Re: [Qemu-devel] [Patch for-2.5 v2 3/6] Add new block driver interface to add/delete a BDS's child

From: Eric Blake <eblake@redhat.com>
To: Wen Congyang <wency@cn.fujitsu.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>
Subject: Re: [Qemu-devel] [Patch for-2.5 v2 3/6] Add new block driver interface to add/delete a BDS's child
Date: Tue, 8 Sep 2015 09:52:07 -0600	[thread overview]
Message-ID: <55EF0427.3020301@redhat.com> (raw)
In-Reply-To: <55EEA5FE.2000507@cn.fujitsu.com>

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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.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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