secchan: Add explanatory comment.

diff --git a/secchan/ofproto.c b/secchan/ofproto.c
index c2a3183792943e28e28054208746cc4ca01f0b6f..8c62115bcdfdaf0d6026ca9b6a2d68e9d0a8cf0d 100644 (file)
--- a/secchan/ofproto.c
+++ b/secchan/ofproto.c
@@ -109,6 +109,17 @@ struct rule {
     uint8_t ip_tos;             /* Last-seen IP type-of-service. */
     tag_type tags;              /* Tags (set only by hooks). */
 
+    /* A subrule with a known super-rule has a non-null 'super' other than
+     * UNKNOWN_SUPER, in which case 'list' is an element of the super-rule's
+     * list of subrules.
+     *
+     * A subrule with an unknown super-rule (which is an optimization that
+     * might well be better removed) has 'super' set to UNKNOWN_SUPER, in
+     * which case 'list' is unused.
+     *
+     * A super-rule has 'super' of NULL, in which case 'list' is the head of a
+     * list of sub-rules.  (A super-rule with no wildcards will never have any
+     * sub-rules.) */
     struct rule *super;
     struct list list;