Re: [PATCH qemu-server 1/2] fix #5032: qemu: sync guest time on resume and snapshot of saved state

[Arthur Bied-Charreton <a.bied-charreton@proxmox.com>]

On Fri, Jun 12, 2026 at 02:29:41PM +0200, Jakob Klocker wrote:

One comment inline, with that addressed consider this:

Reviewed-by: Arthur Bied-Charreton <a.bied-charreton@proxmox.com>
Tested-by: Arthur Bied-Charreton <a.bied-charreton@proxmox.com>

> When a VM is resumed from a saved state (hibernation or snapshot with
> RAM), the guest clock may be stale. A time skew can occur when
> creating a snapshot of a running VM.
> 
> Add a new agent option `set-time-on-resume` to automatically
> synchronize the guest time with the host using the QEMU Guest Agent.
> 
> Trigger time synchronization:
> - after restoring a VM from a saved state or snapshot with RAM
> - after taking a snapshot
> 
> This ensures consistent guest time after rollback, restore, or
> snapshot operations when the guest OS clock does not automatically
> correct itself.
> 
> Link: https://bugzilla.proxmox.com/show_bug.cgi?id=5032
> 
> Signed-off-by: Jakob Klocker <j.klocker@proxmox.com>
> ---
[...]
> diff --git a/src/PVE/QemuServer.pm b/src/PVE/QemuServer.pm
> index 239b0cab..99bdd9f5 100644
> --- a/src/PVE/QemuServer.pm
> +++ b/src/PVE/QemuServer.pm
> @@ -5983,6 +5983,16 @@ sub vm_start_nolock {
>          );
>      }
>  
> +    my $from_saved_state = $resume || ($statefile && !$migratedfrom);
> +
> +    if (
> +        $from_saved_state
> +        && PVE::QemuServer::Agent::should_set_time_on_resume($conf->{agent})
> +    ) {
> +        eval { PVE::QemuServer::Agent::guest_set_time($vmid); 1 }
> +            or warn "could not sync guest time after snapshot - $@";
> +    }
Since this is the resume path, it would make sense to adapt this 
warning message accordingly, would be less confusing and make it easier
to grep for the relevant code when seeing the line in the journal. 
> +
>      return $res;
>  }
[...]