MDEV-7995 : DMLs not getting replicated with log-bin=OFF & binlog-format != ROW

This bug is a side-effect of fix for MDEV-6924, where we completely
stopped a statement-based event from getting into the binlog cache when
binary logging is not enabled (and thus, wsrep_emulate_binlog mode = 1).
As a result, the SBR events were not replicated.

Fixed by allowing the SBR events to be written into the binlog cache.

Note: Only DMLs were affected as DDLs are replicated via TOI.

Merged galera_create_trigger.test from github.com/codership/mysql-wsrep.

mysql-test/suite/galera/r/galera_sbr.result

+SET SESSION binlog_format = 'STATEMENT';
+Warnings:
+Warning	1105	MariaDB Galera does not support binlog format: STATEMENT
+CREATE TABLE t1 (f1 INTEGER PRIMARY KEY) ENGINE=InnoDB;
+INSERT INTO t1 VALUES (1);
+SET SESSION binlog_format = 'MIXED';
+Warnings:
+Warning	1105	MariaDB Galera does not support binlog format: MIXED
+INSERT INTO t1 VALUES (2);
+SELECT COUNT(*) = 2 FROM t1;
+COUNT(*) = 2
+1
+DROP TABLE t1;
+SET GLOBAL binlog_format = 'ROW';

mysql-test/suite/galera/t/galera_sbr.test

+#
+# Test behavior if the user attempts to use statement-based replication
+#
+# SBR is not currently supported but we expect that no crashes or binlog-related assertions will be triggered.
+# 
+
+--source include/have_innodb.inc
+--source include/galera_cluster.inc
+
+--connection node_1
+#SET GLOBAL binlog_format = 'STATEMENT';
+SET SESSION binlog_format = 'STATEMENT';
+
+CREATE TABLE t1 (f1 INTEGER PRIMARY KEY) ENGINE=InnoDB;
+INSERT INTO t1 VALUES (1);
+
+SET SESSION binlog_format = 'MIXED';
+
+INSERT INTO t1 VALUES (2);
+
+--connection node_2
+SELECT COUNT(*) = 2 FROM t1;
+
+DROP TABLE t1;
+
+--connection node_1
+SET GLOBAL binlog_format = 'ROW';

sql/log.cc

@@ -5167,7 +5167,19 @@ bool MYSQL_BIN_LOG::write(Log_event *event_info, my_bool *with_annotate)
   binlog_cache_data *cache_data= 0;
   bool is_trans_cache= FALSE;
   bool using_trans= event_info->use_trans_cache();
-  bool direct= event_info->use_direct_logging();
+  bool direct;
+
+#ifdef WITH_WSREP
+  /*
+    When binary logging is not enabled (--log-bin=0), wsrep-patch partially
+    enables it without opening the binlog file (MSQL_BIN_LOG::open().
+    So, avoid writing directly to binlog file.
+  */
+  if (wsrep_emulate_bin_log)
+    direct= false;
+  else
+#endif /* WITH_WSREP */
+    direct= event_info->use_direct_logging();
 
   if (thd->binlog_evt_union.do_union)
   {
@@ -5948,6 +5960,10 @@ MYSQL_BIN_LOG::write_transaction_to_binlog(THD *thd,
   DBUG_ENTER("MYSQL_BIN_LOG::write_transaction_to_binlog");
 
 #ifdef WITH_WSREP
+  /*
+    Control should not be allowed beyond this point in wsrep_emulate_bin_log
+    mode.
+  */
   if (wsrep_emulate_bin_log) DBUG_RETURN(0);
 #endif /* WITH_WSREP */
   entry.thd= thd;

sql/sql_class.cc

@@ -5885,16 +5885,6 @@ int THD::binlog_query(THD::enum_binlog_query_type qtype, char const *query_arg,
       The MYSQL_LOG::write() function will set the STMT_END_F flag and
       flush the pending rows event if necessary.
     */
-#ifdef WITH_WSREP
-    /*
-      Even though wsrep only supports ROW binary log format, a user can set
-      binlog format to STATEMENT (wsrep_forced_binlog_format). In which case
-      the control might reach here even when binary logging (--log-bin) is
-      not enabled. This is possible because wsrep patch partially enables
-      binary logging by setting wsrep_emulate_binlog.
-    */
-    if (mysql_bin_log.is_open())
-#endif /* WITH_WSREP */
     {
       Query_log_event qinfo(this, query_arg, query_len, is_trans, direct,
                             suppress_use, errcode);