MDEV-6717 : wsrep_data_home_dir should default to @@datadir

Used mysql_real_data_home as wsrep_data_home_dir's default.
Added a test case.

mysql-test/suite/sys_vars/r/wsrep_data_home_dir_basic.result

@@ -2,47 +2,58 @@
 # wsrep_data_home_dir (readonly)
 #
 # default
-SELECT @@global.wsrep_data_home_dir;
-@@global.wsrep_data_home_dir
-
+SELECT COUNT(@@global.wsrep_data_home_dir);
+COUNT(@@global.wsrep_data_home_dir)
+1
 
 # scope
 SELECT @@session.wsrep_data_home_dir;
 ERROR HY000: Variable 'wsrep_data_home_dir' is a GLOBAL variable
 SET @@global.wsrep_data_home_dir='/tmp/data';
 ERROR HY000: Variable 'wsrep_data_home_dir' is a read only variable
-SELECT @@global.wsrep_data_home_dir;
-@@global.wsrep_data_home_dir
-
+SELECT COUNT(@@global.wsrep_data_home_dir);
+COUNT(@@global.wsrep_data_home_dir)
+1
 
 # valid values
 SET @@global.wsrep_data_home_dir='/tmp/data';
 ERROR HY000: Variable 'wsrep_data_home_dir' is a read only variable
-SELECT @@global.wsrep_data_home_dir;
-@@global.wsrep_data_home_dir
-
+SELECT COUNT(@@global.wsrep_data_home_dir);
+COUNT(@@global.wsrep_data_home_dir)
+1
 SET @@global.wsrep_data_home_dir=junk-dir;
 ERROR HY000: Variable 'wsrep_data_home_dir' is a read only variable
-SELECT @@global.wsrep_data_home_dir;
-@@global.wsrep_data_home_dir
-
+SELECT COUNT(@@global.wsrep_data_home_dir);
+COUNT(@@global.wsrep_data_home_dir)
+1
 SET @@global.wsrep_data_home_dir=junk/dir;
 ERROR HY000: Variable 'wsrep_data_home_dir' is a read only variable
-SELECT @@global.wsrep_data_home_dir;
-@@global.wsrep_data_home_dir
-
+SELECT COUNT(@@global.wsrep_data_home_dir);
+COUNT(@@global.wsrep_data_home_dir)
+1
 SET @@global.wsrep_data_home_dir=OFF;
 ERROR HY000: Variable 'wsrep_data_home_dir' is a read only variable
-SELECT @@global.wsrep_data_home_dir;
-@@global.wsrep_data_home_dir
-
+SELECT COUNT(@@global.wsrep_data_home_dir);
+COUNT(@@global.wsrep_data_home_dir)
+1
 SET @@global.wsrep_data_home_dir=default;
 ERROR HY000: Variable 'wsrep_data_home_dir' is a read only variable
-SELECT @@global.wsrep_data_home_dir;
-@@global.wsrep_data_home_dir
-
+SELECT COUNT(@@global.wsrep_data_home_dir);
+COUNT(@@global.wsrep_data_home_dir)
+1
 
 # invalid values
 SET @@global.wsrep_data_home_dir=NULL;
 ERROR HY000: Variable 'wsrep_data_home_dir' is a read only variable
+#
+# MDEV-6717 : wsrep_data_home_dir should default to @@datadir
+#
+SELECT @@GLOBAL.wsrep_data_home_dir = VARIABLE_VALUE FROM
+INFORMATION_SCHEMA.GLOBAL_VARIABLES WHERE VARIABLE_NAME='datadir';
+@@GLOBAL.wsrep_data_home_dir = VARIABLE_VALUE
+1
+SELECT @@GLOBAL.wsrep_data_home_dir = VARIABLE_VALUE FROM
+INFORMATION_SCHEMA.GLOBAL_VARIABLES WHERE VARIABLE_NAME='wsrep_data_home_dir';
+@@GLOBAL.wsrep_data_home_dir = VARIABLE_VALUE
+1
 # End of test

mysql-test/suite/sys_vars/t/wsrep_data_home_dir_basic.test

@@ -5,7 +5,7 @@
 --echo #
 
 --echo # default
-SELECT @@global.wsrep_data_home_dir;
+SELECT COUNT(@@global.wsrep_data_home_dir);
 
 --echo
 --echo # scope
@@ -13,29 +13,37 @@ SELECT @@global.wsrep_data_home_dir;
 SELECT @@session.wsrep_data_home_dir;
 --error ER_INCORRECT_GLOBAL_LOCAL_VAR
 SET @@global.wsrep_data_home_dir='/tmp/data';
-SELECT @@global.wsrep_data_home_dir;
+SELECT COUNT(@@global.wsrep_data_home_dir);
 
 --echo
 --echo # valid values
 --error ER_INCORRECT_GLOBAL_LOCAL_VAR
 SET @@global.wsrep_data_home_dir='/tmp/data';
-SELECT @@global.wsrep_data_home_dir;
+SELECT COUNT(@@global.wsrep_data_home_dir);
 --error ER_INCORRECT_GLOBAL_LOCAL_VAR
 SET @@global.wsrep_data_home_dir=junk-dir;
-SELECT @@global.wsrep_data_home_dir;
+SELECT COUNT(@@global.wsrep_data_home_dir);
 --error ER_INCORRECT_GLOBAL_LOCAL_VAR
 SET @@global.wsrep_data_home_dir=junk/dir;
-SELECT @@global.wsrep_data_home_dir;
+SELECT COUNT(@@global.wsrep_data_home_dir);
 --error ER_INCORRECT_GLOBAL_LOCAL_VAR
 SET @@global.wsrep_data_home_dir=OFF;
-SELECT @@global.wsrep_data_home_dir;
+SELECT COUNT(@@global.wsrep_data_home_dir);
 --error ER_INCORRECT_GLOBAL_LOCAL_VAR
 SET @@global.wsrep_data_home_dir=default;
-SELECT @@global.wsrep_data_home_dir;
+SELECT COUNT(@@global.wsrep_data_home_dir);
 
 --echo
 --echo # invalid values
 --error ER_INCORRECT_GLOBAL_LOCAL_VAR
 SET @@global.wsrep_data_home_dir=NULL;
 
+--echo #
+--echo # MDEV-6717 : wsrep_data_home_dir should default to @@datadir
+--echo #
+SELECT @@GLOBAL.wsrep_data_home_dir = VARIABLE_VALUE FROM
+INFORMATION_SCHEMA.GLOBAL_VARIABLES WHERE VARIABLE_NAME='datadir';
+SELECT @@GLOBAL.wsrep_data_home_dir = VARIABLE_VALUE FROM
+INFORMATION_SCHEMA.GLOBAL_VARIABLES WHERE VARIABLE_NAME='wsrep_data_home_dir';
+
 --echo # End of test

sql/sys_vars.cc

@@ -3707,7 +3707,7 @@ static Sys_var_charptr Sys_wsrep_provider_options(
 static Sys_var_charptr Sys_wsrep_data_home_dir(
        "wsrep_data_home_dir", "home directory for wsrep provider",
        READ_ONLY GLOBAL_VAR(wsrep_data_home_dir), CMD_LINE(REQUIRED_ARG),
-       IN_FS_CHARSET, DEFAULT(""), 
+       IN_FS_CHARSET, DEFAULT(mysql_real_data_home),
        NO_MUTEX_GUARD, NOT_IN_BINLOG);
 
 static Sys_var_charptr Sys_wsrep_cluster_name(

sql/wsrep_mysqld.cc

@@ -538,9 +538,6 @@ int wsrep_init()
             wsrep->provider_vendor,  sizeof(provider_vendor) - 1);
   }
 
-  if (!wsrep_data_home_dir || strlen(wsrep_data_home_dir) == 0)
-    wsrep_data_home_dir = mysql_real_data_home;
-
   char node_addr[512]= { 0, };
   size_t const node_addr_max= sizeof(node_addr) - 1;
   if (!wsrep_node_address || !strcmp(wsrep_node_address, ""))