FreeBSD/Linux Kernel Cross Reference
sys/fs/ntfs/mst.c

     /*
      * 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"
    
    /**
     * post_read_mst_fixup - deprotect multi sector transfer protected data
     * @b:          pointer to the data to deprotect
     * @size:       size in bytes of @b
     *
     * Perform the necessary post read multi sector transfer fixup and detect the
     * presence of incomplete multi sector transfers. - In that case, overwrite the
     * magic of the ntfs record header being processed with "BAAD" (in memory only!)
     * and abort processing.
     *
     * Return 0 on success and -EINVAL on error ("BAAD" magic will be present).
     *
     * NOTE: We consider the absence / invalidity of an update sequence array to
     * mean that the structure is not protected at all and hence doesn't need to
     * be fixed up. Thus, we return success and not failure in this case. This is
     * in contrast to pre_write_mst_fixup(), see below.
     */
    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;
   }
   
   /**
    * pre_write_mst_fixup - apply multi sector transfer protection
    * @b:          pointer to the data to protect
    * @size:       size in bytes of @b
    *
    * Perform the necessary pre write multi sector transfer fixup on the data
    * pointer to by @b of @size.
    *
    * Return 0 if fixup applied (success) or -EINVAL if no fixup was performed
    * (assumed not needed). This is in contrast to post_read_mst_fixup() above.
    *
    * NOTE: We consider the absence / invalidity of an update sequence array to
    * mean that the structure is not subject to protection and hence doesn't need
    * to be fixed up. This means that you have to create a valid update sequence
    * array header in the ntfs record before calling this function, otherwise it
    * will fail (the header needs to contain the position of the update sequence
    * array together with the number of elements in the array). You also need to
    * initialise the update sequence number before calling this function
    * otherwise a random word will be used (whatever was in the record at that
    * position at that time).
    */
   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;
   }
   
   /**
    * post_write_mst_fixup - fast deprotect multi sector transfer protected data
    * @b:          pointer to the data to deprotect
    *
    * Perform the necessary post write multi sector transfer fixup, not checking
    * for any errors, because we assume we have just used pre_write_mst_fixup(),
    * thus the data will be fine or we would never have gotten here.
    */
   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);
           }
   }

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