linux-ext4 - Re: [PATCH 2/6] fiemap: add fe_phys_length and EXTENT_PHYS

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Message-Id: <D8092848-4221-4590-93F6-B99DAC1C9340@dilger.ca>
Date:	Wed, 30 Jul 2014 14:06:16 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	David Sterba <dsterba@...e.cz>
Cc:	linux-fsdevel@...r.kernel.org, hch@...radead.org, mfasheh@...e.com,
	viro@...iv.linux.org.uk, david@...morbit.com, xfs@....sgi.com,
	linux-nilfs@...r.kernel.org, ocfs2-devel@....oracle.com,
	linux-ext4@...r.kernel.org, linux-btrfs@...r.kernel.org
Subject: Re: [PATCH 2/6] fiemap: add fe_phys_length and EXTENT_PHYS_LENGTH flag

On Jul 30, 2014, at 11:18 AM, David Sterba <dsterba@...e.cz> wrote:
> Add a new member to fiemap_extent that represents the physical extent
> length. This value is undefined if the flag EXTENT_PHYS_LENGTH is not
> set.

The description here of PHYS_LENGTH makes sense...

The patch description should also mention the name of the new member,
namely "fe_phys_length"

> +#define FIEMAP_EXTENT_PHYS_LENGTH	0x00000010 /* Physical length of extent
> +						    * not the same as logical */

But the comment doesn't match.  This implies that if PHYS_LENGTH is
set, fe_phys_length != fe_logi_length, but I don't think that is
necessarily correct.  I think it makes more sense to just set
PHYS_LENGTH when fe_phys_length is valid, and if PHYS_LENGTH is not
set then fe_phys_length aware applications should just use
fe_phys_length = fe_logi_length, and older applications would just
use fe_length for both as they would already today.

Cheers, Andreas

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