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 /debugfs/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>