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

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Date:	29 Jan 2007 19:40:50 -0800
From:	Philippe Troin <phil@...i.org>
To:	Denis Vlasenko <vda.linux@...glemail.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: O_NONBLOCK setting "leak" outside of a process??

Denis Vlasenko <vda.linux@...glemail.com> writes:

> Hi,
> 
> I am currently on Linux 2.6.18, x86_64.
> I came across strange behavior while working on one
> of busybox applets. I narrowed it down to these two
> trivial testcases:
> 
> #include <unistd.h>
> #include <fcntl.h>
> int main() {
>         fcntl(0, F_SETFL, fcntl(0, F_GETFL, 0) | O_NONBLOCK);
>         return 0;
> }
> 
> #include <unistd.h>
> #include <fcntl.h>
> 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 exist (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?

Phil.
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