On Wed, 27 Sep 2023 00:13:15 +0200 Lorenzo Bianconi wrote:

+int nfsd_nl_threads_set_doit(struct sk_buff *skb, struct genl_info *info)
+{
+	u32 nthreads;
+	int ret;
+
+	if (!info->attrs[NFSD_A_CONTROL_PLANE_THREADS])
+		return -EINVAL;

Consider using GENL_REQ_ATTR_CHECK(), it will auto-add nice error
message to the reply on error.

+	nthreads = nla_get_u32(info->attrs[NFSD_A_CONTROL_PLANE_THREADS]);
+
+	ret = nfsd_svc(nthreads, genl_info_net(info), get_current_cred());
+	return ret == nthreads ? 0 : ret;
+}
+
+static int nfsd_nl_get_dump(struct sk_buff *skb, struct netlink_callback *cb,
+			    int cmd, int attr, u32 val)

YNL will dutifully return a list for every dump. If you're only getting
a single reply 'do' will be much better.