linux-ext4 - Re: [PATCH 4/7][TAKE5] support new modes in fallocate

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Date:	Wed, 27 Jun 2007 09:26:49 +1000
From:	David Chinner <dgc@....com>
To:	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-ext4@...r.kernel.org, David Chinner <dgc@....com>,
	suparna@...ibm.com, cmm@...ibm.com, xfs@....sgi.com
Subject: Re: [PATCH 4/7][TAKE5] support new modes in fallocate

On Mon, Jun 25, 2007 at 03:52:39PM -0600, Andreas Dilger wrote:
> On Jun 25, 2007  19:15 +0530, Amit K. Arora wrote:
> > +#define FA_FL_DEALLOC	0x01 /* default is allocate */
> > +#define FA_FL_KEEP_SIZE	0x02 /* default is extend/shrink size */
> > +#define FA_FL_DEL_DATA	0x04 /* default is keep written data on DEALLOC */
> 
> In XFS one of the (many) ALLOC modes is to zero existing data on allocate.

No, none of the XFS allocation modes do that.

XFS_IOC_ALLOCSP, which does write zeros to disk, only allocates and
writes zeros in the range between the old file size and the new file size.
XFS_IOC_RESVSP, which alocates unwritten extents, only allocates
where extents do not currently exist. It does not zero existing
extents.

IOWs, you can't overwrite existing data with XFS preallocation.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group
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