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 if (!msblk->stream) 171 goto read_failure; 172 length = squashfs_decompress(msblk, bh, b, offset, length, 173 output); 174 if (length < 0) 175 goto read_failure; 176 } else { 177 /* 178 * Block is uncompressed. 179 */ 180 int in, pg_offset = 0; 181 void *data = squashfs_first_page(output); 182 183 for (bytes = length; k < b; k++) { 184 in = min(bytes, msblk->devblksize - offset); 185 bytes -= in; 186 while (in) { 187 if (pg_offset == PAGE_SIZE) { 188 data = squashfs_next_page(output); 189 pg_offset = 0; 190 } 191 avail = min_t(int, in, PAGE_SIZE - 192 pg_offset); 193 memcpy(data + pg_offset, bh[k]->b_data + offset, 194 avail); 195 in -= avail; 196 pg_offset += avail; 197 offset += avail; 198 } 199 offset = 0; 200 put_bh(bh[k]); 201 } 202 squashfs_finish_page(output); 203 } 204 205 kfree(bh); 206 return length; 207 208 block_release: 209 for (; k < b; k++) 210 put_bh(bh[k]); 211 212 read_failure: 213 ERROR("squashfs_read_data failed to read block 0x%llx\n", 214 (unsigned long long) index); 215 kfree(bh); 216 return -EIO; 217 } 218