connld(7)

connld -- line discipline for unique stream connections

Description

connld is a STREAMS-based module that provides unique connections between server and client processes. It can only be pushed (see streamio(7)) onto one end of a STREAMS-based pipe that may subsequently be attached to a name in the file system name space. 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(7)) 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 the open(2) or creat(2) system call.

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) system calls will fail and return -1 to the originating process.

When the connld module is pushed onto a pipe, messages going back and forth through the pipe are ignored by connld.

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.

References

streamio(7)