1.2 modem devices
IMHO we should change our comm packages for Debian 1.2 to use
/dev/ttyS* instead of /dev/cua*:
Theodore Y. Ts'o wrote:
> From owner-linux-net-outgoing@vger.rutgers.edu Tue May 14 02:34:03 1996
> Date: Mon, 13 May 1996 13:51:04 -0400
> Message-Id: <9605131751.AA13288@dcl.MIT.EDU>
> From: "Theodore Y. Ts'o" <tytso@mit.edu>
> To: Tony Nugent <tonyn@sctnugen.ppp.gu.edu.au>
> Cc: linux-net@vger.rutgers.edu, linux-ppp@vger.rutgers.edu
> In-Reply-To: Tony Nugent's message of Mon, 13 May 1996 07:57:09 +1000,
> <199605122157.HAA03287@sctnugen.ppp.gu.edu.au>
> Subject: Re: /dev/cua? Vs /dev/ttyS? (was: Re: co-existance of pppd and mgetty ?)
> Address: 1 Amherst St., Cambridge, MA 02139
> Phone: (617) 253-8091
> Sender: owner-linux-net@vger.rutgers.edu
> Precedence: bulk
>
> Date: Mon, 13 May 1996 07:57:09 +1000
> From: Tony Nugent <tonyn@sctnugen.ppp.gu.edu.au>
>
> Can someone kindly explain the difference between the /dev/cua? and
> /dev/ttyS? devices?
>
> /dev/ttySxx devices are fully POSIX-compliant TTY devices. If you are
> only going to be using one set of tty devices, you should be using
> /dev/ttySxx.
>
> /dev/cuaXX devices are different from /dev/ttySXX in two ways --- first
> of all, they will allow you to open the device even if CLOCAL is not set
> and the O_NONBLOCK flag was not given to the open device. This allows
> programs that don't use the POSIX-mondated interface for opening
> /dev/ttySxx devices to be able to use /dev/cuaXX to make outgoing phone
> calls on their modem (cu stands for "callout", and is taken from SunOS).
>
> The second way in which /dev/cuaXX differs from /dev/ttySXX is that if
> they are used, they will trigger a simplistic kernel-based locking
> scheme: If /dev/ttySXX is opened by one or more processes, then an
> attempt to open /dev/cuaXX will return EAGAIN. If /dev/cuaXX is opened
> by one or more processes, then an attempt to open /dev/ttySXX will
> result the open blocking until /dev/cuaXX is closed, and the carrier
> detect line goes high.
>
> While this will allow for simple lockouts between a user using a modem
> for callout and a getty listening on the line for logins, it doesn't
> work if you need to arbitrate between multiple programs wanting to do
> dialout --- for example, users wanting to do dialout and UUCP.
>
> I originally implemented the cuaXX/ttySXX lockout mechanism back before
> FSSTND established a standard convention for the use of tty lock files.
> Now that it's there, people should use the tty lock files and not try
> using /dev/cuaXX. The only reason why /dev/cuaXX hasn't disappeared yet
> is for backwards compatibility reasons.
>
> - Ted
>
>
Thanks,
Peter
--
Peter Tobias EMail:
Fachhochschule Ostfriesland tobias@et-inf.fho-emden.de
Fachbereich Elektrotechnik und Informatik tobias@debian.org
Constantiaplatz 4, 26723 Emden, Germany tobias@linux.de
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