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@lougher.demon.co.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_fs_i.h" 38 #include "squashfs.h" 39 #include "decompressor.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 69 return bh; 70 } 71 72 73 /* 74 * Read and decompress a metadata block or datablock. Length is non-zero 75 * if a datablock is being read (the size is stored elsewhere in the 76 * filesystem), otherwise the length is obtained from the first two bytes of 77 * the metadata block. A bit in the length field indicates if the block 78 * is stored uncompressed in the filesystem (usually because compression 79 * generated a larger block - this does occasionally happen with zlib). 80 */ 81 int squashfs_read_data(struct super_block *sb, void **buffer, u64 index, 82 int length, u64 *next_index, int srclength, int pages) 83 { 84 struct squashfs_sb_info *msblk = sb->s_fs_info; 85 struct buffer_head **bh; 86 int offset = index & ((1 << msblk->devblksize_log2) - 1); 87 u64 cur_index = index >> msblk->devblksize_log2; 88 int bytes, compressed, b = 0, k = 0, page = 0, avail; 89 90 bh = kcalloc(((srclength + msblk->devblksize - 1) 91 >> msblk->devblksize_log2) + 1, sizeof(*bh), GFP_KERNEL); 92 if (bh == NULL) 93 return -ENOMEM; 94 95 if (length) { 96 /* 97 * Datablock. 98 */ 99 bytes = -offset; 100 compressed = SQUASHFS_COMPRESSED_BLOCK(length); 101 length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length); 102 if (next_index) 103 *next_index = index + length; 104 105 TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n", 106 index, compressed ? "" : "un", length, srclength); 107 108 if (length < 0 || length > srclength || 109 (index + length) > msblk->bytes_used) 110 goto read_failure; 111 112 for (b = 0; bytes < length; b++, cur_index++) { 113 bh[b] = sb_getblk(sb, cur_index); 114 if (bh[b] == NULL) 115 goto block_release; 116 bytes += msblk->devblksize; 117 } 118 ll_rw_block(READ, b, bh); 119 } else { 120 /* 121 * Metadata block. 122 */ 123 if ((index + 2) > msblk->bytes_used) 124 goto read_failure; 125 126 bh[0] = get_block_length(sb, &cur_index, &offset, &length); 127 if (bh[0] == NULL) 128 goto read_failure; 129 b = 1; 130 131 bytes = msblk->devblksize - offset; 132 compressed = SQUASHFS_COMPRESSED(length); 133 length = SQUASHFS_COMPRESSED_SIZE(length); 134 if (next_index) 135 *next_index = index + length + 2; 136 137 TRACE("Block @ 0x%llx, %scompressed size %d\n", index, 138 compressed ? "" : "un", length); 139 140 if (length < 0 || length > srclength || 141 (index + length) > msblk->bytes_used) 142 goto block_release; 143 144 for (; bytes < length; b++) { 145 bh[b] = sb_getblk(sb, ++cur_index); 146 if (bh[b] == NULL) 147 goto block_release; 148 bytes += msblk->devblksize; 149 } 150 ll_rw_block(READ, b - 1, bh + 1); 151 } 152 153 if (compressed) { 154 length = squashfs_decompress(msblk, buffer, bh, b, offset, 155 length, srclength, pages); 156 if (length < 0) 157 goto read_failure; 158 } else { 159 /* 160 * Block is uncompressed. 161 */ 162 int i, in, pg_offset = 0; 163 164 for (i = 0; i < b; i++) { 165 wait_on_buffer(bh[i]); 166 if (!buffer_uptodate(bh[i])) 167 goto block_release; 168 } 169 170 for (bytes = length; k < b; k++) { 171 in = min(bytes, msblk->devblksize - offset); 172 bytes -= in; 173 while (in) { 174 if (pg_offset == PAGE_CACHE_SIZE) { 175 page++; 176 pg_offset = 0; 177 } 178 avail = min_t(int, in, PAGE_CACHE_SIZE - 179 pg_offset); 180 memcpy(buffer[page] + pg_offset, 181 bh[k]->b_data + offset, avail); 182 in -= avail; 183 pg_offset += avail; 184 offset += avail; 185 } 186 offset = 0; 187 put_bh(bh[k]); 188 } 189 } 190 191 kfree(bh); 192 return length; 193 194 block_release: 195 for (; k < b; k++) 196 put_bh(bh[k]); 197 198 read_failure: 199 ERROR("squashfs_read_data failed to read block 0x%llx\n", 200 (unsigned long long) index); 201 kfree(bh); 202 return -EIO; 203 } 204