[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 16b8fa2175e4..455833a9e31a 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 6cdb10f312df..7f6eda449102 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 000000000000..d27c0a072940
--- /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);