How to transfer file descriptors with UNIX domain sockets?

[Guy Harris]

>I'm sure that it *can* be done - my question is what was it in Oliver
>Laumann's code that informed the kernel that what was in the message was a
>file descriptor?

It was

    msg.msg_accrights = (caddr_t)&fd;
    msg.msg_accrightslen = sizeof (fd);

I.e., the "access rights" in a message sent down a UNIX-domain socket
are, by definition, file descriptors....