Merge branch 'from-miklos' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

[thirdparty/linux.git] / block / bio.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2001 Jens Axboe <axboe@kernel.dk>
 */
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/uio.h>
#include <linux/iocontext.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/mempool.h>
#include <linux/workqueue.h>
#include <linux/cgroup.h>
#include <linux/blk-cgroup.h>
#include <linux/highmem.h>
#include <linux/sched/sysctl.h>

#include <trace/events/block.h>
#include "blk.h"
#include "blk-rq-qos.h"

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

/*
 * if you change this list, also change bvec_alloc or things will
 * break badly! cannot be bigger than what you can fit into an
 * unsigned short
 */
#define BV(x, n) { .nr_vecs = x, .name = "biovec-"#n }
static struct biovec_slab bvec_slabs[BVEC_POOL_NR] __read_mostly = {
        BV(1, 1), BV(4, 4), BV(16, 16), BV(64, 64), BV(128, 128), BV(BIO_MAX_PAGES, max),
};
#undef BV

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

/*
 * Our slab pool management
 */
struct bio_slab {
        struct kmem_cache *slab;
        unsigned int slab_ref;
        unsigned int slab_size;
        char name[8];
};
static DEFINE_MUTEX(bio_slab_lock);
static struct bio_slab *bio_slabs;
static unsigned int bio_slab_nr, bio_slab_max;

static struct kmem_cache *bio_find_or_create_slab(unsigned int extra_size)
{
        unsigned int sz = sizeof(struct bio) + extra_size;
        struct kmem_cache *slab = NULL;
        struct bio_slab *bslab, *new_bio_slabs;
        unsigned int new_bio_slab_max;
        unsigned int i, entry = -1;

        mutex_lock(&bio_slab_lock);

        i = 0;
        while (i < bio_slab_nr) {
                bslab = &bio_slabs[i];

                if (!bslab->slab && entry == -1)
                        entry = i;
                else if (bslab->slab_size == sz) {
                        slab = bslab->slab;
                        bslab->slab_ref++;
                        break;
                }
                i++;
        }

        if (slab)
                goto out_unlock;

        if (bio_slab_nr == bio_slab_max && entry == -1) {
                new_bio_slab_max = bio_slab_max << 1;
                new_bio_slabs = krealloc(bio_slabs,
                                         new_bio_slab_max * sizeof(struct bio_slab),
                                         GFP_KERNEL);
                if (!new_bio_slabs)
                        goto out_unlock;
                bio_slab_max = new_bio_slab_max;
                bio_slabs = new_bio_slabs;
        }
        if (entry == -1)
                entry = bio_slab_nr++;

        bslab = &bio_slabs[entry];

        snprintf(bslab->name, sizeof(bslab->name), "bio-%d", entry);
        slab = kmem_cache_create(bslab->name, sz, ARCH_KMALLOC_MINALIGN,
                                 SLAB_HWCACHE_ALIGN, NULL);
        if (!slab)
                goto out_unlock;

        bslab->slab = slab;
        bslab->slab_ref = 1;
        bslab->slab_size = sz;
out_unlock:
        mutex_unlock(&bio_slab_lock);
        return slab;
}

static void bio_put_slab(struct bio_set *bs)
{
        struct bio_slab *bslab = NULL;
        unsigned int i;

        mutex_lock(&bio_slab_lock);

        for (i = 0; i < bio_slab_nr; i++) {
                if (bs->bio_slab == bio_slabs[i].slab) {
                        bslab = &bio_slabs[i];
                        break;
                }
        }

        if (WARN(!bslab, KERN_ERR "bio: unable to find slab!\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)
{
        if (!idx)
                return;
        idx--;

        BIO_BUG_ON(idx >= BVEC_POOL_NR);

        if (idx == BVEC_POOL_MAX) {
                mempool_free(bv, pool);
        } else {
                struct biovec_slab *bvs = bvec_slabs + idx;

                kmem_cache_free(bvs->slab, bv);
        }
}

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

        /*
         * see comment near bvec_array define!
         */
        switch (nr) {
        case 1:
                *idx = 0;
                break;
        case 2 ... 4:
                *idx = 1;
                break;
        case 5 ... 16:
                *idx = 2;
                break;
        case 17 ... 64:
                *idx = 3;
                break;
        case 65 ... 128:
                *idx = 4;
                break;
        case 129 ... BIO_MAX_PAGES:
                *idx = 5;
                break;
        default:
                return NULL;
        }

        /*
         * idx now points to the pool we want to allocate from. only the
         * 1-vec entry pool is mempool backed.
         */
        if (*idx == BVEC_POOL_MAX) {
fallback:
                bvl = mempool_alloc(pool, gfp_mask);
        } else {
                struct biovec_slab *bvs = bvec_slabs + *idx;
                gfp_t __gfp_mask = gfp_mask & ~(__GFP_DIRECT_RECLAIM | __GFP_IO);

                /*
                 * Make this allocation restricted and don't dump info on
                 * allocation failures, since we'll fallback to the mempool
                 * in case of failure.
                 */
                __gfp_mask |= __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN;

                /*
                 * Try a slab allocation. If this fails and __GFP_DIRECT_RECLAIM
                 * is set, retry with the 1-entry mempool
                 */
                bvl = kmem_cache_alloc(bvs->slab, __gfp_mask);
                if (unlikely(!bvl && (gfp_mask & __GFP_DIRECT_RECLAIM))) {
                        *idx = BVEC_POOL_MAX;
                        goto fallback;
                }
        }

        (*idx)++;
        return bvl;
}

void bio_uninit(struct bio *bio)
{
        bio_disassociate_blkg(bio);

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

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

        bio_uninit(bio);

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

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

                mempool_free(p, &bs->bio_pool);
        } else {
                /* Bio was allocated by bio_kmalloc() */
                kfree(bio);
        }
}

/*
 * Users of this function have their own bio allocation. Subsequently,
 * they must remember to pair any call to bio_init() with bio_uninit()
 * when IO has completed, or when the bio is released.
 */
void bio_init(struct bio *bio, struct bio_vec *table,
              unsigned short max_vecs)
{
        memset(bio, 0, sizeof(*bio));
        atomic_set(&bio->__bi_remaining, 1);
        atomic_set(&bio->__bi_cnt, 1);

        bio->bi_io_vec = table;
        bio->bi_max_vecs = max_vecs;
}
EXPORT_SYMBOL(bio_init);

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

        bio_uninit(bio);

        memset(bio, 0, BIO_RESET_BYTES);
        bio->bi_flags = flags;
        atomic_set(&bio->__bi_remaining, 1);
}
EXPORT_SYMBOL(bio_reset);

static struct bio *__bio_chain_endio(struct bio *bio)
{
        struct bio *parent = bio->bi_private;

        if (!parent->bi_status)
                parent->bi_status = bio->bi_status;
        bio_put(bio);
        return parent;
}

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

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

        bio->bi_private = parent;
        bio->bi_end_io  = bio_chain_endio;
        bio_inc_remaining(parent);
}
EXPORT_SYMBOL(bio_chain);

static void bio_alloc_rescue(struct work_struct *work)
{
        struct bio_set *bs = container_of(work, struct bio_set, rescue_work);
        struct bio *bio;

        while (1) {
                spin_lock(&bs->rescue_lock);
                bio = bio_list_pop(&bs->rescue_list);
                spin_unlock(&bs->rescue_lock);

                if (!bio)
                        break;

                generic_make_request(bio);
        }
}

static void punt_bios_to_rescuer(struct bio_set *bs)
{
        struct bio_list punt, nopunt;
        struct bio *bio;

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

        bio_list_init(&punt);
        bio_list_init(&nopunt);

        while ((bio = bio_list_pop(&current->bio_list[0])))
                bio_list_add(bio->bi_pool == bs ? &punt : &nopunt, bio);
        current->bio_list[0] = nopunt;

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

        spin_lock(&bs->rescue_lock);
        bio_list_merge(&bs->rescue_list, &punt);
        spin_unlock(&bs->rescue_lock);

        queue_work(bs->rescue_workqueue, &bs->rescue_work);
}

/**
 * bio_alloc_bioset - allocate a bio for I/O
 * @gfp_mask:   the GFP_* mask given to the slab allocator
 * @nr_iovecs:  number of iovecs to pre-allocate
 * @bs:         the bio_set to allocate from.
 *
 * Description:
 *   If @bs is NULL, uses kmalloc() to allocate the bio; else the allocation is
 *   backed by the @bs's mempool.
 *
 *   When @bs is not NULL, if %__GFP_DIRECT_RECLAIM is set then bio_alloc will
 *   always be able to allocate a bio. This is due to the mempool guarantees.
 *   To make this work, callers must never allocate more than 1 bio at a time
 *   from this pool. Callers that need to allocate more than 1 bio must always
 *   submit the previously allocated bio for IO before attempting to allocate
 *   a new one. Failure to do so can cause deadlocks under memory pressure.
 *
 *   Note that when running under generic_make_request() (i.e. any block
 *   driver), bios are not submitted until after you return - see the code in
 *   generic_make_request() that converts recursion into iteration, to prevent
 *   stack overflows.
 *
 *   This would normally mean allocating multiple bios under
 *   generic_make_request() would be susceptible to deadlocks, but we have
 *   deadlock avoidance code that resubmits any blocked bios from a rescuer
 *   thread.
 *
 *   However, we do not guarantee forward progress for allocations from other
 *   mempools. Doing multiple allocations from the same mempool under
 *   generic_make_request() should be avoided - instead, use bio_set's front_pad
 *   for per bio allocations.
 *
 *   RETURNS:
 *   Pointer to new bio on success, NULL on failure.
 */
struct bio *bio_alloc_bioset(gfp_t gfp_mask, unsigned int nr_iovecs,
                             struct bio_set *bs)
{
        gfp_t saved_gfp = gfp_mask;
        unsigned front_pad;
        unsigned inline_vecs;
        struct bio_vec *bvl = NULL;
        struct bio *bio;
        void *p;

        if (!bs) {
                if (nr_iovecs > UIO_MAXIOV)
                        return NULL;

                p = kmalloc(sizeof(struct bio) +
                            nr_iovecs * sizeof(struct bio_vec),
                            gfp_mask);
                front_pad = 0;
                inline_vecs = nr_iovecs;
        } else {
                /* should not use nobvec bioset for nr_iovecs > 0 */
                if (WARN_ON_ONCE(!mempool_initialized(&bs->bvec_pool) &&
                                 nr_iovecs > 0))
                        return NULL;
                /*
                 * generic_make_request() converts recursion to iteration; this
                 * means if we're running beneath it, any bios we allocate and
                 * submit will not be submitted (and thus freed) until after we
                 * return.
                 *
                 * This exposes us to a potential deadlock if we allocate
                 * multiple bios from the same bio_set() while running
                 * underneath generic_make_request(). If we were to allocate
                 * multiple bios (say a stacking block driver that was splitting
                 * bios), we would deadlock if we exhausted the mempool's
                 * reserve.
                 *
                 * We solve this, and guarantee forward progress, with a rescuer
                 * workqueue per bio_set. If we go to allocate and there are
                 * bios on current->bio_list, we first try the allocation
                 * without __GFP_DIRECT_RECLAIM; if that fails, we punt those
                 * bios we would be blocking to the rescuer workqueue before
                 * we retry with the original gfp_flags.
                 */

                if (current->bio_list &&
                    (!bio_list_empty(&current->bio_list[0]) ||
                     !bio_list_empty(&current->bio_list[1])) &&
                    bs->rescue_workqueue)
                        gfp_mask &= ~__GFP_DIRECT_RECLAIM;

                p = mempool_alloc(&bs->bio_pool, gfp_mask);
                if (!p && gfp_mask != saved_gfp) {
                        punt_bios_to_rescuer(bs);
                        gfp_mask = saved_gfp;
                        p = mempool_alloc(&bs->bio_pool, gfp_mask);
                }

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

        if (unlikely(!p))
                return NULL;

        bio = p + front_pad;
        bio_init(bio, NULL, 0);

        if (nr_iovecs > inline_vecs) {
                unsigned long idx = 0;

                bvl = bvec_alloc(gfp_mask, nr_iovecs, &idx, &bs->bvec_pool);
                if (!bvl && gfp_mask != saved_gfp) {
                        punt_bios_to_rescuer(bs);
                        gfp_mask = saved_gfp;
                        bvl = bvec_alloc(gfp_mask, nr_iovecs, &idx, &bs->bvec_pool);
                }

                if (unlikely(!bvl))
                        goto err_free;

                bio->bi_flags |= idx << BVEC_POOL_OFFSET;
        } else if (nr_iovecs) {
                bvl = bio->bi_inline_vecs;
        }

        bio->bi_pool = bs;
        bio->bi_max_vecs = nr_iovecs;
        bio->bi_io_vec = bvl;
        return bio;

err_free:
        mempool_free(p, &bs->bio_pool);
        return NULL;
}
EXPORT_SYMBOL(bio_alloc_bioset);

void zero_fill_bio_iter(struct bio *bio, struct bvec_iter start)
{
        unsigned long flags;
        struct bio_vec bv;
        struct bvec_iter iter;

        __bio_for_each_segment(bv, bio, iter, start) {
                char *data = bvec_kmap_irq(&bv, &flags);
                memset(data, 0, bv.bv_len);
                flush_dcache_page(bv.bv_page);
                bvec_kunmap_irq(data, &flags);
        }
}
EXPORT_SYMBOL(zero_fill_bio_iter);

/**
 * bio_truncate - truncate the bio to small size of @new_size
 * @bio:        the bio to be truncated
 * @new_size:   new size for truncating the bio
 *
 * Description:
 *   Truncate the bio to new size of @new_size. If bio_op(bio) is
 *   REQ_OP_READ, zero the truncated part. This function should only
 *   be used for handling corner cases, such as bio eod.
 */
void bio_truncate(struct bio *bio, unsigned new_size)
{
        struct bio_vec bv;
        struct bvec_iter iter;
        unsigned int done = 0;
        bool truncated = false;

        if (new_size >= bio->bi_iter.bi_size)
                return;

        if (bio_op(bio) != REQ_OP_READ)
                goto exit;

        bio_for_each_segment(bv, bio, iter) {
                if (done + bv.bv_len > new_size) {
                        unsigned offset;

                        if (!truncated)
                                offset = new_size - done;
                        else
                                offset = 0;
                        zero_user(bv.bv_page, offset, bv.bv_len - offset);
                        truncated = true;
                }
                done += bv.bv_len;
        }

 exit:
        /*
         * Don't touch bvec table here and make it really immutable, since
         * fs bio user has to retrieve all pages via bio_for_each_segment_all
         * in its .end_bio() callback.
         *
         * It is enough to truncate bio by updating .bi_size since we can make
         * correct bvec with the updated .bi_size for drivers.
         */
        bio->bi_iter.bi_size = new_size;
}

/**
 * guard_bio_eod - truncate a BIO to fit the block device
 * @bio:        bio to truncate
 *
 * This allows us to do IO even on the odd last sectors of a device, even if the
 * block size is some multiple of the physical sector size.
 *
 * We'll just truncate the bio to the size of the device, and clear the end of
 * the buffer head manually.  Truly out-of-range accesses will turn into actual
 * I/O errors, this only handles the "we need to be able to do I/O at the final
 * sector" case.
 */
void guard_bio_eod(struct bio *bio)
{
        sector_t maxsector;
        struct hd_struct *part;

        rcu_read_lock();
        part = __disk_get_part(bio->bi_disk, bio->bi_partno);
        if (part)
                maxsector = part_nr_sects_read(part);
        else
                maxsector = get_capacity(bio->bi_disk);
        rcu_read_unlock();

        if (!maxsector)
                return;

        /*
         * If the *whole* IO is past the end of the device,
         * let it through, and the IO layer will turn it into
         * an EIO.
         */
        if (unlikely(bio->bi_iter.bi_sector >= maxsector))
                return;

        maxsector -= bio->bi_iter.bi_sector;
        if (likely((bio->bi_iter.bi_size >> 9) <= maxsector))
                return;

        bio_truncate(bio, maxsector << 9);
}

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

                /*
                 * last put frees it
                 */
                if (atomic_dec_and_test(&bio->__bi_cnt))
                        bio_free(bio);
        }
}
EXPORT_SYMBOL(bio_put);

/**
 *      __bio_clone_fast - clone a bio that shares the original bio's biovec
 *      @bio: destination bio
 *      @bio_src: bio to clone
 *
 *      Clone a &bio. Caller will own the returned bio, but not
 *      the actual data it points to. Reference count of returned
 *      bio will be one.
 *
 *      Caller must ensure that @bio_src is not freed before @bio.
 */
void __bio_clone_fast(struct bio *bio, struct bio *bio_src)
{
        BUG_ON(bio->bi_pool && BVEC_POOL_IDX(bio));

        /*
         * most users will be overriding ->bi_disk with a new target,
         * so we don't set nor calculate new physical/hw segment counts here
         */
        bio->bi_disk = bio_src->bi_disk;
        bio->bi_partno = bio_src->bi_partno;
        bio_set_flag(bio, BIO_CLONED);
        if (bio_flagged(bio_src, BIO_THROTTLED))
                bio_set_flag(bio, BIO_THROTTLED);
        bio->bi_opf = bio_src->bi_opf;
        bio->bi_ioprio = bio_src->bi_ioprio;
        bio->bi_write_hint = bio_src->bi_write_hint;
        bio->bi_iter = bio_src->bi_iter;
        bio->bi_io_vec = bio_src->bi_io_vec;

        bio_clone_blkg_association(bio, bio_src);
        blkcg_bio_issue_init(bio);
}
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);

const char *bio_devname(struct bio *bio, char *buf)
{
        return disk_name(bio->bi_disk, bio->bi_partno, buf);
}
EXPORT_SYMBOL(bio_devname);

static inline bool page_is_mergeable(const struct bio_vec *bv,
                struct page *page, unsigned int len, unsigned int off,
                bool *same_page)
{
        phys_addr_t vec_end_addr = page_to_phys(bv->bv_page) +
                bv->bv_offset + bv->bv_len - 1;
        phys_addr_t page_addr = page_to_phys(page);

        if (vec_end_addr + 1 != page_addr + off)
                return false;
        if (xen_domain() && !xen_biovec_phys_mergeable(bv, page))
                return false;

        *same_page = ((vec_end_addr & PAGE_MASK) == page_addr);
        if (!*same_page && pfn_to_page(PFN_DOWN(vec_end_addr)) + 1 != page)
                return false;
        return true;
}

static bool bio_try_merge_pc_page(struct request_queue *q, struct bio *bio,
                struct page *page, unsigned len, unsigned offset,
                bool *same_page)
{
        struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
        unsigned long mask = queue_segment_boundary(q);
        phys_addr_t addr1 = page_to_phys(bv->bv_page) + bv->bv_offset;
        phys_addr_t addr2 = page_to_phys(page) + offset + len - 1;

        if ((addr1 | mask) != (addr2 | mask))
                return false;
        if (bv->bv_len + len > queue_max_segment_size(q))
                return false;
        return __bio_try_merge_page(bio, page, len, offset, same_page);
}

/**
 *      __bio_add_pc_page       - attempt to add page to passthrough bio
 *      @q: the target queue
 *      @bio: destination bio
 *      @page: page to add
 *      @len: vec entry length
 *      @offset: vec entry offset
 *      @same_page: return if the merge happen inside the same page
 *
 *      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 passthrough bios.
 */
int __bio_add_pc_page(struct request_queue *q, struct bio *bio,
                struct page *page, unsigned int len, unsigned int offset,
                bool *same_page)
{
        struct bio_vec *bvec;

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

        if (((bio->bi_iter.bi_size + len) >> 9) > queue_max_hw_sectors(q))
                return 0;

        if (bio->bi_vcnt > 0) {
                if (bio_try_merge_pc_page(q, bio, page, len, offset, same_page))
                        return len;

                /*
                 * If the queue doesn't support SG gaps and adding this segment
                 * would create a gap, disallow it.
                 */
                bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
                if (bvec_gap_to_prev(q, bvec, offset))
                        return 0;
        }

        if (bio_full(bio, len))
                return 0;

        if (bio->bi_vcnt >= queue_max_segments(q))
                return 0;

        bvec = &bio->bi_io_vec[bio->bi_vcnt];
        bvec->bv_page = page;
        bvec->bv_len = len;
        bvec->bv_offset = offset;
        bio->bi_vcnt++;
        bio->bi_iter.bi_size += len;
        return len;
}

int bio_add_pc_page(struct request_queue *q, struct bio *bio,
                struct page *page, unsigned int len, unsigned int offset)
{
        bool same_page = false;
        return __bio_add_pc_page(q, bio, page, len, offset, &same_page);
}
EXPORT_SYMBOL(bio_add_pc_page);

/**
 * __bio_try_merge_page - try appending data to an existing bvec.
 * @bio: destination bio
 * @page: start page to add
 * @len: length of the data to add
 * @off: offset of the data relative to @page
 * @same_page: return if the segment has been merged inside the same page
 *
 * Try to add the data at @page + @off to the last bvec of @bio.  This is a
 * a useful optimisation for file systems with a block size smaller than the
 * page size.
 *
 * Warn if (@len, @off) crosses pages in case that @same_page is true.
 *
 * Return %true on success or %false on failure.
 */
bool __bio_try_merge_page(struct bio *bio, struct page *page,
                unsigned int len, unsigned int off, bool *same_page)
{
        if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
                return false;

        if (bio->bi_vcnt > 0) {
                struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];

                if (page_is_mergeable(bv, page, len, off, same_page)) {
                        if (bio->bi_iter.bi_size > UINT_MAX - len)
                                return false;
                        bv->bv_len += len;
                        bio->bi_iter.bi_size += len;
                        return true;
                }
        }
        return false;
}
EXPORT_SYMBOL_GPL(__bio_try_merge_page);

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

        WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED));
        WARN_ON_ONCE(bio_full(bio, len));

        bv->bv_page = page;
        bv->bv_offset = off;
        bv->bv_len = len;

        bio->bi_iter.bi_size += len;
        bio->bi_vcnt++;

        if (!bio_flagged(bio, BIO_WORKINGSET) && unlikely(PageWorkingset(page)))
                bio_set_flag(bio, BIO_WORKINGSET);
}
EXPORT_SYMBOL_GPL(__bio_add_page);

/**
 *      bio_add_page    -       attempt to add page(s) to bio
 *      @bio: destination bio
 *      @page: start page to add
 *      @len: vec entry length, may cross pages
 *      @offset: vec entry offset relative to @page, may cross pages
 *
 *      Attempt to add page(s) to the bio_vec maplist. This will only fail
 *      if either bio->bi_vcnt == bio->bi_max_vecs or it's a cloned bio.
 */
int bio_add_page(struct bio *bio, struct page *page,
                 unsigned int len, unsigned int offset)
{
        bool same_page = false;

        if (!__bio_try_merge_page(bio, page, len, offset, &same_page)) {
                if (bio_full(bio, len))
                        return 0;
                __bio_add_page(bio, page, len, offset);
        }
        return len;
}
EXPORT_SYMBOL(bio_add_page);

void bio_release_pages(struct bio *bio, bool mark_dirty)
{
        struct bvec_iter_all iter_all;
        struct bio_vec *bvec;

        if (bio_flagged(bio, BIO_NO_PAGE_REF))
                return;

        bio_for_each_segment_all(bvec, bio, iter_all) {
                if (mark_dirty && !PageCompound(bvec->bv_page))
                        set_page_dirty_lock(bvec->bv_page);
                put_page(bvec->bv_page);
        }
}

static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter)
{
        const struct bio_vec *bv = iter->bvec;
        unsigned int len;
        size_t size;

        if (WARN_ON_ONCE(iter->iov_offset > bv->bv_len))
                return -EINVAL;

        len = min_t(size_t, bv->bv_len - iter->iov_offset, iter->count);
        size = bio_add_page(bio, bv->bv_page, len,
                                bv->bv_offset + iter->iov_offset);
        if (unlikely(size != len))
                return -EINVAL;
        iov_iter_advance(iter, size);
        return 0;
}

#define PAGE_PTRS_PER_BVEC     (sizeof(struct bio_vec) / sizeof(struct page *))

/**
 * __bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio
 * @bio: bio to add pages to
 * @iter: iov iterator describing the region to be mapped
 *
 * Pins pages from *iter and appends them to @bio's bvec array. The
 * pages will have to be released using put_page() when done.
 * For multi-segment *iter, this function only adds pages from the
 * the next non-empty segment of the iov iterator.
 */
static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
{
        unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt;
        unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt;
        struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
        struct page **pages = (struct page **)bv;
        bool same_page = false;
        ssize_t size, left;
        unsigned len, i;
        size_t offset;

        /*
         * Move page array up in the allocated memory for the bio vecs as far as
         * possible so that we can start filling biovecs from the beginning
         * without overwriting the temporary page array.
        */
        BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2);
        pages += entries_left * (PAGE_PTRS_PER_BVEC - 1);

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

        for (left = size, i = 0; left > 0; left -= len, i++) {
                struct page *page = pages[i];

                len = min_t(size_t, PAGE_SIZE - offset, left);

                if (__bio_try_merge_page(bio, page, len, offset, &same_page)) {
                        if (same_page)
                                put_page(page);
                } else {
                        if (WARN_ON_ONCE(bio_full(bio, len)))
                                return -EINVAL;
                        __bio_add_page(bio, page, len, offset);
                }
                offset = 0;
        }

        iov_iter_advance(iter, size);
        return 0;
}

/**
 * bio_iov_iter_get_pages - add user or kernel pages to a bio
 * @bio: bio to add pages to
 * @iter: iov iterator describing the region to be added
 *
 * This takes either an iterator pointing to user memory, or one pointing to
 * kernel pages (BVEC iterator). If we're adding user pages, we pin them and
 * map them into the kernel. On IO completion, the caller should put those
 * pages. If we're adding kernel pages, and the caller told us it's safe to
 * do so, we just have to add the pages to the bio directly. We don't grab an
 * extra reference to those pages (the user should already have that), and we
 * don't put the page on IO completion. The caller needs to check if the bio is
 * flagged BIO_NO_PAGE_REF on IO completion. If it isn't, then pages should be
 * released.
 *
 * The function tries, but does not guarantee, to pin as many pages as
 * fit into the bio, or are requested in *iter, whatever is smaller. If
 * MM encounters an error pinning the requested pages, it stops. Error
 * is returned only if 0 pages could be pinned.
 */
int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
{
        const bool is_bvec = iov_iter_is_bvec(iter);
        int ret;

        if (WARN_ON_ONCE(bio->bi_vcnt))
                return -EINVAL;

        do {
                if (is_bvec)
                        ret = __bio_iov_bvec_add_pages(bio, iter);
                else
                        ret = __bio_iov_iter_get_pages(bio, iter);
        } while (!ret && iov_iter_count(iter) && !bio_full(bio, 0));

        if (is_bvec)
                bio_set_flag(bio, BIO_NO_PAGE_REF);
        return bio->bi_vcnt ? 0 : ret;
}

static void submit_bio_wait_endio(struct bio *bio)
{
        complete(bio->bi_private);
}

/**
 * submit_bio_wait - submit a bio, and wait until it completes
 * @bio: The &struct bio which describes the I/O
 *
 * Simple wrapper around submit_bio(). Returns 0 on success, or the error from
 * bio_endio() on failure.
 *
 * WARNING: Unlike to how submit_bio() is usually used, this function does not
 * result in bio reference to be consumed. The caller must drop the reference
 * on his own.
 */
int submit_bio_wait(struct bio *bio)
{
        DECLARE_COMPLETION_ONSTACK_MAP(done, bio->bi_disk->lockdep_map);
        unsigned long hang_check;

        bio->bi_private = &done;
        bio->bi_end_io = submit_bio_wait_endio;
        bio->bi_opf |= REQ_SYNC;
        submit_bio(bio);

        /* Prevent hang_check timer from firing at us during very long I/O */
        hang_check = sysctl_hung_task_timeout_secs;
        if (hang_check)
                while (!wait_for_completion_io_timeout(&done,
                                        hang_check * (HZ/2)))
                        ;
        else
                wait_for_completion_io(&done);

        return blk_status_to_errno(bio->bi_status);
}
EXPORT_SYMBOL(submit_bio_wait);

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

        bio_advance_iter(bio, &bio->bi_iter, bytes);
}
EXPORT_SYMBOL(bio_advance);

void bio_copy_data_iter(struct bio *dst, struct bvec_iter *dst_iter,
                        struct bio *src, struct bvec_iter *src_iter)
{
        struct bio_vec src_bv, dst_bv;
        void *src_p, *dst_p;
        unsigned bytes;

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

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

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

                memcpy(dst_p + dst_bv.bv_offset,
                       src_p + src_bv.bv_offset,
                       bytes);

                kunmap_atomic(dst_p);
                kunmap_atomic(src_p);

                flush_dcache_page(dst_bv.bv_page);

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

/**
 * bio_copy_data - copy contents of data buffers from one bio to another
 * @src: source bio
 * @dst: destination bio
 *
 * Stops when it reaches the end of either @src or @dst - that is, copies
 * min(src->bi_size, dst->bi_size) bytes (or the equivalent for lists of bios).
 */
void bio_copy_data(struct bio *dst, struct bio *src)
{
        struct bvec_iter src_iter = src->bi_iter;
        struct bvec_iter dst_iter = dst->bi_iter;

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

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

        while (1) {
                if (!src_iter.bi_size) {
                        src = src->bi_next;
                        if (!src)
                                break;

                        src_iter = src->bi_iter;
                }

                if (!dst_iter.bi_size) {
                        dst = dst->bi_next;
                        if (!dst)
                                break;

                        dst_iter = dst->bi_iter;
                }

                bio_copy_data_iter(dst, &dst_iter, src, &src_iter);
        }
}
EXPORT_SYMBOL(bio_list_copy_data);

void bio_free_pages(struct bio *bio)
{
        struct bio_vec *bvec;
        struct bvec_iter_all iter_all;

        bio_for_each_segment_all(bvec, bio, iter_all)
                __free_page(bvec->bv_page);
}
EXPORT_SYMBOL(bio_free_pages);

/*
 * 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;
        struct bvec_iter_all iter_all;

        bio_for_each_segment_all(bvec, bio, iter_all) {
                if (!PageCompound(bvec->bv_page))
                        set_page_dirty_lock(bvec->bv_page);
        }
}

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

static void bio_dirty_fn(struct work_struct *work);

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

/*
 * This runs in process context
 */
static void bio_dirty_fn(struct work_struct *work)
{
        struct bio *bio, *next;

        spin_lock_irq(&bio_dirty_lock);
        next = bio_dirty_list;
        bio_dirty_list = NULL;
        spin_unlock_irq(&bio_dirty_lock);

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

                bio_release_pages(bio, true);
                bio_put(bio);
        }
}

void bio_check_pages_dirty(struct bio *bio)
{
        struct bio_vec *bvec;
        unsigned long flags;
        struct bvec_iter_all iter_all;

        bio_for_each_segment_all(bvec, bio, iter_all) {
                if (!PageDirty(bvec->bv_page) && !PageCompound(bvec->bv_page))
                        goto defer;
        }

        bio_release_pages(bio, false);
        bio_put(bio);
        return;
defer:
        spin_lock_irqsave(&bio_dirty_lock, flags);
        bio->bi_private = bio_dirty_list;
        bio_dirty_list = bio;
        spin_unlock_irqrestore(&bio_dirty_lock, flags);
        schedule_work(&bio_dirty_work);
}

void update_io_ticks(struct hd_struct *part, unsigned long now, bool end)
{
        unsigned long stamp;
again:
        stamp = READ_ONCE(part->stamp);
        if (unlikely(stamp != now)) {
                if (likely(cmpxchg(&part->stamp, stamp, now) == stamp)) {
                        __part_stat_add(part, io_ticks, end ? now - stamp : 1);
                }
        }
        if (part->partno) {
                part = &part_to_disk(part)->part0;
                goto again;
        }
}

void generic_start_io_acct(struct request_queue *q, int op,
                           unsigned long sectors, struct hd_struct *part)
{
        const int sgrp = op_stat_group(op);

        part_stat_lock();

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

        part_stat_unlock();
}
EXPORT_SYMBOL(generic_start_io_acct);

void generic_end_io_acct(struct request_queue *q, int req_op,
                         struct hd_struct *part, unsigned long start_time)
{
        unsigned long now = jiffies;
        unsigned long duration = now - start_time;
        const int sgrp = op_stat_group(req_op);

        part_stat_lock();

        update_io_ticks(part, now, true);
        part_stat_add(part, nsecs[sgrp], jiffies_to_nsecs(duration));
        part_dec_in_flight(q, part, op_is_write(req_op));

        part_stat_unlock();
}
EXPORT_SYMBOL(generic_end_io_acct);

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

        BUG_ON(atomic_read(&bio->__bi_remaining) <= 0);

        if (atomic_dec_and_test(&bio->__bi_remaining)) {
                bio_clear_flag(bio, BIO_CHAIN);
                return true;
        }

        return false;
}

/**
 * bio_endio - end I/O on a bio
 * @bio:        bio
 *
 * Description:
 *   bio_endio() will end I/O on the whole bio. bio_endio() is the preferred
 *   way to end I/O on a bio. No one should call bi_end_io() directly on a
 *   bio unless they own it and thus know that it has an end_io function.
 *
 *   bio_endio() can be called several times on a bio that has been chained
 *   using bio_chain().  The ->bi_end_io() function will only be called the
 *   last time.  At this point the BLK_TA_COMPLETE tracing event will be
 *   generated if BIO_TRACE_COMPLETION is set.
 **/
void bio_endio(struct bio *bio)
{
again:
        if (!bio_remaining_done(bio))
                return;
        if (!bio_integrity_endio(bio))
                return;

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

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

        if (bio->bi_disk && bio_flagged(bio, BIO_TRACE_COMPLETION)) {
                trace_block_bio_complete(bio->bi_disk->queue, bio,
                                         blk_status_to_errno(bio->bi_status));
                bio_clear_flag(bio, BIO_TRACE_COMPLETION);
        }

        blk_throtl_bio_endio(bio);
        /* release cgroup info */
        bio_uninit(bio);
        if (bio->bi_end_io)
                bio->bi_end_io(bio);
}
EXPORT_SYMBOL(bio_endio);

/**
 * 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.
 *
 * Unless this is a discard request the newly allocated bio will point
 * to @bio's bi_io_vec. It is the caller's responsibility to ensure that
 * neither @bio nor @bs are freed before the split bio.
 */
struct bio *bio_split(struct bio *bio, int sectors,
                      gfp_t gfp, struct bio_set *bs)
{
        struct bio *split;

        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);

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

        if (bio_flagged(bio, BIO_TRACE_COMPLETION))
                bio_set_flag(split, BIO_TRACE_COMPLETION);

        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;

        bio_advance(bio, offset << 9);
        bio->bi_iter.bi_size = size;

        if (bio_integrity(bio))
                bio_integrity_trim(bio);

}
EXPORT_SYMBOL_GPL(bio_trim);

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

        return mempool_init_slab_pool(pool, pool_entries, bp->slab);
}

/*
 * bioset_exit - exit a bioset initialized with bioset_init()
 *
 * May be called on a zeroed but uninitialized bioset (i.e. allocated with
 * kzalloc()).
 */
void bioset_exit(struct bio_set *bs)
{
        if (bs->rescue_workqueue)
                destroy_workqueue(bs->rescue_workqueue);
        bs->rescue_workqueue = NULL;

        mempool_exit(&bs->bio_pool);
        mempool_exit(&bs->bvec_pool);

        bioset_integrity_free(bs);
        if (bs->bio_slab)
                bio_put_slab(bs);
        bs->bio_slab = NULL;
}
EXPORT_SYMBOL(bioset_exit);

/**
 * bioset_init - Initialize a bio_set
 * @bs:         pool to initialize
 * @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
 * @flags:      Flags to modify behavior, currently %BIOSET_NEED_BVECS
 *              and %BIOSET_NEED_RESCUER
 *
 * 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.
 *    If %BIOSET_NEED_BVECS is set in @flags, a separate pool will be allocated
 *    for allocating iovecs.  This pool is not needed e.g. for bio_clone_fast().
 *    If %BIOSET_NEED_RESCUER is set, a workqueue is created which can be used to
 *    dispatch queued requests when the mempool runs out of space.
 *
 */
int bioset_init(struct bio_set *bs,
                unsigned int pool_size,
                unsigned int front_pad,
                int flags)
{
        unsigned int back_pad = BIO_INLINE_VECS * sizeof(struct bio_vec);

        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)
                return -ENOMEM;

        if (mempool_init_slab_pool(&bs->bio_pool, pool_size, bs->bio_slab))
                goto bad;

        if ((flags & BIOSET_NEED_BVECS) &&
            biovec_init_pool(&bs->bvec_pool, pool_size))
                goto bad;

        if (!(flags & BIOSET_NEED_RESCUER))
                return 0;

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

        return 0;
bad:
        bioset_exit(bs);
        return -ENOMEM;
}
EXPORT_SYMBOL(bioset_init);

/*
 * Initialize and setup a new bio_set, based on the settings from
 * another bio_set.
 */
int bioset_init_from_src(struct bio_set *bs, struct bio_set *src)
{
        int flags;

        flags = 0;
        if (src->bvec_pool.min_nr)
                flags |= BIOSET_NEED_BVECS;
        if (src->rescue_workqueue)
                flags |= BIOSET_NEED_RESCUER;

        return bioset_init(bs, src->bio_pool.min_nr, src->front_pad, flags);
}
EXPORT_SYMBOL(bioset_init_from_src);

#ifdef CONFIG_BLK_CGROUP

/**
 * bio_disassociate_blkg - puts back the blkg reference if associated
 * @bio: target bio
 *
 * Helper to disassociate the blkg from @bio if a blkg is associated.
 */
void bio_disassociate_blkg(struct bio *bio)
{
        if (bio->bi_blkg) {
                blkg_put(bio->bi_blkg);
                bio->bi_blkg = NULL;
        }
}
EXPORT_SYMBOL_GPL(bio_disassociate_blkg);

/**
 * __bio_associate_blkg - associate a bio with the a blkg
 * @bio: target bio
 * @blkg: the blkg to associate
 *
 * This tries to associate @bio with the specified @blkg.  Association failure
 * is handled by walking up the blkg tree.  Therefore, the blkg associated can
 * be anything between @blkg and the root_blkg.  This situation only happens
 * when a cgroup is dying and then the remaining bios will spill to the closest
 * alive blkg.
 *
 * A reference will be taken on the @blkg and will be released when @bio is
 * freed.
 */
static void __bio_associate_blkg(struct bio *bio, struct blkcg_gq *blkg)
{
        bio_disassociate_blkg(bio);

        bio->bi_blkg = blkg_tryget_closest(blkg);
}

/**
 * bio_associate_blkg_from_css - associate a bio with a specified css
 * @bio: target bio
 * @css: target css
 *
 * Associate @bio with the blkg found by combining the css's blkg and the
 * request_queue of the @bio.  This falls back to the queue's root_blkg if
 * the association fails with the css.
 */
void bio_associate_blkg_from_css(struct bio *bio,
                                 struct cgroup_subsys_state *css)
{
        struct request_queue *q = bio->bi_disk->queue;
        struct blkcg_gq *blkg;

        rcu_read_lock();

        if (!css || !css->parent)
                blkg = q->root_blkg;
        else
                blkg = blkg_lookup_create(css_to_blkcg(css), q);

        __bio_associate_blkg(bio, blkg);

        rcu_read_unlock();
}
EXPORT_SYMBOL_GPL(bio_associate_blkg_from_css);

#ifdef CONFIG_MEMCG
/**
 * bio_associate_blkg_from_page - associate a bio with the page's blkg
 * @bio: target bio
 * @page: the page to lookup the blkcg from
 *
 * Associate @bio with the blkg from @page's owning memcg and the respective
 * request_queue.  If cgroup_e_css returns %NULL, fall back to the queue's
 * root_blkg.
 */
void bio_associate_blkg_from_page(struct bio *bio, struct page *page)
{
        struct cgroup_subsys_state *css;

        if (!page->mem_cgroup)
                return;

        rcu_read_lock();

        css = cgroup_e_css(page->mem_cgroup->css.cgroup, &io_cgrp_subsys);
        bio_associate_blkg_from_css(bio, css);

        rcu_read_unlock();
}
#endif /* CONFIG_MEMCG */

/**
 * bio_associate_blkg - associate a bio with a blkg
 * @bio: target bio
 *
 * Associate @bio with the blkg found from the bio's css and request_queue.
 * If one is not found, bio_lookup_blkg() creates the blkg.  If a blkg is
 * already associated, the css is reused and association redone as the
 * request_queue may have changed.
 */
void bio_associate_blkg(struct bio *bio)
{
        struct cgroup_subsys_state *css;

        rcu_read_lock();

        if (bio->bi_blkg)
                css = &bio_blkcg(bio)->css;
        else
                css = blkcg_css();

        bio_associate_blkg_from_css(bio, css);

        rcu_read_unlock();
}
EXPORT_SYMBOL_GPL(bio_associate_blkg);

/**
 * bio_clone_blkg_association - clone blkg association from src to dst bio
 * @dst: destination bio
 * @src: source bio
 */
void bio_clone_blkg_association(struct bio *dst, struct bio *src)
{
        rcu_read_lock();

        if (src->bi_blkg)
                __bio_associate_blkg(dst, src->bi_blkg);

        rcu_read_unlock();
}
EXPORT_SYMBOL_GPL(bio_clone_blkg_association);
#endif /* CONFIG_BLK_CGROUP */

static void __init biovec_init_slabs(void)
{
        int i;

        for (i = 0; i < BVEC_POOL_NR; 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 = kcalloc(bio_slab_max, sizeof(struct bio_slab),
                            GFP_KERNEL);

        BUILD_BUG_ON(BIO_FLAG_LAST > BVEC_POOL_OFFSET);

        if (!bio_slabs)
                panic("bio: can't allocate bios\n");

        bio_integrity_init();
        biovec_init_slabs();

        if (bioset_init(&fs_bio_set, BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS))
                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);