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 trace-events-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 #define TRACE_INCLUDE_PATH . 124 #include <trace/define_trace.h> 125