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() 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);