linux-kernel - No NONBLOCK flag for dup3() or epoll

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Message-ID: <48AC4B19.6000206@gmail.com>
Date:	Wed, 20 Aug 2008 18:49:29 +0200
From:	Michael Kerrisk <mtk.manpages@...glemail.com>
To:	Ulrich Drepper <drepper@...hat.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	lkml <linux-kernel@...r.kernel.org>,
	Davide Libenzi <davidel@...ilserver.org>
Subject: No NONBLOCK flag for dup3() or epoll_create1()?

Ulrich

I've been doing some testing (2.6.27-rc3) of your new
file-descriptor-creating syscalls that accept flags.  According to

http://udrepper.livejournal.com/20407.html

all of the system calls should accept a *_NONBLOCK flag.  All of them do,
except for two:
dup3(olfd, newfd, flags)
and
epoll_create1(flags).

For epoll_create1() this certainly appears to be an oversight, since I can't
think of a reason not to support *_NONBLOCK.

For dup3() it is perhaps also an oversight.  However, it's not really clear
to me whether supporting O_NONBLOCK makes sense, since that would change the
file status flags of the open file description that is (also) referred to by
oldfd.  (Furthermore, given a open file description for which O_NONBLOCK is
already enabled, it is not possible to make a dup3() call that disables
O_NONBLOCK, which is an odd asymmetry in the API.)  What are your thoughts on
this?

Cheers,

Michael

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