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-trace 26 27 /* 28 * TRACE_SYSTEM is expected to be a C valid variable (alpha-numeric 29 * and underscore), although it may start with numbers. If for some 30 * reason it is not, you need to add the following lines: 31 */ 32 #undef TRACE_SYSTEM_VAR 33 #define TRACE_SYSTEM_VAR sample_trace 34 /* 35 * But the above is only needed if TRACE_SYSTEM is not alpha-numeric 36 * and underscored. By default, TRACE_SYSTEM_VAR will be equal to 37 * TRACE_SYSTEM. As TRACE_SYSTEM_VAR must be alpha-numeric, if 38 * TRACE_SYSTEM is not, then TRACE_SYSTEM_VAR must be defined with 39 * only alpha-numeric and underscores. 40 * 41 * The TRACE_SYSTEM_VAR is only used internally and not visible to 42 * user space. 43 */ 44 45 /* 46 * Notice that this file is not protected like a normal header. 47 * We also must allow for rereading of this file. The 48 * 49 * || defined(TRACE_HEADER_MULTI_READ) 50 * 51 * serves this purpose. 52 */ 53 #if !defined(_TRACE_EVENT_SAMPLE_H) || defined(TRACE_HEADER_MULTI_READ) 54 #define _TRACE_EVENT_SAMPLE_H 55 56 /* 57 * All trace headers should include tracepoint.h, until we finally 58 * make it into a standard header. 59 */ 60 #include <linux/tracepoint.h> 61 62 /* 63 * The TRACE_EVENT macro is broken up into 5 parts. 64 * 65 * name: name of the trace point. This is also how to enable the tracepoint. 66 * A function called trace_foo_bar() will be created. 67 * 68 * proto: the prototype of the function trace_foo_bar() 69 * Here it is trace_foo_bar(char *foo, int bar). 70 * 71 * args: must match the arguments in the prototype. 72 * Here it is simply "foo, bar". 73 * 74 * struct: This defines the way the data will be stored in the ring buffer. 75 * The items declared here become part of a special structure 76 * called "__entry", which can be used in the fast_assign part of the 77 * TRACE_EVENT macro. 78 * 79 * Here are the currently defined types you can use: 80 * 81 * __field : Is broken up into type and name. Where type can be any 82 * primitive type (integer, long or pointer). 83 * 84 * __field(int, foo) 85 * 86 * __entry->foo = 5; 87 * 88 * __field_struct : This can be any static complex data type (struct, union 89 * but not an array). Be careful using complex types, as each 90 * event is limited in size, and copying large amounts of data 91 * into the ring buffer can slow things down. 92 * 93 * __field_struct(struct bar, foo) 94 * 95 * __entry->bar.x = y; 96 97 * __array: There are three fields (type, name, size). The type is the 98 * type of elements in teh array, the name is the name of the array. 99 * size is the number of items in the array (not the total size). 100 * 101 * __array( char, foo, 10) is the same as saying: char foo[10]; 102 * 103 * Assigning arrays can be done like any array: 104 * 105 * __entry->foo[0] = 'a'; 106 * 107 * memcpy(__entry->foo, bar, 10); 108 * 109 * __dynamic_array: This is similar to array, but can vary is size from 110 * instance to instance of the tracepoint being called. 111 * Like __array, this too has three elements (type, name, size); 112 * type is the type of the element, name is the name of the array. 113 * The size is different than __array. It is not a static number, 114 * but the algorithm to figure out the length of the array for the 115 * specific instance of tracepoint. Again, size is the numebr of 116 * items in the array, not the total length in bytes. 117 * 118 * __dynamic_array( int, foo, bar) is similar to: int foo[bar]; 119 * 120 * Note, unlike arrays, you must use the __get_dynamic_array() macro 121 * to access the array. 122 * 123 * memcpy(__get_dynamic_array(foo), bar, 10); 124 * 125 * Notice, that "__entry" is not needed here. 126 * 127 * __string: This is a special kind of __dynamic_array. It expects to 128 * have a nul terminated character array passed to it (it allows 129 * for NULL too, which would be converted into "(null)"). __string 130 * takes two paramenter (name, src), where name is the name of 131 * the string saved, and src is the string to copy into the 132 * ring buffer. 133 * 134 * __string(foo, bar) is similar to: strcpy(foo, bar) 135 * 136 * To assign a string, use the helper macro __assign_str(). 137 * 138 * __assign_str(foo, bar); 139 * 140 * In most cases, the __assign_str() macro will take the same 141 * parameters as the __string() macro had to declare the string. 142 * 143 * __bitmask: This is another kind of __dynamic_array, but it expects 144 * an array of longs, and the number of bits to parse. It takes 145 * two parameters (name, nr_bits), where name is the name of the 146 * bitmask to save, and the nr_bits is the number of bits to record. 147 * 148 * __bitmask(target_cpu, nr_cpumask_bits) 149 * 150 * To assign a bitmask, use the __assign_bitmask() helper macro. 151 * 152 * __assign_bitmask(target_cpus, cpumask_bits(bar), nr_cpumask_bits); 153 * 154 * 155 * fast_assign: This is a C like function that is used to store the items 156 * into the ring buffer. A special variable called "__entry" will be the 157 * structure that points into the ring buffer and has the same fields as 158 * described by the struct part of TRACE_EVENT above. 159 * 160 * printk: This is a way to print out the data in pretty print. This is 161 * useful if the system crashes and you are logging via a serial line, 162 * the data can be printed to the console using this "printk" method. 163 * This is also used to print out the data from the trace files. 164 * Again, the __entry macro is used to access the data from the ring buffer. 165 * 166 * Note, __dynamic_array, __string, and __bitmask require special helpers 167 * to access the data. 168 * 169 * For __dynamic_array(int, foo, bar) use __get_dynamic_array(foo) 170 * Use __get_dynamic_array_len(foo) to get the length of the array 171 * saved. 172 * 173 * For __string(foo, bar) use __get_str(foo) 174 * 175 * For __bitmask(target_cpus, nr_cpumask_bits) use __get_bitmask(target_cpus) 176 * 177 * 178 * Note, that for both the assign and the printk, __entry is the handler 179 * to the data structure in the ring buffer, and is defined by the 180 * TP_STRUCT__entry. 181 */ 182 183 /* 184 * It is OK to have helper functions in the file, but they need to be protected 185 * from being defined more than once. Remember, this file gets included more 186 * than once. 187 */ 188 #ifndef __TRACE_EVENT_SAMPLE_HELPER_FUNCTIONS 189 #define __TRACE_EVENT_SAMPLE_HELPER_FUNCTIONS 190 static inline int __length_of(const int *list) 191 { 192 int i; 193 194 if (!list) 195 return 0; 196 197 for (i = 0; list[i]; i++) 198 ; 199 return i; 200 } 201 #endif 202 203 TRACE_EVENT(foo_bar, 204 205 TP_PROTO(const char *foo, int bar, const int *lst, 206 const char *string, const struct cpumask *mask), 207 208 TP_ARGS(foo, bar, lst, string, mask), 209 210 TP_STRUCT__entry( 211 __array( char, foo, 10 ) 212 __field( int, bar ) 213 __dynamic_array(int, list, __length_of(lst)) 214 __string( str, string ) 215 __bitmask( cpus, num_possible_cpus() ) 216 ), 217 218 TP_fast_assign( 219 strlcpy(__entry->foo, foo, 10); 220 __entry->bar = bar; 221 memcpy(__get_dynamic_array(list), lst, 222 __length_of(lst) * sizeof(int)); 223 __assign_str(str, string); 224 __assign_bitmask(cpus, cpumask_bits(mask), num_possible_cpus()); 225 ), 226 227 TP_printk("foo %s %d %s %s (%s)", __entry->foo, __entry->bar, 228 __print_array(__get_dynamic_array(list), 229 __get_dynamic_array_len(list), 230 sizeof(int)), 231 __get_str(str), __get_bitmask(cpus)) 232 ); 233 234 /* 235 * There may be a case where a tracepoint should only be called if 236 * some condition is set. Otherwise the tracepoint should not be called. 237 * But to do something like: 238 * 239 * if (cond) 240 * trace_foo(); 241 * 242 * Would cause a little overhead when tracing is not enabled, and that 243 * overhead, even if small, is not something we want. As tracepoints 244 * use static branch (aka jump_labels), where no branch is taken to 245 * skip the tracepoint when not enabled, and a jmp is placed to jump 246 * to the tracepoint code when it is enabled, having a if statement 247 * nullifies that optimization. It would be nice to place that 248 * condition within the static branch. This is where TRACE_EVENT_CONDITION 249 * comes in. 250 * 251 * TRACE_EVENT_CONDITION() is just like TRACE_EVENT, except it adds another 252 * parameter just after args. Where TRACE_EVENT has: 253 * 254 * TRACE_EVENT(name, proto, args, struct, assign, printk) 255 * 256 * the CONDITION version has: 257 * 258 * TRACE_EVENT_CONDITION(name, proto, args, cond, struct, assign, printk) 259 * 260 * Everything is the same as TRACE_EVENT except for the new cond. Think 261 * of the cond variable as: 262 * 263 * if (cond) 264 * trace_foo_bar_with_cond(); 265 * 266 * Except that the logic for the if branch is placed after the static branch. 267 * That is, the if statement that processes the condition will not be 268 * executed unless that traecpoint is enabled. Otherwise it still remains 269 * a nop. 270 */ 271 TRACE_EVENT_CONDITION(foo_bar_with_cond, 272 273 TP_PROTO(const char *foo, int bar), 274 275 TP_ARGS(foo, bar), 276 277 TP_CONDITION(!(bar % 10)), 278 279 TP_STRUCT__entry( 280 __string( foo, foo ) 281 __field( int, bar ) 282 ), 283 284 TP_fast_assign( 285 __assign_str(foo, foo); 286 __entry->bar = bar; 287 ), 288 289 TP_printk("foo %s %d", __get_str(foo), __entry->bar) 290 ); 291 292 void foo_bar_reg(void); 293 void foo_bar_unreg(void); 294 295 /* 296 * Now in the case that some function needs to be called when the 297 * tracepoint is enabled and/or when it is disabled, the 298 * TRACE_EVENT_FN() serves this purpose. This is just like TRACE_EVENT() 299 * but adds two more parameters at the end: 300 * 301 * TRACE_EVENT_FN( name, proto, args, struct, assign, printk, reg, unreg) 302 * 303 * reg and unreg are functions with the prototype of: 304 * 305 * void reg(void) 306 * 307 * The reg function gets called before the tracepoint is enabled, and 308 * the unreg function gets called after the tracepoint is disabled. 309 * 310 * Note, reg and unreg are allowed to be NULL. If you only need to 311 * call a function before enabling, or after disabling, just set one 312 * function and pass in NULL for the other parameter. 313 */ 314 TRACE_EVENT_FN(foo_bar_with_fn, 315 316 TP_PROTO(const char *foo, int bar), 317 318 TP_ARGS(foo, bar), 319 320 TP_STRUCT__entry( 321 __string( foo, foo ) 322 __field( int, bar ) 323 ), 324 325 TP_fast_assign( 326 __assign_str(foo, foo); 327 __entry->bar = bar; 328 ), 329 330 TP_printk("foo %s %d", __get_str(foo), __entry->bar), 331 332 foo_bar_reg, foo_bar_unreg 333 ); 334 335 /* 336 * Each TRACE_EVENT macro creates several helper functions to produce 337 * the code to add the tracepoint, create the files in the trace 338 * directory, hook it to perf, assign the values and to print out 339 * the raw data from the ring buffer. To prevent too much bloat, 340 * if there are more than one tracepoint that uses the same format 341 * for the proto, args, struct, assign and printk, and only the name 342 * is different, it is highly recommended to use the DECLARE_EVENT_CLASS 343 * 344 * DECLARE_EVENT_CLASS() macro creates most of the functions for the 345 * tracepoint. Then DEFINE_EVENT() is use to hook a tracepoint to those 346 * functions. This DEFINE_EVENT() is an instance of the class and can 347 * be enabled and disabled separately from other events (either TRACE_EVENT 348 * or other DEFINE_EVENT()s). 349 * 350 * Note, TRACE_EVENT() itself is simply defined as: 351 * 352 * #define TRACE_EVENT(name, proto, args, tstruct, assign, printk) \ 353 * DEFINE_EVENT_CLASS(name, proto, args, tstruct, assign, printk); \ 354 * DEFINE_EVENT(name, name, proto, args) 355 * 356 * The DEFINE_EVENT() also can be declared with conditions and reg functions: 357 * 358 * DEFINE_EVENT_CONDITION(template, name, proto, args, cond); 359 * DEFINE_EVENT_FN(template, name, proto, args, reg, unreg); 360 */ 361 DECLARE_EVENT_CLASS(foo_template, 362 363 TP_PROTO(const char *foo, int bar), 364 365 TP_ARGS(foo, bar), 366 367 TP_STRUCT__entry( 368 __string( foo, foo ) 369 __field( int, bar ) 370 ), 371 372 TP_fast_assign( 373 __assign_str(foo, foo); 374 __entry->bar = bar; 375 ), 376 377 TP_printk("foo %s %d", __get_str(foo), __entry->bar) 378 ); 379 380 /* 381 * Here's a better way for the previous samples (except, the first 382 * exmaple had more fields and could not be used here). 383 */ 384 DEFINE_EVENT(foo_template, foo_with_template_simple, 385 TP_PROTO(const char *foo, int bar), 386 TP_ARGS(foo, bar)); 387 388 DEFINE_EVENT_CONDITION(foo_template, foo_with_template_cond, 389 TP_PROTO(const char *foo, int bar), 390 TP_ARGS(foo, bar), 391 TP_CONDITION(!(bar % 8))); 392 393 394 DEFINE_EVENT_FN(foo_template, foo_with_template_fn, 395 TP_PROTO(const char *foo, int bar), 396 TP_ARGS(foo, bar), 397 foo_bar_reg, foo_bar_unreg); 398 399 /* 400 * Anytime two events share basically the same values and have 401 * the same output, use the DECLARE_EVENT_CLASS() and DEFINE_EVENT() 402 * when ever possible. 403 */ 404 405 /* 406 * If the event is similar to the DECLARE_EVENT_CLASS, but you need 407 * to have a different output, then use DEFINE_EVENT_PRINT() which 408 * lets you override the TP_printk() of the class. 409 */ 410 411 DEFINE_EVENT_PRINT(foo_template, foo_with_template_print, 412 TP_PROTO(const char *foo, int bar), 413 TP_ARGS(foo, bar), 414 TP_printk("bar %s %d", __get_str(foo), __entry->bar)); 415 416 #endif 417 418 /***** NOTICE! The #if protection ends here. *****/ 419 420 421 /* 422 * There are several ways I could have done this. If I left out the 423 * TRACE_INCLUDE_PATH, then it would default to the kernel source 424 * include/trace/events directory. 425 * 426 * I could specify a path from the define_trace.h file back to this 427 * file. 428 * 429 * #define TRACE_INCLUDE_PATH ../../samples/trace_events 430 * 431 * But the safest and easiest way to simply make it use the directory 432 * that the file is in is to add in the Makefile: 433 * 434 * CFLAGS_trace-events-sample.o := -I$(src) 435 * 436 * This will make sure the current path is part of the include 437 * structure for our file so that define_trace.h can find it. 438 * 439 * I could have made only the top level directory the include: 440 * 441 * CFLAGS_trace-events-sample.o := -I$(PWD) 442 * 443 * And then let the path to this directory be the TRACE_INCLUDE_PATH: 444 * 445 * #define TRACE_INCLUDE_PATH samples/trace_events 446 * 447 * But then if something defines "samples" or "trace_events" as a macro 448 * then we could risk that being converted too, and give us an unexpected 449 * result. 450 */ 451 #undef TRACE_INCLUDE_PATH 452 #undef TRACE_INCLUDE_FILE 453 #define TRACE_INCLUDE_PATH . 454 /* 455 * TRACE_INCLUDE_FILE is not needed if the filename and TRACE_SYSTEM are equal 456 */ 457 #define TRACE_INCLUDE_FILE trace-events-sample 458 #include <trace/define_trace.h> 459