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

To: "Amit K. Arora" <aarora@xxxxxxxxxxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, David Chinner <dgc@xxxxxxx>, suparna@xxxxxxxxxx, cmm@xxxxxxxxxx, xfs@xxxxxxxxxxx
Subject: Re: [PATCH 4/7][TAKE5] support new modes in fallocate
From: David Chinner <dgc@xxxxxxx>
Date: Wed, 27 Jun 2007 09:26:49 +1000
In-reply-to: <20070625215239.GK5181@schatzie.adilger.int>
References: <20070511110301.GB28425@in.ibm.com> <20070512080157.GF85884050@sgi.com> <20070612061652.GA6320@amitarora.in.ibm.com> <20070613235217.GS86004887@sgi.com> <20070614091458.GH5181@schatzie.adilger.int> <20070614120413.GD86004887@sgi.com> <20070614193347.GN5181@schatzie.adilger.int> <20070625132810.GA1951@amitarora.in.ibm.com> <20070625134500.GE1951@amitarora.in.ibm.com> <20070625215239.GK5181@schatzie.adilger.int>
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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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