Line data Source code
1 : /*
2 : * lib/textsearch.c Generic text search interface
3 : *
4 : * This program is free software; you can redistribute it and/or
5 : * modify it under the terms of the GNU General Public License
6 : * as published by the Free Software Foundation; either version
7 : * 2 of the License, or (at your option) any later version.
8 : *
9 : * Authors: Thomas Graf <tgraf@suug.ch>
10 : * Pablo Neira Ayuso <pablo@netfilter.org>
11 : *
12 : * ==========================================================================
13 : *
14 : * INTRODUCTION
15 : *
16 : * The textsearch infrastructure provides text searching facilities for
17 : * both linear and non-linear data. Individual search algorithms are
18 : * implemented in modules and chosen by the user.
19 : *
20 : * ARCHITECTURE
21 : *
22 : * User
23 : * +----------------+
24 : * | finish()|<--------------(6)-----------------+
25 : * |get_next_block()|<--------------(5)---------------+ |
26 : * | | Algorithm | |
27 : * | | +------------------------------+
28 : * | | | init() find() destroy() |
29 : * | | +------------------------------+
30 : * | | Core API ^ ^ ^
31 : * | | +---------------+ (2) (4) (8)
32 : * | (1)|----->| prepare() |---+ | |
33 : * | (3)|----->| find()/next() |-----------+ |
34 : * | (7)|----->| destroy() |----------------------+
35 : * +----------------+ +---------------+
36 : *
37 : * (1) User configures a search by calling _prepare() specifying the
38 : * search parameters such as the pattern and algorithm name.
39 : * (2) Core requests the algorithm to allocate and initialize a search
40 : * configuration according to the specified parameters.
41 : * (3) User starts the search(es) by calling _find() or _next() to
42 : * fetch subsequent occurrences. A state variable is provided
43 : * to the algorithm to store persistent variables.
44 : * (4) Core eventually resets the search offset and forwards the find()
45 : * request to the algorithm.
46 : * (5) Algorithm calls get_next_block() provided by the user continuously
47 : * to fetch the data to be searched in block by block.
48 : * (6) Algorithm invokes finish() after the last call to get_next_block
49 : * to clean up any leftovers from get_next_block. (Optional)
50 : * (7) User destroys the configuration by calling _destroy().
51 : * (8) Core notifies the algorithm to destroy algorithm specific
52 : * allocations. (Optional)
53 : *
54 : * USAGE
55 : *
56 : * Before a search can be performed, a configuration must be created
57 : * by calling textsearch_prepare() specifying the searching algorithm,
58 : * the pattern to look for and flags. As a flag, you can set TS_IGNORECASE
59 : * to perform case insensitive matching. But it might slow down
60 : * performance of algorithm, so you should use it at own your risk.
61 : * The returned configuration may then be used for an arbitrary
62 : * amount of times and even in parallel as long as a separate struct
63 : * ts_state variable is provided to every instance.
64 : *
65 : * The actual search is performed by either calling textsearch_find_-
66 : * continuous() for linear data or by providing an own get_next_block()
67 : * implementation and calling textsearch_find(). Both functions return
68 : * the position of the first occurrence of the pattern or UINT_MAX if
69 : * no match was found. Subsequent occurrences can be found by calling
70 : * textsearch_next() regardless of the linearity of the data.
71 : *
72 : * Once you're done using a configuration it must be given back via
73 : * textsearch_destroy.
74 : *
75 : * EXAMPLE
76 : *
77 : * int pos;
78 : * struct ts_config *conf;
79 : * struct ts_state state;
80 : * const char *pattern = "chicken";
81 : * const char *example = "We dance the funky chicken";
82 : *
83 : * conf = textsearch_prepare("kmp", pattern, strlen(pattern),
84 : * GFP_KERNEL, TS_AUTOLOAD);
85 : * if (IS_ERR(conf)) {
86 : * err = PTR_ERR(conf);
87 : * goto errout;
88 : * }
89 : *
90 : * pos = textsearch_find_continuous(conf, &state, example, strlen(example));
91 : * if (pos != UINT_MAX)
92 : * panic("Oh my god, dancing chickens at %d\n", pos);
93 : *
94 : * textsearch_destroy(conf);
95 : * ==========================================================================
96 : */
97 :
98 : #include <linux/module.h>
99 : #include <linux/types.h>
100 : #include <linux/string.h>
101 : #include <linux/init.h>
102 : #include <linux/rculist.h>
103 : #include <linux/rcupdate.h>
104 : #include <linux/err.h>
105 : #include <linux/textsearch.h>
106 : #include <linux/slab.h>
107 :
108 : static LIST_HEAD(ts_ops);
109 : static DEFINE_SPINLOCK(ts_mod_lock);
110 :
111 : static inline struct ts_ops *lookup_ts_algo(const char *name)
112 : {
113 : struct ts_ops *o;
114 :
115 : rcu_read_lock();
116 0 : list_for_each_entry_rcu(o, &ts_ops, list) {
117 0 : if (!strcmp(name, o->name)) {
118 0 : if (!try_module_get(o->owner))
119 : o = NULL;
120 : rcu_read_unlock();
121 : return o;
122 : }
123 : }
124 : rcu_read_unlock();
125 :
126 : return NULL;
127 : }
128 :
129 : /**
130 : * textsearch_register - register a textsearch module
131 : * @ops: operations lookup table
132 : *
133 : * This function must be called by textsearch modules to announce
134 : * their presence. The specified &@ops must have %name set to a
135 : * unique identifier and the callbacks find(), init(), get_pattern(),
136 : * and get_pattern_len() must be implemented.
137 : *
138 : * Returns 0 or -EEXISTS if another module has already registered
139 : * with same name.
140 : */
141 0 : int textsearch_register(struct ts_ops *ops)
142 : {
143 : int err = -EEXIST;
144 : struct ts_ops *o;
145 :
146 0 : if (ops->name == NULL || ops->find == NULL || ops->init == NULL ||
147 0 : ops->get_pattern == NULL || ops->get_pattern_len == NULL)
148 : return -EINVAL;
149 :
150 : spin_lock(&ts_mod_lock);
151 0 : list_for_each_entry(o, &ts_ops, list) {
152 0 : if (!strcmp(ops->name, o->name))
153 : goto errout;
154 : }
155 :
156 0 : list_add_tail_rcu(&ops->list, &ts_ops);
157 : err = 0;
158 : errout:
159 : spin_unlock(&ts_mod_lock);
160 0 : return err;
161 : }
162 : EXPORT_SYMBOL(textsearch_register);
163 :
164 : /**
165 : * textsearch_unregister - unregister a textsearch module
166 : * @ops: operations lookup table
167 : *
168 : * This function must be called by textsearch modules to announce
169 : * their disappearance for examples when the module gets unloaded.
170 : * The &ops parameter must be the same as the one during the
171 : * registration.
172 : *
173 : * Returns 0 on success or -ENOENT if no matching textsearch
174 : * registration was found.
175 : */
176 0 : int textsearch_unregister(struct ts_ops *ops)
177 : {
178 : int err = 0;
179 : struct ts_ops *o;
180 :
181 : spin_lock(&ts_mod_lock);
182 0 : list_for_each_entry(o, &ts_ops, list) {
183 0 : if (o == ops) {
184 : list_del_rcu(&o->list);
185 : goto out;
186 : }
187 : }
188 :
189 : err = -ENOENT;
190 : out:
191 : spin_unlock(&ts_mod_lock);
192 0 : return err;
193 : }
194 : EXPORT_SYMBOL(textsearch_unregister);
195 :
196 : struct ts_linear_state
197 : {
198 : unsigned int len;
199 : const void *data;
200 : };
201 :
202 0 : static unsigned int get_linear_data(unsigned int consumed, const u8 **dst,
203 : struct ts_config *conf,
204 : struct ts_state *state)
205 : {
206 : struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
207 :
208 0 : if (likely(consumed < st->len)) {
209 0 : *dst = st->data + consumed;
210 0 : return st->len - consumed;
211 : }
212 :
213 : return 0;
214 : }
215 :
216 : /**
217 : * textsearch_find_continuous - search a pattern in continuous/linear data
218 : * @conf: search configuration
219 : * @state: search state
220 : * @data: data to search in
221 : * @len: length of data
222 : *
223 : * A simplified version of textsearch_find() for continuous/linear data.
224 : * Call textsearch_next() to retrieve subsequent matches.
225 : *
226 : * Returns the position of first occurrence of the pattern or
227 : * %UINT_MAX if no occurrence was found.
228 : */
229 0 : unsigned int textsearch_find_continuous(struct ts_config *conf,
230 : struct ts_state *state,
231 : const void *data, unsigned int len)
232 : {
233 : struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
234 :
235 0 : conf->get_next_block = get_linear_data;
236 0 : st->data = data;
237 0 : st->len = len;
238 :
239 0 : return textsearch_find(conf, state);
240 : }
241 : EXPORT_SYMBOL(textsearch_find_continuous);
242 :
243 : /**
244 : * textsearch_prepare - Prepare a search
245 : * @algo: name of search algorithm
246 : * @pattern: pattern data
247 : * @len: length of pattern
248 : * @gfp_mask: allocation mask
249 : * @flags: search flags
250 : *
251 : * Looks up the search algorithm module and creates a new textsearch
252 : * configuration for the specified pattern.
253 : *
254 : * Note: The format of the pattern may not be compatible between
255 : * the various search algorithms.
256 : *
257 : * Returns a new textsearch configuration according to the specified
258 : * parameters or a ERR_PTR(). If a zero length pattern is passed, this
259 : * function returns EINVAL.
260 : */
261 0 : struct ts_config *textsearch_prepare(const char *algo, const void *pattern,
262 : unsigned int len, gfp_t gfp_mask, int flags)
263 : {
264 : int err = -ENOENT;
265 : struct ts_config *conf;
266 : struct ts_ops *ops;
267 :
268 0 : if (len == 0)
269 : return ERR_PTR(-EINVAL);
270 :
271 : ops = lookup_ts_algo(algo);
272 : #ifdef CONFIG_MODULES
273 : /*
274 : * Why not always autoload you may ask. Some users are
275 : * in a situation where requesting a module may deadlock,
276 : * especially when the module is located on a NFS mount.
277 : */
278 0 : if (ops == NULL && flags & TS_AUTOLOAD) {
279 0 : request_module("ts_%s", algo);
280 : ops = lookup_ts_algo(algo);
281 : }
282 : #endif
283 :
284 0 : if (ops == NULL)
285 : goto errout;
286 :
287 0 : conf = ops->init(pattern, len, gfp_mask, flags);
288 0 : if (IS_ERR(conf)) {
289 : err = PTR_ERR(conf);
290 0 : goto errout;
291 : }
292 :
293 0 : conf->ops = ops;
294 0 : return conf;
295 :
296 : errout:
297 0 : if (ops)
298 0 : module_put(ops->owner);
299 :
300 0 : return ERR_PTR(err);
301 : }
302 : EXPORT_SYMBOL(textsearch_prepare);
303 :
304 : /**
305 : * textsearch_destroy - destroy a search configuration
306 : * @conf: search configuration
307 : *
308 : * Releases all references of the configuration and frees
309 : * up the memory.
310 : */
311 0 : void textsearch_destroy(struct ts_config *conf)
312 : {
313 0 : if (conf->ops) {
314 0 : if (conf->ops->destroy)
315 0 : conf->ops->destroy(conf);
316 0 : module_put(conf->ops->owner);
317 : }
318 :
319 0 : kfree(conf);
320 0 : }
321 : EXPORT_SYMBOL(textsearch_destroy);
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