linux-kernel - Re: [PATCH] open: introduce O

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Message-ID: <82ocq0p0ba.fsf@mid.bfk.de>
Date:	Fri, 28 Aug 2009 12:52:57 +0000
From:	Florian Weimer <fweimer@....de>
To:	Eric Blake <ebb9@....net>
Cc:	Davide Libenzi <davidel@...ilserver.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	bug-coreutils@....org, bug-gnulib@....org,
	Ulrich Drepper <drepper@...hat.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] open: introduce O_NOSTD

* Eric Blake:

> Your version fails to clear the cloexec bit of the final fd if the
> original caller didn't request O_CLOEXEC.

Okay, but you can fix that in a race-free manner (but I thought that
this was implied by open_safer).

> If the caller requested O_CLOEXEC, then your version takes 3, 5, or
> 7 syscalls depending on how many std fds were closed, while my
> version takes 3 syscalls regardless of how many std fds were closed.

I really don't see a way around that.  You can't pick a descriptor and
hope that it's unused.

> Also, your suggestion has a definite race in that you are calling
> open() multiple times rather than cloning an existing fd after the
> first open(), such that another process could alter which file is
> visited between your first and last open().

Sure, but this is an unobservable differen.ce

-- 
Florian Weimer                <fweimer@....de>
BFK edv-consulting GmbH       http://www.bfk.de/
Kriegsstraße 100              tel: +49-721-96201-1
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