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Subject[PATCH V3 02/12] perf mmap: factor out function to find ringbuffer position
Date
From: Kan Liang <kan.liang@intel.com>

The perf record has specific codes to calculate the ringbuffer position
for both overwrite and non-overwrite mode.
The perf top will support both modes later.
It is useful to make the specific codes generic.

Introduce a new interface perf_mmap__read_init() to find ringbuffer
position.
Add a check for map->refcnt in perf_mmap__read_init().
'size' is needed for both perf_mmap__read_init() and perf_mmap__push().
Have to calculate in each function.

Signed-off-by: Kan Liang <kan.liang@intel.com>
---
tools/perf/util/mmap.c | 62 ++++++++++++++++++++++++++++++++++----------------
tools/perf/util/mmap.h | 2 ++
2 files changed, 45 insertions(+), 19 deletions(-)

diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
index 05076e6..3fd4f3c 100644
--- a/tools/perf/util/mmap.c
+++ b/tools/perf/util/mmap.c
@@ -267,41 +267,65 @@ static int overwrite_rb_find_range(void *buf, int mask, u64 head, u64 *start, u6
return -1;
}

-int perf_mmap__push(struct perf_mmap *md, bool overwrite,
- void *to, int push(void *to, void *buf, size_t size))
+/*
+ * Report the start and end of the available data in ringbuffer
+ */
+int perf_mmap__read_init(struct perf_mmap *map, bool overwrite,
+ u64 *start, u64 *end)
{
- u64 head = perf_mmap__read_head(md);
- u64 old = md->prev;
- u64 end = head, start = old;
- unsigned char *data = md->base + page_size;
+ u64 head = perf_mmap__read_head(map);
+ u64 old = map->prev;
+ unsigned char *data = map->base + page_size;
unsigned long size;
- void *buf;
- int rc = 0;

- start = overwrite ? head : old;
- end = overwrite ? old : head;
+ /*
+ * Check if event was unmapped due to a POLLHUP/POLLERR.
+ */
+ if (!refcount_read(&map->refcnt))
+ return -EINVAL;

- if (start == end)
- return 0;
+ *start = overwrite ? head : old;
+ *end = overwrite ? old : head;

- size = end - start;
- if (size > (unsigned long)(md->mask) + 1) {
+ if (*start == *end)
+ return -EAGAIN;
+
+ size = *end - *start;
+ if (size > (unsigned long)(map->mask) + 1) {
if (!overwrite) {
WARN_ONCE(1, "failed to keep up with mmap data. (warn only once)\n");

- md->prev = head;
- perf_mmap__consume(md, overwrite);
- return 0;
+ map->prev = head;
+ perf_mmap__consume(map, overwrite);
+ return -EAGAIN;
}

/*
* Backward ring buffer is full. We still have a chance to read
* most of data from it.
*/
- if (overwrite_rb_find_range(data, md->mask, head, &start, &end))
- return -1;
+ if (overwrite_rb_find_range(data, map->mask, head, start, end))
+ return -EINVAL;
}

+ return 0;
+}
+
+int perf_mmap__push(struct perf_mmap *md, bool overwrite,
+ void *to, int push(void *to, void *buf, size_t size))
+{
+ u64 head = perf_mmap__read_head(md);
+ u64 end, start;
+ unsigned char *data = md->base + page_size;
+ unsigned long size;
+ void *buf;
+ int rc;
+
+ rc = perf_mmap__read_init(md, overwrite, &start, &end);
+ if (rc < 0)
+ return (rc == -EAGAIN) ? 0 : -1;
+
+ size = end - start;
if ((start & md->mask) + size != (end & md->mask)) {
buf = &data[start & md->mask];
size = md->mask + 1 - (start & md->mask);
diff --git a/tools/perf/util/mmap.h b/tools/perf/util/mmap.h
index d640273..abe9b9f 100644
--- a/tools/perf/util/mmap.h
+++ b/tools/perf/util/mmap.h
@@ -94,4 +94,6 @@ int perf_mmap__push(struct perf_mmap *md, bool backward,

size_t perf_mmap__mmap_len(struct perf_mmap *map);

+int perf_mmap__read_init(struct perf_mmap *map, bool overwrite,
+ u64 *start, u64 *end);
#endif /*__PERF_MMAP_H */
--
2.5.5
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