[$] User trace events, one year later

The kernel has a well-developed mechanism for the control of tracing ofevents in kernel space. Developers often want to be able to trace user-spaceactivity as well, using the same interfaces, but that mode is rather lesswell supported. One year ago, an attempt toadd an API for the control of user-space trace events ran into troubleand has never been fully enabled. Now, Beau Belgrave is back with areworked API that may finally result in this mechanism becominggenerally available.