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