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 */ 78 TRACE_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