[LIB]: Naive finite state machine based textsearch

A finite state machine consists of n states (struct ts_fsm_token)
representing the pattern as a finite automation. The data is read
sequentially on a octet basis. Every state token specifies the number
of recurrences and the type of value accepted which can be either a
specific character or ctype based set of characters. The available
type of recurrences include 1, (0|1), [0 n], and [1 n].

The algorithm differs between strict/non-strict mode specyfing
whether the pattern has to start at the first octect. Strict mode
is enabled by default and can be disabled by inserting
TS_FSM_HEAD_IGNORE as the first token in the chain.

The runtime performance of the algorithm should be around O(n),
however while in strict mode the average runtime can be better.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 350 insertions, 0 deletions

diff --git a/lib/Kconfig b/lib/Kconfig
index 16b8fa2..455833a 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -80,4 +80,15 @@ config TEXTSEARCH_KMP
 	  To compile this code as a module, choose M here: the
 	  module will be called ts_kmp.
 
+config TEXTSEARCH_FSM
+	depends on TEXTSEARCH
+	tristate "Finite state machine"
+	help
+	  Say Y here if you want to be able to search text using a
+	  naive finite state machine approach implementing a subset
+	  of regular expressions.
+
+	  To compile this code as a module, choose M here: the
+	  module will be called ts_fsm.
+
 endmenu
diff --git a/lib/Makefile b/lib/Makefile
index 6cdb10f..7f6eda4 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -38,6 +38,7 @@ obj-$(CONFIG_REED_SOLOMON) += reed_solomon/
 
 lib-$(CONFIG_TEXTSEARCH) += textsearch.o
 obj-$(CONFIG_TEXTSEARCH_KMP) += ts_kmp.o
+obj-$(CONFIG_TEXTSEARCH_FSM) += ts_fsm.o
 
 hostprogs-y	:= gen_crc32table
 clean-files	:= crc32table.h
diff --git a/lib/ts_fsm.c b/lib/ts_fsm.c
new file mode 100644
index 0000000..d27c0a0
--- /dev/null
+++ b/lib/ts_fsm.c
@@ -0,0 +1,338 @@
+/*
+ * lib/ts_fsm.c	   A naive finite state machine text search approach
+ *
+ *		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>
+ *
+ * ==========================================================================
+ *
+ *   A finite state machine consists of n states (struct ts_fsm_token)
+ *   representing the pattern as a finite automation. The data is read
+ *   sequentially on a octet basis. Every state token specifies the number
+ *   of recurrences and the type of value accepted which can be either a
+ *   specific character or ctype based set of characters. The available
+ *   type of recurrences include 1, (0|1), [0 n], and [1 n].
+ *
+ *   The algorithm differs between strict/non-strict mode specyfing
+ *   whether the pattern has to start at the first octect. Strict mode
+ *   is enabled by default and can be disabled by inserting
+ *   TS_FSM_HEAD_IGNORE as the first token in the chain.
+ *
+ *   The runtime performance of the algorithm should be around O(n),
+ *   however while in strict mode the average runtime can be better.
+ */
+
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/string.h>
+#include <linux/ctype.h>
+#include <linux/textsearch.h>
+#include <linux/textsearch_fsm.h>
+
+struct ts_fsm
+{
+	unsigned int		ntokens;
+	struct ts_fsm_token	tokens[0];
+};
+
+/* other values derived from ctype.h */
+#define _A		0x100 /* ascii */
+#define _W		0x200 /* wildcard */
+
+/* Map to _ctype flags and some magic numbers */
+static u16 token_map[TS_FSM_TYPE_MAX+1] = {
+	[TS_FSM_SPECIFIC] = 0,
+	[TS_FSM_WILDCARD] = _W,
+	[TS_FSM_CNTRL]	  = _C,
+	[TS_FSM_LOWER]	  = _L,
+	[TS_FSM_UPPER]	  = _U,
+	[TS_FSM_PUNCT]	  = _P,
+	[TS_FSM_SPACE]	  = _S,
+	[TS_FSM_DIGIT]	  = _D,
+	[TS_FSM_XDIGIT]	  = _D | _X,
+	[TS_FSM_ALPHA]	  = _U | _L,
+	[TS_FSM_ALNUM]	  = _U | _L | _D,
+	[TS_FSM_PRINT]	  = _P | _U | _L | _D | _SP,
+	[TS_FSM_GRAPH]	  = _P | _U | _L | _D,
+	[TS_FSM_ASCII]	  = _A,
+};
+
+static u16 token_lookup_tbl[256] = {
+_W|_A|_C,      _W|_A|_C,     _W|_A|_C,     _W|_A|_C,		/*   0-  3 */
+_W|_A|_C,      _W|_A|_C,     _W|_A|_C,     _W|_A|_C,		/*   4-  7 */
+_W|_A|_C,      _W|_A|_C|_S,  _W|_A|_C|_S,  _W|_A|_C|_S,		/*   8- 11 */
+_W|_A|_C|_S,   _W|_A|_C|_S,  _W|_A|_C,     _W|_A|_C,		/*  12- 15 */
+_W|_A|_C,      _W|_A|_C,     _W|_A|_C,     _W|_A|_C,		/*  16- 19 */
+_W|_A|_C,      _W|_A|_C,     _W|_A|_C,     _W|_A|_C,		/*  20- 23 */
+_W|_A|_C,      _W|_A|_C,     _W|_A|_C,     _W|_A|_C,		/*  24- 27 */
+_W|_A|_C,      _W|_A|_C,     _W|_A|_C,     _W|_A|_C,		/*  28- 31 */
+_W|_A|_S|_SP,  _W|_A|_P,     _W|_A|_P,     _W|_A|_P,		/*  32- 35 */
+_W|_A|_P,      _W|_A|_P,     _W|_A|_P,     _W|_A|_P,		/*  36- 39 */
+_W|_A|_P,      _W|_A|_P,     _W|_A|_P,     _W|_A|_P,		/*  40- 43 */
+_W|_A|_P,      _W|_A|_P,     _W|_A|_P,     _W|_A|_P,		/*  44- 47 */
+_W|_A|_D,      _W|_A|_D,     _W|_A|_D,     _W|_A|_D,		/*  48- 51 */
+_W|_A|_D,      _W|_A|_D,     _W|_A|_D,     _W|_A|_D,		/*  52- 55 */
+_W|_A|_D,      _W|_A|_D,     _W|_A|_P,     _W|_A|_P,		/*  56- 59 */
+_W|_A|_P,      _W|_A|_P,     _W|_A|_P,     _W|_A|_P,		/*  60- 63 */
+_W|_A|_P,      _W|_A|_U|_X,  _W|_A|_U|_X,  _W|_A|_U|_X,		/*  64- 67 */
+_W|_A|_U|_X,   _W|_A|_U|_X,  _W|_A|_U|_X,  _W|_A|_U,		/*  68- 71 */
+_W|_A|_U,      _W|_A|_U,     _W|_A|_U,     _W|_A|_U,		/*  72- 75 */
+_W|_A|_U,      _W|_A|_U,     _W|_A|_U,     _W|_A|_U,		/*  76- 79 */
+_W|_A|_U,      _W|_A|_U,     _W|_A|_U,     _W|_A|_U,		/*  80- 83 */
+_W|_A|_U,      _W|_A|_U,     _W|_A|_U,     _W|_A|_U,		/*  84- 87 */
+_W|_A|_U,      _W|_A|_U,     _W|_A|_U,     _W|_A|_P,		/*  88- 91 */
+_W|_A|_P,      _W|_A|_P,     _W|_A|_P,     _W|_A|_P,		/*  92- 95 */
+_W|_A|_P,      _W|_A|_L|_X,  _W|_A|_L|_X,  _W|_A|_L|_X,		/*  96- 99 */
+_W|_A|_L|_X,   _W|_A|_L|_X,  _W|_A|_L|_X,  _W|_A|_L,		/* 100-103 */
+_W|_A|_L,      _W|_A|_L,     _W|_A|_L,     _W|_A|_L,		/* 104-107 */
+_W|_A|_L,      _W|_A|_L,     _W|_A|_L,     _W|_A|_L,		/* 108-111 */
+_W|_A|_L,      _W|_A|_L,     _W|_A|_L,     _W|_A|_L,		/* 112-115 */
+_W|_A|_L,      _W|_A|_L,     _W|_A|_L,     _W|_A|_L,		/* 116-119 */
+_W|_A|_L,      _W|_A|_L,     _W|_A|_L,     _W|_A|_P,		/* 120-123 */
+_W|_A|_P,      _W|_A|_P,     _W|_A|_P,     _W|_A|_C,		/* 124-127 */
+_W,            _W,           _W,           _W,			/* 128-131 */
+_W,            _W,           _W,           _W,			/* 132-135 */
+_W,            _W,           _W,           _W,			/* 136-139 */
+_W,            _W,           _W,           _W,			/* 140-143 */
+_W,            _W,           _W,           _W,			/* 144-147 */
+_W,            _W,           _W,           _W,			/* 148-151 */
+_W,            _W,           _W,           _W,			/* 152-155 */
+_W,            _W,           _W,           _W,			/* 156-159 */
+_W|_S|_SP,     _W|_P,        _W|_P,        _W|_P,		/* 160-163 */
+_W|_P,         _W|_P,        _W|_P,        _W|_P,		/* 164-167 */
+_W|_P,         _W|_P,        _W|_P,        _W|_P,		/* 168-171 */
+_W|_P,         _W|_P,        _W|_P,        _W|_P,		/* 172-175 */
+_W|_P,         _W|_P,        _W|_P,        _W|_P,		/* 176-179 */
+_W|_P,         _W|_P,        _W|_P,        _W|_P,		/* 180-183 */
+_W|_P,         _W|_P,        _W|_P,        _W|_P,		/* 184-187 */
+_W|_P,         _W|_P,        _W|_P,        _W|_P,		/* 188-191 */
+_W|_U,         _W|_U,        _W|_U,        _W|_U,		/* 192-195 */
+_W|_U,         _W|_U,        _W|_U,        _W|_U,		/* 196-199 */
+_W|_U,         _W|_U,        _W|_U,        _W|_U,		/* 200-203 */
+_W|_U,         _W|_U,        _W|_U,        _W|_U,		/* 204-207 */
+_W|_U,         _W|_U,        _W|_U,        _W|_U,		/* 208-211 */
+_W|_U,         _W|_U,        _W|_U,        _W|_P,		/* 212-215 */
+_W|_U,         _W|_U,        _W|_U,        _W|_U,		/* 216-219 */
+_W|_U,         _W|_U,        _W|_U,        _W|_L,		/* 220-223 */
+_W|_L,         _W|_L,        _W|_L,        _W|_L,		/* 224-227 */
+_W|_L,         _W|_L,        _W|_L,        _W|_L,		/* 228-231 */
+_W|_L,         _W|_L,        _W|_L,        _W|_L,		/* 232-235 */
+_W|_L,         _W|_L,        _W|_L,        _W|_L,		/* 236-239 */
+_W|_L,         _W|_L,        _W|_L,        _W|_L,		/* 240-243 */
+_W|_L,         _W|_L,        _W|_L,        _W|_P,		/* 244-247 */
+_W|_L,         _W|_L,        _W|_L,        _W|_L,		/* 248-251 */
+_W|_L,         _W|_L,        _W|_L,        _W|_L};		/* 252-255 */
+
+static inline int match_token(struct ts_fsm_token *t, u8 d)
+{
+	if (t->type)
+		return (token_lookup_tbl[d] & t->type) != 0;
+	else
+		return t->value == d;
+}
+
+static unsigned int fsm_find(struct ts_config *conf, struct ts_state *state)
+{
+	struct ts_fsm *fsm = ts_config_priv(conf);
+	struct ts_fsm_token *cur = NULL, *next;
+	unsigned int match_start, block_idx = 0, tok_idx;
+	unsigned block_len = 0, strict, consumed = state->offset;
+	const u8 *data;
+
+#define GET_NEXT_BLOCK()		\
+({	consumed += block_idx;		\
+	block_idx = 0;			\
+	block_len = conf->get_next_block(consumed, &data, conf, state); })
+
+#define TOKEN_MISMATCH()		\
+	do {				\
+		if (strict)		\
+			goto no_match;	\
+		block_idx++;		\
+		goto startover;		\
+	} while(0)
+
+#define end_of_data() unlikely(block_idx >= block_len && !GET_NEXT_BLOCK())
+
+	if (end_of_data())
+		goto no_match;
+
+	strict = fsm->tokens[0].recur != TS_FSM_HEAD_IGNORE;
+
+startover:
+	match_start = consumed + block_idx;
+
+	for (tok_idx = 0; tok_idx < fsm->ntokens; tok_idx++) {
+		cur = &fsm->tokens[tok_idx];
+
+		if (likely(tok_idx < (fsm->ntokens - 1)))
+			next = &fsm->tokens[tok_idx + 1];
+		else
+			next = NULL;
+
+		switch (cur->recur) {
+		case TS_FSM_SINGLE:
+			if (end_of_data())
+				goto no_match;
+
+			if (!match_token(cur, data[block_idx]))
+				TOKEN_MISMATCH();
+			break;
+
+		case TS_FSM_PERHAPS:
+			if (end_of_data() ||
+			    !match_token(cur, data[block_idx]))
+				continue;
+			break;
+
+		case TS_FSM_MULTI:
+			if (end_of_data())
+				goto no_match;
+
+			if (!match_token(cur, data[block_idx]))
+				TOKEN_MISMATCH();
+
+			block_idx++;
+			/* fall through */
+
+		case TS_FSM_ANY:
+			if (next == NULL)
+				goto found_match;
+
+			if (end_of_data())
+				continue;
+
+			while (!match_token(next, data[block_idx])) {
+				if (!match_token(cur, data[block_idx]))
+					TOKEN_MISMATCH();
+				block_idx++;
+				if (end_of_data())
+					goto no_match;
+			}
+			continue;
+
+		/*
+		 * Optimization: Prefer small local loop over jumping
+		 * back and forth until garbage at head is munched.
+		 */
+		case TS_FSM_HEAD_IGNORE:
+			if (end_of_data())
+				continue;
+
+			while (!match_token(next, data[block_idx])) {
+				/*
+				 * Special case, don't start over upon
+				 * a mismatch, give the user the
+				 * chance to specify the type of data
+				 * allowed to be ignored.
+				 */
+				if (!match_token(cur, data[block_idx]))
+					goto no_match;
+
+				block_idx++;
+				if (end_of_data())
+					goto no_match;
+			}
+
+			match_start = consumed + block_idx;
+			continue;
+		}
+
+		block_idx++;
+	}
+
+	if (end_of_data())
+		goto found_match;
+
+no_match:
+	return UINT_MAX;
+
+found_match:
+	state->offset = consumed + block_idx;
+	return match_start;
+}
+
+static struct ts_config *fsm_init(const void *pattern, unsigned int len,
+				     int gfp_mask)
+{
+	int i, err = -EINVAL;
+	struct ts_config *conf;
+	struct ts_fsm *fsm;
+	struct ts_fsm_token *tokens = (struct ts_fsm_token *) pattern;
+	unsigned int ntokens = len / sizeof(*tokens);
+	size_t priv_size = sizeof(*fsm) + len;
+
+	if (len  % sizeof(struct ts_fsm_token) || ntokens < 1)
+		goto errout;
+
+	for (i = 0; i < ntokens; i++) {
+		struct ts_fsm_token *t = &tokens[i];
+
+		if (t->type > TS_FSM_TYPE_MAX || t->recur > TS_FSM_RECUR_MAX)
+			goto errout;
+
+		if (t->recur == TS_FSM_HEAD_IGNORE &&
+		    (i != 0 || i == (ntokens - 1)))
+			goto errout;
+	}
+
+	conf = alloc_ts_config(priv_size, gfp_mask);
+	if (IS_ERR(conf))
+		return conf;
+
+	fsm = ts_config_priv(conf);
+	fsm->ntokens = ntokens;
+	memcpy(fsm->tokens, pattern, len);
+
+	for (i = 0; i < fsm->ntokens; i++) {
+		struct ts_fsm_token *t = &fsm->tokens[i];
+		t->type = token_map[t->type];
+	}
+
+	return conf;
+
+errout:
+	return ERR_PTR(err);
+}
+
+static void *fsm_get_pattern(struct ts_config *conf)
+{
+	struct ts_fsm *fsm = ts_config_priv(conf);
+	return fsm->tokens;
+}
+
+static unsigned int fsm_get_pattern_len(struct ts_config *conf)
+{
+	struct ts_fsm *fsm = ts_config_priv(conf);
+	return fsm->ntokens * sizeof(struct ts_fsm_token);
+}
+
+static struct ts_ops fsm_ops = {
+	.name		  = "fsm",
+	.find		  = fsm_find,
+	.init		  = fsm_init,
+	.get_pattern	  = fsm_get_pattern,
+	.get_pattern_len  = fsm_get_pattern_len,
+	.owner		  = THIS_MODULE,
+	.list		  = LIST_HEAD_INIT(fsm_ops.list)
+};
+
+static int __init init_fsm(void)
+{
+	return textsearch_register(&fsm_ops);
+}
+
+static void __exit exit_fsm(void)
+{
+	textsearch_unregister(&fsm_ops);
+}
+
+MODULE_LICENSE("GPL");
+
+module_init(init_fsm);
+module_exit(exit_fsm);