-#define NBD_REQUEST_SIZE (4 + 2 + 2 + 8 + 8 + 4)
-#define NBD_REPLY_SIZE (4 + 4 + 8)
-#define NBD_REQUEST_MAGIC 0x25609513
-#define NBD_REPLY_MAGIC 0x67446698
-#define NBD_OPTS_MAGIC 0x49484156454F5054LL
-#define NBD_CLIENT_MAGIC 0x0000420281861253LL
-#define NBD_REP_MAGIC 0x0003e889045565a9LL
-
-#define NBD_SET_SOCK _IO(0xab, 0)
-#define NBD_SET_BLKSIZE _IO(0xab, 1)
-#define NBD_SET_SIZE _IO(0xab, 2)
-#define NBD_DO_IT _IO(0xab, 3)
-#define NBD_CLEAR_SOCK _IO(0xab, 4)
-#define NBD_CLEAR_QUE _IO(0xab, 5)
-#define NBD_PRINT_DEBUG _IO(0xab, 6)
-#define NBD_SET_SIZE_BLOCKS _IO(0xab, 7)
-#define NBD_DISCONNECT _IO(0xab, 8)
-#define NBD_SET_TIMEOUT _IO(0xab, 9)
-#define NBD_SET_FLAGS _IO(0xab, 10)
-
-#define NBD_OPT_EXPORT_NAME (1)
-#define NBD_OPT_ABORT (2)
-#define NBD_OPT_LIST (3)
-#define NBD_OPT_PEEK_EXPORT (4)
-#define NBD_OPT_STARTTLS (5)
-
-/* NBD errors are based on errno numbers, so there is a 1:1 mapping,
- * but only a limited set of errno values is specified in the protocol.
- * Everything else is squashed to EINVAL.
+/* Size of all NBD_OPT_*, without payload */
+#define NBD_REQUEST_SIZE (4 + 2 + 2 + 8 + 8 + 4)
+/* Size of all NBD_REP_* sent in answer to most NBD_OPT_*, without payload */
+#define NBD_REPLY_SIZE (4 + 4 + 8)
+/* Size of reply to NBD_OPT_EXPORT_NAME */
+#define NBD_REPLY_EXPORT_NAME_SIZE (8 + 2 + 124)
+/* Size of oldstyle negotiation */
+#define NBD_OLDSTYLE_NEGOTIATE_SIZE (8 + 8 + 8 + 4 + 124)
+
+#define NBD_INIT_MAGIC 0x4e42444d41474943LL /* ASCII "NBDMAGIC" */
+#define NBD_REQUEST_MAGIC 0x25609513
+#define NBD_OPTS_MAGIC 0x49484156454F5054LL /* ASCII "IHAVEOPT" */
+#define NBD_CLIENT_MAGIC 0x0000420281861253LL
+#define NBD_REP_MAGIC 0x0003e889045565a9LL
+
+#define NBD_SET_SOCK _IO(0xab, 0)
+#define NBD_SET_BLKSIZE _IO(0xab, 1)
+#define NBD_SET_SIZE _IO(0xab, 2)
+#define NBD_DO_IT _IO(0xab, 3)
+#define NBD_CLEAR_SOCK _IO(0xab, 4)
+#define NBD_CLEAR_QUE _IO(0xab, 5)
+#define NBD_PRINT_DEBUG _IO(0xab, 6)
+#define NBD_SET_SIZE_BLOCKS _IO(0xab, 7)
+#define NBD_DISCONNECT _IO(0xab, 8)
+#define NBD_SET_TIMEOUT _IO(0xab, 9)
+#define NBD_SET_FLAGS _IO(0xab, 10)
+
+/* nbd_write
+ * Writes @size bytes to @ioc. Returns 0 on success.