libtracefs: Add tracefs_follow_event() API

Add tracefs_follow_event() API that allows to only receive a callback for
a specific event.

Link: https://lore.kernel.org/linux-trace-devel/20221115040838.2456632-4-rostedt@goodmis.org

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
5 files changed