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 i, in, pg_offset = 0; 171 172 for (i = 0; i < b; i++) { 173 wait_on_buffer(bh[i]); 174 if (!buffer_uptodate(bh[i])) 175 goto block_release; 176 } 177 178 for (bytes = length; k < b; k++) { 179 in = min(bytes, msblk->devblksize - offset); 180 bytes -= in; 181 while (in) { 182 if (pg_offset == PAGE_CACHE_SIZE) { 183 page++; 184 pg_offset = 0; 185 } 186 avail = min_t(int, in, PAGE_CACHE_SIZE - 187 pg_offset); 188 memcpy(buffer[page] + pg_offset, 189 bh[k]->b_data + offset, avail); 190 in -= avail; 191 pg_offset += avail; 192 offset += avail; 193 } 194 offset = 0; 195 put_bh(bh[k]); 196 } 197 } 198 199 kfree(bh); 200 return length; 201 202 block_release: 203 for (; k < b; k++) 204 put_bh(bh[k]); 205 206 read_failure: 207 ERROR("squashfs_read_data failed to read block 0x%llx\n", 208 (unsigned long long) index); 209 kfree(bh); 210 return -EIO; 211 } 212