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 
start_nop_trace(struct trace_array * tr)37 static void start_nop_trace(struct trace_array *tr)
38 {
39 	/* Nothing to do! */
40 }
41 
stop_nop_trace(struct trace_array * tr)42 static void stop_nop_trace(struct trace_array *tr)
43 {
44 	/* Nothing to do! */
45 }
46 
nop_trace_init(struct trace_array * tr)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 
nop_trace_reset(struct trace_array * tr)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  */
nop_set_flag(struct trace_array * tr,u32 old_flags,u32 bit,int set)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