// 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?\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, 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\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, 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);
	submit_bio_noacct(&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.\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_SB_CHANGE_DEVS, &mddev->sb_flags);
	pr_err("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;

	pr_debug("MULTIPATH conf printout:\n");
	if (!conf) {
		pr_debug("(conf==NULL)\n");
		return;
	}
	pr_debug(" --- 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)
			pr_debug(" 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;
	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!\n", 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\n",
			       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\n",
			       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;
			submit_bio_noacct(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;
	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)\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)
		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\n",
			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\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:
	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");