[$] Dynamic function tracing events

For as long as the kernel has included tracepoints, developers have arguedover whether those tracepoints are part of the kernel's ABI. Tracepointchanges have had to be reverted in the past because they broke existinguser-space programs that had come to depend on them; meanwhile, fears ofsetting internal code in stone have made it difficult to add tracepoints toa number of kernel subsystems. Now, a new tracing functionality is beingproposed as a way to circumvent all of those problems.