[PATCH V3 02/12] perf mmap: factor out function to find ringbuffer position

[kan . liang]

From: Kan Liang <kan.liang@xxxxxxxxx>

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@xxxxxxxxx>
---
 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