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"
65 /* "Measurement level" of a field. See "Level of Measurement" in the large
66 * comment on struct expr_symbol below for more information. */
70 /* Boolean values are nominal, however because of their simple nature OVN
71 * can allow both equality and inequality tests on them. */
74 /* Ordinal values can at least be ordered on a scale. OVN allows equality
75 * and inequality and relational tests on ordinal values. These are the
76 * fields on which OVS allows bitwise matching. */
80 const char *expr_level_to_string(enum expr_level);
88 * Every symbol must have a name. To be useful, the name must satisfy the
89 * lexer's syntax for an identifier.
95 * Every symbol has a width. For integer symbols, this is the number of bits
96 * in the value; for string symbols, this is 0.
102 * There are three kinds of symbols:
106 * One might, for example, define a field named "vlan.tci" to refer to
107 * MFF_VLAN_TCI. For integer fields, 'field' specifies the referent; for
108 * string fields, 'field' is NULL.
110 * 'expansion' is NULL.
112 * Integer fields can be nominal or ordinal (see below). String fields are
117 * 'expansion' is a string that specifies a subfield of some larger field,
118 * e.g. "vlan.tci[0..11]" for a field that represents a VLAN VID.
122 * Only ordinal fields (see below) may have subfields, and subfields are
127 * A predicate is an arbitrary Boolean expression that can be used in an
128 * expression much like a 1-bit field. 'expansion' specifies the Boolean
129 * expression, e.g. "ip4" might expand to "eth.type == 0x800". The
130 * expansion of a predicate might refer to other predicates, e.g. "icmp4"
131 * might expand to "ip4 && ip4.proto == 1".
135 * A predicate whose expansion refers to any nominal field or predicate
136 * (see below) is nominal; other predicates have Boolean level of
140 * Level of Measurement
141 * ====================
143 * See http://en.wikipedia.org/wiki/Level_of_measurement for the statistical
144 * concept on which this classification is based. There are three levels:
148 * In statistics, ordinal values can be ordered on a scale. Here, we
149 * consider a field (or subfield) to be ordinal if its bits can be examined
150 * individually. This is true for the OpenFlow fields that OpenFlow or
151 * Open vSwitch makes "maskable".
153 * OVN supports all the usual arithmetic relations (== != < <= > >=) on
154 * ordinal fields and their subfields, because all of these can be
155 * implemented as collections of bitwise tests.
159 * In statistics, nominal values cannot be usefully compared except for
160 * equality. This is true of OpenFlow port numbers, Ethernet types, and IP
161 * protocols are examples: all of these are just identifiers assigned
162 * arbitrarily with no deeper meaning. In OpenFlow and Open vSwitch, bits
163 * in these fields generally aren't individually addressable.
165 * OVN only supports arithmetic tests for equality on nominal fields,
166 * because OpenFlow and Open vSwitch provide no way for a flow to
167 * efficiently implement other comparisons on them. (A test for inequality
168 * can be sort of built out of two flows with different priorities, but OVN
169 * matching expressions always generate flows with a single priority.)
171 * String fields are always nominal.
175 * A nominal field that has only two values, 0 and 1, is somewhat
176 * exceptional, since it is easy to support both equality and inequality
177 * tests on such a field: either one can be implemented as a test for 0 or
180 * Only predicates (see above) have a Boolean level of measurement.
182 * This isn't a standard level of measurement.
188 * Any symbol can have prerequisites, which are specified as a string giving an
189 * additional expression that must be true whenever the symbol is referenced.
190 * For example, the "icmp4.type" symbol might have prerequisite "icmp4", which
191 * would cause an expression "icmp4.type == 0" to be interpreted as "icmp4.type
192 * == 0 && icmp4", which would in turn expand to "icmp4.type == 0 && eth.type
193 * == 0x800 && ip4.proto == 1" (assuming "icmp4" is a predicate defined as
194 * suggested under "Types" above).
200 * Ordinarily OVN is willing to consider using any field as a dimension in the
201 * Open vSwitch "conjunctive match" extension (see ovs-ofctl(8)). However,
202 * some fields can't actually be used that way because they are necessary as
203 * prerequisites. For example, from an expression like "tcp.src == {1,2,3}
204 * && tcp.dst == {4,5,6}", OVN might naturally generate flows like this:
206 * conj_id=1,actions=...
207 * ip,actions=conjunction(1,1/3)
208 * ip6,actions=conjunction(1,1/3)
209 * tp_src=1,actions=conjunction(1,2/3)
210 * tp_src=2,actions=conjunction(1,2/3)
211 * tp_src=2,actions=conjunction(1,2/3)
212 * tp_dst=4,actions=conjunction(1,3/3)
213 * tp_dst=5,actions=conjunction(1,3/3)
214 * tp_dst=6,actions=conjunction(1,3/3)
216 * but that's not valid because any flow that matches on tp_src or tp_dst must
217 * also match on either ip or ip6. Thus, one would mark eth.type as "must
218 * crossproduct", to force generating flows like this:
220 * conj_id=1,actions=...
221 * ip,tp_src=1,actions=conjunction(1,1/2)
222 * ip,tp_src=2,actions=conjunction(1,1/2)
223 * ip,tp_src=2,actions=conjunction(1,1/2)
224 * ip6,tp_src=1,actions=conjunction(1,1/2)
225 * ip6,tp_src=2,actions=conjunction(1,1/2)
226 * ip6,tp_src=2,actions=conjunction(1,1/2)
227 * ip,tp_dst=4,actions=conjunction(1,2/2)
228 * ip,tp_dst=5,actions=conjunction(1,2/2)
229 * ip,tp_dst=6,actions=conjunction(1,2/2)
230 * ip6,tp_dst=4,actions=conjunction(1,2/2)
231 * ip6,tp_dst=5,actions=conjunction(1,2/2)
232 * ip6,tp_dst=6,actions=conjunction(1,2/2)
234 * which are acceptable.
240 const struct mf_field *field;
243 enum expr_level level;
246 bool must_crossproduct;
249 struct expr_symbol *expr_symtab_add_field(struct shash *symtab,
250 const char *name, enum mf_field_id,
252 bool must_crossproduct);
253 struct expr_symbol *expr_symtab_add_subfield(struct shash *symtab,
256 const char *subfield);
257 struct expr_symbol *expr_symtab_add_string(struct shash *symtab,
259 const char *prereqs);
260 struct expr_symbol *expr_symtab_add_predicate(struct shash *symtab,
262 const char *expansion);
263 void expr_symtab_destroy(struct shash *symtab);
265 /* Expression type. */
267 EXPR_T_CMP, /* Compare symbol with constant. */
268 EXPR_T_AND, /* Logical AND of 2 or more subexpressions. */
269 EXPR_T_OR, /* Logical OR of 2 or more subexpressions. */
270 EXPR_T_BOOLEAN, /* True or false constant. */
273 /* Relational operator. */
282 const char *expr_relop_to_string(enum expr_relop);
283 bool expr_relop_from_token(enum lex_type type, enum expr_relop *relop);
285 /* An abstract syntax tree for a matching expression.
287 * The expression code maintains and relies on a few important invariants:
289 * - An EXPR_T_AND or EXPR_T_OR node never has a child of the same type.
290 * (Any such children could be merged into their parent.) A node may
291 * have grandchildren of its own type.
293 * As a consequence, every nonterminal node at the same distance from the
294 * root of the root has the same type.
296 * - EXPR_T_AND and EXPR_T_OR nodes must have at least two children.
298 * - An EXPR_T_CMP node always has a nonzero mask, and never has a 1-bit
299 * in its value in a position where the mask is a 0-bit.
301 * The expr_honors_invariants() function can check invariants. */
303 struct ovs_list node; /* In parent EXPR_T_AND or EXPR_T_OR if any. */
304 enum expr_type type; /* Expression type. */
309 * The symbol is on the left, e.g. "field < constant". */
311 const struct expr_symbol *symbol;
312 enum expr_relop relop;
317 union mf_subvalue value;
318 union mf_subvalue mask;
323 /* EXPR_T_AND, EXPR_T_OR. */
324 struct ovs_list andor;
326 /* EXPR_T_BOOLEAN. */
331 struct expr *expr_create_boolean(bool b);
332 struct expr *expr_create_andor(enum expr_type);
333 struct expr *expr_combine(enum expr_type, struct expr *a, struct expr *b);
335 static inline struct expr *
336 expr_from_node(const struct ovs_list *node)
338 return CONTAINER_OF(node, struct expr, node);
341 void expr_format(const struct expr *, struct ds *);
342 void expr_print(const struct expr *);
343 struct expr *expr_parse(struct lexer *, const struct shash *, char **errorp);
344 struct expr *expr_parse_string(const char *, const struct shash *,
347 struct expr *expr_clone(struct expr *);
348 void expr_destroy(struct expr *);
350 struct expr *expr_annotate(struct expr *, const struct shash *, char **errorp);
351 struct expr *expr_simplify(struct expr *);
352 struct expr *expr_normalize(struct expr *);
354 bool expr_honors_invariants(const struct expr *);
355 bool expr_is_simplified(const struct expr *);
356 bool expr_is_normalized(const struct expr *);
359 struct hmap_node hmap_node;
361 struct cls_conjunction *conjunctions;
365 uint32_t expr_to_matches(const struct expr *, struct hmap *);
367 #endif /* ovn/expr.h */