Root/samples/trace_events/trace-events-sample.h

1/*
2 * If TRACE_SYSTEM is defined, that will be the directory created
3 * in the ftrace directory under /sys/kernel/debug/tracing/events/<system>
4 *
5 * The define_trace.h below will also look for a file name of
6 * TRACE_SYSTEM.h where TRACE_SYSTEM is what is defined here.
7 * In this case, it would look for sample.h
8 *
9 * If the header name will be different than the system name
10 * (as in this case), then you can override the header name that
11 * define_trace.h will look up by defining TRACE_INCLUDE_FILE
12 *
13 * This file is called trace-events-sample.h but we want the system
14 * to be called "sample". Therefore we must define the name of this
15 * file:
16 *
17 * #define TRACE_INCLUDE_FILE trace-events-sample
18 *
19 * As we do an the bottom of this file.
20 *
21 * Notice that TRACE_SYSTEM should be defined outside of #if
22 * protection, just like TRACE_INCLUDE_FILE.
23 */
24#undef TRACE_SYSTEM
25#define TRACE_SYSTEM sample
26
27/*
28 * Notice that this file is not protected like a normal header.
29 * We also must allow for rereading of this file. The
30 *
31 * || defined(TRACE_HEADER_MULTI_READ)
32 *
33 * serves this purpose.
34 */
35#if !defined(_TRACE_EVENT_SAMPLE_H) || defined(TRACE_HEADER_MULTI_READ)
36#define _TRACE_EVENT_SAMPLE_H
37
38/*
39 * All trace headers should include tracepoint.h, until we finally
40 * make it into a standard header.
41 */
42#include <linux/tracepoint.h>
43
44/*
45 * The TRACE_EVENT macro is broken up into 5 parts.
46 *
47 * name: name of the trace point. This is also how to enable the tracepoint.
48 * A function called trace_foo_bar() will be created.
49 *
50 * proto: the prototype of the function trace_foo_bar()
51 * Here it is trace_foo_bar(char *foo, int bar).
52 *
53 * args: must match the arguments in the prototype.
54 * Here it is simply "foo, bar".
55 *
56 * struct: This defines the way the data will be stored in the ring buffer.
57 * There are currently two types of elements. __field and __array.
58 * a __field is broken up into (type, name). Where type can be any
59 * type but an array.
60 * For an array. there are three fields. (type, name, size). The
61 * type of elements in the array, the name of the field and the size
62 * of the array.
63 *
64 * __array( char, foo, 10) is the same as saying char foo[10].
65 *
66 * fast_assign: This is a C like function that is used to store the items
67 * into the ring buffer.
68 *
69 * printk: This is a way to print out the data in pretty print. This is
70 * useful if the system crashes and you are logging via a serial line,
71 * the data can be printed to the console using this "printk" method.
72 *
73 * Note, that for both the assign and the printk, __entry is the handler
74 * to the data structure in the ring buffer, and is defined by the
75 * TP_STRUCT__entry.
76 */
77TRACE_EVENT(foo_bar,
78
79    TP_PROTO(char *foo, int bar),
80
81    TP_ARGS(foo, bar),
82
83    TP_STRUCT__entry(
84        __array( char, foo, 10 )
85        __field( int, bar )
86    ),
87
88    TP_fast_assign(
89        strncpy(__entry->foo, foo, 10);
90        __entry->bar = bar;
91    ),
92
93    TP_printk("foo %s %d", __entry->foo, __entry->bar)
94);
95#endif
96
97/***** NOTICE! The #if protection ends here. *****/
98
99
100/*
101 * There are several ways I could have done this. If I left out the
102 * TRACE_INCLUDE_PATH, then it would default to the kernel source
103 * include/trace/events directory.
104 *
105 * I could specify a path from the define_trace.h file back to this
106 * file.
107 *
108 * #define TRACE_INCLUDE_PATH ../../samples/trace_events
109 *
110 * But the safest and easiest way to simply make it use the directory
111 * that the file is in is to add in the Makefile:
112 *
113 * CFLAGS_trace-events-sample.o := -I$(src)
114 *
115 * This will make sure the current path is part of the include
116 * structure for our file so that define_trace.h can find it.
117 *
118 * I could have made only the top level directory the include:
119 *
120 * CFLAGS_trace-events-sample.o := -I$(PWD)
121 *
122 * And then let the path to this directory be the TRACE_INCLUDE_PATH:
123 *
124 * #define TRACE_INCLUDE_PATH samples/trace_events
125 *
126 * But then if something defines "samples" or "trace_events" as a macro
127 * then we could risk that being converted too, and give us an unexpected
128 * result.
129 */
130#undef TRACE_INCLUDE_PATH
131#undef TRACE_INCLUDE_FILE
132#define TRACE_INCLUDE_PATH .
133/*
134 * TRACE_INCLUDE_FILE is not needed if the filename and TRACE_SYSTEM are equal
135 */
136#define TRACE_INCLUDE_FILE trace-events-sample
137#include <trace/define_trace.h>
138

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