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Date: Thu, 23 Apr 2015 17:14:59 +0800
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Subject: Re: [Qemu-devel] [PATCH COLO v3 01/14] docs: block replication's
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To: Kevin Wolf <kwolf@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>
Cc: Fam Zheng <famz@redhat.com>, Lai Jiangshan <laijs@cn.fujitsu.com>, qemu block <qemu-block@nongnu.org>, Jiang Yunhong <yunhong.jiang@intel.com>, Dong Eddie <eddie.dong@intel.com>, qemu devel <qemu-devel@nongnu.org>, Max Reitz <mreitz@redhat.com>, Gonglei <arei.gonglei@huawei.com>, Stefan Hajnoczi <stefanha@redhat.com>, Yang Hongyang <yanghy@cn.fujitsu.com>, "Dr. David
	Alan Gilbert" <dgilbert@redhat.com>, zhanghailiang <zhang.zhanghailiang@huawei.com>

On 04/23/2015 05:00 PM, Kevin Wolf wrote:
> Am 22.04.2015 um 12:12 hat Paolo Bonzini geschrieben:
>> On 22/04/2015 11:31, Kevin Wolf wrote:
>>>> Actually I liked the "foo+colo" names.
>>>>
>>>> These are just internal details of the implementations and the
>>>> primary/secondary disks actually can be any format.
>>>>
>>>> Stefan, what was your worry with the +colo block drivers?
>>>
>>> I haven't read the patches yet, so I may be misunderstanding, but
>>> wouldn't a separate filter driver be more appropriate than modifying
>>> qcow2 with logic that has nothing to do with the image format?
>>
>> Possibly; on the other hand, why multiply the size of the test matrix
>> with options that no one will use and that will bitrot?
> 
> Because it may be the right design.
> 
> If you're really worried about the test matrix, put a check in the
> filter block driver that its bs->file is qcow2. Of course, such an
> artificial restriction looks a bit ugly, but using a bad design just
> in order to get the same restriction is even worse.

The bs->file->driver should support backing file, and use backing reference
already.

What about the primary side? We should control when to connect to NBD server,
not in nbd_open().

Thanks
Wen Congyang

> 
> Stefan originally wanted to put image streaming in the QED driver. I
> think we'll agree today that it was right to reject that. It's simply
> not functionality related to the format. Adding replication logic to
> qcow2 looks similar to me in that respect.
> 
> Kevin
> .
>