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

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Date:	02 Feb 2007 10:59:42 -0800
From:	Philippe Troin <phil@...i.org>
To:	Roland Kuhn <rkuhn@....physik.tu-muenchen.de>
Cc:	"Guillaume Chazarain" <guichaz@...il.com>,
	"Denis Vlasenko" <vda.linux@...glemail.com>,
	linux-kernel@...r.kernel.org
Subject: Re: O_NONBLOCK setting "leak" outside of a process??

Roland Kuhn <rkuhn@....physik.tu-muenchen.de> writes:

> Hi Guillaume!
> 
> On 2 Feb 2007, at 14:48, Guillaume Chazarain wrote:
> 
> > 2007/2/2, Roland Kuhn <rkuhn@....physik.tu-muenchen.de>:
> >
> >> That's a bug, right?
> >
> > No, if you want something like: (echo toto; date; echo titi) > file
> > to work in your shell, you'll be happy to have the seek position
> > shared in the processes.

Absolutely right.  This has been part of Unix since the beginning.

> As a naive user I'd probably expect that each of the above adds to
> the output, which perfectly fits the O_APPEND flag (to be set by the
> shell, of course).

No, no, O_APPEND has slightly different semantics.

> The immediate point was about the flags, though, and having
> O_NONBLOCK on or off certainly is a _design_ choice when writing a
> program. If I remove O_NONBLOCK, I have a right to expect that I/O
> functions do not return EAGAIN!

Generally you don't want to mess with shared resouces like stdin,
stdout and stderr.

Phil.
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