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
  15 /**
  16  * DOC: ts_intro
  17  * INTRODUCTION
  18  *
  19  *   The textsearch infrastructure provides text searching facilities for
  20  *   both linear and non-linear data. Individual search algorithms are
  21  *   implemented in modules and chosen by the user.
  22  *
  23  * ARCHITECTURE
  24  *
  25  * .. code-block:: none
  26  *
  27  *     User
  28  *     +----------------+
  29  *     |        finish()|<--------------(6)-----------------+
  30  *     |get_next_block()|<--------------(5)---------------+ |
  31  *     |                |                     Algorithm   | |
  32  *     |                |                    +------------------------------+
  33  *     |                |                    |  init()   find()   destroy() |
  34  *     |                |                    +------------------------------+
  35  *     |                |       Core API           ^       ^          ^
  36  *     |                |      +---------------+  (2)     (4)        (8)
  37  *     |             (1)|----->| prepare()     |---+       |          |
  38  *     |             (3)|----->| find()/next() |-----------+          |
  39  *     |             (7)|----->| destroy()     |----------------------+
  40  *     +----------------+      +---------------+
  41  *
  42  *   (1) User configures a search by calling textsearch_prepare() specifying
  43  *       the search parameters such as the pattern and algorithm name.
  44  *   (2) Core requests the algorithm to allocate and initialize a search
  45  *       configuration according to the specified parameters.
  46  *   (3) User starts the search(es) by calling textsearch_find() or
  47  *       textsearch_next() to fetch subsequent occurrences. A state variable
  48  *       is provided to the algorithm to store persistent variables.
  49  *   (4) Core eventually resets the search offset and forwards the find()
  50  *       request to the algorithm.
  51  *   (5) Algorithm calls get_next_block() provided by the user continuously
  52  *       to fetch the data to be searched in block by block.
  53  *   (6) Algorithm invokes finish() after the last call to get_next_block
  54  *       to clean up any leftovers from get_next_block. (Optional)
  55  *   (7) User destroys the configuration by calling textsearch_destroy().
  56  *   (8) Core notifies the algorithm to destroy algorithm specific
  57  *       allocations. (Optional)
  58  *
  59  * USAGE
  60  *
  61  *   Before a search can be performed, a configuration must be created
  62  *   by calling textsearch_prepare() specifying the searching algorithm,
  63  *   the pattern to look for and flags. As a flag, you can set TS_IGNORECASE
  64  *   to perform case insensitive matching. But it might slow down
  65  *   performance of algorithm, so you should use it at own your risk.
  66  *   The returned configuration may then be used for an arbitrary
  67  *   amount of times and even in parallel as long as a separate struct
  68  *   ts_state variable is provided to every instance.
  69  *
  70  *   The actual search is performed by either calling
  71  *   textsearch_find_continuous() for linear data or by providing
  72  *   an own get_next_block() implementation and
  73  *   calling textsearch_find(). Both functions return
  74  *   the position of the first occurrence of the pattern or UINT_MAX if
  75  *   no match was found. Subsequent occurrences can be found by calling
  76  *   textsearch_next() regardless of the linearity of the data.
  77  *
  78  *   Once you're done using a configuration it must be given back via
  79  *   textsearch_destroy.
  80  *
  81  * EXAMPLE::
  82  *
  83  *   int pos;
  84  *   struct ts_config *conf;
  85  *   struct ts_state state;
  86  *   const char *pattern = "chicken";
  87  *   const char *example = "We dance the funky chicken";
  88  *
  89  *   conf = textsearch_prepare("kmp", pattern, strlen(pattern),
  90  *                             GFP_KERNEL, TS_AUTOLOAD);
  91  *   if (IS_ERR(conf)) {
  92  *       err = PTR_ERR(conf);
  93  *       goto errout;
  94  *   }
  95  *
  96  *   pos = textsearch_find_continuous(conf, \&state, example, strlen(example));
  97  *   if (pos != UINT_MAX)
  98  *       panic("Oh my god, dancing chickens at \%d\n", pos);
  99  *
 100  *   textsearch_destroy(conf);
 101  */
 102 /* ========================================================================== */
 103
 104 #include <linux/module.h>
 105 #include <linux/types.h>
 106 #include <linux/string.h>
 107 #include <linux/init.h>
 108 #include <linux/rculist.h>
 109 #include <linux/rcupdate.h>
 110 #include <linux/err.h>
 111 #include <linux/textsearch.h>
 112 #include <linux/slab.h>
 113
 114 static LIST_HEAD(ts_ops);
 115 static DEFINE_SPINLOCK(ts_mod_lock);
 116
 117 static inline struct ts_ops *lookup_ts_algo(const char *name)
 118 {
 119         struct ts_ops *o;
 120
 121         rcu_read_lock();
 122         list_for_each_entry_rcu(o, &ts_ops, list) {
 123                 if (!strcmp(name, o->name)) {
 124                         if (!try_module_get(o->owner))
 125                                 o = NULL;
 126                         rcu_read_unlock();
 127                         return o;
 128                 }
 129         }
 130         rcu_read_unlock();
 131
 132         return NULL;
 133 }
 134
 135 /**
 136  * textsearch_register - register a textsearch module
 137  * @ops: operations lookup table
 138  *
 139  * This function must be called by textsearch modules to announce
 140  * their presence. The specified &@ops must have %name set to a
 141  * unique identifier and the callbacks find(), init(), get_pattern(),
 142  * and get_pattern_len() must be implemented.
 143  *
 144  * Returns 0 or -EEXISTS if another module has already registered
 145  * with same name.
 146  */
 147 int textsearch_register(struct ts_ops *ops)
 148 {
 149         int err = -EEXIST;
 150         struct ts_ops *o;
 151
 152         if (ops->name == NULL || ops->find == NULL || ops->init == NULL ||
 153             ops->get_pattern == NULL || ops->get_pattern_len == NULL)
 154                 return -EINVAL;
 155
 156         spin_lock(&ts_mod_lock);
 157         list_for_each_entry(o, &ts_ops, list) {
 158                 if (!strcmp(ops->name, o->name))
 159                         goto errout;
 160         }
 161
 162         list_add_tail_rcu(&ops->list, &ts_ops);
 163         err = 0;
 164 errout:
 165         spin_unlock(&ts_mod_lock);
 166         return err;
 167 }
 168 EXPORT_SYMBOL(textsearch_register);
 169
 170 /**
 171  * textsearch_unregister - unregister a textsearch module
 172  * @ops: operations lookup table
 173  *
 174  * This function must be called by textsearch modules to announce
 175  * their disappearance for examples when the module gets unloaded.
 176  * The &ops parameter must be the same as the one during the
 177  * registration.
 178  *
 179  * Returns 0 on success or -ENOENT if no matching textsearch
 180  * registration was found.
 181  */
 182 int textsearch_unregister(struct ts_ops *ops)
 183 {
 184         int err = 0;
 185         struct ts_ops *o;
 186
 187         spin_lock(&ts_mod_lock);
 188         list_for_each_entry(o, &ts_ops, list) {
 189                 if (o == ops) {
 190                         list_del_rcu(&o->list);
 191                         goto out;
 192                 }
 193         }
 194
 195         err = -ENOENT;
 196 out:
 197         spin_unlock(&ts_mod_lock);
 198         return err;
 199 }
 200 EXPORT_SYMBOL(textsearch_unregister);
 201
 202 struct ts_linear_state
 203 {
 204         unsigned int    len;
 205         const void      *data;
 206 };
 207
 208 static unsigned int get_linear_data(unsigned int consumed, const u8 **dst,
 209                                     struct ts_config *conf,
 210                                     struct ts_state *state)
 211 {
 212         struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
 213
 214         if (likely(consumed < st->len)) {
 215                 *dst = st->data + consumed;
 216                 return st->len - consumed;
 217         }
 218
 219         return 0;
 220 }
 221
 222 /**
 223  * textsearch_find_continuous - search a pattern in continuous/linear data
 224  * @conf: search configuration
 225  * @state: search state
 226  * @data: data to search in
 227  * @len: length of data
 228  *
 229  * A simplified version of textsearch_find() for continuous/linear data.
 230  * Call textsearch_next() to retrieve subsequent matches.
 231  *
 232  * Returns the position of first occurrence of the pattern or
 233  * %UINT_MAX if no occurrence was found.
 234  */
 235 unsigned int textsearch_find_continuous(struct ts_config *conf,
 236                                         struct ts_state *state,
 237                                         const void *data, unsigned int len)
 238 {
 239         struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
 240
 241         conf->get_next_block = get_linear_data;
 242         st->data = data;
 243         st->len = len;
 244
 245         return textsearch_find(conf, state);
 246 }
 247 EXPORT_SYMBOL(textsearch_find_continuous);
 248
 249 /**
 250  * textsearch_prepare - Prepare a search
 251  * @algo: name of search algorithm
 252  * @pattern: pattern data
 253  * @len: length of pattern
 254  * @gfp_mask: allocation mask
 255  * @flags: search flags
 256  *
 257  * Looks up the search algorithm module and creates a new textsearch
 258  * configuration for the specified pattern.
 259  *
 260  * Note: The format of the pattern may not be compatible between
 261  *       the various search algorithms.
 262  *
 263  * Returns a new textsearch configuration according to the specified
 264  * parameters or a ERR_PTR(). If a zero length pattern is passed, this
 265  * function returns EINVAL.
 266  */
 267 struct ts_config *textsearch_prepare(const char *algo, const void *pattern,
 268                                      unsigned int len, gfp_t gfp_mask, int flags)
 269 {
 270         int err = -ENOENT;
 271         struct ts_config *conf;
 272         struct ts_ops *ops;
 273
 274         if (len == 0)
 275                 return ERR_PTR(-EINVAL);
 276
 277         ops = lookup_ts_algo(algo);
 278 #ifdef CONFIG_MODULES
 279         /*
 280          * Why not always autoload you may ask. Some users are
 281          * in a situation where requesting a module may deadlock,
 282          * especially when the module is located on a NFS mount.
 283          */
 284         if (ops == NULL && flags & TS_AUTOLOAD) {
 285                 request_module("ts_%s", algo);
 286                 ops = lookup_ts_algo(algo);
 287         }
 288 #endif
 289
 290         if (ops == NULL)
 291                 goto errout;
 292
 293         conf = ops->init(pattern, len, gfp_mask, flags);
 294         if (IS_ERR(conf)) {
 295                 err = PTR_ERR(conf);
 296                 goto errout;
 297         }
 298
 299         conf->ops = ops;
 300         return conf;
 301
 302 errout:
 303         if (ops)
 304                 module_put(ops->owner);
 305
 306         return ERR_PTR(err);
 307 }
 308 EXPORT_SYMBOL(textsearch_prepare);
 309
 310 /**
 311  * textsearch_destroy - destroy a search configuration
 312  * @conf: search configuration
 313  *
 314  * Releases all references of the configuration and frees
 315  * up the memory.
 316  */
 317 void textsearch_destroy(struct ts_config *conf)
 318 {
 319         if (conf->ops) {
 320                 if (conf->ops->destroy)
 321                         conf->ops->destroy(conf);
 322                 module_put(conf->ops->owner);
 323         }
 324
 325         kfree(conf);
 326 }
 327 EXPORT_SYMBOL(textsearch_destroy);