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