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From: Wen Congyang <wency@cn.fujitsu.com>
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Date: Fri, 6 Nov 2015 08:50:56 +0800
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Subject: Re: [Qemu-devel] [PATCH v6 3/4] qmp: add monitor command to
	add/remove a child
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To: Alberto Garcia <berto@igalia.com>, qemu devel <qemu-devel@nongnu.org>, Eric Blake <eblake@redhat.com>, Markus Armbruster <armbru@redhat.com>, Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>
Cc: 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 11/05/2015 09:49 PM, Alberto Garcia wrote:
> On Fri 16 Oct 2015 10:57:45 AM CEST, Wen Congyang <wency@cn.fujitsu.com> wrote:
> 
>> The new QMP command name is x-blockdev-change. It justs for
>> adding/removing quorum's child now, and don't support all kinds of
>> children, all kinds of operations, nor all block drivers. So it is
>> experimental now.
> 
> I might have missed some discussion, why were the -add and -delete 

This monitor command can be used to implement: add, delete, insert, remove,
replace... Currently, I only implement add and delete operation.

> 
>> +# @x-blockdev-change
>> +#
>> +# Dynamic reconfigure the block driver state graph. It can be used to
>> +# add, remove, insert, replace a block driver state. Currently only
>> +# the Quorum driver implements this feature to add and remove its child.
>> +# This is useful to fix a broken quorum child.
>> +#
>> +# @operation: the chanage operation. It can be add, delete.
>> +#
>> +# @parent: the id or node name of which node will be changed.
>> +#
>> +# @child: the child node-name which will be deleted.
>> +#
>> +# @node: the new node-name which will be added.
>> +#
>> +# Note: this command is experimental, and not a stable API.
>> +#
>> +# Since: 2.5
>> +##
>> +{ 'command': 'x-blockdev-change',
>> +  'data' : { 'operation': 'ChangeOperation',
>> +             'parent': 'str',
>> +             '*child': 'str',
>> +             '*node': 'str' } }
> 
> Do you really need two separate 'child' and 'node' parameters? If the
> operation is 'add' you can only use 'node', if it is 'delete, you can
> only use 'child'. It seems to me that you can simply have one 'node'
> parameter and use it for both ...

parent and child already exist in the BDS graph, and node is a new node.
In the furture, we may need to implement insert opetioan, and this operation
needs such three BDSes.

Thanks
Wen Congyang

> 
> Berto
> .
>