rtla/trace: Save event histogram output to a file

The hist: trigger generates a histogram in the file sys/event/hist.
If the hist: trigger is used, automatically save the histogram output of
the event sys:event in the sys_event_hist.txt file.

Link: https://lkml.kernel.org/r/b5c906af31d4e022ffe87fb0848fac5c089087c8.1646247211.git.bristot@kernel.org

Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Documentation/tools/rtla/common_options.rst

@@ -23,7 +23,15 @@
         Filter the previous **-e** *sys:event* event with *<filter>*. For further information about event filtering see https://www.kernel.org/doc/html/latest/trace/events.html#event-filtering.
 
 **--trigger** *<trigger>*
-        Enable a trace event trigger to the previous **-e** *sys:event*. For further information about event trigger see https://www.kernel.org/doc/html/latest/trace/events.html#event-triggers.
+        Enable a trace event trigger to the previous **-e** *sys:event*.
+        If the *hist:* trigger is activated, the output histogram will be automatically saved to a file named *system_event_hist.txt*.
+        For example, the command:
+
+        rtla <command> <mode> -t -e osnoise:irq_noise --trigger="hist:key=desc,duration/1000:sort=desc,duration/1000:vals=hitcount"
+
+        Will automatically save the content of the histogram associated to *osnoise:irq_noise* event in *osnoise_irq_noise_hist.txt*.
+
+        For further information about event trigger see https://www.kernel.org/doc/html/latest/trace/events.html#event-triggers.
 
 **-P**, **--priority** *o:prio|r:prio|f:prio|d:runtime:period*
 

tools/tracing/rtla/src/trace.c

@@ -296,6 +296,57 @@ static void trace_event_disable_filter(struct trace_instance *instance,
 			tevent->event ? : "*", tevent->filter);
 }
 
+/*
+ * trace_event_save_hist - save the content of an event hist
+ *
+ * If the trigger is a hist: one, save the content of the hist file.
+ */
+static void trace_event_save_hist(struct trace_instance *instance,
+				  struct trace_events *tevent)
+{
+	int retval, index, out_fd;
+	mode_t mode = 0644;
+	char path[1024];
+	char *hist;
+
+	if (!tevent)
+		return;
+
+	/* trigger enables hist */
+	if (!tevent->trigger)
+		return;
+
+	/* is this a hist: trigger? */
+	retval = strncmp(tevent->trigger, "hist:", strlen("hist:"));
+	if (retval)
+		return;
+
+	snprintf(path, 1024, "%s_%s_hist.txt", tevent->system, tevent->event);
+
+	printf("  Saving event %s:%s hist to %s\n", tevent->system, tevent->event, path);
+
+	out_fd = creat(path, mode);
+	if (out_fd < 0) {
+		err_msg("  Failed to create %s output file\n", path);
+		return;
+	}
+
+	hist = tracefs_event_file_read(instance->inst, tevent->system, tevent->event, "hist", 0);
+	if (!hist) {
+		err_msg("  Failed to read %s:%s hist file\n", tevent->system, tevent->event);
+		goto out_close;
+	}
+
+	index = 0;
+	do {
+		index += write(out_fd, &hist[index], strlen(hist) - index);
+	} while (index < strlen(hist));
+
+	free(hist);
+out_close:
+	close(out_fd);
+}
+
 /*
  * trace_event_disable_trigger - disable an event trigger
  */
@@ -314,6 +365,8 @@ static void trace_event_disable_trigger(struct trace_instance *instance,
 	debug_msg("Disabling %s:%s trigger %s\n", tevent->system,
 		  tevent->event ? : "*", tevent->trigger);
 
+	trace_event_save_hist(instance, tevent);
+
 	snprintf(trigger, 1024, "!%s\n", tevent->trigger);
 
 	retval = tracefs_event_file_write(instance->inst, tevent->system,