mtdswap.c

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/*
 * 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 <[email protected]>
 *
 * 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 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 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

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\n", offset);
    ret = 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 = 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\n",
            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\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 (mtd_can_have_bb(d->mtd) && 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_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->ecclayout->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\n", 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\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) {
            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 || 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)\n", 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)\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 = -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->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 && !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\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 %zd\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: %u\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 = 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(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 (!oinfo) {
        printk(KERN_ERR "%s: mtd%d does not have OOB\n",
            MTDSWAP_PREFIX, mtd->index);
        return;
    }

    if (!mtd->oobsize || oinfo->oobavail < MTDSWAP_OOBSIZE) {
        printk(KERN_ERR "%s: Not enough free bytes in OOB, "
            "%d available, %zu 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 <[email protected]>");
MODULE_DESCRIPTION("Block device access to an MTD suitable for using as "
        "swap space");