libbpf: Add ring__size

Add ring__size to get the total size of a given ringbuffer.

Signed-off-by: Martin Kelly <martin.kelly@crowdstrike.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230925215045.2375758-10-martin.kelly@crowdstrike.com

src/libbpf.h

@@ -1293,6 +1293,16 @@ LIBBPF_API unsigned long ring__producer_pos(const struct ring *r);
  */
 LIBBPF_API size_t ring__avail_data_size(const struct ring *r);
 
+/**
+ * @brief **ring__size()** returns the total size of the ringbuffer's map data
+ * area (excluding special producer/consumer pages). Effectively this gives the
+ * amount of usable bytes of data inside the ringbuffer.
+ *
+ * @param r A ringbuffer object.
+ * @return The total size of the ringbuffer map data area.
+ */
+LIBBPF_API size_t ring__size(const struct ring *r);
+
 struct user_ring_buffer_opts {
 	size_t sz; /* size of this struct, for forward/backward compatibility */
 };