// SPDX-License-Identifier: GPL-2.0-only

  /*
   * Swap block device support for MTDs
   * Turns an MTD device into a swap device with block wear leveling
   *
   * Copyright © 2007,2011 Nokia Corporation. All rights reserved.
   *
   * Authors: Jarkko Lavinen <jarkko.lavinen@nokia.com>
   *
   * Based on Richard Purdie's earlier implementation in 2007. Background
   * support and lock-less operation written by Adrian Hunter.

   */
  
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/mtd/mtd.h>
  #include <linux/mtd/blktrans.h>
  #include <linux/rbtree.h>
  #include <linux/sched.h>
  #include <linux/slab.h>
  #include <linux/vmalloc.h>
  #include <linux/genhd.h>
  #include <linux/swap.h>
  #include <linux/debugfs.h>
  #include <linux/seq_file.h>
  #include <linux/device.h>
  #include <linux/math64.h>
  
  #define MTDSWAP_PREFIX "mtdswap"
  
  /*
   * The number of free eraseblocks when GC should stop
   */
  #define CLEAN_BLOCK_THRESHOLD	20
  
  /*
   * Number of free eraseblocks below which GC can also collect low frag
   * blocks.
   */

  #define LOW_FRAG_GC_THRESHOLD	5

  
  /*
   * Wear level cost amortization. We want to do wear leveling on the background
   * without disturbing gc too much. This is made by defining max GC frequency.
   * Frequency value 6 means 1/6 of the GC passes will pick an erase block based
   * on the biggest wear difference rather than the biggest dirtiness.
   *
   * The lower freq2 should be chosen so that it makes sure the maximum erase
   * difference will decrease even if a malicious application is deliberately
   * trying to make erase differences large.
   */
  #define MAX_ERASE_DIFF		4000
  #define COLLECT_NONDIRTY_BASE	MAX_ERASE_DIFF
  #define COLLECT_NONDIRTY_FREQ1	6
  #define COLLECT_NONDIRTY_FREQ2	4
  
  #define PAGE_UNDEF		UINT_MAX
  #define BLOCK_UNDEF		UINT_MAX
  #define BLOCK_ERROR		(UINT_MAX - 1)
  #define BLOCK_MAX		(UINT_MAX - 2)
  
  #define EBLOCK_BAD		(1 << 0)
  #define EBLOCK_NOMAGIC		(1 << 1)
  #define EBLOCK_BITFLIP		(1 << 2)
  #define EBLOCK_FAILED		(1 << 3)
  #define EBLOCK_READERR		(1 << 4)
  #define EBLOCK_IDX_SHIFT	5
  
  struct swap_eb {
  	struct rb_node rb;
  	struct rb_root *root;
  
  	unsigned int flags;
  	unsigned int active_count;
  	unsigned int erase_count;

  	unsigned int pad;		/* speeds up pointer decrement */

  };
  
  #define MTDSWAP_ECNT_MIN(rbroot) (rb_entry(rb_first(rbroot), struct swap_eb, \
  				rb)->erase_count)
  #define MTDSWAP_ECNT_MAX(rbroot) (rb_entry(rb_last(rbroot), struct swap_eb, \
  				rb)->erase_count)
  
  struct mtdswap_tree {
  	struct rb_root root;
  	unsigned int count;
  };
  
  enum {
  	MTDSWAP_CLEAN,
  	MTDSWAP_USED,
  	MTDSWAP_LOWFRAG,
  	MTDSWAP_HIFRAG,
  	MTDSWAP_DIRTY,
  	MTDSWAP_BITFLIP,
  	MTDSWAP_FAILING,
  	MTDSWAP_TREE_CNT,
  };
  
  struct mtdswap_dev {
  	struct mtd_blktrans_dev *mbd_dev;
  	struct mtd_info *mtd;
  	struct device *dev;
  
  	unsigned int *page_data;
  	unsigned int *revmap;
  
  	unsigned int eblks;
  	unsigned int spare_eblks;
  	unsigned int pages_per_eblk;
  	unsigned int max_erase_count;
  	struct swap_eb *eb_data;
  
  	struct mtdswap_tree trees[MTDSWAP_TREE_CNT];
  
  	unsigned long long sect_read_count;
  	unsigned long long sect_write_count;
  	unsigned long long mtd_write_count;
  	unsigned long long mtd_read_count;
  	unsigned long long discard_count;
  	unsigned long long discard_page_count;
  
  	unsigned int curr_write_pos;
  	struct swap_eb *curr_write;
  
  	char *page_buf;
  	char *oob_buf;

  };
  
  struct mtdswap_oobdata {
  	__le16 magic;
  	__le32 count;

  } __packed;

  
  #define MTDSWAP_MAGIC_CLEAN	0x2095
  #define MTDSWAP_MAGIC_DIRTY	(MTDSWAP_MAGIC_CLEAN + 1)
  #define MTDSWAP_TYPE_CLEAN	0
  #define MTDSWAP_TYPE_DIRTY	1
  #define MTDSWAP_OOBSIZE		sizeof(struct mtdswap_oobdata)
  
  #define MTDSWAP_ERASE_RETRIES	3 /* Before marking erase block bad */
  #define MTDSWAP_IO_RETRIES	3

  enum {
  	MTDSWAP_SCANNED_CLEAN,
  	MTDSWAP_SCANNED_DIRTY,
  	MTDSWAP_SCANNED_BITFLIP,
  	MTDSWAP_SCANNED_BAD,
  };
  
  /*
   * In the worst case mtdswap_writesect() has allocated the last clean
   * page from the current block and is then pre-empted by the GC
   * thread. The thread can consume a full erase block when moving a
   * block.
   */
  #define MIN_SPARE_EBLOCKS	2
  #define MIN_ERASE_BLOCKS	(MIN_SPARE_EBLOCKS + 1)
  
  #define TREE_ROOT(d, name) (&d->trees[MTDSWAP_ ## name].root)
  #define TREE_EMPTY(d, name) (TREE_ROOT(d, name)->rb_node == NULL)
  #define TREE_NONEMPTY(d, name) (!TREE_EMPTY(d, name))
  #define TREE_COUNT(d, name) (d->trees[MTDSWAP_ ## name].count)
  
  #define MTDSWAP_MBD_TO_MTDSWAP(dev) ((struct mtdswap_dev *)dev->priv)
  
  static char partitions[128] = "";
  module_param_string(partitions, partitions, sizeof(partitions), 0444);
  MODULE_PARM_DESC(partitions, "MTD partition numbers to use as swap "
  		"partitions=\"1,3,5\"");
  
  static unsigned int spare_eblocks = 10;
  module_param(spare_eblocks, uint, 0444);
  MODULE_PARM_DESC(spare_eblocks, "Percentage of spare erase blocks for "
  		"garbage collection (default 10%)");
  
  static bool header; /* false */
  module_param(header, bool, 0444);
  MODULE_PARM_DESC(header,
  		"Include builtin swap header (default 0, without header)");
  
  static int mtdswap_gc(struct mtdswap_dev *d, unsigned int background);
  
  static loff_t mtdswap_eb_offset(struct mtdswap_dev *d, struct swap_eb *eb)
  {
  	return (loff_t)(eb - d->eb_data) * d->mtd->erasesize;
  }
  
  static void mtdswap_eb_detach(struct mtdswap_dev *d, struct swap_eb *eb)
  {
  	unsigned int oldidx;
  	struct mtdswap_tree *tp;
  
  	if (eb->root) {
  		tp = container_of(eb->root, struct mtdswap_tree, root);
  		oldidx = tp - &d->trees[0];
  
  		d->trees[oldidx].count--;
  		rb_erase(&eb->rb, eb->root);
  	}
  }
  
  static void __mtdswap_rb_add(struct rb_root *root, struct swap_eb *eb)
  {
  	struct rb_node **p, *parent = NULL;
  	struct swap_eb *cur;
  
  	p = &root->rb_node;
  	while (*p) {
  		parent = *p;
  		cur = rb_entry(parent, struct swap_eb, rb);
  		if (eb->erase_count > cur->erase_count)
  			p = &(*p)->rb_right;
  		else
  			p = &(*p)->rb_left;
  	}
  
  	rb_link_node(&eb->rb, parent, p);
  	rb_insert_color(&eb->rb, root);
  }
  
  static void mtdswap_rb_add(struct mtdswap_dev *d, struct swap_eb *eb, int idx)
  {
  	struct rb_root *root;
  
  	if (eb->root == &d->trees[idx].root)
  		return;
  
  	mtdswap_eb_detach(d, eb);
  	root = &d->trees[idx].root;
  	__mtdswap_rb_add(root, eb);
  	eb->root = root;
  	d->trees[idx].count++;
  }
  
  static struct rb_node *mtdswap_rb_index(struct rb_root *root, unsigned int idx)
  {
  	struct rb_node *p;
  	unsigned int i;
  
  	p = rb_first(root);
  	i = 0;
  	while (i < idx && p) {
  		p = rb_next(p);
  		i++;
  	}
  
  	return p;
  }
  
  static int mtdswap_handle_badblock(struct mtdswap_dev *d, struct swap_eb *eb)
  {
  	int ret;
  	loff_t offset;
  
  	d->spare_eblks--;
  	eb->flags |= EBLOCK_BAD;
  	mtdswap_eb_detach(d, eb);
  	eb->root = NULL;
  
  	/* badblocks not supported */

  	if (!mtd_can_have_bb(d->mtd))

  		return 1;
  
  	offset = mtdswap_eb_offset(d, eb);
  	dev_warn(d->dev, "Marking bad block at %08llx
  ", offset);

  	ret = mtd_block_markbad(d->mtd, offset);

  
  	if (ret) {
  		dev_warn(d->dev, "Mark block bad failed for block at %08llx "
  			"error %d
  ", offset, ret);
  		return ret;
  	}
  
  	return 1;
  
  }
  
  static int mtdswap_handle_write_error(struct mtdswap_dev *d, struct swap_eb *eb)
  {
  	unsigned int marked = eb->flags & EBLOCK_FAILED;
  	struct swap_eb *curr_write = d->curr_write;
  
  	eb->flags |= EBLOCK_FAILED;
  	if (curr_write == eb) {
  		d->curr_write = NULL;
  
  		if (!marked && d->curr_write_pos != 0) {
  			mtdswap_rb_add(d, eb, MTDSWAP_FAILING);
  			return 0;
  		}
  	}
  
  	return mtdswap_handle_badblock(d, eb);
  }
  
  static int mtdswap_read_oob(struct mtdswap_dev *d, loff_t from,
  			struct mtd_oob_ops *ops)
  {

  	int ret = mtd_read_oob(d->mtd, from, ops);

  	if (mtd_is_bitflip(ret))

  		return ret;
  
  	if (ret) {
  		dev_warn(d->dev, "Read OOB failed %d for block at %08llx
  ",
  			ret, from);
  		return ret;
  	}
  
  	if (ops->oobretlen < ops->ooblen) {
  		dev_warn(d->dev, "Read OOB return short read (%zd bytes not "

  			"%zd) for block at %08llx
  ",

  			ops->oobretlen, ops->ooblen, from);
  		return -EIO;
  	}
  
  	return 0;
  }
  
  static int mtdswap_read_markers(struct mtdswap_dev *d, struct swap_eb *eb)
  {
  	struct mtdswap_oobdata *data, *data2;
  	int ret;
  	loff_t offset;
  	struct mtd_oob_ops ops;
  
  	offset = mtdswap_eb_offset(d, eb);
  
  	/* Check first if the block is bad. */

  	if (mtd_can_have_bb(d->mtd) && mtd_block_isbad(d->mtd, offset))

  		return MTDSWAP_SCANNED_BAD;

  	ops.ooblen = 2 * d->mtd->oobavail;

  	ops.oobbuf = d->oob_buf;
  	ops.ooboffs = 0;
  	ops.datbuf = NULL;

  	ops.mode = MTD_OPS_AUTO_OOB;

  
  	ret = mtdswap_read_oob(d, offset, &ops);

  	if (ret && !mtd_is_bitflip(ret))

  		return ret;
  
  	data = (struct mtdswap_oobdata *)d->oob_buf;
  	data2 = (struct mtdswap_oobdata *)

  		(d->oob_buf + d->mtd->oobavail);

  
  	if (le16_to_cpu(data->magic) == MTDSWAP_MAGIC_CLEAN) {
  		eb->erase_count = le32_to_cpu(data->count);

  		if (mtd_is_bitflip(ret))

  			ret = MTDSWAP_SCANNED_BITFLIP;
  		else {
  			if (le16_to_cpu(data2->magic) == MTDSWAP_MAGIC_DIRTY)
  				ret = MTDSWAP_SCANNED_DIRTY;
  			else
  				ret = MTDSWAP_SCANNED_CLEAN;
  		}
  	} else {
  		eb->flags |= EBLOCK_NOMAGIC;
  		ret = MTDSWAP_SCANNED_DIRTY;
  	}
  
  	return ret;
  }
  
  static int mtdswap_write_marker(struct mtdswap_dev *d, struct swap_eb *eb,
  				u16 marker)
  {
  	struct mtdswap_oobdata n;
  	int ret;
  	loff_t offset;
  	struct mtd_oob_ops ops;
  
  	ops.ooboffs = 0;
  	ops.oobbuf = (uint8_t *)&n;

  	ops.mode = MTD_OPS_AUTO_OOB;

  	ops.datbuf = NULL;
  
  	if (marker == MTDSWAP_TYPE_CLEAN) {
  		n.magic = cpu_to_le16(MTDSWAP_MAGIC_CLEAN);
  		n.count = cpu_to_le32(eb->erase_count);
  		ops.ooblen = MTDSWAP_OOBSIZE;
  		offset = mtdswap_eb_offset(d, eb);
  	} else {
  		n.magic = cpu_to_le16(MTDSWAP_MAGIC_DIRTY);
  		ops.ooblen = sizeof(n.magic);
  		offset = mtdswap_eb_offset(d, eb) + d->mtd->writesize;
  	}

  	ret = mtd_write_oob(d->mtd, offset, &ops);

  
  	if (ret) {
  		dev_warn(d->dev, "Write OOB failed for block at %08llx "
  			"error %d
  ", offset, ret);

  		if (ret == -EIO || mtd_is_eccerr(ret))

  			mtdswap_handle_write_error(d, eb);
  		return ret;
  	}
  
  	if (ops.oobretlen != ops.ooblen) {
  		dev_warn(d->dev, "Short OOB write for block at %08llx: "

  			"%zd not %zd
  ",

  			offset, ops.oobretlen, ops.ooblen);
  		return ret;
  	}
  
  	return 0;
  }
  
  /*
   * Are there any erase blocks without MAGIC_CLEAN header, presumably
   * because power was cut off after erase but before header write? We
   * need to guestimate the erase count.
   */
  static void mtdswap_check_counts(struct mtdswap_dev *d)
  {
  	struct rb_root hist_root = RB_ROOT;
  	struct rb_node *medrb;
  	struct swap_eb *eb;
  	unsigned int i, cnt, median;
  
  	cnt = 0;
  	for (i = 0; i < d->eblks; i++) {
  		eb = d->eb_data + i;
  
  		if (eb->flags & (EBLOCK_NOMAGIC | EBLOCK_BAD | EBLOCK_READERR))
  			continue;
  
  		__mtdswap_rb_add(&hist_root, eb);
  		cnt++;
  	}
  
  	if (cnt == 0)
  		return;
  
  	medrb = mtdswap_rb_index(&hist_root, cnt / 2);
  	median = rb_entry(medrb, struct swap_eb, rb)->erase_count;
  
  	d->max_erase_count = MTDSWAP_ECNT_MAX(&hist_root);
  
  	for (i = 0; i < d->eblks; i++) {
  		eb = d->eb_data + i;
  
  		if (eb->flags & (EBLOCK_NOMAGIC | EBLOCK_READERR))
  			eb->erase_count = median;
  
  		if (eb->flags & (EBLOCK_NOMAGIC | EBLOCK_BAD | EBLOCK_READERR))
  			continue;
  
  		rb_erase(&eb->rb, &hist_root);
  	}
  }
  
  static void mtdswap_scan_eblks(struct mtdswap_dev *d)
  {
  	int status;
  	unsigned int i, idx;
  	struct swap_eb *eb;
  
  	for (i = 0; i < d->eblks; i++) {
  		eb = d->eb_data + i;
  
  		status = mtdswap_read_markers(d, eb);
  		if (status < 0)
  			eb->flags |= EBLOCK_READERR;
  		else if (status == MTDSWAP_SCANNED_BAD) {
  			eb->flags |= EBLOCK_BAD;
  			continue;
  		}
  
  		switch (status) {
  		case MTDSWAP_SCANNED_CLEAN:
  			idx = MTDSWAP_CLEAN;
  			break;
  		case MTDSWAP_SCANNED_DIRTY:
  		case MTDSWAP_SCANNED_BITFLIP:
  			idx = MTDSWAP_DIRTY;
  			break;
  		default:
  			idx = MTDSWAP_FAILING;
  		}
  
  		eb->flags |= (idx << EBLOCK_IDX_SHIFT);
  	}
  
  	mtdswap_check_counts(d);
  
  	for (i = 0; i < d->eblks; i++) {
  		eb = d->eb_data + i;
  
  		if (eb->flags & EBLOCK_BAD)
  			continue;
  
  		idx = eb->flags >> EBLOCK_IDX_SHIFT;
  		mtdswap_rb_add(d, eb, idx);
  	}
  }
  
  /*
   * Place eblk into a tree corresponding to its number of active blocks
   * it contains.
   */
  static void mtdswap_store_eb(struct mtdswap_dev *d, struct swap_eb *eb)
  {
  	unsigned int weight = eb->active_count;
  	unsigned int maxweight = d->pages_per_eblk;
  
  	if (eb == d->curr_write)
  		return;
  
  	if (eb->flags & EBLOCK_BITFLIP)
  		mtdswap_rb_add(d, eb, MTDSWAP_BITFLIP);
  	else if (eb->flags & (EBLOCK_READERR | EBLOCK_FAILED))
  		mtdswap_rb_add(d, eb, MTDSWAP_FAILING);
  	if (weight == maxweight)
  		mtdswap_rb_add(d, eb, MTDSWAP_USED);
  	else if (weight == 0)
  		mtdswap_rb_add(d, eb, MTDSWAP_DIRTY);
  	else if (weight > (maxweight/2))
  		mtdswap_rb_add(d, eb, MTDSWAP_LOWFRAG);
  	else
  		mtdswap_rb_add(d, eb, MTDSWAP_HIFRAG);
  }

  static int mtdswap_erase_block(struct mtdswap_dev *d, struct swap_eb *eb)
  {
  	struct mtd_info *mtd = d->mtd;
  	struct erase_info erase;

  	unsigned int retries = 0;
  	int ret;
  
  	eb->erase_count++;
  	if (eb->erase_count > d->max_erase_count)
  		d->max_erase_count = eb->erase_count;
  
  retry:

  	memset(&erase, 0, sizeof(struct erase_info));

  	erase.addr	= mtdswap_eb_offset(d, eb);
  	erase.len	= mtd->erasesize;

  	ret = mtd_erase(mtd, &erase);

  	if (ret) {

  		if (retries++ < MTDSWAP_ERASE_RETRIES) {

  			dev_warn(d->dev,
  				"erase of erase block %#llx on %s failed",
  				erase.addr, mtd->name);
  			yield();
  			goto retry;
  		}
  
  		dev_err(d->dev, "Cannot erase erase block %#llx on %s
  ",
  			erase.addr, mtd->name);
  
  		mtdswap_handle_badblock(d, eb);
  		return -EIO;
  	}

  	return 0;
  }
  
  static int mtdswap_map_free_block(struct mtdswap_dev *d, unsigned int page,
  				unsigned int *block)
  {
  	int ret;
  	struct swap_eb *old_eb = d->curr_write;
  	struct rb_root *clean_root;
  	struct swap_eb *eb;
  
  	if (old_eb == NULL || d->curr_write_pos >= d->pages_per_eblk) {
  		do {
  			if (TREE_EMPTY(d, CLEAN))
  				return -ENOSPC;
  
  			clean_root = TREE_ROOT(d, CLEAN);
  			eb = rb_entry(rb_first(clean_root), struct swap_eb, rb);
  			rb_erase(&eb->rb, clean_root);
  			eb->root = NULL;
  			TREE_COUNT(d, CLEAN)--;
  
  			ret = mtdswap_write_marker(d, eb, MTDSWAP_TYPE_DIRTY);

  		} while (ret == -EIO || mtd_is_eccerr(ret));

  
  		if (ret)
  			return ret;
  
  		d->curr_write_pos = 0;
  		d->curr_write = eb;
  		if (old_eb)
  			mtdswap_store_eb(d, old_eb);
  	}
  
  	*block = (d->curr_write - d->eb_data) * d->pages_per_eblk +
  		d->curr_write_pos;
  
  	d->curr_write->active_count++;
  	d->revmap[*block] = page;
  	d->curr_write_pos++;
  
  	return 0;
  }
  
  static unsigned int mtdswap_free_page_cnt(struct mtdswap_dev *d)
  {
  	return TREE_COUNT(d, CLEAN) * d->pages_per_eblk +
  		d->pages_per_eblk - d->curr_write_pos;
  }
  
  static unsigned int mtdswap_enough_free_pages(struct mtdswap_dev *d)
  {
  	return mtdswap_free_page_cnt(d) > d->pages_per_eblk;
  }
  
  static int mtdswap_write_block(struct mtdswap_dev *d, char *buf,
  			unsigned int page, unsigned int *bp, int gc_context)
  {
  	struct mtd_info *mtd = d->mtd;
  	struct swap_eb *eb;
  	size_t retlen;
  	loff_t writepos;
  	int ret;
  
  retry:
  	if (!gc_context)
  		while (!mtdswap_enough_free_pages(d))
  			if (mtdswap_gc(d, 0) > 0)
  				return -ENOSPC;
  
  	ret = mtdswap_map_free_block(d, page, bp);
  	eb = d->eb_data + (*bp / d->pages_per_eblk);

  	if (ret == -EIO || mtd_is_eccerr(ret)) {

  		d->curr_write = NULL;
  		eb->active_count--;
  		d->revmap[*bp] = PAGE_UNDEF;
  		goto retry;
  	}
  
  	if (ret < 0)
  		return ret;
  
  	writepos = (loff_t)*bp << PAGE_SHIFT;

  	ret =  mtd_write(mtd, writepos, PAGE_SIZE, &retlen, buf);

  	if (ret == -EIO || mtd_is_eccerr(ret)) {

  		d->curr_write_pos--;
  		eb->active_count--;
  		d->revmap[*bp] = PAGE_UNDEF;
  		mtdswap_handle_write_error(d, eb);
  		goto retry;
  	}
  
  	if (ret < 0) {

  		dev_err(d->dev, "Write to MTD device failed: %d (%zd written)",

  			ret, retlen);
  		goto err;
  	}
  
  	if (retlen != PAGE_SIZE) {

  		dev_err(d->dev, "Short write to MTD device: %zd written",

  			retlen);
  		ret = -EIO;
  		goto err;
  	}
  
  	return ret;
  
  err:
  	d->curr_write_pos--;
  	eb->active_count--;
  	d->revmap[*bp] = PAGE_UNDEF;
  
  	return ret;
  }
  
  static int mtdswap_move_block(struct mtdswap_dev *d, unsigned int oldblock,
  		unsigned int *newblock)
  {
  	struct mtd_info *mtd = d->mtd;
  	struct swap_eb *eb, *oldeb;
  	int ret;
  	size_t retlen;
  	unsigned int page, retries;
  	loff_t readpos;
  
  	page = d->revmap[oldblock];
  	readpos = (loff_t) oldblock << PAGE_SHIFT;
  	retries = 0;
  
  retry:

  	ret = mtd_read(mtd, readpos, PAGE_SIZE, &retlen, d->page_buf);

  	if (ret < 0 && !mtd_is_bitflip(ret)) {

  		oldeb = d->eb_data + oldblock / d->pages_per_eblk;
  		oldeb->flags |= EBLOCK_READERR;
  
  		dev_err(d->dev, "Read Error: %d (block %u)
  ", ret,
  			oldblock);
  		retries++;
  		if (retries < MTDSWAP_IO_RETRIES)
  			goto retry;
  
  		goto read_error;
  	}
  
  	if (retlen != PAGE_SIZE) {

  		dev_err(d->dev, "Short read: %zd (block %u)
  ", retlen,

  		       oldblock);
  		ret = -EIO;
  		goto read_error;
  	}
  
  	ret = mtdswap_write_block(d, d->page_buf, page, newblock, 1);
  	if (ret < 0) {
  		d->page_data[page] = BLOCK_ERROR;
  		dev_err(d->dev, "Write error: %d
  ", ret);
  		return ret;
  	}
  
  	eb = d->eb_data + *newblock / d->pages_per_eblk;
  	d->page_data[page] = *newblock;
  	d->revmap[oldblock] = PAGE_UNDEF;
  	eb = d->eb_data + oldblock / d->pages_per_eblk;
  	eb->active_count--;
  
  	return 0;
  
  read_error:
  	d->page_data[page] = BLOCK_ERROR;
  	d->revmap[oldblock] = PAGE_UNDEF;
  	return ret;
  }
  
  static int mtdswap_gc_eblock(struct mtdswap_dev *d, struct swap_eb *eb)
  {
  	unsigned int i, block, eblk_base, newblock;
  	int ret, errcode;
  
  	errcode = 0;
  	eblk_base = (eb - d->eb_data) * d->pages_per_eblk;
  
  	for (i = 0; i < d->pages_per_eblk; i++) {
  		if (d->spare_eblks < MIN_SPARE_EBLOCKS)
  			return -ENOSPC;
  
  		block = eblk_base + i;
  		if (d->revmap[block] == PAGE_UNDEF)
  			continue;
  
  		ret = mtdswap_move_block(d, block, &newblock);
  		if (ret < 0 && !errcode)
  			errcode = ret;
  	}
  
  	return errcode;
  }
  
  static int __mtdswap_choose_gc_tree(struct mtdswap_dev *d)
  {
  	int idx, stopat;

  	if (TREE_COUNT(d, CLEAN) < LOW_FRAG_GC_THRESHOLD)

  		stopat = MTDSWAP_LOWFRAG;
  	else
  		stopat = MTDSWAP_HIFRAG;
  
  	for (idx = MTDSWAP_BITFLIP; idx >= stopat; idx--)
  		if (d->trees[idx].root.rb_node != NULL)
  			return idx;
  
  	return -1;
  }
  
  static int mtdswap_wlfreq(unsigned int maxdiff)
  {
  	unsigned int h, x, y, dist, base;
  
  	/*
  	 * Calculate linear ramp down from f1 to f2 when maxdiff goes from
  	 * MAX_ERASE_DIFF to MAX_ERASE_DIFF + COLLECT_NONDIRTY_BASE.  Similar
  	 * to triangle with height f1 - f1 and width COLLECT_NONDIRTY_BASE.
  	 */
  
  	dist = maxdiff - MAX_ERASE_DIFF;
  	if (dist > COLLECT_NONDIRTY_BASE)
  		dist = COLLECT_NONDIRTY_BASE;
  
  	/*
  	 * Modelling the slop as right angular triangle with base
  	 * COLLECT_NONDIRTY_BASE and height freq1 - freq2. The ratio y/x is
  	 * equal to the ratio h/base.
  	 */
  	h = COLLECT_NONDIRTY_FREQ1 - COLLECT_NONDIRTY_FREQ2;
  	base = COLLECT_NONDIRTY_BASE;
  
  	x = dist - base;
  	y = (x * h + base / 2) / base;
  
  	return COLLECT_NONDIRTY_FREQ2 + y;
  }
  
  static int mtdswap_choose_wl_tree(struct mtdswap_dev *d)
  {
  	static unsigned int pick_cnt;

  	unsigned int i, idx = -1, wear, max;

  	struct rb_root *root;
  
  	max = 0;
  	for (i = 0; i <= MTDSWAP_DIRTY; i++) {
  		root = &d->trees[i].root;
  		if (root->rb_node == NULL)
  			continue;
  
  		wear = d->max_erase_count - MTDSWAP_ECNT_MIN(root);
  		if (wear > max) {
  			max = wear;
  			idx = i;
  		}
  	}
  
  	if (max > MAX_ERASE_DIFF && pick_cnt >= mtdswap_wlfreq(max) - 1) {
  		pick_cnt = 0;
  		return idx;
  	}
  
  	pick_cnt++;
  	return -1;
  }
  
  static int mtdswap_choose_gc_tree(struct mtdswap_dev *d,
  				unsigned int background)
  {
  	int idx;
  
  	if (TREE_NONEMPTY(d, FAILING) &&
  		(background || (TREE_EMPTY(d, CLEAN) && TREE_EMPTY(d, DIRTY))))
  		return MTDSWAP_FAILING;
  
  	idx = mtdswap_choose_wl_tree(d);
  	if (idx >= MTDSWAP_CLEAN)
  		return idx;
  
  	return __mtdswap_choose_gc_tree(d);
  }
  
  static struct swap_eb *mtdswap_pick_gc_eblk(struct mtdswap_dev *d,
  					unsigned int background)
  {
  	struct rb_root *rp = NULL;
  	struct swap_eb *eb = NULL;
  	int idx;
  
  	if (background && TREE_COUNT(d, CLEAN) > CLEAN_BLOCK_THRESHOLD &&
  		TREE_EMPTY(d, DIRTY) && TREE_EMPTY(d, FAILING))
  		return NULL;
  
  	idx = mtdswap_choose_gc_tree(d, background);
  	if (idx < 0)
  		return NULL;
  
  	rp = &d->trees[idx].root;
  	eb = rb_entry(rb_first(rp), struct swap_eb, rb);
  
  	rb_erase(&eb->rb, rp);
  	eb->root = NULL;
  	d->trees[idx].count--;
  	return eb;
  }
  
  static unsigned int mtdswap_test_patt(unsigned int i)
  {
  	return i % 2 ? 0x55555555 : 0xAAAAAAAA;
  }
  
  static unsigned int mtdswap_eblk_passes(struct mtdswap_dev *d,
  					struct swap_eb *eb)
  {
  	struct mtd_info *mtd = d->mtd;
  	unsigned int test, i, j, patt, mtd_pages;
  	loff_t base, pos;
  	unsigned int *p1 = (unsigned int *)d->page_buf;
  	unsigned char *p2 = (unsigned char *)d->oob_buf;
  	struct mtd_oob_ops ops;
  	int ret;

  	ops.mode = MTD_OPS_AUTO_OOB;

  	ops.len = mtd->writesize;

  	ops.ooblen = mtd->oobavail;

  	ops.ooboffs = 0;
  	ops.datbuf = d->page_buf;
  	ops.oobbuf = d->oob_buf;
  	base = mtdswap_eb_offset(d, eb);
  	mtd_pages = d->pages_per_eblk * PAGE_SIZE / mtd->writesize;
  
  	for (test = 0; test < 2; test++) {
  		pos = base;
  		for (i = 0; i < mtd_pages; i++) {
  			patt = mtdswap_test_patt(test + i);
  			memset(d->page_buf, patt, mtd->writesize);

  			memset(d->oob_buf, patt, mtd->oobavail);

  			ret = mtd_write_oob(mtd, pos, &ops);

  			if (ret)
  				goto error;
  
  			pos += mtd->writesize;
  		}
  
  		pos = base;
  		for (i = 0; i < mtd_pages; i++) {

  			ret = mtd_read_oob(mtd, pos, &ops);

  			if (ret)
  				goto error;
  
  			patt = mtdswap_test_patt(test + i);
  			for (j = 0; j < mtd->writesize/sizeof(int); j++)
  				if (p1[j] != patt)
  					goto error;

  			for (j = 0; j < mtd->oobavail; j++)

  				if (p2[j] != (unsigned char)patt)
  					goto error;
  
  			pos += mtd->writesize;
  		}
  
  		ret = mtdswap_erase_block(d, eb);
  		if (ret)
  			goto error;
  	}
  
  	eb->flags &= ~EBLOCK_READERR;
  	return 1;
  
  error:
  	mtdswap_handle_badblock(d, eb);
  	return 0;
  }
  
  static int mtdswap_gc(struct mtdswap_dev *d, unsigned int background)
  {
  	struct swap_eb *eb;
  	int ret;
  
  	if (d->spare_eblks < MIN_SPARE_EBLOCKS)
  		return 1;
  
  	eb = mtdswap_pick_gc_eblk(d, background);
  	if (!eb)
  		return 1;
  
  	ret = mtdswap_gc_eblock(d, eb);
  	if (ret == -ENOSPC)
  		return 1;
  
  	if (eb->flags & EBLOCK_FAILED) {
  		mtdswap_handle_badblock(d, eb);
  		return 0;
  	}
  
  	eb->flags &= ~EBLOCK_BITFLIP;
  	ret = mtdswap_erase_block(d, eb);
  	if ((eb->flags & EBLOCK_READERR) &&
  		(ret || !mtdswap_eblk_passes(d, eb)))
  		return 0;
  
  	if (ret == 0)
  		ret = mtdswap_write_marker(d, eb, MTDSWAP_TYPE_CLEAN);
  
  	if (ret == 0)
  		mtdswap_rb_add(d, eb, MTDSWAP_CLEAN);

  	else if (ret != -EIO && !mtd_is_eccerr(ret))

  		mtdswap_rb_add(d, eb, MTDSWAP_DIRTY);
  
  	return 0;
  }
  
  static void mtdswap_background(struct mtd_blktrans_dev *dev)
  {
  	struct mtdswap_dev *d = MTDSWAP_MBD_TO_MTDSWAP(dev);
  	int ret;
  
  	while (1) {
  		ret = mtdswap_gc(d, 1);
  		if (ret || mtd_blktrans_cease_background(dev))
  			return;
  	}
  }
  
  static void mtdswap_cleanup(struct mtdswap_dev *d)
  {
  	vfree(d->eb_data);
  	vfree(d->revmap);
  	vfree(d->page_data);
  	kfree(d->oob_buf);
  	kfree(d->page_buf);
  }
  
  static int mtdswap_flush(struct mtd_blktrans_dev *dev)
  {
  	struct mtdswap_dev *d = MTDSWAP_MBD_TO_MTDSWAP(dev);

  	mtd_sync(d->mtd);

  	return 0;
  }
  
  static unsigned int mtdswap_badblocks(struct mtd_info *mtd, uint64_t size)
  {
  	loff_t offset;
  	unsigned int badcnt;
  
  	badcnt = 0;

  	if (mtd_can_have_bb(mtd))

  		for (offset = 0; offset < size; offset += mtd->erasesize)

  			if (mtd_block_isbad(mtd, offset))

  				badcnt++;
  
  	return badcnt;
  }
  
  static int mtdswap_writesect(struct mtd_blktrans_dev *dev,
  			unsigned long page, char *buf)
  {
  	struct mtdswap_dev *d = MTDSWAP_MBD_TO_MTDSWAP(dev);
  	unsigned int newblock, mapped;
  	struct swap_eb *eb;
  	int ret;
  
  	d->sect_write_count++;
  
  	if (d->spare_eblks < MIN_SPARE_EBLOCKS)
  		return -ENOSPC;
  
  	if (header) {
  		/* Ignore writes to the header page */
  		if (unlikely(page == 0))
  			return 0;
  
  		page--;
  	}
  
  	mapped = d->page_data[page];
  	if (mapped <= BLOCK_MAX) {
  		eb = d->eb_data + (mapped / d->pages_per_eblk);
  		eb->active_count--;
  		mtdswap_store_eb(d, eb);
  		d->page_data[page] = BLOCK_UNDEF;
  		d->revmap[mapped] = PAGE_UNDEF;
  	}
  
  	ret = mtdswap_write_block(d, buf, page, &newblock, 0);
  	d->mtd_write_count++;
  
  	if (ret < 0)
  		return ret;
  
  	eb = d->eb_data + (newblock / d->pages_per_eblk);
  	d->page_data[page] = newblock;
  
  	return 0;
  }
  
  /* Provide a dummy swap header for the kernel */
  static int mtdswap_auto_header(struct mtdswap_dev *d, char *buf)
  {
  	union swap_header *hd = (union swap_header *)(buf);
  
  	memset(buf, 0, PAGE_SIZE - 10);
  
  	hd->info.version = 1;
  	hd->info.last_page = d->mbd_dev->size - 1;
  	hd->info.nr_badpages = 0;
  
  	memcpy(buf + PAGE_SIZE - 10, "SWAPSPACE2", 10);
  
  	return 0;
  }
  
  static int mtdswap_readsect(struct mtd_blktrans_dev *dev,
  			unsigned long page, char *buf)
  {
  	struct mtdswap_dev *d = MTDSWAP_MBD_TO_MTDSWAP(dev);
  	struct mtd_info *mtd = d->mtd;
  	unsigned int realblock, retries;
  	loff_t readpos;
  	struct swap_eb *eb;
  	size_t retlen;
  	int ret;
  
  	d->sect_read_count++;
  
  	if (header) {
  		if (unlikely(page == 0))
  			return mtdswap_auto_header(d, buf);
  
  		page--;
  	}
  
  	realblock = d->page_data[page];
  	if (realblock > BLOCK_MAX) {
  		memset(buf, 0x0, PAGE_SIZE);
  		if (realblock == BLOCK_UNDEF)
  			return 0;
  		else
  			return -EIO;
  	}
  
  	eb = d->eb_data + (realblock / d->pages_per_eblk);
  	BUG_ON(d->revmap[realblock] == PAGE_UNDEF);
  
  	readpos = (loff_t)realblock << PAGE_SHIFT;
  	retries = 0;
  
  retry:

  	ret = mtd_read(mtd, readpos, PAGE_SIZE, &retlen, buf);

  
  	d->mtd_read_count++;

  	if (mtd_is_bitflip(ret)) {

  		eb->flags |= EBLOCK_BITFLIP;
  		mtdswap_rb_add(d, eb, MTDSWAP_BITFLIP);
  		ret = 0;
  	}
  
  	if (ret < 0) {
  		dev_err(d->dev, "Read error %d
  ", ret);
  		eb->flags |= EBLOCK_READERR;
  		mtdswap_rb_add(d, eb, MTDSWAP_FAILING);
  		retries++;
  		if (retries < MTDSWAP_IO_RETRIES)
  			goto retry;
  
  		return ret;
  	}
  
  	if (retlen != PAGE_SIZE) {

  		dev_err(d->dev, "Short read %zd
  ", retlen);

  		return -EIO;
  	}
  
  	return 0;
  }
  
  static int mtdswap_discard(struct mtd_blktrans_dev *dev, unsigned long first,
  			unsigned nr_pages)
  {
  	struct mtdswap_dev *d = MTDSWAP_MBD_TO_MTDSWAP(dev);
  	unsigned long page;
  	struct swap_eb *eb;
  	unsigned int mapped;
  
  	d->discard_count++;
  
  	for (page = first; page < first + nr_pages; page++) {
  		mapped = d->page_data[page];
  		if (mapped <= BLOCK_MAX) {
  			eb = d->eb_data + (mapped / d->pages_per_eblk);
  			eb->active_count--;
  			mtdswap_store_eb(d, eb);
  			d->page_data[page] = BLOCK_UNDEF;
  			d->revmap[mapped] = PAGE_UNDEF;
  			d->discard_page_count++;
  		} else if (mapped == BLOCK_ERROR) {
  			d->page_data[page] = BLOCK_UNDEF;
  			d->discard_page_count++;
  		}
  	}
  
  	return 0;
  }
  
  static int mtdswap_show(struct seq_file *s, void *data)
  {
  	struct mtdswap_dev *d = (struct mtdswap_dev *) s->private;
  	unsigned long sum;
  	unsigned int count[MTDSWAP_TREE_CNT];
  	unsigned int min[MTDSWAP_TREE_CNT];
  	unsigned int max[MTDSWAP_TREE_CNT];
  	unsigned int i, cw = 0, cwp = 0, cwecount = 0, bb_cnt, mapped, pages;
  	uint64_t use_size;

  	static const char * const name[] = {
  		"clean", "used", "low", "high", "dirty", "bitflip", "failing"
  	};

  
  	mutex_lock(&d->mbd_dev->lock);
  
  	for (i = 0; i < MTDSWAP_TREE_CNT; i++) {
  		struct rb_root *root = &d->trees[i].root;
  
  		if (root->rb_node) {
  			count[i] = d->trees[i].count;

  			min[i] = MTDSWAP_ECNT_MIN(root);
  			max[i] = MTDSWAP_ECNT_MAX(root);

  		} else
  			count[i] = 0;
  	}
  
  	if (d->curr_write) {
  		cw = 1;
  		cwp = d->curr_write_pos;
  		cwecount = d->curr_write->erase_count;
  	}
  
  	sum = 0;
  	for (i = 0; i < d->eblks; i++)
  		sum += d->eb_data[i].erase_count;
  
  	use_size = (uint64_t)d->eblks * d->mtd->erasesize;
  	bb_cnt = mtdswap_badblocks(d->mtd, use_size);
  
  	mapped = 0;
  	pages = d->mbd_dev->size;
  	for (i = 0; i < pages; i++)
  		if (d->page_data[i] != BLOCK_UNDEF)
  			mapped++;
  
  	mutex_unlock(&d->mbd_dev->lock);
  
  	for (i = 0; i < MTDSWAP_TREE_CNT; i++) {
  		if (!count[i])
  			continue;
  
  		if (min[i] != max[i])
  			seq_printf(s, "%s:\t%5d erase blocks, erased min %d, "
  				"max %d times
  ",
  				name[i], count[i], min[i], max[i]);
  		else
  			seq_printf(s, "%s:\t%5d erase blocks, all erased %d "
  				"times
  ", name[i], count[i], min[i]);
  	}
  
  	if (bb_cnt)
  		seq_printf(s, "bad:\t%5u erase blocks
  ", bb_cnt);
  
  	if (cw)
  		seq_printf(s, "current erase block: %u pages used, %u free, "
  			"erased %u times
  ",
  			cwp, d->pages_per_eblk - cwp, cwecount);
  
  	seq_printf(s, "total erasures: %lu
  ", sum);

  	seq_puts(s, "
  ");

  
  	seq_printf(s, "mtdswap_readsect count: %llu
  ", d->sect_read_count);
  	seq_printf(s, "mtdswap_writesect count: %llu
  ", d->sect_write_count);
  	seq_printf(s, "mtdswap_discard count: %llu
  ", d->discard_count);
  	seq_printf(s, "mtd read count: %llu
  ", d->mtd_read_count);
  	seq_printf(s, "mtd write count: %llu
  ", d->mtd_write_count);
  	seq_printf(s, "discarded pages count: %llu
  ", d->discard_page_count);

  	seq_puts(s, "
  ");

  	seq_printf(s, "total pages: %u
  ", pages);

  	seq_printf(s, "pages mapped: %u
  ", mapped);
  
  	return 0;
  }

  DEFINE_SHOW_ATTRIBUTE(mtdswap);

  
  static int mtdswap_add_debugfs(struct mtdswap_dev *d)
  {

  	struct dentry *root = d->mtd->dbg.dfs_dir;

  	if (!IS_ENABLED(CONFIG_DEBUG_FS))

  		return 0;

  	if (IS_ERR_OR_NULL(root))

  		return -1;

  	debugfs_create_file("mtdswap_stats", S_IRUSR, root, d, &mtdswap_fops);

  
  	return 0;
  }
  
  static int mtdswap_init(struct mtdswap_dev *d, unsigned int eblocks,
  			unsigned int spare_cnt)
  {
  	struct mtd_info *mtd = d->mbd_dev->mtd;
  	unsigned int i, eblk_bytes, pages, blocks;
  	int ret = -ENOMEM;
  
  	d->mtd = mtd;
  	d->eblks = eblocks;
  	d->spare_eblks = spare_cnt;
  	d->pages_per_eblk = mtd->erasesize >> PAGE_SHIFT;
  
  	pages = d->mbd_dev->size;
  	blocks = eblocks * d->pages_per_eblk;
  
  	for (i = 0; i < MTDSWAP_TREE_CNT; i++)
  		d->trees[i].root = RB_ROOT;

  	d->page_data = vmalloc(array_size(pages, sizeof(int)));

  	if (!d->page_data)
  		goto page_data_fail;

  	d->revmap = vmalloc(array_size(blocks, sizeof(int)));

  	if (!d->revmap)
  		goto revmap_fail;
  
  	eblk_bytes = sizeof(struct swap_eb)*d->eblks;

  	d->eb_data = vzalloc(eblk_bytes);

  	if (!d->eb_data)
  		goto eb_data_fail;

  	for (i = 0; i < pages; i++)
  		d->page_data[i] = BLOCK_UNDEF;
  
  	for (i = 0; i < blocks; i++)
  		d->revmap[i] = PAGE_UNDEF;
  
  	d->page_buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
  	if (!d->page_buf)
  		goto page_buf_fail;

  	d->oob_buf = kmalloc_array(2, mtd->oobavail, GFP_KERNEL);

  	if (!d->oob_buf)
  		goto oob_buf_fail;
  
  	mtdswap_scan_eblks(d);
  
  	return 0;
  
  oob_buf_fail:
  	kfree(d->page_buf);
  page_buf_fail:
  	vfree(d->eb_data);
  eb_data_fail:
  	vfree(d->revmap);
  revmap_fail:
  	vfree(d->page_data);
  page_data_fail:
  	printk(KERN_ERR "%s: init failed (%d)
  ", MTDSWAP_PREFIX, ret);
  	return ret;
  }
  
  static void mtdswap_add_mtd(struct mtd_blktrans_ops *tr, struct mtd_info *mtd)
  {
  	struct mtdswap_dev *d;
  	struct mtd_blktrans_dev *mbd_dev;
  	char *parts;
  	char *this_opt;
  	unsigned long part;
  	unsigned int eblocks, eavailable, bad_blocks, spare_cnt;
  	uint64_t swap_size, use_size, size_limit;

  	int ret;
  
  	parts = &partitions[0];
  	if (!*parts)
  		return;
  
  	while ((this_opt = strsep(&parts, ",")) != NULL) {

  		if (kstrtoul(this_opt, 0, &part) < 0)

  			return;
  
  		if (mtd->index == part)
  			break;
  	}
  
  	if (mtd->index != part)
  		return;
  
  	if (mtd->erasesize < PAGE_SIZE || mtd->erasesize % PAGE_SIZE) {
  		printk(KERN_ERR "%s: Erase size %u not multiple of PAGE_SIZE "
  			"%lu
  ", MTDSWAP_PREFIX, mtd->erasesize, PAGE_SIZE);
  		return;
  	}
  
  	if (PAGE_SIZE % mtd->writesize || mtd->writesize > PAGE_SIZE) {
  		printk(KERN_ERR "%s: PAGE_SIZE %lu not multiple of write size"
  			" %u
  ", MTDSWAP_PREFIX, PAGE_SIZE, mtd->writesize);
  		return;
  	}

  	if (!mtd->oobsize || mtd->oobavail < MTDSWAP_OOBSIZE) {

  		printk(KERN_ERR "%s: Not enough free bytes in OOB, "

  			"%d available, %zu needed.
  ",

  			MTDSWAP_PREFIX, mtd->oobavail, MTDSWAP_OOBSIZE);

  		return;
  	}
  
  	if (spare_eblocks > 100)
  		spare_eblocks = 100;
  
  	use_size = mtd->size;
  	size_limit = (uint64_t) BLOCK_MAX * PAGE_SIZE;
  
  	if (mtd->size > size_limit) {
  		printk(KERN_WARNING "%s: Device too large. Limiting size to "
  			"%llu bytes
  ", MTDSWAP_PREFIX, size_limit);
  		use_size = size_limit;
  	}
  
  	eblocks = mtd_div_by_eb(use_size, mtd);

  	use_size = (uint64_t)eblocks * mtd->erasesize;

  	bad_blocks = mtdswap_badblocks(mtd, use_size);
  	eavailable = eblocks - bad_blocks;
  
  	if (eavailable < MIN_ERASE_BLOCKS) {
  		printk(KERN_ERR "%s: Not enough erase blocks. %u available, "
  			"%d needed
  ", MTDSWAP_PREFIX, eavailable,
  			MIN_ERASE_BLOCKS);
  		return;
  	}
  
  	spare_cnt = div_u64((uint64_t)eavailable * spare_eblocks, 100);
  
  	if (spare_cnt < MIN_SPARE_EBLOCKS)
  		spare_cnt = MIN_SPARE_EBLOCKS;
  
  	if (spare_cnt > eavailable - 1)
  		spare_cnt = eavailable - 1;
  
  	swap_size = (uint64_t)(eavailable - spare_cnt) * mtd->erasesize +
  		(header ? PAGE_SIZE : 0);
  
  	printk(KERN_INFO "%s: Enabling MTD swap on device %lu, size %llu KB, "
  		"%u spare, %u bad blocks
  ",
  		MTDSWAP_PREFIX, part, swap_size / 1024, spare_cnt, bad_blocks);
  
  	d = kzalloc(sizeof(struct mtdswap_dev), GFP_KERNEL);
  	if (!d)
  		return;
  
  	mbd_dev = kzalloc(sizeof(struct mtd_blktrans_dev), GFP_KERNEL);
  	if (!mbd_dev) {
  		kfree(d);
  		return;
  	}
  
  	d->mbd_dev = mbd_dev;
  	mbd_dev->priv = d;
  
  	mbd_dev->mtd = mtd;
  	mbd_dev->devnum = mtd->index;
  	mbd_dev->size = swap_size >> PAGE_SHIFT;
  	mbd_dev->tr = tr;
  
  	if (!(mtd->flags & MTD_WRITEABLE))
  		mbd_dev->readonly = 1;
  
  	if (mtdswap_init(d, eblocks, spare_cnt) < 0)
  		goto init_failed;
  
  	if (add_mtd_blktrans_dev(mbd_dev) < 0)
  		goto cleanup;
  
  	d->dev = disk_to_dev(mbd_dev->disk);
  
  	ret = mtdswap_add_debugfs(d);
  	if (ret < 0)
  		goto debugfs_failed;
  
  	return;
  
  debugfs_failed:
  	del_mtd_blktrans_dev(mbd_dev);
  
  cleanup:
  	mtdswap_cleanup(d);
  
  init_failed:
  	kfree(mbd_dev);
  	kfree(d);
  }
  
  static void mtdswap_remove_dev(struct mtd_blktrans_dev *dev)
  {
  	struct mtdswap_dev *d = MTDSWAP_MBD_TO_MTDSWAP(dev);

  	del_mtd_blktrans_dev(dev);
  	mtdswap_cleanup(d);
  	kfree(d);
  }
  
  static struct mtd_blktrans_ops mtdswap_ops = {
  	.name		= "mtdswap",
  	.major		= 0,
  	.part_bits	= 0,
  	.blksize	= PAGE_SIZE,
  	.flush		= mtdswap_flush,
  	.readsect	= mtdswap_readsect,
  	.writesect	= mtdswap_writesect,
  	.discard	= mtdswap_discard,
  	.background	= mtdswap_background,
  	.add_mtd	= mtdswap_add_mtd,
  	.remove_dev	= mtdswap_remove_dev,
  	.owner		= THIS_MODULE,
  };
  
  static int __init mtdswap_modinit(void)
  {
  	return register_mtd_blktrans(&mtdswap_ops);
  }
  
  static void __exit mtdswap_modexit(void)
  {
  	deregister_mtd_blktrans(&mtdswap_ops);
  }
  
  module_init(mtdswap_modinit);
  module_exit(mtdswap_modexit);
  
  
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Jarkko Lavinen <jarkko.lavinen@nokia.com>");
  MODULE_DESCRIPTION("Block device access to an MTD suitable for using as "
  		"swap space");