mst.c

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/*
 * mst.c - NTFS multi sector transfer protection handling code. Part of the
 *     Linux-NTFS project.
 *
 * Copyright (c) 2001-2004 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
 */

#include "ntfs.h"

int post_read_mst_fixup(NTFS_RECORD *b, const u32 size)
{
    u16 usa_ofs, usa_count, usn;
    u16 *usa_pos, *data_pos;

    /* Setup the variables. */
    usa_ofs = le16_to_cpu(b->usa_ofs);
    /* Decrement usa_count to get number of fixups. */
    usa_count = le16_to_cpu(b->usa_count) - 1;
    /* Size and alignment checks. */
    if ( size & (NTFS_BLOCK_SIZE - 1)   ||
         usa_ofs & 1            ||
         usa_ofs + (usa_count * 2) > size   ||
         (size >> NTFS_BLOCK_SIZE_BITS) != usa_count)
        return 0;
    /* Position of usn in update sequence array. */
    usa_pos = (u16*)b + usa_ofs/sizeof(u16);
    /*
     * The update sequence number which has to be equal to each of the
     * u16 values before they are fixed up. Note no need to care for
     * endianness since we are comparing and moving data for on disk
     * structures which means the data is consistent. - If it is
     * consistenty the wrong endianness it doesn't make any difference.
     */
    usn = *usa_pos;
    /*
     * Position in protected data of first u16 that needs fixing up.
     */
    data_pos = (u16*)b + NTFS_BLOCK_SIZE/sizeof(u16) - 1;
    /*
     * Check for incomplete multi sector transfer(s).
     */
    while (usa_count--) {
        if (*data_pos != usn) {
            /*
             * Incomplete multi sector transfer detected! )-:
             * Set the magic to "BAAD" and return failure.
             * Note that magic_BAAD is already converted to le32.
             */
            b->magic = magic_BAAD;
            return -EINVAL;
        }
        data_pos += NTFS_BLOCK_SIZE/sizeof(u16);
    }
    /* Re-setup the variables. */
    usa_count = le16_to_cpu(b->usa_count) - 1;
    data_pos = (u16*)b + NTFS_BLOCK_SIZE/sizeof(u16) - 1;
    /* Fixup all sectors. */
    while (usa_count--) {
        /*
         * Increment position in usa and restore original data from
         * the usa into the data buffer.
         */
        *data_pos = *(++usa_pos);
        /* Increment position in data as well. */
        data_pos += NTFS_BLOCK_SIZE/sizeof(u16);
    }
    return 0;
}

int pre_write_mst_fixup(NTFS_RECORD *b, const u32 size)
{
    le16 *usa_pos, *data_pos;
    u16 usa_ofs, usa_count, usn;
    le16 le_usn;

    /* Sanity check + only fixup if it makes sense. */
    if (!b || ntfs_is_baad_record(b->magic) ||
            ntfs_is_hole_record(b->magic))
        return -EINVAL;
    /* Setup the variables. */
    usa_ofs = le16_to_cpu(b->usa_ofs);
    /* Decrement usa_count to get number of fixups. */
    usa_count = le16_to_cpu(b->usa_count) - 1;
    /* Size and alignment checks. */
    if ( size & (NTFS_BLOCK_SIZE - 1)   ||
         usa_ofs & 1            ||
         usa_ofs + (usa_count * 2) > size   ||
         (size >> NTFS_BLOCK_SIZE_BITS) != usa_count)
        return -EINVAL;
    /* Position of usn in update sequence array. */
    usa_pos = (le16*)((u8*)b + usa_ofs);
    /*
     * Cyclically increment the update sequence number
     * (skipping 0 and -1, i.e. 0xffff).
     */
    usn = le16_to_cpup(usa_pos) + 1;
    if (usn == 0xffff || !usn)
        usn = 1;
    le_usn = cpu_to_le16(usn);
    *usa_pos = le_usn;
    /* Position in data of first u16 that needs fixing up. */
    data_pos = (le16*)b + NTFS_BLOCK_SIZE/sizeof(le16) - 1;
    /* Fixup all sectors. */
    while (usa_count--) {
        /*
         * Increment the position in the usa and save the
         * original data from the data buffer into the usa.
         */
        *(++usa_pos) = *data_pos;
        /* Apply fixup to data. */
        *data_pos = le_usn;
        /* Increment position in data as well. */
        data_pos += NTFS_BLOCK_SIZE/sizeof(le16);
    }
    return 0;
}

void post_write_mst_fixup(NTFS_RECORD *b)
{
    le16 *usa_pos, *data_pos;

    u16 usa_ofs = le16_to_cpu(b->usa_ofs);
    u16 usa_count = le16_to_cpu(b->usa_count) - 1;

    /* Position of usn in update sequence array. */
    usa_pos = (le16*)b + usa_ofs/sizeof(le16);

    /* Position in protected data of first u16 that needs fixing up. */
    data_pos = (le16*)b + NTFS_BLOCK_SIZE/sizeof(le16) - 1;

    /* Fixup all sectors. */
    while (usa_count--) {
        /*
         * Increment position in usa and restore original data from
         * the usa into the data buffer.
         */
        *data_pos = *(++usa_pos);

        /* Increment position in data as well. */
        data_pos += NTFS_BLOCK_SIZE/sizeof(le16);
    }
}