Linux Kernel  3.7.1
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fragment.c
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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 <[email protected]>
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 
40 #include "squashfs_fs.h"
41 #include "squashfs_fs_sb.h"
42 #include "squashfs.h"
43 
44 /*
45  * Look-up fragment using the fragment index table. Return the on disk
46  * location of the fragment and its compressed size
47  */
48 int squashfs_frag_lookup(struct super_block *sb, unsigned int fragment,
49  u64 *fragment_block)
50 {
51  struct squashfs_sb_info *msblk = sb->s_fs_info;
52  int block = SQUASHFS_FRAGMENT_INDEX(fragment);
53  int offset = SQUASHFS_FRAGMENT_INDEX_OFFSET(fragment);
54  u64 start_block = le64_to_cpu(msblk->fragment_index[block]);
55  struct squashfs_fragment_entry fragment_entry;
56  int size;
57 
58  size = squashfs_read_metadata(sb, &fragment_entry, &start_block,
59  &offset, sizeof(fragment_entry));
60  if (size < 0)
61  return size;
62 
63  *fragment_block = le64_to_cpu(fragment_entry.start_block);
64  size = le32_to_cpu(fragment_entry.size);
65 
66  return size;
67 }
68 
69 
70 /*
71  * Read the uncompressed fragment lookup table indexes off disk into memory
72  */
74  u64 fragment_table_start, u64 next_table, unsigned int fragments)
75 {
76  unsigned int length = SQUASHFS_FRAGMENT_INDEX_BYTES(fragments);
77  __le64 *table;
78 
79  /*
80  * Sanity check, length bytes should not extend into the next table -
81  * this check also traps instances where fragment_table_start is
82  * incorrectly larger than the next table start
83  */
84  if (fragment_table_start + length > next_table)
85  return ERR_PTR(-EINVAL);
86 
87  table = squashfs_read_table(sb, fragment_table_start, length);
88 
89  /*
90  * table[0] points to the first fragment table metadata block, this
91  * should be less than fragment_table_start
92  */
93  if (!IS_ERR(table) && le64_to_cpu(table[0]) >= fragment_table_start) {
94  kfree(table);
95  return ERR_PTR(-EINVAL);
96  }
97 
98  return table;
99 }