erts: Add erlang:system_flag(system_logger,_)

This flag allows logger and other components to set the
process which log messages from ERTS are to be sent.

7 files changed, 196 insertions, 98 deletions

diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml
index a42323b13d..7699f64c25 100644
--- a/erts/doc/src/erlang.xml
+++ b/erts/doc/src/erlang.xml
@@ -7539,7 +7539,39 @@ ok
     </func>
 
     <func>
-      <name name="system_flag" arity="2" clause_i="14" since=""/>
+      <name name="system_flag" arity="2" clause_i="14" since="OTP 21.3"/>
+      <fsummary>Set system logger process.</fsummary>
+      <desc>
+        <p>Sets the process that will receive the logging
+        messages generated by ERTS. If set to <c>undefined</c>,
+        all logging messages generated by ERTS will be dropped.
+        The messages will be in the format:</p>
+        <code>
+{log,Level,Format,ArgList,Metadata} where
+
+Level = atom(),
+Format = string(),
+ArgList = list(term()),
+Metadata = #{ pid => pid(),
+   group_leader => pid(),
+   time := logger:timestamp(),
+   error_logger := #{ emulator := true, tag := atom() }
+        </code>
+        <p>If the <c>system_logger</c> process dies,
+        this flag will be reset to <c>logger</c>.</p>
+        <p>The default is the process named <c>logger</c>.</p>
+        <p>Returns the old value of the flag.</p>
+        <note><p>This function is designed to be used by the
+        KERNEL <seealso marker="kernel:logger"><c>logger</c></seealso>.
+        Be careful if you change it to something else as
+        log messages may be lost. If you want to intercept
+        emulator log messages, do it by adding a specialized handler
+        to the KERNEL logger.</p></note>
+      </desc>
+    </func>
+
+    <func>
+      <name name="system_flag" arity="2" clause_i="15" since=""/>
       <fsummary>Set system flag trace_control_word.</fsummary>
       <desc>
         <p>Sets the value of the node trace control word to
@@ -7553,7 +7585,7 @@ ok
     </func>
 
     <func>
-      <name name="system_flag" arity="2" clause_i="15"
+      <name name="system_flag" arity="2" clause_i="16"
 	    anchor="system_flag_time_offset" since="?"/>
       <fsummary>Finalize the time offset.</fsummary>
       <desc>
@@ -7703,8 +7735,9 @@ ok
               <seealso marker="#system_info_nif_version"><c>nif_version</c></seealso>,
               <seealso marker="#system_info_otp_release"><c>otp_release</c></seealso>,
               <seealso marker="#system_info_port_parallelism"><c>port_parallelism</c></seealso>,
-              <seealso marker="#system_info_system_version"><c>system_version</c></seealso>,
               <seealso marker="#system_info_system_architecture"><c>system_architecture</c></seealso>,
+              <seealso marker="#system_info_system_logger"><c>system_logger</c></seealso>,
+              <seealso marker="#system_info_system_version"><c>system_version</c></seealso>,
               <seealso marker="#system_info_trace_control_word"><c>trace_control_word</c></seealso>,
               <seealso marker="#system_info_version"><c>version</c></seealso>,
               <seealso marker="#system_info_wordsize"><c>wordsize</c></seealso>
@@ -7876,7 +7909,7 @@ ok
 	    anchor="system_info_cpu_topology" since=""/>           <!-- cpu_topology -->
       <name name="system_info" arity="1" clause_i="13" since=""/>  <!-- {cpu_topology, _} -->
       <name name="system_info" arity="1" clause_i="38" since=""/>  <!-- logical_processors -->
-      <name name="system_info" arity="1" clause_i="73" since="?"/>  <!-- update_cpu_info -->
+      <name name="system_info" arity="1" clause_i="74" since="?"/>  <!-- update_cpu_info -->
       <fsummary>Information about the CPU topology of the system.</fsummary>
       <type name="cpu_topology"/>
       <type name="level_entry"/>
@@ -8231,10 +8264,10 @@ ok
       <name name="system_info" arity="1" clause_i="50" since="OTP 18.0"/>  <!-- os_monotonic_time_source -->
       <name name="system_info" arity="1" clause_i="51" since="OTP 18.0"/>  <!-- os_system_time_source -->
       <name name="system_info" arity="1" clause_i="63" since="OTP 18.0"/>  <!-- start_time -->
-      <name name="system_info" arity="1" clause_i="68" since="OTP 18.0"/>  <!-- time_correction -->
-      <name name="system_info" arity="1" clause_i="69" since="OTP 18.0"/>  <!-- time_offset -->
-      <name name="system_info" arity="1" clause_i="70" since="OTP 18.0"/>  <!-- time_warp_mode -->
-      <name name="system_info" arity="1" clause_i="71" since="?"/>  <!-- tolerant_timeofday -->
+      <name name="system_info" arity="1" clause_i="69" since="OTP 18.0"/>  <!-- time_correction -->
+      <name name="system_info" arity="1" clause_i="70" since="OTP 18.0"/>  <!-- time_offset -->
+      <name name="system_info" arity="1" clause_i="71" since="OTP 18.0"/>  <!-- time_warp_mode -->
+      <name name="system_info" arity="1" clause_i="72" since="?"/>  <!-- tolerant_timeofday -->
       <fsummary>Information about system time.</fsummary>
       <desc>
         <marker id="system_info_time_tags"/>
@@ -8466,8 +8499,8 @@ ok
       <name name="system_info" arity="1" clause_i="60" since=""/>  <!-- scheduler_id -->
       <name name="system_info" arity="1" clause_i="61" since=""/>  <!-- schedulers -->
       <name name="system_info" arity="1" clause_i="62" since=""/>  <!-- smp_support -->
-      <name name="system_info" arity="1" clause_i="66" since=""/>  <!-- threads -->
-      <name name="system_info" arity="1" clause_i="67" since=""/>  <!-- thread_pool_size -->
+      <name name="system_info" arity="1" clause_i="67" since=""/>  <!-- threads -->
+      <name name="system_info" arity="1" clause_i="68" since=""/>  <!-- thread_pool_size -->
       <fsummary>Information about system schedulers.</fsummary>
       <desc>
         <marker id="system_info_scheduler_tags"/>
@@ -8889,19 +8922,20 @@ ok
       <!-- <name name="system_info" arity="1" clause_i="61"/>  schedulers -->
       <!-- <name name="system_info" arity="1" clause_i="62"/>  smp_support -->
       <!-- <name name="system_info" arity="1" clause_i="63"/>  start_time -->
-      <name name="system_info" arity="1" clause_i="64" since=""/>  <!-- system_version -->
-      <name name="system_info" arity="1" clause_i="65" since=""/>  <!-- system_architecture -->
-      <!-- <name name="system_info" arity="1" clause_i="66"/>  threads -->
-      <!-- <name name="system_info" arity="1" clause_i="67"/>  thread_pool_size -->
-      <!-- <name name="system_info" arity="1" clause_i="68"/>  time_correction -->
-      <!-- <name name="system_info" arity="1" clause_i="69"/>  time_offset -->
-      <!-- <name name="system_info" arity="1" clause_i="70"/>  time_warp_mode -->
-      <!-- <name name="system_info" arity="1" clause_i="71"/>  tolerant_timeofday -->
-      <name name="system_info" arity="1" clause_i="72" since=""/>  <!-- trace_control_word -->
-      <!-- <name name="system_info" arity="1" clause_i="73"/>  update_cpu_info -->
-      <name name="system_info" arity="1" clause_i="74" since=""/>  <!-- version -->
-      <name name="system_info" arity="1" clause_i="75" since=""/>  <!-- wordsize -->
-      <!-- <name name="system_info" arity="1" clause_i="76"/>  overview -->
+      <name name="system_info" arity="1" clause_i="64" since=""/>  <!-- system_architecture -->
+      <name name="system_info" arity="1" clause_i="65" since="OTP 21.3"/>  <!-- system_logger -->
+      <name name="system_info" arity="1" clause_i="66" since=""/>  <!-- system_version -->
+      <!-- <name name="system_info" arity="1" clause_i="67"/>  threads -->
+      <!-- <name name="system_info" arity="1" clause_i="68"/>  thread_pool_size -->
+      <!-- <name name="system_info" arity="1" clause_i="69"/>  time_correction -->
+      <!-- <name name="system_info" arity="1" clause_i="70"/>  time_offset -->
+      <!-- <name name="system_info" arity="1" clause_i="71"/>  time_warp_mode -->
+      <!-- <name name="system_info" arity="1" clause_i="72"/>  tolerant_timeofday -->
+      <name name="system_info" arity="1" clause_i="73" since=""/>  <!-- trace_control_word -->
+      <!-- <name name="system_info" arity="1" clause_i="74"/>  update_cpu_info -->
+      <name name="system_info" arity="1" clause_i="75" since=""/>  <!-- version -->
+      <name name="system_info" arity="1" clause_i="76" since=""/>  <!-- wordsize -->
+      <!-- <name name="system_info" arity="1" clause_i="77"/>  overview -->
       <fsummary>Information about the system.</fsummary>
       <desc>
         <marker id="system_info_misc_tags"/>
@@ -9057,18 +9091,24 @@ ok
               <seealso marker="erl#+spp"><c>+spp</c></seealso>
               in <c>erl(1)</c>.</p>
           </item>
-          <tag><marker id="system_info_system_version"/>
-            <c>system_version</c></tag>
-          <item>
-            <p>Returns a string containing version number and
-              some important properties, such as the number of schedulers.</p>
-          </item>
           <tag><marker id="system_info_system_architecture"/>
             <c>system_architecture</c></tag>
           <item>
             <p>Returns a string containing the processor and OS
               architecture the emulator is built for.</p>
           </item>
+          <tag><marker id="system_info_system_logger"/>
+            <c>system_logger</c></tag>
+          <item>
+            <p>Returns the current <c>system_logger</c> as set by
+            <seealso marker="#system_flag/2"><c>erlang:system_flag(system_logger, _)</c></seealso>.</p>
+          </item>
+          <tag><marker id="system_info_system_version"/>
+            <c>system_version</c></tag>
+          <item>
+            <p>Returns a string containing version number and
+              some important properties, such as the number of schedulers.</p>
+          </item>
           <tag><marker id="system_info_trace_control_word"/>
             <c>trace_control_word</c></tag>
           <item>
diff --git a/erts/emulator/beam/bif.c b/erts/emulator/beam/bif.c
index f1fac7f8d0..b13c6c90c6 100644
--- a/erts/emulator/beam/bif.c
+++ b/erts/emulator/beam/bif.c
@@ -4701,6 +4701,9 @@ BIF_RETTYPE system_flag_2(BIF_ALIST_2)
 	return erts_bind_schedulers(BIF_P, BIF_ARG_2);
     } else if (ERTS_IS_ATOM_STR("erts_alloc", BIF_ARG_1)) {
         return erts_alloc_set_dyn_param(BIF_P, BIF_ARG_2);
+    } else if (ERTS_IS_ATOM_STR("system_logger", BIF_ARG_1)) {
+        Eterm res = erts_set_system_logger(BIF_ARG_2);
+        if (is_value(res)) BIF_RET(res);
     }
     error:
     BIF_ERROR(BIF_P, BADARG);
@@ -5203,61 +5206,6 @@ erts_call_dirty_bif(ErtsSchedulerData *esdp, Process *c_p, BeamInstr *I, Eterm *
     return exiting;
 }
 
-
-
-#ifdef HARDDEBUG
-/*
-You'll need this line in bif.tab to be able to use this debug bif
-
-bif erlang:send_to_logger/2
-
-*/
-BIF_RETTYPE send_to_logger_2(BIF_ALIST_2)
-{
-    byte *buf;
-    ErlDrvSizeT len;
-    if (!is_atom(BIF_ARG_1) || !(is_list(BIF_ARG_2) ||
-				 is_nil(BIF_ARG_1))) {
-	BIF_ERROR(BIF_P,BADARG);
-    }
-    if (erts_iolist_size(BIF_ARG_2, &len) != 0)
-	BIF_ERROR(BIF_P,BADARG);
-    else if (len == 0)
-	buf = "";
-    else {
-#ifdef DEBUG
-	ErlDrvSizeT len2;
-#endif
-	buf = (byte *) erts_alloc(ERTS_ALC_T_TMP, len+1);
-#ifdef DEBUG
-	len2 =
-#else
-	(void)
-#endif
-	    erts_iolist_to_buf(BIF_ARG_2, buf, len);
-	ASSERT(len2 == len);
-	buf[len] = '\0';
-	switch (BIF_ARG_1) {
-	case am_info:
-	    erts_send_info_to_logger(BIF_P->group_leader, buf, len);
-	    break;
-	case am_warning:
-	    erts_send_warning_to_logger(BIF_P->group_leader, buf, len);
-	    break;
-	case am_error:
-	    erts_send_error_to_logger(BIF_P->group_leader, buf, len);
-	    break;
-	default:
-	{
-	    BIF_ERROR(BIF_P,BADARG);
-	}
-	}
-	erts_free(ERTS_ALC_T_TMP, (void *) buf);
-    }
-    BIF_RET(am_true);
-}
-#endif /* HARDDEBUG */
-
 BIF_RETTYPE get_module_info_1(BIF_ALIST_1)
 {
     Eterm ret = erts_module_info_0(BIF_P, BIF_ARG_1);
diff --git a/erts/emulator/beam/erl_bif_info.c b/erts/emulator/beam/erl_bif_info.c
index 7fada0d548..9cc95a5c09 100644
--- a/erts/emulator/beam/erl_bif_info.c
+++ b/erts/emulator/beam/erl_bif_info.c
@@ -3139,6 +3139,8 @@ BIF_RETTYPE system_info_1(BIF_ALIST_1)
 	DECL_AM(tag);
 	BIF_RET(AM_tag);
 #endif
+    } else if (ERTS_IS_ATOM_STR("system_logger", BIF_ARG_1)) {
+        BIF_RET(erts_get_system_logger());
     }
 
     BIF_ERROR(BIF_P, BADARG);
diff --git a/erts/emulator/beam/erl_trace.c b/erts/emulator/beam/erl_trace.c
index 2350d4c02f..701fb38147 100644
--- a/erts/emulator/beam/erl_trace.c
+++ b/erts/emulator/beam/erl_trace.c
@@ -72,6 +72,7 @@ static ErtsTracer default_port_tracer;
 
 static Eterm system_monitor;
 static Eterm system_profile;
+static erts_aint_t system_logger;
 
 #ifdef HAVE_ERTS_NOW_CPU
 int erts_cpu_timestamp;
@@ -340,6 +341,7 @@ void erts_init_trace(void) {
     default_port_trace_flags = F_INITIAL_TRACE_FLAGS;
     default_port_tracer = erts_tracer_nil;
     system_seq_tracer = erts_tracer_nil;
+    erts_atomic_init_nob(&system_logger, am_logger);
     init_sys_msg_dispatcher();
     init_tracer_nif();
 }
@@ -2027,10 +2029,24 @@ enqueue_sys_msg(enum ErtsSysMsgType type,
     erts_mtx_unlock(&smq_mtx);
 }
 
+Eterm
+erts_get_system_logger(void)
+{
+    return (Eterm)erts_atomic_read_nob(&system_logger);
+}
+
+Eterm
+erts_set_system_logger(Eterm logger)
+{
+    if (logger != am_logger && logger != am_undefined && !is_internal_pid(logger))
+        return THE_NON_VALUE;
+    return (Eterm)erts_atomic_xchg_nob(&system_logger, logger);
+}
+
 void
 erts_queue_error_logger_message(Eterm from, Eterm msg, ErlHeapFragment *bp)
 {
-    enqueue_sys_msg(SYS_MSG_TYPE_ERRLGR, from, am_logger, msg, bp);
+    enqueue_sys_msg(SYS_MSG_TYPE_ERRLGR, from, erts_get_system_logger(), msg, bp);
 }
 
 void
@@ -2271,7 +2287,7 @@ sys_msg_dispatcher_func(void *unused)
 		}
 		break;
 	    case SYS_MSG_TYPE_ERRLGR:
-		receiver = am_logger;
+		receiver = smqp->to;
 		break;
 	    default:
 		receiver = NIL;
@@ -2285,8 +2301,15 @@ sys_msg_dispatcher_func(void *unused)
 	    if (is_internal_pid(receiver)) {
 		proc = erts_pid2proc(NULL, 0, receiver, proc_locks);
 		if (!proc) {
-		    /* Bad tracer */
-		    goto failure;
+                    if (smqp->type == SYS_MSG_TYPE_ERRLGR) {
+                        /* Bad logger process, send to kernel 'logger' process */
+                        erts_set_system_logger(am_logger);
+                        receiver = erts_get_system_logger();
+                        goto logger;
+                    } else {
+                        /* Bad tracer */
+                        goto failure;
+                    }
 		}
 		else {
 		    ErtsMessage *mp;
@@ -2299,9 +2322,9 @@ sys_msg_dispatcher_func(void *unused)
 #endif
 		    erts_proc_unlock(proc, proc_locks);
 		}
-	    }
-	    else if (receiver == am_logger) {
-		proc = erts_whereis_process(NULL,0,receiver,proc_locks,0);
+	    } else if (receiver == am_logger) {
+            logger:
+		proc = erts_whereis_process(NULL,0,am_logger,proc_locks,0);
 		if (!proc)
 		    goto failure;
 		else if (smqp->from == proc->common.id)
@@ -2309,7 +2332,10 @@ sys_msg_dispatcher_func(void *unused)
 		else
 		    goto queue_proc_msg;
 	    }
-	    else if (is_internal_port(receiver)) {
+            else if (receiver == am_undefined) {
+                goto drop_sys_msg;
+	    }
+            else if (is_internal_port(receiver)) {
 		port = erts_thr_id2port_sflgs(receiver,
 					      ERTS_PORT_SFLGS_INVALID_TRACER_LOOKUP);
 		if (!port)
@@ -2366,7 +2392,7 @@ erts_foreach_sys_msg_in_q(void (*func)(Eterm,
 	    to = erts_get_system_profile();
 	    break;
 	case SYS_MSG_TYPE_ERRLGR:
-	    to = am_logger;
+	    to = erts_get_system_logger();
 	    break;
 	default:
 	    to = NIL;
diff --git a/erts/emulator/beam/erl_trace.h b/erts/emulator/beam/erl_trace.h
index bccf31606e..b7844d1cb0 100644
--- a/erts/emulator/beam/erl_trace.h
+++ b/erts/emulator/beam/erl_trace.h
@@ -94,6 +94,8 @@ void erts_foreach_sys_msg_in_q(void (*func)(Eterm,
 					    Eterm,
 					    Eterm,
 					    ErlHeapFragment *));
+Eterm erts_set_system_logger(Eterm);
+Eterm erts_get_system_logger(void);
 void erts_queue_error_logger_message(Eterm, Eterm, ErlHeapFragment *);
 void erts_send_sys_msg_proc(Eterm, Eterm, Eterm, ErlHeapFragment *);
 
diff --git a/erts/emulator/test/system_info_SUITE.erl b/erts/emulator/test/system_info_SUITE.erl
index 21ab6b378a..4e663fed7f 100644
--- a/erts/emulator/test/system_info_SUITE.erl
+++ b/erts/emulator/test/system_info_SUITE.erl
@@ -37,8 +37,9 @@
 
 -export([process_count/1, system_version/1, misc_smoke_tests/1,
          heap_size/1, wordsize/1, memory/1, ets_limit/1, atom_limit/1,
-         ets_count/1,
-         atom_count/1]).
+         ets_count/1, atom_count/1, system_logger/1]).
+
+-export([init/1, handle_event/2, handle_call/2]).
 
 suite() ->
     [{ct_hooks,[ts_install_cth]},
@@ -46,8 +47,8 @@ suite() ->
 
 all() -> 
     [process_count, system_version, misc_smoke_tests,
-     ets_count,
-     heap_size, wordsize, memory, ets_limit, atom_limit, atom_count].
+     ets_count, heap_size, wordsize, memory, ets_limit, atom_limit, atom_count,
+     system_logger].
 
 %%%
 %%% The test cases -------------------------------------------------------------
@@ -573,3 +574,78 @@ atom_count(Config) when is_list(Config) ->
     true = Limit >= Count2,
     true = Count2 > Count1,
     ok.
+
+
+system_logger(Config) when is_list(Config) ->
+
+    TC = self(),
+
+    ok = error_logger:add_report_handler(?MODULE, [TC]),
+
+    generate_log_event(),
+
+    flush(1, report_handler),
+
+    Initial = erlang:system_info(system_logger),
+
+    {Logger,_} = spawn_monitor(fun F() -> receive M -> TC ! {system_logger,M}, F() end end),
+
+    Initial = erlang:system_flag(system_logger, Logger),
+    Logger = erlang:system_info(system_logger),
+
+    generate_log_event(),
+    flush(1, system_logger),
+
+    Logger = erlang:system_flag(system_logger, Logger),
+
+    generate_log_event(),
+    flush(1, system_logger),
+
+    exit(Logger, die),
+    receive {'DOWN',_,_,_,_} -> ok end,
+
+    generate_log_event(),
+    flush(1, report_handler),
+
+    logger = erlang:system_info(system_logger),
+
+    logger = erlang:system_flag(system_logger, undefined),
+    generate_log_event(),
+    flush(),
+
+    undefined = erlang:system_flag(system_logger, Initial),
+
+    ok.
+
+flush() ->
+    receive
+        M ->
+            ct:fail({unexpected_message, M})
+    after 0 ->
+            ok
+    end.
+
+flush(0, _Pat) ->
+    flush();
+flush(Cnt, Pat) ->
+    receive
+        M when element(1,M) =:= Pat ->
+            ct:log("~p",[M]),
+            flush(Cnt-1, Pat)
+    after 500 ->
+            ct:fail({missing, Cnt, Pat})
+    end.
+
+generate_log_event() ->
+    {_Pid, Ref} = spawn_monitor(fun() -> ok = nok end),
+    receive {'DOWN', Ref, _, _, _} -> ok end.
+
+init([To]) ->
+    {ok, To}.
+
+handle_call(Msg, State) ->
+    {ok, Msg, State}.
+
+handle_event(Event, State) ->
+    State ! {report_handler, Event},
+    {ok, State}.
diff --git a/erts/preloaded/src/erlang.erl b/erts/preloaded/src/erlang.erl
index c20082a545..5730e999cb 100644
--- a/erts/preloaded/src/erlang.erl
+++ b/erts/preloaded/src/erlang.erl
@@ -2526,6 +2526,9 @@ subtract(_,_) ->
                                 OldSchedulersOnline when
       SchedulersOnline :: pos_integer(),
       OldSchedulersOnline :: pos_integer();
+                        (system_logger, Logger) -> PrevLogger when
+      Logger :: logger | undefined | pid(),
+      PrevLogger :: logger | undefined | pid();
                         (trace_control_word, TCW) -> OldTCW when
       TCW :: non_neg_integer(),
       OldTCW :: non_neg_integer();
@@ -2731,8 +2734,9 @@ tuple_to_list(_Tuple) ->
          (schedulers | schedulers_online) -> pos_integer();
          (smp_support) -> boolean();
          (start_time) -> integer();
-         (system_version) -> string();
          (system_architecture) -> string();
+         (system_logger) -> logger | undefined | pid();
+         (system_version) -> string();
          (threads) -> boolean();
          (thread_pool_size) -> non_neg_integer();
          (time_correction) -> true | false;