1 /* SPDX-License-Identifier: GPL-2.0 */ 2 /* 3 * If TRACE_SYSTEM is defined, that will be the directory created 4 * in the ftrace directory under /sys/kernel/tracing/events/<system> 5 * 6 * The define_trace.h below will also look for a file name of 7 * TRACE_SYSTEM.h where TRACE_SYSTEM is what is defined here. 8 * In this case, it would look for sample-trace.h 9 * 10 * If the header name will be different than the system name 11 * (as in this case), then you can override the header name that 12 * define_trace.h will look up by defining TRACE_INCLUDE_FILE 13 * 14 * This file is called trace-events-sample.h but we want the system 15 * to be called "sample-trace". Therefore we must define the name of this 16 * file: 17 * 18 * #define TRACE_INCLUDE_FILE trace-events-sample 19 * 20 * As we do an the bottom of this file. 21 * 22 * Notice that TRACE_SYSTEM should be defined outside of #if 23 * protection, just like TRACE_INCLUDE_FILE. 24 */ 25 #undef TRACE_SYSTEM 26 #define TRACE_SYSTEM sample-trace 27 28 /* 29 * TRACE_SYSTEM is expected to be a C valid variable (alpha-numeric 30 * and underscore), although it may start with numbers. If for some 31 * reason it is not, you need to add the following lines: 32 */ 33 #undef TRACE_SYSTEM_VAR 34 #define TRACE_SYSTEM_VAR sample_trace 35 /* 36 * But the above is only needed if TRACE_SYSTEM is not alpha-numeric 37 * and underscored. By default, TRACE_SYSTEM_VAR will be equal to 38 * TRACE_SYSTEM. As TRACE_SYSTEM_VAR must be alpha-numeric, if 39 * TRACE_SYSTEM is not, then TRACE_SYSTEM_VAR must be defined with 40 * only alpha-numeric and underscores. 41 * 42 * The TRACE_SYSTEM_VAR is only used internally and not visible to 43 * user space. 44 */ 45 46 /* 47 * Notice that this file is not protected like a normal header. 48 * We also must allow for rereading of this file. The 49 * 50 * || defined(TRACE_HEADER_MULTI_READ) 51 * 52 * serves this purpose. 53 */ 54 #if !defined(_TRACE_EVENT_SAMPLE_H) || defined(TRACE_HEADER_MULTI_READ) 55 #define _TRACE_EVENT_SAMPLE_H 56 57 /* 58 * All trace headers should include tracepoint.h, until we finally 59 * make it into a standard header. 60 */ 61 #include <linux/tracepoint.h> 62 63 /* 64 * The TRACE_EVENT macro is broken up into 5 parts. 65 * 66 * name: name of the trace point. This is also how to enable the tracepoint. 67 * A function called trace_foo_bar() will be created. 68 * 69 * proto: the prototype of the function trace_foo_bar() 70 * Here it is trace_foo_bar(char *foo, int bar). 71 * 72 * args: must match the arguments in the prototype. 73 * Here it is simply "foo, bar". 74 * 75 * struct: This defines the way the data will be stored in the ring buffer. 76 * The items declared here become part of a special structure 77 * called "__entry", which can be used in the fast_assign part of the 78 * TRACE_EVENT macro. 79 * 80 * Here are the currently defined types you can use: 81 * 82 * __field : Is broken up into type and name. Where type can be any 83 * primitive type (integer, long or pointer). 84 * 85 * __field(int, foo) 86 * 87 * __entry->foo = 5; 88 * 89 * __field_struct : This can be any static complex data type (struct, union 90 * but not an array). Be careful using complex types, as each 91 * event is limited in size, and copying large amounts of data 92 * into the ring buffer can slow things down. 93 * 94 * __field_struct(struct bar, foo) 95 * 96 * __entry->bar.x = y; 97 98 * __array: There are three fields (type, name, size). The type is the 99 * type of elements in the array, the name is the name of the array. 100 * size is the number of items in the array (not the total size). 101 * 102 * __array( char, foo, 10) is the same as saying: char foo[10]; 103 * 104 * Assigning arrays can be done like any array: 105 * 106 * __entry->foo[0] = 'a'; 107 * 108 * memcpy(__entry->foo, bar, 10); 109 * 110 * __dynamic_array: This is similar to array, but can vary its size from 111 * instance to instance of the tracepoint being called. 112 * Like __array, this too has three elements (type, name, size); 113 * type is the type of the element, name is the name of the array. 114 * The size is different than __array. It is not a static number, 115 * but the algorithm to figure out the length of the array for the 116 * specific instance of tracepoint. Again, size is the number of 117 * items in the array, not the total length in bytes. 118 * 119 * __dynamic_array( int, foo, bar) is similar to: int foo[bar]; 120 * 121 * Note, unlike arrays, you must use the __get_dynamic_array() macro 122 * to access the array. 123 * 124 * memcpy(__get_dynamic_array(foo), bar, 10); 125 * 126 * Notice, that "__entry" is not needed here. 127 * 128 * __string: This is a special kind of __dynamic_array. It expects to 129 * have a null terminated character array passed to it (it allows 130 * for NULL too, which would be converted into "(null)"). __string 131 * takes two parameter (name, src), where name is the name of 132 * the string saved, and src is the string to copy into the 133 * ring buffer. 134 * 135 * __string(foo, bar) is similar to: strcpy(foo, bar) 136 * 137 * To assign a string, use the helper macro __assign_str(). 138 * 139 * __assign_str(foo, bar); 140 * 141 * In most cases, the __assign_str() macro will take the same 142 * parameters as the __string() macro had to declare the string. 143 * 144 * __bitmask: This is another kind of __dynamic_array, but it expects 145 * an array of longs, and the number of bits to parse. It takes 146 * two parameters (name, nr_bits), where name is the name of the 147 * bitmask to save, and the nr_bits is the number of bits to record. 148 * 149 * __bitmask(target_cpu, nr_cpumask_bits) 150 * 151 * To assign a bitmask, use the __assign_bitmask() helper macro. 152 * 153 * __assign_bitmask(target_cpus, cpumask_bits(bar), nr_cpumask_bits); 154 * 155 * 156 * fast_assign: This is a C like function that is used to store the items 157 * into the ring buffer. A special variable called "__entry" will be the 158 * structure that points into the ring buffer and has the same fields as 159 * described by the struct part of TRACE_EVENT above. 160 * 161 * printk: This is a way to print out the data in pretty print. This is 162 * useful if the system crashes and you are logging via a serial line, 163 * the data can be printed to the console using this "printk" method. 164 * This is also used to print out the data from the trace files. 165 * Again, the __entry macro is used to access the data from the ring buffer. 166 * 167 * Note, __dynamic_array, __string, and __bitmask require special helpers 168 * to access the data. 169 * 170 * For __dynamic_array(int, foo, bar) use __get_dynamic_array(foo) 171 * Use __get_dynamic_array_len(foo) to get the length of the array 172 * saved. Note, __get_dynamic_array_len() returns the total allocated 173 * length of the dynamic array; __print_array() expects the second 174 * parameter to be the number of elements. To get that, the array length 175 * needs to be divided by the element size. 176 * 177 * For __string(foo, bar) use __get_str(foo) 178 * 179 * For __bitmask(target_cpus, nr_cpumask_bits) use __get_bitmask(target_cpus) 180 * 181 * 182 * Note, that for both the assign and the printk, __entry is the handler 183 * to the data structure in the ring buffer, and is defined by the 184 * TP_STRUCT__entry. 185 */ 186 187 /* 188 * It is OK to have helper functions in the file, but they need to be protected 189 * from being defined more than once. Remember, this file gets included more 190 * than once. 191 */ 192 #ifndef __TRACE_EVENT_SAMPLE_HELPER_FUNCTIONS 193 #define __TRACE_EVENT_SAMPLE_HELPER_FUNCTIONS 194 static inline int __length_of(const int *list) 195 { 196 int i; 197 198 if (!list) 199 return 0; 200 201 for (i = 0; list[i]; i++) 202 ; 203 return i; 204 } 205 206 enum { 207 TRACE_SAMPLE_FOO = 2, 208 TRACE_SAMPLE_BAR = 4, 209 TRACE_SAMPLE_ZOO = 8, 210 }; 211 #endif 212 213 /* 214 * If enums are used in the TP_printk(), their names will be shown in 215 * format files and not their values. This can cause problems with user 216 * space programs that parse the format files to know how to translate 217 * the raw binary trace output into human readable text. 218 * 219 * To help out user space programs, any enum that is used in the TP_printk() 220 * should be defined by TRACE_DEFINE_ENUM() macro. All that is needed to 221 * be done is to add this macro with the enum within it in the trace 222 * header file, and it will be converted in the output. 223 */ 224 225 TRACE_DEFINE_ENUM(TRACE_SAMPLE_FOO); 226 TRACE_DEFINE_ENUM(TRACE_SAMPLE_BAR); 227 TRACE_DEFINE_ENUM(TRACE_SAMPLE_ZOO); 228 229 TRACE_EVENT(foo_bar, 230 231 TP_PROTO(const char *foo, int bar, const int *lst, 232 const char *string, const struct cpumask *mask), 233 234 TP_ARGS(foo, bar, lst, string, mask), 235 236 TP_STRUCT__entry( 237 __array( char, foo, 10 ) 238 __field( int, bar ) 239 __dynamic_array(int, list, __length_of(lst)) 240 __string( str, string ) 241 __bitmask( cpus, num_possible_cpus() ) 242 ), 243 244 TP_fast_assign( 245 strlcpy(__entry->foo, foo, 10); 246 __entry->bar = bar; 247 memcpy(__get_dynamic_array(list), lst, 248 __length_of(lst) * sizeof(int)); 249 __assign_str(str, string); 250 __assign_bitmask(cpus, cpumask_bits(mask), num_possible_cpus()); 251 ), 252 253 TP_printk("foo %s %d %s %s %s %s (%s)", __entry->foo, __entry->bar, 254 255 /* 256 * Notice here the use of some helper functions. This includes: 257 * 258 * __print_symbolic( variable, { value, "string" }, ... ), 259 * 260 * The variable is tested against each value of the { } pair. If 261 * the variable matches one of the values, then it will print the 262 * string in that pair. If non are matched, it returns a string 263 * version of the number (if __entry->bar == 7 then "7" is returned). 264 */ 265 __print_symbolic(__entry->bar, 266 { 0, "zero" }, 267 { TRACE_SAMPLE_FOO, "TWO" }, 268 { TRACE_SAMPLE_BAR, "FOUR" }, 269 { TRACE_SAMPLE_ZOO, "EIGHT" }, 270 { 10, "TEN" } 271 ), 272 273 /* 274 * __print_flags( variable, "delim", { value, "flag" }, ... ), 275 * 276 * This is similar to __print_symbolic, except that it tests the bits 277 * of the value. If ((FLAG & variable) == FLAG) then the string is 278 * printed. If more than one flag matches, then each one that does is 279 * also printed with delim in between them. 280 * If not all bits are accounted for, then the not found bits will be 281 * added in hex format: 0x506 will show BIT2|BIT4|0x500 282 */ 283 __print_flags(__entry->bar, "|", 284 { 1, "BIT1" }, 285 { 2, "BIT2" }, 286 { 4, "BIT3" }, 287 { 8, "BIT4" } 288 ), 289 /* 290 * __print_array( array, len, element_size ) 291 * 292 * This prints out the array that is defined by __array in a nice format. 293 */ 294 __print_array(__get_dynamic_array(list), 295 __get_dynamic_array_len(list) / sizeof(int), 296 sizeof(int)), 297 __get_str(str), __get_bitmask(cpus)) 298 ); 299 300 /* 301 * There may be a case where a tracepoint should only be called if 302 * some condition is set. Otherwise the tracepoint should not be called. 303 * But to do something like: 304 * 305 * if (cond) 306 * trace_foo(); 307 * 308 * Would cause a little overhead when tracing is not enabled, and that 309 * overhead, even if small, is not something we want. As tracepoints 310 * use static branch (aka jump_labels), where no branch is taken to 311 * skip the tracepoint when not enabled, and a jmp is placed to jump 312 * to the tracepoint code when it is enabled, having a if statement 313 * nullifies that optimization. It would be nice to place that 314 * condition within the static branch. This is where TRACE_EVENT_CONDITION 315 * comes in. 316 * 317 * TRACE_EVENT_CONDITION() is just like TRACE_EVENT, except it adds another 318 * parameter just after args. Where TRACE_EVENT has: 319 * 320 * TRACE_EVENT(name, proto, args, struct, assign, printk) 321 * 322 * the CONDITION version has: 323 * 324 * TRACE_EVENT_CONDITION(name, proto, args, cond, struct, assign, printk) 325 * 326 * Everything is the same as TRACE_EVENT except for the new cond. Think 327 * of the cond variable as: 328 * 329 * if (cond) 330 * trace_foo_bar_with_cond(); 331 * 332 * Except that the logic for the if branch is placed after the static branch. 333 * That is, the if statement that processes the condition will not be 334 * executed unless that traecpoint is enabled. Otherwise it still remains 335 * a nop. 336 */ 337 TRACE_EVENT_CONDITION(foo_bar_with_cond, 338 339 TP_PROTO(const char *foo, int bar), 340 341 TP_ARGS(foo, bar), 342 343 TP_CONDITION(!(bar % 10)), 344 345 TP_STRUCT__entry( 346 __string( foo, foo ) 347 __field( int, bar ) 348 ), 349 350 TP_fast_assign( 351 __assign_str(foo, foo); 352 __entry->bar = bar; 353 ), 354 355 TP_printk("foo %s %d", __get_str(foo), __entry->bar) 356 ); 357 358 int foo_bar_reg(void); 359 void foo_bar_unreg(void); 360 361 /* 362 * Now in the case that some function needs to be called when the 363 * tracepoint is enabled and/or when it is disabled, the 364 * TRACE_EVENT_FN() serves this purpose. This is just like TRACE_EVENT() 365 * but adds two more parameters at the end: 366 * 367 * TRACE_EVENT_FN( name, proto, args, struct, assign, printk, reg, unreg) 368 * 369 * reg and unreg are functions with the prototype of: 370 * 371 * void reg(void) 372 * 373 * The reg function gets called before the tracepoint is enabled, and 374 * the unreg function gets called after the tracepoint is disabled. 375 * 376 * Note, reg and unreg are allowed to be NULL. If you only need to 377 * call a function before enabling, or after disabling, just set one 378 * function and pass in NULL for the other parameter. 379 */ 380 TRACE_EVENT_FN(foo_bar_with_fn, 381 382 TP_PROTO(const char *foo, int bar), 383 384 TP_ARGS(foo, bar), 385 386 TP_STRUCT__entry( 387 __string( foo, foo ) 388 __field( int, bar ) 389 ), 390 391 TP_fast_assign( 392 __assign_str(foo, foo); 393 __entry->bar = bar; 394 ), 395 396 TP_printk("foo %s %d", __get_str(foo), __entry->bar), 397 398 foo_bar_reg, foo_bar_unreg 399 ); 400 401 /* 402 * Each TRACE_EVENT macro creates several helper functions to produce 403 * the code to add the tracepoint, create the files in the trace 404 * directory, hook it to perf, assign the values and to print out 405 * the raw data from the ring buffer. To prevent too much bloat, 406 * if there are more than one tracepoint that uses the same format 407 * for the proto, args, struct, assign and printk, and only the name 408 * is different, it is highly recommended to use the DECLARE_EVENT_CLASS 409 * 410 * DECLARE_EVENT_CLASS() macro creates most of the functions for the 411 * tracepoint. Then DEFINE_EVENT() is use to hook a tracepoint to those 412 * functions. This DEFINE_EVENT() is an instance of the class and can 413 * be enabled and disabled separately from other events (either TRACE_EVENT 414 * or other DEFINE_EVENT()s). 415 * 416 * Note, TRACE_EVENT() itself is simply defined as: 417 * 418 * #define TRACE_EVENT(name, proto, args, tstruct, assign, printk) \ 419 * DECLARE_EVENT_CLASS(name, proto, args, tstruct, assign, printk); \ 420 * DEFINE_EVENT(name, name, proto, args) 421 * 422 * The DEFINE_EVENT() also can be declared with conditions and reg functions: 423 * 424 * DEFINE_EVENT_CONDITION(template, name, proto, args, cond); 425 * DEFINE_EVENT_FN(template, name, proto, args, reg, unreg); 426 */ 427 DECLARE_EVENT_CLASS(foo_template, 428 429 TP_PROTO(const char *foo, int bar), 430 431 TP_ARGS(foo, bar), 432 433 TP_STRUCT__entry( 434 __string( foo, foo ) 435 __field( int, bar ) 436 ), 437 438 TP_fast_assign( 439 __assign_str(foo, foo); 440 __entry->bar = bar; 441 ), 442 443 TP_printk("foo %s %d", __get_str(foo), __entry->bar) 444 ); 445 446 /* 447 * Here's a better way for the previous samples (except, the first 448 * example had more fields and could not be used here). 449 */ 450 DEFINE_EVENT(foo_template, foo_with_template_simple, 451 TP_PROTO(const char *foo, int bar), 452 TP_ARGS(foo, bar)); 453 454 DEFINE_EVENT_CONDITION(foo_template, foo_with_template_cond, 455 TP_PROTO(const char *foo, int bar), 456 TP_ARGS(foo, bar), 457 TP_CONDITION(!(bar % 8))); 458 459 460 DEFINE_EVENT_FN(foo_template, foo_with_template_fn, 461 TP_PROTO(const char *foo, int bar), 462 TP_ARGS(foo, bar), 463 foo_bar_reg, foo_bar_unreg); 464 465 /* 466 * Anytime two events share basically the same values and have 467 * the same output, use the DECLARE_EVENT_CLASS() and DEFINE_EVENT() 468 * when ever possible. 469 */ 470 471 /* 472 * If the event is similar to the DECLARE_EVENT_CLASS, but you need 473 * to have a different output, then use DEFINE_EVENT_PRINT() which 474 * lets you override the TP_printk() of the class. 475 */ 476 477 DEFINE_EVENT_PRINT(foo_template, foo_with_template_print, 478 TP_PROTO(const char *foo, int bar), 479 TP_ARGS(foo, bar), 480 TP_printk("bar %s %d", __get_str(foo), __entry->bar)); 481 482 #endif 483 484 /***** NOTICE! The #if protection ends here. *****/ 485 486 487 /* 488 * There are several ways I could have done this. If I left out the 489 * TRACE_INCLUDE_PATH, then it would default to the kernel source 490 * include/trace/events directory. 491 * 492 * I could specify a path from the define_trace.h file back to this 493 * file. 494 * 495 * #define TRACE_INCLUDE_PATH ../../samples/trace_events 496 * 497 * But the safest and easiest way to simply make it use the directory 498 * that the file is in is to add in the Makefile: 499 * 500 * CFLAGS_trace-events-sample.o := -I$(src) 501 * 502 * This will make sure the current path is part of the include 503 * structure for our file so that define_trace.h can find it. 504 * 505 * I could have made only the top level directory the include: 506 * 507 * CFLAGS_trace-events-sample.o := -I$(PWD) 508 * 509 * And then let the path to this directory be the TRACE_INCLUDE_PATH: 510 * 511 * #define TRACE_INCLUDE_PATH samples/trace_events 512 * 513 * But then if something defines "samples" or "trace_events" as a macro 514 * then we could risk that being converted too, and give us an unexpected 515 * result. 516 */ 517 #undef TRACE_INCLUDE_PATH 518 #undef TRACE_INCLUDE_FILE 519 #define TRACE_INCLUDE_PATH . 520 /* 521 * TRACE_INCLUDE_FILE is not needed if the filename and TRACE_SYSTEM are equal 522 */ 523 #define TRACE_INCLUDE_FILE trace-events-sample 524 #include <trace/define_trace.h> 525