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Nir Soffer

2021-Jan-06 15:16 UTC

[ovirt-devel] Issue: Device path changed after adding disks to guest VM

On Wed, Dec 2, 2020 at 4:57 PM Joy Li <joooy.li at gmail.com>
wrote:>
> Thanks a lot Nir! Good to know that oVirt cannot guarantee the disk names
so that I don't need to spend more time trying to enable such a feature.
>
> I can always reproduce the problem via my application, basically, the
procedure is as following:
>
> 1. create a VM
Which guest OS? Can you share the guest disk image or ISO image used
to instal it?
> 2. add disks to the VM (e.g.: disk names: disk1, disk3)
> 3. check the disk mappings via `virsh domblklist `
Please shared the libvirt domain xml (virsh dumpxml vm-name)
> 4. add another disk (let's say, disk2, give a name alphabetically
before some existing disks)
Add disk while the vm is running (hotplug)?
> 5. shutdown the VM via hypervisor and start it again (reboot won't
work)
What do you mean by "reboot does not work?"
> 6. `virsh domblklist` again, then you might see the problem I mentioned
before
Mapping is different compared with state before the reboot?
> There are no virtio devices inside /dev/disk/by-id/xxx of my guest VM.
Maybe you don't have systemd-udev installed?

The links in /dev/disk/... are created by udev during startup, and
when detecting a new disk.
> And I just noticed that the disks mapping information given by hypervisor
(from VM configuration or virsh command) is different from the reality inside
the VM. The disk name inside the VM was actually not changed.
>
> So now my issue is that given a disk name (/dev/vdb) of a VM, how can I get
its wwid? Before I got it from the hypervisor, but now the hypervisor's
information is not reliable, and since the disk is unformatted, I cannot use
UUID.
You can use:

# udevadm info /dev/vda
P: /devices/pci0000:00/0000:00:02.5/0000:06:00.0/virtio4/block/vda
N: vda
L: 0
S: disk/by-path/pci-0000:06:00.0
S: disk/by-id/virtio-b97e68b2-87ea-45ca-9
S: disk/by-path/virtio-pci-0000:06:00.0
E: DEVPATH=/devices/pci0000:00/0000:00:02.5/0000:06:00.0/virtio4/block/vda
E: DEVNAME=/dev/vda
E: DEVTYPE=disk
E: MAJOR=252
E: MINOR=0
E: SUBSYSTEM=block
E: USEC_INITIALIZED=10518442
E: ID_SERIAL=b97e68b2-87ea-45ca-9
E: ID_PATH=pci-0000:06:00.0
E: ID_PATH_TAG=pci-0000_06_00_0
E: DEVLINKS=/dev/disk/by-path/pci-0000:06:00.0
/dev/disk/by-id/virtio-b97e68b2-87ea-45ca-9
/dev/disk/by-path/virtio-pci-0000:06:00.0
E: TAGS=:systemd:

I tried to reproduce you issue 4.4.5 development build:

Starting vm with 2 direct LUN disks:

# virsh -r dumpxml disk-mapping
...
    <disk type='block' device='disk'
snapshot='no'>
      <driver name='qemu' type='qcow2' cache='none'
error_policy='stop' io='native' discard='unmap'/>
      <source
dev='/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5'
index='3'>
        <seclabel model='dac' relabel='no'/>
      </source>
      <backingStore type='block' index='5'>
        <format type='qcow2'/>
        <source
dev='/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/ad891316-b80a-4ab5-895b-400108bd0ca1'>
          <seclabel model='dac' relabel='no'/>
        </source>
        <backingStore/>
      </backingStore>
      <target dev='sda' bus='scsi'/>
      <serial>40018b33-2b11-4d10-82e4-604a5b135fb2</serial>
      <boot order='1'/>
      <alias name='ua-40018b33-2b11-4d10-82e4-604a5b135fb2'/>
      <address type='drive' controller='0' bus='0'
target='0' unit='0'/>
    </disk>
    <disk type='block' device='disk'
snapshot='no'>
      <driver name='qemu' type='raw' cache='none'
error_policy='stop'
io='native' iothread='1'/>
      <source dev='/dev/mapper/3600140594af345ed76d42058f2b1a454'
index='2'>
        <seclabel model='dac' relabel='no'/>
      </source>
      <backingStore/>
      <target dev='vda' bus='virtio'/>
      <serial>b97e68b2-87ea-45ca-94fb-277d5b30baa2</serial>
      <alias name='ua-b97e68b2-87ea-45ca-94fb-277d5b30baa2'/>
      <address type='pci' domain='0x0000' bus='0x06'
slot='0x00'
function='0x0'/>
    </disk>
    <disk type='block' device='disk'
snapshot='no'>
      <driver name='qemu' type='raw' cache='none'
error_policy='stop'
io='native' iothread='1'/>
      <source dev='/dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5'
index='1'>
        <seclabel model='dac' relabel='no'/>
      </source>
      <backingStore/>
      <target dev='vdb' bus='virtio'/>
      <serial>d9a29187-f492-4a0d-aea2-7d5216c957d7</serial>
      <alias name='ua-d9a29187-f492-4a0d-aea2-7d5216c957d7'/>
      <address type='pci' domain='0x0000' bus='0x07'
slot='0x00'
function='0x0'/>
    </disk>
...

# virsh -r domblklist disk-mapping
 Target   Source
---------------------------------------------------------------------------------------------------------------------------------------------------------------
 sdc      -
 sda     
/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5
 vda      /dev/mapper/3600140594af345ed76d42058f2b1a454
 vdb      /dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5

In guest:

# ls -lh /dev/disk/by-id/virtio-*
lrwxrwxrwx. 1 root root 9 Jan  6 09:42
/dev/disk/by-id/virtio-b97e68b2-87ea-45ca-9 -> ../../vda
lrwxrwxrwx. 1 root root 9 Jan  6 09:42
/dev/disk/by-id/virtio-d9a29187-f492-4a0d-a -> ../../vdb

NOTE: "d9a29187-f492-4a0d-a" are the first characters of the disk id:
"d9a29187-f492-4a0d-aea2-7d5216c957d7"
seen in oVirt:
https://my-engine/ovirt-engine/webadmin/?locale=en_US#disks-general;id=d9a29187-f492-4a0d-aea2-7d5216c957d7


Adding another disk in sorted in the middle (while the vm is running):

# virsh -r dumpxml disk-mapping
...
    <disk type='block' device='disk'
snapshot='no'>
      <driver name='qemu' type='qcow2' cache='none'
error_policy='stop' io='native' discard='unmap'/>
      <source
dev='/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5'
index='3'>
        <seclabel model='dac' relabel='no'/>
      </source>
      <backingStore type='block' index='5'>
        <format type='qcow2'/>
        <source
dev='/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/ad891316-b80a-4ab5-895b-400108bd0ca1'>
          <seclabel model='dac' relabel='no'/>
        </source>
        <backingStore/>
      </backingStore>
      <target dev='sda' bus='scsi'/>
      <serial>40018b33-2b11-4d10-82e4-604a5b135fb2</serial>
      <boot order='1'/>
      <alias name='ua-40018b33-2b11-4d10-82e4-604a5b135fb2'/>
      <address type='drive' controller='0' bus='0'
target='0' unit='0'/>
    </disk>
    <disk type='block' device='disk'
snapshot='no'>
      <driver name='qemu' type='raw' cache='none'
error_policy='stop'
io='native' iothread='1'/>
      <source dev='/dev/mapper/3600140594af345ed76d42058f2b1a454'
index='2'>
        <seclabel model='dac' relabel='no'/>
      </source>
      <backingStore/>
      <target dev='vda' bus='virtio'/>
      <serial>b97e68b2-87ea-45ca-94fb-277d5b30baa2</serial>
      <alias name='ua-b97e68b2-87ea-45ca-94fb-277d5b30baa2'/>
      <address type='pci' domain='0x0000' bus='0x06'
slot='0x00'
function='0x0'/>
    </disk>
    <disk type='block' device='disk'
snapshot='no'>
      <driver name='qemu' type='raw' cache='none'
error_policy='stop'
io='native' iothread='1'/>
      <source dev='/dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5'
index='1'>
        <seclabel model='dac' relabel='no'/>
      </source>
      <backingStore/>
      <target dev='vdb' bus='virtio'/>
      <serial>d9a29187-f492-4a0d-aea2-7d5216c957d7</serial>
      <alias name='ua-d9a29187-f492-4a0d-aea2-7d5216c957d7'/>
      <address type='pci' domain='0x0000' bus='0x07'
slot='0x00'
function='0x0'/>
    </disk>
    <disk type='block' device='disk'
snapshot='no'>
      <driver name='qemu' type='raw' cache='none'
error_policy='stop'
io='native' iothread='1'/>
      <source dev='/dev/mapper/36001405b4d0c0b7544d47438b21296ef'
index='7'>
        <seclabel model='dac' relabel='no'/>
      </source>
      <backingStore/>
      <target dev='vdc' bus='virtio'/>
      <serial>e801c2e4-dc2e-4c53-b17b-bf6de99f16ed</serial>
      <alias name='ua-e801c2e4-dc2e-4c53-b17b-bf6de99f16ed'/>
      <address type='pci' domain='0x0000' bus='0x09'
slot='0x00'
function='0x0'/>
    </disk>
...


# virsh -r domblklist disk-mapping
 Target   Source
---------------------------------------------------------------------------------------------------------------------------------------------------------------
 sdc      -
 sda     
/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5
 vda      /dev/mapper/3600140594af345ed76d42058f2b1a454
 vdb      /dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5
 vdc      /dev/mapper/36001405b4d0c0b7544d47438b21296ef

In the guest:

# ls -lh /dev/disk/by-id/virtio-*
lrwxrwxrwx. 1 root root 9 Jan  6 09:42
/dev/disk/by-id/virtio-b97e68b2-87ea-45ca-9 -> ../../vda
lrwxrwxrwx. 1 root root 9 Jan  6 09:42
/dev/disk/by-id/virtio-d9a29187-f492-4a0d-a -> ../../vdb
lrwxrwxrwx. 1 root root 9 Jan  6 09:51
/dev/disk/by-id/virtio-e801c2e4-dc2e-4c53-b -> ../../vdc


Shutdown VM and start it again

# virsh -r dumpxml disk-mapping
...
    <disk type='block' device='disk'
snapshot='no'>
      <driver name='qemu' type='qcow2' cache='none'
error_policy='stop' io='native' discard='unmap'/>
      <source
dev='/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5'
index='4'>
        <seclabel model='dac' relabel='no'/>
      </source>
      <backingStore type='block' index='6'>
        <format type='qcow2'/>
        <source
dev='/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/ad891316-b80a-4ab5-895b-400108bd0ca1'>
          <seclabel model='dac' relabel='no'/>
        </source>
        <backingStore/>
      </backingStore>
      <target dev='sda' bus='scsi'/>
      <serial>40018b33-2b11-4d10-82e4-604a5b135fb2</serial>
      <boot order='1'/>
      <alias name='ua-40018b33-2b11-4d10-82e4-604a5b135fb2'/>
      <address type='drive' controller='0' bus='0'
target='0' unit='0'/>
    </disk>
    <disk type='block' device='disk'
snapshot='no'>
      <driver name='qemu' type='raw' cache='none'
error_policy='stop'
io='native' iothread='1'/>
      <source dev='/dev/mapper/3600140594af345ed76d42058f2b1a454'
index='3'>
        <seclabel model='dac' relabel='no'/>
      </source>
      <backingStore/>
      <target dev='vda' bus='virtio'/>
      <serial>b97e68b2-87ea-45ca-94fb-277d5b30baa2</serial>
      <alias name='ua-b97e68b2-87ea-45ca-94fb-277d5b30baa2'/>
      <address type='pci' domain='0x0000' bus='0x06'
slot='0x00'
function='0x0'/>
    </disk>
    <disk type='block' device='disk'
snapshot='no'>
      <driver name='qemu' type='raw' cache='none'
error_policy='stop'
io='native' iothread='1'/>
      <source dev='/dev/mapper/36001405b4d0c0b7544d47438b21296ef'
index='2'>
        <seclabel model='dac' relabel='no'/>
      </source>
      <backingStore/>
      <target dev='vdb' bus='virtio'/>
      <serial>e801c2e4-dc2e-4c53-b17b-bf6de99f16ed</serial>
      <alias name='ua-e801c2e4-dc2e-4c53-b17b-bf6de99f16ed'/>
      <address type='pci' domain='0x0000' bus='0x09'
slot='0x00'
function='0x0'/>
    </disk>
    <disk type='block' device='disk'
snapshot='no'>
      <driver name='qemu' type='raw' cache='none'
error_policy='stop'
io='native' iothread='1'/>
      <source dev='/dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5'
index='1'>
        <seclabel model='dac' relabel='no'/>
      </source>
      <backingStore/>
      <target dev='vdc' bus='virtio'/>
      <serial>d9a29187-f492-4a0d-aea2-7d5216c957d7</serial>
      <alias name='ua-d9a29187-f492-4a0d-aea2-7d5216c957d7'/>
      <address type='pci' domain='0x0000' bus='0x07'
slot='0x00'
function='0x0'/>
    </disk>
...

# virsh -r domblklist disk-mapping
 Target   Source
---------------------------------------------------------------------------------------------------------------------------------------------------------------
 sdc      -
 sda     
/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5
 vda      /dev/mapper/3600140594af345ed76d42058f2b1a454
 vdb      /dev/mapper/36001405b4d0c0b7544d47438b21296ef
 vdc      /dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5


In the guest:

# ls -lh /dev/disk/by-id/virtio-*
lrwxrwxrwx. 1 root root 9 Jan  6 09:55
/dev/disk/by-id/virtio-b97e68b2-87ea-45ca-9 -> ../../vda
lrwxrwxrwx. 1 root root 9 Jan  6 09:55
/dev/disk/by-id/virtio-d9a29187-f492-4a0d-a -> ../../vdb
lrwxrwxrwx. 1 root root 9 Jan  6 09:55
/dev/disk/by-id/virtio-e801c2e4-dc2e-4c53-b -> ../../vdc

Comparing to state before reboot:

# virsh -r domblklist disk-mapping
 Target   Source
---------------------------------------------------------------------------------------------------------------------------------------------------------------
 sdc      -
 sda     
/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5
 vda      /dev/mapper/3600140594af345ed76d42058f2b1a454
 vdb      /dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5
 vdc      /dev/mapper/36001405b4d0c0b7544d47438b21296ef

# ls -lh /dev/disk/by-id/virtio-*
lrwxrwxrwx. 1 root root 9 Jan  6 09:42
/dev/disk/by-id/virtio-b97e68b2-87ea-45ca-9 -> ../../vda
lrwxrwxrwx. 1 root root 9 Jan  6 09:42
/dev/disk/by-id/virtio-d9a29187-f492-4a0d-a -> ../../vdb
lrwxrwxrwx. 1 root root 9 Jan  6 09:51
/dev/disk/by-id/virtio-e801c2e4-dc2e-4c53-b -> ../../vdc

In the guest disks are mapped to the same device name.

It looks like libivrt domblklist is not correct - vdb and vdc are switched.
Peter, this expected?

Nir
>
> Joy
>
> On Wed, Dec 2, 2020 at 1:28 PM Nir Soffer <nsoffer at redhat.com>
wrote:
>>
>> On Wed, Dec 2, 2020 at 10:27 AM Joy Li <joooy.li at gmail.com>
wrote:
>> >
>> > Hi All,
>> >
>> > I'm facing the problem that after adding disks to guest VM,
the device target path changed (My ovirt version is 4.3). For example:
>> >
>> > Before adding a disk:
>> >
>> > virsh # domblklist <vmname>
>> > Target   Source
>> > ---------------------------------------------------------
>> >  hdc      -
>> >  vda      /dev/mapper/3600a09803830386546244a546d494f53
>> >  vdb      /dev/mapper/3600a09803830386546244a546d494f54
>> >  vdc      /dev/mapper/3600a09803830386546244a546d494f55
>> >  vdd      /dev/mapper/3600a09803830386546244a546d494f56
>> >  vde      /dev/mapper/3600a09803830386546244a546d494f57
>> >  vdf      /dev/mapper/3600a09803830386546244a546d494f58
>> >
>> > After adding a disk, and then shutdown and start the VM:
>> >
>> > virsh # domblklist <vmname>
>> > Target   Source
>> > ---------------------------------------------------------
>> >  hdc      -
>> >  vda      /dev/mapper/3600a09803830386546244a546d494f53
>> >  vdb      /dev/mapper/3600a09803830386546244a546d494f54
>> >  vdc      /dev/mapper/3600a09803830386546244a546d494f6c
>> >  vdd      /dev/mapper/3600a09803830386546244a546d494f55
>> >  vde      /dev/mapper/3600a09803830386546244a546d494f56
>> >  vdf      /dev/mapper/3600a09803830386546244a546d494f57
>> >  vdg      /dev/mapper/3600a09803830386546244a546d494f58
>> >
>> > The devices' multipath doesn't map to the same target path
as before, so in my VM the /dev/vdc doesn't point to the old
/dev/mapper/3600a09803830386546244a546d494f55 anymore.
>> >
>> > Anybody knows how can I make the device path mapping fixed without
being changed after adding or removing disks.
>>
>> Device nodes are not stable, and oVirt cannot guarantee that you will
>> get the same
>> node in the guest in all runs.
>>
>> You should use /dev/disk/by-id/xxx links to located devices, and blkid
to create
>> fstab mounts that do not depend on node names.
>>
>> Regardless, oVirt try to keep devices stable as possible. Do you know
>> how to reproduce
>> this issue reliably?
>>
>> Nir
>>

Peter Krempa

2021-Jan-06 15:36 UTC

head link

[ovirt-devel] Issue: Device path changed after adding disks to guest VM

On Wed, Jan 06, 2021 at 17:16:24 +0200, Nir Soffer
wrote:> On Wed, Dec 2, 2020 at 4:57 PM Joy Li <joooy.li at gmail.com> wrote:
[...]
> Comparing to state before reboot:
> 
> # virsh -r domblklist disk-mapping
>  Target   Source
>
---------------------------------------------------------------------------------------------------------------------------------------------------------------
>  sdc      -
>  sda     
/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5
>  vda      /dev/mapper/3600140594af345ed76d42058f2b1a454
>  vdb      /dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5
>  vdc      /dev/mapper/36001405b4d0c0b7544d47438b21296ef
> 
> # ls -lh /dev/disk/by-id/virtio-*
> lrwxrwxrwx. 1 root root 9 Jan  6 09:42
> /dev/disk/by-id/virtio-b97e68b2-87ea-45ca-9 -> ../../vda
> lrwxrwxrwx. 1 root root 9 Jan  6 09:42
> /dev/disk/by-id/virtio-d9a29187-f492-4a0d-a -> ../../vdb
> lrwxrwxrwx. 1 root root 9 Jan  6 09:51
> /dev/disk/by-id/virtio-e801c2e4-dc2e-4c53-b -> ../../vdc
> 
> In the guest disks are mapped to the same device name.
> 
> It looks like libivrt domblklist is not correct - vdb and vdc are switched.
> Peter, this expected?
The names in 'virsh domblklist' are unfortunately and confusingly chosen
to match the expected /dev/ device node name, but it's at kernel's
discretion to name /dev/ nodes.

This means that it's not guaranteed that what you see in 'virsh
domblklist' will match the state in the guest.

In this case I think the reorder happens as the PCI address of vdb is
larger than the address of vdc.

A partial workaround can be to use the data provided by the qemu guest
agent, for exampe via 'virsh domfsinfo':

$ virsh domfsinfo fedora32
 Mountpoint   Name   Type   Target
------------------------------------
 /            dm-0   xfs    vda
 /boot        vda1   xfs    vda

Here the guest-host matching is established via the PCI address so the
'Target' field accurately refers to the target in the VM XML.

Similarly the linux kernel recently changed enumeration of SCSI devices
so they are not guaranteed to match either. Libguestfs for example
needed a workaround.

https://github.com/libguestfs/libguestfs/commit/bca9b94fc593771b3801b09b95e477f160517909

libvirt users - Jan 2021 - [ovirt-devel] Issue: Device path changed after adding disks to guest VM

[ovirt-devel] Issue: Device path changed after adding disks to guest VM

[ovirt-devel] Issue: Device path changed after adding disks to guest VM