[pve-devel] [PATCH pve-storage 8/9] lvmplugin: add qcow2 snapshot - Alexandre Derumier via pve-devel

From: Alexandre Derumier via pve-devel <pve-devel@lists.proxmox.com>
To: pve-devel@lists.proxmox.com
Cc: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>
Subject: [pve-devel] [PATCH pve-storage 8/9] lvmplugin: add qcow2 snapshot
Date: Tue,  3 Jun 2025 09:55:52 +0200	[thread overview]
Message-ID: <mailman.225.1748937433.395.pve-devel@lists.proxmox.com> (raw)
In-Reply-To: <20250603075558.627850-1-alexandre.derumier@groupe-cyllene.com>

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From: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>
To: pve-devel@lists.proxmox.com
Subject: [PATCH pve-storage 8/9] lvmplugin: add qcow2 snapshot
Date: Tue,  3 Jun 2025 09:55:52 +0200
Message-ID: <20250603075558.627850-18-alexandre.derumier@groupe-cyllene.com>

we format lvm logical volume with qcow2 to handle snapshot chain.

like for qcow2 file, when a snapshot is taken, the current lvm volume
is renamed to snap volname, and a new current lvm volume is created
with the snap volname as backing file

Signed-off-by: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>
---
 src/PVE/Storage/LVMPlugin.pm | 450 ++++++++++++++++++++++++++++++-----
 1 file changed, 385 insertions(+), 65 deletions(-)

diff --git a/src/PVE/Storage/LVMPlugin.pm b/src/PVE/Storage/LVMPlugin.pm
index 25268a4..af50b91 100644
--- a/src/PVE/Storage/LVMPlugin.pm
+++ b/src/PVE/Storage/LVMPlugin.pm
@@ -11,6 +11,8 @@ use PVE::JSONSchema qw(get_standard_option);
 
 use PVE::Storage::Common;
 
+use JSON;
+
 use base qw(PVE::Storage::Plugin);
 
 # lvm helper functions
@@ -209,6 +211,59 @@ sub lvm_list_volumes {
     return $lvs;
 }
 
+sub free_lvm_volumes {
+    my ($class, $scfg, $storeid, $volnames) = @_;
+
+    my $vg = $scfg->{vgname};
+
+    # we need to zero out LVM data for security reasons
+    # and to allow thin provisioning
+    my $zero_out_worker = sub {
+	# wipe throughput up to 10MB/s by default; may be overwritten with saferemove_throughput
+	my $throughput = '-10485760';
+	if ($scfg->{saferemove_throughput}) {
+		$throughput = $scfg->{saferemove_throughput};
+	}
+	for my $name (@$volnames) {
+	    print "zero-out data on image $name (/dev/$vg/del-$name)\n";
+
+	    my $cmd = [
+		'/usr/bin/cstream',
+		'-i', '/dev/zero',
+		'-o', "/dev/$vg/del-$name",
+		'-T', '10',
+		'-v', '1',
+		'-b', '1048576',
+		'-t', "$throughput"
+	    ];
+	    eval { run_command($cmd, errmsg => "zero out finished (note: 'No space left on device' is ok here)"); };
+	    warn $@ if $@;
+
+	    $class->cluster_lock_storage($storeid, $scfg->{shared}, undef, sub {
+		my $cmd = ['/sbin/lvremove', '-f', "$vg/del-$name"];
+		run_command($cmd, errmsg => "lvremove '$vg/del-$name' error");
+	    });
+	    print "successfully removed volume $name ($vg/del-$name)\n";
+	}
+    };
+
+    if ($scfg->{saferemove}) {
+	for my $name (@$volnames) {
+	    # avoid long running task, so we only rename here
+	    my $cmd = ['/sbin/lvrename', $vg, $name, "del-$name"];
+	    run_command($cmd, errmsg => "lvrename '$vg/$name' error");
+	}
+	return $zero_out_worker;
+    } else {
+	for my $name (@$volnames) {
+	    my $tmpvg = $scfg->{vgname};
+	    my $cmd = ['/sbin/lvremove', '-f', "$tmpvg/$name"];
+	    run_command($cmd, errmsg => "lvremove '$tmpvg/$name' error");
+	}
+    }
+}
+
+
 # Configuration
 
 sub type {
@@ -218,6 +273,7 @@ sub type {
 sub plugindata {
     return {
 	content => [ {images => 1, rootdir => 1}, { images => 1 }],
+	format => [ { raw => 1, qcow2 => 1 } , 'raw' ],
 	'sensitive-properties' => {},
     };
 }
@@ -294,7 +350,10 @@ sub parse_volname {
     PVE::Storage::Plugin::parse_lvm_name($volname);
 
     if ($volname =~ m/^(vm-(\d+)-\S+)$/) {
-	return ('images', $1, $2, undef, undef, undef, 'raw');
+	my $name = $1;
+	my $vmid = $2;
+	my $format = $volname =~ m/\.qcow2$/ ? 'qcow2' : 'raw';
+	return ('images', $name, $vmid, undef, undef, undef, $format);
     }
 
     die "unable to parse lvm volume name '$volname'\n";
@@ -303,11 +362,13 @@ sub parse_volname {
 sub filesystem_path {
     my ($class, $scfg, $volname, $snapname) = @_;
 
-    die "lvm snapshot is not implemented"if defined($snapname);
+    my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) =
+	$class->parse_volname($volname);
 
-    my ($vtype, $name, $vmid) = $class->parse_volname($volname);
+    die "snapshot is working with qcow2 format only" if defined($snapname) && $format ne 'qcow2';
 
     my $vg = $scfg->{vgname};
+    $name = $class->get_snap_name($volname, $snapname) if $snapname;
 
     my $path = "/dev/$vg/$name";
 
@@ -335,7 +396,9 @@ sub find_free_diskname {
 
     my $disk_list = [ keys %{$lvs->{$vg}} ];
 
-    return PVE::Storage::Plugin::get_next_vm_diskname($disk_list, $storeid, $vmid, undef, $scfg);
+    $add_fmt_suffix = $fmt eq 'qcow2' ? 1 : undef;
+
+    return PVE::Storage::Plugin::get_next_vm_diskname($disk_list, $storeid, $vmid, $fmt, $scfg, $add_fmt_suffix);
 }
 
 sub lvcreate {
@@ -363,13 +426,47 @@ sub lvrename {
     );
 }
 
-sub alloc_image {
-    my ($class, $storeid, $scfg, $vmid, $fmt, $name, $size) = @_;
+my sub lvm_qcow2_format {
+    my ($class, $storeid, $scfg, $name, $fmt, $backing_snap, $size) = @_;
 
-    die "unsupported format '$fmt'" if $fmt ne 'raw';
+    die "Can't format the volume, the format is not qcow2" if $fmt ne 'qcow2';
+
+    $class->activate_volume($storeid, $scfg, $name);
+    my $path = $class->path($scfg, $name, $storeid);
+
+    if ($backing_snap) {
+	my $backing_path = $class->path($scfg, $name, $storeid, $backing_snap);
+	PVE::Storage::Common::qemu_img_create_qcow2_backed($scfg, $path, $backing_path, $fmt);
+    } else {
+	PVE::Storage::Common::qemu_img_create($scfg, $fmt, $size, $path);
+    }
+}
+
+my sub calculate_lvm_size {
+    my ($size, $fmt, $backing_snap) = @_;
+    #input size = qcow2 image size in kb
+
+    return $size if $fmt ne 'qcow2';
+
+    my $json = PVE::Storage::Common::qemu_img_measure($size, $fmt, 5, $backing_snap);
+    die "failed to query file information with qemu-img measure\n" if !$json;
+    my $info = eval { decode_json($json) };
+    if ($@) {
+        die "Invalid JSON: $@\n";
+    }
+
+    die "Missing fully-allocated value from json" if !$info->{'fully-allocated'};
+
+    return $info->{'fully-allocated'} / 1024;
+}
+
+my sub alloc_lvm_image {
+    my ($class, $storeid, $scfg, $vmid, $fmt, $name, $size, $backing_snap) = @_;
+
+    die "unsupported format '$fmt'" if $fmt !~ m/(raw|qcow2)/;
 
     die "illegal name '$name' - should be 'vm-$vmid-*'\n"
-	if  $name && $name !~ m/^vm-$vmid-/;
+	if $name !~ m/^vm-$vmid-/;
 
     my $vgs = lvm_vgs();
 
@@ -378,70 +475,94 @@ sub alloc_image {
     die "no such volume group '$vg'\n" if !defined ($vgs->{$vg});
 
     my $free = int($vgs->{$vg}->{free});
+    my $lvmsize = calculate_lvm_size($size, $fmt, $backing_snap);
 
     die "not enough free space ($free < $size)\n" if $free < $size;
 
-    $name = $class->find_free_diskname($storeid, $scfg, $vmid)
+    my $tags = ["pve-vm-$vmid"];
+    #tags all snapshots volumes with the main volume tag for easier activation of the whole group
+    push @$tags, "\@pve-$name" if $fmt eq 'qcow2';
+    lvcreate($vg, $name, $lvmsize, $tags);
+
+    return if $fmt ne 'qcow2';
+
+    #format the lvm volume with qcow2 format
+    eval { lvm_qcow2_format($class, $storeid, $scfg, $name, $fmt, $backing_snap, $size) };
+    if ($@) {
+	my $err = $@;
+	#no need to safe cleanup as the volume is still empty
+	eval {
+	    my $cmd = ['/sbin/lvremove', '-f', "$vg/$name"];
+	    run_command($cmd, errmsg => "lvremove '$vg/$name' error");
+	};
+	die $err;
+    }
+}
+
+sub alloc_image {
+    my ($class, $storeid, $scfg, $vmid, $fmt, $name, $size) = @_;
+
+    $name = $class->find_free_diskname($storeid, $scfg, $vmid, $fmt)
 	if !$name;
 
-    lvcreate($vg, $name, $size, ["pve-vm-$vmid"]);
+    alloc_lvm_image($class, $storeid, $scfg, $vmid, $fmt, $name, $size);
 
     return $name;
 }
 
-sub free_image {
-    my ($class, $storeid, $scfg, $volname, $isBase) = @_;
+sub alloc_snap_image {
+    my ($class, $storeid, $scfg, $volname, $backing_snap) = @_;
 
-    my $vg = $scfg->{vgname};
+    my ($vmid, $format) = ($class->parse_volname($volname))[2,6];
+    my $path = $class->path($scfg, $volname, $storeid, $backing_snap);
 
-    # we need to zero out LVM data for security reasons
-    # and to allow thin provisioning
+    #we need to use same size than the backing image qcow2 virtual-size
+    my $size = PVE::Storage::Plugin::file_size_info($path, 5, $format);
+    $size = $size / 1024;  #we use kb in lvcreate
 
-    my $zero_out_worker = sub {
-	print "zero-out data on image $volname (/dev/$vg/del-$volname)\n";
+    alloc_lvm_image($class, $storeid, $scfg, $vmid, $format, $volname, $size, $backing_snap);
+}
 
-	# wipe throughput up to 10MB/s by default; may be overwritten with saferemove_throughput
-	my $throughput = '-10485760';
-	if ($scfg->{saferemove_throughput}) {
-		$throughput = $scfg->{saferemove_throughput};
-	}
+sub free_snap_image {
+    my ($class, $storeid, $scfg, $volname, $snap) = @_;
 
-	my $cmd = [
-		'/usr/bin/cstream',
-		'-i', '/dev/zero',
-		'-o', "/dev/$vg/del-$volname",
-		'-T', '10',
-		'-v', '1',
-		'-b', '1048576',
-		'-t', "$throughput"
-	];
-	eval { run_command($cmd, errmsg => "zero out finished (note: 'No space left on device' is ok here)"); };
-	warn $@ if $@;
+    #activate only the snapshot volume
+    my $path = $class->path($scfg, $volname, $storeid, $snap);
+    my $cmd = ['/sbin/lvchange', '-aly', $path];
+    run_command($cmd, errmsg => "can't activate LV '$path' to zero-out its data");
+    $cmd = ['/sbin/lvchange', '--refresh', $path];
+    run_command($cmd, errmsg => "can't refresh LV '$path' to zero-out its data");
 
-	$class->cluster_lock_storage($storeid, $scfg->{shared}, undef, sub {
-	    my $cmd = ['/sbin/lvremove', '-f', "$vg/del-$volname"];
-	    run_command($cmd, errmsg => "lvremove '$vg/del-$volname' error");
-	});
-	print "successfully removed volume $volname ($vg/del-$volname)\n";
-    };
+    my $snap_volname = $class->get_snap_volname($volname, $snap);
+    return $class->free_lvm_volumes($scfg, $storeid, [$snap_volname]);
+}
 
-    my $cmd = ['/sbin/lvchange', '-aly', "$vg/$volname"];
-    run_command($cmd, errmsg => "can't activate LV '$vg/$volname' to zero-out its data");
-    $cmd = ['/sbin/lvchange', '--refresh', "$vg/$volname"];
-    run_command($cmd, errmsg => "can't refresh LV '$vg/$volname' to zero-out its data");
+sub free_image {
+    my ($class, $storeid, $scfg, $volname, $isBase, $format) = @_;
 
-    if ($scfg->{saferemove}) {
-	# avoid long running task, so we only rename here
-	$cmd = ['/sbin/lvrename', $vg, $volname, "del-$volname"];
-	run_command($cmd, errmsg => "lvrename '$vg/$volname' error");
-	return $zero_out_worker;
-    } else {
-	my $tmpvg = $scfg->{vgname};
-	$cmd = ['/sbin/lvremove', '-f', "$tmpvg/$volname"];
-	run_command($cmd, errmsg => "lvremove '$tmpvg/$volname' error");
+    my $name = ($class->parse_volname($volname))[1];
+
+    #activate volumes && snapshot volumes
+    my $path = $class->path($scfg, $volname, $storeid);
+    $path = "\@pve-$name" if $format && $format eq 'qcow2';
+    my $cmd = ['/sbin/lvchange', '-aly', $path];
+    run_command($cmd, errmsg => "can't activate LV '$path' to zero-out its data");
+    $cmd = ['/sbin/lvchange', '--refresh', $path];
+    run_command($cmd, errmsg => "can't refresh LV '$path' to zero-out its data");
+
+    my $volnames = [];
+    my $snapshots =  $class->volume_snapshot_info($scfg, $storeid, $volname);
+    for my $snapid (sort { $snapshots->{$b}->{order} <=> $snapshots->{$a}->{order} } keys %$snapshots) {
+	my $snap = $snapshots->{$snapid};
+	next if $snapid eq 'current';
+	next if !$snap->{volid};
+	next if !$snap->{ext};
+	my ($snap_storeid, $snap_volname) = PVE::Storage::parse_volume_id($snap->{volid});
+	push @$volnames, $snap_volname;
     }
+    push @$volnames, $volname;
 
-    return undef;
+    return $class->free_lvm_volumes($scfg, $storeid, $volnames);
 }
 
 my $check_tags = sub {
@@ -539,6 +660,12 @@ sub activate_volume {
 
     my $lvm_activate_mode = 'ey';
 
+    #activate volume && all snapshots volumes by tag
+    my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) =
+	$class->parse_volname($volname);
+
+    $path = "\@pve-$name" if $format eq 'qcow2';
+
     my $cmd = ['/sbin/lvchange', "-a$lvm_activate_mode", $path];
     run_command($cmd, errmsg => "can't activate LV '$path'");
     $cmd = ['/sbin/lvchange', '--refresh', $path];
@@ -551,6 +678,10 @@ sub deactivate_volume {
     my $path = $class->path($scfg, $volname, $storeid, $snapname);
     return if ! -b $path;
 
+    my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) =
+	$class->parse_volname($volname);
+    $path = "\@pve-$name" if $format eq 'qcow2';
+
     my $cmd = ['/sbin/lvchange', '-aln', $path];
     run_command($cmd, errmsg => "can't deactivate LV '$path'");
 }
@@ -558,21 +689,31 @@ sub deactivate_volume {
 sub volume_resize {
     my ($class, $scfg, $storeid, $volname, $size, $running) = @_;
 
-    $size = ($size/1024/1024) . "M";
+    my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) =
+	$class->parse_volname($volname);
+
+    my $lvmsize = calculate_lvm_size($size/1024, $format);
+    $lvmsize = "${lvmsize}k";
 
     my $path = $class->path($scfg, $volname);
-    my $cmd = ['/sbin/lvextend', '-L', $size, $path];
+    my $cmd = ['/sbin/lvextend', '-L', $lvmsize, $path];
 
     $class->cluster_lock_storage($storeid, $scfg->{shared}, undef, sub {
 	run_command($cmd, errmsg => "error resizing volume '$path'");
     });
 
+    if(!$running && $format eq 'qcow2') {
+	my $prealloc_opt = PVE::Storage::Plugin::preallocation_cmd_option($scfg, $format);
+	my $cmd = ['/usr/bin/qemu-img', 'resize', "--$prealloc_opt", '-f', $format, $path , $size];
+	run_command($cmd, timeout => 10);
+    }
+
     return 1;
 }
 
 sub volume_size_info {
-    my ($class, $scfg, $storeid, $volname, $timeout) = @_;
-    my $path = $class->filesystem_path($scfg, $volname);
+    my ($class, $scfg, $storeid, $volname, $timeout, $snap) = @_;
+    my $path = $class->filesystem_path($scfg, $volname, $snap);
 
     my $cmd = ['/sbin/lvs', '--separator', ':', '--noheadings', '--units', 'b',
 	       '--unbuffered', '--nosuffix', '--options', 'lv_size', $path];
@@ -588,30 +729,181 @@ sub volume_size_info {
 sub volume_snapshot {
     my ($class, $scfg, $storeid, $volname, $snap, $running) = @_;
 
-    die "lvm snapshot is not implemented";
+    my ($vmid, $format) = ($class->parse_volname($volname))[2,6];
+
+    die "can't snapshot this image format\n" if $format ne 'qcow2';
+
+    if ($running) {
+        #rename with blockdev-reopen is done at qemu level when running
+        $class->alloc_snap_image($storeid, $scfg, $volname, $snap);
+	if ($@) {
+	    die "can't allocate new volume $volname: $@\n";
+	}
+        return;
+    }
+
+    #rename current volume to snap volume
+    eval { $class->rename_volume($scfg, $storeid, $volname, $vmid, undef, 'current', $snap) };
+    die "error rename $volname to $snap\n" if $@;
+
+    eval { $class->alloc_snap_image($storeid, $scfg, $volname, $snap) };
+    if ($@) {
+	my $err = $@;
+        eval { $class->rename_volume($scfg, $storeid, $volname, $vmid, undef, $snap, 'current') };
+        die $err;
+    }
+}
+
+sub volume_rollback_is_possible {
+    my ($class, $scfg, $storeid, $volname, $snap, $blockers) = @_;
+
+    my $snap_path = $class->path($scfg, $volname, $storeid, $snap);
+
+    $class->activate_volume($storeid, $scfg, $volname, undef, {});
+    my $snapshots = $class->volume_snapshot_info($scfg, $storeid, $volname);
+    my $parent_snap = $snapshots->{current}->{parent};
+
+    return 1 if $parent_snap eq $snap;
+    die "can't rollback, '$snap' is not most recent snapshot on '$volname'\n";
+
+    return 1;
 }
 
 sub volume_snapshot_rollback {
     my ($class, $scfg, $storeid, $volname, $snap) = @_;
 
-    die "lvm snapshot rollback is not implemented";
+    my $format = ($class->parse_volname($volname))[6];
+
+    die "can't rollback snapshot for this image format\n" if $format ne 'qcow2';
+
+    $class->activate_volume($storeid, $scfg, $volname, undef, {});
+
+    # we can simply reformat the current lvm volume to avoid
+    # a long safe remove.(not needed here, as the allocated space
+    # is still the same owner)
+    eval { lvm_qcow2_format($class, $storeid, $scfg, $volname, $format, $snap) };
+    if($@) {
+	die "can't rollback. Error reformating current $volname\n";
+    }
+    return undef;
 }
 
 sub volume_snapshot_delete {
-    my ($class, $scfg, $storeid, $volname, $snap) = @_;
+    my ($class, $scfg, $storeid, $volname, $snap, $running) = @_;
 
-    die "lvm snapshot delete is not implemented";
+    my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) = $class->parse_volname($volname);
+
+    die "can't delete snapshot for this image format\n" if $format ne 'qcow2';
+
+    if ($running) {
+	my $cleanup_worker = eval { $class->free_snap_image($storeid, $scfg, $volname, $snap); };
+	die "error deleting snapshot $snap $@\n" if $@;
+
+	if ($cleanup_worker) {
+	    my $rpcenv = PVE::RPCEnvironment::get();
+	    my $authuser = $rpcenv->get_user();
+	    $rpcenv->fork_worker('imgdel', undef, $authuser, $cleanup_worker);
+	}
+	return;
+    }
+
+    my $cmd = "";
+    my $path = $class->filesystem_path($scfg, $volname);
+
+    $class->activate_volume($storeid, $scfg, $volname);
+
+    my $snapshots = $class->volume_snapshot_info($scfg, $storeid, $volname);
+    my $snappath = $snapshots->{$snap}->{file};
+    my $snapvolname = $snapshots->{$snap}->{volname};
+    die "volume $snappath is missing" if !-e $snappath;
+
+    my $parentsnap = $snapshots->{$snap}->{parent};
+
+    my $childsnap = $snapshots->{$snap}->{child};
+    my $childpath = $snapshots->{$childsnap}->{file};
+    my $childvolname = $snapshots->{$childsnap}->{volname};
+
+    my $cleanup_worker = undef;
+    my $err = undef;
+    #if first snapshot,as it should be bigger,  we merge child, and rename the snapshot to child
+    if(!$parentsnap) {
+        print "$volname: deleting snapshot '$snap' by commiting snapshot '$childsnap'\n";
+        print "running 'qemu-img commit $childpath'\n";
+	#can't use -d here, as it's an lvm volume
+	$cmd = ['/usr/bin/qemu-img', 'commit', $childpath];
+	eval {	run_command($cmd) };
+	if ($@) {
+	    warn "The state of $snap is now invalid. Don't try to clone or rollback it. You can only try to delete it again later\n";
+	    die "error commiting $childsnap to $snap; $@\n";
+	}
+	print"delete $childvolname\n";
+	$cleanup_worker = eval { $class->free_snap_image($storeid, $scfg, $volname, $childsnap) };
+	if ($@) {
+	    die "error delete old snapshot volume $childvolname: $@\n";
+	}
+
+	print"rename $snapvolname to $childvolname\n";
+	my $vg = $scfg->{vgname};
+	eval { lvrename($vg, $snapvolname, $childvolname) };
+	if ($@) {
+	    warn $@;
+	    $err = "error renaming snapshot: $@\n";
+	}
+
+    } else {
+	#we rebase the child image on the parent as new backing image
+	my $parentpath = $snapshots->{$parentsnap}->{file};
+        print "$volname: deleting snapshot '$snap' by rebasing '$childsnap' on top of '$parentsnap'\n";
+        print "running 'qemu-img rebase -b $parentpath -F qcow -f qcow2 $childpath'\n";
+	$cmd = ['/usr/bin/qemu-img', 'rebase', '-b', $parentpath, '-F', 'qcow2', '-f', 'qcow2', $childpath];
+	eval { run_command($cmd) };
+	if ($@) {
+	    #in case of abort, the state of the snap is still clean, just a little bit bigger
+	    die "error rebase $childsnap from $parentsnap; $@\n";
+	}
+	#delete the snapshot
+	eval { $cleanup_worker = $class->free_snap_image($storeid, $scfg, $volname, $snap); };
+	if ($@) {
+	    die "error deleting old snapshot volume $snapvolname\n";
+	}
+    }
+
+    if ($cleanup_worker) {
+	my $rpcenv = PVE::RPCEnvironment::get();
+	my $authuser = $rpcenv->get_user();
+	$rpcenv->fork_worker('imgdel', undef, $authuser, $cleanup_worker);
+    }
+
+    die $err if $err;
 }
 
 sub volume_has_feature {
     my ($class, $scfg, $feature, $storeid, $volname, $snapname, $running) = @_;
 
     my $features = {
-	copy => { base => 1, current => 1},
-	rename => {current => 1},
+        copy => {
+            base => { qcow2 => 1, raw => 1 },
+            current => { qcow2 => 1, raw => 1},
+            snap => { qcow2 => 1 },
+        },
+        'rename' => {
+            current => { qcow2 => 1, raw => 1},
+        },
+        snapshot => {
+            current => { qcow2 => 1 },
+            snap => { qcow2 => 1 },
+        },
+#	fixme: add later ? (we need to handle basepath, volume activation,...)
+#	template => {
+#	    current => { raw => 1, qcow2 => 1},
+#	},
+#	clone => {
+#	    base => { qcow2 => 1 },
+#	},
     };
 
-    my ($vtype, $name, $vmid, $basename, $basevmid, $isBase) =
+
+    my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) =
 	$class->parse_volname($volname);
 
     my $key = undef;
@@ -620,7 +912,7 @@ sub volume_has_feature {
     }else{
 	$key =  $isBase ? 'base' : 'current';
     }
-    return 1 if $features->{$feature}->{$key};
+    return 1 if defined($features->{$feature}->{$key}->{$format});
 
     return undef;
 }
@@ -745,4 +1037,32 @@ sub rename_volume {
     return "${storeid}:${target_volname}";
 }
 
+sub qemu_blockdev_options {
+    my ($class, $scfg, $storeid, $volname, $options) = @_;
+
+    my ($path) = $class->filesystem_path($scfg, $volname, $options->{'snapshot-name'});
+
+    my $format = ($class->parse_volname($volname))[6];
+    die "can attach only the snapshot of a qcow2 image\n"
+        if $options->{'snapshot-name'} && $format ne 'qcow2';
+
+    my $blockdev = { driver => 'host_device', filename => $path };
+
+    return $blockdev;
+}
+
+sub get_snap_name {
+    my ($class, $volname, $snapname) = @_;
+
+    my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) = $class->parse_volname($volname);
+    $name = !$snapname || $snapname eq 'current' ? $name : "snap-$snapname-$name";
+    return $name;
+}
+
+sub get_snap_volname {
+    my ($class, $volname, $snapname) = @_;
+
+    return $class->get_snap_name($volname, $snapname);
+}
+
 1;
-- 
2.39.5



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