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# $Id: debian.device,v 1.1 2000/02/21 03:52:51 jeff Exp $
This exchange of messages should help clarify the problem people have
been experiencing with diald. Bottom line: DO NOT USE /dev/cua? devices.
--
Date: Mon, 20 Nov 1995 15:05:32 EST
To: Jeffrey Ebert <jebert@ix.netcom.com>
cc: debian-user@Pixar.com, giuseppe@deselby.xs4all.nl,
linux-diald@vger.rutgers.edu
From: "Eric Schenk" <schenk@cs.toronto.edu>
Subject: Re: diald and pppd problems
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Jeffrey Ebert <jebert@ix.netcom.com> writes:
[Reports a problem with diald and ppp-2.2.0c not working, and failing
with "PPP not available" messages, yet pppd works fine from the command line.]
>Eric Schenk wrote:
>> (2) There were reports of a problem when starting pppd from inittab.
>> This was a result of pppd relying on having a controlling terminal,
>> which it does not when started from inittab. This problem may
>> be related to what you are seeing. The way the test code is
>> written the ppp_available routine would fail if it was run and it
>> could not actually open /dev/cua0.
>>
>> Check the following:
>> the permissions on /dev/cua0.
>> that you are running diald as root.
>> You might also try running diald with /dev/ttyS0 instead (this is
>> a shot in the dark, but it's worth a try).
> If any of this works I'll be happy to explain why :-)
>
>Thanks for the help, Eric. I am now executing diald with /dev/ttyS0 and
>it works very nicely. Now, how about the explanation?
Ok. Here is what I think is happening (I haven't tested this yet, but
it makes sense to me). Ppd needs to open up a terminal line at various
times, just to be able to do various ioctl's. Most critically this occurs
in ppp_available. Now, the way pppd gets a terminal is it opens the controling
terminal /dev/tty. When pppd is invoked from the command line this doesn't
cause a problem. But, when pppd is invoked by diald, the controling terminal
IS /dev/cua0. Since /dev/cua0 can't be opened by multiple processes at once,
and it is already open, the reopen fails. Panic ensues.
In any case, I'll look further into this and see if I can't set things up so
diald doesn't cause this problem to occur. In the worst case, if I can't avoid
this problem, I'll at least document it in the FAQ (and change the manual
page examples so they don't use /dev/cua*).
Thanks for reporting this,
-- eric
---------------------------------------------------------------------------
Eric Schenk www: http://www.cs.toronto.edu/~schenk
Department of Computer Science email: schenk@cs.toronto.edu
University of Toronto
----------------------------------------------------------------------
From: ncm@cantrip.org (Nathan Myers)
Can someone kindly explain the difference between the /dev/cua? and
/dev/ttyS? devices?
Ted T'so Mon (13 May 1996):
/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.
-----------------------------------------------------------------------
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