- write message fid-value reply! error!procedure
This corresponds to a 9P Twrite request. The message is a list of three elements, the fid of the file, the offset to write to, and the data to write as a u8vector.
If the write succeeds, reply! should be called with a list of a single element, the number of bytes actually written.
If the write fails, error! should be called with a suitable error message.
The default implementation calls error! with a message stating that writing is not supported.