recovery.c

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/*
 * This file is part of UBIFS.
 *
 * Copyright (C) 2006-2008 Nokia Corporation
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published by
 * the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 51
 * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * Authors: Adrian Hunter
 *          Artem Bityutskiy (Битюцкий Артём)
 */

/*
 * This file implements functions needed to recover from unclean un-mounts.
 * When UBIFS is mounted, it checks a flag on the master node to determine if
 * an un-mount was completed successfully. If not, the process of mounting
 * incorporates additional checking and fixing of on-flash data structures.
 * UBIFS always cleans away all remnants of an unclean un-mount, so that
 * errors do not accumulate. However UBIFS defers recovery if it is mounted
 * read-only, and the flash is not modified in that case.
 *
 * The general UBIFS approach to the recovery is that it recovers from
 * corruptions which could be caused by power cuts, but it refuses to recover
 * from corruption caused by other reasons. And UBIFS tries to distinguish
 * between these 2 reasons of corruptions and silently recover in the former
 * case and loudly complain in the latter case.
 *
 * UBIFS writes only to erased LEBs, so it writes only to the flash space
 * containing only 0xFFs. UBIFS also always writes strictly from the beginning
 * of the LEB to the end. And UBIFS assumes that the underlying flash media
 * writes in @c->max_write_size bytes at a time.
 *
 * Hence, if UBIFS finds a corrupted node at offset X, it expects only the min.
 * I/O unit corresponding to offset X to contain corrupted data, all the
 * following min. I/O units have to contain empty space (all 0xFFs). If this is
 * not true, the corruption cannot be the result of a power cut, and UBIFS
 * refuses to mount.
 */

#include <linux/crc32.h>
#include <linux/slab.h>
#include "ubifs.h"

static int is_empty(void *buf, int len)
{
    uint8_t *p = buf;
    int i;

    for (i = 0; i < len; i++)
        if (*p++ != 0xff)
            return 0;
    return 1;
}

static int first_non_ff(void *buf, int len)
{
    uint8_t *p = buf;
    int i;

    for (i = 0; i < len; i++)
        if (*p++ != 0xff)
            return i;
    return -1;
}

static int get_master_node(const struct ubifs_info *c, int lnum, void **pbuf,
               struct ubifs_mst_node **mst, void **cor)
{
    const int sz = c->mst_node_alsz;
    int err, offs, len;
    void *sbuf, *buf;

    sbuf = vmalloc(c->leb_size);
    if (!sbuf)
        return -ENOMEM;

    err = ubifs_leb_read(c, lnum, sbuf, 0, c->leb_size, 0);
    if (err && err != -EBADMSG)
        goto out_free;

    /* Find the first position that is definitely not a node */
    offs = 0;
    buf = sbuf;
    len = c->leb_size;
    while (offs + UBIFS_MST_NODE_SZ <= c->leb_size) {
        struct ubifs_ch *ch = buf;

        if (le32_to_cpu(ch->magic) != UBIFS_NODE_MAGIC)
            break;
        offs += sz;
        buf  += sz;
        len  -= sz;
    }
    /* See if there was a valid master node before that */
    if (offs) {
        int ret;

        offs -= sz;
        buf  -= sz;
        len  += sz;
        ret = ubifs_scan_a_node(c, buf, len, lnum, offs, 1);
        if (ret != SCANNED_A_NODE && offs) {
            /* Could have been corruption so check one place back */
            offs -= sz;
            buf  -= sz;
            len  += sz;
            ret = ubifs_scan_a_node(c, buf, len, lnum, offs, 1);
            if (ret != SCANNED_A_NODE)
                /*
                 * We accept only one area of corruption because
                 * we are assuming that it was caused while
                 * trying to write a master node.
                 */
                goto out_err;
        }
        if (ret == SCANNED_A_NODE) {
            struct ubifs_ch *ch = buf;

            if (ch->node_type != UBIFS_MST_NODE)
                goto out_err;
            dbg_rcvry("found a master node at %d:%d", lnum, offs);
            *mst = buf;
            offs += sz;
            buf  += sz;
            len  -= sz;
        }
    }
    /* Check for corruption */
    if (offs < c->leb_size) {
        if (!is_empty(buf, min_t(int, len, sz))) {
            *cor = buf;
            dbg_rcvry("found corruption at %d:%d", lnum, offs);
        }
        offs += sz;
        buf  += sz;
        len  -= sz;
    }
    /* Check remaining empty space */
    if (offs < c->leb_size)
        if (!is_empty(buf, len))
            goto out_err;
    *pbuf = sbuf;
    return 0;

out_err:
    err = -EINVAL;
out_free:
    vfree(sbuf);
    *mst = NULL;
    *cor = NULL;
    return err;
}

static int write_rcvrd_mst_node(struct ubifs_info *c,
                struct ubifs_mst_node *mst)
{
    int err = 0, lnum = UBIFS_MST_LNUM, sz = c->mst_node_alsz;
    __le32 save_flags;

    dbg_rcvry("recovery");

    save_flags = mst->flags;
    mst->flags |= cpu_to_le32(UBIFS_MST_RCVRY);

    ubifs_prepare_node(c, mst, UBIFS_MST_NODE_SZ, 1);
    err = ubifs_leb_change(c, lnum, mst, sz);
    if (err)
        goto out;
    err = ubifs_leb_change(c, lnum + 1, mst, sz);
    if (err)
        goto out;
out:
    mst->flags = save_flags;
    return err;
}

int ubifs_recover_master_node(struct ubifs_info *c)
{
    void *buf1 = NULL, *buf2 = NULL, *cor1 = NULL, *cor2 = NULL;
    struct ubifs_mst_node *mst1 = NULL, *mst2 = NULL, *mst;
    const int sz = c->mst_node_alsz;
    int err, offs1, offs2;

    dbg_rcvry("recovery");

    err = get_master_node(c, UBIFS_MST_LNUM, &buf1, &mst1, &cor1);
    if (err)
        goto out_free;

    err = get_master_node(c, UBIFS_MST_LNUM + 1, &buf2, &mst2, &cor2);
    if (err)
        goto out_free;

    if (mst1) {
        offs1 = (void *)mst1 - buf1;
        if ((le32_to_cpu(mst1->flags) & UBIFS_MST_RCVRY) &&
            (offs1 == 0 && !cor1)) {
            /*
             * mst1 was written by recovery at offset 0 with no
             * corruption.
             */
            dbg_rcvry("recovery recovery");
            mst = mst1;
        } else if (mst2) {
            offs2 = (void *)mst2 - buf2;
            if (offs1 == offs2) {
                /* Same offset, so must be the same */
                if (memcmp((void *)mst1 + UBIFS_CH_SZ,
                       (void *)mst2 + UBIFS_CH_SZ,
                       UBIFS_MST_NODE_SZ - UBIFS_CH_SZ))
                    goto out_err;
                mst = mst1;
            } else if (offs2 + sz == offs1) {
                /* 1st LEB was written, 2nd was not */
                if (cor1)
                    goto out_err;
                mst = mst1;
            } else if (offs1 == 0 &&
                   c->leb_size - offs2 - sz < sz) {
                /* 1st LEB was unmapped and written, 2nd not */
                if (cor1)
                    goto out_err;
                mst = mst1;
            } else
                goto out_err;
        } else {
            /*
             * 2nd LEB was unmapped and about to be written, so
             * there must be only one master node in the first LEB
             * and no corruption.
             */
            if (offs1 != 0 || cor1)
                goto out_err;
            mst = mst1;
        }
    } else {
        if (!mst2)
            goto out_err;
        /*
         * 1st LEB was unmapped and about to be written, so there must
         * be no room left in 2nd LEB.
         */
        offs2 = (void *)mst2 - buf2;
        if (offs2 + sz + sz <= c->leb_size)
            goto out_err;
        mst = mst2;
    }

    ubifs_msg("recovered master node from LEB %d",
          (mst == mst1 ? UBIFS_MST_LNUM : UBIFS_MST_LNUM + 1));

    memcpy(c->mst_node, mst, UBIFS_MST_NODE_SZ);

    if (c->ro_mount) {
        /* Read-only mode. Keep a copy for switching to rw mode */
        c->rcvrd_mst_node = kmalloc(sz, GFP_KERNEL);
        if (!c->rcvrd_mst_node) {
            err = -ENOMEM;
            goto out_free;
        }
        memcpy(c->rcvrd_mst_node, c->mst_node, UBIFS_MST_NODE_SZ);

        /*
         * We had to recover the master node, which means there was an
         * unclean reboot. However, it is possible that the master node
         * is clean at this point, i.e., %UBIFS_MST_DIRTY is not set.
         * E.g., consider the following chain of events:
         *
         * 1. UBIFS was cleanly unmounted, so the master node is clean
         * 2. UBIFS is being mounted R/W and starts changing the master
         *    node in the first (%UBIFS_MST_LNUM). A power cut happens,
         *    so this LEB ends up with some amount of garbage at the
         *    end.
         * 3. UBIFS is being mounted R/O. We reach this place and
         *    recover the master node from the second LEB
         *    (%UBIFS_MST_LNUM + 1). But we cannot update the media
         *    because we are being mounted R/O. We have to defer the
         *    operation.
         * 4. However, this master node (@c->mst_node) is marked as
         *    clean (since the step 1). And if we just return, the
         *    mount code will be confused and won't recover the master
         *    node when it is re-mounter R/W later.
         *
         *    Thus, to force the recovery by marking the master node as
         *    dirty.
         */
        c->mst_node->flags |= cpu_to_le32(UBIFS_MST_DIRTY);
    } else {
        /* Write the recovered master node */
        c->max_sqnum = le64_to_cpu(mst->ch.sqnum) - 1;
        err = write_rcvrd_mst_node(c, c->mst_node);
        if (err)
            goto out_free;
    }

    vfree(buf2);
    vfree(buf1);

    return 0;

out_err:
    err = -EINVAL;
out_free:
    ubifs_err("failed to recover master node");
    if (mst1) {
        ubifs_err("dumping first master node");
        ubifs_dump_node(c, mst1);
    }
    if (mst2) {
        ubifs_err("dumping second master node");
        ubifs_dump_node(c, mst2);
    }
    vfree(buf2);
    vfree(buf1);
    return err;
}

int ubifs_write_rcvrd_mst_node(struct ubifs_info *c)
{
    int err;

    if (!c->rcvrd_mst_node)
        return 0;
    c->rcvrd_mst_node->flags |= cpu_to_le32(UBIFS_MST_DIRTY);
    c->mst_node->flags |= cpu_to_le32(UBIFS_MST_DIRTY);
    err = write_rcvrd_mst_node(c, c->rcvrd_mst_node);
    if (err)
        return err;
    kfree(c->rcvrd_mst_node);
    c->rcvrd_mst_node = NULL;
    return 0;
}

static int is_last_write(const struct ubifs_info *c, void *buf, int offs)
{
    int empty_offs, check_len;
    uint8_t *p;

    /*
     * Round up to the next @c->max_write_size boundary i.e. @offs is in
     * the last wbuf written. After that should be empty space.
     */
    empty_offs = ALIGN(offs + 1, c->max_write_size);
    check_len = c->leb_size - empty_offs;
    p = buf + empty_offs - offs;
    return is_empty(p, check_len);
}

static void clean_buf(const struct ubifs_info *c, void **buf, int lnum,
              int *offs, int *len)
{
    int empty_offs, pad_len;

    lnum = lnum;
    dbg_rcvry("cleaning corruption at %d:%d", lnum, *offs);

    ubifs_assert(!(*offs & 7));
    empty_offs = ALIGN(*offs, c->min_io_size);
    pad_len = empty_offs - *offs;
    ubifs_pad(c, *buf, pad_len);
    *offs += pad_len;
    *buf += pad_len;
    *len -= pad_len;
    memset(*buf, 0xff, c->leb_size - empty_offs);
}

static int no_more_nodes(const struct ubifs_info *c, void *buf, int len,
            int lnum, int offs)
{
    struct ubifs_ch *ch = buf;
    int skip, dlen = le32_to_cpu(ch->len);

    /* Check for empty space after the corrupt node's common header */
    skip = ALIGN(offs + UBIFS_CH_SZ, c->max_write_size) - offs;
    if (is_empty(buf + skip, len - skip))
        return 1;
    /*
     * The area after the common header size is not empty, so the common
     * header must be intact. Check it.
     */
    if (ubifs_check_node(c, buf, lnum, offs, 1, 0) != -EUCLEAN) {
        dbg_rcvry("unexpected bad common header at %d:%d", lnum, offs);
        return 0;
    }
    /* Now we know the corrupt node's length we can skip over it */
    skip = ALIGN(offs + dlen, c->max_write_size) - offs;
    /* After which there should be empty space */
    if (is_empty(buf + skip, len - skip))
        return 1;
    dbg_rcvry("unexpected data at %d:%d", lnum, offs + skip);
    return 0;
}

static int fix_unclean_leb(struct ubifs_info *c, struct ubifs_scan_leb *sleb,
               int start)
{
    int lnum = sleb->lnum, endpt = start;

    /* Get the end offset of the last node we are keeping */
    if (!list_empty(&sleb->nodes)) {
        struct ubifs_scan_node *snod;

        snod = list_entry(sleb->nodes.prev,
                  struct ubifs_scan_node, list);
        endpt = snod->offs + snod->len;
    }

    if (c->ro_mount && !c->remounting_rw) {
        /* Add to recovery list */
        struct ubifs_unclean_leb *ucleb;

        dbg_rcvry("need to fix LEB %d start %d endpt %d",
              lnum, start, sleb->endpt);
        ucleb = kzalloc(sizeof(struct ubifs_unclean_leb), GFP_NOFS);
        if (!ucleb)
            return -ENOMEM;
        ucleb->lnum = lnum;
        ucleb->endpt = endpt;
        list_add_tail(&ucleb->list, &c->unclean_leb_list);
    } else {
        /* Write the fixed LEB back to flash */
        int err;

        dbg_rcvry("fixing LEB %d start %d endpt %d",
              lnum, start, sleb->endpt);
        if (endpt == 0) {
            err = ubifs_leb_unmap(c, lnum);
            if (err)
                return err;
        } else {
            int len = ALIGN(endpt, c->min_io_size);

            if (start) {
                err = ubifs_leb_read(c, lnum, sleb->buf, 0,
                             start, 1);
                if (err)
                    return err;
            }
            /* Pad to min_io_size */
            if (len > endpt) {
                int pad_len = len - ALIGN(endpt, 8);

                if (pad_len > 0) {
                    void *buf = sleb->buf + len - pad_len;

                    ubifs_pad(c, buf, pad_len);
                }
            }
            err = ubifs_leb_change(c, lnum, sleb->buf, len);
            if (err)
                return err;
        }
    }
    return 0;
}

static void drop_last_group(struct ubifs_scan_leb *sleb, int *offs)
{
    while (!list_empty(&sleb->nodes)) {
        struct ubifs_scan_node *snod;
        struct ubifs_ch *ch;

        snod = list_entry(sleb->nodes.prev, struct ubifs_scan_node,
                  list);
        ch = snod->node;
        if (ch->group_type != UBIFS_IN_NODE_GROUP)
            break;

        dbg_rcvry("dropping grouped node at %d:%d",
              sleb->lnum, snod->offs);
        *offs = snod->offs;
        list_del(&snod->list);
        kfree(snod);
        sleb->nodes_cnt -= 1;
    }
}

static void drop_last_node(struct ubifs_scan_leb *sleb, int *offs)
{
    struct ubifs_scan_node *snod;

    if (!list_empty(&sleb->nodes)) {
        snod = list_entry(sleb->nodes.prev, struct ubifs_scan_node,
                  list);

        dbg_rcvry("dropping last node at %d:%d",
              sleb->lnum, snod->offs);
        *offs = snod->offs;
        list_del(&snod->list);
        kfree(snod);
        sleb->nodes_cnt -= 1;
    }
}

struct ubifs_scan_leb *ubifs_recover_leb(struct ubifs_info *c, int lnum,
                     int offs, void *sbuf, int jhead)
{
    int ret = 0, err, len = c->leb_size - offs, start = offs, min_io_unit;
    int grouped = jhead == -1 ? 0 : c->jheads[jhead].grouped;
    struct ubifs_scan_leb *sleb;
    void *buf = sbuf + offs;

    dbg_rcvry("%d:%d, jhead %d, grouped %d", lnum, offs, jhead, grouped);

    sleb = ubifs_start_scan(c, lnum, offs, sbuf);
    if (IS_ERR(sleb))
        return sleb;

    ubifs_assert(len >= 8);
    while (len >= 8) {
        dbg_scan("look at LEB %d:%d (%d bytes left)",
             lnum, offs, len);

        cond_resched();

        /*
         * Scan quietly until there is an error from which we cannot
         * recover
         */
        ret = ubifs_scan_a_node(c, buf, len, lnum, offs, 1);
        if (ret == SCANNED_A_NODE) {
            /* A valid node, and not a padding node */
            struct ubifs_ch *ch = buf;
            int node_len;

            err = ubifs_add_snod(c, sleb, buf, offs);
            if (err)
                goto error;
            node_len = ALIGN(le32_to_cpu(ch->len), 8);
            offs += node_len;
            buf += node_len;
            len -= node_len;
        } else if (ret > 0) {
            /* Padding bytes or a valid padding node */
            offs += ret;
            buf += ret;
            len -= ret;
        } else if (ret == SCANNED_EMPTY_SPACE ||
               ret == SCANNED_GARBAGE     ||
               ret == SCANNED_A_BAD_PAD_NODE ||
               ret == SCANNED_A_CORRUPT_NODE) {
            dbg_rcvry("found corruption (%d) at %d:%d",
                  ret, lnum, offs);
            break;
        } else {
            ubifs_err("unexpected return value %d", ret);
            err = -EINVAL;
            goto error;
        }
    }

    if (ret == SCANNED_GARBAGE || ret == SCANNED_A_BAD_PAD_NODE) {
        if (!is_last_write(c, buf, offs))
            goto corrupted_rescan;
    } else if (ret == SCANNED_A_CORRUPT_NODE) {
        if (!no_more_nodes(c, buf, len, lnum, offs))
            goto corrupted_rescan;
    } else if (!is_empty(buf, len)) {
        if (!is_last_write(c, buf, offs)) {
            int corruption = first_non_ff(buf, len);

            /*
             * See header comment for this file for more
             * explanations about the reasons we have this check.
             */
            ubifs_err("corrupt empty space LEB %d:%d, corruption starts at %d",
                  lnum, offs, corruption);
            /* Make sure we dump interesting non-0xFF data */
            offs += corruption;
            buf += corruption;
            goto corrupted;
        }
    }

    min_io_unit = round_down(offs, c->min_io_size);
    if (grouped)
        /*
         * If nodes are grouped, always drop the incomplete group at
         * the end.
         */
        drop_last_group(sleb, &offs);

    if (jhead == GCHD) {
        /*
         * If this LEB belongs to the GC head then while we are in the
         * middle of the same min. I/O unit keep dropping nodes. So
         * basically, what we want is to make sure that the last min.
         * I/O unit where we saw the corruption is dropped completely
         * with all the uncorrupted nodes which may possibly sit there.
         *
         * In other words, let's name the min. I/O unit where the
         * corruption starts B, and the previous min. I/O unit A. The
         * below code tries to deal with a situation when half of B
         * contains valid nodes or the end of a valid node, and the
         * second half of B contains corrupted data or garbage. This
         * means that UBIFS had been writing to B just before the power
         * cut happened. I do not know how realistic is this scenario
         * that half of the min. I/O unit had been written successfully
         * and the other half not, but this is possible in our 'failure
         * mode emulation' infrastructure at least.
         *
         * So what is the problem, why we need to drop those nodes? Why
         * can't we just clean-up the second half of B by putting a
         * padding node there? We can, and this works fine with one
         * exception which was reproduced with power cut emulation
         * testing and happens extremely rarely.
         *
         * Imagine the file-system is full, we run GC which starts
         * moving valid nodes from LEB X to LEB Y (obviously, LEB Y is
         * the current GC head LEB). The @c->gc_lnum is -1, which means
         * that GC will retain LEB X and will try to continue. Imagine
         * that LEB X is currently the dirtiest LEB, and the amount of
         * used space in LEB Y is exactly the same as amount of free
         * space in LEB X.
         *
         * And a power cut happens when nodes are moved from LEB X to
         * LEB Y. We are here trying to recover LEB Y which is the GC
         * head LEB. We find the min. I/O unit B as described above.
         * Then we clean-up LEB Y by padding min. I/O unit. And later
         * 'ubifs_rcvry_gc_commit()' function fails, because it cannot
         * find a dirty LEB which could be GC'd into LEB Y! Even LEB X
         * does not match because the amount of valid nodes there does
         * not fit the free space in LEB Y any more! And this is
         * because of the padding node which we added to LEB Y. The
         * user-visible effect of this which I once observed and
         * analysed is that we cannot mount the file-system with
         * -ENOSPC error.
         *
         * So obviously, to make sure that situation does not happen we
         * should free min. I/O unit B in LEB Y completely and the last
         * used min. I/O unit in LEB Y should be A. This is basically
         * what the below code tries to do.
         */
        while (offs > min_io_unit)
            drop_last_node(sleb, &offs);
    }

    buf = sbuf + offs;
    len = c->leb_size - offs;

    clean_buf(c, &buf, lnum, &offs, &len);
    ubifs_end_scan(c, sleb, lnum, offs);

    err = fix_unclean_leb(c, sleb, start);
    if (err)
        goto error;

    return sleb;

corrupted_rescan:
    /* Re-scan the corrupted data with verbose messages */
    ubifs_err("corruption %d", ret);
    ubifs_scan_a_node(c, buf, len, lnum, offs, 1);
corrupted:
    ubifs_scanned_corruption(c, lnum, offs, buf);
    err = -EUCLEAN;
error:
    ubifs_err("LEB %d scanning failed", lnum);
    ubifs_scan_destroy(sleb);
    return ERR_PTR(err);
}

static int get_cs_sqnum(struct ubifs_info *c, int lnum, int offs,
            unsigned long long *cs_sqnum)
{
    struct ubifs_cs_node *cs_node = NULL;
    int err, ret;

    dbg_rcvry("at %d:%d", lnum, offs);
    cs_node = kmalloc(UBIFS_CS_NODE_SZ, GFP_KERNEL);
    if (!cs_node)
        return -ENOMEM;
    if (c->leb_size - offs < UBIFS_CS_NODE_SZ)
        goto out_err;
    err = ubifs_leb_read(c, lnum, (void *)cs_node, offs,
                 UBIFS_CS_NODE_SZ, 0);
    if (err && err != -EBADMSG)
        goto out_free;
    ret = ubifs_scan_a_node(c, cs_node, UBIFS_CS_NODE_SZ, lnum, offs, 0);
    if (ret != SCANNED_A_NODE) {
        ubifs_err("Not a valid node");
        goto out_err;
    }
    if (cs_node->ch.node_type != UBIFS_CS_NODE) {
        ubifs_err("Node a CS node, type is %d", cs_node->ch.node_type);
        goto out_err;
    }
    if (le64_to_cpu(cs_node->cmt_no) != c->cmt_no) {
        ubifs_err("CS node cmt_no %llu != current cmt_no %llu",
              (unsigned long long)le64_to_cpu(cs_node->cmt_no),
              c->cmt_no);
        goto out_err;
    }
    *cs_sqnum = le64_to_cpu(cs_node->ch.sqnum);
    dbg_rcvry("commit start sqnum %llu", *cs_sqnum);
    kfree(cs_node);
    return 0;

out_err:
    err = -EINVAL;
out_free:
    ubifs_err("failed to get CS sqnum");
    kfree(cs_node);
    return err;
}

struct ubifs_scan_leb *ubifs_recover_log_leb(struct ubifs_info *c, int lnum,
                         int offs, void *sbuf)
{
    struct ubifs_scan_leb *sleb;
    int next_lnum;

    dbg_rcvry("LEB %d", lnum);
    next_lnum = lnum + 1;
    if (next_lnum >= UBIFS_LOG_LNUM + c->log_lebs)
        next_lnum = UBIFS_LOG_LNUM;
    if (next_lnum != c->ltail_lnum) {
        /*
         * We can only recover at the end of the log, so check that the
         * next log LEB is empty or out of date.
         */
        sleb = ubifs_scan(c, next_lnum, 0, sbuf, 0);
        if (IS_ERR(sleb))
            return sleb;
        if (sleb->nodes_cnt) {
            struct ubifs_scan_node *snod;
            unsigned long long cs_sqnum = c->cs_sqnum;

            snod = list_entry(sleb->nodes.next,
                      struct ubifs_scan_node, list);
            if (cs_sqnum == 0) {
                int err;

                err = get_cs_sqnum(c, lnum, offs, &cs_sqnum);
                if (err) {
                    ubifs_scan_destroy(sleb);
                    return ERR_PTR(err);
                }
            }
            if (snod->sqnum > cs_sqnum) {
                ubifs_err("unrecoverable log corruption in LEB %d",
                      lnum);
                ubifs_scan_destroy(sleb);
                return ERR_PTR(-EUCLEAN);
            }
        }
        ubifs_scan_destroy(sleb);
    }
    return ubifs_recover_leb(c, lnum, offs, sbuf, -1);
}

static int recover_head(struct ubifs_info *c, int lnum, int offs, void *sbuf)
{
    int len = c->max_write_size, err;

    if (offs + len > c->leb_size)
        len = c->leb_size - offs;

    if (!len)
        return 0;

    /* Read at the head location and check it is empty flash */
    err = ubifs_leb_read(c, lnum, sbuf, offs, len, 1);
    if (err || !is_empty(sbuf, len)) {
        dbg_rcvry("cleaning head at %d:%d", lnum, offs);
        if (offs == 0)
            return ubifs_leb_unmap(c, lnum);
        err = ubifs_leb_read(c, lnum, sbuf, 0, offs, 1);
        if (err)
            return err;
        return ubifs_leb_change(c, lnum, sbuf, offs);
    }

    return 0;
}

int ubifs_recover_inl_heads(struct ubifs_info *c, void *sbuf)
{
    int err;

    ubifs_assert(!c->ro_mount || c->remounting_rw);

    dbg_rcvry("checking index head at %d:%d", c->ihead_lnum, c->ihead_offs);
    err = recover_head(c, c->ihead_lnum, c->ihead_offs, sbuf);
    if (err)
        return err;

    dbg_rcvry("checking LPT head at %d:%d", c->nhead_lnum, c->nhead_offs);
    err = recover_head(c, c->nhead_lnum, c->nhead_offs, sbuf);
    if (err)
        return err;

    return 0;
}

static int clean_an_unclean_leb(struct ubifs_info *c,
                struct ubifs_unclean_leb *ucleb, void *sbuf)
{
    int err, lnum = ucleb->lnum, offs = 0, len = ucleb->endpt, quiet = 1;
    void *buf = sbuf;

    dbg_rcvry("LEB %d len %d", lnum, len);

    if (len == 0) {
        /* Nothing to read, just unmap it */
        err = ubifs_leb_unmap(c, lnum);
        if (err)
            return err;
        return 0;
    }

    err = ubifs_leb_read(c, lnum, buf, offs, len, 0);
    if (err && err != -EBADMSG)
        return err;

    while (len >= 8) {
        int ret;

        cond_resched();

        /* Scan quietly until there is an error */
        ret = ubifs_scan_a_node(c, buf, len, lnum, offs, quiet);

        if (ret == SCANNED_A_NODE) {
            /* A valid node, and not a padding node */
            struct ubifs_ch *ch = buf;
            int node_len;

            node_len = ALIGN(le32_to_cpu(ch->len), 8);
            offs += node_len;
            buf += node_len;
            len -= node_len;
            continue;
        }

        if (ret > 0) {
            /* Padding bytes or a valid padding node */
            offs += ret;
            buf += ret;
            len -= ret;
            continue;
        }

        if (ret == SCANNED_EMPTY_SPACE) {
            ubifs_err("unexpected empty space at %d:%d",
                  lnum, offs);
            return -EUCLEAN;
        }

        if (quiet) {
            /* Redo the last scan but noisily */
            quiet = 0;
            continue;
        }

        ubifs_scanned_corruption(c, lnum, offs, buf);
        return -EUCLEAN;
    }

    /* Pad to min_io_size */
    len = ALIGN(ucleb->endpt, c->min_io_size);
    if (len > ucleb->endpt) {
        int pad_len = len - ALIGN(ucleb->endpt, 8);

        if (pad_len > 0) {
            buf = c->sbuf + len - pad_len;
            ubifs_pad(c, buf, pad_len);
        }
    }

    /* Write back the LEB atomically */
    err = ubifs_leb_change(c, lnum, sbuf, len);
    if (err)
        return err;

    dbg_rcvry("cleaned LEB %d", lnum);

    return 0;
}

int ubifs_clean_lebs(struct ubifs_info *c, void *sbuf)
{
    dbg_rcvry("recovery");
    while (!list_empty(&c->unclean_leb_list)) {
        struct ubifs_unclean_leb *ucleb;
        int err;

        ucleb = list_entry(c->unclean_leb_list.next,
                   struct ubifs_unclean_leb, list);
        err = clean_an_unclean_leb(c, ucleb, sbuf);
        if (err)
            return err;
        list_del(&ucleb->list);
        kfree(ucleb);
    }
    return 0;
}

static int grab_empty_leb(struct ubifs_info *c)
{
    int lnum, err;

    /*
     * Note, it is very important to first search for an empty LEB and then
     * run the commit, not vice-versa. The reason is that there might be
     * only one empty LEB at the moment, the one which has been the
     * @c->gc_lnum just before the power cut happened. During the regular
     * UBIFS operation (not now) @c->gc_lnum is marked as "taken", so no
     * one but GC can grab it. But at this moment this single empty LEB is
     * not marked as taken, so if we run commit - what happens? Right, the
     * commit will grab it and write the index there. Remember that the
     * index always expands as long as there is free space, and it only
     * starts consolidating when we run out of space.
     *
     * IOW, if we run commit now, we might not be able to find a free LEB
     * after this.
     */
    lnum = ubifs_find_free_leb_for_idx(c);
    if (lnum < 0) {
        ubifs_err("could not find an empty LEB");
        ubifs_dump_lprops(c);
        ubifs_dump_budg(c, &c->bi);
        return lnum;
    }

    /* Reset the index flag */
    err = ubifs_change_one_lp(c, lnum, LPROPS_NC, LPROPS_NC, 0,
                  LPROPS_INDEX, 0);
    if (err)
        return err;

    c->gc_lnum = lnum;
    dbg_rcvry("found empty LEB %d, run commit", lnum);

    return ubifs_run_commit(c);
}

int ubifs_rcvry_gc_commit(struct ubifs_info *c)
{
    struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
    struct ubifs_lprops lp;
    int err;

    dbg_rcvry("GC head LEB %d, offs %d", wbuf->lnum, wbuf->offs);

    c->gc_lnum = -1;
    if (wbuf->lnum == -1 || wbuf->offs == c->leb_size)
        return grab_empty_leb(c);

    err = ubifs_find_dirty_leb(c, &lp, wbuf->offs, 2);
    if (err) {
        if (err != -ENOSPC)
            return err;

        dbg_rcvry("could not find a dirty LEB");
        return grab_empty_leb(c);
    }

    ubifs_assert(!(lp.flags & LPROPS_INDEX));
    ubifs_assert(lp.free + lp.dirty >= wbuf->offs);

    /*
     * We run the commit before garbage collection otherwise subsequent
     * mounts will see the GC and orphan deletion in a different order.
     */
    dbg_rcvry("committing");
    err = ubifs_run_commit(c);
    if (err)
        return err;

    dbg_rcvry("GC'ing LEB %d", lp.lnum);
    mutex_lock_nested(&wbuf->io_mutex, wbuf->jhead);
    err = ubifs_garbage_collect_leb(c, &lp);
    if (err >= 0) {
        int err2 = ubifs_wbuf_sync_nolock(wbuf);

        if (err2)
            err = err2;
    }
    mutex_unlock(&wbuf->io_mutex);
    if (err < 0) {
        ubifs_err("GC failed, error %d", err);
        if (err == -EAGAIN)
            err = -EINVAL;
        return err;
    }

    ubifs_assert(err == LEB_RETAINED);
    if (err != LEB_RETAINED)
        return -EINVAL;

    err = ubifs_leb_unmap(c, c->gc_lnum);
    if (err)
        return err;

    dbg_rcvry("allocated LEB %d for GC", lp.lnum);
    return 0;
}

struct size_entry {
    struct rb_node rb;
    ino_t inum;
    loff_t i_size;
    loff_t d_size;
    int exists;
    struct inode *inode;
};

static int add_ino(struct ubifs_info *c, ino_t inum, loff_t i_size,
           loff_t d_size, int exists)
{
    struct rb_node **p = &c->size_tree.rb_node, *parent = NULL;
    struct size_entry *e;

    while (*p) {
        parent = *p;
        e = rb_entry(parent, struct size_entry, rb);
        if (inum < e->inum)
            p = &(*p)->rb_left;
        else
            p = &(*p)->rb_right;
    }

    e = kzalloc(sizeof(struct size_entry), GFP_KERNEL);
    if (!e)
        return -ENOMEM;

    e->inum = inum;
    e->i_size = i_size;
    e->d_size = d_size;
    e->exists = exists;

    rb_link_node(&e->rb, parent, p);
    rb_insert_color(&e->rb, &c->size_tree);

    return 0;
}

static struct size_entry *find_ino(struct ubifs_info *c, ino_t inum)
{
    struct rb_node *p = c->size_tree.rb_node;
    struct size_entry *e;

    while (p) {
        e = rb_entry(p, struct size_entry, rb);
        if (inum < e->inum)
            p = p->rb_left;
        else if (inum > e->inum)
            p = p->rb_right;
        else
            return e;
    }
    return NULL;
}

static void remove_ino(struct ubifs_info *c, ino_t inum)
{
    struct size_entry *e = find_ino(c, inum);

    if (!e)
        return;
    rb_erase(&e->rb, &c->size_tree);
    kfree(e);
}

void ubifs_destroy_size_tree(struct ubifs_info *c)
{
    struct rb_node *this = c->size_tree.rb_node;
    struct size_entry *e;

    while (this) {
        if (this->rb_left) {
            this = this->rb_left;
            continue;
        } else if (this->rb_right) {
            this = this->rb_right;
            continue;
        }
        e = rb_entry(this, struct size_entry, rb);
        if (e->inode)
            iput(e->inode);
        this = rb_parent(this);
        if (this) {
            if (this->rb_left == &e->rb)
                this->rb_left = NULL;
            else
                this->rb_right = NULL;
        }
        kfree(e);
    }
    c->size_tree = RB_ROOT;
}

int ubifs_recover_size_accum(struct ubifs_info *c, union ubifs_key *key,
                 int deletion, loff_t new_size)
{
    ino_t inum = key_inum(c, key);
    struct size_entry *e;
    int err;

    switch (key_type(c, key)) {
    case UBIFS_INO_KEY:
        if (deletion)
            remove_ino(c, inum);
        else {
            e = find_ino(c, inum);
            if (e) {
                e->i_size = new_size;
                e->exists = 1;
            } else {
                err = add_ino(c, inum, new_size, 0, 1);
                if (err)
                    return err;
            }
        }
        break;
    case UBIFS_DATA_KEY:
        e = find_ino(c, inum);
        if (e) {
            if (new_size > e->d_size)
                e->d_size = new_size;
        } else {
            err = add_ino(c, inum, 0, new_size, 0);
            if (err)
                return err;
        }
        break;
    case UBIFS_TRUN_KEY:
        e = find_ino(c, inum);
        if (e)
            e->d_size = new_size;
        break;
    }
    return 0;
}

static int fix_size_in_place(struct ubifs_info *c, struct size_entry *e)
{
    struct ubifs_ino_node *ino = c->sbuf;
    unsigned char *p;
    union ubifs_key key;
    int err, lnum, offs, len;
    loff_t i_size;
    uint32_t crc;

    /* Locate the inode node LEB number and offset */
    ino_key_init(c, &key, e->inum);
    err = ubifs_tnc_locate(c, &key, ino, &lnum, &offs);
    if (err)
        goto out;
    /*
     * If the size recorded on the inode node is greater than the size that
     * was calculated from nodes in the journal then don't change the inode.
     */
    i_size = le64_to_cpu(ino->size);
    if (i_size >= e->d_size)
        return 0;
    /* Read the LEB */
    err = ubifs_leb_read(c, lnum, c->sbuf, 0, c->leb_size, 1);
    if (err)
        goto out;
    /* Change the size field and recalculate the CRC */
    ino = c->sbuf + offs;
    ino->size = cpu_to_le64(e->d_size);
    len = le32_to_cpu(ino->ch.len);
    crc = crc32(UBIFS_CRC32_INIT, (void *)ino + 8, len - 8);
    ino->ch.crc = cpu_to_le32(crc);
    /* Work out where data in the LEB ends and free space begins */
    p = c->sbuf;
    len = c->leb_size - 1;
    while (p[len] == 0xff)
        len -= 1;
    len = ALIGN(len + 1, c->min_io_size);
    /* Atomically write the fixed LEB back again */
    err = ubifs_leb_change(c, lnum, c->sbuf, len);
    if (err)
        goto out;
    dbg_rcvry("inode %lu at %d:%d size %lld -> %lld",
          (unsigned long)e->inum, lnum, offs, i_size, e->d_size);
    return 0;

out:
    ubifs_warn("inode %lu failed to fix size %lld -> %lld error %d",
           (unsigned long)e->inum, e->i_size, e->d_size, err);
    return err;
}

int ubifs_recover_size(struct ubifs_info *c)
{
    struct rb_node *this = rb_first(&c->size_tree);

    while (this) {
        struct size_entry *e;
        int err;

        e = rb_entry(this, struct size_entry, rb);
        if (!e->exists) {
            union ubifs_key key;

            ino_key_init(c, &key, e->inum);
            err = ubifs_tnc_lookup(c, &key, c->sbuf);
            if (err && err != -ENOENT)
                return err;
            if (err == -ENOENT) {
                /* Remove data nodes that have no inode */
                dbg_rcvry("removing ino %lu",
                      (unsigned long)e->inum);
                err = ubifs_tnc_remove_ino(c, e->inum);
                if (err)
                    return err;
            } else {
                struct ubifs_ino_node *ino = c->sbuf;

                e->exists = 1;
                e->i_size = le64_to_cpu(ino->size);
            }
        }

        if (e->exists && e->i_size < e->d_size) {
            if (c->ro_mount) {
                /* Fix the inode size and pin it in memory */
                struct inode *inode;
                struct ubifs_inode *ui;

                ubifs_assert(!e->inode);

                inode = ubifs_iget(c->vfs_sb, e->inum);
                if (IS_ERR(inode))
                    return PTR_ERR(inode);

                ui = ubifs_inode(inode);
                if (inode->i_size < e->d_size) {
                    dbg_rcvry("ino %lu size %lld -> %lld",
                          (unsigned long)e->inum,
                          inode->i_size, e->d_size);
                    inode->i_size = e->d_size;
                    ui->ui_size = e->d_size;
                    ui->synced_i_size = e->d_size;
                    e->inode = inode;
                    this = rb_next(this);
                    continue;
                }
                iput(inode);
            } else {
                /* Fix the size in place */
                err = fix_size_in_place(c, e);
                if (err)
                    return err;
                if (e->inode)
                    iput(e->inode);
            }
        }

        this = rb_next(this);
        rb_erase(&e->rb, &c->size_tree);
        kfree(e);
    }

    return 0;
}