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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

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


Dave Chinner
Principal Engineer
SGI Australian Software Group

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