Much has been written on LWN about dynamically instrumenting kernel
code. These features are also available to user-space code with a
special kind of probe known as a User Statically-Defined Tracing
(USDT) probe. These probes provide a low-overhead way of
instrumenting user-space code and provide a convenient way to debug applications
running in production. In this final article of the BPF and BCC series
we'll look at where USDT probes come from and how you can use them to
understand the behavior of your own applications.