Fix for bug #29131: SHOW VARIABLES reports variable 'log' but SET

doesn't recognize it

This is a 5.0 version of the patch, it will be null-merged to 5.1

Problem:

'log' and 'log_slow_queries' were "fixed" variables, i.e. they showed up
in SHOW VARIABLES, but could not be used in expressions like 
"select @@log". Also, using them in the SET statement produced an 
incorrect "unknown system variable" error.

Solution:

Make 'log' and 'log_slow_queries' read-only dynamic variables to make 
them available for use in expressions, and produce a correct error 
about the variable being read-only when used in the SET statement.


mysql-test/r/variables.result:
  Added a test case for bug #29131.
mysql-test/t/variables.test:
  Added a test case for bug #29131.
sql/mysql_priv.h:
  Changed the type of opt_log and opt_slow_log to my_bool to 
  align with the interfaces in set_var.cc
sql/mysqld.cc:
  Changed the type of opt_log and opt_slow_log to my_bool to 
  align with the interfaces in set_var.cc
sql/set_var.cc:
  Made 'log' and 'log_slow_queries' to be read-only dynamic system 
  variable, i.e. available for use in expressions with the @@var syntax.
sql/set_var.h:
  Added a new system variable class representing a read-only boolean
  variable.

mysql-test/r/variables.result

@@ -791,6 +791,22 @@ ERROR HY000: Variable 'hostname' is a read only variable
 show variables like 'hostname';
 Variable_name	Value
 hostname	#
+SHOW VARIABLES LIKE 'log';
+Variable_name	Value
+log	ON
+SELECT @@log;
+@@log
+1
+SET GLOBAL log=0;
+ERROR HY000: Variable 'log' is a read only variable
+SHOW VARIABLES LIKE 'log_slow_queries';
+Variable_name	Value
+log_slow_queries	ON
+SELECT @@log_slow_queries;
+@@log_slow_queries
+1
+SET GLOBAL log_slow_queries=0;
+ERROR HY000: Variable 'log_slow_queries' is a read only variable
 End of 5.0 tests
 set global binlog_cache_size         =@my_binlog_cache_size;
 set global connect_timeout           =@my_connect_timeout;

mysql-test/t/variables.test

@@ -674,6 +674,20 @@ set @@hostname= "anothername";
 --replace_column 2 #
 show variables like 'hostname';
 
+#
+# Bug #29131: SHOW VARIABLES reports variable 'log' but SET doesn't recognize it
+#
+
+SHOW VARIABLES LIKE 'log';
+SELECT @@log;
+--error 1238
+SET GLOBAL log=0;
+
+SHOW VARIABLES LIKE 'log_slow_queries';
+SELECT @@log_slow_queries;
+--error 1238
+SET GLOBAL log_slow_queries=0;
+
 --echo End of 5.0 tests
 
 # This is at the very after the versioned tests, since it involves doing

sql/mysql_priv.h

@@ -1306,8 +1306,8 @@ extern bool opt_endinfo, using_udf_functions;
 extern my_bool locked_in_memory;
 extern bool opt_using_transactions, mysqld_embedded;
 extern bool using_update_log, opt_large_files, server_id_supplied;
-extern bool opt_log, opt_update_log, opt_bin_log, opt_slow_log, opt_error_log;
-extern my_bool opt_log_queries_not_using_indexes;
+extern bool opt_update_log, opt_bin_log, opt_error_log;
+extern my_bool opt_log, opt_slow_log, opt_log_queries_not_using_indexes;
 extern bool opt_disable_networking, opt_skip_show_db;
 extern my_bool opt_character_set_client_handshake;
 extern bool volatile abort_loop, shutdown_in_progress, grant_option;

sql/mysqld.cc

@@ -339,8 +339,8 @@ static my_bool opt_sync_bdb_logs;
 
 /* Global variables */
 
-bool opt_log, opt_update_log, opt_bin_log, opt_slow_log;
-my_bool opt_log_queries_not_using_indexes= 0;
+bool opt_update_log, opt_bin_log;
+my_bool opt_log, opt_slow_log, opt_log_queries_not_using_indexes= 0;
 bool opt_error_log= IF_WIN(1,0);
 bool opt_disable_networking=0, opt_skip_show_db=0;
 my_bool opt_character_set_client_handshake= 1;

sql/set_var.cc

@@ -201,6 +201,7 @@ sys_var_key_cache_long  sys_key_cache_age_threshold("key_cache_age_threshold",
 							      param_age_threshold));
 sys_var_bool_ptr	sys_local_infile("local_infile",
 					 &opt_local_infile);
+sys_var_bool_const_ptr sys_log("log", &opt_log);
 sys_var_trust_routine_creators
 sys_trust_routine_creators("log_bin_trust_routine_creators",
                            &trust_function_creators);
@@ -213,6 +214,7 @@ sys_var_bool_ptr
 sys_var_thd_ulong	sys_log_warnings("log_warnings", &SV::log_warnings);
 sys_var_thd_ulong	sys_long_query_time("long_query_time",
 					     &SV::long_query_time);
+sys_var_bool_const_ptr sys_log_slow("log_slow_queries", &opt_slow_log);
 sys_var_thd_bool	sys_low_priority_updates("low_priority_updates",
 						 &SV::low_priority_updates,
 						 fix_low_priority_updates);
@@ -665,9 +667,11 @@ sys_var *sys_variables[]=
   &sys_lc_time_names,
   &sys_license,
   &sys_local_infile,
+  &sys_log,
   &sys_log_binlog,
   &sys_log_off,
   &sys_log_queries_not_using_indexes,
+  &sys_log_slow,
   &sys_log_update,
   &sys_log_warnings,
   &sys_long_query_time,
@@ -946,7 +950,7 @@ struct show_var_st init_vars[]= {
 #ifdef HAVE_MLOCKALL
   {"locked_in_memory",	      (char*) &locked_in_memory,	    SHOW_BOOL},
 #endif
-  {"log",                     (char*) &opt_log,                     SHOW_BOOL},
+  {sys_log.name,              (char*) &sys_log,                     SHOW_SYS},
   {"log_bin",                 (char*) &opt_bin_log,                 SHOW_BOOL},
   {sys_trust_function_creators.name,(char*) &sys_trust_function_creators, SHOW_SYS},
   {"log_error",               (char*) log_error_file,               SHOW_CHAR},
@@ -955,7 +959,7 @@ struct show_var_st init_vars[]= {
 #ifdef HAVE_REPLICATION
   {"log_slave_updates",       (char*) &opt_log_slave_updates,       SHOW_MY_BOOL},
 #endif
-  {"log_slow_queries",        (char*) &opt_slow_log,                SHOW_BOOL},
+  {sys_log_slow.name,         (char*) &sys_log_slow,                SHOW_SYS},
   {sys_log_warnings.name,     (char*) &sys_log_warnings,	    SHOW_SYS},
   {sys_long_query_time.name,  (char*) &sys_long_query_time, 	    SHOW_SYS},
   {sys_low_priority_updates.name, (char*) &sys_low_priority_updates, SHOW_SYS},

sql/set_var.h

@@ -160,6 +160,28 @@ class sys_var_bool_ptr :public sys_var
 };
 
 
+class sys_var_bool_const_ptr : public sys_var
+{
+public:
+  my_bool *value;
+  sys_var_bool_const_ptr(const char *name_arg, my_bool *value_arg)
+    :sys_var(name_arg),value(value_arg)
+  {}
+  bool check(THD *thd, set_var *var)
+  {
+    return 1;
+  }
+  bool update(THD *thd, set_var *var)
+  {
+    return 1;
+  }
+  SHOW_TYPE show_type() { return SHOW_MY_BOOL; }
+  byte *value_ptr(THD *thd, enum_var_type type, LEX_STRING *base)
+  { return (byte*) value; }
+  bool check_update_type(Item_result type) { return 0; }
+  bool is_readonly() const { return 1; }
+};
+
 class sys_var_str :public sys_var
 {
 public: