libvirt users - Mar 2023 - Upgrade machine type during migration

Hi,


I have an old system. The guest there is defined with:

 ? <os>
 ??? <type arch='x86_64'
machine='pc-q35-rhel8.2.0'>hvm</type>
 ? </os>


When I try to migrate this guest to a new system I get the error:

error: internal error: unable to execute QEMU command 'blockdev-add': 
Failed to connect socket: Permission denied

On the new host I see the log entries:

libvirtd[22411]: Domain id=18 name='test02' 
uuid=9bad33a8-d18e-4c68-bdbe-dad34142dc22 is tainted: deprecated-config 
(machine type 'pc-q35-rhel8.2.0')
systemd-machined[9980]: New machine qemu-18-test02.
systemd[1]: Started Virtual Machine qemu-18-test02.
systemd-networkd[3914]: vnet20: Link DOWN
systemd-networkd[3914]: vnet20: Lost carrier
kernel: br1: port 3(vnet20) entered disabled state
kernel: device vnet20 left promiscuous mode
kernel: br1: port 3(vnet20) entered disabled state
systemd[1]: machine-qemu\x2d18\x2dtest02.scope: Deactivated successfully.
systemd-machined[9980]: Machine qemu-18-test02 terminated.
libvirtd[22411]: migration successfully aborted


It seems there is no possible combination of machine types that is 
compatible for both hosts. The old host only can start rhel8.2 guests, 
the new one only rhel9.0.


Is there a possibility to change the machine type during a migration? Is 
such a migration possible? Or do I have so shut down the guest?

Michael Schwartzkopff

On Sat, Mar 11, 2023 at 06:35:20PM +0100, Michael Schwartzkopff
wrote:
> Hi,
> 
> 
> I have an old system. The guest there is defined with:
> 
> ? <os>
> ??? <type arch='x86_64'
machine='pc-q35-rhel8.2.0'>hvm</type>
> ? </os>
> 
> 
> When I try to migrate this guest to a new system I get the error:
> 
> error: internal error: unable to execute QEMU command
'blockdev-add': Failed
> to connect socket: Permission denied
> 
> On the new host I see the log entries:
> 
> libvirtd[22411]: Domain id=18 name='test02'
> uuid=9bad33a8-d18e-4c68-bdbe-dad34142dc22 is tainted: deprecated-config
> (machine type 'pc-q35-rhel8.2.0')
> systemd-machined[9980]: New machine qemu-18-test02.
> systemd[1]: Started Virtual Machine qemu-18-test02.
> systemd-networkd[3914]: vnet20: Link DOWN
> systemd-networkd[3914]: vnet20: Lost carrier
> kernel: br1: port 3(vnet20) entered disabled state
> kernel: device vnet20 left promiscuous mode
> kernel: br1: port 3(vnet20) entered disabled state
> systemd[1]: machine-qemu\x2d18\x2dtest02.scope: Deactivated successfully.
> systemd-machined[9980]: Machine qemu-18-test02 terminated.
> libvirtd[22411]: migration successfully aborted
> 
> 
> It seems there is no possible combination of machine types that is
> compatible for both hosts. The old host only can start rhel8.2 guests, the
> new one only rhel9.0.
RHEL-9 is capable of running all rhel8.x machine types, so there shold
be no compatibility problems here.

The message you see about deprecation is simply a warning that continuing
to use this rhel8.2 machine type is discouraged, because you won't be
able to live migrate it onto future RHEL-10 hosts.
> Is there a possibility to change the machine type during a migration? Is
> such a migration possible? Or do I have so shut down the guest?
Changing machine types during live migration is impossible as that's
a guest visible hardware change. That shouldn't matter foir your
case though, as RHEL-9 is capable fo running rhel8.2 machine types.

I'd suggeest checking the /var/log/libvirt/qemu/$GUEST.log file
for details of why it might have actually failed.

With regards,
Daniel
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On Sat, Mar 11, 2023 at 18:35:20 +0100, Michael Schwartzkopff
wrote:
> Hi,
> 
> 
> I have an old system. The guest there is defined with:
> 
> ? <os>
> ??? <type arch='x86_64'
machine='pc-q35-rhel8.2.0'>hvm</type>
> ? </os>
> 
> 
> When I try to migrate this guest to a new system I get the error:
> 
> error: internal error: unable to execute QEMU command
'blockdev-add': Failed
> to connect socket: Permission denied
You seem to be using migration with non-shared storage. Could you please
post the full set of parameters you are passing to the migration API?

(or the full virsh commandline arguments)

This error seems to be a problem with setting up the disk migration
connection and (as also Daniel pointed out) has nothing to do with the
machine type.

Michael Schwartzkopff schrieb:
> It seems there is no possible combination of machine types that is 
> compatible for both hosts. The old host only can start rhel8.2 guests, 
> the new one only rhel9.0.
that depends on the host, but to be honour, I don't think, that you 
can't use different versions of guest-os.

On my Xen- and KVM-environments, we have running CentOS 5 upto 8 guests, 
plus some with Ubuntu. No problem with migration from one host to the other.
> Is there a possibility to change the machine type during a migration? Is 
> such a migration possible? Or do I have so shut down the guest?
I do not know that, what does the "machine type" mean? Your guest is a
RHEL 8.2? If so you would have to upgrade the guest os to RHEL 9.

But I think this will not solve the problem, according to the error you 
get "execute QEMU command 'blockdev-add': Failed to connect socket:
Permission denied" it's more a problem of your new host-machine.

-- 

kind regards,

thg