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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.
* namei.c
* This file implements code to do filename lookup in directories.
* Like inodes, directories are packed into compressed metadata blocks, stored
* in a directory table. Directories are accessed using the start address of
* the metablock containing the directory and the offset into the
* decompressed block (<block, offset>).
* Directories are organised in a slightly complex way, and are not simply
* a list of file names. The organisation takes advantage of the
* fact that (in most cases) the inodes of the files will be in the same
* compressed metadata block, and therefore, can share the start block.
* Directories are therefore organised in a two level list, a directory
* header containing the shared start block value, and a sequence of directory
* entries, each of which share the shared start block. A new directory header
* is written once/if the inode start block changes. The directory
* header/directory entry list is repeated as many times as necessary.
* Directories are sorted, and can contain a directory index to speed up
* file lookup. Directory indexes store one entry per metablock, each entry
* storing the index/filename mapping to the first directory header
* in each metadata block. Directories are sorted in alphabetical order,
* and at lookup the index is scanned linearly looking for the first filename
* alphabetically larger than the filename being looked up. At this point the
* location of the metadata block the filename is in has been found.
* The general idea of the index is ensure only one metadata block needs to be
* decompressed to do a lookup irrespective of the length of the directory.
* This scheme has the advantage that it doesn't require extra memory overhead
* and doesn't require much extra storage on disk.
#include <linux/fs.h>
#include <linux/vfs.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/dcache.h>
#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs_fs_i.h"
#include "squashfs.h"
* Lookup name in the directory index, returning the location of the metadata
* block containing it, and the directory index this represents.
* If we get an error reading the index then return the part of the index
* (if any) we have managed to read - the index isn't essential, just
* quicker.
static int get_dir_index_using_name(struct super_block *sb,
u64 *next_block, int *next_offset, u64 index_start,
int index_offset, int i_count, const char *name,
int len)
struct squashfs_sb_info *msblk = sb->s_fs_info;
int i, size, length = 0, err;
struct squashfs_dir_index *index;
char *str;
TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count);
index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN * 2 + 2, GFP_KERNEL);
if (index == NULL) {
ERROR("Failed to allocate squashfs_dir_index\n");
goto out;
str = &index->name[SQUASHFS_NAME_LEN + 1];
strncpy(str, name, len);
str[len] = '\0';
for (i = 0; i < i_count; i++) {
err = squashfs_read_metadata(sb, index, &index_start,
&index_offset, sizeof(*index));
if (err < 0)
size = le32_to_cpu(index->size) + 1;
err = squashfs_read_metadata(sb, index->name, &index_start,
&index_offset, size);
if (err < 0)
index->name[size] = '\0';
if (strcmp(index->name, str) > 0)
length = le32_to_cpu(index->index);
*next_block = le32_to_cpu(index->start_block) +
*next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;
* Return index (f_pos) of the looked up metadata block. Translate
* from internal f_pos to external f_pos which is offset by 3 because
* we invent "." and ".." entries which are not actually stored in the
* directory.
return length + 3;
static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry,
struct nameidata *nd)
const unsigned char *name = dentry->;
int len = dentry->d_name.len;
struct inode *inode = NULL;
struct squashfs_sb_info *msblk = dir->i_sb->s_fs_info;
struct squashfs_dir_header dirh;
struct squashfs_dir_entry *dire;
u64 block = squashfs_i(dir)->start + msblk->directory_table;
int offset = squashfs_i(dir)->offset;
int err, length = 0, dir_count, size;
TRACE("Entered squashfs_lookup [%llx:%x]\n", block, offset);
dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
if (dire == NULL) {
ERROR("Failed to allocate squashfs_dir_entry\n");
return ERR_PTR(-ENOMEM);
if (len > SQUASHFS_NAME_LEN) {
goto failed;
length = get_dir_index_using_name(dir->i_sb, &block, &offset,
squashfs_i(dir)->dir_idx_cnt, name, len);
while (length < i_size_read(dir)) {
* Read directory header.
err = squashfs_read_metadata(dir->i_sb, &dirh, &block,
&offset, sizeof(dirh));
if (err < 0)
goto read_failure;
length += sizeof(dirh);
dir_count = le32_to_cpu(dirh.count) + 1;
while (dir_count--) {
* Read directory entry.
err = squashfs_read_metadata(dir->i_sb, dire, &block,
&offset, sizeof(*dire));
if (err < 0)
goto read_failure;
size = le16_to_cpu(dire->size) + 1;
err = squashfs_read_metadata(dir->i_sb, dire->name,
&block, &offset, size);
if (err < 0)
goto read_failure;
length += sizeof(*dire) + size;
if (name[0] < dire->name[0])
goto exit_lookup;
if (len == size && !strncmp(name, dire->name, len)) {
unsigned int blk, off, ino_num;
long long ino;
blk = le32_to_cpu(dirh.start_block);
off = le16_to_cpu(dire->offset);
ino_num = le32_to_cpu(dirh.inode_number) +
(short) le16_to_cpu(dire->inode_number);
ino = SQUASHFS_MKINODE(blk, off);
TRACE("calling squashfs_iget for directory "
"entry %s, inode %x:%x, %d\n", name,
blk, off, ino_num);
inode = squashfs_iget(dir->i_sb, ino, ino_num);
if (IS_ERR(inode)) {
err = PTR_ERR(inode);
goto failed;
goto exit_lookup;
if (inode)
return d_splice_alias(inode, dentry);
d_add(dentry, inode);
return ERR_PTR(0);
ERROR("Unable to read directory block [%llx:%x]\n",
squashfs_i(dir)->start + msblk->directory_table,
return ERR_PTR(err);
const struct inode_operations squashfs_dir_inode_ops = {
.lookup = squashfs_lookup