System Status Variables plugin
At the end of the chapter, let's try to create a different Daemon plugin. This plugin, called sys_status, does not start any threads and does not do anything in the background. It uses the status variables to provide access to the getrusage() statistics. The getrusage() system call returns information about the process resource usage such as number of page faults, number of signals received, and number of context switches. How could we let MySQL users see this information?
As we remember, status variables are defined in terms of pointers to data. That is, SHOW STATUS takes the st_mysql_show_var structure and shows the data pointed to by its value member. It works well when a value to show is stored in a variable; for example, in our vars plugin, where we have stored the value in a status_vars C variable. But in this case we want to show the result of a function call. In other words, we need to use SHOW_FUNC type of a "status variable". And because we...
