MDEV-30120 Update the wsrep_provider_options read_only value in the system_variables table.

When wsrep-provider-options plugin is initialized we need to update
wsrep-provider-options variable as READ_ONLY.

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

@@ -11,7 +11,7 @@ CREATE TABLE t1 (f1 INT PRIMARY KEY) ENGINE=InnoDB;
 SET GLOBAL wsrep_provider_repl_max_ws_size=1;
 SHOW VARIABLES LIKE 'wsrep_provider_repl_max_ws_size';
 
---error ER_ERROR_DURING_COMMIT
+--error ER_UNKNOWN_ERROR
 INSERT INTO t1 VALUES (1);
 
 SET GLOBAL wsrep_provider_repl_max_ws_size=DEFAULT;
@@ -31,3 +31,8 @@ DROP TABLE t1;
 
 CALL mtr.add_suppression("transaction size limit");
 CALL mtr.add_suppression("rbr write fail");
+
+#
+# MDEV-30120 :Update the wsrep_provider_options read_only value in the system_variables table.
+#
+SELECT VARIABLE_NAME,READ_ONLY FROM information_schema.system_variables where VARIABLE_NAME like '%wsrep_provider_options%';

sql/CMakeLists.txt

@@ -38,7 +38,8 @@ IF(WITH_WSREP AND NOT EMBEDDED_LIBRARY)
     wsrep_schema.cc
     wsrep_plugin.cc
     service_wsrep.cc
-  )
+    )
+  MYSQL_ADD_PLUGIN(wsrep_provider ${WSREP_SOURCES} DEFAULT NOT_EMBEDDED LINK_LIBRARIES wsrep-lib wsrep_api_v26)
   MYSQL_ADD_PLUGIN(wsrep ${WSREP_SOURCES} MANDATORY NOT_EMBEDDED LINK_LIBRARIES wsrep-lib wsrep_api_v26)
   IF(VISIBILITY_HIDDEN_FLAG AND TARGET wsrep)
     # wsrep_info plugin needs some wsrep symbols from inside mysqld

sql/set_var.h

@@ -134,6 +134,8 @@ class sys_var: protected Value_source // for double_from_string_with_check
     return system_charset_info;
   }
   bool is_readonly() const { return flags & READONLY; }
+  void update_flags(int new_flags) { flags = new_flags; }
+  int get_flags() const { return flags; }
   /**
     the following is only true for keycache variables,
     that support the syntax @@keycache_name.variable_name

sql/wsrep_plugin.cc

@@ -20,6 +20,11 @@
   in favor of single options which are initialized from provider.
 */
 
+#include "sql_plugin.h"
+#include "sql_priv.h"
+#include "sql_class.h"
+#include "set_var.h"
+
 #include "my_global.h"
 #include "mysqld_error.h"
 #include <mysql/plugin.h>
@@ -272,12 +277,21 @@ static int wsrep_provider_plugin_init(void *p)
 {
   WSREP_DEBUG("wsrep_provider_plugin_init()");
   provider_plugin_enabled= true;
+
+  // When plugin-wsrep-provider is enabled we set
+  // wsrep_provider_options parameter as READ_ONLY
+  sys_var *my_var= find_sys_var(current_thd, "wsrep_provider_options");
+  int flags= my_var->get_flags();
+  my_var->update_flags(flags |= (int)sys_var::READONLY);
   return 0;
 }
 
 static int wsrep_provider_plugin_deinit(void *p)
 {
   WSREP_DEBUG("wsrep_provider_plugin_deinit()");
+  sys_var *my_var= find_sys_var(current_thd, "wsrep_provider_options");
+  int flags= my_var->get_flags();
+  my_var->update_flags(flags &= (int)~sys_var::READONLY);
   return 0;
 }