the request type (see below; 'type'), a 64 bit handle ('handle'), a 64
bit data offset ('from'), and a 32 bit length ('len'). In case of a
write request, the header is immediately followed by 'len' bytes of
-data.
+data. In the case of NBD_CMD_FLUSH, the offset and length are
+ignored.
The reply contains three fields: a 32 bit magic number ('magic'), a 32
bit error code ('error'; 0, unless an error occurred in which case it is