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cantab.net!aia21
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/*
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* compress.c - Compressed attribute handling code. Part of the Linux-NTFS
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* project.
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*
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* Copyright (c) 2004 Anton Altaparmakov
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*
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* This program/include file is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as published
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* by the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program/include file is distributed in the hope that it will be
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* useful, but WITHOUT ANY WARRANTY; without even the implied warranty
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* of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program (in the main directory of the Linux-NTFS
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* distribution in the file COPYING); if not, write to the Free Software
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* Foundation,Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#include <stdio.h>
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#include <string.h>
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#include <stdlib.h>
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#include <errno.h>
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#include "attrib.h"
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#include "debug.h"
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#include "volume.h"
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#include "types.h"
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#include "layout.h"
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#include "runlist.h"
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/**
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* ntfs_compressed_attr_pread - read from a compressed attribute
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* @na: ntfs attribute to read from
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* @pos: byte position in the attribute to begin reading from
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* @count: number of bytes to read
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* @b: output data buffer
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*
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* NOTE: You probably want to be using attrib.c::ntfs_attr_pread() instead.
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*
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* This function will read @count bytes starting at offset @pos from the
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* compressed ntfs attribute @na into the data buffer @b.
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*
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* On success, return the number of successfully read bytes. If this number
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* is lower than @count this means that the read reached end of file or that
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* an error was encountered during the read so that the read is partial.
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* 0 means end of file or nothing was read (also return 0 when @count is 0).
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*
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* On error and nothing has been read, return -1 with errno set appropriately
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* to the return code of ntfs_pread(), or to EINVAL in case of invalid
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* arguments.
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*/
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s64 ntfs_compressed_attr_pread(ntfs_attr *na, const s64 pos, s64 count,
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void *b)
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{
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s64 br, to_read, ofs, total, total2;
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u64 cb_size_mask;
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VCN start_vcn, end_vcn;
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ntfs_volume *vol;
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runlist_element *rl;
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u8 *ntfs_compression_buffer, *ntfs_uncompressed_buffer;
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u8 *cb, *cb_pos, *cb_end;
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u32 cb_size;
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unsigned int nr_cbs, cb_clusters;
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Dprintf("%s(): Entering for inode 0x%Lx, attr 0x%x, pos 0x%Lx, "
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"count 0x%Lx.\n", __FUNCTION__,
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(unsigned long long)na->ni->mft_no, na->type,
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(long long)pos, (long long)count);
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if (!na || !NAttrCompressed(na) || !na->ni || !na->ni->vol || !b ||
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pos < 0 || count < 0) {
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errno = EINVAL;
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return -1;
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}
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/*
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* Encrypted attributes are not supported. We return access denied,
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* which is what Windows NT4 does, too.
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*/
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if (NAttrEncrypted(na)) {
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errno = EACCES;
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return -1;
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}
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if (!count)
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return 0;
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/* Truncate reads beyond end of attribute. */
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if (pos + count > na->data_size) {
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if (pos >= na->data_size)
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return 0;
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count = na->data_size - pos;
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}
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/* If it is a resident attribute, simply use ntfs_attr_pread(). */
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if (!NAttrNonResident(na))
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return ntfs_attr_pread(na, pos, count, b);
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total = total2 = 0;
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/* Zero out reads beyond initialized size. */
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if (pos + count > na->initialized_size) {
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if (pos >= na->initialized_size) {
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memset(b, 0, count);
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return count;
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}
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total2 = pos + count - na->initialized_size;
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count -= total2;
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memset((u8*)b + count, 0, total2);
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}
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vol = na->ni->vol;
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cb_size = na->compression_block_size;
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cb_size_mask = cb_size - 1UL;
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cb_clusters = na->compression_block_clusters;
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/* Need a temporary buffer for each loaded compression block. */
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ntfs_compression_buffer = malloc(cb_size);
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if (!ntfs_compression_buffer)
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return -1;
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/* Need a temporary buffer for each uncompressed block. */
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ntfs_uncompressed_buffer = malloc(cb_size);
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if (!ntfs_uncompressed_buffer) {
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int eo = errno;
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free(ntfs_compression_buffer);
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errno = eo;
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return -1;
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}
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/*
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* The first vcn in the first compression block (cb) which we need to
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* decompress.
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*/
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start_vcn = (pos & ~cb_size_mask) >> vol->cluster_size_bits;
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/*
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* The first vcn in the cb after the last cb which we need to
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* decompress.
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*/
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end_vcn = ((pos + count + cb_size - 1) & ~cb_size_mask) >>
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vol->cluster_size_bits;
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/* Number of compression blocks (cbs) in the wanted vcn range. */
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nr_cbs = (end_vcn - start_vcn) << vol->cluster_size_bits >>
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na->compression_block_size_bits;
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do_next_cb:
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nr_cbs--;
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cb_pos = cb = ntfs_compression_buffer;
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cb_end = cb + cb_size;
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// FIXME: I am here... (AIA)
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free(ntfs_compression_buffer);
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free(ntfs_uncompressed_buffer);
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errno = ENOTSUP;
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return -1;
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/* Find the runlist element containing the vcn. */
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rl = ntfs_attr_find_vcn(na, pos >> vol->cluster_size_bits);
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if (!rl) {
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/*
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* If the vcn is not present it is an out of bounds read.
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* However, we already truncated the read to the data_size,
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* so getting this here is an error.
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*/
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if (errno == ENOENT)
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errno = EIO;
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return -1;
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}
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/*
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* Gather the requested data into the linear destination buffer. Note,
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* a partial final vcn is taken care of by the @count capping of read
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* length.
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*/
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ofs = pos - (rl->vcn << vol->cluster_size_bits);
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for (; count; rl++, ofs = 0) {
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if (!rl->length)
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goto rl_err_out;
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if (rl->lcn < (LCN)0) {
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if (rl->lcn != (LCN)LCN_HOLE)
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goto rl_err_out;
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/* It is a hole, just zero the matching @b range. */
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to_read = min(count, (rl->length <<
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vol->cluster_size_bits) - ofs);
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memset(b, 0, to_read);
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/* Update progress counters. */
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total += to_read;
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count -= to_read;
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(u8*)b += to_read;
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continue;
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}
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/* It is a real lcn, read it into @dst. */
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to_read = min(count, (rl->length << vol->cluster_size_bits) -
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ofs);
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retry:
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Dprintf("%s(): Reading 0x%Lx bytes from vcn 0x%Lx, lcn 0x%Lx, "
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"ofs 0x%Lx.\n", __FUNCTION__, to_read,
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rl->vcn, rl->lcn, ofs);
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br = ntfs_pread(vol->dev, (rl->lcn << vol->cluster_size_bits) +
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ofs, to_read, b);
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/* If everything ok, update progress counters and continue. */
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if (br > 0) {
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total += br;
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count -= br;
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(u8*)b += br;
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continue;
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}
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/* If the syscall was interrupted, try again. */
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if (br == (s64)-1 && errno == EINTR)
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goto retry;
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if (total)
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return total;
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if (!br)
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errno = EIO;
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return -1;
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}
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/* Finally, return the number of bytes read. */
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return total + total2;
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rl_err_out:
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if (total)
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return total;
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errno = EIO;
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return -1;
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}
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