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

To: Andreas Dilger <adilger@xxxxxxxxx>
Subject: Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)
From: Theodore Tso <tytso@xxxxxxx>
Date: Sat, 16 Apr 2011 08:21:28 -0400
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, 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: <E7438588-5C5A-42B9-9B6C-FADF7CAC6D3A@xxxxxxxxx>
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> <E7438588-5C5A-42B9-9B6C-FADF7CAC6D3A@xxxxxxxxx>
On Apr 16, 2011, at 1:11 AM, Andreas Dilger wrote:

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

Except that if someone is copying a large delay allocated file, it will cause 
the file to immediately snapped to disk, which might not be the greatest
thing in the world.  Christoph is write, SEEK_HOLE and SEEK_DATA are
a much better API for what cp woulld lke to do.  Unfortunately it hasn't
been implemented yet in the VFS...

- Ted
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