From c64420ee0c50958c61958fcec4947fbbe721a661 Mon Sep 17 00:00:00 2001
From: Siri Hansen <siri@erlang.org>
Date: Fri, 30 Nov 2018 17:45:18 +0100
Subject: [logger] Re-create log file if deleted

This is an update to logger_std_h, which makes it play well with tools
like logrotate.
---
 lib/kernel/src/logger_std_h.erl        | 45 +++++++++++++++++++++++-----------
 lib/kernel/test/logger_std_h_SUITE.erl | 23 ++++++++++++++---
 2 files changed, 51 insertions(+), 17 deletions(-)

(limited to 'lib')

diff --git a/lib/kernel/src/logger_std_h.erl b/lib/kernel/src/logger_std_h.erl
index ebe741e331..63d1dbaba2 100644
--- a/lib/kernel/src/logger_std_h.erl
+++ b/lib/kernel/src/logger_std_h.erl
@@ -328,27 +328,30 @@ file_ctrl_loop(Fd, DevName, Synced,
     receive
         %% asynchronous event
         {log,Bin} ->
-            Result = write_to_dev(Fd, Bin, DevName, PrevWriteResult, HandlerName),
-            file_ctrl_loop(Fd, DevName, false,
+            Fd1 = ensure(Fd, DevName),
+            Result = write_to_dev(Fd1, Bin, DevName, PrevWriteResult, HandlerName),
+            file_ctrl_loop(Fd1, DevName, false,
                            Result, PrevSyncResult, HandlerName);
 
         %% synchronous event
         {{log,Bin},{From,MRef}} ->
-            check_exist(Fd, DevName),
-            Result = write_to_dev(Fd, Bin, DevName, PrevWriteResult, HandlerName),
+            Fd1 = ensure(Fd, DevName),
+            Result = write_to_dev(Fd1, Bin, DevName, PrevWriteResult, HandlerName),
             From ! {MRef,ok},
-            file_ctrl_loop(Fd, DevName, false,
+            file_ctrl_loop(Fd1, DevName, false,
                            Result, PrevSyncResult, HandlerName);
 
         filesync ->
-            Result = sync_dev(Fd, DevName, Synced, PrevSyncResult, HandlerName),
-            file_ctrl_loop(Fd, DevName, true,
+            Fd1 = ensure(Fd, DevName),
+            Result = sync_dev(Fd1, DevName, Synced, PrevSyncResult, HandlerName),
+            file_ctrl_loop(Fd1, DevName, true,
                            PrevWriteResult, Result, HandlerName);
 
         {filesync,{From,MRef}} ->
-            Result = sync_dev(Fd, DevName, Synced, PrevSyncResult, HandlerName),
+            Fd1 = ensure(Fd, DevName),
+            Result = sync_dev(Fd1, DevName, Synced, PrevSyncResult, HandlerName),
             From ! {MRef,ok},
-            file_ctrl_loop(Fd, DevName, true,
+            file_ctrl_loop(Fd1, DevName, true,
                            PrevWriteResult, Result, HandlerName);
 
         stop ->
@@ -356,11 +359,25 @@ file_ctrl_loop(Fd, DevName, Synced,
             stopped
     end.
 
-check_exist(DevName, DevName) when is_atom(DevName) ->
-    ok;
-check_exist(_Fd, FileName) ->
-    _ = spawn_link(fun() -> {ok,_} = file:read_file_info(FileName) end),
-    ok.
+%% In order to play well with tools like logrotate, we need to be able
+%% to re-create the file if it has disappeared (e.g. if rotated by
+%% logrotate)
+ensure(Fd,DevName) when is_atom(DevName) ->
+    Fd;
+ensure(Fd,FileName) ->
+    case file:read_file_info(FileName) of
+        {ok,_} ->
+            Fd;
+        _ ->
+            _ = file:close(Fd),
+            _ = file:close(Fd), % delayed_write cause close not to close
+            case do_open_log_file({file,FileName}) of
+                {ok,Fd1} ->
+                    Fd1;
+                Error ->
+                    exit({could_not_reopen_file,Error})
+            end
+    end.
 
 write_to_dev(DevName, Bin, _DevName, _PrevWriteResult, _HandlerName)
   when is_atom(DevName) ->
diff --git a/lib/kernel/test/logger_std_h_SUITE.erl b/lib/kernel/test/logger_std_h_SUITE.erl
index a1159f280c..eb17a6d857 100644
--- a/lib/kernel/test/logger_std_h_SUITE.erl
+++ b/lib/kernel/test/logger_std_h_SUITE.erl
@@ -136,7 +136,8 @@ all() ->
      mem_kill_new,
      mem_kill_std,
      restart_after,
-     handler_requests_under_load
+     handler_requests_under_load,
+     recreate_deleted_log
     ].
 
 add_remove_instance_tty(_Config) ->
@@ -1255,6 +1256,22 @@ handler_requests_under_load(Config) ->
 handler_requests_under_load(cleanup, _Config) ->
     ok = stop_handler(?MODULE).
 
+recreate_deleted_log(Config) ->
+    {Log,_HConfig,_StdHConfig} =
+        start_handler(?MODULE, ?FUNCTION_NAME, Config),
+    logger:notice("first",?domain),
+    logger_std_h:filesync(?MODULE),
+    ok = file:rename(Log,Log++".old"),
+    logger:notice("second",?domain),
+    logger_std_h:filesync(?MODULE),
+    {ok,<<"first\n">>} = file:read_file(Log++".old"),
+    {ok,<<"second\n">>} = file:read_file(Log),
+    ok.
+recreate_deleted_log(cleanup, _Config) ->
+    ok = stop_handler(?MODULE).
+
+%%%-----------------------------------------------------------------
+%%%
 send_requests(HName, TO, Reqs = [{Req,Res}|Rs]) ->
     receive
         {From,finish} ->
@@ -1276,8 +1293,8 @@ send_requests(HName, TO, Reqs = [{Req,Res}|Rs]) ->
 
 %%%-----------------------------------------------------------------
 %%% 
-start_handler(Name, TTY, Config) when TTY == standard_io;
-                                      TTY == standard_error->
+start_handler(Name, TTY, _Config) when TTY == standard_io;
+                                       TTY == standard_error->
     ok = logger:add_handler(Name,
                             logger_std_h,
                             #{config => #{type => TTY},
-- 
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