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

[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?

>  }
>  
>  # Stops the dbus-vmstate helper D-Bus service daemon and removes the associated
> -- 
> 2.47.3
> 
> 
> 
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