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