snapshots are breaking shred

Corinna Vinschen corinna-cygwin@cygwin.com
Thu Feb 17 19:38:00 GMT 2005


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@cygwin.com
Red Hat, Inc.

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