mtd: Add mtdswap block driver

Add a driver for allowing an mtd device to be used as a block device for
swapping. The block device is volatile, and the mapping of swapped pages
is not stored on flash.

Signed-off-by: Jarkko Lavinen <[e-mail]>
Tested-by: Artem Bityutskiy <[e-mail]>
Signed-off-by: David Woodhouse <[e-mail]>

drivers/mtd/Kconfig

···
 	  To use, add console=ttyMTDx to the kernel command line,
 	  where x is the MTD device number to use.
 
+config MTD_SWAP
+	tristate "Swap on MTD device support"
+	depends on MTD && SWAP
+	select MTD_BLKDEVS
+	help
+	  Provides volatile block device driver on top of mtd partition
+          suitable for swapping.  The mapping of written blocks is not saved.
+	  The driver provides wear leveling by storing erase counter into the
+	  OOB.
+
+config MTD_SWAP_STRICT
+       bool "Strict erase error handling"
+       depends on MTD_SWAP
+       help
+	 Enables strict tolerance on failed erasures, marking erase blocks bad
+	 right after the first failed operation. With non-strict mode the
+	 erase operation is retried.
+
 source "drivers/mtd/chips/Kconfig"
 
 source "drivers/mtd/maps/Kconfig"

drivers/mtd/Makefile

···
 obj-$(CONFIG_SSFDC)		+= ssfdc.o
 obj-$(CONFIG_SM_FTL)		+= sm_ftl.o
 obj-$(CONFIG_MTD_OOPS)		+= mtdoops.o
+obj-$(CONFIG_MTD_SWAP)		+= mtdswap.o
 
 nftl-objs		:= nftlcore.o nftlmount.o
 inftl-objs		:= inftlcore.o inftlmount.o

drivers/mtd/mtdswap.c

···
+/*
+ * 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 <[e-mail]>
+ *
+ * Based on Richard Purdie's earlier implementation in 2007. Background
+ * support and lock-less operation written by Adrian Hunter.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
+ * 02110-1301 USA
+ */
+
+#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_TRESHOLD	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 decremtnt */
+};
+
+#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 dentry *debugfs_root;
+};
+
+struct mtdswap_oobdata {
+	__le16 magic;
+	__le32 count;
+} __attribute__((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
+
+#ifdef CONFIG_MTD_SWAP_STRICT
+#define MTDSWAP_STRICT		1
+#else
+#define MTDSWAP_STRICT		0
+#endif
+
+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 (!d->mtd->block_markbad)
+		return 1;
+
+	offset = mtdswap_eb_offset(d, eb);
+	dev_warn(d->dev, "Marking bad block at %08llx\n", offset);
+	ret = d->mtd->block_markbad(d->mtd, offset);
+
+	if (ret) {
+		dev_warn(d->dev, "Mark block bad failed for block at %08llx "
+			"error %d\n", 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 = d->mtd->read_oob(d->mtd, from, ops);
+
+	if (ret == -EUCLEAN)
+		return ret;
+
+	if (ret) {
+		dev_warn(d->dev, "Read OOB failed %d for block at %08llx\n",
+			ret, from);
+		return ret;
+	}
+
+	if (ops->oobretlen < ops->ooblen) {
+		dev_warn(d->dev, "Read OOB return short read (%zd bytes not "
+			"%d) for block at %08llx\n",
+			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 (d->mtd->block_isbad && d->mtd->block_isbad(d->mtd, offset))
+		return MTDSWAP_SCANNED_BAD;
+
+	ops.ooblen = 2 * d->mtd->ecclayout->oobavail;
+	ops.oobbuf = d->oob_buf;
+	ops.ooboffs = 0;
+	ops.datbuf = NULL;
+	ops.mode = MTD_OOB_AUTO;
+
+	ret = mtdswap_read_oob(d, offset, &ops);
+
+	if (ret && ret != -EUCLEAN)
+		return ret;
+
+	data = (struct mtdswap_oobdata *)d->oob_buf;
+	data2 = (struct mtdswap_oobdata *)
+		(d->oob_buf + d->mtd->ecclayout->oobavail);
+
+	if (le16_to_cpu(data->magic) == MTDSWAP_MAGIC_CLEAN) {
+		eb->erase_count = le32_to_cpu(data->count);
+		if (ret == -EUCLEAN)
+			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_OOB_AUTO;
+	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 = d->mtd->write_oob(d->mtd, offset , &ops);
+
+	if (ret) {
+		dev_warn(d->dev, "Write OOB failed for block at %08llx "
+			"error %d\n", offset, ret);
+		if (ret == -EIO || ret == -EBADMSG)
+			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 %d\n",
+			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 void mtdswap_erase_callback(struct erase_info *done)
+{
+	wait_queue_head_t *wait_q = (wait_queue_head_t *)done->priv;
+	wake_up(wait_q);
+}
+
+static int mtdswap_erase_block(struct mtdswap_dev *d, struct swap_eb *eb)
+{
+	struct mtd_info *mtd = d->mtd;
+	struct erase_info erase;
+	wait_queue_head_t wq;
+	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:
+	init_waitqueue_head(&wq);
+	memset(&erase, 0, sizeof(struct erase_info));
+
+	erase.mtd	= mtd;
+	erase.callback	= mtdswap_erase_callback;
+	erase.addr	= mtdswap_eb_offset(d, eb);
+	erase.len	= mtd->erasesize;
+	erase.priv	= (u_long)&wq;
+
+	ret = mtd->erase(mtd, &erase);
+	if (ret) {
+		if (retries++ < MTDSWAP_ERASE_RETRIES && !MTDSWAP_STRICT) {
+			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\n",
+			erase.addr, mtd->name);
+
+		mtdswap_handle_badblock(d, eb);
+		return -EIO;
+	}
+
+	ret = wait_event_interruptible(wq, erase.state == MTD_ERASE_DONE ||
+					   erase.state == MTD_ERASE_FAILED);
+	if (ret) {
+		dev_err(d->dev, "Interrupted erase block %#llx erassure on %s",
+			erase.addr, mtd->name);
+		return -EINTR;
+	}
+
+	if (erase.state == MTD_ERASE_FAILED) {
+		if (retries++ < MTDSWAP_ERASE_RETRIES) {
+			dev_warn(d->dev,
+				"erase of erase block %#llx on %s failed",
+				erase.addr, mtd->name);
+			yield();
+			goto retry;
+		}
+
+		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 || ret == -EBADMSG);
+
+		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 || ret == -EBADMSG) {
+		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 || ret == -EBADMSG) {
+		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 (%d written)",
+			ret, retlen);
+		goto err;
+	}
+
+	if (retlen != PAGE_SIZE) {
+		dev_err(d->dev, "Short write to MTD device: %d 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 && ret != -EUCLEAN) {
+		oldeb = d->eb_data + oldblock / d->pages_per_eblk;
+		oldeb->flags |= EBLOCK_READERR;
+
+		dev_err(d->dev, "Read Error: %d (block %u)\n", ret,
+			oldblock);
+		retries++;
+		if (retries < MTDSWAP_IO_RETRIES)
+			goto retry;
+
+		goto read_error;
+	}
+
+	if (retlen != PAGE_SIZE) {
+		dev_err(d->dev, "Short read: %d (block %u)\n", 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\n", 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_TRESHOLD)
+		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, 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_OOB_AUTO;
+	ops.len = mtd->writesize;
+	ops.ooblen = mtd->ecclayout->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->ecclayout->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->ecclayout->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 && ret != -EBADMSG)
+		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);
+
+	if (d->mtd->sync)
+		d->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->block_isbad)
+		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 (ret == -EUCLEAN) {
+		eb->flags |= EBLOCK_BITFLIP;
+		mtdswap_rb_add(d, eb, MTDSWAP_BITFLIP);
+		ret = 0;
+	}
+
+	if (ret < 0) {
+		dev_err(d->dev, "Read error %d\n", 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 %d\n", 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;
+	char *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] = rb_entry(rb_first(root), struct swap_eb,
+					rb)->erase_count;
+			max[i] = rb_entry(rb_last(root), struct swap_eb,
+					rb)->erase_count;
+		} 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\n",
+				name[i], count[i], min[i], max[i]);
+		else
+			seq_printf(s, "%s:\t%5d erase blocks, all erased %d "
+				"times\n", name[i], count[i], min[i]);
+	}
+
+	if (bb_cnt)
+		seq_printf(s, "bad:\t%5u erase blocks\n", bb_cnt);
+
+	if (cw)
+		seq_printf(s, "current erase block: %u pages used, %u free, "
+			"erased %u times\n",
+			cwp, d->pages_per_eblk - cwp, cwecount);
+
+	seq_printf(s, "total erasures: %lu\n", sum);
+
+	seq_printf(s, "\n");
+
+	seq_printf(s, "mtdswap_readsect count: %llu\n", d->sect_read_count);
+	seq_printf(s, "mtdswap_writesect count: %llu\n", d->sect_write_count);
+	seq_printf(s, "mtdswap_discard count: %llu\n", d->discard_count);
+	seq_printf(s, "mtd read count: %llu\n", d->mtd_read_count);
+	seq_printf(s, "mtd write count: %llu\n", d->mtd_write_count);
+	seq_printf(s, "discarded pages count: %llu\n", d->discard_page_count);
+
+	seq_printf(s, "\n");
+	seq_printf(s, "total pages: %lu\n", pages);
+	seq_printf(s, "pages mapped: %u\n", mapped);
+
+	return 0;
+}
+
+static int mtdswap_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, mtdswap_show, inode->i_private);
+}
+
+static const struct file_operations mtdswap_fops = {
+	.open		= mtdswap_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
+static int mtdswap_add_debugfs(struct mtdswap_dev *d)
+{
+	struct gendisk *gd = d->mbd_dev->disk;
+	struct device *dev = disk_to_dev(gd);
+
+	struct dentry *root;
+	struct dentry *dent;
+
+	root = debugfs_create_dir(gd->disk_name, NULL);
+	if (IS_ERR(root))
+		return 0;
+
+	if (!root) {
+		dev_err(dev, "failed to initialize debugfs\n");
+		return -1;
+	}
+
+	d->debugfs_root = root;
+
+	dent = debugfs_create_file("stats", S_IRUSR, root, d,
+				&mtdswap_fops);
+	if (!dent) {
+		dev_err(d->dev, "debugfs_create_file failed\n");
+		debugfs_remove_recursive(root);
+		d->debugfs_root = NULL;
+		return -1;
+	}
+
+	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(sizeof(int)*pages);
+	if (!d->page_data)
+		goto page_data_fail;
+
+	d->revmap = vmalloc(sizeof(int)*blocks);
+	if (!d->revmap)
+		goto revmap_fail;
+
+	eblk_bytes = sizeof(struct swap_eb)*d->eblks;
+	d->eb_data = vmalloc(eblk_bytes);
+	if (!d->eb_data)
+		goto eb_data_fail;
+
+	memset(d->eb_data, 0, eblk_bytes);
+	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(2 * mtd->ecclayout->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)\n", 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;
+	struct nand_ecclayout *oinfo;
+	int ret;
+
+	parts = &partitions[0];
+	if (!*parts)
+		return;
+
+	while ((this_opt = strsep(&parts, ",")) != NULL) {
+		if (strict_strtoul(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\n", 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\n", MTDSWAP_PREFIX, PAGE_SIZE, mtd->writesize);
+		return;
+	}
+
+	oinfo = mtd->ecclayout;
+	if (!mtd->oobsize || !oinfo || oinfo->oobavail < MTDSWAP_OOBSIZE) {
+		printk(KERN_ERR "%s: Not enough free bytes in OOB, "
+			"%d available, %u needed.\n",
+			MTDSWAP_PREFIX, oinfo->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\n", MTDSWAP_PREFIX, size_limit);
+		use_size = size_limit;
+	}
+
+	eblocks = mtd_div_by_eb(use_size, mtd);
+	use_size = 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\n", 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\n",
+		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);
+
+	debugfs_remove_recursive(d->debugfs_root);
+	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 <[e-mail]>");
+MODULE_DESCRIPTION("Block device access to an MTD suitable for using as "
+		"swap space");