[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>

include/linux/textsearch_fsm.h

+#ifndef __LINUX_TEXTSEARCH_FSM_H
+#define __LINUX_TEXTSEARCH_FSM_H
+
+#include <linux/types.h>
+
+enum {
+	TS_FSM_SPECIFIC,	/* specific character */
+	TS_FSM_WILDCARD,	/* any character */
+	TS_FSM_DIGIT,		/* isdigit() */
+	TS_FSM_XDIGIT,		/* isxdigit() */
+	TS_FSM_PRINT,		/* isprint() */
+	TS_FSM_ALPHA,		/* isalpha() */
+	TS_FSM_ALNUM,		/* isalnum() */
+	TS_FSM_ASCII,		/* isascii() */
+	TS_FSM_CNTRL,		/* iscntrl() */
+	TS_FSM_GRAPH,		/* isgraph() */
+	TS_FSM_LOWER,		/* islower() */
+	TS_FSM_UPPER,		/* isupper() */
+	TS_FSM_PUNCT,		/* ispunct() */
+	TS_FSM_SPACE,		/* isspace() */
+	__TS_FSM_TYPE_MAX,
+};
+#define TS_FSM_TYPE_MAX (__TS_FSM_TYPE_MAX - 1)
+
+enum {
+	TS_FSM_SINGLE,		/* 1 occurrence */
+	TS_FSM_PERHAPS,		/* 1 or 0 occurrence */
+	TS_FSM_ANY,		/* 0..n occurrences */
+	TS_FSM_MULTI,		/* 1..n occurrences */
+	TS_FSM_HEAD_IGNORE,	/* 0..n ignored occurrences at head */
+	__TS_FSM_RECUR_MAX,
+};
+#define TS_FSM_RECUR_MAX (__TS_FSM_RECUR_MAX - 1)
+
+/**
+ * struct ts_fsm_token - state machine token (state)
+ * @type: type of token
+ * @recur: number of recurrences
+ * @value: character value for TS_FSM_SPECIFIC
+ */
+struct ts_fsm_token
+{
+	__u16		type;
+	__u8		recur;
+	__u8		value;
+};
+
+#endif

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

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