Re: [pve-devel] [PATCH qemu-server 13/14] blockdev: add backing_chain support

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

> Alexandre Derumier via pve-devel <pve-devel@lists.proxmox.com> hat am 22.04.2025 13:51 CEST geschrieben:
> We need to define name-nodes for all backing chain images,
> to be able to live rename them with blockdev-reopen
> 
> For linked clone, we don't need to definebase image(s) chain.
> They are auto added with #block nodename.
> 
> Signed-off-by: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>
> ---
>  PVE/QemuServer/Drive.pm | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
> 
> diff --git a/PVE/QemuServer/Drive.pm b/PVE/QemuServer/Drive.pm
> index 08b893a1..0737034d 100644
> --- a/PVE/QemuServer/Drive.pm
> +++ b/PVE/QemuServer/Drive.pm
> @@ -1249,6 +1249,37 @@ sub generate_format_blockdev {
>      return $blockdev;
>  }
>  
> +sub generate_backing_blockdev {

make this private?

> +    my ($storecfg, $snapshots, $deviceid, $drive, $snap_id) = @_;
> +
> +    my $snapshot = $snapshots->{$snap_id};
> +    my $parentid = $snapshot->{parent};
> +
> +    my $volid = $drive->{file};
> +
> +    my $snap_file_blockdev = generate_file_blockdev($storecfg, $drive, $snap_id);
> +    $snap_file_blockdev->{filename} = $snapshot->{file};
> +    $drive->{ro} = 1;
> +    my $snap_fmt_blockdev = generate_format_blockdev($storecfg, $drive, $snap_file_blockdev, $snap_id);
> +    $snap_fmt_blockdev->{backing} = generate_backing_blockdev($storecfg, $snapshots, $deviceid, $drive, $parentid) if $parentid;
> +    return $snap_fmt_blockdev;
> +}
> +
> +sub generate_backing_chain_blockdev {
> +    my ($storecfg, $deviceid, $drive) = @_;
> +
> +    my $volid = $drive->{file};
> +    my $snapshot_type = PVE::Storage::volume_has_feature($storecfg, 'snapshot', $volid);
> +    return if !$snapshot_type || $snapshot_type != 3;

this can just be $snapshot_type != 3.. should we move this check to the caller?
and make this helper private?

> +
> +    my $chain_blockdev = undef;

drop this

> +    PVE::Storage::activate_volumes($storecfg, [$volid]);
> +    my $snapshots = PVE::Storage::volume_snapshot_info($storecfg, $volid);
> +    my $parentid = $snapshots->{'current'}->{parent};

return undef if !$parentid;

> +    $chain_blockdev = generate_backing_blockdev($storecfg, $snapshots, $deviceid, $drive, $parentid) if $parentid;

return generate_backing_blockdev(...);

> +    return $chain_blockdev;
> +}
> +
>  sub generate_drive_blockdev {
>      my ($storecfg, $drive, $live_restore_name) = @_;
>  
> @@ -1266,6 +1297,8 @@ sub generate_drive_blockdev {
>  
>      my $blockdev_file = generate_file_blockdev($storecfg, $drive);
>      my $blockdev_format = generate_format_blockdev($storecfg, $drive, $blockdev_file);
> +    my $backing_chain  = generate_backing_chain_blockdev($storecfg, "drive-$drive_id", $drive);
> +    $blockdev_format->{backing} = $backing_chain if $backing_chain;
>  
>      #pflash0 don't support throttle-filter
>      return $blockdev_format if $drive_id eq 'pflash0';
> -- 
> 2.39.5


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