textsearch.c

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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 <[email protected]>
 *      Pablo Neira Ayuso <[email protected]>
 *
 * ==========================================================================
 *
 * 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;
}

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;
}

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;
}

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);
}

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);
}

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);