/*
   * 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
  ", 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;
  }
  EXPORT_SYMBOL(textsearch_register);
  
  /**
   * 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;
  }
  EXPORT_SYMBOL(textsearch_unregister);
  
  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);
  }
  EXPORT_SYMBOL(textsearch_find_continuous);
  
  /**
   * 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.
   *
   * 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);
  }
  EXPORT_SYMBOL(textsearch_prepare);
  
  /**
   * 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_destroy);