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