samples/trace_events/trace-events-sample.h

   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
 274 void foo_bar_reg(void);
 275 void foo_bar_unreg(void);
 276
 277 /*
 278  * Now in the case that some function needs to be called when the
 279  * tracepoint is enabled and/or when it is disabled, the
 280  * TRACE_EVENT_FN() serves this purpose. This is just like TRACE_EVENT()
 281  * but adds two more parameters at the end:
 282  *
 283  * TRACE_EVENT_FN( name, proto, args, struct, assign, printk, reg, unreg)
 284  *
 285  * reg and unreg are functions with the prototype of:
 286  *
 287  *    void reg(void)
 288  *
 289  * The reg function gets called before the tracepoint is enabled, and
 290  * the unreg function gets called after the tracepoint is disabled.
 291  *
 292  * Note, reg and unreg are allowed to be NULL. If you only need to
 293  * call a function before enabling, or after disabling, just set one
 294  * function and pass in NULL for the other parameter.
 295  */
 296 TRACE_EVENT_FN(foo_bar_with_fn,
 297
 298         TP_PROTO(const char *foo, int bar),
 299
 300         TP_ARGS(foo, bar),
 301
 302         TP_STRUCT__entry(
 303                 __string(       foo,    foo             )
 304                 __field(        int,    bar             )
 305         ),
 306
 307         TP_fast_assign(
 308                 __assign_str(foo, foo);
 309                 __entry->bar    = bar;
 310         ),
 311
 312         TP_printk("foo %s %d", __get_str(foo), __entry->bar),
 313
 314         foo_bar_reg, foo_bar_unreg
 315 );
 316
 317 /*
 318  * Each TRACE_EVENT macro creates several helper functions to produce
 319  * the code to add the tracepoint, create the files in the trace
 320  * directory, hook it to perf, assign the values and to print out
 321  * the raw data from the ring buffer. To prevent too much bloat,
 322  * if there are more than one tracepoint that uses the same format
 323  * for the proto, args, struct, assign and printk, and only the name
 324  * is different, it is highly recommended to use the DECLARE_EVENT_CLASS
 325  *
 326  * DECLARE_EVENT_CLASS() macro creates most of the functions for the
 327  * tracepoint. Then DEFINE_EVENT() is use to hook a tracepoint to those
 328  * functions. This DEFINE_EVENT() is an instance of the class and can
 329  * be enabled and disabled separately from other events (either TRACE_EVENT
 330  * or other DEFINE_EVENT()s).
 331  *
 332  * Note, TRACE_EVENT() itself is simply defined as:
 333  *
 334  * #define TRACE_EVENT(name, proto, args, tstruct, assign, printk)  \
 335  *  DEFINE_EVENT_CLASS(name, proto, args, tstruct, assign, printk); \
 336  *  DEFINE_EVENT(name, name, proto, args)
 337  *
 338  * The DEFINE_EVENT() also can be declared with conditions and reg functions:
 339  *
 340  * DEFINE_EVENT_CONDITION(template, name, proto, args, cond);
 341  * DEFINE_EVENT_FN(template, name, proto, args, reg, unreg);
 342  */
 343 DECLARE_EVENT_CLASS(foo_template,
 344
 345         TP_PROTO(const char *foo, int bar),
 346
 347         TP_ARGS(foo, bar),
 348
 349         TP_STRUCT__entry(
 350                 __string(       foo,    foo             )
 351                 __field(        int,    bar             )
 352         ),
 353
 354         TP_fast_assign(
 355                 __assign_str(foo, foo);
 356                 __entry->bar    = bar;
 357         ),
 358
 359         TP_printk("foo %s %d", __get_str(foo), __entry->bar)
 360 );
 361
 362 /*
 363  * Here's a better way for the previous samples (except, the first
 364  * exmaple had more fields and could not be used here).
 365  */
 366 DEFINE_EVENT(foo_template, foo_with_template_simple,
 367         TP_PROTO(const char *foo, int bar),
 368         TP_ARGS(foo, bar));
 369
 370 DEFINE_EVENT_CONDITION(foo_template, foo_with_template_cond,
 371         TP_PROTO(const char *foo, int bar),
 372         TP_ARGS(foo, bar),
 373         TP_CONDITION(!(bar % 8)));
 374
 375
 376 DEFINE_EVENT_FN(foo_template, foo_with_template_fn,
 377         TP_PROTO(const char *foo, int bar),
 378         TP_ARGS(foo, bar),
 379         foo_bar_reg, foo_bar_unreg);
 380
 381 /*
 382  * Anytime two events share basically the same values and have
 383  * the same output, use the DECLARE_EVENT_CLASS() and DEFINE_EVENT()
 384  * when ever possible.
 385  */
 386
 387 /*
 388  * If the event is similar to the DECLARE_EVENT_CLASS, but you need
 389  * to have a different output, then use DEFINE_EVENT_PRINT() which
 390  * lets you override the TP_printk() of the class.
 391  */
 392
 393 DEFINE_EVENT_PRINT(foo_template, foo_with_template_print,
 394         TP_PROTO(const char *foo, int bar),
 395         TP_ARGS(foo, bar),
 396         TP_printk("bar %s %d", __get_str(foo), __entry->bar));
 397
 398 #endif
 399
 400 /***** NOTICE! The #if protection ends here. *****/
 401
 402
 403 /*
 404  * There are several ways I could have done this. If I left out the
 405  * TRACE_INCLUDE_PATH, then it would default to the kernel source
 406  * include/trace/events directory.
 407  *
 408  * I could specify a path from the define_trace.h file back to this
 409  * file.
 410  *
 411  * #define TRACE_INCLUDE_PATH ../../samples/trace_events
 412  *
 413  * But the safest and easiest way to simply make it use the directory
 414  * that the file is in is to add in the Makefile:
 415  *
 416  * CFLAGS_trace-events-sample.o := -I$(src)
 417  *
 418  * This will make sure the current path is part of the include
 419  * structure for our file so that define_trace.h can find it.
 420  *
 421  * I could have made only the top level directory the include:
 422  *
 423  * CFLAGS_trace-events-sample.o := -I$(PWD)
 424  *
 425  * And then let the path to this directory be the TRACE_INCLUDE_PATH:
 426  *
 427  * #define TRACE_INCLUDE_PATH samples/trace_events
 428  *
 429  * But then if something defines "samples" or "trace_events" as a macro
 430  * then we could risk that being converted too, and give us an unexpected
 431  * result.
 432  */
 433 #undef TRACE_INCLUDE_PATH
 434 #undef TRACE_INCLUDE_FILE
 435 #define TRACE_INCLUDE_PATH .
 436 /*
 437  * TRACE_INCLUDE_FILE is not needed if the filename and TRACE_SYSTEM are equal
 438  */
 439 #define TRACE_INCLUDE_FILE trace-events-sample
 440 #include <trace/define_trace.h>