dm.c

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/*
 * Copyright (C) 2001, 2002 Sistina Software (UK) Limited.
 * Copyright (C) 2004-2008 Red Hat, Inc. All rights reserved.
 *
 * This file is released under the GPL.
 */

#include "dm.h"
#include "dm-uevent.h"

#include <linux/init.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/moduleparam.h>
#include <linux/blkpg.h>
#include <linux/bio.h>
#include <linux/mempool.h>
#include <linux/slab.h>
#include <linux/idr.h>
#include <linux/hdreg.h>
#include <linux/delay.h>

#include <trace/events/block.h>

#define DM_MSG_PREFIX "core"

#ifdef CONFIG_PRINTK
/*
 * ratelimit state to be used in DMXXX_LIMIT().
 */
DEFINE_RATELIMIT_STATE(dm_ratelimit_state,
               DEFAULT_RATELIMIT_INTERVAL,
               DEFAULT_RATELIMIT_BURST);
EXPORT_SYMBOL(dm_ratelimit_state);
#endif

/*
 * Cookies are numeric values sent with CHANGE and REMOVE
 * uevents while resuming, removing or renaming the device.
 */
#define DM_COOKIE_ENV_VAR_NAME "DM_COOKIE"
#define DM_COOKIE_LENGTH 24

static const char *_name = DM_NAME;

static unsigned int major = 0;
static unsigned int _major = 0;

static DEFINE_IDR(_minor_idr);

static DEFINE_SPINLOCK(_minor_lock);
/*
 * For bio-based dm.
 * One of these is allocated per bio.
 */
struct dm_io {
    struct mapped_device *md;
    int error;
    atomic_t io_count;
    struct bio *bio;
    unsigned long start_time;
    spinlock_t endio_lock;
};

/*
 * For bio-based dm.
 * One of these is allocated per target within a bio.  Hopefully
 * this will be simplified out one day.
 */
struct dm_target_io {
    struct dm_io *io;
    struct dm_target *ti;
    union map_info info;
    struct bio clone;
};

/*
 * For request-based dm.
 * One of these is allocated per request.
 */
struct dm_rq_target_io {
    struct mapped_device *md;
    struct dm_target *ti;
    struct request *orig, clone;
    int error;
    union map_info info;
};

/*
 * For request-based dm - the bio clones we allocate are embedded in these
 * structs.
 *
 * We allocate these with bio_alloc_bioset, using the front_pad parameter when
 * the bioset is created - this means the bio has to come at the end of the
 * struct.
 */
struct dm_rq_clone_bio_info {
    struct bio *orig;
    struct dm_rq_target_io *tio;
    struct bio clone;
};

union map_info *dm_get_mapinfo(struct bio *bio)
{
    if (bio && bio->bi_private)
        return &((struct dm_target_io *)bio->bi_private)->info;
    return NULL;
}

union map_info *dm_get_rq_mapinfo(struct request *rq)
{
    if (rq && rq->end_io_data)
        return &((struct dm_rq_target_io *)rq->end_io_data)->info;
    return NULL;
}
EXPORT_SYMBOL_GPL(dm_get_rq_mapinfo);

#define MINOR_ALLOCED ((void *)-1)

/*
 * Bits for the md->flags field.
 */
#define DMF_BLOCK_IO_FOR_SUSPEND 0
#define DMF_SUSPENDED 1
#define DMF_FROZEN 2
#define DMF_FREEING 3
#define DMF_DELETING 4
#define DMF_NOFLUSH_SUSPENDING 5
#define DMF_MERGE_IS_OPTIONAL 6

/*
 * Work processed by per-device workqueue.
 */
struct mapped_device {
    struct rw_semaphore io_lock;
    struct mutex suspend_lock;
    rwlock_t map_lock;
    atomic_t holders;
    atomic_t open_count;

    unsigned long flags;

    struct request_queue *queue;
    unsigned type;
    /* Protect queue and type against concurrent access. */
    struct mutex type_lock;

    struct target_type *immutable_target_type;

    struct gendisk *disk;
    char name[16];

    void *interface_ptr;

    /*
     * A list of ios that arrived while we were suspended.
     */
    atomic_t pending[2];
    wait_queue_head_t wait;
    struct work_struct work;
    struct bio_list deferred;
    spinlock_t deferred_lock;

    /*
     * Processing queue (flush)
     */
    struct workqueue_struct *wq;

    /*
     * The current mapping.
     */
    struct dm_table *map;

    /*
     * io objects are allocated from here.
     */
    mempool_t *io_pool;
    mempool_t *tio_pool;

    struct bio_set *bs;

    /*
     * Event handling.
     */
    atomic_t event_nr;
    wait_queue_head_t eventq;
    atomic_t uevent_seq;
    struct list_head uevent_list;
    spinlock_t uevent_lock; /* Protect access to uevent_list */

    /*
     * freeze/thaw support require holding onto a super block
     */
    struct super_block *frozen_sb;
    struct block_device *bdev;

    /* forced geometry settings */
    struct hd_geometry geometry;

    /* sysfs handle */
    struct kobject kobj;

    /* zero-length flush that will be cloned and submitted to targets */
    struct bio flush_bio;
};

/*
 * For mempools pre-allocation at the table loading time.
 */
struct dm_md_mempools {
    mempool_t *io_pool;
    mempool_t *tio_pool;
    struct bio_set *bs;
};

#define MIN_IOS 256
static struct kmem_cache *_io_cache;
static struct kmem_cache *_rq_tio_cache;

/*
 * Unused now, and needs to be deleted. But since io_pool is overloaded and it's
 * still used for _io_cache, I'm leaving this for a later cleanup
 */
static struct kmem_cache *_rq_bio_info_cache;

static int __init local_init(void)
{
    int r = -ENOMEM;

    /* allocate a slab for the dm_ios */
    _io_cache = KMEM_CACHE(dm_io, 0);
    if (!_io_cache)
        return r;

    _rq_tio_cache = KMEM_CACHE(dm_rq_target_io, 0);
    if (!_rq_tio_cache)
        goto out_free_io_cache;

    _rq_bio_info_cache = KMEM_CACHE(dm_rq_clone_bio_info, 0);
    if (!_rq_bio_info_cache)
        goto out_free_rq_tio_cache;

    r = dm_uevent_init();
    if (r)
        goto out_free_rq_bio_info_cache;

    _major = major;
    r = register_blkdev(_major, _name);
    if (r < 0)
        goto out_uevent_exit;

    if (!_major)
        _major = r;

    return 0;

out_uevent_exit:
    dm_uevent_exit();
out_free_rq_bio_info_cache:
    kmem_cache_destroy(_rq_bio_info_cache);
out_free_rq_tio_cache:
    kmem_cache_destroy(_rq_tio_cache);
out_free_io_cache:
    kmem_cache_destroy(_io_cache);

    return r;
}

static void local_exit(void)
{
    kmem_cache_destroy(_rq_bio_info_cache);
    kmem_cache_destroy(_rq_tio_cache);
    kmem_cache_destroy(_io_cache);
    unregister_blkdev(_major, _name);
    dm_uevent_exit();

    _major = 0;

    DMINFO("cleaned up");
}

static int (*_inits[])(void) __initdata = {
    local_init,
    dm_target_init,
    dm_linear_init,
    dm_stripe_init,
    dm_io_init,
    dm_kcopyd_init,
    dm_interface_init,
};

static void (*_exits[])(void) = {
    local_exit,
    dm_target_exit,
    dm_linear_exit,
    dm_stripe_exit,
    dm_io_exit,
    dm_kcopyd_exit,
    dm_interface_exit,
};

static int __init dm_init(void)
{
    const int count = ARRAY_SIZE(_inits);

    int r, i;

    for (i = 0; i < count; i++) {
        r = _inits[i]();
        if (r)
            goto bad;
    }

    return 0;

      bad:
    while (i--)
        _exits[i]();

    return r;
}

static void __exit dm_exit(void)
{
    int i = ARRAY_SIZE(_exits);

    while (i--)
        _exits[i]();

    /*
     * Should be empty by this point.
     */
    idr_remove_all(&_minor_idr);
    idr_destroy(&_minor_idr);
}

/*
 * Block device functions
 */
int dm_deleting_md(struct mapped_device *md)
{
    return test_bit(DMF_DELETING, &md->flags);
}

static int dm_blk_open(struct block_device *bdev, fmode_t mode)
{
    struct mapped_device *md;

    spin_lock(&_minor_lock);

    md = bdev->bd_disk->private_data;
    if (!md)
        goto out;

    if (test_bit(DMF_FREEING, &md->flags) ||
        dm_deleting_md(md)) {
        md = NULL;
        goto out;
    }

    dm_get(md);
    atomic_inc(&md->open_count);

out:
    spin_unlock(&_minor_lock);

    return md ? 0 : -ENXIO;
}

static int dm_blk_close(struct gendisk *disk, fmode_t mode)
{
    struct mapped_device *md = disk->private_data;

    spin_lock(&_minor_lock);

    atomic_dec(&md->open_count);
    dm_put(md);

    spin_unlock(&_minor_lock);

    return 0;
}

int dm_open_count(struct mapped_device *md)
{
    return atomic_read(&md->open_count);
}

/*
 * Guarantees nothing is using the device before it's deleted.
 */
int dm_lock_for_deletion(struct mapped_device *md)
{
    int r = 0;

    spin_lock(&_minor_lock);

    if (dm_open_count(md))
        r = -EBUSY;
    else
        set_bit(DMF_DELETING, &md->flags);

    spin_unlock(&_minor_lock);

    return r;
}

static int dm_blk_getgeo(struct block_device *bdev, struct hd_geometry *geo)
{
    struct mapped_device *md = bdev->bd_disk->private_data;

    return dm_get_geometry(md, geo);
}

static int dm_blk_ioctl(struct block_device *bdev, fmode_t mode,
            unsigned int cmd, unsigned long arg)
{
    struct mapped_device *md = bdev->bd_disk->private_data;
    struct dm_table *map = dm_get_live_table(md);
    struct dm_target *tgt;
    int r = -ENOTTY;

    if (!map || !dm_table_get_size(map))
        goto out;

    /* We only support devices that have a single target */
    if (dm_table_get_num_targets(map) != 1)
        goto out;

    tgt = dm_table_get_target(map, 0);

    if (dm_suspended_md(md)) {
        r = -EAGAIN;
        goto out;
    }

    if (tgt->type->ioctl)
        r = tgt->type->ioctl(tgt, cmd, arg);

out:
    dm_table_put(map);

    return r;
}

static struct dm_io *alloc_io(struct mapped_device *md)
{
    return mempool_alloc(md->io_pool, GFP_NOIO);
}

static void free_io(struct mapped_device *md, struct dm_io *io)
{
    mempool_free(io, md->io_pool);
}

static void free_tio(struct mapped_device *md, struct dm_target_io *tio)
{
    bio_put(&tio->clone);
}

static struct dm_rq_target_io *alloc_rq_tio(struct mapped_device *md,
                        gfp_t gfp_mask)
{
    return mempool_alloc(md->tio_pool, gfp_mask);
}

static void free_rq_tio(struct dm_rq_target_io *tio)
{
    mempool_free(tio, tio->md->tio_pool);
}

static int md_in_flight(struct mapped_device *md)
{
    return atomic_read(&md->pending[READ]) +
           atomic_read(&md->pending[WRITE]);
}

static void start_io_acct(struct dm_io *io)
{
    struct mapped_device *md = io->md;
    int cpu;
    int rw = bio_data_dir(io->bio);

    io->start_time = jiffies;

    cpu = part_stat_lock();
    part_round_stats(cpu, &dm_disk(md)->part0);
    part_stat_unlock();
    atomic_set(&dm_disk(md)->part0.in_flight[rw],
        atomic_inc_return(&md->pending[rw]));
}

static void end_io_acct(struct dm_io *io)
{
    struct mapped_device *md = io->md;
    struct bio *bio = io->bio;
    unsigned long duration = jiffies - io->start_time;
    int pending, cpu;
    int rw = bio_data_dir(bio);

    cpu = part_stat_lock();
    part_round_stats(cpu, &dm_disk(md)->part0);
    part_stat_add(cpu, &dm_disk(md)->part0, ticks[rw], duration);
    part_stat_unlock();

    /*
     * After this is decremented the bio must not be touched if it is
     * a flush.
     */
    pending = atomic_dec_return(&md->pending[rw]);
    atomic_set(&dm_disk(md)->part0.in_flight[rw], pending);
    pending += atomic_read(&md->pending[rw^0x1]);

    /* nudge anyone waiting on suspend queue */
    if (!pending)
        wake_up(&md->wait);
}

/*
 * Add the bio to the list of deferred io.
 */
static void queue_io(struct mapped_device *md, struct bio *bio)
{
    unsigned long flags;

    spin_lock_irqsave(&md->deferred_lock, flags);
    bio_list_add(&md->deferred, bio);
    spin_unlock_irqrestore(&md->deferred_lock, flags);
    queue_work(md->wq, &md->work);
}

/*
 * Everyone (including functions in this file), should use this
 * function to access the md->map field, and make sure they call
 * dm_table_put() when finished.
 */
struct dm_table *dm_get_live_table(struct mapped_device *md)
{
    struct dm_table *t;
    unsigned long flags;

    read_lock_irqsave(&md->map_lock, flags);
    t = md->map;
    if (t)
        dm_table_get(t);
    read_unlock_irqrestore(&md->map_lock, flags);

    return t;
}

/*
 * Get the geometry associated with a dm device
 */
int dm_get_geometry(struct mapped_device *md, struct hd_geometry *geo)
{
    *geo = md->geometry;

    return 0;
}

/*
 * Set the geometry of a device.
 */
int dm_set_geometry(struct mapped_device *md, struct hd_geometry *geo)
{
    sector_t sz = (sector_t)geo->cylinders * geo->heads * geo->sectors;

    if (geo->start > sz) {
        DMWARN("Start sector is beyond the geometry limits.");
        return -EINVAL;
    }

    md->geometry = *geo;

    return 0;
}

/*-----------------------------------------------------------------
 * CRUD START:
 *   A more elegant soln is in the works that uses the queue
 *   merge fn, unfortunately there are a couple of changes to
 *   the block layer that I want to make for this.  So in the
 *   interests of getting something for people to use I give
 *   you this clearly demarcated crap.
 *---------------------------------------------------------------*/

static int __noflush_suspending(struct mapped_device *md)
{
    return test_bit(DMF_NOFLUSH_SUSPENDING, &md->flags);
}

/*
 * Decrements the number of outstanding ios that a bio has been
 * cloned into, completing the original io if necc.
 */
static void dec_pending(struct dm_io *io, int error)
{
    unsigned long flags;
    int io_error;
    struct bio *bio;
    struct mapped_device *md = io->md;

    /* Push-back supersedes any I/O errors */
    if (unlikely(error)) {
        spin_lock_irqsave(&io->endio_lock, flags);
        if (!(io->error > 0 && __noflush_suspending(md)))
            io->error = error;
        spin_unlock_irqrestore(&io->endio_lock, flags);
    }

    if (atomic_dec_and_test(&io->io_count)) {
        if (io->error == DM_ENDIO_REQUEUE) {
            /*
             * Target requested pushing back the I/O.
             */
            spin_lock_irqsave(&md->deferred_lock, flags);
            if (__noflush_suspending(md))
                bio_list_add_head(&md->deferred, io->bio);
            else
                /* noflush suspend was interrupted. */
                io->error = -EIO;
            spin_unlock_irqrestore(&md->deferred_lock, flags);
        }

        io_error = io->error;
        bio = io->bio;
        end_io_acct(io);
        free_io(md, io);

        if (io_error == DM_ENDIO_REQUEUE)
            return;

        if ((bio->bi_rw & REQ_FLUSH) && bio->bi_size) {
            /*
             * Preflush done for flush with data, reissue
             * without REQ_FLUSH.
             */
            bio->bi_rw &= ~REQ_FLUSH;
            queue_io(md, bio);
        } else {
            /* done with normal IO or empty flush */
            trace_block_bio_complete(md->queue, bio, io_error);
            bio_endio(bio, io_error);
        }
    }
}

static void clone_endio(struct bio *bio, int error)
{
    int r = 0;
    struct dm_target_io *tio = bio->bi_private;
    struct dm_io *io = tio->io;
    struct mapped_device *md = tio->io->md;
    dm_endio_fn endio = tio->ti->type->end_io;

    if (!bio_flagged(bio, BIO_UPTODATE) && !error)
        error = -EIO;

    if (endio) {
        r = endio(tio->ti, bio, error, &tio->info);
        if (r < 0 || r == DM_ENDIO_REQUEUE)
            /*
             * error and requeue request are handled
             * in dec_pending().
             */
            error = r;
        else if (r == DM_ENDIO_INCOMPLETE)
            /* The target will handle the io */
            return;
        else if (r) {
            DMWARN("unimplemented target endio return value: %d", r);
            BUG();
        }
    }

    free_tio(md, tio);
    dec_pending(io, error);
}

/*
 * Partial completion handling for request-based dm
 */
static void end_clone_bio(struct bio *clone, int error)
{
    struct dm_rq_clone_bio_info *info = clone->bi_private;
    struct dm_rq_target_io *tio = info->tio;
    struct bio *bio = info->orig;
    unsigned int nr_bytes = info->orig->bi_size;

    bio_put(clone);

    if (tio->error)
        /*
         * An error has already been detected on the request.
         * Once error occurred, just let clone->end_io() handle
         * the remainder.
         */
        return;
    else if (error) {
        /*
         * Don't notice the error to the upper layer yet.
         * The error handling decision is made by the target driver,
         * when the request is completed.
         */
        tio->error = error;
        return;
    }

    /*
     * I/O for the bio successfully completed.
     * Notice the data completion to the upper layer.
     */

    /*
     * bios are processed from the head of the list.
     * So the completing bio should always be rq->bio.
     * If it's not, something wrong is happening.
     */
    if (tio->orig->bio != bio)
        DMERR("bio completion is going in the middle of the request");

    /*
     * Update the original request.
     * Do not use blk_end_request() here, because it may complete
     * the original request before the clone, and break the ordering.
     */
    blk_update_request(tio->orig, 0, nr_bytes);
}

/*
 * Don't touch any member of the md after calling this function because
 * the md may be freed in dm_put() at the end of this function.
 * Or do dm_get() before calling this function and dm_put() later.
 */
static void rq_completed(struct mapped_device *md, int rw, int run_queue)
{
    atomic_dec(&md->pending[rw]);

    /* nudge anyone waiting on suspend queue */
    if (!md_in_flight(md))
        wake_up(&md->wait);

    /*
     * Run this off this callpath, as drivers could invoke end_io while
     * inside their request_fn (and holding the queue lock). Calling
     * back into ->request_fn() could deadlock attempting to grab the
     * queue lock again.
     */
    if (run_queue)
        blk_run_queue_async(md->queue);

    /*
     * dm_put() must be at the end of this function. See the comment above
     */
    dm_put(md);
}

static void free_rq_clone(struct request *clone)
{
    struct dm_rq_target_io *tio = clone->end_io_data;

    blk_rq_unprep_clone(clone);
    free_rq_tio(tio);
}

/*
 * Complete the clone and the original request.
 * Must be called without queue lock.
 */
static void dm_end_request(struct request *clone, int error)
{
    int rw = rq_data_dir(clone);
    struct dm_rq_target_io *tio = clone->end_io_data;
    struct mapped_device *md = tio->md;
    struct request *rq = tio->orig;

    if (rq->cmd_type == REQ_TYPE_BLOCK_PC) {
        rq->errors = clone->errors;
        rq->resid_len = clone->resid_len;

        if (rq->sense)
            /*
             * We are using the sense buffer of the original
             * request.
             * So setting the length of the sense data is enough.
             */
            rq->sense_len = clone->sense_len;
    }

    free_rq_clone(clone);
    blk_end_request_all(rq, error);
    rq_completed(md, rw, true);
}

static void dm_unprep_request(struct request *rq)
{
    struct request *clone = rq->special;

    rq->special = NULL;
    rq->cmd_flags &= ~REQ_DONTPREP;

    free_rq_clone(clone);
}

/*
 * Requeue the original request of a clone.
 */
void dm_requeue_unmapped_request(struct request *clone)
{
    int rw = rq_data_dir(clone);
    struct dm_rq_target_io *tio = clone->end_io_data;
    struct mapped_device *md = tio->md;
    struct request *rq = tio->orig;
    struct request_queue *q = rq->q;
    unsigned long flags;

    dm_unprep_request(rq);

    spin_lock_irqsave(q->queue_lock, flags);
    blk_requeue_request(q, rq);
    spin_unlock_irqrestore(q->queue_lock, flags);

    rq_completed(md, rw, 0);
}
EXPORT_SYMBOL_GPL(dm_requeue_unmapped_request);

static void __stop_queue(struct request_queue *q)
{
    blk_stop_queue(q);
}

static void stop_queue(struct request_queue *q)
{
    unsigned long flags;

    spin_lock_irqsave(q->queue_lock, flags);
    __stop_queue(q);
    spin_unlock_irqrestore(q->queue_lock, flags);
}

static void __start_queue(struct request_queue *q)
{
    if (blk_queue_stopped(q))
        blk_start_queue(q);
}

static void start_queue(struct request_queue *q)
{
    unsigned long flags;

    spin_lock_irqsave(q->queue_lock, flags);
    __start_queue(q);
    spin_unlock_irqrestore(q->queue_lock, flags);
}

static void dm_done(struct request *clone, int error, bool mapped)
{
    int r = error;
    struct dm_rq_target_io *tio = clone->end_io_data;
    dm_request_endio_fn rq_end_io = NULL;

    if (tio->ti) {
        rq_end_io = tio->ti->type->rq_end_io;

        if (mapped && rq_end_io)
            r = rq_end_io(tio->ti, clone, error, &tio->info);
    }

    if (r <= 0)
        /* The target wants to complete the I/O */
        dm_end_request(clone, r);
    else if (r == DM_ENDIO_INCOMPLETE)
        /* The target will handle the I/O */
        return;
    else if (r == DM_ENDIO_REQUEUE)
        /* The target wants to requeue the I/O */
        dm_requeue_unmapped_request(clone);
    else {
        DMWARN("unimplemented target endio return value: %d", r);
        BUG();
    }
}

/*
 * Request completion handler for request-based dm
 */
static void dm_softirq_done(struct request *rq)
{
    bool mapped = true;
    struct request *clone = rq->completion_data;
    struct dm_rq_target_io *tio = clone->end_io_data;

    if (rq->cmd_flags & REQ_FAILED)
        mapped = false;

    dm_done(clone, tio->error, mapped);
}

/*
 * Complete the clone and the original request with the error status
 * through softirq context.
 */
static void dm_complete_request(struct request *clone, int error)
{
    struct dm_rq_target_io *tio = clone->end_io_data;
    struct request *rq = tio->orig;

    tio->error = error;
    rq->completion_data = clone;
    blk_complete_request(rq);
}

/*
 * Complete the not-mapped clone and the original request with the error status
 * through softirq context.
 * Target's rq_end_io() function isn't called.
 * This may be used when the target's map_rq() function fails.
 */
void dm_kill_unmapped_request(struct request *clone, int error)
{
    struct dm_rq_target_io *tio = clone->end_io_data;
    struct request *rq = tio->orig;

    rq->cmd_flags |= REQ_FAILED;
    dm_complete_request(clone, error);
}
EXPORT_SYMBOL_GPL(dm_kill_unmapped_request);

/*
 * Called with the queue lock held
 */
static void end_clone_request(struct request *clone, int error)
{
    /*
     * For just cleaning up the information of the queue in which
     * the clone was dispatched.
     * The clone is *NOT* freed actually here because it is alloced from
     * dm own mempool and REQ_ALLOCED isn't set in clone->cmd_flags.
     */
    __blk_put_request(clone->q, clone);

    /*
     * Actual request completion is done in a softirq context which doesn't
     * hold the queue lock.  Otherwise, deadlock could occur because:
     *     - another request may be submitted by the upper level driver
     *       of the stacking during the completion
     *     - the submission which requires queue lock may be done
     *       against this queue
     */
    dm_complete_request(clone, error);
}

/*
 * Return maximum size of I/O possible at the supplied sector up to the current
 * target boundary.
 */
static sector_t max_io_len_target_boundary(sector_t sector, struct dm_target *ti)
{
    sector_t target_offset = dm_target_offset(ti, sector);

    return ti->len - target_offset;
}

static sector_t max_io_len(sector_t sector, struct dm_target *ti)
{
    sector_t len = max_io_len_target_boundary(sector, ti);
    sector_t offset, max_len;

    /*
     * Does the target need to split even further?
     */
    if (ti->max_io_len) {
        offset = dm_target_offset(ti, sector);
        if (unlikely(ti->max_io_len & (ti->max_io_len - 1)))
            max_len = sector_div(offset, ti->max_io_len);
        else
            max_len = offset & (ti->max_io_len - 1);
        max_len = ti->max_io_len - max_len;

        if (len > max_len)
            len = max_len;
    }

    return len;
}

int dm_set_target_max_io_len(struct dm_target *ti, sector_t len)
{
    if (len > UINT_MAX) {
        DMERR("Specified maximum size of target IO (%llu) exceeds limit (%u)",
              (unsigned long long)len, UINT_MAX);
        ti->error = "Maximum size of target IO is too large";
        return -EINVAL;
    }

    ti->max_io_len = (uint32_t) len;

    return 0;
}
EXPORT_SYMBOL_GPL(dm_set_target_max_io_len);

static void __map_bio(struct dm_target *ti, struct dm_target_io *tio)
{
    int r;
    sector_t sector;
    struct mapped_device *md;
    struct bio *clone = &tio->clone;

    clone->bi_end_io = clone_endio;
    clone->bi_private = tio;

    /*
     * Map the clone.  If r == 0 we don't need to do
     * anything, the target has assumed ownership of
     * this io.
     */
    atomic_inc(&tio->io->io_count);
    sector = clone->bi_sector;
    r = ti->type->map(ti, clone, &tio->info);
    if (r == DM_MAPIO_REMAPPED) {
        /* the bio has been remapped so dispatch it */

        trace_block_bio_remap(bdev_get_queue(clone->bi_bdev), clone,
                      tio->io->bio->bi_bdev->bd_dev, sector);

        generic_make_request(clone);
    } else if (r < 0 || r == DM_MAPIO_REQUEUE) {
        /* error the io and bail out, or requeue it if needed */
        md = tio->io->md;
        dec_pending(tio->io, r);
        free_tio(md, tio);
    } else if (r) {
        DMWARN("unimplemented target map return value: %d", r);
        BUG();
    }
}

struct clone_info {
    struct mapped_device *md;
    struct dm_table *map;
    struct bio *bio;
    struct dm_io *io;
    sector_t sector;
    sector_t sector_count;
    unsigned short idx;
};

/*
 * Creates a little bio that just does part of a bvec.
 */
static void split_bvec(struct dm_target_io *tio, struct bio *bio,
               sector_t sector, unsigned short idx, unsigned int offset,
               unsigned int len, struct bio_set *bs)
{
    struct bio *clone = &tio->clone;
    struct bio_vec *bv = bio->bi_io_vec + idx;

    *clone->bi_io_vec = *bv;

    clone->bi_sector = sector;
    clone->bi_bdev = bio->bi_bdev;
    clone->bi_rw = bio->bi_rw;
    clone->bi_vcnt = 1;
    clone->bi_size = to_bytes(len);
    clone->bi_io_vec->bv_offset = offset;
    clone->bi_io_vec->bv_len = clone->bi_size;
    clone->bi_flags |= 1 << BIO_CLONED;

    if (bio_integrity(bio)) {
        bio_integrity_clone(clone, bio, GFP_NOIO);
        bio_integrity_trim(clone,
                   bio_sector_offset(bio, idx, offset), len);
    }
}

/*
 * Creates a bio that consists of range of complete bvecs.
 */
static void clone_bio(struct dm_target_io *tio, struct bio *bio,
              sector_t sector, unsigned short idx,
              unsigned short bv_count, unsigned int len,
              struct bio_set *bs)
{
    struct bio *clone = &tio->clone;

    __bio_clone(clone, bio);
    clone->bi_sector = sector;
    clone->bi_idx = idx;
    clone->bi_vcnt = idx + bv_count;
    clone->bi_size = to_bytes(len);
    clone->bi_flags &= ~(1 << BIO_SEG_VALID);

    if (bio_integrity(bio)) {
        bio_integrity_clone(clone, bio, GFP_NOIO);

        if (idx != bio->bi_idx || clone->bi_size < bio->bi_size)
            bio_integrity_trim(clone,
                       bio_sector_offset(bio, idx, 0), len);
    }
}

static struct dm_target_io *alloc_tio(struct clone_info *ci,
                      struct dm_target *ti, int nr_iovecs)
{
    struct dm_target_io *tio;
    struct bio *clone;

    clone = bio_alloc_bioset(GFP_NOIO, nr_iovecs, ci->md->bs);
    tio = container_of(clone, struct dm_target_io, clone);

    tio->io = ci->io;
    tio->ti = ti;
    memset(&tio->info, 0, sizeof(tio->info));

    return tio;
}

static void __issue_target_request(struct clone_info *ci, struct dm_target *ti,
                   unsigned request_nr, sector_t len)
{
    struct dm_target_io *tio = alloc_tio(ci, ti, ci->bio->bi_max_vecs);
    struct bio *clone = &tio->clone;

    tio->info.target_request_nr = request_nr;

    /*
     * Discard requests require the bio's inline iovecs be initialized.
     * ci->bio->bi_max_vecs is BIO_INLINE_VECS anyway, for both flush
     * and discard, so no need for concern about wasted bvec allocations.
     */

     __bio_clone(clone, ci->bio);
    if (len) {
        clone->bi_sector = ci->sector;
        clone->bi_size = to_bytes(len);
    }

    __map_bio(ti, tio);
}

static void __issue_target_requests(struct clone_info *ci, struct dm_target *ti,
                    unsigned num_requests, sector_t len)
{
    unsigned request_nr;

    for (request_nr = 0; request_nr < num_requests; request_nr++)
        __issue_target_request(ci, ti, request_nr, len);
}

static int __clone_and_map_empty_flush(struct clone_info *ci)
{
    unsigned target_nr = 0;
    struct dm_target *ti;

    BUG_ON(bio_has_data(ci->bio));
    while ((ti = dm_table_get_target(ci->map, target_nr++)))
        __issue_target_requests(ci, ti, ti->num_flush_requests, 0);

    return 0;
}

/*
 * Perform all io with a single clone.
 */
static void __clone_and_map_simple(struct clone_info *ci, struct dm_target *ti)
{
    struct bio *bio = ci->bio;
    struct dm_target_io *tio;

    tio = alloc_tio(ci, ti, bio->bi_max_vecs);
    clone_bio(tio, bio, ci->sector, ci->idx, bio->bi_vcnt - ci->idx,
          ci->sector_count, ci->md->bs);
    __map_bio(ti, tio);
    ci->sector_count = 0;
}

static int __clone_and_map_discard(struct clone_info *ci)
{
    struct dm_target *ti;
    sector_t len;

    do {
        ti = dm_table_find_target(ci->map, ci->sector);
        if (!dm_target_is_valid(ti))
            return -EIO;

        /*
         * Even though the device advertised discard support,
         * that does not mean every target supports it, and
         * reconfiguration might also have changed that since the
         * check was performed.
         */
        if (!ti->num_discard_requests)
            return -EOPNOTSUPP;

        if (!ti->split_discard_requests)
            len = min(ci->sector_count, max_io_len_target_boundary(ci->sector, ti));
        else
            len = min(ci->sector_count, max_io_len(ci->sector, ti));

        __issue_target_requests(ci, ti, ti->num_discard_requests, len);

        ci->sector += len;
    } while (ci->sector_count -= len);

    return 0;
}

static int __clone_and_map(struct clone_info *ci)
{
    struct bio *bio = ci->bio;
    struct dm_target *ti;
    sector_t len = 0, max;
    struct dm_target_io *tio;

    if (unlikely(bio->bi_rw & REQ_DISCARD))
        return __clone_and_map_discard(ci);

    ti = dm_table_find_target(ci->map, ci->sector);
    if (!dm_target_is_valid(ti))
        return -EIO;

    max = max_io_len(ci->sector, ti);

    if (ci->sector_count <= max) {
        /*
         * Optimise for the simple case where we can do all of
         * the remaining io with a single clone.
         */
        __clone_and_map_simple(ci, ti);

    } else if (to_sector(bio->bi_io_vec[ci->idx].bv_len) <= max) {
        /*
         * There are some bvecs that don't span targets.
         * Do as many of these as possible.
         */
        int i;
        sector_t remaining = max;
        sector_t bv_len;

        for (i = ci->idx; remaining && (i < bio->bi_vcnt); i++) {
            bv_len = to_sector(bio->bi_io_vec[i].bv_len);

            if (bv_len > remaining)
                break;

            remaining -= bv_len;
            len += bv_len;
        }

        tio = alloc_tio(ci, ti, bio->bi_max_vecs);
        clone_bio(tio, bio, ci->sector, ci->idx, i - ci->idx, len,
              ci->md->bs);
        __map_bio(ti, tio);

        ci->sector += len;
        ci->sector_count -= len;
        ci->idx = i;

    } else {
        /*
         * Handle a bvec that must be split between two or more targets.
         */
        struct bio_vec *bv = bio->bi_io_vec + ci->idx;
        sector_t remaining = to_sector(bv->bv_len);
        unsigned int offset = 0;

        do {
            if (offset) {
                ti = dm_table_find_target(ci->map, ci->sector);
                if (!dm_target_is_valid(ti))
                    return -EIO;

                max = max_io_len(ci->sector, ti);
            }

            len = min(remaining, max);

            tio = alloc_tio(ci, ti, 1);
            split_bvec(tio, bio, ci->sector, ci->idx,
                   bv->bv_offset + offset, len, ci->md->bs);

            __map_bio(ti, tio);

            ci->sector += len;
            ci->sector_count -= len;
            offset += to_bytes(len);
        } while (remaining -= len);

        ci->idx++;
    }

    return 0;
}

/*
 * Split the bio into several clones and submit it to targets.
 */
static void __split_and_process_bio(struct mapped_device *md, struct bio *bio)
{
    struct clone_info ci;
    int error = 0;

    ci.map = dm_get_live_table(md);
    if (unlikely(!ci.map)) {
        bio_io_error(bio);
        return;
    }

    ci.md = md;
    ci.io = alloc_io(md);
    ci.io->error = 0;
    atomic_set(&ci.io->io_count, 1);
    ci.io->bio = bio;
    ci.io->md = md;
    spin_lock_init(&ci.io->endio_lock);
    ci.sector = bio->bi_sector;
    ci.idx = bio->bi_idx;

    start_io_acct(ci.io);
    if (bio->bi_rw & REQ_FLUSH) {
        ci.bio = &ci.md->flush_bio;
        ci.sector_count = 0;
        error = __clone_and_map_empty_flush(&ci);
        /* dec_pending submits any data associated with flush */
    } else {
        ci.bio = bio;
        ci.sector_count = bio_sectors(bio);
        while (ci.sector_count && !error)
            error = __clone_and_map(&ci);
    }

    /* drop the extra reference count */
    dec_pending(ci.io, error);
    dm_table_put(ci.map);
}
/*-----------------------------------------------------------------
 * CRUD END
 *---------------------------------------------------------------*/

static int dm_merge_bvec(struct request_queue *q,
             struct bvec_merge_data *bvm,
             struct bio_vec *biovec)
{
    struct mapped_device *md = q->queuedata;
    struct dm_table *map = dm_get_live_table(md);
    struct dm_target *ti;
    sector_t max_sectors;
    int max_size = 0;

    if (unlikely(!map))
        goto out;

    ti = dm_table_find_target(map, bvm->bi_sector);
    if (!dm_target_is_valid(ti))
        goto out_table;

    /*
     * Find maximum amount of I/O that won't need splitting
     */
    max_sectors = min(max_io_len(bvm->bi_sector, ti),
              (sector_t) BIO_MAX_SECTORS);
    max_size = (max_sectors << SECTOR_SHIFT) - bvm->bi_size;
    if (max_size < 0)
        max_size = 0;

    /*
     * merge_bvec_fn() returns number of bytes
     * it can accept at this offset
     * max is precomputed maximal io size
     */
    if (max_size && ti->type->merge)
        max_size = ti->type->merge(ti, bvm, biovec, max_size);
    /*
     * If the target doesn't support merge method and some of the devices
     * provided their merge_bvec method (we know this by looking at
     * queue_max_hw_sectors), then we can't allow bios with multiple vector
     * entries.  So always set max_size to 0, and the code below allows
     * just one page.
     */
    else if (queue_max_hw_sectors(q) <= PAGE_SIZE >> 9)

        max_size = 0;

out_table:
    dm_table_put(map);

out:
    /*
     * Always allow an entire first page
     */
    if (max_size <= biovec->bv_len && !(bvm->bi_size >> SECTOR_SHIFT))
        max_size = biovec->bv_len;

    return max_size;
}

/*
 * The request function that just remaps the bio built up by
 * dm_merge_bvec.
 */
static void _dm_request(struct request_queue *q, struct bio *bio)
{
    int rw = bio_data_dir(bio);
    struct mapped_device *md = q->queuedata;
    int cpu;

    down_read(&md->io_lock);

    cpu = part_stat_lock();
    part_stat_inc(cpu, &dm_disk(md)->part0, ios[rw]);
    part_stat_add(cpu, &dm_disk(md)->part0, sectors[rw], bio_sectors(bio));
    part_stat_unlock();

    /* if we're suspended, we have to queue this io for later */
    if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags))) {
        up_read(&md->io_lock);

        if (bio_rw(bio) != READA)
            queue_io(md, bio);
        else
            bio_io_error(bio);
        return;
    }

    __split_and_process_bio(md, bio);
    up_read(&md->io_lock);
    return;
}

static int dm_request_based(struct mapped_device *md)
{
    return blk_queue_stackable(md->queue);
}

static void dm_request(struct request_queue *q, struct bio *bio)
{
    struct mapped_device *md = q->queuedata;

    if (dm_request_based(md))
        blk_queue_bio(q, bio);
    else
        _dm_request(q, bio);
}

void dm_dispatch_request(struct request *rq)
{
    int r;

    if (blk_queue_io_stat(rq->q))
        rq->cmd_flags |= REQ_IO_STAT;

    rq->start_time = jiffies;
    r = blk_insert_cloned_request(rq->q, rq);
    if (r)
        dm_complete_request(rq, r);
}
EXPORT_SYMBOL_GPL(dm_dispatch_request);

static int dm_rq_bio_constructor(struct bio *bio, struct bio *bio_orig,
                 void *data)
{
    struct dm_rq_target_io *tio = data;
    struct dm_rq_clone_bio_info *info =
        container_of(bio, struct dm_rq_clone_bio_info, clone);

    info->orig = bio_orig;
    info->tio = tio;
    bio->bi_end_io = end_clone_bio;
    bio->bi_private = info;

    return 0;
}

static int setup_clone(struct request *clone, struct request *rq,
               struct dm_rq_target_io *tio)
{
    int r;

    r = blk_rq_prep_clone(clone, rq, tio->md->bs, GFP_ATOMIC,
                  dm_rq_bio_constructor, tio);
    if (r)
        return r;

    clone->cmd = rq->cmd;
    clone->cmd_len = rq->cmd_len;
    clone->sense = rq->sense;
    clone->buffer = rq->buffer;
    clone->end_io = end_clone_request;
    clone->end_io_data = tio;

    return 0;
}

static struct request *clone_rq(struct request *rq, struct mapped_device *md,
                gfp_t gfp_mask)
{
    struct request *clone;
    struct dm_rq_target_io *tio;

    tio = alloc_rq_tio(md, gfp_mask);
    if (!tio)
        return NULL;

    tio->md = md;
    tio->ti = NULL;
    tio->orig = rq;
    tio->error = 0;
    memset(&tio->info, 0, sizeof(tio->info));

    clone = &tio->clone;
    if (setup_clone(clone, rq, tio)) {
        /* -ENOMEM */
        free_rq_tio(tio);
        return NULL;
    }

    return clone;
}

/*
 * Called with the queue lock held.
 */
static int dm_prep_fn(struct request_queue *q, struct request *rq)
{
    struct mapped_device *md = q->queuedata;
    struct request *clone;

    if (unlikely(rq->special)) {
        DMWARN("Already has something in rq->special.");
        return BLKPREP_KILL;
    }

    clone = clone_rq(rq, md, GFP_ATOMIC);
    if (!clone)
        return BLKPREP_DEFER;

    rq->special = clone;
    rq->cmd_flags |= REQ_DONTPREP;

    return BLKPREP_OK;
}

/*
 * Returns:
 * 0  : the request has been processed (not requeued)
 * !0 : the request has been requeued
 */
static int map_request(struct dm_target *ti, struct request *clone,
               struct mapped_device *md)
{
    int r, requeued = 0;
    struct dm_rq_target_io *tio = clone->end_io_data;

    tio->ti = ti;
    r = ti->type->map_rq(ti, clone, &tio->info);
    switch (r) {
    case DM_MAPIO_SUBMITTED:
        /* The target has taken the I/O to submit by itself later */
        break;
    case DM_MAPIO_REMAPPED:
        /* The target has remapped the I/O so dispatch it */
        trace_block_rq_remap(clone->q, clone, disk_devt(dm_disk(md)),
                     blk_rq_pos(tio->orig));
        dm_dispatch_request(clone);
        break;
    case DM_MAPIO_REQUEUE:
        /* The target wants to requeue the I/O */
        dm_requeue_unmapped_request(clone);
        requeued = 1;
        break;
    default:
        if (r > 0) {
            DMWARN("unimplemented target map return value: %d", r);
            BUG();
        }

        /* The target wants to complete the I/O */
        dm_kill_unmapped_request(clone, r);
        break;
    }

    return requeued;
}

static struct request *dm_start_request(struct mapped_device *md, struct request *orig)
{
    struct request *clone;

    blk_start_request(orig);
    clone = orig->special;
    atomic_inc(&md->pending[rq_data_dir(clone)]);

    /*
     * Hold the md reference here for the in-flight I/O.
     * We can't rely on the reference count by device opener,
     * because the device may be closed during the request completion
     * when all bios are completed.
     * See the comment in rq_completed() too.
     */
    dm_get(md);

    return clone;
}

/*
 * q->request_fn for request-based dm.
 * Called with the queue lock held.
 */
static void dm_request_fn(struct request_queue *q)
{
    struct mapped_device *md = q->queuedata;
    struct dm_table *map = dm_get_live_table(md);
    struct dm_target *ti;
    struct request *rq, *clone;
    sector_t pos;

    /*
     * For suspend, check blk_queue_stopped() and increment
     * ->pending within a single queue_lock not to increment the
     * number of in-flight I/Os after the queue is stopped in
     * dm_suspend().
     */
    while (!blk_queue_stopped(q)) {
        rq = blk_peek_request(q);
        if (!rq)
            goto delay_and_out;

        /* always use block 0 to find the target for flushes for now */
        pos = 0;
        if (!(rq->cmd_flags & REQ_FLUSH))
            pos = blk_rq_pos(rq);

        ti = dm_table_find_target(map, pos);
        if (!dm_target_is_valid(ti)) {
            /*
             * Must perform setup, that dm_done() requires,
             * before calling dm_kill_unmapped_request
             */
            DMERR_LIMIT("request attempted access beyond the end of device");
            clone = dm_start_request(md, rq);
            dm_kill_unmapped_request(clone, -EIO);
            continue;
        }

        if (ti->type->busy && ti->type->busy(ti))
            goto delay_and_out;

        clone = dm_start_request(md, rq);

        spin_unlock(q->queue_lock);
        if (map_request(ti, clone, md))
            goto requeued;

        BUG_ON(!irqs_disabled());
        spin_lock(q->queue_lock);
    }

    goto out;

requeued:
    BUG_ON(!irqs_disabled());
    spin_lock(q->queue_lock);

delay_and_out:
    blk_delay_queue(q, HZ / 10);
out:
    dm_table_put(map);
}

int dm_underlying_device_busy(struct request_queue *q)
{
    return blk_lld_busy(q);
}
EXPORT_SYMBOL_GPL(dm_underlying_device_busy);

static int dm_lld_busy(struct request_queue *q)
{
    int r;
    struct mapped_device *md = q->queuedata;
    struct dm_table *map = dm_get_live_table(md);

    if (!map || test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags))
        r = 1;
    else
        r = dm_table_any_busy_target(map);

    dm_table_put(map);

    return r;
}

static int dm_any_congested(void *congested_data, int bdi_bits)
{
    int r = bdi_bits;
    struct mapped_device *md = congested_data;
    struct dm_table *map;

    if (!test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) {
        map = dm_get_live_table(md);
        if (map) {
            /*
             * Request-based dm cares about only own queue for
             * the query about congestion status of request_queue
             */
            if (dm_request_based(md))
                r = md->queue->backing_dev_info.state &
                    bdi_bits;
            else
                r = dm_table_any_congested(map, bdi_bits);

            dm_table_put(map);
        }
    }

    return r;
}

/*-----------------------------------------------------------------
 * An IDR is used to keep track of allocated minor numbers.
 *---------------------------------------------------------------*/
static void free_minor(int minor)
{
    spin_lock(&_minor_lock);
    idr_remove(&_minor_idr, minor);
    spin_unlock(&_minor_lock);
}

/*
 * See if the device with a specific minor # is free.
 */
static int specific_minor(int minor)
{
    int r, m;

    if (minor >= (1 << MINORBITS))
        return -EINVAL;

    r = idr_pre_get(&_minor_idr, GFP_KERNEL);
    if (!r)
        return -ENOMEM;

    spin_lock(&_minor_lock);

    if (idr_find(&_minor_idr, minor)) {
        r = -EBUSY;
        goto out;
    }

    r = idr_get_new_above(&_minor_idr, MINOR_ALLOCED, minor, &m);
    if (r)
        goto out;

    if (m != minor) {
        idr_remove(&_minor_idr, m);
        r = -EBUSY;
        goto out;
    }

out:
    spin_unlock(&_minor_lock);
    return r;
}

static int next_free_minor(int *minor)
{
    int r, m;

    r = idr_pre_get(&_minor_idr, GFP_KERNEL);
    if (!r)
        return -ENOMEM;

    spin_lock(&_minor_lock);

    r = idr_get_new(&_minor_idr, MINOR_ALLOCED, &m);
    if (r)
        goto out;

    if (m >= (1 << MINORBITS)) {
        idr_remove(&_minor_idr, m);
        r = -ENOSPC;
        goto out;
    }

    *minor = m;

out:
    spin_unlock(&_minor_lock);
    return r;
}

static const struct block_device_operations dm_blk_dops;

static void dm_wq_work(struct work_struct *work);

static void dm_init_md_queue(struct mapped_device *md)
{
    /*
     * Request-based dm devices cannot be stacked on top of bio-based dm
     * devices.  The type of this dm device has not been decided yet.
     * The type is decided at the first table loading time.
     * To prevent problematic device stacking, clear the queue flag
     * for request stacking support until then.
     *
     * This queue is new, so no concurrency on the queue_flags.
     */
    queue_flag_clear_unlocked(QUEUE_FLAG_STACKABLE, md->queue);

    md->queue->queuedata = md;
    md->queue->backing_dev_info.congested_fn = dm_any_congested;
    md->queue->backing_dev_info.congested_data = md;
    blk_queue_make_request(md->queue, dm_request);
    blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);
    blk_queue_merge_bvec(md->queue, dm_merge_bvec);
}

/*
 * Allocate and initialise a blank device with a given minor.
 */
static struct mapped_device *alloc_dev(int minor)
{
    int r;
    struct mapped_device *md = kzalloc(sizeof(*md), GFP_KERNEL);
    void *old_md;

    if (!md) {
        DMWARN("unable to allocate device, out of memory.");
        return NULL;
    }

    if (!try_module_get(THIS_MODULE))
        goto bad_module_get;

    /* get a minor number for the dev */
    if (minor == DM_ANY_MINOR)
        r = next_free_minor(&minor);
    else
        r = specific_minor(minor);
    if (r < 0)
        goto bad_minor;

    md->type = DM_TYPE_NONE;
    init_rwsem(&md->io_lock);
    mutex_init(&md->suspend_lock);
    mutex_init(&md->type_lock);
    spin_lock_init(&md->deferred_lock);
    rwlock_init(&md->map_lock);
    atomic_set(&md->holders, 1);
    atomic_set(&md->open_count, 0);
    atomic_set(&md->event_nr, 0);
    atomic_set(&md->uevent_seq, 0);
    INIT_LIST_HEAD(&md->uevent_list);
    spin_lock_init(&md->uevent_lock);

    md->queue = blk_alloc_queue(GFP_KERNEL);
    if (!md->queue)
        goto bad_queue;

    dm_init_md_queue(md);

    md->disk = alloc_disk(1);
    if (!md->disk)
        goto bad_disk;

    atomic_set(&md->pending[0], 0);
    atomic_set(&md->pending[1], 0);
    init_waitqueue_head(&md->wait);
    INIT_WORK(&md->work, dm_wq_work);
    init_waitqueue_head(&md->eventq);

    md->disk->major = _major;
    md->disk->first_minor = minor;
    md->disk->fops = &dm_blk_dops;
    md->disk->queue = md->queue;
    md->disk->private_data = md;
    sprintf(md->disk->disk_name, "dm-%d", minor);
    add_disk(md->disk);
    format_dev_t(md->name, MKDEV(_major, minor));

    md->wq = alloc_workqueue("kdmflush",
                 WQ_NON_REENTRANT | WQ_MEM_RECLAIM, 0);
    if (!md->wq)
        goto bad_thread;

    md->bdev = bdget_disk(md->disk, 0);
    if (!md->bdev)
        goto bad_bdev;

    bio_init(&md->flush_bio);
    md->flush_bio.bi_bdev = md->bdev;
    md->flush_bio.bi_rw = WRITE_FLUSH;

    /* Populate the mapping, nobody knows we exist yet */
    spin_lock(&_minor_lock);
    old_md = idr_replace(&_minor_idr, md, minor);
    spin_unlock(&_minor_lock);

    BUG_ON(old_md != MINOR_ALLOCED);

    return md;

bad_bdev:
    destroy_workqueue(md->wq);
bad_thread:
    del_gendisk(md->disk);
    put_disk(md->disk);
bad_disk:
    blk_cleanup_queue(md->queue);
bad_queue:
    free_minor(minor);
bad_minor:
    module_put(THIS_MODULE);
bad_module_get:
    kfree(md);
    return NULL;
}

static void unlock_fs(struct mapped_device *md);

static void free_dev(struct mapped_device *md)
{
    int minor = MINOR(disk_devt(md->disk));

    unlock_fs(md);
    bdput(md->bdev);
    destroy_workqueue(md->wq);
    if (md->tio_pool)
        mempool_destroy(md->tio_pool);
    if (md->io_pool)
        mempool_destroy(md->io_pool);
    if (md->bs)
        bioset_free(md->bs);
    blk_integrity_unregister(md->disk);
    del_gendisk(md->disk);
    free_minor(minor);

    spin_lock(&_minor_lock);
    md->disk->private_data = NULL;
    spin_unlock(&_minor_lock);

    put_disk(md->disk);
    blk_cleanup_queue(md->queue);
    module_put(THIS_MODULE);
    kfree(md);
}

static void __bind_mempools(struct mapped_device *md, struct dm_table *t)
{
    struct dm_md_mempools *p;

    if (md->io_pool && (md->tio_pool || dm_table_get_type(t) == DM_TYPE_BIO_BASED) && md->bs)
        /* the md already has necessary mempools */
        goto out;

    p = dm_table_get_md_mempools(t);
    BUG_ON(!p || md->io_pool || md->tio_pool || md->bs);

    md->io_pool = p->io_pool;
    p->io_pool = NULL;
    md->tio_pool = p->tio_pool;
    p->tio_pool = NULL;
    md->bs = p->bs;
    p->bs = NULL;

out:
    /* mempool bind completed, now no need any mempools in the table */
    dm_table_free_md_mempools(t);
}

/*
 * Bind a table to the device.
 */
static void event_callback(void *context)
{
    unsigned long flags;
    LIST_HEAD(uevents);
    struct mapped_device *md = (struct mapped_device *) context;

    spin_lock_irqsave(&md->uevent_lock, flags);
    list_splice_init(&md->uevent_list, &uevents);
    spin_unlock_irqrestore(&md->uevent_lock, flags);

    dm_send_uevents(&uevents, &disk_to_dev(md->disk)->kobj);

    atomic_inc(&md->event_nr);
    wake_up(&md->eventq);
}

/*
 * Protected by md->suspend_lock obtained by dm_swap_table().
 */
static void __set_size(struct mapped_device *md, sector_t size)
{
    set_capacity(md->disk, size);

    i_size_write(md->bdev->bd_inode, (loff_t)size << SECTOR_SHIFT);
}

/*
 * Return 1 if the queue has a compulsory merge_bvec_fn function.
 *
 * If this function returns 0, then the device is either a non-dm
 * device without a merge_bvec_fn, or it is a dm device that is
 * able to split any bios it receives that are too big.
 */
int dm_queue_merge_is_compulsory(struct request_queue *q)
{
    struct mapped_device *dev_md;

    if (!q->merge_bvec_fn)
        return 0;

    if (q->make_request_fn == dm_request) {
        dev_md = q->queuedata;
        if (test_bit(DMF_MERGE_IS_OPTIONAL, &dev_md->flags))
            return 0;
    }

    return 1;
}

static int dm_device_merge_is_compulsory(struct dm_target *ti,
                     struct dm_dev *dev, sector_t start,
                     sector_t len, void *data)
{
    struct block_device *bdev = dev->bdev;
    struct request_queue *q = bdev_get_queue(bdev);

    return dm_queue_merge_is_compulsory(q);
}

/*
 * Return 1 if it is acceptable to ignore merge_bvec_fn based
 * on the properties of the underlying devices.
 */
static int dm_table_merge_is_optional(struct dm_table *table)
{
    unsigned i = 0;
    struct dm_target *ti;

    while (i < dm_table_get_num_targets(table)) {
        ti = dm_table_get_target(table, i++);

        if (ti->type->iterate_devices &&
            ti->type->iterate_devices(ti, dm_device_merge_is_compulsory, NULL))
            return 0;
    }

    return 1;
}

/*
 * Returns old map, which caller must destroy.
 */
static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t,
                   struct queue_limits *limits)
{
    struct dm_table *old_map;
    struct request_queue *q = md->queue;
    sector_t size;
    unsigned long flags;
    int merge_is_optional;

    size = dm_table_get_size(t);

    /*
     * Wipe any geometry if the size of the table changed.
     */
    if (size != get_capacity(md->disk))
        memset(&md->geometry, 0, sizeof(md->geometry));

    __set_size(md, size);

    dm_table_event_callback(t, event_callback, md);

    /*
     * The queue hasn't been stopped yet, if the old table type wasn't
     * for request-based during suspension.  So stop it to prevent
     * I/O mapping before resume.
     * This must be done before setting the queue restrictions,
     * because request-based dm may be run just after the setting.
     */
    if (dm_table_request_based(t) && !blk_queue_stopped(q))
        stop_queue(q);

    __bind_mempools(md, t);

    merge_is_optional = dm_table_merge_is_optional(t);

    write_lock_irqsave(&md->map_lock, flags);
    old_map = md->map;
    md->map = t;
    md->immutable_target_type = dm_table_get_immutable_target_type(t);

    dm_table_set_restrictions(t, q, limits);
    if (merge_is_optional)
        set_bit(DMF_MERGE_IS_OPTIONAL, &md->flags);
    else
        clear_bit(DMF_MERGE_IS_OPTIONAL, &md->flags);
    write_unlock_irqrestore(&md->map_lock, flags);

    return old_map;
}

/*
 * Returns unbound table for the caller to free.
 */
static struct dm_table *__unbind(struct mapped_device *md)
{
    struct dm_table *map = md->map;
    unsigned long flags;

    if (!map)
        return NULL;

    dm_table_event_callback(map, NULL, NULL);
    write_lock_irqsave(&md->map_lock, flags);
    md->map = NULL;
    write_unlock_irqrestore(&md->map_lock, flags);

    return map;
}

/*
 * Constructor for a new device.
 */
int dm_create(int minor, struct mapped_device **result)
{
    struct mapped_device *md;

    md = alloc_dev(minor);
    if (!md)
        return -ENXIO;

    dm_sysfs_init(md);

    *result = md;
    return 0;
}

/*
 * Functions to manage md->type.
 * All are required to hold md->type_lock.
 */
void dm_lock_md_type(struct mapped_device *md)
{
    mutex_lock(&md->type_lock);
}

void dm_unlock_md_type(struct mapped_device *md)
{
    mutex_unlock(&md->type_lock);
}

void dm_set_md_type(struct mapped_device *md, unsigned type)
{
    md->type = type;
}

unsigned dm_get_md_type(struct mapped_device *md)
{
    return md->type;
}

struct target_type *dm_get_immutable_target_type(struct mapped_device *md)
{
    return md->immutable_target_type;
}

/*
 * Fully initialize a request-based queue (->elevator, ->request_fn, etc).
 */
static int dm_init_request_based_queue(struct mapped_device *md)
{
    struct request_queue *q = NULL;

    if (md->queue->elevator)
        return 1;

    /* Fully initialize the queue */
    q = blk_init_allocated_queue(md->queue, dm_request_fn, NULL);
    if (!q)
        return 0;

    md->queue = q;
    dm_init_md_queue(md);
    blk_queue_softirq_done(md->queue, dm_softirq_done);
    blk_queue_prep_rq(md->queue, dm_prep_fn);
    blk_queue_lld_busy(md->queue, dm_lld_busy);

    elv_register_queue(md->queue);

    return 1;
}

/*
 * Setup the DM device's queue based on md's type
 */
int dm_setup_md_queue(struct mapped_device *md)
{
    if ((dm_get_md_type(md) == DM_TYPE_REQUEST_BASED) &&
        !dm_init_request_based_queue(md)) {
        DMWARN("Cannot initialize queue for request-based mapped device");
        return -EINVAL;
    }

    return 0;
}

static struct mapped_device *dm_find_md(dev_t dev)
{
    struct mapped_device *md;
    unsigned minor = MINOR(dev);

    if (MAJOR(dev) != _major || minor >= (1 << MINORBITS))
        return NULL;

    spin_lock(&_minor_lock);

    md = idr_find(&_minor_idr, minor);
    if (md && (md == MINOR_ALLOCED ||
           (MINOR(disk_devt(dm_disk(md))) != minor) ||
           dm_deleting_md(md) ||
           test_bit(DMF_FREEING, &md->flags))) {
        md = NULL;
        goto out;
    }

out:
    spin_unlock(&_minor_lock);

    return md;
}

struct mapped_device *dm_get_md(dev_t dev)
{
    struct mapped_device *md = dm_find_md(dev);

    if (md)
        dm_get(md);

    return md;
}
EXPORT_SYMBOL_GPL(dm_get_md);

void *dm_get_mdptr(struct mapped_device *md)
{
    return md->interface_ptr;
}

void dm_set_mdptr(struct mapped_device *md, void *ptr)
{
    md->interface_ptr = ptr;
}

void dm_get(struct mapped_device *md)
{
    atomic_inc(&md->holders);
    BUG_ON(test_bit(DMF_FREEING, &md->flags));
}

const char *dm_device_name(struct mapped_device *md)
{
    return md->name;
}
EXPORT_SYMBOL_GPL(dm_device_name);

static void __dm_destroy(struct mapped_device *md, bool wait)
{
    struct dm_table *map;

    might_sleep();

    spin_lock(&_minor_lock);
    map = dm_get_live_table(md);
    idr_replace(&_minor_idr, MINOR_ALLOCED, MINOR(disk_devt(dm_disk(md))));
    set_bit(DMF_FREEING, &md->flags);
    spin_unlock(&_minor_lock);

    if (!dm_suspended_md(md)) {
        dm_table_presuspend_targets(map);
        dm_table_postsuspend_targets(map);
    }

    /*
     * Rare, but there may be I/O requests still going to complete,
     * for example.  Wait for all references to disappear.
     * No one should increment the reference count of the mapped_device,
     * after the mapped_device state becomes DMF_FREEING.
     */
    if (wait)
        while (atomic_read(&md->holders))
            msleep(1);
    else if (atomic_read(&md->holders))
        DMWARN("%s: Forcibly removing mapped_device still in use! (%d users)",
               dm_device_name(md), atomic_read(&md->holders));

    dm_sysfs_exit(md);
    dm_table_put(map);
    dm_table_destroy(__unbind(md));
    free_dev(md);
}

void dm_destroy(struct mapped_device *md)
{
    __dm_destroy(md, true);
}

void dm_destroy_immediate(struct mapped_device *md)
{
    __dm_destroy(md, false);
}

void dm_put(struct mapped_device *md)
{
    atomic_dec(&md->holders);
}
EXPORT_SYMBOL_GPL(dm_put);

static int dm_wait_for_completion(struct mapped_device *md, int interruptible)
{
    int r = 0;
    DECLARE_WAITQUEUE(wait, current);

    add_wait_queue(&md->wait, &wait);

    while (1) {
        set_current_state(interruptible);

        if (!md_in_flight(md))
            break;

        if (interruptible == TASK_INTERRUPTIBLE &&
            signal_pending(current)) {
            r = -EINTR;
            break;
        }

        io_schedule();
    }
    set_current_state(TASK_RUNNING);

    remove_wait_queue(&md->wait, &wait);

    return r;
}

/*
 * Process the deferred bios
 */
static void dm_wq_work(struct work_struct *work)
{
    struct mapped_device *md = container_of(work, struct mapped_device,
                        work);
    struct bio *c;

    down_read(&md->io_lock);

    while (!test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) {
        spin_lock_irq(&md->deferred_lock);
        c = bio_list_pop(&md->deferred);
        spin_unlock_irq(&md->deferred_lock);

        if (!c)
            break;

        up_read(&md->io_lock);

        if (dm_request_based(md))
            generic_make_request(c);
        else
            __split_and_process_bio(md, c);

        down_read(&md->io_lock);
    }

    up_read(&md->io_lock);
}

static void dm_queue_flush(struct mapped_device *md)
{
    clear_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags);
    smp_mb__after_clear_bit();
    queue_work(md->wq, &md->work);
}

/*
 * Swap in a new table, returning the old one for the caller to destroy.
 */
struct dm_table *dm_swap_table(struct mapped_device *md, struct dm_table *table)
{
    struct dm_table *live_map, *map = ERR_PTR(-EINVAL);
    struct queue_limits limits;
    int r;

    mutex_lock(&md->suspend_lock);

    /* device must be suspended */
    if (!dm_suspended_md(md))
        goto out;

    /*
     * If the new table has no data devices, retain the existing limits.
     * This helps multipath with queue_if_no_path if all paths disappear,
     * then new I/O is queued based on these limits, and then some paths
     * reappear.
     */
    if (dm_table_has_no_data_devices(table)) {
        live_map = dm_get_live_table(md);
        if (live_map)
            limits = md->queue->limits;
        dm_table_put(live_map);
    }

    r = dm_calculate_queue_limits(table, &limits);
    if (r) {
        map = ERR_PTR(r);
        goto out;
    }

    map = __bind(md, table, &limits);

out:
    mutex_unlock(&md->suspend_lock);
    return map;
}

/*
 * Functions to lock and unlock any filesystem running on the
 * device.
 */
static int lock_fs(struct mapped_device *md)
{
    int r;

    WARN_ON(md->frozen_sb);

    md->frozen_sb = freeze_bdev(md->bdev);
    if (IS_ERR(md->frozen_sb)) {
        r = PTR_ERR(md->frozen_sb);
        md->frozen_sb = NULL;
        return r;
    }

    set_bit(DMF_FROZEN, &md->flags);

    return 0;
}

static void unlock_fs(struct mapped_device *md)
{
    if (!test_bit(DMF_FROZEN, &md->flags))
        return;

    thaw_bdev(md->bdev, md->frozen_sb);
    md->frozen_sb = NULL;
    clear_bit(DMF_FROZEN, &md->flags);
}

/*
 * We need to be able to change a mapping table under a mounted
 * filesystem.  For example we might want to move some data in
 * the background.  Before the table can be swapped with
 * dm_bind_table, dm_suspend must be called to flush any in
 * flight bios and ensure that any further io gets deferred.
 */
/*
 * Suspend mechanism in request-based dm.
 *
 * 1. Flush all I/Os by lock_fs() if needed.
 * 2. Stop dispatching any I/O by stopping the request_queue.
 * 3. Wait for all in-flight I/Os to be completed or requeued.
 *
 * To abort suspend, start the request_queue.
 */
int dm_suspend(struct mapped_device *md, unsigned suspend_flags)
{
    struct dm_table *map = NULL;
    int r = 0;
    int do_lockfs = suspend_flags & DM_SUSPEND_LOCKFS_FLAG ? 1 : 0;
    int noflush = suspend_flags & DM_SUSPEND_NOFLUSH_FLAG ? 1 : 0;

    mutex_lock(&md->suspend_lock);

    if (dm_suspended_md(md)) {
        r = -EINVAL;
        goto out_unlock;
    }

    map = dm_get_live_table(md);

    /*
     * DMF_NOFLUSH_SUSPENDING must be set before presuspend.
     * This flag is cleared before dm_suspend returns.
     */
    if (noflush)
        set_bit(DMF_NOFLUSH_SUSPENDING, &md->flags);

    /* This does not get reverted if there's an error later. */
    dm_table_presuspend_targets(map);

    /*
     * Flush I/O to the device.
     * Any I/O submitted after lock_fs() may not be flushed.
     * noflush takes precedence over do_lockfs.
     * (lock_fs() flushes I/Os and waits for them to complete.)
     */
    if (!noflush && do_lockfs) {
        r = lock_fs(md);
        if (r)
            goto out;
    }

    /*
     * Here we must make sure that no processes are submitting requests
     * to target drivers i.e. no one may be executing
     * __split_and_process_bio. This is called from dm_request and
     * dm_wq_work.
     *
     * To get all processes out of __split_and_process_bio in dm_request,
     * we take the write lock. To prevent any process from reentering
     * __split_and_process_bio from dm_request and quiesce the thread
     * (dm_wq_work), we set BMF_BLOCK_IO_FOR_SUSPEND and call
     * flush_workqueue(md->wq).
     */
    down_write(&md->io_lock);
    set_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags);
    up_write(&md->io_lock);

    /*
     * Stop md->queue before flushing md->wq in case request-based
     * dm defers requests to md->wq from md->queue.
     */
    if (dm_request_based(md))
        stop_queue(md->queue);

    flush_workqueue(md->wq);

    /*
     * At this point no more requests are entering target request routines.
     * We call dm_wait_for_completion to wait for all existing requests
     * to finish.
     */
    r = dm_wait_for_completion(md, TASK_INTERRUPTIBLE);

    down_write(&md->io_lock);
    if (noflush)
        clear_bit(DMF_NOFLUSH_SUSPENDING, &md->flags);
    up_write(&md->io_lock);

    /* were we interrupted ? */
    if (r < 0) {
        dm_queue_flush(md);

        if (dm_request_based(md))
            start_queue(md->queue);

        unlock_fs(md);
        goto out; /* pushback list is already flushed, so skip flush */
    }

    /*
     * If dm_wait_for_completion returned 0, the device is completely
     * quiescent now. There is no request-processing activity. All new
     * requests are being added to md->deferred list.
     */

    set_bit(DMF_SUSPENDED, &md->flags);

    dm_table_postsuspend_targets(map);

out:
    dm_table_put(map);

out_unlock:
    mutex_unlock(&md->suspend_lock);
    return r;
}

int dm_resume(struct mapped_device *md)
{
    int r = -EINVAL;
    struct dm_table *map = NULL;

    mutex_lock(&md->suspend_lock);
    if (!dm_suspended_md(md))
        goto out;

    map = dm_get_live_table(md);
    if (!map || !dm_table_get_size(map))
        goto out;

    r = dm_table_resume_targets(map);
    if (r)
        goto out;

    dm_queue_flush(md);

    /*
     * Flushing deferred I/Os must be done after targets are resumed
     * so that mapping of targets can work correctly.
     * Request-based dm is queueing the deferred I/Os in its request_queue.
     */
    if (dm_request_based(md))
        start_queue(md->queue);

    unlock_fs(md);

    clear_bit(DMF_SUSPENDED, &md->flags);

    r = 0;
out:
    dm_table_put(map);
    mutex_unlock(&md->suspend_lock);

    return r;
}

/*-----------------------------------------------------------------
 * Event notification.
 *---------------------------------------------------------------*/
int dm_kobject_uevent(struct mapped_device *md, enum kobject_action action,
               unsigned cookie)
{
    char udev_cookie[DM_COOKIE_LENGTH];
    char *envp[] = { udev_cookie, NULL };

    if (!cookie)
        return kobject_uevent(&disk_to_dev(md->disk)->kobj, action);
    else {
        snprintf(udev_cookie, DM_COOKIE_LENGTH, "%s=%u",
             DM_COOKIE_ENV_VAR_NAME, cookie);
        return kobject_uevent_env(&disk_to_dev(md->disk)->kobj,
                      action, envp);
    }
}

uint32_t dm_next_uevent_seq(struct mapped_device *md)
{
    return atomic_add_return(1, &md->uevent_seq);
}

uint32_t dm_get_event_nr(struct mapped_device *md)
{
    return atomic_read(&md->event_nr);
}

int dm_wait_event(struct mapped_device *md, int event_nr)
{
    return wait_event_interruptible(md->eventq,
            (event_nr != atomic_read(&md->event_nr)));
}

void dm_uevent_add(struct mapped_device *md, struct list_head *elist)
{
    unsigned long flags;

    spin_lock_irqsave(&md->uevent_lock, flags);
    list_add(elist, &md->uevent_list);
    spin_unlock_irqrestore(&md->uevent_lock, flags);
}

/*
 * The gendisk is only valid as long as you have a reference
 * count on 'md'.
 */
struct gendisk *dm_disk(struct mapped_device *md)
{
    return md->disk;
}

struct kobject *dm_kobject(struct mapped_device *md)
{
    return &md->kobj;
}

/*
 * struct mapped_device should not be exported outside of dm.c
 * so use this check to verify that kobj is part of md structure
 */
struct mapped_device *dm_get_from_kobject(struct kobject *kobj)
{
    struct mapped_device *md;

    md = container_of(kobj, struct mapped_device, kobj);
    if (&md->kobj != kobj)
        return NULL;

    if (test_bit(DMF_FREEING, &md->flags) ||
        dm_deleting_md(md))
        return NULL;

    dm_get(md);
    return md;
}

int dm_suspended_md(struct mapped_device *md)
{
    return test_bit(DMF_SUSPENDED, &md->flags);
}

int dm_suspended(struct dm_target *ti)
{
    return dm_suspended_md(dm_table_get_md(ti->table));
}
EXPORT_SYMBOL_GPL(dm_suspended);

int dm_noflush_suspending(struct dm_target *ti)
{
    return __noflush_suspending(dm_table_get_md(ti->table));
}
EXPORT_SYMBOL_GPL(dm_noflush_suspending);

struct dm_md_mempools *dm_alloc_md_mempools(unsigned type, unsigned integrity)
{
    struct dm_md_mempools *pools = kmalloc(sizeof(*pools), GFP_KERNEL);
    unsigned int pool_size = (type == DM_TYPE_BIO_BASED) ? 16 : MIN_IOS;

    if (!pools)
        return NULL;

    pools->io_pool = (type == DM_TYPE_BIO_BASED) ?
             mempool_create_slab_pool(MIN_IOS, _io_cache) :
             mempool_create_slab_pool(MIN_IOS, _rq_bio_info_cache);
    if (!pools->io_pool)
        goto free_pools_and_out;

    pools->tio_pool = NULL;
    if (type == DM_TYPE_REQUEST_BASED) {
        pools->tio_pool = mempool_create_slab_pool(MIN_IOS, _rq_tio_cache);
        if (!pools->tio_pool)
            goto free_io_pool_and_out;
    }

    pools->bs = (type == DM_TYPE_BIO_BASED) ?
        bioset_create(pool_size,
                  offsetof(struct dm_target_io, clone)) :
        bioset_create(pool_size,
                  offsetof(struct dm_rq_clone_bio_info, clone));
    if (!pools->bs)
        goto free_tio_pool_and_out;

    if (integrity && bioset_integrity_create(pools->bs, pool_size))
        goto free_bioset_and_out;

    return pools;

free_bioset_and_out:
    bioset_free(pools->bs);

free_tio_pool_and_out:
    if (pools->tio_pool)
        mempool_destroy(pools->tio_pool);

free_io_pool_and_out:
    mempool_destroy(pools->io_pool);

free_pools_and_out:
    kfree(pools);

    return NULL;
}

void dm_free_md_mempools(struct dm_md_mempools *pools)
{
    if (!pools)
        return;

    if (pools->io_pool)
        mempool_destroy(pools->io_pool);

    if (pools->tio_pool)
        mempool_destroy(pools->tio_pool);

    if (pools->bs)
        bioset_free(pools->bs);

    kfree(pools);
}

static const struct block_device_operations dm_blk_dops = {
    .open = dm_blk_open,
    .release = dm_blk_close,
    .ioctl = dm_blk_ioctl,
    .getgeo = dm_blk_getgeo,
    .owner = THIS_MODULE
};

EXPORT_SYMBOL(dm_get_mapinfo);

/*
 * module hooks
 */
module_init(dm_init);
module_exit(dm_exit);

module_param(major, uint, 0);
MODULE_PARM_DESC(major, "The major number of the device mapper");
MODULE_DESCRIPTION(DM_NAME " driver");
MODULE_AUTHOR("Joe Thornber <[email protected]>");
MODULE_LICENSE("GPL");