1 // SPDX-License-Identifier: GPL-2.0-or-later
3 * Squashfs - a compressed read only filesystem for Linux
5 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
6 * Phillip Lougher <phillip@squashfs.org.uk>
12 * This file implements code to do filename lookup in directories.
14 * Like inodes, directories are packed into compressed metadata blocks, stored
15 * in a directory table. Directories are accessed using the start address of
16 * the metablock containing the directory and the offset into the
17 * decompressed block (<block, offset>).
19 * Directories are organised in a slightly complex way, and are not simply
20 * a list of file names. The organisation takes advantage of the
21 * fact that (in most cases) the inodes of the files will be in the same
22 * compressed metadata block, and therefore, can share the start block.
23 * Directories are therefore organised in a two level list, a directory
24 * header containing the shared start block value, and a sequence of directory
25 * entries, each of which share the shared start block. A new directory header
26 * is written once/if the inode start block changes. The directory
27 * header/directory entry list is repeated as many times as necessary.
29 * Directories are sorted, and can contain a directory index to speed up
30 * file lookup. Directory indexes store one entry per metablock, each entry
31 * storing the index/filename mapping to the first directory header
32 * in each metadata block. Directories are sorted in alphabetical order,
33 * and at lookup the index is scanned linearly looking for the first filename
34 * alphabetically larger than the filename being looked up. At this point the
35 * location of the metadata block the filename is in has been found.
36 * The general idea of the index is ensure only one metadata block needs to be
37 * decompressed to do a lookup irrespective of the length of the directory.
38 * This scheme has the advantage that it doesn't require extra memory overhead
39 * and doesn't require much extra storage on disk.
43 #include <linux/vfs.h>
44 #include <linux/slab.h>
45 #include <linux/string.h>
46 #include <linux/dcache.h>
47 #include <linux/xattr.h>
49 #include "squashfs_fs.h"
50 #include "squashfs_fs_sb.h"
51 #include "squashfs_fs_i.h"
56 * Lookup name in the directory index, returning the location of the metadata
57 * block containing it, and the directory index this represents.
59 * If we get an error reading the index then return the part of the index
60 * (if any) we have managed to read - the index isn't essential, just
63 static int get_dir_index_using_name(struct super_block *sb,
64 u64 *next_block, int *next_offset, u64 index_start,
65 int index_offset, int i_count, const char *name)
67 struct squashfs_sb_info *msblk = sb->s_fs_info;
68 int i, length = 0, err;
70 struct squashfs_dir_index *index;
72 TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count);
74 index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
76 ERROR("Failed to allocate squashfs_dir_index\n");
80 for (i = 0; i < i_count; i++) {
81 err = squashfs_read_metadata(sb, index, &index_start,
82 &index_offset, sizeof(*index));
87 size = le32_to_cpu(index->size) + 1;
88 if (size > SQUASHFS_NAME_LEN)
91 err = squashfs_read_metadata(sb, index->name, &index_start,
96 index->name[size] = '\0';
98 if (strcmp(index->name, name) > 0)
101 length = le32_to_cpu(index->index);
102 *next_block = le32_to_cpu(index->start_block) +
103 msblk->directory_table;
106 *next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;
111 * Return index (f_pos) of the looked up metadata block. Translate
112 * from internal f_pos to external f_pos which is offset by 3 because
113 * we invent "." and ".." entries which are not actually stored in the
120 static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry,
123 const unsigned char *name = dentry->d_name.name;
124 int len = dentry->d_name.len;
125 struct inode *inode = NULL;
126 struct squashfs_sb_info *msblk = dir->i_sb->s_fs_info;
127 struct squashfs_dir_header dirh;
128 struct squashfs_dir_entry *dire;
129 u64 block = squashfs_i(dir)->start + msblk->directory_table;
130 int offset = squashfs_i(dir)->offset;
132 unsigned int dir_count, size;
134 TRACE("Entered squashfs_lookup [%llx:%x]\n", block, offset);
136 dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
138 ERROR("Failed to allocate squashfs_dir_entry\n");
139 return ERR_PTR(-ENOMEM);
142 if (len > SQUASHFS_NAME_LEN) {
147 length = get_dir_index_using_name(dir->i_sb, &block, &offset,
148 squashfs_i(dir)->dir_idx_start,
149 squashfs_i(dir)->dir_idx_offset,
150 squashfs_i(dir)->dir_idx_cnt, name);
152 while (length < i_size_read(dir)) {
154 * Read directory header.
156 err = squashfs_read_metadata(dir->i_sb, &dirh, &block,
157 &offset, sizeof(dirh));
161 length += sizeof(dirh);
163 dir_count = le32_to_cpu(dirh.count) + 1;
165 if (dir_count > SQUASHFS_DIR_COUNT)
168 while (dir_count--) {
170 * Read directory entry.
172 err = squashfs_read_metadata(dir->i_sb, dire, &block,
173 &offset, sizeof(*dire));
177 size = le16_to_cpu(dire->size) + 1;
179 /* size should never be larger than SQUASHFS_NAME_LEN */
180 if (size > SQUASHFS_NAME_LEN)
183 err = squashfs_read_metadata(dir->i_sb, dire->name,
184 &block, &offset, size);
188 length += sizeof(*dire) + size;
190 if (name[0] < dire->name[0])
193 if (len == size && !strncmp(name, dire->name, len)) {
194 unsigned int blk, off, ino_num;
196 blk = le32_to_cpu(dirh.start_block);
197 off = le16_to_cpu(dire->offset);
198 ino_num = le32_to_cpu(dirh.inode_number) +
199 (short) le16_to_cpu(dire->inode_number);
200 ino = SQUASHFS_MKINODE(blk, off);
202 TRACE("calling squashfs_iget for directory "
203 "entry %s, inode %x:%x, %d\n", name,
206 inode = squashfs_iget(dir->i_sb, ino, ino_num);
214 return d_splice_alias(inode, dentry);
220 ERROR("Unable to read directory block [%llx:%x]\n",
221 squashfs_i(dir)->start + msblk->directory_table,
222 squashfs_i(dir)->offset);
229 const struct inode_operations squashfs_dir_inode_ops = {
230 .lookup = squashfs_lookup,
231 .listxattr = squashfs_listxattr