dm sysfs: fix a module unload race

[mirror_ubuntu-artful-kernel.git] / drivers / md / dm.c

/*
 * 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);

static void do_deferred_remove(struct work_struct *w);

static DECLARE_WORK(deferred_remove_work, do_deferred_remove);

/*
 * 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;
        struct dm_stats_aux stats_aux;
};

/*
 * 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
#define DMF_DEFERRED_REMOVE 7

/*
 * A dummy definition to make RCU happy.
 * struct dm_table should never be dereferenced in this file.
 */
struct dm_table {
        int undefined__;
};

/*
 * Work processed by per-device workqueue.
 */
struct mapped_device {
        struct srcu_struct io_barrier;
        struct mutex suspend_lock;
        atomic_t holders;
        atomic_t open_count;

        /*
         * The current mapping.
         * Use dm_get_live_table{_fast} or take suspend_lock for
         * dereference.
         */
        struct dm_table *map;

        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;

        /*
         * io objects are allocated from here.
         */
        mempool_t *io_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;

        /* kobject and completion */
        struct dm_kobject_holder kobj_holder;

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

        struct dm_stats stats;
};

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

#define RESERVED_BIO_BASED_IOS          16
#define RESERVED_REQUEST_BASED_IOS      256
#define RESERVED_MAX_IOS                1024
static struct kmem_cache *_io_cache;
static struct kmem_cache *_rq_tio_cache;

/*
 * Bio-based DM's mempools' reserved IOs set by the user.
 */
static unsigned reserved_bio_based_ios = RESERVED_BIO_BASED_IOS;

/*
 * Request-based DM's mempools' reserved IOs set by the user.
 */
static unsigned reserved_rq_based_ios = RESERVED_REQUEST_BASED_IOS;

static unsigned __dm_get_reserved_ios(unsigned *reserved_ios,
                                      unsigned def, unsigned max)
{
        unsigned ios = ACCESS_ONCE(*reserved_ios);
        unsigned modified_ios = 0;

        if (!ios)
                modified_ios = def;
        else if (ios > max)
                modified_ios = max;

        if (modified_ios) {
                (void)cmpxchg(reserved_ios, ios, modified_ios);
                ios = modified_ios;
        }

        return ios;
}

unsigned dm_get_reserved_bio_based_ios(void)
{
        return __dm_get_reserved_ios(&reserved_bio_based_ios,
                                     RESERVED_BIO_BASED_IOS, RESERVED_MAX_IOS);
}
EXPORT_SYMBOL_GPL(dm_get_reserved_bio_based_ios);

unsigned dm_get_reserved_rq_based_ios(void)
{
        return __dm_get_reserved_ios(&reserved_rq_based_ios,
                                     RESERVED_REQUEST_BASED_IOS, RESERVED_MAX_IOS);
}
EXPORT_SYMBOL_GPL(dm_get_reserved_rq_based_ios);

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;

        r = dm_uevent_init();
        if (r)
                goto out_free_rq_tio_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_tio_cache:
        kmem_cache_destroy(_rq_tio_cache);
out_free_io_cache:
        kmem_cache_destroy(_io_cache);

        return r;
}

static void local_exit(void)
{
        flush_scheduled_work();

        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,
        dm_statistics_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,
        dm_statistics_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_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 void dm_blk_close(struct gendisk *disk, fmode_t mode)
{
        struct mapped_device *md = disk->private_data;

        spin_lock(&_minor_lock);

        if (atomic_dec_and_test(&md->open_count) &&
            (test_bit(DMF_DEFERRED_REMOVE, &md->flags)))
                schedule_work(&deferred_remove_work);

        dm_put(md);

        spin_unlock(&_minor_lock);
}

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, bool mark_deferred, bool only_deferred)
{
        int r = 0;

        spin_lock(&_minor_lock);

        if (dm_open_count(md)) {
                r = -EBUSY;
                if (mark_deferred)
                        set_bit(DMF_DEFERRED_REMOVE, &md->flags);
        } else if (only_deferred && !test_bit(DMF_DEFERRED_REMOVE, &md->flags))
                r = -EEXIST;
        else
                set_bit(DMF_DELETING, &md->flags);

        spin_unlock(&_minor_lock);

        return r;
}

int dm_cancel_deferred_remove(struct mapped_device *md)
{
        int r = 0;

        spin_lock(&_minor_lock);

        if (test_bit(DMF_DELETING, &md->flags))
                r = -EBUSY;
        else
                clear_bit(DMF_DEFERRED_REMOVE, &md->flags);

        spin_unlock(&_minor_lock);

        return r;
}

static void do_deferred_remove(struct work_struct *w)
{
        dm_deferred_remove();
}

sector_t dm_get_size(struct mapped_device *md)
{
        return get_capacity(md->disk);
}

struct dm_stats *dm_get_stats(struct mapped_device *md)
{
        return &md->stats;
}

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;
        int srcu_idx;
        struct dm_table *map;
        struct dm_target *tgt;
        int r = -ENOTTY;

retry:
        map = dm_get_live_table(md, &srcu_idx);

        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_put_live_table(md, srcu_idx);

        if (r == -ENOTCONN) {
                msleep(10);
                goto retry;
        }

        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->io_pool, gfp_mask);
}

static void free_rq_tio(struct dm_rq_target_io *tio)
{
        mempool_free(tio, tio->md->io_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;
        struct bio *bio = io->bio;
        int cpu;
        int rw = bio_data_dir(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]));

        if (unlikely(dm_stats_used(&md->stats)))
                dm_stats_account_io(&md->stats, bio->bi_rw, bio->bi_sector,
                                    bio_sectors(bio), false, 0, &io->stats_aux);
}

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();

        if (unlikely(dm_stats_used(&md->stats)))
                dm_stats_account_io(&md->stats, bio->bi_rw, bio->bi_sector,
                                    bio_sectors(bio), true, duration, &io->stats_aux);

        /*
         * 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_put_live_table() when finished.
 */
struct dm_table *dm_get_live_table(struct mapped_device *md, int *srcu_idx) __acquires(md->io_barrier)
{
        *srcu_idx = srcu_read_lock(&md->io_barrier);

        return srcu_dereference(md->map, &md->io_barrier);
}

void dm_put_live_table(struct mapped_device *md, int srcu_idx) __releases(md->io_barrier)
{
        srcu_read_unlock(&md->io_barrier, srcu_idx);
}

void dm_sync_table(struct mapped_device *md)
{
        synchronize_srcu(&md->io_barrier);
        synchronize_rcu_expedited();
}

/*
 * A fast alternative to dm_get_live_table/dm_put_live_table.
 * The caller must not block between these two functions.
 */
static struct dm_table *dm_get_live_table_fast(struct mapped_device *md) __acquires(RCU)
{
        rcu_read_lock();
        return rcu_dereference(md->map);
}

static void dm_put_live_table_fast(struct mapped_device *md) __releases(RCU)
{
        rcu_read_unlock();
}

/*
 * 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);
                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_io *tio)
{
        int r;
        sector_t sector;
        struct mapped_device *md;
        struct bio *clone = &tio->clone;
        struct dm_target *ti = tio->ti;

        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);
        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;
};

static void bio_setup_sector(struct bio *bio, sector_t sector, sector_t len)
{
        bio->bi_sector = sector;
        bio->bi_size = to_bytes(len);
}

static void bio_setup_bv(struct bio *bio, unsigned short idx, unsigned short bv_count)
{
        bio->bi_idx = idx;
        bio->bi_vcnt = idx + bv_count;
        bio->bi_flags &= ~(1 << BIO_SEG_VALID);
}

static void clone_bio_integrity(struct bio *bio, struct bio *clone,
                                unsigned short idx, unsigned len, unsigned offset,
                                unsigned trim)
{
        if (!bio_integrity(bio))
                return;

        bio_integrity_clone(clone, bio, GFP_NOIO);

        if (trim)
                bio_integrity_trim(clone, bio_sector_offset(bio, idx, offset), len);
}

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

        *clone->bi_io_vec = *bv;

        bio_setup_sector(clone, sector, len);

        clone->bi_bdev = bio->bi_bdev;
        clone->bi_rw = bio->bi_rw;
        clone->bi_vcnt = 1;
        clone->bi_io_vec->bv_offset = offset;
        clone->bi_io_vec->bv_len = clone->bi_size;
        clone->bi_flags |= 1 << BIO_CLONED;

        clone_bio_integrity(bio, clone, idx, len, offset, 1);
}

/*
 * 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 len)
{
        struct bio *clone = &tio->clone;
        unsigned trim = 0;

        __bio_clone(clone, bio);
        bio_setup_sector(clone, sector, len);
        bio_setup_bv(clone, idx, bv_count);

        if (idx != bio->bi_idx || clone->bi_size < bio->bi_size)
                trim = 1;
        clone_bio_integrity(bio, clone, idx, len, 0, trim);
}

static struct dm_target_io *alloc_tio(struct clone_info *ci,
                                      struct dm_target *ti, int nr_iovecs,
                                      unsigned target_bio_nr)
{
        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));
        tio->target_bio_nr = target_bio_nr;

        return tio;
}

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

        /*
         * 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)
                bio_setup_sector(clone, ci->sector, len);

        __map_bio(tio);
}

static void __send_duplicate_bios(struct clone_info *ci, struct dm_target *ti,
                                  unsigned num_bios, sector_t len)
{
        unsigned target_bio_nr;

        for (target_bio_nr = 0; target_bio_nr < num_bios; target_bio_nr++)
                __clone_and_map_simple_bio(ci, ti, target_bio_nr, len);
}

static int __send_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++)))
                __send_duplicate_bios(ci, ti, ti->num_flush_bios, 0);

        return 0;
}

static void __clone_and_map_data_bio(struct clone_info *ci, struct dm_target *ti,
                                     sector_t sector, int nr_iovecs,
                                     unsigned short idx, unsigned short bv_count,
                                     unsigned offset, unsigned len,
                                     unsigned split_bvec)
{
        struct bio *bio = ci->bio;
        struct dm_target_io *tio;
        unsigned target_bio_nr;
        unsigned num_target_bios = 1;

        /*
         * Does the target want to receive duplicate copies of the bio?
         */
        if (bio_data_dir(bio) == WRITE && ti->num_write_bios)
                num_target_bios = ti->num_write_bios(ti, bio);

        for (target_bio_nr = 0; target_bio_nr < num_target_bios; target_bio_nr++) {
                tio = alloc_tio(ci, ti, nr_iovecs, target_bio_nr);
                if (split_bvec)
                        clone_split_bio(tio, bio, sector, idx, offset, len);
                else
                        clone_bio(tio, bio, sector, idx, bv_count, len);
                __map_bio(tio);
        }
}

typedef unsigned (*get_num_bios_fn)(struct dm_target *ti);

static unsigned get_num_discard_bios(struct dm_target *ti)
{
        return ti->num_discard_bios;
}

static unsigned get_num_write_same_bios(struct dm_target *ti)
{
        return ti->num_write_same_bios;
}

typedef bool (*is_split_required_fn)(struct dm_target *ti);

static bool is_split_required_for_discard(struct dm_target *ti)
{
        return ti->split_discard_bios;
}

static int __send_changing_extent_only(struct clone_info *ci,
                                       get_num_bios_fn get_num_bios,
                                       is_split_required_fn is_split_required)
{
        struct dm_target *ti;
        sector_t len;
        unsigned num_bios;

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

                /*
                 * Even though the device advertised support for this type of
                 * request, that does not mean every target supports it, and
                 * reconfiguration might also have changed that since the
                 * check was performed.
                 */
                num_bios = get_num_bios ? get_num_bios(ti) : 0;
                if (!num_bios)
                        return -EOPNOTSUPP;

                if (is_split_required && !is_split_required(ti))
                        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));

                __send_duplicate_bios(ci, ti, num_bios, len);

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

        return 0;
}

static int __send_discard(struct clone_info *ci)
{
        return __send_changing_extent_only(ci, get_num_discard_bios,
                                           is_split_required_for_discard);
}

static int __send_write_same(struct clone_info *ci)
{
        return __send_changing_extent_only(ci, get_num_write_same_bios, NULL);
}

/*
 * Find maximum number of sectors / bvecs we can process with a single bio.
 */
static sector_t __len_within_target(struct clone_info *ci, sector_t max, int *idx)
{
        struct bio *bio = ci->bio;
        sector_t bv_len, total_len = 0;

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

                if (bv_len > max)
                        break;

                max -= bv_len;
                total_len += bv_len;
        }

        return total_len;
}

static int __split_bvec_across_targets(struct clone_info *ci,
                                       struct dm_target *ti, sector_t max)
{
        struct bio *bio = ci->bio;
        struct bio_vec *bv = bio->bi_io_vec + ci->idx;
        sector_t remaining = to_sector(bv->bv_len);
        unsigned offset = 0;
        sector_t len;

        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);

                __clone_and_map_data_bio(ci, ti, ci->sector, 1, ci->idx, 0,
                                         bv->bv_offset + offset, len, 1);

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

        ci->idx++;

        return 0;
}

/*
 * Select the correct strategy for processing a non-flush bio.
 */
static int __split_and_process_non_flush(struct clone_info *ci)
{
        struct bio *bio = ci->bio;
        struct dm_target *ti;
        sector_t len, max;
        int idx;

        if (unlikely(bio->bi_rw & REQ_DISCARD))
                return __send_discard(ci);
        else if (unlikely(bio->bi_rw & REQ_WRITE_SAME))
                return __send_write_same(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);

        /*
         * Optimise for the simple case where we can do all of
         * the remaining io with a single clone.
         */
        if (ci->sector_count <= max) {
                __clone_and_map_data_bio(ci, ti, ci->sector, bio->bi_max_vecs,
                                         ci->idx, bio->bi_vcnt - ci->idx, 0,
                                         ci->sector_count, 0);
                ci->sector_count = 0;
                return 0;
        }

        /*
         * There are some bvecs that don't span targets.
         * Do as many of these as possible.
         */
        if (to_sector(bio->bi_io_vec[ci->idx].bv_len) <= max) {
                len = __len_within_target(ci, max, &idx);

                __clone_and_map_data_bio(ci, ti, ci->sector, bio->bi_max_vecs,
                                         ci->idx, idx - ci->idx, 0, len, 0);

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

                return 0;
        }

        /*
         * Handle a bvec that must be split between two or more targets.
         */
        return __split_bvec_across_targets(ci, ti, max);
}

/*
 * Entry point to split a bio into clones and submit them to the targets.
 */
static void __split_and_process_bio(struct mapped_device *md,
                                    struct dm_table *map, struct bio *bio)
{
        struct clone_info ci;
        int error = 0;

        if (unlikely(!map)) {
                bio_io_error(bio);
                return;
        }

        ci.map = map;
        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 = __send_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 = __split_and_process_non_flush(&ci);
        }

        /* drop the extra reference count */
        dec_pending(ci.io, error);
}
/*-----------------------------------------------------------------
 * 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_fast(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;

        /*
         * 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:
        dm_put_live_table_fast(md);
        /*
         * 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;
        int srcu_idx;
        struct dm_table *map;

        map = dm_get_live_table(md, &srcu_idx);

        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))) {
                dm_put_live_table(md, srcu_idx);

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

        __split_and_process_bio(md, map, bio);
        dm_put_live_table(md, srcu_idx);
        return;
}

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;
        int srcu_idx;
        struct dm_table *map = dm_get_live_table(md, &srcu_idx);
        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_put_live_table(md, srcu_idx);
}

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_fast(md);

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

        dm_put_live_table_fast(md);

        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_fast(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_put_live_table_fast(md);
        }

        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;

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

        idr_preload(GFP_KERNEL);
        spin_lock(&_minor_lock);

        r = idr_alloc(&_minor_idr, MINOR_ALLOCED, minor, minor + 1, GFP_NOWAIT);

        spin_unlock(&_minor_lock);
        idr_preload_end();
        if (r < 0)
                return r == -ENOSPC ? -EBUSY : r;
        return 0;
}

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

        idr_preload(GFP_KERNEL);
        spin_lock(&_minor_lock);

        r = idr_alloc(&_minor_idr, MINOR_ALLOCED, 0, 1 << MINORBITS, GFP_NOWAIT);

        spin_unlock(&_minor_lock);
        idr_preload_end();
        if (r < 0)
                return r;
        *minor = r;
        return 0;
}

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;

        r = init_srcu_struct(&md->io_barrier);
        if (r < 0)
                goto bad_io_barrier;

        md->type = DM_TYPE_NONE;
        mutex_init(&md->suspend_lock);
        mutex_init(&md->type_lock);
        spin_lock_init(&md->deferred_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);
        init_completion(&md->kobj_holder.completion);

        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_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;

        dm_stats_init(&md->stats);

        /* 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:
        cleanup_srcu_struct(&md->io_barrier);
bad_io_barrier:
        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->io_pool)
                mempool_destroy(md->io_pool);
        if (md->bs)
                bioset_free(md->bs);
        blk_integrity_unregister(md->disk);
        del_gendisk(md->disk);
        cleanup_srcu_struct(&md->io_barrier);
        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);
        dm_stats_cleanup(&md->stats);
        module_put(THIS_MODULE);
        kfree(md);
}

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

        if (md->io_pool && md->bs) {
                /* The md already has necessary mempools. */
                if (dm_table_get_type(t) == DM_TYPE_BIO_BASED) {
                        /*
                         * Reload bioset because front_pad may have changed
                         * because a different table was loaded.
                         */
                        bioset_free(md->bs);
                        md->bs = p->bs;
                        p->bs = NULL;
                } else if (dm_table_get_type(t) == DM_TYPE_REQUEST_BASED) {
                        /*
                         * There's no need to reload with request-based dm
                         * because the size of front_pad doesn't change.
                         * Note for future: If you are to reload bioset,
                         * prep-ed requests in the queue may refer
                         * to bio from the old bioset, so you must walk
                         * through the queue to unprep.
                         */
                }
                goto out;
        }

        BUG_ON(!p || md->io_pool || md->bs);

        md->io_pool = p->io_pool;
        p->io_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;
        int merge_is_optional;

        size = dm_table_get_size(t);

        /*
         * Wipe any geometry if the size of the table changed.
         */
        if (size != dm_get_size(md))
                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);

        old_map = md->map;
        rcu_assign_pointer(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);
        dm_sync_table(md);

        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;

        if (!map)
                return NULL;

        dm_table_event_callback(map, NULL, NULL);
        rcu_assign_pointer(md->map, NULL);
        dm_sync_table(md);

        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)
{
        BUG_ON(!mutex_is_locked(&md->type_lock));
        md->type = type;
}

unsigned dm_get_md_type(struct mapped_device *md)
{
        BUG_ON(!mutex_is_locked(&md->type_lock));
        return md->type;
}

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

/*
 * The queue_limits are only valid as long as you have a reference
 * count on 'md'.
 */
struct queue_limits *dm_get_queue_limits(struct mapped_device *md)
{
        BUG_ON(!atomic_read(&md->holders));
        return &md->queue->limits;
}
EXPORT_SYMBOL_GPL(dm_get_queue_limits);

/*
 * 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;
        int srcu_idx;

        might_sleep();

        spin_lock(&_minor_lock);
        map = dm_get_live_table(md, &srcu_idx);
        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);
        }

        /* dm_put_live_table must be before msleep, otherwise deadlock is possible */
        dm_put_live_table(md, srcu_idx);

        /*
         * 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_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;
        int srcu_idx;
        struct dm_table *map;

        map = dm_get_live_table(md, &srcu_idx);

        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;

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

        dm_put_live_table(md, srcu_idx);
}

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 = NULL, *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_fast(md);
                if (live_map)
                        limits = md->queue->limits;
                dm_put_live_table_fast(md);
        }

        if (!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 = md->map;

        /*
         * 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_unlock;
        }

        /*
         * 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).
         */
        set_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags);
        synchronize_srcu(&md->io_barrier);

        /*
         * 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);

        if (noflush)
                clear_bit(DMF_NOFLUSH_SUSPENDING, &md->flags);
        synchronize_srcu(&md->io_barrier);

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

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

                unlock_fs(md);
                goto out_unlock; /* 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_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 = md->map;
        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:
        mutex_unlock(&md->suspend_lock);

        return r;
}

/*
 * Internal suspend/resume works like userspace-driven suspend. It waits
 * until all bios finish and prevents issuing new bios to the target drivers.
 * It may be used only from the kernel.
 *
 * Internal suspend holds md->suspend_lock, which prevents interaction with
 * userspace-driven suspend.
 */

void dm_internal_suspend(struct mapped_device *md)
{
        mutex_lock(&md->suspend_lock);
        if (dm_suspended_md(md))
                return;

        set_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags);
        synchronize_srcu(&md->io_barrier);
        flush_workqueue(md->wq);
        dm_wait_for_completion(md, TASK_UNINTERRUPTIBLE);
}

void dm_internal_resume(struct mapped_device *md)
{
        if (dm_suspended_md(md))
                goto done;

        dm_queue_flush(md);

done:
        mutex_unlock(&md->suspend_lock);
}

/*-----------------------------------------------------------------
 * 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_holder.kobj;
}

struct mapped_device *dm_get_from_kobject(struct kobject *kobj)
{
        struct mapped_device *md;

        md = container_of(kobj, struct mapped_device, kobj_holder.kobj);

        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_test_deferred_remove_flag(struct mapped_device *md)
{
        return test_bit(DMF_DEFERRED_REMOVE, &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, unsigned per_bio_data_size)
{
        struct dm_md_mempools *pools = kzalloc(sizeof(*pools), GFP_KERNEL);
        struct kmem_cache *cachep;
        unsigned int pool_size;
        unsigned int front_pad;

        if (!pools)
                return NULL;

        if (type == DM_TYPE_BIO_BASED) {
                cachep = _io_cache;
                pool_size = dm_get_reserved_bio_based_ios();
                front_pad = roundup(per_bio_data_size, __alignof__(struct dm_target_io)) + offsetof(struct dm_target_io, clone);
        } else if (type == DM_TYPE_REQUEST_BASED) {
                cachep = _rq_tio_cache;
                pool_size = dm_get_reserved_rq_based_ios();
                front_pad = offsetof(struct dm_rq_clone_bio_info, clone);
                /* per_bio_data_size is not used. See __bind_mempools(). */
                WARN_ON(per_bio_data_size != 0);
        } else
                goto out;

        pools->io_pool = mempool_create_slab_pool(pool_size, cachep);
        if (!pools->io_pool)
                goto out;

        pools->bs = bioset_create(pool_size, front_pad);
        if (!pools->bs)
                goto out;

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

        return pools;

out:
        dm_free_md_mempools(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->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_param(reserved_bio_based_ios, uint, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(reserved_bio_based_ios, "Reserved IOs in bio-based mempools");

module_param(reserved_rq_based_ios, uint, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(reserved_rq_based_ios, "Reserved IOs in request-based mempools");

MODULE_DESCRIPTION(DM_NAME " driver");
MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
MODULE_LICENSE("GPL");