fix(sessds): Prevent hot update of session_persistence.enable config

apps/emqx/src/emqx_config.erl

@@ -715,6 +715,7 @@ add_handlers() ->
     ok = emqx_config_logger:add_handler(),
     ok = emqx_config_zones:add_handler(),
     emqx_sys_mon:add_handler(),
+    emqx_persistent_message:add_handler(),
     ok.
 
 remove_handlers() ->

apps/emqx/src/emqx_persistent_message.erl

@@ -16,11 +16,16 @@
 
 -module(emqx_persistent_message).
 
+-behaviour(emqx_config_handler).
+
 -include("emqx.hrl").
 
 -export([init/0]).
 -export([is_persistence_enabled/0, force_ds/0]).
 
+%% Config handler
+-export([add_handler/0, pre_config_update/3]).
+
 %% Message persistence
 -export([
     persist/1
@@ -66,6 +71,19 @@ storage_backend(Path) ->
 
 %%--------------------------------------------------------------------
 
+-spec add_handler() -> ok.
+add_handler() ->
+    emqx_conf:add_handler([session_persistence], ?MODULE).
+
+pre_config_update([session_persistence], #{<<"enable">> := New}, #{<<"enable">> := Old}) when
+    New =/= Old
+->
+    {error, "Hot update of session_persistence.enable parameter is currently not supported"};
+pre_config_update(_Root, _NewConf, _OldConf) ->
+    ok.
+
+%%--------------------------------------------------------------------
+
 -spec persist(emqx_types:message()) ->
     ok | {skipped, _Reason} | {error, _TODO}.
 persist(Msg) ->