LXR linux/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 *    primitive type (integer, long or pointer). __field_struct() can
  60 *    be any static complex data value (struct, union, but not an array).
  61 *    For an array. there are three fields. (type, name, size). The
  62 *    type of elements in the array, the name of the field and the size
  63 *    of the array.
  64 *
  65 *    __array( char, foo, 10) is the same as saying   char foo[10].
  66 *
  67 * fast_assign: This is a C like function that is used to store the items
  68 *    into the ring buffer.
  69 *
  70 * printk: This is a way to print out the data in pretty print. This is
  71 *    useful if the system crashes and you are logging via a serial line,
  72 *    the data can be printed to the console using this "printk" method.
  73 *
  74 * Note, that for both the assign and the printk, __entry is the handler
  75 * to the data structure in the ring buffer, and is defined by the
  76 * TP_STRUCT__entry.
  77 */
  78TRACE_EVENT(foo_bar,
  79
  80        TP_PROTO(char *foo, int bar),
  81
  82        TP_ARGS(foo, bar),
  83
  84        TP_STRUCT__entry(
  85                __array(        char,   foo,    10              )
  86                __field(        int,    bar                     )
  87        ),
  88
  89        TP_fast_assign(
  90                strncpy(__entry->foo, foo, 10);
  91                __entry->bar    = bar;
  92        ),
  93
  94        TP_printk("foo %s %d", __entry->foo, __entry->bar)
  95);
  96#endif
  97
  98/***** NOTICE! The #if protection ends here. *****/
  99
 100
 101/*
 102 * There are several ways I could have done this. If I left out the
 103 * TRACE_INCLUDE_PATH, then it would default to the kernel source
 104 * include/trace/events directory.
 105 *
 106 * I could specify a path from the define_trace.h file back to this
 107 * file.
 108 *
 109 * #define TRACE_INCLUDE_PATH ../../samples/trace_events
 110 *
 111 * But the safest and easiest way to simply make it use the directory
 112 * that the file is in is to add in the Makefile:
 113 *
 114 * CFLAGS_trace-events-sample.o := -I$(src)
 115 *
 116 * This will make sure the current path is part of the include
 117 * structure for our file so that define_trace.h can find it.
 118 *
 119 * I could have made only the top level directory the include:
 120 *
 121 * CFLAGS_trace-events-sample.o := -I$(PWD)
 122 *
 123 * And then let the path to this directory be the TRACE_INCLUDE_PATH:
 124 *
 125 * #define TRACE_INCLUDE_PATH samples/trace_events
 126 *
 127 * But then if something defines "samples" or "trace_events" as a macro
 128 * then we could risk that being converted too, and give us an unexpected
 129 * result.
 130 */
 131#undef TRACE_INCLUDE_PATH
 132#undef TRACE_INCLUDE_FILE
 133#define TRACE_INCLUDE_PATH .
 134/*
 135 * TRACE_INCLUDE_FILE is not needed if the filename and TRACE_SYSTEM are equal
 136 */
 137#define TRACE_INCLUDE_FILE trace-events-sample
 138#include <trace/define_trace.h>
 139