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

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Message-ID: <alpine.DEB.2.00.0908251420190.18518@makko.or.mcafeemobile.com>
Date:	Tue, 25 Aug 2009 14:53:54 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Eric Blake <ebb9@....net>
cc:	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

On Tue, 25 Aug 2009, Eric Blake wrote:

> Another solution is for the application to sanitize all newly-created
> fds: GNU coreutils provides a wrapper open_safer, which does nothing
> extra in the common case that open() returned 3 or larger, but calls
> fcntl(n,F_DUPFD,3)/close(n) before returning if n was less than 3.
> However, this leads to triple the syscall cost for every open() call
> if the process starts life with a std fd closed; and if O_CLOEXEC is
> not used, still leaves a window of time where the fd can be leaked
> through another thread's use of fork/exec.

I think we can say that the vast majority of the software is not going to 
notice the proposed open_safer(), performance-wise, since the first three 
fds are always filled. So IMO the performance impact argument is a weak one.
If CLOEXEC semantics are needed in the open operation, F_DUPFD_CLOEXEC can 
be used to match it.
While the patch is simple, IMO this is something that can be easily taken 
care in glibc layers w/out huge drawbacks.


- Davide


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