linux/fs/squashfs/fragment.c
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   1/*
   2 * Squashfs - a compressed read only filesystem for Linux
   3 *
   4 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
   5 * Phillip Lougher <phillip@squashfs.org.uk>
   6 *
   7 * This program is free software; you can redistribute it and/or
   8 * modify it under the terms of the GNU General Public License
   9 * as published by the Free Software Foundation; either version 2,
  10 * or (at your option) any later version.
  11 *
  12 * This program is distributed in the hope that it will be useful,
  13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 * GNU General Public License for more details.
  16 *
  17 * You should have received a copy of the GNU General Public License
  18 * along with this program; if not, write to the Free Software
  19 * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  20 *
  21 * fragment.c
  22 */
  23
  24/*
  25 * This file implements code to handle compressed fragments (tail-end packed
  26 * datablocks).
  27 *
  28 * Regular files contain a fragment index which is mapped to a fragment
  29 * location on disk and compressed size using a fragment lookup table.
  30 * Like everything in Squashfs this fragment lookup table is itself stored
  31 * compressed into metadata blocks.  A second index table is used to locate
  32 * these.  This second index table for speed of access (and because it
  33 * is small) is read at mount time and cached in memory.
  34 */
  35
  36#include <linux/fs.h>
  37#include <linux/vfs.h>
  38#include <linux/slab.h>
  39
  40#include "squashfs_fs.h"
  41#include "squashfs_fs_sb.h"
  42#include "squashfs.h"
  43
  44/*
  45 * Look-up fragment using the fragment index table.  Return the on disk
  46 * location of the fragment and its compressed size
  47 */
  48int squashfs_frag_lookup(struct super_block *sb, unsigned int fragment,
  49                                u64 *fragment_block)
  50{
  51        struct squashfs_sb_info *msblk = sb->s_fs_info;
  52        int block = SQUASHFS_FRAGMENT_INDEX(fragment);
  53        int offset = SQUASHFS_FRAGMENT_INDEX_OFFSET(fragment);
  54        u64 start_block = le64_to_cpu(msblk->fragment_index[block]);
  55        struct squashfs_fragment_entry fragment_entry;
  56        int size;
  57
  58        size = squashfs_read_metadata(sb, &fragment_entry, &start_block,
  59                                        &offset, sizeof(fragment_entry));
  60        if (size < 0)
  61                return size;
  62
  63        *fragment_block = le64_to_cpu(fragment_entry.start_block);
  64        size = le32_to_cpu(fragment_entry.size);
  65
  66        return size;
  67}
  68
  69
  70/*
  71 * Read the uncompressed fragment lookup table indexes off disk into memory
  72 */
  73__le64 *squashfs_read_fragment_index_table(struct super_block *sb,
  74        u64 fragment_table_start, u64 next_table, unsigned int fragments)
  75{
  76        unsigned int length = SQUASHFS_FRAGMENT_INDEX_BYTES(fragments);
  77        __le64 *table;
  78
  79        /*
  80         * Sanity check, length bytes should not extend into the next table -
  81         * this check also traps instances where fragment_table_start is
  82         * incorrectly larger than the next table start
  83         */
  84        if (fragment_table_start + length > next_table)
  85                return ERR_PTR(-EINVAL);
  86
  87        table = squashfs_read_table(sb, fragment_table_start, length);
  88
  89        /*
  90         * table[0] points to the first fragment table metadata block, this
  91         * should be less than fragment_table_start
  92         */
  93        if (!IS_ERR(table) && le64_to_cpu(table[0]) >= fragment_table_start) {
  94                kfree(table);
  95                return ERR_PTR(-EINVAL);
  96        }
  97
  98        return table;
  99}
 100
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