/*
 * Copyright (C) 2002 Sistina Software (UK) Limited.
 * Copyright (C) 2006 Red Hat GmbH
 *
 * This file is released under the GPL.
 *
 * Kcopyd provides a simple interface for copying an area of one
 * block-device to one or more other block-devices, with an asynchronous
 * completion notification.
 */

#include <linux/types.h>
#include <linux/atomic.h>
#include <linux/blkdev.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/mempool.h>
#include <linux/module.h>
#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/workqueue.h>
#include <linux/mutex.h>
#include <linux/delay.h>
#include <linux/device-mapper.h>
#include <linux/dm-kcopyd.h>

#include "dm-core.h"

#define SUB_JOB_SIZE    128
#define SPLIT_COUNT     8
#define MIN_JOBS        8
#define RESERVE_PAGES   (DIV_ROUND_UP(SUB_JOB_SIZE << SECTOR_SHIFT, PAGE_SIZE))

/*-----------------------------------------------------------------
 * Each kcopyd client has its own little pool of preallocated
 * pages for kcopyd io.
 *---------------------------------------------------------------*/
struct dm_kcopyd_client {
        struct page_list *pages;
        unsigned nr_reserved_pages;
        unsigned nr_free_pages;

        struct dm_io_client *io_client;

        wait_queue_head_t destroyq;

        mempool_t job_pool;

        struct workqueue_struct *kcopyd_wq;
        struct work_struct kcopyd_work;

        struct dm_kcopyd_throttle *throttle;

        atomic_t nr_jobs;

/*
 * We maintain four lists of jobs:
 *
 * i)   jobs waiting for pages
 * ii)  jobs that have pages, and are waiting for the io to be issued.
 * iii) jobs that don't need to do any IO and just run a callback
 * iv) jobs that have completed.
 *
 * All four of these are protected by job_lock.
 */
        spinlock_t job_lock;
        struct list_head callback_jobs;
        struct list_head complete_jobs;
        struct list_head io_jobs;
        struct list_head pages_jobs;
};

static struct page_list zero_page_list;

static DEFINE_SPINLOCK(throttle_spinlock);

/*
 * IO/IDLE accounting slowly decays after (1 << ACCOUNT_INTERVAL_SHIFT) period.
 * When total_period >= (1 << ACCOUNT_INTERVAL_SHIFT) the counters are divided
 * by 2.
 */
#define ACCOUNT_INTERVAL_SHIFT          SHIFT_HZ

/*
 * Sleep this number of milliseconds.
 *
 * The value was decided experimentally.
 * Smaller values seem to cause an increased copy rate above the limit.
 * The reason for this is unknown but possibly due to jiffies rounding errors
 * or read/write cache inside the disk.
 */
#define SLEEP_MSEC                      100

/*
 * Maximum number of sleep events. There is a theoretical livelock if more
 * kcopyd clients do work simultaneously which this limit avoids.
 */
#define MAX_SLEEPS                      10

static void io_job_start(struct dm_kcopyd_throttle *t)
{
        unsigned throttle, now, difference;
        int slept = 0, skew;

        if (unlikely(!t))
                return;

try_again:
        spin_lock_irq(&throttle_spinlock);

        throttle = READ_ONCE(t->throttle);

        if (likely(throttle >= 100))
                goto skip_limit;

        now = jiffies;
        difference = now - t->last_jiffies;
        t->last_jiffies = now;
        if (t->num_io_jobs)
                t->io_period += difference;
        t->total_period += difference;

        /*
         * Maintain sane values if we got a temporary overflow.
         */
        if (unlikely(t->io_period > t->total_period))
                t->io_period = t->total_period;

        if (unlikely(t->total_period >= (1 << ACCOUNT_INTERVAL_SHIFT))) {
                int shift = fls(t->total_period >> ACCOUNT_INTERVAL_SHIFT);
                t->total_period >>= shift;
                t->io_period >>= shift;
        }

        skew = t->io_period - throttle * t->total_period / 100;

        if (unlikely(skew > 0) && slept < MAX_SLEEPS) {
                slept++;
                spin_unlock_irq(&throttle_spinlock);
                msleep(SLEEP_MSEC);
                goto try_again;
        }

skip_limit:
        t->num_io_jobs++;

        spin_unlock_irq(&throttle_spinlock);
}

static void io_job_finish(struct dm_kcopyd_throttle *t)
{
        unsigned long flags;

        if (unlikely(!t))
                return;

        spin_lock_irqsave(&throttle_spinlock, flags);

        t->num_io_jobs--;

        if (likely(READ_ONCE(t->throttle) >= 100))
                goto skip_limit;

        if (!t->num_io_jobs) {
                unsigned now, difference;

                now = jiffies;
                difference = now - t->last_jiffies;
                t->last_jiffies = now;

                t->io_period += difference;
                t->total_period += difference;

                /*
                 * Maintain sane values if we got a temporary overflow.
                 */
                if (unlikely(t->io_period > t->total_period))
                        t->io_period = t->total_period;
        }

skip_limit:
        spin_unlock_irqrestore(&throttle_spinlock, flags);
}


static void wake(struct dm_kcopyd_client *kc)
{
        queue_work(kc->kcopyd_wq, &kc->kcopyd_work);
}

/*
 * Obtain one page for the use of kcopyd.
 */
static struct page_list *alloc_pl(gfp_t gfp)
{
        struct page_list *pl;

        pl = kmalloc(sizeof(*pl), gfp);
        if (!pl)
                return NULL;

        pl->page = alloc_page(gfp);
        if (!pl->page) {
                kfree(pl);
                return NULL;
        }

        return pl;
}

static void free_pl(struct page_list *pl)
{
        __free_page(pl->page);
        kfree(pl);
}

/*
 * Add the provided pages to a client's free page list, releasing
 * back to the system any beyond the reserved_pages limit.
 */
static void kcopyd_put_pages(struct dm_kcopyd_client *kc, struct page_list *pl)
{
        struct page_list *next;

        do {
                next = pl->next;

                if (kc->nr_free_pages >= kc->nr_reserved_pages)
                        free_pl(pl);
                else {
                        pl->next = kc->pages;
                        kc->pages = pl;
                        kc->nr_free_pages++;
                }

                pl = next;
        } while (pl);
}

static int kcopyd_get_pages(struct dm_kcopyd_client *kc,
                            unsigned int nr, struct page_list **pages)
{
        struct page_list *pl;

        *pages = NULL;

        do {
                pl = alloc_pl(__GFP_NOWARN | __GFP_NORETRY | __GFP_KSWAPD_RECLAIM);
                if (unlikely(!pl)) {
                        /* Use reserved pages */
                        pl = kc->pages;
                        if (unlikely(!pl))
                                goto out_of_memory;
                        kc->pages = pl->next;
                        kc->nr_free_pages--;
                }
                pl->next = *pages;
                *pages = pl;
        } while (--nr);

        return 0;

out_of_memory:
        if (*pages)
                kcopyd_put_pages(kc, *pages);
        return -ENOMEM;
}

/*
 * These three functions resize the page pool.
 */
static void drop_pages(struct page_list *pl)
{
        struct page_list *next;

        while (pl) {
                next = pl->next;
                free_pl(pl);
                pl = next;
        }
}

/*
 * Allocate and reserve nr_pages for the use of a specific client.
 */
static int client_reserve_pages(struct dm_kcopyd_client *kc, unsigned nr_pages)
{
        unsigned i;
        struct page_list *pl = NULL, *next;

        for (i = 0; i < nr_pages; i++) {
                next = alloc_pl(GFP_KERNEL);
                if (!next) {
                        if (pl)
                                drop_pages(pl);
                        return -ENOMEM;
                }
                next->next = pl;
                pl = next;
        }

        kc->nr_reserved_pages += nr_pages;
        kcopyd_put_pages(kc, pl);

        return 0;
}

static void client_free_pages(struct dm_kcopyd_client *kc)
{
        BUG_ON(kc->nr_free_pages != kc->nr_reserved_pages);
        drop_pages(kc->pages);
        kc->pages = NULL;
        kc->nr_free_pages = kc->nr_reserved_pages = 0;
}

/*-----------------------------------------------------------------
 * kcopyd_jobs need to be allocated by the *clients* of kcopyd,
 * for this reason we use a mempool to prevent the client from
 * ever having to do io (which could cause a deadlock).
 *---------------------------------------------------------------*/
struct kcopyd_job {
        struct dm_kcopyd_client *kc;
        struct list_head list;
        unsigned long flags;

        /*
         * Error state of the job.
         */
        int read_err;
        unsigned long write_err;

        /*
         * Either READ or WRITE
         */
        int rw;
        struct dm_io_region source;

        /*
         * The destinations for the transfer.
         */
        unsigned int num_dests;
        struct dm_io_region dests[DM_KCOPYD_MAX_REGIONS];

        struct page_list *pages;

        /*
         * Set this to ensure you are notified when the job has
         * completed.  'context' is for callback to use.
         */
        dm_kcopyd_notify_fn fn;
        void *context;

        /*
         * These fields are only used if the job has been split
         * into more manageable parts.
         */
        struct mutex lock;
        atomic_t sub_jobs;
        sector_t progress;
        sector_t write_offset;

        struct kcopyd_job *master_job;
};

static struct kmem_cache *_job_cache;

int __init dm_kcopyd_init(void)
{
        _job_cache = kmem_cache_create("kcopyd_job",
                                sizeof(struct kcopyd_job) * (SPLIT_COUNT + 1),
                                __alignof__(struct kcopyd_job), 0, NULL);
        if (!_job_cache)
                return -ENOMEM;

        zero_page_list.next = &zero_page_list;
        zero_page_list.page = ZERO_PAGE(0);

        return 0;
}

void dm_kcopyd_exit(void)
{
        kmem_cache_destroy(_job_cache);
        _job_cache = NULL;
}

/*
 * Functions to push and pop a job onto the head of a given job
 * list.
 */
static struct kcopyd_job *pop_io_job(struct list_head *jobs,
                                     struct dm_kcopyd_client *kc)
{
        struct kcopyd_job *job;

        /*
         * For I/O jobs, pop any read, any write without sequential write
         * constraint and sequential writes that are at the right position.
         */
        list_for_each_entry(job, jobs, list) {
                if (job->rw == READ || !test_bit(DM_KCOPYD_WRITE_SEQ, &job->flags)) {
                        list_del(&job->list);
                        return job;
                }

                if (job->write_offset == job->master_job->write_offset) {
                        job->master_job->write_offset += job->source.count;
                        list_del(&job->list);
                        return job;
                }
        }

        return NULL;
}

static struct kcopyd_job *pop(struct list_head *jobs,
                              struct dm_kcopyd_client *kc)
{
        struct kcopyd_job *job = NULL;
        unsigned long flags;

        spin_lock_irqsave(&kc->job_lock, flags);

        if (!list_empty(jobs)) {
                if (jobs == &kc->io_jobs)
                        job = pop_io_job(jobs, kc);
                else {
                        job = list_entry(jobs->next, struct kcopyd_job, list);
                        list_del(&job->list);
                }
        }
        spin_unlock_irqrestore(&kc->job_lock, flags);

        return job;
}

static void push(struct list_head *jobs, struct kcopyd_job *job)
{
        unsigned long flags;
        struct dm_kcopyd_client *kc = job->kc;

        spin_lock_irqsave(&kc->job_lock, flags);
        list_add_tail(&job->list, jobs);
        spin_unlock_irqrestore(&kc->job_lock, flags);
}


static void push_head(struct list_head *jobs, struct kcopyd_job *job)
{
        unsigned long flags;
        struct dm_kcopyd_client *kc = job->kc;

        spin_lock_irqsave(&kc->job_lock, flags);
        list_add(&job->list, jobs);
        spin_unlock_irqrestore(&kc->job_lock, flags);
}

/*
 * These three functions process 1 item from the corresponding
 * job list.
 *
 * They return:
 * < 0: error
 *   0: success
 * > 0: can't process yet.
 */
static int run_complete_job(struct kcopyd_job *job)
{
        void *context = job->context;
        int read_err = job->read_err;
        unsigned long write_err = job->write_err;
        dm_kcopyd_notify_fn fn = job->fn;
        struct dm_kcopyd_client *kc = job->kc;

        if (job->pages && job->pages != &zero_page_list)
                kcopyd_put_pages(kc, job->pages);
        /*
         * If this is the master job, the sub jobs have already
         * completed so we can free everything.
         */
        if (job->master_job == job) {
                mutex_destroy(&job->lock);
                mempool_free(job, &kc->job_pool);
        }
        fn(read_err, write_err, context);

        if (atomic_dec_and_test(&kc->nr_jobs))
                wake_up(&kc->destroyq);

        cond_resched();

        return 0;
}

static void complete_io(unsigned long error, void *context)
{
        struct kcopyd_job *job = (struct kcopyd_job *) context;
        struct dm_kcopyd_client *kc = job->kc;

        io_job_finish(kc->throttle);

        if (error) {
                if (op_is_write(job->rw))
                        job->write_err |= error;
                else
                        job->read_err = 1;

                if (!test_bit(DM_KCOPYD_IGNORE_ERROR, &job->flags)) {
                        push(&kc->complete_jobs, job);
                        wake(kc);
                        return;
                }
        }

        if (op_is_write(job->rw))
                push(&kc->complete_jobs, job);

        else {
                job->rw = WRITE;
                push(&kc->io_jobs, job);
        }

        wake(kc);
}

/*
 * Request io on as many buffer heads as we can currently get for
 * a particular job.
 */
static int run_io_job(struct kcopyd_job *job)
{
        int r;
        struct dm_io_request io_req = {
                .bi_op = job->rw,
                .bi_op_flags = 0,
                .mem.type = DM_IO_PAGE_LIST,
                .mem.ptr.pl = job->pages,
                .mem.offset = 0,
                .notify.fn = complete_io,
                .notify.context = job,
                .client = job->kc->io_client,
        };

        /*
         * If we need to write sequentially and some reads or writes failed,
         * no point in continuing.
         */
        if (test_bit(DM_KCOPYD_WRITE_SEQ, &job->flags) &&
            job->master_job->write_err)
                return -EIO;

        io_job_start(job->kc->throttle);

        if (job->rw == READ)
                r = dm_io(&io_req, 1, &job->source, NULL);
        else
                r = dm_io(&io_req, job->num_dests, job->dests, NULL);

        return r;
}

static int run_pages_job(struct kcopyd_job *job)
{
        int r;
        unsigned nr_pages = dm_div_up(job->dests[0].count, PAGE_SIZE >> 9);

        r = kcopyd_get_pages(job->kc, nr_pages, &job->pages);
        if (!r) {
                /* this job is ready for io */
                push(&job->kc->io_jobs, job);
                return 0;
        }

        if (r == -ENOMEM)
                /* can't complete now */
                return 1;

        return r;
}

/*
 * Run through a list for as long as possible.  Returns the count
 * of successful jobs.
 */
static int process_jobs(struct list_head *jobs, struct dm_kcopyd_client *kc,
                        int (*fn) (struct kcopyd_job *))
{
        struct kcopyd_job *job;
        int r, count = 0;

        while ((job = pop(jobs, kc))) {

                r = fn(job);

                if (r < 0) {
                        /* error this rogue job */
                        if (op_is_write(job->rw))
                                job->write_err = (unsigned long) -1L;
                        else
                                job->read_err = 1;
                        push(&kc->complete_jobs, job);
                        break;
                }

                if (r > 0) {
                        /*
                         * We couldn't service this job ATM, so
                         * push this job back onto the list.
                         */
                        push_head(jobs, job);
                        break;
                }

                count++;
        }

        return count;
}

/*
 * kcopyd does this every time it's woken up.
 */
static void do_work(struct work_struct *work)
{
        struct dm_kcopyd_client *kc = container_of(work,
                                        struct dm_kcopyd_client, kcopyd_work);
        struct blk_plug plug;
        unsigned long flags;

        /*
         * The order that these are called is *very* important.
         * complete jobs can free some pages for pages jobs.
         * Pages jobs when successful will jump onto the io jobs
         * list.  io jobs call wake when they complete and it all
         * starts again.
         */
        spin_lock_irqsave(&kc->job_lock, flags);
        list_splice_tail_init(&kc->callback_jobs, &kc->complete_jobs);
        spin_unlock_irqrestore(&kc->job_lock, flags);

        blk_start_plug(&plug);
        process_jobs(&kc->complete_jobs, kc, run_complete_job);
        process_jobs(&kc->pages_jobs, kc, run_pages_job);
        process_jobs(&kc->io_jobs, kc, run_io_job);
        blk_finish_plug(&plug);
}

/*
 * If we are copying a small region we just dispatch a single job
 * to do the copy, otherwise the io has to be split up into many
 * jobs.
 */
static void dispatch_job(struct kcopyd_job *job)
{
        struct dm_kcopyd_client *kc = job->kc;
        atomic_inc(&kc->nr_jobs);
        if (unlikely(!job->source.count))
                push(&kc->callback_jobs, job);
        else if (job->pages == &zero_page_list)
                push(&kc->io_jobs, job);
        else
                push(&kc->pages_jobs, job);
        wake(kc);
}

static void segment_complete(int read_err, unsigned long write_err,
                             void *context)
{
        /* FIXME: tidy this function */
        sector_t progress = 0;
        sector_t count = 0;
        struct kcopyd_job *sub_job = (struct kcopyd_job *) context;
        struct kcopyd_job *job = sub_job->master_job;
        struct dm_kcopyd_client *kc = job->kc;

        mutex_lock(&job->lock);

        /* update the error */
        if (read_err)
                job->read_err = 1;

        if (write_err)
                job->write_err |= write_err;

        /*
         * Only dispatch more work if there hasn't been an error.
         */
        if ((!job->read_err && !job->write_err) ||
            test_bit(DM_KCOPYD_IGNORE_ERROR, &job->flags)) {
                /* get the next chunk of work */
                progress = job->progress;
                count = job->source.count - progress;
                if (count) {
                        if (count > SUB_JOB_SIZE)
                                count = SUB_JOB_SIZE;

                        job->progress += count;
                }
        }
        mutex_unlock(&job->lock);

        if (count) {
                int i;

                *sub_job = *job;
                sub_job->write_offset = progress;
                sub_job->source.sector += progress;
                sub_job->source.count = count;

                for (i = 0; i < job->num_dests; i++) {
                        sub_job->dests[i].sector += progress;
                        sub_job->dests[i].count = count;
                }

                sub_job->fn = segment_complete;
                sub_job->context = sub_job;
                dispatch_job(sub_job);

        } else if (atomic_dec_and_test(&job->sub_jobs)) {

                /*
                 * Queue the completion callback to the kcopyd thread.
                 *
                 * Some callers assume that all the completions are called
                 * from a single thread and don't race with each other.
                 *
                 * We must not call the callback directly here because this
                 * code may not be executing in the thread.
                 */
                push(&kc->complete_jobs, job);
                wake(kc);
        }
}

/*
 * Create some sub jobs to share the work between them.
 */
static void split_job(struct kcopyd_job *master_job)
{
        int i;

        atomic_inc(&master_job->kc->nr_jobs);

        atomic_set(&master_job->sub_jobs, SPLIT_COUNT);
        for (i = 0; i < SPLIT_COUNT; i++) {
                master_job[i + 1].master_job = master_job;
                segment_complete(0, 0u, &master_job[i + 1]);
        }
}

void dm_kcopyd_copy(struct dm_kcopyd_client *kc, struct dm_io_region *from,
                    unsigned int num_dests, struct dm_io_region *dests,
                    unsigned int flags, dm_kcopyd_notify_fn fn, void *context)
{
        struct kcopyd_job *job;
        int i;

        /*
         * Allocate an array of jobs consisting of one master job
         * followed by SPLIT_COUNT sub jobs.
         */
        job = mempool_alloc(&kc->job_pool, GFP_NOIO);
        mutex_init(&job->lock);

        /*
         * set up for the read.
         */
        job->kc = kc;
        job->flags = flags;
        job->read_err = 0;
        job->write_err = 0;

        job->num_dests = num_dests;
        memcpy(&job->dests, dests, sizeof(*dests) * num_dests);

        /*
         * If one of the destination is a host-managed zoned block device,
         * we need to write sequentially. If one of the destination is a
         * host-aware device, then leave it to the caller to choose what to do.
         */
        if (!test_bit(DM_KCOPYD_WRITE_SEQ, &job->flags)) {
                for (i = 0; i < job->num_dests; i++) {
                        if (bdev_zoned_model(dests[i].bdev) == BLK_ZONED_HM) {
                                set_bit(DM_KCOPYD_WRITE_SEQ, &job->flags);
                                break;
                        }
                }
        }

        /*
         * If we need to write sequentially, errors cannot be ignored.
         */
        if (test_bit(DM_KCOPYD_WRITE_SEQ, &job->flags) &&
            test_bit(DM_KCOPYD_IGNORE_ERROR, &job->flags))
                clear_bit(DM_KCOPYD_IGNORE_ERROR, &job->flags);

        if (from) {
                job->source = *from;
                job->pages = NULL;
                job->rw = READ;
        } else {
                memset(&job->source, 0, sizeof job->source);
                job->source.count = job->dests[0].count;
                job->pages = &zero_page_list;

                /*
                 * Use WRITE ZEROES to optimize zeroing if all dests support it.
                 */
                job->rw = REQ_OP_WRITE_ZEROES;
                for (i = 0; i < job->num_dests; i++)
                        if (!bdev_write_zeroes_sectors(job->dests[i].bdev)) {
                                job->rw = WRITE;
                                break;
                        }
        }

        job->fn = fn;
        job->context = context;
        job->master_job = job;
        job->write_offset = 0;

        if (job->source.count <= SUB_JOB_SIZE)
                dispatch_job(job);
        else {
                job->progress = 0;
                split_job(job);
        }
}
EXPORT_SYMBOL(dm_kcopyd_copy);

void dm_kcopyd_zero(struct dm_kcopyd_client *kc,
                    unsigned num_dests, struct dm_io_region *dests,
                    unsigned flags, dm_kcopyd_notify_fn fn, void *context)
{
        dm_kcopyd_copy(kc, NULL, num_dests, dests, flags, fn, context);
}
EXPORT_SYMBOL(dm_kcopyd_zero);

void *dm_kcopyd_prepare_callback(struct dm_kcopyd_client *kc,
                                 dm_kcopyd_notify_fn fn, void *context)
{
        struct kcopyd_job *job;

        job = mempool_alloc(&kc->job_pool, GFP_NOIO);

        memset(job, 0, sizeof(struct kcopyd_job));
        job->kc = kc;
        job->fn = fn;
        job->context = context;
        job->master_job = job;

        atomic_inc(&kc->nr_jobs);

        return job;
}
EXPORT_SYMBOL(dm_kcopyd_prepare_callback);

void dm_kcopyd_do_callback(void *j, int read_err, unsigned long write_err)
{
        struct kcopyd_job *job = j;
        struct dm_kcopyd_client *kc = job->kc;

        job->read_err = read_err;
        job->write_err = write_err;

        push(&kc->callback_jobs, job);
        wake(kc);
}
EXPORT_SYMBOL(dm_kcopyd_do_callback);

/*
 * Cancels a kcopyd job, eg. someone might be deactivating a
 * mirror.
 */
#if 0
int kcopyd_cancel(struct kcopyd_job *job, int block)
{
        /* FIXME: finish */
        return -1;
}
#endif  /*  0  */

/*-----------------------------------------------------------------
 * Client setup
 *---------------------------------------------------------------*/
struct dm_kcopyd_client *dm_kcopyd_client_create(struct dm_kcopyd_throttle *throttle)
{
        int r;
        struct dm_kcopyd_client *kc;

        kc = kzalloc(sizeof(*kc), GFP_KERNEL);
        if (!kc)
                return ERR_PTR(-ENOMEM);

        spin_lock_init(&kc->job_lock);
        INIT_LIST_HEAD(&kc->callback_jobs);
        INIT_LIST_HEAD(&kc->complete_jobs);
        INIT_LIST_HEAD(&kc->io_jobs);
        INIT_LIST_HEAD(&kc->pages_jobs);
        kc->throttle = throttle;

        r = mempool_init_slab_pool(&kc->job_pool, MIN_JOBS, _job_cache);
        if (r)
                goto bad_slab;

        INIT_WORK(&kc->kcopyd_work, do_work);
        kc->kcopyd_wq = alloc_workqueue("kcopyd", WQ_MEM_RECLAIM, 0);
        if (!kc->kcopyd_wq) {
                r = -ENOMEM;
                goto bad_workqueue;
        }

        kc->pages = NULL;
        kc->nr_reserved_pages = kc->nr_free_pages = 0;
        r = client_reserve_pages(kc, RESERVE_PAGES);
        if (r)
                goto bad_client_pages;

        kc->io_client = dm_io_client_create();
        if (IS_ERR(kc->io_client)) {
                r = PTR_ERR(kc->io_client);
                goto bad_io_client;
        }

        init_waitqueue_head(&kc->destroyq);
        atomic_set(&kc->nr_jobs, 0);

        return kc;

bad_io_client:
        client_free_pages(kc);
bad_client_pages:
        destroy_workqueue(kc->kcopyd_wq);
bad_workqueue:
        mempool_exit(&kc->job_pool);
bad_slab:
        kfree(kc);

        return ERR_PTR(r);
}
EXPORT_SYMBOL(dm_kcopyd_client_create);

void dm_kcopyd_client_destroy(struct dm_kcopyd_client *kc)
{
        /* Wait for completion of all jobs submitted by this client. */
        wait_event(kc->destroyq, !atomic_read(&kc->nr_jobs));

        BUG_ON(!list_empty(&kc->callback_jobs));
        BUG_ON(!list_empty(&kc->complete_jobs));
        BUG_ON(!list_empty(&kc->io_jobs));
        BUG_ON(!list_empty(&kc->pages_jobs));
        destroy_workqueue(kc->kcopyd_wq);
        dm_io_client_destroy(kc->io_client);
        client_free_pages(kc);
        mempool_exit(&kc->job_pool);
        kfree(kc);
}
EXPORT_SYMBOL(dm_kcopyd_client_destroy);