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To: cygwin AT cygwin DOT com
Subject: Re: symlinks to unlinked but open files should work
References: <op DOT yjxvo5gyofd6j1 AT frascati DOT upc DOT de> <20160703111436 DOT GA6301 AT calimero DOT vinschen DOT de>
Date: Sun, 03 Jul 2016 13:48:17 +0200
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From: "Helmut Karlowski" <helmut DOT karlowski AT ish DOT de>
Message-ID: <op.yj0werznofd6j1@frascati.upc.de>
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Am 03.07.2016, 13:14 Uhr, schrieb Corinna Vinschen:

> You don't even need a symlink.  This will show the same result:
>
>   exec >out1
>   rm out1
>   [[ -w /dev/fd/1 ]] || echo /dev/fd/1 not writable 1>&2

I noticed that too meanwhile, but I thought you would not need that  
information ;)
It's only about the /dev/fd-symlinks, otherwise cygwin seems to be  
correct: they don't work anywhere on an open but deleted file:

ln -sf out1 lout1
exec >out1
[[ -w lout1 ]] || echo lout1 not writable-1 1>&2
rm out1
[[ -w lout1 ]] || echo lout1 not writable-2 1>&2
rm lout1

correctly prints the second message.

> In Cygwin we move a deleted but still open file out of the way (into
> the trash) so the path is incorrect afterwards but even if we wouldn't
> do that, the underlying problem can't be solved:
>
> The problem is that a deleted file in Windows can't be opened anymore.
> If you translate the above -w <file> into a libc call access
> ("/dev/fd/1", W_OK) or its Windows equivalent, that call will always
> fail on a deleted file.  Same for open/CreateFile, etc.
>
> Sorry, but off the top of my head I don't see a feasible workaround for
> this problem.

Not a big issue - I don't know any situation this would break except the  
above /dev/fd-test.

-Helmut


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