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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@squashfs.org.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 * namei.c
22 */
23
24/*
25 * This file implements code to do filename lookup in directories.
26 *
27 * Like inodes, directories are packed into compressed metadata blocks, stored
28 * in a directory table. Directories are accessed using the start address of
29 * the metablock containing the directory and the offset into the
30 * decompressed block (<block, offset>).
31 *
32 * Directories are organised in a slightly complex way, and are not simply
33 * a list of file names. The organisation takes advantage of the
34 * fact that (in most cases) the inodes of the files will be in the same
35 * compressed metadata block, and therefore, can share the start block.
36 * Directories are therefore organised in a two level list, a directory
37 * header containing the shared start block value, and a sequence of directory
38 * entries, each of which share the shared start block. A new directory header
39 * is written once/if the inode start block changes. The directory
40 * header/directory entry list is repeated as many times as necessary.
41 *
42 * Directories are sorted, and can contain a directory index to speed up
43 * file lookup. Directory indexes store one entry per metablock, each entry
44 * storing the index/filename mapping to the first directory header
45 * in each metadata block. Directories are sorted in alphabetical order,
46 * and at lookup the index is scanned linearly looking for the first filename
47 * alphabetically larger than the filename being looked up. At this point the
48 * location of the metadata block the filename is in has been found.
49 * The general idea of the index is ensure only one metadata block needs to be
50 * decompressed to do a lookup irrespective of the length of the directory.
51 * This scheme has the advantage that it doesn't require extra memory overhead
52 * and doesn't require much extra storage on disk.
53 */
54
55#include <linux/fs.h>
56#include <linux/vfs.h>
57#include <linux/slab.h>
58#include <linux/string.h>
59#include <linux/dcache.h>
60#include <linux/xattr.h>
61
62#include "squashfs_fs.h"
63#include "squashfs_fs_sb.h"
64#include "squashfs_fs_i.h"
65#include "squashfs.h"
66#include "xattr.h"
67
68/*
69 * Lookup name in the directory index, returning the location of the metadata
70 * block containing it, and the directory index this represents.
71 *
72 * If we get an error reading the index then return the part of the index
73 * (if any) we have managed to read - the index isn't essential, just
74 * quicker.
75 */
76static int get_dir_index_using_name(struct super_block *sb,
77 u64 *next_block, int *next_offset, u64 index_start,
78 int index_offset, int i_count, const char *name,
79 int len)
80{
81 struct squashfs_sb_info *msblk = sb->s_fs_info;
82 int i, size, length = 0, err;
83 struct squashfs_dir_index *index;
84 char *str;
85
86 TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count);
87
88 index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN * 2 + 2, GFP_KERNEL);
89 if (index == NULL) {
90 ERROR("Failed to allocate squashfs_dir_index\n");
91 goto out;
92 }
93
94 str = &index->name[SQUASHFS_NAME_LEN + 1];
95 strncpy(str, name, len);
96 str[len] = '\0';
97
98 for (i = 0; i < i_count; i++) {
99 err = squashfs_read_metadata(sb, index, &index_start,
100 &index_offset, sizeof(*index));
101 if (err < 0)
102 break;
103
104
105 size = le32_to_cpu(index->size) + 1;
106
107 err = squashfs_read_metadata(sb, index->name, &index_start,
108 &index_offset, size);
109 if (err < 0)
110 break;
111
112 index->name[size] = '\0';
113
114 if (strcmp(index->name, str) > 0)
115 break;
116
117 length = le32_to_cpu(index->index);
118 *next_block = le32_to_cpu(index->start_block) +
119 msblk->directory_table;
120 }
121
122 *next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;
123 kfree(index);
124
125out:
126 /*
127 * Return index (f_pos) of the looked up metadata block. Translate
128 * from internal f_pos to external f_pos which is offset by 3 because
129 * we invent "." and ".." entries which are not actually stored in the
130 * directory.
131 */
132 return length + 3;
133}
134
135
136static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry,
137 struct nameidata *nd)
138{
139 const unsigned char *name = dentry->d_name.name;
140 int len = dentry->d_name.len;
141 struct inode *inode = NULL;
142 struct squashfs_sb_info *msblk = dir->i_sb->s_fs_info;
143 struct squashfs_dir_header dirh;
144 struct squashfs_dir_entry *dire;
145 u64 block = squashfs_i(dir)->start + msblk->directory_table;
146 int offset = squashfs_i(dir)->offset;
147 int err, length, dir_count, size;
148
149 TRACE("Entered squashfs_lookup [%llx:%x]\n", block, offset);
150
151 dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
152 if (dire == NULL) {
153 ERROR("Failed to allocate squashfs_dir_entry\n");
154 return ERR_PTR(-ENOMEM);
155 }
156
157 if (len > SQUASHFS_NAME_LEN) {
158 err = -ENAMETOOLONG;
159 goto failed;
160 }
161
162 length = get_dir_index_using_name(dir->i_sb, &block, &offset,
163 squashfs_i(dir)->dir_idx_start,
164 squashfs_i(dir)->dir_idx_offset,
165 squashfs_i(dir)->dir_idx_cnt, name, len);
166
167 while (length < i_size_read(dir)) {
168 /*
169 * Read directory header.
170 */
171 err = squashfs_read_metadata(dir->i_sb, &dirh, &block,
172 &offset, sizeof(dirh));
173 if (err < 0)
174 goto read_failure;
175
176 length += sizeof(dirh);
177
178 dir_count = le32_to_cpu(dirh.count) + 1;
179
180 if (dir_count > SQUASHFS_DIR_COUNT)
181 goto data_error;
182
183 while (dir_count--) {
184 /*
185 * Read directory entry.
186 */
187 err = squashfs_read_metadata(dir->i_sb, dire, &block,
188 &offset, sizeof(*dire));
189 if (err < 0)
190 goto read_failure;
191
192 size = le16_to_cpu(dire->size) + 1;
193
194 /* size should never be larger than SQUASHFS_NAME_LEN */
195 if (size > SQUASHFS_NAME_LEN)
196 goto data_error;
197
198 err = squashfs_read_metadata(dir->i_sb, dire->name,
199 &block, &offset, size);
200 if (err < 0)
201 goto read_failure;
202
203 length += sizeof(*dire) + size;
204
205 if (name[0] < dire->name[0])
206 goto exit_lookup;
207
208 if (len == size && !strncmp(name, dire->name, len)) {
209 unsigned int blk, off, ino_num;
210 long long ino;
211 blk = le32_to_cpu(dirh.start_block);
212 off = le16_to_cpu(dire->offset);
213 ino_num = le32_to_cpu(dirh.inode_number) +
214 (short) le16_to_cpu(dire->inode_number);
215 ino = SQUASHFS_MKINODE(blk, off);
216
217 TRACE("calling squashfs_iget for directory "
218 "entry %s, inode %x:%x, %d\n", name,
219 blk, off, ino_num);
220
221 inode = squashfs_iget(dir->i_sb, ino, ino_num);
222 goto exit_lookup;
223 }
224 }
225 }
226
227exit_lookup:
228 kfree(dire);
229 return d_splice_alias(inode, dentry);
230
231data_error:
232 err = -EIO;
233
234read_failure:
235 ERROR("Unable to read directory block [%llx:%x]\n",
236 squashfs_i(dir)->start + msblk->directory_table,
237 squashfs_i(dir)->offset);
238failed:
239 kfree(dire);
240 return ERR_PTR(err);
241}
242
243
244const struct inode_operations squashfs_dir_inode_ops = {
245 .lookup = squashfs_lookup,
246 .getxattr = generic_getxattr,
247 .listxattr = squashfs_listxattr
248};