--- /dev/null
+/*
+ * 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);
+ }
+}
Code Review / kvmfornfv.git / blobdiff