xref: /openbmc/linux/lib/textsearch.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
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@eurodev.net>
11  *
12  * ==========================================================================
13  *
14  * INTRODUCTION
15  *
16  *   The textsearch infrastructure provides text searching facitilies 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 continously
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() specyfing the searching algorithm and
58  *   the pattern to look for. The returned configuration may then be used
59  *   for an arbitary amount of times and even in parallel as long as a
60  *   separate struct ts_state variable is provided to every instance.
61  *
62  *   The actual search is performed by either calling textsearch_find_-
63  *   continuous() for linear data or by providing an own get_next_block()
64  *   implementation and calling textsearch_find(). Both functions return
65  *   the position of the first occurrence of the patern or UINT_MAX if
66  *   no match was found. Subsequent occurences can be found by calling
67  *   textsearch_next() regardless of the linearity of the data.
68  *
69  *   Once you're done using a configuration it must be given back via
70  *   textsearch_destroy.
71  *
72  * EXAMPLE
73  *
74  *   int pos;
75  *   struct ts_config *conf;
76  *   struct ts_state state;
77  *   const char *pattern = "chicken";
78  *   const char *example = "We dance the funky chicken";
79  *
80  *   conf = textsearch_prepare("kmp", pattern, strlen(pattern),
81  *                             GFP_KERNEL, TS_AUTOLOAD);
82  *   if (IS_ERR(conf)) {
83  *       err = PTR_ERR(conf);
84  *       goto errout;
85  *   }
86  *
87  *   pos = textsearch_find_continuous(conf, &state, example, strlen(example));
88  *   if (pos != UINT_MAX)
89  *       panic("Oh my god, dancing chickens at %d\n", pos);
90  *
91  *   textsearch_destroy(conf);
92  *
93  * ==========================================================================
94  */
95 
96 #include <linux/module.h>
97 #include <linux/types.h>
98 #include <linux/string.h>
99 #include <linux/init.h>
100 #include <linux/rcupdate.h>
101 #include <linux/err.h>
102 #include <linux/textsearch.h>
103 
104 static LIST_HEAD(ts_ops);
105 static DEFINE_SPINLOCK(ts_mod_lock);
106 
107 static inline struct ts_ops *lookup_ts_algo(const char *name)
108 {
109 	struct ts_ops *o;
110 
111 	rcu_read_lock();
112 	list_for_each_entry_rcu(o, &ts_ops, list) {
113 		if (!strcmp(name, o->name)) {
114 			if (!try_module_get(o->owner))
115 				o = NULL;
116 			rcu_read_unlock();
117 			return o;
118 		}
119 	}
120 	rcu_read_unlock();
121 
122 	return NULL;
123 }
124 
125 /**
126  * textsearch_register - register a textsearch module
127  * @ops: operations lookup table
128  *
129  * This function must be called by textsearch modules to announce
130  * their presence. The specified &@ops must have %name set to a
131  * unique identifier and the callbacks find(), init(), get_pattern(),
132  * and get_pattern_len() must be implemented.
133  *
134  * Returns 0 or -EEXISTS if another module has already registered
135  * with same name.
136  */
137 int textsearch_register(struct ts_ops *ops)
138 {
139 	int err = -EEXIST;
140 	struct ts_ops *o;
141 
142 	if (ops->name == NULL || ops->find == NULL || ops->init == NULL ||
143 	    ops->get_pattern == NULL || ops->get_pattern_len == NULL)
144 		return -EINVAL;
145 
146 	spin_lock(&ts_mod_lock);
147 	list_for_each_entry(o, &ts_ops, list) {
148 		if (!strcmp(ops->name, o->name))
149 			goto errout;
150 	}
151 
152 	list_add_tail_rcu(&ops->list, &ts_ops);
153 	err = 0;
154 errout:
155 	spin_unlock(&ts_mod_lock);
156 	return err;
157 }
158 
159 /**
160  * textsearch_unregister - unregister a textsearch module
161  * @ops: operations lookup table
162  *
163  * This function must be called by textsearch modules to announce
164  * their disappearance for examples when the module gets unloaded.
165  * The &ops parameter must be the same as the one during the
166  * registration.
167  *
168  * Returns 0 on success or -ENOENT if no matching textsearch
169  * registration was found.
170  */
171 int textsearch_unregister(struct ts_ops *ops)
172 {
173 	int err = 0;
174 	struct ts_ops *o;
175 
176 	spin_lock(&ts_mod_lock);
177 	list_for_each_entry(o, &ts_ops, list) {
178 		if (o == ops) {
179 			list_del_rcu(&o->list);
180 			goto out;
181 		}
182 	}
183 
184 	err = -ENOENT;
185 out:
186 	spin_unlock(&ts_mod_lock);
187 	return err;
188 }
189 
190 struct ts_linear_state
191 {
192 	unsigned int	len;
193 	const void	*data;
194 };
195 
196 static unsigned int get_linear_data(unsigned int consumed, const u8 **dst,
197 				    struct ts_config *conf,
198 				    struct ts_state *state)
199 {
200 	struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
201 
202 	if (likely(consumed < st->len)) {
203 		*dst = st->data + consumed;
204 		return st->len - consumed;
205 	}
206 
207 	return 0;
208 }
209 
210 /**
211  * textsearch_find_continuous - search a pattern in continuous/linear data
212  * @conf: search configuration
213  * @state: search state
214  * @data: data to search in
215  * @len: length of data
216  *
217  * A simplified version of textsearch_find() for continuous/linear data.
218  * Call textsearch_next() to retrieve subsequent matches.
219  *
220  * Returns the position of first occurrence of the pattern or
221  * %UINT_MAX if no occurrence was found.
222  */
223 unsigned int textsearch_find_continuous(struct ts_config *conf,
224 					struct ts_state *state,
225 					const void *data, unsigned int len)
226 {
227 	struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
228 
229 	conf->get_next_block = get_linear_data;
230 	st->data = data;
231 	st->len = len;
232 
233 	return textsearch_find(conf, state);
234 }
235 
236 /**
237  * textsearch_prepare - Prepare a search
238  * @algo: name of search algorithm
239  * @pattern: pattern data
240  * @len: length of pattern
241  * @gfp_mask: allocation mask
242  * @flags: search flags
243  *
244  * Looks up the search algorithm module and creates a new textsearch
245  * configuration for the specified pattern. Upon completion all
246  * necessary refcnts are held and the configuration must be put back
247  * using textsearch_put() after usage.
248  *
249  * Note: The format of the pattern may not be compatible between
250  *       the various search algorithms.
251  *
252  * Returns a new textsearch configuration according to the specified
253  *         parameters or a ERR_PTR().
254  */
255 struct ts_config *textsearch_prepare(const char *algo, const void *pattern,
256 				     unsigned int len, gfp_t gfp_mask, int flags)
257 {
258 	int err = -ENOENT;
259 	struct ts_config *conf;
260 	struct ts_ops *ops;
261 
262 	ops = lookup_ts_algo(algo);
263 #ifdef CONFIG_KMOD
264 	/*
265 	 * Why not always autoload you may ask. Some users are
266 	 * in a situation where requesting a module may deadlock,
267 	 * especially when the module is located on a NFS mount.
268 	 */
269 	if (ops == NULL && flags & TS_AUTOLOAD) {
270 		request_module("ts_%s", algo);
271 		ops = lookup_ts_algo(algo);
272 	}
273 #endif
274 
275 	if (ops == NULL)
276 		goto errout;
277 
278 	conf = ops->init(pattern, len, gfp_mask);
279 	if (IS_ERR(conf)) {
280 		err = PTR_ERR(conf);
281 		goto errout;
282 	}
283 
284 	conf->ops = ops;
285 	return conf;
286 
287 errout:
288 	if (ops)
289 		module_put(ops->owner);
290 
291 	return ERR_PTR(err);
292 }
293 
294 /**
295  * textsearch_destroy - destroy a search configuration
296  * @conf: search configuration
297  *
298  * Releases all references of the configuration and frees
299  * up the memory.
300  */
301 void textsearch_destroy(struct ts_config *conf)
302 {
303 	if (conf->ops) {
304 		if (conf->ops->destroy)
305 			conf->ops->destroy(conf);
306 		module_put(conf->ops->owner);
307 	}
308 
309 	kfree(conf);
310 }
311 
312 EXPORT_SYMBOL(textsearch_register);
313 EXPORT_SYMBOL(textsearch_unregister);
314 EXPORT_SYMBOL(textsearch_prepare);
315 EXPORT_SYMBOL(textsearch_find_continuous);
316 EXPORT_SYMBOL(textsearch_destroy);
317