From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:43674)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <wency@cn.fujitsu.com>) id 1ZZYfK-0004Nr-Um
	for qemu-devel@nongnu.org; Wed, 09 Sep 2015 02:15:31 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <wency@cn.fujitsu.com>) id 1ZZYfK-0003zF-2b
	for qemu-devel@nongnu.org; Wed, 09 Sep 2015 02:15:30 -0400
References: <1439279489-13338-1-git-send-email-wency@cn.fujitsu.com>
	<1439279489-13338-4-git-send-email-wency@cn.fujitsu.com>
	<55E4917A.9010703@redhat.com> <55E4F4FF.1000504@cn.fujitsu.com>
	<55E5C4B0.1080301@redhat.com> <55EEA5FE.2000507@cn.fujitsu.com>
	<55EF0427.3020301@redhat.com>
From: Wen Congyang <wency@cn.fujitsu.com>
Message-ID: <55EFCE5B.50102@cn.fujitsu.com>
Date: Wed, 9 Sep 2015 14:14:51 +0800
MIME-Version: 1.0
In-Reply-To: <55EF0427.3020301@redhat.com>
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [Patch for-2.5 v2 3/6] Add new block driver
 interface to add/delete a BDS's child
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/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: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Eric Blake <eblake@redhat.com>, qemu devel <qemu-devel@nongnu.org>, Markus Armbruster <armbru@redhat.com>, Alberto Garcia <berto@igalia.com>, Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, zhanghailiang <zhang.zhanghailiang@huawei.com>, qemu block <qemu-block@nongnu.org>, Jiang Yunhong <yunhong.jiang@intel.com>, Dong Eddie <eddie.dong@intel.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Gonglei <arei.gonglei@huawei.com>, Yang Hongyang <yanghy@cn.fujitsu.com>

On 09/08/2015 11:52 PM, Eric Blake wrote:
> On 09/08/2015 03:10 AM, Wen Congyang wrote:
> 
>>> Design-wise, I think we really want to have the add-child operation be
>>> handed a pre-opened BDS, rather than the options dictionary to open the
>>> BDS itself.  That is, we should use the existing blockdev-add (and
>>> enhance it to support everything) to open the BDS, and then this command
>>> should just attach that BDS as the new child (which is why it IS
>>> important that we validate that the new BDS being added doesn't create
>>> an invalid loop).
>>>
>>
>> How to check it? The parent BDS can get all children. But the child doesn't
>> know if it is some BDS's child.
> 
> If I'm not mistaken, a child DOES know what its parent(s) are, once we
> have Max's series for NULL BDS representing a BB without media.
> 

Which patch? I don't find it.

Thanks
Wen Congyang