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() 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/rculist.h> 101 #include <linux/rcupdate.h> 102 #include <linux/err.h> 103 #include <linux/textsearch.h> 104 105 static LIST_HEAD(ts_ops); 106 static DEFINE_SPINLOCK(ts_mod_lock); 107 108 static inline struct ts_ops *lookup_ts_algo(const char *name) 109 { 110 struct ts_ops *o; 111 112 rcu_read_lock(); 113 list_for_each_entry_rcu(o, &ts_ops, list) { 114 if (!strcmp(name, o->name)) { 115 if (!try_module_get(o->owner)) 116 o = NULL; 117 rcu_read_unlock(); 118 return o; 119 } 120 } 121 rcu_read_unlock(); 122 123 return NULL; 124 } 125 126 /** 127 * textsearch_register - register a textsearch module 128 * @ops: operations lookup table 129 * 130 * This function must be called by textsearch modules to announce 131 * their presence. The specified &@ops must have %name set to a 132 * unique identifier and the callbacks find(), init(), get_pattern(), 133 * and get_pattern_len() must be implemented. 134 * 135 * Returns 0 or -EEXISTS if another module has already registered 136 * with same name. 137 */ 138 int textsearch_register(struct ts_ops *ops) 139 { 140 int err = -EEXIST; 141 struct ts_ops *o; 142 143 if (ops->name == NULL || ops->find == NULL || ops->init == NULL || 144 ops->get_pattern == NULL || ops->get_pattern_len == NULL) 145 return -EINVAL; 146 147 spin_lock(&ts_mod_lock); 148 list_for_each_entry(o, &ts_ops, list) { 149 if (!strcmp(ops->name, o->name)) 150 goto errout; 151 } 152 153 list_add_tail_rcu(&ops->list, &ts_ops); 154 err = 0; 155 errout: 156 spin_unlock(&ts_mod_lock); 157 return err; 158 } 159 160 /** 161 * textsearch_unregister - unregister a textsearch module 162 * @ops: operations lookup table 163 * 164 * This function must be called by textsearch modules to announce 165 * their disappearance for examples when the module gets unloaded. 166 * The &ops parameter must be the same as the one during the 167 * registration. 168 * 169 * Returns 0 on success or -ENOENT if no matching textsearch 170 * registration was found. 171 */ 172 int textsearch_unregister(struct ts_ops *ops) 173 { 174 int err = 0; 175 struct ts_ops *o; 176 177 spin_lock(&ts_mod_lock); 178 list_for_each_entry(o, &ts_ops, list) { 179 if (o == ops) { 180 list_del_rcu(&o->list); 181 goto out; 182 } 183 } 184 185 err = -ENOENT; 186 out: 187 spin_unlock(&ts_mod_lock); 188 return err; 189 } 190 191 struct ts_linear_state 192 { 193 unsigned int len; 194 const void *data; 195 }; 196 197 static unsigned int get_linear_data(unsigned int consumed, const u8 **dst, 198 struct ts_config *conf, 199 struct ts_state *state) 200 { 201 struct ts_linear_state *st = (struct ts_linear_state *) state->cb; 202 203 if (likely(consumed < st->len)) { 204 *dst = st->data + consumed; 205 return st->len - consumed; 206 } 207 208 return 0; 209 } 210 211 /** 212 * textsearch_find_continuous - search a pattern in continuous/linear data 213 * @conf: search configuration 214 * @state: search state 215 * @data: data to search in 216 * @len: length of data 217 * 218 * A simplified version of textsearch_find() for continuous/linear data. 219 * Call textsearch_next() to retrieve subsequent matches. 220 * 221 * Returns the position of first occurrence of the pattern or 222 * %UINT_MAX if no occurrence was found. 223 */ 224 unsigned int textsearch_find_continuous(struct ts_config *conf, 225 struct ts_state *state, 226 const void *data, unsigned int len) 227 { 228 struct ts_linear_state *st = (struct ts_linear_state *) state->cb; 229 230 conf->get_next_block = get_linear_data; 231 st->data = data; 232 st->len = len; 233 234 return textsearch_find(conf, state); 235 } 236 237 /** 238 * textsearch_prepare - Prepare a search 239 * @algo: name of search algorithm 240 * @pattern: pattern data 241 * @len: length of pattern 242 * @gfp_mask: allocation mask 243 * @flags: search flags 244 * 245 * Looks up the search algorithm module and creates a new textsearch 246 * configuration for the specified pattern. Upon completion all 247 * necessary refcnts are held and the configuration must be put back 248 * using textsearch_put() after usage. 249 * 250 * Note: The format of the pattern may not be compatible between 251 * the various search algorithms. 252 * 253 * Returns a new textsearch configuration according to the specified 254 * parameters or a ERR_PTR(). If a zero length pattern is passed, this 255 * function returns EINVAL. 256 */ 257 struct ts_config *textsearch_prepare(const char *algo, const void *pattern, 258 unsigned int len, gfp_t gfp_mask, int flags) 259 { 260 int err = -ENOENT; 261 struct ts_config *conf; 262 struct ts_ops *ops; 263 264 if (len == 0) 265 return ERR_PTR(-EINVAL); 266 267 ops = lookup_ts_algo(algo); 268 #ifdef CONFIG_KMOD 269 /* 270 * Why not always autoload you may ask. Some users are 271 * in a situation where requesting a module may deadlock, 272 * especially when the module is located on a NFS mount. 273 */ 274 if (ops == NULL && flags & TS_AUTOLOAD) { 275 request_module("ts_%s", algo); 276 ops = lookup_ts_algo(algo); 277 } 278 #endif 279 280 if (ops == NULL) 281 goto errout; 282 283 conf = ops->init(pattern, len, gfp_mask); 284 if (IS_ERR(conf)) { 285 err = PTR_ERR(conf); 286 goto errout; 287 } 288 289 conf->ops = ops; 290 return conf; 291 292 errout: 293 if (ops) 294 module_put(ops->owner); 295 296 return ERR_PTR(err); 297 } 298 299 /** 300 * textsearch_destroy - destroy a search configuration 301 * @conf: search configuration 302 * 303 * Releases all references of the configuration and frees 304 * up the memory. 305 */ 306 void textsearch_destroy(struct ts_config *conf) 307 { 308 if (conf->ops) { 309 if (conf->ops->destroy) 310 conf->ops->destroy(conf); 311 module_put(conf->ops->owner); 312 } 313 314 kfree(conf); 315 } 316 317 EXPORT_SYMBOL(textsearch_register); 318 EXPORT_SYMBOL(textsearch_unregister); 319 EXPORT_SYMBOL(textsearch_prepare); 320 EXPORT_SYMBOL(textsearch_find_continuous); 321 EXPORT_SYMBOL(textsearch_destroy); 322