samples/trace_events/trace-events-sample.h

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