From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from [140.186.70.92] (port=44220 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1PR3BX-0004or-AN
	for qemu-devel@nongnu.org; Fri, 10 Dec 2010 08:38:59 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <hch@lst.de>) id 1PR3BT-0004LY-P3
	for qemu-devel@nongnu.org; Fri, 10 Dec 2010 08:38:55 -0500
Received: from verein.lst.de ([213.95.11.210]:52553)
	by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from <hch@lst.de>)
	id 1PR3BT-0004Ig-G4
	for qemu-devel@nongnu.org; Fri, 10 Dec 2010 08:38:51 -0500
Date: Fri, 10 Dec 2010 14:38:43 +0100
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [Qemu-devel] [PATCH 1/5] block: add discard support
Message-ID: <20101210133843.GA28846@lst.de>
References: <20101125135657.GA2814@lst.de> <20101201153504.GA6056@lst.de>
	<20101201153514.GA6310@lst.de> <4CF78D1D.3060107@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <4CF78D1D.3060107@redhat.com>
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Kevin Wolf <kwolf@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>, qemu-devel@nongnu.org

On Thu, Dec 02, 2010 at 01:12:13PM +0100, Kevin Wolf wrote:
> >      DEFINE_PROP_UINT16("physical_block_size", _state,                   \
> >                         _conf.physical_block_size, 512),                 \
> >      DEFINE_PROP_UINT16("min_io_size", _state, _conf.min_io_size, 0),  \
> > -    DEFINE_PROP_UINT32("opt_io_size", _state, _conf.opt_io_size, 0)
> > +    DEFINE_PROP_UINT32("opt_io_size", _state, _conf.opt_io_size, 0), \
> > +    DEFINE_PROP_UINT32("discard_granularity", _state, \
> > +                       _conf.discard_granularity, 0)
> 
> Is there no way to get this value automatically?
> 
> At least for non-raw images (and it should be trivial to implement this
> in qcow2) I guess we'll want to set it to the cluster size of the image
> instead of requiring the user to set this value.

It's guest visible state, so it must not change due to migrations.  For
the current implementation all values for it work anyway - if it's
smaller than the block size we'll zero out the remainder of the block.