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Squashfs: fragment block operations

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Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
This commit is contained in:
Phillip Lougher 2009-01-05 08:46:25 +00:00
parent 122601408d
commit 122edd1514
1 changed files with 98 additions and 0 deletions
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fs/squashfs/fragment.c Normal file
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/*
* Squashfs - a compressed read only filesystem for Linux
*
* Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
* Phillip Lougher <phillip@lougher.demon.co.uk>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2,
* or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
* fragment.c
*/
/*
* This file implements code to handle compressed fragments (tail-end packed
* datablocks).
*
* Regular files contain a fragment index which is mapped to a fragment
* location on disk and compressed size using a fragment lookup table.
* Like everything in Squashfs this fragment lookup table is itself stored
* compressed into metadata blocks. A second index table is used to locate
* these. This second index table for speed of access (and because it
* is small) is read at mount time and cached in memory.
*/
#include <linux/fs.h>
#include <linux/vfs.h>
#include <linux/slab.h>
#include <linux/zlib.h>
#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs_fs_i.h"
#include "squashfs.h"
/*
* Look-up fragment using the fragment index table. Return the on disk
* location of the fragment and its compressed size
*/
int squashfs_frag_lookup(struct super_block *sb, unsigned int fragment,
u64 *fragment_block)
{
struct squashfs_sb_info *msblk = sb->s_fs_info;
int block = SQUASHFS_FRAGMENT_INDEX(fragment);
int offset = SQUASHFS_FRAGMENT_INDEX_OFFSET(fragment);
u64 start_block = le64_to_cpu(msblk->fragment_index[block]);
struct squashfs_fragment_entry fragment_entry;
int size;
size = squashfs_read_metadata(sb, &fragment_entry, &start_block,
&offset, sizeof(fragment_entry));
if (size < 0)
return size;
*fragment_block = le64_to_cpu(fragment_entry.start_block);
size = le32_to_cpu(fragment_entry.size);
return size;
}
/*
* Read the uncompressed fragment lookup table indexes off disk into memory
*/
__le64 *squashfs_read_fragment_index_table(struct super_block *sb,
u64 fragment_table_start, unsigned int fragments)
{
unsigned int length = SQUASHFS_FRAGMENT_INDEX_BYTES(fragments);
__le64 *fragment_index;
int err;
/* Allocate fragment lookup table indexes */
fragment_index = kmalloc(length, GFP_KERNEL);
if (fragment_index == NULL) {
ERROR("Failed to allocate fragment index table\n");
return ERR_PTR(-ENOMEM);
}
err = squashfs_read_table(sb, fragment_index, fragment_table_start,
length);
if (err < 0) {
ERROR("unable to read fragment index table\n");
kfree(fragment_index);
return ERR_PTR(err);
}
return fragment_index;
}