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
  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 compression
  87  * algorithms).
  88  */
  89 int 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 in, pg_offset = 0;
 171
 172                 for (bytes = length; k < b; k++) {
 173                         in = min(bytes, msblk->devblksize - offset);
 174                         bytes -= in;
 175                         wait_on_buffer(bh[k]);
 176                         if (!buffer_uptodate(bh[k]))
 177                                 goto block_release;
 178                         while (in) {
 179                                 if (pg_offset == PAGE_CACHE_SIZE) {
 180                                         page++;
 181                                         pg_offset = 0;
 182                                 }
 183                                 avail = min_t(int, in, PAGE_CACHE_SIZE -
 184                                                 pg_offset);
 185                                 memcpy(buffer[page] + pg_offset,
 186                                                 bh[k]->b_data + offset, avail);
 187                                 in -= avail;
 188                                 pg_offset += avail;
 189                                 offset += avail;
 190                         }
 191                         offset = 0;
 192                         put_bh(bh[k]);
 193                 }
 194         }
 195
 196         kfree(bh);
 197         return length;
 198
 199 block_release:
 200         for (; k < b; k++)
 201                 put_bh(bh[k]);
 202
 203 read_failure:
 204         ERROR("squashfs_read_data failed to read block 0x%llx\n",
 205                                         (unsigned long long) index);
 206         kfree(bh);
 207         return -EIO;
 208 }