linux-kernel - Re: O_NONBLOCK setting "leak" outside of a process??

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Message-Id: <200702020000.40524.vda.linux@googlemail.com>
Date:	Fri, 2 Feb 2007 00:00:40 +0100
From:	Denis Vlasenko <vda.linux@...glemail.com>
To:	Philippe Troin <phil@...i.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: O_NONBLOCK setting "leak" outside of a process??

On Tuesday 30 January 2007 04:40, Philippe Troin wrote:
> > int main() {
> >         fcntl(0, F_SETFL, fcntl(0, F_GETFL, 0) | O_NONBLOCK);
> >         return 0;
> > }
> > 
> > int main() {
> >         fcntl(0, F_SETFL, fcntl(0, F_GETFL, 0) & ~O_NONBLOCK);
> >         return 0;
> > }
> > 
> > If I run "nonblock" in Midnight Commander in KDE's Konsole,
> > screen redraw starts to work ~5 times slower. For example,
> > Ctrl-O ("show/hide panels" in MC) takes ~0.5 sec to redraw.
> > This persists after the program exits (which it
> > does immediately as you see).
> > Running "block" reverts things to normal.
> > 
> > I mean: how can O_NONBLOCK _issued in a process which
> > already exited_ have any effect whatsoever on MC or Konsole?
> > They can't even know that it did it, right?
> > 
> > Either I do not know something subtle about Unix or some sort
> > of bug is at work.
> 
> Because they all share the same stdin file descriptor, therefore they
> share the same file descriptor flags?

What share the same file descriptor? MC and programs started from it?

I thought after exec() fds atre either closed (if CLOEXEC) or
becoming independent from parent process
(i.e. it you seek, close, etc your fd, parent would not notice that).

Am I wrong?
--
vda
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