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c88da2c9 PL |
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@lougher.demon.co.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> | |
c88da2c9 PL |
60 | |
61 | #include "squashfs_fs.h" | |
62 | #include "squashfs_fs_sb.h" | |
63 | #include "squashfs_fs_i.h" | |
64 | #include "squashfs.h" | |
65 | ||
66 | /* | |
67 | * Lookup name in the directory index, returning the location of the metadata | |
68 | * block containing it, and the directory index this represents. | |
69 | * | |
70 | * If we get an error reading the index then return the part of the index | |
71 | * (if any) we have managed to read - the index isn't essential, just | |
72 | * quicker. | |
73 | */ | |
74 | static int get_dir_index_using_name(struct super_block *sb, | |
75 | u64 *next_block, int *next_offset, u64 index_start, | |
76 | int index_offset, int i_count, const char *name, | |
77 | int len) | |
78 | { | |
79 | struct squashfs_sb_info *msblk = sb->s_fs_info; | |
80 | int i, size, length = 0, err; | |
81 | struct squashfs_dir_index *index; | |
82 | char *str; | |
83 | ||
84 | TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count); | |
85 | ||
86 | index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN * 2 + 2, GFP_KERNEL); | |
87 | if (index == NULL) { | |
88 | ERROR("Failed to allocate squashfs_dir_index\n"); | |
89 | goto out; | |
90 | } | |
91 | ||
92 | str = &index->name[SQUASHFS_NAME_LEN + 1]; | |
93 | strncpy(str, name, len); | |
94 | str[len] = '\0'; | |
95 | ||
96 | for (i = 0; i < i_count; i++) { | |
97 | err = squashfs_read_metadata(sb, index, &index_start, | |
98 | &index_offset, sizeof(*index)); | |
99 | if (err < 0) | |
100 | break; | |
101 | ||
102 | ||
103 | size = le32_to_cpu(index->size) + 1; | |
104 | ||
105 | err = squashfs_read_metadata(sb, index->name, &index_start, | |
106 | &index_offset, size); | |
107 | if (err < 0) | |
108 | break; | |
109 | ||
110 | index->name[size] = '\0'; | |
111 | ||
112 | if (strcmp(index->name, str) > 0) | |
113 | break; | |
114 | ||
115 | length = le32_to_cpu(index->index); | |
116 | *next_block = le32_to_cpu(index->start_block) + | |
117 | msblk->directory_table; | |
118 | } | |
119 | ||
120 | *next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE; | |
121 | kfree(index); | |
122 | ||
123 | out: | |
124 | /* | |
125 | * Return index (f_pos) of the looked up metadata block. Translate | |
126 | * from internal f_pos to external f_pos which is offset by 3 because | |
127 | * we invent "." and ".." entries which are not actually stored in the | |
128 | * directory. | |
129 | */ | |
130 | return length + 3; | |
131 | } | |
132 | ||
133 | ||
134 | static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry, | |
135 | struct nameidata *nd) | |
136 | { | |
137 | const unsigned char *name = dentry->d_name.name; | |
138 | int len = dentry->d_name.len; | |
139 | struct inode *inode = NULL; | |
140 | struct squashfs_sb_info *msblk = dir->i_sb->s_fs_info; | |
141 | struct squashfs_dir_header dirh; | |
142 | struct squashfs_dir_entry *dire; | |
143 | u64 block = squashfs_i(dir)->start + msblk->directory_table; | |
144 | int offset = squashfs_i(dir)->offset; | |
145 | int err, length = 0, dir_count, size; | |
146 | ||
147 | TRACE("Entered squashfs_lookup [%llx:%x]\n", block, offset); | |
148 | ||
149 | dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL); | |
150 | if (dire == NULL) { | |
151 | ERROR("Failed to allocate squashfs_dir_entry\n"); | |
152 | return ERR_PTR(-ENOMEM); | |
153 | } | |
154 | ||
155 | if (len > SQUASHFS_NAME_LEN) { | |
156 | err = -ENAMETOOLONG; | |
157 | goto failed; | |
158 | } | |
159 | ||
160 | length = get_dir_index_using_name(dir->i_sb, &block, &offset, | |
161 | squashfs_i(dir)->dir_idx_start, | |
162 | squashfs_i(dir)->dir_idx_offset, | |
163 | squashfs_i(dir)->dir_idx_cnt, name, len); | |
164 | ||
165 | while (length < i_size_read(dir)) { | |
166 | /* | |
167 | * Read directory header. | |
168 | */ | |
169 | err = squashfs_read_metadata(dir->i_sb, &dirh, &block, | |
170 | &offset, sizeof(dirh)); | |
171 | if (err < 0) | |
172 | goto read_failure; | |
173 | ||
174 | length += sizeof(dirh); | |
175 | ||
176 | dir_count = le32_to_cpu(dirh.count) + 1; | |
177 | while (dir_count--) { | |
178 | /* | |
179 | * Read directory entry. | |
180 | */ | |
181 | err = squashfs_read_metadata(dir->i_sb, dire, &block, | |
182 | &offset, sizeof(*dire)); | |
183 | if (err < 0) | |
184 | goto read_failure; | |
185 | ||
186 | size = le16_to_cpu(dire->size) + 1; | |
187 | ||
188 | err = squashfs_read_metadata(dir->i_sb, dire->name, | |
189 | &block, &offset, size); | |
190 | if (err < 0) | |
191 | goto read_failure; | |
192 | ||
193 | length += sizeof(*dire) + size; | |
194 | ||
195 | if (name[0] < dire->name[0]) | |
196 | goto exit_lookup; | |
197 | ||
198 | if (len == size && !strncmp(name, dire->name, len)) { | |
199 | unsigned int blk, off, ino_num; | |
200 | long long ino; | |
201 | blk = le32_to_cpu(dirh.start_block); | |
202 | off = le16_to_cpu(dire->offset); | |
203 | ino_num = le32_to_cpu(dirh.inode_number) + | |
204 | (short) le16_to_cpu(dire->inode_number); | |
205 | ino = SQUASHFS_MKINODE(blk, off); | |
206 | ||
207 | TRACE("calling squashfs_iget for directory " | |
208 | "entry %s, inode %x:%x, %d\n", name, | |
209 | blk, off, ino_num); | |
210 | ||
211 | inode = squashfs_iget(dir->i_sb, ino, ino_num); | |
212 | if (IS_ERR(inode)) { | |
213 | err = PTR_ERR(inode); | |
214 | goto failed; | |
215 | } | |
216 | ||
217 | goto exit_lookup; | |
218 | } | |
219 | } | |
220 | } | |
221 | ||
222 | exit_lookup: | |
223 | kfree(dire); | |
224 | if (inode) | |
225 | return d_splice_alias(inode, dentry); | |
226 | d_add(dentry, inode); | |
227 | return ERR_PTR(0); | |
228 | ||
229 | read_failure: | |
230 | ERROR("Unable to read directory block [%llx:%x]\n", | |
231 | squashfs_i(dir)->start + msblk->directory_table, | |
232 | squashfs_i(dir)->offset); | |
233 | failed: | |
234 | kfree(dire); | |
235 | return ERR_PTR(err); | |
236 | } | |
237 | ||
238 | ||
239 | const struct inode_operations squashfs_dir_inode_ops = { | |
240 | .lookup = squashfs_lookup | |
241 | }; |