FreeBSD/Linux Kernel Cross Reference
sys/lib/textsearch.c

     /*
      * lib/textsearch.c     Generic text search interface
      *
      *              This program is free software; you can redistribute it and/or
      *              modify it under the terms of the GNU General Public License
      *              as published by the Free Software Foundation; either version
      *              2 of the License, or (at your option) any later version.
      *
      * Authors:     Thomas Graf <tgraf@suug.ch>
     *              Pablo Neira Ayuso <pablo@netfilter.org>
     *
     * ==========================================================================
     *
     * INTRODUCTION
     *
     *   The textsearch infrastructure provides text searching facilities for
     *   both linear and non-linear data. Individual search algorithms are
     *   implemented in modules and chosen by the user.
     *
     * ARCHITECTURE
     *
     *      User
     *     +----------------+
     *     |        finish()|<--------------(6)-----------------+
     *     |get_next_block()|<--------------(5)---------------+ |
     *     |                |                     Algorithm   | |
     *     |                |                    +------------------------------+
     *     |                |                    |  init()   find()   destroy() |
     *     |                |                    +------------------------------+
     *     |                |       Core API           ^       ^          ^
     *     |                |      +---------------+  (2)     (4)        (8)
     *     |             (1)|----->| prepare()     |---+       |          |
     *     |             (3)|----->| find()/next() |-----------+          |
     *     |             (7)|----->| destroy()     |----------------------+
     *     +----------------+      +---------------+
     *  
     *   (1) User configures a search by calling _prepare() specifying the
     *       search parameters such as the pattern and algorithm name.
     *   (2) Core requests the algorithm to allocate and initialize a search
     *       configuration according to the specified parameters.
     *   (3) User starts the search(es) by calling _find() or _next() to
     *       fetch subsequent occurrences. A state variable is provided
     *       to the algorithm to store persistent variables.
     *   (4) Core eventually resets the search offset and forwards the find()
     *       request to the algorithm.
     *   (5) Algorithm calls get_next_block() provided by the user continuously
     *       to fetch the data to be searched in block by block.
     *   (6) Algorithm invokes finish() after the last call to get_next_block
     *       to clean up any leftovers from get_next_block. (Optional)
     *   (7) User destroys the configuration by calling _destroy().
     *   (8) Core notifies the algorithm to destroy algorithm specific
     *       allocations. (Optional)
     *
     * USAGE
     *
     *   Before a search can be performed, a configuration must be created
     *   by calling textsearch_prepare() specifying the searching algorithm,
     *   the pattern to look for and flags. As a flag, you can set TS_IGNORECASE
     *   to perform case insensitive matching. But it might slow down
     *   performance of algorithm, so you should use it at own your risk.
     *   The returned configuration may then be used for an arbitrary
     *   amount of times and even in parallel as long as a separate struct
     *   ts_state variable is provided to every instance.
     *
     *   The actual search is performed by either calling textsearch_find_-
     *   continuous() for linear data or by providing an own get_next_block()
     *   implementation and calling textsearch_find(). Both functions return
     *   the position of the first occurrence of the pattern or UINT_MAX if
     *   no match was found. Subsequent occurrences can be found by calling
     *   textsearch_next() regardless of the linearity of the data.
     *
     *   Once you're done using a configuration it must be given back via
     *   textsearch_destroy.
     *
     * EXAMPLE
     *
     *   int pos;
     *   struct ts_config *conf;
     *   struct ts_state state;
     *   const char *pattern = "chicken";
     *   const char *example = "We dance the funky chicken";
     *
     *   conf = textsearch_prepare("kmp", pattern, strlen(pattern),
     *                             GFP_KERNEL, TS_AUTOLOAD);
     *   if (IS_ERR(conf)) {
     *       err = PTR_ERR(conf);
     *       goto errout;
     *   }
     *
     *   pos = textsearch_find_continuous(conf, &state, example, strlen(example));
     *   if (pos != UINT_MAX)
     *       panic("Oh my god, dancing chickens at %d\n", pos);
     *
     *   textsearch_destroy(conf);
     * ==========================================================================
     */
    
    #include <linux/module.h>
    #include <linux/types.h>
   #include <linux/string.h>
   #include <linux/init.h>
   #include <linux/rculist.h>
   #include <linux/rcupdate.h>
   #include <linux/err.h>
   #include <linux/textsearch.h>
   #include <linux/slab.h>
   
   static LIST_HEAD(ts_ops);
   static DEFINE_SPINLOCK(ts_mod_lock);
   
   static inline struct ts_ops *lookup_ts_algo(const char *name)
   {
           struct ts_ops *o;
   
           rcu_read_lock();
           list_for_each_entry_rcu(o, &ts_ops, list) {
                   if (!strcmp(name, o->name)) {
                           if (!try_module_get(o->owner))
                                   o = NULL;
                           rcu_read_unlock();
                           return o;
                   }
           }
           rcu_read_unlock();
   
           return NULL;
   }
   
   /**
    * textsearch_register - register a textsearch module
    * @ops: operations lookup table
    *
    * This function must be called by textsearch modules to announce
    * their presence. The specified &@ops must have %name set to a
    * unique identifier and the callbacks find(), init(), get_pattern(),
    * and get_pattern_len() must be implemented.
    *
    * Returns 0 or -EEXISTS if another module has already registered
    * with same name.
    */
   int textsearch_register(struct ts_ops *ops)
   {
           int err = -EEXIST;
           struct ts_ops *o;
   
           if (ops->name == NULL || ops->find == NULL || ops->init == NULL ||
               ops->get_pattern == NULL || ops->get_pattern_len == NULL)
                   return -EINVAL;
   
           spin_lock(&ts_mod_lock);
           list_for_each_entry(o, &ts_ops, list) {
                   if (!strcmp(ops->name, o->name))
                           goto errout;
           }
   
           list_add_tail_rcu(&ops->list, &ts_ops);
           err = 0;
   errout:
           spin_unlock(&ts_mod_lock);
           return err;
   }
   
   /**
    * textsearch_unregister - unregister a textsearch module
    * @ops: operations lookup table
    *
    * This function must be called by textsearch modules to announce
    * their disappearance for examples when the module gets unloaded.
    * The &ops parameter must be the same as the one during the
    * registration.
    *
    * Returns 0 on success or -ENOENT if no matching textsearch
    * registration was found.
    */
   int textsearch_unregister(struct ts_ops *ops)
   {
           int err = 0;
           struct ts_ops *o;
   
           spin_lock(&ts_mod_lock);
           list_for_each_entry(o, &ts_ops, list) {
                   if (o == ops) {
                           list_del_rcu(&o->list);
                           goto out;
                   }
           }
   
           err = -ENOENT;
   out:
           spin_unlock(&ts_mod_lock);
           return err;
   }
   
   struct ts_linear_state
   {
           unsigned int    len;
           const void      *data;
   };
   
   static unsigned int get_linear_data(unsigned int consumed, const u8 **dst,
                                       struct ts_config *conf,
                                       struct ts_state *state)
   {
           struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
   
           if (likely(consumed < st->len)) {
                   *dst = st->data + consumed;
                   return st->len - consumed;
           }
   
           return 0;
   }
   
   /**
    * textsearch_find_continuous - search a pattern in continuous/linear data
    * @conf: search configuration
    * @state: search state
    * @data: data to search in
    * @len: length of data
    *
    * A simplified version of textsearch_find() for continuous/linear data.
    * Call textsearch_next() to retrieve subsequent matches.
    *
    * Returns the position of first occurrence of the pattern or
    * %UINT_MAX if no occurrence was found.
    */ 
   unsigned int textsearch_find_continuous(struct ts_config *conf,
                                           struct ts_state *state,
                                           const void *data, unsigned int len)
   {
           struct ts_linear_state *st = (struct ts_linear_state *) state->cb;
   
           conf->get_next_block = get_linear_data;
           st->data = data;
           st->len = len;
   
           return textsearch_find(conf, state);
   }
   
   /**
    * textsearch_prepare - Prepare a search
    * @algo: name of search algorithm
    * @pattern: pattern data
    * @len: length of pattern
    * @gfp_mask: allocation mask
    * @flags: search flags
    *
    * Looks up the search algorithm module and creates a new textsearch
    * configuration for the specified pattern. Upon completion all
    * necessary refcnts are held and the configuration must be put back
    * using textsearch_put() after usage.
    *
    * Note: The format of the pattern may not be compatible between
    *       the various search algorithms.
    *
    * Returns a new textsearch configuration according to the specified
    * parameters or a ERR_PTR(). If a zero length pattern is passed, this
    * function returns EINVAL.
    */
   struct ts_config *textsearch_prepare(const char *algo, const void *pattern,
                                        unsigned int len, gfp_t gfp_mask, int flags)
   {
           int err = -ENOENT;
           struct ts_config *conf;
           struct ts_ops *ops;
           
           if (len == 0)
                   return ERR_PTR(-EINVAL);
   
           ops = lookup_ts_algo(algo);
   #ifdef CONFIG_MODULES
           /*
            * Why not always autoload you may ask. Some users are
            * in a situation where requesting a module may deadlock,
            * especially when the module is located on a NFS mount.
            */
           if (ops == NULL && flags & TS_AUTOLOAD) {
                   request_module("ts_%s", algo);
                   ops = lookup_ts_algo(algo);
           }
   #endif
   
           if (ops == NULL)
                   goto errout;
   
           conf = ops->init(pattern, len, gfp_mask, flags);
           if (IS_ERR(conf)) {
                   err = PTR_ERR(conf);
                   goto errout;
           }
   
           conf->ops = ops;
           return conf;
   
   errout:
           if (ops)
                   module_put(ops->owner);
                   
           return ERR_PTR(err);
   }
   
   /**
    * textsearch_destroy - destroy a search configuration
    * @conf: search configuration
    *
    * Releases all references of the configuration and frees
    * up the memory.
    */
   void textsearch_destroy(struct ts_config *conf)
   {
           if (conf->ops) {
                   if (conf->ops->destroy)
                           conf->ops->destroy(conf);
                   module_put(conf->ops->owner);
           }
   
           kfree(conf);
   }
   
   EXPORT_SYMBOL(textsearch_register);
   EXPORT_SYMBOL(textsearch_unregister);
   EXPORT_SYMBOL(textsearch_prepare);
   EXPORT_SYMBOL(textsearch_find_continuous);
   EXPORT_SYMBOL(textsearch_destroy);

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