From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from [140.186.70.92] (port=45165 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1PzrZ2-0007SI-97
	for qemu-devel@nongnu.org; Wed, 16 Mar 2011 10:19:05 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <cs5070214@cse.iitd.ac.in>) id 1PzrZ0-0003Mp-Q6
	for qemu-devel@nongnu.org; Wed, 16 Mar 2011 10:19:04 -0400
Received: from smtp2.iitd.ernet.in ([202.141.68.44]:57473)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <cs5070214@cse.iitd.ac.in>) id 1PzrZ0-0003E8-3k
	for qemu-devel@nongnu.org; Wed, 16 Mar 2011 10:19:02 -0400
Message-ID: <4D80C693.6040704@cse.iitd.ac.in>
Date: Wed, 16 Mar 2011 19:47:55 +0530
From: Dushyant Bansal <cs5070214@cse.iitd.ac.in>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] Re: KVM call agenda for Jan 25
References: <20110124132559.GA25236@x200.localdomain>	<4D3DF7EA.4010807@codemonkey.ws>	<20110125115727.5f2b495e@doriath>	<20110125120244.5b18863d@doriath>	<AANLkTi=px6_UZ6vYFm=wvS8aTmecQbA1_Z3ra9UH9ecm@mail.gmail.com>	<4D43F0F5.10206@cse.iitd.ac.in>	<4D67E9EB.7090606@cse.iitd.ac.in>	<AANLkTik6de8nkuS6xz6btOkqjTMTKmOm_B+Jy9DCa2Tk@mail.gmail.com>	<4D6975B0.4060309@cse.iitd.ac.in>	<AANLkTikGeDvT7zq4UbBh-FpCUDrSQ-uoNBp_mJVpKx68@mail.gmail.com>	<4D6C087B.90603@cse.iitd.ac.in>	<AANLkTimMyCmy6yYJM6+5QdAt0DjCQq=WHE1iOwpJJHAq@mail.gmail.com>
	<4D7E309B.6080800@cse.iitd.ac.in> <4D7F3EFC.3050106@redhat.com>
In-Reply-To: <4D7F3EFC.3050106@redhat.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: Kevin Wolf <kwolf@redhat.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel@nongnu.org


>> 1. header_size: variable in qed, equals to cluster size in qcow2:
>> When will it be larger than 1 cluster in qed? So, what will happen to
>> that extra data on qed->qcow2 conversion.
>>      
> If you have an feature that is used in the original image, but cannot be
> represented in the new format, I think you should just get an error.
>
>    
>> 2. L2 table size: equals to L1 table size in qed, equals to cluster size
>> in qcow2:
>> we need to take it into account during conversion.
>>      
> Right. I think we'll have to rewrite all of the metadata.
>
> I wonder if we can manage to have a nice block driver interface for
> in-place image conversions so that we don't only get a qed<->qcow2
> converter, but also can implement the interface in e.g. VMDK and get
> VMDK<->qcow2 and VMDK<->qed as well.
>    
>> 3. refcount table:
>> qcow2->qed:we do not keep refcount structure
>> qed->qcow2: initialize refcount structure
>>      
> Yes, refcounts can be rebuilt after the mapping has been converted.
>
>    
>> So, a qcow2->qed->qcow2 conversion means if earlier, qcow2 image was
>> using additional features{1-4}, all information related to that will be
>> lost.
>>      
> We shouldn't lose anything but just abort if a conversion isn't
> possible. The user can still use qemu-img convert for the more
> complicated cases, for example for removing encryption or compression.
>
>    
Thanks for clearing up those issues.

--
Dushyant