[libvirt] [SPDK] [Qemu-devel] Qemu migration with vhost-user-blk on top of local storage

[Wodkowski, PawelX]

On Wed, 2019-01-09 at 21:23 +0800, wuzhouhui wrote:
> > -----Original Messages-----
> > From: "Stefan Hajnoczi" <stefanha at gmail.com>
> > Sent Time: 2019-01-09 20:42:58 (Wednesday)
> > To: wuzhouhui <wuzhouhui14 at mails.ucas.ac.cn>
> > Cc: qemu-devel at nongnu.org, xieyongji at baidu.com, lilin24 at baidu.com, 
> > libvir-list at redhat.com, spdk at lists.01.org
> > Subject: Re: [Qemu-devel] Qemu migration with vhost-user-blk on top
> > of local storage
> > 
> > On Wed, Jan 09, 2019 at 06:23:42PM +0800, wuzhouhui wrote:
> > > Hi everyone,
> > > 
> > > I'm working qemu with vhost target (e.g. spdk), and I attempt to
> > > migrate VM with
> > > 2 local storages. One local storage is a regular file, e.g.
> > > /tmp/c74.qcow2, and
> > > the other is a malloc bdev that spdk created. This malloc bdev
> > > will exported to
> > > VM via vhost-user-blk. When I execute following command:
> > > 
> > >   virsh migrate --live --persistent --unsafe --undefinesource --
> > > copy-storage-all \
> > >      --p2p --auto-converge --verbose --desturi
> > > qemu+tcp://<uri>/system vm0
> > > 
> > > The libvirt reports:
> > > 
> > >   qemu-2.12.1: error: internal error: unable to execute QEMU
> > > command \
> > >     'nbd-server-add': Cannot find device=drive-virtio-disk1 nor \
> > >     node_name=drive-virtio-disk1
> > 
> > Please post your libvirt domain XML.
> 
> My libvirt is based on libvirt-1.1.1-29.el7, and add many patches to
> satisfy our
> own needs, e.g. add support for vhost-user-blk. Post domain xml may
> not useful.
> Anyway, following is full contents of XML:
> 
>   <domain type='kvm'>
>     <name>wzh</name>
>     <uuid>a84e96e6-2c53-408d-986b-c709bc6a0e51</uuid>
>     <memory unit='MiB'>4096</memory>
>     <memoryBacking>
>       <hugepages/>
>     </memoryBacking>
>     <currentMemory unit='MiB'>4096</currentMemory>
>     <vcpu placement='static' cpuset='16-31'>2</vcpu>
>     <os>
>       <type arch='x86_64' machine='pc'>hvm</type>
>       <boot dev='hd'/>
>     </os>
>     <features>
>       <acpi/>
>     </features>
>     <clock offset='utc'>
>       <timer name='rtc' tickpolicy='catchup'/>
>     </clock>
>     <on_poweroff>destroy</on_poweroff>
>     <on_reboot>restart</on_reboot>
>     <on_crash>destroy</on_crash>
>     <devices>
>       <emulator>/data/wzh/x86_64-softmmu/qemu-system-
> x86_64</emulator>
>       <disk type='file' device='disk'>
> 	<driver name='qemu' type='qcow2' cache='none'/>
> 	<source file='/data/wzh/c74.qcow2'/>
> 	<target dev='vda' bus='virtio'/>
> 	<alias name='virtio-disk0'/>
>       </disk>
> 
>       <disk type='vhost-user-blk' device='disk'>
> 	<source type='unix' path='/var/tmp/lv0' mode='client'>
> 	</source>
> 	<target dev='vdb' bus='virtio'/>
> 	<driver queues='4'/>
>       </disk>
> 
>       <controller type='usb' index='0'>
> 	<alias name='usb0'/>
>       </controller>
>       <controller type='pci' index='0' model='pci-root'>
> 	<alias name='pci.0'/>
>       </controller>
>       <serial type='pty'>
> 	<target port='0'/>
> 	<alias name='serial0'/>
>       </serial>
>       <serial type='pty'>
> 	<target port='1'/>
> 	<alias name='serial1'/>
>       </serial>
>       <input type='tablet' bus='usb'>
> 	<alias name='input0'/>
>       </input>
>       <input type='mouse' bus='ps2'/>
>       <graphics type='vnc' autoport='yes' listen='0.0.0.0'
> keymap='en-us'>
> 	<listen type='address' address='0.0.0.0'/>
>       </graphics>
>       <video>
> 	<model type='cirrus' vram='9216' heads='1'/>
> 	<alias name='video0'/>
>       </video>
>     </devices>
>     <seclabel type='none'/>
>   </domain>
> 
> > 
> > > Does it means that qemu with spdk on top of local storage don't
> > > support migration?
> > > 
> > > QEMU: 2.12.1
> > > SPDK: 18.10
> > 
> > vhost-user-blk bypasses the QEMU block layer, so NBD storage
> > migration
> > at the QEMU level will not work for the vhost-user-blk disk.
> > 
> > Stefan


Don't know if this is the case that wuzhouhui is using but generally
migration should work if all storages are accesible from both machines.
The QEMU image and Malloc bdev should be exposed using some kind of
network sharing. SPDK on migration target should be configured the same
way as on source machine.

We are testing this issuing QEMU monitor commands so I can't help with
libvirt here.

Example setup/test case we are using in one of our tests:

Machine1:
  Expose VM image over SSHF
  Expose some block device using SPDK nvmf target
  SPDK nvmf initiator:
     - connects to Machine1 SPDK nvmf target to access block device
  SPDK vhost-scsi:
    - presents block device to QEMU from SPDK nvmf initiator:
  QEMU VM uses
    - shared VM image
    - block device from SPDK nvmf  initiator over vhost-user-scsi

Machine2:  
  SPDK nvmf initiator:
     - connects to Machine1 SPDK nvmf target to access block device
  SPDK vhost-scsi:
    - presents block device to QEMU from nvmf
initiator:
  QEMU instance - waiting for incoming migration
    - shared VM image over SSHFS
    - block device from SPDK nvmf  initiator over vhost-user-scsi

Some traffic is generated using FIO and then we just migrate VM from
Machine1 to Machine2.

Pawel

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