samples/trace_events/trace-events-sample.h

   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>