wrstuden@loki.stanford.edu (Bill Studenmund) writes:

> 
> As an example, the mac port supports two types of crtscts flow
> control. The first is for modems, where we shut up when CTS says,
> and we use DTR to hang up the modem. The second is where we use CTS
> and DTR (in place of RTS) for handshaking. RTS is unavailable as it
> drives the transmit trancievers. 

I see absolutely no reason why it would make sense to sysctl(8) for
this.  If anything, you should create another tty flag, a la CRTSCTS.