[RFC PATCH v4 18/22] tracing/boot: Add synthetic event support

[Masami Hiramatsu]

Add synthetic event node support to boot time tracing.
The synthetic event is a kind of event node, but the group
name is "synthetic".

 - ftrace.event.synthetic.EVENT.fields = FIELD[, FIELD2...]
   Defines new synthetic event with FIELDs. Each field should be
   "type varname".

The synthetic node requires "fields" string arraies, which defines
the fields as same as tracing/synth_events interface.

Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
 kernel/trace/trace_boot.c        |   47 ++++++++++++++++++++++++++++++++++++++
 kernel/trace/trace_events_hist.c |    5 ++++
 2 files changed, 52 insertions(+)

diff --git a/kernel/trace/trace_boot.c b/kernel/trace/trace_boot.c
index a11dc60299fb..3054921b0877 100644
--- a/kernel/trace/trace_boot.c
+++ b/kernel/trace/trace_boot.c
@@ -118,6 +118,50 @@ trace_boot_add_kprobe_event(struct xbc_node *node, const char *event)
 }
 #endif
 
+#ifdef CONFIG_HIST_TRIGGERS
+extern int synth_event_run_command(const char *command);
+
+static int __init
+trace_boot_add_synth_event(struct xbc_node *node, const char *event)
+{
+	struct xbc_node *anode;
+	char buf[MAX_BUF_LEN], *q;
+	const char *p;
+	int len, delta, ret;
+
+	len = ARRAY_SIZE(buf);
+	delta = snprintf(buf, len, "%s", event);
+	if (delta >= len) {
+		pr_err("Event name is too long: %s\n", event);
+		return -E2BIG;
+	}
+	len -= delta; q = buf + delta;
+
+	xbc_node_for_each_array_value(node, "fields", anode, p) {
+		delta = snprintf(q, len, " %s;", p);
+		if (delta >= len) {
+			pr_err("fields string is too long: %s\n", p);
+			return -E2BIG;
+		}
+		len -= delta; q += delta;
+	}
+
+	ret = synth_event_run_command(buf);
+	if (ret < 0)
+		pr_err("Failed to add synthetic event: %s\n", buf);
+
+
+	return ret;
+}
+#else
+static inline int __init
+trace_boot_add_synth_event(struct xbc_node *node, const char *event)
+{
+	pr_err("Synthetic event is not supported.\n");
+	return -ENOTSUPP;
+}
+#endif
+
 static void __init
 trace_boot_init_one_event(struct trace_array *tr, struct xbc_node *gnode,
 			  struct xbc_node *enode)
@@ -133,6 +177,9 @@ trace_boot_init_one_event(struct trace_array *tr, struct xbc_node *gnode,
 	if (!strcmp(group, "kprobes"))
 		if (trace_boot_add_kprobe_event(enode, event) < 0)
 			return;
+	if (!strcmp(group, "synthetic"))
+		if (trace_boot_add_synth_event(enode, event) < 0)
+			return;
 
 	mutex_lock(&event_mutex);
 	file = find_event_file(tr, group, event);
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index d902a61775c4..806ad38bec95 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1365,6 +1365,11 @@ static int create_or_delete_synth_event(int argc, char **argv)
 	return ret == -ECANCELED ? -EINVAL : ret;
 }
 
+int synth_event_run_command(const char *command)
+{
+	return trace_run_command(command, create_or_delete_synth_event);
+}
+
 static int synth_event_create(int argc, const char **argv)
 {
 	const char *name = argv[0];