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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 "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 <asm/atomic.h>

#define DM_MSG_PREFIX "multipath"
#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 dm_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 pg_init_in_progress; /* Only one pg_init allowed at once */

      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 saved_queue_if_no_path;/* Saved state during suspension */
      unsigned pg_init_retries;     /* Number of times to retry pg_init */
      unsigned pg_init_count;       /* Number of times pg_init called */

      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 dm_mpath_io structs so that we
       * can resubmit bios on error.
       */
      mempool_t *mpio_pool;
};

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

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

#define MIN_IOS 256     /* Mempool size */

static struct kmem_cache *_mpio_cache;

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


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

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

      if (pgpath)
            pgpath->path.is_active = 1;

      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;

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

      m = kzalloc(sizeof(*m), GFP_KERNEL);
      if (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);
            INIT_WORK(&m->trigger_event, trigger_event);
            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;
      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;
      }

      m->pg_init_count = 0;
}

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

/*
 * 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 bio *bio,
              struct dm_mpath_io *mpio, unsigned was_queued)
{
      int r = DM_MAPIO_REMAPPED;
      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)) {
            /* Queue for the daemon to resubmit */
            bio_list_add(&m->queued_ios, bio);
            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)
            bio->bi_bdev = pgpath->path.dev->bdev;
      else if (__must_push_back(m))
            r = DM_MAPIO_REQUEUE;
      else
            r = -EIO;   /* Failed */

      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 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;
      struct bio *bio = NULL, *next;
      struct dm_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, r);
            else if (r == DM_MAPIO_REMAPPED)
                  generic_make_request(bio);
            else if (r == DM_MAPIO_REQUEUE)
                  bio_endio(bio, -EIO);

            bio = next;
      }
}

static void process_queued_ios(struct work_struct *work)
{
      struct multipath *m =
            container_of(work, struct multipath, process_queued_ios);
      struct hw_handler *hwh = &m->hw_handler;
      struct pgpath *pgpath = NULL;
      unsigned init_required = 0, must_queue = 1;
      unsigned long flags;

      spin_lock_irqsave(&m->lock, flags);

      if (!m->queue_size)
            goto out;

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

      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) {
            m->pg_init_count++;
            m->pg_init_required = 0;
            m->pg_init_in_progress = 1;
            init_required = 1;
      }

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

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, "invalid number of path selector args"},
      };

      pst = dm_get_path_selector(shift(as));
      if (!pst) {
            ti->error = "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 = "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 = "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 = "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)
{
      static struct param _params[] = {
            {1, 1024, "invalid number of paths"},
            {0, 1024, "invalid number of selector args"}
      };

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

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

      pg = alloc_priority_group();
      if (!pg) {
            ti->error = "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)
{
      int r;
      struct hw_handler_type *hwht;
      unsigned hw_argc;
      struct dm_target *ti = m->ti;

      static struct param _params[] = {
            {0, 1024, "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 = "unknown hardware handler type";
            return -EINVAL;
      }

      m->hw_handler.md = dm_table_get_md(ti->table);
      dm_put(m->hw_handler.md);

      r = hwht->create(&m->hw_handler, hw_argc - 1, as->argv);
      if (r) {
            dm_put_hw_handler(hwht);
            ti->error = "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)
{
      int r;
      unsigned argc;
      struct dm_target *ti = m->ti;
      const char *param_name;

      static struct param _params[] = {
            {0, 3, "invalid number of feature args"},
            {1, 50, "pg_init_retries must be between 1 and 50"},
      };

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

      if (!argc)
            return 0;

      do {
            param_name = shift(as);
            argc--;

            if (!strnicmp(param_name, MESG_STR("queue_if_no_path"))) {
                  r = queue_if_no_path(m, 1, 0);
                  continue;
            }

            if (!strnicmp(param_name, MESG_STR("pg_init_retries")) &&
                (argc >= 1)) {
                  r = read_param(_params + 1, shift(as),
                               &m->pg_init_retries, &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 parameters */
      static struct param _params[] = {
            {1, 1024, "invalid number of priority groups"},
            {1, 1024, "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(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 = 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);
            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 = "priority group count mismatch";
            r = -EINVAL;
            goto bad;
      }

      return 0;

 bad:
      free_multipath(m);
      return r;
}

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

      flush_workqueue(kmultipathd);
      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 dm_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 || r == DM_MAPIO_REQUEUE)
            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("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;

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

      queue_work(kmultipathd, &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++ && m->queue_size)
            queue_work(kmultipathd, &m->process_queued_ios);

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

      queue_work(kmultipathd, &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);

      queue_work(kmultipathd, &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);

      queue_work(kmultipathd, &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;
}

/*
 * 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;
}

/*
 * pg_init must call this when it has completed its initialisation
 */
void dm_pg_init_complete(struct dm_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;

      /*
       * If requested, retry pg_init until maximum number of retries exceeded.
       * If retry not requested and PG already bypassed, always fail the path.
       */
      if (err_flags & MP_RETRY) {
            if (pg_init_limit_reached(m, pgpath))
                  err_flags |= MP_FAIL_PATH;
      } else 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 & ~MP_RETRY) {
            m->current_pgpath = NULL;
            m->current_pg = NULL;
      } else if (!m->pg_init_required)
            m->queue_io = 0;

      m->pg_init_in_progress = 0;
      queue_work(kmultipathd, &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 dm_mpath_io *mpio)
{
      struct hw_handler *hwh = &m->hw_handler;
      unsigned err_flags = MP_FAIL_PATH;  /* Default behavior */
      unsigned long flags;

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

      if ((error == -EWOULDBLOCK) && bio_rw_ahead(bio))
            return error;

      if (error == -EOPNOTSUPP)
            return error;

      spin_lock_irqsave(&m->lock, flags);
      if (!m->nr_valid_paths) {
            if (__must_push_back(m)) {
                  spin_unlock_irqrestore(&m->lock, flags);
                  return DM_ENDIO_REQUEUE;
            } else if (!m->queue_if_no_path) {
                  spin_unlock_irqrestore(&m->lock, flags);
                  return -EIO;
            } else {
                  spin_unlock_irqrestore(&m->lock, flags);
                  goto requeue;
            }
      }
      spin_unlock_irqrestore(&m->lock, flags);

      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_irqsave(&m->lock, flags);
      bio_list_add(&m->queued_ios, bio);
      m->queue_size++;
      if (!m->queue_io)
            queue_work(kmultipathd, &m->process_queued_ios);
      spin_unlock_irqrestore(&m->lock, flags);

      return DM_ENDIO_INCOMPLETE;   /* 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 = ti->private;
      struct dm_mpath_io *mpio = 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 != DM_ENDIO_INCOMPLETE)
            mempool_free(mpio, m->mpio_pool);

      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);
}

/*
 * 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,
                      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("2 %u %u ", m->queue_size, m->pg_init_count);
      else {
            DMEMIT("%u ", m->queue_if_no_path +
                        (m->pg_init_retries > 0) * 2);
            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 (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, 0);
            else if (!strnicmp(argv[0], MESG_STR("fail_if_no_path")))
                  return queue_if_no_path(m, 0, 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("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;
}

static int multipath_ioctl(struct dm_target *ti, struct inode *inode,
                     struct file *filp, unsigned int cmd,
                     unsigned long arg)
{
      struct multipath *m = (struct multipath *) ti->private;
      struct block_device *bdev = NULL;
      unsigned long flags;
      struct file fake_file = {};
      struct dentry fake_dentry = {};
      int r = 0;

      fake_file.f_path.dentry = &fake_dentry;

      spin_lock_irqsave(&m->lock, flags);

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

      if (m->current_pgpath) {
            bdev = m->current_pgpath->path.dev->bdev;
            fake_dentry.d_inode = bdev->bd_inode;
            fake_file.f_mode = m->current_pgpath->path.dev->mode;
      }

      if (m->queue_io)
            r = -EAGAIN;
      else if (!bdev)
            r = -EIO;

      spin_unlock_irqrestore(&m->lock, flags);

      return r ? : blkdev_driver_ioctl(bdev->bd_inode, &fake_file,
                               bdev->bd_disk, cmd, arg);
}

/*-----------------------------------------------------------------
 * Module setup
 *---------------------------------------------------------------*/
static struct target_type multipath_target = {
      .name = "multipath",
      .version = {1, 0, 5},
      .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,
      .ioctl  = multipath_ioctl,
};

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 = create_workqueue("kmpathd");
      if (!kmultipathd) {
            DMERR("failed to create workqueue kmpathd");
            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)
{
      int r;

      destroy_workqueue(kmultipathd);

      r = dm_unregister_target(&multipath_target);
      if (r < 0)
            DMERR("target unregister failed %d", 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");

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