2fb2882f0fa7b1a1b656f68596ec740d10650cd9
[linux-3.10.git] / fs / squashfs / block.c
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.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
68         return bh;
69 }
70
71
72 /*
73  * Read and decompress a metadata block or datablock.  Length is non-zero
74  * if a datablock is being read (the size is stored elsewhere in the
75  * filesystem), otherwise the length is obtained from the first two bytes of
76  * the metadata block.  A bit in the length field indicates if the block
77  * is stored uncompressed in the filesystem (usually because compression
78  * generated a larger block - this does occasionally happen with zlib).
79  */
80 int squashfs_read_data(struct super_block *sb, void **buffer, u64 index,
81                         int length, u64 *next_index, int srclength, int pages)
82 {
83         struct squashfs_sb_info *msblk = sb->s_fs_info;
84         struct buffer_head **bh;
85         int offset = index & ((1 << msblk->devblksize_log2) - 1);
86         u64 cur_index = index >> msblk->devblksize_log2;
87         int bytes, compressed, b = 0, k = 0, page = 0, avail;
88
89         bh = kcalloc(((srclength + msblk->devblksize - 1)
90                 >> msblk->devblksize_log2) + 1, sizeof(*bh), GFP_KERNEL);
91         if (bh == NULL)
92                 return -ENOMEM;
93
94         if (length) {
95                 /*
96                  * Datablock.
97                  */
98                 bytes = -offset;
99                 compressed = SQUASHFS_COMPRESSED_BLOCK(length);
100                 length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
101                 if (next_index)
102                         *next_index = index + length;
103
104                 TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
105                         index, compressed ? "" : "un", length, srclength);
106
107                 if (length < 0 || length > srclength ||
108                                 (index + length) > msblk->bytes_used)
109                         goto read_failure;
110
111                 for (b = 0; bytes < length; b++, cur_index++) {
112                         bh[b] = sb_getblk(sb, cur_index);
113                         if (bh[b] == NULL)
114                                 goto block_release;
115                         bytes += msblk->devblksize;
116                 }
117                 ll_rw_block(READ, b, bh);
118         } else {
119                 /*
120                  * Metadata block.
121                  */
122                 if ((index + 2) > msblk->bytes_used)
123                         goto read_failure;
124
125                 bh[0] = get_block_length(sb, &cur_index, &offset, &length);
126                 if (bh[0] == NULL)
127                         goto read_failure;
128                 b = 1;
129
130                 bytes = msblk->devblksize - offset;
131                 compressed = SQUASHFS_COMPRESSED(length);
132                 length = SQUASHFS_COMPRESSED_SIZE(length);
133                 if (next_index)
134                         *next_index = index + length + 2;
135
136                 TRACE("Block @ 0x%llx, %scompressed size %d\n", index,
137                                 compressed ? "" : "un", length);
138
139                 if (length < 0 || length > srclength ||
140                                         (index + length) > msblk->bytes_used)
141                         goto block_release;
142
143                 for (; bytes < length; b++) {
144                         bh[b] = sb_getblk(sb, ++cur_index);
145                         if (bh[b] == NULL)
146                                 goto block_release;
147                         bytes += msblk->devblksize;
148                 }
149                 ll_rw_block(READ, b - 1, bh + 1);
150         }
151
152         if (compressed) {
153                 length = squashfs_decompress(msblk, buffer, bh, b, offset,
154                          length, srclength, pages);
155                 if (length < 0)
156                         goto read_failure;
157         } else {
158                 /*
159                  * Block is uncompressed.
160                  */
161                 int i, in, pg_offset = 0;
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                 for (bytes = length; k < b; k++) {
170                         in = min(bytes, msblk->devblksize - offset);
171                         bytes -= in;
172                         while (in) {
173                                 if (pg_offset == PAGE_CACHE_SIZE) {
174                                         page++;
175                                         pg_offset = 0;
176                                 }
177                                 avail = min_t(int, in, PAGE_CACHE_SIZE -
178                                                 pg_offset);
179                                 memcpy(buffer[page] + pg_offset,
180                                                 bh[k]->b_data + offset, avail);
181                                 in -= avail;
182                                 pg_offset += avail;
183                                 offset += avail;
184                         }
185                         offset = 0;
186                         put_bh(bh[k]);
187                 }
188         }
189
190         kfree(bh);
191         return length;
192
193 block_release:
194         for (; k < b; k++)
195                 put_bh(bh[k]);
196
197 read_failure:
198         ERROR("squashfs_read_data failed to read block 0x%llx\n",
199                                         (unsigned long long) index);
200         kfree(bh);
201         return -EIO;
202 }