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From: mpl@sfsup.UUCP (M.P.Lindner)
Newsgroups: comp.unix.questions
Subject: Re: catching signals while writing to a tty-line
Message-ID: <2021@sfsup.UUCP>
Date: Thu, 10-Sep-87 16:21:22 EDT
Article-I.D.: sfsup.2021
Posted: Thu Sep 10 16:21:22 1987
Date-Received: Sat, 12-Sep-87 15:49:50 EDT
References: <589@euraiv1.UUCP>
Organization: AT&T-IS, Summit N.J. USA
Lines: 29
Summary: System V is broken

In article <589@euraiv1.UUCP>, aiv@euraiv1.UUCP writes:
> 	"when a signal that is to be caught occurs during a read, a write,
	...
> 	will be executed and the interrupted system call will return -1 to
> 	the calling process with errno set to EINTR."
> 
> (btw, I use System V release 2.0 on an AT&T 3B2/300)
> 
> The problem is of course to detect the number of characters that has
> already been written so that we don't send chars twice or not at all.
> 
> Eelco van Asperen.

Previous versions of UNIX(R) behaved as you'd like it to - write returned the
number of characters actually written.  However, in System V UNIX, the
behaviour was modified to return -1.  Consider that write *should* return -1
*on an error*.  It seems that a signal you're expecting is now considered
an error!

As for a solution, there is none, other than to modify the kernel.  This
behaviour broke some of my programs and several applications I know of.
It doesn't happen on *all* implementations of system V yet, but it will.

Call your support rep and complain.  I think this is something that should
be changed back, but heck, I only *work* on UNIX, so they won't listen to
me :{).

Mike Lindner
Disclaimer:  The above opinions are contrary to those of my employer!