linux/fs/squashfs/block.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 * block.c
  22 */
  23
  24/*
  25 * This file implements the low-level routines to read and decompress
  26 * datablocks and metadata blocks.
  27 */
  28
  29#include <linux/fs.h>
  30#include <linux/vfs.h>
  31#include <linux/slab.h>
  32#include <linux/string.h>
  33#include <linux/buffer_head.h>
  34
  35#include "squashfs_fs.h"
  36#include "squashfs_fs_sb.h"
  37#include "squashfs.h"
  38#include "decompressor.h"
  39
  40/*
  41 * Read the metadata block length, this is stored in the first two
  42 * bytes of the metadata block.
  43 */
  44static struct buffer_head *get_block_length(struct super_block *sb,
  45                        u64 *cur_index, int *offset, int *length)
  46{
  47        struct squashfs_sb_info *msblk = sb->s_fs_info;
  48        struct buffer_head *bh;
  49
  50        bh = sb_bread(sb, *cur_index);
  51        if (bh == NULL)
  52                return NULL;
  53
  54        if (msblk->devblksize - *offset == 1) {
  55                *length = (unsigned char) bh->b_data[*offset];
  56                put_bh(bh);
  57                bh = sb_bread(sb, ++(*cur_index));
  58                if (bh == NULL)
  59                        return NULL;
  60                *length |= (unsigned char) bh->b_data[0] << 8;
  61                *offset = 1;
  62        } else {
  63                *length = (unsigned char) bh->b_data[*offset] |
  64                        (unsigned char) bh->b_data[*offset + 1] << 8;
  65                *offset += 2;
  66
  67                if (*offset == msblk->devblksize) {
  68                        put_bh(bh);
  69                        bh = sb_bread(sb, ++(*cur_index));
  70                        if (bh == NULL)
  71                                return NULL;
  72                        *offset = 0;
  73                }
  74        }
  75
  76        return bh;
  77}
  78
  79
  80/*
  81 * Read and decompress a metadata block or datablock.  Length is non-zero
  82 * if a datablock is being read (the size is stored elsewhere in the
  83 * filesystem), otherwise the length is obtained from the first two bytes of
  84 * the metadata block.  A bit in the length field indicates if the block
  85 * is stored uncompressed in the filesystem (usually because compression
  86 * generated a larger block - this does occasionally happen with compression
  87 * algorithms).
  88 */
  89int squashfs_read_data(struct super_block *sb, void **buffer, u64 index,
  90                        int length, u64 *next_index, int srclength, int pages)
  91{
  92        struct squashfs_sb_info *msblk = sb->s_fs_info;
  93        struct buffer_head **bh;
  94        int offset = index & ((1 << msblk->devblksize_log2) - 1);
  95        u64 cur_index = index >> msblk->devblksize_log2;
  96        int bytes, compressed, b = 0, k = 0, page = 0, avail;
  97
  98        bh = kcalloc(((srclength + msblk->devblksize - 1)
  99                >> msblk->devblksize_log2) + 1, sizeof(*bh), GFP_KERNEL);
 100        if (bh == NULL)
 101                return -ENOMEM;
 102
 103        if (length) {
 104                /*
 105                 * Datablock.
 106                 */
 107                bytes = -offset;
 108                compressed = SQUASHFS_COMPRESSED_BLOCK(length);
 109                length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
 110                if (next_index)
 111                        *next_index = index + length;
 112
 113                TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
 114                        index, compressed ? "" : "un", length, srclength);
 115
 116                if (length < 0 || length > srclength ||
 117                                (index + length) > msblk->bytes_used)
 118                        goto read_failure;
 119
 120                for (b = 0; bytes < length; b++, cur_index++) {
 121                        bh[b] = sb_getblk(sb, cur_index);
 122                        if (bh[b] == NULL)
 123                                goto block_release;
 124                        bytes += msblk->devblksize;
 125                }
 126                ll_rw_block(READ, b, bh);
 127        } else {
 128                /*
 129                 * Metadata block.
 130                 */
 131                if ((index + 2) > msblk->bytes_used)
 132                        goto read_failure;
 133
 134                bh[0] = get_block_length(sb, &cur_index, &offset, &length);
 135                if (bh[0] == NULL)
 136                        goto read_failure;
 137                b = 1;
 138
 139                bytes = msblk->devblksize - offset;
 140                compressed = SQUASHFS_COMPRESSED(length);
 141                length = SQUASHFS_COMPRESSED_SIZE(length);
 142                if (next_index)
 143                        *next_index = index + length + 2;
 144
 145                TRACE("Block @ 0x%llx, %scompressed size %d\n", index,
 146                                compressed ? "" : "un", length);
 147
 148                if (length < 0 || length > srclength ||
 149                                        (index + length) > msblk->bytes_used)
 150                        goto block_release;
 151
 152                for (; bytes < length; b++) {
 153                        bh[b] = sb_getblk(sb, ++cur_index);
 154                        if (bh[b] == NULL)
 155                                goto block_release;
 156                        bytes += msblk->devblksize;
 157                }
 158                ll_rw_block(READ, b - 1, bh + 1);
 159        }
 160
 161        if (compressed) {
 162                length = squashfs_decompress(msblk, buffer, bh, b, offset,
 163                         length, srclength, pages);
 164                if (length < 0)
 165                        goto read_failure;
 166        } else {
 167                /*
 168                 * Block is uncompressed.
 169                 */
 170                int i, in, pg_offset = 0;
 171
 172                for (i = 0; i < b; i++) {
 173                        wait_on_buffer(bh[i]);
 174                        if (!buffer_uptodate(bh[i]))
 175                                goto block_release;
 176                }
 177
 178                for (bytes = length; k < b; k++) {
 179                        in = min(bytes, msblk->devblksize - offset);
 180                        bytes -= in;
 181                        while (in) {
 182                                if (pg_offset == PAGE_CACHE_SIZE) {
 183                                        page++;
 184                                        pg_offset = 0;
 185                                }
 186                                avail = min_t(int, in, PAGE_CACHE_SIZE -
 187                                                pg_offset);
 188                                memcpy(buffer[page] + pg_offset,
 189                                                bh[k]->b_data + offset, avail);
 190                                in -= avail;
 191                                pg_offset += avail;
 192                                offset += avail;
 193                        }
 194                        offset = 0;
 195                        put_bh(bh[k]);
 196                }
 197        }
 198
 199        kfree(bh);
 200        return length;
 201
 202block_release:
 203        for (; k < b; k++)
 204                put_bh(bh[k]);
 205
 206read_failure:
 207        ERROR("squashfs_read_data failed to read block 0x%llx\n",
 208                                        (unsigned long long) index);
 209        kfree(bh);
 210        return -EIO;
 211}
 212
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