logfile.c

Go to the documentation of this file.

/*
 * logfile.c - NTFS kernel journal handling. Part of the Linux-NTFS project.
 *
 * Copyright (c) 2002-2007 Anton Altaparmakov
 *
 * This program/include file 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/include file 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 (in the main directory of the Linux-NTFS
 * distribution in the file COPYING); if not, write to the Free Software
 * Foundation,Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#ifdef NTFS_RW

#include <linux/types.h>
#include <linux/fs.h>
#include <linux/highmem.h>
#include <linux/buffer_head.h>
#include <linux/bitops.h>
#include <linux/log2.h>

#include "attrib.h"
#include "aops.h"
#include "debug.h"
#include "logfile.h"
#include "malloc.h"
#include "volume.h"
#include "ntfs.h"

static bool ntfs_check_restart_page_header(struct inode *vi,
        RESTART_PAGE_HEADER *rp, s64 pos)
{
    u32 logfile_system_page_size, logfile_log_page_size;
    u16 ra_ofs, usa_count, usa_ofs, usa_end = 0;
    bool have_usa = true;

    ntfs_debug("Entering.");
    /*
     * If the system or log page sizes are smaller than the ntfs block size
     * or either is not a power of 2 we cannot handle this log file.
     */
    logfile_system_page_size = le32_to_cpu(rp->system_page_size);
    logfile_log_page_size = le32_to_cpu(rp->log_page_size);
    if (logfile_system_page_size < NTFS_BLOCK_SIZE ||
            logfile_log_page_size < NTFS_BLOCK_SIZE ||
            logfile_system_page_size &
            (logfile_system_page_size - 1) ||
            !is_power_of_2(logfile_log_page_size)) {
        ntfs_error(vi->i_sb, "$LogFile uses unsupported page size.");
        return false;
    }
    /*
     * We must be either at !pos (1st restart page) or at pos = system page
     * size (2nd restart page).
     */
    if (pos && pos != logfile_system_page_size) {
        ntfs_error(vi->i_sb, "Found restart area in incorrect "
                "position in $LogFile.");
        return false;
    }
    /* We only know how to handle version 1.1. */
    if (sle16_to_cpu(rp->major_ver) != 1 ||
            sle16_to_cpu(rp->minor_ver) != 1) {
        ntfs_error(vi->i_sb, "$LogFile version %i.%i is not "
                "supported.  (This driver supports version "
                "1.1 only.)", (int)sle16_to_cpu(rp->major_ver),
                (int)sle16_to_cpu(rp->minor_ver));
        return false;
    }
    /*
     * If chkdsk has been run the restart page may not be protected by an
     * update sequence array.
     */
    if (ntfs_is_chkd_record(rp->magic) && !le16_to_cpu(rp->usa_count)) {
        have_usa = false;
        goto skip_usa_checks;
    }
    /* Verify the size of the update sequence array. */
    usa_count = 1 + (logfile_system_page_size >> NTFS_BLOCK_SIZE_BITS);
    if (usa_count != le16_to_cpu(rp->usa_count)) {
        ntfs_error(vi->i_sb, "$LogFile restart page specifies "
                "inconsistent update sequence array count.");
        return false;
    }
    /* Verify the position of the update sequence array. */
    usa_ofs = le16_to_cpu(rp->usa_ofs);
    usa_end = usa_ofs + usa_count * sizeof(u16);
    if (usa_ofs < sizeof(RESTART_PAGE_HEADER) ||
            usa_end > NTFS_BLOCK_SIZE - sizeof(u16)) {
        ntfs_error(vi->i_sb, "$LogFile restart page specifies "
                "inconsistent update sequence array offset.");
        return false;
    }
skip_usa_checks:
    /*
     * Verify the position of the restart area.  It must be:
     *  - aligned to 8-byte boundary,
     *  - after the update sequence array, and
     *  - within the system page size.
     */
    ra_ofs = le16_to_cpu(rp->restart_area_offset);
    if (ra_ofs & 7 || (have_usa ? ra_ofs < usa_end :
            ra_ofs < sizeof(RESTART_PAGE_HEADER)) ||
            ra_ofs > logfile_system_page_size) {
        ntfs_error(vi->i_sb, "$LogFile restart page specifies "
                "inconsistent restart area offset.");
        return false;
    }
    /*
     * Only restart pages modified by chkdsk are allowed to have chkdsk_lsn
     * set.
     */
    if (!ntfs_is_chkd_record(rp->magic) && sle64_to_cpu(rp->chkdsk_lsn)) {
        ntfs_error(vi->i_sb, "$LogFile restart page is not modified "
                "by chkdsk but a chkdsk LSN is specified.");
        return false;
    }
    ntfs_debug("Done.");
    return true;
}

static bool ntfs_check_restart_area(struct inode *vi, RESTART_PAGE_HEADER *rp)
{
    u64 file_size;
    RESTART_AREA *ra;
    u16 ra_ofs, ra_len, ca_ofs;
    u8 fs_bits;

    ntfs_debug("Entering.");
    ra_ofs = le16_to_cpu(rp->restart_area_offset);
    ra = (RESTART_AREA*)((u8*)rp + ra_ofs);
    /*
     * Everything before ra->file_size must be before the first word
     * protected by an update sequence number.  This ensures that it is
     * safe to access ra->client_array_offset.
     */
    if (ra_ofs + offsetof(RESTART_AREA, file_size) >
            NTFS_BLOCK_SIZE - sizeof(u16)) {
        ntfs_error(vi->i_sb, "$LogFile restart area specifies "
                "inconsistent file offset.");
        return false;
    }
    /*
     * Now that we can access ra->client_array_offset, make sure everything
     * up to the log client array is before the first word protected by an
     * update sequence number.  This ensures we can access all of the
     * restart area elements safely.  Also, the client array offset must be
     * aligned to an 8-byte boundary.
     */
    ca_ofs = le16_to_cpu(ra->client_array_offset);
    if (((ca_ofs + 7) & ~7) != ca_ofs ||
            ra_ofs + ca_ofs > NTFS_BLOCK_SIZE - sizeof(u16)) {
        ntfs_error(vi->i_sb, "$LogFile restart area specifies "
                "inconsistent client array offset.");
        return false;
    }
    /*
     * The restart area must end within the system page size both when
     * calculated manually and as specified by ra->restart_area_length.
     * Also, the calculated length must not exceed the specified length.
     */
    ra_len = ca_ofs + le16_to_cpu(ra->log_clients) *
            sizeof(LOG_CLIENT_RECORD);
    if (ra_ofs + ra_len > le32_to_cpu(rp->system_page_size) ||
            ra_ofs + le16_to_cpu(ra->restart_area_length) >
            le32_to_cpu(rp->system_page_size) ||
            ra_len > le16_to_cpu(ra->restart_area_length)) {
        ntfs_error(vi->i_sb, "$LogFile restart area is out of bounds "
                "of the system page size specified by the "
                "restart page header and/or the specified "
                "restart area length is inconsistent.");
        return false;
    }
    /*
     * The ra->client_free_list and ra->client_in_use_list must be either
     * LOGFILE_NO_CLIENT or less than ra->log_clients or they are
     * overflowing the client array.
     */
    if ((ra->client_free_list != LOGFILE_NO_CLIENT &&
            le16_to_cpu(ra->client_free_list) >=
            le16_to_cpu(ra->log_clients)) ||
            (ra->client_in_use_list != LOGFILE_NO_CLIENT &&
            le16_to_cpu(ra->client_in_use_list) >=
            le16_to_cpu(ra->log_clients))) {
        ntfs_error(vi->i_sb, "$LogFile restart area specifies "
                "overflowing client free and/or in use lists.");
        return false;
    }
    /*
     * Check ra->seq_number_bits against ra->file_size for consistency.
     * We cannot just use ffs() because the file size is not a power of 2.
     */
    file_size = (u64)sle64_to_cpu(ra->file_size);
    fs_bits = 0;
    while (file_size) {
        file_size >>= 1;
        fs_bits++;
    }
    if (le32_to_cpu(ra->seq_number_bits) != 67 - fs_bits) {
        ntfs_error(vi->i_sb, "$LogFile restart area specifies "
                "inconsistent sequence number bits.");
        return false;
    }
    /* The log record header length must be a multiple of 8. */
    if (((le16_to_cpu(ra->log_record_header_length) + 7) & ~7) !=
            le16_to_cpu(ra->log_record_header_length)) {
        ntfs_error(vi->i_sb, "$LogFile restart area specifies "
                "inconsistent log record header length.");
        return false;
    }
    /* Dito for the log page data offset. */
    if (((le16_to_cpu(ra->log_page_data_offset) + 7) & ~7) !=
            le16_to_cpu(ra->log_page_data_offset)) {
        ntfs_error(vi->i_sb, "$LogFile restart area specifies "
                "inconsistent log page data offset.");
        return false;
    }
    ntfs_debug("Done.");
    return true;
}

static bool ntfs_check_log_client_array(struct inode *vi,
        RESTART_PAGE_HEADER *rp)
{
    RESTART_AREA *ra;
    LOG_CLIENT_RECORD *ca, *cr;
    u16 nr_clients, idx;
    bool in_free_list, idx_is_first;

    ntfs_debug("Entering.");
    ra = (RESTART_AREA*)((u8*)rp + le16_to_cpu(rp->restart_area_offset));
    ca = (LOG_CLIENT_RECORD*)((u8*)ra +
            le16_to_cpu(ra->client_array_offset));
    /*
     * Check the ra->client_free_list first and then check the
     * ra->client_in_use_list.  Check each of the log client records in
     * each of the lists and check that the array does not overflow the
     * ra->log_clients value.  Also keep track of the number of records
     * visited as there cannot be more than ra->log_clients records and
     * that way we detect eventual loops in within a list.
     */
    nr_clients = le16_to_cpu(ra->log_clients);
    idx = le16_to_cpu(ra->client_free_list);
    in_free_list = true;
check_list:
    for (idx_is_first = true; idx != LOGFILE_NO_CLIENT_CPU; nr_clients--,
            idx = le16_to_cpu(cr->next_client)) {
        if (!nr_clients || idx >= le16_to_cpu(ra->log_clients))
            goto err_out;
        /* Set @cr to the current log client record. */
        cr = ca + idx;
        /* The first log client record must not have a prev_client. */
        if (idx_is_first) {
            if (cr->prev_client != LOGFILE_NO_CLIENT)
                goto err_out;
            idx_is_first = false;
        }
    }
    /* Switch to and check the in use list if we just did the free list. */
    if (in_free_list) {
        in_free_list = false;
        idx = le16_to_cpu(ra->client_in_use_list);
        goto check_list;
    }
    ntfs_debug("Done.");
    return true;
err_out:
    ntfs_error(vi->i_sb, "$LogFile log client array is corrupt.");
    return false;
}

static int ntfs_check_and_load_restart_page(struct inode *vi,
        RESTART_PAGE_HEADER *rp, s64 pos, RESTART_PAGE_HEADER **wrp,
        LSN *lsn)
{
    RESTART_AREA *ra;
    RESTART_PAGE_HEADER *trp;
    int size, err;

    ntfs_debug("Entering.");
    /* Check the restart page header for consistency. */
    if (!ntfs_check_restart_page_header(vi, rp, pos)) {
        /* Error output already done inside the function. */
        return -EINVAL;
    }
    /* Check the restart area for consistency. */
    if (!ntfs_check_restart_area(vi, rp)) {
        /* Error output already done inside the function. */
        return -EINVAL;
    }
    ra = (RESTART_AREA*)((u8*)rp + le16_to_cpu(rp->restart_area_offset));
    /*
     * Allocate a buffer to store the whole restart page so we can multi
     * sector transfer deprotect it.
     */
    trp = ntfs_malloc_nofs(le32_to_cpu(rp->system_page_size));
    if (!trp) {
        ntfs_error(vi->i_sb, "Failed to allocate memory for $LogFile "
                "restart page buffer.");
        return -ENOMEM;
    }
    /*
     * Read the whole of the restart page into the buffer.  If it fits
     * completely inside @rp, just copy it from there.  Otherwise map all
     * the required pages and copy the data from them.
     */
    size = PAGE_CACHE_SIZE - (pos & ~PAGE_CACHE_MASK);
    if (size >= le32_to_cpu(rp->system_page_size)) {
        memcpy(trp, rp, le32_to_cpu(rp->system_page_size));
    } else {
        pgoff_t idx;
        struct page *page;
        int have_read, to_read;

        /* First copy what we already have in @rp. */
        memcpy(trp, rp, size);
        /* Copy the remaining data one page at a time. */
        have_read = size;
        to_read = le32_to_cpu(rp->system_page_size) - size;
        idx = (pos + size) >> PAGE_CACHE_SHIFT;
        BUG_ON((pos + size) & ~PAGE_CACHE_MASK);
        do {
            page = ntfs_map_page(vi->i_mapping, idx);
            if (IS_ERR(page)) {
                ntfs_error(vi->i_sb, "Error mapping $LogFile "
                        "page (index %lu).", idx);
                err = PTR_ERR(page);
                if (err != -EIO && err != -ENOMEM)
                    err = -EIO;
                goto err_out;
            }
            size = min_t(int, to_read, PAGE_CACHE_SIZE);
            memcpy((u8*)trp + have_read, page_address(page), size);
            ntfs_unmap_page(page);
            have_read += size;
            to_read -= size;
            idx++;
        } while (to_read > 0);
    }
    /*
     * Perform the multi sector transfer deprotection on the buffer if the
     * restart page is protected.
     */
    if ((!ntfs_is_chkd_record(trp->magic) || le16_to_cpu(trp->usa_count))
            && post_read_mst_fixup((NTFS_RECORD*)trp,
            le32_to_cpu(rp->system_page_size))) {
        /*
         * A multi sector tranfer error was detected.  We only need to
         * abort if the restart page contents exceed the multi sector
         * transfer fixup of the first sector.
         */
        if (le16_to_cpu(rp->restart_area_offset) +
                le16_to_cpu(ra->restart_area_length) >
                NTFS_BLOCK_SIZE - sizeof(u16)) {
            ntfs_error(vi->i_sb, "Multi sector transfer error "
                    "detected in $LogFile restart page.");
            err = -EINVAL;
            goto err_out;
        }
    }
    /*
     * If the restart page is modified by chkdsk or there are no active
     * logfile clients, the logfile is consistent.  Otherwise, need to
     * check the log client records for consistency, too.
     */
    err = 0;
    if (ntfs_is_rstr_record(rp->magic) &&
            ra->client_in_use_list != LOGFILE_NO_CLIENT) {
        if (!ntfs_check_log_client_array(vi, trp)) {
            err = -EINVAL;
            goto err_out;
        }
    }
    if (lsn) {
        if (ntfs_is_rstr_record(rp->magic))
            *lsn = sle64_to_cpu(ra->current_lsn);
        else /* if (ntfs_is_chkd_record(rp->magic)) */
            *lsn = sle64_to_cpu(rp->chkdsk_lsn);
    }
    ntfs_debug("Done.");
    if (wrp)
        *wrp = trp;
    else {
err_out:
        ntfs_free(trp);
    }
    return err;
}

bool ntfs_check_logfile(struct inode *log_vi, RESTART_PAGE_HEADER **rp)
{
    s64 size, pos;
    LSN rstr1_lsn, rstr2_lsn;
    ntfs_volume *vol = NTFS_SB(log_vi->i_sb);
    struct address_space *mapping = log_vi->i_mapping;
    struct page *page = NULL;
    u8 *kaddr = NULL;
    RESTART_PAGE_HEADER *rstr1_ph = NULL;
    RESTART_PAGE_HEADER *rstr2_ph = NULL;
    int log_page_size, log_page_mask, err;
    bool logfile_is_empty = true;
    u8 log_page_bits;

    ntfs_debug("Entering.");
    /* An empty $LogFile must have been clean before it got emptied. */
    if (NVolLogFileEmpty(vol))
        goto is_empty;
    size = i_size_read(log_vi);
    /* Make sure the file doesn't exceed the maximum allowed size. */
    if (size > MaxLogFileSize)
        size = MaxLogFileSize;
    /*
     * Truncate size to a multiple of the page cache size or the default
     * log page size if the page cache size is between the default log page
     * log page size if the page cache size is between the default log page
     * size and twice that.
     */
    if (PAGE_CACHE_SIZE >= DefaultLogPageSize && PAGE_CACHE_SIZE <=
            DefaultLogPageSize * 2)
        log_page_size = DefaultLogPageSize;
    else
        log_page_size = PAGE_CACHE_SIZE;
    log_page_mask = log_page_size - 1;
    /*
     * Use ntfs_ffs() instead of ffs() to enable the compiler to
     * optimize log_page_size and log_page_bits into constants.
     */
    log_page_bits = ntfs_ffs(log_page_size) - 1;
    size &= ~(s64)(log_page_size - 1);
    /*
     * Ensure the log file is big enough to store at least the two restart
     * pages and the minimum number of log record pages.
     */
    if (size < log_page_size * 2 || (size - log_page_size * 2) >>
            log_page_bits < MinLogRecordPages) {
        ntfs_error(vol->sb, "$LogFile is too small.");
        return false;
    }
    /*
     * Read through the file looking for a restart page.  Since the restart
     * page header is at the beginning of a page we only need to search at
     * what could be the beginning of a page (for each page size) rather
     * than scanning the whole file byte by byte.  If all potential places
     * contain empty and uninitialzed records, the log file can be assumed
     * to be empty.
     */
    for (pos = 0; pos < size; pos <<= 1) {
        pgoff_t idx = pos >> PAGE_CACHE_SHIFT;
        if (!page || page->index != idx) {
            if (page)
                ntfs_unmap_page(page);
            page = ntfs_map_page(mapping, idx);
            if (IS_ERR(page)) {
                ntfs_error(vol->sb, "Error mapping $LogFile "
                        "page (index %lu).", idx);
                goto err_out;
            }
        }
        kaddr = (u8*)page_address(page) + (pos & ~PAGE_CACHE_MASK);
        /*
         * A non-empty block means the logfile is not empty while an
         * empty block after a non-empty block has been encountered
         * means we are done.
         */
        if (!ntfs_is_empty_recordp((le32*)kaddr))
            logfile_is_empty = false;
        else if (!logfile_is_empty)
            break;
        /*
         * A log record page means there cannot be a restart page after
         * this so no need to continue searching.
         */
        if (ntfs_is_rcrd_recordp((le32*)kaddr))
            break;
        /* If not a (modified by chkdsk) restart page, continue. */
        if (!ntfs_is_rstr_recordp((le32*)kaddr) &&
                !ntfs_is_chkd_recordp((le32*)kaddr)) {
            if (!pos)
                pos = NTFS_BLOCK_SIZE >> 1;
            continue;
        }
        /*
         * Check the (modified by chkdsk) restart page for consistency
         * and get a copy of the complete multi sector transfer
         * deprotected restart page.
         */
        err = ntfs_check_and_load_restart_page(log_vi,
                (RESTART_PAGE_HEADER*)kaddr, pos,
                !rstr1_ph ? &rstr1_ph : &rstr2_ph,
                !rstr1_ph ? &rstr1_lsn : &rstr2_lsn);
        if (!err) {
            /*
             * If we have now found the first (modified by chkdsk)
             * restart page, continue looking for the second one.
             */
            if (!pos) {
                pos = NTFS_BLOCK_SIZE >> 1;
                continue;
            }
            /*
             * We have now found the second (modified by chkdsk)
             * restart page, so we can stop looking.
             */
            break;
        }
        /*
         * Error output already done inside the function.  Note, we do
         * not abort if the restart page was invalid as we might still
         * find a valid one further in the file.
         */
        if (err != -EINVAL) {
            ntfs_unmap_page(page);
            goto err_out;
        }
        /* Continue looking. */
        if (!pos)
            pos = NTFS_BLOCK_SIZE >> 1;
    }
    if (page)
        ntfs_unmap_page(page);
    if (logfile_is_empty) {
        NVolSetLogFileEmpty(vol);
is_empty:
        ntfs_debug("Done.  ($LogFile is empty.)");
        return true;
    }
    if (!rstr1_ph) {
        BUG_ON(rstr2_ph);
        ntfs_error(vol->sb, "Did not find any restart pages in "
                "$LogFile and it was not empty.");
        return false;
    }
    /* If both restart pages were found, use the more recent one. */
    if (rstr2_ph) {
        /*
         * If the second restart area is more recent, switch to it.
         * Otherwise just throw it away.
         */
        if (rstr2_lsn > rstr1_lsn) {
            ntfs_debug("Using second restart page as it is more "
                    "recent.");
            ntfs_free(rstr1_ph);
            rstr1_ph = rstr2_ph;
            /* rstr1_lsn = rstr2_lsn; */
        } else {
            ntfs_debug("Using first restart page as it is more "
                    "recent.");
            ntfs_free(rstr2_ph);
        }
        rstr2_ph = NULL;
    }
    /* All consistency checks passed. */
    if (rp)
        *rp = rstr1_ph;
    else
        ntfs_free(rstr1_ph);
    ntfs_debug("Done.");
    return true;
err_out:
    if (rstr1_ph)
        ntfs_free(rstr1_ph);
    return false;
}

bool ntfs_is_logfile_clean(struct inode *log_vi, const RESTART_PAGE_HEADER *rp)
{
    ntfs_volume *vol = NTFS_SB(log_vi->i_sb);
    RESTART_AREA *ra;

    ntfs_debug("Entering.");
    /* An empty $LogFile must have been clean before it got emptied. */
    if (NVolLogFileEmpty(vol)) {
        ntfs_debug("Done.  ($LogFile is empty.)");
        return true;
    }
    BUG_ON(!rp);
    if (!ntfs_is_rstr_record(rp->magic) &&
            !ntfs_is_chkd_record(rp->magic)) {
        ntfs_error(vol->sb, "Restart page buffer is invalid.  This is "
                "probably a bug in that the $LogFile should "
                "have been consistency checked before calling "
                "this function.");
        return false;
    }
    ra = (RESTART_AREA*)((u8*)rp + le16_to_cpu(rp->restart_area_offset));
    /*
     * If the $LogFile has active clients, i.e. it is open, and we do not
     * have the RESTART_VOLUME_IS_CLEAN bit set in the restart area flags,
     * we assume there was an unclean shutdown.
     */
    if (ra->client_in_use_list != LOGFILE_NO_CLIENT &&
            !(ra->flags & RESTART_VOLUME_IS_CLEAN)) {
        ntfs_debug("Done.  $LogFile indicates a dirty shutdown.");
        return false;
    }
    /* $LogFile indicates a clean shutdown. */
    ntfs_debug("Done.  $LogFile indicates a clean shutdown.");
    return true;
}

bool ntfs_empty_logfile(struct inode *log_vi)
{
    VCN vcn, end_vcn;
    ntfs_inode *log_ni = NTFS_I(log_vi);
    ntfs_volume *vol = log_ni->vol;
    struct super_block *sb = vol->sb;
    runlist_element *rl;
    unsigned long flags;
    unsigned block_size, block_size_bits;
    int err;
    bool should_wait = true;

    ntfs_debug("Entering.");
    if (NVolLogFileEmpty(vol)) {
        ntfs_debug("Done.");
        return true;
    }
    /*
     * We cannot use ntfs_attr_set() because we may be still in the middle
     * of a mount operation.  Thus we do the emptying by hand by first
     * zapping the page cache pages for the $LogFile/$DATA attribute and
     * then emptying each of the buffers in each of the clusters specified
     * by the runlist by hand.
     */
    block_size = sb->s_blocksize;
    block_size_bits = sb->s_blocksize_bits;
    vcn = 0;
    read_lock_irqsave(&log_ni->size_lock, flags);
    end_vcn = (log_ni->initialized_size + vol->cluster_size_mask) >>
            vol->cluster_size_bits;
    read_unlock_irqrestore(&log_ni->size_lock, flags);
    truncate_inode_pages(log_vi->i_mapping, 0);
    down_write(&log_ni->runlist.lock);
    rl = log_ni->runlist.rl;
    if (unlikely(!rl || vcn < rl->vcn || !rl->length)) {
map_vcn:
        err = ntfs_map_runlist_nolock(log_ni, vcn, NULL);
        if (err) {
            ntfs_error(sb, "Failed to map runlist fragment (error "
                    "%d).", -err);
            goto err;
        }
        rl = log_ni->runlist.rl;
        BUG_ON(!rl || vcn < rl->vcn || !rl->length);
    }
    /* Seek to the runlist element containing @vcn. */
    while (rl->length && vcn >= rl[1].vcn)
        rl++;
    do {
        LCN lcn;
        sector_t block, end_block;
        s64 len;

        /*
         * If this run is not mapped map it now and start again as the
         * runlist will have been updated.
         */
        lcn = rl->lcn;
        if (unlikely(lcn == LCN_RL_NOT_MAPPED)) {
            vcn = rl->vcn;
            goto map_vcn;
        }
        /* If this run is not valid abort with an error. */
        if (unlikely(!rl->length || lcn < LCN_HOLE))
            goto rl_err;
        /* Skip holes. */
        if (lcn == LCN_HOLE)
            continue;
        block = lcn << vol->cluster_size_bits >> block_size_bits;
        len = rl->length;
        if (rl[1].vcn > end_vcn)
            len = end_vcn - rl->vcn;
        end_block = (lcn + len) << vol->cluster_size_bits >>
                block_size_bits;
        /* Iterate over the blocks in the run and empty them. */
        do {
            struct buffer_head *bh;

            /* Obtain the buffer, possibly not uptodate. */
            bh = sb_getblk(sb, block);
            BUG_ON(!bh);
            /* Setup buffer i/o submission. */
            lock_buffer(bh);
            bh->b_end_io = end_buffer_write_sync;
            get_bh(bh);
            /* Set the entire contents of the buffer to 0xff. */
            memset(bh->b_data, -1, block_size);
            if (!buffer_uptodate(bh))
                set_buffer_uptodate(bh);
            if (buffer_dirty(bh))
                clear_buffer_dirty(bh);
            /*
             * Submit the buffer and wait for i/o to complete but
             * only for the first buffer so we do not miss really
             * serious i/o errors.  Once the first buffer has
             * completed ignore errors afterwards as we can assume
             * that if one buffer worked all of them will work.
             */
            submit_bh(WRITE, bh);
            if (should_wait) {
                should_wait = false;
                wait_on_buffer(bh);
                if (unlikely(!buffer_uptodate(bh)))
                    goto io_err;
            }
            brelse(bh);
        } while (++block < end_block);
    } while ((++rl)->vcn < end_vcn);
    up_write(&log_ni->runlist.lock);
    /*
     * Zap the pages again just in case any got instantiated whilst we were
     * emptying the blocks by hand.  FIXME: We may not have completed
     * writing to all the buffer heads yet so this may happen too early.
     * We really should use a kernel thread to do the emptying
     * asynchronously and then we can also set the volume dirty and output
     * an error message if emptying should fail.
     */
    truncate_inode_pages(log_vi->i_mapping, 0);
    /* Set the flag so we do not have to do it again on remount. */
    NVolSetLogFileEmpty(vol);
    ntfs_debug("Done.");
    return true;
io_err:
    ntfs_error(sb, "Failed to write buffer.  Unmount and run chkdsk.");
    goto dirty_err;
rl_err:
    ntfs_error(sb, "Runlist is corrupt.  Unmount and run chkdsk.");
dirty_err:
    NVolSetErrors(vol);
    err = -EIO;
err:
    up_write(&log_ni->runlist.lock);
    ntfs_error(sb, "Failed to fill $LogFile with 0xff bytes (error %d).",
            -err);
    return false;
}

#endif /* NTFS_RW */