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* Squashfs - a compressed read only filesystem for Linux
* Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
* Phillip Lougher <>
* 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
* 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.
* export.c
* This file implements code to make Squashfs filesystems exportable (NFS etc.)
* The export code uses an inode lookup table to map inode numbers passed in
* filehandles to an inode location on disk. This table is 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.
* The inode lookup table is used only by the export code, inode disk
* locations are directly encoded in directories, enabling direct access
* without an intermediate lookup for all operations except the export ops.
#include <linux/fs.h>
#include <linux/vfs.h>
#include <linux/dcache.h>
#include <linux/exportfs.h>
#include <linux/slab.h>
#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs_fs_i.h"
#include "squashfs.h"
* Look-up inode number (ino) in table, returning the inode location.
static long long squashfs_inode_lookup(struct super_block *sb, int ino_num)
struct squashfs_sb_info *msblk = sb->s_fs_info;
int blk = SQUASHFS_LOOKUP_BLOCK(ino_num - 1);
int offset = SQUASHFS_LOOKUP_BLOCK_OFFSET(ino_num - 1);
u64 start = le64_to_cpu(msblk->inode_lookup_table[blk]);
__le64 ino;
int err;
TRACE("Entered squashfs_inode_lookup, inode_number = %d\n", ino_num);
err = squashfs_read_metadata(sb, &ino, &start, &offset, sizeof(ino));
if (err < 0)
return err;
TRACE("squashfs_inode_lookup, inode = 0x%llx\n",
(u64) le64_to_cpu(ino));
return le64_to_cpu(ino);
static struct dentry *squashfs_export_iget(struct super_block *sb,
unsigned int ino_num)
long long ino;
struct dentry *dentry = ERR_PTR(-ENOENT);
TRACE("Entered squashfs_export_iget\n");
ino = squashfs_inode_lookup(sb, ino_num);
if (ino >= 0)
dentry = d_obtain_alias(squashfs_iget(sb, ino, ino_num));
return dentry;
static struct dentry *squashfs_fh_to_dentry(struct super_block *sb,
struct fid *fid, int fh_len, int fh_type)
if ((fh_type != FILEID_INO32_GEN && fh_type != FILEID_INO32_GEN_PARENT)
|| fh_len < 2)
return NULL;
return squashfs_export_iget(sb, fid->i32.ino);
static struct dentry *squashfs_fh_to_parent(struct super_block *sb,
struct fid *fid, int fh_len, int fh_type)
if (fh_type != FILEID_INO32_GEN_PARENT || fh_len < 4)
return NULL;
return squashfs_export_iget(sb, fid->i32.parent_ino);
static struct dentry *squashfs_get_parent(struct dentry *child)
struct inode *inode = child->d_inode;
unsigned int parent_ino = squashfs_i(inode)->parent;
return squashfs_export_iget(inode->i_sb, parent_ino);
* Read uncompressed inode lookup table indexes off disk into memory
__le64 *squashfs_read_inode_lookup_table(struct super_block *sb,
u64 lookup_table_start, unsigned int inodes)
unsigned int length = SQUASHFS_LOOKUP_BLOCK_BYTES(inodes);
__le64 *inode_lookup_table;
int err;
TRACE("In read_inode_lookup_table, length %d\n", length);
/* Allocate inode lookup table indexes */
inode_lookup_table = kmalloc(length, GFP_KERNEL);
if (inode_lookup_table == NULL) {
ERROR("Failed to allocate inode lookup table\n");
return ERR_PTR(-ENOMEM);
err = squashfs_read_table(sb, inode_lookup_table, lookup_table_start,
if (err < 0) {
ERROR("unable to read inode lookup table\n");
return ERR_PTR(err);
return inode_lookup_table;
const struct export_operations squashfs_export_ops = {
.fh_to_dentry = squashfs_fh_to_dentry,
.fh_to_parent = squashfs_fh_to_parent,
.get_parent = squashfs_get_parent