| Phillip Lougher | 122edd1 | 2009-01-05 08:46:25 +0000 | [diff] [blame] | 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 | } |