man/man4m/connld.4m

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 CONNLD 4M "June 19, 2021"
 NAME
connld - line discipline for unique stream connections
 SYNOPSIS
int ioctl(fd, I_PUSH, "connld");


 DESCRIPTION
connld is a STREAMS-based module that provides unique connections between
server and client processes. It can only be pushed (see streamio(4I))
onto one end of a STREAMS-based pipe that may subsequently be attached to a
name in the file system name space with fattach(3C). After the pipe end
is attached, a new pipe is created internally when an originating process
attempts to open(2) or creat(2) the file system name. A file
descriptor for one end of the new pipe is packaged into a message identical to
that for the ioctl I_SENDFD (see streamio(4I)) and is transmitted
along the stream to the server process on the other end. The originating
process is blocked until the server responds.

The server responds to the I_SENDFD request by accepting the file
descriptor through the I_RECVFD ioctl message. When this happens, the
file descriptor associated with the other end of the new pipe is transmitted to
the originating process as the file descriptor returned from open(2) or
creat(2).

If the server does not respond to the I_SENDFD request, the stream that
the connld module is pushed on becomes uni-directional because the server
will not be able to retrieve any data off the stream until the I_RECVFD
request is issued. If the server process exits before issuing the
I_RECVFD request, the open(2) or the creat(2) invocation will
fail and return -1 to the originating process.

When the connld module is pushed onto a pipe, it ignores messages going
back and forth through the pipe.
 ERRORS
On success, an open of connld returns 0. On failure, errno is set
to the following values:
EINVAL

A stream onto which connld is being pushed is not a pipe or the pipe does
not have a write queue pointer pointing to a stream head read queue.


EINVAL

The other end of the pipe onto which connld is being pushed is linked
under a multiplexor.


EPIPE

connld is being pushed onto a pipe end whose other end is no longer
there.


ENOMEM

An internal pipe could not be created.


ENXIO

An M_HANGUP message is at the stream head of the pipe onto which
connld is being pushed.


EAGAIN

Internal data structures could not be allocated.


ENFILE

A file table entry could not be allocated.


 SEE ALSO
 creat (2),  open (2),  fattach (3C),  streamio (4I)
STREAMS Programming Guide