trace: print a warning if user tries to enable an unknown trace event

There was no warning if a bad trace event name was given to
'trace-event' command, thus the user could think that the command
was successful even if this was not the case.

Print a warning if the user tries to enable a trace event which is not
known.
Acked-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

monitor.c

@@ -549,7 +549,11 @@ static void do_change_trace_event_state(Monitor *mon, const QDict *qdict)
 {
     const char *tp_name = qdict_get_str(qdict, "name");
     bool new_state = qdict_get_bool(qdict, "option");
-    st_change_trace_event_state(tp_name, new_state);
+    int ret = st_change_trace_event_state(tp_name, new_state);
+
+    if (!ret) {
+        monitor_printf(mon, "unknown event name \"%s\"\n", tp_name);
+    }
 }
 
 static void do_trace_file(Monitor *mon, const QDict *qdict)

simpletrace.c

@@ -246,12 +246,14 @@ static TraceEvent* find_trace_event_by_name(const char *tname)
     return NULL; /* indicates end of list reached without a match */
 }
 
-void st_change_trace_event_state(const char *tname, bool tstate)
+bool st_change_trace_event_state(const char *tname, bool tstate)
 {
     TraceEvent *tp;
 
     tp = find_trace_event_by_name(tname);
     if (tp) {
         tp->state = tstate;
+        return true;
     }
+    return false;
 }

simpletrace.h

@@ -31,7 +31,7 @@ void trace5(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, uint64_t
 void trace6(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, uint64_t x4, uint64_t x5, uint64_t x6);
 void st_print_trace(FILE *stream, int (*stream_printf)(FILE *stream, const char *fmt, ...));
 void st_print_trace_events(FILE *stream, int (*stream_printf)(FILE *stream, const char *fmt, ...));
-void st_change_trace_event_state(const char *tname, bool tstate);
+bool st_change_trace_event_state(const char *tname, bool tstate);
 void st_print_trace_file_status(FILE *stream, int (*stream_printf)(FILE *stream, const char *fmt, ...));
 void st_set_trace_file_enabled(bool enable);
 bool st_set_trace_file(const char *file);