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 */ 77TRACE_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