How to hot plugin a new vhost-user-blk-pci device to running VM?

[Liang Chaojun]

Thanks Peter for your quickly response. Is there any workaround to do that？As you know we must take care the risk of using latest version in product environment.


Thanks a lot!

> 在 2021年5月13日，22:25，Peter Krempa <pkrempa at redhat.com> 写道：
> 
> On Thu, May 13, 2021 at 15:25:23 +0800, 梁朝军 wrote:
>>   Hi Guy,
>> 
>>   Does  anyone clear how to hot plugin a new vhost-user-blk-pci device to a
>>   running VM?
>> 
>>   Before staring vm , I pass the disk through QEMU command line  like below.
>> 
>>   <qemu:commandline>
>>    <qemu:arg value='-object'/>
>>    <qemu:arg
>>   value='memory-backend-file,id=mem0,size=4G,mem-path=/dev/hugepages,share=on'/>
>>    <qemu:arg value='-numa'/>
>>    <qemu:arg value='node,memdev=mem0'/>
>>    <qemu:arg value='-chardev'/>
>>    <qemu:arg
>>   value='socket,id=spdk_vhost_blk721ea46a-b306-11eb-a280-525400a98761,path=/var/tmp/vhost.721ea46a-b306-11eb-a280-525400a98761,reconnect=1'/>
>>    <qemu:arg value='-device'/>
>>    <qemu:arg
>>   value='vhost-user-blk-pci,chardev=spdk_vhost_blk721ea46a-b306-11eb-a280-525400a98761,bootindex=1,num-queues=4'/>
>>    <qemu:arg value='-chardev'/>
>>    <qemu:arg
>>   value='socket,id=spdk_vhost_blk2f699c58-d222-4629-9fdc-400c3aadc55e,path=/var/tmp/vhost.2f699c58-d222-4629-9fdc-400c3aadc55e,reconnect=1'/>
>>    <qemu:arg value='-device'/>
>>    <qemu:arg
>>   value='vhost-user-blk-pci,chardev=spdk_vhost_blk2f699c58-d222-4629-9fdc-400c3aadc55e,num-queues=4'/>
>>   </qemu:commandline>
>> 
>>   But I don**t know how to live add a vhost-user-blk-pci device on running
>>   VM even with calling attachDevice API now.
> 
> You need to use the proper and supported way to use vhost-user-blk:
> 
>  <disk type='vhostuser' device='disk'>
>    <driver name='qemu' type='raw'/>
>    <source type='unix' path='/tmp/vhost-blk.sock'>
>      <reconnect enabled='yes' timeout='10'/>
>    </source>
>    <target dev='vdf' bus='virtio'/>
>  </disk>
> 
> That works also with attachDevice.
> 
> 
>>   OS: redhat 7.4 Libvirt version: 3.4
> 
> This is obviously way too old for it. You'll need at least libvirt-7.1
> for that.
>