Re: [PATCH qemu-server 1/1] fix #8030: snapshot: avoid orphaned vmstate volume on failure

["Elias Huhsovitz" <e.huhsovitz@proxmox.com>]

Sensible change! The state information should be allocated as late as
possible on disk.

Tested using the same methodology as the bug reporter. The state-file
was not orphaned and after releasing the QMP socket, operations and
snapshots continued working as normal.

Therefore:

Reviewed-by: Elias Huhsovitz <e.huhsovitz@proxmox.com>
Tested-by: Elias Huhsovitz <e.huhsovitz@proxmox.com>

On Mon Sep 14, 2026 at 4:05 PM CEST, Michael Köppl wrote:
> The state volume was allocated before the running instance was queried
> for its machine type, CPU argument and network MTUs. Those queries can
> fail (e.g. the 'query-machines' QMP command, which can run into a
> timeout while QEMU's is busy [0]).
>
> The helper is called from __snapshot_prepare() before write_config(), so
> the config never records the snapshot, snapshot_create() dies before it
> gets to its cleanup path. Such a failure leaves behind the just
> allocated volume.
>
> Query the running instance first, which makes the allocation the last
> step of the function that can fail.
>
> [0] https://bugzilla.proxmox.com/show_bug.cgi?id=8030
>
> Signed-off-by: Michael Köppl <m.koeppl@proxmox.com>
> ---
> Tested this pretty much as described in the Bugzilla entry, but using a
> Perl script to connect to the QMP socket instead of socat.
>
>  src/PVE/QemuConfig.pm | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/src/PVE/QemuConfig.pm b/src/PVE/QemuConfig.pm
> index 26f0fda2..2ef6c075 100644
> --- a/src/PVE/QemuConfig.pm
> +++ b/src/PVE/QemuConfig.pm
> @@ -238,8 +238,6 @@ sub __snapshot_save_vmstate {
>      my $name = "vm-$vmid-state-$snapname";
>      $name .= ".raw" if $scfg->{path}; # add filename extension for file base storage
>  
> -    my $statefile =
> -        PVE::Storage::vdisk_alloc($storecfg, $target, $vmid, 'raw', $name, $size * 1024);
>      my $runningmachine = PVE::QemuServer::Machine::get_current_qemu_machine($vmid);
>  
>      # get current QEMU -cpu argument to ensure consistency of custom CPU models
> @@ -249,6 +247,11 @@ sub __snapshot_save_vmstate {
>  
>      my $nets_host_mtu = PVE::QemuServer::Network::get_nets_host_mtu($vmid, $conf);
>  
> +    # allocate only after querying the running instance, nothing below can fail, so a failed
> +    # query cannot leave an orphaned state volume behind
> +    my $statefile =
> +        PVE::Storage::vdisk_alloc($storecfg, $target, $vmid, 'raw', $name, $size * 1024);
> +
>      if (!$suspend) {
>          $conf = $conf->{snapshots}->{$snapname};
>      }