fs/squashfs/block.c

   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 #include "page_actor.h"
  40
  41 /*
  42  * Read the metadata block length, this is stored in the first two
  43  * bytes of the metadata block.
  44  */
  45 static struct buffer_head *get_block_length(struct super_block *sb,
  46                         u64 *cur_index, int *offset, int *length)
  47 {
  48         struct squashfs_sb_info *msblk = sb->s_fs_info;
  49         struct buffer_head *bh;
  50
  51         bh = sb_bread(sb, *cur_index);
  52         if (bh == NULL)
  53                 return NULL;
  54
  55         if (msblk->devblksize - *offset == 1) {
  56                 *length = (unsigned char) bh->b_data[*offset];
  57                 put_bh(bh);
  58                 bh = sb_bread(sb, ++(*cur_index));
  59                 if (bh == NULL)
  60                         return NULL;
  61                 *length |= (unsigned char) bh->b_data[0] << 8;
  62                 *offset = 1;
  63         } else {
  64                 *length = (unsigned char) bh->b_data[*offset] |
  65                         (unsigned char) bh->b_data[*offset + 1] << 8;
  66                 *offset += 2;
  67
  68                 if (*offset == msblk->devblksize) {
  69                         put_bh(bh);
  70                         bh = sb_bread(sb, ++(*cur_index));
  71                         if (bh == NULL)
  72                                 return NULL;
  73                         *offset = 0;
  74                 }
  75         }
  76
  77         return bh;
  78 }
  79
  80
  81 /*
  82  * Read and decompress a metadata block or datablock.  Length is non-zero
  83  * if a datablock is being read (the size is stored elsewhere in the
  84  * filesystem), otherwise the length is obtained from the first two bytes of
  85  * the metadata block.  A bit in the length field indicates if the block
  86  * is stored uncompressed in the filesystem (usually because compression
  87  * generated a larger block - this does occasionally happen with compression
  88  * algorithms).
  89  */
  90 int squashfs_read_data(struct super_block *sb, u64 index, int length,
  91                 u64 *next_index, struct squashfs_page_actor *output)
  92 {
  93         struct squashfs_sb_info *msblk = sb->s_fs_info;
  94         struct buffer_head **bh;
  95         int offset = index & ((1 << msblk->devblksize_log2) - 1);
  96         u64 cur_index = index >> msblk->devblksize_log2;
  97         int bytes, compressed, b = 0, k = 0, avail, i;
  98
  99         bh = kcalloc(((output->length + msblk->devblksize - 1)
 100                 >> msblk->devblksize_log2) + 1, sizeof(*bh), GFP_KERNEL);
 101         if (bh == NULL)
 102                 return -ENOMEM;
 103
 104         if (length) {
 105                 /*
 106                  * Datablock.
 107                  */
 108                 bytes = -offset;
 109                 compressed = SQUASHFS_COMPRESSED_BLOCK(length);
 110                 length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
 111                 if (next_index)
 112                         *next_index = index + length;
 113
 114                 TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
 115                         index, compressed ? "" : "un", length, output->length);
 116
 117                 if (length < 0 || length > output->length ||
 118                                 (index + length) > msblk->bytes_used)
 119                         goto read_failure;
 120
 121                 for (b = 0; bytes < length; b++, cur_index++) {
 122                         bh[b] = sb_getblk(sb, cur_index);
 123                         if (bh[b] == NULL)
 124                                 goto block_release;
 125                         bytes += msblk->devblksize;
 126                 }
 127                 ll_rw_block(READ, b, bh);
 128         } else {
 129                 /*
 130                  * Metadata block.
 131                  */
 132                 if ((index + 2) > msblk->bytes_used)
 133                         goto read_failure;
 134
 135                 bh[0] = get_block_length(sb, &cur_index, &offset, &length);
 136                 if (bh[0] == NULL)
 137                         goto read_failure;
 138                 b = 1;
 139
 140                 bytes = msblk->devblksize - offset;
 141                 compressed = SQUASHFS_COMPRESSED(length);
 142                 length = SQUASHFS_COMPRESSED_SIZE(length);
 143                 if (next_index)
 144                         *next_index = index + length + 2;
 145
 146                 TRACE("Block @ 0x%llx, %scompressed size %d\n", index,
 147                                 compressed ? "" : "un", length);
 148
 149                 if (length < 0 || length > output->length ||
 150                                         (index + length) > msblk->bytes_used)
 151                         goto block_release;
 152
 153                 for (; bytes < length; b++) {
 154                         bh[b] = sb_getblk(sb, ++cur_index);
 155                         if (bh[b] == NULL)
 156                                 goto block_release;
 157                         bytes += msblk->devblksize;
 158                 }
 159                 ll_rw_block(READ, b - 1, bh + 1);
 160         }
 161
 162         for (i = 0; i < b; i++) {
 163                 wait_on_buffer(bh[i]);
 164                 if (!buffer_uptodate(bh[i]))
 165                         goto block_release;
 166         }
 167
 168         if (compressed) {
 169                 length = squashfs_decompress(msblk, bh, b, offset, length,
 170                         output);
 171                 if (length < 0)
 172                         goto read_failure;
 173         } else {
 174                 /*
 175                  * Block is uncompressed.
 176                  */
 177                 int in, pg_offset = 0;
 178                 void *data = squashfs_first_page(output);
 179
 180                 for (bytes = length; k < b; k++) {
 181                         in = min(bytes, msblk->devblksize - offset);
 182                         bytes -= in;
 183                         while (in) {
 184                                 if (pg_offset == PAGE_CACHE_SIZE) {
 185                                         data = squashfs_next_page(output);
 186                                         pg_offset = 0;
 187                                 }
 188                                 avail = min_t(int, in, PAGE_CACHE_SIZE -
 189                                                 pg_offset);
 190                                 memcpy(data + pg_offset, bh[k]->b_data + offset,
 191                                                 avail);
 192                                 in -= avail;
 193                                 pg_offset += avail;
 194                                 offset += avail;
 195                         }
 196                         offset = 0;
 197                         put_bh(bh[k]);
 198                 }
 199                 squashfs_finish_page(output);
 200         }
 201
 202         kfree(bh);
 203         return length;
 204
 205 block_release:
 206         for (; k < b; k++)
 207                 put_bh(bh[k]);
 208
 209 read_failure:
 210         ERROR("squashfs_read_data failed to read block 0x%llx\n",
 211                                         (unsigned long long) index);
 212         kfree(bh);
 213         return -EIO;
 214 }