[safe/jmp/linux-2.6] / drivers / md / dm-raid1.c

/*
 * 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_IO_PAGES 64
#define DM_KCOPYD_PAGES 64

#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_BARRIER,
                .mem.type = DM_IO_KMEM,
                .mem.ptr.bvec = 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 + (bio->bi_sector - m->ms->ti->begin);
}

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)
{
        /*
         * If device is suspended, complete the bio.
         */
        if (atomic_read(&ms->suspend)) {
                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.
         */
        spin_lock_irq(&ms->lock);
        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_BARRIER),
                .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,
        };

        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 (unlikely(bio_empty_barrier(bio))) {
                        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);

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

/*-----------------------------------------------------------------
 * 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(DM_IO_PAGES);
        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;

        if (sscanf(argv[1], "%llu", &offset) != 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;

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

        if (sscanf(argv[1], "%u", &param_count) != 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;

        *args_used = 0;

        if (!argc)
                return 0;

        if (sscanf(argv[0], "%u", &num_features) != 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;

        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 > 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;
        ti->split_io = dm_rh_get_region_size(ms->rh);
        ti->num_flush_requests = 1;

        ms->kmirrord_wq = create_singlethread_workqueue("kmirrord");
        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;
        }

        r = dm_kcopyd_client_create(DM_KCOPYD_PAGES, &ms->kcopyd_client);
        if (r)
                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_scheduled_work();
        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 (likely(!bio_empty_barrier(bio)))
                        dm_rh_dec(ms->rh, map_context->ll);
                return error;
        }

        if (error == -EOPNOTSUPP)
                goto out;

        if ((error == -EWOULDBLOCK) && bio_rw_flagged(bio, BIO_RW_AHEAD))
                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);

        /*
         * 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);

        /*
         * Now set ms->suspend is set and the workqueue flushed, no more
         * entries can be added to ms->hold list, so process it.
         *
         * Bios can still arrive concurrently with or after this
         * presuspend function, but they cannot join 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);
}

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,
                         char *result, unsigned int 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, 0},
        .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");