Moved, renamed, and deleted files

The original directory structure was scattered and unorganized.
Changes are basically to make it look like kernel structure.

1 files changed, 1723 insertions, 0 deletions

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
new file mode 100644
index 00000000..754f38f8
--- /dev/null
+++ b/drivers/md/dm-mpath.c
@@ -0,0 +1,1723 @@
+/*
+ * 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 <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;
+
+	spinlock_t lock;
+
+	const char *hw_handler_name;
+	char *hw_handler_params;
+
+	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;		/* 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 */
+	unsigned pg_init_delay_msecs;	/* Number of msecs before pg_init retry */
+
+	struct work_struct process_queued_ios;
+	struct list_head 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;
+
+	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.
+	 */
+	do {
+		list_for_each_entry(pg, &m->priority_groups, list) {
+			if (pg->bypassed == bypassed)
+				continue;
+			if (!__choose_path_in_pg(m, pg, nr_bytes))
+				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->queue_size)
+		goto out;
+
+	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);
+
+out:
+	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;
+
+	/* 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->hw_handler_name) {
+		struct request_queue *q = bdev_get_queue(p->path.dev->bdev);
+
+		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, 5, "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, "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_sync(&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 = mpio->pgpath;
+	struct path_selector *ps;
+	int r;
+
+	BUG_ON(!mpio);
+
+	r  = do_end_io(m, clone, error, mpio);
+	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,
+			    char *result, unsigned int 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);
+		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->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 = (struct multipath *) ti->private;
+	struct block_device *bdev = NULL;
+	fmode_t mode = 0;
+	unsigned long flags;
+	int r = 0;
+
+	spin_lock_irqsave(&m->lock, flags);
+
+	if (!m->current_pgpath)
+		__choose_pgpath(m, 0);
+
+	if (m->current_pgpath) {
+		bdev = m->current_pgpath->path.dev->bdev;
+		mode = m->current_pgpath->path.dev->mode;
+	}
+
+	if (m->queue_io)
+		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);
+
+	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, 3, 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 <dm-devel@redhat.com>");
+MODULE_LICENSE("GPL");