UBI: add a comment

[linux-2.6] / drivers / mtd / ubi / vtbl.c

/*
 * Copyright (c) International Business Machines Corp., 2006
 * Copyright (c) Nokia Corporation, 2006, 2007
 *
 * 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)
 */

/*
 * This file includes volume table manipulation code. The volume table is an
 * on-flash table containing volume meta-data like name, number of reserved
 * physical eraseblocks, type, etc. The volume table is stored in the so-called
 * "layout volume".
 *
 * The layout volume is an internal volume which is organized as follows. It
 * consists of two logical eraseblocks - LEB 0 and LEB 1. Each logical
 * eraseblock stores one volume table copy, i.e. LEB 0 and LEB 1 duplicate each
 * other. This redundancy guarantees robustness to unclean reboots. The volume
 * table is basically an array of volume table records. Each record contains
 * full information about the volume and protected by a CRC checksum.
 *
 * The volume table is changed, it is first changed in RAM. Then LEB 0 is
 * erased, and the updated volume table is written back to LEB 0. Then same for
 * LEB 1. This scheme guarantees recoverability from unclean reboots.
 *
 * In this UBI implementation the on-flash volume table does not contain any
 * information about how many data static volumes contain. This information may
 * be found from the scanning data.
 *
 * But it would still be beneficial to store this information in the volume
 * table. For example, suppose we have a static volume X, and all its physical
 * eraseblocks became bad for some reasons. Suppose we are attaching the
 * corresponding MTD device, the scanning has found no logical eraseblocks
 * corresponding to the volume X. According to the volume table volume X does
 * exist. So we don't know whether it is just empty or all its physical
 * eraseblocks went bad. So we cannot alarm the user about this corruption.
 *
 * The volume table also stores so-called "update marker", which is used for
 * volume updates. Before updating the volume, the update marker is set, and
 * after the update operation is finished, the update marker is cleared. So if
 * the update operation was interrupted (e.g. by an unclean reboot) - the
 * update marker is still there and we know that the volume's contents is
 * damaged.
 */

#include <linux/crc32.h>
#include <linux/err.h>
#include <asm/div64.h>
#include "ubi.h"

#ifdef CONFIG_MTD_UBI_DEBUG_PARANOID
static void paranoid_vtbl_check(const struct ubi_device *ubi);
#else
#define paranoid_vtbl_check(ubi)
#endif

/* Empty volume table record */
static struct ubi_vtbl_record empty_vtbl_record;

/**
 * ubi_change_vtbl_record - change volume table record.
 * @ubi: UBI device description object
 * @idx: table index to change
 * @vtbl_rec: new volume table record
 *
 * This function changes volume table record @idx. If @vtbl_rec is %NULL, empty
 * volume table record is written. The caller does not have to calculate CRC of
 * the record as it is done by this function. Returns zero in case of success
 * and a negative error code in case of failure.
 */
int ubi_change_vtbl_record(struct ubi_device *ubi, int idx,
                           struct ubi_vtbl_record *vtbl_rec)
{
        int i, err;
        uint32_t crc;
        struct ubi_volume *layout_vol;

        ubi_assert(idx >= 0 && idx < ubi->vtbl_slots);
        layout_vol = ubi->volumes[vol_id2idx(ubi, UBI_LAYOUT_VOLUME_ID)];

        if (!vtbl_rec)
                vtbl_rec = &empty_vtbl_record;
        else {
                crc = crc32(UBI_CRC32_INIT, vtbl_rec, UBI_VTBL_RECORD_SIZE_CRC);
                vtbl_rec->crc = cpu_to_be32(crc);
        }

        memcpy(&ubi->vtbl[idx], vtbl_rec, sizeof(struct ubi_vtbl_record));
        for (i = 0; i < UBI_LAYOUT_VOLUME_EBS; i++) {
                err = ubi_eba_unmap_leb(ubi, layout_vol, i);
                if (err)
                        return err;

                err = ubi_eba_write_leb(ubi, layout_vol, i, ubi->vtbl, 0,
                                        ubi->vtbl_size, UBI_LONGTERM);
                if (err)
                        return err;
        }

        paranoid_vtbl_check(ubi);
        return 0;
}

/**
 * vtbl_check - check if volume table is not corrupted and contains sensible
 *              data.
 * @ubi: UBI device description object
 * @vtbl: volume table
 *
 * This function returns zero if @vtbl is all right, %1 if CRC is incorrect,
 * and %-EINVAL if it contains inconsistent data.
 */
static int vtbl_check(const struct ubi_device *ubi,
                      const struct ubi_vtbl_record *vtbl)
{
        int i, n, reserved_pebs, alignment, data_pad, vol_type, name_len;
        int upd_marker, err;
        uint32_t crc;
        const char *name;

        for (i = 0; i < ubi->vtbl_slots; i++) {
                cond_resched();

                reserved_pebs = be32_to_cpu(vtbl[i].reserved_pebs);
                alignment = be32_to_cpu(vtbl[i].alignment);
                data_pad = be32_to_cpu(vtbl[i].data_pad);
                upd_marker = vtbl[i].upd_marker;
                vol_type = vtbl[i].vol_type;
                name_len = be16_to_cpu(vtbl[i].name_len);
                name = &vtbl[i].name[0];

                crc = crc32(UBI_CRC32_INIT, &vtbl[i], UBI_VTBL_RECORD_SIZE_CRC);
                if (be32_to_cpu(vtbl[i].crc) != crc) {
                        ubi_err("bad CRC at record %u: %#08x, not %#08x",
                                 i, crc, be32_to_cpu(vtbl[i].crc));
                        ubi_dbg_dump_vtbl_record(&vtbl[i], i);
                        return 1;
                }

                if (reserved_pebs == 0) {
                        if (memcmp(&vtbl[i], &empty_vtbl_record,
                                                UBI_VTBL_RECORD_SIZE)) {
                                err = 2;
                                goto bad;
                        }
                        continue;
                }

                if (reserved_pebs < 0 || alignment < 0 || data_pad < 0 ||
                    name_len < 0) {
                        err = 3;
                        goto bad;
                }

                if (alignment > ubi->leb_size || alignment == 0) {
                        err = 4;
                        goto bad;
                }

                n = alignment % ubi->min_io_size;
                if (alignment != 1 && n) {
                        err = 5;
                        goto bad;
                }

                n = ubi->leb_size % alignment;
                if (data_pad != n) {
                        dbg_err("bad data_pad, has to be %d", n);
                        err = 6;
                        goto bad;
                }

                if (vol_type != UBI_VID_DYNAMIC && vol_type != UBI_VID_STATIC) {
                        err = 7;
                        goto bad;
                }

                if (upd_marker != 0 && upd_marker != 1) {
                        err = 8;
                        goto bad;
                }

                if (reserved_pebs > ubi->good_peb_count) {
                        dbg_err("too large reserved_pebs, good PEBs %d",
                                ubi->good_peb_count);
                        err = 9;
                        goto bad;
                }

                if (name_len > UBI_VOL_NAME_MAX) {
                        err = 10;
                        goto bad;
                }

                if (name[0] == '\0') {
                        err = 11;
                        goto bad;
                }

                if (name_len != strnlen(name, name_len + 1)) {
                        err = 12;
                        goto bad;
                }
        }

        /* Checks that all names are unique */
        for (i = 0; i < ubi->vtbl_slots - 1; i++) {
                for (n = i + 1; n < ubi->vtbl_slots; n++) {
                        int len1 = be16_to_cpu(vtbl[i].name_len);
                        int len2 = be16_to_cpu(vtbl[n].name_len);

                        if (len1 > 0 && len1 == len2 &&
                            !strncmp(vtbl[i].name, vtbl[n].name, len1)) {
                                ubi_err("volumes %d and %d have the same name"
                                        " \"%s\"", i, n, vtbl[i].name);
                                ubi_dbg_dump_vtbl_record(&vtbl[i], i);
                                ubi_dbg_dump_vtbl_record(&vtbl[n], n);
                                return -EINVAL;
                        }
                }
        }

        return 0;

bad:
        ubi_err("volume table check failed: record %d, error %d", i, err);
        ubi_dbg_dump_vtbl_record(&vtbl[i], i);
        return -EINVAL;
}

/**
 * create_vtbl - create a copy of volume table.
 * @ubi: UBI device description object
 * @si: scanning information
 * @copy: number of the volume table copy
 * @vtbl: contents of the volume table
 *
 * This function returns zero in case of success and a negative error code in
 * case of failure.
 */
static int create_vtbl(struct ubi_device *ubi, struct ubi_scan_info *si,
                       int copy, void *vtbl)
{
        int err, tries = 0;
        static struct ubi_vid_hdr *vid_hdr;
        struct ubi_scan_volume *sv;
        struct ubi_scan_leb *new_seb, *old_seb = NULL;

        ubi_msg("create volume table (copy #%d)", copy + 1);

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

        /*
         * Check if there is a logical eraseblock which would have to contain
         * this volume table copy was found during scanning. It has to be wiped
         * out.
         */
        sv = ubi_scan_find_sv(si, UBI_LAYOUT_VOLUME_ID);
        if (sv)
                old_seb = ubi_scan_find_seb(sv, copy);

retry:
        new_seb = ubi_scan_get_free_peb(ubi, si);
        if (IS_ERR(new_seb)) {
                err = PTR_ERR(new_seb);
                goto out_free;
        }

        vid_hdr->vol_type = UBI_VID_DYNAMIC;
        vid_hdr->vol_id = cpu_to_be32(UBI_LAYOUT_VOLUME_ID);
        vid_hdr->compat = UBI_LAYOUT_VOLUME_COMPAT;
        vid_hdr->data_size = vid_hdr->used_ebs =
                             vid_hdr->data_pad = cpu_to_be32(0);
        vid_hdr->lnum = cpu_to_be32(copy);
        vid_hdr->sqnum = cpu_to_be64(++si->max_sqnum);
        vid_hdr->leb_ver = cpu_to_be32(old_seb ? old_seb->leb_ver + 1: 0);

        /* The EC header is already there, write the VID header */
        err = ubi_io_write_vid_hdr(ubi, new_seb->pnum, vid_hdr);
        if (err)
                goto write_error;

        /* Write the layout volume contents */
        err = ubi_io_write_data(ubi, vtbl, new_seb->pnum, 0, ubi->vtbl_size);
        if (err)
                goto write_error;

        /*
         * And add it to the scanning information. Don't delete the old
         * @old_seb as it will be deleted and freed in 'ubi_scan_add_used()'.
         */
        err = ubi_scan_add_used(ubi, si, new_seb->pnum, new_seb->ec,
                                vid_hdr, 0);
        kfree(new_seb);
        ubi_free_vid_hdr(ubi, vid_hdr);
        return err;

write_error:
        if (err == -EIO && ++tries <= 5) {
                /*
                 * Probably this physical eraseblock went bad, try to pick
                 * another one.
                 */
                list_add_tail(&new_seb->u.list, &si->corr);
                goto retry;
        }
        kfree(new_seb);
out_free:
        ubi_free_vid_hdr(ubi, vid_hdr);
        return err;

}

/**
 * process_lvol - process the layout volume.
 * @ubi: UBI device description object
 * @si: scanning information
 * @sv: layout volume scanning information
 *
 * This function is responsible for reading the layout volume, ensuring it is
 * not corrupted, and recovering from corruptions if needed. Returns volume
 * table in case of success and a negative error code in case of failure.
 */
static struct ubi_vtbl_record *process_lvol(struct ubi_device *ubi,
                                            struct ubi_scan_info *si,
                                            struct ubi_scan_volume *sv)
{
        int err;
        struct rb_node *rb;
        struct ubi_scan_leb *seb;
        struct ubi_vtbl_record *leb[UBI_LAYOUT_VOLUME_EBS] = { NULL, NULL };
        int leb_corrupted[UBI_LAYOUT_VOLUME_EBS] = {1, 1};

        /*
         * UBI goes through the following steps when it changes the layout
         * volume:
         * a. erase LEB 0;
         * b. write new data to LEB 0;
         * c. erase LEB 1;
         * d. write new data to LEB 1.
         *
         * Before the change, both LEBs contain the same data.
         *
         * Due to unclean reboots, the contents of LEB 0 may be lost, but there
         * should LEB 1. So it is OK if LEB 0 is corrupted while LEB 1 is not.
         * Similarly, LEB 1 may be lost, but there should be LEB 0. And
         * finally, unclean reboots may result in a situation when neither LEB
         * 0 nor LEB 1 are corrupted, but they are different. In this case, LEB
         * 0 contains more recent information.
         *
         * So the plan is to first check LEB 0. Then
         * a. if LEB 0 is OK, it must be containing the most resent data; then
         *    we compare it with LEB 1, and if they are different, we copy LEB
         *    0 to LEB 1;
         * b. if LEB 0 is corrupted, but LEB 1 has to be OK, and we copy LEB 1
         *    to LEB 0.
         */

        dbg_msg("check layout volume");

        /* Read both LEB 0 and LEB 1 into memory */
        ubi_rb_for_each_entry(rb, seb, &sv->root, u.rb) {
                leb[seb->lnum] = vmalloc(ubi->vtbl_size);
                if (!leb[seb->lnum]) {
                        err = -ENOMEM;
                        goto out_free;
                }
                memset(leb[seb->lnum], 0, ubi->vtbl_size);

                err = ubi_io_read_data(ubi, leb[seb->lnum], seb->pnum, 0,
                                       ubi->vtbl_size);
                if (err == UBI_IO_BITFLIPS || err == -EBADMSG)
                        /*
                         * Scrub the PEB later. Note, -EBADMSG indicates an
                         * uncorrectable ECC error, but we have our own CRC and
                         * the data will be checked later. If the data is OK,
                         * the PEB will be scrubbed (because we set
                         * seb->scrub). If the data is not OK, the contents of
                         * the PEB will be recovered from the second copy, and
                         * seb->scrub will be cleared in
                         * 'ubi_scan_add_used()'.
                         */
                        seb->scrub = 1;
                else if (err)
                        goto out_free;
        }

        err = -EINVAL;
        if (leb[0]) {
                leb_corrupted[0] = vtbl_check(ubi, leb[0]);
                if (leb_corrupted[0] < 0)
                        goto out_free;
        }

        if (!leb_corrupted[0]) {
                /* LEB 0 is OK */
                if (leb[1])
                        leb_corrupted[1] = memcmp(leb[0], leb[1], ubi->vtbl_size);
                if (leb_corrupted[1]) {
                        ubi_warn("volume table copy #2 is corrupted");
                        err = create_vtbl(ubi, si, 1, leb[0]);
                        if (err)
                                goto out_free;
                        ubi_msg("volume table was restored");
                }

                /* Both LEB 1 and LEB 2 are OK and consistent */
                vfree(leb[1]);
                return leb[0];
        } else {
                /* LEB 0 is corrupted or does not exist */
                if (leb[1]) {
                        leb_corrupted[1] = vtbl_check(ubi, leb[1]);
                        if (leb_corrupted[1] < 0)
                                goto out_free;
                }
                if (leb_corrupted[1]) {
                        /* Both LEB 0 and LEB 1 are corrupted */
                        ubi_err("both volume tables are corrupted");
                        goto out_free;
                }

                ubi_warn("volume table copy #1 is corrupted");
                err = create_vtbl(ubi, si, 0, leb[1]);
                if (err)
                        goto out_free;
                ubi_msg("volume table was restored");

                vfree(leb[0]);
                return leb[1];
        }

out_free:
        vfree(leb[0]);
        vfree(leb[1]);
        return ERR_PTR(err);
}

/**
 * create_empty_lvol - create empty layout volume.
 * @ubi: UBI device description object
 * @si: scanning information
 *
 * This function returns volume table contents in case of success and a
 * negative error code in case of failure.
 */
static struct ubi_vtbl_record *create_empty_lvol(struct ubi_device *ubi,
                                                 struct ubi_scan_info *si)
{
        int i;
        struct ubi_vtbl_record *vtbl;

        vtbl = vmalloc(ubi->vtbl_size);
        if (!vtbl)
                return ERR_PTR(-ENOMEM);
        memset(vtbl, 0, ubi->vtbl_size);

        for (i = 0; i < ubi->vtbl_slots; i++)
                memcpy(&vtbl[i], &empty_vtbl_record, UBI_VTBL_RECORD_SIZE);

        for (i = 0; i < UBI_LAYOUT_VOLUME_EBS; i++) {
                int err;

                err = create_vtbl(ubi, si, i, vtbl);
                if (err) {
                        vfree(vtbl);
                        return ERR_PTR(err);
                }
        }

        return vtbl;
}

/**
 * init_volumes - initialize volume information for existing volumes.
 * @ubi: UBI device description object
 * @si: scanning information
 * @vtbl: volume table
 *
 * This function allocates volume description objects for existing volumes.
 * Returns zero in case of success and a negative error code in case of
 * failure.
 */
static int init_volumes(struct ubi_device *ubi, const struct ubi_scan_info *si,
                        const struct ubi_vtbl_record *vtbl)
{
        int i, reserved_pebs = 0;
        struct ubi_scan_volume *sv;
        struct ubi_volume *vol;

        for (i = 0; i < ubi->vtbl_slots; i++) {
                cond_resched();

                if (be32_to_cpu(vtbl[i].reserved_pebs) == 0)
                        continue; /* Empty record */

                vol = kzalloc(sizeof(struct ubi_volume), GFP_KERNEL);
                if (!vol)
                        return -ENOMEM;

                vol->reserved_pebs = be32_to_cpu(vtbl[i].reserved_pebs);
                vol->alignment = be32_to_cpu(vtbl[i].alignment);
                vol->data_pad = be32_to_cpu(vtbl[i].data_pad);
                vol->vol_type = vtbl[i].vol_type == UBI_VID_DYNAMIC ?
                                        UBI_DYNAMIC_VOLUME : UBI_STATIC_VOLUME;
                vol->name_len = be16_to_cpu(vtbl[i].name_len);
                vol->usable_leb_size = ubi->leb_size - vol->data_pad;
                memcpy(vol->name, vtbl[i].name, vol->name_len);
                vol->name[vol->name_len] = '\0';
                vol->vol_id = i;

                if (vtbl[i].flags & UBI_VTBL_AUTORESIZE_FLG) {
                        /* Auto re-size flag may be set only for one volume */
                        if (ubi->autoresize_vol_id != -1) {
                                ubi_err("more then one auto-resize volume (%d "
                                        "and %d)", ubi->autoresize_vol_id, i);
                                kfree(vol);
                                return -EINVAL;
                        }

                        ubi->autoresize_vol_id = i;
                }

                ubi_assert(!ubi->volumes[i]);
                ubi->volumes[i] = vol;
                ubi->vol_count += 1;
                vol->ubi = ubi;
                reserved_pebs += vol->reserved_pebs;

                /*
                 * In case of dynamic volume UBI knows nothing about how many
                 * data is stored there. So assume the whole volume is used.
                 */
                if (vol->vol_type == UBI_DYNAMIC_VOLUME) {
                        vol->used_ebs = vol->reserved_pebs;
                        vol->last_eb_bytes = vol->usable_leb_size;
                        vol->used_bytes =
                                (long long)vol->used_ebs * vol->usable_leb_size;
                        continue;
                }

                /* Static volumes only */
                sv = ubi_scan_find_sv(si, i);
                if (!sv) {
                        /*
                         * No eraseblocks belonging to this volume found. We
                         * don't actually know whether this static volume is
                         * completely corrupted or just contains no data. And
                         * we cannot know this as long as data size is not
                         * stored on flash. So we just assume the volume is
                         * empty. FIXME: this should be handled.
                         */
                        continue;
                }

                if (sv->leb_count != sv->used_ebs) {
                        /*
                         * We found a static volume which misses several
                         * eraseblocks. Treat it as corrupted.
                         */
                        ubi_warn("static volume %d misses %d LEBs - corrupted",
                                 sv->vol_id, sv->used_ebs - sv->leb_count);
                        vol->corrupted = 1;
                        continue;
                }

                vol->used_ebs = sv->used_ebs;
                vol->used_bytes =
                        (long long)(vol->used_ebs - 1) * vol->usable_leb_size;
                vol->used_bytes += sv->last_data_size;
                vol->last_eb_bytes = sv->last_data_size;
        }

        /* And add the layout volume */
        vol = kzalloc(sizeof(struct ubi_volume), GFP_KERNEL);
        if (!vol)
                return -ENOMEM;

        vol->reserved_pebs = UBI_LAYOUT_VOLUME_EBS;
        vol->alignment = 1;
        vol->vol_type = UBI_DYNAMIC_VOLUME;
        vol->name_len = sizeof(UBI_LAYOUT_VOLUME_NAME) - 1;
        memcpy(vol->name, UBI_LAYOUT_VOLUME_NAME, vol->name_len + 1);
        vol->usable_leb_size = ubi->leb_size;
        vol->used_ebs = vol->reserved_pebs;
        vol->last_eb_bytes = vol->reserved_pebs;
        vol->used_bytes =
                (long long)vol->used_ebs * (ubi->leb_size - vol->data_pad);
        vol->vol_id = UBI_LAYOUT_VOLUME_ID;
        vol->ref_count = 1;

        ubi_assert(!ubi->volumes[i]);
        ubi->volumes[vol_id2idx(ubi, vol->vol_id)] = vol;
        reserved_pebs += vol->reserved_pebs;
        ubi->vol_count += 1;
        vol->ubi = ubi;

        if (reserved_pebs > ubi->avail_pebs)
                ubi_err("not enough PEBs, required %d, available %d",
                        reserved_pebs, ubi->avail_pebs);
        ubi->rsvd_pebs += reserved_pebs;
        ubi->avail_pebs -= reserved_pebs;

        return 0;
}

/**
 * check_sv - check volume scanning information.
 * @vol: UBI volume description object
 * @sv: volume scanning information
 *
 * This function returns zero if the volume scanning information is consistent
 * to the data read from the volume tabla, and %-EINVAL if not.
 */
static int check_sv(const struct ubi_volume *vol,
                    const struct ubi_scan_volume *sv)
{
        int err;

        if (sv->highest_lnum >= vol->reserved_pebs) {
                err = 1;
                goto bad;
        }
        if (sv->leb_count > vol->reserved_pebs) {
                err = 2;
                goto bad;
        }
        if (sv->vol_type != vol->vol_type) {
                err = 3;
                goto bad;
        }
        if (sv->used_ebs > vol->reserved_pebs) {
                err = 4;
                goto bad;
        }
        if (sv->data_pad != vol->data_pad) {
                err = 5;
                goto bad;
        }
        return 0;

bad:
        ubi_err("bad scanning information, error %d", err);
        ubi_dbg_dump_sv(sv);
        ubi_dbg_dump_vol_info(vol);
        return -EINVAL;
}

/**
 * check_scanning_info - check that scanning information.
 * @ubi: UBI device description object
 * @si: scanning information
 *
 * Even though we protect on-flash data by CRC checksums, we still don't trust
 * the media. This function ensures that scanning information is consistent to
 * the information read from the volume table. Returns zero if the scanning
 * information is OK and %-EINVAL if it is not.
 */
static int check_scanning_info(const struct ubi_device *ubi,
                               struct ubi_scan_info *si)
{
        int err, i;
        struct ubi_scan_volume *sv;
        struct ubi_volume *vol;

        if (si->vols_found > UBI_INT_VOL_COUNT + ubi->vtbl_slots) {
                ubi_err("scanning found %d volumes, maximum is %d + %d",
                        si->vols_found, UBI_INT_VOL_COUNT, ubi->vtbl_slots);
                return -EINVAL;
        }

        if (si->highest_vol_id >= ubi->vtbl_slots + UBI_INT_VOL_COUNT&&
            si->highest_vol_id < UBI_INTERNAL_VOL_START) {
                ubi_err("too large volume ID %d found by scanning",
                        si->highest_vol_id);
                return -EINVAL;
        }


        for (i = 0; i < ubi->vtbl_slots + UBI_INT_VOL_COUNT; i++) {
                cond_resched();

                sv = ubi_scan_find_sv(si, i);
                vol = ubi->volumes[i];
                if (!vol) {
                        if (sv)
                                ubi_scan_rm_volume(si, sv);
                        continue;
                }

                if (vol->reserved_pebs == 0) {
                        ubi_assert(i < ubi->vtbl_slots);

                        if (!sv)
                                continue;

                        /*
                         * During scanning we found a volume which does not
                         * exist according to the information in the volume
                         * table. This must have happened due to an unclean
                         * reboot while the volume was being removed. Discard
                         * these eraseblocks.
                         */
                        ubi_msg("finish volume %d removal", sv->vol_id);
                        ubi_scan_rm_volume(si, sv);
                } else if (sv) {
                        err = check_sv(vol, sv);
                        if (err)
                                return err;
                }
        }

        return 0;
}

/**
 * ubi_read_volume_table - read volume table.
 * information.
 * @ubi: UBI device description object
 * @si: scanning information
 *
 * This function reads volume table, checks it, recover from errors if needed,
 * or creates it if needed. Returns zero in case of success and a negative
 * error code in case of failure.
 */
int ubi_read_volume_table(struct ubi_device *ubi, struct ubi_scan_info *si)
{
        int i, err;
        struct ubi_scan_volume *sv;

        empty_vtbl_record.crc = cpu_to_be32(0xf116c36b);

        /*
         * The number of supported volumes is limited by the eraseblock size
         * and by the UBI_MAX_VOLUMES constant.
         */
        ubi->vtbl_slots = ubi->leb_size / UBI_VTBL_RECORD_SIZE;
        if (ubi->vtbl_slots > UBI_MAX_VOLUMES)
                ubi->vtbl_slots = UBI_MAX_VOLUMES;

        ubi->vtbl_size = ubi->vtbl_slots * UBI_VTBL_RECORD_SIZE;
        ubi->vtbl_size = ALIGN(ubi->vtbl_size, ubi->min_io_size);

        sv = ubi_scan_find_sv(si, UBI_LAYOUT_VOLUME_ID);
        if (!sv) {
                /*
                 * No logical eraseblocks belonging to the layout volume were
                 * found. This could mean that the flash is just empty. In
                 * this case we create empty layout volume.
                 *
                 * But if flash is not empty this must be a corruption or the
                 * MTD device just contains garbage.
                 */
                if (si->is_empty) {
                        ubi->vtbl = create_empty_lvol(ubi, si);
                        if (IS_ERR(ubi->vtbl))
                                return PTR_ERR(ubi->vtbl);
                } else {
                        ubi_err("the layout volume was not found");
                        return -EINVAL;
                }
        } else {
                if (sv->leb_count > UBI_LAYOUT_VOLUME_EBS) {
                        /* This must not happen with proper UBI images */
                        dbg_err("too many LEBs (%d) in layout volume",
                                sv->leb_count);
                        return -EINVAL;
                }

                ubi->vtbl = process_lvol(ubi, si, sv);
                if (IS_ERR(ubi->vtbl))
                        return PTR_ERR(ubi->vtbl);
        }

        ubi->avail_pebs = ubi->good_peb_count;

        /*
         * The layout volume is OK, initialize the corresponding in-RAM data
         * structures.
         */
        err = init_volumes(ubi, si, ubi->vtbl);
        if (err)
                goto out_free;

        /*
         * Get sure that the scanning information is consistent to the
         * information stored in the volume table.
         */
        err = check_scanning_info(ubi, si);
        if (err)
                goto out_free;

        return 0;

out_free:
        vfree(ubi->vtbl);
        for (i = 0; i < ubi->vtbl_slots + UBI_INT_VOL_COUNT; i++)
                if (ubi->volumes[i]) {
                        kfree(ubi->volumes[i]);
                        ubi->volumes[i] = NULL;
                }
        return err;
}

#ifdef CONFIG_MTD_UBI_DEBUG_PARANOID

/**
 * paranoid_vtbl_check - check volume table.
 * @ubi: UBI device description object
 */
static void paranoid_vtbl_check(const struct ubi_device *ubi)
{
        if (vtbl_check(ubi, ubi->vtbl)) {
                ubi_err("paranoid check failed");
                BUG();
        }
}

#endif /* CONFIG_MTD_UBI_DEBUG_PARANOID */