linux-ext4 - Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)

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Message-Id: <E7438588-5C5A-42B9-9B6C-FADF7CAC6D3A@dilger.ca>
Date:	Fri, 15 Apr 2011 23:11:23 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Dave Chinner <david@...morbit.com>
Cc:	Pádraig Brady <P@...igBrady.com>,
	Eric Sandeen <sandeen@...deen.net>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"coreutils@....org" <coreutils@....org>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	xfs-oss <xfs@....sgi.com>
Subject: Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)

On 2011-04-15, at 6:50 PM, Dave Chinner <david@...morbit.com> wrote:
> What you are suggesting is that FIEMAP needs to be page cache
> coherent, and that is far, far away from the intended use of the
> interface. Even consiering that you need to looking for active pages
> in the page cache when mapping extents say to me that you are
> doing something very wrong.
> 
> Unwritten extents remain unwritten until the data is physically
> written to them. Therefore, to change their state, you need to sync
> the data covering the range.

In that case, it means cp should just always use FIEMAP_FLAG_SYNC, which is fine. 

Cheers, Andreas

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