linux-ext4 - Re: [PATCH 0/3] Fiemap, an extent mapping ioctl

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Date:	Wed, 10 Sep 2008 11:46:12 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mark Fasheh <mfasheh@...e.com>
Cc:	Andreas Dilger <adilger@....com>,
	Eric Sandeen <esandeen@...hat.com>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 0/3] Fiemap, an extent mapping ioctl

On Wed, 10 Sep 2008 05:49:34 -0700 Mark Fasheh <mfasheh@...e.com> wrote:

> Hello,
> 
> 	The following patches are the latest attempt at implementing a
> fiemap ioctl, which can be used by userspace software to get extent
> information for an inode in an efficient manner.

As these are applicable to all filesystems, Cc:ing only linux-ext4 is
not sufficient.  All filesystem developers (at least) need an
opportunity to review and understand these changes.

> 
> ...
>
> The fiemap ioctl is an efficient method for userspace to get file
> extent mappings. Instead of block-by-block mapping (such as bmap), fiemap
> returns a list of extents.
> 

The above is, afacit, the only offered rationale for the addition of
these new feature.  I don't recall seeing anyone complain about bmap()
inefficiency.  In fact I rarely hear of anyone using bmap() at all.

This rationale needs expanding, please.  A lot.
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