From mboxrd@z Thu Jan  1 00:00:00 1970
From: lm@mcvoy.com (Larry McVoy)
Date: Thu, 10 Jul 2014 07:45:03 -0700
Subject: [TUHS] Excise process from a pipe
In-Reply-To: <201407101204.s6AC4hKQ026601@coolidge.cs.dartmouth.edu>
References: <201407100249.s6A2nMh3017869@coolidge.cs.dartmouth.edu>
 <20140710045223.GA19076@www.oztivo.net>
 <201407101204.s6AC4hKQ026601@coolidge.cs.dartmouth.edu>
Message-ID: <20140710144502.GA24876@mcvoy.com>

I'm pretty aware of the various flavors of Unix and unless the process 
in question is willing to help I can't see how this could work.

There are system calls for passing file descriptors but you have the 
problem that the pipe itself is a buffer of some size and you'd have
the problem of draining it.

Every utility that you put in a pipeline would have to be reworked
to pass file descriptors around, it would be really unpleasant and
not at all Unix like.

On Thu, Jul 10, 2014 at 08:04:43AM -0400, Doug McIlroy wrote:
> In the suggested answer, the code changes but the process survives.
> 
> I suspect the answer to my original question is no, but I know only a tiny
> fraction of the cumulative API of the extended Unix family.
> 
> Doug
> 
> >> Was there ever a
> >> flavor of Unix in which a process could excise itself
> >> from a pipeline without breaking the pipeline?
> >
> > If in the middle of a pipeline, all I can think of is:
> >
> >       close fd 0 and fd 1
> >       dup() read end of pipe 1 to be stdin (fd 0)
> >       dup() write end of pipe 2 to be stdout (fd 1)
> >       exec("/bin/cat")
> _______________________________________________
> TUHS mailing list
> TUHS at minnie.tuhs.org
> https://minnie.tuhs.org/mailman/listinfo/tuhs

-- 
---
Larry McVoy            	     lm at mcvoy.com             http://www.mcvoy.com/lm