-#define RELAY_GET_N_SUBBUFS _IOR(0xF5, 0x02,__u32)
-/* returns the size of the sub buffers. */
-#define RELAY_GET_SUBBUF_SIZE _IOR(0xF5, 0x03,__u32)
+#define RELAY_GET_N_SB _IOR(0xF5, 0x02,__u32)
+/* returns the size of the current sub buffer. */
+#define RELAY_GET_SB_SIZE _IOR(0xF5, 0x03, __u32)
+/* returns the size of data to consume in the current sub-buffer. */
+#define RELAY_GET_MAX_SB_SIZE _IOR(0xF5, 0x04, __u32)
+