attach.c

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/*
 * Copyright (c) International Business Machines Corp., 2006
 *
 * 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 *
 * Author: Artem Bityutskiy (Битюцкий Артём)
 */

/*
 * UBI attaching sub-system.
 *
 * This sub-system is responsible for attaching MTD devices and it also
 * implements flash media scanning.
 *
 * The attaching information is represented by a &struct ubi_attach_info'
 * object. Information about volumes is represented by &struct ubi_ainf_volume
 * objects which are kept in volume RB-tree with root at the @volumes field.
 * The RB-tree is indexed by the volume ID.
 *
 * Logical eraseblocks are represented by &struct ubi_ainf_peb objects. These
 * objects are kept in per-volume RB-trees with the root at the corresponding
 * &struct ubi_ainf_volume object. To put it differently, we keep an RB-tree of
 * per-volume objects and each of these objects is the root of RB-tree of
 * per-LEB objects.
 *
 * Corrupted physical eraseblocks are put to the @corr list, free physical
 * eraseblocks are put to the @free list and the physical eraseblock to be
 * erased are put to the @erase list.
 *
 * About corruptions
 * ~~~~~~~~~~~~~~~~~
 *
 * UBI protects EC and VID headers with CRC-32 checksums, so it can detect
 * whether the headers are corrupted or not. Sometimes UBI also protects the
 * data with CRC-32, e.g., when it executes the atomic LEB change operation, or
 * when it moves the contents of a PEB for wear-leveling purposes.
 *
 * UBI tries to distinguish between 2 types of corruptions.
 *
 * 1. Corruptions caused by power cuts. These are expected corruptions and UBI
 * tries to handle them gracefully, without printing too many warnings and
 * error messages. The idea is that we do not lose important data in these
 * cases - we may lose only the data which were being written to the media just
 * before the power cut happened, and the upper layers (e.g., UBIFS) are
 * supposed to handle such data losses (e.g., by using the FS journal).
 *
 * When UBI detects a corruption (CRC-32 mismatch) in a PEB, and it looks like
 * the reason is a power cut, UBI puts this PEB to the @erase list, and all
 * PEBs in the @erase list are scheduled for erasure later.
 *
 * 2. Unexpected corruptions which are not caused by power cuts. During
 * attaching, such PEBs are put to the @corr list and UBI preserves them.
 * Obviously, this lessens the amount of available PEBs, and if at some  point
 * UBI runs out of free PEBs, it switches to R/O mode. UBI also loudly informs
 * about such PEBs every time the MTD device is attached.
 *
 * However, it is difficult to reliably distinguish between these types of
 * corruptions and UBI's strategy is as follows (in case of attaching by
 * scanning). UBI assumes corruption type 2 if the VID header is corrupted and
 * the data area does not contain all 0xFFs, and there were no bit-flips or
 * integrity errors (e.g., ECC errors in case of NAND) while reading the data
 * area.  Otherwise UBI assumes corruption type 1. So the decision criteria
 * are as follows.
 *   o If the data area contains only 0xFFs, there are no data, and it is safe
 *     to just erase this PEB - this is corruption type 1.
 *   o If the data area has bit-flips or data integrity errors (ECC errors on
 *     NAND), it is probably a PEB which was being erased when power cut
 *     happened, so this is corruption type 1. However, this is just a guess,
 *     which might be wrong.
 *   o Otherwise this is corruption type 2.
 */

#include <linux/err.h>
#include <linux/slab.h>
#include <linux/crc32.h>
#include <linux/math64.h>
#include <linux/random.h>
#include "ubi.h"

static int self_check_ai(struct ubi_device *ubi, struct ubi_attach_info *ai);

/* Temporary variables used during scanning */
static struct ubi_ec_hdr *ech;
static struct ubi_vid_hdr *vidh;

static int add_to_list(struct ubi_attach_info *ai, int pnum, int vol_id,
               int lnum, int ec, int to_head, struct list_head *list)
{
    struct ubi_ainf_peb *aeb;

    if (list == &ai->free) {
        dbg_bld("add to free: PEB %d, EC %d", pnum, ec);
    } else if (list == &ai->erase) {
        dbg_bld("add to erase: PEB %d, EC %d", pnum, ec);
    } else if (list == &ai->alien) {
        dbg_bld("add to alien: PEB %d, EC %d", pnum, ec);
        ai->alien_peb_count += 1;
    } else
        BUG();

    aeb = kmem_cache_alloc(ai->aeb_slab_cache, GFP_KERNEL);
    if (!aeb)
        return -ENOMEM;

    aeb->pnum = pnum;
    aeb->vol_id = vol_id;
    aeb->lnum = lnum;
    aeb->ec = ec;
    if (to_head)
        list_add(&aeb->u.list, list);
    else
        list_add_tail(&aeb->u.list, list);
    return 0;
}

static int add_corrupted(struct ubi_attach_info *ai, int pnum, int ec)
{
    struct ubi_ainf_peb *aeb;

    dbg_bld("add to corrupted: PEB %d, EC %d", pnum, ec);

    aeb = kmem_cache_alloc(ai->aeb_slab_cache, GFP_KERNEL);
    if (!aeb)
        return -ENOMEM;

    ai->corr_peb_count += 1;
    aeb->pnum = pnum;
    aeb->ec = ec;
    list_add(&aeb->u.list, &ai->corr);
    return 0;
}

static int validate_vid_hdr(const struct ubi_vid_hdr *vid_hdr,
                const struct ubi_ainf_volume *av, int pnum)
{
    int vol_type = vid_hdr->vol_type;
    int vol_id = be32_to_cpu(vid_hdr->vol_id);
    int used_ebs = be32_to_cpu(vid_hdr->used_ebs);
    int data_pad = be32_to_cpu(vid_hdr->data_pad);

    if (av->leb_count != 0) {
        int av_vol_type;

        /*
         * This is not the first logical eraseblock belonging to this
         * volume. Ensure that the data in its VID header is consistent
         * to the data in previous logical eraseblock headers.
         */

        if (vol_id != av->vol_id) {
            ubi_err("inconsistent vol_id");
            goto bad;
        }

        if (av->vol_type == UBI_STATIC_VOLUME)
            av_vol_type = UBI_VID_STATIC;
        else
            av_vol_type = UBI_VID_DYNAMIC;

        if (vol_type != av_vol_type) {
            ubi_err("inconsistent vol_type");
            goto bad;
        }

        if (used_ebs != av->used_ebs) {
            ubi_err("inconsistent used_ebs");
            goto bad;
        }

        if (data_pad != av->data_pad) {
            ubi_err("inconsistent data_pad");
            goto bad;
        }
    }

    return 0;

bad:
    ubi_err("inconsistent VID header at PEB %d", pnum);
    ubi_dump_vid_hdr(vid_hdr);
    ubi_dump_av(av);
    return -EINVAL;
}

static struct ubi_ainf_volume *add_volume(struct ubi_attach_info *ai,
                      int vol_id, int pnum,
                      const struct ubi_vid_hdr *vid_hdr)
{
    struct ubi_ainf_volume *av;
    struct rb_node **p = &ai->volumes.rb_node, *parent = NULL;

    ubi_assert(vol_id == be32_to_cpu(vid_hdr->vol_id));

    /* Walk the volume RB-tree to look if this volume is already present */
    while (*p) {
        parent = *p;
        av = rb_entry(parent, struct ubi_ainf_volume, rb);

        if (vol_id == av->vol_id)
            return av;

        if (vol_id > av->vol_id)
            p = &(*p)->rb_left;
        else
            p = &(*p)->rb_right;
    }

    /* The volume is absent - add it */
    av = kmalloc(sizeof(struct ubi_ainf_volume), GFP_KERNEL);
    if (!av)
        return ERR_PTR(-ENOMEM);

    av->highest_lnum = av->leb_count = 0;
    av->vol_id = vol_id;
    av->root = RB_ROOT;
    av->used_ebs = be32_to_cpu(vid_hdr->used_ebs);
    av->data_pad = be32_to_cpu(vid_hdr->data_pad);
    av->compat = vid_hdr->compat;
    av->vol_type = vid_hdr->vol_type == UBI_VID_DYNAMIC ? UBI_DYNAMIC_VOLUME
                                : UBI_STATIC_VOLUME;
    if (vol_id > ai->highest_vol_id)
        ai->highest_vol_id = vol_id;

    rb_link_node(&av->rb, parent, p);
    rb_insert_color(&av->rb, &ai->volumes);
    ai->vols_found += 1;
    dbg_bld("added volume %d", vol_id);
    return av;
}

int ubi_compare_lebs(struct ubi_device *ubi, const struct ubi_ainf_peb *aeb,
            int pnum, const struct ubi_vid_hdr *vid_hdr)
{
    void *buf;
    int len, err, second_is_newer, bitflips = 0, corrupted = 0;
    uint32_t data_crc, crc;
    struct ubi_vid_hdr *vh = NULL;
    unsigned long long sqnum2 = be64_to_cpu(vid_hdr->sqnum);

    if (sqnum2 == aeb->sqnum) {
        /*
         * This must be a really ancient UBI image which has been
         * created before sequence numbers support has been added. At
         * that times we used 32-bit LEB versions stored in logical
         * eraseblocks. That was before UBI got into mainline. We do not
         * support these images anymore. Well, those images still work,
         * but only if no unclean reboots happened.
         */
        ubi_err("unsupported on-flash UBI format");
        return -EINVAL;
    }

    /* Obviously the LEB with lower sequence counter is older */
    second_is_newer = (sqnum2 > aeb->sqnum);

    /*
     * Now we know which copy is newer. If the copy flag of the PEB with
     * newer version is not set, then we just return, otherwise we have to
     * check data CRC. For the second PEB we already have the VID header,
     * for the first one - we'll need to re-read it from flash.
     *
     * Note: this may be optimized so that we wouldn't read twice.
     */

    if (second_is_newer) {
        if (!vid_hdr->copy_flag) {
            /* It is not a copy, so it is newer */
            dbg_bld("second PEB %d is newer, copy_flag is unset",
                pnum);
            return 1;
        }
    } else {
        if (!aeb->copy_flag) {
            /* It is not a copy, so it is newer */
            dbg_bld("first PEB %d is newer, copy_flag is unset",
                pnum);
            return bitflips << 1;
        }

        vh = ubi_zalloc_vid_hdr(ubi, GFP_KERNEL);
        if (!vh)
            return -ENOMEM;

        pnum = aeb->pnum;
        err = ubi_io_read_vid_hdr(ubi, pnum, vh, 0);
        if (err) {
            if (err == UBI_IO_BITFLIPS)
                bitflips = 1;
            else {
                ubi_err("VID of PEB %d header is bad, but it was OK earlier, err %d",
                    pnum, err);
                if (err > 0)
                    err = -EIO;

                goto out_free_vidh;
            }
        }

        vid_hdr = vh;
    }

    /* Read the data of the copy and check the CRC */

    len = be32_to_cpu(vid_hdr->data_size);
    buf = vmalloc(len);
    if (!buf) {
        err = -ENOMEM;
        goto out_free_vidh;
    }

    err = ubi_io_read_data(ubi, buf, pnum, 0, len);
    if (err && err != UBI_IO_BITFLIPS && !mtd_is_eccerr(err))
        goto out_free_buf;

    data_crc = be32_to_cpu(vid_hdr->data_crc);
    crc = crc32(UBI_CRC32_INIT, buf, len);
    if (crc != data_crc) {
        dbg_bld("PEB %d CRC error: calculated %#08x, must be %#08x",
            pnum, crc, data_crc);
        corrupted = 1;
        bitflips = 0;
        second_is_newer = !second_is_newer;
    } else {
        dbg_bld("PEB %d CRC is OK", pnum);
        bitflips = !!err;
    }

    vfree(buf);
    ubi_free_vid_hdr(ubi, vh);

    if (second_is_newer)
        dbg_bld("second PEB %d is newer, copy_flag is set", pnum);
    else
        dbg_bld("first PEB %d is newer, copy_flag is set", pnum);

    return second_is_newer | (bitflips << 1) | (corrupted << 2);

out_free_buf:
    vfree(buf);
out_free_vidh:
    ubi_free_vid_hdr(ubi, vh);
    return err;
}

int ubi_add_to_av(struct ubi_device *ubi, struct ubi_attach_info *ai, int pnum,
          int ec, const struct ubi_vid_hdr *vid_hdr, int bitflips)
{
    int err, vol_id, lnum;
    unsigned long long sqnum;
    struct ubi_ainf_volume *av;
    struct ubi_ainf_peb *aeb;
    struct rb_node **p, *parent = NULL;

    vol_id = be32_to_cpu(vid_hdr->vol_id);
    lnum = be32_to_cpu(vid_hdr->lnum);
    sqnum = be64_to_cpu(vid_hdr->sqnum);

    dbg_bld("PEB %d, LEB %d:%d, EC %d, sqnum %llu, bitflips %d",
        pnum, vol_id, lnum, ec, sqnum, bitflips);

    av = add_volume(ai, vol_id, pnum, vid_hdr);
    if (IS_ERR(av))
        return PTR_ERR(av);

    if (ai->max_sqnum < sqnum)
        ai->max_sqnum = sqnum;

    /*
     * Walk the RB-tree of logical eraseblocks of volume @vol_id to look
     * if this is the first instance of this logical eraseblock or not.
     */
    p = &av->root.rb_node;
    while (*p) {
        int cmp_res;

        parent = *p;
        aeb = rb_entry(parent, struct ubi_ainf_peb, u.rb);
        if (lnum != aeb->lnum) {
            if (lnum < aeb->lnum)
                p = &(*p)->rb_left;
            else
                p = &(*p)->rb_right;
            continue;
        }

        /*
         * There is already a physical eraseblock describing the same
         * logical eraseblock present.
         */

        dbg_bld("this LEB already exists: PEB %d, sqnum %llu, EC %d",
            aeb->pnum, aeb->sqnum, aeb->ec);

        /*
         * Make sure that the logical eraseblocks have different
         * sequence numbers. Otherwise the image is bad.
         *
         * However, if the sequence number is zero, we assume it must
         * be an ancient UBI image from the era when UBI did not have
         * sequence numbers. We still can attach these images, unless
         * there is a need to distinguish between old and new
         * eraseblocks, in which case we'll refuse the image in
         * 'ubi_compare_lebs()'. In other words, we attach old clean
         * images, but refuse attaching old images with duplicated
         * logical eraseblocks because there was an unclean reboot.
         */
        if (aeb->sqnum == sqnum && sqnum != 0) {
            ubi_err("two LEBs with same sequence number %llu",
                sqnum);
            ubi_dump_aeb(aeb, 0);
            ubi_dump_vid_hdr(vid_hdr);
            return -EINVAL;
        }

        /*
         * Now we have to drop the older one and preserve the newer
         * one.
         */
        cmp_res = ubi_compare_lebs(ubi, aeb, pnum, vid_hdr);
        if (cmp_res < 0)
            return cmp_res;

        if (cmp_res & 1) {
            /*
             * This logical eraseblock is newer than the one
             * found earlier.
             */
            err = validate_vid_hdr(vid_hdr, av, pnum);
            if (err)
                return err;

            err = add_to_list(ai, aeb->pnum, aeb->vol_id,
                      aeb->lnum, aeb->ec, cmp_res & 4,
                      &ai->erase);
            if (err)
                return err;

            aeb->ec = ec;
            aeb->pnum = pnum;
            aeb->vol_id = vol_id;
            aeb->lnum = lnum;
            aeb->scrub = ((cmp_res & 2) || bitflips);
            aeb->copy_flag = vid_hdr->copy_flag;
            aeb->sqnum = sqnum;

            if (av->highest_lnum == lnum)
                av->last_data_size =
                    be32_to_cpu(vid_hdr->data_size);

            return 0;
        } else {
            /*
             * This logical eraseblock is older than the one found
             * previously.
             */
            return add_to_list(ai, pnum, vol_id, lnum, ec,
                       cmp_res & 4, &ai->erase);
        }
    }

    /*
     * We've met this logical eraseblock for the first time, add it to the
     * attaching information.
     */

    err = validate_vid_hdr(vid_hdr, av, pnum);
    if (err)
        return err;

    aeb = kmem_cache_alloc(ai->aeb_slab_cache, GFP_KERNEL);
    if (!aeb)
        return -ENOMEM;

    aeb->ec = ec;
    aeb->pnum = pnum;
    aeb->vol_id = vol_id;
    aeb->lnum = lnum;
    aeb->scrub = bitflips;
    aeb->copy_flag = vid_hdr->copy_flag;
    aeb->sqnum = sqnum;

    if (av->highest_lnum <= lnum) {
        av->highest_lnum = lnum;
        av->last_data_size = be32_to_cpu(vid_hdr->data_size);
    }

    av->leb_count += 1;
    rb_link_node(&aeb->u.rb, parent, p);
    rb_insert_color(&aeb->u.rb, &av->root);
    return 0;
}

struct ubi_ainf_volume *ubi_find_av(const struct ubi_attach_info *ai,
                    int vol_id)
{
    struct ubi_ainf_volume *av;
    struct rb_node *p = ai->volumes.rb_node;

    while (p) {
        av = rb_entry(p, struct ubi_ainf_volume, rb);

        if (vol_id == av->vol_id)
            return av;

        if (vol_id > av->vol_id)
            p = p->rb_left;
        else
            p = p->rb_right;
    }

    return NULL;
}

void ubi_remove_av(struct ubi_attach_info *ai, struct ubi_ainf_volume *av)
{
    struct rb_node *rb;
    struct ubi_ainf_peb *aeb;

    dbg_bld("remove attaching information about volume %d", av->vol_id);

    while ((rb = rb_first(&av->root))) {
        aeb = rb_entry(rb, struct ubi_ainf_peb, u.rb);
        rb_erase(&aeb->u.rb, &av->root);
        list_add_tail(&aeb->u.list, &ai->erase);
    }

    rb_erase(&av->rb, &ai->volumes);
    kfree(av);
    ai->vols_found -= 1;
}

static int early_erase_peb(struct ubi_device *ubi,
               const struct ubi_attach_info *ai, int pnum, int ec)
{
    int err;
    struct ubi_ec_hdr *ec_hdr;

    if ((long long)ec >= UBI_MAX_ERASECOUNTER) {
        /*
         * Erase counter overflow. Upgrade UBI and use 64-bit
         * erase counters internally.
         */
        ubi_err("erase counter overflow at PEB %d, EC %d", pnum, ec);
        return -EINVAL;
    }

    ec_hdr = kzalloc(ubi->ec_hdr_alsize, GFP_KERNEL);
    if (!ec_hdr)
        return -ENOMEM;

    ec_hdr->ec = cpu_to_be64(ec);

    err = ubi_io_sync_erase(ubi, pnum, 0);
    if (err < 0)
        goto out_free;

    err = ubi_io_write_ec_hdr(ubi, pnum, ec_hdr);

out_free:
    kfree(ec_hdr);
    return err;
}

struct ubi_ainf_peb *ubi_early_get_peb(struct ubi_device *ubi,
                       struct ubi_attach_info *ai)
{
    int err = 0;
    struct ubi_ainf_peb *aeb, *tmp_aeb;

    if (!list_empty(&ai->free)) {
        aeb = list_entry(ai->free.next, struct ubi_ainf_peb, u.list);
        list_del(&aeb->u.list);
        dbg_bld("return free PEB %d, EC %d", aeb->pnum, aeb->ec);
        return aeb;
    }

    /*
     * We try to erase the first physical eraseblock from the erase list
     * and pick it if we succeed, or try to erase the next one if not. And
     * so forth. We don't want to take care about bad eraseblocks here -
     * they'll be handled later.
     */
    list_for_each_entry_safe(aeb, tmp_aeb, &ai->erase, u.list) {
        if (aeb->ec == UBI_UNKNOWN)
            aeb->ec = ai->mean_ec;

        err = early_erase_peb(ubi, ai, aeb->pnum, aeb->ec+1);
        if (err)
            continue;

        aeb->ec += 1;
        list_del(&aeb->u.list);
        dbg_bld("return PEB %d, EC %d", aeb->pnum, aeb->ec);
        return aeb;
    }

    ubi_err("no free eraseblocks");
    return ERR_PTR(-ENOSPC);
}

static int check_corruption(struct ubi_device *ubi, struct ubi_vid_hdr *vid_hdr,
                int pnum)
{
    int err;

    mutex_lock(&ubi->buf_mutex);
    memset(ubi->peb_buf, 0x00, ubi->leb_size);

    err = ubi_io_read(ubi, ubi->peb_buf, pnum, ubi->leb_start,
              ubi->leb_size);
    if (err == UBI_IO_BITFLIPS || mtd_is_eccerr(err)) {
        /*
         * Bit-flips or integrity errors while reading the data area.
         * It is difficult to say for sure what type of corruption is
         * this, but presumably a power cut happened while this PEB was
         * erased, so it became unstable and corrupted, and should be
         * erased.
         */
        err = 0;
        goto out_unlock;
    }

    if (err)
        goto out_unlock;

    if (ubi_check_pattern(ubi->peb_buf, 0xFF, ubi->leb_size))
        goto out_unlock;

    ubi_err("PEB %d contains corrupted VID header, and the data does not contain all 0xFF",
        pnum);
    ubi_err("this may be a non-UBI PEB or a severe VID header corruption which requires manual inspection");
    ubi_dump_vid_hdr(vid_hdr);
    pr_err("hexdump of PEB %d offset %d, length %d",
           pnum, ubi->leb_start, ubi->leb_size);
    ubi_dbg_print_hex_dump(KERN_DEBUG, "", DUMP_PREFIX_OFFSET, 32, 1,
                   ubi->peb_buf, ubi->leb_size, 1);
    err = 1;

out_unlock:
    mutex_unlock(&ubi->buf_mutex);
    return err;
}

static int scan_peb(struct ubi_device *ubi, struct ubi_attach_info *ai,
            int pnum, int *vid, unsigned long long *sqnum)
{
    long long uninitialized_var(ec);
    int err, bitflips = 0, vol_id = -1, ec_err = 0;

    dbg_bld("scan PEB %d", pnum);

    /* Skip bad physical eraseblocks */
    err = ubi_io_is_bad(ubi, pnum);
    if (err < 0)
        return err;
    else if (err) {
        ai->bad_peb_count += 1;
        return 0;
    }

    err = ubi_io_read_ec_hdr(ubi, pnum, ech, 0);
    if (err < 0)
        return err;
    switch (err) {
    case 0:
        break;
    case UBI_IO_BITFLIPS:
        bitflips = 1;
        break;
    case UBI_IO_FF:
        ai->empty_peb_count += 1;
        return add_to_list(ai, pnum, UBI_UNKNOWN, UBI_UNKNOWN,
                   UBI_UNKNOWN, 0, &ai->erase);
    case UBI_IO_FF_BITFLIPS:
        ai->empty_peb_count += 1;
        return add_to_list(ai, pnum, UBI_UNKNOWN, UBI_UNKNOWN,
                   UBI_UNKNOWN, 1, &ai->erase);
    case UBI_IO_BAD_HDR_EBADMSG:
    case UBI_IO_BAD_HDR:
        /*
         * We have to also look at the VID header, possibly it is not
         * corrupted. Set %bitflips flag in order to make this PEB be
         * moved and EC be re-created.
         */
        ec_err = err;
        ec = UBI_UNKNOWN;
        bitflips = 1;
        break;
    default:
        ubi_err("'ubi_io_read_ec_hdr()' returned unknown code %d", err);
        return -EINVAL;
    }

    if (!ec_err) {
        int image_seq;

        /* Make sure UBI version is OK */
        if (ech->version != UBI_VERSION) {
            ubi_err("this UBI version is %d, image version is %d",
                UBI_VERSION, (int)ech->version);
            return -EINVAL;
        }

        ec = be64_to_cpu(ech->ec);
        if (ec > UBI_MAX_ERASECOUNTER) {
            /*
             * Erase counter overflow. The EC headers have 64 bits
             * reserved, but we anyway make use of only 31 bit
             * values, as this seems to be enough for any existing
             * flash. Upgrade UBI and use 64-bit erase counters
             * internally.
             */
            ubi_err("erase counter overflow, max is %d",
                UBI_MAX_ERASECOUNTER);
            ubi_dump_ec_hdr(ech);
            return -EINVAL;
        }

        /*
         * Make sure that all PEBs have the same image sequence number.
         * This allows us to detect situations when users flash UBI
         * images incorrectly, so that the flash has the new UBI image
         * and leftovers from the old one. This feature was added
         * relatively recently, and the sequence number was always
         * zero, because old UBI implementations always set it to zero.
         * For this reasons, we do not panic if some PEBs have zero
         * sequence number, while other PEBs have non-zero sequence
         * number.
         */
        image_seq = be32_to_cpu(ech->image_seq);
        if (!ubi->image_seq && image_seq)
            ubi->image_seq = image_seq;
        if (ubi->image_seq && image_seq &&
            ubi->image_seq != image_seq) {
            ubi_err("bad image sequence number %d in PEB %d, expected %d",
                image_seq, pnum, ubi->image_seq);
            ubi_dump_ec_hdr(ech);
            return -EINVAL;
        }
    }

    /* OK, we've done with the EC header, let's look at the VID header */

    err = ubi_io_read_vid_hdr(ubi, pnum, vidh, 0);
    if (err < 0)
        return err;
    switch (err) {
    case 0:
        break;
    case UBI_IO_BITFLIPS:
        bitflips = 1;
        break;
    case UBI_IO_BAD_HDR_EBADMSG:
        if (ec_err == UBI_IO_BAD_HDR_EBADMSG)
            /*
             * Both EC and VID headers are corrupted and were read
             * with data integrity error, probably this is a bad
             * PEB, bit it is not marked as bad yet. This may also
             * be a result of power cut during erasure.
             */
            ai->maybe_bad_peb_count += 1;
    case UBI_IO_BAD_HDR:
        if (ec_err)
            /*
             * Both headers are corrupted. There is a possibility
             * that this a valid UBI PEB which has corresponding
             * LEB, but the headers are corrupted. However, it is
             * impossible to distinguish it from a PEB which just
             * contains garbage because of a power cut during erase
             * operation. So we just schedule this PEB for erasure.
             *
             * Besides, in case of NOR flash, we deliberately
             * corrupt both headers because NOR flash erasure is
             * slow and can start from the end.
             */
            err = 0;
        else
            /*
             * The EC was OK, but the VID header is corrupted. We
             * have to check what is in the data area.
             */
            err = check_corruption(ubi, vidh, pnum);

        if (err < 0)
            return err;
        else if (!err)
            /* This corruption is caused by a power cut */
            err = add_to_list(ai, pnum, UBI_UNKNOWN,
                      UBI_UNKNOWN, ec, 1, &ai->erase);
        else
            /* This is an unexpected corruption */
            err = add_corrupted(ai, pnum, ec);
        if (err)
            return err;
        goto adjust_mean_ec;
    case UBI_IO_FF_BITFLIPS:
        err = add_to_list(ai, pnum, UBI_UNKNOWN, UBI_UNKNOWN,
                  ec, 1, &ai->erase);
        if (err)
            return err;
        goto adjust_mean_ec;
    case UBI_IO_FF:
        if (ec_err || bitflips)
            err = add_to_list(ai, pnum, UBI_UNKNOWN,
                      UBI_UNKNOWN, ec, 1, &ai->erase);
        else
            err = add_to_list(ai, pnum, UBI_UNKNOWN,
                      UBI_UNKNOWN, ec, 0, &ai->free);
        if (err)
            return err;
        goto adjust_mean_ec;
    default:
        ubi_err("'ubi_io_read_vid_hdr()' returned unknown code %d",
            err);
        return -EINVAL;
    }

    vol_id = be32_to_cpu(vidh->vol_id);
    if (vid)
        *vid = vol_id;
    if (sqnum)
        *sqnum = be64_to_cpu(vidh->sqnum);
    if (vol_id > UBI_MAX_VOLUMES && vol_id != UBI_LAYOUT_VOLUME_ID) {
        int lnum = be32_to_cpu(vidh->lnum);

        /* Unsupported internal volume */
        switch (vidh->compat) {
        case UBI_COMPAT_DELETE:
            if (vol_id != UBI_FM_SB_VOLUME_ID
                && vol_id != UBI_FM_DATA_VOLUME_ID) {
                ubi_msg("\"delete\" compatible internal volume %d:%d found, will remove it",
                    vol_id, lnum);
            }
            err = add_to_list(ai, pnum, vol_id, lnum,
                      ec, 1, &ai->erase);
            if (err)
                return err;
            return 0;

        case UBI_COMPAT_RO:
            ubi_msg("read-only compatible internal volume %d:%d found, switch to read-only mode",
                vol_id, lnum);
            ubi->ro_mode = 1;
            break;

        case UBI_COMPAT_PRESERVE:
            ubi_msg("\"preserve\" compatible internal volume %d:%d found",
                vol_id, lnum);
            err = add_to_list(ai, pnum, vol_id, lnum,
                      ec, 0, &ai->alien);
            if (err)
                return err;
            return 0;

        case UBI_COMPAT_REJECT:
            ubi_err("incompatible internal volume %d:%d found",
                vol_id, lnum);
            return -EINVAL;
        }
    }

    if (ec_err)
        ubi_warn("valid VID header but corrupted EC header at PEB %d",
             pnum);
    err = ubi_add_to_av(ubi, ai, pnum, ec, vidh, bitflips);
    if (err)
        return err;

adjust_mean_ec:
    if (!ec_err) {
        ai->ec_sum += ec;
        ai->ec_count += 1;
        if (ec > ai->max_ec)
            ai->max_ec = ec;
        if (ec < ai->min_ec)
            ai->min_ec = ec;
    }

    return 0;
}

static int late_analysis(struct ubi_device *ubi, struct ubi_attach_info *ai)
{
    struct ubi_ainf_peb *aeb;
    int max_corr, peb_count;

    peb_count = ubi->peb_count - ai->bad_peb_count - ai->alien_peb_count;
    max_corr = peb_count / 20 ?: 8;

    /*
     * Few corrupted PEBs is not a problem and may be just a result of
     * unclean reboots. However, many of them may indicate some problems
     * with the flash HW or driver.
     */
    if (ai->corr_peb_count) {
        ubi_err("%d PEBs are corrupted and preserved",
            ai->corr_peb_count);
        pr_err("Corrupted PEBs are:");
        list_for_each_entry(aeb, &ai->corr, u.list)
            pr_cont(" %d", aeb->pnum);
        pr_cont("\n");

        /*
         * If too many PEBs are corrupted, we refuse attaching,
         * otherwise, only print a warning.
         */
        if (ai->corr_peb_count >= max_corr) {
            ubi_err("too many corrupted PEBs, refusing");
            return -EINVAL;
        }
    }

    if (ai->empty_peb_count + ai->maybe_bad_peb_count == peb_count) {
        /*
         * All PEBs are empty, or almost all - a couple PEBs look like
         * they may be bad PEBs which were not marked as bad yet.
         *
         * This piece of code basically tries to distinguish between
         * the following situations:
         *
         * 1. Flash is empty, but there are few bad PEBs, which are not
         *    marked as bad so far, and which were read with error. We
         *    want to go ahead and format this flash. While formatting,
         *    the faulty PEBs will probably be marked as bad.
         *
         * 2. Flash contains non-UBI data and we do not want to format
         *    it and destroy possibly important information.
         */
        if (ai->maybe_bad_peb_count <= 2) {
            ai->is_empty = 1;
            ubi_msg("empty MTD device detected");
            get_random_bytes(&ubi->image_seq,
                     sizeof(ubi->image_seq));
        } else {
            ubi_err("MTD device is not UBI-formatted and possibly contains non-UBI data - refusing it");
            return -EINVAL;
        }

    }

    return 0;
}

static void destroy_av(struct ubi_attach_info *ai, struct ubi_ainf_volume *av)
{
    struct ubi_ainf_peb *aeb;
    struct rb_node *this = av->root.rb_node;

    while (this) {
        if (this->rb_left)
            this = this->rb_left;
        else if (this->rb_right)
            this = this->rb_right;
        else {
            aeb = rb_entry(this, struct ubi_ainf_peb, u.rb);
            this = rb_parent(this);
            if (this) {
                if (this->rb_left == &aeb->u.rb)
                    this->rb_left = NULL;
                else
                    this->rb_right = NULL;
            }

            kmem_cache_free(ai->aeb_slab_cache, aeb);
        }
    }
    kfree(av);
}

static void destroy_ai(struct ubi_attach_info *ai)
{
    struct ubi_ainf_peb *aeb, *aeb_tmp;
    struct ubi_ainf_volume *av;
    struct rb_node *rb;

    list_for_each_entry_safe(aeb, aeb_tmp, &ai->alien, u.list) {
        list_del(&aeb->u.list);
        kmem_cache_free(ai->aeb_slab_cache, aeb);
    }
    list_for_each_entry_safe(aeb, aeb_tmp, &ai->erase, u.list) {
        list_del(&aeb->u.list);
        kmem_cache_free(ai->aeb_slab_cache, aeb);
    }
    list_for_each_entry_safe(aeb, aeb_tmp, &ai->corr, u.list) {
        list_del(&aeb->u.list);
        kmem_cache_free(ai->aeb_slab_cache, aeb);
    }
    list_for_each_entry_safe(aeb, aeb_tmp, &ai->free, u.list) {
        list_del(&aeb->u.list);
        kmem_cache_free(ai->aeb_slab_cache, aeb);
    }

    /* Destroy the volume RB-tree */
    rb = ai->volumes.rb_node;
    while (rb) {
        if (rb->rb_left)
            rb = rb->rb_left;
        else if (rb->rb_right)
            rb = rb->rb_right;
        else {
            av = rb_entry(rb, struct ubi_ainf_volume, rb);

            rb = rb_parent(rb);
            if (rb) {
                if (rb->rb_left == &av->rb)
                    rb->rb_left = NULL;
                else
                    rb->rb_right = NULL;
            }

            destroy_av(ai, av);
        }
    }

    if (ai->aeb_slab_cache)
        kmem_cache_destroy(ai->aeb_slab_cache);

    kfree(ai);
}

static int scan_all(struct ubi_device *ubi, struct ubi_attach_info *ai,
            int start)
{
    int err, pnum;
    struct rb_node *rb1, *rb2;
    struct ubi_ainf_volume *av;
    struct ubi_ainf_peb *aeb;

    err = -ENOMEM;

    ech = kzalloc(ubi->ec_hdr_alsize, GFP_KERNEL);
    if (!ech)
        return err;

    vidh = ubi_zalloc_vid_hdr(ubi, GFP_KERNEL);
    if (!vidh)
        goto out_ech;

    for (pnum = start; pnum < ubi->peb_count; pnum++) {
        cond_resched();

        dbg_gen("process PEB %d", pnum);
        err = scan_peb(ubi, ai, pnum, NULL, NULL);
        if (err < 0)
            goto out_vidh;
    }

    ubi_msg("scanning is finished");

    /* Calculate mean erase counter */
    if (ai->ec_count)
        ai->mean_ec = div_u64(ai->ec_sum, ai->ec_count);

    err = late_analysis(ubi, ai);
    if (err)
        goto out_vidh;

    /*
     * In case of unknown erase counter we use the mean erase counter
     * value.
     */
    ubi_rb_for_each_entry(rb1, av, &ai->volumes, rb) {
        ubi_rb_for_each_entry(rb2, aeb, &av->root, u.rb)
            if (aeb->ec == UBI_UNKNOWN)
                aeb->ec = ai->mean_ec;
    }

    list_for_each_entry(aeb, &ai->free, u.list) {
        if (aeb->ec == UBI_UNKNOWN)
            aeb->ec = ai->mean_ec;
    }

    list_for_each_entry(aeb, &ai->corr, u.list)
        if (aeb->ec == UBI_UNKNOWN)
            aeb->ec = ai->mean_ec;

    list_for_each_entry(aeb, &ai->erase, u.list)
        if (aeb->ec == UBI_UNKNOWN)
            aeb->ec = ai->mean_ec;

    err = self_check_ai(ubi, ai);
    if (err)
        goto out_vidh;

    ubi_free_vid_hdr(ubi, vidh);
    kfree(ech);

    return 0;

out_vidh:
    ubi_free_vid_hdr(ubi, vidh);
out_ech:
    kfree(ech);
    return err;
}

#ifdef CONFIG_MTD_UBI_FASTMAP

static int scan_fast(struct ubi_device *ubi, struct ubi_attach_info *ai)
{
    int err, pnum, fm_anchor = -1;
    unsigned long long max_sqnum = 0;

    err = -ENOMEM;

    ech = kzalloc(ubi->ec_hdr_alsize, GFP_KERNEL);
    if (!ech)
        goto out;

    vidh = ubi_zalloc_vid_hdr(ubi, GFP_KERNEL);
    if (!vidh)
        goto out_ech;

    for (pnum = 0; pnum < UBI_FM_MAX_START; pnum++) {
        int vol_id = -1;
        unsigned long long sqnum = -1;
        cond_resched();

        dbg_gen("process PEB %d", pnum);
        err = scan_peb(ubi, ai, pnum, &vol_id, &sqnum);
        if (err < 0)
            goto out_vidh;

        if (vol_id == UBI_FM_SB_VOLUME_ID && sqnum > max_sqnum) {
            max_sqnum = sqnum;
            fm_anchor = pnum;
        }
    }

    ubi_free_vid_hdr(ubi, vidh);
    kfree(ech);

    if (fm_anchor < 0)
        return UBI_NO_FASTMAP;

    return ubi_scan_fastmap(ubi, ai, fm_anchor);

out_vidh:
    ubi_free_vid_hdr(ubi, vidh);
out_ech:
    kfree(ech);
out:
    return err;
}

#endif

static struct ubi_attach_info *alloc_ai(const char *slab_name)
{
    struct ubi_attach_info *ai;

    ai = kzalloc(sizeof(struct ubi_attach_info), GFP_KERNEL);
    if (!ai)
        return ai;

    INIT_LIST_HEAD(&ai->corr);
    INIT_LIST_HEAD(&ai->free);
    INIT_LIST_HEAD(&ai->erase);
    INIT_LIST_HEAD(&ai->alien);
    ai->volumes = RB_ROOT;
    ai->aeb_slab_cache = kmem_cache_create(slab_name,
                           sizeof(struct ubi_ainf_peb),
                           0, 0, NULL);
    if (!ai->aeb_slab_cache) {
        kfree(ai);
        ai = NULL;
    }

    return ai;
}

int ubi_attach(struct ubi_device *ubi, int force_scan)
{
    int err;
    struct ubi_attach_info *ai;

    ai = alloc_ai("ubi_aeb_slab_cache");
    if (!ai)
        return -ENOMEM;

#ifdef CONFIG_MTD_UBI_FASTMAP
    /* On small flash devices we disable fastmap in any case. */
    if ((int)mtd_div_by_eb(ubi->mtd->size, ubi->mtd) <= UBI_FM_MAX_START) {
        ubi->fm_disabled = 1;
        force_scan = 1;
    }

    if (force_scan)
        err = scan_all(ubi, ai, 0);
    else {
        err = scan_fast(ubi, ai);
        if (err > 0) {
            if (err != UBI_NO_FASTMAP) {
                destroy_ai(ai);
                ai = alloc_ai("ubi_aeb_slab_cache2");
                if (!ai)
                    return -ENOMEM;
            }

            err = scan_all(ubi, ai, UBI_FM_MAX_START);
        }
    }
#else
    err = scan_all(ubi, ai, 0);
#endif
    if (err)
        goto out_ai;

    ubi->bad_peb_count = ai->bad_peb_count;
    ubi->good_peb_count = ubi->peb_count - ubi->bad_peb_count;
    ubi->corr_peb_count = ai->corr_peb_count;
    ubi->max_ec = ai->max_ec;
    ubi->mean_ec = ai->mean_ec;
    dbg_gen("max. sequence number:       %llu", ai->max_sqnum);

    err = ubi_read_volume_table(ubi, ai);
    if (err)
        goto out_ai;

    err = ubi_wl_init(ubi, ai);
    if (err)
        goto out_vtbl;

    err = ubi_eba_init(ubi, ai);
    if (err)
        goto out_wl;

#ifdef CONFIG_MTD_UBI_FASTMAP
    if (ubi->fm && ubi->dbg->chk_gen) {
        struct ubi_attach_info *scan_ai;

        scan_ai = alloc_ai("ubi_ckh_aeb_slab_cache");
        if (!scan_ai)
            goto out_wl;

        err = scan_all(ubi, scan_ai, 0);
        if (err) {
            destroy_ai(scan_ai);
            goto out_wl;
        }

        err = self_check_eba(ubi, ai, scan_ai);
        destroy_ai(scan_ai);

        if (err)
            goto out_wl;
    }
#endif

    destroy_ai(ai);
    return 0;

out_wl:
    ubi_wl_close(ubi);
out_vtbl:
    ubi_free_internal_volumes(ubi);
    vfree(ubi->vtbl);
out_ai:
    destroy_ai(ai);
    return err;
}

static int self_check_ai(struct ubi_device *ubi, struct ubi_attach_info *ai)
{
    int pnum, err, vols_found = 0;
    struct rb_node *rb1, *rb2;
    struct ubi_ainf_volume *av;
    struct ubi_ainf_peb *aeb, *last_aeb;
    uint8_t *buf;

    if (!ubi->dbg->chk_gen)
        return 0;

    /*
     * At first, check that attaching information is OK.
     */
    ubi_rb_for_each_entry(rb1, av, &ai->volumes, rb) {
        int leb_count = 0;

        cond_resched();

        vols_found += 1;

        if (ai->is_empty) {
            ubi_err("bad is_empty flag");
            goto bad_av;
        }

        if (av->vol_id < 0 || av->highest_lnum < 0 ||
            av->leb_count < 0 || av->vol_type < 0 || av->used_ebs < 0 ||
            av->data_pad < 0 || av->last_data_size < 0) {
            ubi_err("negative values");
            goto bad_av;
        }

        if (av->vol_id >= UBI_MAX_VOLUMES &&
            av->vol_id < UBI_INTERNAL_VOL_START) {
            ubi_err("bad vol_id");
            goto bad_av;
        }

        if (av->vol_id > ai->highest_vol_id) {
            ubi_err("highest_vol_id is %d, but vol_id %d is there",
                ai->highest_vol_id, av->vol_id);
            goto out;
        }

        if (av->vol_type != UBI_DYNAMIC_VOLUME &&
            av->vol_type != UBI_STATIC_VOLUME) {
            ubi_err("bad vol_type");
            goto bad_av;
        }

        if (av->data_pad > ubi->leb_size / 2) {
            ubi_err("bad data_pad");
            goto bad_av;
        }

        last_aeb = NULL;
        ubi_rb_for_each_entry(rb2, aeb, &av->root, u.rb) {
            cond_resched();

            last_aeb = aeb;
            leb_count += 1;

            if (aeb->pnum < 0 || aeb->ec < 0) {
                ubi_err("negative values");
                goto bad_aeb;
            }

            if (aeb->ec < ai->min_ec) {
                ubi_err("bad ai->min_ec (%d), %d found",
                    ai->min_ec, aeb->ec);
                goto bad_aeb;
            }

            if (aeb->ec > ai->max_ec) {
                ubi_err("bad ai->max_ec (%d), %d found",
                    ai->max_ec, aeb->ec);
                goto bad_aeb;
            }

            if (aeb->pnum >= ubi->peb_count) {
                ubi_err("too high PEB number %d, total PEBs %d",
                    aeb->pnum, ubi->peb_count);
                goto bad_aeb;
            }

            if (av->vol_type == UBI_STATIC_VOLUME) {
                if (aeb->lnum >= av->used_ebs) {
                    ubi_err("bad lnum or used_ebs");
                    goto bad_aeb;
                }
            } else {
                if (av->used_ebs != 0) {
                    ubi_err("non-zero used_ebs");
                    goto bad_aeb;
                }
            }

            if (aeb->lnum > av->highest_lnum) {
                ubi_err("incorrect highest_lnum or lnum");
                goto bad_aeb;
            }
        }

        if (av->leb_count != leb_count) {
            ubi_err("bad leb_count, %d objects in the tree",
                leb_count);
            goto bad_av;
        }

        if (!last_aeb)
            continue;

        aeb = last_aeb;

        if (aeb->lnum != av->highest_lnum) {
            ubi_err("bad highest_lnum");
            goto bad_aeb;
        }
    }

    if (vols_found != ai->vols_found) {
        ubi_err("bad ai->vols_found %d, should be %d",
            ai->vols_found, vols_found);
        goto out;
    }

    /* Check that attaching information is correct */
    ubi_rb_for_each_entry(rb1, av, &ai->volumes, rb) {
        last_aeb = NULL;
        ubi_rb_for_each_entry(rb2, aeb, &av->root, u.rb) {
            int vol_type;

            cond_resched();

            last_aeb = aeb;

            err = ubi_io_read_vid_hdr(ubi, aeb->pnum, vidh, 1);
            if (err && err != UBI_IO_BITFLIPS) {
                ubi_err("VID header is not OK (%d)", err);
                if (err > 0)
                    err = -EIO;
                return err;
            }

            vol_type = vidh->vol_type == UBI_VID_DYNAMIC ?
                   UBI_DYNAMIC_VOLUME : UBI_STATIC_VOLUME;
            if (av->vol_type != vol_type) {
                ubi_err("bad vol_type");
                goto bad_vid_hdr;
            }

            if (aeb->sqnum != be64_to_cpu(vidh->sqnum)) {
                ubi_err("bad sqnum %llu", aeb->sqnum);
                goto bad_vid_hdr;
            }

            if (av->vol_id != be32_to_cpu(vidh->vol_id)) {
                ubi_err("bad vol_id %d", av->vol_id);
                goto bad_vid_hdr;
            }

            if (av->compat != vidh->compat) {
                ubi_err("bad compat %d", vidh->compat);
                goto bad_vid_hdr;
            }

            if (aeb->lnum != be32_to_cpu(vidh->lnum)) {
                ubi_err("bad lnum %d", aeb->lnum);
                goto bad_vid_hdr;
            }

            if (av->used_ebs != be32_to_cpu(vidh->used_ebs)) {
                ubi_err("bad used_ebs %d", av->used_ebs);
                goto bad_vid_hdr;
            }

            if (av->data_pad != be32_to_cpu(vidh->data_pad)) {
                ubi_err("bad data_pad %d", av->data_pad);
                goto bad_vid_hdr;
            }
        }

        if (!last_aeb)
            continue;

        if (av->highest_lnum != be32_to_cpu(vidh->lnum)) {
            ubi_err("bad highest_lnum %d", av->highest_lnum);
            goto bad_vid_hdr;
        }

        if (av->last_data_size != be32_to_cpu(vidh->data_size)) {
            ubi_err("bad last_data_size %d", av->last_data_size);
            goto bad_vid_hdr;
        }
    }

    /*
     * Make sure that all the physical eraseblocks are in one of the lists
     * or trees.
     */
    buf = kzalloc(ubi->peb_count, GFP_KERNEL);
    if (!buf)
        return -ENOMEM;

    for (pnum = 0; pnum < ubi->peb_count; pnum++) {
        err = ubi_io_is_bad(ubi, pnum);
        if (err < 0) {
            kfree(buf);
            return err;
        } else if (err)
            buf[pnum] = 1;
    }

    ubi_rb_for_each_entry(rb1, av, &ai->volumes, rb)
        ubi_rb_for_each_entry(rb2, aeb, &av->root, u.rb)
            buf[aeb->pnum] = 1;

    list_for_each_entry(aeb, &ai->free, u.list)
        buf[aeb->pnum] = 1;

    list_for_each_entry(aeb, &ai->corr, u.list)
        buf[aeb->pnum] = 1;

    list_for_each_entry(aeb, &ai->erase, u.list)
        buf[aeb->pnum] = 1;

    list_for_each_entry(aeb, &ai->alien, u.list)
        buf[aeb->pnum] = 1;

    err = 0;
    for (pnum = 0; pnum < ubi->peb_count; pnum++)
        if (!buf[pnum]) {
            ubi_err("PEB %d is not referred", pnum);
            err = 1;
        }

    kfree(buf);
    if (err)
        goto out;
    return 0;

bad_aeb:
    ubi_err("bad attaching information about LEB %d", aeb->lnum);
    ubi_dump_aeb(aeb, 0);
    ubi_dump_av(av);
    goto out;

bad_av:
    ubi_err("bad attaching information about volume %d", av->vol_id);
    ubi_dump_av(av);
    goto out;

bad_vid_hdr:
    ubi_err("bad attaching information about volume %d", av->vol_id);
    ubi_dump_av(av);
    ubi_dump_vid_hdr(vidh);

out:
    dump_stack();
    return -EINVAL;
}