From: Ondřej Surý <ondrej@isc.org>
Date: Thu, 4 Jun 2026 08:25:42 +0000 (+0200)
Subject: Use variable size struct for zonecut ndata to avoid allocation
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=43a85a5bcae6ef6074b36432b12951a91e4e57c6;p=thirdparty%2Fbind9.git

Use variable size struct for zonecut ndata to avoid allocation

Previously, the node_deleg_t would do double allocation, one for the
struct itself and one for the zonecut.  This has been changed to use
variable sized struct with the zonecut .ndata buffer attached to the end
of node_deleg_t structure.
---

diff --git a/lib/dns/deleg.c b/lib/dns/deleg.c
index d0ae712a7ff..249e7c5502b 100644
--- a/lib/dns/deleg.c
+++ b/lib/dns/deleg.c
@@ -119,11 +119,17 @@ struct delegdb_node {
 	/*
 	 * Immutable node data
 	 */
-	size_t size;
-	dns_name_t zonecut;
 	dns_delegset_t *delegset;
+
+	dns_name_t zonecut;
+	uint8_t zonecut_buffer[];
 };
 
+static size_t
+delegdb_node_size(const delegdb_node_t *node) {
+	return sizeof(*node) + node->zonecut.length;
+}
+
 static void
 delegdb_node_destroy(delegdb_node_t *node) {
 	REQUIRE(VALID_DELEGDB_NODE(node));
@@ -133,10 +139,9 @@ delegdb_node_destroy(delegdb_node_t *node) {
 
 	node->magic = 0;
 
-	dns_name_free(&node->zonecut, qplru->mctx);
 	dns_delegset_detach(&node->delegset);
 
-	isc_mem_put(qplru->mctx, node, sizeof(*node));
+	isc_mem_put(qplru->mctx, node, delegdb_node_size(node));
 
 	qplru_detach(&qplru);
 }
@@ -450,6 +455,9 @@ dns_delegset_addns(dns_delegset_t *delegset, dns_deleg_t *deleg,
 	addname(delegset, &deleg->names, name);
 }
 
+static size_t
+delegset_size(dns_delegset_t *delegset);
+
 static void
 delegdb_cleanup(dns_delegdb_t *delegdb, dns_qp_t *qp, size_t requested) {
 	delegdb_node_t *node = NULL;
@@ -467,7 +475,8 @@ delegdb_cleanup(dns_delegdb_t *delegdb, dns_qp_t *qp, size_t requested) {
 		if (node == NULL) {
 			break;
 		}
-		reclaimed += node->size;
+		reclaimed += delegdb_node_size(node) +
+			     delegset_size(node->delegset);
 
 		if (LIBDNS_DELEGDB_EVICT_ENABLED()) {
 			char namebuf[DNS_NAME_FORMATSIZE];
@@ -507,17 +516,6 @@ delegset_size(dns_delegset_t *delegset) {
 	return sz;
 }
 
-static size_t
-delegdb_node_size(const dns_name_t *zonecut, dns_delegset_t *delegset) {
-	size_t sz = 0;
-
-	sz += sizeof(delegdb_node_t);
-	sz += dns_name_size(zonecut);
-	sz += delegset_size(delegset);
-
-	return sz;
-}
-
 static size_t
 delegdb_node_prepare(qplru_t *qplru, isc_stdtime_t now, dns_ttl_t ttl,
 		     const dns_name_t *zonecut, dns_delegset_t *delegset,
@@ -527,21 +525,28 @@ delegdb_node_prepare(qplru_t *qplru, isc_stdtime_t now, dns_ttl_t ttl,
 	}
 	delegset->expires = ttl + now;
 
-	*nodep = isc_mem_get(qplru->mctx, sizeof(**nodep));
-	**nodep = (delegdb_node_t){
+	isc_region_t zonecut_r = { 0 };
+	dns_name_toregion(zonecut, &zonecut_r);
+
+	delegdb_node_t *node = isc_mem_get(qplru->mctx,
+					   sizeof(*node) + zonecut_r.length);
+	*node = (delegdb_node_t){
 		.magic = DELEGDB_NODE_MAGIC,
 		.references = ISC_REFCOUNT_INITIALIZER(1),
-		.zonecut = DNS_NAME_INITEMPTY,
 		.link = ISC_LINK_INITIALIZER,
 		.deadlink = ISC_LINK_INITIALIZER,
-		.size = delegdb_node_size(zonecut, delegset),
+		.zonecut = DNS_NAME_INITEMPTY,
 		.qplru = qplru_ref(qplru),
 	};
+	dns_delegset_attach(delegset, &node->delegset);
+
+	memmove(node->zonecut_buffer, zonecut_r.base, zonecut_r.length);
+	zonecut_r.base = node->zonecut_buffer;
+	dns_name_fromregion(&node->zonecut, &zonecut_r);
 
-	dns_delegset_attach(delegset, &(*nodep)->delegset);
-	dns_name_dup(zonecut, qplru->mctx, &(*nodep)->zonecut);
+	*nodep = node;
 
-	return sizeof(**nodep) + (*nodep)->size;
+	return delegdb_node_size(node);
 }
 
 isc_result_t
@@ -594,7 +599,8 @@ dns_delegset_insert(dns_delegdb_t *delegdb, const dns_name_t *zonecut,
 	 * initialize a new node.
 	 */
 	size_t requested = delegdb_node_prepare(delegdb->qplru, now, ttl,
-						zonecut, delegset, &node);
+						zonecut, delegset, &node) +
+			   delegset_size(delegset);
 
 	/*
 	 * Add the node in the DB