drivers/md/multipath.c - kernel/msm-4.9 - Gitiles

 /*
  * multipath.c : Multiple Devices driver for Linux
  *
  * Copyright (C) 1999, 2000, 2001 Ingo Molnar, Red Hat
  *
  * Copyright (C) 1996, 1997, 1998 Ingo Molnar, Miguel de Icaza, Gadi Oxman
  *
  * MULTIPATH management functions.
  *
  * derived from raid1.c.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2, or (at your option)
  * any later version.
  *
  * You should have received a copy of the GNU General Public License
  * (for example /usr/src/linux/COPYING); if not, write to the Free
  * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */

 #include <linux/blkdev.h>
 #include <linux/module.h>
 #include <linux/raid/md_u.h>
 #include <linux/seq_file.h>
 #include <linux/slab.h>
 #include "md.h"
 #include "multipath.h"

 #define MAX_WORK_PER_DISK 128

 #define	NR_RESERVED_BUFS	32

 static int multipath_map (struct mpconf *conf)
 {
 	int i, disks = conf->raid_disks;

 	/*
 	 * Later we do read balancing on the read side
 	 * now we use the first available disk.
 	 */

 	rcu_read_lock();
 	for (i = 0; i < disks; i++) {
 		struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);
 		if (rdev && test_bit(In_sync, &rdev->flags)) {
 			atomic_inc(&rdev->nr_pending);
 			rcu_read_unlock();
 			return i;
 		}
 	}
 	rcu_read_unlock();

 	printk(KERN_ERR "multipath_map(): no more operational IO paths?\n");
 	return (-1);
 }

 static void multipath_reschedule_retry (struct multipath_bh *mp_bh)
 {
 	unsigned long flags;
 	struct mddev *mddev = mp_bh->mddev;
 	struct mpconf *conf = mddev->private;

 	spin_lock_irqsave(&conf->device_lock, flags);
 	list_add(&mp_bh->retry_list, &conf->retry_list);
 	spin_unlock_irqrestore(&conf->device_lock, flags);
 	md_wakeup_thread(mddev->thread);
 }

 /*
  * multipath_end_bh_io() is called when we have finished servicing a multipathed
  * operation and are ready to return a success/failure code to the buffer
  * cache layer.
  */
 static void multipath_end_bh_io (struct multipath_bh *mp_bh, int err)
 {
 	struct bio *bio = mp_bh->master_bio;
 	struct mpconf *conf = mp_bh->mddev->private;

 	bio_endio(bio, err);
 	mempool_free(mp_bh, conf->pool);
 }

 static void multipath_end_request(struct bio *bio, int error)
 {
 	int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
 	struct multipath_bh *mp_bh = bio->bi_private;
 	struct mpconf *conf = mp_bh->mddev->private;
 	struct md_rdev *rdev = conf->multipaths[mp_bh->path].rdev;

 	if (uptodate)
 		multipath_end_bh_io(mp_bh, 0);
 	else if (!(bio->bi_rw & REQ_RAHEAD)) {
 		/*
 		 * oops, IO error:
 		 */
 		char b[BDEVNAME_SIZE];
 		md_error (mp_bh->mddev, rdev);
 		printk(KERN_ERR "multipath: %s: rescheduling sector %llu\n",
 		       bdevname(rdev->bdev,b),
 		       (unsigned long long)bio->bi_iter.bi_sector);
 		multipath_reschedule_retry(mp_bh);
 	} else
 		multipath_end_bh_io(mp_bh, error);
 	rdev_dec_pending(rdev, conf->mddev);
 }

 static void multipath_make_request(struct mddev *mddev, struct bio * bio)
 {
 	struct mpconf *conf = mddev->private;
 	struct multipath_bh * mp_bh;
 	struct multipath_info *multipath;

 	if (unlikely(bio->bi_rw & REQ_FLUSH)) {
 		md_flush_request(mddev, bio);
 		return;
 	}

 	mp_bh = mempool_alloc(conf->pool, GFP_NOIO);

 	mp_bh->master_bio = bio;
 	mp_bh->mddev = mddev;

 	mp_bh->path = multipath_map(conf);
 	if (mp_bh->path < 0) {
 		bio_endio(bio, -EIO);
 		mempool_free(mp_bh, conf->pool);
 		return;
 	}
 	multipath = conf->multipaths + mp_bh->path;

 	mp_bh->bio = *bio;
 	mp_bh->bio.bi_iter.bi_sector += multipath->rdev->data_offset;
 	mp_bh->bio.bi_bdev = multipath->rdev->bdev;
 	mp_bh->bio.bi_rw |= REQ_FAILFAST_TRANSPORT;
 	mp_bh->bio.bi_end_io = multipath_end_request;
 	mp_bh->bio.bi_private = mp_bh;
 	generic_make_request(&mp_bh->bio);
 	return;
 }

 static void multipath_status (struct seq_file *seq, struct mddev *mddev)
 {
 	struct mpconf *conf = mddev->private;
 	int i;

 	seq_printf (seq, " [%d/%d] [", conf->raid_disks,
 		    conf->raid_disks - mddev->degraded);
 	for (i = 0; i < conf->raid_disks; i++)
 		seq_printf (seq, "%s",
 			       conf->multipaths[i].rdev &&
 			       test_bit(In_sync, &conf->multipaths[i].rdev->flags) ? "U" : "_");
 	seq_printf (seq, "]");
 }

 static int multipath_congested(struct mddev *mddev, int bits)
 {
 	struct mpconf *conf = mddev->private;
 	int i, ret = 0;

 	rcu_read_lock();
 	for (i = 0; i < mddev->raid_disks ; i++) {
 		struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);
 		if (rdev && !test_bit(Faulty, &rdev->flags)) {
 			struct request_queue *q = bdev_get_queue(rdev->bdev);

 			ret |= bdi_congested(&q->backing_dev_info, bits);
 			/* Just like multipath_map, we just check the
 			 * first available device
 			 */
 			break;
 		}
 	}
 	rcu_read_unlock();
 	return ret;
 }

 /*
  * Careful, this can execute in IRQ contexts as well!
  */
 static void multipath_error (struct mddev *mddev, struct md_rdev *rdev)
 {
 	struct mpconf *conf = mddev->private;
 	char b[BDEVNAME_SIZE];

 	if (conf->raid_disks - mddev->degraded <= 1) {
 		/*
 		 * Uh oh, we can do nothing if this is our last path, but
 		 * first check if this is a queued request for a device
 		 * which has just failed.
 		 */
 		printk(KERN_ALERT
 		       "multipath: only one IO path left and IO error.\n");
 		/* leave it active... it's all we have */
 		return;
 	}
 	/*
 	 * Mark disk as unusable
 	 */
 	if (test_and_clear_bit(In_sync, &rdev->flags)) {
 		unsigned long flags;
 		spin_lock_irqsave(&conf->device_lock, flags);
 		mddev->degraded++;
 		spin_unlock_irqrestore(&conf->device_lock, flags);
 	}
 	set_bit(Faulty, &rdev->flags);
 	set_bit(MD_CHANGE_DEVS, &mddev->flags);
 	printk(KERN_ALERT "multipath: IO failure on %s,"
 	       " disabling IO path.\n"
 	       "multipath: Operation continuing"
 	       " on %d IO paths.\n",
 	       bdevname(rdev->bdev, b),
 	       conf->raid_disks - mddev->degraded);
 }

 static void print_multipath_conf (struct mpconf *conf)
 {
 	int i;
 	struct multipath_info *tmp;

 	printk("MULTIPATH conf printout:\n");
 	if (!conf) {
 		printk("(conf==NULL)\n");
 		return;
 	}
 	printk(" --- wd:%d rd:%d\n", conf->raid_disks - conf->mddev->degraded,
 			 conf->raid_disks);

 	for (i = 0; i < conf->raid_disks; i++) {
 		char b[BDEVNAME_SIZE];
 		tmp = conf->multipaths + i;
 		if (tmp->rdev)
 			printk(" disk%d, o:%d, dev:%s\n",
 				i,!test_bit(Faulty, &tmp->rdev->flags),
 			       bdevname(tmp->rdev->bdev,b));
 	}
 }

 static int multipath_add_disk(struct mddev *mddev, struct md_rdev *rdev)
 {
 	struct mpconf *conf = mddev->private;
 	struct request_queue *q;
 	int err = -EEXIST;
 	int path;
 	struct multipath_info *p;
 	int first = 0;
 	int last = mddev->raid_disks - 1;

 	if (rdev->raid_disk >= 0)
 		first = last = rdev->raid_disk;

 	print_multipath_conf(conf);

 	for (path = first; path <= last; path++)
 		if ((p=conf->multipaths+path)->rdev == NULL) {
 			q = rdev->bdev->bd_disk->queue;
 			disk_stack_limits(mddev->gendisk, rdev->bdev,
 					  rdev->data_offset << 9);

 		/* as we don't honour merge_bvec_fn, we must never risk
 		 * violating it, so limit ->max_segments to one, lying
 		 * within a single page.
 		 * (Note: it is very unlikely that a device with
 		 * merge_bvec_fn will be involved in multipath.)
 		 */
 			if (q->merge_bvec_fn) {
 				blk_queue_max_segments(mddev->queue, 1);
 				blk_queue_segment_boundary(mddev->queue,
 							   PAGE_CACHE_SIZE - 1);
 			}

 			spin_lock_irq(&conf->device_lock);
 			mddev->degraded--;
 			rdev->raid_disk = path;
 			set_bit(In_sync, &rdev->flags);
 			spin_unlock_irq(&conf->device_lock);
 			rcu_assign_pointer(p->rdev, rdev);
 			err = 0;
 			md_integrity_add_rdev(rdev, mddev);
 			break;
 		}

 	print_multipath_conf(conf);

 	return err;
 }

 static int multipath_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
 {
 	struct mpconf *conf = mddev->private;
 	int err = 0;
 	int number = rdev->raid_disk;
 	struct multipath_info *p = conf->multipaths + number;

 	print_multipath_conf(conf);

 	if (rdev == p->rdev) {
 		if (test_bit(In_sync, &rdev->flags) ||
 		    atomic_read(&rdev->nr_pending)) {
 			printk(KERN_ERR "hot-remove-disk, slot %d is identified"
 			       " but is still operational!\n", number);
 			err = -EBUSY;
 			goto abort;
 		}
 		p->rdev = NULL;
 		synchronize_rcu();
 		if (atomic_read(&rdev->nr_pending)) {
 			/* lost the race, try later */
 			err = -EBUSY;
 			p->rdev = rdev;
 			goto abort;
 		}
 		err = md_integrity_register(mddev);
 	}
 abort:

 	print_multipath_conf(conf);
 	return err;
 }

 /*
  * This is a kernel thread which:
  *
  *	1.	Retries failed read operations on working multipaths.
  *	2.	Updates the raid superblock when problems encounter.
  *	3.	Performs writes following reads for array syncronising.
  */

 static void multipathd(struct md_thread *thread)
 {
 	struct mddev *mddev = thread->mddev;
 	struct multipath_bh *mp_bh;
 	struct bio *bio;
 	unsigned long flags;
 	struct mpconf *conf = mddev->private;
 	struct list_head *head = &conf->retry_list;

 	md_check_recovery(mddev);
 	for (;;) {
 		char b[BDEVNAME_SIZE];
 		spin_lock_irqsave(&conf->device_lock, flags);
 		if (list_empty(head))
 			break;
 		mp_bh = list_entry(head->prev, struct multipath_bh, retry_list);
 		list_del(head->prev);
 		spin_unlock_irqrestore(&conf->device_lock, flags);

 		bio = &mp_bh->bio;
 		bio->bi_iter.bi_sector = mp_bh->master_bio->bi_iter.bi_sector;

 		if ((mp_bh->path = multipath_map (conf))<0) {
 			printk(KERN_ALERT "multipath: %s: unrecoverable IO read"
 				" error for block %llu\n",
 				bdevname(bio->bi_bdev,b),
 				(unsigned long long)bio->bi_iter.bi_sector);
 			multipath_end_bh_io(mp_bh, -EIO);
 		} else {
 			printk(KERN_ERR "multipath: %s: redirecting sector %llu"
 				" to another IO path\n",
 				bdevname(bio->bi_bdev,b),
 				(unsigned long long)bio->bi_iter.bi_sector);
 			*bio = *(mp_bh->master_bio);
 			bio->bi_iter.bi_sector +=
 				conf->multipaths[mp_bh->path].rdev->data_offset;
 			bio->bi_bdev = conf->multipaths[mp_bh->path].rdev->bdev;
 			bio->bi_rw |= REQ_FAILFAST_TRANSPORT;
 			bio->bi_end_io = multipath_end_request;
 			bio->bi_private = mp_bh;
 			generic_make_request(bio);
 		}
 	}
 	spin_unlock_irqrestore(&conf->device_lock, flags);
 }

 static sector_t multipath_size(struct mddev *mddev, sector_t sectors, int raid_disks)
 {
 	WARN_ONCE(sectors || raid_disks,
 		  "%s does not support generic reshape\n", __func__);

 	return mddev->dev_sectors;
 }

 static int multipath_run (struct mddev *mddev)
 {
 	struct mpconf *conf;
 	int disk_idx;
 	struct multipath_info *disk;
 	struct md_rdev *rdev;
 	int working_disks;

 	if (md_check_no_bitmap(mddev))
 		return -EINVAL;

 	if (mddev->level != LEVEL_MULTIPATH) {
 		printk("multipath: %s: raid level not set to multipath IO (%d)\n",
 		       mdname(mddev), mddev->level);
 		goto out;
 	}
 	/*
 	 * copy the already verified devices into our private MULTIPATH
 	 * bookkeeping area. [whatever we allocate in multipath_run(),
 	 * should be freed in multipath_free()]
 	 */

 	conf = kzalloc(sizeof(struct mpconf), GFP_KERNEL);
 	mddev->private = conf;
 	if (!conf) {
 		printk(KERN_ERR
 			"multipath: couldn't allocate memory for %s\n",
 			mdname(mddev));
 		goto out;
 	}

 	conf->multipaths = kzalloc(sizeof(struct multipath_info)*mddev->raid_disks,
 				   GFP_KERNEL);
 	if (!conf->multipaths) {
 		printk(KERN_ERR
 			"multipath: couldn't allocate memory for %s\n",
 			mdname(mddev));
 		goto out_free_conf;
 	}

 	working_disks = 0;
 	rdev_for_each(rdev, mddev) {
 		disk_idx = rdev->raid_disk;
 		if (disk_idx < 0 ||
 		    disk_idx >= mddev->raid_disks)
 			continue;

 		disk = conf->multipaths + disk_idx;
 		disk->rdev = rdev;
 		disk_stack_limits(mddev->gendisk, rdev->bdev,
 				  rdev->data_offset << 9);

 		/* as we don't honour merge_bvec_fn, we must never risk
 		 * violating it, not that we ever expect a device with
 		 * a merge_bvec_fn to be involved in multipath */
 		if (rdev->bdev->bd_disk->queue->merge_bvec_fn) {
 			blk_queue_max_segments(mddev->queue, 1);
 			blk_queue_segment_boundary(mddev->queue,
 						   PAGE_CACHE_SIZE - 1);
 		}

 		if (!test_bit(Faulty, &rdev->flags))
 			working_disks++;
 	}

 	conf->raid_disks = mddev->raid_disks;
 	conf->mddev = mddev;
 	spin_lock_init(&conf->device_lock);
 	INIT_LIST_HEAD(&conf->retry_list);

 	if (!working_disks) {
 		printk(KERN_ERR "multipath: no operational IO paths for %s\n",
 			mdname(mddev));
 		goto out_free_conf;
 	}
 	mddev->degraded = conf->raid_disks - working_disks;

 	conf->pool = mempool_create_kmalloc_pool(NR_RESERVED_BUFS,
 						 sizeof(struct multipath_bh));
 	if (conf->pool == NULL) {
 		printk(KERN_ERR
 			"multipath: couldn't allocate memory for %s\n",
 			mdname(mddev));
 		goto out_free_conf;
 	}

 	{
 		mddev->thread = md_register_thread(multipathd, mddev,
 						   "multipath");
 		if (!mddev->thread) {
 			printk(KERN_ERR "multipath: couldn't allocate thread"
 				" for %s\n", mdname(mddev));
 			goto out_free_conf;
 		}
 	}

 	printk(KERN_INFO
 		"multipath: array %s active with %d out of %d IO paths\n",
 		mdname(mddev), conf->raid_disks - mddev->degraded,
 	       mddev->raid_disks);
 	/*
 	 * Ok, everything is just fine now
 	 */
 	md_set_array_sectors(mddev, multipath_size(mddev, 0, 0));

 	if (md_integrity_register(mddev))
 		goto out_free_conf;

 	return 0;

 out_free_conf:
 	if (conf->pool)
 		mempool_destroy(conf->pool);
 	kfree(conf->multipaths);
 	kfree(conf);
 	mddev->private = NULL;
 out:
 	return -EIO;
 }

 static void multipath_free(struct mddev *mddev, void *priv)
 {
 	struct mpconf *conf = priv;

 	mempool_destroy(conf->pool);
 	kfree(conf->multipaths);
 	kfree(conf);
 }

 static struct md_personality multipath_personality =
 {
 	.name		= "multipath",
 	.level		= LEVEL_MULTIPATH,
 	.owner		= THIS_MODULE,
 	.make_request	= multipath_make_request,
 	.run		= multipath_run,
 	.free		= multipath_free,
 	.status		= multipath_status,
 	.error_handler	= multipath_error,
 	.hot_add_disk	= multipath_add_disk,
 	.hot_remove_disk= multipath_remove_disk,
 	.size		= multipath_size,
 	.congested	= multipath_congested,
 };

 static int __init multipath_init (void)
 {
 	return register_md_personality (&multipath_personality);
 }

 static void __exit multipath_exit (void)
 {
 	unregister_md_personality (&multipath_personality);
 }

 module_init(multipath_init);
 module_exit(multipath_exit);
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("simple multi-path personality for MD");
 MODULE_ALIAS("md-personality-7"); /* MULTIPATH */
 MODULE_ALIAS("md-multipath");
 MODULE_ALIAS("md-level--4");
	/*
	* multipath.c : Multiple Devices driver for Linux
	*
	* Copyright (C) 1999, 2000, 2001 Ingo Molnar, Red Hat
	*
	* Copyright (C) 1996, 1997, 1998 Ingo Molnar, Miguel de Icaza, Gadi Oxman
	*
	* MULTIPATH management functions.
	*
	* derived from raid1.c.
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2, or (at your option)
	* any later version.
	*
	* You should have received a copy of the GNU General Public License
	* (for example /usr/src/linux/COPYING); if not, write to the Free
	* Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
	*/

	#include <linux/blkdev.h>
	#include <linux/module.h>
	#include <linux/raid/md_u.h>
	#include <linux/seq_file.h>
	#include <linux/slab.h>
	#include "md.h"
	#include "multipath.h"

	#define MAX_WORK_PER_DISK 128

	#define NR_RESERVED_BUFS 32

	static int multipath_map (struct mpconf *conf)
	{
	int i, disks = conf->raid_disks;

	/*
	* Later we do read balancing on the read side
	* now we use the first available disk.
	*/

	rcu_read_lock();
	for (i = 0; i < disks; i++) {
	struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);
	if (rdev && test_bit(In_sync, &rdev->flags)) {
	atomic_inc(&rdev->nr_pending);
	rcu_read_unlock();
	return i;
	}
	}
	rcu_read_unlock();

	printk(KERN_ERR "multipath_map(): no more operational IO paths?\n");
	return (-1);
	}

	static void multipath_reschedule_retry (struct multipath_bh *mp_bh)
	{
	unsigned long flags;
	struct mddev *mddev = mp_bh->mddev;
	struct mpconf *conf = mddev->private;

	spin_lock_irqsave(&conf->device_lock, flags);
	list_add(&mp_bh->retry_list, &conf->retry_list);
	spin_unlock_irqrestore(&conf->device_lock, flags);
	md_wakeup_thread(mddev->thread);
	}

	/*
	* multipath_end_bh_io() is called when we have finished servicing a multipathed
	* operation and are ready to return a success/failure code to the buffer
	* cache layer.
	*/
	static void multipath_end_bh_io (struct multipath_bh *mp_bh, int err)
	{
	struct bio *bio = mp_bh->master_bio;
	struct mpconf *conf = mp_bh->mddev->private;

	bio_endio(bio, err);
	mempool_free(mp_bh, conf->pool);
	}

	static void multipath_end_request(struct bio *bio, int error)
	{
	int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
	struct multipath_bh *mp_bh = bio->bi_private;
	struct mpconf *conf = mp_bh->mddev->private;
	struct md_rdev *rdev = conf->multipaths[mp_bh->path].rdev;

	if (uptodate)
	multipath_end_bh_io(mp_bh, 0);
	else if (!(bio->bi_rw & REQ_RAHEAD)) {
	/*
	* oops, IO error:
	*/
	char b[BDEVNAME_SIZE];
	md_error (mp_bh->mddev, rdev);
	printk(KERN_ERR "multipath: %s: rescheduling sector %llu\n",
	bdevname(rdev->bdev,b),
	(unsigned long long)bio->bi_iter.bi_sector);
	multipath_reschedule_retry(mp_bh);
	} else
	multipath_end_bh_io(mp_bh, error);
	rdev_dec_pending(rdev, conf->mddev);
	}

	static void multipath_make_request(struct mddev mddev, struct bio bio)
	{
	struct mpconf *conf = mddev->private;
	struct multipath_bh * mp_bh;
	struct multipath_info *multipath;

	if (unlikely(bio->bi_rw & REQ_FLUSH)) {
	md_flush_request(mddev, bio);
	return;
	}

	mp_bh = mempool_alloc(conf->pool, GFP_NOIO);

	mp_bh->master_bio = bio;
	mp_bh->mddev = mddev;

	mp_bh->path = multipath_map(conf);
	if (mp_bh->path < 0) {
	bio_endio(bio, -EIO);
	mempool_free(mp_bh, conf->pool);
	return;
	}
	multipath = conf->multipaths + mp_bh->path;

	mp_bh->bio = *bio;
	mp_bh->bio.bi_iter.bi_sector += multipath->rdev->data_offset;
	mp_bh->bio.bi_bdev = multipath->rdev->bdev;
	mp_bh->bio.bi_rw \|= REQ_FAILFAST_TRANSPORT;
	mp_bh->bio.bi_end_io = multipath_end_request;
	mp_bh->bio.bi_private = mp_bh;
	generic_make_request(&mp_bh->bio);
	return;
	}

	static void multipath_status (struct seq_file seq, struct mddev mddev)
	{
	struct mpconf *conf = mddev->private;
	int i;

	seq_printf (seq, " [%d/%d] [", conf->raid_disks,
	conf->raid_disks - mddev->degraded);
	for (i = 0; i < conf->raid_disks; i++)
	seq_printf (seq, "%s",
	conf->multipaths[i].rdev &&
	test_bit(In_sync, &conf->multipaths[i].rdev->flags) ? "U" : "_");
	seq_printf (seq, "]");
	}

	static int multipath_congested(struct mddev *mddev, int bits)
	{
	struct mpconf *conf = mddev->private;
	int i, ret = 0;

	rcu_read_lock();
	for (i = 0; i < mddev->raid_disks ; i++) {
	struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);
	if (rdev && !test_bit(Faulty, &rdev->flags)) {
	struct request_queue *q = bdev_get_queue(rdev->bdev);

	ret \|= bdi_congested(&q->backing_dev_info, bits);
	/* Just like multipath_map, we just check the
	* first available device
	*/
	break;
	}
	}
	rcu_read_unlock();
	return ret;
	}

	/*
	* Careful, this can execute in IRQ contexts as well!
	*/
	static void multipath_error (struct mddev mddev, struct md_rdev rdev)
	{
	struct mpconf *conf = mddev->private;
	char b[BDEVNAME_SIZE];

	if (conf->raid_disks - mddev->degraded <= 1) {
	/*
	* Uh oh, we can do nothing if this is our last path, but
	* first check if this is a queued request for a device
	* which has just failed.
	*/
	printk(KERN_ALERT
	"multipath: only one IO path left and IO error.\n");
	/* leave it active... it's all we have */
	return;
	}
	/*
	* Mark disk as unusable
	*/
	if (test_and_clear_bit(In_sync, &rdev->flags)) {
	unsigned long flags;
	spin_lock_irqsave(&conf->device_lock, flags);
	mddev->degraded++;
	spin_unlock_irqrestore(&conf->device_lock, flags);
	}
	set_bit(Faulty, &rdev->flags);
	set_bit(MD_CHANGE_DEVS, &mddev->flags);
	printk(KERN_ALERT "multipath: IO failure on %s,"
	" disabling IO path.\n"
	"multipath: Operation continuing"
	" on %d IO paths.\n",
	bdevname(rdev->bdev, b),
	conf->raid_disks - mddev->degraded);
	}

	static void print_multipath_conf (struct mpconf *conf)
	{
	int i;
	struct multipath_info *tmp;

	printk("MULTIPATH conf printout:\n");
	if (!conf) {
	printk("(conf==NULL)\n");
	return;
	}
	printk(" --- wd:%d rd:%d\n", conf->raid_disks - conf->mddev->degraded,
	conf->raid_disks);

	for (i = 0; i < conf->raid_disks; i++) {
	char b[BDEVNAME_SIZE];
	tmp = conf->multipaths + i;
	if (tmp->rdev)
	printk(" disk%d, o:%d, dev:%s\n",
	i,!test_bit(Faulty, &tmp->rdev->flags),
	bdevname(tmp->rdev->bdev,b));
	}
	}

	static int multipath_add_disk(struct mddev mddev, struct md_rdev rdev)
	{
	struct mpconf *conf = mddev->private;
	struct request_queue *q;
	int err = -EEXIST;
	int path;
	struct multipath_info *p;
	int first = 0;
	int last = mddev->raid_disks - 1;

	if (rdev->raid_disk >= 0)
	first = last = rdev->raid_disk;

	print_multipath_conf(conf);

	for (path = first; path <= last; path++)
	if ((p=conf->multipaths+path)->rdev == NULL) {
	q = rdev->bdev->bd_disk->queue;
	disk_stack_limits(mddev->gendisk, rdev->bdev,
	rdev->data_offset << 9);

	/* as we don't honour merge_bvec_fn, we must never risk
	* violating it, so limit ->max_segments to one, lying
	* within a single page.
	* (Note: it is very unlikely that a device with
	* merge_bvec_fn will be involved in multipath.)
	*/
	if (q->merge_bvec_fn) {
	blk_queue_max_segments(mddev->queue, 1);
	blk_queue_segment_boundary(mddev->queue,
	PAGE_CACHE_SIZE - 1);
	}

	spin_lock_irq(&conf->device_lock);
	mddev->degraded--;
	rdev->raid_disk = path;
	set_bit(In_sync, &rdev->flags);
	spin_unlock_irq(&conf->device_lock);
	rcu_assign_pointer(p->rdev, rdev);
	err = 0;
	md_integrity_add_rdev(rdev, mddev);
	break;
	}

	print_multipath_conf(conf);

	return err;
	}

	static int multipath_remove_disk(struct mddev mddev, struct md_rdev rdev)
	{
	struct mpconf *conf = mddev->private;
	int err = 0;
	int number = rdev->raid_disk;
	struct multipath_info *p = conf->multipaths + number;

	print_multipath_conf(conf);

	if (rdev == p->rdev) {
	if (test_bit(In_sync, &rdev->flags) \|\|
	atomic_read(&rdev->nr_pending)) {
	printk(KERN_ERR "hot-remove-disk, slot %d is identified"
	" but is still operational!\n", number);
	err = -EBUSY;
	goto abort;
	}
	p->rdev = NULL;
	synchronize_rcu();
	if (atomic_read(&rdev->nr_pending)) {
	/* lost the race, try later */
	err = -EBUSY;
	p->rdev = rdev;
	goto abort;
	}
	err = md_integrity_register(mddev);
	}
	abort:

	print_multipath_conf(conf);
	return err;
	}

	/*
	* This is a kernel thread which:
	*
	* 1. Retries failed read operations on working multipaths.
	* 2. Updates the raid superblock when problems encounter.
	* 3. Performs writes following reads for array syncronising.
	*/

	static void multipathd(struct md_thread *thread)
	{
	struct mddev *mddev = thread->mddev;
	struct multipath_bh *mp_bh;
	struct bio *bio;
	unsigned long flags;
	struct mpconf *conf = mddev->private;
	struct list_head *head = &conf->retry_list;

	md_check_recovery(mddev);
	for (;;) {
	char b[BDEVNAME_SIZE];
	spin_lock_irqsave(&conf->device_lock, flags);
	if (list_empty(head))
	break;
	mp_bh = list_entry(head->prev, struct multipath_bh, retry_list);
	list_del(head->prev);
	spin_unlock_irqrestore(&conf->device_lock, flags);

	bio = &mp_bh->bio;
	bio->bi_iter.bi_sector = mp_bh->master_bio->bi_iter.bi_sector;

	if ((mp_bh->path = multipath_map (conf))<0) {
	printk(KERN_ALERT "multipath: %s: unrecoverable IO read"
	" error for block %llu\n",
	bdevname(bio->bi_bdev,b),
	(unsigned long long)bio->bi_iter.bi_sector);
	multipath_end_bh_io(mp_bh, -EIO);
	} else {
	printk(KERN_ERR "multipath: %s: redirecting sector %llu"
	" to another IO path\n",
	bdevname(bio->bi_bdev,b),
	(unsigned long long)bio->bi_iter.bi_sector);
	bio = (mp_bh->master_bio);
	bio->bi_iter.bi_sector +=
	conf->multipaths[mp_bh->path].rdev->data_offset;
	bio->bi_bdev = conf->multipaths[mp_bh->path].rdev->bdev;
	bio->bi_rw \|= REQ_FAILFAST_TRANSPORT;
	bio->bi_end_io = multipath_end_request;
	bio->bi_private = mp_bh;
	generic_make_request(bio);
	}
	}
	spin_unlock_irqrestore(&conf->device_lock, flags);
	}

	static sector_t multipath_size(struct mddev *mddev, sector_t sectors, int raid_disks)
	{
	WARN_ONCE(sectors \|\| raid_disks,
	"%s does not support generic reshape\n", __func__);

	return mddev->dev_sectors;
	}

	static int multipath_run (struct mddev *mddev)
	{
	struct mpconf *conf;
	int disk_idx;
	struct multipath_info *disk;
	struct md_rdev *rdev;
	int working_disks;

	if (md_check_no_bitmap(mddev))
	return -EINVAL;

	if (mddev->level != LEVEL_MULTIPATH) {
	printk("multipath: %s: raid level not set to multipath IO (%d)\n",
	mdname(mddev), mddev->level);
	goto out;
	}
	/*
	* copy the already verified devices into our private MULTIPATH
	* bookkeeping area. [whatever we allocate in multipath_run(),
	* should be freed in multipath_free()]
	*/

	conf = kzalloc(sizeof(struct mpconf), GFP_KERNEL);
	mddev->private = conf;
	if (!conf) {
	printk(KERN_ERR
	"multipath: couldn't allocate memory for %s\n",
	mdname(mddev));
	goto out;
	}

	conf->multipaths = kzalloc(sizeof(struct multipath_info)*mddev->raid_disks,
	GFP_KERNEL);
	if (!conf->multipaths) {
	printk(KERN_ERR
	"multipath: couldn't allocate memory for %s\n",
	mdname(mddev));
	goto out_free_conf;
	}

	working_disks = 0;
	rdev_for_each(rdev, mddev) {
	disk_idx = rdev->raid_disk;
	if (disk_idx < 0 \|\|
	disk_idx >= mddev->raid_disks)
	continue;

	disk = conf->multipaths + disk_idx;
	disk->rdev = rdev;
	disk_stack_limits(mddev->gendisk, rdev->bdev,
	rdev->data_offset << 9);

	/* as we don't honour merge_bvec_fn, we must never risk
	* violating it, not that we ever expect a device with
	* a merge_bvec_fn to be involved in multipath */
	if (rdev->bdev->bd_disk->queue->merge_bvec_fn) {
	blk_queue_max_segments(mddev->queue, 1);
	blk_queue_segment_boundary(mddev->queue,
	PAGE_CACHE_SIZE - 1);
	}

	if (!test_bit(Faulty, &rdev->flags))
	working_disks++;
	}

	conf->raid_disks = mddev->raid_disks;
	conf->mddev = mddev;
	spin_lock_init(&conf->device_lock);
	INIT_LIST_HEAD(&conf->retry_list);

	if (!working_disks) {
	printk(KERN_ERR "multipath: no operational IO paths for %s\n",
	mdname(mddev));
	goto out_free_conf;
	}
	mddev->degraded = conf->raid_disks - working_disks;

	conf->pool = mempool_create_kmalloc_pool(NR_RESERVED_BUFS,
	sizeof(struct multipath_bh));
	if (conf->pool == NULL) {
	printk(KERN_ERR
	"multipath: couldn't allocate memory for %s\n",
	mdname(mddev));
	goto out_free_conf;
	}

	{
	mddev->thread = md_register_thread(multipathd, mddev,
	"multipath");
	if (!mddev->thread) {
	printk(KERN_ERR "multipath: couldn't allocate thread"
	" for %s\n", mdname(mddev));
	goto out_free_conf;
	}
	}

	printk(KERN_INFO
	"multipath: array %s active with %d out of %d IO paths\n",
	mdname(mddev), conf->raid_disks - mddev->degraded,
	mddev->raid_disks);
	/*
	* Ok, everything is just fine now
	*/
	md_set_array_sectors(mddev, multipath_size(mddev, 0, 0));

	if (md_integrity_register(mddev))
	goto out_free_conf;

	return 0;

	out_free_conf:
	if (conf->pool)
	mempool_destroy(conf->pool);
	kfree(conf->multipaths);
	kfree(conf);
	mddev->private = NULL;
	out:
	return -EIO;
	}

	static void multipath_free(struct mddev mddev, void priv)
	{
	struct mpconf *conf = priv;

	mempool_destroy(conf->pool);
	kfree(conf->multipaths);
	kfree(conf);
	}

	static struct md_personality multipath_personality =
	{
	.name = "multipath",
	.level = LEVEL_MULTIPATH,
	.owner = THIS_MODULE,
	.make_request = multipath_make_request,
	.run = multipath_run,
	.free = multipath_free,
	.status = multipath_status,
	.error_handler = multipath_error,
	.hot_add_disk = multipath_add_disk,
	.hot_remove_disk= multipath_remove_disk,
	.size = multipath_size,
	.congested = multipath_congested,
	};

	static int __init multipath_init (void)
	{
	return register_md_personality (&multipath_personality);
	}

	static void __exit multipath_exit (void)
	{
	unregister_md_personality (&multipath_personality);
	}

	module_init(multipath_init);
	module_exit(multipath_exit);
	MODULE_LICENSE("GPL");
	MODULE_DESCRIPTION("simple multi-path personality for MD");
	MODULE_ALIAS("md-personality-7"); /* MULTIPATH */
	MODULE_ALIAS("md-multipath");
	MODULE_ALIAS("md-level--4");