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Date: Tue, 21 Jul 2009 15:58:48 +0200
From: Corinna Vinschen <vinschen AT redhat DOT com>
To: newlib AT sourceware DOT org, cygwin AT cygwin DOT com
Subject: Re: close on exec atomics
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On Jul 21 07:04, Eric Blake wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> It seems like it would be pretty easy to add several new close-on-exec
> features required by POSIX 2008:
> 
> open(name, O_RDONLY | O_CLOEXEC);
> // skips the need to use fcntl
> 
> fcntl(fd, F_DUPFD_CLOEXEC);
> // like F_DUPFD, but closes window without having to use
> // fcntl(fd, F_SETFD, fcntl(fd, F_GETFD))
> 
> and those provided by glibc as extensions:
> 
> fopen(name, "re");
> // like fopen "r", but with cloexec set
> 
> The argument is that in multi-threaded apps, if one thread opens a file
> but has not yet turned on the close-on-exec bit while another thread does
> a fork-and-exec, then you leaked the fd into the child; and these new
> flags close the window.
> 
> Should I go ahead and prepare a patch for the newlib side?

It's not that easy to implement, especially not the fcntl which requires
to redefine the dup2 methods throughout to allow atomic operation on the
target OS handles.  open (O_CLOEXEC) is much easier.  Anyway, can we
wait until after Cygwin 1.7.1?


Corinna

-- 
Corinna Vinschen
Cygwin Project Co-Leader
Red Hat

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