1// SPDX-License-Identifier: GPL-2.0
2/*
3 * nop tracer
4 *
5 * Copyright (C) 2008 Steven Noonan <steven@uplinklabs.net>
6 *
7 */
8
9#include <linux/module.h>
10#include <linux/ftrace.h>
11
12#include "trace.h"
13
14/* Our two options */
15enum {
16 TRACE_NOP_OPT_ACCEPT = 0x1,
17 TRACE_NOP_OPT_REFUSE = 0x2
18};
19
20/* Options for the tracer (see trace_options file) */
21static struct tracer_opt nop_opts[] = {
22 /* Option that will be accepted by set_flag callback */
23 { TRACER_OPT(test_nop_accept, TRACE_NOP_OPT_ACCEPT) },
24 /* Option that will be refused by set_flag callback */
25 { TRACER_OPT(test_nop_refuse, TRACE_NOP_OPT_REFUSE) },
26 { } /* Always set a last empty entry */
27};
28
29static struct tracer_flags nop_flags = {
30 /* You can check your flags value here when you want. */
31 .val = 0, /* By default: all flags disabled */
32 .opts = nop_opts
33};
34
35static struct trace_array *ctx_trace;
36
37static void start_nop_trace(struct trace_array *tr)
38{
39 /* Nothing to do! */
40}
41
42static void stop_nop_trace(struct trace_array *tr)
43{
44 /* Nothing to do! */
45}
46
47static int nop_trace_init(struct trace_array *tr)
48{
49 ctx_trace = tr;
50 start_nop_trace(tr);
51 return 0;
52}
53
54static void nop_trace_reset(struct trace_array *tr)
55{
56 stop_nop_trace(tr);
57}
58
59/* It only serves as a signal handler and a callback to
60 * accept or refuse the setting of a flag.
61 * If you don't implement it, then the flag setting will be
62 * automatically accepted.
63 */
64static int nop_set_flag(struct trace_array *tr, u32 old_flags, u32 bit, int set)
65{
66 /*
67 * Note that you don't need to update nop_flags.val yourself.
68 * The tracing Api will do it automatically if you return 0
69 */
70 if (bit == TRACE_NOP_OPT_ACCEPT) {
71 printk(KERN_DEBUG "nop_test_accept flag set to %d: we accept."
72 " Now cat trace_options to see the result\n",
73 set);
74 return 0;
75 }
76
77 if (bit == TRACE_NOP_OPT_REFUSE) {
78 printk(KERN_DEBUG "nop_test_refuse flag set to %d: we refuse."
79 " Now cat trace_options to see the result\n",
80 set);
81 return -EINVAL;
82 }
83
84 return 0;
85}
86
87
88struct tracer nop_trace __read_mostly =
89{
90 .name = "nop",
91 .init = nop_trace_init,
92 .reset = nop_trace_reset,
93#ifdef CONFIG_FTRACE_SELFTEST
94 .selftest = trace_selftest_startup_nop,
95#endif
96 .flags = &nop_flags,
97 .set_flag = nop_set_flag,
98 .allow_instances = true,
99};
100
101