// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * NTFS kernel journal handling.
 *
 * Copyright (c) 2002-2007 Anton Altaparmakov
 */

#include <linux/blkdev.h>

#include "attrib.h"
#include "logfile.h"
#include "ntfs.h"

/*
 * ntfs_check_restart_page_header - check the page header for consistency
 * @vi:         LogFile inode to which the restart page header belongs
 * @rp:         restart page header to check
 * @pos:        position in @vi at which the restart page header resides
 *
 * Check the restart page header @rp for consistency and return 'true' if it is
 * consistent and 'false' otherwise.
 *
 * This function only needs NTFS_BLOCK_SIZE bytes in @rp, i.e. it does not
 * require the full restart page.
 */
static bool ntfs_check_restart_page_header(struct inode *vi,
                struct 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 (le16_to_cpu(rp->major_ver) != 1 ||
            le16_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)le16_to_cpu(rp->major_ver),
                        (int)le16_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(struct 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(struct 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) && le64_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;
}

/*
 * ntfs_check_restart_area - check the restart area for consistency
 * @vi:         LogFile inode to which the restart page belongs
 * @rp:         restart page whose restart area to check
 *
 * Check the restart area of the restart page @rp for consistency and return
 * 'true' if it is consistent and 'false' otherwise.
 *
 * This function assumes that the restart page header has already been
 * consistency checked.
 *
 * This function only needs NTFS_BLOCK_SIZE bytes in @rp, i.e. it does not
 * require the full restart page.
 */
static bool ntfs_check_restart_area(struct inode *vi, struct restart_page_header *rp)
{
        u64 file_size;
        struct restart_area *ra;
        u32 ra_ofs, ra_len, ca_ofs;
        u8 fs_bits;

        ntfs_debug("Entering.");
        ra_ofs = le16_to_cpu(rp->restart_area_offset);
        ra = (struct 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(struct 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(struct 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 = le64_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;
}

/*
 * ntfs_check_log_client_array - check the log client array for consistency
 * @vi:         LogFile inode to which the restart page belongs
 * @rp:         restart page whose log client array to check
 *
 * Check the log client array of the restart page @rp for consistency and
 * return 'true' if it is consistent and 'false' otherwise.
 *
 * This function assumes that the restart page header and the restart area have
 * already been consistency checked.
 *
 * Unlike ntfs_check_restart_page_header() and ntfs_check_restart_area(), this
 * function needs @rp->system_page_size bytes in @rp, i.e. it requires the full
 * restart page and the page must be multi sector transfer deprotected.
 */
static bool ntfs_check_log_client_array(struct inode *vi,
                struct restart_page_header *rp)
{
        struct restart_area *ra;
        struct log_client_record *ca, *cr;
        u16 nr_clients, idx;
        bool in_free_list, idx_is_first;

        ntfs_debug("Entering.");
        ra = (struct restart_area *)((u8 *)rp + le16_to_cpu(rp->restart_area_offset));
        ca = (struct 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;
}

/*
 * ntfs_check_and_load_restart_page - check the restart page for consistency
 * @vi:         LogFile inode to which the restart page belongs
 * @rp:         restart page to check
 * @pos:        position in @vi at which the restart page resides
 * @wrp:        [OUT] copy of the multi sector transfer deprotected restart page
 * @lsn:        [OUT] set to the current logfile lsn on success
 *
 * Check the restart page @rp for consistency and return 0 if it is consistent
 * and -errno otherwise.  The restart page may have been modified by chkdsk in
 * which case its magic is CHKD instead of RSTR.
 *
 * This function only needs NTFS_BLOCK_SIZE bytes in @rp, i.e. it does not
 * require the full restart page.
 *
 * If @wrp is not NULL, on success, *@wrp will point to a buffer containing a
 * copy of the complete multi sector transfer deprotected page.  On failure,
 * *@wrp is undefined.
 *
 * Simillarly, if @lsn is not NULL, on success *@lsn will be set to the current
 * logfile lsn according to this restart page.  On failure, *@lsn is undefined.
 *
 * The following error codes are defined:
 *      -EINVAL - The restart page is inconsistent.
 *      -ENOMEM - Not enough memory to load the restart page.
 *      -EIO    - Failed to reading from LogFile.
 */
static int ntfs_check_and_load_restart_page(struct inode *vi,
                struct restart_page_header *rp, s64 pos, struct restart_page_header **wrp,
                s64 *lsn)
{
        struct restart_area *ra;
        struct 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 = (struct 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 = kvzalloc(le32_to_cpu(rp->system_page_size), GFP_NOFS);
        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_SIZE - (pos & ~PAGE_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 folio *folio;
                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_SHIFT;
                do {
                        folio = read_mapping_folio(vi->i_mapping, idx, NULL);
                        if (IS_ERR(folio)) {
                                ntfs_error(vi->i_sb, "Error mapping LogFile page (index %lu).",
                                                idx);
                                err = PTR_ERR(folio);
                                if (err != -EIO && err != -ENOMEM)
                                        err = -EIO;
                                goto err_out;
                        }
                        size = min_t(int, to_read, PAGE_SIZE);
                        memcpy((u8 *)trp + have_read, folio_address(folio), size);
                        folio_put(folio);
                        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((struct ntfs_record *)trp, le32_to_cpu(rp->system_page_size))) {
                /*
                 * A multi sector transfer 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 = le64_to_cpu(ra->current_lsn);
                else /* if (ntfs_is_chkd_record(rp->magic)) */
                        *lsn = le64_to_cpu(rp->chkdsk_lsn);
        }
        ntfs_debug("Done.");
        if (wrp)
                *wrp = trp;
        else {
err_out:
                kvfree(trp);
        }
        return err;
}

/*
 * ntfs_check_logfile - check the journal for consistency
 * @log_vi:     struct inode of loaded journal LogFile to check
 * @rp:         [OUT] on success this is a copy of the current restart page
 *
 * Check the LogFile journal for consistency and return 'true' if it is
 * consistent and 'false' if not.  On success, the current restart page is
 * returned in *@rp.  Caller must call kvfree(*@rp) when finished with it.
 *
 * At present we only check the two restart pages and ignore the log record
 * pages.
 *
 * Note that the MstProtected flag is not set on the LogFile inode and hence
 * when reading pages they are not deprotected.  This is because we do not know
 * if the LogFile was created on a system with a different page size to ours
 * yet and mst deprotection would fail if our page size is smaller.
 */
bool ntfs_check_logfile(struct inode *log_vi, struct restart_page_header **rp)
{
        s64 size, pos;
        s64 rstr1_lsn, rstr2_lsn;
        struct ntfs_volume *vol = NTFS_SB(log_vi->i_sb);
        struct address_space *mapping = log_vi->i_mapping;
        struct folio *folio = NULL;
        u8 *kaddr = NULL;
        struct restart_page_header *rstr1_ph = NULL;
        struct restart_page_header *rstr2_ph = NULL;
        int log_page_size, 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 (DefaultLogPageSize <= PAGE_SIZE &&
            DefaultLogPageSize * 2 <= PAGE_SIZE)
                log_page_size = DefaultLogPageSize;
        else
                log_page_size = PAGE_SIZE;
        /*
         * 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_SHIFT;

                if (!folio || folio->index != idx) {
                        if (folio) {
                                kunmap_local(kaddr);
                                folio_put(folio);
                        }
                        folio = read_mapping_folio(mapping, idx, NULL);
                        if (IS_ERR(folio)) {
                                ntfs_error(vol->sb, "Error mapping LogFile page (index %lu).",
                                                idx);
                                goto err_out;
                        }
                }
                kaddr = (u8 *)kmap_local_folio(folio, 0) + (pos & ~PAGE_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,
                                (struct 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) {
                        kunmap_local(kaddr);
                        folio_put(folio);
                        goto err_out;
                }
                /* Continue looking. */
                if (!pos)
                        pos = NTFS_BLOCK_SIZE >> 1;
        }
        if (folio) {
                kunmap_local(kaddr);
                folio_put(folio);
        }
        if (logfile_is_empty) {
                NVolSetLogFileEmpty(vol);
is_empty:
                ntfs_debug("Done.  (LogFile is empty.)");
                return true;
        }
        if (!rstr1_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.");
                        kvfree(rstr1_ph);
                        rstr1_ph = rstr2_ph;
                        /* rstr1_lsn = rstr2_lsn; */
                } else {
                        ntfs_debug("Using first restart page as it is more recent.");
                        kvfree(rstr2_ph);
                }
                rstr2_ph = NULL;
        }
        /* All consistency checks passed. */
        if (rp)
                *rp = rstr1_ph;
        else
                kvfree(rstr1_ph);
        ntfs_debug("Done.");
        return true;
err_out:
        kvfree(rstr1_ph);
        return false;
}

/*
 * ntfs_empty_logfile - empty the contents of the LogFile journal
 * @log_vi:     struct inode of loaded journal LogFile to empty
 *
 * Empty the contents of the LogFile journal @log_vi and return 'true' on
 * success and 'false' on error.
 *
 * This function assumes that the LogFile journal has already been consistency
 * checked by a call to ntfs_check_logfile() and that ntfs_is_logfile_clean()
 * has been used to ensure that the LogFile is clean.
 */
bool ntfs_empty_logfile(struct inode *log_vi)
{
        s64 vcn, end_vcn;
        struct ntfs_inode *log_ni = NTFS_I(log_vi);
        struct ntfs_volume *vol = log_ni->vol;
        struct super_block *sb = vol->sb;
        struct runlist_element *rl;
        unsigned long flags;
        int err;
        bool should_wait = true;
        char *empty_buf = NULL;
        struct file_ra_state *ra = NULL;

        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.
         */
        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;
        }
        /* Seek to the runlist element containing @vcn. */
        while (rl->length && vcn >= rl[1].vcn)
                rl++;

        err = -ENOMEM;
        empty_buf = kvzalloc(vol->cluster_size, GFP_NOFS);
        if (!empty_buf)
                goto err;

        memset(empty_buf, 0xff, vol->cluster_size);

        ra = kzalloc(sizeof(*ra), GFP_NOFS);
        if (!ra)
                goto err;

        file_ra_state_init(ra, sb->s_bdev->bd_mapping);
        do {
                s64 lcn;
                loff_t start, end;
                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;
                        kvfree(empty_buf);
                        empty_buf = NULL;
                        kfree(ra);
                        ra = NULL;
                        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;
                start = NTFS_CLU_TO_B(vol, lcn);
                len = rl->length;
                if (rl[1].vcn > end_vcn)
                        len = end_vcn - rl->vcn;
                end = NTFS_CLU_TO_B(vol, lcn + len);

                page_cache_sync_readahead(sb->s_bdev->bd_mapping, ra, NULL,
                        start >> PAGE_SHIFT, (end - start) >> PAGE_SHIFT);

                do {
                        err = ntfs_bdev_write(sb, empty_buf, start,
                                                  vol->cluster_size);
                        if (err) {
                                ntfs_error(sb, "ntfs_dev_write failed, err : %d\n", err);
                                goto io_err;
                        }

                        /*
                         * 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.
                         */
                        if (should_wait) {
                                should_wait = false;
                                err = filemap_write_and_wait_range(sb->s_bdev->bd_mapping,
                                                start, start + vol->cluster_size);
                                if (err)
                                        goto io_err;
                        }
                        start += vol->cluster_size;
                } while (start < end);
        } while ((++rl)->vcn < end_vcn);
        up_write(&log_ni->runlist.lock);
        kvfree(empty_buf);
        kfree(ra);
        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:
        kvfree(empty_buf);
        kfree(ra);
        up_write(&log_ni->runlist.lock);
        ntfs_error(sb, "Failed to fill LogFile with 0xff bytes (error %d).",
                        -err);
        return false;
}