+#define LTT_MAGIC_NUMBER 0x00D6B7ED
+#define LTT_REV_MAGIC_NUMBER 0xEDB7D600
+
+/* Returns the size of a subbuffer size. This is the size that
+ * will need to be written to disk.
+ *
+ * @subbuffer: pointer to the beginning of the subbuffer (the
+ * beginning of its header)
+ */
+
+size_t subbuffer_data_size(void *subbuf)
+{
+ struct ltt_subbuffer_header *header = subbuf;
+ int reverse;
+ u32 data_size;
+
+ if(header->magic_number == LTT_MAGIC_NUMBER) {
+ reverse = 0;
+ }
+ else if(header->magic_number == LTT_REV_MAGIC_NUMBER) {
+ reverse = 1;
+ }
+ else {
+ return -1;
+ }
+
+ data_size = header->sb_size;
+ if(reverse)
+ data_size = bswap_32(data_size);
+
+ return data_size;
+}
+
+