trace-events-sample.h 17 KB

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