perf record: Read from backward ring buffer

	return record__write(rec, event, event->header.size);

}

static int

backward_rb_find_range(void *buf, int mask, u64 head, u64 *start, u64 *end)

{

	struct perf_event_header *pheader;

	u64 evt_head = head;

	int size = mask + 1;

	pr_debug2("backward_rb_find_range: buf=%p, head=%"PRIx64"\n", buf, head);

	pheader = (struct perf_event_header *)(buf + (head & mask));

	*start = head;

	while (true) {

		if (evt_head - head >= (unsigned int)size) {

			pr_debug("Finshed reading backward ring buffer: rewind\n");

			if (evt_head - head > (unsigned int)size)

				evt_head -= pheader->size;

			*end = evt_head;

			return 0;

		}

		pheader = (struct perf_event_header *)(buf + (evt_head & mask));

		if (pheader->size == 0) {

			pr_debug("Finshed reading backward ring buffer: get start\n");

			*end = evt_head;

			return 0;

		}

		evt_head += pheader->size;

		pr_debug3("move evt_head: %"PRIx64"\n", evt_head);

	}

	WARN_ONCE(1, "Shouldn't get here\n");

	return -1;

}

static int

rb_find_range(struct perf_evlist *evlist,

	      void *data, int mask, u64 head, u64 old,

	      u64 *start, u64 *end)

{

	if (!evlist->backward) {

		*start = old;

		*end = head;

		return 0;

	}

	return backward_rb_find_range(data, mask, head, start, end);

}

static int record__mmap_read(struct record *rec, int idx)

{

	struct perf_mmap *md = &rec->evlist->mmap[idx];

	void *buf;

	int rc = 0;

	if (rb_find_range(rec->evlist, data, md->mask, head,

			  old, &start, &end))

		return -1;

	if (start == end)

		return 0;

	perf_evlist__set_maps(evlist, cpus, threads);

	fdarray__init(&evlist->pollfd, 64);

	evlist->workload.pid = -1;

	evlist->backward = false;

}

struct perf_evlist *perf_evlist__new(void)

	bool		 overwrite;

	bool		 enabled;

	bool		 has_user_cpus;

	bool		 backward;

	size_t		 mmap_len;

	int		 id_pos;

	int		 is_pos;