How to detect CD loss?

[Russell Cook]

I'v got a '386 running SCO Xenix 2.3.1 (kid=5.34).  I'm connecting a serial
device which acts one heck of a lot like a modem.  That is, when the
device drops CD, I need to know about it so I can take the appropriate
action.  (That's just like uucp does it.)

The problem is that I never seem to get the CD loss notification.  I've tried
ports with and without modem control (in conjunction with and without
CLOCAL in my ioctl() call).  SCO sent me some source code that said the
most common mistake is to not use setpgrp() so I tried that just before
opening the port.  It didn't help.

Does anyone have a code snippet they can provide me that shows how to open
a port, configure it with ioctl() and then get notified when CD is lost?
I'd be satisfied with a setup that returns -1 on a read()/write() of the
port when CD is gone.

BTW, I trap ALL signals and receive nothing when CD is lost.