fix default handler for tunable update

Signed-off-by: Emelia Lei <wlei29@bloomberg.net>

Author: emelialei88

db/db_tunables.c

@@ -1261,13 +1261,6 @@ static int file_copier_update(void *context, void *value)
     return 0;
 }
 
-static int iam_metrics_namespace_update(void *context, void *value)
-{
-    comdb2_tunable *tunable = (comdb2_tunable *)context;
-    *(char **)tunable->var = intern((char *)value);
-    return 0;
-}
-
 static void *file_permissions_value(void *context)
 {
     static char val[15];
@@ -1407,6 +1400,15 @@ int register_tunable(comdb2_tunable *tunable)
     /* Keep tunable names in lower case (to be consistent). */
     tunable_tolower(t->name);
 
+    // Ensure the initial value for tunables without an update function
+    // is heap-allocated so the default update handler can safely free() it.
+    if ((tunable->type == TUNABLE_STRING || tunable->type == TUNABLE_RAW) &&
+         !tunable->update) {
+        if (tunable->var && *(char **)tunable->var) {
+            *((char **)tunable->var) = strdup(*(char **)tunable->var);
+        }
+    }
+
     t->descr = tunable->descr;
 
     if (tunable->type >= TUNABLE_INVALID) {

db/db_tunables.h

@@ -2583,8 +2583,7 @@ REGISTER_TUNABLE("iam_base_bri",
                  TUNABLE_STRING, &gbl_iam_base_bri, READEARLY | READONLY, NULL,
                  NULL, NULL, NULL);
 REGISTER_TUNABLE("iam_metrics_namespace", "metrics namespace for IAM user metrics (default: comdb2-iam)",
-                 TUNABLE_STRING, &gbl_iam_metrics_namespace, READEARLY | READONLY, NULL, NULL,
-                 iam_metrics_namespace_update, NULL);
+                 TUNABLE_STRING, &gbl_iam_metrics_namespace, READEARLY | READONLY, NULL, NULL, NULL, NULL);
 REGISTER_TUNABLE("queue_nonodh_scan_limit", "For comdb2_queues, stop queue scan at this depth (Default: 10000)", TUNABLE_INTEGER, &gbl_nonodh_queue_scan_limit, 0, NULL, NULL, NULL, NULL);
 REGISTER_TUNABLE("always_request_log_req", "Always request the next log record on replicant if there is a gap (default: off)", TUNABLE_BOOLEAN, &gbl_always_request_log_req, 0, NULL, NULL, NULL, NULL);
 REGISTER_TUNABLE("nudge_replication_when_idle",