Linux-2.6.12-rc2

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / drivers / md / dm-mpath.c

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

#include "dm.h"
#include "dm-path-selector.h"
#include "dm-hw-handler.h"
#include "dm-bio-list.h"
#include "dm-bio-record.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 <asm/atomic.h>

#define MESG_STR(x) x, sizeof(x)

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

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

        struct path 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;

        spinlock_t lock;

        struct hw_handler hw_handler;
        unsigned nr_priority_groups;
        struct list_head priority_groups;
        unsigned pg_init_required;      /* pg_init needs calling? */

        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;              /* Must we queue all I/O? */
        unsigned queue_if_no_path;      /* Queue I/O if last path fails? */
        unsigned suspended;             /* Has dm core suspended our I/O? */

        struct work_struct process_queued_ios;
        struct bio_list queued_ios;
        unsigned queue_size;

        struct work_struct trigger_event;

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

/*
 * Context information attached to each bio we process.
 */
struct mpath_io {
        struct pgpath *pgpath;
        struct dm_bio_details details;
};

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

#define MIN_IOS 256     /* Mempool size */

static kmem_cache_t *_mpio_cache;

static void process_queued_ios(void *data);
static void trigger_event(void *data);


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

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

        if (pgpath) {
                memset(pgpath, 0, sizeof(*pgpath));
                pgpath->path.is_active = 1;
        }

        return pgpath;
}

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

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

        pg = kmalloc(sizeof(*pg), GFP_KERNEL);
        if (!pg)
                return NULL;

        memset(pg, 0, sizeof(*pg));
        INIT_LIST_HEAD(&pg->pgpaths);

        return pg;
}

static void free_pgpaths(struct list_head *pgpaths, struct dm_target *ti)
{
        struct pgpath *pgpath, *tmp;

        list_for_each_entry_safe(pgpath, tmp, pgpaths, list) {
                list_del(&pgpath->list);
                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(void)
{
        struct multipath *m;

        m = kmalloc(sizeof(*m), GFP_KERNEL);
        if (m) {
                memset(m, 0, sizeof(*m));
                INIT_LIST_HEAD(&m->priority_groups);
                spin_lock_init(&m->lock);
                m->queue_io = 1;
                INIT_WORK(&m->process_queued_ios, process_queued_ios, m);
                INIT_WORK(&m->trigger_event, trigger_event, m);
                m->mpio_pool = mempool_create(MIN_IOS, mempool_alloc_slab,
                                              mempool_free_slab, _mpio_cache);
                if (!m->mpio_pool) {
                        kfree(m);
                        return NULL;
                }
        }

        return m;
}

static void free_multipath(struct multipath *m)
{
        struct priority_group *pg, *tmp;
        struct hw_handler *hwh = &m->hw_handler;

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

        if (hwh->type) {
                hwh->type->destroy(hwh);
                dm_put_hw_handler(hwh->type);
        }

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


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

static void __switch_pg(struct multipath *m, struct pgpath *pgpath)
{
        struct hw_handler *hwh = &m->hw_handler;

        m->current_pg = pgpath->pg;

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

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

        path = pg->ps.type->select_path(&pg->ps, &m->repeat_count);
        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)
{
        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))
                        return;
        }

        /* Don't change PG until it has no remaining paths */
        if (m->current_pg && !__choose_path_in_pg(m, m->current_pg))
                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.
         */
        do {
                list_for_each_entry(pg, &m->priority_groups, list) {
                        if (pg->bypassed == bypassed)
                                continue;
                        if (!__choose_path_in_pg(m, pg))
                                return;
                }
        } while (bypassed--);

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

static int map_io(struct multipath *m, struct bio *bio, struct mpath_io *mpio,
                  unsigned was_queued)
{
        int r = 1;
        unsigned long flags;
        struct pgpath *pgpath;

        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);

        pgpath = m->current_pgpath;

        if (was_queued)
                m->queue_size--;

        if ((pgpath && m->queue_io) ||
            (!pgpath && m->queue_if_no_path && !m->suspended)) {
                /* Queue for the daemon to resubmit */
                bio_list_add(&m->queued_ios, bio);
                m->queue_size++;
                if (m->pg_init_required || !m->queue_io)
                        schedule_work(&m->process_queued_ios);
                pgpath = NULL;
                r = 0;
        } else if (!pgpath)
                r = -EIO;               /* Failed */
        else
                bio->bi_bdev = pgpath->path.dev->bdev;

        mpio->pgpath = pgpath;

        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 long flags;

        spin_lock_irqsave(&m->lock, flags);

        m->queue_if_no_path = queue_if_no_path;
        if (!m->queue_if_no_path)
                schedule_work(&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;
        struct bio *bio = NULL, *next;
        struct mpath_io *mpio;
        union map_info *info;

        spin_lock_irqsave(&m->lock, flags);
        bio = bio_list_get(&m->queued_ios);
        spin_unlock_irqrestore(&m->lock, flags);

        while (bio) {
                next = bio->bi_next;
                bio->bi_next = NULL;

                info = dm_get_mapinfo(bio);
                mpio = info->ptr;

                r = map_io(m, bio, mpio, 1);
                if (r < 0)
                        bio_endio(bio, bio->bi_size, r);
                else if (r == 1)
                        generic_make_request(bio);

                bio = next;
        }
}

static void process_queued_ios(void *data)
{
        struct multipath *m = (struct multipath *) data;
        struct hw_handler *hwh = &m->hw_handler;
        struct pgpath *pgpath;
        unsigned init_required, must_queue = 0;
        unsigned long flags;

        spin_lock_irqsave(&m->lock, flags);

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

        pgpath = m->current_pgpath;

        if ((pgpath && m->queue_io) ||
            (!pgpath && m->queue_if_no_path && !m->suspended))
                must_queue = 1;

        init_required = m->pg_init_required;
        if (init_required)
                m->pg_init_required = 0;

        spin_unlock_irqrestore(&m->lock, flags);

        if (init_required)
                hwh->type->pg_init(hwh, pgpath->pg->bypassed, &pgpath->path);

        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(void *data)
{
        struct multipath *m = (struct multipath *) data;

        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>]* ]+ ]+
 *---------------------------------------------------------------*/
struct param {
        unsigned min;
        unsigned max;
        char *error;
};

#define ESTR(s) ("dm-multipath: " s)

static int read_param(struct param *param, char *str, unsigned *v, char **error)
{
        if (!str ||
            (sscanf(str, "%u", v) != 1) ||
            (*v < param->min) ||
            (*v > param->max)) {
                *error = param->error;
                return -EINVAL;
        }

        return 0;
}

struct arg_set {
        unsigned argc;
        char **argv;
};

static char *shift(struct arg_set *as)
{
        char *r;

        if (as->argc) {
                as->argc--;
                r = *as->argv;
                as->argv++;
                return r;
        }

        return NULL;
}

static void consume(struct arg_set *as, unsigned n)
{
        BUG_ON (as->argc < n);
        as->argc -= n;
        as->argv += n;
}

static int parse_path_selector(struct arg_set *as, struct priority_group *pg,
                               struct dm_target *ti)
{
        int r;
        struct path_selector_type *pst;
        unsigned ps_argc;

        static struct param _params[] = {
                {0, 1024, ESTR("invalid number of path selector args")},
        };

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

        r = read_param(_params, shift(as), &ps_argc, &ti->error);
        if (r)
                return -EINVAL;

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

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

        return 0;
}

static struct pgpath *parse_path(struct arg_set *as, struct path_selector *ps,
                               struct dm_target *ti)
{
        int r;
        struct pgpath *p;

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

        p = alloc_pgpath();
        if (!p)
                return NULL;

        r = dm_get_device(ti, shift(as), ti->begin, ti->len,
                          dm_table_get_mode(ti->table), &p->path.dev);
        if (r) {
                ti->error = ESTR("error getting device");
                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 NULL;
}

static struct priority_group *parse_priority_group(struct arg_set *as,
                                                   struct multipath *m,
                                                   struct dm_target *ti)
{
        static struct param _params[] = {
                {1, 1024, ESTR("invalid number of paths")},
                {0, 1024, ESTR("invalid number of selector args")}
        };

        int r;
        unsigned i, nr_selector_args, nr_params;
        struct priority_group *pg;

        if (as->argc < 2) {
                as->argc = 0;
                ti->error = ESTR("not enough priority group aruments");
                return NULL;
        }

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

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

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

        r = read_param(_params + 1, shift(as), &nr_selector_args, &ti->error);
        if (r)
                goto bad;

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

                if (as->argc < nr_params)
                        goto bad;

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

                pgpath = parse_path(&path_args, &pg->ps, ti);
                if (!pgpath)
                        goto bad;

                pgpath->pg = pg;
                list_add_tail(&pgpath->list, &pg->pgpaths);
                consume(as, nr_params);
        }

        return pg;

 bad:
        free_priority_group(pg, ti);
        return NULL;
}

static int parse_hw_handler(struct arg_set *as, struct multipath *m,
                            struct dm_target *ti)
{
        int r;
        struct hw_handler_type *hwht;
        unsigned hw_argc;

        static struct param _params[] = {
                {0, 1024, ESTR("invalid number of hardware handler args")},
        };

        r = read_param(_params, shift(as), &hw_argc, &ti->error);
        if (r)
                return -EINVAL;

        if (!hw_argc)
                return 0;

        hwht = dm_get_hw_handler(shift(as));
        if (!hwht) {
                ti->error = ESTR("unknown hardware handler type");
                return -EINVAL;
        }

        r = hwht->create(&m->hw_handler, hw_argc - 1, as->argv);
        if (r) {
                dm_put_hw_handler(hwht);
                ti->error = ESTR("hardware handler constructor failed");
                return r;
        }

        m->hw_handler.type = hwht;
        consume(as, hw_argc - 1);

        return 0;
}

static int parse_features(struct arg_set *as, struct multipath *m,
                          struct dm_target *ti)
{
        int r;
        unsigned argc;

        static struct param _params[] = {
                {0, 1, ESTR("invalid number of feature args")},
        };

        r = read_param(_params, shift(as), &argc, &ti->error);
        if (r)
                return -EINVAL;

        if (!argc)
                return 0;

        if (!strnicmp(shift(as), MESG_STR("queue_if_no_path")))
                return queue_if_no_path(m, 1);
        else {
                ti->error = "Unrecognised multipath feature request";
                return -EINVAL;
        }
}

static int multipath_ctr(struct dm_target *ti, unsigned int argc,
                         char **argv)
{
        /* target parameters */
        static struct param _params[] = {
                {1, 1024, ESTR("invalid number of priority groups")},
                {1, 1024, ESTR("invalid initial priority group number")},
        };

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

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

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

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

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

        r = read_param(_params, shift(&as), &m->nr_priority_groups, &ti->error);
        if (r)
                goto bad;

        r = read_param(_params + 1, shift(&as), &next_pg_num, &ti->error);
        if (r)
                goto bad;

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

                pg = parse_priority_group(&as, m, ti);
                if (!pg) {
                        r = -EINVAL;
                        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 = ESTR("priority group count mismatch");
                r = -EINVAL;
                goto bad;
        }

        ti->private = m;
        m->ti = ti;

        return 0;

 bad:
        free_multipath(m);
        return r;
}

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

/*
 * Map bios, recording original fields for later in case we have to resubmit
 */
static int multipath_map(struct dm_target *ti, struct bio *bio,
                         union map_info *map_context)
{
        int r;
        struct mpath_io *mpio;
        struct multipath *m = (struct multipath *) ti->private;

        mpio = mempool_alloc(m->mpio_pool, GFP_NOIO);
        dm_bio_record(&mpio->details, bio);

        map_context->ptr = mpio;
        bio->bi_rw |= (1 << BIO_RW_FAILFAST);
        r = map_io(m, bio, mpio, 0);
        if (r < 0)
                mempool_free(mpio, m->mpio_pool);

        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->path.is_active)
                goto out;

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

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

        m->nr_valid_paths--;

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

        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->path.is_active)
                goto out;

        if (!pgpath->pg->ps.type) {
                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->path.is_active = 1;

        m->current_pgpath = NULL;
        if (!m->nr_valid_paths++)
                schedule_work(&m->process_queued_ios);

        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 = 0;
        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;

        if (!pgstr || (sscanf(pgstr, "%u", &pgnum) != 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;

        if (!pgstr || (sscanf(pgstr, "%u", &pgnum) != 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;
}

/*
 * pg_init must call this when it has completed its initialisation
 */
void dm_pg_init_complete(struct path *path, unsigned err_flags)
{
        struct pgpath *pgpath = path_to_pgpath(path);
        struct priority_group *pg = pgpath->pg;
        struct multipath *m = pg->m;
        unsigned long flags;

        /* We insist on failing the path if the PG is already bypassed. */
        if (err_flags && pg->bypassed)
                err_flags |= MP_FAIL_PATH;

        if (err_flags & MP_FAIL_PATH)
                fail_path(pgpath);

        if (err_flags & MP_BYPASS_PG)
                bypass_pg(m, pg, 1);

        spin_lock_irqsave(&m->lock, flags);
        if (!err_flags)
                m->queue_io = 0;
        else {
                m->current_pgpath = NULL;
                m->current_pg = NULL;
        }
        schedule_work(&m->process_queued_ios);
        spin_unlock_irqrestore(&m->lock, flags);
}

/*
 * end_io handling
 */
static int do_end_io(struct multipath *m, struct bio *bio,
                     int error, struct mpath_io *mpio)
{
        struct hw_handler *hwh = &m->hw_handler;
        unsigned err_flags = MP_FAIL_PATH;      /* Default behavior */

        if (!error)
                return 0;       /* I/O complete */

        spin_lock(&m->lock);
        if (!m->nr_valid_paths) {
                if (!m->queue_if_no_path || m->suspended) {
                        spin_unlock(&m->lock);
                        return -EIO;
                } else {
                        spin_unlock(&m->lock);
                        goto requeue;
                }
        }
        spin_unlock(&m->lock);

        if (hwh->type && hwh->type->error)
                err_flags = hwh->type->error(hwh, bio);

        if (mpio->pgpath) {
                if (err_flags & MP_FAIL_PATH)
                        fail_path(mpio->pgpath);

                if (err_flags & MP_BYPASS_PG)
                        bypass_pg(m, mpio->pgpath->pg, 1);
        }

        if (err_flags & MP_ERROR_IO)
                return -EIO;

      requeue:
        dm_bio_restore(&mpio->details, bio);

        /* queue for the daemon to resubmit or fail */
        spin_lock(&m->lock);
        bio_list_add(&m->queued_ios, bio);
        m->queue_size++;
        if (!m->queue_io)
                schedule_work(&m->process_queued_ios);
        spin_unlock(&m->lock);

        return 1;       /* io not complete */
}

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

        r  = do_end_io(m, bio, error, mpio);
        if (pgpath) {
                ps = &pgpath->pg->ps;
                if (ps->type->end_io)
                        ps->type->end_io(ps, &pgpath->path);
        }
        if (r <= 0)
                mempool_free(mpio, m->mpio_pool);

        return r;
}

/*
 * Suspend can't complete until all the I/O is processed so if
 * the last path failed we will now error any queued I/O.
 */
static void multipath_presuspend(struct dm_target *ti)
{
        struct multipath *m = (struct multipath *) ti->private;
        unsigned long flags;

        spin_lock_irqsave(&m->lock, flags);
        m->suspended = 1;
        if (m->queue_if_no_path)
                schedule_work(&m->process_queued_ios);
        spin_unlock_irqrestore(&m->lock, flags);
}

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->suspended = 0;
        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,
                            char *result, unsigned int maxlen)
{
        int sz = 0;
        unsigned long flags;
        struct multipath *m = (struct multipath *) ti->private;
        struct hw_handler *hwh = &m->hw_handler;
        struct priority_group *pg;
        struct pgpath *p;
        unsigned pg_num;
        char state;

        spin_lock_irqsave(&m->lock, flags);

        /* Features */
        if (type == STATUSTYPE_INFO)
                DMEMIT("1 %u ", m->queue_size);
        else if (m->queue_if_no_path)
                DMEMIT("1 queue_if_no_path ");
        else
                DMEMIT("0 ");

        if (hwh->type && hwh->type->status)
                sz += hwh->type->status(hwh, type, result + sz, maxlen - sz);
        else if (!hwh->type || type == STATUSTYPE_INFO)
                DMEMIT("0 ");
        else
                DMEMIT("1 %s ", hwh->type->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 = 1;

        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->path.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;
        struct dm_dev *dev;
        struct multipath *m = (struct multipath *) ti->private;
        action_fn action;

        if (argc == 1) {
                if (!strnicmp(argv[0], MESG_STR("queue_if_no_path")))
                        return queue_if_no_path(m, 1);
                else if (!strnicmp(argv[0], MESG_STR("fail_if_no_path")))
                        return queue_if_no_path(m, 0);
        }

        if (argc != 2)
                goto error;

        if (!strnicmp(argv[0], MESG_STR("disable_group")))
                return bypass_pg_num(m, argv[1], 1);
        else if (!strnicmp(argv[0], MESG_STR("enable_group")))
                return bypass_pg_num(m, argv[1], 0);
        else if (!strnicmp(argv[0], MESG_STR("switch_group")))
                return switch_pg_num(m, argv[1]);
        else if (!strnicmp(argv[0], MESG_STR("reinstate_path")))
                action = reinstate_path;
        else if (!strnicmp(argv[0], MESG_STR("fail_path")))
                action = fail_path;
        else
                goto error;

        r = dm_get_device(ti, argv[1], ti->begin, ti->len,
                          dm_table_get_mode(ti->table), &dev);
        if (r) {
                DMWARN("dm-multipath message: error getting device %s",
                       argv[1]);
                return -EINVAL;
        }

        r = action_dev(m, dev, action);

        dm_put_device(ti, dev);

        return r;

error:
        DMWARN("Unrecognised multipath message received.");
        return -EINVAL;
}

/*-----------------------------------------------------------------
 * Module setup
 *---------------------------------------------------------------*/
static struct target_type multipath_target = {
        .name = "multipath",
        .version = {1, 0, 4},
        .module = THIS_MODULE,
        .ctr = multipath_ctr,
        .dtr = multipath_dtr,
        .map = multipath_map,
        .end_io = multipath_end_io,
        .presuspend = multipath_presuspend,
        .resume = multipath_resume,
        .status = multipath_status,
        .message = multipath_message,
};

static int __init dm_multipath_init(void)
{
        int r;

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

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

        DMINFO("dm-multipath 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)
{
        int r;

        r = dm_unregister_target(&multipath_target);
        if (r < 0)
                DMERR("%s: target unregister failed %d",
                      multipath_target.name, r);
        kmem_cache_destroy(_mpio_cache);
}

EXPORT_SYMBOL_GPL(dm_pg_init_complete);

module_init(dm_multipath_init);
module_exit(dm_multipath_exit);

MODULE_DESCRIPTION(DM_NAME " multipath target");
MODULE_AUTHOR("Sistina Software <dm-devel@redhat.com>");
MODULE_LICENSE("GPL");