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

27 Oct 2023


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-----Original Messages-----
From: "Stefan Hajnoczi" <stefanha@gmail.com>
Sent Time: 2019-01-09 20:42:58 (Wednesday)
To: wuzhouhui <wuzhouhui14@mails.ucas.ac.cn>
Cc: qemu-devel@nongnu.org, xieyongji@baidu.com, lilin24@baidu.com, libvir-list@redhat.com, spdk@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:
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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>
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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