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 for investigation issues  because
we can't know  which role the server was started with.

Solution:
I added a new read-only status variable init_rpl_role that captures
the value of rpl_status right after startup  and keeps it unchanged.

ex usage: SHOW STATUS LIKE 'init_rpl_role'; SHOW GLOBAL STATUS LIKE 'init_rpl_role';

Author: Mahmoud-kh1

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

@@ -0,0 +1,12 @@
+#  
+# MDEV-38202: add init_rpl_role in output of "show variables"   
+#  
+# it should show SLAVE as it is set in opt file
+SHOW STATUS LIKE 'init_rpl_role';
+Variable_name	Value
+Init_rpl_role	SLAVE
+SHOW GLOBAL STATUS LIKE 'init_rpl_role';
+Variable_name	Value
+Init_rpl_role	SLAVE
+Init_rpl_role is: SLAVE  
+# End of 13.0 tests

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

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

mysql-test/suite/rpl/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
+SHOW STATUS LIKE 'init_rpl_role';
+SHOW GLOBAL STATUS LIKE 'init_rpl_role';
+
+let $init_role= query_get_value(SHOW STATUS LIKE 'Init_rpl_role', Value, 1);  
+--echo Init_rpl_role is: $init_role  
+  
+if (`SELECT strcmp("SLAVE", "$init_role") != 0`)  
+{  
+  --die init_rpl_role should be SLAVE
+}
+
+--echo # End of 13.0 tests

sql/mysqld.cc

@@ -7315,6 +7315,13 @@ static int show_rpl_status(THD *, SHOW_VAR *var, void *, system_status_var *,
   return 0;
 }
 
+static int show_init_rpl_role(THD *, SHOW_VAR *var, void *, system_status_var *,  
+                              enum_var_type)  
+{  
+  var->type= SHOW_CHAR;  
+  var->value= const_cast<char*>(rpl_role_type[init_rpl_role_val]);  
+  return 0;  
+}
 static int show_slave_running(THD *thd, SHOW_VAR *var, void *buff,
                               system_status_var *, enum_var_type)
 {
@@ -7979,6 +7986,7 @@ SHOW_VAR status_vars[]= {
   {"Questions",                (char*) offsetof(STATUS_VAR, questions), SHOW_LONG_STATUS},
 #ifdef HAVE_REPLICATION
   {"Rpl_status",               (char*) &show_rpl_status,          SHOW_SIMPLE_FUNC},
+  {"Init_rpl_role",            (char*) &show_init_rpl_role,       SHOW_SIMPLE_FUNC},  
 #endif
   {"Select_full_join",         (char*) offsetof(STATUS_VAR, select_full_join_count_), SHOW_LONG_STATUS},
   {"Select_full_range_join",   (char*) offsetof(STATUS_VAR, select_full_range_join_count_), SHOW_LONG_STATUS},
@@ -9141,6 +9149,7 @@ static int get_options(int *argc_ptr, char ***argv_ptr)
     flush_time= 0;
 
 #ifdef HAVE_REPLICATION
+  init_rpl_role_val = rpl_status;
   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;