Root/lib/textsearch.c

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 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() 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 arbitary
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 patern or UINT_MAX if
69 * no match was found. Subsequent occurences 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
108static LIST_HEAD(ts_ops);
109static DEFINE_SPINLOCK(ts_mod_lock);
110
111static 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 */
141int 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;
158errout:
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 */
175int 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;
189out:
190    spin_unlock(&ts_mod_lock);
191    return err;
192}
193
194struct ts_linear_state
195{
196    unsigned int len;
197    const void *data;
198};
199
200static 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 */
227unsigned 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 */
260struct 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
295errout:
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 */
309void 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
320EXPORT_SYMBOL(textsearch_register);
321EXPORT_SYMBOL(textsearch_unregister);
322EXPORT_SYMBOL(textsearch_prepare);
323EXPORT_SYMBOL(textsearch_find_continuous);
324EXPORT_SYMBOL(textsearch_destroy);
325

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