database: Allocate subnets list only once

This is a performance improvement when exporting networks flattened. For
the subnet search, we allocate an empty list many times which is often
not required.

This patch changes this behaviour that (if needed) the lists will be
allocated and will stay around and cleared if necessary.
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

src/database.c

@@ -125,6 +125,7 @@ struct loc_database_enumerator {
 
 	// For subnet search and bogons
 	struct loc_network_list* stack;
+	struct loc_network_list* subnets;
 
 	// For bogons
 	struct in6_addr gap6_start;
@@ -984,6 +985,9 @@ static void loc_database_enumerator_free(struct loc_database_enumerator* enumera
 	if (enumerator->stack)
 		loc_network_list_unref(enumerator->stack);
 
+	if (enumerator->subnets)
+		loc_network_list_unref(enumerator->subnets);
+
 	free(enumerator);
 }
 
@@ -1301,12 +1305,13 @@ static int __loc_database_enumerator_next_network_flattened(
 		return 0;
 
 	struct loc_network* subnet = NULL;
-	struct loc_network_list* subnets;
 
 	// Create a list with all subnets
-	r = loc_network_list_new(enumerator->ctx, &subnets);
-	if (r)
-		return r;
+	if (!enumerator->subnets) {
+		r = loc_network_list_new(enumerator->ctx, &enumerator->subnets);
+		if (r)
+			return r;
+	}
 
 	// Search all subnets from the database
 	while (1) {
@@ -1314,7 +1319,7 @@ static int __loc_database_enumerator_next_network_flattened(
 		r = __loc_database_enumerator_next_network(enumerator, &subnet, 0);
 		if (r) {
 			loc_network_unref(subnet);
-			loc_network_list_unref(subnets);
+			loc_network_list_clear(enumerator->subnets);
 
 			return r;
 		}
@@ -1325,10 +1330,10 @@ static int __loc_database_enumerator_next_network_flattened(
 
 		// Collect all subnets in a list
 		if (loc_network_is_subnet(*network, subnet)) {
-			r = loc_network_list_push(subnets, subnet);
+			r = loc_network_list_push(enumerator->subnets, subnet);
 			if (r) {
 				loc_network_unref(subnet);
-				loc_network_list_unref(subnets);
+				loc_network_list_clear(enumerator->subnets);
 
 				return r;
 			}
@@ -1341,7 +1346,7 @@ static int __loc_database_enumerator_next_network_flattened(
 		r = loc_network_list_push(enumerator->stack, subnet);
 		if (r) {
 			loc_network_unref(subnet);
-			loc_network_list_unref(subnets);
+			loc_network_list_clear(enumerator->subnets);
 
 			return r;
 		}
@@ -1350,27 +1355,28 @@ static int __loc_database_enumerator_next_network_flattened(
 		break;
 	}
 
-	DEBUG(enumerator->ctx, "Found %zu subnet(s)\n", loc_network_list_size(subnets));
+	DEBUG(enumerator->ctx, "Found %zu subnet(s)\n",
+		loc_network_list_size(enumerator->subnets));
 
 	// We can abort here if the network has no subnets
-	if (loc_network_list_empty(subnets)) {
-		loc_network_list_unref(subnets);
+	if (loc_network_list_empty(enumerator->subnets)) {
+		loc_network_list_clear(enumerator->subnets);
 
 		return 0;
 	}
 
 	// If the network has any subnets, we will break it into smaller parts
 	// without the subnets.
-	struct loc_network_list* excluded = loc_network_exclude_list(*network, subnets);
+	struct loc_network_list* excluded = loc_network_exclude_list(*network, enumerator->subnets);
 	if (!excluded) {
-		loc_network_list_unref(subnets);
+		loc_network_list_clear(enumerator->subnets);
 		return -1;
 	}
 
 	// Merge subnets onto the stack
-	r = loc_network_list_merge(enumerator->stack, subnets);
+	r = loc_network_list_merge(enumerator->stack, enumerator->subnets);
 	if (r) {
-		loc_network_list_unref(subnets);
+		loc_network_list_clear(enumerator->subnets);
 		loc_network_list_unref(excluded);
 
 		return r;
@@ -1379,13 +1385,13 @@ static int __loc_database_enumerator_next_network_flattened(
 	// Push excluded list onto the stack
 	r = loc_network_list_merge(enumerator->stack, excluded);
 	if (r) {
-		loc_network_list_unref(subnets);
+		loc_network_list_clear(enumerator->subnets);
 		loc_network_list_unref(excluded);
 
 		return r;
 	}
 
-	loc_network_list_unref(subnets);
+	loc_network_list_clear(enumerator->subnets);
 	loc_network_list_unref(excluded);
 
 	// Drop the network and restart the whole process again to pick the next network