linux-ext4 - Re: [Ext4 punch hole 1/5] Ext4 Punch Hole Support: Convert Blocks to Uninit Exts

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Message-ID: <20110302202313.GA15097@dastard>
Date:	Thu, 3 Mar 2011 07:23:13 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Andreas Dilger <adilger@...ger.ca>
Cc:	Allison Henderson <achender@...ux.vnet.ibm.com>,
	linux-ext4@...r.kernel.org
Subject: Re: [Ext4 punch hole 1/5] Ext4 Punch Hole Support: Convert Blocks
 to Uninit Exts

On Mon, Feb 28, 2011 at 11:42:48PM -0700, Andreas Dilger wrote:
> On 2011-02-28, at 8:08 PM, Allison Henderson wrote:
> > This first patch adds a function to convert a range of blocks
> > to an uninitialized extent.  This function will
> > be used to first convert the blocks to extents before
> > punching them out.
> 
> This was proposed as a separate function for FALLOCATE by Dave
> Chinner (based on XFS_IOC_ZERO_RANGE), so this is useful as a
> standalone function.

XFS_IOC_ZERO_RANGE converts a range to unwritten extents, not
uninitialised extents. An uninitialised extent is one that is
allocated but had not data written to it (i.e. contains stale data),
while an unwritten/preallocated extent is guaranteed to contain
zeros.  This may be just a terminology issue, but we should try to
use the same jargon across all filesystems...

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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