kernel/trace/ring_buffer.c

   1 /*
   2  * Generic ring buffer
   3  *
   4  * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
   5  */
   6 #include <linux/ring_buffer.h>
   7 #include <linux/spinlock.h>
   8 #include <linux/debugfs.h>
   9 #include <linux/uaccess.h>
  10 #include <linux/module.h>
  11 #include <linux/percpu.h>
  12 #include <linux/mutex.h>
  13 #include <linux/sched.h>        /* used for sched_clock() (for now) */
  14 #include <linux/init.h>
  15 #include <linux/hash.h>
  16 #include <linux/list.h>
  17 #include <linux/fs.h>
  18
  19 /* Up this if you want to test the TIME_EXTENTS and normalization */
  20 #define DEBUG_SHIFT 0
  21
  22 /* FIXME!!! */
  23 u64 ring_buffer_time_stamp(int cpu)
  24 {
  25         /* shift to debug/test normalization and TIME_EXTENTS */
  26         return sched_clock() << DEBUG_SHIFT;
  27 }
  28
  29 void ring_buffer_normalize_time_stamp(int cpu, u64 *ts)
  30 {
  31         /* Just stupid testing the normalize function and deltas */
  32         *ts >>= DEBUG_SHIFT;
  33 }
  34
  35 #define RB_EVNT_HDR_SIZE (sizeof(struct ring_buffer_event))
  36 #define RB_ALIGNMENT_SHIFT      2
  37 #define RB_ALIGNMENT            (1 << RB_ALIGNMENT_SHIFT)
  38 #define RB_MAX_SMALL_DATA       28
  39
  40 enum {
  41         RB_LEN_TIME_EXTEND = 8,
  42         RB_LEN_TIME_STAMP = 16,
  43 };
  44
  45 /* inline for ring buffer fast paths */
  46 static inline unsigned
  47 rb_event_length(struct ring_buffer_event *event)
  48 {
  49         unsigned length;
  50
  51         switch (event->type) {
  52         case RINGBUF_TYPE_PADDING:
  53                 /* undefined */
  54                 return -1;
  55
  56         case RINGBUF_TYPE_TIME_EXTEND:
  57                 return RB_LEN_TIME_EXTEND;
  58
  59         case RINGBUF_TYPE_TIME_STAMP:
  60                 return RB_LEN_TIME_STAMP;
  61
  62         case RINGBUF_TYPE_DATA:
  63                 if (event->len)
  64                         length = event->len << RB_ALIGNMENT_SHIFT;
  65                 else
  66                         length = event->array[0];
  67                 return length + RB_EVNT_HDR_SIZE;
  68         default:
  69                 BUG();
  70         }
  71         /* not hit */
  72         return 0;
  73 }
  74
  75 /**
  76  * ring_buffer_event_length - return the length of the event
  77  * @event: the event to get the length of
  78  */
  79 unsigned ring_buffer_event_length(struct ring_buffer_event *event)
  80 {
  81         return rb_event_length(event);
  82 }
  83
  84 /* inline for ring buffer fast paths */
  85 static inline void *
  86 rb_event_data(struct ring_buffer_event *event)
  87 {
  88         BUG_ON(event->type != RINGBUF_TYPE_DATA);
  89         /* If length is in len field, then array[0] has the data */
  90         if (event->len)
  91                 return (void *)&event->array[0];
  92         /* Otherwise length is in array[0] and array[1] has the data */
  93         return (void *)&event->array[1];
  94 }
  95
  96 /**
  97  * ring_buffer_event_data - return the data of the event
  98  * @event: the event to get the data from
  99  */
 100 void *ring_buffer_event_data(struct ring_buffer_event *event)
 101 {
 102         return rb_event_data(event);
 103 }
 104
 105 #define for_each_buffer_cpu(buffer, cpu)                \
 106         for_each_cpu_mask(cpu, buffer->cpumask)
 107
 108 #define TS_SHIFT        27
 109 #define TS_MASK         ((1ULL << TS_SHIFT) - 1)
 110 #define TS_DELTA_TEST   (~TS_MASK)
 111
 112 /*
 113  * This hack stolen from mm/slob.c.
 114  * We can store per page timing information in the page frame of the page.
 115  * Thanks to Peter Zijlstra for suggesting this idea.
 116  */
 117 struct buffer_page {
 118         u64              time_stamp;    /* page time stamp */
 119         local_t          write;         /* index for next write */
 120         local_t          commit;        /* write commited index */
 121         unsigned         read;          /* index for next read */
 122         struct list_head list;          /* list of free pages */
 123         void *page;                     /* Actual data page */
 124 };
 125
 126 /*
 127  * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
 128  * this issue out.
 129  */
 130 static inline void free_buffer_page(struct buffer_page *bpage)
 131 {
 132         if (bpage->page)
 133                 __free_page(bpage->page);
 134         kfree(bpage);
 135 }
 136
 137 /*
 138  * We need to fit the time_stamp delta into 27 bits.
 139  */
 140 static inline int test_time_stamp(u64 delta)
 141 {
 142         if (delta & TS_DELTA_TEST)
 143                 return 1;
 144         return 0;
 145 }
 146
 147 #define BUF_PAGE_SIZE PAGE_SIZE
 148
 149 /*
 150  * head_page == tail_page && head == tail then buffer is empty.
 151  */
 152 struct ring_buffer_per_cpu {
 153         int                             cpu;
 154         struct ring_buffer              *buffer;
 155         spinlock_t                      lock;
 156         struct lock_class_key           lock_key;
 157         struct list_head                pages;
 158         struct buffer_page              *head_page;     /* read from head */
 159         struct buffer_page              *tail_page;     /* write to tail */
 160         struct buffer_page              *commit_page;   /* commited pages */
 161         struct buffer_page              *reader_page;
 162         unsigned long                   overrun;
 163         unsigned long                   entries;
 164         u64                             write_stamp;
 165         u64                             read_stamp;
 166         atomic_t                        record_disabled;
 167 };
 168
 169 struct ring_buffer {
 170         unsigned long                   size;
 171         unsigned                        pages;
 172         unsigned                        flags;
 173         int                             cpus;
 174         cpumask_t                       cpumask;
 175         atomic_t                        record_disabled;
 176
 177         struct mutex                    mutex;
 178
 179         struct ring_buffer_per_cpu      **buffers;
 180 };
 181
 182 struct ring_buffer_iter {
 183         struct ring_buffer_per_cpu      *cpu_buffer;
 184         unsigned long                   head;
 185         struct buffer_page              *head_page;
 186         u64                             read_stamp;
 187 };
 188
 189 #define RB_WARN_ON(buffer, cond)                                \
 190         do {                                                    \
 191                 if (unlikely(cond)) {                           \
 192                         atomic_inc(&buffer->record_disabled);   \
 193                         WARN_ON(1);                             \
 194                 }                                               \
 195         } while (0)
 196
 197 #define RB_WARN_ON_RET(buffer, cond)                            \
 198         do {                                                    \
 199                 if (unlikely(cond)) {                           \
 200                         atomic_inc(&buffer->record_disabled);   \
 201                         WARN_ON(1);                             \
 202                         return -1;                              \
 203                 }                                               \
 204         } while (0)
 205
 206 #define RB_WARN_ON_ONCE(buffer, cond)                           \
 207         do {                                                    \
 208                 static int once;                                \
 209                 if (unlikely(cond) && !once) {                  \
 210                         once++;                                 \
 211                         atomic_inc(&buffer->record_disabled);   \
 212                         WARN_ON(1);                             \
 213                 }                                               \
 214         } while (0)
 215
 216 /**
 217  * check_pages - integrity check of buffer pages
 218  * @cpu_buffer: CPU buffer with pages to test
 219  *
 220  * As a safty measure we check to make sure the data pages have not
 221  * been corrupted.
 222  */
 223 static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
 224 {
 225         struct list_head *head = &cpu_buffer->pages;
 226         struct buffer_page *page, *tmp;
 227
 228         RB_WARN_ON_RET(cpu_buffer, head->next->prev != head);
 229         RB_WARN_ON_RET(cpu_buffer, head->prev->next != head);
 230
 231         list_for_each_entry_safe(page, tmp, head, list) {
 232                 RB_WARN_ON_RET(cpu_buffer,
 233                                page->list.next->prev != &page->list);
 234                 RB_WARN_ON_RET(cpu_buffer,
 235                                page->list.prev->next != &page->list);
 236         }
 237
 238         return 0;
 239 }
 240
 241 static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 242                              unsigned nr_pages)
 243 {
 244         struct list_head *head = &cpu_buffer->pages;
 245         struct buffer_page *page, *tmp;
 246         unsigned long addr;
 247         LIST_HEAD(pages);
 248         unsigned i;
 249
 250         for (i = 0; i < nr_pages; i++) {
 251                 page = kzalloc_node(ALIGN(sizeof(*page), cache_line_size()),
 252                                     GFP_KERNEL, cpu_to_node(cpu_buffer->cpu));
 253                 if (!page)
 254                         goto free_pages;
 255                 list_add(&page->list, &pages);
 256
 257                 addr = __get_free_page(GFP_KERNEL);
 258                 if (!addr)
 259                         goto free_pages;
 260                 page->page = (void *)addr;
 261         }
 262
 263         list_splice(&pages, head);
 264
 265         rb_check_pages(cpu_buffer);
 266
 267         return 0;
 268
 269  free_pages:
 270         list_for_each_entry_safe(page, tmp, &pages, list) {
 271                 list_del_init(&page->list);
 272                 free_buffer_page(page);
 273         }
 274         return -ENOMEM;
 275 }
 276
 277 static struct ring_buffer_per_cpu *
 278 rb_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu)
 279 {
 280         struct ring_buffer_per_cpu *cpu_buffer;
 281         struct buffer_page *page;
 282         unsigned long addr;
 283         int ret;
 284
 285         cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
 286                                   GFP_KERNEL, cpu_to_node(cpu));
 287         if (!cpu_buffer)
 288                 return NULL;
 289
 290         cpu_buffer->cpu = cpu;
 291         cpu_buffer->buffer = buffer;
 292         spin_lock_init(&cpu_buffer->lock);
 293         INIT_LIST_HEAD(&cpu_buffer->pages);
 294
 295         page = kzalloc_node(ALIGN(sizeof(*page), cache_line_size()),
 296                             GFP_KERNEL, cpu_to_node(cpu));
 297         if (!page)
 298                 goto fail_free_buffer;
 299
 300         cpu_buffer->reader_page = page;
 301         addr = __get_free_page(GFP_KERNEL);
 302         if (!addr)
 303                 goto fail_free_reader;
 304         page->page = (void *)addr;
 305
 306         INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
 307
 308         ret = rb_allocate_pages(cpu_buffer, buffer->pages);
 309         if (ret < 0)
 310                 goto fail_free_reader;
 311
 312         cpu_buffer->head_page
 313                 = list_entry(cpu_buffer->pages.next, struct buffer_page, list);
 314         cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
 315
 316         return cpu_buffer;
 317
 318  fail_free_reader:
 319         free_buffer_page(cpu_buffer->reader_page);
 320
 321  fail_free_buffer:
 322         kfree(cpu_buffer);
 323         return NULL;
 324 }
 325
 326 static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
 327 {
 328         struct list_head *head = &cpu_buffer->pages;
 329         struct buffer_page *page, *tmp;
 330
 331         list_del_init(&cpu_buffer->reader_page->list);
 332         free_buffer_page(cpu_buffer->reader_page);
 333
 334         list_for_each_entry_safe(page, tmp, head, list) {
 335                 list_del_init(&page->list);
 336                 free_buffer_page(page);
 337         }
 338         kfree(cpu_buffer);
 339 }
 340
 341 /*
 342  * Causes compile errors if the struct buffer_page gets bigger
 343  * than the struct page.
 344  */
 345 extern int ring_buffer_page_too_big(void);
 346
 347 /**
 348  * ring_buffer_alloc - allocate a new ring_buffer
 349  * @size: the size in bytes that is needed.
 350  * @flags: attributes to set for the ring buffer.
 351  *
 352  * Currently the only flag that is available is the RB_FL_OVERWRITE
 353  * flag. This flag means that the buffer will overwrite old data
 354  * when the buffer wraps. If this flag is not set, the buffer will
 355  * drop data when the tail hits the head.
 356  */
 357 struct ring_buffer *ring_buffer_alloc(unsigned long size, unsigned flags)
 358 {
 359         struct ring_buffer *buffer;
 360         int bsize;
 361         int cpu;
 362
 363         /* Paranoid! Optimizes out when all is well */
 364         if (sizeof(struct buffer_page) > sizeof(struct page))
 365                 ring_buffer_page_too_big();
 366
 367
 368         /* keep it in its own cache line */
 369         buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
 370                          GFP_KERNEL);
 371         if (!buffer)
 372                 return NULL;
 373
 374         buffer->pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
 375         buffer->flags = flags;
 376
 377         /* need at least two pages */
 378         if (buffer->pages == 1)
 379                 buffer->pages++;
 380
 381         buffer->cpumask = cpu_possible_map;
 382         buffer->cpus = nr_cpu_ids;
 383
 384         bsize = sizeof(void *) * nr_cpu_ids;
 385         buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()),
 386                                   GFP_KERNEL);
 387         if (!buffer->buffers)
 388                 goto fail_free_buffer;
 389
 390         for_each_buffer_cpu(buffer, cpu) {
 391                 buffer->buffers[cpu] =
 392                         rb_allocate_cpu_buffer(buffer, cpu);
 393                 if (!buffer->buffers[cpu])
 394                         goto fail_free_buffers;
 395         }
 396
 397         mutex_init(&buffer->mutex);
 398
 399         return buffer;
 400
 401  fail_free_buffers:
 402         for_each_buffer_cpu(buffer, cpu) {
 403                 if (buffer->buffers[cpu])
 404                         rb_free_cpu_buffer(buffer->buffers[cpu]);
 405         }
 406         kfree(buffer->buffers);
 407
 408  fail_free_buffer:
 409         kfree(buffer);
 410         return NULL;
 411 }
 412
 413 /**
 414  * ring_buffer_free - free a ring buffer.
 415  * @buffer: the buffer to free.
 416  */
 417 void
 418 ring_buffer_free(struct ring_buffer *buffer)
 419 {
 420         int cpu;
 421
 422         for_each_buffer_cpu(buffer, cpu)
 423                 rb_free_cpu_buffer(buffer->buffers[cpu]);
 424
 425         kfree(buffer);
 426 }
 427
 428 static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
 429
 430 static void
 431 rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages)
 432 {
 433         struct buffer_page *page;
 434         struct list_head *p;
 435         unsigned i;
 436
 437         atomic_inc(&cpu_buffer->record_disabled);
 438         synchronize_sched();
 439
 440         for (i = 0; i < nr_pages; i++) {
 441                 BUG_ON(list_empty(&cpu_buffer->pages));
 442                 p = cpu_buffer->pages.next;
 443                 page = list_entry(p, struct buffer_page, list);
 444                 list_del_init(&page->list);
 445                 free_buffer_page(page);
 446         }
 447         BUG_ON(list_empty(&cpu_buffer->pages));
 448
 449         rb_reset_cpu(cpu_buffer);
 450
 451         rb_check_pages(cpu_buffer);
 452
 453         atomic_dec(&cpu_buffer->record_disabled);
 454
 455 }
 456
 457 static void
 458 rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer,
 459                 struct list_head *pages, unsigned nr_pages)
 460 {
 461         struct buffer_page *page;
 462         struct list_head *p;
 463         unsigned i;
 464
 465         atomic_inc(&cpu_buffer->record_disabled);
 466         synchronize_sched();
 467
 468         for (i = 0; i < nr_pages; i++) {
 469                 BUG_ON(list_empty(pages));
 470                 p = pages->next;
 471                 page = list_entry(p, struct buffer_page, list);
 472                 list_del_init(&page->list);
 473                 list_add_tail(&page->list, &cpu_buffer->pages);
 474         }
 475         rb_reset_cpu(cpu_buffer);
 476
 477         rb_check_pages(cpu_buffer);
 478
 479         atomic_dec(&cpu_buffer->record_disabled);
 480 }
 481
 482 /**
 483  * ring_buffer_resize - resize the ring buffer
 484  * @buffer: the buffer to resize.
 485  * @size: the new size.
 486  *
 487  * The tracer is responsible for making sure that the buffer is
 488  * not being used while changing the size.
 489  * Note: We may be able to change the above requirement by using
 490  *  RCU synchronizations.
 491  *
 492  * Minimum size is 2 * BUF_PAGE_SIZE.
 493  *
 494  * Returns -1 on failure.
 495  */
 496 int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
 497 {
 498         struct ring_buffer_per_cpu *cpu_buffer;
 499         unsigned nr_pages, rm_pages, new_pages;
 500         struct buffer_page *page, *tmp;
 501         unsigned long buffer_size;
 502         unsigned long addr;
 503         LIST_HEAD(pages);
 504         int i, cpu;
 505
 506         size = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
 507         size *= BUF_PAGE_SIZE;
 508         buffer_size = buffer->pages * BUF_PAGE_SIZE;
 509
 510         /* we need a minimum of two pages */
 511         if (size < BUF_PAGE_SIZE * 2)
 512                 size = BUF_PAGE_SIZE * 2;
 513
 514         if (size == buffer_size)
 515                 return size;
 516
 517         mutex_lock(&buffer->mutex);
 518
 519         nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
 520
 521         if (size < buffer_size) {
 522
 523                 /* easy case, just free pages */
 524                 BUG_ON(nr_pages >= buffer->pages);
 525
 526                 rm_pages = buffer->pages - nr_pages;
 527
 528                 for_each_buffer_cpu(buffer, cpu) {
 529                         cpu_buffer = buffer->buffers[cpu];
 530                         rb_remove_pages(cpu_buffer, rm_pages);
 531                 }
 532                 goto out;
 533         }
 534
 535         /*
 536          * This is a bit more difficult. We only want to add pages
 537          * when we can allocate enough for all CPUs. We do this
 538          * by allocating all the pages and storing them on a local
 539          * link list. If we succeed in our allocation, then we
 540          * add these pages to the cpu_buffers. Otherwise we just free
 541          * them all and return -ENOMEM;
 542          */
 543         BUG_ON(nr_pages <= buffer->pages);
 544         new_pages = nr_pages - buffer->pages;
 545
 546         for_each_buffer_cpu(buffer, cpu) {
 547                 for (i = 0; i < new_pages; i++) {
 548                         page = kzalloc_node(ALIGN(sizeof(*page),
 549                                                   cache_line_size()),
 550                                             GFP_KERNEL, cpu_to_node(cpu));
 551                         if (!page)
 552                                 goto free_pages;
 553                         list_add(&page->list, &pages);
 554                         addr = __get_free_page(GFP_KERNEL);
 555                         if (!addr)
 556                                 goto free_pages;
 557                         page->page = (void *)addr;
 558                 }
 559         }
 560
 561         for_each_buffer_cpu(buffer, cpu) {
 562                 cpu_buffer = buffer->buffers[cpu];
 563                 rb_insert_pages(cpu_buffer, &pages, new_pages);
 564         }
 565
 566         BUG_ON(!list_empty(&pages));
 567
 568  out:
 569         buffer->pages = nr_pages;
 570         mutex_unlock(&buffer->mutex);
 571
 572         return size;
 573
 574  free_pages:
 575         list_for_each_entry_safe(page, tmp, &pages, list) {
 576                 list_del_init(&page->list);
 577                 free_buffer_page(page);
 578         }
 579         return -ENOMEM;
 580 }
 581
 582 static inline int rb_null_event(struct ring_buffer_event *event)
 583 {
 584         return event->type == RINGBUF_TYPE_PADDING;
 585 }
 586
 587 static inline void *__rb_page_index(struct buffer_page *page, unsigned index)
 588 {
 589         return page->page + index;
 590 }
 591
 592 static inline struct ring_buffer_event *
 593 rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
 594 {
 595         return __rb_page_index(cpu_buffer->reader_page,
 596                                cpu_buffer->reader_page->read);
 597 }
 598
 599 static inline struct ring_buffer_event *
 600 rb_head_event(struct ring_buffer_per_cpu *cpu_buffer)
 601 {
 602         return __rb_page_index(cpu_buffer->head_page,
 603                                cpu_buffer->head_page->read);
 604 }
 605
 606 static inline struct ring_buffer_event *
 607 rb_iter_head_event(struct ring_buffer_iter *iter)
 608 {
 609         return __rb_page_index(iter->head_page, iter->head);
 610 }
 611
 612 static inline unsigned rb_page_write(struct buffer_page *bpage)
 613 {
 614         return local_read(&bpage->write);
 615 }
 616
 617 static inline unsigned rb_page_commit(struct buffer_page *bpage)
 618 {
 619         return local_read(&bpage->commit);
 620 }
 621
 622 /* Size is determined by what has been commited */
 623 static inline unsigned rb_page_size(struct buffer_page *bpage)
 624 {
 625         return rb_page_commit(bpage);
 626 }
 627
 628 static inline unsigned
 629 rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
 630 {
 631         return rb_page_commit(cpu_buffer->commit_page);
 632 }
 633
 634 static inline unsigned rb_head_size(struct ring_buffer_per_cpu *cpu_buffer)
 635 {
 636         return rb_page_commit(cpu_buffer->head_page);
 637 }
 638
 639 /*
 640  * When the tail hits the head and the buffer is in overwrite mode,
 641  * the head jumps to the next page and all content on the previous
 642  * page is discarded. But before doing so, we update the overrun
 643  * variable of the buffer.
 644  */
 645 static void rb_update_overflow(struct ring_buffer_per_cpu *cpu_buffer)
 646 {
 647         struct ring_buffer_event *event;
 648         unsigned long head;
 649
 650         for (head = 0; head < rb_head_size(cpu_buffer);
 651              head += rb_event_length(event)) {
 652
 653                 event = __rb_page_index(cpu_buffer->head_page, head);
 654                 BUG_ON(rb_null_event(event));
 655                 /* Only count data entries */
 656                 if (event->type != RINGBUF_TYPE_DATA)
 657                         continue;
 658                 cpu_buffer->overrun++;
 659                 cpu_buffer->entries--;
 660         }
 661 }
 662
 663 static inline void rb_inc_page(struct ring_buffer_per_cpu *cpu_buffer,
 664                                struct buffer_page **page)
 665 {
 666         struct list_head *p = (*page)->list.next;
 667
 668         if (p == &cpu_buffer->pages)
 669                 p = p->next;
 670
 671         *page = list_entry(p, struct buffer_page, list);
 672 }
 673
 674 static inline unsigned
 675 rb_event_index(struct ring_buffer_event *event)
 676 {
 677         unsigned long addr = (unsigned long)event;
 678
 679         return (addr & ~PAGE_MASK) - (PAGE_SIZE - BUF_PAGE_SIZE);
 680 }
 681
 682 static inline int
 683 rb_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
 684              struct ring_buffer_event *event)
 685 {
 686         unsigned long addr = (unsigned long)event;
 687         unsigned long index;
 688
 689         index = rb_event_index(event);
 690         addr &= PAGE_MASK;
 691
 692         return cpu_buffer->commit_page->page == (void *)addr &&
 693                 rb_commit_index(cpu_buffer) == index;
 694 }
 695
 696 static inline void
 697 rb_set_commit_event(struct ring_buffer_per_cpu *cpu_buffer,
 698                     struct ring_buffer_event *event)
 699 {
 700         unsigned long addr = (unsigned long)event;
 701         unsigned long index;
 702
 703         index = rb_event_index(event);
 704         addr &= PAGE_MASK;
 705
 706         while (cpu_buffer->commit_page->page != (void *)addr) {
 707                 RB_WARN_ON(cpu_buffer,
 708                            cpu_buffer->commit_page == cpu_buffer->tail_page);
 709                 cpu_buffer->commit_page->commit =
 710                         cpu_buffer->commit_page->write;
 711                 rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
 712                 cpu_buffer->write_stamp = cpu_buffer->commit_page->time_stamp;
 713         }
 714
 715         /* Now set the commit to the event's index */
 716         local_set(&cpu_buffer->commit_page->commit, index);
 717 }
 718
 719 static inline void
 720 rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
 721 {
 722         /*
 723          * We only race with interrupts and NMIs on this CPU.
 724          * If we own the commit event, then we can commit
 725          * all others that interrupted us, since the interruptions
 726          * are in stack format (they finish before they come
 727          * back to us). This allows us to do a simple loop to
 728          * assign the commit to the tail.
 729          */
 730         while (cpu_buffer->commit_page != cpu_buffer->tail_page) {
 731                 cpu_buffer->commit_page->commit =
 732                         cpu_buffer->commit_page->write;
 733                 rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
 734                 cpu_buffer->write_stamp = cpu_buffer->commit_page->time_stamp;
 735                 /* add barrier to keep gcc from optimizing too much */
 736                 barrier();
 737         }
 738         while (rb_commit_index(cpu_buffer) !=
 739                rb_page_write(cpu_buffer->commit_page)) {
 740                 cpu_buffer->commit_page->commit =
 741                         cpu_buffer->commit_page->write;
 742                 barrier();
 743         }
 744 }
 745
 746 static void rb_reset_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
 747 {
 748         cpu_buffer->read_stamp = cpu_buffer->reader_page->time_stamp;
 749         cpu_buffer->reader_page->read = 0;
 750 }
 751
 752 static inline void rb_inc_iter(struct ring_buffer_iter *iter)
 753 {
 754         struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
 755
 756         /*
 757          * The iterator could be on the reader page (it starts there).
 758          * But the head could have moved, since the reader was
 759          * found. Check for this case and assign the iterator
 760          * to the head page instead of next.
 761          */
 762         if (iter->head_page == cpu_buffer->reader_page)
 763                 iter->head_page = cpu_buffer->head_page;
 764         else
 765                 rb_inc_page(cpu_buffer, &iter->head_page);
 766
 767         iter->read_stamp = iter->head_page->time_stamp;
 768         iter->head = 0;
 769 }
 770
 771 /**
 772  * ring_buffer_update_event - update event type and data
 773  * @event: the even to update
 774  * @type: the type of event
 775  * @length: the size of the event field in the ring buffer
 776  *
 777  * Update the type and data fields of the event. The length
 778  * is the actual size that is written to the ring buffer,
 779  * and with this, we can determine what to place into the
 780  * data field.
 781  */
 782 static inline void
 783 rb_update_event(struct ring_buffer_event *event,
 784                          unsigned type, unsigned length)
 785 {
 786         event->type = type;
 787
 788         switch (type) {
 789
 790         case RINGBUF_TYPE_PADDING:
 791                 break;
 792
 793         case RINGBUF_TYPE_TIME_EXTEND:
 794                 event->len =
 795                         (RB_LEN_TIME_EXTEND + (RB_ALIGNMENT-1))
 796                         >> RB_ALIGNMENT_SHIFT;
 797                 break;
 798
 799         case RINGBUF_TYPE_TIME_STAMP:
 800                 event->len =
 801                         (RB_LEN_TIME_STAMP + (RB_ALIGNMENT-1))
 802                         >> RB_ALIGNMENT_SHIFT;
 803                 break;
 804
 805         case RINGBUF_TYPE_DATA:
 806                 length -= RB_EVNT_HDR_SIZE;
 807                 if (length > RB_MAX_SMALL_DATA) {
 808                         event->len = 0;
 809                         event->array[0] = length;
 810                 } else
 811                         event->len =
 812                                 (length + (RB_ALIGNMENT-1))
 813                                 >> RB_ALIGNMENT_SHIFT;
 814                 break;
 815         default:
 816                 BUG();
 817         }
 818 }
 819
 820 static inline unsigned rb_calculate_event_length(unsigned length)
 821 {
 822         struct ring_buffer_event event; /* Used only for sizeof array */
 823
 824         /* zero length can cause confusions */
 825         if (!length)
 826                 length = 1;
 827
 828         if (length > RB_MAX_SMALL_DATA)
 829                 length += sizeof(event.array[0]);
 830
 831         length += RB_EVNT_HDR_SIZE;
 832         length = ALIGN(length, RB_ALIGNMENT);
 833
 834         return length;
 835 }
 836
 837 static struct ring_buffer_event *
 838 __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
 839                   unsigned type, unsigned long length, u64 *ts)
 840 {
 841         struct buffer_page *tail_page, *head_page, *reader_page;
 842         unsigned long tail, write;
 843         struct ring_buffer *buffer = cpu_buffer->buffer;
 844         struct ring_buffer_event *event;
 845         unsigned long flags;
 846
 847         tail_page = cpu_buffer->tail_page;
 848         write = local_add_return(length, &tail_page->write);
 849         tail = write - length;
 850
 851         /* See if we shot pass the end of this buffer page */
 852         if (write > BUF_PAGE_SIZE) {
 853                 struct buffer_page *next_page = tail_page;
 854
 855                 spin_lock_irqsave(&cpu_buffer->lock, flags);
 856
 857                 rb_inc_page(cpu_buffer, &next_page);
 858
 859                 head_page = cpu_buffer->head_page;
 860                 reader_page = cpu_buffer->reader_page;
 861
 862                 /* we grabbed the lock before incrementing */
 863                 RB_WARN_ON(cpu_buffer, next_page == reader_page);
 864
 865                 /*
 866                  * If for some reason, we had an interrupt storm that made
 867                  * it all the way around the buffer, bail, and warn
 868                  * about it.
 869                  */
 870                 if (unlikely(next_page == cpu_buffer->commit_page)) {
 871                         WARN_ON_ONCE(1);
 872                         goto out_unlock;
 873                 }
 874
 875                 if (next_page == head_page) {
 876                         if (!(buffer->flags & RB_FL_OVERWRITE)) {
 877                                 /* reset write */
 878                                 if (tail <= BUF_PAGE_SIZE)
 879                                         local_set(&tail_page->write, tail);
 880                                 goto out_unlock;
 881                         }
 882
 883                         /* tail_page has not moved yet? */
 884                         if (tail_page == cpu_buffer->tail_page) {
 885                                 /* count overflows */
 886                                 rb_update_overflow(cpu_buffer);
 887
 888                                 rb_inc_page(cpu_buffer, &head_page);
 889                                 cpu_buffer->head_page = head_page;
 890                                 cpu_buffer->head_page->read = 0;
 891                         }
 892                 }
 893
 894                 /*
 895                  * If the tail page is still the same as what we think
 896                  * it is, then it is up to us to update the tail
 897                  * pointer.
 898                  */
 899                 if (tail_page == cpu_buffer->tail_page) {
 900                         local_set(&next_page->write, 0);
 901                         local_set(&next_page->commit, 0);
 902                         cpu_buffer->tail_page = next_page;
 903
 904                         /* reread the time stamp */
 905                         *ts = ring_buffer_time_stamp(cpu_buffer->cpu);
 906                         cpu_buffer->tail_page->time_stamp = *ts;
 907                 }
 908
 909                 /*
 910                  * The actual tail page has moved forward.
 911                  */
 912                 if (tail < BUF_PAGE_SIZE) {
 913                         /* Mark the rest of the page with padding */
 914                         event = __rb_page_index(tail_page, tail);
 915                         event->type = RINGBUF_TYPE_PADDING;
 916                 }
 917
 918                 if (tail <= BUF_PAGE_SIZE)
 919                         /* Set the write back to the previous setting */
 920                         local_set(&tail_page->write, tail);
 921
 922                 /*
 923                  * If this was a commit entry that failed,
 924                  * increment that too
 925                  */
 926                 if (tail_page == cpu_buffer->commit_page &&
 927                     tail == rb_commit_index(cpu_buffer)) {
 928                         rb_set_commit_to_write(cpu_buffer);
 929                 }
 930
 931                 spin_unlock_irqrestore(&cpu_buffer->lock, flags);
 932
 933                 /* fail and let the caller try again */
 934                 return ERR_PTR(-EAGAIN);
 935         }
 936
 937         /* We reserved something on the buffer */
 938
 939         BUG_ON(write > BUF_PAGE_SIZE);
 940
 941         event = __rb_page_index(tail_page, tail);
 942         rb_update_event(event, type, length);
 943
 944         /*
 945          * If this is a commit and the tail is zero, then update
 946          * this page's time stamp.
 947          */
 948         if (!tail && rb_is_commit(cpu_buffer, event))
 949                 cpu_buffer->commit_page->time_stamp = *ts;
 950
 951         return event;
 952
 953  out_unlock:
 954         spin_unlock_irqrestore(&cpu_buffer->lock, flags);
 955         return NULL;
 956 }
 957
 958 static int
 959 rb_add_time_stamp(struct ring_buffer_per_cpu *cpu_buffer,
 960                   u64 *ts, u64 *delta)
 961 {
 962         struct ring_buffer_event *event;
 963         static int once;
 964         int ret;
 965
 966         if (unlikely(*delta > (1ULL << 59) && !once++)) {
 967                 printk(KERN_WARNING "Delta way too big! %llu"
 968                        " ts=%llu write stamp = %llu\n",
 969                        *delta, *ts, cpu_buffer->write_stamp);
 970                 WARN_ON(1);
 971         }
 972
 973         /*
 974          * The delta is too big, we to add a
 975          * new timestamp.
 976          */
 977         event = __rb_reserve_next(cpu_buffer,
 978                                   RINGBUF_TYPE_TIME_EXTEND,
 979                                   RB_LEN_TIME_EXTEND,
 980                                   ts);
 981         if (!event)
 982                 return -EBUSY;
 983
 984         if (PTR_ERR(event) == -EAGAIN)
 985                 return -EAGAIN;
 986
 987         /* Only a commited time event can update the write stamp */
 988         if (rb_is_commit(cpu_buffer, event)) {
 989                 /*
 990                  * If this is the first on the page, then we need to
 991                  * update the page itself, and just put in a zero.
 992                  */
 993                 if (rb_event_index(event)) {
 994                         event->time_delta = *delta & TS_MASK;
 995                         event->array[0] = *delta >> TS_SHIFT;
 996                 } else {
 997                         cpu_buffer->commit_page->time_stamp = *ts;
 998                         event->time_delta = 0;
 999                         event->array[0] = 0;
1000                 }
1001                 cpu_buffer->write_stamp = *ts;
1002                 /* let the caller know this was the commit */
1003                 ret = 1;
1004         } else {
1005                 /* Darn, this is just wasted space */
1006                 event->time_delta = 0;
1007                 event->array[0] = 0;
1008                 ret = 0;
1009         }
1010
1011         *delta = 0;
1012
1013         return ret;
1014 }
1015
1016 static struct ring_buffer_event *
1017 rb_reserve_next_event(struct ring_buffer_per_cpu *cpu_buffer,
1018                       unsigned type, unsigned long length)
1019 {
1020         struct ring_buffer_event *event;
1021         u64 ts, delta;
1022         int commit = 0;
1023
1024  again:
1025         ts = ring_buffer_time_stamp(cpu_buffer->cpu);
1026
1027         /*
1028          * Only the first commit can update the timestamp.
1029          * Yes there is a race here. If an interrupt comes in
1030          * just after the conditional and it traces too, then it
1031          * will also check the deltas. More than one timestamp may
1032          * also be made. But only the entry that did the actual
1033          * commit will be something other than zero.
1034          */
1035         if (cpu_buffer->tail_page == cpu_buffer->commit_page &&
1036             rb_page_write(cpu_buffer->tail_page) ==
1037             rb_commit_index(cpu_buffer)) {
1038
1039                 delta = ts - cpu_buffer->write_stamp;
1040
1041                 /* make sure this delta is calculated here */
1042                 barrier();
1043
1044                 /* Did the write stamp get updated already? */
1045                 if (unlikely(ts < cpu_buffer->write_stamp))
1046                         goto again;
1047
1048                 if (test_time_stamp(delta)) {
1049
1050                         commit = rb_add_time_stamp(cpu_buffer, &ts, &delta);
1051
1052                         if (commit == -EBUSY)
1053                                 return NULL;
1054
1055                         if (commit == -EAGAIN)
1056                                 goto again;
1057
1058                         RB_WARN_ON(cpu_buffer, commit < 0);
1059                 }
1060         } else
1061                 /* Non commits have zero deltas */
1062                 delta = 0;
1063
1064         event = __rb_reserve_next(cpu_buffer, type, length, &ts);
1065         if (PTR_ERR(event) == -EAGAIN)
1066                 goto again;
1067
1068         if (!event) {
1069                 if (unlikely(commit))
1070                         /*
1071                          * Ouch! We needed a timestamp and it was commited. But
1072                          * we didn't get our event reserved.
1073                          */
1074                         rb_set_commit_to_write(cpu_buffer);
1075                 return NULL;
1076         }
1077
1078         /*
1079          * If the timestamp was commited, make the commit our entry
1080          * now so that we will update it when needed.
1081          */
1082         if (commit)
1083                 rb_set_commit_event(cpu_buffer, event);
1084         else if (!rb_is_commit(cpu_buffer, event))
1085                 delta = 0;
1086
1087         event->time_delta = delta;
1088
1089         return event;
1090 }
1091
1092 static DEFINE_PER_CPU(int, rb_need_resched);
1093
1094 /**
1095  * ring_buffer_lock_reserve - reserve a part of the buffer
1096  * @buffer: the ring buffer to reserve from
1097  * @length: the length of the data to reserve (excluding event header)
1098  * @flags: a pointer to save the interrupt flags
1099  *
1100  * Returns a reseverd event on the ring buffer to copy directly to.
1101  * The user of this interface will need to get the body to write into
1102  * and can use the ring_buffer_event_data() interface.
1103  *
1104  * The length is the length of the data needed, not the event length
1105  * which also includes the event header.
1106  *
1107  * Must be paired with ring_buffer_unlock_commit, unless NULL is returned.
1108  * If NULL is returned, then nothing has been allocated or locked.
1109  */
1110 struct ring_buffer_event *
1111 ring_buffer_lock_reserve(struct ring_buffer *buffer,
1112                          unsigned long length,
1113                          unsigned long *flags)
1114 {
1115         struct ring_buffer_per_cpu *cpu_buffer;
1116         struct ring_buffer_event *event;
1117         int cpu, resched;
1118
1119         if (atomic_read(&buffer->record_disabled))
1120                 return NULL;
1121
1122         /* If we are tracing schedule, we don't want to recurse */
1123         resched = need_resched();
1124         preempt_disable_notrace();
1125
1126         cpu = raw_smp_processor_id();
1127
1128         if (!cpu_isset(cpu, buffer->cpumask))
1129                 goto out;
1130
1131         cpu_buffer = buffer->buffers[cpu];
1132
1133         if (atomic_read(&cpu_buffer->record_disabled))
1134                 goto out;
1135
1136         length = rb_calculate_event_length(length);
1137         if (length > BUF_PAGE_SIZE)
1138                 goto out;
1139
1140         event = rb_reserve_next_event(cpu_buffer, RINGBUF_TYPE_DATA, length);
1141         if (!event)
1142                 goto out;
1143
1144         /*
1145          * Need to store resched state on this cpu.
1146          * Only the first needs to.
1147          */
1148
1149         if (preempt_count() == 1)
1150                 per_cpu(rb_need_resched, cpu) = resched;
1151
1152         return event;
1153
1154  out:
1155         if (resched)
1156                 preempt_enable_notrace();
1157         else
1158                 preempt_enable_notrace();
1159         return NULL;
1160 }
1161
1162 static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
1163                       struct ring_buffer_event *event)
1164 {
1165         cpu_buffer->entries++;
1166
1167         /* Only process further if we own the commit */
1168         if (!rb_is_commit(cpu_buffer, event))
1169                 return;
1170
1171         cpu_buffer->write_stamp += event->time_delta;
1172
1173         rb_set_commit_to_write(cpu_buffer);
1174 }
1175
1176 /**
1177  * ring_buffer_unlock_commit - commit a reserved
1178  * @buffer: The buffer to commit to
1179  * @event: The event pointer to commit.
1180  * @flags: the interrupt flags received from ring_buffer_lock_reserve.
1181  *
1182  * This commits the data to the ring buffer, and releases any locks held.
1183  *
1184  * Must be paired with ring_buffer_lock_reserve.
1185  */
1186 int ring_buffer_unlock_commit(struct ring_buffer *buffer,
1187                               struct ring_buffer_event *event,
1188                               unsigned long flags)
1189 {
1190         struct ring_buffer_per_cpu *cpu_buffer;
1191         int cpu = raw_smp_processor_id();
1192
1193         cpu_buffer = buffer->buffers[cpu];
1194
1195         rb_commit(cpu_buffer, event);
1196
1197         /*
1198          * Only the last preempt count needs to restore preemption.
1199          */
1200         if (preempt_count() == 1) {
1201                 if (per_cpu(rb_need_resched, cpu))
1202                         preempt_enable_no_resched_notrace();
1203                 else
1204                         preempt_enable_notrace();
1205         } else
1206                 preempt_enable_no_resched_notrace();
1207
1208         return 0;
1209 }
1210
1211 /**
1212  * ring_buffer_write - write data to the buffer without reserving
1213  * @buffer: The ring buffer to write to.
1214  * @length: The length of the data being written (excluding the event header)
1215  * @data: The data to write to the buffer.
1216  *
1217  * This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as
1218  * one function. If you already have the data to write to the buffer, it
1219  * may be easier to simply call this function.
1220  *
1221  * Note, like ring_buffer_lock_reserve, the length is the length of the data
1222  * and not the length of the event which would hold the header.
1223  */
1224 int ring_buffer_write(struct ring_buffer *buffer,
1225                         unsigned long length,
1226                         void *data)
1227 {
1228         struct ring_buffer_per_cpu *cpu_buffer;
1229         struct ring_buffer_event *event;
1230         unsigned long event_length;
1231         void *body;
1232         int ret = -EBUSY;
1233         int cpu, resched;
1234
1235         if (atomic_read(&buffer->record_disabled))
1236                 return -EBUSY;
1237
1238         resched = need_resched();
1239         preempt_disable_notrace();
1240
1241         cpu = raw_smp_processor_id();
1242
1243         if (!cpu_isset(cpu, buffer->cpumask))
1244                 goto out;
1245
1246         cpu_buffer = buffer->buffers[cpu];
1247
1248         if (atomic_read(&cpu_buffer->record_disabled))
1249                 goto out;
1250
1251         event_length = rb_calculate_event_length(length);
1252         event = rb_reserve_next_event(cpu_buffer,
1253                                       RINGBUF_TYPE_DATA, event_length);
1254         if (!event)
1255                 goto out;
1256
1257         body = rb_event_data(event);
1258
1259         memcpy(body, data, length);
1260
1261         rb_commit(cpu_buffer, event);
1262
1263         ret = 0;
1264  out:
1265         if (resched)
1266                 preempt_enable_no_resched_notrace();
1267         else
1268                 preempt_enable_notrace();
1269
1270         return ret;
1271 }
1272
1273 static inline int rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
1274 {
1275         struct buffer_page *reader = cpu_buffer->reader_page;
1276         struct buffer_page *head = cpu_buffer->head_page;
1277         struct buffer_page *commit = cpu_buffer->commit_page;
1278
1279         return reader->read == rb_page_commit(reader) &&
1280                 (commit == reader ||
1281                  (commit == head &&
1282                   head->read == rb_page_commit(commit)));
1283 }
1284
1285 /**
1286  * ring_buffer_record_disable - stop all writes into the buffer
1287  * @buffer: The ring buffer to stop writes to.
1288  *
1289  * This prevents all writes to the buffer. Any attempt to write
1290  * to the buffer after this will fail and return NULL.
1291  *
1292  * The caller should call synchronize_sched() after this.
1293  */
1294 void ring_buffer_record_disable(struct ring_buffer *buffer)
1295 {
1296         atomic_inc(&buffer->record_disabled);
1297 }
1298
1299 /**
1300  * ring_buffer_record_enable - enable writes to the buffer
1301  * @buffer: The ring buffer to enable writes
1302  *
1303  * Note, multiple disables will need the same number of enables
1304  * to truely enable the writing (much like preempt_disable).
1305  */
1306 void ring_buffer_record_enable(struct ring_buffer *buffer)
1307 {
1308         atomic_dec(&buffer->record_disabled);
1309 }
1310
1311 /**
1312  * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
1313  * @buffer: The ring buffer to stop writes to.
1314  * @cpu: The CPU buffer to stop
1315  *
1316  * This prevents all writes to the buffer. Any attempt to write
1317  * to the buffer after this will fail and return NULL.
1318  *
1319  * The caller should call synchronize_sched() after this.
1320  */
1321 void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu)
1322 {
1323         struct ring_buffer_per_cpu *cpu_buffer;
1324
1325         if (!cpu_isset(cpu, buffer->cpumask))
1326                 return;
1327
1328         cpu_buffer = buffer->buffers[cpu];
1329         atomic_inc(&cpu_buffer->record_disabled);
1330 }
1331
1332 /**
1333  * ring_buffer_record_enable_cpu - enable writes to the buffer
1334  * @buffer: The ring buffer to enable writes
1335  * @cpu: The CPU to enable.
1336  *
1337  * Note, multiple disables will need the same number of enables
1338  * to truely enable the writing (much like preempt_disable).
1339  */
1340 void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu)
1341 {
1342         struct ring_buffer_per_cpu *cpu_buffer;
1343
1344         if (!cpu_isset(cpu, buffer->cpumask))
1345                 return;
1346
1347         cpu_buffer = buffer->buffers[cpu];
1348         atomic_dec(&cpu_buffer->record_disabled);
1349 }
1350
1351 /**
1352  * ring_buffer_entries_cpu - get the number of entries in a cpu buffer
1353  * @buffer: The ring buffer
1354  * @cpu: The per CPU buffer to get the entries from.
1355  */
1356 unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
1357 {
1358         struct ring_buffer_per_cpu *cpu_buffer;
1359
1360         if (!cpu_isset(cpu, buffer->cpumask))
1361                 return 0;
1362
1363         cpu_buffer = buffer->buffers[cpu];
1364         return cpu_buffer->entries;
1365 }
1366
1367 /**
1368  * ring_buffer_overrun_cpu - get the number of overruns in a cpu_buffer
1369  * @buffer: The ring buffer
1370  * @cpu: The per CPU buffer to get the number of overruns from
1371  */
1372 unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
1373 {
1374         struct ring_buffer_per_cpu *cpu_buffer;
1375
1376         if (!cpu_isset(cpu, buffer->cpumask))
1377                 return 0;
1378
1379         cpu_buffer = buffer->buffers[cpu];
1380         return cpu_buffer->overrun;
1381 }
1382
1383 /**
1384  * ring_buffer_entries - get the number of entries in a buffer
1385  * @buffer: The ring buffer
1386  *
1387  * Returns the total number of entries in the ring buffer
1388  * (all CPU entries)
1389  */
1390 unsigned long ring_buffer_entries(struct ring_buffer *buffer)
1391 {
1392         struct ring_buffer_per_cpu *cpu_buffer;
1393         unsigned long entries = 0;
1394         int cpu;
1395
1396         /* if you care about this being correct, lock the buffer */
1397         for_each_buffer_cpu(buffer, cpu) {
1398                 cpu_buffer = buffer->buffers[cpu];
1399                 entries += cpu_buffer->entries;
1400         }
1401
1402         return entries;
1403 }
1404
1405 /**
1406  * ring_buffer_overrun_cpu - get the number of overruns in buffer
1407  * @buffer: The ring buffer
1408  *
1409  * Returns the total number of overruns in the ring buffer
1410  * (all CPU entries)
1411  */
1412 unsigned long ring_buffer_overruns(struct ring_buffer *buffer)
1413 {
1414         struct ring_buffer_per_cpu *cpu_buffer;
1415         unsigned long overruns = 0;
1416         int cpu;
1417
1418         /* if you care about this being correct, lock the buffer */
1419         for_each_buffer_cpu(buffer, cpu) {
1420                 cpu_buffer = buffer->buffers[cpu];
1421                 overruns += cpu_buffer->overrun;
1422         }
1423
1424         return overruns;
1425 }
1426
1427 /**
1428  * ring_buffer_iter_reset - reset an iterator
1429  * @iter: The iterator to reset
1430  *
1431  * Resets the iterator, so that it will start from the beginning
1432  * again.
1433  */
1434 void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
1435 {
1436         struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
1437
1438         /* Iterator usage is expected to have record disabled */
1439         if (list_empty(&cpu_buffer->reader_page->list)) {
1440                 iter->head_page = cpu_buffer->head_page;
1441                 iter->head = cpu_buffer->head_page->read;
1442         } else {
1443                 iter->head_page = cpu_buffer->reader_page;
1444                 iter->head = cpu_buffer->reader_page->read;
1445         }
1446         if (iter->head)
1447                 iter->read_stamp = cpu_buffer->read_stamp;
1448         else
1449                 iter->read_stamp = iter->head_page->time_stamp;
1450 }
1451
1452 /**
1453  * ring_buffer_iter_empty - check if an iterator has no more to read
1454  * @iter: The iterator to check
1455  */
1456 int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
1457 {
1458         struct ring_buffer_per_cpu *cpu_buffer;
1459
1460         cpu_buffer = iter->cpu_buffer;
1461
1462         return iter->head_page == cpu_buffer->commit_page &&
1463                 iter->head == rb_commit_index(cpu_buffer);
1464 }
1465
1466 static void
1467 rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
1468                      struct ring_buffer_event *event)
1469 {
1470         u64 delta;
1471
1472         switch (event->type) {
1473         case RINGBUF_TYPE_PADDING:
1474                 return;
1475
1476         case RINGBUF_TYPE_TIME_EXTEND:
1477                 delta = event->array[0];
1478                 delta <<= TS_SHIFT;
1479                 delta += event->time_delta;
1480                 cpu_buffer->read_stamp += delta;
1481                 return;
1482
1483         case RINGBUF_TYPE_TIME_STAMP:
1484                 /* FIXME: not implemented */
1485                 return;
1486
1487         case RINGBUF_TYPE_DATA:
1488                 cpu_buffer->read_stamp += event->time_delta;
1489                 return;
1490
1491         default:
1492                 BUG();
1493         }
1494         return;
1495 }
1496
1497 static void
1498 rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
1499                           struct ring_buffer_event *event)
1500 {
1501         u64 delta;
1502
1503         switch (event->type) {
1504         case RINGBUF_TYPE_PADDING:
1505                 return;
1506
1507         case RINGBUF_TYPE_TIME_EXTEND:
1508                 delta = event->array[0];
1509                 delta <<= TS_SHIFT;
1510                 delta += event->time_delta;
1511                 iter->read_stamp += delta;
1512                 return;
1513
1514         case RINGBUF_TYPE_TIME_STAMP:
1515                 /* FIXME: not implemented */
1516                 return;
1517
1518         case RINGBUF_TYPE_DATA:
1519                 iter->read_stamp += event->time_delta;
1520                 return;
1521
1522         default:
1523                 BUG();
1524         }
1525         return;
1526 }
1527
1528 static struct buffer_page *
1529 rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
1530 {
1531         struct buffer_page *reader = NULL;
1532         unsigned long flags;
1533
1534         spin_lock_irqsave(&cpu_buffer->lock, flags);
1535
1536  again:
1537         reader = cpu_buffer->reader_page;
1538
1539         /* If there's more to read, return this page */
1540         if (cpu_buffer->reader_page->read < rb_page_size(reader))
1541                 goto out;
1542
1543         /* Never should we have an index greater than the size */
1544         RB_WARN_ON(cpu_buffer,
1545                    cpu_buffer->reader_page->read > rb_page_size(reader));
1546
1547         /* check if we caught up to the tail */
1548         reader = NULL;
1549         if (cpu_buffer->commit_page == cpu_buffer->reader_page)
1550                 goto out;
1551
1552         /*
1553          * Splice the empty reader page into the list around the head.
1554          * Reset the reader page to size zero.
1555          */
1556
1557         reader = cpu_buffer->head_page;
1558         cpu_buffer->reader_page->list.next = reader->list.next;
1559         cpu_buffer->reader_page->list.prev = reader->list.prev;
1560
1561         local_set(&cpu_buffer->reader_page->write, 0);
1562         local_set(&cpu_buffer->reader_page->commit, 0);
1563
1564         /* Make the reader page now replace the head */
1565         reader->list.prev->next = &cpu_buffer->reader_page->list;
1566         reader->list.next->prev = &cpu_buffer->reader_page->list;
1567
1568         /*
1569          * If the tail is on the reader, then we must set the head
1570          * to the inserted page, otherwise we set it one before.
1571          */
1572         cpu_buffer->head_page = cpu_buffer->reader_page;
1573
1574         if (cpu_buffer->commit_page != reader)
1575                 rb_inc_page(cpu_buffer, &cpu_buffer->head_page);
1576
1577         /* Finally update the reader page to the new head */
1578         cpu_buffer->reader_page = reader;
1579         rb_reset_reader_page(cpu_buffer);
1580
1581         goto again;
1582
1583  out:
1584         spin_unlock_irqrestore(&cpu_buffer->lock, flags);
1585
1586         return reader;
1587 }
1588
1589 static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
1590 {
1591         struct ring_buffer_event *event;
1592         struct buffer_page *reader;
1593         unsigned length;
1594
1595         reader = rb_get_reader_page(cpu_buffer);
1596
1597         /* This function should not be called when buffer is empty */
1598         BUG_ON(!reader);
1599
1600         event = rb_reader_event(cpu_buffer);
1601
1602         if (event->type == RINGBUF_TYPE_DATA)
1603                 cpu_buffer->entries--;
1604
1605         rb_update_read_stamp(cpu_buffer, event);
1606
1607         length = rb_event_length(event);
1608         cpu_buffer->reader_page->read += length;
1609 }
1610
1611 static void rb_advance_iter(struct ring_buffer_iter *iter)
1612 {
1613         struct ring_buffer *buffer;
1614         struct ring_buffer_per_cpu *cpu_buffer;
1615         struct ring_buffer_event *event;
1616         unsigned length;
1617
1618         cpu_buffer = iter->cpu_buffer;
1619         buffer = cpu_buffer->buffer;
1620
1621         /*
1622          * Check if we are at the end of the buffer.
1623          */
1624         if (iter->head >= rb_page_size(iter->head_page)) {
1625                 BUG_ON(iter->head_page == cpu_buffer->commit_page);
1626                 rb_inc_iter(iter);
1627                 return;
1628         }
1629
1630         event = rb_iter_head_event(iter);
1631
1632         length = rb_event_length(event);
1633
1634         /*
1635          * This should not be called to advance the header if we are
1636          * at the tail of the buffer.
1637          */
1638         BUG_ON((iter->head_page == cpu_buffer->commit_page) &&
1639                (iter->head + length > rb_commit_index(cpu_buffer)));
1640
1641         rb_update_iter_read_stamp(iter, event);
1642
1643         iter->head += length;
1644
1645         /* check for end of page padding */
1646         if ((iter->head >= rb_page_size(iter->head_page)) &&
1647             (iter->head_page != cpu_buffer->commit_page))
1648                 rb_advance_iter(iter);
1649 }
1650
1651 /**
1652  * ring_buffer_peek - peek at the next event to be read
1653  * @buffer: The ring buffer to read
1654  * @cpu: The cpu to peak at
1655  * @ts: The timestamp counter of this event.
1656  *
1657  * This will return the event that will be read next, but does
1658  * not consume the data.
1659  */
1660 struct ring_buffer_event *
1661 ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
1662 {
1663         struct ring_buffer_per_cpu *cpu_buffer;
1664         struct ring_buffer_event *event;
1665         struct buffer_page *reader;
1666
1667         if (!cpu_isset(cpu, buffer->cpumask))
1668                 return NULL;
1669
1670         cpu_buffer = buffer->buffers[cpu];
1671
1672  again:
1673         reader = rb_get_reader_page(cpu_buffer);
1674         if (!reader)
1675                 return NULL;
1676
1677         event = rb_reader_event(cpu_buffer);
1678
1679         switch (event->type) {
1680         case RINGBUF_TYPE_PADDING:
1681                 RB_WARN_ON(cpu_buffer, 1);
1682                 rb_advance_reader(cpu_buffer);
1683                 return NULL;
1684
1685         case RINGBUF_TYPE_TIME_EXTEND:
1686                 /* Internal data, OK to advance */
1687                 rb_advance_reader(cpu_buffer);
1688                 goto again;
1689
1690         case RINGBUF_TYPE_TIME_STAMP:
1691                 /* FIXME: not implemented */
1692                 rb_advance_reader(cpu_buffer);
1693                 goto again;
1694
1695         case RINGBUF_TYPE_DATA:
1696                 if (ts) {
1697                         *ts = cpu_buffer->read_stamp + event->time_delta;
1698                         ring_buffer_normalize_time_stamp(cpu_buffer->cpu, ts);
1699                 }
1700                 return event;
1701
1702         default:
1703                 BUG();
1704         }
1705
1706         return NULL;
1707 }
1708
1709 /**
1710  * ring_buffer_iter_peek - peek at the next event to be read
1711  * @iter: The ring buffer iterator
1712  * @ts: The timestamp counter of this event.
1713  *
1714  * This will return the event that will be read next, but does
1715  * not increment the iterator.
1716  */
1717 struct ring_buffer_event *
1718 ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
1719 {
1720         struct ring_buffer *buffer;
1721         struct ring_buffer_per_cpu *cpu_buffer;
1722         struct ring_buffer_event *event;
1723
1724         if (ring_buffer_iter_empty(iter))
1725                 return NULL;
1726
1727         cpu_buffer = iter->cpu_buffer;
1728         buffer = cpu_buffer->buffer;
1729
1730  again:
1731         if (rb_per_cpu_empty(cpu_buffer))
1732                 return NULL;
1733
1734         event = rb_iter_head_event(iter);
1735
1736         switch (event->type) {
1737         case RINGBUF_TYPE_PADDING:
1738                 rb_inc_iter(iter);
1739                 goto again;
1740
1741         case RINGBUF_TYPE_TIME_EXTEND:
1742                 /* Internal data, OK to advance */
1743                 rb_advance_iter(iter);
1744                 goto again;
1745
1746         case RINGBUF_TYPE_TIME_STAMP:
1747                 /* FIXME: not implemented */
1748                 rb_advance_iter(iter);
1749                 goto again;
1750
1751         case RINGBUF_TYPE_DATA:
1752                 if (ts) {
1753                         *ts = iter->read_stamp + event->time_delta;
1754                         ring_buffer_normalize_time_stamp(cpu_buffer->cpu, ts);
1755                 }
1756                 return event;
1757
1758         default:
1759                 BUG();
1760         }
1761
1762         return NULL;
1763 }
1764
1765 /**
1766  * ring_buffer_consume - return an event and consume it
1767  * @buffer: The ring buffer to get the next event from
1768  *
1769  * Returns the next event in the ring buffer, and that event is consumed.
1770  * Meaning, that sequential reads will keep returning a different event,
1771  * and eventually empty the ring buffer if the producer is slower.
1772  */
1773 struct ring_buffer_event *
1774 ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts)
1775 {
1776         struct ring_buffer_per_cpu *cpu_buffer;
1777         struct ring_buffer_event *event;
1778
1779         if (!cpu_isset(cpu, buffer->cpumask))
1780                 return NULL;
1781
1782         event = ring_buffer_peek(buffer, cpu, ts);
1783         if (!event)
1784                 return NULL;
1785
1786         cpu_buffer = buffer->buffers[cpu];
1787         rb_advance_reader(cpu_buffer);
1788
1789         return event;
1790 }
1791
1792 /**
1793  * ring_buffer_read_start - start a non consuming read of the buffer
1794  * @buffer: The ring buffer to read from
1795  * @cpu: The cpu buffer to iterate over
1796  *
1797  * This starts up an iteration through the buffer. It also disables
1798  * the recording to the buffer until the reading is finished.
1799  * This prevents the reading from being corrupted. This is not
1800  * a consuming read, so a producer is not expected.
1801  *
1802  * Must be paired with ring_buffer_finish.
1803  */
1804 struct ring_buffer_iter *
1805 ring_buffer_read_start(struct ring_buffer *buffer, int cpu)
1806 {
1807         struct ring_buffer_per_cpu *cpu_buffer;
1808         struct ring_buffer_iter *iter;
1809         unsigned long flags;
1810
1811         if (!cpu_isset(cpu, buffer->cpumask))
1812                 return NULL;
1813
1814         iter = kmalloc(sizeof(*iter), GFP_KERNEL);
1815         if (!iter)
1816                 return NULL;
1817
1818         cpu_buffer = buffer->buffers[cpu];
1819
1820         iter->cpu_buffer = cpu_buffer;
1821
1822         atomic_inc(&cpu_buffer->record_disabled);
1823         synchronize_sched();
1824
1825         spin_lock_irqsave(&cpu_buffer->lock, flags);
1826         ring_buffer_iter_reset(iter);
1827         spin_unlock_irqrestore(&cpu_buffer->lock, flags);
1828
1829         return iter;
1830 }
1831
1832 /**
1833  * ring_buffer_finish - finish reading the iterator of the buffer
1834  * @iter: The iterator retrieved by ring_buffer_start
1835  *
1836  * This re-enables the recording to the buffer, and frees the
1837  * iterator.
1838  */
1839 void
1840 ring_buffer_read_finish(struct ring_buffer_iter *iter)
1841 {
1842         struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
1843
1844         atomic_dec(&cpu_buffer->record_disabled);
1845         kfree(iter);
1846 }
1847
1848 /**
1849  * ring_buffer_read - read the next item in the ring buffer by the iterator
1850  * @iter: The ring buffer iterator
1851  * @ts: The time stamp of the event read.
1852  *
1853  * This reads the next event in the ring buffer and increments the iterator.
1854  */
1855 struct ring_buffer_event *
1856 ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts)
1857 {
1858         struct ring_buffer_event *event;
1859
1860         event = ring_buffer_iter_peek(iter, ts);
1861         if (!event)
1862                 return NULL;
1863
1864         rb_advance_iter(iter);
1865
1866         return event;
1867 }
1868
1869 /**
1870  * ring_buffer_size - return the size of the ring buffer (in bytes)
1871  * @buffer: The ring buffer.
1872  */
1873 unsigned long ring_buffer_size(struct ring_buffer *buffer)
1874 {
1875         return BUF_PAGE_SIZE * buffer->pages;
1876 }
1877
1878 static void
1879 rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
1880 {
1881         cpu_buffer->head_page
1882                 = list_entry(cpu_buffer->pages.next, struct buffer_page, list);
1883         local_set(&cpu_buffer->head_page->write, 0);
1884         local_set(&cpu_buffer->head_page->commit, 0);
1885
1886         cpu_buffer->head_page->read = 0;
1887
1888         cpu_buffer->tail_page = cpu_buffer->head_page;
1889         cpu_buffer->commit_page = cpu_buffer->head_page;
1890
1891         INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
1892         local_set(&cpu_buffer->reader_page->write, 0);
1893         local_set(&cpu_buffer->reader_page->commit, 0);
1894         cpu_buffer->reader_page->read = 0;
1895
1896         cpu_buffer->overrun = 0;
1897         cpu_buffer->entries = 0;
1898 }
1899
1900 /**
1901  * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
1902  * @buffer: The ring buffer to reset a per cpu buffer of
1903  * @cpu: The CPU buffer to be reset
1904  */
1905 void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
1906 {
1907         struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
1908         unsigned long flags;
1909
1910         if (!cpu_isset(cpu, buffer->cpumask))
1911                 return;
1912
1913         spin_lock_irqsave(&cpu_buffer->lock, flags);
1914
1915         rb_reset_cpu(cpu_buffer);
1916
1917         spin_unlock_irqrestore(&cpu_buffer->lock, flags);
1918 }
1919
1920 /**
1921  * ring_buffer_reset - reset a ring buffer
1922  * @buffer: The ring buffer to reset all cpu buffers
1923  */
1924 void ring_buffer_reset(struct ring_buffer *buffer)
1925 {
1926         int cpu;
1927
1928         for_each_buffer_cpu(buffer, cpu)
1929                 ring_buffer_reset_cpu(buffer, cpu);
1930 }
1931
1932 /**
1933  * rind_buffer_empty - is the ring buffer empty?
1934  * @buffer: The ring buffer to test
1935  */
1936 int ring_buffer_empty(struct ring_buffer *buffer)
1937 {
1938         struct ring_buffer_per_cpu *cpu_buffer;
1939         int cpu;
1940
1941         /* yes this is racy, but if you don't like the race, lock the buffer */
1942         for_each_buffer_cpu(buffer, cpu) {
1943                 cpu_buffer = buffer->buffers[cpu];
1944                 if (!rb_per_cpu_empty(cpu_buffer))
1945                         return 0;
1946         }
1947         return 1;
1948 }
1949
1950 /**
1951  * ring_buffer_empty_cpu - is a cpu buffer of a ring buffer empty?
1952  * @buffer: The ring buffer
1953  * @cpu: The CPU buffer to test
1954  */
1955 int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
1956 {
1957         struct ring_buffer_per_cpu *cpu_buffer;
1958
1959         if (!cpu_isset(cpu, buffer->cpumask))
1960                 return 1;
1961
1962         cpu_buffer = buffer->buffers[cpu];
1963         return rb_per_cpu_empty(cpu_buffer);
1964 }
1965
1966 /**
1967  * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
1968  * @buffer_a: One buffer to swap with
1969  * @buffer_b: The other buffer to swap with
1970  *
1971  * This function is useful for tracers that want to take a "snapshot"
1972  * of a CPU buffer and has another back up buffer lying around.
1973  * it is expected that the tracer handles the cpu buffer not being
1974  * used at the moment.
1975  */
1976 int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
1977                          struct ring_buffer *buffer_b, int cpu)
1978 {
1979         struct ring_buffer_per_cpu *cpu_buffer_a;
1980         struct ring_buffer_per_cpu *cpu_buffer_b;
1981
1982         if (!cpu_isset(cpu, buffer_a->cpumask) ||
1983             !cpu_isset(cpu, buffer_b->cpumask))
1984                 return -EINVAL;
1985
1986         /* At least make sure the two buffers are somewhat the same */
1987         if (buffer_a->size != buffer_b->size ||
1988             buffer_a->pages != buffer_b->pages)
1989                 return -EINVAL;
1990
1991         cpu_buffer_a = buffer_a->buffers[cpu];
1992         cpu_buffer_b = buffer_b->buffers[cpu];
1993
1994         /*
1995          * We can't do a synchronize_sched here because this
1996          * function can be called in atomic context.
1997          * Normally this will be called from the same CPU as cpu.
1998          * If not it's up to the caller to protect this.
1999          */
2000         atomic_inc(&cpu_buffer_a->record_disabled);
2001         atomic_inc(&cpu_buffer_b->record_disabled);
2002
2003         buffer_a->buffers[cpu] = cpu_buffer_b;
2004         buffer_b->buffers[cpu] = cpu_buffer_a;
2005
2006         cpu_buffer_b->buffer = buffer_a;
2007         cpu_buffer_a->buffer = buffer_b;
2008
2009         atomic_dec(&cpu_buffer_a->record_disabled);
2010         atomic_dec(&cpu_buffer_b->record_disabled);
2011
2012         return 0;
2013 }
2014