// SPDX-License-Identifier: GPL-2.0-or-later

  /*
   * 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.

   */

  #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 "md-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) &&
  		    !test_bit(Faulty, &rdev->flags)) {

  			atomic_inc(&rdev->nr_pending);
  			rcu_read_unlock();
  			return i;
  		}
  	}
  	rcu_read_unlock();

  	pr_crit_ratelimited("multipath_map(): no more operational IO paths?
  ");

  	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, blk_status_t status)

  {
  	struct bio *bio = mp_bh->master_bio;

  	struct mpconf *conf = mp_bh->mddev->private;

  	bio->bi_status = status;

  	bio_endio(bio);

  	mempool_free(mp_bh, &conf->pool);

  }

  static void multipath_end_request(struct bio *bio)

  {

  	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 (!bio->bi_status)

  		multipath_end_bh_io(mp_bh, 0);

  	else if (!(bio->bi_opf & REQ_RAHEAD)) {

  		/*
  		 * oops, IO error:
  		 */
  		char b[BDEVNAME_SIZE];
  		md_error (mp_bh->mddev, rdev);

  		pr_info("multipath: %s: rescheduling sector %llu
  ",
  			bdevname(rdev->bdev,b),
  			(unsigned long long)bio->bi_iter.bi_sector);

  		multipath_reschedule_retry(mp_bh);
  	} else

  		multipath_end_bh_io(mp_bh, bio->bi_status);

  	rdev_dec_pending(rdev, conf->mddev);

  }

  static bool 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_opf & REQ_PREFLUSH)
  	    && md_flush_request(mddev, bio))

  		return true;

  	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_io_error(bio);

  		mempool_free(mp_bh, &conf->pool);

  		return true;

  	}
  	multipath = conf->multipaths + mp_bh->path;

  	bio_init(&mp_bh->bio, NULL, 0);

  	__bio_clone_fast(&mp_bh->bio, bio);

  	mp_bh->bio.bi_iter.bi_sector += multipath->rdev->data_offset;

  	bio_set_dev(&mp_bh->bio, multipath->rdev->bdev);

  	mp_bh->bio.bi_opf |= REQ_FAILFAST_TRANSPORT;

  	mp_bh->bio.bi_end_io = multipath_end_request;
  	mp_bh->bio.bi_private = mp_bh;

  	mddev_check_writesame(mddev, &mp_bh->bio);

  	mddev_check_write_zeroes(mddev, &mp_bh->bio);

  	generic_make_request(&mp_bh->bio);

  	return true;

  }

  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);

  	rcu_read_lock();
  	for (i = 0; i < conf->raid_disks; i++) {
  		struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);
  		seq_printf (seq, "%s", rdev && test_bit(In_sync, &rdev->flags) ? "U" : "_");
  	}
  	rcu_read_unlock();

  	seq_putc(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.
  		 */

  		pr_warn("multipath: only one IO path left and IO error.
  ");

  		/* 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_SB_CHANGE_DEVS, &mddev->sb_flags);

  	pr_err("multipath: IO failure on %s, disabling IO path.
  "
  	       "multipath: Operation continuing on %d IO paths.
  ",

  	       bdevname(rdev->bdev, b),
  	       conf->raid_disks - mddev->degraded);

  }

  static void print_multipath_conf (struct mpconf *conf)

  {
  	int i;
  	struct multipath_info *tmp;

  	pr_debug("MULTIPATH conf printout:
  ");

  	if (!conf) {

  		pr_debug("(conf==NULL)
  ");

  		return;
  	}

  	pr_debug(" --- wd:%d rd:%d
  ", 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)

  			pr_debug(" disk%d, o:%d, dev:%s
  ",
  				 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;

  	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) {

  			disk_stack_limits(mddev->gendisk, rdev->bdev,
  					  rdev->data_offset << 9);

  			err = md_integrity_add_rdev(rdev, mddev);
  			if (err)
  				break;

  			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;
  			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)) {

  			pr_warn("hot-remove-disk, slot %d is identified but is still operational!
  ", number);

  			err = -EBUSY;
  			goto abort;
  		}
  		p->rdev = NULL;

  		if (!test_bit(RemoveSynchronized, &rdev->flags)) {
  			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) {

  			pr_err("multipath: %s: unrecoverable IO read error for block %llu
  ",

  			       bio_devname(bio, b),

  			       (unsigned long long)bio->bi_iter.bi_sector);

  			multipath_end_bh_io(mp_bh, BLK_STS_IOERR);

  		} else {

  			pr_err("multipath: %s: redirecting sector %llu to another IO path
  ",

  			       bio_devname(bio, 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_set_dev(bio, conf->multipaths[mp_bh->path].rdev->bdev);

  			bio->bi_opf |= 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
  ", __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;

  	int ret;

  	if (md_check_no_bitmap(mddev))
  		return -EINVAL;

  	if (mddev->level != LEVEL_MULTIPATH) {

  		pr_warn("multipath: %s: raid level not set to multipath IO (%d)
  ",
  			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)

  		goto out;

  	conf->multipaths = kcalloc(mddev->raid_disks,
  				   sizeof(struct multipath_info),

  				   GFP_KERNEL);

  	if (!conf->multipaths)

  		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);

  		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) {

  		pr_warn("multipath: no operational IO paths for %s
  ",

  			mdname(mddev));
  		goto out_free_conf;
  	}

  	mddev->degraded = conf->raid_disks - working_disks;

  	ret = mempool_init_kmalloc_pool(&conf->pool, NR_RESERVED_BUFS,
  					sizeof(struct multipath_bh));
  	if (ret)

  		goto out_free_conf;

  	mddev->thread = md_register_thread(multipathd, mddev,
  					   "multipath");
  	if (!mddev->thread)
  		goto out_free_conf;

  	pr_info("multipath: array %s active with %d out of %d IO paths
  ",

  		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:

  	mempool_exit(&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_exit(&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");