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

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

On 2015/06/24 14:57, Michael S. Tsirkin wrote:
>>>>>> Also, if QEMU or the backend is closed unexpectedly, there is no way to
>>>>>> recover without restarting both applications.
>>>>> This was previously discussed:
>>>>> https://lists.gnu.org/archive/html/qemu-devel/2014-03/msg00585.html
>>>>> It doesn't look like any of the issues have been addressed.
>>>>>
>>>>> In my opinion, the right way to handle this requires
>>>>> guest cooperation.  For example, we can extend virtio 1 to allow a
>>>>> single queue to reset.
>>>>>
>>>>> We then can do something like the following:
>>>>> - hypervisor detects queue backend disconnect.
>>>>> - hypervisor sets flag and notifies guest
>>>>> - guest resets queue, optionally discarding queued packets
>>>>> - hypervisor detects (or requests if it's a client), backend reconnect
>>>>> - hypervisor detects guest queue reset
>>>>> - hypervisor notifies guests about backend reconnect
>>>>> - hypervisor sends hypervisor device state (e.g. queue addresses and
>>>>>   indices) to backend
>>>>>
>>>>> Reconnect isn't robust without such an extension.
>>>> I appreciate your all comments. It's truly helpful.
>>>> Do you have any plans to support such queue reset features in virtio spec?
>>> Maybe, but I don't have the time to work on this :(
>>> You are welcome to contribute this.
>> To do that, I need to talk around my boss to join OASIS :'(
> That's not true at all. Non members can submit feedback.
> You do need permission from your employer, but
> no need to join and pay fees if you don't want to.
> See
> https://www.oasis-open.org/committees/comments/index.php?wg_abbrev=virtio
> for the details.

Thanks so much for correcting.

>> Probably it's not so easy, so I will just wait, if we need to change
>> spec itself.
> The QEMU patch that allows handling backend disconnect similar to
> disk errors can be implemented without guest/spec changes
> let me know if you need more explanation.

Could you please describe it more?
I want to try to implement it.

Regards,
Tetsuya