openfd request behaves like open, except that it prepares and returns
a Unix file descriptor corresponding to the opened fid.
After a successful
fid is considered by the client to have been clunked
and can be reused.
The returned Unix file descriptor is one end of a Unix pipe.
A proxy process at the other end transfers data between
the pipe and the 9P server.
Because it is a pipe, errors on reads and writes are discarded
mode must be
OWRITE; it cannot be
Openfd is implemented by
9P servers that post their services using
(or indirectly via
will never see a