Merge branch 'i7300_idle' into release
[linux-2.6] / 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