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From: Andreas Dilger <adilger@sun.com>
Subject: Re: [RFC][PATCH 0/5] Fiemap, an extent mapping ioctl
Date: Thu, 29 May 2008 17:20:38 -0600
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Cc: jim owens <jowens@hp.com>, Christoph Hellwig <hch@infradead.org>,
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To: Joel Becker <Joel.Becker@oracle.com>
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On May 29, 2008  14:47 -0700, Joel Becker wrote:
> On Thu, May 29, 2008 at 03:41:23PM -0600, Andreas Dilger wrote:
> > So, to clarify, you are suggesting that FIEMAP_FLAG_NUM_EXTENTS isn't
> > needed, and returning the extent count should just be detected by calling
> > FIEMAP with fm_extent_count == 0?  I'm OK with that also, since calling
> > it with fm_extent_count == 0 doesn't make sense otherwise.
> 
> 	I'd always set fm_extent_count to whatever covers the range.
> So, like snprintf(3), you always know when you were truncated and by how
> much.  Then, passing fm_extent_count=0 in is just a special case of it.
> Like estimating a printf buffer with len = snprintf(NULL, 0, fmt, ...);

I totally agree, I just didn't remember to include the start/end range
in my email, though I think they are necessary.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.