fs/squashfs/fragment.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  * 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  */
  73 __le64 *squashfs_read_fragment_index_table(struct super_block *sb,
  74         u64 fragment_table_start, unsigned int fragments)
  75 {
  76         unsigned int length = SQUASHFS_FRAGMENT_INDEX_BYTES(fragments);
  77         __le64 *fragment_index;
  78         int err;
  79
  80         /* Allocate fragment lookup table indexes */
  81         fragment_index = kmalloc(length, GFP_KERNEL);
  82         if (fragment_index == NULL) {
  83                 ERROR("Failed to allocate fragment index table\n");
  84                 return ERR_PTR(-ENOMEM);
  85         }
  86
  87         err = squashfs_read_table(sb, fragment_index, fragment_table_start,
  88                         length);
  89         if (err < 0) {
  90                 ERROR("unable to read fragment index table\n");
  91                 kfree(fragment_index);
  92                 return ERR_PTR(err);
  93         }
  94
  95         return fragment_index;
  96 }