text: /*
   * 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/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 (multipath_conf_t *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++) {
  		mdk_rdev_t *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;
  	mddev_t *mddev = mp_bh->mddev;
  	multipath_conf_t *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;
  	multipath_conf_t *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;
  	multipath_conf_t *conf = mp_bh->mddev->private;
  	mdk_rdev_t *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_sector);
  		multipath_reschedule_retry(mp_bh);
  	} else
  		multipath_end_bh_io(mp_bh, error);
  	rdev_dec_pending(rdev, conf->mddev);
  }
  
  static int multipath_make_request(mddev_t *mddev, struct bio * bio)
  {
  	multipath_conf_t *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 0;
  	}
  
  	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 0;
  	}
  	multipath = conf->multipaths + mp_bh->path;
  
  	mp_bh->bio = *bio;
  	mp_bh->bio.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 0;
  }
  
  static void multipath_status (struct seq_file *seq, mddev_t *mddev)
  {
  	multipath_conf_t *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(void *data, int bits)
  {
  	mddev_t *mddev = data;
  	multipath_conf_t *conf = mddev->private;
  	int i, ret = 0;
  
  	if (mddev_congested(mddev, bits))
  		return 1;
  
  	rcu_read_lock();
  	for (i = 0; i < mddev->raid_disks ; i++) {
  		mdk_rdev_t *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 (mddev_t *mddev, mdk_rdev_t *rdev)
  {
  	multipath_conf_t *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 (multipath_conf_t *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(mddev_t *mddev, mdk_rdev_t *rdev)
  {
  	multipath_conf_t *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(mddev_t *mddev, int number)
  {
  	multipath_conf_t *conf = mddev->private;
  	int err = 0;
  	mdk_rdev_t *rdev;
  	struct multipath_info *p = conf->multipaths + number;
  
  	print_multipath_conf(conf);
  
  	rdev = p->rdev;
  	if (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 (mddev_t *mddev)
  {
  	struct multipath_bh *mp_bh;
  	struct bio *bio;
  	unsigned long flags;
  	multipath_conf_t *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_sector = mp_bh->master_bio->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_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_sector);
  			*bio = *(mp_bh->master_bio);
  			bio->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(mddev_t *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 (mddev_t *mddev)
  {
  	multipath_conf_t *conf;
  	int disk_idx;
  	struct multipath_info *disk;
  	mdk_rdev_t *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_stop()]
  	 */
  
  	conf = kzalloc(sizeof(multipath_conf_t), 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;
  	list_for_each_entry(rdev, &mddev->disks, same_set) {
  		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, NULL);
  		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));
  
  	mddev->queue->backing_dev_info.congested_fn = multipath_congested;
  	mddev->queue->backing_dev_info.congested_data = mddev;
  
  	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 int multipath_stop (mddev_t *mddev)
  {
  	multipath_conf_t *conf = mddev->private;
  
  	md_unregister_thread(mddev->thread);
  	mddev->thread = NULL;
  	blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
  	mempool_destroy(conf->pool);
  	kfree(conf->multipaths);
  	kfree(conf);
  	mddev->private = NULL;
  	return 0;
  }
  
  static struct mdk_personality multipath_personality =
  {
  	.name		= "multipath",
  	.level		= LEVEL_MULTIPATH,
  	.owner		= THIS_MODULE,
  	.make_request	= multipath_make_request,
  	.run		= multipath_run,
  	.stop		= multipath_stop,
  	.status		= multipath_status,
  	.error_handler	= multipath_error,
  	.hot_add_disk	= multipath_add_disk,
  	.hot_remove_disk= multipath_remove_disk,
  	.size		= multipath_size,
  };
  
  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");
  