From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from [140.186.70.92] (port=34660 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1P5L5Z-0004hR-Ql
	for qemu-devel@nongnu.org; Mon, 11 Oct 2010 12:19:06 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1P5L5T-0004Pr-To
	for qemu-devel@nongnu.org; Mon, 11 Oct 2010 12:19:01 -0400
Received: from mail-yx0-f173.google.com ([209.85.213.173]:52797)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1P5L5T-0004Pn-Qg
	for qemu-devel@nongnu.org; Mon, 11 Oct 2010 12:18:55 -0400
Received: by yxn35 with SMTP id 35so774347yxn.4
	for <qemu-devel@nongnu.org>; Mon, 11 Oct 2010 09:18:55 -0700 (PDT)
Message-ID: <4CB338EC.3080504@codemonkey.ws>
Date: Mon, 11 Oct 2010 11:18:52 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] Re: [PATCH v2 3/7] docs: Add QED image format
	specification
References: <1286552914-27014-1-git-send-email-stefanha@linux.vnet.ibm.com>	<1286552914-27014-4-git-send-email-stefanha@linux.vnet.ibm.com>	<4CB317EF.7070504@redhat.com>	<20101011153039.GD5439@stefan-thinkpad.transitives.com>	<4CB32F95.8040301@redhat.com>
	<20101011154656.GE5439@stefan-thinkpad.transitives.com>
In-Reply-To: <20101011154656.GE5439@stefan-thinkpad.transitives.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
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: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Christoph Hellwig <hch@lst.de>, Avi Kivity <avi@redhat.com>, qemu-devel@nongnu.org

On 10/11/2010 10:46 AM, Stefan Hajnoczi wrote:
> On Mon, Oct 11, 2010 at 05:39:01PM +0200, Avi Kivity wrote:
>    
>>   On 10/11/2010 05:30 PM, Stefan Hajnoczi wrote:
>>      
>>>>   It was discussed before, but I don't think we came to a conclusion. Are
>>>>   there any circumstances under which you don't want to set the
>>>>   QED_CF_BACKING_FORMAT flag?
>>>>          
>>> I suggest the following:
>>>
>>> QED_CF_BACKING_FORMAT_RAW = 0x1
>>>
>>> When set, the backing file is a raw image and should not be probed for
>>> its file format.  The default (unset) means that the backing image file
>>> format may be probed.
>>>
>>> Now the backing_fmt_{offset,size} are no longer necessary.
>>>        
>> Should it not be an incompatible option?  If the backing disk starts
>> with a format magic, it will be probed by an older qemu,
>> incorrectly.
>>      
> Agreed, it should be a non-compat feature bit.
>    

If it's just raw or not raw, then I agree it should be non-compat.

I think we just need a feature bit then that indicates that the backing 
file is non-probeable which certainly simplifies the implementation.

QED_F_BACKING_FORMAT_NOPROBE maybe?

Regards,

Anthony Liguori

> Stefan
>
>