Add delegdb configuration struct

Instead of having independent APIs to configure various aspects of the
delegdb (i.e. cache size, other settings that may come up later), a
single configuration struct is passed to `dns_delegdb_setconfig()`, which
internally does all the plumbing. To avoid relying on
atomics/synchronization, `dns_delegdb_setconfig()` must be called from
exclusive mode (for now).

The configuration can be retrieved at any time (not necessarily from
exclusive mode) using `dns_delegdb_getconfig()`. This is useful, for
instance, to flush the delegdb without losing its parameters.

bin/named/server.c

@@ -4334,7 +4334,9 @@ configure_view(dns_view_t *view, dns_viewlist_t *viewlist, cfg_obj_t *config,
 	} else {
 		dns_delegdb_create(&view->deleg);
 	}
-	dns_delegdb_setsize(view->deleg, cache_size_slice);
+	dns_delegdb_setconfig(
+		view->deleg,
+		&(dns_delegdb_config_t){ .dbsize = cache_size_slice });
 
 	/*
 	 * The previous view isn't needed anymore.

lib/dns/deleg.c

@@ -70,6 +70,8 @@ struct dns_delegdb {
 	 * (After decrementing `owners`.)
 	 */
 	isc_refcount_t owners;
+
+	dns_delegdb_config_t config;
 };
 
 static void
@@ -217,7 +219,8 @@ dns_delegdb_create(dns_delegdb_t **delegdbp) {
 				    .mctx = mctx,
 				    .references = ISC_REFCOUNT_INITIALIZER(1),
 				    .nloops = isc_loopmgr_nloops(),
-				    .owners = ISC_REFCOUNT_INITIALIZER(1) };
+				    .owners = ISC_REFCOUNT_INITIALIZER(1),
+				    .config = {} };
 
 	dns_qpmulti_create(mctx, &qpmethods, &delegdb->nodes, &delegdb->nodes);
 
@@ -1033,8 +1036,8 @@ dns_delegdb_shutdown(dns_delegdb_t *delegdb) {
 	}
 }
 
-void
-dns_delegdb_setsize(dns_delegdb_t *delegdb, size_t size) {
+static void
+delegdb_setsize(dns_delegdb_t *delegdb, size_t size) {
 	size_t lowater;
 	size_t hiwater;
 
@@ -1058,3 +1061,20 @@ dns_delegdb_setsize(dns_delegdb_t *delegdb, size_t size) {
 		isc_mem_setwater(delegdb->mctx, hiwater, lowater);
 	}
 }
+
+dns_delegdb_config_t
+dns_delegdb_getconfig(dns_delegdb_t *delegdb) {
+	REQUIRE(VALID_DELEGDB(delegdb));
+	return delegdb->config;
+}
+
+void
+dns_delegdb_setconfig(dns_delegdb_t *delegdb,
+		      const dns_delegdb_config_t *config) {
+	REQUIRE(isc_loop_get(isc_tid()) == isc_loop_main());
+	REQUIRE(VALID_DELEGDB(delegdb));
+
+	delegdb->config = *config;
+
+	delegdb_setsize(delegdb, delegdb->config.dbsize);
+}

lib/dns/include/dns/deleg.h

@@ -18,6 +18,19 @@
 
 #include <dns/types.h>
 
+/*
+ * `dns_delegdb_config_t` centralizes all configurable parameters
+ * for the delegation database.
+ */
+typedef struct {
+	/*
+	 * Defines the size of the delegation cache. Whenever the effective
+	 * cache size comes close to this size, least recently used cache
+	 * entries are discarded. Value `0` means there is no limitation.
+	 */
+	size_t dbsize;
+} dns_delegdb_config_t;
+
 /*
  * A `dns_deleg_t` object represents either:
  *
@@ -94,6 +107,21 @@ typedef struct dns_delegdb dns_delegdb_t;
 void
 dns_delegdb_create(dns_delegdb_t **delegdbp);
 
+/*
+ * Configure the delegation database. Must be called from the exclusive mode
+ * only.
+ */
+void
+dns_delegdb_setconfig(dns_delegdb_t		 *delegdb,
+		      const dns_delegdb_config_t *config);
+
+/*
+ * Returns a copy of the current configuration of the delegation database. Can
+ * be called anytime.
+ */
+dns_delegdb_config_t
+dns_delegdb_getconfig(dns_delegdb_t *delegdb);
+
 /*
  * Attach a delegation DB from an existing view to another view. Used when
  * reloading the server and the delegation DB is reused.
@@ -222,12 +250,4 @@ dns_delegset_fromnsrdataset(isc_mem_t *mctx, dns_rdataset_t *rdataset,
 isc_result_t
 dns_delegdb_delete(dns_delegdb_t *db, const dns_name_t *name, bool tree);
 
-/*
- * Defines the size of the delegation cache. Whenever the effective cache
- * size comes close to this size, least recently used cache entries are
- * discarded. Value `0` means there is no limitation.
- */
-void
-dns_delegdb_setsize(dns_delegdb_t *db, size_t size);
-
 ISC_REFCOUNT_DECL(dns_delegdb);

tests/dns/deleg_test.c

@@ -659,16 +659,18 @@ cleanuptests(ISC_ATTR_UNUSED void *arg) {
 	dns_deleg_t *deleg = NULL;
 	dns_delegset_t *delegset = NULL;
 
+	/*
+	 * hiwater is 4375000 = 5000000 - (5000000 >> 3)
+	 * lowater is 3750000 = 5000000 - (5000000 >> 2)
+	 */
+	dns_delegdb_config_t config = { .dbsize = 5000000 };
+
 	dns_delegdb_create(&db);
 	assert_non_null(db);
 
 	ctx = (cleanup_ctx_t){ .db = db, .now = isc_stdtime_now() };
 
-	/*
-	 * hiwater is 4375000 = 5000000 - (5000000 >> 3)
-	 * lowater is 3750000 = 5000000 - (5000000 >> 2)
-	 */
-	dns_delegdb_setsize(db, 5000000);
+	dns_delegdb_setconfig(db, &config);
 
 	/*
 	 * A valid record