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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() 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 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/rculist.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_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);
|
