tracing_set_clock
ret = tracing_set_clock(&global_trace, trace_boot_clock);
tracing_set_clock(&global_trace, "global");
ret = tracing_set_clock(tr, clockstr);
tracing_set_clock(tr, trace_clocks[tscratch->clock_id].name) < 0) {
extern int tracing_set_clock(struct trace_array *tr, const char *clockstr);
if (tracing_set_clock(tr, p) < 0)
ret = tracing_set_clock(file->tr, hist_data->attrs->clock);