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

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)
From: Andreas Dilger <adilger@xxxxxxxxx>
Date: Fri, 15 Apr 2011 23:11:23 -0600
Cc: Pádraig Brady <P@xxxxxxxxxxxxxx>, Eric Sandeen <sandeen@xxxxxxxxxxx>, "linux-ext4@xxxxxxxxxxxxxxx" <linux-ext4@xxxxxxxxxxxxxxx>, "coreutils@xxxxxxx" <coreutils@xxxxxxx>, Markus Trippelsdorf <markus@xxxxxxxxxxxxxxx>, xfs-oss <xfs@xxxxxxxxxxx>
In-reply-to: <20110416005040.GP21395@dastard>
References: <20110414102608.GA1678@xxxxxxxxxxxxxx> <20110414120635.GB1678@xxxxxxxxxxxxxx> <20110414140222.GB1679@xxxxxxxxxxxxxx> <4DA70BD3.1070409@xxxxxxxxxxxxxx> <4DA717B2.3020305@xxxxxxxxxxx> <20110414225904.GK21395@dastard> <4DA7836A.5040604@xxxxxxxxxxxxxx> <20110415000940.GL21395@dastard> <76FFF648-CA02-494B-A862-566C66A8CB82@xxxxxxxxx> <20110416005040.GP21395@dastard>
On 2011-04-15, at 6:50 PM, Dave Chinner <david@xxxxxxxxxxxxx> 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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