include/linux/ftrace_event.h

   1
   2 #ifndef _LINUX_FTRACE_EVENT_H
   3 #define _LINUX_FTRACE_EVENT_H
   4
   5 #include <linux/ring_buffer.h>
   6 #include <linux/trace_seq.h>
   7 #include <linux/percpu.h>
   8 #include <linux/hardirq.h>
   9 #include <linux/perf_event.h>
  10 #include <linux/tracepoint.h>
  11
  12 struct trace_array;
  13 struct trace_buffer;
  14 struct tracer;
  15 struct dentry;
  16
  17 struct trace_print_flags {
  18         unsigned long           mask;
  19         const char              *name;
  20 };
  21
  22 struct trace_print_flags_u64 {
  23         unsigned long long      mask;
  24         const char              *name;
  25 };
  26
  27 const char *ftrace_print_flags_seq(struct trace_seq *p, const char *delim,
  28                                    unsigned long flags,
  29                                    const struct trace_print_flags *flag_array);
  30
  31 const char *ftrace_print_symbols_seq(struct trace_seq *p, unsigned long val,
  32                                      const struct trace_print_flags *symbol_array);
  33
  34 #if BITS_PER_LONG == 32
  35 const char *ftrace_print_symbols_seq_u64(struct trace_seq *p,
  36                                          unsigned long long val,
  37                                          const struct trace_print_flags_u64
  38                                                                  *symbol_array);
  39 #endif
  40
  41 const char *ftrace_print_hex_seq(struct trace_seq *p,
  42                                  const unsigned char *buf, int len);
  43
  44 struct trace_iterator;
  45 struct trace_event;
  46
  47 int ftrace_raw_output_prep(struct trace_iterator *iter,
  48                            struct trace_event *event);
  49
  50 /*
  51  * The trace entry - the most basic unit of tracing. This is what
  52  * is printed in the end as a single line in the trace output, such as:
  53  *
  54  *     bash-15816 [01]   235.197585: idle_cpu <- irq_enter
  55  */
  56 struct trace_entry {
  57         unsigned short          type;
  58         unsigned char           flags;
  59         unsigned char           preempt_count;
  60         int                     pid;
  61 };
  62
  63 #define FTRACE_MAX_EVENT                                                \
  64         ((1 << (sizeof(((struct trace_entry *)0)->type) * 8)) - 1)
  65
  66 /*
  67  * Trace iterator - used by printout routines who present trace
  68  * results to users and which routines might sleep, etc:
  69  */
  70 struct trace_iterator {
  71         struct trace_array      *tr;
  72         struct tracer           *trace;
  73         struct trace_buffer     *trace_buffer;
  74         void                    *private;
  75         int                     cpu_file;
  76         struct mutex            mutex;
  77         struct ring_buffer_iter **buffer_iter;
  78         unsigned long           iter_flags;
  79
  80         /* trace_seq for __print_flags() and __print_symbolic() etc. */
  81         struct trace_seq        tmp_seq;
  82
  83         cpumask_var_t           started;
  84
  85         /* it's true when current open file is snapshot */
  86         bool                    snapshot;
  87
  88         /* The below is zeroed out in pipe_read */
  89         struct trace_seq        seq;
  90         struct trace_entry      *ent;
  91         unsigned long           lost_events;
  92         int                     leftover;
  93         int                     ent_size;
  94         int                     cpu;
  95         u64                     ts;
  96
  97         loff_t                  pos;
  98         long                    idx;
  99
 100         /* All new field here will be zeroed out in pipe_read */
 101 };
 102
 103 enum trace_iter_flags {
 104         TRACE_FILE_LAT_FMT      = 1,
 105         TRACE_FILE_ANNOTATE     = 2,
 106         TRACE_FILE_TIME_IN_NS   = 4,
 107 };
 108
 109
 110 typedef enum print_line_t (*trace_print_func)(struct trace_iterator *iter,
 111                                       int flags, struct trace_event *event);
 112
 113 struct trace_event_functions {
 114         trace_print_func        trace;
 115         trace_print_func        raw;
 116         trace_print_func        hex;
 117         trace_print_func        binary;
 118 };
 119
 120 struct trace_event {
 121         struct hlist_node               node;
 122         struct list_head                list;
 123         int                             type;
 124         struct trace_event_functions    *funcs;
 125 };
 126
 127 extern int register_ftrace_event(struct trace_event *event);
 128 extern int unregister_ftrace_event(struct trace_event *event);
 129
 130 /* Return values for print_line callback */
 131 enum print_line_t {
 132         TRACE_TYPE_PARTIAL_LINE = 0,    /* Retry after flushing the seq */
 133         TRACE_TYPE_HANDLED      = 1,
 134         TRACE_TYPE_UNHANDLED    = 2,    /* Relay to other output functions */
 135         TRACE_TYPE_NO_CONSUME   = 3     /* Handled but ask to not consume */
 136 };
 137
 138 void tracing_generic_entry_update(struct trace_entry *entry,
 139                                   unsigned long flags,
 140                                   int pc);
 141 struct ftrace_event_file;
 142
 143 struct ring_buffer_event *
 144 trace_event_buffer_lock_reserve(struct ring_buffer **current_buffer,
 145                                 struct ftrace_event_file *ftrace_file,
 146                                 int type, unsigned long len,
 147                                 unsigned long flags, int pc);
 148 struct ring_buffer_event *
 149 trace_current_buffer_lock_reserve(struct ring_buffer **current_buffer,
 150                                   int type, unsigned long len,
 151                                   unsigned long flags, int pc);
 152 void trace_current_buffer_unlock_commit(struct ring_buffer *buffer,
 153                                         struct ring_buffer_event *event,
 154                                         unsigned long flags, int pc);
 155 void trace_buffer_unlock_commit(struct ring_buffer *buffer,
 156                                 struct ring_buffer_event *event,
 157                                 unsigned long flags, int pc);
 158 void trace_buffer_unlock_commit_regs(struct ring_buffer *buffer,
 159                                      struct ring_buffer_event *event,
 160                                      unsigned long flags, int pc,
 161                                      struct pt_regs *regs);
 162 void trace_current_buffer_discard_commit(struct ring_buffer *buffer,
 163                                          struct ring_buffer_event *event);
 164
 165 void tracing_record_cmdline(struct task_struct *tsk);
 166
 167 int ftrace_output_call(struct trace_iterator *iter, char *name, char *fmt, ...);
 168
 169 struct event_filter;
 170
 171 enum trace_reg {
 172         TRACE_REG_REGISTER,
 173         TRACE_REG_UNREGISTER,
 174 #ifdef CONFIG_PERF_EVENTS
 175         TRACE_REG_PERF_REGISTER,
 176         TRACE_REG_PERF_UNREGISTER,
 177         TRACE_REG_PERF_OPEN,
 178         TRACE_REG_PERF_CLOSE,
 179         TRACE_REG_PERF_ADD,
 180         TRACE_REG_PERF_DEL,
 181 #endif
 182 };
 183
 184 struct ftrace_event_call;
 185
 186 struct ftrace_event_class {
 187         char                    *system;
 188         void                    *probe;
 189 #ifdef CONFIG_PERF_EVENTS
 190         void                    *perf_probe;
 191 #endif
 192         int                     (*reg)(struct ftrace_event_call *event,
 193                                        enum trace_reg type, void *data);
 194         int                     (*define_fields)(struct ftrace_event_call *);
 195         struct list_head        *(*get_fields)(struct ftrace_event_call *);
 196         struct list_head        fields;
 197         int                     (*raw_init)(struct ftrace_event_call *);
 198 };
 199
 200 extern int ftrace_event_reg(struct ftrace_event_call *event,
 201                             enum trace_reg type, void *data);
 202
 203 int ftrace_output_event(struct trace_iterator *iter, struct ftrace_event_call *event,
 204                         char *fmt, ...);
 205
 206 int ftrace_event_define_field(struct ftrace_event_call *call,
 207                               char *type, int len, char *item, int offset,
 208                               int field_size, int sign, int filter);
 209
 210 struct ftrace_event_buffer {
 211         struct ring_buffer              *buffer;
 212         struct ring_buffer_event        *event;
 213         struct ftrace_event_file        *ftrace_file;
 214         void                            *entry;
 215         unsigned long                   flags;
 216         int                             pc;
 217 };
 218
 219 void *ftrace_event_buffer_reserve(struct ftrace_event_buffer *fbuffer,
 220                                   struct ftrace_event_file *ftrace_file,
 221                                   unsigned long len);
 222
 223 void ftrace_event_buffer_commit(struct ftrace_event_buffer *fbuffer);
 224
 225 int ftrace_event_define_field(struct ftrace_event_call *call,
 226                               char *type, int len, char *item, int offset,
 227                               int field_size, int sign, int filter);
 228
 229 enum {
 230         TRACE_EVENT_FL_FILTERED_BIT,
 231         TRACE_EVENT_FL_CAP_ANY_BIT,
 232         TRACE_EVENT_FL_NO_SET_FILTER_BIT,
 233         TRACE_EVENT_FL_IGNORE_ENABLE_BIT,
 234         TRACE_EVENT_FL_WAS_ENABLED_BIT,
 235         TRACE_EVENT_FL_USE_CALL_FILTER_BIT,
 236         TRACE_EVENT_FL_TRACEPOINT_BIT,
 237 };
 238
 239 /*
 240  * Event flags:
 241  *  FILTERED      - The event has a filter attached
 242  *  CAP_ANY       - Any user can enable for perf
 243  *  NO_SET_FILTER - Set when filter has error and is to be ignored
 244  *  IGNORE_ENABLE - For ftrace internal events, do not enable with debugfs file
 245  *  WAS_ENABLED   - Set and stays set when an event was ever enabled
 246  *                    (used for module unloading, if a module event is enabled,
 247  *                     it is best to clear the buffers that used it).
 248  *  USE_CALL_FILTER - For ftrace internal events, don't use file filter
 249  *  TRACEPOINT    - Event is a tracepoint
 250  */
 251 enum {
 252         TRACE_EVENT_FL_FILTERED         = (1 << TRACE_EVENT_FL_FILTERED_BIT),
 253         TRACE_EVENT_FL_CAP_ANY          = (1 << TRACE_EVENT_FL_CAP_ANY_BIT),
 254         TRACE_EVENT_FL_NO_SET_FILTER    = (1 << TRACE_EVENT_FL_NO_SET_FILTER_BIT),
 255         TRACE_EVENT_FL_IGNORE_ENABLE    = (1 << TRACE_EVENT_FL_IGNORE_ENABLE_BIT),
 256         TRACE_EVENT_FL_WAS_ENABLED      = (1 << TRACE_EVENT_FL_WAS_ENABLED_BIT),
 257         TRACE_EVENT_FL_USE_CALL_FILTER  = (1 << TRACE_EVENT_FL_USE_CALL_FILTER_BIT),
 258         TRACE_EVENT_FL_TRACEPOINT       = (1 << TRACE_EVENT_FL_TRACEPOINT_BIT),
 259 };
 260
 261 struct ftrace_event_call {
 262         struct list_head        list;
 263         struct ftrace_event_class *class;
 264         union {
 265                 char                    *name;
 266                 /* Set TRACE_EVENT_FL_TRACEPOINT flag when using "tp" */
 267                 struct tracepoint       *tp;
 268         };
 269         struct trace_event      event;
 270         const char              *print_fmt;
 271         struct event_filter     *filter;
 272         struct list_head        *files;
 273         void                    *mod;
 274         void                    *data;
 275         /*
 276          *   bit 0:             filter_active
 277          *   bit 1:             allow trace by non root (cap any)
 278          *   bit 2:             failed to apply filter
 279          *   bit 3:             ftrace internal event (do not enable)
 280          *   bit 4:             Event was enabled by module
 281          *   bit 5:             use call filter rather than file filter
 282          *   bit 6:             Event is a tracepoint
 283          */
 284         int                     flags; /* static flags of different events */
 285
 286 #ifdef CONFIG_PERF_EVENTS
 287         int                             perf_refcount;
 288         struct hlist_head __percpu      *perf_events;
 289
 290         int     (*perf_perm)(struct ftrace_event_call *,
 291                              struct perf_event *);
 292 #endif
 293 };
 294
 295 static inline const char *
 296 ftrace_event_name(struct ftrace_event_call *call)
 297 {
 298         if (call->flags & TRACE_EVENT_FL_TRACEPOINT)
 299                 return call->tp ? call->tp->name : NULL;
 300         else
 301                 return call->name;
 302 }
 303
 304 struct trace_array;
 305 struct ftrace_subsystem_dir;
 306
 307 enum {
 308         FTRACE_EVENT_FL_ENABLED_BIT,
 309         FTRACE_EVENT_FL_RECORDED_CMD_BIT,
 310         FTRACE_EVENT_FL_FILTERED_BIT,
 311         FTRACE_EVENT_FL_NO_SET_FILTER_BIT,
 312         FTRACE_EVENT_FL_SOFT_MODE_BIT,
 313         FTRACE_EVENT_FL_SOFT_DISABLED_BIT,
 314         FTRACE_EVENT_FL_TRIGGER_MODE_BIT,
 315         FTRACE_EVENT_FL_TRIGGER_COND_BIT,
 316 };
 317
 318 /*
 319  * Ftrace event file flags:
 320  *  ENABLED       - The event is enabled
 321  *  RECORDED_CMD  - The comms should be recorded at sched_switch
 322  *  FILTERED      - The event has a filter attached
 323  *  NO_SET_FILTER - Set when filter has error and is to be ignored
 324  *  SOFT_MODE     - The event is enabled/disabled by SOFT_DISABLED
 325  *  SOFT_DISABLED - When set, do not trace the event (even though its
 326  *                   tracepoint may be enabled)
 327  *  TRIGGER_MODE  - When set, invoke the triggers associated with the event
 328  *  TRIGGER_COND  - When set, one or more triggers has an associated filter
 329  */
 330 enum {
 331         FTRACE_EVENT_FL_ENABLED         = (1 << FTRACE_EVENT_FL_ENABLED_BIT),
 332         FTRACE_EVENT_FL_RECORDED_CMD    = (1 << FTRACE_EVENT_FL_RECORDED_CMD_BIT),
 333         FTRACE_EVENT_FL_FILTERED        = (1 << FTRACE_EVENT_FL_FILTERED_BIT),
 334         FTRACE_EVENT_FL_NO_SET_FILTER   = (1 << FTRACE_EVENT_FL_NO_SET_FILTER_BIT),
 335         FTRACE_EVENT_FL_SOFT_MODE       = (1 << FTRACE_EVENT_FL_SOFT_MODE_BIT),
 336         FTRACE_EVENT_FL_SOFT_DISABLED   = (1 << FTRACE_EVENT_FL_SOFT_DISABLED_BIT),
 337         FTRACE_EVENT_FL_TRIGGER_MODE    = (1 << FTRACE_EVENT_FL_TRIGGER_MODE_BIT),
 338         FTRACE_EVENT_FL_TRIGGER_COND    = (1 << FTRACE_EVENT_FL_TRIGGER_COND_BIT),
 339 };
 340
 341 struct ftrace_event_file {
 342         struct list_head                list;
 343         struct ftrace_event_call        *event_call;
 344         struct event_filter             *filter;
 345         struct dentry                   *dir;
 346         struct trace_array              *tr;
 347         struct ftrace_subsystem_dir     *system;
 348         struct list_head                triggers;
 349
 350         /*
 351          * 32 bit flags:
 352          *   bit 0:             enabled
 353          *   bit 1:             enabled cmd record
 354          *   bit 2:             enable/disable with the soft disable bit
 355          *   bit 3:             soft disabled
 356          *   bit 4:             trigger enabled
 357          *
 358          * Note: The bits must be set atomically to prevent races
 359          * from other writers. Reads of flags do not need to be in
 360          * sync as they occur in critical sections. But the way flags
 361          * is currently used, these changes do not affect the code
 362          * except that when a change is made, it may have a slight
 363          * delay in propagating the changes to other CPUs due to
 364          * caching and such. Which is mostly OK ;-)
 365          */
 366         unsigned long           flags;
 367         atomic_t                sm_ref; /* soft-mode reference counter */
 368         atomic_t                tm_ref; /* trigger-mode reference counter */
 369 };
 370
 371 #define __TRACE_EVENT_FLAGS(name, value)                                \
 372         static int __init trace_init_flags_##name(void)                 \
 373         {                                                               \
 374                 event_##name.flags |= value;                            \
 375                 return 0;                                               \
 376         }                                                               \
 377         early_initcall(trace_init_flags_##name);
 378
 379 #define __TRACE_EVENT_PERF_PERM(name, expr...)                          \
 380         static int perf_perm_##name(struct ftrace_event_call *tp_event, \
 381                                     struct perf_event *p_event)         \
 382         {                                                               \
 383                 return ({ expr; });                                     \
 384         }                                                               \
 385         static int __init trace_init_perf_perm_##name(void)             \
 386         {                                                               \
 387                 event_##name.perf_perm = &perf_perm_##name;             \
 388                 return 0;                                               \
 389         }                                                               \
 390         early_initcall(trace_init_perf_perm_##name);
 391
 392 #define PERF_MAX_TRACE_SIZE     2048
 393
 394 #define MAX_FILTER_STR_VAL      256     /* Should handle KSYM_SYMBOL_LEN */
 395
 396 enum event_trigger_type {
 397         ETT_NONE                = (0),
 398         ETT_TRACE_ONOFF         = (1 << 0),
 399         ETT_SNAPSHOT            = (1 << 1),
 400         ETT_STACKTRACE          = (1 << 2),
 401         ETT_EVENT_ENABLE        = (1 << 3),
 402 };
 403
 404 extern void destroy_preds(struct ftrace_event_file *file);
 405 extern void destroy_call_preds(struct ftrace_event_call *call);
 406 extern int filter_match_preds(struct event_filter *filter, void *rec);
 407
 408 extern int filter_check_discard(struct ftrace_event_file *file, void *rec,
 409                                 struct ring_buffer *buffer,
 410                                 struct ring_buffer_event *event);
 411 extern int call_filter_check_discard(struct ftrace_event_call *call, void *rec,
 412                                      struct ring_buffer *buffer,
 413                                      struct ring_buffer_event *event);
 414 extern enum event_trigger_type event_triggers_call(struct ftrace_event_file *file,
 415                                                    void *rec);
 416 extern void event_triggers_post_call(struct ftrace_event_file *file,
 417                                      enum event_trigger_type tt);
 418
 419 /**
 420  * ftrace_trigger_soft_disabled - do triggers and test if soft disabled
 421  * @file: The file pointer of the event to test
 422  *
 423  * If any triggers without filters are attached to this event, they
 424  * will be called here. If the event is soft disabled and has no
 425  * triggers that require testing the fields, it will return true,
 426  * otherwise false.
 427  */
 428 static inline bool
 429 ftrace_trigger_soft_disabled(struct ftrace_event_file *file)
 430 {
 431         unsigned long eflags = file->flags;
 432
 433         if (!(eflags & FTRACE_EVENT_FL_TRIGGER_COND)) {
 434                 if (eflags & FTRACE_EVENT_FL_TRIGGER_MODE)
 435                         event_triggers_call(file, NULL);
 436                 if (eflags & FTRACE_EVENT_FL_SOFT_DISABLED)
 437                         return true;
 438         }
 439         return false;
 440 }
 441
 442 /*
 443  * Helper function for event_trigger_unlock_commit{_regs}().
 444  * If there are event triggers attached to this event that requires
 445  * filtering against its fields, then they wil be called as the
 446  * entry already holds the field information of the current event.
 447  *
 448  * It also checks if the event should be discarded or not.
 449  * It is to be discarded if the event is soft disabled and the
 450  * event was only recorded to process triggers, or if the event
 451  * filter is active and this event did not match the filters.
 452  *
 453  * Returns true if the event is discarded, false otherwise.
 454  */
 455 static inline bool
 456 __event_trigger_test_discard(struct ftrace_event_file *file,
 457                              struct ring_buffer *buffer,
 458                              struct ring_buffer_event *event,
 459                              void *entry,
 460                              enum event_trigger_type *tt)
 461 {
 462         unsigned long eflags = file->flags;
 463
 464         if (eflags & FTRACE_EVENT_FL_TRIGGER_COND)
 465                 *tt = event_triggers_call(file, entry);
 466
 467         if (test_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, &file->flags))
 468                 ring_buffer_discard_commit(buffer, event);
 469         else if (!filter_check_discard(file, entry, buffer, event))
 470                 return false;
 471
 472         return true;
 473 }
 474
 475 /**
 476  * event_trigger_unlock_commit - handle triggers and finish event commit
 477  * @file: The file pointer assoctiated to the event
 478  * @buffer: The ring buffer that the event is being written to
 479  * @event: The event meta data in the ring buffer
 480  * @entry: The event itself
 481  * @irq_flags: The state of the interrupts at the start of the event
 482  * @pc: The state of the preempt count at the start of the event.
 483  *
 484  * This is a helper function to handle triggers that require data
 485  * from the event itself. It also tests the event against filters and
 486  * if the event is soft disabled and should be discarded.
 487  */
 488 static inline void
 489 event_trigger_unlock_commit(struct ftrace_event_file *file,
 490                             struct ring_buffer *buffer,
 491                             struct ring_buffer_event *event,
 492                             void *entry, unsigned long irq_flags, int pc)
 493 {
 494         enum event_trigger_type tt = ETT_NONE;
 495
 496         if (!__event_trigger_test_discard(file, buffer, event, entry, &tt))
 497                 trace_buffer_unlock_commit(buffer, event, irq_flags, pc);
 498
 499         if (tt)
 500                 event_triggers_post_call(file, tt);
 501 }
 502
 503 /**
 504  * event_trigger_unlock_commit_regs - handle triggers and finish event commit
 505  * @file: The file pointer assoctiated to the event
 506  * @buffer: The ring buffer that the event is being written to
 507  * @event: The event meta data in the ring buffer
 508  * @entry: The event itself
 509  * @irq_flags: The state of the interrupts at the start of the event
 510  * @pc: The state of the preempt count at the start of the event.
 511  *
 512  * This is a helper function to handle triggers that require data
 513  * from the event itself. It also tests the event against filters and
 514  * if the event is soft disabled and should be discarded.
 515  *
 516  * Same as event_trigger_unlock_commit() but calls
 517  * trace_buffer_unlock_commit_regs() instead of trace_buffer_unlock_commit().
 518  */
 519 static inline void
 520 event_trigger_unlock_commit_regs(struct ftrace_event_file *file,
 521                                  struct ring_buffer *buffer,
 522                                  struct ring_buffer_event *event,
 523                                  void *entry, unsigned long irq_flags, int pc,
 524                                  struct pt_regs *regs)
 525 {
 526         enum event_trigger_type tt = ETT_NONE;
 527
 528         if (!__event_trigger_test_discard(file, buffer, event, entry, &tt))
 529                 trace_buffer_unlock_commit_regs(buffer, event,
 530                                                 irq_flags, pc, regs);
 531
 532         if (tt)
 533                 event_triggers_post_call(file, tt);
 534 }
 535
 536 enum {
 537         FILTER_OTHER = 0,
 538         FILTER_STATIC_STRING,
 539         FILTER_DYN_STRING,
 540         FILTER_PTR_STRING,
 541         FILTER_TRACE_FN,
 542 };
 543
 544 extern int trace_event_raw_init(struct ftrace_event_call *call);
 545 extern int trace_define_field(struct ftrace_event_call *call, const char *type,
 546                               const char *name, int offset, int size,
 547                               int is_signed, int filter_type);
 548 extern int trace_add_event_call(struct ftrace_event_call *call);
 549 extern int trace_remove_event_call(struct ftrace_event_call *call);
 550
 551 #define is_signed_type(type)    (((type)(-1)) < (type)1)
 552
 553 int trace_set_clr_event(const char *system, const char *event, int set);
 554
 555 /*
 556  * The double __builtin_constant_p is because gcc will give us an error
 557  * if we try to allocate the static variable to fmt if it is not a
 558  * constant. Even with the outer if statement optimizing out.
 559  */
 560 #define event_trace_printk(ip, fmt, args...)                            \
 561 do {                                                                    \
 562         __trace_printk_check_format(fmt, ##args);                       \
 563         tracing_record_cmdline(current);                                \
 564         if (__builtin_constant_p(fmt)) {                                \
 565                 static const char *trace_printk_fmt                     \
 566                   __attribute__((section("__trace_printk_fmt"))) =      \
 567                         __builtin_constant_p(fmt) ? fmt : NULL;         \
 568                                                                         \
 569                 __trace_bprintk(ip, trace_printk_fmt, ##args);          \
 570         } else                                                          \
 571                 __trace_printk(ip, fmt, ##args);                        \
 572 } while (0)
 573
 574 /**
 575  * tracepoint_string - register constant persistent string to trace system
 576  * @str - a constant persistent string that will be referenced in tracepoints
 577  *
 578  * If constant strings are being used in tracepoints, it is faster and
 579  * more efficient to just save the pointer to the string and reference
 580  * that with a printf "%s" instead of saving the string in the ring buffer
 581  * and wasting space and time.
 582  *
 583  * The problem with the above approach is that userspace tools that read
 584  * the binary output of the trace buffers do not have access to the string.
 585  * Instead they just show the address of the string which is not very
 586  * useful to users.
 587  *
 588  * With tracepoint_string(), the string will be registered to the tracing
 589  * system and exported to userspace via the debugfs/tracing/printk_formats
 590  * file that maps the string address to the string text. This way userspace
 591  * tools that read the binary buffers have a way to map the pointers to
 592  * the ASCII strings they represent.
 593  *
 594  * The @str used must be a constant string and persistent as it would not
 595  * make sense to show a string that no longer exists. But it is still fine
 596  * to be used with modules, because when modules are unloaded, if they
 597  * had tracepoints, the ring buffers are cleared too. As long as the string
 598  * does not change during the life of the module, it is fine to use
 599  * tracepoint_string() within a module.
 600  */
 601 #define tracepoint_string(str)                                          \
 602         ({                                                              \
 603                 static const char *___tp_str __tracepoint_string = str; \
 604                 ___tp_str;                                              \
 605         })
 606 #define __tracepoint_string     __attribute__((section("__tracepoint_str")))
 607
 608 #ifdef CONFIG_PERF_EVENTS
 609 struct perf_event;
 610
 611 DECLARE_PER_CPU(struct pt_regs, perf_trace_regs);
 612
 613 extern int  perf_trace_init(struct perf_event *event);
 614 extern void perf_trace_destroy(struct perf_event *event);
 615 extern int  perf_trace_add(struct perf_event *event, int flags);
 616 extern void perf_trace_del(struct perf_event *event, int flags);
 617 extern int  ftrace_profile_set_filter(struct perf_event *event, int event_id,
 618                                      char *filter_str);
 619 extern void ftrace_profile_free_filter(struct perf_event *event);
 620 extern void *perf_trace_buf_prepare(int size, unsigned short type,
 621                                     struct pt_regs *regs, int *rctxp);
 622
 623 static inline void
 624 perf_trace_buf_submit(void *raw_data, int size, int rctx, u64 addr,
 625                        u64 count, struct pt_regs *regs, void *head,
 626                        struct task_struct *task)
 627 {
 628         perf_tp_event(addr, count, raw_data, size, regs, head, rctx, task);
 629 }
 630 #endif
 631
 632 #endif /* _LINUX_FTRACE_EVENT_H */