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Date: Thu, 17 Feb 2005 13:14:43 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: snapshots are breaking shred
Message-ID: <20050217121443.GS2597@cygbert.vinschen.de>
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References: <020920051745 DOT 590 DOT 420A4C2A000CF0230000024E22058864420A050E040D0C079D0A AT comcast DOT net> <20050209192812 DOT GU2597 AT cygbert DOT vinschen DOT de> <loom DOT 20050214T215335-693 AT post DOT gmane DOT org>
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On Feb 14 21:19, Eric Blake wrote:
> Corinna Vinschen <corinna-cygwin <at> cygwin.com> writes:
> > > With coreutils 5.3.0-2 and various snapshots, I am seeing regressions in 
> shred(1)caused by cygwin changes:
> > 
> > As far as fsync is affected, I don't see how that could ever fail, except
> > the Windows call fails for some reason.  The fsync code hasn't changed
> > for quite some time.
> 
> I found what is causing this.  Coreutils shred uses the following code:
> int dir_fd = open (dir, O_WRONLY | O_NOCTTY);

So it tries to open directories for writing despite of POSIX not allowing
this?  How weird.

> POSIX requires that open fail with EISDIR on open with O_WRONLY or O_RDWR on a 
> directory, and you implemented that in a patch on Jan 6.  So with 1.5.12, shred 
> got a writeable fd from the first open, but with snapshots after Jan 6 it has 
> only a readable fd from the second open.  But fsync() is implemented with 
> FlushFileBuffers, which requires write access to the handle it is about to 
> flush, so it now fails with EACCES.
> 
> I don't know if it is better to patch open_fs() to additionally grant 
> GENERIC_WRITE access when opening directories as O_RDONLY (since that is the 
> only way to open a directory), or to patch fsync() to temporarily grant write 
> access to a directory for the duration of the flush.  But it is a definite 
> regression from 1.5.12 that should be fixed.
> 
> I also think that fsync() could be patched to return EINVAL on non-directory 
> file descriptors that were opened as O_RDONLY, rather than performing a failed 
> FlushFileBuffers and getting EACCES, as a closer match to the errors allowed by 
> POSIX.  http://www.opengroup.org/onlinepubs/009695399/functions/fsync.html

I'm pretty busy with non-Cygwin stuff at the moment.  But you know,
http://cygwin.com/acronyms/#PTC .


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          mailto:cygwin AT cygwin DOT com
Red Hat, Inc.

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