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From: Wen Congyang <wency@cn.fujitsu.com>
Message-ID: <55FA122F.8080608@cn.fujitsu.com>
Date: Thu, 17 Sep 2015 09:06:55 +0800
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Subject: Re: [Qemu-devel] [Qemu-block] [PATCH v3 1/5] support nbd driver in
 blockdev-add
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To: Eric Blake <eblake@redhat.com>, Markus Armbruster <armbru@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>, qemu devel <qemu-devel@nongnu.org>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Gonglei <arei.gonglei@huawei.com>, Stefan Hajnoczi <stefanha@redhat.com>, Yang Hongyang <yanghy@cn.fujitsu.com>

On 09/16/2015 10:53 PM, Eric Blake wrote:
> On 09/16/2015 05:18 AM, Markus Armbruster wrote:
> 
>>>>>>>> Perhaps it could be as simple as
>>>>>>>>
>>>>>>>>     { 'struct': 'BlockdevOptionsNBD',
>>>>>>>>       'data': { 'addr: 'SocketAddress', 'export': 'str' } }
>>>>>>>
>>>>>>> The problem is that: NBD doesn't use the fd.
>>>>>>
>>>>>> Is that fundamental, or just a matter of implementation?
>>>>
>>>> Question still open.
>>
>> Question still open.
> 
> Dan's patches didn't address it...
> 
>> Long term, I'd like to see us get rid of the conversions between
>> QAPI-generated types and QDict / QemuOpts.
>>
>> Short term, you need to co-evolve the QDict-based code such as
>> nbd_config() with the QAPI interfaces.
> 
> ...but DO affect the short-term, by starting the conversion over to
> using the QAPI type more fully:
> https://lists.gnu.org/archive/html/qemu-devel/2015-09/msg04383.html

The problem still exists with this patch, because we pass "addr.data.host"
to nbd_open().

Thanks
Wen Congyang

> 
>>
>> Keeping the QAPI interface clean is more important than minimizing the
>> implementation work, because we're free to mess with the implementation,
>> but releasing a QAPI interface makes it ABI, so we better get it right.
> 
> Especially once the QAPI interface is actually used by a QMP command
> (there are places where we are using qapi internally for ease in command
> line handling, but not exposing the structures through QMP yet).
>