linux-kernel - Re: [PATCH 05/39] whiteout/NFSD: Don't return information about whiteouts to userspace

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Date:	Mon, 17 May 2010 15:51:45 -0400
From:	Valerie Aurora <vaurora@...hat.com>
To:	Neil Brown <neilb@...e.de>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Jan Blunck <jblunck@...e.de>,
	David Woodhouse <dwmw2@...radead.org>,
	linux-nfs@...r.kernel.org, "J. Bruce Fields" <bfields@...ldses.org>
Subject: Re: [PATCH 05/39] whiteout/NFSD: Don't return information about whiteouts to userspace

On Fri, May 07, 2010 at 07:18:08AM +1000, Neil Brown wrote:
> On Thu, 6 May 2010 14:01:51 -0400
> Valerie Aurora <vaurora@...hat.com> wrote:
> 
> > On Tue, May 04, 2010 at 09:37:31AM +1000, Neil Brown wrote:
> > > On Mon,  3 May 2010 16:12:04 -0700
> > > Valerie Aurora <vaurora@...hat.com> wrote:
> > > 
> > > > From: Jan Blunck <jblunck@...e.de>
> > > > 
> > > > Userspace isn't ready for handling another file type, so silently drop
> > > > whiteout directory entries before they leave the kernel.
> > > 
> > > Feels very intrusive doesn't it....
> > > 
> > > Have you considered something like the following?
> > 
> > Hrm, I see how that could be more elegant, but I'd rather avoid yet
> > another layer of function pointer passing around.  This code is
> > already hard enough to review...
> 
>  Yes, the extra indirection is a bit of a negative, but I don't think this
>  patch is harder to review than the alternate.
>  From a numerical perspective, with this patch you only need to look at the
>  various places that ->readdir is called to be sure it is always correct.
>  There are about 3.  With the original you need to look at ever filldir
>  function.  Jan has found 9.  
> 
>  And from a maintainability perspective, I think my approach is safer.  Given
>  that there are 9 filldir functions already, the chance that a need will be
>  found for another seems good, and the chance that the coder will know to
>  check for DT_WHT is a best even.  Conversely if another call to ->readdir
>  were added it is likely that nothing would need to be done.
> 
>  Of course just counting things doesn't give a completely picture but I think
>  it can be indicative.

Okay, good points.  Let me try it out after getting this next rewrite done.

Thanks,

-VAL
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