MDEV-38202: Make init_rpl_role visible at runtime

Problem:
The --init-rpl-role option can be set in the .cnf file or command
line to configure the server replication role at startup (MASTER or
SLAVE), but there was no way to check this value at runtime. This
made it hard to investigate issues because we could not know which
role the server was started with.

Solution:
I added a new read-only system variable init_rpl_role that is set
after startup and kept unchanged.

Example usage:
* SHOW GLOBAL VARIABLES LIKE 'init_rpl_role'
* SELECT @@GLOBAL.init_rpl_role

Reviewed-by: ParadoxV5 <paradox.ver5@gmail.com>
Reviewed-by: Georgi (Joro) Kodinov <joro@mariadb.org>

Author: Mahmoud-kh1

mysql-test/main/information_schema.result

@@ -1939,6 +1939,7 @@ drop table if exists t1;drop table if exists t1;
 drop table if exists t1;drop table if exists t1;
 drop table if exists t1;drop table if exists t1;
 INIT_FILE	
+INIT_RPL_ROLE	MASTER
 INIT_SLAVE	
 set global init_connect="";
 create table t0 select * from information_schema.global_status where VARIABLE_NAME='COM_SELECT';

mysql-test/main/mysqld--help.result

@@ -465,7 +465,9 @@ The following specify which files/extra groups are read (specified before remain
  (unless the user has SUPER privilege)
  --init-file=name    Read SQL commands from this file at startup
  --init-rpl-role=name 
- Set the replication role. One of: MASTER, SLAVE
+ The replication role the server starts with. Can be set
+ to help recover special semi-sync replication situations.
+ Possible values are MASTER and SLAVE
  --init-slave=name   Command(s) that are executed by a slave server each time
  the SQL thread starts
  --interactive-timeout=# 

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

@@ -0,0 +1,17 @@
+#
+# MDEV-38202: add init_rpl_role in output of "show variables"
+#
+# It should show SLAVE as it is set in opt file
+SELECT @@GLOBAL.init_rpl_role;
+@@GLOBAL.init_rpl_role
+SLAVE
+SHOW GLOBAL VARIABLES LIKE 'init_rpl_role';
+Variable_name	Value
+init_rpl_role	SLAVE
+# Verify that it's a global scope only.
+SELECT @@SESSION.init_rpl_role;
+ERROR HY000: Variable 'init_rpl_role' is a GLOBAL variable
+# Verify it's read-only.
+SET @@GLOBAL.init_rpl_role = 'MASTER';
+ERROR HY000: Variable 'init_rpl_role' is a read only variable
+# End of 13.0 tests

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

@@ -1582,6 +1582,16 @@ NUMERIC_BLOCK_SIZE	NULL
 ENUM_VALUE_LIST	NULL
 READ_ONLY	YES
 COMMAND_LINE_ARGUMENT	REQUIRED
+VARIABLE_NAME	INIT_RPL_ROLE
+VARIABLE_SCOPE	GLOBAL
+VARIABLE_TYPE	ENUM
+VARIABLE_COMMENT	The replication role the server starts with. Can be set to help recover special semi-sync replication situations. Possible values are MASTER and SLAVE
+NUMERIC_MIN_VALUE	NULL
+NUMERIC_MAX_VALUE	NULL
+NUMERIC_BLOCK_SIZE	NULL
+ENUM_VALUE_LIST	MASTER,SLAVE
+READ_ONLY	YES
+COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	INIT_SLAVE
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	VARCHAR

mysql-test/suite/sys_vars/t/init_rpl_role_variable_basic.opt

@@ -0,0 +1 @@
+--init-rpl-role=SLAVE

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

@@ -0,0 +1,18 @@
+--source include/not_embedded.inc
+--echo #
+--echo # MDEV-38202: add init_rpl_role in output of "show variables"
+--echo #
+
+--echo # It should show SLAVE as it is set in opt file
+SELECT @@GLOBAL.init_rpl_role;
+SHOW GLOBAL VARIABLES LIKE 'init_rpl_role';
+
+--echo # Verify that it's a global scope only.
+--error ER_INCORRECT_GLOBAL_LOCAL_VAR
+SELECT @@SESSION.init_rpl_role;
+
+--echo # Verify it's read-only.
+--error ER_INCORRECT_GLOBAL_LOCAL_VAR
+SET @@GLOBAL.init_rpl_role = 'MASTER';
+
+--echo # End of 13.0 tests

sql/mysqld.cc

@@ -7086,9 +7086,6 @@ struct my_option my_long_options[]=
    "which is whether to validate the master's certificate in TLS replication",
    &master_ssl_verify_server_cert, nullptr, nullptr, GET_BOOL, NO_ARG,
    master_ssl_verify_server_cert, 0, 0, nullptr, 0, nullptr},
-  {"init-rpl-role", 0, "Set the replication role",
-   &rpl_status, &rpl_status, &rpl_role_typelib,
-   GET_ENUM, REQUIRED_ARG, RPL_AUTH_MASTER, 0, 0, 0, 0, 0},
 #endif /* HAVE_REPLICATION */
   {"memlock", 0, "Lock mariadbd process in memory", &locked_in_memory,
    &locked_in_memory, 0, GET_BOOL, NO_ARG, 0, 0, 0, 0, 0, 0},
@@ -9141,6 +9138,7 @@ static int get_options(int *argc_ptr, char ***argv_ptr)
     flush_time= 0;
 
 #ifdef HAVE_REPLICATION
+  rpl_status= init_rpl_role_val;
   if (init_slave_skip_errors(opt_slave_skip_errors))
     return 1;
   if (init_slave_transaction_retry_errors(opt_slave_transaction_retry_errors))

sql/repl_failsafe.cc

@@ -52,6 +52,7 @@ struct Slave_info
 
 Atomic_counter<uint32_t> binlog_dump_thread_count;
 ulong rpl_status=RPL_NULL;
+ulong init_rpl_role_val= 0;
 mysql_mutex_t LOCK_rpl_status;
 
 const char *rpl_role_type[] = {"MASTER","SLAVE",NullS};

sql/repl_failsafe.h

@@ -29,6 +29,7 @@ typedef enum {RPL_AUTH_MASTER=0,RPL_IDLE_SLAVE,RPL_ACTIVE_SLAVE,
 	      RPL_ANY /* wild card used by change_rpl_status */ } RPL_STATUS;
 extern ulong rpl_status;
 
+extern ulong init_rpl_role_val;
 extern mysql_mutex_t LOCK_rpl_status;
 extern mysql_cond_t COND_rpl_status;
 extern TYPELIB rpl_role_typelib;

sql/sys_vars.cc

@@ -67,6 +67,7 @@
 #include "semisync_master.h"
 #include "semisync_slave.h"
 #include <ssl_compat.h>
+#include "repl_failsafe.h"
 #ifdef WITH_WSREP
 #include "wsrep_mysqld.h"
 #endif
@@ -1505,6 +1506,16 @@ Sys_init_slave(
        DEFAULT(""), &PLock_sys_init_slave,
        NOT_IN_BINLOG, ON_CHECK(check_init_string));
 
+#ifdef HAVE_REPLICATION 
+static Sys_var_enum Sys_init_rpl_role(  
+       "init_rpl_role",  
+       "The replication role the server starts with."  
+       "Can be set to help recover "  
+       "special semi-sync replication situations."  
+       "Possible values are MASTER and SLAVE",  
+       READ_ONLY GLOBAL_VAR(init_rpl_role_val), CMD_LINE(REQUIRED_ARG),  
+       rpl_role_type, DEFAULT(RPL_AUTH_MASTER));  
+#endif
 static Sys_var_ulong Sys_interactive_timeout(
        "interactive_timeout",
        "The number of seconds the server waits for activity on an interactive "