/* Just in case... We could replace this with BUG() some day. */
return (LCN)LCN_ENOENT;
}
+
+/**
+ * ntfs_get_nr_significant_bytes - get number of bytes needed to store a number
+ * @n: number for which to get the number of bytes for
+ *
+ * Return the number of bytes required to store @n unambiguously as
+ * a signed number.
+ *
+ * This is used in the context of the mapping pairs array to determine how
+ * many bytes will be needed in the array to store a given logical cluster
+ * number (lcn) or a specific run length.
+ *
+ * Return the number of bytes written. This function cannot fail.
+ */
+static inline int ntfs_get_nr_significant_bytes(const s64 n)
+{
+ s64 l = n;
+ int i;
+ s8 j;
+
+ i = 0;
+ do {
+ l >>= 8;
+ i++;
+ } while (l != 0 && l != -1);
+ j = (n >> 8 * (i - 1)) & 0xff;
+ /* If the sign bit is wrong, we need an extra byte. */
+ if ((n < 0 && j >= 0) || (n > 0 && j < 0))
+ i++;
+ return i;
+}
+
+/**
+ * ntfs_get_size_for_mapping_pairs - get bytes needed for mapping pairs array
+ * @vol: ntfs volume (needed for the ntfs version)
+ * @rl: locked runlist to determine the size of the mapping pairs of
+ * @start_vcn: vcn at which to start the mapping pairs array
+ *
+ * Walk the locked runlist @rl and calculate the size in bytes of the mapping
+ * pairs array corresponding to the runlist @rl, starting at vcn @start_vcn.
+ * This for example allows us to allocate a buffer of the right size when
+ * building the mapping pairs array.
+ *
+ * If @rl is NULL, just return 1 (for the single terminator byte).
+ *
+ * Return the calculated size in bytes on success. On error, return -errno.
+ * The following error codes are defined:
+ * -EINVAL - Run list contains unmapped elements. Make sure to only pass
+ * fully mapped runlists to this function.
+ * -EIO - The runlist is corrupt.
+ *
+ * Locking: @rl must be locked on entry (either for reading or writing), it
+ * remains locked throughout, and is left locked upon return.
+ */
+int ntfs_get_size_for_mapping_pairs(const ntfs_volume *vol,
+ const runlist_element *rl, const VCN start_vcn)
+{
+ LCN prev_lcn;
+ int rls;
+
+ BUG_ON(start_vcn < 0);
+ if (!rl) {
+ BUG_ON(start_vcn);
+ return 1;
+ }
+ /* Skip to runlist element containing @start_vcn. */
+ while (rl->length && start_vcn >= rl[1].vcn)
+ rl++;
+ if ((!rl->length && start_vcn > rl->vcn) || start_vcn < rl->vcn)
+ return -EINVAL;
+ prev_lcn = 0;
+ /* Always need the termining zero byte. */
+ rls = 1;
+ /* Do the first partial run if present. */
+ if (start_vcn > rl->vcn) {
+ s64 delta;
+
+ /* We know rl->length != 0 already. */
+ if (rl->length < 0 || rl->lcn < LCN_HOLE)
+ goto err_out;
+ delta = start_vcn - rl->vcn;
+ /* Header byte + length. */
+ rls += 1 + ntfs_get_nr_significant_bytes(rl->length - delta);
+ /*
+ * If the logical cluster number (lcn) denotes a hole and we
+ * are on NTFS 3.0+, we don't store it at all, i.e. we need
+ * zero space. On earlier NTFS versions we just store the lcn.
+ * Note: this assumes that on NTFS 1.2-, holes are stored with
+ * an lcn of -1 and not a delta_lcn of -1 (unless both are -1).
+ */
+ if (rl->lcn >= 0 || vol->major_ver < 3) {
+ prev_lcn = rl->lcn;
+ if (rl->lcn >= 0)
+ prev_lcn += delta;
+ /* Change in lcn. */
+ rls += ntfs_get_nr_significant_bytes(prev_lcn);
+ }
+ /* Go to next runlist element. */
+ rl++;
+ }
+ /* Do the full runs. */
+ for (; rl->length; rl++) {
+ if (rl->length < 0 || rl->lcn < LCN_HOLE)
+ goto err_out;
+ /* Header byte + length. */
+ rls += 1 + ntfs_get_nr_significant_bytes(rl->length);
+ /*
+ * If the logical cluster number (lcn) denotes a hole and we
+ * are on NTFS 3.0+, we don't store it at all, i.e. we need
+ * zero space. On earlier NTFS versions we just store the lcn.
+ * Note: this assumes that on NTFS 1.2-, holes are stored with
+ * an lcn of -1 and not a delta_lcn of -1 (unless both are -1).
+ */
+ if (rl->lcn >= 0 || vol->major_ver < 3) {
+ /* Change in lcn. */
+ rls += ntfs_get_nr_significant_bytes(rl->lcn -
+ prev_lcn);
+ prev_lcn = rl->lcn;
+ }
+ }
+ return rls;
+err_out:
+ if (rl->lcn == LCN_RL_NOT_MAPPED)
+ rls = -EINVAL;
+ else
+ rls = -EIO;
+ return rls;
+}
+
+/**
+ * ntfs_write_significant_bytes - write the significant bytes of a number
+ * @dst: destination buffer to write to
+ * @dst_max: pointer to last byte of destination buffer for bounds checking
+ * @n: number whose significant bytes to write
+ *
+ * Store in @dst, the minimum bytes of the number @n which are required to
+ * identify @n unambiguously as a signed number, taking care not to exceed
+ * @dest_max, the maximum position within @dst to which we are allowed to
+ * write.
+ *
+ * This is used when building the mapping pairs array of a runlist to compress
+ * a given logical cluster number (lcn) or a specific run length to the minumum
+ * size possible.
+ *
+ * Return the number of bytes written on success. On error, i.e. the
+ * destination buffer @dst is too small, return -ENOSPC.
+ */
+static inline int ntfs_write_significant_bytes(s8 *dst, const s8 *dst_max,
+ const s64 n)
+{
+ s64 l = n;
+ int i;
+ s8 j;
+
+ i = 0;
+ do {
+ if (dst > dst_max)
+ goto err_out;
+ *dst++ = l & 0xffll;
+ l >>= 8;
+ i++;
+ } while (l != 0 && l != -1);
+ j = (n >> 8 * (i - 1)) & 0xff;
+ /* If the sign bit is wrong, we need an extra byte. */
+ if (n < 0 && j >= 0) {
+ if (dst > dst_max)
+ goto err_out;
+ i++;
+ *dst = (s8)-1;
+ } else if (n > 0 && j < 0) {
+ if (dst > dst_max)
+ goto err_out;
+ i++;
+ *dst = (s8)0;
+ }
+ return i;
+err_out:
+ return -ENOSPC;
+}
+
+/**
+ * ntfs_mapping_pairs_build - build the mapping pairs array from a runlist
+ * @vol: ntfs volume (needed for the ntfs version)
+ * @dst: destination buffer to which to write the mapping pairs array
+ * @dst_len: size of destination buffer @dst in bytes
+ * @rl: locked runlist for which to build the mapping pairs array
+ * @start_vcn: vcn at which to start the mapping pairs array
+ * @stop_vcn: first vcn outside destination buffer on success or -ENOSPC
+ *
+ * Create the mapping pairs array from the locked runlist @rl, starting at vcn
+ * @start_vcn and save the array in @dst. @dst_len is the size of @dst in
+ * bytes and it should be at least equal to the value obtained by calling
+ * ntfs_get_size_for_mapping_pairs().
+ *
+ * If @rl is NULL, just write a single terminator byte to @dst.
+ *
+ * On success or -ENOSPC error, if @stop_vcn is not NULL, *@stop_vcn is set to
+ * the first vcn outside the destination buffer. Note that on error, @dst has
+ * been filled with all the mapping pairs that will fit, thus it can be treated
+ * as partial success, in that a new attribute extent needs to be created or
+ * the next extent has to be used and the mapping pairs build has to be
+ * continued with @start_vcn set to *@stop_vcn.
+ *
+ * Return 0 on success and -errno on error. The following error codes are
+ * defined:
+ * -EINVAL - Run list contains unmapped elements. Make sure to only pass
+ * fully mapped runlists to this function.
+ * -EIO - The runlist is corrupt.
+ * -ENOSPC - The destination buffer is too small.
+ *
+ * Locking: @rl must be locked on entry (either for reading or writing), it
+ * remains locked throughout, and is left locked upon return.
+ */
+int ntfs_mapping_pairs_build(const ntfs_volume *vol, s8 *dst,
+ const int dst_len, const runlist_element *rl,
+ const VCN start_vcn, VCN *const stop_vcn)
+{
+ LCN prev_lcn;
+ s8 *dst_max, *dst_next;
+ int err = -ENOSPC;
+ s8 len_len, lcn_len;
+
+ BUG_ON(start_vcn < 0);
+ BUG_ON(dst_len < 1);
+ if (!rl) {
+ BUG_ON(start_vcn);
+ if (stop_vcn)
+ *stop_vcn = 0;
+ /* Terminator byte. */
+ *dst = 0;
+ return 0;
+ }
+ /* Skip to runlist element containing @start_vcn. */
+ while (rl->length && start_vcn >= rl[1].vcn)
+ rl++;
+ if ((!rl->length && start_vcn > rl->vcn) || start_vcn < rl->vcn)
+ return -EINVAL;
+ /*
+ * @dst_max is used for bounds checking in
+ * ntfs_write_significant_bytes().
+ */
+ dst_max = dst + dst_len - 1;
+ prev_lcn = 0;
+ /* Do the first partial run if present. */
+ if (start_vcn > rl->vcn) {
+ s64 delta;
+
+ /* We know rl->length != 0 already. */
+ if (rl->length < 0 || rl->lcn < LCN_HOLE)
+ goto err_out;
+ delta = start_vcn - rl->vcn;
+ /* Write length. */
+ len_len = ntfs_write_significant_bytes(dst + 1, dst_max,
+ rl->length - delta);
+ if (len_len < 0)
+ goto size_err;
+ /*
+ * If the logical cluster number (lcn) denotes a hole and we
+ * are on NTFS 3.0+, we don't store it at all, i.e. we need
+ * zero space. On earlier NTFS versions we just write the lcn
+ * change. FIXME: Do we need to write the lcn change or just
+ * the lcn in that case? Not sure as I have never seen this
+ * case on NT4. - We assume that we just need to write the lcn
+ * change until someone tells us otherwise... (AIA)
+ */
+ if (rl->lcn >= 0 || vol->major_ver < 3) {
+ prev_lcn = rl->lcn;
+ if (rl->lcn >= 0)
+ prev_lcn += delta;
+ /* Write change in lcn. */
+ lcn_len = ntfs_write_significant_bytes(dst + 1 +
+ len_len, dst_max, prev_lcn);
+ if (lcn_len < 0)
+ goto size_err;
+ } else
+ lcn_len = 0;
+ dst_next = dst + len_len + lcn_len + 1;
+ if (dst_next > dst_max)
+ goto size_err;
+ /* Update header byte. */
+ *dst = lcn_len << 4 | len_len;
+ /* Position at next mapping pairs array element. */
+ dst = dst_next;
+ /* Go to next runlist element. */
+ rl++;
+ }
+ /* Do the full runs. */
+ for (; rl->length; rl++) {
+ if (rl->length < 0 || rl->lcn < LCN_HOLE)
+ goto err_out;
+ /* Write length. */
+ len_len = ntfs_write_significant_bytes(dst + 1, dst_max,
+ rl->length);
+ if (len_len < 0)
+ goto size_err;
+ /*
+ * If the logical cluster number (lcn) denotes a hole and we
+ * are on NTFS 3.0+, we don't store it at all, i.e. we need
+ * zero space. On earlier NTFS versions we just write the lcn
+ * change. FIXME: Do we need to write the lcn change or just
+ * the lcn in that case? Not sure as I have never seen this
+ * case on NT4. - We assume that we just need to write the lcn
+ * change until someone tells us otherwise... (AIA)
+ */
+ if (rl->lcn >= 0 || vol->major_ver < 3) {
+ /* Write change in lcn. */
+ lcn_len = ntfs_write_significant_bytes(dst + 1 +
+ len_len, dst_max, rl->lcn - prev_lcn);
+ if (lcn_len < 0)
+ goto size_err;
+ prev_lcn = rl->lcn;
+ } else
+ lcn_len = 0;
+ dst_next = dst + len_len + lcn_len + 1;
+ if (dst_next > dst_max)
+ goto size_err;
+ /* Update header byte. */
+ *dst = lcn_len << 4 | len_len;
+ /* Position at next mapping pairs array element. */
+ dst = dst_next;
+ }
+ /* Success. */
+ err = 0;
+size_err:
+ /* Set stop vcn. */
+ if (stop_vcn)
+ *stop_vcn = rl->vcn;
+ /* Add terminator byte. */
+ *dst = 0;
+ return err;
+err_out:
+ if (rl->lcn == LCN_RL_NOT_MAPPED)
+ err = -EINVAL;
+ else
+ err = -EIO;
+ return err;
+}
projects / linux / commitdiff