[logger] Start using handler callback changing_config/3 in built-in handlers

The new parameter to this function, SetOrUpdate, indicates how
unspecified configuration data fields shall be set. The rule is that
if SetOrUpdate equals set, then default values shall be used, and if
SetOrUpdate equals update, then existing configuration values shall be
used. Consequently, these examples now apply to logger_std_h and
logger_disk_log_h:

set_handler_config(default, config, #{sync_mode_qlen => 20}) sets the
value of sync_mode_qlen to 20, and resets all other (writable) fields
in the config map to their default values.

update_handler_config(default, config, #{sync_mode_qlen => 20}) sets
the value of sync_mode_qlen to 20, and leaves all other fields in the
config map unchanged.

1 files changed, 35 insertions, 26 deletions

diff --git a/lib/kernel/src/logger_std_h.erl b/lib/kernel/src/logger_std_h.erl
index 66fa6b6ab6..6bbf75e0ab 100644
--- a/lib/kernel/src/logger_std_h.erl
+++ b/lib/kernel/src/logger_std_h.erl
@@ -35,7 +35,7 @@
          terminate/2, code_change/3]).
 
 %% logger callbacks
--export([log/2, adding_handler/1, removing_handler/1, changing_config/2]).
+-export([log/2, adding_handler/1, removing_handler/1, changing_config/3]).
 
 %% handler internal
 -export([log_handler_info/4]).
@@ -116,9 +116,8 @@ reset(Name) ->
 %%% Handler being added
 adding_handler(#{id:=Name}=Config) ->
     case check_config(adding, Config) of
-        {ok, Config1} ->
+        {ok, #{config:=HConfig}=Config1} ->
             %% create initial handler state by merging defaults with config
-            HConfig = maps:get(config, Config1, #{}),
             HState = maps:merge(get_init_state(), HConfig),
             case logger_h_common:overload_levels_ok(HState) of
                 true ->
@@ -135,22 +134,31 @@ adding_handler(#{id:=Name}=Config) ->
 
 %%%-----------------------------------------------------------------
 %%% Updating handler config
-changing_config(OldConfig=#{id:=Name, config:=OldHConfig},
-                NewConfig=#{id:=Name}) ->
-    #{type:=Type, handler_pid:=HPid, mode_tab:=ModeTab} = OldHConfig,
-    NewHConfig = maps:get(config, NewConfig, #{}),
-    case maps:get(type, NewHConfig, Type) of
-        Type ->
-            NewHConfig1 = NewHConfig#{type=>Type,
-                                      handler_pid=>HPid,
-                                      mode_tab=>ModeTab},
-            changing_config1(HPid, OldConfig,
-                             NewConfig#{config=>NewHConfig1});
-        _ ->
-            {error,{illegal_config_change,OldConfig,NewConfig}}
-    end;
-changing_config(OldConfig, NewConfig) ->
-    {error,{illegal_config_change,OldConfig,NewConfig}}.
+changing_config(SetOrUpdate,OldConfig=#{config:=OldHConfig},NewConfig) ->
+    WriteOnce = maps:with([type],OldHConfig),
+    ReadOnly = maps:with([handler_pid,mode_tab],OldHConfig),
+    NewHConfig0 = maps:get(config, NewConfig, #{}),
+    Default =
+        case SetOrUpdate of
+            set ->
+                %% Do not reset write-once fields to defaults
+                maps:merge(get_default_config(),WriteOnce);
+            update ->
+                OldHConfig
+        end,
+
+    %% Allow (accidentially) included read-only fields - just overwrite them
+    NewHConfig = maps:merge(maps:merge(Default, NewHConfig0),ReadOnly),
+
+    %% But fail if write-once fields are changed
+    case maps:with([type],NewHConfig) of
+        WriteOnce ->
+            changing_config1(maps:get(handler_pid,OldHConfig),
+                             OldConfig,
+                             NewConfig#{config=>NewHConfig});
+        Other ->
+            {error,{illegal_config_change,#{config=>WriteOnce},#{config=>Other}}}
+    end.
 
 changing_config1(HPid, OldConfig, NewConfig) ->
     case check_config(changing, NewConfig) of
@@ -169,8 +177,7 @@ changing_config1(HPid, OldConfig, NewConfig) ->
 check_config(adding, Config) ->
     %% Merge in defaults on handler level
     HConfig0 = maps:get(config, Config, #{}),
-    HConfig = maps:merge(#{type => standard_io},
-                         HConfig0),
+    HConfig = maps:merge(get_default_config(),HConfig0),
     case check_h_config(maps:to_list(HConfig)) of
         ok ->
             {ok,Config#{config=>HConfig}};
@@ -428,8 +435,9 @@ code_change(_OldVsn, State, _Extra) ->
 
 %%%-----------------------------------------------------------------
 %%%
-get_init_state() ->
-     #{sync_mode_qlen              => ?SYNC_MODE_QLEN,
+get_default_config() ->
+     #{type                        => standard_io,
+       sync_mode_qlen              => ?SYNC_MODE_QLEN,
        drop_mode_qlen              => ?DROP_MODE_QLEN,
        flush_qlen                  => ?FLUSH_QLEN,
        burst_limit_enable          => ?BURST_LIMIT_ENABLE,
@@ -439,10 +447,12 @@ get_init_state() ->
        overload_kill_qlen          => ?OVERLOAD_KILL_QLEN,
        overload_kill_mem_size      => ?OVERLOAD_KILL_MEM_SIZE,
        overload_kill_restart_after => ?OVERLOAD_KILL_RESTART_AFTER,
-       file_ctrl_sync_int          => ?CONTROLLER_SYNC_INTERVAL,
-       filesync_ok_qlen            => ?FILESYNC_OK_QLEN,
        filesync_repeat_interval    => ?FILESYNC_REPEAT_INTERVAL}.
 
+get_init_state() ->
+    #{file_ctrl_sync_int          => ?CONTROLLER_SYNC_INTERVAL,
+      filesync_ok_qlen            => ?FILESYNC_OK_QLEN}.
+
 %%%-----------------------------------------------------------------
 %%% Add a standard handler to the logger.
 %%% This starts a dedicated handler process which should always
@@ -825,4 +835,3 @@ sync_dev(Fd, DevName, PrevSyncResult, HandlerName) ->
             logger_h_common:error_notify({HandlerName,filesync,DevName,Error}),
             Error
     end.
-