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 */
15 enum {
16 TRACE_NOP_OPT_ACCEPT = 0x1,
17 TRACE_NOP_OPT_REFUSE = 0x2
18 };
19
20 /* Options for the tracer (see trace_options file) */
21 static 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
29 static 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
35 static struct trace_array *ctx_trace;
36
37 static void start_nop_trace(struct trace_array *tr)
38 {
39 /* Nothing to do! */
40 }
41
42 static void stop_nop_trace(struct trace_array *tr)
43 {
44 /* Nothing to do! */
45 }
46
47 static int nop_trace_init(struct trace_array *tr)
48 {
49 ctx_trace = tr;
50 start_nop_trace(tr);
51 return 0;
52 }
53
54 static 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 */
64 static 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
88 struct 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
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