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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 | */ |
77 | TRACE_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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