[deliverable/linux.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/buffer_head.h>
#include <linux/mempool.h>
#include <linux/slab.h>
#include <linux/idr.h>
#include <linux/hdreg.h>

#include <trace/events/block.h>

#define DM_MSG_PREFIX "core"

static const char *_name = DM_NAME;

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

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;
};

/*
 * 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;
};

/*
 * 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.
 * One of these is allocated per bio.
 */
struct dm_rq_clone_bio_info {
        struct bio *orig;
        struct request *rq;
};

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;
}

#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_QUEUE_IO_TO_THREAD 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;
        struct gendisk *disk;
        char name[16];

        void *interface_ptr;

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

        /*
         * An error from the barrier request currently being processed.
         */
        int barrier_error;

        /*
         * Processing queue (flush/barriers)
         */
        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 barrier that will be cloned and submitted to targets */
        struct bio barrier_bio;
};

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

        /* allocate a slab for the target ios */
        _tio_cache = KMEM_CACHE(dm_target_io, 0);
        if (!_tio_cache)
                goto out_free_io_cache;

        _rq_tio_cache = KMEM_CACHE(dm_rq_target_io, 0);
        if (!_rq_tio_cache)
                goto out_free_tio_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_tio_cache:
        kmem_cache_destroy(_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(_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_kcopyd_init,
        dm_interface_init,
};

static void (*_exits[])(void) = {
        local_exit,
        dm_target_exit,
        dm_linear_exit,
        dm_stripe_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]();
}

/*
 * Block device functions
 */
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) ||
            test_bit(DMF_DELETING, &md->flags)) {
                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;
        atomic_dec(&md->open_count);
        dm_put(md);
        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_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)) {
                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)
{
        mempool_free(tio, md->tio_pool);
}

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

        io->start_time = jiffies;

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

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 barrier.
         */
        dm_disk(md)->part0.in_flight = pending =
                atomic_dec_return(&md->pending);

        /* 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)
{
        down_write(&md->io_lock);

        spin_lock_irq(&md->deferred_lock);
        bio_list_add(&md->deferred, bio);
        spin_unlock_irq(&md->deferred_lock);

        if (!test_and_set_bit(DMF_QUEUE_IO_TO_THREAD, &md->flags))
                queue_work(md->wq, &md->work);

        up_write(&md->io_lock);
}

/*
 * 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_table(struct mapped_device *md)
{
        struct dm_table *t;

        read_lock(&md->map_lock);
        t = md->map;
        if (t)
                dm_table_get(t);
        read_unlock(&md->map_lock);

        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 (error && !(io->error > 0 && __noflush_suspending(md)))
                io->error = error;

        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)) {
                                if (!bio_barrier(io->bio))
                                        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;

                if (bio_barrier(bio)) {
                        /*
                         * There can be just one barrier request so we use
                         * a per-device variable for error reporting.
                         * Note that you can't touch the bio after end_io_acct
                         */
                        if (!md->barrier_error && io_error != -EOPNOTSUPP)
                                md->barrier_error = io_error;
                        end_io_acct(io);
                } else {
                        end_io_acct(io);

                        if (io_error != DM_ENDIO_REQUEUE) {
                                trace_block_bio_complete(md->queue, bio);

                                bio_endio(bio, io_error);
                        }
                }

                free_io(md, io);
        }
}

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();
                }
        }

        /*
         * Store md for cleanup instead of tio which is about to get freed.
         */
        bio->bi_private = md->bs;

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

static sector_t max_io_len(struct mapped_device *md,
                           sector_t sector, struct dm_target *ti)
{
        sector_t offset = sector - ti->begin;
        sector_t len = ti->len - offset;

        /*
         * Does the target need to split even further ?
         */
        if (ti->split_io) {
                sector_t boundary;
                boundary = ((offset + ti->split_io) & ~(ti->split_io - 1))
                           - offset;
                if (len > boundary)
                        len = boundary;
        }

        return len;
}

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

        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_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);
                /*
                 * Store bio_set for cleanup.
                 */
                clone->bi_private = md->bs;
                bio_put(clone);
                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 dm_bio_destructor(struct bio *bio)
{
        struct bio_set *bs = bio->bi_private;

        bio_free(bio, bs);
}

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

        clone = bio_alloc_bioset(GFP_NOIO, 1, bs);
        clone->bi_destructor = dm_bio_destructor;
        *clone->bi_io_vec = *bv;

        clone->bi_sector = sector;
        clone->bi_bdev = bio->bi_bdev;
        clone->bi_rw = bio->bi_rw & ~(1 << BIO_RW_BARRIER);
        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);
        }

        return clone;
}

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

        clone = bio_alloc_bioset(GFP_NOIO, bio->bi_max_vecs, bs);
        __bio_clone(clone, bio);
        clone->bi_rw &= ~(1 << BIO_RW_BARRIER);
        clone->bi_destructor = dm_bio_destructor;
        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);
        }

        return clone;
}

static struct dm_target_io *alloc_tio(struct clone_info *ci,
                                      struct dm_target *ti)
{
        struct dm_target_io *tio = mempool_alloc(ci->md->tio_pool, GFP_NOIO);

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

        return tio;
}

static void __flush_target(struct clone_info *ci, struct dm_target *ti,
                          unsigned flush_nr)
{
        struct dm_target_io *tio = alloc_tio(ci, ti);
        struct bio *clone;

        tio->info.flush_request = flush_nr;

        clone = bio_alloc_bioset(GFP_NOIO, 0, ci->md->bs);
        __bio_clone(clone, ci->bio);
        clone->bi_destructor = dm_bio_destructor;

        __map_bio(ti, clone, tio);
}

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

        while ((ti = dm_table_get_target(ci->map, target_nr++)))
                for (flush_nr = 0; flush_nr < ti->num_flush_requests;
                     flush_nr++)
                        __flush_target(ci, ti, flush_nr);

        ci->sector_count = 0;

        return 0;
}

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

        if (unlikely(bio_empty_barrier(bio)))
                return __clone_and_map_empty_barrier(ci);

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

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

        /*
         * Allocate a target io object.
         */
        tio = alloc_tio(ci, 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 = clone_bio(bio, ci->sector, ci->idx,
                                  bio->bi_vcnt - ci->idx, ci->sector_count,
                                  ci->md->bs);
                __map_bio(ti, clone, tio);
                ci->sector_count = 0;

        } 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;
                }

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

                                tio = alloc_tio(ci, ti);
                        }

                        len = min(remaining, max);

                        clone = split_bvec(bio, ci->sector, ci->idx,
                                           bv->bv_offset + offset, len,
                                           ci->md->bs);

                        __map_bio(ti, clone, 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_table(md);
        if (unlikely(!ci.map)) {
                if (!bio_barrier(bio))
                        bio_io_error(bio);
                else
                        if (!md->barrier_error)
                                md->barrier_error = -EIO;
                return;
        }

        ci.md = md;
        ci.bio = bio;
        ci.io = alloc_io(md);
        ci.io->error = 0;
        atomic_set(&ci.io->io_count, 1);
        ci.io->bio = bio;
        ci.io->md = md;
        ci.sector = bio->bi_sector;
        ci.sector_count = bio_sectors(bio);
        if (unlikely(bio_empty_barrier(bio)))
                ci.sector_count = 1;
        ci.idx = bio->bi_idx;

        start_io_acct(ci.io);
        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_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(md, 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 int 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 or the thread is processing barriers
         * we have to queue this io for later.
         */
        if (unlikely(test_bit(DMF_QUEUE_IO_TO_THREAD, &md->flags)) ||
            unlikely(bio_barrier(bio))) {
                up_read(&md->io_lock);

                if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) &&
                    bio_rw(bio) == READA) {
                        bio_io_error(bio);
                        return 0;
                }

                queue_io(md, bio);

                return 0;
        }

        __split_and_process_bio(md, bio);
        up_read(&md->io_lock);
        return 0;
}

static void dm_unplug_all(struct request_queue *q)
{
        struct mapped_device *md = q->queuedata;
        struct dm_table *map = dm_get_table(md);

        if (map) {
                dm_table_unplug_all(map);
                dm_table_put(map);
        }
}

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_table(md);
                if (map) {
                        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 DEFINE_IDR(_minor_idr);

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 struct block_device_operations dm_blk_dops;

static void dm_wq_work(struct work_struct *work);

/*
 * 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;

        init_rwsem(&md->io_lock);
        mutex_init(&md->suspend_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;

        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_ordered(md->queue, QUEUE_ORDERED_DRAIN, NULL);
        blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);
        md->queue->unplug_fn = dm_unplug_all;
        blk_queue_merge_bvec(md->queue, dm_merge_bvec);

        md->io_pool = mempool_create_slab_pool(MIN_IOS, _io_cache);
        if (!md->io_pool)
                goto bad_io_pool;

        md->tio_pool = mempool_create_slab_pool(MIN_IOS, _tio_cache);
        if (!md->tio_pool)
                goto bad_tio_pool;

        md->bs = bioset_create(16, 0);
        if (!md->bs)
                goto bad_no_bioset;

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

        atomic_set(&md->pending, 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 = create_singlethread_workqueue("kdmflush");
        if (!md->wq)
                goto bad_thread;

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

        /* 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:
        put_disk(md->disk);
bad_disk:
        bioset_free(md->bs);
bad_no_bioset:
        mempool_destroy(md->tio_pool);
bad_tio_pool:
        mempool_destroy(md->io_pool);
bad_io_pool:
        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);
        mempool_destroy(md->tio_pool);
        mempool_destroy(md->io_pool);
        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);
}

/*
 * 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);
}

static void __set_size(struct mapped_device *md, sector_t size)
{
        set_capacity(md->disk, size);

        mutex_lock(&md->bdev->bd_inode->i_mutex);
        i_size_write(md->bdev->bd_inode, (loff_t)size << SECTOR_SHIFT);
        mutex_unlock(&md->bdev->bd_inode->i_mutex);
}

static int __bind(struct mapped_device *md, struct dm_table *t)
{
        struct request_queue *q = md->queue;
        sector_t size;

        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);

        if (!size) {
                dm_table_destroy(t);
                return 0;
        }

        dm_table_event_callback(t, event_callback, md);

        write_lock(&md->map_lock);
        md->map = t;
        dm_table_set_restrictions(t, q);
        write_unlock(&md->map_lock);

        return 0;
}

static void __unbind(struct mapped_device *md)
{
        struct dm_table *map = md->map;

        if (!map)
                return;

        dm_table_event_callback(map, NULL, NULL);
        write_lock(&md->map_lock);
        md->map = NULL;
        write_unlock(&md->map_lock);
        dm_table_destroy(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;
}

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) ||
                   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;
}

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);
}

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

void dm_put(struct mapped_device *md)
{
        struct dm_table *map;

        BUG_ON(test_bit(DMF_FREEING, &md->flags));

        if (atomic_dec_and_lock(&md->holders, &_minor_lock)) {
                map = dm_get_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)) {
                        dm_table_presuspend_targets(map);
                        dm_table_postsuspend_targets(map);
                }
                dm_sysfs_exit(md);
                dm_table_put(map);
                __unbind(md);
                free_dev(md);
        }
}
EXPORT_SYMBOL_GPL(dm_put);

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

        dm_unplug_all(md->queue);

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

        while (1) {
                set_current_state(interruptible);

                smp_mb();
                if (!atomic_read(&md->pending))
                        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;
}

static void dm_flush(struct mapped_device *md)
{
        dm_wait_for_completion(md, TASK_UNINTERRUPTIBLE);

        bio_init(&md->barrier_bio);
        md->barrier_bio.bi_bdev = md->bdev;
        md->barrier_bio.bi_rw = WRITE_BARRIER;
        __split_and_process_bio(md, &md->barrier_bio);

        dm_wait_for_completion(md, TASK_UNINTERRUPTIBLE);
}

static void process_barrier(struct mapped_device *md, struct bio *bio)
{
        md->barrier_error = 0;

        dm_flush(md);

        if (!bio_empty_barrier(bio)) {
                __split_and_process_bio(md, bio);
                dm_flush(md);
        }

        if (md->barrier_error != DM_ENDIO_REQUEUE)
                bio_endio(bio, md->barrier_error);
        else {
                spin_lock_irq(&md->deferred_lock);
                bio_list_add_head(&md->deferred, bio);
                spin_unlock_irq(&md->deferred_lock);
        }
}

/*
 * 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_write(&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) {
                        clear_bit(DMF_QUEUE_IO_TO_THREAD, &md->flags);
                        break;
                }

                up_write(&md->io_lock);

                if (bio_barrier(c))
                        process_barrier(md, c);
                else
                        __split_and_process_bio(md, c);

                down_write(&md->io_lock);
        }

        up_write(&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 (destroying old one).
 */
int dm_swap_table(struct mapped_device *md, struct dm_table *table)
{
        int r = -EINVAL;

        mutex_lock(&md->suspend_lock);

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

        __unbind(md);
        r = __bind(md, table);

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

/*
 * 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.
 */
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)) {
                r = -EINVAL;
                goto out_unlock;
        }

        map = dm_get_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. noflush supersedes do_lockfs,
         * because lock_fs() needs to flush I/Os.
         */
        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, we set
         * DMF_QUEUE_IO_TO_THREAD.
         *
         * To quiesce the thread (dm_wq_work), we set DMF_BLOCK_IO_FOR_SUSPEND
         * and call flush_workqueue(md->wq). flush_workqueue will wait until
         * dm_wq_work exits and DMF_BLOCK_IO_FOR_SUSPEND will prevent any
         * further calls to __split_and_process_bio from dm_wq_work.
         */
        down_write(&md->io_lock);
        set_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags);
        set_bit(DMF_QUEUE_IO_TO_THREAD, &md->flags);
        up_write(&md->io_lock);

        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);

                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.
         */

        dm_table_postsuspend_targets(map);

        set_bit(DMF_SUSPENDED, &md->flags);

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))
                goto out;

        map = dm_get_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);

        unlock_fs(md);

        clear_bit(DMF_SUSPENDED, &md->flags);

        dm_table_unplug_all(map);

        dm_kobject_uevent(md);

        r = 0;

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

        return r;
}

/*-----------------------------------------------------------------
 * Event notification.
 *---------------------------------------------------------------*/
void dm_kobject_uevent(struct mapped_device *md)
{
        kobject_uevent(&disk_to_dev(md->disk)->kobj, KOBJ_CHANGE);
}

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) ||
            test_bit(DMF_DELETING, &md->flags))
                return NULL;

        dm_get(md);
        return md;
}

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

int dm_noflush_suspending(struct dm_target *ti)
{
        struct mapped_device *md = dm_table_get_md(ti->table);
        int r = __noflush_suspending(md);

        dm_put(md);

        return r;
}
EXPORT_SYMBOL_GPL(dm_noflush_suspending);

static 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 <dm-devel@redhat.com>");
MODULE_LICENSE("GPL");