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 */
get_block_length(struct super_block * sb,u64 * cur_index,int * offset,int * length)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 */
squashfs_read_data(struct super_block * sb,u64 index,int length,u64 * next_index,struct squashfs_page_actor * output)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