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 | |