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 } 215