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Linux/lib/textsearch.c

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  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         list_for_each_entry_rcu(o, &ts_ops, list) {
117                 if (!strcmp(name, o->name)) {
118                         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 int textsearch_register(struct ts_ops *ops)
142 {
143         int err = -EEXIST;
144         struct ts_ops *o;
145 
146         if (ops->name == NULL || ops->find == NULL || ops->init == NULL ||
147             ops->get_pattern == NULL || ops->get_pattern_len == NULL)
148                 return -EINVAL;
149 
150         spin_lock(&ts_mod_lock);
151         list_for_each_entry(o, &ts_ops, list) {
152                 if (!strcmp(ops->name, o->name))
153                         goto errout;
154         }
155 
156         list_add_tail_rcu(&ops->list, &ts_ops);
157         err = 0;
158 errout:
159         spin_unlock(&ts_mod_lock);
160         return err;
161 }
162 
163 /**
164  * textsearch_unregister - unregister a textsearch module
165  * @ops: operations lookup table
166  *
167  * This function must be called by textsearch modules to announce
168  * their disappearance for examples when the module gets unloaded.
169  * The &ops parameter must be the same as the one during the
170  * registration.
171  *
172  * Returns 0 on success or -ENOENT if no matching textsearch
173  * registration was found.
174  */
175 int textsearch_unregister(struct ts_ops *ops)
176 {
177         int err = 0;
178         struct ts_ops *o;
179 
180         spin_lock(&ts_mod_lock);
181         list_for_each_entry(o, &ts_ops, list) {
182                 if (o == ops) {
183                         list_del_rcu(&o->list);
184                         goto out;
185                 }
186         }
187 
188         err = -ENOENT;
189 out:
190         spin_unlock(&ts_mod_lock);
191         return err;
192 }
193 
194 struct ts_linear_state
195 {
196         unsigned int    len;
197         const void      *data;
198 };
199 
200 static unsigned int get_linear_data(unsigned int consumed, const u8 **dst,
201                                     struct ts_config *conf,
202                                     struct ts_state *state)
203 {
204         struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
205 
206         if (likely(consumed < st->len)) {
207                 *dst = st->data + consumed;
208                 return st->len - consumed;
209         }
210 
211         return 0;
212 }
213 
214 /**
215  * textsearch_find_continuous - search a pattern in continuous/linear data
216  * @conf: search configuration
217  * @state: search state
218  * @data: data to search in
219  * @len: length of data
220  *
221  * A simplified version of textsearch_find() for continuous/linear data.
222  * Call textsearch_next() to retrieve subsequent matches.
223  *
224  * Returns the position of first occurrence of the pattern or
225  * %UINT_MAX if no occurrence was found.
226  */ 
227 unsigned int textsearch_find_continuous(struct ts_config *conf,
228                                         struct ts_state *state,
229                                         const void *data, unsigned int len)
230 {
231         struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
232 
233         conf->get_next_block = get_linear_data;
234         st->data = data;
235         st->len = len;
236 
237         return textsearch_find(conf, state);
238 }
239 
240 /**
241  * textsearch_prepare - Prepare a search
242  * @algo: name of search algorithm
243  * @pattern: pattern data
244  * @len: length of pattern
245  * @gfp_mask: allocation mask
246  * @flags: search flags
247  *
248  * Looks up the search algorithm module and creates a new textsearch
249  * configuration for the specified pattern. Upon completion all
250  * necessary refcnts are held and the configuration must be put back
251  * using textsearch_put() after usage.
252  *
253  * Note: The format of the pattern may not be compatible between
254  *       the various search algorithms.
255  *
256  * Returns a new textsearch configuration according to the specified
257  * parameters or a ERR_PTR(). If a zero length pattern is passed, this
258  * function returns EINVAL.
259  */
260 struct ts_config *textsearch_prepare(const char *algo, const void *pattern,
261                                      unsigned int len, gfp_t gfp_mask, int flags)
262 {
263         int err = -ENOENT;
264         struct ts_config *conf;
265         struct ts_ops *ops;
266         
267         if (len == 0)
268                 return ERR_PTR(-EINVAL);
269 
270         ops = lookup_ts_algo(algo);
271 #ifdef CONFIG_MODULES
272         /*
273          * Why not always autoload you may ask. Some users are
274          * in a situation where requesting a module may deadlock,
275          * especially when the module is located on a NFS mount.
276          */
277         if (ops == NULL && flags & TS_AUTOLOAD) {
278                 request_module("ts_%s", algo);
279                 ops = lookup_ts_algo(algo);
280         }
281 #endif
282 
283         if (ops == NULL)
284                 goto errout;
285 
286         conf = ops->init(pattern, len, gfp_mask, flags);
287         if (IS_ERR(conf)) {
288                 err = PTR_ERR(conf);
289                 goto errout;
290         }
291 
292         conf->ops = ops;
293         return conf;
294 
295 errout:
296         if (ops)
297                 module_put(ops->owner);
298                 
299         return ERR_PTR(err);
300 }
301 
302 /**
303  * textsearch_destroy - destroy a search configuration
304  * @conf: search configuration
305  *
306  * Releases all references of the configuration and frees
307  * up the memory.
308  */
309 void textsearch_destroy(struct ts_config *conf)
310 {
311         if (conf->ops) {
312                 if (conf->ops->destroy)
313                         conf->ops->destroy(conf);
314                 module_put(conf->ops->owner);
315         }
316 
317         kfree(conf);
318 }
319 
320 EXPORT_SYMBOL(textsearch_register);
321 EXPORT_SYMBOL(textsearch_unregister);
322 EXPORT_SYMBOL(textsearch_prepare);
323 EXPORT_SYMBOL(textsearch_find_continuous);
324 EXPORT_SYMBOL(textsearch_destroy);
325 

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