Re: [pve-devel] [PATCH qemu-server 12/14] qemu_img convert : add external snapshot support

["Fabian Grünbichler" <f.gruenbichler@proxmox.com>]

the commit title is a bit weird, this actually adapts the qemu_img_convert helper
to the new volume_has_feature values, supporting external snapshots is a side effect
of that..

> Alexandre Derumier via pve-devel <pve-devel@lists.proxmox.com> hat am 22.04.2025 13:51 CEST geschrieben:
> for external snapshot, we simply use snap volname as src.
> don't use internal snapshot option in the command line.
> 
> Signed-off-by: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>
> ---
>  PVE/QemuServer.pm | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
> index 12d60cad..5cce7094 100644
> --- a/PVE/QemuServer.pm
> +++ b/PVE/QemuServer.pm
> @@ -7906,11 +7906,11 @@ sub qemu_img_convert {
>      my $dst_format = checked_volume_format($storecfg, $dst_volid);
>      my $dst_path = PVE::Storage::path($storecfg, $dst_volid);
>      my $dst_is_iscsi = ($dst_path =~ m|^iscsi://|);
> +    my $snapshot_type = PVE::Storage::volume_has_feature($storecfg, 'snapshot', $src_volid);
>  
>      my $cmd = [];
>      push @$cmd, '/usr/bin/qemu-img', 'convert', '-p', '-n';
> -    push @$cmd, '-l', "snapshot.name=$snapname"
> -	if $snapname && $src_format && $src_format eq "qcow2";
> +    push @$cmd, '-l', "snapshot.name=$snapname" if $snapname && $snapshot_type == 2;

this breaks backwards compatibility with external plugins that override volume_has_features, and
thus still return '1' while using internal qcow2 snapshots.. I think we need to detect that and
fallback here? or we need to differentiate all four cases:

1: plugin not changed, fallback to format-based decision
2: storage snapshot, no need to pass snapshot name to qemu-img
3: qcow2-internal snapshot, need to pass snapshot name to qemu-img
4: qcow2-external snapshot, no need to pass snapshot name to qemu-img

?

at that point, it might make more sense to actually name those values:

1: plugin not changed, 'legacy' snapshot support
'storage': same semantics as '1', but plugin was updated/doesn't override volume_has_features
'file-internal': same as 3 above
'file-external': same as 4 above

? or if we want to keep volume_has_features the same, we could introduce a new helper that
returns the snapshot type?

>      push @$cmd, '-t', 'none' if $dst_scfg->{type} eq 'zfspool';
>      push @$cmd, '-T', $cachemode if defined($cachemode);
>      push @$cmd, '-r', "${bwlimit}K" if defined($bwlimit);
> -- 
> 2.39.5


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