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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 |