Re: [pve-devel] [PATCH v3 pve-storage 2/3] lvmplugin: add qcow2 snapshot

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

one downside with this part in particular - we have to always allocate full-size LVs (+qcow2 overhead), even if most of them will end up storing just a single snapshot delta which might be a tiny part of that full-size.. hopefully if discard is working across the whole stack this doesn't actually explode space usage on the storage side, but it makes everything a bit hard to track.. OTOH, while we could in theory extend/reduce the LVs and qcow2 images on them when modifying the backing chain, the additional complexity is probably not worth it at the moment..

> Alexandre Derumier via pve-devel <pve-devel@lists.proxmox.com> hat am 16.12.2024 10:12 CET geschrieben:
> Signed-off-by: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>
> ---
>  src/PVE/Storage/LVMPlugin.pm | 231 ++++++++++++++++++++++++++++++++---
>  1 file changed, 213 insertions(+), 18 deletions(-)
> 
> diff --git a/src/PVE/Storage/LVMPlugin.pm b/src/PVE/Storage/LVMPlugin.pm
> index 88fd612..1257cd3 100644
> --- a/src/PVE/Storage/LVMPlugin.pm
> +++ b/src/PVE/Storage/LVMPlugin.pm
> @@ -4,6 +4,7 @@ use strict;
>  use warnings;
>  
>  use IO::File;
> +use POSIX qw/ceil/;
>  
>  use PVE::Tools qw(run_command trim);
>  use PVE::Storage::Plugin;
> @@ -216,6 +217,7 @@ sub type {
>  sub plugindata {
>      return {
>  	content => [ {images => 1, rootdir => 1}, { images => 1 }],
> +	format => [ { raw => 1, qcow2 => 1 } , 'raw' ],

I wonder if we want to guard the snapshotting-related parts below with an additional "snapext" option here as well? or even the usage of qcow2 altogether?

>      };
>  }
>  
> @@ -291,7 +293,10 @@ 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";
> @@ -300,11 +305,13 @@ 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 = $class->get_snap_volname($volname, $snapname) if $snapname;
>  
>      my $path = "/dev/$vg/$name";
>  
> @@ -332,7 +339,9 @@ 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, $add_fmt_suffix);
>  }
>  
>  sub lvcreate {
> @@ -363,7 +372,15 @@ sub lvrename {
>  sub alloc_image {
>      my ($class, $storeid, $scfg, $vmid, $fmt, $name, $size) = @_;
>  
> -    die "unsupported format '$fmt'" if $fmt ne 'raw';
> +    die "unsupported format '$fmt'" if $fmt !~ m/(raw|qcow2)/;
> +
> +    $name = $class->alloc_new_image($storeid, $scfg, $vmid, $fmt, $name, $size);
> +    $class->format_qcow2($storeid, $scfg, $name, $size) if $fmt eq 'qcow2';
> +    return $name;
> +}
> +
> +sub alloc_new_image {
> +    my ($class, $storeid, $scfg, $vmid, $fmt, $name, $size) = @_;
>  
>      die "illegal name '$name' - should be 'vm-$vmid-*'\n"
>  	if  $name && $name !~ m/^vm-$vmid-/;
> @@ -376,16 +393,45 @@ sub alloc_image {
>  
>      my $free = int($vgs->{$vg}->{free});
>  
> +
> +    #add extra space for qcow2 metadatas
> +    #without sub-allocated clusters : For 1TB storage : l2_size = disk_size × 8 / cluster_size
> +    #with sub-allocated clusters : For 1TB storage : l2_size = disk_size × 8 / cluster_size / 16
> +                                   #4MB overhead for 1TB with extented l2 clustersize=128k
> +
> +    my $qcow2_overhead = ceil($size/1024/1024/1024) * 4096;

there's "qemu-img measure", which seems like it would do exactly what we want ;)

> +
> +    my $lvmsize = $size;
> +    $lvmsize += $qcow2_overhead if $fmt eq 'qcow2';
> +
>      die "not enough free space ($free < $size)\n" if $free < $size;
>  
> -    $name = $class->find_free_diskname($storeid, $scfg, $vmid)
> +    $name = $class->find_free_diskname($storeid, $scfg, $vmid, $fmt)
>  	if !$name;
>  
> -    lvcreate($vg, $name, $size, ["pve-vm-$vmid"]);
> -
> +    my $tags = ["pve-vm-$vmid"];
> +    push @$tags, "\@pve-$name" if $fmt eq 'qcow2';

that's a creative way to avoid the need to discover and activate snapshots one by one below, but it might warrant a comment ;)

> +    lvcreate($vg, $name, $lvmsize, $tags);
>      return $name;
>  }
>  
> +sub format_qcow2 {
> +    my ($class, $storeid, $scfg, $name, $size, $backing_file) = @_;
> +
> +    # activate volume
> +    $class->activate_volume($storeid, $scfg, $name, undef, {});
> +    my $path = $class->path($scfg, $name, $storeid);
> +    # create the qcow2 fs
> +    my $cmd = ['/usr/bin/qemu-img', 'create'];
> +    push @$cmd, '-b', $backing_file, '-F', 'qcow2' if $backing_file;
> +    push @$cmd, '-f', 'qcow2', $path;
> +    push @$cmd, "${size}K" if $size;
> +    my $options = "extended_l2=on,";
> +    $options .= PVE::Storage::Plugin::preallocation_cmd_option($scfg, 'qcow2');
> +    push @$cmd, '-o', $options;
> +    run_command($cmd);
> +}
> +
>  sub free_image {
>      my ($class, $storeid, $scfg, $volname, $isBase) = @_;
>  
> @@ -536,6 +582,12 @@ 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];
> @@ -548,6 +600,10 @@ 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 '$path'");
>  }
> @@ -555,15 +611,27 @@ sub deactivate_volume {
>  sub volume_resize {
>      my ($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 = $size / 1024;
> +    my $qcow2_overhead = ceil($size/1024/1024/1024/1024) * 4096;

see above

> +    $lvmsize += $qcow2_overhead if $format eq 'qcow2';
> +    $lvmsize = "${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;
>  }
>  
> @@ -585,30 +653,149 @@ sub volume_size_info {
>  sub volume_snapshot {
>      my ($class, $scfg, $storeid, $volname, $snap) = @_;
>  
> -    die "lvm snapshot is not implemented";
> +    my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) =
> +        $class->parse_volname($volname);
> +
> +    die "can't snapshot this image format\n" if $format ne 'qcow2';
> +
> +    $class->activate_volume($storeid, $scfg, $volname, undef, {});
> +
> +    my $snap_volname = $class->get_snap_volname($volname, $snap);
> +    my $snap_path = $class->path($scfg, $volname, $storeid, $snap);
> +
> +    my $size = $class->volume_size_info($scfg, $storeid, $volname, 5);
> +
> +    #rename current lvm volume to snap volume
> +    my $vg = $scfg->{vgname};
> +    print"rename $volname to $snap_volname\n";
> +    eval { lvrename($vg, $volname, $snap_volname) } ;

missing error handling..

> +
> +
> +    #allocate a new lvm volume
> +    $class->alloc_new_image($storeid, $scfg, $vmid, 'qcow2', $volname, $size/1024);

missing error handling

> +    eval {
> +        $class->format_qcow2($storeid, $scfg, $volname, undef, $snap_path);
> +    };
> +
> +    if ($@) {
> +        eval { $class->free_image($storeid, $scfg, $volname, 0) };
> +        warn $@ if $@;
> +    }
> +}
> +
> +sub volume_rollback_is_possible {
> +    my ($class, $scfg, $storeid, $volname, $snap, $blockers) = @_;
> +
> +    my $snap_path = $class->path($scfg, $volname, $storeid, $snap);
> +
> +    my $snapshots = $class->volume_snapshot_info($scfg, $storeid, $volname);
> +    my $parent_snap = $snapshots->{current}->{parent};
> +
> +    return 1 if !-e $snap_path || $snapshots->{$parent_snap}->{file} eq $snap_path;

the first condition here seems wrong, see storage patch #1

> +    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";
> +    die "can't rollback snapshot this image format\n" if $volname !~ m/\.(qcow2|qed)$/;

above we only have qcow2, which IMHO makes more sense..

> +
> +    my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) =
> +        $class->parse_volname($volname);
> +
> +    $class->activate_volume($storeid, $scfg, $volname, undef, {});
> +    my $size = $class->volume_size_info($scfg, $storeid, $volname, 5);
> +    my $snap_path = $class->path($scfg, $volname, $storeid, $snap);
> +
> +    #simply delete the current snapshot and recreate it
> +    $class->free_image($storeid, $scfg, $volname, 0);
> +    $class->alloc_new_image($storeid, $scfg, $vmid, 'qcow2', $volname, $size/1024);
> +    $class->format_qcow2($storeid, $scfg, $volname, undef, $snap_path);

missing error handling..

> +
> +    return undef;
>  }
>  
>  sub volume_snapshot_delete {
> -    my ($class, $scfg, $storeid, $volname, $snap) = @_;
> +    my ($class, $scfg, $storeid, $volname, $snap, $running) = @_;
> +
> +   die "can't delete snapshot for this image format\n" if $volname !~ m/\.(qcow2|qed)$/;

same as above

> +
> +   return 1 if $running;
> +
> +   my $cmd = "";
> +   my $path = $class->filesystem_path($scfg, $volname);
> +
> +
> +   my $snapshots = $class->volume_snapshot_info($scfg, $storeid, $volname);
> +   my $snap_path = $snapshots->{$snap}->{file};
> +   my $snap_volname = $snapshots->{$snap}->{volname};
> +   return if !-e $snap_path;  #already deleted ?

should maybe be a die?

> +
> +   my $parent_snap = $snapshots->{$snap}->{parent};
> +   my $child_snap = $snapshots->{$snap}->{child};
> +
> +   my $parent_path = $snapshots->{$parent_snap}->{file} if $parent_snap;
> +   my $child_path = $snapshots->{$child_snap}->{file} if $child_snap;
> +   my $child_volname = $snapshots->{$child_snap}->{volname} if $child_snap;
> +
> +
> +   #if first snapshot, we merge child, and rename the snapshot to child
> +   if(!$parent_snap) {
> +        #we use commit here, as it's faster than rebase
> +        #https://lists.gnu.org/archive/html/qemu-discuss/2019-08/msg00041.html
> +        print"commit $child_path\n";
> +        $cmd = ['/usr/bin/qemu-img', 'commit', $child_path];
> +        run_command($cmd);
> +        print"delete $child_volname\n";
> +        $class->free_image($storeid, $scfg, $child_volname, 0);
> +
> +        print"rename $snap_volname to $child_volname\n";
> +	my $vg = $scfg->{vgname};
> +        lvrename($vg, $snap_volname, $child_volname);

missing error handling..

> +    } else {
> +        print"commit $snap_path\n";
> +        $cmd = ['/usr/bin/qemu-img', 'commit', $snap_path];

leftover?

> +        #if we delete an intermediate snapshot, we need to link upper snapshot to base snapshot
> +        die "missing parentsnap snapshot to rebase child $child_path\n" if !$parent_path;
> +        print "link $child_snap to $parent_snap\n";
> +        $cmd = ['/usr/bin/qemu-img', 'rebase', '-u', '-b', $parent_path, '-F', 'qcow2', '-f', 'qcow2', $child_path];
> +        run_command($cmd);

same as for patch #1, I am not sure the -u here is correct..

> +        #delete the snapshot
> +        $class->free_image($storeid, $scfg, $snap_volname, 0);
> +    }
>  
> -    die "lvm snapshot delete is not implemented";
>  }
>  
>  sub volume_has_feature {
>      my ($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 },
> +        },
> +        template => {
> +            current => { qcow2 => 1, raw => 1},
> +        },
> +#	don't allow to clone as we can't activate the base on multiple host at the same time
> +#       clone => {
> +#           base => { qcow2 => 1, raw => 1},
> +#       },

I think activating the base would actually be okay, we just must never write to it? ;)

>      };
>  
> -    my ($vtype, $name, $vmid, $basename, $basevmid, $isBase) =
> +
> +    my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) =
>  	$class->parse_volname($volname);
>  
>      my $key = undef;
> @@ -617,7 +804,7 @@ sub volume_has_feature {
>      }else{
>  	$key =  $isBase ? 'base' : 'current';
>      }
> -    return 1 if $features->{$feature}->{$key};
> +    return 1 if defined($features->{$feature}->{$key}->{$format});
>  
>      return undef;
>  }
> @@ -738,4 +925,12 @@ sub rename_volume {
>      return "${storeid}:${target_volname}";
>  }
>  
> +sub get_snap_volname {
> +    my ($class, $volname, $snapname) = @_;
> +
> +    my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) = $class->parse_volname($volname);
> +    $name = !$snapname || $snapname eq 'current' ? $volname : "snap-$snapname-$name";
> +    return $name;
> +}
> +
>  1;
> -- 
> 2.39.5


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