mtdconcat.c

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/*
 * MTD device concatenation layer
 *
 * Copyright © 2002 Robert Kaiser <[email protected]>
 * Copyright © 2002-2010 David Woodhouse <[email protected]>
 *
 * NAND support by Christian Gan <[email protected]>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * 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/slab.h>
#include <linux/sched.h>
#include <linux/types.h>
#include <linux/backing-dev.h>

#include <linux/mtd/mtd.h>
#include <linux/mtd/concat.h>

#include <asm/div64.h>

/*
 * Our storage structure:
 * Subdev points to an array of pointers to struct mtd_info objects
 * which is allocated along with this structure
 *
 */
struct mtd_concat {
    struct mtd_info mtd;
    int num_subdev;
    struct mtd_info **subdev;
};

/*
 * how to calculate the size required for the above structure,
 * including the pointer array subdev points to:
 */
#define SIZEOF_STRUCT_MTD_CONCAT(num_subdev)    \
    ((sizeof(struct mtd_concat) + (num_subdev) * sizeof(struct mtd_info *)))

/*
 * Given a pointer to the MTD object in the mtd_concat structure,
 * we can retrieve the pointer to that structure with this macro.
 */
#define CONCAT(x)  ((struct mtd_concat *)(x))

/*
 * MTD methods which look up the relevant subdevice, translate the
 * effective address and pass through to the subdevice.
 */

static int
concat_read(struct mtd_info *mtd, loff_t from, size_t len,
        size_t * retlen, u_char * buf)
{
    struct mtd_concat *concat = CONCAT(mtd);
    int ret = 0, err;
    int i;

    for (i = 0; i < concat->num_subdev; i++) {
        struct mtd_info *subdev = concat->subdev[i];
        size_t size, retsize;

        if (from >= subdev->size) {
            /* Not destined for this subdev */
            size = 0;
            from -= subdev->size;
            continue;
        }
        if (from + len > subdev->size)
            /* First part goes into this subdev */
            size = subdev->size - from;
        else
            /* Entire transaction goes into this subdev */
            size = len;

        err = mtd_read(subdev, from, size, &retsize, buf);

        /* Save information about bitflips! */
        if (unlikely(err)) {
            if (mtd_is_eccerr(err)) {
                mtd->ecc_stats.failed++;
                ret = err;
            } else if (mtd_is_bitflip(err)) {
                mtd->ecc_stats.corrected++;
                /* Do not overwrite -EBADMSG !! */
                if (!ret)
                    ret = err;
            } else
                return err;
        }

        *retlen += retsize;
        len -= size;
        if (len == 0)
            return ret;

        buf += size;
        from = 0;
    }
    return -EINVAL;
}

static int
concat_write(struct mtd_info *mtd, loff_t to, size_t len,
         size_t * retlen, const u_char * buf)
{
    struct mtd_concat *concat = CONCAT(mtd);
    int err = -EINVAL;
    int i;

    for (i = 0; i < concat->num_subdev; i++) {
        struct mtd_info *subdev = concat->subdev[i];
        size_t size, retsize;

        if (to >= subdev->size) {
            size = 0;
            to -= subdev->size;
            continue;
        }
        if (to + len > subdev->size)
            size = subdev->size - to;
        else
            size = len;

        err = mtd_write(subdev, to, size, &retsize, buf);
        if (err)
            break;

        *retlen += retsize;
        len -= size;
        if (len == 0)
            break;

        err = -EINVAL;
        buf += size;
        to = 0;
    }
    return err;
}

static int
concat_writev(struct mtd_info *mtd, const struct kvec *vecs,
        unsigned long count, loff_t to, size_t * retlen)
{
    struct mtd_concat *concat = CONCAT(mtd);
    struct kvec *vecs_copy;
    unsigned long entry_low, entry_high;
    size_t total_len = 0;
    int i;
    int err = -EINVAL;

    /* Calculate total length of data */
    for (i = 0; i < count; i++)
        total_len += vecs[i].iov_len;

    /* Check alignment */
    if (mtd->writesize > 1) {
        uint64_t __to = to;
        if (do_div(__to, mtd->writesize) || (total_len % mtd->writesize))
            return -EINVAL;
    }

    /* make a copy of vecs */
    vecs_copy = kmemdup(vecs, sizeof(struct kvec) * count, GFP_KERNEL);
    if (!vecs_copy)
        return -ENOMEM;

    entry_low = 0;
    for (i = 0; i < concat->num_subdev; i++) {
        struct mtd_info *subdev = concat->subdev[i];
        size_t size, wsize, retsize, old_iov_len;

        if (to >= subdev->size) {
            to -= subdev->size;
            continue;
        }

        size = min_t(uint64_t, total_len, subdev->size - to);
        wsize = size; /* store for future use */

        entry_high = entry_low;
        while (entry_high < count) {
            if (size <= vecs_copy[entry_high].iov_len)
                break;
            size -= vecs_copy[entry_high++].iov_len;
        }

        old_iov_len = vecs_copy[entry_high].iov_len;
        vecs_copy[entry_high].iov_len = size;

        err = mtd_writev(subdev, &vecs_copy[entry_low],
                 entry_high - entry_low + 1, to, &retsize);

        vecs_copy[entry_high].iov_len = old_iov_len - size;
        vecs_copy[entry_high].iov_base += size;

        entry_low = entry_high;

        if (err)
            break;

        *retlen += retsize;
        total_len -= wsize;

        if (total_len == 0)
            break;

        err = -EINVAL;
        to = 0;
    }

    kfree(vecs_copy);
    return err;
}

static int
concat_read_oob(struct mtd_info *mtd, loff_t from, struct mtd_oob_ops *ops)
{
    struct mtd_concat *concat = CONCAT(mtd);
    struct mtd_oob_ops devops = *ops;
    int i, err, ret = 0;

    ops->retlen = ops->oobretlen = 0;

    for (i = 0; i < concat->num_subdev; i++) {
        struct mtd_info *subdev = concat->subdev[i];

        if (from >= subdev->size) {
            from -= subdev->size;
            continue;
        }

        /* partial read ? */
        if (from + devops.len > subdev->size)
            devops.len = subdev->size - from;

        err = mtd_read_oob(subdev, from, &devops);
        ops->retlen += devops.retlen;
        ops->oobretlen += devops.oobretlen;

        /* Save information about bitflips! */
        if (unlikely(err)) {
            if (mtd_is_eccerr(err)) {
                mtd->ecc_stats.failed++;
                ret = err;
            } else if (mtd_is_bitflip(err)) {
                mtd->ecc_stats.corrected++;
                /* Do not overwrite -EBADMSG !! */
                if (!ret)
                    ret = err;
            } else
                return err;
        }

        if (devops.datbuf) {
            devops.len = ops->len - ops->retlen;
            if (!devops.len)
                return ret;
            devops.datbuf += devops.retlen;
        }
        if (devops.oobbuf) {
            devops.ooblen = ops->ooblen - ops->oobretlen;
            if (!devops.ooblen)
                return ret;
            devops.oobbuf += ops->oobretlen;
        }

        from = 0;
    }
    return -EINVAL;
}

static int
concat_write_oob(struct mtd_info *mtd, loff_t to, struct mtd_oob_ops *ops)
{
    struct mtd_concat *concat = CONCAT(mtd);
    struct mtd_oob_ops devops = *ops;
    int i, err;

    if (!(mtd->flags & MTD_WRITEABLE))
        return -EROFS;

    ops->retlen = ops->oobretlen = 0;

    for (i = 0; i < concat->num_subdev; i++) {
        struct mtd_info *subdev = concat->subdev[i];

        if (to >= subdev->size) {
            to -= subdev->size;
            continue;
        }

        /* partial write ? */
        if (to + devops.len > subdev->size)
            devops.len = subdev->size - to;

        err = mtd_write_oob(subdev, to, &devops);
        ops->retlen += devops.oobretlen;
        if (err)
            return err;

        if (devops.datbuf) {
            devops.len = ops->len - ops->retlen;
            if (!devops.len)
                return 0;
            devops.datbuf += devops.retlen;
        }
        if (devops.oobbuf) {
            devops.ooblen = ops->ooblen - ops->oobretlen;
            if (!devops.ooblen)
                return 0;
            devops.oobbuf += devops.oobretlen;
        }
        to = 0;
    }
    return -EINVAL;
}

static void concat_erase_callback(struct erase_info *instr)
{
    wake_up((wait_queue_head_t *) instr->priv);
}

static int concat_dev_erase(struct mtd_info *mtd, struct erase_info *erase)
{
    int err;
    wait_queue_head_t waitq;
    DECLARE_WAITQUEUE(wait, current);

    /*
     * This code was stol^H^H^H^Hinspired by mtdchar.c
     */
    init_waitqueue_head(&waitq);

    erase->mtd = mtd;
    erase->callback = concat_erase_callback;
    erase->priv = (unsigned long) &waitq;

    /*
     * FIXME: Allow INTERRUPTIBLE. Which means
     * not having the wait_queue head on the stack.
     */
    err = mtd_erase(mtd, erase);
    if (!err) {
        set_current_state(TASK_UNINTERRUPTIBLE);
        add_wait_queue(&waitq, &wait);
        if (erase->state != MTD_ERASE_DONE
            && erase->state != MTD_ERASE_FAILED)
            schedule();
        remove_wait_queue(&waitq, &wait);
        set_current_state(TASK_RUNNING);

        err = (erase->state == MTD_ERASE_FAILED) ? -EIO : 0;
    }
    return err;
}

static int concat_erase(struct mtd_info *mtd, struct erase_info *instr)
{
    struct mtd_concat *concat = CONCAT(mtd);
    struct mtd_info *subdev;
    int i, err;
    uint64_t length, offset = 0;
    struct erase_info *erase;

    /*
     * Check for proper erase block alignment of the to-be-erased area.
     * It is easier to do this based on the super device's erase
     * region info rather than looking at each particular sub-device
     * in turn.
     */
    if (!concat->mtd.numeraseregions) {
        /* the easy case: device has uniform erase block size */
        if (instr->addr & (concat->mtd.erasesize - 1))
            return -EINVAL;
        if (instr->len & (concat->mtd.erasesize - 1))
            return -EINVAL;
    } else {
        /* device has variable erase size */
        struct mtd_erase_region_info *erase_regions =
            concat->mtd.eraseregions;

        /*
         * Find the erase region where the to-be-erased area begins:
         */
        for (i = 0; i < concat->mtd.numeraseregions &&
             instr->addr >= erase_regions[i].offset; i++) ;
        --i;

        /*
         * Now erase_regions[i] is the region in which the
         * to-be-erased area begins. Verify that the starting
         * offset is aligned to this region's erase size:
         */
        if (i < 0 || instr->addr & (erase_regions[i].erasesize - 1))
            return -EINVAL;

        /*
         * now find the erase region where the to-be-erased area ends:
         */
        for (; i < concat->mtd.numeraseregions &&
             (instr->addr + instr->len) >= erase_regions[i].offset;
             ++i) ;
        --i;
        /*
         * check if the ending offset is aligned to this region's erase size
         */
        if (i < 0 || ((instr->addr + instr->len) &
                    (erase_regions[i].erasesize - 1)))
            return -EINVAL;
    }

    /* make a local copy of instr to avoid modifying the caller's struct */
    erase = kmalloc(sizeof (struct erase_info), GFP_KERNEL);

    if (!erase)
        return -ENOMEM;

    *erase = *instr;
    length = instr->len;

    /*
     * find the subdevice where the to-be-erased area begins, adjust
     * starting offset to be relative to the subdevice start
     */
    for (i = 0; i < concat->num_subdev; i++) {
        subdev = concat->subdev[i];
        if (subdev->size <= erase->addr) {
            erase->addr -= subdev->size;
            offset += subdev->size;
        } else {
            break;
        }
    }

    /* must never happen since size limit has been verified above */
    BUG_ON(i >= concat->num_subdev);

    /* now do the erase: */
    err = 0;
    for (; length > 0; i++) {
        /* loop for all subdevices affected by this request */
        subdev = concat->subdev[i]; /* get current subdevice */

        /* limit length to subdevice's size: */
        if (erase->addr + length > subdev->size)
            erase->len = subdev->size - erase->addr;
        else
            erase->len = length;

        length -= erase->len;
        if ((err = concat_dev_erase(subdev, erase))) {
            /* sanity check: should never happen since
             * block alignment has been checked above */
            BUG_ON(err == -EINVAL);
            if (erase->fail_addr != MTD_FAIL_ADDR_UNKNOWN)
                instr->fail_addr = erase->fail_addr + offset;
            break;
        }
        /*
         * erase->addr specifies the offset of the area to be
         * erased *within the current subdevice*. It can be
         * non-zero only the first time through this loop, i.e.
         * for the first subdevice where blocks need to be erased.
         * All the following erases must begin at the start of the
         * current subdevice, i.e. at offset zero.
         */
        erase->addr = 0;
        offset += subdev->size;
    }
    instr->state = erase->state;
    kfree(erase);
    if (err)
        return err;

    if (instr->callback)
        instr->callback(instr);
    return 0;
}

static int concat_lock(struct mtd_info *mtd, loff_t ofs, uint64_t len)
{
    struct mtd_concat *concat = CONCAT(mtd);
    int i, err = -EINVAL;

    for (i = 0; i < concat->num_subdev; i++) {
        struct mtd_info *subdev = concat->subdev[i];
        uint64_t size;

        if (ofs >= subdev->size) {
            size = 0;
            ofs -= subdev->size;
            continue;
        }
        if (ofs + len > subdev->size)
            size = subdev->size - ofs;
        else
            size = len;

        err = mtd_lock(subdev, ofs, size);
        if (err)
            break;

        len -= size;
        if (len == 0)
            break;

        err = -EINVAL;
        ofs = 0;
    }

    return err;
}

static int concat_unlock(struct mtd_info *mtd, loff_t ofs, uint64_t len)
{
    struct mtd_concat *concat = CONCAT(mtd);
    int i, err = 0;

    for (i = 0; i < concat->num_subdev; i++) {
        struct mtd_info *subdev = concat->subdev[i];
        uint64_t size;

        if (ofs >= subdev->size) {
            size = 0;
            ofs -= subdev->size;
            continue;
        }
        if (ofs + len > subdev->size)
            size = subdev->size - ofs;
        else
            size = len;

        err = mtd_unlock(subdev, ofs, size);
        if (err)
            break;

        len -= size;
        if (len == 0)
            break;

        err = -EINVAL;
        ofs = 0;
    }

    return err;
}

static void concat_sync(struct mtd_info *mtd)
{
    struct mtd_concat *concat = CONCAT(mtd);
    int i;

    for (i = 0; i < concat->num_subdev; i++) {
        struct mtd_info *subdev = concat->subdev[i];
        mtd_sync(subdev);
    }
}

static int concat_suspend(struct mtd_info *mtd)
{
    struct mtd_concat *concat = CONCAT(mtd);
    int i, rc = 0;

    for (i = 0; i < concat->num_subdev; i++) {
        struct mtd_info *subdev = concat->subdev[i];
        if ((rc = mtd_suspend(subdev)) < 0)
            return rc;
    }
    return rc;
}

static void concat_resume(struct mtd_info *mtd)
{
    struct mtd_concat *concat = CONCAT(mtd);
    int i;

    for (i = 0; i < concat->num_subdev; i++) {
        struct mtd_info *subdev = concat->subdev[i];
        mtd_resume(subdev);
    }
}

static int concat_block_isbad(struct mtd_info *mtd, loff_t ofs)
{
    struct mtd_concat *concat = CONCAT(mtd);
    int i, res = 0;

    if (!mtd_can_have_bb(concat->subdev[0]))
        return res;

    for (i = 0; i < concat->num_subdev; i++) {
        struct mtd_info *subdev = concat->subdev[i];

        if (ofs >= subdev->size) {
            ofs -= subdev->size;
            continue;
        }

        res = mtd_block_isbad(subdev, ofs);
        break;
    }

    return res;
}

static int concat_block_markbad(struct mtd_info *mtd, loff_t ofs)
{
    struct mtd_concat *concat = CONCAT(mtd);
    int i, err = -EINVAL;

    for (i = 0; i < concat->num_subdev; i++) {
        struct mtd_info *subdev = concat->subdev[i];

        if (ofs >= subdev->size) {
            ofs -= subdev->size;
            continue;
        }

        err = mtd_block_markbad(subdev, ofs);
        if (!err)
            mtd->ecc_stats.badblocks++;
        break;
    }

    return err;
}

/*
 * try to support NOMMU mmaps on concatenated devices
 * - we don't support subdev spanning as we can't guarantee it'll work
 */
static unsigned long concat_get_unmapped_area(struct mtd_info *mtd,
                          unsigned long len,
                          unsigned long offset,
                          unsigned long flags)
{
    struct mtd_concat *concat = CONCAT(mtd);
    int i;

    for (i = 0; i < concat->num_subdev; i++) {
        struct mtd_info *subdev = concat->subdev[i];

        if (offset >= subdev->size) {
            offset -= subdev->size;
            continue;
        }

        return mtd_get_unmapped_area(subdev, len, offset, flags);
    }

    return (unsigned long) -ENOSYS;
}

/*
 * This function constructs a virtual MTD device by concatenating
 * num_devs MTD devices. A pointer to the new device object is
 * stored to *new_dev upon success. This function does _not_
 * register any devices: this is the caller's responsibility.
 */
struct mtd_info *mtd_concat_create(struct mtd_info *subdev[],   /* subdevices to concatenate */
                   int num_devs,    /* number of subdevices      */
                   const char *name)
{               /* name for the new device   */
    int i;
    size_t size;
    struct mtd_concat *concat;
    uint32_t max_erasesize, curr_erasesize;
    int num_erase_region;
    int max_writebufsize = 0;

    printk(KERN_NOTICE "Concatenating MTD devices:\n");
    for (i = 0; i < num_devs; i++)
        printk(KERN_NOTICE "(%d): \"%s\"\n", i, subdev[i]->name);
    printk(KERN_NOTICE "into device \"%s\"\n", name);

    /* allocate the device structure */
    size = SIZEOF_STRUCT_MTD_CONCAT(num_devs);
    concat = kzalloc(size, GFP_KERNEL);
    if (!concat) {
        printk
            ("memory allocation error while creating concatenated device \"%s\"\n",
             name);
        return NULL;
    }
    concat->subdev = (struct mtd_info **) (concat + 1);

    /*
     * Set up the new "super" device's MTD object structure, check for
     * incompatibilities between the subdevices.
     */
    concat->mtd.type = subdev[0]->type;
    concat->mtd.flags = subdev[0]->flags;
    concat->mtd.size = subdev[0]->size;
    concat->mtd.erasesize = subdev[0]->erasesize;
    concat->mtd.writesize = subdev[0]->writesize;

    for (i = 0; i < num_devs; i++)
        if (max_writebufsize < subdev[i]->writebufsize)
            max_writebufsize = subdev[i]->writebufsize;
    concat->mtd.writebufsize = max_writebufsize;

    concat->mtd.subpage_sft = subdev[0]->subpage_sft;
    concat->mtd.oobsize = subdev[0]->oobsize;
    concat->mtd.oobavail = subdev[0]->oobavail;
    if (subdev[0]->_writev)
        concat->mtd._writev = concat_writev;
    if (subdev[0]->_read_oob)
        concat->mtd._read_oob = concat_read_oob;
    if (subdev[0]->_write_oob)
        concat->mtd._write_oob = concat_write_oob;
    if (subdev[0]->_block_isbad)
        concat->mtd._block_isbad = concat_block_isbad;
    if (subdev[0]->_block_markbad)
        concat->mtd._block_markbad = concat_block_markbad;

    concat->mtd.ecc_stats.badblocks = subdev[0]->ecc_stats.badblocks;

    concat->mtd.backing_dev_info = subdev[0]->backing_dev_info;

    concat->subdev[0] = subdev[0];

    for (i = 1; i < num_devs; i++) {
        if (concat->mtd.type != subdev[i]->type) {
            kfree(concat);
            printk("Incompatible device type on \"%s\"\n",
                   subdev[i]->name);
            return NULL;
        }
        if (concat->mtd.flags != subdev[i]->flags) {
            /*
             * Expect all flags except MTD_WRITEABLE to be
             * equal on all subdevices.
             */
            if ((concat->mtd.flags ^ subdev[i]->
                 flags) & ~MTD_WRITEABLE) {
                kfree(concat);
                printk("Incompatible device flags on \"%s\"\n",
                       subdev[i]->name);
                return NULL;
            } else
                /* if writeable attribute differs,
                   make super device writeable */
                concat->mtd.flags |=
                    subdev[i]->flags & MTD_WRITEABLE;
        }

        /* only permit direct mapping if the BDIs are all the same
         * - copy-mapping is still permitted
         */
        if (concat->mtd.backing_dev_info !=
            subdev[i]->backing_dev_info)
            concat->mtd.backing_dev_info =
                &default_backing_dev_info;

        concat->mtd.size += subdev[i]->size;
        concat->mtd.ecc_stats.badblocks +=
            subdev[i]->ecc_stats.badblocks;
        if (concat->mtd.writesize   !=  subdev[i]->writesize ||
            concat->mtd.subpage_sft != subdev[i]->subpage_sft ||
            concat->mtd.oobsize    !=  subdev[i]->oobsize ||
            !concat->mtd._read_oob  != !subdev[i]->_read_oob ||
            !concat->mtd._write_oob != !subdev[i]->_write_oob) {
            kfree(concat);
            printk("Incompatible OOB or ECC data on \"%s\"\n",
                   subdev[i]->name);
            return NULL;
        }
        concat->subdev[i] = subdev[i];

    }

    concat->mtd.ecclayout = subdev[0]->ecclayout;

    concat->num_subdev = num_devs;
    concat->mtd.name = name;

    concat->mtd._erase = concat_erase;
    concat->mtd._read = concat_read;
    concat->mtd._write = concat_write;
    concat->mtd._sync = concat_sync;
    concat->mtd._lock = concat_lock;
    concat->mtd._unlock = concat_unlock;
    concat->mtd._suspend = concat_suspend;
    concat->mtd._resume = concat_resume;
    concat->mtd._get_unmapped_area = concat_get_unmapped_area;

    /*
     * Combine the erase block size info of the subdevices:
     *
     * first, walk the map of the new device and see how
     * many changes in erase size we have
     */
    max_erasesize = curr_erasesize = subdev[0]->erasesize;
    num_erase_region = 1;
    for (i = 0; i < num_devs; i++) {
        if (subdev[i]->numeraseregions == 0) {
            /* current subdevice has uniform erase size */
            if (subdev[i]->erasesize != curr_erasesize) {
                /* if it differs from the last subdevice's erase size, count it */
                ++num_erase_region;
                curr_erasesize = subdev[i]->erasesize;
                if (curr_erasesize > max_erasesize)
                    max_erasesize = curr_erasesize;
            }
        } else {
            /* current subdevice has variable erase size */
            int j;
            for (j = 0; j < subdev[i]->numeraseregions; j++) {

                /* walk the list of erase regions, count any changes */
                if (subdev[i]->eraseregions[j].erasesize !=
                    curr_erasesize) {
                    ++num_erase_region;
                    curr_erasesize =
                        subdev[i]->eraseregions[j].
                        erasesize;
                    if (curr_erasesize > max_erasesize)
                        max_erasesize = curr_erasesize;
                }
            }
        }
    }

    if (num_erase_region == 1) {
        /*
         * All subdevices have the same uniform erase size.
         * This is easy:
         */
        concat->mtd.erasesize = curr_erasesize;
        concat->mtd.numeraseregions = 0;
    } else {
        uint64_t tmp64;

        /*
         * erase block size varies across the subdevices: allocate
         * space to store the data describing the variable erase regions
         */
        struct mtd_erase_region_info *erase_region_p;
        uint64_t begin, position;

        concat->mtd.erasesize = max_erasesize;
        concat->mtd.numeraseregions = num_erase_region;
        concat->mtd.eraseregions = erase_region_p =
            kmalloc(num_erase_region *
                sizeof (struct mtd_erase_region_info), GFP_KERNEL);
        if (!erase_region_p) {
            kfree(concat);
            printk
                ("memory allocation error while creating erase region list"
                 " for device \"%s\"\n", name);
            return NULL;
        }

        /*
         * walk the map of the new device once more and fill in
         * in erase region info:
         */
        curr_erasesize = subdev[0]->erasesize;
        begin = position = 0;
        for (i = 0; i < num_devs; i++) {
            if (subdev[i]->numeraseregions == 0) {
                /* current subdevice has uniform erase size */
                if (subdev[i]->erasesize != curr_erasesize) {
                    /*
                     *  fill in an mtd_erase_region_info structure for the area
                     *  we have walked so far:
                     */
                    erase_region_p->offset = begin;
                    erase_region_p->erasesize =
                        curr_erasesize;
                    tmp64 = position - begin;
                    do_div(tmp64, curr_erasesize);
                    erase_region_p->numblocks = tmp64;
                    begin = position;

                    curr_erasesize = subdev[i]->erasesize;
                    ++erase_region_p;
                }
                position += subdev[i]->size;
            } else {
                /* current subdevice has variable erase size */
                int j;
                for (j = 0; j < subdev[i]->numeraseregions; j++) {
                    /* walk the list of erase regions, count any changes */
                    if (subdev[i]->eraseregions[j].
                        erasesize != curr_erasesize) {
                        erase_region_p->offset = begin;
                        erase_region_p->erasesize =
                            curr_erasesize;
                        tmp64 = position - begin;
                        do_div(tmp64, curr_erasesize);
                        erase_region_p->numblocks = tmp64;
                        begin = position;

                        curr_erasesize =
                            subdev[i]->eraseregions[j].
                            erasesize;
                        ++erase_region_p;
                    }
                    position +=
                        subdev[i]->eraseregions[j].
                        numblocks * (uint64_t)curr_erasesize;
                }
            }
        }
        /* Now write the final entry */
        erase_region_p->offset = begin;
        erase_region_p->erasesize = curr_erasesize;
        tmp64 = position - begin;
        do_div(tmp64, curr_erasesize);
        erase_region_p->numblocks = tmp64;
    }

    return &concat->mtd;
}

/*
 * This function destroys an MTD object obtained from concat_mtd_devs()
 */

void mtd_concat_destroy(struct mtd_info *mtd)
{
    struct mtd_concat *concat = CONCAT(mtd);
    if (concat->mtd.numeraseregions)
        kfree(concat->mtd.eraseregions);
    kfree(concat);
}

EXPORT_SYMBOL(mtd_concat_create);
EXPORT_SYMBOL(mtd_concat_destroy);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Robert Kaiser <[email protected]>");
MODULE_DESCRIPTION("Generic support for concatenating of MTD devices");