When one try to set a nonexistent tracer, no error is returned
as if the name of the tracer was correct.
We should return -EINVAL.
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Acked-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>