MySQL Bugs: #34905: Plugin variables of type enum don't receive their default value

Bug #34905	Plugin variables of type enum don't receive their default value
Submitted:	27 Feb 2008 21:14	Modified:	5 Sep 2008 6:26
Reporter:	Bill Mitchell	Email Updates:
Status:	Can't repeat	Impact on me:	None
Category:	MySQL Server	Severity:	S3 (Non-critical)
Version:	5.1.22	OS:	Any
Assigned to:		CPU Architecture:	Any

Description:
For handler plugin variables of type enum, there is a problem that the default value is not loaded into the variable upon startup.  Even though the variable is declared as having a nonzero default value, a show variables statement after startup shows the value is still zero.  

How to repeat:
In a plugin, declare a variable of type ENUM that has a non-zero default value, e.g.:

static const char *log_level_names[] =
{ "CRITICAL", "ERROR", "WARNING", "INFO", "DEBUG", "USER", "TRACE",
  NullS};
static TYPELIB log_level_typelib= {array_elements(log_level_names)-1,"",
			       log_level_names, NULL};

static unsigned long test_level = 0;
static MYSQL_SYSVAR_ENUM(test_level, test_level, PLUGIN_VAR_OPCMDARG,
  "The value of the logging level: Critical, Error, Warning, etc... ",
  NULL, NULL, 3, &log_level_typelib);

After loading the handler, use SHOW VARIABLES LIKE ... to dump the value.  It will have a value of CRITICAL, not INFO matching the default.  

Suggested fix:
Near the end of the logic in construct_options(), there is a guard that skips code when the variable type is PLUGIN_VAR_ENUM or PLUGIN_VAR_SET.  It appears this logic calculates the memory address for the variable, without which no default is assigned.  After commenting out the guard for PLUGIN_VAR_ENUM, the global variable received its default value.

The block:
    if ((opt->flags & PLUGIN_VAR_TYPEMASK) != PLUGIN_VAR_ENUM &&
        (opt->flags & PLUGIN_VAR_TYPEMASK) != PLUGIN_VAR_SET)
    {
      if (opt->flags & PLUGIN_VAR_THDLOCAL)
        options->value= options->u_max_value= (uchar**)
          (global_system_variables.dynamic_variables_ptr + offset);
      else
        options->value= options->u_max_value= *(uchar***) (opt + 1);
    }
should read:

    if ((opt->flags & PLUGIN_VAR_TYPEMASK) != PLUGIN_VAR_ENUM &&
    if ((opt->flags & PLUGIN_VAR_TYPEMASK) != PLUGIN_VAR_SET)
    {
      if (opt->flags & PLUGIN_VAR_THDLOCAL)
        options->value= options->u_max_value= (uchar**)
          (global_system_variables.dynamic_variables_ptr + offset);
      else
        options->value= options->u_max_value= *(uchar***) (opt + 1);
    }

Of course, it may be that the guard should be removed entirely.  I did not define a variable of type SET so I did not investigate whether these have the same problem of not receiving a default value.  

By inspection, it appears this same problem is still in 5.1.23, and the above code fragment is from sql_plugin.cc in 5.1.23.  I did uncover a separate problem that a plugin that declared a variable of type MYSQL_THDVAR_ENUM was diagnosed as invalid in register_var(), but that bug appears fixed in the 5.1.23 source.

Obviously there is a typo in the corrected fix, when I did the cut-and-paste.  The suggested fix should read:
 
    if ((opt->flags & PLUGIN_VAR_TYPEMASK) != PLUGIN_VAR_SET)
    {
      if (opt->flags & PLUGIN_VAR_THDLOCAL)
        options->value= options->u_max_value= (uchar**)
          (global_system_variables.dynamic_variables_ptr + offset);
      else
        options->value= options->u_max_value= *(uchar***) (opt + 1);
    }

Please try with newer version: MySQL 5.1.23.

On Windows, with 5.1.23, I cannot get my plugin enum variable set from my option file whereas other options are.
The default check_func_enum() is never called.
Could both problems be related?

No feedback was provided for this bug for over a month, so it is
being suspended automatically. If you are able to provide the
information that was originally requested, please do so and change
the status of the bug back to "Open".

Please, try to repeat with a newer version, 5.1.26, and inform about the results.

It's OK with 5.1.26-rc: the enum plugin variable gets its default value as set by the macro MYSQL_SYSVAR_ENUM, and is also properly set from an option file.

So we can close this bug report?

Yes, thanks.

No feedback was provided for this bug for over a month, so it is
being suspended automatically. If you are able to provide the
information that was originally requested, please do so and change
the status of the bug back to "Open".

Closed as it seems fixed in 5.1.26.