> ...but you still need some smarts in the `dial in' program.  It will
> wake up when the dial-out program establishes {fake, real} carrier, so
> it needs to know things like how to find UUCP-style lock files and honor
> them by ignoring the serial line until it can acquire the lock file.
> Likewise, dial-out programs must obtain the lock before opening and
> manipulating the serial line.

Right on both counts.  These problems are cleanly solved
*and* none of the old programs break if allowing-dialin-or-
dialout-based-on-a-minor-number-bit hack is added to the com
driver(s).  I have never understood why this hack is
considered so bad.  If you don't use it, it is completely
harmless and allows use of the standard POSIX behavior for
those who want to use it.