1 /* 2 * If TRACE_SYSTEM is defined, that will be the directory created 3 * in the ftrace directory under /sys/kernel/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 * The items declared here become part of a special structure 58 * called "__entry", which can be used in the fast_assign part of the 59 * TRACE_EVENT macro. 60 * 61 * Here are the currently defined types you can use: 62 * 63 * __field : Is broken up into type and name. Where type can be any 64 * primitive type (integer, long or pointer). 65 * 66 * __field(int, foo) 67 * 68 * __entry->foo = 5; 69 * 70 * __field_struct : This can be any static complex data type (struct, union 71 * but not an array). Be careful using complex types, as each 72 * event is limited in size, and copying large amounts of data 73 * into the ring buffer can slow things down. 74 * 75 * __field_struct(struct bar, foo) 76 * 77 * __entry->bar.x = y; 78 79 * __array: There are three fields (type, name, size). The type is the 80 * type of elements in teh array, the name is the name of the array. 81 * size is the number of items in the array (not the total size). 82 * 83 * __array( char, foo, 10) is the same as saying: char foo[10]; 84 * 85 * Assigning arrays can be done like any array: 86 * 87 * __entry->foo[0] = 'a'; 88 * 89 * memcpy(__entry->foo, bar, 10); 90 * 91 * __dynamic_array: This is similar to array, but can vary is size from 92 * instance to instance of the tracepoint being called. 93 * Like __array, this too has three elements (type, name, size); 94 * type is the type of the element, name is the name of the array. 95 * The size is different than __array. It is not a static number, 96 * but the algorithm to figure out the length of the array for the 97 * specific instance of tracepoint. Again, size is the numebr of 98 * items in the array, not the total length in bytes. 99 * 100 * __dynamic_array( int, foo, bar) is similar to: int foo[bar]; 101 * 102 * Note, unlike arrays, you must use the __get_dynamic_array() macro 103 * to access the array. 104 * 105 * memcpy(__get_dynamic_array(foo), bar, 10); 106 * 107 * Notice, that "__entry" is not needed here. 108 * 109 * __string: This is a special kind of __dynamic_array. It expects to 110 * have a nul terminated character array passed to it (it allows 111 * for NULL too, which would be converted into "(null)"). __string 112 * takes two paramenter (name, src), where name is the name of 113 * the string saved, and src is the string to copy into the 114 * ring buffer. 115 * 116 * __string(foo, bar) is similar to: strcpy(foo, bar) 117 * 118 * To assign a string, use the helper macro __assign_str(). 119 * 120 * __assign_str(foo, bar); 121 * 122 * In most cases, the __assign_str() macro will take the same 123 * parameters as the __string() macro had to declare the string. 124 * 125 * __bitmask: This is another kind of __dynamic_array, but it expects 126 * an array of longs, and the number of bits to parse. It takes 127 * two parameters (name, nr_bits), where name is the name of the 128 * bitmask to save, and the nr_bits is the number of bits to record. 129 * 130 * __bitmask(target_cpu, nr_cpumask_bits) 131 * 132 * To assign a bitmask, use the __assign_bitmask() helper macro. 133 * 134 * __assign_bitmask(target_cpus, cpumask_bits(bar), nr_cpumask_bits); 135 * 136 * 137 * fast_assign: This is a C like function that is used to store the items 138 * into the ring buffer. A special variable called "__entry" will be the 139 * structure that points into the ring buffer and has the same fields as 140 * described by the struct part of TRACE_EVENT above. 141 * 142 * printk: This is a way to print out the data in pretty print. This is 143 * useful if the system crashes and you are logging via a serial line, 144 * the data can be printed to the console using this "printk" method. 145 * This is also used to print out the data from the trace files. 146 * Again, the __entry macro is used to access the data from the ring buffer. 147 * 148 * Note, __dynamic_array, __string, and __bitmask require special helpers 149 * to access the data. 150 * 151 * For __dynamic_array(int, foo, bar) use __get_dynamic_array(foo) 152 * Use __get_dynamic_array_len(foo) to get the length of the array 153 * saved. 154 * 155 * For __string(foo, bar) use __get_str(foo) 156 * 157 * For __bitmask(target_cpus, nr_cpumask_bits) use __get_bitmask(target_cpus) 158 * 159 * 160 * Note, that for both the assign and the printk, __entry is the handler 161 * to the data structure in the ring buffer, and is defined by the 162 * TP_STRUCT__entry. 163 */ 164 165 /* 166 * It is OK to have helper functions in the file, but they need to be protected 167 * from being defined more than once. Remember, this file gets included more 168 * than once. 169 */ 170 #ifndef __TRACE_EVENT_SAMPLE_HELPER_FUNCTIONS 171 #define __TRACE_EVENT_SAMPLE_HELPER_FUNCTIONS 172 static inline int __length_of(const int *list) 173 { 174 int i; 175 176 if (!list) 177 return 0; 178 179 for (i = 0; list[i]; i++) 180 ; 181 return i; 182 } 183 #endif 184 185 TRACE_EVENT(foo_bar, 186 187 TP_PROTO(const char *foo, int bar, const int *lst, 188 const char *string, const struct cpumask *mask), 189 190 TP_ARGS(foo, bar, lst, string, mask), 191 192 TP_STRUCT__entry( 193 __array( char, foo, 10 ) 194 __field( int, bar ) 195 __dynamic_array(int, list, __length_of(lst)) 196 __string( str, string ) 197 __bitmask( cpus, num_possible_cpus() ) 198 ), 199 200 TP_fast_assign( 201 strlcpy(__entry->foo, foo, 10); 202 __entry->bar = bar; 203 memcpy(__get_dynamic_array(list), lst, 204 __length_of(lst) * sizeof(int)); 205 __assign_str(str, string); 206 __assign_bitmask(cpus, cpumask_bits(mask), num_possible_cpus()); 207 ), 208 209 TP_printk("foo %s %d %s %s (%s)", __entry->foo, __entry->bar, 210 __print_array(__get_dynamic_array(list), 211 __get_dynamic_array_len(list), 212 sizeof(int)), 213 __get_str(str), __get_bitmask(cpus)) 214 ); 215 216 /* 217 * There may be a case where a tracepoint should only be called if 218 * some condition is set. Otherwise the tracepoint should not be called. 219 * But to do something like: 220 * 221 * if (cond) 222 * trace_foo(); 223 * 224 * Would cause a little overhead when tracing is not enabled, and that 225 * overhead, even if small, is not something we want. As tracepoints 226 * use static branch (aka jump_labels), where no branch is taken to 227 * skip the tracepoint when not enabled, and a jmp is placed to jump 228 * to the tracepoint code when it is enabled, having a if statement 229 * nullifies that optimization. It would be nice to place that 230 * condition within the static branch. This is where TRACE_EVENT_CONDITION 231 * comes in. 232 * 233 * TRACE_EVENT_CONDITION() is just like TRACE_EVENT, except it adds another 234 * parameter just after args. Where TRACE_EVENT has: 235 * 236 * TRACE_EVENT(name, proto, args, struct, assign, printk) 237 * 238 * the CONDITION version has: 239 * 240 * TRACE_EVENT_CONDITION(name, proto, args, cond, struct, assign, printk) 241 * 242 * Everything is the same as TRACE_EVENT except for the new cond. Think 243 * of the cond variable as: 244 * 245 * if (cond) 246 * trace_foo_bar_with_cond(); 247 * 248 * Except that the logic for the if branch is placed after the static branch. 249 * That is, the if statement that processes the condition will not be 250 * executed unless that traecpoint is enabled. Otherwise it still remains 251 * a nop. 252 */ 253 TRACE_EVENT_CONDITION(foo_bar_with_cond, 254 255 TP_PROTO(const char *foo, int bar), 256 257 TP_ARGS(foo, bar), 258 259 TP_CONDITION(!(bar % 10)), 260 261 TP_STRUCT__entry( 262 __string( foo, foo ) 263 __field( int, bar ) 264 ), 265 266 TP_fast_assign( 267 __assign_str(foo, foo); 268 __entry->bar = bar; 269 ), 270 271 TP_printk("foo %s %d", __get_str(foo), __entry->bar) 272 ); 273 #endif 274 275 /***** NOTICE! The #if protection ends here. *****/ 276 277 278 /* 279 * There are several ways I could have done this. If I left out the 280 * TRACE_INCLUDE_PATH, then it would default to the kernel source 281 * include/trace/events directory. 282 * 283 * I could specify a path from the define_trace.h file back to this 284 * file. 285 * 286 * #define TRACE_INCLUDE_PATH ../../samples/trace_events 287 * 288 * But the safest and easiest way to simply make it use the directory 289 * that the file is in is to add in the Makefile: 290 * 291 * CFLAGS_trace-events-sample.o := -I$(src) 292 * 293 * This will make sure the current path is part of the include 294 * structure for our file so that define_trace.h can find it. 295 * 296 * I could have made only the top level directory the include: 297 * 298 * CFLAGS_trace-events-sample.o := -I$(PWD) 299 * 300 * And then let the path to this directory be the TRACE_INCLUDE_PATH: 301 * 302 * #define TRACE_INCLUDE_PATH samples/trace_events 303 * 304 * But then if something defines "samples" or "trace_events" as a macro 305 * then we could risk that being converted too, and give us an unexpected 306 * result. 307 */ 308 #undef TRACE_INCLUDE_PATH 309 #undef TRACE_INCLUDE_FILE 310 #define TRACE_INCLUDE_PATH . 311 /* 312 * TRACE_INCLUDE_FILE is not needed if the filename and TRACE_SYSTEM are equal 313 */ 314 #define TRACE_INCLUDE_FILE trace-events-sample 315 #include <trace/define_trace.h> 316