Re: Problem creating files on network drives with cygwin 1.5.10-3 and tar

[Corinna Vinschen <corinna-cygwin at cygwin dot com>]

On Jun 16 21:47, Pierre A. Humblet wrote:
> On Wed, Jun 16, 2004 at 06:10:03PM -0700, Rick Rankin wrote:
> > It seems to be the O_TRUNC flag that's causing the problem. If I remove it, the
> > open succeeds when the file doesn't exist.
> > 
> > Here's the output of 'strace opentest /cygdrive/m/foo | fgrep NtCreateFile'
> > when /cygdrive/m/foo exists and with the O_TRUNC flag (1 line):
> > 
> >  1081  154650 [main] opentest 1796 fhandler_base::open: 0 = NtCreateFile
> > (0x32C, 40100080, m:\foo, io, NULL, 80, 7, 0, 20, NULL, 0)
>  
> The most likely explanation is that one of your network drives does not fully
> support the FILE_SUPERSEDE creation flag. Perhaps one could use FILE_OVERWRITE_IF
> instead. The difference is slight and according to 
> http://www.osronline.com/article.cfm?id=302 
> this is how CREATE_ALWAYS is implemented. CREATE_ALWAYS was used up to 
> 1.5.9 on NT systems.

That's what the Windows DDK docs have to say about this:

"The CreateDisposition value FILE_SUPERSEDE requires that the caller have
 DELETE access to a existing file object. If so, a successful call to
 ZwCreateFile with FILE_SUPERSEDE on an existing file effectively deletes
 that file, and then recreates it. [...] Note that this type of disposition
 is consistent with the POSIX style of overwriting files.
 [...]
 Overwriting a file is semantically equivalent to a supersede operation,
 except for the following: 

 The caller must have write access to the file, rather than delete access.
 [...]"

Except for Pierre's guess of the file system not supporting FILE_SUPERSEDE,
there's perhaps the other possible explanation, that you don't have the
DELETE permission given in the directories security descriptor.

I've applied a patch which substitutes FILE_SUPERSEDE with FILE_OVERWRITE_IF
in Cygwin.  It shows up in the next developers snapshot.  Please give it
a try.


Thanks for your help in tracking this down,
Corinna

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

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