todo-list: update
probe: support os.probe("tp:subsystem:event", eventfun)

Two function call is same for user:
os.trace("subsystem:event", eventfun)
os.probe("tp:subsystem:event", eventfun)

but the backend implementation is different,
first is based on tracing expose work directly,
second is based on perf, with minor change on tracing code.

In future, first one will be removed, so then all perf based.

(tracing expose patch set still have valued, for unify tracing and perf
code in include/trace/ftrace.h, and remove duplicated syscall tracing,
the kernel size shinked a lot after apply that patch set)