/*
 * 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 scanning unit.
 *
 * This unit is responsible for scanning the flash media, checking UBI
 * headers and providing complete information about the UBI flash image.
 *
 * The scanning information is represented by a &struct ubi_scan_info' object.
 * Information about found volumes is represented by &struct ubi_scan_volume
 * objects which are kept in volume RB-tree with root at the @volumes field.
 * The RB-tree is indexed by the volume ID.
 *
 * Found logical eraseblocks are represented by &struct ubi_scan_leb objects.
 * These objects are kept in per-volume RB-trees with the root at the
 * corresponding &struct ubi_scan_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-eraseblock 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.
 */

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

#ifdef CONFIG_MTD_UBI_DEBUG_PARANOID
static int paranoid_check_si(struct ubi_device *ubi, struct ubi_scan_info *si);
#else
#define paranoid_check_si(ubi, si) 0
#endif

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

/**
 * add_to_list - add physical eraseblock to a list.
 * @si: scanning information
 * @pnum: physical eraseblock number to add
 * @ec: erase counter of the physical eraseblock
 * @list: the list to add to
 *
 * This function adds physical eraseblock @pnum to free, erase, corrupted or
 * alien lists. Returns zero in case of success and a negative error code in
 * case of failure.
 */
static int add_to_list(struct ubi_scan_info *si, int pnum, int ec,
                       struct list_head *list)
{
        struct ubi_scan_leb *seb;

        if (list == &si->free)
                dbg_bld("add to free: PEB %d, EC %d", pnum, ec);
        else if (list == &si->erase)
                dbg_bld("add to erase: PEB %d, EC %d", pnum, ec);
        else if (list == &si->corr)
                dbg_bld("add to corrupted: PEB %d, EC %d", pnum, ec);
        else if (list == &si->alien)
                dbg_bld("add to alien: PEB %d, EC %d", pnum, ec);
        else
                BUG();

        seb = kmalloc(sizeof(struct ubi_scan_leb), GFP_KERNEL);
        if (!seb)
                return -ENOMEM;

        seb->pnum = pnum;
        seb->ec = ec;
        list_add_tail(&seb->u.list, list);
        return 0;
}

/**
 * commit_to_mean_value - commit intermediate results to the final mean erase
 * counter value.
 * @si: scanning information
 *
 * This is a helper function which calculates partial mean erase counter mean
 * value and adds it to the resulting mean value. As we can work only in
 * integer arithmetic and we want to calculate the mean value of erase counter
 * accurately, we first sum erase counter values in @si->ec_sum variable and
 * count these components in @si->ec_count. If this temporary @si->ec_sum is
 * going to overflow, we calculate the partial mean value
 * (@si->ec_sum/@si->ec_count) and add it to @si->mean_ec.
 */
static void commit_to_mean_value(struct ubi_scan_info *si)
{
        si->ec_sum /= si->ec_count;
        if (si->ec_sum % si->ec_count >= si->ec_count / 2)
                si->mean_ec += 1;
        si->mean_ec += si->ec_sum;
}

/**
 * validate_vid_hdr - check that volume identifier header is correct and
 * consistent.
 * @vid_hdr: the volume identifier header to check
 * @sv: information about the volume this logical eraseblock belongs to
 * @pnum: physical eraseblock number the VID header came from
 *
 * This function checks that data stored in @vid_hdr is consistent. Returns
 * non-zero if an inconsistency was found and zero if not.
 *
 * Note, UBI does sanity check of everything it reads from the flash media.
 * Most of the checks are done in the I/O unit. Here we check that the
 * information in the VID header is consistent to the information in other VID
 * headers of the same volume.
 */
static int validate_vid_hdr(const struct ubi_vid_hdr *vid_hdr,
                            const struct ubi_scan_volume *sv, 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 (sv->leb_count != 0) {
                int sv_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 != sv->vol_id) {
                        dbg_err("inconsistent vol_id");
                        goto bad;
                }

                if (sv->vol_type == UBI_STATIC_VOLUME)
                        sv_vol_type = UBI_VID_STATIC;
                else
                        sv_vol_type = UBI_VID_DYNAMIC;

                if (vol_type != sv_vol_type) {
                        dbg_err("inconsistent vol_type");
                        goto bad;
                }

                if (used_ebs != sv->used_ebs) {
                        dbg_err("inconsistent used_ebs");
                        goto bad;
                }

                if (data_pad != sv->data_pad) {
                        dbg_err("inconsistent data_pad");
                        goto bad;
                }
        }

        return 0;

bad:
        ubi_err("inconsistent VID header at PEB %d", pnum);
        ubi_dbg_dump_vid_hdr(vid_hdr);
        ubi_dbg_dump_sv(sv);
        return -EINVAL;
}

/**
 * add_volume - add volume to the scanning information.
 * @si: scanning information
 * @vol_id: ID of the volume to add
 * @pnum: physical eraseblock number
 * @vid_hdr: volume identifier header
 *
 * If the volume corresponding to the @vid_hdr logical eraseblock is already
 * present in the scanning information, this function does nothing. Otherwise
 * it adds corresponding volume to the scanning information. Returns a pointer
 * to the scanning volume object in case of success and a negative error code
 * in case of failure.
 */
static struct ubi_scan_volume *add_volume(struct ubi_scan_info *si, int vol_id,
                                          int pnum,
                                          const struct ubi_vid_hdr *vid_hdr)
{
        struct ubi_scan_volume *sv;
        struct rb_node **p = &si->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;
                sv = rb_entry(parent, struct ubi_scan_volume, rb);

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

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

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

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

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

/**
 * compare_lebs - find out which logical eraseblock is newer.
 * @ubi: UBI device description object
 * @seb: first logical eraseblock to compare
 * @pnum: physical eraseblock number of the second logical eraseblock to
 * compare
 * @vid_hdr: volume identifier header of the second logical eraseblock
 *
 * This function compares 2 copies of a LEB and informs which one is newer. In
 * case of success this function returns a positive value, in case of failure, a
 * negative error code is returned. The success return codes use the following
 * bits:
 *     o bit 0 is cleared: the first PEB (described by @seb) is newer then the
 *       second PEB (described by @pnum and @vid_hdr);
 *     o bit 0 is set: the second PEB is newer;
 *     o bit 1 is cleared: no bit-flips were detected in the newer LEB;
 *     o bit 1 is set: bit-flips were detected in the newer LEB;
 *     o bit 2 is cleared: the older LEB is not corrupted;
 *     o bit 2 is set: the older LEB is corrupted.
 */
static int compare_lebs(struct ubi_device *ubi, const struct ubi_scan_leb *seb,
                        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 (seb->sqnum == 0 && sqnum2 == 0) {
                long long abs, v1 = seb->leb_ver, v2 = be32_to_cpu(vid_hdr->leb_ver);

                /*
                 * UBI constantly increases the logical eraseblock version
                 * number and it can overflow. Thus, we have to bear in mind
                 * that versions that are close to %0xFFFFFFFF are less then
                 * versions that are close to %0.
                 *
                 * The UBI WL unit guarantees that the number of pending tasks
                 * is not greater then %0x7FFFFFFF. So, if the difference
                 * between any two versions is greater or equivalent to
                 * %0x7FFFFFFF, there was an overflow and the logical
                 * eraseblock with lower version is actually newer then the one
                 * with higher version.
                 *
                 * FIXME: but this is anyway obsolete and will be removed at
                 * some point.
                 */
                dbg_bld("using old crappy leb_ver stuff");

                if (v1 == v2) {
                        ubi_err("PEB %d and PEB %d have the same version %lld",
                                seb->pnum, pnum, v1);
                        return -EINVAL;
                }

                abs = v1 - v2;
                if (abs < 0)
                        abs = -abs;

                if (abs < 0x7FFFFFFF)
                        /* Non-overflow situation */
                        second_is_newer = (v2 > v1);
                else
                        second_is_newer = (v2 < v1);
        } else
                /* Obviously the LEB with lower sequence counter is older */
                second_is_newer = sqnum2 > seb->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.
         *
         * FIXME: 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 {
                pnum = seb->pnum;

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

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

                                goto out_free_vidh;
                        }
                }

                if (!vh->copy_flag) {
                        /* It is not a copy, so it is newer */
                        dbg_bld("first PEB %d is newer, copy_flag is unset",
                                pnum);
                        err = bitflips << 1;
                        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)
                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;
}

/**
 * ubi_scan_add_used - add information about a physical eraseblock to the
 * scanning information.
 * @ubi: UBI device description object
 * @si: scanning information
 * @pnum: the physical eraseblock number
 * @ec: erase counter
 * @vid_hdr: the volume identifier header
 * @bitflips: if bit-flips were detected when this physical eraseblock was read
 *
 * This function adds information about a used physical eraseblock to the
 * 'used' tree of the corresponding volume. The function is rather complex
 * because it has to handle cases when this is not the first physical
 * eraseblock belonging to the same logical eraseblock, and the newer one has
 * to be picked, while the older one has to be dropped. This function returns
 * zero in case of success and a negative error code in case of failure.
 */
int ubi_scan_add_used(struct ubi_device *ubi, struct ubi_scan_info *si,
                      int pnum, int ec, const struct ubi_vid_hdr *vid_hdr,
                      int bitflips)
{
        int err, vol_id, lnum;
        uint32_t leb_ver;
        unsigned long long sqnum;
        struct ubi_scan_volume *sv;
        struct ubi_scan_leb *seb;
        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);
        leb_ver = be32_to_cpu(vid_hdr->leb_ver);

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

        sv = add_volume(si, vol_id, pnum, vid_hdr);
        if (IS_ERR(sv) < 0)
                return PTR_ERR(sv);

        if (si->max_sqnum < sqnum)
                si->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 = &sv->root.rb_node;
        while (*p) {
                int cmp_res;

                parent = *p;
                seb = rb_entry(parent, struct ubi_scan_leb, u.rb);
                if (lnum != seb->lnum) {
                        if (lnum < seb->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, "
                        "LEB ver %u, EC %d", seb->pnum, seb->sqnum,
                        seb->leb_ver, seb->ec);

                /*
                 * Make sure that the logical eraseblocks have different
                 * versions. Otherwise the image is bad.
                 */
                if (seb->leb_ver == leb_ver && leb_ver != 0) {
                        ubi_err("two LEBs with same version %u", leb_ver);
                        ubi_dbg_dump_seb(seb, 0);
                        ubi_dbg_dump_vid_hdr(vid_hdr);
                        return -EINVAL;
                }

                /*
                 * Make sure that the logical eraseblocks have different
                 * sequence numbers. Otherwise the image is bad.
                 *
                 * FIXME: remove 'sqnum != 0' check when leb_ver is removed.
                 */
                if (seb->sqnum == sqnum && sqnum != 0) {
                        ubi_err("two LEBs with same sequence number %llu",
                                sqnum);
                        ubi_dbg_dump_seb(seb, 0);
                        ubi_dbg_dump_vid_hdr(vid_hdr);
                        return -EINVAL;
                }

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

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

                        if (cmp_res & 4)
                                err = add_to_list(si, seb->pnum, seb->ec,
                                                  &si->corr);
                        else
                                err = add_to_list(si, seb->pnum, seb->ec,
                                                  &si->erase);
                        if (err)
                                return err;

                        seb->ec = ec;
                        seb->pnum = pnum;
                        seb->scrub = ((cmp_res & 2) || bitflips);
                        seb->sqnum = sqnum;
                        seb->leb_ver = leb_ver;

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

                        return 0;
                } else {
                        /*
                         * This logical eraseblock is older then the one found
                         * previously.
                         */
                        if (cmp_res & 4)
                                return add_to_list(si, pnum, ec, &si->corr);
                        else
                                return add_to_list(si, pnum, ec, &si->erase);
                }
        }

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

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

        seb = kmalloc(sizeof(struct ubi_scan_leb), GFP_KERNEL);
        if (!seb)
                return -ENOMEM;

        seb->ec = ec;
        seb->pnum = pnum;
        seb->lnum = lnum;
        seb->sqnum = sqnum;
        seb->scrub = bitflips;
        seb->leb_ver = leb_ver;

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

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

/**
 * ubi_scan_find_sv - find information about a particular volume in the
 * scanning information.
 * @si: scanning information
 * @vol_id: the requested volume ID
 *
 * This function returns a pointer to the volume description or %NULL if there
 * are no data about this volume in the scanning information.
 */
struct ubi_scan_volume *ubi_scan_find_sv(const struct ubi_scan_info *si,
                                         int vol_id)
{
        struct ubi_scan_volume *sv;
        struct rb_node *p = si->volumes.rb_node;

        while (p) {
                sv = rb_entry(p, struct ubi_scan_volume, rb);

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

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

        return NULL;
}

/**
 * ubi_scan_find_seb - find information about a particular logical
 * eraseblock in the volume scanning information.
 * @sv: a pointer to the volume scanning information
 * @lnum: the requested logical eraseblock
 *
 * This function returns a pointer to the scanning logical eraseblock or %NULL
 * if there are no data about it in the scanning volume information.
 */
struct ubi_scan_leb *ubi_scan_find_seb(const struct ubi_scan_volume *sv,
                                       int lnum)
{
        struct ubi_scan_leb *seb;
        struct rb_node *p = sv->root.rb_node;

        while (p) {
                seb = rb_entry(p, struct ubi_scan_leb, u.rb);

                if (lnum == seb->lnum)
                        return seb;

                if (lnum > seb->lnum)
                        p = p->rb_left;
                else
                        p = p->rb_right;
        }

        return NULL;
}

/**
 * ubi_scan_rm_volume - delete scanning information about a volume.
 * @si: scanning information
 * @sv: the volume scanning information to delete
 */
void ubi_scan_rm_volume(struct ubi_scan_info *si, struct ubi_scan_volume *sv)
{
        struct rb_node *rb;
        struct ubi_scan_leb *seb;

        dbg_bld("remove scanning information about volume %d", sv->vol_id);

        while ((rb = rb_first(&sv->root))) {
                seb = rb_entry(rb, struct ubi_scan_leb, u.rb);
                rb_erase(&seb->u.rb, &sv->root);
                list_add_tail(&seb->u.list, &si->erase);
        }

        rb_erase(&sv->rb, &si->volumes);
        kfree(sv);
        si->vols_found -= 1;
}

/**
 * ubi_scan_erase_peb - erase a physical eraseblock.
 * @ubi: UBI device description object
 * @si: scanning information
 * @pnum: physical eraseblock number to erase;
 * @ec: erase counter value to write (%UBI_SCAN_UNKNOWN_EC if it is unknown)
 *
 * This function erases physical eraseblock 'pnum', and writes the erase
 * counter header to it. This function should only be used on UBI device
 * initialization stages, when the EBA unit had not been yet initialized. This
 * function returns zero in case of success and a negative error code in case
 * of failure.
 */
int ubi_scan_erase_peb(struct ubi_device *ubi, const struct ubi_scan_info *si,
                       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;
}

/**
 * ubi_scan_get_free_peb - get a free physical eraseblock.
 * @ubi: UBI device description object
 * @si: scanning information
 *
 * This function returns a free physical eraseblock. It is supposed to be
 * called on the UBI initialization stages when the wear-leveling unit is not
 * initialized yet. This function picks a physical eraseblocks from one of the
 * lists, writes the EC header if it is needed, and removes it from the list.
 *
 * This function returns scanning physical eraseblock information in case of
 * success and an error code in case of failure.
 */
struct ubi_scan_leb *ubi_scan_get_free_peb(struct ubi_device *ubi,
                                           struct ubi_scan_info *si)
{
        int err = 0, i;
        struct ubi_scan_leb *seb;

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

        for (i = 0; i < 2; i++) {
                struct list_head *head;
                struct ubi_scan_leb *tmp_seb;

                if (i == 0)
                        head = &si->erase;
                else
                        head = &si->corr;

                /*
                 * We try to erase the first physical eraseblock from the @head
                 * 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(seb, tmp_seb, head, u.list) {
                        if (seb->ec == UBI_SCAN_UNKNOWN_EC)
                                seb->ec = si->mean_ec;

                        err = ubi_scan_erase_peb(ubi, si, seb->pnum, seb->ec+1);
                        if (err)
                                continue;

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

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

/**
 * process_eb - read UBI headers, check them and add corresponding data
 * to the scanning information.
 * @ubi: UBI device description object
 * @si: scanning information
 * @pnum: the physical eraseblock number
 *
 * This function returns a zero if the physical eraseblock was successfully
 * handled and a negative error code in case of failure.
 */
static int process_eb(struct ubi_device *ubi, struct ubi_scan_info *si, int pnum)
{
        long long uninitialized_var(ec);
        int err, bitflips = 0, vol_id, ec_corr = 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) {
                /*
                 * FIXME: this is actually duty of the I/O unit to initialize
                 * this, but MTD does not provide enough information.
                 */
                si->bad_peb_count += 1;
                return 0;
        }

        err = ubi_io_read_ec_hdr(ubi, pnum, ech, 0);
        if (err < 0)
                return err;
        else if (err == UBI_IO_BITFLIPS)
                bitflips = 1;
        else if (err == UBI_IO_PEB_EMPTY)
                return add_to_list(si, pnum, UBI_SCAN_UNKNOWN_EC, &si->erase);
        else if (err == UBI_IO_BAD_EC_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_corr = 1;
                ec = UBI_SCAN_UNKNOWN_EC;
                bitflips = 1;
        }

        si->is_empty = 0;

        if (!ec_corr) {
                /* 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_dbg_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;
        else if (err == UBI_IO_BITFLIPS)
                bitflips = 1;
        else if (err == UBI_IO_BAD_VID_HDR ||
                 (err == UBI_IO_PEB_FREE && ec_corr)) {
                /* VID header is corrupted */
                err = add_to_list(si, pnum, ec, &si->corr);
                if (err)
                        return err;
                goto adjust_mean_ec;
        } else if (err == UBI_IO_PEB_FREE) {
                /* No VID header - the physical eraseblock is free */
                err = add_to_list(si, pnum, ec, &si->free);
                if (err)
                        return err;
                goto adjust_mean_ec;
        }

        vol_id = be32_to_cpu(vidh->vol_id);
        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:
                        ubi_msg("\"delete\" compatible internal volume %d:%d"
                                " found, remove it", vol_id, lnum);
                        err = add_to_list(si, pnum, ec, &si->corr);
                        if (err)
                                return err;
                        break;

                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(si, pnum, ec, &si->alien);
                        if (err)
                                return err;
                        si->alien_peb_count += 1;
                        return 0;

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

        /* Both UBI headers seem to be fine */
        err = ubi_scan_add_used(ubi, si, pnum, ec, vidh, bitflips);
        if (err)
                return err;

adjust_mean_ec:
        if (!ec_corr) {
                if (si->ec_sum + ec < ec) {
                        commit_to_mean_value(si);
                        si->ec_sum = 0;
                        si->ec_count = 0;
                } else {
                        si->ec_sum += ec;
                        si->ec_count += 1;
                }

                if (ec > si->max_ec)
                        si->max_ec = ec;
                if (ec < si->min_ec)
                        si->min_ec = ec;
        }

        return 0;
}

/**
 * ubi_scan - scan an MTD device.
 * @ubi: UBI device description object
 *
 * This function does full scanning of an MTD device and returns complete
 * information about it. In case of failure, an error code is returned.
 */
struct ubi_scan_info *ubi_scan(struct ubi_device *ubi)
{
        int err, pnum;
        struct rb_node *rb1, *rb2;
        struct ubi_scan_volume *sv;
        struct ubi_scan_leb *seb;
        struct ubi_scan_info *si;

        si = kzalloc(sizeof(struct ubi_scan_info), GFP_KERNEL);
        if (!si)
                return ERR_PTR(-ENOMEM);

        INIT_LIST_HEAD(&si->corr);
        INIT_LIST_HEAD(&si->free);
        INIT_LIST_HEAD(&si->erase);
        INIT_LIST_HEAD(&si->alien);
        si->volumes = RB_ROOT;
        si->is_empty = 1;

        err = -ENOMEM;
        ech = kzalloc(ubi->ec_hdr_alsize, GFP_KERNEL);
        if (!ech)
                goto out_si;

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

        for (pnum = 0; pnum < ubi->peb_count; pnum++) {
                cond_resched();

                dbg_msg("process PEB %d", pnum);
                err = process_eb(ubi, si, pnum);
                if (err < 0)
                        goto out_vidh;
        }

        dbg_msg("scanning is finished");

        /* Finish mean erase counter calculations */
        if (si->ec_count)
                commit_to_mean_value(si);

        if (si->is_empty)
                ubi_msg("empty MTD device detected");

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

        list_for_each_entry(seb, &si->free, u.list) {
                if (seb->ec == UBI_SCAN_UNKNOWN_EC)
                        seb->ec = si->mean_ec;
        }

        list_for_each_entry(seb, &si->corr, u.list)
                if (seb->ec == UBI_SCAN_UNKNOWN_EC)
                        seb->ec = si->mean_ec;

        list_for_each_entry(seb, &si->erase, u.list)
                if (seb->ec == UBI_SCAN_UNKNOWN_EC)
                        seb->ec = si->mean_ec;

        err = paranoid_check_si(ubi, si);
        if (err) {
                if (err > 0)

                        err = -EINVAL;
                goto out_vidh;
        }

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

        return si;

out_vidh:
        ubi_free_vid_hdr(ubi, vidh);
out_ech:
        kfree(ech);
out_si:
        ubi_scan_destroy_si(si);
        return ERR_PTR(err);
}

/**
 * destroy_sv - free the scanning volume information
 * @sv: scanning volume information
 *
 * This function destroys the volume RB-tree (@sv->root) and the scanning
 * volume information.
 */
static void destroy_sv(struct ubi_scan_volume *sv)
{
        struct ubi_scan_leb *seb;
        struct rb_node *this = sv->root.rb_node;

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

                        kfree(seb);
                }
        }
        kfree(sv);
}

/**
 * ubi_scan_destroy_si - destroy scanning information.
 * @si: scanning information
 */
void ubi_scan_destroy_si(struct ubi_scan_info *si)
{
        struct ubi_scan_leb *seb, *seb_tmp;
        struct ubi_scan_volume *sv;
        struct rb_node *rb;

        list_for_each_entry_safe(seb, seb_tmp, &si->alien, u.list) {
                list_del(&seb->u.list);
                kfree(seb);
        }
        list_for_each_entry_safe(seb, seb_tmp, &si->erase, u.list) {
                list_del(&seb->u.list);
                kfree(seb);
        }
        list_for_each_entry_safe(seb, seb_tmp, &si->corr, u.list) {
                list_del(&seb->u.list);
                kfree(seb);
        }
        list_for_each_entry_safe(seb, seb_tmp, &si->free, u.list) {
                list_del(&seb->u.list);
                kfree(seb);
        }

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

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

                        destroy_sv(sv);
                }
        }

        kfree(si);
}

#ifdef CONFIG_MTD_UBI_DEBUG_PARANOID

/**
 * paranoid_check_si - check if the scanning information is correct and
 * consistent.
 * @ubi: UBI device description object
 * @si: scanning information
 *
 * This function returns zero if the scanning information is all right, %1 if
 * not and a negative error code if an error occurred.
 */
static int paranoid_check_si(struct ubi_device *ubi, struct ubi_scan_info *si)
{
        int pnum, err, vols_found = 0;
        struct rb_node *rb1, *rb2;
        struct ubi_scan_volume *sv;
        struct ubi_scan_leb *seb, *last_seb;
        uint8_t *buf;

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

                cond_resched();

                vols_found += 1;

                if (si->is_empty) {
                        ubi_err("bad is_empty flag");
                        goto bad_sv;
                }

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

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

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

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

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

                last_seb = NULL;
                ubi_rb_for_each_entry(rb2, seb, &sv->root, u.rb) {
                        cond_resched();

                        last_seb = seb;
                        leb_count += 1;

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

                        if (seb->ec < si->min_ec) {
                                ubi_err("bad si->min_ec (%d), %d found",
                                        si->min_ec, seb->ec);
                                goto bad_seb;
                        }

                        if (seb->ec > si->max_ec) {
                                ubi_err("bad si->max_ec (%d), %d found",
                                        si->max_ec, seb->ec);
                                goto bad_seb;
                        }

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

                        if (sv->vol_type == UBI_STATIC_VOLUME) {
                                if (seb->lnum >= sv->used_ebs) {
                                        ubi_err("bad lnum or used_ebs");
                                        goto bad_seb;
                                }
                        } else {
                                if (sv->used_ebs != 0) {
                                        ubi_err("non-zero used_ebs");
                                        goto bad_seb;
                                }
                        }

                        if (seb->lnum > sv->highest_lnum) {
                                ubi_err("incorrect highest_lnum or lnum");
                                goto bad_seb;
                        }
                }

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

                if (!last_seb)
                        continue;

                seb = last_seb;

                if (seb->lnum != sv->highest_lnum) {
                        ubi_err("bad highest_lnum");
                        goto bad_seb;
                }
        }

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

        /* Check that scanning information is correct */
        ubi_rb_for_each_entry(rb1, sv, &si->volumes, rb) {
                last_seb = NULL;
                ubi_rb_for_each_entry(rb2, seb, &sv->root, u.rb) {
                        int vol_type;

                        cond_resched();

                        last_seb = seb;

                        err = ubi_io_read_vid_hdr(ubi, seb->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 (sv->vol_type != vol_type) {
                                ubi_err("bad vol_type");
                                goto bad_vid_hdr;
                        }

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

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

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

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

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

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

                        if (seb->leb_ver != be32_to_cpu(vidh->leb_ver)) {
                                ubi_err("bad leb_ver %u", seb->leb_ver);
                                goto bad_vid_hdr;
                        }
                }

                if (!last_seb)
                        continue;

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

                if (sv->last_data_size != be32_to_cpu(vidh->data_size)) {
                        ubi_err("bad last_data_size %d", sv->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, sv, &si->volumes, rb)
                ubi_rb_for_each_entry(rb2, seb, &sv->root, u.rb)
                        buf[seb->pnum] = 1;

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

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

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

        list_for_each_entry(seb, &si->alien, u.list)
                buf[seb->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_seb:
        ubi_err("bad scanning information about LEB %d", seb->lnum);
        ubi_dbg_dump_seb(seb, 0);
        ubi_dbg_dump_sv(sv);
        goto out;

bad_sv:
        ubi_err("bad scanning information about volume %d", sv->vol_id);
        ubi_dbg_dump_sv(sv);
        goto out;

bad_vid_hdr:
        ubi_err("bad scanning information about volume %d", sv->vol_id);
        ubi_dbg_dump_sv(sv);
        ubi_dbg_dump_vid_hdr(vidh);

out:
        ubi_dbg_dump_stack();
        return 1;
}

#endif /* CONFIG_MTD_UBI_DEBUG_PARANOID */