[pve-devel] [PATCH qemu-server 3/3] migration: conntrack: avoid crash when dbus-vmstate object cannot be added (quickly enough)

[Fiona Ebner]

Am 03.10.25 um 1:42 PM schrieb Fabian Grünbichler:
> On September 29, 2025 2:24 pm, Fiona Ebner wrote:
>> As reported in the community forum [0], it might happen that the
>> dbus-vmstate object is not added (quickly enough) to the target QEMU
>> instance, before the migration state is loaded. This would result in
>> a crash of the target instance:
>>
>>> kvm: Unknown savevm section or instance 'dbus-vmstate/dbus-vmstate'
>>> 0. Make sure that your current VM setup matches your saved VM setup,
>>> including any hotplugged devices
>>> kvm: load of migration failed: Invalid argument
>>
>> This is after the configuration is already moved and thus there also
>> is no source instance running anymore.
>>
>> Make sure that the qemu_add_dbus_vmstate() function only returns
>> success when the object is successfully added.
>>
>> [0]: https://forum.proxmox.com/threads/172588/
>>
>> Signed-off-by: Fiona Ebner <f.ebner at proxmox.com>
>> ---
>>  src/PVE/QemuServer/DBusVMState.pm | 10 ++++++++++
>>  1 file changed, 10 insertions(+)
>>
>> diff --git a/src/PVE/QemuServer/DBusVMState.pm b/src/PVE/QemuServer/DBusVMState.pm
>> index a72d6dd2..354602a7 100644
>> --- a/src/PVE/QemuServer/DBusVMState.pm
>> +++ b/src/PVE/QemuServer/DBusVMState.pm
>> @@ -11,6 +11,7 @@ use PVE::Systemd;
>>  use PVE::Tools;
>>  
>>  use PVE::QemuServer::Helpers;
>> +use PVE::QemuServer::Monitor qw(mon_cmd);
>>  
>>  use constant {
>>      DBUS_VMSTATE_EXE => '/usr/libexec/qemu-server/dbus-vmstate',
>> @@ -59,6 +60,15 @@ sub qemu_add_dbus_vmstate {
>>      if (my $err = $@) {
>>          die "failed to start DBus VMState service for VM $vmid: $err\n";
>>      }
>> +
>> +    # Need to wait for the object to be added by the started service.
>> +    for (my $i = 0; $i < 5; $i++) {
>> +        my $qom_list = mon_cmd($vmid, 'qom-list', path => '/objects');
>> +        return if grep { $_->{name} eq 'pve-vmstate' } $qom_list->@*;
>> +        sleep 1;
>> +    }
>> +
>> +    die "timeout waiting for pve-vmstate object to show up\n";
> 
> wouldn't this be better handled by making the service started here
> type=notify?

Yes, good idea! Will send a v2.