dm-raid1.c

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/*
 * Copyright (C) 2003 Sistina Software Limited.
 * Copyright (C) 2005-2008 Red Hat, Inc. All rights reserved.
 *
 * This file is released under the GPL.
 */

#include "dm-bio-record.h"

#include <linux/init.h>
#include <linux/mempool.h>
#include <linux/module.h>
#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/workqueue.h>
#include <linux/device-mapper.h>
#include <linux/dm-io.h>
#include <linux/dm-dirty-log.h>
#include <linux/dm-kcopyd.h>
#include <linux/dm-region-hash.h>

#define DM_MSG_PREFIX "raid1"

#define MAX_RECOVERY 1  /* Maximum number of regions recovered in parallel. */

#define DM_RAID1_HANDLE_ERRORS 0x01
#define errors_handled(p)   ((p)->features & DM_RAID1_HANDLE_ERRORS)

static DECLARE_WAIT_QUEUE_HEAD(_kmirrord_recovery_stopped);

/*-----------------------------------------------------------------
 * Mirror set structures.
 *---------------------------------------------------------------*/
enum dm_raid1_error {
    DM_RAID1_WRITE_ERROR,
    DM_RAID1_FLUSH_ERROR,
    DM_RAID1_SYNC_ERROR,
    DM_RAID1_READ_ERROR
};

struct mirror {
    struct mirror_set *ms;
    atomic_t error_count;
    unsigned long error_type;
    struct dm_dev *dev;
    sector_t offset;
};

struct mirror_set {
    struct dm_target *ti;
    struct list_head list;

    uint64_t features;

    spinlock_t lock;    /* protects the lists */
    struct bio_list reads;
    struct bio_list writes;
    struct bio_list failures;
    struct bio_list holds;  /* bios are waiting until suspend */

    struct dm_region_hash *rh;
    struct dm_kcopyd_client *kcopyd_client;
    struct dm_io_client *io_client;
    mempool_t *read_record_pool;

    /* recovery */
    region_t nr_regions;
    int in_sync;
    int log_failure;
    int leg_failure;
    atomic_t suspend;

    atomic_t default_mirror;    /* Default mirror */

    struct workqueue_struct *kmirrord_wq;
    struct work_struct kmirrord_work;
    struct timer_list timer;
    unsigned long timer_pending;

    struct work_struct trigger_event;

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

static void wakeup_mirrord(void *context)
{
    struct mirror_set *ms = context;

    queue_work(ms->kmirrord_wq, &ms->kmirrord_work);
}

static void delayed_wake_fn(unsigned long data)
{
    struct mirror_set *ms = (struct mirror_set *) data;

    clear_bit(0, &ms->timer_pending);
    wakeup_mirrord(ms);
}

static void delayed_wake(struct mirror_set *ms)
{
    if (test_and_set_bit(0, &ms->timer_pending))
        return;

    ms->timer.expires = jiffies + HZ / 5;
    ms->timer.data = (unsigned long) ms;
    ms->timer.function = delayed_wake_fn;
    add_timer(&ms->timer);
}

static void wakeup_all_recovery_waiters(void *context)
{
    wake_up_all(&_kmirrord_recovery_stopped);
}

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

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

    if (should_wake)
        wakeup_mirrord(ms);
}

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

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

#define MIN_READ_RECORDS 20
struct dm_raid1_read_record {
    struct mirror *m;
    struct dm_bio_details details;
};

static struct kmem_cache *_dm_raid1_read_record_cache;

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

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

static void bio_set_m(struct bio *bio, struct mirror *m)
{
    bio->bi_next = (struct bio *) m;
}

static struct mirror *get_default_mirror(struct mirror_set *ms)
{
    return &ms->mirror[atomic_read(&ms->default_mirror)];
}

static void set_default_mirror(struct mirror *m)
{
    struct mirror_set *ms = m->ms;
    struct mirror *m0 = &(ms->mirror[0]);

    atomic_set(&ms->default_mirror, m - m0);
}

static struct mirror *get_valid_mirror(struct mirror_set *ms)
{
    struct mirror *m;

    for (m = ms->mirror; m < ms->mirror + ms->nr_mirrors; m++)
        if (!atomic_read(&m->error_count))
            return m;

    return NULL;
}

/* fail_mirror
 * @m: mirror device to fail
 * @error_type: one of the enum's, DM_RAID1_*_ERROR
 *
 * If errors are being handled, record the type of
 * error encountered for this device.  If this type
 * of error has already been recorded, we can return;
 * otherwise, we must signal userspace by triggering
 * an event.  Additionally, if the device is the
 * primary device, we must choose a new primary, but
 * only if the mirror is in-sync.
 *
 * This function must not block.
 */
static void fail_mirror(struct mirror *m, enum dm_raid1_error error_type)
{
    struct mirror_set *ms = m->ms;
    struct mirror *new;

    ms->leg_failure = 1;

    /*
     * error_count is used for nothing more than a
     * simple way to tell if a device has encountered
     * errors.
     */
    atomic_inc(&m->error_count);

    if (test_and_set_bit(error_type, &m->error_type))
        return;

    if (!errors_handled(ms))
        return;

    if (m != get_default_mirror(ms))
        goto out;

    if (!ms->in_sync) {
        /*
         * Better to issue requests to same failing device
         * than to risk returning corrupt data.
         */
        DMERR("Primary mirror (%s) failed while out-of-sync: "
              "Reads may fail.", m->dev->name);
        goto out;
    }

    new = get_valid_mirror(ms);
    if (new)
        set_default_mirror(new);
    else
        DMWARN("All sides of mirror have failed.");

out:
    schedule_work(&ms->trigger_event);
}

static int mirror_flush(struct dm_target *ti)
{
    struct mirror_set *ms = ti->private;
    unsigned long error_bits;

    unsigned int i;
    struct dm_io_region io[ms->nr_mirrors];
    struct mirror *m;
    struct dm_io_request io_req = {
        .bi_rw = WRITE_FLUSH,
        .mem.type = DM_IO_KMEM,
        .mem.ptr.addr = NULL,
        .client = ms->io_client,
    };

    for (i = 0, m = ms->mirror; i < ms->nr_mirrors; i++, m++) {
        io[i].bdev = m->dev->bdev;
        io[i].sector = 0;
        io[i].count = 0;
    }

    error_bits = -1;
    dm_io(&io_req, ms->nr_mirrors, io, &error_bits);
    if (unlikely(error_bits != 0)) {
        for (i = 0; i < ms->nr_mirrors; i++)
            if (test_bit(i, &error_bits))
                fail_mirror(ms->mirror + i,
                        DM_RAID1_FLUSH_ERROR);
        return -EIO;
    }

    return 0;
}

/*-----------------------------------------------------------------
 * 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 long write_err,
                  void *context)
{
    struct dm_region *reg = context;
    struct mirror_set *ms = dm_rh_region_context(reg);
    int m, bit = 0;

    if (read_err) {
        /* Read error means the failure of default mirror. */
        DMERR_LIMIT("Unable to read primary mirror during recovery");
        fail_mirror(get_default_mirror(ms), DM_RAID1_SYNC_ERROR);
    }

    if (write_err) {
        DMERR_LIMIT("Write error during recovery (error = 0x%lx)",
                write_err);
        /*
         * Bits correspond to devices (excluding default mirror).
         * The default mirror cannot change during recovery.
         */
        for (m = 0; m < ms->nr_mirrors; m++) {
            if (&ms->mirror[m] == get_default_mirror(ms))
                continue;
            if (test_bit(bit, &write_err))
                fail_mirror(ms->mirror + m,
                        DM_RAID1_SYNC_ERROR);
            bit++;
        }
    }

    dm_rh_recovery_end(reg, !(read_err || write_err));
}

static int recover(struct mirror_set *ms, struct dm_region *reg)
{
    int r;
    unsigned i;
    struct dm_io_region from, to[DM_KCOPYD_MAX_REGIONS], *dest;
    struct mirror *m;
    unsigned long flags = 0;
    region_t key = dm_rh_get_region_key(reg);
    sector_t region_size = dm_rh_get_region_size(ms->rh);

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

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

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

    /* hand to kcopyd */
    if (!errors_handled(ms))
        set_bit(DM_KCOPYD_IGNORE_ERROR, &flags);

    r = dm_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)
{
    struct dm_region *reg;
    struct dm_dirty_log *log = dm_rh_dirty_log(ms->rh);
    int r;

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

    /*
     * Copy any already quiesced regions.
     */
    while ((reg = dm_rh_recovery_start(ms->rh))) {
        r = recover(ms, reg);
        if (r)
            dm_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)
{
    struct mirror *m = get_default_mirror(ms);

    do {
        if (likely(!atomic_read(&m->error_count)))
            return m;

        if (m-- == ms->mirror)
            m += ms->nr_mirrors;
    } while (m != get_default_mirror(ms));

    return NULL;
}

static int default_ok(struct mirror *m)
{
    struct mirror *default_mirror = get_default_mirror(m->ms);

    return !atomic_read(&default_mirror->error_count);
}

static int mirror_available(struct mirror_set *ms, struct bio *bio)
{
    struct dm_dirty_log *log = dm_rh_dirty_log(ms->rh);
    region_t region = dm_rh_bio_to_region(ms->rh, bio);

    if (log->type->in_sync(log, region, 0))
        return choose_mirror(ms,  bio->bi_sector) ? 1 : 0;

    return 0;
}

/*
 * remap a buffer to a particular mirror.
 */
static sector_t map_sector(struct mirror *m, struct bio *bio)
{
    if (unlikely(!bio->bi_size))
        return 0;
    return m->offset + dm_target_offset(m->ms->ti, bio->bi_sector);
}

static void map_bio(struct mirror *m, struct bio *bio)
{
    bio->bi_bdev = m->dev->bdev;
    bio->bi_sector = map_sector(m, bio);
}

static void map_region(struct dm_io_region *io, struct mirror *m,
               struct bio *bio)
{
    io->bdev = m->dev->bdev;
    io->sector = map_sector(m, bio);
    io->count = bio->bi_size >> 9;
}

static void hold_bio(struct mirror_set *ms, struct bio *bio)
{
    /*
     * Lock is required to avoid race condition during suspend
     * process.
     */
    spin_lock_irq(&ms->lock);

    if (atomic_read(&ms->suspend)) {
        spin_unlock_irq(&ms->lock);

        /*
         * If device is suspended, complete the bio.
         */
        if (dm_noflush_suspending(ms->ti))
            bio_endio(bio, DM_ENDIO_REQUEUE);
        else
            bio_endio(bio, -EIO);
        return;
    }

    /*
     * Hold bio until the suspend is complete.
     */
    bio_list_add(&ms->holds, bio);
    spin_unlock_irq(&ms->lock);
}

/*-----------------------------------------------------------------
 * Reads
 *---------------------------------------------------------------*/
static void read_callback(unsigned long error, void *context)
{
    struct bio *bio = context;
    struct mirror *m;

    m = bio_get_m(bio);
    bio_set_m(bio, NULL);

    if (likely(!error)) {
        bio_endio(bio, 0);
        return;
    }

    fail_mirror(m, DM_RAID1_READ_ERROR);

    if (likely(default_ok(m)) || mirror_available(m->ms, bio)) {
        DMWARN_LIMIT("Read failure on mirror device %s.  "
                 "Trying alternative device.",
                 m->dev->name);
        queue_bio(m->ms, bio, bio_rw(bio));
        return;
    }

    DMERR_LIMIT("Read failure on mirror device %s.  Failing I/O.",
            m->dev->name);
    bio_endio(bio, -EIO);
}

/* Asynchronous read. */
static void read_async_bio(struct mirror *m, struct bio *bio)
{
    struct dm_io_region io;
    struct dm_io_request io_req = {
        .bi_rw = READ,
        .mem.type = DM_IO_BVEC,
        .mem.ptr.bvec = bio->bi_io_vec + bio->bi_idx,
        .notify.fn = read_callback,
        .notify.context = bio,
        .client = m->ms->io_client,
    };

    map_region(&io, m, bio);
    bio_set_m(bio, m);
    BUG_ON(dm_io(&io_req, 1, &io, NULL));
}

static inline int region_in_sync(struct mirror_set *ms, region_t region,
                 int may_block)
{
    int state = dm_rh_get_state(ms->rh, region, may_block);
    return state == DM_RH_CLEAN || state == DM_RH_DIRTY;
}

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 = dm_rh_bio_to_region(ms->rh, bio);
        m = get_default_mirror(ms);

        /*
         * We can only read balance if the region is in sync.
         */
        if (likely(region_in_sync(ms, region, 1)))
            m = choose_mirror(ms, bio->bi_sector);
        else if (m && atomic_read(&m->error_count))
            m = NULL;

        if (likely(m))
            read_async_bio(m, bio);
        else
            bio_endio(bio, -EIO);
    }
}

/*-----------------------------------------------------------------
 * 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 i, ret = 0;
    struct bio *bio = (struct bio *) context;
    struct mirror_set *ms;
    int should_wake = 0;
    unsigned long flags;

    ms = bio_get_m(bio)->ms;
    bio_set_m(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 (likely(!error)) {
        bio_endio(bio, ret);
        return;
    }

    for (i = 0; i < ms->nr_mirrors; i++)
        if (test_bit(i, &error))
            fail_mirror(ms->mirror + i, DM_RAID1_WRITE_ERROR);

    /*
     * Need to raise event.  Since raising
     * events can block, we need to do it in
     * the main thread.
     */
    spin_lock_irqsave(&ms->lock, flags);
    if (!ms->failures.head)
        should_wake = 1;
    bio_list_add(&ms->failures, bio);
    spin_unlock_irqrestore(&ms->lock, flags);
    if (should_wake)
        wakeup_mirrord(ms);
}

static void do_write(struct mirror_set *ms, struct bio *bio)
{
    unsigned int i;
    struct dm_io_region io[ms->nr_mirrors], *dest = io;
    struct mirror *m;
    struct dm_io_request io_req = {
        .bi_rw = WRITE | (bio->bi_rw & WRITE_FLUSH_FUA),
        .mem.type = DM_IO_BVEC,
        .mem.ptr.bvec = bio->bi_io_vec + bio->bi_idx,
        .notify.fn = write_callback,
        .notify.context = bio,
        .client = ms->io_client,
    };

    if (bio->bi_rw & REQ_DISCARD) {
        io_req.bi_rw |= REQ_DISCARD;
        io_req.mem.type = DM_IO_KMEM;
        io_req.mem.ptr.addr = NULL;
    }

    for (i = 0, m = ms->mirror; i < ms->nr_mirrors; i++, m++)
        map_region(dest++, m, bio);

    /*
     * Use default mirror because we only need it to retrieve the reference
     * to the mirror set in write_callback().
     */
    bio_set_m(bio, get_default_mirror(ms));

    BUG_ON(dm_io(&io_req, ms->nr_mirrors, io, NULL));
}

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;
    struct bio_list requeue;
    struct dm_dirty_log *log = dm_rh_dirty_log(ms->rh);
    region_t region;

    if (!writes->head)
        return;

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

    while ((bio = bio_list_pop(writes))) {
        if ((bio->bi_rw & REQ_FLUSH) ||
            (bio->bi_rw & REQ_DISCARD)) {
            bio_list_add(&sync, bio);
            continue;
        }

        region = dm_rh_bio_to_region(ms->rh, bio);

        if (log->type->is_remote_recovering &&
            log->type->is_remote_recovering(log, region)) {
            bio_list_add(&requeue, bio);
            continue;
        }

        state = dm_rh_get_state(ms->rh, region, 1);
        switch (state) {
        case DM_RH_CLEAN:
        case DM_RH_DIRTY:
            this_list = &sync;
            break;

        case DM_RH_NOSYNC:
            this_list = &nosync;
            break;

        case DM_RH_RECOVERING:
            this_list = &recover;
            break;
        }

        bio_list_add(this_list, bio);
    }

    /*
     * Add bios that are delayed due to remote recovery
     * back on to the write queue
     */
    if (unlikely(requeue.head)) {
        spin_lock_irq(&ms->lock);
        bio_list_merge(&ms->writes, &requeue);
        spin_unlock_irq(&ms->lock);
        delayed_wake(ms);
    }

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

    /*
     * If the flush fails on a previous call and succeeds here,
     * we must not reset the log_failure variable.  We need
     * userspace interaction to do that.
     */
    ms->log_failure = dm_rh_flush(ms->rh) ? 1 : ms->log_failure;

    /*
     * Dispatch io.
     */
    if (unlikely(ms->log_failure) && errors_handled(ms)) {
        spin_lock_irq(&ms->lock);
        bio_list_merge(&ms->failures, &sync);
        spin_unlock_irq(&ms->lock);
        wakeup_mirrord(ms);
    } else
        while ((bio = bio_list_pop(&sync)))
            do_write(ms, bio);

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

    while ((bio = bio_list_pop(&nosync))) {
        if (unlikely(ms->leg_failure) && errors_handled(ms)) {
            spin_lock_irq(&ms->lock);
            bio_list_add(&ms->failures, bio);
            spin_unlock_irq(&ms->lock);
            wakeup_mirrord(ms);
        } else {
            map_bio(get_default_mirror(ms), bio);
            generic_make_request(bio);
        }
    }
}

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

    if (likely(!failures->head))
        return;

    /*
     * If the log has failed, unattempted writes are being
     * put on the holds list.  We can't issue those writes
     * until a log has been marked, so we must store them.
     *
     * If a 'noflush' suspend is in progress, we can requeue
     * the I/O's to the core.  This give userspace a chance
     * to reconfigure the mirror, at which point the core
     * will reissue the writes.  If the 'noflush' flag is
     * not set, we have no choice but to return errors.
     *
     * Some writes on the failures list may have been
     * submitted before the log failure and represent a
     * failure to write to one of the devices.  It is ok
     * for us to treat them the same and requeue them
     * as well.
     */
    while ((bio = bio_list_pop(failures))) {
        if (!ms->log_failure) {
            ms->in_sync = 0;
            dm_rh_mark_nosync(ms->rh, bio);
        }

        /*
         * If all the legs are dead, fail the I/O.
         * If we have been told to handle errors, hold the bio
         * and wait for userspace to deal with the problem.
         * Otherwise pretend that the I/O succeeded. (This would
         * be wrong if the failed leg returned after reboot and
         * got replicated back to the good legs.)
         */
        if (!get_valid_mirror(ms))
            bio_endio(bio, -EIO);
        else if (errors_handled(ms))
            hold_bio(ms, bio);
        else
            bio_endio(bio, 0);
    }
}

static void trigger_event(struct work_struct *work)
{
    struct mirror_set *ms =
        container_of(work, struct mirror_set, trigger_event);

    dm_table_event(ms->ti->table);
}

/*-----------------------------------------------------------------
 * kmirrord
 *---------------------------------------------------------------*/
static void do_mirror(struct work_struct *work)
{
    struct mirror_set *ms = container_of(work, struct mirror_set,
                         kmirrord_work);
    struct bio_list reads, writes, failures;
    unsigned long flags;

    spin_lock_irqsave(&ms->lock, flags);
    reads = ms->reads;
    writes = ms->writes;
    failures = ms->failures;
    bio_list_init(&ms->reads);
    bio_list_init(&ms->writes);
    bio_list_init(&ms->failures);
    spin_unlock_irqrestore(&ms->lock, flags);

    dm_rh_update_states(ms->rh, errors_handled(ms));
    do_recovery(ms);
    do_reads(ms, &reads);
    do_writes(ms, &writes);
    do_failures(ms, &failures);
}

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

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

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

    spin_lock_init(&ms->lock);
    bio_list_init(&ms->reads);
    bio_list_init(&ms->writes);
    bio_list_init(&ms->failures);
    bio_list_init(&ms->holds);

    ms->ti = ti;
    ms->nr_mirrors = nr_mirrors;
    ms->nr_regions = dm_sector_div_up(ti->len, region_size);
    ms->in_sync = 0;
    ms->log_failure = 0;
    ms->leg_failure = 0;
    atomic_set(&ms->suspend, 0);
    atomic_set(&ms->default_mirror, DEFAULT_MIRROR);

    ms->read_record_pool = mempool_create_slab_pool(MIN_READ_RECORDS,
                        _dm_raid1_read_record_cache);

    if (!ms->read_record_pool) {
        ti->error = "Error creating mirror read_record_pool";
        kfree(ms);
        return NULL;
    }

    ms->io_client = dm_io_client_create();
    if (IS_ERR(ms->io_client)) {
        ti->error = "Error creating dm_io client";
        mempool_destroy(ms->read_record_pool);
        kfree(ms);
        return NULL;
    }

    ms->rh = dm_region_hash_create(ms, dispatch_bios, wakeup_mirrord,
                       wakeup_all_recovery_waiters,
                       ms->ti->begin, MAX_RECOVERY,
                       dl, region_size, ms->nr_regions);
    if (IS_ERR(ms->rh)) {
        ti->error = "Error creating dirty region hash";
        dm_io_client_destroy(ms->io_client);
        mempool_destroy(ms->read_record_pool);
        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);

    dm_io_client_destroy(ms->io_client);
    dm_region_hash_destroy(ms->rh);
    mempool_destroy(ms->read_record_pool);
    kfree(ms);
}

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

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

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

    ms->mirror[mirror].ms = ms;
    atomic_set(&(ms->mirror[mirror].error_count), 0);
    ms->mirror[mirror].error_type = 0;
    ms->mirror[mirror].offset = offset;

    return 0;
}

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

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

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

    *args_used = 2 + param_count;

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

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

    return dl;
}

static int parse_features(struct mirror_set *ms, unsigned argc, char **argv,
              unsigned *args_used)
{
    unsigned num_features;
    struct dm_target *ti = ms->ti;
    char dummy;

    *args_used = 0;

    if (!argc)
        return 0;

    if (sscanf(argv[0], "%u%c", &num_features, &dummy) != 1) {
        ti->error = "Invalid number of features";
        return -EINVAL;
    }

    argc--;
    argv++;
    (*args_used)++;

    if (num_features > argc) {
        ti->error = "Not enough arguments to support feature count";
        return -EINVAL;
    }

    if (!strcmp("handle_errors", argv[0]))
        ms->features |= DM_RAID1_HANDLE_ERRORS;
    else {
        ti->error = "Unrecognised feature requested";
        return -EINVAL;
    }

    (*args_used)++;

    return 0;
}

/*
 * Construct a mirror mapping:
 *
 * log_type #log_params <log_params>
 * #mirrors [mirror_path offset]{2,}
 * [#features <features>]
 *
 * log_type is "core" or "disk"
 * #log_params is between 1 and 3
 *
 * If present, features must be "handle_errors".
 */
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 dm_dirty_log *dl;
    char dummy;

    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%c", &nr_mirrors, &dummy) != 1 ||
        nr_mirrors < 2 || nr_mirrors > DM_KCOPYD_MAX_REGIONS + 1) {
        ti->error = "Invalid number of mirrors";
        dm_dirty_log_destroy(dl);
        return -EINVAL;
    }

    argv++, argc--;

    if (argc < nr_mirrors * 2) {
        ti->error = "Too few mirror arguments";
        dm_dirty_log_destroy(dl);
        return -EINVAL;
    }

    ms = alloc_context(nr_mirrors, dl->type->get_region_size(dl), ti, dl);
    if (!ms) {
        dm_dirty_log_destroy(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;

    r = dm_set_target_max_io_len(ti, dm_rh_get_region_size(ms->rh));
    if (r)
        goto err_free_context;

    ti->num_flush_requests = 1;
    ti->num_discard_requests = 1;
    ti->discard_zeroes_data_unsupported = true;

    ms->kmirrord_wq = alloc_workqueue("kmirrord",
                      WQ_NON_REENTRANT | WQ_MEM_RECLAIM, 0);
    if (!ms->kmirrord_wq) {
        DMERR("couldn't start kmirrord");
        r = -ENOMEM;
        goto err_free_context;
    }
    INIT_WORK(&ms->kmirrord_work, do_mirror);
    init_timer(&ms->timer);
    ms->timer_pending = 0;
    INIT_WORK(&ms->trigger_event, trigger_event);

    r = parse_features(ms, argc, argv, &args_used);
    if (r)
        goto err_destroy_wq;

    argv += args_used;
    argc -= args_used;

    /*
     * Any read-balancing addition depends on the
     * DM_RAID1_HANDLE_ERRORS flag being present.
     * This is because the decision to balance depends
     * on the sync state of a region.  If the above
     * flag is not present, we ignore errors; and
     * the sync state may be inaccurate.
     */

    if (argc) {
        ti->error = "Too many mirror arguments";
        r = -EINVAL;
        goto err_destroy_wq;
    }

    ms->kcopyd_client = dm_kcopyd_client_create();
    if (IS_ERR(ms->kcopyd_client)) {
        r = PTR_ERR(ms->kcopyd_client);
        goto err_destroy_wq;
    }

    wakeup_mirrord(ms);
    return 0;

err_destroy_wq:
    destroy_workqueue(ms->kmirrord_wq);
err_free_context:
    free_context(ms, ti, ms->nr_mirrors);
    return r;
}

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

    del_timer_sync(&ms->timer);
    flush_workqueue(ms->kmirrord_wq);
    flush_work(&ms->trigger_event);
    dm_kcopyd_client_destroy(ms->kcopyd_client);
    destroy_workqueue(ms->kmirrord_wq);
    free_context(ms, ti, ms->nr_mirrors);
}

/*
 * 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;
    struct dm_raid1_read_record *read_record = NULL;
    struct dm_dirty_log *log = dm_rh_dirty_log(ms->rh);

    if (rw == WRITE) {
        /* Save region for mirror_end_io() handler */
        map_context->ll = dm_rh_bio_to_region(ms->rh, bio);
        queue_bio(ms, bio, rw);
        return DM_MAPIO_SUBMITTED;
    }

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

    /*
     * If region is not in-sync queue the bio.
     */
    if (!r || (r == -EWOULDBLOCK)) {
        if (rw == READA)
            return -EWOULDBLOCK;

        queue_bio(ms, bio, rw);
        return DM_MAPIO_SUBMITTED;
    }

    /*
     * The region is in-sync and we can perform reads directly.
     * Store enough information so we can retry if it fails.
     */
    m = choose_mirror(ms, bio->bi_sector);
    if (unlikely(!m))
        return -EIO;

    read_record = mempool_alloc(ms->read_record_pool, GFP_NOIO);
    if (likely(read_record)) {
        dm_bio_record(&read_record->details, bio);
        map_context->ptr = read_record;
        read_record->m = m;
    }

    map_bio(m, bio);

    return DM_MAPIO_REMAPPED;
}

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;
    struct mirror *m = NULL;
    struct dm_bio_details *bd = NULL;
    struct dm_raid1_read_record *read_record = map_context->ptr;

    /*
     * We need to dec pending if this was a write.
     */
    if (rw == WRITE) {
        if (!(bio->bi_rw & (REQ_FLUSH | REQ_DISCARD)))
            dm_rh_dec(ms->rh, map_context->ll);
        return error;
    }

    if (error == -EOPNOTSUPP)
        goto out;

    if ((error == -EWOULDBLOCK) && (bio->bi_rw & REQ_RAHEAD))
        goto out;

    if (unlikely(error)) {
        if (!read_record) {
            /*
             * There wasn't enough memory to record necessary
             * information for a retry or there was no other
             * mirror in-sync.
             */
            DMERR_LIMIT("Mirror read failed.");
            return -EIO;
        }

        m = read_record->m;

        DMERR("Mirror read failed from %s. Trying alternative device.",
              m->dev->name);

        fail_mirror(m, DM_RAID1_READ_ERROR);

        /*
         * A failed read is requeued for another attempt using an intact
         * mirror.
         */
        if (default_ok(m) || mirror_available(ms, bio)) {
            bd = &read_record->details;

            dm_bio_restore(bd, bio);
            mempool_free(read_record, ms->read_record_pool);
            map_context->ptr = NULL;
            queue_bio(ms, bio, rw);
            return 1;
        }
        DMERR("All replicated volumes dead, failing I/O");
    }

out:
    if (read_record) {
        mempool_free(read_record, ms->read_record_pool);
        map_context->ptr = NULL;
    }

    return error;
}

static void mirror_presuspend(struct dm_target *ti)
{
    struct mirror_set *ms = (struct mirror_set *) ti->private;
    struct dm_dirty_log *log = dm_rh_dirty_log(ms->rh);

    struct bio_list holds;
    struct bio *bio;

    atomic_set(&ms->suspend, 1);

    /*
     * Process bios in the hold list to start recovery waiting
     * for bios in the hold list. After the process, no bio has
     * a chance to be added in the hold list because ms->suspend
     * is set.
     */
    spin_lock_irq(&ms->lock);
    holds = ms->holds;
    bio_list_init(&ms->holds);
    spin_unlock_irq(&ms->lock);

    while ((bio = bio_list_pop(&holds)))
        hold_bio(ms, bio);

    /*
     * We must finish up all the work that we've
     * generated (i.e. recovery work).
     */
    dm_rh_stop_recovery(ms->rh);

    wait_event(_kmirrord_recovery_stopped,
           !dm_rh_recovery_in_flight(ms->rh));

    if (log->type->presuspend && log->type->presuspend(log))
        /* FIXME: need better error handling */
        DMWARN("log presuspend failed");

    /*
     * Now that recovery is complete/stopped and the
     * delayed bios are queued, we need to wait for
     * the worker thread to complete.  This way,
     * we know that all of our I/O has been pushed.
     */
    flush_workqueue(ms->kmirrord_wq);
}

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

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

static void mirror_resume(struct dm_target *ti)
{
    struct mirror_set *ms = ti->private;
    struct dm_dirty_log *log = dm_rh_dirty_log(ms->rh);

    atomic_set(&ms->suspend, 0);
    if (log->type->resume && log->type->resume(log))
        /* FIXME: need better error handling */
        DMWARN("log resume failed");
    dm_rh_start_recovery(ms->rh);
}

/*
 * device_status_char
 * @m: mirror device/leg we want the status of
 *
 * We return one character representing the most severe error
 * we have encountered.
 *    A => Alive - No failures
 *    D => Dead - A write failure occurred leaving mirror out-of-sync
 *    S => Sync - A sychronization failure occurred, mirror out-of-sync
 *    R => Read - A read failure occurred, mirror data unaffected
 *
 * Returns: <char>
 */
static char device_status_char(struct mirror *m)
{
    if (!atomic_read(&(m->error_count)))
        return 'A';

    return (test_bit(DM_RAID1_FLUSH_ERROR, &(m->error_type))) ? 'F' :
        (test_bit(DM_RAID1_WRITE_ERROR, &(m->error_type))) ? 'D' :
        (test_bit(DM_RAID1_SYNC_ERROR, &(m->error_type))) ? 'S' :
        (test_bit(DM_RAID1_READ_ERROR, &(m->error_type))) ? 'R' : 'U';
}


static int mirror_status(struct dm_target *ti, status_type_t type,
             unsigned status_flags, char *result, unsigned maxlen)
{
    unsigned int m, sz = 0;
    struct mirror_set *ms = (struct mirror_set *) ti->private;
    struct dm_dirty_log *log = dm_rh_dirty_log(ms->rh);
    char buffer[ms->nr_mirrors + 1];

    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);
            buffer[m] = device_status_char(&(ms->mirror[m]));
        }
        buffer[m] = '\0';

        DMEMIT("%llu/%llu 1 %s ",
              (unsigned long long)log->type->get_sync_count(log),
              (unsigned long long)ms->nr_regions, buffer);

        sz += log->type->status(log, type, result+sz, maxlen-sz);

        break;

    case STATUSTYPE_TABLE:
        sz = log->type->status(log, type, result, maxlen);

        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);

        if (ms->features & DM_RAID1_HANDLE_ERRORS)
            DMEMIT(" 1 handle_errors");
    }

    return 0;
}

static int mirror_iterate_devices(struct dm_target *ti,
                  iterate_devices_callout_fn fn, void *data)
{
    struct mirror_set *ms = ti->private;
    int ret = 0;
    unsigned i;

    for (i = 0; !ret && i < ms->nr_mirrors; i++)
        ret = fn(ti, ms->mirror[i].dev,
             ms->mirror[i].offset, ti->len, data);

    return ret;
}

static struct target_type mirror_target = {
    .name    = "mirror",
    .version = {1, 12, 1},
    .module  = THIS_MODULE,
    .ctr     = mirror_ctr,
    .dtr     = mirror_dtr,
    .map     = mirror_map,
    .end_io  = mirror_end_io,
    .presuspend = mirror_presuspend,
    .postsuspend = mirror_postsuspend,
    .resume  = mirror_resume,
    .status  = mirror_status,
    .iterate_devices = mirror_iterate_devices,
};

static int __init dm_mirror_init(void)
{
    int r;

    _dm_raid1_read_record_cache = KMEM_CACHE(dm_raid1_read_record, 0);
    if (!_dm_raid1_read_record_cache) {
        DMERR("Can't allocate dm_raid1_read_record cache");
        r = -ENOMEM;
        goto bad_cache;
    }

    r = dm_register_target(&mirror_target);
    if (r < 0) {
        DMERR("Failed to register mirror target");
        goto bad_target;
    }

    return 0;

bad_target:
    kmem_cache_destroy(_dm_raid1_read_record_cache);
bad_cache:
    return r;
}

static void __exit dm_mirror_exit(void)
{
    dm_unregister_target(&mirror_target);
    kmem_cache_destroy(_dm_raid1_read_record_cache);
}

/* 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");