linux-kernel - Re: [PATCH 0/5] fallocate system call

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Message-ID: <20070430055632.GR32602149@melbourne.sgi.com>
Date:	Mon, 30 Apr 2007 15:56:32 +1000
From:	David Chinner <dgc@....com>
To:	Chris Wedgwood <cw@...f.org>
Cc:	David Chinner <dgc@....com>,
	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>, torvalds@...l.org,
	akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org,
	xfs@....sgi.com, suparna@...ibm.com, cmm@...ibm.com
Subject: Re: [PATCH 0/5] fallocate system call

On Sun, Apr 29, 2007 at 10:25:59PM -0700, Chris Wedgwood wrote:
> On Mon, Apr 30, 2007 at 10:47:02AM +1000, David Chinner wrote:
> 
> > For FA_ALLOCATE, it's supposed to change the file size if we
> > allocate past EOF, right?
> 
> I would argue no.  Use truncate for that.

I'm going from the ext4 implementation because the semantics
have not been documented yet.

IIRC, the argument for FA_ALLOCATE changing file size is that
posix_fallocate() is supposed to change the file size. I think
that having a mode for real preallocation and another for
posix_fallocate is a valid thing to do...

Note that the way XFS implements growing the file size after the
allocation is via a truncate....

> > For FA_DEALLOCATE, does it change the filesize at all?
> 
> Same as above.
> 
> > Or does
> > it just punch a hole in the file?
> 
> Yes.

That's would what I did because otherwise you'd use ftruncate64().
Without documented behaviour or an ext4 implementation, I have to
ask what it's supposed to do, though ;)

Cheers,

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