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Re: [Qemu-devel] [PATCH v2 0/5] Add feature to start QEMU without vhost-

From: Tetsuya Mukawa
Subject: Re: [Qemu-devel] [PATCH v2 0/5] Add feature to start QEMU without vhost-user backend
Date: Wed, 22 Jul 2015 11:44:28 +0900
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

On 2015/07/19 21:48, Michael S. Tsirkin wrote:
> On Wed, Jun 24, 2015 at 07:57:45AM +0200, Michael S. Tsirkin wrote:
>> On Wed, Jun 24, 2015 at 02:46:30PM +0900, Tetsuya Mukawa wrote:
>>> On 2015/06/23 18:41, Michael S. Tsirkin wrote:
>>>> On Tue, Jun 23, 2015 at 05:31:06PM +0900, Tetsuya Mukawa wrote:
>>>>> On 2015/06/22 17:14, Michael S. Tsirkin wrote:
>>>>>> On Mon, Jun 22, 2015 at 12:50:43PM +0900, Tetsuya Mukawa wrote:
>>>>>>> Hi guys,
>>>>>>> Here are patches to add feature to start QEMU without vhost-user 
>>>>>>> backend.
>>>>>>> Currently, if we want to use vhost-user backend, the backend must start 
>>>>>>> before
>>>>>>> QEMU.
>>>>>> Aren't you looking for something like xinetd?
>>>>> It will help for restricting starting order, but not help for
>>>>> reconnection of vhost-user backend.
>>>> At this point, I suggest that we always connect at vm start.
>>>> With that, you can add an option to reset the VM
>>>> on backend disconnect.
>>>> So
>>>>    - detect backend disconnect
>>>>    - reset and stop (notifying management)
>>>>    - reconnect or detect backend reconnect
>>>>    - proceed with boot
>>>> As I tried to explain below, getting the full functionality
>>>> will require guest driver changes. They aren't hard to get
>>>> done, patches welcome.
>>> Could you please let me know your thinking about using
>>> DEVICE_NEEDS_RESET for vhost-user reconnection?
>>> If it's works, I will try to submit it.
>> DEVICE_NEEDS_RESET is hard to handle correctly in guest:
>> you need to reconfigure a bunch of state,
>> so far no one wrote the necessary support.
> But yes, if you write the guest code, I think
> it can work.
> We probably want a feature bit so host can know guest can
> handle reconnections, but that's a minor detail, it
> would be easy to add afterwards.

Hi Michael,

I appreciate for your suggestion.
I will check the virtio-net driver of linux and the virtio-net device of
QEMU to know how difficult to implement DEVICE_NEEDS_RESET.


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