关于mysql plugin 自定义系统变量

1. 定义
/*
  Plugin system variables.
*/
static long     sysvar_one_value;
static char     *sysvar_two_value;
static MYSQL_SYSVAR_LONG(simple_sysvar_one, sysvar_one_value,
  PLUGIN_VAR_RQCMDARG,
  "Simple fulltext parser example system variable number one. Give a number.",
  NULL, NULL, 77L, 7L, 777L, 0);
static MYSQL_SYSVAR_STR(simple_sysvar_two, sysvar_two_value,
  PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_MEMALLOC,
  "Simple fulltext parser example system variable number two. Give a string.",
  NULL, NULL, "simple sysvar two default");
static MYSQL_THDVAR_LONG(simple_thdvar_one,
  PLUGIN_VAR_RQCMDARG,
  "Simple fulltext parser example thread variable number one. Give a number.",
  NULL, NULL, 88L, 8L, 888L, 0);
static MYSQL_THDVAR_STR(simple_thdvar_two,
  PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_MEMALLOC,
  "Simple fulltext parser example thread variable number two. Give a string.",
  NULL, NULL, "simple thdvar two default");
static struct st_mysql_sys_var* simple_system_variables[]= {
  MYSQL_SYSVAR(simple_sysvar_one),
  MYSQL_SYSVAR(simple_sysvar_two),
  MYSQL_SYSVAR(simple_thdvar_one),
  MYSQL_SYSVAR(simple_thdvar_two),
  NULL
};
/*
  Plugin library descriptor
*/
mysql_declare_plugin(ftexample)
{
  MYSQL_FTPARSER_PLUGIN,      /* type                            */
  &simple_parser_descriptor,  /* descriptor                      */
  "simple_parser",            /* name                            */
  "MySQL AB",