text: /**
   * mst.c - Multi sector fixup handling code. Originated from the Linux-NTFS project.
   *
   * Copyright (c) 2000-2004 Anton Altaparmakov
   * Copyright (c) 2006-2009 Szabolcs Szakacsits
   *
   * 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 NTFS-3G
   * 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 HAVE_CONFIG_H
  #include "config.h"
  #endif
  
  #ifdef HAVE_ERRNO_H
  #include <errno.h>
  #endif
  
  #include "mst.h"
  #include "logging.h"
  
  /**
   * ntfs_mst_post_read_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 fixups 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 -1 on error, with errno set to the error code. The
   * following error codes are defined:
   *	EINVAL	Invalid arguments or invalid NTFS record in buffer @b.
   *	EIO	Multi sector transfer error was detected. Magic of the NTFS
   *		record in @b will have been set to "BAAD".
   */
  int ntfs_mst_post_read_fixup_warn(NTFS_RECORD *b, const u32 size,
  					BOOL warn)
  {
  	u16 usa_ofs, usa_count, usn;
  	u16 *usa_pos, *data_pos;
  
  	ntfs_log_trace("Entering\n");
  
  	/* 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 ||
  			(u32)(usa_ofs + (usa_count * 2)) > size ||
  			(size >> NTFS_BLOCK_SIZE_BITS) != usa_count) {
  		errno = EINVAL;
  		if (warn) {
  			ntfs_log_perror("%s: magic: 0x%08lx  size: %ld "
  					"  usa_ofs: %d  usa_count: %u",
  					 __FUNCTION__,
  					(long)le32_to_cpu(*(le32 *)b),
  					(long)size, (int)usa_ofs,
  					(unsigned int)usa_count);
  		}
  		return -1;
  	}
  	/* 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
  	 * consistency 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.
  			 */
  			errno = EIO;
  			ntfs_log_perror("Incomplete multi-sector transfer: "
  				"magic: 0x%08x  size: %d  usa_ofs: %d  usa_count:"
  				" %d  data: %d  usn: %d", *(le32 *)b, size,
  				usa_ofs, usa_count, *data_pos, usn);
  			b->magic = magic_BAAD;
  			return -1;
  		}
  		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;
  }
  
  /*
   *		Deprotect multi sector transfer protected data
   *	with a warning if an error is found.
   */
  
  int ntfs_mst_post_read_fixup(NTFS_RECORD *b, const u32 size)
  {
  	return (ntfs_mst_post_read_fixup_warn(b,size,TRUE));
  }
  
  /**
   * ntfs_mst_pre_write_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 fixups applied successfully or -1 if no fixups were performed
   * due to errors. In that case errno i set to the error code (EINVAL).
   *
   * NOTE: We consider the absence / invalidity of an update sequence array to
   * mean error. 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 ntfs_mst_pre_write_fixup(NTFS_RECORD *b, const u32 size)
  {
  	u16 usa_ofs, usa_count, usn;
  	u16 *usa_pos, *data_pos;
  
  	ntfs_log_trace("Entering\n");
  
  	/* Sanity check + only fixup if it makes sense. */
  	if (!b || ntfs_is_baad_record(b->magic) ||
  			ntfs_is_hole_record(b->magic)) {
  		errno = EINVAL;
  		ntfs_log_perror("%s: bad argument", __FUNCTION__);
  		return -1;
  	}
  	/* 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 ||
  			(u32)(usa_ofs + (usa_count * 2)) > size ||
  			(size >> NTFS_BLOCK_SIZE_BITS) != usa_count) {
  		errno = EINVAL;
  		ntfs_log_perror("%s", __FUNCTION__);
  		return -1;
  	}
  	/* Position of usn in update sequence array. */
  	usa_pos = (u16*)((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;
  	usn = cpu_to_le16(usn);
  	*usa_pos = usn;
  	/* Position in data of first u16 that needs fixing up. */
  	data_pos = (u16*)b + NTFS_BLOCK_SIZE/sizeof(u16) - 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 = usn;
  		/* Increment position in data as well. */
  		data_pos += NTFS_BLOCK_SIZE/sizeof(u16);
  	}
  	return 0;
  }
  
  /**
   * ntfs_mst_post_write_fixup - 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
   * ntfs_mst_pre_write_fixup(), thus the data will be fine or we would never
   * have gotten here.
   */
  void ntfs_mst_post_write_fixup(NTFS_RECORD *b)
  {
  	u16 *usa_pos, *data_pos;
  
  	u16 usa_ofs = le16_to_cpu(b->usa_ofs);
  	u16 usa_count = le16_to_cpu(b->usa_count) - 1;
  
  	ntfs_log_trace("Entering\n");
  
  	/* Position of usn in update sequence array. */
  	usa_pos = (u16*)b + usa_ofs/sizeof(u16);
  
  	/* Position in protected data of first u16 that needs fixing up. */
  	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);
  	}
  }
  
  