Re: [PATCH qemu-server] api: create disks: use correct volume name for cloudinit on a snapshot-as-volume-chain storage

["Max R. Carrara" <m.carrara@proxmox.com>]

On Fri Aug 7, 2026 at 1:59 PM CEST, Fiona Ebner wrote:
> The pve-storage commit 05032c5 ("fix #7811: storage: lvm: reject
> allocation on format and volume name mismatch") exposed an issue with
> handling the name of the cloudinit name on an LVM storage with
> snapshot-as-volume-chain. The guest layer passes a fixed name for the
> cloudinit drive, but this does not match what the storage layer needs,
> because it was missing the .qcow2 extension. Fix the issue by catching
> that case.
>
> This is a stop-gap fix. In the long run, constructing the name should
> not be done in the guest layer, rather the storage plugin should be
> queried for a valid name first.
>
> Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
> ---

Just gave this a spin and can confirm that it works as expected.

Before applying this patch, the LVM storage w/ SaVC enabled refused the
cloudinit drive ('does not match requested format "qcow2"') -- with the
patch applied, the cloudinit drive can be added again without issues.

Unless there's something I have missed, this LGTM. Nice job!

Consider:

Tested-by: Max R. Carrara <m.carrara@proxmox.com>

>  src/PVE/API2/Qemu.pm | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/src/PVE/API2/Qemu.pm b/src/PVE/API2/Qemu.pm
> index 39c725d0..3320313c 100644
> --- a/src/PVE/API2/Qemu.pm
> +++ b/src/PVE/API2/Qemu.pm
> @@ -495,6 +495,9 @@ my sub create_disks : prototype($$$$$$$$$$$) {
>              if ($scfg->{path}) {
>                  $fmt = $disk->{format} // "qcow2";
>                  $name .= ".$fmt";
> +            } elsif ($scfg->{'snapshot-as-volume-chain'}) {
> +                $fmt = $disk->{format} // "qcow2";
> +                $name .= ".$fmt" if $fmt eq 'qcow2';
>              } else {
>                  $fmt = $disk->{format} // "raw";
>              }