1 files changed, 100 insertions, 0 deletions
diff --git a/kernel/trace/trace_nop.c b/kernel/trace/trace_nop.c
new file mode 100644
index 000000000..50523f953
--- /dev/null
+++ b/kernel/trace/trace_nop.c
@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * nop tracer
+ *
+ * Copyright (C) 2008 Steven Noonan <steven@uplinklabs.net>
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/ftrace.h>
+
+#include "trace.h"
+
+/* Our two options */
+enum {
+	TRACE_NOP_OPT_ACCEPT = 0x1,
+	TRACE_NOP_OPT_REFUSE = 0x2
+};
+
+/* Options for the tracer (see trace_options file) */
+static struct tracer_opt nop_opts[] = {
+	/* Option that will be accepted by set_flag callback */
+	{ TRACER_OPT(test_nop_accept, TRACE_NOP_OPT_ACCEPT) },
+	/* Option that will be refused by set_flag callback */
+	{ TRACER_OPT(test_nop_refuse, TRACE_NOP_OPT_REFUSE) },
+	{ } /* Always set a last empty entry */
+};
+
+static struct tracer_flags nop_flags = {
+	/* You can check your flags value here when you want. */
+	.val = 0, /* By default: all flags disabled */
+	.opts = nop_opts
+};
+
+static struct trace_array	*ctx_trace;
+
+static void start_nop_trace(struct trace_array *tr)
+{
+	/* Nothing to do! */
+}
+
+static void stop_nop_trace(struct trace_array *tr)
+{
+	/* Nothing to do! */
+}
+
+static int nop_trace_init(struct trace_array *tr)
+{
+	ctx_trace = tr;
+	start_nop_trace(tr);
+	return 0;
+}
+
+static void nop_trace_reset(struct trace_array *tr)
+{
+	stop_nop_trace(tr);
+}
+
+/* It only serves as a signal handler and a callback to
+ * accept or refuse the setting of a flag.
+ * If you don't implement it, then the flag setting will be
+ * automatically accepted.
+ */
+static int nop_set_flag(struct trace_array *tr, u32 old_flags, u32 bit, int set)
+{
+	/*
+	 * Note that you don't need to update nop_flags.val yourself.
+	 * The tracing Api will do it automatically if you return 0
+	 */
+	if (bit == TRACE_NOP_OPT_ACCEPT) {
+		printk(KERN_DEBUG "nop_test_accept flag set to %d: we accept."
+			" Now cat trace_options to see the result\n",
+			set);
+		return 0;
+	}
+
+	if (bit == TRACE_NOP_OPT_REFUSE) {
+		printk(KERN_DEBUG "nop_test_refuse flag set to %d: we refuse."
+			" Now cat trace_options to see the result\n",
+			set);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+
+struct tracer nop_trace __read_mostly =
+{
+	.name		= "nop",
+	.init		= nop_trace_init,
+	.reset		= nop_trace_reset,
+#ifdef CONFIG_FTRACE_SELFTEST
+	.selftest	= trace_selftest_startup_nop,
+#endif
+	.flags		= &nop_flags,
+	.set_flag	= nop_set_flag,
+	.allow_instances = true,
+};
+