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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 */
44static 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 */
89int 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
202block_release:
203 for (; k < b; k++)
204 put_bh(bh[k]);
205
206read_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}