MDEV-4222: Assertion `( ((global_system_variables.wsrep_on) &&

  (thd && thd->variables.wsrep_on)) && wsrep_emulate_bin_log) ||
  mysql_bin_log .is_open()' fails on SAVEPOINT with disabled
  wsrep_provider

As wsrep_on system variable is ON by default the binlog handlerton
is implicitly enabled during the server initialization phase. Later,
while wsrep plugin is getting initialized, wsrep_on in corrected &
turned OFF in case wsrep provider is not specified (leaving binlog
in ON state!). This leads to the reported assertion.

Fixed by adding another check for wsrep provider before binlog
is enabled.

Added a test case.

mysql-test/suite/wsrep/r/trans.result

+#
+# MDEV-4222 : Assertion `( ((global_system_variables.wsrep_on) &&
+#            (thd && thd->variables.wsrep_on)) && srep_emulate_bin_log)
+#            || mysql_bin_log .is_open()' fails on SAVEPOINT with
+#            disabled wsrep_provider
+#
+START TRANSACTION WITH CONSISTENT SNAPSHOT;
+SAVEPOINT A;
+End of test.

mysql-test/suite/wsrep/t/trans.test

+--source include/have_innodb.inc
+
+--echo #
+--echo # MDEV-4222 : Assertion `( ((global_system_variables.wsrep_on) &&
+--echo #            (thd && thd->variables.wsrep_on)) && srep_emulate_bin_log)
+--echo #            || mysql_bin_log .is_open()' fails on SAVEPOINT with
+--echo #            disabled wsrep_provider
+--echo #
+
+START TRANSACTION WITH CONSISTENT SNAPSHOT;
+SAVEPOINT A;
+
+--echo End of test.

sql/log.cc

@@ -1708,7 +1708,7 @@ int binlog_init(void *p)
 {
   binlog_hton= (handlerton *)p;
 #ifdef WITH_WSREP
-  if (WSREP_ON) 
+  if (WSREP_ON && WSREP_PROVIDER_EXISTS)
     binlog_hton->state= SHOW_OPTION_YES;
   else
   {

sql/mysqld.cc

@@ -4909,7 +4909,7 @@ pthread_handler_t start_wsrep_THD(void *arg)
 
 void wsrep_create_rollbacker()
 {
-  if (wsrep_provider && strcasecmp(wsrep_provider, "none"))
+  if (WSREP_PROVIDER_EXISTS)
   {
     pthread_t hThread;
     /* create rollbacker */
@@ -4925,7 +4925,7 @@ void wsrep_create_appliers(long threads)
   {
     /* see wsrep_replication_start() for the logic */
     if (wsrep_cluster_address && strlen(wsrep_cluster_address) &&
-        wsrep_provider && strcasecmp(wsrep_provider, "none"))
+        WSREP_PROVIDER_EXISTS)
     {
       WSREP_ERROR("Trying to launch slave threads before creating "
                   "connection at '%s'", wsrep_cluster_address);

sql/wsrep_mysqld.cc

@@ -438,8 +438,7 @@ int wsrep_init()
     }
   }
 
-  if (strlen(wsrep_provider)== 0 ||
-      !strcmp(wsrep_provider, WSREP_NONE))
+  if (!WSREP_PROVIDER_EXISTS)
   {
     // enable normal operation in case no provider is specified
     wsrep_ready_set(TRUE);
@@ -662,8 +661,7 @@ bool wsrep_start_replication()
     if provider is trivial, don't even try to connect,
     but resume local node operation
   */
-  if (strlen(wsrep_provider)== 0 ||
-      !strcmp(wsrep_provider, WSREP_NONE))
+  if (!WSREP_PROVIDER_EXISTS)
   {
     // enable normal operation in case no provider is specified
     wsrep_ready_set(TRUE);

sql/wsrep_mysqld.h

@@ -286,6 +286,9 @@ extern wsrep_seqno_t wsrep_locked_seqno;
     if (victim_thd) WSREP_LOG_CONFLICT_THD(victim_thd, "Victim thread");       \
   }
 
+#define WSREP_PROVIDER_EXISTS                                                  \
+  (wsrep_provider && strncasecmp(wsrep_provider, WSREP_NONE, FN_REFLEN))
+
 /*! Synchronizes applier thread start with init thread */
 extern void wsrep_sst_grab();
 /*! Init thread waits for SST completion */