The rctl_walk() function provides a mechanism for the application author to examine all active resource controls (rctls) on the current system. The callback function provided by the application is given the name of an rctl at each invocation and can use
the walk_data to record its own state. The callback function should return non-zero if it encounters an error condition or attempts to terminate the walk prematurely; otherwise the callback function should return 0.
Upon successful completion, rctl_walk() returns 0. It returns -1 if the callback function returned a non-zero value or if the walk encountered an error, in which case errno is set to indicate the error.