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/*

 * 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 facitilies 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 continously

 *       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() specyfing the searching algorithm and

 *   the pattern to look for. The returned configuration may then be used

 *   for an arbitary 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 patern or UINT_MAX if

 *   no match was found. Subsequent occurences 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/rcupdate.h>

#include <linux/err.h>

#include <linux/textsearch.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_KMOD

        /*

         * 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);

        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);