Linux-2.6.12-rc2

[people/ms/linux.git] / drivers / md / dm.c

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

#include "dm.h"
#include "dm-bio-list.h"

#include <linux/init.h>
#include <linux/module.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>

static const char *_name = DM_NAME;

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

/*
 * One of these is allocated per bio.
 */
struct dm_io {
        struct mapped_device *md;
        int error;
        struct bio *bio;
        atomic_t io_count;
};

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

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

/*
 * Bits for the md->flags field.
 */
#define DMF_BLOCK_IO 0
#define DMF_SUSPENDED 1
#define DMF_FS_LOCKED 2

struct mapped_device {
        struct rw_semaphore lock;
        rwlock_t map_lock;
        atomic_t holders;

        unsigned long flags;

        request_queue_t *queue;
        struct gendisk *disk;

        void *interface_ptr;

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

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

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

        /*
         * Event handling.
         */
        atomic_t event_nr;
        wait_queue_head_t eventq;

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

#define MIN_IOS 256
static kmem_cache_t *_io_cache;
static kmem_cache_t *_tio_cache;

static struct bio_set *dm_set;

static int __init local_init(void)
{
        int r;

        dm_set = bioset_create(16, 16, 4);
        if (!dm_set)
                return -ENOMEM;

        /* allocate a slab for the dm_ios */
        _io_cache = kmem_cache_create("dm_io",
                                      sizeof(struct dm_io), 0, 0, NULL, NULL);
        if (!_io_cache)
                return -ENOMEM;

        /* allocate a slab for the target ios */
        _tio_cache = kmem_cache_create("dm_tio", sizeof(struct target_io),
                                       0, 0, NULL, NULL);
        if (!_tio_cache) {
                kmem_cache_destroy(_io_cache);
                return -ENOMEM;
        }

        _major = major;
        r = register_blkdev(_major, _name);
        if (r < 0) {
                kmem_cache_destroy(_tio_cache);
                kmem_cache_destroy(_io_cache);
                return r;
        }

        if (!_major)
                _major = r;

        return 0;
}

static void local_exit(void)
{
        kmem_cache_destroy(_tio_cache);
        kmem_cache_destroy(_io_cache);

        bioset_free(dm_set);

        if (unregister_blkdev(_major, _name) < 0)
                DMERR("devfs_unregister_blkdev failed");

        _major = 0;

        DMINFO("cleaned up");
}

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

void (*_exits[])(void) = {
        local_exit,
        dm_target_exit,
        dm_linear_exit,
        dm_stripe_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 inode *inode, struct file *file)
{
        struct mapped_device *md;

        md = inode->i_bdev->bd_disk->private_data;
        dm_get(md);
        return 0;
}

static int dm_blk_close(struct inode *inode, struct file *file)
{
        struct mapped_device *md;

        md = inode->i_bdev->bd_disk->private_data;
        dm_put(md);
        return 0;
}

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

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

static inline struct target_io *alloc_tio(struct mapped_device *md)
{
        return mempool_alloc(md->tio_pool, GFP_NOIO);
}

static inline void free_tio(struct mapped_device *md, struct target_io *tio)
{
        mempool_free(tio, md->tio_pool);
}

/*
 * Add the bio to the list of deferred io.
 */
static int queue_io(struct mapped_device *md, struct bio *bio)
{
        down_write(&md->lock);

        if (!test_bit(DMF_BLOCK_IO, &md->flags)) {
                up_write(&md->lock);
                return 1;
        }

        bio_list_add(&md->deferred, bio);

        up_write(&md->lock);
        return 0;               /* deferred successfully */
}

/*
 * 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;
}

/*-----------------------------------------------------------------
 * 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.
 *---------------------------------------------------------------*/

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

        if (atomic_dec_and_test(&io->io_count)) {
                if (atomic_dec_and_test(&io->md->pending))
                        /* nudge anyone waiting on suspend queue */
                        wake_up(&io->md->wait);

                bio_endio(io->bio, io->bio->bi_size, io->error);
                free_io(io->md, io);
        }
}

static int clone_endio(struct bio *bio, unsigned int done, int error)
{
        int r = 0;
        struct target_io *tio = bio->bi_private;
        struct dm_io *io = tio->io;
        dm_endio_fn endio = tio->ti->type->end_io;

        if (bio->bi_size)
                return 1;

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

        if (endio) {
                r = endio(tio->ti, bio, error, &tio->info);
                if (r < 0)
                        error = r;

                else if (r > 0)
                        /* the target wants another shot at the io */
                        return 1;
        }

        free_tio(io->md, tio);
        dec_pending(io, error);
        bio_put(bio);
        return r;
}

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 target_io *tio)
{
        int r;

        /*
         * Sanity checks.
         */
        BUG_ON(!clone->bi_size);

        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);
        r = ti->type->map(ti, clone, &tio->info);
        if (r > 0)
                /* the bio has been remapped so dispatch it */
                generic_make_request(clone);

        else if (r < 0) {
                /* error the io and bail out */
                struct dm_io *io = tio->io;
                free_tio(tio->io->md, tio);
                dec_pending(io, -EIO);
                bio_put(clone);
        }
}

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

/*
 * Creates a little bio that 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 *clone;
        struct bio_vec *bv = bio->bi_io_vec + idx;

        clone = bio_alloc_bioset(GFP_NOIO, 1, dm_set);
        *clone->bi_io_vec = *bv;

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

        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 *clone;

        clone = bio_clone(bio, GFP_NOIO);
        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);

        return clone;
}

static void __clone_and_map(struct clone_info *ci)
{
        struct bio *clone, *bio = ci->bio;
        struct dm_target *ti = dm_table_find_target(ci->map, ci->sector);
        sector_t len = 0, max = max_io_len(ci->md, ci->sector, ti);
        struct target_io *tio;

        /*
         * Allocate a target io object.
         */
        tio = alloc_tio(ci->md);
        tio->io = ci->io;
        tio->ti = ti;
        memset(&tio->info, 0, sizeof(tio->info));

        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);
                __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);
                __map_bio(ti, clone, tio);

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

        } else {
                /*
                 * Create two copy bios to deal with io that has
                 * been split across a target.
                 */
                struct bio_vec *bv = bio->bi_io_vec + ci->idx;

                clone = split_bvec(bio, ci->sector, ci->idx,
                                   bv->bv_offset, max);
                __map_bio(ti, clone, tio);

                ci->sector += max;
                ci->sector_count -= max;
                ti = dm_table_find_target(ci->map, ci->sector);

                len = to_sector(bv->bv_len) - max;
                clone = split_bvec(bio, ci->sector, ci->idx,
                                   bv->bv_offset + to_bytes(max), len);
                tio = alloc_tio(ci->md);
                tio->io = ci->io;
                tio->ti = ti;
                memset(&tio->info, 0, sizeof(tio->info));
                __map_bio(ti, clone, tio);

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

/*
 * Split the bio into several clones.
 */
static void __split_bio(struct mapped_device *md, struct bio *bio)
{
        struct clone_info ci;

        ci.map = dm_get_table(md);
        if (!ci.map) {
                bio_io_error(bio, bio->bi_size);
                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);
        ci.idx = bio->bi_idx;

        atomic_inc(&md->pending);
        while (ci.sector_count)
                __clone_and_map(&ci);

        /* drop the extra reference count */
        dec_pending(ci.io, 0);
        dm_table_put(ci.map);
}
/*-----------------------------------------------------------------
 * CRUD END
 *---------------------------------------------------------------*/

/*
 * The request function that just remaps the bio built up by
 * dm_merge_bvec.
 */
static int dm_request(request_queue_t *q, struct bio *bio)
{
        int r;
        struct mapped_device *md = q->queuedata;

        down_read(&md->lock);

        /*
         * If we're suspended we have to queue
         * this io for later.
         */
        while (test_bit(DMF_BLOCK_IO, &md->flags)) {
                up_read(&md->lock);

                if (bio_rw(bio) == READA) {
                        bio_io_error(bio, bio->bi_size);
                        return 0;
                }

                r = queue_io(md, bio);
                if (r < 0) {
                        bio_io_error(bio, bio->bi_size);
                        return 0;

                } else if (r == 0)
                        return 0;       /* deferred successfully */

                /*
                 * We're in a while loop, because someone could suspend
                 * before we get to the following read lock.
                 */
                down_read(&md->lock);
        }

        __split_bio(md, bio);
        up_read(&md->lock);
        return 0;
}

static int dm_flush_all(request_queue_t *q, struct gendisk *disk,
                        sector_t *error_sector)
{
        struct mapped_device *md = q->queuedata;
        struct dm_table *map = dm_get_table(md);
        int ret = -ENXIO;

        if (map) {
                ret = dm_table_flush_all(md->map);
                dm_table_put(map);
        }

        return ret;
}

static void dm_unplug_all(request_queue_t *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;
        struct mapped_device *md = (struct mapped_device *) congested_data;
        struct dm_table *map = dm_get_table(md);

        if (!map || test_bit(DMF_BLOCK_IO, &md->flags))
                r = bdi_bits;
        else
                r = dm_table_any_congested(map, bdi_bits);

        dm_table_put(map);
        return r;
}

/*-----------------------------------------------------------------
 * An IDR is used to keep track of allocated minor numbers.
 *---------------------------------------------------------------*/
static DECLARE_MUTEX(_minor_lock);
static DEFINE_IDR(_minor_idr);

static void free_minor(unsigned int minor)
{
        down(&_minor_lock);
        idr_remove(&_minor_idr, minor);
        up(&_minor_lock);
}

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

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

        down(&_minor_lock);

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

        r = idr_pre_get(&_minor_idr, GFP_KERNEL);
        if (!r) {
                r = -ENOMEM;
                goto out;
        }

        r = idr_get_new_above(&_minor_idr, md, minor, &m);
        if (r) {
                goto out;
        }

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

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

static int next_free_minor(struct mapped_device *md, unsigned int *minor)
{
        int r;
        unsigned int m;

        down(&_minor_lock);

        r = idr_pre_get(&_minor_idr, GFP_KERNEL);
        if (!r) {
                r = -ENOMEM;
                goto out;
        }

        r = idr_get_new(&_minor_idr, md, &m);
        if (r) {
                goto out;
        }

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

        *minor = m;

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

static struct block_device_operations dm_blk_dops;

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

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

        /* get a minor number for the dev */
        r = persistent ? specific_minor(md, minor) : next_free_minor(md, &minor);
        if (r < 0)
                goto bad1;

        memset(md, 0, sizeof(*md));
        init_rwsem(&md->lock);
        rwlock_init(&md->map_lock);
        atomic_set(&md->holders, 1);
        atomic_set(&md->event_nr, 0);

        md->queue = blk_alloc_queue(GFP_KERNEL);
        if (!md->queue)
                goto bad1;

        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);
        md->queue->unplug_fn = dm_unplug_all;
        md->queue->issue_flush_fn = dm_flush_all;

        md->io_pool = mempool_create(MIN_IOS, mempool_alloc_slab,
                                     mempool_free_slab, _io_cache);
        if (!md->io_pool)
                goto bad2;

        md->tio_pool = mempool_create(MIN_IOS, mempool_alloc_slab,
                                      mempool_free_slab, _tio_cache);
        if (!md->tio_pool)
                goto bad3;

        md->disk = alloc_disk(1);
        if (!md->disk)
                goto bad4;

        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);

        atomic_set(&md->pending, 0);
        init_waitqueue_head(&md->wait);
        init_waitqueue_head(&md->eventq);

        return md;

 bad4:
        mempool_destroy(md->tio_pool);
 bad3:
        mempool_destroy(md->io_pool);
 bad2:
        blk_put_queue(md->queue);
        free_minor(minor);
 bad1:
        kfree(md);
        return NULL;
}

static void free_dev(struct mapped_device *md)
{
        free_minor(md->disk->first_minor);
        mempool_destroy(md->tio_pool);
        mempool_destroy(md->io_pool);
        del_gendisk(md->disk);
        put_disk(md->disk);
        blk_put_queue(md->queue);
        kfree(md);
}

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

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

static void __set_size(struct gendisk *disk, sector_t size)
{
        struct block_device *bdev;

        set_capacity(disk, size);
        bdev = bdget_disk(disk, 0);
        if (bdev) {
                down(&bdev->bd_inode->i_sem);
                i_size_write(bdev->bd_inode, (loff_t)size << SECTOR_SHIFT);
                up(&bdev->bd_inode->i_sem);
                bdput(bdev);
        }
}

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

        size = dm_table_get_size(t);
        __set_size(md->disk, size);
        if (size == 0)
                return 0;

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

        dm_table_get(t);
        dm_table_event_callback(md->map, event_callback, md);
        dm_table_set_restrictions(t, q);
        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_put(map);
}

/*
 * Constructor for a new device.
 */
static int create_aux(unsigned int minor, int persistent,
                      struct mapped_device **result)
{
        struct mapped_device *md;

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

        *result = md;
        return 0;
}

int dm_create(struct mapped_device **result)
{
        return create_aux(0, 0, result);
}

int dm_create_with_minor(unsigned int minor, struct mapped_device **result)
{
        return create_aux(minor, 1, result);
}

void *dm_get_mdptr(dev_t dev)
{
        struct mapped_device *md;
        void *mdptr = NULL;
        unsigned minor = MINOR(dev);

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

        down(&_minor_lock);

        md = idr_find(&_minor_idr, minor);

        if (md && (dm_disk(md)->first_minor == minor))
                mdptr = md->interface_ptr;

        up(&_minor_lock);

        return mdptr;
}

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);
}

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

        if (atomic_dec_and_test(&md->holders)) {
                if (!test_bit(DMF_SUSPENDED, &md->flags) && map) {
                        dm_table_presuspend_targets(map);
                        dm_table_postsuspend_targets(map);
                }
                __unbind(md);
                free_dev(md);
        }

        dm_table_put(map);
}

/*
 * Process the deferred bios
 */
static void __flush_deferred_io(struct mapped_device *md, struct bio *c)
{
        struct bio *n;

        while (c) {
                n = c->bi_next;
                c->bi_next = NULL;
                __split_bio(md, c);
                c = n;
        }
}

/*
 * Swap in a new table (destroying old one).
 */
int dm_swap_table(struct mapped_device *md, struct dm_table *table)
{
        int r;

        down_write(&md->lock);

        /* device must be suspended */
        if (!test_bit(DMF_SUSPENDED, &md->flags)) {
                up_write(&md->lock);
                return -EPERM;
        }

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

        up_write(&md->lock);
        return 0;
}

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

        if (test_and_set_bit(DMF_FS_LOCKED, &md->flags))
                return 0;

        bdev = bdget_disk(md->disk, 0);
        if (!bdev) {
                DMWARN("bdget failed in __lock_fs");
                return -ENOMEM;
        }

        WARN_ON(md->frozen_sb);
        md->frozen_sb = freeze_bdev(bdev);
        /* don't bdput right now, we don't want the bdev
         * to go away while it is locked.  We'll bdput
         * in __unlock_fs
         */
        return 0;
}

static int __unlock_fs(struct mapped_device *md)
{
        struct block_device *bdev;

        if (!test_and_clear_bit(DMF_FS_LOCKED, &md->flags))
                return 0;

        bdev = bdget_disk(md->disk, 0);
        if (!bdev) {
                DMWARN("bdget failed in __unlock_fs");
                return -ENOMEM;
        }

        thaw_bdev(bdev, md->frozen_sb);
        md->frozen_sb = NULL;
        bdput(bdev);
        bdput(bdev);
        return 0;
}

/*
 * 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)
{
        struct dm_table *map;
        DECLARE_WAITQUEUE(wait, current);

        /* Flush I/O to the device. */
        down_read(&md->lock);
        if (test_bit(DMF_BLOCK_IO, &md->flags)) {
                up_read(&md->lock);
                return -EINVAL;
        }

        map = dm_get_table(md);
        if (map)
                dm_table_presuspend_targets(map);
        __lock_fs(md);

        up_read(&md->lock);

        /*
         * First we set the BLOCK_IO flag so no more ios will be
         * mapped.
         */
        down_write(&md->lock);
        if (test_bit(DMF_BLOCK_IO, &md->flags)) {
                /*
                 * If we get here we know another thread is
                 * trying to suspend as well, so we leave the fs
                 * locked for this thread.
                 */
                up_write(&md->lock);
                return -EINVAL;
        }

        set_bit(DMF_BLOCK_IO, &md->flags);
        add_wait_queue(&md->wait, &wait);
        up_write(&md->lock);

        /* unplug */
        if (map) {
                dm_table_unplug_all(map);
                dm_table_put(map);
        }

        /*
         * Then we wait for the already mapped ios to
         * complete.
         */
        while (1) {
                set_current_state(TASK_INTERRUPTIBLE);

                if (!atomic_read(&md->pending) || signal_pending(current))
                        break;

                io_schedule();
        }
        set_current_state(TASK_RUNNING);

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

        /* were we interrupted ? */
        if (atomic_read(&md->pending)) {
                __unlock_fs(md);
                clear_bit(DMF_BLOCK_IO, &md->flags);
                up_write(&md->lock);
                return -EINTR;
        }

        set_bit(DMF_SUSPENDED, &md->flags);

        map = dm_get_table(md);
        if (map)
                dm_table_postsuspend_targets(map);
        dm_table_put(map);
        up_write(&md->lock);

        return 0;
}

int dm_resume(struct mapped_device *md)
{
        struct bio *def;
        struct dm_table *map = dm_get_table(md);

        down_write(&md->lock);
        if (!map ||
            !test_bit(DMF_SUSPENDED, &md->flags) ||
            !dm_table_get_size(map)) {
                up_write(&md->lock);
                dm_table_put(map);
                return -EINVAL;
        }

        dm_table_resume_targets(map);
        clear_bit(DMF_SUSPENDED, &md->flags);
        clear_bit(DMF_BLOCK_IO, &md->flags);

        def = bio_list_get(&md->deferred);
        __flush_deferred_io(md, def);
        up_write(&md->lock);
        __unlock_fs(md);
        dm_table_unplug_all(map);
        dm_table_put(map);

        return 0;
}

/*-----------------------------------------------------------------
 * Event notification.
 *---------------------------------------------------------------*/
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)));
}

/*
 * 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;
}

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

static struct block_device_operations dm_blk_dops = {
        .open = dm_blk_open,
        .release = dm_blk_close,
        .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");