linux/lib/textsearch.c
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   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
 107static LIST_HEAD(ts_ops);
 108static DEFINE_SPINLOCK(ts_mod_lock);
 109
 110static 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 */
 140int 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;
 157errout:
 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 */
 174int 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;
 188out:
 189        spin_unlock(&ts_mod_lock);
 190        return err;
 191}
 192
 193struct ts_linear_state
 194{
 195        unsigned int    len;
 196        const void      *data;
 197};
 198
 199static 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 */ 
 226unsigned 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 */
 259struct 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
 294errout:
 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 */
 308void 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
 319EXPORT_SYMBOL(textsearch_register);
 320EXPORT_SYMBOL(textsearch_unregister);
 321EXPORT_SYMBOL(textsearch_prepare);
 322EXPORT_SYMBOL(textsearch_find_continuous);
 323EXPORT_SYMBOL(textsearch_destroy);
 324
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