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122edd15 PL |
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 | * fragment.c | |
22 | */ | |
23 | ||
24 | /* | |
25 | * This file implements code to handle compressed fragments (tail-end packed | |
26 | * datablocks). | |
27 | * | |
28 | * Regular files contain a fragment index which is mapped to a fragment | |
29 | * location on disk and compressed size using a fragment lookup table. | |
30 | * Like everything in Squashfs this fragment lookup table is itself stored | |
31 | * compressed into metadata blocks. A second index table is used to locate | |
32 | * these. This second index table for speed of access (and because it | |
33 | * is small) is read at mount time and cached in memory. | |
34 | */ | |
35 | ||
36 | #include <linux/fs.h> | |
37 | #include <linux/vfs.h> | |
38 | #include <linux/slab.h> | |
39 | #include <linux/zlib.h> | |
40 | ||
41 | #include "squashfs_fs.h" | |
42 | #include "squashfs_fs_sb.h" | |
43 | #include "squashfs_fs_i.h" | |
44 | #include "squashfs.h" | |
45 | ||
46 | /* | |
47 | * Look-up fragment using the fragment index table. Return the on disk | |
48 | * location of the fragment and its compressed size | |
49 | */ | |
50 | int squashfs_frag_lookup(struct super_block *sb, unsigned int fragment, | |
51 | u64 *fragment_block) | |
52 | { | |
53 | struct squashfs_sb_info *msblk = sb->s_fs_info; | |
54 | int block = SQUASHFS_FRAGMENT_INDEX(fragment); | |
55 | int offset = SQUASHFS_FRAGMENT_INDEX_OFFSET(fragment); | |
56 | u64 start_block = le64_to_cpu(msblk->fragment_index[block]); | |
57 | struct squashfs_fragment_entry fragment_entry; | |
58 | int size; | |
59 | ||
60 | size = squashfs_read_metadata(sb, &fragment_entry, &start_block, | |
61 | &offset, sizeof(fragment_entry)); | |
62 | if (size < 0) | |
63 | return size; | |
64 | ||
65 | *fragment_block = le64_to_cpu(fragment_entry.start_block); | |
66 | size = le32_to_cpu(fragment_entry.size); | |
67 | ||
68 | return size; | |
69 | } | |
70 | ||
71 | ||
72 | /* | |
73 | * Read the uncompressed fragment lookup table indexes off disk into memory | |
74 | */ | |
75 | __le64 *squashfs_read_fragment_index_table(struct super_block *sb, | |
76 | u64 fragment_table_start, unsigned int fragments) | |
77 | { | |
78 | unsigned int length = SQUASHFS_FRAGMENT_INDEX_BYTES(fragments); | |
79 | __le64 *fragment_index; | |
80 | int err; | |
81 | ||
82 | /* Allocate fragment lookup table indexes */ | |
83 | fragment_index = kmalloc(length, GFP_KERNEL); | |
84 | if (fragment_index == NULL) { | |
85 | ERROR("Failed to allocate fragment index table\n"); | |
86 | return ERR_PTR(-ENOMEM); | |
87 | } | |
88 | ||
89 | err = squashfs_read_table(sb, fragment_index, fragment_table_start, | |
90 | length); | |
91 | if (err < 0) { | |
92 | ERROR("unable to read fragment index table\n"); | |
93 | kfree(fragment_index); | |
94 | return ERR_PTR(err); | |
95 | } | |
96 | ||
97 | return fragment_index; | |
98 | } |