Re: [Qemu-devel] [PATCH for-4.0 0/6] vhost-user-blk: Add support for backend reconnecting

[Jason Wang <jasowang@redhat.com>]

On 2018/12/6 下午9:57, Jason Wang wrote:
>
> On 2018/12/6 下午2:35, elohimes@gmail.com wrote:
>> From: Xie Yongji <xieyongji@baidu.com>
>>
>> This patchset is aimed at supporting qemu to reconnect
>> vhost-user-blk backend after vhost-user-blk backend crash or
>> restart.
>>
>> The patch 1 tries to implenment the sync connection for
>> "reconnect socket".
>>
>> The patch 2 introduces a new message VHOST_USER_SET_VRING_INFLIGHT
>> to support offering shared memory to backend to record
>> its inflight I/O.
>>
>> The patch 3,4 are the corresponding libvhost-user patches of
>> patch 2. Make libvhost-user support VHOST_USER_SET_VRING_INFLIGHT.
>>
>> The patch 5 supports vhost-user-blk to reconnect backend when
>> connection closed.
>>
>> The patch 6 tells qemu that we support reconnecting now.
>>
>> To use it, we could start qemu with:
>>
>> qemu-system-x86_64 \
>>          -chardev 
>> socket,id=char0,path=/path/vhost.socket,reconnect=1,wait \
>>          -device vhost-user-blk-pci,chardev=char0 \
>>
>> and start vhost-user-blk backend with:
>>
>> vhost-user-blk -b /path/file -s /path/vhost.socket
>>
>> Then we can restart vhost-user-blk at any time during VM running.
>
>
> I wonder whether or not it's better to handle this at the level of 
> virtio protocol itself instead of vhost-user level. E.g expose 
> last_avail_idx to driver might be sufficient?
>
> Another possible issue is, looks like you need to deal with different 
> kinds of ring layouts e.g packed virtqueues.
>
> Thanks 


Cc Maxime who wrote vhost-user reconnecting for more thoughts.

Thanks