[PATCH] ppc32: add 440GX erratum 440_43 workaround

[linux-2.6/openmoko-kernel/knife-kernel.git] / drivers / md / dm-raid1.c

/*
 * Copyright (C) 2003 Sistina Software Limited.
 *
 * This file is released under the GPL.
 */

#include "dm.h"
#include "dm-bio-list.h"
#include "dm-io.h"
#include "dm-log.h"
#include "kcopyd.h"

#include <linux/ctype.h>
#include <linux/init.h>
#include <linux/mempool.h>
#include <linux/module.h>
#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/vmalloc.h>
#include <linux/workqueue.h>

static struct workqueue_struct *_kmirrord_wq;
static struct work_struct _kmirrord_work;

static inline void wake(void)
{
        queue_work(_kmirrord_wq, &_kmirrord_work);
}

/*-----------------------------------------------------------------
 * Region hash
 *
 * The mirror splits itself up into discrete regions.  Each
 * region can be in one of three states: clean, dirty,
 * nosync.  There is no need to put clean regions in the hash.
 *
 * In addition to being present in the hash table a region _may_
 * be present on one of three lists.
 *
 *   clean_regions: Regions on this list have no io pending to
 *   them, they are in sync, we are no longer interested in them,
 *   they are dull.  rh_update_states() will remove them from the
 *   hash table.
 *
 *   quiesced_regions: These regions have been spun down, ready
 *   for recovery.  rh_recovery_start() will remove regions from
 *   this list and hand them to kmirrord, which will schedule the
 *   recovery io with kcopyd.
 *
 *   recovered_regions: Regions that kcopyd has successfully
 *   recovered.  rh_update_states() will now schedule any delayed
 *   io, up the recovery_count, and remove the region from the
 *   hash.
 *
 * There are 2 locks:
 *   A rw spin lock 'hash_lock' protects just the hash table,
 *   this is never held in write mode from interrupt context,
 *   which I believe means that we only have to disable irqs when
 *   doing a write lock.
 *
 *   An ordinary spin lock 'region_lock' that protects the three
 *   lists in the region_hash, with the 'state', 'list' and
 *   'bhs_delayed' fields of the regions.  This is used from irq
 *   context, so all other uses will have to suspend local irqs.
 *---------------------------------------------------------------*/
struct mirror_set;
struct region_hash {
        struct mirror_set *ms;
        uint32_t region_size;
        unsigned region_shift;

        /* holds persistent region state */
        struct dirty_log *log;

        /* hash table */
        rwlock_t hash_lock;
        mempool_t *region_pool;
        unsigned int mask;
        unsigned int nr_buckets;
        struct list_head *buckets;

        spinlock_t region_lock;
        struct semaphore recovery_count;
        struct list_head clean_regions;
        struct list_head quiesced_regions;
        struct list_head recovered_regions;
};

enum {
        RH_CLEAN,
        RH_DIRTY,
        RH_NOSYNC,
        RH_RECOVERING
};

struct region {
        struct region_hash *rh; /* FIXME: can we get rid of this ? */
        region_t key;
        int state;

        struct list_head hash_list;
        struct list_head list;

        atomic_t pending;
        struct bio_list delayed_bios;
};

/*
 * Conversion fns
 */
static inline region_t bio_to_region(struct region_hash *rh, struct bio *bio)
{
        return bio->bi_sector >> rh->region_shift;
}

static inline sector_t region_to_sector(struct region_hash *rh, region_t region)
{
        return region << rh->region_shift;
}

/* FIXME move this */
static void queue_bio(struct mirror_set *ms, struct bio *bio, int rw);

#define MIN_REGIONS 64
#define MAX_RECOVERY 1
static int rh_init(struct region_hash *rh, struct mirror_set *ms,
                   struct dirty_log *log, uint32_t region_size,
                   region_t nr_regions)
{
        unsigned int nr_buckets, max_buckets;
        size_t i;

        /*
         * Calculate a suitable number of buckets for our hash
         * table.
         */
        max_buckets = nr_regions >> 6;
        for (nr_buckets = 128u; nr_buckets < max_buckets; nr_buckets <<= 1)
                ;
        nr_buckets >>= 1;

        rh->ms = ms;
        rh->log = log;
        rh->region_size = region_size;
        rh->region_shift = ffs(region_size) - 1;
        rwlock_init(&rh->hash_lock);
        rh->mask = nr_buckets - 1;
        rh->nr_buckets = nr_buckets;

        rh->buckets = vmalloc(nr_buckets * sizeof(*rh->buckets));
        if (!rh->buckets) {
                DMERR("unable to allocate region hash memory");
                return -ENOMEM;
        }

        for (i = 0; i < nr_buckets; i++)
                INIT_LIST_HEAD(rh->buckets + i);

        spin_lock_init(&rh->region_lock);
        sema_init(&rh->recovery_count, 0);
        INIT_LIST_HEAD(&rh->clean_regions);
        INIT_LIST_HEAD(&rh->quiesced_regions);
        INIT_LIST_HEAD(&rh->recovered_regions);

        rh->region_pool = mempool_create_kmalloc_pool(MIN_REGIONS,
                                                      sizeof(struct region));
        if (!rh->region_pool) {
                vfree(rh->buckets);
                rh->buckets = NULL;
                return -ENOMEM;
        }

        return 0;
}

static void rh_exit(struct region_hash *rh)
{
        unsigned int h;
        struct region *reg, *nreg;

        BUG_ON(!list_empty(&rh->quiesced_regions));
        for (h = 0; h < rh->nr_buckets; h++) {
                list_for_each_entry_safe(reg, nreg, rh->buckets + h, hash_list) {
                        BUG_ON(atomic_read(&reg->pending));
                        mempool_free(reg, rh->region_pool);
                }
        }

        if (rh->log)
                dm_destroy_dirty_log(rh->log);
        if (rh->region_pool)
                mempool_destroy(rh->region_pool);
        vfree(rh->buckets);
}

#define RH_HASH_MULT 2654435387U

static inline unsigned int rh_hash(struct region_hash *rh, region_t region)
{
        return (unsigned int) ((region * RH_HASH_MULT) >> 12) & rh->mask;
}

static struct region *__rh_lookup(struct region_hash *rh, region_t region)
{
        struct region *reg;

        list_for_each_entry (reg, rh->buckets + rh_hash(rh, region), hash_list)
                if (reg->key == region)
                        return reg;

        return NULL;
}

static void __rh_insert(struct region_hash *rh, struct region *reg)
{
        unsigned int h = rh_hash(rh, reg->key);
        list_add(&reg->hash_list, rh->buckets + h);
}

static struct region *__rh_alloc(struct region_hash *rh, region_t region)
{
        struct region *reg, *nreg;

        read_unlock(&rh->hash_lock);
        nreg = mempool_alloc(rh->region_pool, GFP_NOIO);
        nreg->state = rh->log->type->in_sync(rh->log, region, 1) ?
                RH_CLEAN : RH_NOSYNC;
        nreg->rh = rh;
        nreg->key = region;

        INIT_LIST_HEAD(&nreg->list);

        atomic_set(&nreg->pending, 0);
        bio_list_init(&nreg->delayed_bios);
        write_lock_irq(&rh->hash_lock);

        reg = __rh_lookup(rh, region);
        if (reg)
                /* we lost the race */
                mempool_free(nreg, rh->region_pool);

        else {
                __rh_insert(rh, nreg);
                if (nreg->state == RH_CLEAN) {
                        spin_lock(&rh->region_lock);
                        list_add(&nreg->list, &rh->clean_regions);
                        spin_unlock(&rh->region_lock);
                }
                reg = nreg;
        }
        write_unlock_irq(&rh->hash_lock);
        read_lock(&rh->hash_lock);

        return reg;
}

static inline struct region *__rh_find(struct region_hash *rh, region_t region)
{
        struct region *reg;

        reg = __rh_lookup(rh, region);
        if (!reg)
                reg = __rh_alloc(rh, region);

        return reg;
}

static int rh_state(struct region_hash *rh, region_t region, int may_block)
{
        int r;
        struct region *reg;

        read_lock(&rh->hash_lock);
        reg = __rh_lookup(rh, region);
        read_unlock(&rh->hash_lock);

        if (reg)
                return reg->state;

        /*
         * The region wasn't in the hash, so we fall back to the
         * dirty log.
         */
        r = rh->log->type->in_sync(rh->log, region, may_block);

        /*
         * Any error from the dirty log (eg. -EWOULDBLOCK) gets
         * taken as a RH_NOSYNC
         */
        return r == 1 ? RH_CLEAN : RH_NOSYNC;
}

static inline int rh_in_sync(struct region_hash *rh,
                             region_t region, int may_block)
{
        int state = rh_state(rh, region, may_block);
        return state == RH_CLEAN || state == RH_DIRTY;
}

static void dispatch_bios(struct mirror_set *ms, struct bio_list *bio_list)
{
        struct bio *bio;

        while ((bio = bio_list_pop(bio_list))) {
                queue_bio(ms, bio, WRITE);
        }
}

static void rh_update_states(struct region_hash *rh)
{
        struct region *reg, *next;

        LIST_HEAD(clean);
        LIST_HEAD(recovered);

        /*
         * Quickly grab the lists.
         */
        write_lock_irq(&rh->hash_lock);
        spin_lock(&rh->region_lock);
        if (!list_empty(&rh->clean_regions)) {
                list_splice(&rh->clean_regions, &clean);
                INIT_LIST_HEAD(&rh->clean_regions);

                list_for_each_entry (reg, &clean, list) {
                        rh->log->type->clear_region(rh->log, reg->key);
                        list_del(&reg->hash_list);
                }
        }

        if (!list_empty(&rh->recovered_regions)) {
                list_splice(&rh->recovered_regions, &recovered);
                INIT_LIST_HEAD(&rh->recovered_regions);

                list_for_each_entry (reg, &recovered, list)
                        list_del(&reg->hash_list);
        }
        spin_unlock(&rh->region_lock);
        write_unlock_irq(&rh->hash_lock);

        /*
         * All the regions on the recovered and clean lists have
         * now been pulled out of the system, so no need to do
         * any more locking.
         */
        list_for_each_entry_safe (reg, next, &recovered, list) {
                rh->log->type->clear_region(rh->log, reg->key);
                rh->log->type->complete_resync_work(rh->log, reg->key, 1);
                dispatch_bios(rh->ms, &reg->delayed_bios);
                up(&rh->recovery_count);
                mempool_free(reg, rh->region_pool);
        }

        if (!list_empty(&recovered))
                rh->log->type->flush(rh->log);

        list_for_each_entry_safe (reg, next, &clean, list)
                mempool_free(reg, rh->region_pool);
}

static void rh_inc(struct region_hash *rh, region_t region)
{
        struct region *reg;

        read_lock(&rh->hash_lock);
        reg = __rh_find(rh, region);

        spin_lock_irq(&rh->region_lock);
        atomic_inc(&reg->pending);

        if (reg->state == RH_CLEAN) {
                reg->state = RH_DIRTY;
                list_del_init(&reg->list);      /* take off the clean list */
                spin_unlock_irq(&rh->region_lock);

                rh->log->type->mark_region(rh->log, reg->key);
        } else
                spin_unlock_irq(&rh->region_lock);


        read_unlock(&rh->hash_lock);
}

static void rh_inc_pending(struct region_hash *rh, struct bio_list *bios)
{
        struct bio *bio;

        for (bio = bios->head; bio; bio = bio->bi_next)
                rh_inc(rh, bio_to_region(rh, bio));
}

static void rh_dec(struct region_hash *rh, region_t region)
{
        unsigned long flags;
        struct region *reg;
        int should_wake = 0;

        read_lock(&rh->hash_lock);
        reg = __rh_lookup(rh, region);
        read_unlock(&rh->hash_lock);

        spin_lock_irqsave(&rh->region_lock, flags);
        if (atomic_dec_and_test(&reg->pending)) {
                /*
                 * There is no pending I/O for this region.
                 * We can move the region to corresponding list for next action.
                 * At this point, the region is not yet connected to any list.
                 *
                 * If the state is RH_NOSYNC, the region should be kept off
                 * from clean list.
                 * The hash entry for RH_NOSYNC will remain in memory
                 * until the region is recovered or the map is reloaded.
                 */

                /* do nothing for RH_NOSYNC */
                if (reg->state == RH_RECOVERING) {
                        list_add_tail(&reg->list, &rh->quiesced_regions);
                } else if (reg->state == RH_DIRTY) {
                        reg->state = RH_CLEAN;
                        list_add(&reg->list, &rh->clean_regions);
                }
                should_wake = 1;
        }
        spin_unlock_irqrestore(&rh->region_lock, flags);

        if (should_wake)
                wake();
}

/*
 * Starts quiescing a region in preparation for recovery.
 */
static int __rh_recovery_prepare(struct region_hash *rh)
{
        int r;
        struct region *reg;
        region_t region;

        /*
         * Ask the dirty log what's next.
         */
        r = rh->log->type->get_resync_work(rh->log, &region);
        if (r <= 0)
                return r;

        /*
         * Get this region, and start it quiescing by setting the
         * recovering flag.
         */
        read_lock(&rh->hash_lock);
        reg = __rh_find(rh, region);
        read_unlock(&rh->hash_lock);

        spin_lock_irq(&rh->region_lock);
        reg->state = RH_RECOVERING;

        /* Already quiesced ? */
        if (atomic_read(&reg->pending))
                list_del_init(&reg->list);

        else {
                list_del_init(&reg->list);
                list_add(&reg->list, &rh->quiesced_regions);
        }
        spin_unlock_irq(&rh->region_lock);

        return 1;
}

static void rh_recovery_prepare(struct region_hash *rh)
{
        while (!down_trylock(&rh->recovery_count))
                if (__rh_recovery_prepare(rh) <= 0) {
                        up(&rh->recovery_count);
                        break;
                }
}

/*
 * Returns any quiesced regions.
 */
static struct region *rh_recovery_start(struct region_hash *rh)
{
        struct region *reg = NULL;

        spin_lock_irq(&rh->region_lock);
        if (!list_empty(&rh->quiesced_regions)) {
                reg = list_entry(rh->quiesced_regions.next,
                                 struct region, list);
                list_del_init(&reg->list);      /* remove from the quiesced list */
        }
        spin_unlock_irq(&rh->region_lock);

        return reg;
}

/* FIXME: success ignored for now */
static void rh_recovery_end(struct region *reg, int success)
{
        struct region_hash *rh = reg->rh;

        spin_lock_irq(&rh->region_lock);
        list_add(&reg->list, &reg->rh->recovered_regions);
        spin_unlock_irq(&rh->region_lock);

        wake();
}

static void rh_flush(struct region_hash *rh)
{
        rh->log->type->flush(rh->log);
}

static void rh_delay(struct region_hash *rh, struct bio *bio)
{
        struct region *reg;

        read_lock(&rh->hash_lock);
        reg = __rh_find(rh, bio_to_region(rh, bio));
        bio_list_add(&reg->delayed_bios, bio);
        read_unlock(&rh->hash_lock);
}

static void rh_stop_recovery(struct region_hash *rh)
{
        int i;

        /* wait for any recovering regions */
        for (i = 0; i < MAX_RECOVERY; i++)
                down(&rh->recovery_count);
}

static void rh_start_recovery(struct region_hash *rh)
{
        int i;

        for (i = 0; i < MAX_RECOVERY; i++)
                up(&rh->recovery_count);

        wake();
}

/*-----------------------------------------------------------------
 * Mirror set structures.
 *---------------------------------------------------------------*/
struct mirror {
        atomic_t error_count;
        struct dm_dev *dev;
        sector_t offset;
};

struct mirror_set {
        struct dm_target *ti;
        struct list_head list;
        struct region_hash rh;
        struct kcopyd_client *kcopyd_client;

        spinlock_t lock;        /* protects the next two lists */
        struct bio_list reads;
        struct bio_list writes;

        /* recovery */
        region_t nr_regions;
        int in_sync;

        struct mirror *default_mirror;  /* Default mirror */

        unsigned int nr_mirrors;
        struct mirror mirror[0];
};

/*
 * Every mirror should look like this one.
 */
#define DEFAULT_MIRROR 0

/*
 * This is yucky.  We squirrel the mirror_set struct away inside
 * bi_next for write buffers.  This is safe since the bh
 * doesn't get submitted to the lower levels of block layer.
 */
static struct mirror_set *bio_get_ms(struct bio *bio)
{
        return (struct mirror_set *) bio->bi_next;
}

static void bio_set_ms(struct bio *bio, struct mirror_set *ms)
{
        bio->bi_next = (struct bio *) ms;
}

/*-----------------------------------------------------------------
 * Recovery.
 *
 * When a mirror is first activated we may find that some regions
 * are in the no-sync state.  We have to recover these by
 * recopying from the default mirror to all the others.
 *---------------------------------------------------------------*/
static void recovery_complete(int read_err, unsigned int write_err,
                              void *context)
{
        struct region *reg = (struct region *) context;

        /* FIXME: better error handling */
        rh_recovery_end(reg, read_err || write_err);
}

static int recover(struct mirror_set *ms, struct region *reg)
{
        int r;
        unsigned int i;
        struct io_region from, to[KCOPYD_MAX_REGIONS], *dest;
        struct mirror *m;
        unsigned long flags = 0;

        /* fill in the source */
        m = ms->default_mirror;
        from.bdev = m->dev->bdev;
        from.sector = m->offset + region_to_sector(reg->rh, reg->key);
        if (reg->key == (ms->nr_regions - 1)) {
                /*
                 * The final region may be smaller than
                 * region_size.
                 */
                from.count = ms->ti->len & (reg->rh->region_size - 1);
                if (!from.count)
                        from.count = reg->rh->region_size;
        } else
                from.count = reg->rh->region_size;

        /* fill in the destinations */
        for (i = 0, dest = to; i < ms->nr_mirrors; i++) {
                if (&ms->mirror[i] == ms->default_mirror)
                        continue;

                m = ms->mirror + i;
                dest->bdev = m->dev->bdev;
                dest->sector = m->offset + region_to_sector(reg->rh, reg->key);
                dest->count = from.count;
                dest++;
        }

        /* hand to kcopyd */
        set_bit(KCOPYD_IGNORE_ERROR, &flags);
        r = kcopyd_copy(ms->kcopyd_client, &from, ms->nr_mirrors - 1, to, flags,
                        recovery_complete, reg);

        return r;
}

static void do_recovery(struct mirror_set *ms)
{
        int r;
        struct region *reg;
        struct dirty_log *log = ms->rh.log;

        /*
         * Start quiescing some regions.
         */
        rh_recovery_prepare(&ms->rh);

        /*
         * Copy any already quiesced regions.
         */
        while ((reg = rh_recovery_start(&ms->rh))) {
                r = recover(ms, reg);
                if (r)
                        rh_recovery_end(reg, 0);
        }

        /*
         * Update the in sync flag.
         */
        if (!ms->in_sync &&
            (log->type->get_sync_count(log) == ms->nr_regions)) {
                /* the sync is complete */
                dm_table_event(ms->ti->table);
                ms->in_sync = 1;
        }
}

/*-----------------------------------------------------------------
 * Reads
 *---------------------------------------------------------------*/
static struct mirror *choose_mirror(struct mirror_set *ms, sector_t sector)
{
        /* FIXME: add read balancing */
        return ms->default_mirror;
}

/*
 * remap a buffer to a particular mirror.
 */
static void map_bio(struct mirror_set *ms, struct mirror *m, struct bio *bio)
{
        bio->bi_bdev = m->dev->bdev;
        bio->bi_sector = m->offset + (bio->bi_sector - ms->ti->begin);
}

static void do_reads(struct mirror_set *ms, struct bio_list *reads)
{
        region_t region;
        struct bio *bio;
        struct mirror *m;

        while ((bio = bio_list_pop(reads))) {
                region = bio_to_region(&ms->rh, bio);

                /*
                 * We can only read balance if the region is in sync.
                 */
                if (rh_in_sync(&ms->rh, region, 0))
                        m = choose_mirror(ms, bio->bi_sector);
                else
                        m = ms->default_mirror;

                map_bio(ms, m, bio);
                generic_make_request(bio);
        }
}

/*-----------------------------------------------------------------
 * Writes.
 *
 * We do different things with the write io depending on the
 * state of the region that it's in:
 *
 * SYNC:        increment pending, use kcopyd to write to *all* mirrors
 * RECOVERING:  delay the io until recovery completes
 * NOSYNC:      increment pending, just write to the default mirror
 *---------------------------------------------------------------*/
static void write_callback(unsigned long error, void *context)
{
        unsigned int i;
        int uptodate = 1;
        struct bio *bio = (struct bio *) context;
        struct mirror_set *ms;

        ms = bio_get_ms(bio);
        bio_set_ms(bio, NULL);

        /*
         * NOTE: We don't decrement the pending count here,
         * instead it is done by the targets endio function.
         * This way we handle both writes to SYNC and NOSYNC
         * regions with the same code.
         */

        if (error) {
                /*
                 * only error the io if all mirrors failed.
                 * FIXME: bogus
                 */
                uptodate = 0;
                for (i = 0; i < ms->nr_mirrors; i++)
                        if (!test_bit(i, &error)) {
                                uptodate = 1;
                                break;
                        }
        }
        bio_endio(bio, bio->bi_size, 0);
}

static void do_write(struct mirror_set *ms, struct bio *bio)
{
        unsigned int i;
        struct io_region io[KCOPYD_MAX_REGIONS+1];
        struct mirror *m;

        for (i = 0; i < ms->nr_mirrors; i++) {
                m = ms->mirror + i;

                io[i].bdev = m->dev->bdev;
                io[i].sector = m->offset + (bio->bi_sector - ms->ti->begin);
                io[i].count = bio->bi_size >> 9;
        }

        bio_set_ms(bio, ms);
        dm_io_async_bvec(ms->nr_mirrors, io, WRITE,
                         bio->bi_io_vec + bio->bi_idx,
                         write_callback, bio);
}

static void do_writes(struct mirror_set *ms, struct bio_list *writes)
{
        int state;
        struct bio *bio;
        struct bio_list sync, nosync, recover, *this_list = NULL;

        if (!writes->head)
                return;

        /*
         * Classify each write.
         */
        bio_list_init(&sync);
        bio_list_init(&nosync);
        bio_list_init(&recover);

        while ((bio = bio_list_pop(writes))) {
                state = rh_state(&ms->rh, bio_to_region(&ms->rh, bio), 1);
                switch (state) {
                case RH_CLEAN:
                case RH_DIRTY:
                        this_list = &sync;
                        break;

                case RH_NOSYNC:
                        this_list = &nosync;
                        break;

                case RH_RECOVERING:
                        this_list = &recover;
                        break;
                }

                bio_list_add(this_list, bio);
        }

        /*
         * Increment the pending counts for any regions that will
         * be written to (writes to recover regions are going to
         * be delayed).
         */
        rh_inc_pending(&ms->rh, &sync);
        rh_inc_pending(&ms->rh, &nosync);
        rh_flush(&ms->rh);

        /*
         * Dispatch io.
         */
        while ((bio = bio_list_pop(&sync)))
                do_write(ms, bio);

        while ((bio = bio_list_pop(&recover)))
                rh_delay(&ms->rh, bio);

        while ((bio = bio_list_pop(&nosync))) {
                map_bio(ms, ms->default_mirror, bio);
                generic_make_request(bio);
        }
}

/*-----------------------------------------------------------------
 * kmirrord
 *---------------------------------------------------------------*/
static LIST_HEAD(_mirror_sets);
static DECLARE_RWSEM(_mirror_sets_lock);

static void do_mirror(struct mirror_set *ms)
{
        struct bio_list reads, writes;

        spin_lock(&ms->lock);
        reads = ms->reads;
        writes = ms->writes;
        bio_list_init(&ms->reads);
        bio_list_init(&ms->writes);
        spin_unlock(&ms->lock);

        rh_update_states(&ms->rh);
        do_recovery(ms);
        do_reads(ms, &reads);
        do_writes(ms, &writes);
}

static void do_work(void *ignored)
{
        struct mirror_set *ms;

        down_read(&_mirror_sets_lock);
        list_for_each_entry (ms, &_mirror_sets, list)
                do_mirror(ms);
        up_read(&_mirror_sets_lock);
}

/*-----------------------------------------------------------------
 * Target functions
 *---------------------------------------------------------------*/
static struct mirror_set *alloc_context(unsigned int nr_mirrors,
                                        uint32_t region_size,
                                        struct dm_target *ti,
                                        struct dirty_log *dl)
{
        size_t len;
        struct mirror_set *ms = NULL;

        if (array_too_big(sizeof(*ms), sizeof(ms->mirror[0]), nr_mirrors))
                return NULL;

        len = sizeof(*ms) + (sizeof(ms->mirror[0]) * nr_mirrors);

        ms = kmalloc(len, GFP_KERNEL);
        if (!ms) {
                ti->error = "dm-mirror: Cannot allocate mirror context";
                return NULL;
        }

        memset(ms, 0, len);
        spin_lock_init(&ms->lock);

        ms->ti = ti;
        ms->nr_mirrors = nr_mirrors;
        ms->nr_regions = dm_sector_div_up(ti->len, region_size);
        ms->in_sync = 0;
        ms->default_mirror = &ms->mirror[DEFAULT_MIRROR];

        if (rh_init(&ms->rh, ms, dl, region_size, ms->nr_regions)) {
                ti->error = "dm-mirror: Error creating dirty region hash";
                kfree(ms);
                return NULL;
        }

        return ms;
}

static void free_context(struct mirror_set *ms, struct dm_target *ti,
                         unsigned int m)
{
        while (m--)
                dm_put_device(ti, ms->mirror[m].dev);

        rh_exit(&ms->rh);
        kfree(ms);
}

static inline int _check_region_size(struct dm_target *ti, uint32_t size)
{
        return !(size % (PAGE_SIZE >> 9) || (size & (size - 1)) ||
                 size > ti->len);
}

static int get_mirror(struct mirror_set *ms, struct dm_target *ti,
                      unsigned int mirror, char **argv)
{
        unsigned long long offset;

        if (sscanf(argv[1], "%llu", &offset) != 1) {
                ti->error = "dm-mirror: Invalid offset";
                return -EINVAL;
        }

        if (dm_get_device(ti, argv[0], offset, ti->len,
                          dm_table_get_mode(ti->table),
                          &ms->mirror[mirror].dev)) {
                ti->error = "dm-mirror: Device lookup failure";
                return -ENXIO;
        }

        ms->mirror[mirror].offset = offset;

        return 0;
}

static int add_mirror_set(struct mirror_set *ms)
{
        down_write(&_mirror_sets_lock);
        list_add_tail(&ms->list, &_mirror_sets);
        up_write(&_mirror_sets_lock);
        wake();

        return 0;
}

static void del_mirror_set(struct mirror_set *ms)
{
        down_write(&_mirror_sets_lock);
        list_del(&ms->list);
        up_write(&_mirror_sets_lock);
}

/*
 * Create dirty log: log_type #log_params <log_params>
 */
static struct dirty_log *create_dirty_log(struct dm_target *ti,
                                          unsigned int argc, char **argv,
                                          unsigned int *args_used)
{
        unsigned int param_count;
        struct dirty_log *dl;

        if (argc < 2) {
                ti->error = "dm-mirror: Insufficient mirror log arguments";
                return NULL;
        }

        if (sscanf(argv[1], "%u", &param_count) != 1) {
                ti->error = "dm-mirror: Invalid mirror log argument count";
                return NULL;
        }

        *args_used = 2 + param_count;

        if (argc < *args_used) {
                ti->error = "dm-mirror: Insufficient mirror log arguments";
                return NULL;
        }

        dl = dm_create_dirty_log(argv[0], ti, param_count, argv + 2);
        if (!dl) {
                ti->error = "dm-mirror: Error creating mirror dirty log";
                return NULL;
        }

        if (!_check_region_size(ti, dl->type->get_region_size(dl))) {
                ti->error = "dm-mirror: Invalid region size";
                dm_destroy_dirty_log(dl);
                return NULL;
        }

        return dl;
}

/*
 * Construct a mirror mapping:
 *
 * log_type #log_params <log_params>
 * #mirrors [mirror_path offset]{2,}
 *
 * log_type is "core" or "disk"
 * #log_params is between 1 and 3
 */
#define DM_IO_PAGES 64
static int mirror_ctr(struct dm_target *ti, unsigned int argc, char **argv)
{
        int r;
        unsigned int nr_mirrors, m, args_used;
        struct mirror_set *ms;
        struct dirty_log *dl;

        dl = create_dirty_log(ti, argc, argv, &args_used);
        if (!dl)
                return -EINVAL;

        argv += args_used;
        argc -= args_used;

        if (!argc || sscanf(argv[0], "%u", &nr_mirrors) != 1 ||
            nr_mirrors < 2 || nr_mirrors > KCOPYD_MAX_REGIONS + 1) {
                ti->error = "dm-mirror: Invalid number of mirrors";
                dm_destroy_dirty_log(dl);
                return -EINVAL;
        }

        argv++, argc--;

        if (argc != nr_mirrors * 2) {
                ti->error = "dm-mirror: Wrong number of mirror arguments";
                dm_destroy_dirty_log(dl);
                return -EINVAL;
        }

        ms = alloc_context(nr_mirrors, dl->type->get_region_size(dl), ti, dl);
        if (!ms) {
                dm_destroy_dirty_log(dl);
                return -ENOMEM;
        }

        /* Get the mirror parameter sets */
        for (m = 0; m < nr_mirrors; m++) {
                r = get_mirror(ms, ti, m, argv);
                if (r) {
                        free_context(ms, ti, m);
                        return r;
                }
                argv += 2;
                argc -= 2;
        }

        ti->private = ms;
        ti->split_io = ms->rh.region_size;

        r = kcopyd_client_create(DM_IO_PAGES, &ms->kcopyd_client);
        if (r) {
                free_context(ms, ti, ms->nr_mirrors);
                return r;
        }

        add_mirror_set(ms);
        return 0;
}

static void mirror_dtr(struct dm_target *ti)
{
        struct mirror_set *ms = (struct mirror_set *) ti->private;

        del_mirror_set(ms);
        kcopyd_client_destroy(ms->kcopyd_client);
        free_context(ms, ti, ms->nr_mirrors);
}

static void queue_bio(struct mirror_set *ms, struct bio *bio, int rw)
{
        int should_wake = 0;
        struct bio_list *bl;

        bl = (rw == WRITE) ? &ms->writes : &ms->reads;
        spin_lock(&ms->lock);
        should_wake = !(bl->head);
        bio_list_add(bl, bio);
        spin_unlock(&ms->lock);

        if (should_wake)
                wake();
}

/*
 * Mirror mapping function
 */
static int mirror_map(struct dm_target *ti, struct bio *bio,
                      union map_info *map_context)
{
        int r, rw = bio_rw(bio);
        struct mirror *m;
        struct mirror_set *ms = ti->private;

        map_context->ll = bio->bi_sector >> ms->rh.region_shift;

        if (rw == WRITE) {
                queue_bio(ms, bio, rw);
                return 0;
        }

        r = ms->rh.log->type->in_sync(ms->rh.log,
                                      bio_to_region(&ms->rh, bio), 0);
        if (r < 0 && r != -EWOULDBLOCK)
                return r;

        if (r == -EWOULDBLOCK)  /* FIXME: ugly */
                r = 0;

        /*
         * We don't want to fast track a recovery just for a read
         * ahead.  So we just let it silently fail.
         * FIXME: get rid of this.
         */
        if (!r && rw == READA)
                return -EIO;

        if (!r) {
                /* Pass this io over to the daemon */
                queue_bio(ms, bio, rw);
                return 0;
        }

        m = choose_mirror(ms, bio->bi_sector);
        if (!m)
                return -EIO;

        map_bio(ms, m, bio);
        return 1;
}

static int mirror_end_io(struct dm_target *ti, struct bio *bio,
                         int error, union map_info *map_context)
{
        int rw = bio_rw(bio);
        struct mirror_set *ms = (struct mirror_set *) ti->private;
        region_t region = map_context->ll;

        /*
         * We need to dec pending if this was a write.
         */
        if (rw == WRITE)
                rh_dec(&ms->rh, region);

        return 0;
}

static void mirror_postsuspend(struct dm_target *ti)
{
        struct mirror_set *ms = (struct mirror_set *) ti->private;
        struct dirty_log *log = ms->rh.log;

        rh_stop_recovery(&ms->rh);
        if (log->type->suspend && log->type->suspend(log))
                /* FIXME: need better error handling */
                DMWARN("log suspend failed");
}

static void mirror_resume(struct dm_target *ti)
{
        struct mirror_set *ms = (struct mirror_set *) ti->private;
        struct dirty_log *log = ms->rh.log;
        if (log->type->resume && log->type->resume(log))
                /* FIXME: need better error handling */
                DMWARN("log resume failed");
        rh_start_recovery(&ms->rh);
}

static int mirror_status(struct dm_target *ti, status_type_t type,
                         char *result, unsigned int maxlen)
{
        unsigned int m, sz;
        struct mirror_set *ms = (struct mirror_set *) ti->private;

        sz = ms->rh.log->type->status(ms->rh.log, type, result, maxlen);

        switch (type) {
        case STATUSTYPE_INFO:
                DMEMIT("%d ", ms->nr_mirrors);
                for (m = 0; m < ms->nr_mirrors; m++)
                        DMEMIT("%s ", ms->mirror[m].dev->name);

                DMEMIT("%llu/%llu",
                        (unsigned long long)ms->rh.log->type->
                                get_sync_count(ms->rh.log),
                        (unsigned long long)ms->nr_regions);
                break;

        case STATUSTYPE_TABLE:
                DMEMIT("%d ", ms->nr_mirrors);
                for (m = 0; m < ms->nr_mirrors; m++)
                        DMEMIT("%s %llu ", ms->mirror[m].dev->name,
                                (unsigned long long)ms->mirror[m].offset);
        }

        return 0;
}

static struct target_type mirror_target = {
        .name    = "mirror",
        .version = {1, 0, 1},
        .module  = THIS_MODULE,
        .ctr     = mirror_ctr,
        .dtr     = mirror_dtr,
        .map     = mirror_map,
        .end_io  = mirror_end_io,
        .postsuspend = mirror_postsuspend,
        .resume  = mirror_resume,
        .status  = mirror_status,
};

static int __init dm_mirror_init(void)
{
        int r;

        r = dm_dirty_log_init();
        if (r)
                return r;

        _kmirrord_wq = create_singlethread_workqueue("kmirrord");
        if (!_kmirrord_wq) {
                DMERR("couldn't start kmirrord");
                dm_dirty_log_exit();
                return r;
        }
        INIT_WORK(&_kmirrord_work, do_work, NULL);

        r = dm_register_target(&mirror_target);
        if (r < 0) {
                DMERR("%s: Failed to register mirror target",
                      mirror_target.name);
                dm_dirty_log_exit();
                destroy_workqueue(_kmirrord_wq);
        }

        return r;
}

static void __exit dm_mirror_exit(void)
{
        int r;

        r = dm_unregister_target(&mirror_target);
        if (r < 0)
                DMERR("%s: unregister failed %d", mirror_target.name, r);

        destroy_workqueue(_kmirrord_wq);
        dm_dirty_log_exit();
}

/* Module hooks */
module_init(dm_mirror_init);
module_exit(dm_mirror_exit);

MODULE_DESCRIPTION(DM_NAME " mirror target");
MODULE_AUTHOR("Joe Thornber");
MODULE_LICENSE("GPL");