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

[David Chinner <dgc@xxxxxxx>]

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