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@lougher.demon.co.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  */
  44 static 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 zlib).
  87  */
  88 int squashfs_read_data(struct super_block *sb, void **buffer, u64 index,
  89                         int length, u64 *next_index, int srclength, int pages)
  90 {
  91         struct squashfs_sb_info *msblk = sb->s_fs_info;
  92         struct buffer_head **bh;
  93         int offset = index & ((1 << msblk->devblksize_log2) - 1);
  94         u64 cur_index = index >> msblk->devblksize_log2;
  95         int bytes, compressed, b = 0, k = 0, page = 0, avail;
  96
  97         bh = kcalloc(((srclength + msblk->devblksize - 1)
  98                 >> msblk->devblksize_log2) + 1, sizeof(*bh), GFP_KERNEL);
  99         if (bh == NULL)
 100                 return -ENOMEM;
 101
 102         if (length) {
 103                 /*
 104                  * Datablock.
 105                  */
 106                 bytes = -offset;
 107                 compressed = SQUASHFS_COMPRESSED_BLOCK(length);
 108                 length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
 109                 if (next_index)
 110                         *next_index = index + length;
 111
 112                 TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
 113                         index, compressed ? "" : "un", length, srclength);
 114
 115                 if (length < 0 || length > srclength ||
 116                                 (index + length) > msblk->bytes_used)
 117                         goto read_failure;
 118
 119                 for (b = 0; bytes < length; b++, cur_index++) {
 120                         bh[b] = sb_getblk(sb, cur_index);
 121                         if (bh[b] == NULL)
 122                                 goto block_release;
 123                         bytes += msblk->devblksize;
 124                 }
 125                 ll_rw_block(READ, b, bh);
 126         } else {
 127                 /*
 128                  * Metadata block.
 129                  */
 130                 if ((index + 2) > msblk->bytes_used)
 131                         goto read_failure;
 132
 133                 bh[0] = get_block_length(sb, &cur_index, &offset, &length);
 134                 if (bh[0] == NULL)
 135                         goto read_failure;
 136                 b = 1;
 137
 138                 bytes = msblk->devblksize - offset;
 139                 compressed = SQUASHFS_COMPRESSED(length);
 140                 length = SQUASHFS_COMPRESSED_SIZE(length);
 141                 if (next_index)
 142                         *next_index = index + length + 2;
 143
 144                 TRACE("Block @ 0x%llx, %scompressed size %d\n", index,
 145                                 compressed ? "" : "un", length);
 146
 147                 if (length < 0 || length > srclength ||
 148                                         (index + length) > msblk->bytes_used)
 149                         goto block_release;
 150
 151                 for (; bytes < length; b++) {
 152                         bh[b] = sb_getblk(sb, ++cur_index);
 153                         if (bh[b] == NULL)
 154                                 goto block_release;
 155                         bytes += msblk->devblksize;
 156                 }
 157                 ll_rw_block(READ, b - 1, bh + 1);
 158         }
 159
 160         if (compressed) {
 161                 length = squashfs_decompress(msblk, buffer, bh, b, offset,
 162                          length, srclength, pages);
 163                 if (length < 0)
 164                         goto read_failure;
 165         } else {
 166                 /*
 167                  * Block is uncompressed.
 168                  */
 169                 int i, in, pg_offset = 0;
 170
 171                 for (i = 0; i < b; i++) {
 172                         wait_on_buffer(bh[i]);
 173                         if (!buffer_uptodate(bh[i]))
 174                                 goto block_release;
 175                 }
 176
 177                 for (bytes = length; k < b; k++) {
 178                         in = min(bytes, msblk->devblksize - offset);
 179                         bytes -= in;
 180                         while (in) {
 181                                 if (pg_offset == PAGE_CACHE_SIZE) {
 182                                         page++;
 183                                         pg_offset = 0;
 184                                 }
 185                                 avail = min_t(int, in, PAGE_CACHE_SIZE -
 186                                                 pg_offset);
 187                                 memcpy(buffer[page] + pg_offset,
 188                                                 bh[k]->b_data + offset, avail);
 189                                 in -= avail;
 190                                 pg_offset += avail;
 191                                 offset += avail;
 192                         }
 193                         offset = 0;
 194                         put_bh(bh[k]);
 195                 }
 196         }
 197
 198         kfree(bh);
 199         return length;
 200
 201 block_release:
 202         for (; k < b; k++)
 203                 put_bh(bh[k]);
 204
 205 read_failure:
 206         ERROR("squashfs_read_data failed to read block 0x%llx\n",
 207                                         (unsigned long long) index);
 208         kfree(bh);
 209         return -EIO;
 210 }