dm-mpath.c

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/*
 * Copyright (C) 2003 Sistina Software Limited.
 * Copyright (C) 2004-2005 Red Hat, Inc. All rights reserved.
 *
 * This file is released under the GPL.
 */

#include <linux/device-mapper.h>

#include "dm-path-selector.h"
#include "dm-uevent.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/workqueue.h>
#include <linux/delay.h>
#include <scsi/scsi_dh.h>
#include <linux/atomic.h>

#define DM_MSG_PREFIX "multipath"
#define DM_PG_INIT_DELAY_MSECS 2000
#define DM_PG_INIT_DELAY_DEFAULT ((unsigned) -1)

/* Path properties */
struct pgpath {
    struct list_head list;

    struct priority_group *pg;  /* Owning PG */
    unsigned is_active;     /* Path status */
    unsigned fail_count;        /* Cumulative failure count */

    struct dm_path path;
    struct delayed_work activate_path;
};

#define path_to_pgpath(__pgp) container_of((__pgp), struct pgpath, path)

/*
 * Paths are grouped into Priority Groups and numbered from 1 upwards.
 * Each has a path selector which controls which path gets used.
 */
struct priority_group {
    struct list_head list;

    struct multipath *m;        /* Owning multipath instance */
    struct path_selector ps;

    unsigned pg_num;        /* Reference number */
    unsigned bypassed;      /* Temporarily bypass this PG? */

    unsigned nr_pgpaths;        /* Number of paths in PG */
    struct list_head pgpaths;
};

/* Multipath context */
struct multipath {
    struct list_head list;
    struct dm_target *ti;

    const char *hw_handler_name;
    char *hw_handler_params;

    spinlock_t lock;

    unsigned nr_priority_groups;
    struct list_head priority_groups;

    wait_queue_head_t pg_init_wait; /* Wait for pg_init completion */

    unsigned pg_init_required;  /* pg_init needs calling? */
    unsigned pg_init_in_progress;   /* Only one pg_init allowed at once */
    unsigned pg_init_delay_retry;   /* Delay pg_init retry? */

    unsigned nr_valid_paths;    /* Total number of usable paths */
    struct pgpath *current_pgpath;
    struct priority_group *current_pg;
    struct priority_group *next_pg; /* Switch to this PG if set */
    unsigned repeat_count;      /* I/Os left before calling PS again */

    unsigned queue_io:1;        /* Must we queue all I/O? */
    unsigned queue_if_no_path:1;    /* Queue I/O if last path fails? */
    unsigned saved_queue_if_no_path:1; /* Saved state during suspension */
    unsigned retain_attached_hw_handler:1; /* If there's already a hw_handler present, don't change it. */

    unsigned pg_init_retries;   /* Number of times to retry pg_init */
    unsigned pg_init_count;     /* Number of times pg_init called */
    unsigned pg_init_delay_msecs;   /* Number of msecs before pg_init retry */

    unsigned queue_size;
    struct work_struct process_queued_ios;
    struct list_head queued_ios;

    struct work_struct trigger_event;

    /*
     * We must use a mempool of dm_mpath_io structs so that we
     * can resubmit bios on error.
     */
    mempool_t *mpio_pool;

    struct mutex work_mutex;
};

/*
 * Context information attached to each bio we process.
 */
struct dm_mpath_io {
    struct pgpath *pgpath;
    size_t nr_bytes;
};

typedef int (*action_fn) (struct pgpath *pgpath);

#define MIN_IOS 256 /* Mempool size */

static struct kmem_cache *_mpio_cache;

static struct workqueue_struct *kmultipathd, *kmpath_handlerd;
static void process_queued_ios(struct work_struct *work);
static void trigger_event(struct work_struct *work);
static void activate_path(struct work_struct *work);


/*-----------------------------------------------
 * Allocation routines
 *-----------------------------------------------*/

static struct pgpath *alloc_pgpath(void)
{
    struct pgpath *pgpath = kzalloc(sizeof(*pgpath), GFP_KERNEL);

    if (pgpath) {
        pgpath->is_active = 1;
        INIT_DELAYED_WORK(&pgpath->activate_path, activate_path);
    }

    return pgpath;
}

static void free_pgpath(struct pgpath *pgpath)
{
    kfree(pgpath);
}

static struct priority_group *alloc_priority_group(void)
{
    struct priority_group *pg;

    pg = kzalloc(sizeof(*pg), GFP_KERNEL);

    if (pg)
        INIT_LIST_HEAD(&pg->pgpaths);

    return pg;
}

static void free_pgpaths(struct list_head *pgpaths, struct dm_target *ti)
{
    struct pgpath *pgpath, *tmp;
    struct multipath *m = ti->private;

    list_for_each_entry_safe(pgpath, tmp, pgpaths, list) {
        list_del(&pgpath->list);
        if (m->hw_handler_name)
            scsi_dh_detach(bdev_get_queue(pgpath->path.dev->bdev));
        dm_put_device(ti, pgpath->path.dev);
        free_pgpath(pgpath);
    }
}

static void free_priority_group(struct priority_group *pg,
                struct dm_target *ti)
{
    struct path_selector *ps = &pg->ps;

    if (ps->type) {
        ps->type->destroy(ps);
        dm_put_path_selector(ps->type);
    }

    free_pgpaths(&pg->pgpaths, ti);
    kfree(pg);
}

static struct multipath *alloc_multipath(struct dm_target *ti)
{
    struct multipath *m;

    m = kzalloc(sizeof(*m), GFP_KERNEL);
    if (m) {
        INIT_LIST_HEAD(&m->priority_groups);
        INIT_LIST_HEAD(&m->queued_ios);
        spin_lock_init(&m->lock);
        m->queue_io = 1;
        m->pg_init_delay_msecs = DM_PG_INIT_DELAY_DEFAULT;
        INIT_WORK(&m->process_queued_ios, process_queued_ios);
        INIT_WORK(&m->trigger_event, trigger_event);
        init_waitqueue_head(&m->pg_init_wait);
        mutex_init(&m->work_mutex);
        m->mpio_pool = mempool_create_slab_pool(MIN_IOS, _mpio_cache);
        if (!m->mpio_pool) {
            kfree(m);
            return NULL;
        }
        m->ti = ti;
        ti->private = m;
    }

    return m;
}

static void free_multipath(struct multipath *m)
{
    struct priority_group *pg, *tmp;

    list_for_each_entry_safe(pg, tmp, &m->priority_groups, list) {
        list_del(&pg->list);
        free_priority_group(pg, m->ti);
    }

    kfree(m->hw_handler_name);
    kfree(m->hw_handler_params);
    mempool_destroy(m->mpio_pool);
    kfree(m);
}

static int set_mapinfo(struct multipath *m, union map_info *info)
{
    struct dm_mpath_io *mpio;

    mpio = mempool_alloc(m->mpio_pool, GFP_ATOMIC);
    if (!mpio)
        return -ENOMEM;

    memset(mpio, 0, sizeof(*mpio));
    info->ptr = mpio;

    return 0;
}

static void clear_mapinfo(struct multipath *m, union map_info *info)
{
    struct dm_mpath_io *mpio = info->ptr;

    info->ptr = NULL;
    mempool_free(mpio, m->mpio_pool);
}

/*-----------------------------------------------
 * Path selection
 *-----------------------------------------------*/

static void __pg_init_all_paths(struct multipath *m)
{
    struct pgpath *pgpath;
    unsigned long pg_init_delay = 0;

    m->pg_init_count++;
    m->pg_init_required = 0;
    if (m->pg_init_delay_retry)
        pg_init_delay = msecs_to_jiffies(m->pg_init_delay_msecs != DM_PG_INIT_DELAY_DEFAULT ?
                         m->pg_init_delay_msecs : DM_PG_INIT_DELAY_MSECS);
    list_for_each_entry(pgpath, &m->current_pg->pgpaths, list) {
        /* Skip failed paths */
        if (!pgpath->is_active)
            continue;
        if (queue_delayed_work(kmpath_handlerd, &pgpath->activate_path,
                       pg_init_delay))
            m->pg_init_in_progress++;
    }
}

static void __switch_pg(struct multipath *m, struct pgpath *pgpath)
{
    m->current_pg = pgpath->pg;

    /* Must we initialise the PG first, and queue I/O till it's ready? */
    if (m->hw_handler_name) {
        m->pg_init_required = 1;
        m->queue_io = 1;
    } else {
        m->pg_init_required = 0;
        m->queue_io = 0;
    }

    m->pg_init_count = 0;
}

static int __choose_path_in_pg(struct multipath *m, struct priority_group *pg,
                   size_t nr_bytes)
{
    struct dm_path *path;

    path = pg->ps.type->select_path(&pg->ps, &m->repeat_count, nr_bytes);
    if (!path)
        return -ENXIO;

    m->current_pgpath = path_to_pgpath(path);

    if (m->current_pg != pg)
        __switch_pg(m, m->current_pgpath);

    return 0;
}

static void __choose_pgpath(struct multipath *m, size_t nr_bytes)
{
    struct priority_group *pg;
    unsigned bypassed = 1;

    if (!m->nr_valid_paths)
        goto failed;

    /* Were we instructed to switch PG? */
    if (m->next_pg) {
        pg = m->next_pg;
        m->next_pg = NULL;
        if (!__choose_path_in_pg(m, pg, nr_bytes))
            return;
    }

    /* Don't change PG until it has no remaining paths */
    if (m->current_pg && !__choose_path_in_pg(m, m->current_pg, nr_bytes))
        return;

    /*
     * Loop through priority groups until we find a valid path.
     * First time we skip PGs marked 'bypassed'.
     * Second time we only try the ones we skipped, but set
     * pg_init_delay_retry so we do not hammer controllers.
     */
    do {
        list_for_each_entry(pg, &m->priority_groups, list) {
            if (pg->bypassed == bypassed)
                continue;
            if (!__choose_path_in_pg(m, pg, nr_bytes)) {
                if (!bypassed)
                    m->pg_init_delay_retry = 1;
                return;
            }
        }
    } while (bypassed--);

failed:
    m->current_pgpath = NULL;
    m->current_pg = NULL;
}

/*
 * Check whether bios must be queued in the device-mapper core rather
 * than here in the target.
 *
 * m->lock must be held on entry.
 *
 * If m->queue_if_no_path and m->saved_queue_if_no_path hold the
 * same value then we are not between multipath_presuspend()
 * and multipath_resume() calls and we have no need to check
 * for the DMF_NOFLUSH_SUSPENDING flag.
 */
static int __must_push_back(struct multipath *m)
{
    return (m->queue_if_no_path != m->saved_queue_if_no_path &&
        dm_noflush_suspending(m->ti));
}

static int map_io(struct multipath *m, struct request *clone,
          union map_info *map_context, unsigned was_queued)
{
    int r = DM_MAPIO_REMAPPED;
    size_t nr_bytes = blk_rq_bytes(clone);
    unsigned long flags;
    struct pgpath *pgpath;
    struct block_device *bdev;
    struct dm_mpath_io *mpio = map_context->ptr;

    spin_lock_irqsave(&m->lock, flags);

    /* Do we need to select a new pgpath? */
    if (!m->current_pgpath ||
        (!m->queue_io && (m->repeat_count && --m->repeat_count == 0)))
        __choose_pgpath(m, nr_bytes);

    pgpath = m->current_pgpath;

    if (was_queued)
        m->queue_size--;

    if ((pgpath && m->queue_io) ||
        (!pgpath && m->queue_if_no_path)) {
        /* Queue for the daemon to resubmit */
        list_add_tail(&clone->queuelist, &m->queued_ios);
        m->queue_size++;
        if ((m->pg_init_required && !m->pg_init_in_progress) ||
            !m->queue_io)
            queue_work(kmultipathd, &m->process_queued_ios);
        pgpath = NULL;
        r = DM_MAPIO_SUBMITTED;
    } else if (pgpath) {
        bdev = pgpath->path.dev->bdev;
        clone->q = bdev_get_queue(bdev);
        clone->rq_disk = bdev->bd_disk;
    } else if (__must_push_back(m))
        r = DM_MAPIO_REQUEUE;
    else
        r = -EIO;   /* Failed */

    mpio->pgpath = pgpath;
    mpio->nr_bytes = nr_bytes;

    if (r == DM_MAPIO_REMAPPED && pgpath->pg->ps.type->start_io)
        pgpath->pg->ps.type->start_io(&pgpath->pg->ps, &pgpath->path,
                          nr_bytes);

    spin_unlock_irqrestore(&m->lock, flags);

    return r;
}

/*
 * If we run out of usable paths, should we queue I/O or error it?
 */
static int queue_if_no_path(struct multipath *m, unsigned queue_if_no_path,
                unsigned save_old_value)
{
    unsigned long flags;

    spin_lock_irqsave(&m->lock, flags);

    if (save_old_value)
        m->saved_queue_if_no_path = m->queue_if_no_path;
    else
        m->saved_queue_if_no_path = queue_if_no_path;
    m->queue_if_no_path = queue_if_no_path;
    if (!m->queue_if_no_path && m->queue_size)
        queue_work(kmultipathd, &m->process_queued_ios);

    spin_unlock_irqrestore(&m->lock, flags);

    return 0;
}

/*-----------------------------------------------------------------
 * The multipath daemon is responsible for resubmitting queued ios.
 *---------------------------------------------------------------*/

static void dispatch_queued_ios(struct multipath *m)
{
    int r;
    unsigned long flags;
    union map_info *info;
    struct request *clone, *n;
    LIST_HEAD(cl);

    spin_lock_irqsave(&m->lock, flags);
    list_splice_init(&m->queued_ios, &cl);
    spin_unlock_irqrestore(&m->lock, flags);

    list_for_each_entry_safe(clone, n, &cl, queuelist) {
        list_del_init(&clone->queuelist);

        info = dm_get_rq_mapinfo(clone);

        r = map_io(m, clone, info, 1);
        if (r < 0) {
            clear_mapinfo(m, info);
            dm_kill_unmapped_request(clone, r);
        } else if (r == DM_MAPIO_REMAPPED)
            dm_dispatch_request(clone);
        else if (r == DM_MAPIO_REQUEUE) {
            clear_mapinfo(m, info);
            dm_requeue_unmapped_request(clone);
        }
    }
}

static void process_queued_ios(struct work_struct *work)
{
    struct multipath *m =
        container_of(work, struct multipath, process_queued_ios);
    struct pgpath *pgpath = NULL;
    unsigned must_queue = 1;
    unsigned long flags;

    spin_lock_irqsave(&m->lock, flags);

    if (!m->current_pgpath)
        __choose_pgpath(m, 0);

    pgpath = m->current_pgpath;

    if ((pgpath && !m->queue_io) ||
        (!pgpath && !m->queue_if_no_path))
        must_queue = 0;

    if (m->pg_init_required && !m->pg_init_in_progress && pgpath)
        __pg_init_all_paths(m);

    spin_unlock_irqrestore(&m->lock, flags);
    if (!must_queue)
        dispatch_queued_ios(m);
}

/*
 * An event is triggered whenever a path is taken out of use.
 * Includes path failure and PG bypass.
 */
static void trigger_event(struct work_struct *work)
{
    struct multipath *m =
        container_of(work, struct multipath, trigger_event);

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

/*-----------------------------------------------------------------
 * Constructor/argument parsing:
 * <#multipath feature args> [<arg>]*
 * <#hw_handler args> [hw_handler [<arg>]*]
 * <#priority groups>
 * <initial priority group>
 *     [<selector> <#selector args> [<arg>]*
 *      <#paths> <#per-path selector args>
 *         [<path> [<arg>]* ]+ ]+
 *---------------------------------------------------------------*/
static int parse_path_selector(struct dm_arg_set *as, struct priority_group *pg,
                   struct dm_target *ti)
{
    int r;
    struct path_selector_type *pst;
    unsigned ps_argc;

    static struct dm_arg _args[] = {
        {0, 1024, "invalid number of path selector args"},
    };

    pst = dm_get_path_selector(dm_shift_arg(as));
    if (!pst) {
        ti->error = "unknown path selector type";
        return -EINVAL;
    }

    r = dm_read_arg_group(_args, as, &ps_argc, &ti->error);
    if (r) {
        dm_put_path_selector(pst);
        return -EINVAL;
    }

    r = pst->create(&pg->ps, ps_argc, as->argv);
    if (r) {
        dm_put_path_selector(pst);
        ti->error = "path selector constructor failed";
        return r;
    }

    pg->ps.type = pst;
    dm_consume_args(as, ps_argc);

    return 0;
}

static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps,
                   struct dm_target *ti)
{
    int r;
    struct pgpath *p;
    struct multipath *m = ti->private;
    struct request_queue *q = NULL;
    const char *attached_handler_name;

    /* we need at least a path arg */
    if (as->argc < 1) {
        ti->error = "no device given";
        return ERR_PTR(-EINVAL);
    }

    p = alloc_pgpath();
    if (!p)
        return ERR_PTR(-ENOMEM);

    r = dm_get_device(ti, dm_shift_arg(as), dm_table_get_mode(ti->table),
              &p->path.dev);
    if (r) {
        ti->error = "error getting device";
        goto bad;
    }

    if (m->retain_attached_hw_handler || m->hw_handler_name)
        q = bdev_get_queue(p->path.dev->bdev);

    if (m->retain_attached_hw_handler) {
        attached_handler_name = scsi_dh_attached_handler_name(q, GFP_KERNEL);
        if (attached_handler_name) {
            /*
             * Reset hw_handler_name to match the attached handler
             * and clear any hw_handler_params associated with the
             * ignored handler.
             *
             * NB. This modifies the table line to show the actual
             * handler instead of the original table passed in.
             */
            kfree(m->hw_handler_name);
            m->hw_handler_name = attached_handler_name;

            kfree(m->hw_handler_params);
            m->hw_handler_params = NULL;
        }
    }

    if (m->hw_handler_name) {
        /*
         * Increments scsi_dh reference, even when using an
         * already-attached handler.
         */
        r = scsi_dh_attach(q, m->hw_handler_name);
        if (r == -EBUSY) {
            /*
             * Already attached to different hw_handler:
             * try to reattach with correct one.
             */
            scsi_dh_detach(q);
            r = scsi_dh_attach(q, m->hw_handler_name);
        }

        if (r < 0) {
            ti->error = "error attaching hardware handler";
            dm_put_device(ti, p->path.dev);
            goto bad;
        }

        if (m->hw_handler_params) {
            r = scsi_dh_set_params(q, m->hw_handler_params);
            if (r < 0) {
                ti->error = "unable to set hardware "
                            "handler parameters";
                scsi_dh_detach(q);
                dm_put_device(ti, p->path.dev);
                goto bad;
            }
        }
    }

    r = ps->type->add_path(ps, &p->path, as->argc, as->argv, &ti->error);
    if (r) {
        dm_put_device(ti, p->path.dev);
        goto bad;
    }

    return p;

 bad:
    free_pgpath(p);
    return ERR_PTR(r);
}

static struct priority_group *parse_priority_group(struct dm_arg_set *as,
                           struct multipath *m)
{
    static struct dm_arg _args[] = {
        {1, 1024, "invalid number of paths"},
        {0, 1024, "invalid number of selector args"}
    };

    int r;
    unsigned i, nr_selector_args, nr_args;
    struct priority_group *pg;
    struct dm_target *ti = m->ti;

    if (as->argc < 2) {
        as->argc = 0;
        ti->error = "not enough priority group arguments";
        return ERR_PTR(-EINVAL);
    }

    pg = alloc_priority_group();
    if (!pg) {
        ti->error = "couldn't allocate priority group";
        return ERR_PTR(-ENOMEM);
    }
    pg->m = m;

    r = parse_path_selector(as, pg, ti);
    if (r)
        goto bad;

    /*
     * read the paths
     */
    r = dm_read_arg(_args, as, &pg->nr_pgpaths, &ti->error);
    if (r)
        goto bad;

    r = dm_read_arg(_args + 1, as, &nr_selector_args, &ti->error);
    if (r)
        goto bad;

    nr_args = 1 + nr_selector_args;
    for (i = 0; i < pg->nr_pgpaths; i++) {
        struct pgpath *pgpath;
        struct dm_arg_set path_args;

        if (as->argc < nr_args) {
            ti->error = "not enough path parameters";
            r = -EINVAL;
            goto bad;
        }

        path_args.argc = nr_args;
        path_args.argv = as->argv;

        pgpath = parse_path(&path_args, &pg->ps, ti);
        if (IS_ERR(pgpath)) {
            r = PTR_ERR(pgpath);
            goto bad;
        }

        pgpath->pg = pg;
        list_add_tail(&pgpath->list, &pg->pgpaths);
        dm_consume_args(as, nr_args);
    }

    return pg;

 bad:
    free_priority_group(pg, ti);
    return ERR_PTR(r);
}

static int parse_hw_handler(struct dm_arg_set *as, struct multipath *m)
{
    unsigned hw_argc;
    int ret;
    struct dm_target *ti = m->ti;

    static struct dm_arg _args[] = {
        {0, 1024, "invalid number of hardware handler args"},
    };

    if (dm_read_arg_group(_args, as, &hw_argc, &ti->error))
        return -EINVAL;

    if (!hw_argc)
        return 0;

    m->hw_handler_name = kstrdup(dm_shift_arg(as), GFP_KERNEL);
    if (!try_then_request_module(scsi_dh_handler_exist(m->hw_handler_name),
                     "scsi_dh_%s", m->hw_handler_name)) {
        ti->error = "unknown hardware handler type";
        ret = -EINVAL;
        goto fail;
    }

    if (hw_argc > 1) {
        char *p;
        int i, j, len = 4;

        for (i = 0; i <= hw_argc - 2; i++)
            len += strlen(as->argv[i]) + 1;
        p = m->hw_handler_params = kzalloc(len, GFP_KERNEL);
        if (!p) {
            ti->error = "memory allocation failed";
            ret = -ENOMEM;
            goto fail;
        }
        j = sprintf(p, "%d", hw_argc - 1);
        for (i = 0, p+=j+1; i <= hw_argc - 2; i++, p+=j+1)
            j = sprintf(p, "%s", as->argv[i]);
    }
    dm_consume_args(as, hw_argc - 1);

    return 0;
fail:
    kfree(m->hw_handler_name);
    m->hw_handler_name = NULL;
    return ret;
}

static int parse_features(struct dm_arg_set *as, struct multipath *m)
{
    int r;
    unsigned argc;
    struct dm_target *ti = m->ti;
    const char *arg_name;

    static struct dm_arg _args[] = {
        {0, 6, "invalid number of feature args"},
        {1, 50, "pg_init_retries must be between 1 and 50"},
        {0, 60000, "pg_init_delay_msecs must be between 0 and 60000"},
    };

    r = dm_read_arg_group(_args, as, &argc, &ti->error);
    if (r)
        return -EINVAL;

    if (!argc)
        return 0;

    do {
        arg_name = dm_shift_arg(as);
        argc--;

        if (!strcasecmp(arg_name, "queue_if_no_path")) {
            r = queue_if_no_path(m, 1, 0);
            continue;
        }

        if (!strcasecmp(arg_name, "retain_attached_hw_handler")) {
            m->retain_attached_hw_handler = 1;
            continue;
        }

        if (!strcasecmp(arg_name, "pg_init_retries") &&
            (argc >= 1)) {
            r = dm_read_arg(_args + 1, as, &m->pg_init_retries, &ti->error);
            argc--;
            continue;
        }

        if (!strcasecmp(arg_name, "pg_init_delay_msecs") &&
            (argc >= 1)) {
            r = dm_read_arg(_args + 2, as, &m->pg_init_delay_msecs, &ti->error);
            argc--;
            continue;
        }

        ti->error = "Unrecognised multipath feature request";
        r = -EINVAL;
    } while (argc && !r);

    return r;
}

static int multipath_ctr(struct dm_target *ti, unsigned int argc,
             char **argv)
{
    /* target arguments */
    static struct dm_arg _args[] = {
        {0, 1024, "invalid number of priority groups"},
        {0, 1024, "invalid initial priority group number"},
    };

    int r;
    struct multipath *m;
    struct dm_arg_set as;
    unsigned pg_count = 0;
    unsigned next_pg_num;

    as.argc = argc;
    as.argv = argv;

    m = alloc_multipath(ti);
    if (!m) {
        ti->error = "can't allocate multipath";
        return -EINVAL;
    }

    r = parse_features(&as, m);
    if (r)
        goto bad;

    r = parse_hw_handler(&as, m);
    if (r)
        goto bad;

    r = dm_read_arg(_args, &as, &m->nr_priority_groups, &ti->error);
    if (r)
        goto bad;

    r = dm_read_arg(_args + 1, &as, &next_pg_num, &ti->error);
    if (r)
        goto bad;

    if ((!m->nr_priority_groups && next_pg_num) ||
        (m->nr_priority_groups && !next_pg_num)) {
        ti->error = "invalid initial priority group";
        r = -EINVAL;
        goto bad;
    }

    /* parse the priority groups */
    while (as.argc) {
        struct priority_group *pg;

        pg = parse_priority_group(&as, m);
        if (IS_ERR(pg)) {
            r = PTR_ERR(pg);
            goto bad;
        }

        m->nr_valid_paths += pg->nr_pgpaths;
        list_add_tail(&pg->list, &m->priority_groups);
        pg_count++;
        pg->pg_num = pg_count;
        if (!--next_pg_num)
            m->next_pg = pg;
    }

    if (pg_count != m->nr_priority_groups) {
        ti->error = "priority group count mismatch";
        r = -EINVAL;
        goto bad;
    }

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

    return 0;

 bad:
    free_multipath(m);
    return r;
}

static void multipath_wait_for_pg_init_completion(struct multipath *m)
{
    DECLARE_WAITQUEUE(wait, current);
    unsigned long flags;

    add_wait_queue(&m->pg_init_wait, &wait);

    while (1) {
        set_current_state(TASK_UNINTERRUPTIBLE);

        spin_lock_irqsave(&m->lock, flags);
        if (!m->pg_init_in_progress) {
            spin_unlock_irqrestore(&m->lock, flags);
            break;
        }
        spin_unlock_irqrestore(&m->lock, flags);

        io_schedule();
    }
    set_current_state(TASK_RUNNING);

    remove_wait_queue(&m->pg_init_wait, &wait);
}

static void flush_multipath_work(struct multipath *m)
{
    flush_workqueue(kmpath_handlerd);
    multipath_wait_for_pg_init_completion(m);
    flush_workqueue(kmultipathd);
    flush_work(&m->trigger_event);
}

static void multipath_dtr(struct dm_target *ti)
{
    struct multipath *m = ti->private;

    flush_multipath_work(m);
    free_multipath(m);
}

/*
 * Map cloned requests
 */
static int multipath_map(struct dm_target *ti, struct request *clone,
             union map_info *map_context)
{
    int r;
    struct multipath *m = (struct multipath *) ti->private;

    if (set_mapinfo(m, map_context) < 0)
        /* ENOMEM, requeue */
        return DM_MAPIO_REQUEUE;

    clone->cmd_flags |= REQ_FAILFAST_TRANSPORT;
    r = map_io(m, clone, map_context, 0);
    if (r < 0 || r == DM_MAPIO_REQUEUE)
        clear_mapinfo(m, map_context);

    return r;
}

/*
 * Take a path out of use.
 */
static int fail_path(struct pgpath *pgpath)
{
    unsigned long flags;
    struct multipath *m = pgpath->pg->m;

    spin_lock_irqsave(&m->lock, flags);

    if (!pgpath->is_active)
        goto out;

    DMWARN("Failing path %s.", pgpath->path.dev->name);

    pgpath->pg->ps.type->fail_path(&pgpath->pg->ps, &pgpath->path);
    pgpath->is_active = 0;
    pgpath->fail_count++;

    m->nr_valid_paths--;

    if (pgpath == m->current_pgpath)
        m->current_pgpath = NULL;

    dm_path_uevent(DM_UEVENT_PATH_FAILED, m->ti,
              pgpath->path.dev->name, m->nr_valid_paths);

    schedule_work(&m->trigger_event);

out:
    spin_unlock_irqrestore(&m->lock, flags);

    return 0;
}

/*
 * Reinstate a previously-failed path
 */
static int reinstate_path(struct pgpath *pgpath)
{
    int r = 0;
    unsigned long flags;
    struct multipath *m = pgpath->pg->m;

    spin_lock_irqsave(&m->lock, flags);

    if (pgpath->is_active)
        goto out;

    if (!pgpath->pg->ps.type->reinstate_path) {
        DMWARN("Reinstate path not supported by path selector %s",
               pgpath->pg->ps.type->name);
        r = -EINVAL;
        goto out;
    }

    r = pgpath->pg->ps.type->reinstate_path(&pgpath->pg->ps, &pgpath->path);
    if (r)
        goto out;

    pgpath->is_active = 1;

    if (!m->nr_valid_paths++ && m->queue_size) {
        m->current_pgpath = NULL;
        queue_work(kmultipathd, &m->process_queued_ios);
    } else if (m->hw_handler_name && (m->current_pg == pgpath->pg)) {
        if (queue_work(kmpath_handlerd, &pgpath->activate_path.work))
            m->pg_init_in_progress++;
    }

    dm_path_uevent(DM_UEVENT_PATH_REINSTATED, m->ti,
              pgpath->path.dev->name, m->nr_valid_paths);

    schedule_work(&m->trigger_event);

out:
    spin_unlock_irqrestore(&m->lock, flags);

    return r;
}

/*
 * Fail or reinstate all paths that match the provided struct dm_dev.
 */
static int action_dev(struct multipath *m, struct dm_dev *dev,
              action_fn action)
{
    int r = -EINVAL;
    struct pgpath *pgpath;
    struct priority_group *pg;

    list_for_each_entry(pg, &m->priority_groups, list) {
        list_for_each_entry(pgpath, &pg->pgpaths, list) {
            if (pgpath->path.dev == dev)
                r = action(pgpath);
        }
    }

    return r;
}

/*
 * Temporarily try to avoid having to use the specified PG
 */
static void bypass_pg(struct multipath *m, struct priority_group *pg,
              int bypassed)
{
    unsigned long flags;

    spin_lock_irqsave(&m->lock, flags);

    pg->bypassed = bypassed;
    m->current_pgpath = NULL;
    m->current_pg = NULL;

    spin_unlock_irqrestore(&m->lock, flags);

    schedule_work(&m->trigger_event);
}

/*
 * Switch to using the specified PG from the next I/O that gets mapped
 */
static int switch_pg_num(struct multipath *m, const char *pgstr)
{
    struct priority_group *pg;
    unsigned pgnum;
    unsigned long flags;
    char dummy;

    if (!pgstr || (sscanf(pgstr, "%u%c", &pgnum, &dummy) != 1) || !pgnum ||
        (pgnum > m->nr_priority_groups)) {
        DMWARN("invalid PG number supplied to switch_pg_num");
        return -EINVAL;
    }

    spin_lock_irqsave(&m->lock, flags);
    list_for_each_entry(pg, &m->priority_groups, list) {
        pg->bypassed = 0;
        if (--pgnum)
            continue;

        m->current_pgpath = NULL;
        m->current_pg = NULL;
        m->next_pg = pg;
    }
    spin_unlock_irqrestore(&m->lock, flags);

    schedule_work(&m->trigger_event);
    return 0;
}

/*
 * Set/clear bypassed status of a PG.
 * PGs are numbered upwards from 1 in the order they were declared.
 */
static int bypass_pg_num(struct multipath *m, const char *pgstr, int bypassed)
{
    struct priority_group *pg;
    unsigned pgnum;
    char dummy;

    if (!pgstr || (sscanf(pgstr, "%u%c", &pgnum, &dummy) != 1) || !pgnum ||
        (pgnum > m->nr_priority_groups)) {
        DMWARN("invalid PG number supplied to bypass_pg");
        return -EINVAL;
    }

    list_for_each_entry(pg, &m->priority_groups, list) {
        if (!--pgnum)
            break;
    }

    bypass_pg(m, pg, bypassed);
    return 0;
}

/*
 * Should we retry pg_init immediately?
 */
static int pg_init_limit_reached(struct multipath *m, struct pgpath *pgpath)
{
    unsigned long flags;
    int limit_reached = 0;

    spin_lock_irqsave(&m->lock, flags);

    if (m->pg_init_count <= m->pg_init_retries)
        m->pg_init_required = 1;
    else
        limit_reached = 1;

    spin_unlock_irqrestore(&m->lock, flags);

    return limit_reached;
}

static void pg_init_done(void *data, int errors)
{
    struct pgpath *pgpath = data;
    struct priority_group *pg = pgpath->pg;
    struct multipath *m = pg->m;
    unsigned long flags;
    unsigned delay_retry = 0;

    /* device or driver problems */
    switch (errors) {
    case SCSI_DH_OK:
        break;
    case SCSI_DH_NOSYS:
        if (!m->hw_handler_name) {
            errors = 0;
            break;
        }
        DMERR("Could not failover the device: Handler scsi_dh_%s "
              "Error %d.", m->hw_handler_name, errors);
        /*
         * Fail path for now, so we do not ping pong
         */
        fail_path(pgpath);
        break;
    case SCSI_DH_DEV_TEMP_BUSY:
        /*
         * Probably doing something like FW upgrade on the
         * controller so try the other pg.
         */
        bypass_pg(m, pg, 1);
        break;
    case SCSI_DH_RETRY:
        /* Wait before retrying. */
        delay_retry = 1;
    case SCSI_DH_IMM_RETRY:
    case SCSI_DH_RES_TEMP_UNAVAIL:
        if (pg_init_limit_reached(m, pgpath))
            fail_path(pgpath);
        errors = 0;
        break;
    default:
        /*
         * We probably do not want to fail the path for a device
         * error, but this is what the old dm did. In future
         * patches we can do more advanced handling.
         */
        fail_path(pgpath);
    }

    spin_lock_irqsave(&m->lock, flags);
    if (errors) {
        if (pgpath == m->current_pgpath) {
            DMERR("Could not failover device. Error %d.", errors);
            m->current_pgpath = NULL;
            m->current_pg = NULL;
        }
    } else if (!m->pg_init_required)
        pg->bypassed = 0;

    if (--m->pg_init_in_progress)
        /* Activations of other paths are still on going */
        goto out;

    if (!m->pg_init_required)
        m->queue_io = 0;

    m->pg_init_delay_retry = delay_retry;
    queue_work(kmultipathd, &m->process_queued_ios);

    /*
     * Wake up any thread waiting to suspend.
     */
    wake_up(&m->pg_init_wait);

out:
    spin_unlock_irqrestore(&m->lock, flags);
}

static void activate_path(struct work_struct *work)
{
    struct pgpath *pgpath =
        container_of(work, struct pgpath, activate_path.work);

    scsi_dh_activate(bdev_get_queue(pgpath->path.dev->bdev),
                pg_init_done, pgpath);
}

/*
 * end_io handling
 */
static int do_end_io(struct multipath *m, struct request *clone,
             int error, struct dm_mpath_io *mpio)
{
    /*
     * We don't queue any clone request inside the multipath target
     * during end I/O handling, since those clone requests don't have
     * bio clones.  If we queue them inside the multipath target,
     * we need to make bio clones, that requires memory allocation.
     * (See drivers/md/dm.c:end_clone_bio() about why the clone requests
     *  don't have bio clones.)
     * Instead of queueing the clone request here, we queue the original
     * request into dm core, which will remake a clone request and
     * clone bios for it and resubmit it later.
     */
    int r = DM_ENDIO_REQUEUE;
    unsigned long flags;

    if (!error && !clone->errors)
        return 0;   /* I/O complete */

    if (error == -EOPNOTSUPP || error == -EREMOTEIO || error == -EILSEQ)
        return error;

    if (mpio->pgpath)
        fail_path(mpio->pgpath);

    spin_lock_irqsave(&m->lock, flags);
    if (!m->nr_valid_paths) {
        if (!m->queue_if_no_path) {
            if (!__must_push_back(m))
                r = -EIO;
        } else {
            if (error == -EBADE)
                r = error;
        }
    }
    spin_unlock_irqrestore(&m->lock, flags);

    return r;
}

static int multipath_end_io(struct dm_target *ti, struct request *clone,
                int error, union map_info *map_context)
{
    struct multipath *m = ti->private;
    struct dm_mpath_io *mpio = map_context->ptr;
    struct pgpath *pgpath;
    struct path_selector *ps;
    int r;

    BUG_ON(!mpio);

    r  = do_end_io(m, clone, error, mpio);
    pgpath = mpio->pgpath;
    if (pgpath) {
        ps = &pgpath->pg->ps;
        if (ps->type->end_io)
            ps->type->end_io(ps, &pgpath->path, mpio->nr_bytes);
    }
    clear_mapinfo(m, map_context);

    return r;
}

/*
 * Suspend can't complete until all the I/O is processed so if
 * the last path fails we must error any remaining I/O.
 * Note that if the freeze_bdev fails while suspending, the
 * queue_if_no_path state is lost - userspace should reset it.
 */
static void multipath_presuspend(struct dm_target *ti)
{
    struct multipath *m = (struct multipath *) ti->private;

    queue_if_no_path(m, 0, 1);
}

static void multipath_postsuspend(struct dm_target *ti)
{
    struct multipath *m = ti->private;

    mutex_lock(&m->work_mutex);
    flush_multipath_work(m);
    mutex_unlock(&m->work_mutex);
}

/*
 * Restore the queue_if_no_path setting.
 */
static void multipath_resume(struct dm_target *ti)
{
    struct multipath *m = (struct multipath *) ti->private;
    unsigned long flags;

    spin_lock_irqsave(&m->lock, flags);
    m->queue_if_no_path = m->saved_queue_if_no_path;
    spin_unlock_irqrestore(&m->lock, flags);
}

/*
 * Info output has the following format:
 * num_multipath_feature_args [multipath_feature_args]*
 * num_handler_status_args [handler_status_args]*
 * num_groups init_group_number
 *            [A|D|E num_ps_status_args [ps_status_args]*
 *             num_paths num_selector_args
 *             [path_dev A|F fail_count [selector_args]* ]+ ]+
 *
 * Table output has the following format (identical to the constructor string):
 * num_feature_args [features_args]*
 * num_handler_args hw_handler [hw_handler_args]*
 * num_groups init_group_number
 *     [priority selector-name num_ps_args [ps_args]*
 *      num_paths num_selector_args [path_dev [selector_args]* ]+ ]+
 */
static int multipath_status(struct dm_target *ti, status_type_t type,
                unsigned status_flags, char *result, unsigned maxlen)
{
    int sz = 0;
    unsigned long flags;
    struct multipath *m = (struct multipath *) ti->private;
    struct priority_group *pg;
    struct pgpath *p;
    unsigned pg_num;
    char state;

    spin_lock_irqsave(&m->lock, flags);

    /* Features */
    if (type == STATUSTYPE_INFO)
        DMEMIT("2 %u %u ", m->queue_size, m->pg_init_count);
    else {
        DMEMIT("%u ", m->queue_if_no_path +
                  (m->pg_init_retries > 0) * 2 +
                  (m->pg_init_delay_msecs != DM_PG_INIT_DELAY_DEFAULT) * 2 +
                  m->retain_attached_hw_handler);
        if (m->queue_if_no_path)
            DMEMIT("queue_if_no_path ");
        if (m->pg_init_retries)
            DMEMIT("pg_init_retries %u ", m->pg_init_retries);
        if (m->pg_init_delay_msecs != DM_PG_INIT_DELAY_DEFAULT)
            DMEMIT("pg_init_delay_msecs %u ", m->pg_init_delay_msecs);
        if (m->retain_attached_hw_handler)
            DMEMIT("retain_attached_hw_handler ");
    }

    if (!m->hw_handler_name || type == STATUSTYPE_INFO)
        DMEMIT("0 ");
    else
        DMEMIT("1 %s ", m->hw_handler_name);

    DMEMIT("%u ", m->nr_priority_groups);

    if (m->next_pg)
        pg_num = m->next_pg->pg_num;
    else if (m->current_pg)
        pg_num = m->current_pg->pg_num;
    else
        pg_num = (m->nr_priority_groups ? 1 : 0);

    DMEMIT("%u ", pg_num);

    switch (type) {
    case STATUSTYPE_INFO:
        list_for_each_entry(pg, &m->priority_groups, list) {
            if (pg->bypassed)
                state = 'D';    /* Disabled */
            else if (pg == m->current_pg)
                state = 'A';    /* Currently Active */
            else
                state = 'E';    /* Enabled */

            DMEMIT("%c ", state);

            if (pg->ps.type->status)
                sz += pg->ps.type->status(&pg->ps, NULL, type,
                              result + sz,
                              maxlen - sz);
            else
                DMEMIT("0 ");

            DMEMIT("%u %u ", pg->nr_pgpaths,
                   pg->ps.type->info_args);

            list_for_each_entry(p, &pg->pgpaths, list) {
                DMEMIT("%s %s %u ", p->path.dev->name,
                       p->is_active ? "A" : "F",
                       p->fail_count);
                if (pg->ps.type->status)
                    sz += pg->ps.type->status(&pg->ps,
                          &p->path, type, result + sz,
                          maxlen - sz);
            }
        }
        break;

    case STATUSTYPE_TABLE:
        list_for_each_entry(pg, &m->priority_groups, list) {
            DMEMIT("%s ", pg->ps.type->name);

            if (pg->ps.type->status)
                sz += pg->ps.type->status(&pg->ps, NULL, type,
                              result + sz,
                              maxlen - sz);
            else
                DMEMIT("0 ");

            DMEMIT("%u %u ", pg->nr_pgpaths,
                   pg->ps.type->table_args);

            list_for_each_entry(p, &pg->pgpaths, list) {
                DMEMIT("%s ", p->path.dev->name);
                if (pg->ps.type->status)
                    sz += pg->ps.type->status(&pg->ps,
                          &p->path, type, result + sz,
                          maxlen - sz);
            }
        }
        break;
    }

    spin_unlock_irqrestore(&m->lock, flags);

    return 0;
}

static int multipath_message(struct dm_target *ti, unsigned argc, char **argv)
{
    int r = -EINVAL;
    struct dm_dev *dev;
    struct multipath *m = (struct multipath *) ti->private;
    action_fn action;

    mutex_lock(&m->work_mutex);

    if (dm_suspended(ti)) {
        r = -EBUSY;
        goto out;
    }

    if (argc == 1) {
        if (!strcasecmp(argv[0], "queue_if_no_path")) {
            r = queue_if_no_path(m, 1, 0);
            goto out;
        } else if (!strcasecmp(argv[0], "fail_if_no_path")) {
            r = queue_if_no_path(m, 0, 0);
            goto out;
        }
    }

    if (argc != 2) {
        DMWARN("Unrecognised multipath message received.");
        goto out;
    }

    if (!strcasecmp(argv[0], "disable_group")) {
        r = bypass_pg_num(m, argv[1], 1);
        goto out;
    } else if (!strcasecmp(argv[0], "enable_group")) {
        r = bypass_pg_num(m, argv[1], 0);
        goto out;
    } else if (!strcasecmp(argv[0], "switch_group")) {
        r = switch_pg_num(m, argv[1]);
        goto out;
    } else if (!strcasecmp(argv[0], "reinstate_path"))
        action = reinstate_path;
    else if (!strcasecmp(argv[0], "fail_path"))
        action = fail_path;
    else {
        DMWARN("Unrecognised multipath message received.");
        goto out;
    }

    r = dm_get_device(ti, argv[1], dm_table_get_mode(ti->table), &dev);
    if (r) {
        DMWARN("message: error getting device %s",
               argv[1]);
        goto out;
    }

    r = action_dev(m, dev, action);

    dm_put_device(ti, dev);

out:
    mutex_unlock(&m->work_mutex);
    return r;
}

static int multipath_ioctl(struct dm_target *ti, unsigned int cmd,
               unsigned long arg)
{
    struct multipath *m = ti->private;
    struct pgpath *pgpath;
    struct block_device *bdev;
    fmode_t mode;
    unsigned long flags;
    int r;

again:
    bdev = NULL;
    mode = 0;
    r = 0;

    spin_lock_irqsave(&m->lock, flags);

    if (!m->current_pgpath)
        __choose_pgpath(m, 0);

    pgpath = m->current_pgpath;

    if (pgpath) {
        bdev = pgpath->path.dev->bdev;
        mode = pgpath->path.dev->mode;
    }

    if ((pgpath && m->queue_io) || (!pgpath && m->queue_if_no_path))
        r = -EAGAIN;
    else if (!bdev)
        r = -EIO;

    spin_unlock_irqrestore(&m->lock, flags);

    /*
     * Only pass ioctls through if the device sizes match exactly.
     */
    if (!r && ti->len != i_size_read(bdev->bd_inode) >> SECTOR_SHIFT)
        r = scsi_verify_blk_ioctl(NULL, cmd);

    if (r == -EAGAIN && !fatal_signal_pending(current)) {
        queue_work(kmultipathd, &m->process_queued_ios);
        msleep(10);
        goto again;
    }

    return r ? : __blkdev_driver_ioctl(bdev, mode, cmd, arg);
}

static int multipath_iterate_devices(struct dm_target *ti,
                     iterate_devices_callout_fn fn, void *data)
{
    struct multipath *m = ti->private;
    struct priority_group *pg;
    struct pgpath *p;
    int ret = 0;

    list_for_each_entry(pg, &m->priority_groups, list) {
        list_for_each_entry(p, &pg->pgpaths, list) {
            ret = fn(ti, p->path.dev, ti->begin, ti->len, data);
            if (ret)
                goto out;
        }
    }

out:
    return ret;
}

static int __pgpath_busy(struct pgpath *pgpath)
{
    struct request_queue *q = bdev_get_queue(pgpath->path.dev->bdev);

    return dm_underlying_device_busy(q);
}

/*
 * We return "busy", only when we can map I/Os but underlying devices
 * are busy (so even if we map I/Os now, the I/Os will wait on
 * the underlying queue).
 * In other words, if we want to kill I/Os or queue them inside us
 * due to map unavailability, we don't return "busy".  Otherwise,
 * dm core won't give us the I/Os and we can't do what we want.
 */
static int multipath_busy(struct dm_target *ti)
{
    int busy = 0, has_active = 0;
    struct multipath *m = ti->private;
    struct priority_group *pg;
    struct pgpath *pgpath;
    unsigned long flags;

    spin_lock_irqsave(&m->lock, flags);

    /* Guess which priority_group will be used at next mapping time */
    if (unlikely(!m->current_pgpath && m->next_pg))
        pg = m->next_pg;
    else if (likely(m->current_pg))
        pg = m->current_pg;
    else
        /*
         * We don't know which pg will be used at next mapping time.
         * We don't call __choose_pgpath() here to avoid to trigger
         * pg_init just by busy checking.
         * So we don't know whether underlying devices we will be using
         * at next mapping time are busy or not. Just try mapping.
         */
        goto out;

    /*
     * If there is one non-busy active path at least, the path selector
     * will be able to select it. So we consider such a pg as not busy.
     */
    busy = 1;
    list_for_each_entry(pgpath, &pg->pgpaths, list)
        if (pgpath->is_active) {
            has_active = 1;

            if (!__pgpath_busy(pgpath)) {
                busy = 0;
                break;
            }
        }

    if (!has_active)
        /*
         * No active path in this pg, so this pg won't be used and
         * the current_pg will be changed at next mapping time.
         * We need to try mapping to determine it.
         */
        busy = 0;

out:
    spin_unlock_irqrestore(&m->lock, flags);

    return busy;
}

/*-----------------------------------------------------------------
 * Module setup
 *---------------------------------------------------------------*/
static struct target_type multipath_target = {
    .name = "multipath",
    .version = {1, 5, 0},
    .module = THIS_MODULE,
    .ctr = multipath_ctr,
    .dtr = multipath_dtr,
    .map_rq = multipath_map,
    .rq_end_io = multipath_end_io,
    .presuspend = multipath_presuspend,
    .postsuspend = multipath_postsuspend,
    .resume = multipath_resume,
    .status = multipath_status,
    .message = multipath_message,
    .ioctl  = multipath_ioctl,
    .iterate_devices = multipath_iterate_devices,
    .busy = multipath_busy,
};

static int __init dm_multipath_init(void)
{
    int r;

    /* allocate a slab for the dm_ios */
    _mpio_cache = KMEM_CACHE(dm_mpath_io, 0);
    if (!_mpio_cache)
        return -ENOMEM;

    r = dm_register_target(&multipath_target);
    if (r < 0) {
        DMERR("register failed %d", r);
        kmem_cache_destroy(_mpio_cache);
        return -EINVAL;
    }

    kmultipathd = alloc_workqueue("kmpathd", WQ_MEM_RECLAIM, 0);
    if (!kmultipathd) {
        DMERR("failed to create workqueue kmpathd");
        dm_unregister_target(&multipath_target);
        kmem_cache_destroy(_mpio_cache);
        return -ENOMEM;
    }

    /*
     * A separate workqueue is used to handle the device handlers
     * to avoid overloading existing workqueue. Overloading the
     * old workqueue would also create a bottleneck in the
     * path of the storage hardware device activation.
     */
    kmpath_handlerd = alloc_ordered_workqueue("kmpath_handlerd",
                          WQ_MEM_RECLAIM);
    if (!kmpath_handlerd) {
        DMERR("failed to create workqueue kmpath_handlerd");
        destroy_workqueue(kmultipathd);
        dm_unregister_target(&multipath_target);
        kmem_cache_destroy(_mpio_cache);
        return -ENOMEM;
    }

    DMINFO("version %u.%u.%u loaded",
           multipath_target.version[0], multipath_target.version[1],
           multipath_target.version[2]);

    return r;
}

static void __exit dm_multipath_exit(void)
{
    destroy_workqueue(kmpath_handlerd);
    destroy_workqueue(kmultipathd);

    dm_unregister_target(&multipath_target);
    kmem_cache_destroy(_mpio_cache);
}

module_init(dm_multipath_init);
module_exit(dm_multipath_exit);

MODULE_DESCRIPTION(DM_NAME " multipath target");
MODULE_AUTHOR("Sistina Software <[email protected]>");
MODULE_LICENSE("GPL");