1/*
2 * nop tracer
3 *
4 * Copyright (C) 2008 Steven Noonan <steven@uplinklabs.net>
5 *
6 */
7
8#include <linux/module.h>
9#include <linux/ftrace.h>
10
11#include "trace.h"
12
13/* Our two options */
14enum {
15	TRACE_NOP_OPT_ACCEPT = 0x1,
16	TRACE_NOP_OPT_REFUSE = 0x2
17};
18
19/* Options for the tracer (see trace_options file) */
20static struct tracer_opt nop_opts[] = {
21	/* Option that will be accepted by set_flag callback */
22	{ TRACER_OPT(test_nop_accept, TRACE_NOP_OPT_ACCEPT) },
23	/* Option that will be refused by set_flag callback */
24	{ TRACER_OPT(test_nop_refuse, TRACE_NOP_OPT_REFUSE) },
25	{ } /* Always set a last empty entry */
26};
27
28static struct tracer_flags nop_flags = {
29	/* You can check your flags value here when you want. */
30	.val = 0, /* By default: all flags disabled */
31	.opts = nop_opts
32};
33
34static struct trace_array	*ctx_trace;
35
36static void start_nop_trace(struct trace_array *tr)
37{
38	/* Nothing to do! */
39}
40
41static void stop_nop_trace(struct trace_array *tr)
42{
43	/* Nothing to do! */
44}
45
46static int nop_trace_init(struct trace_array *tr)
47{
48	ctx_trace = tr;
49	start_nop_trace(tr);
50	return 0;
51}
52
53static void nop_trace_reset(struct trace_array *tr)
54{
55	stop_nop_trace(tr);
56}
57
58/* It only serves as a signal handler and a callback to
59 * accept or refuse tthe setting of a flag.
60 * If you don't implement it, then the flag setting will be
61 * automatically accepted.
62 */
63static int nop_set_flag(struct trace_array *tr, u32 old_flags, u32 bit, int set)
64{
65	/*
66	 * Note that you don't need to update nop_flags.val yourself.
67	 * The tracing Api will do it automatically if you return 0
68	 */
69	if (bit == TRACE_NOP_OPT_ACCEPT) {
70		printk(KERN_DEBUG "nop_test_accept flag set to %d: we accept."
71			" Now cat trace_options to see the result\n",
72			set);
73		return 0;
74	}
75
76	if (bit == TRACE_NOP_OPT_REFUSE) {
77		printk(KERN_DEBUG "nop_test_refuse flag set to %d: we refuse."
78			"Now cat trace_options to see the result\n",
79			set);
80		return -EINVAL;
81	}
82
83	return 0;
84}
85
86
87struct tracer nop_trace __read_mostly =
88{
89	.name		= "nop",
90	.init		= nop_trace_init,
91	.reset		= nop_trace_reset,
92#ifdef CONFIG_FTRACE_SELFTEST
93	.selftest	= trace_selftest_startup_nop,
94#endif
95	.flags		= &nop_flags,
96	.set_flag	= nop_set_flag,
97	.allow_instances = true,
98};
99
100