source: src/linux/universal/linux-4.9/fs/squashfs/namei.c @ 31630

Last change on this file since 31630 was 31630, checked in by brainslayer, 3 months ago

new fs is compatible with standard squashfs, just smaller

File size: 7.4 KB
Line 
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, length = 0, err;
83        unsigned int size;
84        struct squashfs_dir_index *index;
85        char *str;
86
87        TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count);
88
89        index = kmalloc(sizeof(*index) + SQUASHFS_NAME_LEN * 2 + 2, GFP_KERNEL);
90        if (index == NULL) {
91                ERROR("Failed to allocate squashfs_dir_index\n");
92                goto out;
93        }
94
95        str = &index->name[SQUASHFS_NAME_LEN + 1];
96        strncpy(str, name, len);
97        str[len] = '\0';
98
99        for (i = 0; i < i_count; i++) {
100                err = squashfs_read_metadata(sb, index, &index_start,
101                                        &index_offset, sizeof(*index));
102                if (err < 0)
103                        break;
104
105
106                size = le32_to_cpu(index->size) + 1;
107                if (size > SQUASHFS_NAME_LEN)
108                        break;
109
110                err = squashfs_read_metadata(sb, index->name, &index_start,
111                                        &index_offset, size);
112                if (err < 0)
113                        break;
114
115                index->name[size] = '\0';
116
117                if (strcmp(index->name, str) > 0)
118                        break;
119
120                length = le32_to_cpu(index->index);
121                *next_block = le32_to_cpu(index->start_block) +
122                                        msblk->directory_table;
123        }
124
125        *next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;
126        kfree(index);
127
128out:
129        /*
130         * Return index (f_pos) of the looked up metadata block.  Translate
131         * from internal f_pos to external f_pos which is offset by 3 because
132         * we invent "." and ".." entries which are not actually stored in the
133         * directory.
134         */
135        return length + 3;
136}
137
138
139static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry,
140                                 unsigned int flags)
141{
142        const unsigned char *name = dentry->d_name.name;
143        int len = dentry->d_name.len;
144        struct inode *inode = NULL;
145        struct squashfs_sb_info *msblk = dir->i_sb->s_fs_info;
146        struct squashfs_dir_header dirh;
147        struct squashfs_dir_entry *dire;
148        u64 block = squashfs_i(dir)->start + msblk->directory_table;
149        int offset = squashfs_i(dir)->offset;
150        int err, length;
151        unsigned int dir_count, size;
152
153        TRACE("Entered squashfs_lookup [%llx:%x]\n", block, offset);
154
155        dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
156        if (dire == NULL) {
157                ERROR("Failed to allocate squashfs_dir_entry\n");
158                return ERR_PTR(-ENOMEM);
159        }
160
161        if (len > SQUASHFS_NAME_LEN) {
162                err = -ENAMETOOLONG;
163                goto failed;
164        }
165
166        length = get_dir_index_using_name(dir->i_sb, &block, &offset,
167                                squashfs_i(dir)->dir_idx_start,
168                                squashfs_i(dir)->dir_idx_offset,
169                                squashfs_i(dir)->dir_idx_cnt, name, len);
170
171        while (length < i_size_read(dir)) {
172                /*
173                 * Read directory header.
174                 */
175                err = squashfs_read_metadata(dir->i_sb, &dirh, &block,
176                                &offset, sizeof(dirh));
177                if (err < 0)
178                        goto read_failure;
179
180                length += sizeof(dirh);
181
182                dir_count = le32_to_cpu(dirh.count) + 1;
183
184                if (dir_count > SQUASHFS_DIR_COUNT)
185                        goto data_error;
186
187                while (dir_count--) {
188                        /*
189                         * Read directory entry.
190                         */
191                        err = squashfs_read_metadata(dir->i_sb, dire, &block,
192                                        &offset, sizeof(*dire));
193                        if (err < 0)
194                                goto read_failure;
195
196                        size = le16_to_cpu(dire->size) + 1;
197
198                        /* size should never be larger than SQUASHFS_NAME_LEN */
199                        if (size > SQUASHFS_NAME_LEN)
200                                goto data_error;
201
202                        err = squashfs_read_metadata(dir->i_sb, dire->name,
203                                        &block, &offset, size);
204                        if (err < 0)
205                                goto read_failure;
206
207                        length += sizeof(*dire) + size;
208
209                        if (name[0] < dire->name[0])
210                                goto exit_lookup;
211
212                        if (len == size && !strncmp(name, dire->name, len)) {
213                                unsigned int blk, off, ino_num;
214                                long long ino;
215                                blk = le32_to_cpu(dirh.start_block);
216                                off = le16_to_cpu(dire->offset);
217                                ino_num = le32_to_cpu(dirh.inode_number) +
218                                        (short) le16_to_cpu(dire->inode_number);
219                                ino = SQUASHFS_MKINODE(blk, off);
220
221                                TRACE("calling squashfs_iget for directory "
222                                        "entry %s, inode  %x:%x, %d\n", name,
223                                        blk, off, ino_num);
224
225                                inode = squashfs_iget(dir->i_sb, ino, ino_num);
226                                goto exit_lookup;
227                        }
228                }
229        }
230
231exit_lookup:
232        kfree(dire);
233        return d_splice_alias(inode, dentry);
234
235data_error:
236        err = -EIO;
237
238read_failure:
239        ERROR("Unable to read directory block [%llx:%x]\n",
240                squashfs_i(dir)->start + msblk->directory_table,
241                squashfs_i(dir)->offset);
242failed:
243        kfree(dire);
244        return ERR_PTR(err);
245}
246
247
248const struct inode_operations squashfs_dir_inode_ops = {
249        .lookup = squashfs_lookup,
250        .listxattr = squashfs_listxattr
251};
Note: See TracBrowser for help on using the repository browser.