bvec)))
                bio->bi_flags &= ~(1 << BIO_SEG_VALID);

        bio->bi_vcnt++;
        bio->bi_phys_segments++;
        bio->bi_hw_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, q->max_hw_sectors);
}

/**
 *      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, q->max_sectors);
}

struct bio_map_data {
        struct bio_vec *iovecs;
        int nr_sgvecs;
        struct sg_iovec *sgvecs;
};

static void bio_set_map_data(struct bio_map_data *bmd, struct bio *bio,
                             struct sg_iovec *iov, int iov_count)
{
        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;
        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)
{
        struct bio_map_data *bmd = kmalloc(sizeof(*bmd), GFP_KERNEL);

        if (!bmd)
                return NULL;

        bmd->iovecs = kmalloc(sizeof(struct bio_vec) * nr_segs, GFP_KERNEL);
        if (!bmd->iovecs) {
                kfree(bmd);
                return NULL;
        }

        bmd->sgvecs = kmalloc(sizeof(struct sg_iovec) * iov_count, GFP_KERNEL);
        if (bmd->sgvecs)
                return bmd;

        kfree(bmd->iovecs);
        kfree(bmd);
        return NULL;
}

static int __bio_copy_iov(struct bio *bio, struct sg_iovec *iov, int iov_count,
                          int uncopy)
{
        int ret = 0, i;
        struct bio_vec *bvec;
        int iov_idx = 0;
        unsigned int iov_off = 0;
        int read = bio_data_dir(bio) == READ;

        __bio_for_each_segment(bvec, bio, i, 0) {
                char *bv_addr = page_address(bvec->bv_page);
                unsigned int bv_len = bvec->bv_len;

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

                        bytes = min_t(unsigned int,
                                      iov[iov_idx].iov_len - iov_off, bv_len);
                        iov_addr = iov[iov_idx].iov_base + iov_off;

                        if (!ret) {
                                if (!read && !uncopy)
                                        ret = copy_from_user(bv_addr, iov_addr,
                                                             bytes);
                                if (read && uncopy)
                                        ret = copy_to_user(iov_addr, bv_addr,
                                                           bytes);

                                if (ret)
                                        ret = -EFAULT;
                        }

                        bv_len -= bytes;
                        bv_addr += bytes;
                        iov_addr += bytes;
                        iov_off += bytes;

                        if (iov[iov_idx].iov_len == iov_off) {
                                iov_idx++;
                                iov_off = 0;
                        }
                }

                if (uncopy)
                        __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;

        ret = __bio_copy_iov(bio, bmd->sgvecs, bmd->nr_sgvecs, 1);

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

/**
 *      bio_copy_user_iov       -       copy user data to bio
 *      @q: destination block queue
 *      @iov:   the iovec.
 *      @iov_count: number of elements in the iovec
 *      @write_to_vm: bool indicating writing to pages or not
 *
 *      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 sg_iovec *iov,
                              int iov_count, int write_to_vm)
{
        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;

        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;
        }

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

        ret = -ENOMEM;
        bio = bio_alloc(GFP_KERNEL, nr_pages);
        if (!bio)
                goto out_bmd;

        bio->bi_rw |= (!write_to_vm << BIO_RW);

        ret = 0;
        while (len) {
                unsigned int bytes = PAGE_SIZE;

                if (bytes > len)
                        bytes = len;

                page = alloc_page(q->bounce_gfp | GFP_KERNEL);
                if (!page) {
                        ret = -ENOMEM;
                        break;
                }

                if (bio_add_pc_page(q, bio, page, bytes, 0) < bytes)
                        break;

                len -= bytes;
        }

        if (ret)
                goto cleanup;

        /*
         * success
         */
        if (!write_to_vm) {
                ret = __bio_copy_iov(bio, iov, iov_count, 0);
                if (ret)
                        goto cleanup;
        }

        bio_set_map_data(bmd, bio, iov, iov_count);
        return bio;
cleanup:
        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
 *      @uaddr: start of user address
 *      @len: length in bytes
 *      @write_to_vm: bool indicating writing to pages or not
 *
 *      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, unsigned long uaddr,
                          unsigned int len, int write_to_vm)
{
        struct sg_iovec iov;

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

        return bio_copy_user_iov(q, &iov, 1, write_to_vm);
}

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)
{
        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_alloc(GFP_KERNEL, nr_pages);
        if (!bio)
                return ERR_PTR(-ENOMEM);

        ret = -ENOMEM;
        pages = kcalloc(nr_pages, sizeof(struct page *), GFP_KERNEL);
        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;
                
                down_read(&current->mm->mmap_sem);
                ret = get_user_pages(current, current->mm, uaddr,
                                     local_nr_pages,
                                     write_to_vm, 0, &pages[cur_page], NULL);
                up_read(&current->mm->mmap_sem);

                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
 *
 *      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)
{
        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);
}

/**
 *      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
 *
 *      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)
{
        struct bio *bio;

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

        if (IS_ERR(bio))
                return bio;

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

        return bio;
}

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

        /*
         * make sure we dirty pages we wrote to
         */
        __bio_for_each_segment(bvec, bio, i, 0) {
                if (bio_data_dir(bio) == READ)
                        set_page_dirty_lock(bvec->bv_page);

                page_cache_release(bvec->bv_page);
        }

        bio_put(bio);
}

/**
 *      bio_unmap_user  -       unmap a bio
 *      @bio:           the bio being unmapped
 *
 *      Unmap a bio previously mapped by bio_map_user(). Must be called with
 *      a process context.
 *
 *      bio_unmap_user() may sleep.
 */
void bio_unmap_user(struct bio *bio)
{
        __bio_unmap_user(bio);
        bio_put(bio);
}

static void bio_map_kern_endio(struct bio *bio, int err)
{
        bio_put(bio);
}


static struct bio *__bio_map_kern(struct request_queue *q, void *data,
                                  unsigned int len, gfp_t gfp_mask)
{
        unsigned long kaddr = (unsigned long)data;
        unsigned long end = (kaddr + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
        unsigned long start = kaddr >> PAGE_SHIFT;
        const int nr_pages = end - start;
        int offset, i;
        struct bio *bio;

        bio = bio_alloc(gfp_mask, nr_pages);
        if (!bio)
                return ERR_PTR(-ENOMEM);

        offset = offset_in_page(kaddr);
        for (i = 0; i < nr_pages; i++) {
                unsigned int bytes = PAGE_SIZE - offset;

                if (len <= 0)
                        break;

                if (bytes > len)
                        bytes = len;

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

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

        bio->bi_end_io = bio_map_kern_endio;
        return bio;
}

/**
 *      bio_map_kern    -       map kernel address into bio
 *      @q: the struct request_queue for the bio
 *      @data: pointer to buffer to map
 *      @len: length in bytes
 *      @gfp_mask: allocation flags for bio allocation
 *
 *      Map the kernel address into a bio suitable for io to a block
 *      device. Returns an error pointer in case of error.
 */
struct bio *bio_map_kern(struct request_queue *q, void *data, unsigned int len,
                         gfp_t gfp_mask)
{
        struct bio *bio;

        bio = __bio_map_kern(q, data, len, gfp_mask);
        if (IS_ERR(bio))
                return bio;

        if (bio->bi_size == len)
                return bio;

        /*
         * Don't support partial mappings.
         */
        bio_put(bio);
        return ERR_PTR(-EINVAL);
}

static void bio_copy_kern_endio(struct bio *bio, int err)
{
        struct bio_vec *bvec;
        const int read = bio_data_dir(bio) == READ;
        char *p = bio->bi_private;
        int i;

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

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

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

        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)
{
        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;
        struct bio *bio;
        struct bio_vec *bvec;
        int i, ret;

        bio = bio_alloc(gfp_mask, nr_pages);
        if (!bio)
                return ERR_PTR(-ENOMEM);

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

                if (bytes > len)
                        bytes = len;

                page = alloc_page(q->bounce_gfp | gfp_mask);
                if (!page) {
                        ret = -ENOMEM;
                        goto cleanup;
                }

                if (bio_add_pc_page(q, bio, page, bytes, 0) < bytes) {
                        ret = -EINVAL;
                        goto cleanup;
                }

                len -= bytes;
        }

        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_private = data;
        bio->bi_end_io = bio_copy_kern_endio;
        return bio;
cleanup:
        bio_for_each_segment(bvec, bio, i)
                __free_page(bvec->bv_page);

        bio_put(bio);

        return ERR_PTR(ret);
}

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

/*
 * bio_set_pages_dirty() will mark all the bio's pages as dirty.
 */
void bio_set_pages_dirty(struct bio *bio)
{
        struct bio_vec *bvec = bio->bi_io_vec;
        int i;

        for (i = 0; i < bio->bi_vcnt; i++) {
                struct page *page = bvec[i].bv_page;

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

static void bio_release_pages(struct bio *bio)
{
        struct bio_vec *bvec = bio->bi_io_vec;
        int i;

        for (i = 0; i < bio->bi_vcnt; i++) {
                struct page *page = bvec[i].bv_page;

                if (page)
                        put_page(page);
        }
}

/*
 * bio_check_pages_dirty() will check that all the BIO's pages are still dirty.
 * If they are, then fine.  If, however, some pages are clean then they must
 * have been written out during the direct-IO read.  So we take another ref on
 * the BIO and the offending pages and re-dirty the pages in process context.
 *
 * It is expected that bio_check_pages_dirty() will wholly own the BIO from
 * here on.  It will run one page_cache_release() against each page and will
 * run one bio_put() against the BIO.
 */

static void bio_dirty_fn(struct work_struct *work);

static DECLARE_WORK(bio_dirty_work, bio_dirty_fn);
static DEFINE_SPINLOCK(bio_dirty_lock);
static struct bio *bio_dirty_list;

/*
 * This runs in process context
 */
static void bio_dirty_fn(struct work_struct *work)
{
        unsigned long flags;
        struct bio *bio;

        spin_lock_irqsave(&bio_dirty_lock, flags);
        bio = bio_dirty_list;
        bio_dirty_list = NULL;
        spin_unlock_irqrestore(&bio_dirty_lock, flags);

        while (bio) {
                struct bio *next = bio->bi_private;

                bio_set_pages_dirty(bio);
                bio_release_pages(bio);
                bio_put(bio);
                bio = next;
        }
}

void bio_check_pages_dirty(struct bio *bio)
{
        struct bio_vec *bvec = bio->bi_io_vec;
        int nr_clean_pages = 0;
        int i;

        for (i = 0; i < bio->bi_vcnt; i++) {
                struct page *page = bvec[i].bv_page;

                if (PageDirty(page) || PageCompound(page)) {
                        page_cache_release(page);
                        bvec[i].bv_page = NULL;
                } else {
                        nr_clean_pages++;
                }
        }

        if (nr_clean_pages) {
                unsigned long flags;

                spin_lock_irqsave(&bio_dirty_lock, flags);
                bio->bi_private = bio_dirty_list;
                bio_dirty_list = bio;
                spin_unlock_irqrestore(&bio_dirty_lock, flags);
                schedule_work(&bio_dirty_work);
        } else {
                bio_put(bio);
        }
}

/**
 * bio_endio - end I/O on a bio
 * @bio:        bio
 * @error:      error, if any
 *
 * Description:
 *   bio_endio() will end I/O on the whole bio. bio_endio() is the
 *   preferred way to end I/O on a bio, it takes care of clearing
 *   BIO_UPTODATE on error. @error is 0 on success, and and one of the
 *   established -Exxxx (-EIO, for instance) error values in case
 *   something went wrong. Noone should call bi_end_io() directly on a
 *   bio unless they own it and thus know that it has an end_io
 *   function.
 **/
void bio_endio(struct bio *bio, int error)
{
        if (error)
                clear_bit(BIO_UPTODATE, &bio->bi_flags);
        else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
                error = -EIO;

        if (bio->bi_end_io)
                bio->bi_end_io(bio, error);
}

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

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

static void bio_pair_end_1(struct bio *bi, int err)
{
        struct bio_pair *bp = container_of(bi, struct bio_pair, bio1);

        if (err)
                bp->error = err;

        bio_pair_release(bp);
}

static void bio_pair_end_2(struct bio *bi, int err)
{
        struct bio_pair *bp = container_of(bi, struct bio_pair, bio2);

        if (err)
                bp->error = err;

        bio_pair_release(bp);
}

/*
 * split a bio - only worry about a bio with a single page
 * in it's iovec
 */
struct bio_pair *bio_split(struct bio *bi, mempool_t *pool, int first_sectors)
{
        struct bio_pair *bp = mempool_alloc(pool, GFP_NOIO);

        if (!bp)
                return bp;

        blk_add_trace_pdu_int(bdev_get_queue(bi->bi_bdev), BLK_TA_SPLIT, 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 = pool;

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

        return bp;
}


/*
 * 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)
{
        int i;

        for (i = 0; i < BIOVEC_NR_POOLS; i++) {
                struct biovec_slab *bp = bvec_slabs + i;
                mempool_t **bvp = bs->bvec_pools + i;

                *bvp = mempool_create_slab_pool(pool_entries, bp->slab);
                if (!*bvp)
                        return -ENOMEM;
        }
        return 0;
}

static void biovec_free_pools(struct bio_set *bs)
{
        int i;

        for (i = 0; i < BIOVEC_NR_POOLS; i++) {
                mempool_t *bvp = bs->bvec_pools[i];

                if (bvp)
                        mempool_destroy(bvp);
        }

}

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

        bioset_integrity_free(bs);
        biovec_free_pools(bs);

        kfree(bs);
}

struct bio_set *bioset_create(int bio_pool_size, int bvec_pool_size)
{
        struct bio_set *bs = kzalloc(sizeof(*bs), GFP_KERNEL);

        if (!bs)
                return NULL;

        bs->bio_pool = mempool_create_slab_pool(bio_pool_size, bio_slab);
        if (!bs->bio_pool)
                goto bad;

        if (bioset_integrity_create(bs, bio_pool_size))
                goto bad;

        if (!biovec_create_pools(bs, bvec_pool_size))
                return bs;

bad:
        bioset_free(bs);
        return NULL;
}

static void __init biovec_init_slabs(void)
{
        int i;

        for (i = 0; i < BIOVEC_NR_POOLS; i++) {
                int size;
                struct biovec_slab *bvs = bvec_slabs + i;

                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 = KMEM_CACHE(bio, SLAB_HWCACHE_ALIGN|SLAB_PANIC);

        bio_integrity_init_slab();
        biovec_init_slabs();

        fs_bio_set = bioset_create(BIO_POOL_SIZE, 2);
        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);

EXPORT_SYMBOL(bio_alloc);
EXPORT_SYMBOL(bio_put);
EXPORT_SYMBOL(bio_free);
EXPORT_SYMBOL(bio_endio);
EXPORT_SYMBOL(bio_init);
EXPORT_SYMBOL(__bio_clone);
EXPORT_SYMBOL(bio_clone);
EXPORT_SYMBOL(bio_phys_segments);
EXPORT_SYMBOL(bio_hw_segments);
EXPORT_SYMBOL(bio_add_page);
EXPORT_SYMBOL(bio_add_pc_page);
EXPORT_SYMBOL(bio_get_nr_vecs);
EXPORT_SYMBOL(bio_map_user);
EXPORT_SYMBOL(bio_unmap_user);
EXPORT_SYMBOL(bio_map_kern);
EXPORT_SYMBOL(bio_copy_kern);
EXPORT_SYMBOL(bio_pair_release);
EXPORT_SYMBOL(bio_split);
EXPORT_SYMBOL(bio_split_pool);
EXPORT_SYMBOL(bio_copy_user);
EXPORT_SYMBOL(bio_uncopy_user);
EXPORT_SYMBOL(bioset_create);
EXPORT_SYMBOL(bioset_free);
EXPORT_SYMBOL(bio_alloc_bioset);