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

[Tetsuya Mukawa <mukawa@igel.co.jp>]

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.

Regards,
Tetsuya