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 #include <linux/bio.h>
  35
  36 #include "squashfs_fs.h"
  37 #include "squashfs_fs_sb.h"
  38 #include "squashfs.h"
  39 #include "decompressor.h"
  40 #include "page_actor.h"
  41
  42 /*
  43  * Read the metadata block length, this is stored in the first two
  44  * bytes of the metadata block.
  45  */
  46 static struct buffer_head *get_block_length(struct super_block *sb,
  47                         u64 *cur_index, int *offset, int *length)
  48 {
  49         struct squashfs_sb_info *msblk = sb->s_fs_info;
  50         struct buffer_head *bh;
  51
  52         bh = sb_bread(sb, *cur_index);
  53         if (bh == NULL)
  54                 return NULL;
  55
  56         if (msblk->devblksize - *offset == 1) {
  57                 *length = (unsigned char) bh->b_data[*offset];
  58                 put_bh(bh);
  59                 bh = sb_bread(sb, ++(*cur_index));
  60                 if (bh == NULL)
  61                         return NULL;
  62                 *length |= (unsigned char) bh->b_data[0] << 8;
  63                 *offset = 1;
  64         } else {
  65                 *length = (unsigned char) bh->b_data[*offset] |
  66                         (unsigned char) bh->b_data[*offset + 1] << 8;
  67                 *offset += 2;
  68
  69                 if (*offset == msblk->devblksize) {
  70                         put_bh(bh);
  71                         bh = sb_bread(sb, ++(*cur_index));
  72                         if (bh == NULL)
  73                                 return NULL;
  74                         *offset = 0;
  75                 }
  76         }
  77
  78         return bh;
  79 }
  80
  81
  82 /*
  83  * Read and decompress a metadata block or datablock.  Length is non-zero
  84  * if a datablock is being read (the size is stored elsewhere in the
  85  * filesystem), otherwise the length is obtained from the first two bytes of
  86  * the metadata block.  A bit in the length field indicates if the block
  87  * is stored uncompressed in the filesystem (usually because compression
  88  * generated a larger block - this does occasionally happen with compression
  89  * algorithms).
  90  */
  91 int squashfs_read_data(struct super_block *sb, u64 index, int length,
  92                 u64 *next_index, struct squashfs_page_actor *output)
  93 {
  94         struct squashfs_sb_info *msblk = sb->s_fs_info;
  95         struct buffer_head **bh;
  96         int offset = index & ((1 << msblk->devblksize_log2) - 1);
  97         u64 cur_index = index >> msblk->devblksize_log2;
  98         int bytes, compressed, b = 0, k = 0, avail, i;
  99
 100         bh = kcalloc(((output->length + msblk->devblksize - 1)
 101                 >> msblk->devblksize_log2) + 1, sizeof(*bh), GFP_KERNEL);
 102         if (bh == NULL)
 103                 return -ENOMEM;
 104
 105         if (length) {
 106                 /*
 107                  * Datablock.
 108                  */
 109                 bytes = -offset;
 110                 compressed = SQUASHFS_COMPRESSED_BLOCK(length);
 111                 length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
 112                 if (next_index)
 113                         *next_index = index + length;
 114
 115                 TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
 116                         index, compressed ? "" : "un", length, output->length);
 117
 118                 if (length < 0 || length > output->length ||
 119                                 (index + length) > msblk->bytes_used)
 120                         goto read_failure;
 121
 122                 for (b = 0; bytes < length; b++, cur_index++) {
 123                         bh[b] = sb_getblk(sb, cur_index);
 124                         if (bh[b] == NULL)
 125                                 goto block_release;
 126                         bytes += msblk->devblksize;
 127                 }
 128                 ll_rw_block(REQ_OP_READ, 0, b, bh);
 129         } else {
 130                 /*
 131                  * Metadata block.
 132                  */
 133                 if ((index + 2) > msblk->bytes_used)
 134                         goto read_failure;
 135
 136                 bh[0] = get_block_length(sb, &cur_index, &offset, &length);
 137                 if (bh[0] == NULL)
 138                         goto read_failure;
 139                 b = 1;
 140
 141                 bytes = msblk->devblksize - offset;
 142                 compressed = SQUASHFS_COMPRESSED(length);
 143                 length = SQUASHFS_COMPRESSED_SIZE(length);
 144                 if (next_index)
 145                         *next_index = index + length + 2;
 146
 147                 TRACE("Block @ 0x%llx, %scompressed size %d\n", index,
 148                                 compressed ? "" : "un", length);
 149
 150                 if (length < 0 || length > output->length ||
 151                                         (index + length) > msblk->bytes_used)
 152                         goto block_release;
 153
 154                 for (; bytes < length; b++) {
 155                         bh[b] = sb_getblk(sb, ++cur_index);
 156                         if (bh[b] == NULL)
 157                                 goto block_release;
 158                         bytes += msblk->devblksize;
 159                 }
 160                 ll_rw_block(REQ_OP_READ, 0, b - 1, bh + 1);
 161         }
 162
 163         for (i = 0; i < b; i++) {
 164                 wait_on_buffer(bh[i]);
 165                 if (!buffer_uptodate(bh[i]))
 166                         goto block_release;
 167         }
 168
 169         if (compressed) {
 170                 length = squashfs_decompress(msblk, bh, b, offset, length,
 171                         output);
 172                 if (length < 0)
 173                         goto read_failure;
 174         } else {
 175                 /*
 176                  * Block is uncompressed.
 177                  */
 178                 int in, pg_offset = 0;
 179                 void *data = squashfs_first_page(output);
 180
 181                 for (bytes = length; k < b; k++) {
 182                         in = min(bytes, msblk->devblksize - offset);
 183                         bytes -= in;
 184                         while (in) {
 185                                 if (pg_offset == PAGE_SIZE) {
 186                                         data = squashfs_next_page(output);
 187                                         pg_offset = 0;
 188                                 }
 189                                 avail = min_t(int, in, PAGE_SIZE -
 190                                                 pg_offset);
 191                                 memcpy(data + pg_offset, bh[k]->b_data + offset,
 192                                                 avail);
 193                                 in -= avail;
 194                                 pg_offset += avail;
 195                                 offset += avail;
 196                         }
 197                         offset = 0;
 198                         put_bh(bh[k]);
 199                 }
 200                 squashfs_finish_page(output);
 201         }
 202
 203         kfree(bh);
 204         return length;
 205
 206 block_release:
 207         for (; k < b; k++)
 208                 put_bh(bh[k]);
 209
 210 read_failure:
 211         ERROR("squashfs_read_data failed to read block 0x%llx\n",
 212                                         (unsigned long long) index);
 213         kfree(bh);
 214         return -EIO;
 215 }