with the -s flag, we should read 9P messages from
standard *INPUT* (fd 0) and write responses to
standard *OUTPUT* (fd 1).
before these servers where reading from fd 1,
assuming they where both the same files.
when we get eof, stop the loop immidiately and do not
rely on the read to eventually return an error.
when convM2S() fails to decode the message, error out
and stop the loop. there is no point in continuing.
