2 * Copyright (c) 2015 Nicira, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at:
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
20 /* OVN matching expression tree
21 * ============================
23 * The data structures here form an abstract expression tree for matching
26 * The abstract syntax tree representation of a matching expression is one of:
28 * - A Boolean literal ("true" or "false").
30 * - A comparison of a field (or part of a field) against a constant
31 * with one of the operators == != < <= > >=.
33 * - The logical AND or OR of two or more matching expressions.
35 * Literals and comparisons are called "terminal" nodes, logical AND and OR
36 * nodes are "nonterminal" nodes.
38 * The syntax for expressions includes a few other concepts that are not part
39 * of the abstract syntax tree. In these examples, x is a field, a, b, and c
40 * are constants, and e1 and e2 are arbitrary expressions:
42 * - Logical NOT. The parser implements NOT by inverting the sense of the
43 * operand: !(x == a) becomes x != a, !(e1 && e2) becomes !e1 || !e2, and
46 * - Set membership. The parser translates x == {a, b, c} into
47 * x == a || x == b || x == c.
49 * - Reversed comparisons. The parser translates a < x into x > a.
51 * - Range expressions. The parser translates a < x < b into
55 #include "classifier.h"
60 #include "meta-flow.h"
67 /* "Measurement level" of a field. See "Level of Measurement" in the large
68 * comment on struct expr_symbol below for more information. */
72 /* Boolean values are nominal, however because of their simple nature OVN
73 * can allow both equality and inequality tests on them. */
76 /* Ordinal values can at least be ordered on a scale. OVN allows equality
77 * and inequality and relational tests on ordinal values. These are the
78 * fields on which OVS allows bitwise matching. */
82 const char *expr_level_to_string(enum expr_level);
90 * Every symbol must have a name. To be useful, the name must satisfy the
91 * lexer's syntax for an identifier.
97 * Every symbol has a width. For integer symbols, this is the number of bits
98 * in the value; for string symbols, this is 0.
104 * There are three kinds of symbols:
108 * One might, for example, define a field named "vlan.tci" to refer to
109 * MFF_VLAN_TCI. For integer fields, 'field' specifies the referent; for
110 * string fields, 'field' is NULL.
112 * 'expansion' is NULL.
114 * Integer fields can be nominal or ordinal (see below). String fields are
119 * 'expansion' is a string that specifies a subfield of some larger field,
120 * e.g. "vlan.tci[0..11]" for a field that represents a VLAN VID.
124 * Only ordinal fields (see below) may have subfields, and subfields are
129 * A predicate is an arbitrary Boolean expression that can be used in an
130 * expression much like a 1-bit field. 'expansion' specifies the Boolean
131 * expression, e.g. "ip4" might expand to "eth.type == 0x800". The
132 * expansion of a predicate might refer to other predicates, e.g. "icmp4"
133 * might expand to "ip4 && ip4.proto == 1".
137 * A predicate whose expansion refers to any nominal field or predicate
138 * (see below) is nominal; other predicates have Boolean level of
142 * Level of Measurement
143 * ====================
145 * See http://en.wikipedia.org/wiki/Level_of_measurement for the statistical
146 * concept on which this classification is based. There are three levels:
150 * In statistics, ordinal values can be ordered on a scale. Here, we
151 * consider a field (or subfield) to be ordinal if its bits can be examined
152 * individually. This is true for the OpenFlow fields that OpenFlow or
153 * Open vSwitch makes "maskable".
155 * OVN supports all the usual arithmetic relations (== != < <= > >=) on
156 * ordinal fields and their subfields, because all of these can be
157 * implemented as collections of bitwise tests.
161 * In statistics, nominal values cannot be usefully compared except for
162 * equality. This is true of OpenFlow port numbers, Ethernet types, and IP
163 * protocols are examples: all of these are just identifiers assigned
164 * arbitrarily with no deeper meaning. In OpenFlow and Open vSwitch, bits
165 * in these fields generally aren't individually addressable.
167 * OVN only supports arithmetic tests for equality on nominal fields,
168 * because OpenFlow and Open vSwitch provide no way for a flow to
169 * efficiently implement other comparisons on them. (A test for inequality
170 * can be sort of built out of two flows with different priorities, but OVN
171 * matching expressions always generate flows with a single priority.)
173 * String fields are always nominal.
177 * A nominal field that has only two values, 0 and 1, is somewhat
178 * exceptional, since it is easy to support both equality and inequality
179 * tests on such a field: either one can be implemented as a test for 0 or
182 * Only predicates (see above) have a Boolean level of measurement.
184 * This isn't a standard level of measurement.
190 * Any symbol can have prerequisites, which are specified as a string giving an
191 * additional expression that must be true whenever the symbol is referenced.
192 * For example, the "icmp4.type" symbol might have prerequisite "icmp4", which
193 * would cause an expression "icmp4.type == 0" to be interpreted as "icmp4.type
194 * == 0 && icmp4", which would in turn expand to "icmp4.type == 0 && eth.type
195 * == 0x800 && ip4.proto == 1" (assuming "icmp4" is a predicate defined as
196 * suggested under "Types" above).
202 * Ordinarily OVN is willing to consider using any field as a dimension in the
203 * Open vSwitch "conjunctive match" extension (see ovs-ofctl(8)). However,
204 * some fields can't actually be used that way because they are necessary as
205 * prerequisites. For example, from an expression like "tcp.src == {1,2,3}
206 * && tcp.dst == {4,5,6}", OVN might naturally generate flows like this:
208 * conj_id=1,actions=...
209 * ip,actions=conjunction(1,1/3)
210 * ip6,actions=conjunction(1,1/3)
211 * tp_src=1,actions=conjunction(1,2/3)
212 * tp_src=2,actions=conjunction(1,2/3)
213 * tp_src=3,actions=conjunction(1,2/3)
214 * tp_dst=4,actions=conjunction(1,3/3)
215 * tp_dst=5,actions=conjunction(1,3/3)
216 * tp_dst=6,actions=conjunction(1,3/3)
218 * but that's not valid because any flow that matches on tp_src or tp_dst must
219 * also match on either ip or ip6. Thus, one would mark eth.type as "must
220 * crossproduct", to force generating flows like this:
222 * conj_id=1,actions=...
223 * ip,tp_src=1,actions=conjunction(1,1/2)
224 * ip,tp_src=2,actions=conjunction(1,1/2)
225 * ip,tp_src=3,actions=conjunction(1,1/2)
226 * ip6,tp_src=1,actions=conjunction(1,1/2)
227 * ip6,tp_src=2,actions=conjunction(1,1/2)
228 * ip6,tp_src=3,actions=conjunction(1,1/2)
229 * ip,tp_dst=4,actions=conjunction(1,2/2)
230 * ip,tp_dst=5,actions=conjunction(1,2/2)
231 * ip,tp_dst=6,actions=conjunction(1,2/2)
232 * ip6,tp_dst=4,actions=conjunction(1,2/2)
233 * ip6,tp_dst=5,actions=conjunction(1,2/2)
234 * ip6,tp_dst=6,actions=conjunction(1,2/2)
236 * which are acceptable.
242 const struct mf_field *field;
245 enum expr_level level;
248 bool must_crossproduct;
251 struct expr_symbol *expr_symtab_add_field(struct shash *symtab,
252 const char *name, enum mf_field_id,
254 bool must_crossproduct);
255 struct expr_symbol *expr_symtab_add_subfield(struct shash *symtab,
258 const char *subfield);
259 struct expr_symbol *expr_symtab_add_string(struct shash *symtab,
260 const char *name, enum mf_field_id,
261 const char *prereqs);
262 struct expr_symbol *expr_symtab_add_predicate(struct shash *symtab,
264 const char *expansion);
265 void expr_symtab_destroy(struct shash *symtab);
267 /* Expression type. */
269 EXPR_T_CMP, /* Compare symbol with constant. */
270 EXPR_T_AND, /* Logical AND of 2 or more subexpressions. */
271 EXPR_T_OR, /* Logical OR of 2 or more subexpressions. */
272 EXPR_T_BOOLEAN, /* True or false constant. */
275 /* Relational operator. */
284 const char *expr_relop_to_string(enum expr_relop);
285 bool expr_relop_from_token(enum lex_type type, enum expr_relop *relop);
287 /* An abstract syntax tree for a matching expression.
289 * The expression code maintains and relies on a few important invariants:
291 * - An EXPR_T_AND or EXPR_T_OR node never has a child of the same type.
292 * (Any such children could be merged into their parent.) A node may
293 * have grandchildren of its own type.
295 * As a consequence, every nonterminal node at the same distance from the
296 * root has the same type.
298 * - EXPR_T_AND and EXPR_T_OR nodes must have at least two children.
300 * - An EXPR_T_CMP node always has a nonzero mask, and never has a 1-bit
301 * in its value in a position where the mask is a 0-bit.
303 * The expr_honors_invariants() function can check invariants. */
305 struct ovs_list node; /* In parent EXPR_T_AND or EXPR_T_OR if any. */
306 enum expr_type type; /* Expression type. */
311 * The symbol is on the left, e.g. "field < constant". */
313 const struct expr_symbol *symbol;
314 enum expr_relop relop;
319 union mf_subvalue value;
320 union mf_subvalue mask;
325 /* EXPR_T_AND, EXPR_T_OR. */
326 struct ovs_list andor;
328 /* EXPR_T_BOOLEAN. */
333 struct expr *expr_create_boolean(bool b);
334 struct expr *expr_create_andor(enum expr_type);
335 struct expr *expr_combine(enum expr_type, struct expr *a, struct expr *b);
337 static inline struct expr *
338 expr_from_node(const struct ovs_list *node)
340 return CONTAINER_OF(node, struct expr, node);
343 void expr_format(const struct expr *, struct ds *);
344 void expr_print(const struct expr *);
345 struct expr *expr_parse(struct lexer *, const struct shash *symtab,
347 struct expr *expr_parse_string(const char *, const struct shash *symtab,
350 struct expr *expr_clone(struct expr *);
351 void expr_destroy(struct expr *);
353 struct expr *expr_annotate(struct expr *, const struct shash *symtab,
355 struct expr *expr_simplify(struct expr *);
356 struct expr *expr_normalize(struct expr *);
358 bool expr_honors_invariants(const struct expr *);
359 bool expr_is_simplified(const struct expr *);
360 bool expr_is_normalized(const struct expr *);
362 /* Converting expressions to OpenFlow flows. */
364 /* An OpenFlow match generated from a Boolean expression. See
365 * expr_to_matches() for more information. */
367 struct hmap_node hmap_node;
369 struct cls_conjunction *conjunctions;
373 uint32_t expr_to_matches(const struct expr *, const struct simap *ports,
374 struct hmap *matches);
375 void expr_matches_destroy(struct hmap *matches);
376 void expr_matches_print(const struct hmap *matches, FILE *);
378 /* Action parsing helper. */
380 char *expr_parse_assignment(struct lexer *lexer, const struct shash *symtab,
381 const struct simap *ports, struct ofpbuf *ofpacts,
382 struct expr **prereqsp);
384 #endif /* ovn/expr.h */