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