expr: New module for Boolean expressions on fields, for use in OVN.

Known weaknesses:

    * String fields can't be converted to flows yet.  A subsequent commit
      will fix this.

    * Flows aren't optimal in some situations likely to be common.
      I don't think either of those is a reason not to commit this;
      this is a solid base to build on.

Signed-off-by: Ben Pfaff <[email protected]>
Acked-by: Russell Bryant <[email protected]>

ovn/TODO

@@ -4,31 +4,6 @@
   the same syntax and I imagine the same code ought to be useful in
   ovn-nbd for ACL match expressions.
 
-** Definition of data structures to represent a match expression as a
-   syntax tree.
-
-** Definition of data structures to represent variables (fields).
-
-   Fields need names and prerequisites.  Most fields are numeric and
-   thus need widths.  We need also need a way to represent nominal
-   fields (currently just logical port names).  It might be
-   appropriate to associate fields directly with OXM/NXM code points;
-   we have to decide whether we want OVN to use the OVS flow structure
-   or work with OXM more directly.
-
-   Probably should be defined so that the data structure is also
-   useful for references to fields in action parsing.
-
-** Parsing into syntax tree.
-
-** Semantic checking against variable definitions.
-
-** Applying prerequisites.
-
-** Simplification into conjunction-of-disjunctions (CoD) form.
-
-** Transformation from CoD form into OXM matches.
-
 * ovn-controller
 
 ** Flow table handling in ovn-controller.

ovn/lib/automake.mk

@@ -1,2 +1,6 @@
 lib_LTLIBRARIES += ovn/lib/libovn.la
-ovn_lib_libovn_la_SOURCES = ovn/lib/lex.c ovn/lib/lex.h
+ovn_lib_libovn_la_SOURCES = \
+	ovn/lib/expr.c \
+	ovn/lib/expr.h \
+	ovn/lib/lex.c \
+	ovn/lib/lex.h