[PATCH v9 04/10] tracing: Add 'snapshot' event trigger command

[Tom Zanussi]

Add 'snapshot' event_command.  snapshot event triggers are added by
the user via this command in a similar way and using practically the
same syntax as the analogous 'snapshot' ftrace function command, but
instead of writing to the set_ftrace_filter file, the snapshot event
trigger is written to the per-event 'trigger' files:

    echo 'snapshot' > .../somesys/someevent/trigger

The above command will turn on snapshots for someevent i.e. whenever
someevent is hit, a snapshot will be done.

This also adds a 'count' version that limits the number of times the
command will be invoked:

    echo 'snapshot:N' > .../somesys/someevent/trigger

Where N is the number of times the command will be invoked.

The above command will snapshot N times for someevent i.e. whenever
someevent is hit N times, a snapshot will be done.

Also adds a new ftrace_alloc_snapshot() function - the ftrace snapshot
command defines code that allocates a snapshot, which would be nice to
be able to reuse, which this does.

Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
---
 include/linux/ftrace_event.h        |  1 +
 kernel/trace/trace.c                |  9 +++++
 kernel/trace/trace.h                |  1 +
 kernel/trace/trace_events_trigger.c | 74 +++++++++++++++++++++++++++++++++++++
 4 files changed, 85 insertions(+)

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 239738c..bfd81f3 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -319,6 +319,7 @@ struct ftrace_event_file {
 enum event_trigger_type {
 	ETT_NONE		= (0),
 	ETT_TRACE_ONOFF		= (1 << 0),
+	ETT_SNAPSHOT		= (1 << 1),
 };
 
 extern void destroy_preds(struct ftrace_event_call *call);
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 7974ba2..53bd5e1 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5355,6 +5355,15 @@ static const struct file_operations tracing_dyn_info_fops = {
 };
 #endif /* CONFIG_DYNAMIC_FTRACE */
 
+#if defined(CONFIG_TRACER_SNAPSHOT)
+int ftrace_alloc_snapshot(void)
+{
+	return alloc_snapshot(&global_trace);
+}
+#else
+int ftrace_alloc_snapshot(void) { return -ENOSYS; }
+#endif
+
 #if defined(CONFIG_TRACER_SNAPSHOT) && defined(CONFIG_DYNAMIC_FTRACE)
 static void
 ftrace_snapshot(unsigned long ip, unsigned long parent_ip, void **data)
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index e9e7c1b..e2afe25 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1200,6 +1200,7 @@ struct event_command {
 
 extern int trace_event_enable_disable(struct ftrace_event_file *file,
 				      int enable, int soft_disable);
+extern int ftrace_alloc_snapshot(void);
 
 extern const char *__start___trace_bprintk_fmt[];
 extern const char *__stop___trace_bprintk_fmt[];
diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index 3634061..f32fa31 100644
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -696,6 +696,74 @@ static struct event_command trigger_traceoff_cmd = {
 	.get_trigger_ops	= onoff_get_trigger_ops,
 };
 
+static void
+snapshot_trigger(struct event_trigger_data *data)
+{
+	tracing_snapshot();
+}
+
+static void
+snapshot_count_trigger(struct event_trigger_data *data)
+{
+	if (!data->count)
+		return;
+
+	if (data->count != -1)
+		(data->count)--;
+
+	snapshot_trigger(data);
+}
+
+static int
+register_snapshot_trigger(char *glob, struct event_trigger_ops *ops,
+			  struct event_trigger_data *data,
+			  struct ftrace_event_file *file)
+{
+	int ret = register_trigger(glob, ops, data, file);
+
+	if (ret > 0)
+		ftrace_alloc_snapshot();
+
+	return ret;
+}
+
+static int
+snapshot_trigger_print(struct seq_file *m, struct event_trigger_ops *ops,
+		       struct event_trigger_data *data)
+{
+	return event_trigger_print("snapshot", m, (void *)data->count,
+				   data->filter_str);
+}
+
+static struct event_trigger_ops snapshot_trigger_ops = {
+	.func			= snapshot_trigger,
+	.print			= snapshot_trigger_print,
+	.init			= event_trigger_init,
+	.free			= event_trigger_free,
+};
+
+static struct event_trigger_ops snapshot_count_trigger_ops = {
+	.func			= snapshot_count_trigger,
+	.print			= snapshot_trigger_print,
+	.init			= event_trigger_init,
+	.free			= event_trigger_free,
+};
+
+static struct event_trigger_ops *
+snapshot_get_trigger_ops(char *cmd, char *param)
+{
+	return param ? &snapshot_count_trigger_ops : &snapshot_trigger_ops;
+}
+
+static struct event_command trigger_snapshot_cmd = {
+	.name			= "snapshot",
+	.trigger_type		= ETT_SNAPSHOT,
+	.func			= event_trigger_callback,
+	.reg			= register_snapshot_trigger,
+	.unreg			= unregister_trigger,
+	.get_trigger_ops	= snapshot_get_trigger_ops,
+};
+
 static __init void unregister_trigger_traceon_traceoff_cmds(void)
 {
 	unregister_event_command(&trigger_traceon_cmd);
@@ -726,5 +794,11 @@ __init int register_trigger_cmds(void)
 		return ret;
 	}
 
+	ret = register_event_command(&trigger_snapshot_cmd);
+	if (WARN_ON(ret < 0)) {
+		unregister_trigger_traceon_traceoff_cmds();
+		return ret;
+	}
+
 	return 0;
 }
-- 
1.7.11.4

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