From mboxrd@z Thu Jan  1 00:00:00 1970
From: rudi.j.blom@gmail.com (Rudi Blom)
Date: Tue, 7 Mar 2017 11:16:56 +0700
Subject: [TUHS] communication files: interprocess IO before pipes
Message-ID: <CAMYpm87_dNaDL4kqjzxroffigpoS9L4+yZcaMsCrfKiHr0YgJQ@mail.gmail.com>

On SCO UNIX 3.2V4 pipes where simulated as follows

	int fd[2]
	struct strfdinsert	ins;

	/*
	 * First open the stream clone device "/dev/spx" twice,
	 * obtaining the two file descriptors.
	 */
	if ( (fd[0] = open(SPX_DEVICE, O_RDWR)) < 0)
	{
		gen_trace(gtr_flag, "-gen_pipe(): -open(fd[0]): %s\n", strerror(errno));
		break;
	}
	if ( (fd[1] = open(SPX_DEVICE, O_RDWR)) < 0)
	{
		gen_trace(gtr_flag, ">gen_pipe(): -open(fd[1]): %s\n", strerror(errno));
		close(fd[0]);
		break;
	}

	/*
	 * Now link these two streams together with an
	 * I_FDINSERT ioctl.
	 */
	ins.ctlbuf.buf     = (char *) &pointer; /* no ctl info, just the ptr */
	ins.ctlbuf.maxlen  = sizeof(queue_t *);
	ins.ctlbuf.len     = sizeof(queue_t *);
	ins.databuf.buf    = (char *) 0;        /* no data to send */
	ins.databuf.len    = -1; /* magic: must be -1, not 0, for stream pipe */
	ins.databuf.maxlen = 0;
	ins.fildes = fd[1];     /* the fd to connect with fd[0] */
	ins.flags  = 0;         /* nonpriority message */
	ins.offset = 0;         /* offset of pointer in control buffer */

	if (ioctl(fd[0], I_FDINSERT, (char * ) &ins) < 0)
	{
		gen_trace(gtr_flag, ">gen_pipe(): -ioctl(I_FDINSERT): %s\n", strerror(errno));
		close(fd[0]);
		close(fd[1]);
		break;
	}

	/*
	 * reset close_on_exec flag
	 */
	gen_trace(gtr_flag, ">gen_pipe(): +fcntl()\n");
	if ((rc = fcntl(fd[0], F_SETFD, 0)) == -1)
		gen_trace(gtr_flag, ">gen_pipe(): -fcntl(fd0, close_on_exec): %s\n",
			strerror(errno));
	if ((rc = fcntl(fd[1], F_SETFD, 0)) == -1)
		gen_trace(gtr_flag, ">gen_pipe(): -fcntl(fd1, close_on_exec): %s\n",
			strerror(errno));
	rc = 0;
	break;