tracing: Save the last hist command's associated event name

In preparation for making use of the new trace error log, save the
subsystem and event name associated with the last hist command - it
will be passed as the location param in the event_log_err() calls.

Link: http://lkml.kernel.org/r/eb0fd1362be8f39facb86c83eecf441b7a5876f8.1554072478.git.tom.zanussi@linux.intel.comAcked-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_events_hist.c

@@ -535,15 +535,34 @@ static struct track_data *track_data_alloc(unsigned int key_len,
 	return data;
 }
 
-static char last_hist_cmd[MAX_FILTER_STR_VAL];
+static char last_cmd[MAX_FILTER_STR_VAL];
+static char last_cmd_loc[MAX_FILTER_STR_VAL];
+
 static char hist_err_str[MAX_FILTER_STR_VAL];
 
-static void last_cmd_set(char *str)
+static void last_cmd_set(struct trace_event_file *file, char *str)
 {
+	const char *system = NULL, *name = NULL;
+	struct trace_event_call *call;
+
 	if (!str)
 		return;
 
-	strncpy(last_hist_cmd, str, MAX_FILTER_STR_VAL - 1);
+	strncpy(last_cmd, str, MAX_FILTER_STR_VAL - 1);
+
+	if (file) {
+		call = file->event_call;
+
+		system = call->class->system;
+		if (system) {
+			name = trace_event_name(call);
+			if (!name)
+				system = NULL;
+		}
+	}
+
+	if (system)
+		snprintf(last_cmd_loc, MAX_FILTER_STR_VAL, "hist:%s:%s", system, name);
 }
 
 static void hist_err(char *str, char *var)
@@ -583,6 +602,8 @@ static void hist_err_event(char *str, char *system, char *event, char *var)
 static void hist_err_clear(void)
 {
 	hist_err_str[0] = '\0';
+	last_cmd[0] = '\0';
+	last_cmd_loc[0] = '\0';
 }
 
 static bool have_hist_err(void)
@@ -5438,8 +5459,8 @@ static int hist_show(struct seq_file *m, void *v)
 	}
 
 	if (have_hist_err()) {
-		seq_printf(m, "\nERROR: %s\n", hist_err_str);
-		seq_printf(m, "  Last command: %s\n", last_hist_cmd);
+		seq_printf(m, "\n%s: error: \n", hist_err_str);
+		seq_printf(m, "  Last command: %s\n", last_cmd);
 	}
 
  out_unlock:
@@ -6043,8 +6064,8 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 	lockdep_assert_held(&event_mutex);
 
 	if (glob && strlen(glob)) {
-		last_cmd_set(param);
 		hist_err_clear();
+		last_cmd_set(file, param);
 	}
 
 	if (!param)