lib/cache: improve internal docs

diff --git a/lib/cache/impl.h b/lib/cache/impl.h
index b12e16b124fff597897a3b10a2056554394b58ed..7887341d4e4a329561cbb5997c0e38dfe04c7fbe 100644 (file)
--- a/lib/cache/impl.h
+++ b/lib/cache/impl.h
@@ -175,8 +175,16 @@ struct entry_apex {
        bool has_cname : 1;
        bool has_dname : 1;
 
-       uint8_t pad_; /**< Weird: 1 byte + 2 bytes + x bytes; let's do 2+2+x. */
-       int8_t nsecs[ENTRY_APEX_NSECS_CNT]; /**< values:  0: none, 1: NSEC, 3: NSEC3 */
+       uint8_t pad_; /**< 1 byte + 2 bytes + x bytes would be weird; let's do 2+2+x. */
+
+       /** We have two slots for NSEC* parameters.
+        *
+        * This array describes how they're filled;
+        * values:  0: none, 1: NSEC, 3: NSEC3.
+        *
+        * Two slots are a compromise to smoothly handle normal rollovers
+        * (either changing NSEC3 parameters or between NSEC and NSEC3). */
+       int8_t nsecs[ENTRY_APEX_NSECS_CNT];
        uint8_t data[];
        /* XXX: if not first, stamp of last being the first?
         * Purpose: save cache operations if rolled the algo/params long ago. */