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.

1 files changed, 22 insertions, 0 deletions

diff --git a/sql/set_var.h b/sql/set_var.h
index 6000e155db9..7b3f864f44c 100644
--- a/sql/set_var.h
+++ b/sql/set_var.h
@@ -160,6 +160,28 @@ public:
 };
 
 
+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: