tracing_set_tracer
WARN_ON(tracing_set_tracer(&global_trace, type->name) < 0);
int tracing_set_tracer(struct trace_array *tr, const char *buf);
err = tracing_set_tracer(tr, name);
extern int tracing_set_tracer(struct trace_array *tr, const char *buf);
if (tracing_set_tracer(tr, p) < 0)