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From: Wen Congyang <wency@cn.fujitsu.com>
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Date: Wed, 2 Sep 2015 09:25:58 +0800
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Subject: Re: [Qemu-devel] [Patch for-2.5 v2 5/6] qmp: add monitor command to
 add/remove a child
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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 09/01/2015 11:34 PM, Eric Blake wrote:
> On 08/31/2015 06:55 PM, Wen Congyang wrote:
> 
>>>> +This command is still a work in progress. It doesn't support all
>>>> +block drivers. Stay away from it unless you want it to help with
>>>> +its development.
>>>
>>> Maybe we should name it 'x-child-add' for now, so that we aren't baking
>>> ourselves into a corner.
>>
>> Do you mean the command name should be x-child-add? It is OK.
> 
> Use of the 'x-' prefix means a command is experimental and may change or
> be withdrawn.  It gives us a way to test if an interface is useful
> without committing to that interface long term.  We've still got time
> before 2.5 to get blockdev-add working everywhere, in which case I think
> we are better off using blockdev-add to create a new unattached BDS and
> then have this command pass the node name to be made the new child,
> rather than all the options for opening the child from scratch.
> 

Good idea. The unattached BDS created by the command blockdev-add always
have BB. So it may be used by the device created by the command device_add
later. So I think we should have an API to check it. What about the following
patches?
http://lists.nongnu.org/archive/html/qemu-devel/2015-07/msg01591.html
http://lists.nongnu.org/archive/html/qemu-devel/2015-07/msg01590.html

Thanks
Wen Congyang