> Well, yeah, every port that wants to support bidirectional serial lines.

  Seems like a good kernel configuration option to me.

> > How do you do neat stuff like recognizing fax vs voice vs data?
> 
> I thought the modems handled that.

  The modem does that, and then says "CONNECT FAX" or something. How
does the "getty" know not to say "login:" in that case? The reality is
that tty devices have gotten a bit long in the tooth.

> This amounts to making mgetty a (user-land) part of the terminal
> driver, as I assume you realize.  I'm not sure how I feel about
> layering a user-land process on top of the kernel tty driver.  It
> hadn't occurred to me as a possibility.

  Neither am I. I prefer to keep it in userland. I'd even be willing to throw all
of the line discipline stuff away and have a "getty" process that 
read characters and fed them into a pty if cooked mode is useful. 
  E.g. optimize the RS-232 TTY driver to do PPP, FAX and maybe UUCP.
Let interactive login (which is getting rarer) be the exceptional
case.