[pve-devel] [PATCH pve-storage 2/5] qcow2: add external snapshot support

[Alexandre Derumier via pve-devel <pve-devel@lists.proxmox.com>]

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From: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>
To: pve-devel@lists.proxmox.com
Subject: [PATCH pve-storage 2/5] qcow2: add external snapshot support
Date: Tue, 22 Apr 2025 13:51:26 +0200
Message-ID: <20250422115141.808427-6-alexandre.derumier@groupe-cyllene.com>

add a snapext option to enable the feature

When a snapshot is taken, the current volume is renamed to snap volname
and a current image is created with the snap volume as backing file

Signed-off-by: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>
---
 src/PVE/Storage.pm           |   5 +-
 src/PVE/Storage/DirPlugin.pm |   1 +
 src/PVE/Storage/Plugin.pm    | 277 ++++++++++++++++++++++++++++++-----
 3 files changed, 242 insertions(+), 41 deletions(-)

diff --git a/src/PVE/Storage.pm b/src/PVE/Storage.pm
index 1a37cc8..db9d190 100755
--- a/src/PVE/Storage.pm
+++ b/src/PVE/Storage.pm
@@ -348,13 +348,13 @@ sub volume_rollback_is_possible {
 }
 
 sub volume_snapshot {
-    my ($cfg, $volid, $snap) = @_;
+    my ($cfg, $volid, $snap, $running) = @_;
 
     my ($storeid, $volname) = parse_volume_id($volid, 1);
     if ($storeid) {
 	my $scfg = storage_config($cfg, $storeid);
 	my $plugin = PVE::Storage::Plugin->lookup($scfg->{type});
-	return $plugin->volume_snapshot($scfg, $storeid, $volname, $snap);
+	return $plugin->volume_snapshot($scfg, $storeid, $volname, $snap, $running);
     } elsif ($volid =~ m|^(/.+)$| && -e $volid) {
 	die "snapshot file/device '$volid' is not possible\n";
     } else {
@@ -378,7 +378,6 @@ sub volume_snapshot_rollback {
     }
 }
 
-# FIXME PVE 8.x remove $running parameter (needs APIAGE reset)
 sub volume_snapshot_delete {
     my ($cfg, $volid, $snap, $running) = @_;
 
diff --git a/src/PVE/Storage/DirPlugin.pm b/src/PVE/Storage/DirPlugin.pm
index 734309f..54d8d74 100644
--- a/src/PVE/Storage/DirPlugin.pm
+++ b/src/PVE/Storage/DirPlugin.pm
@@ -83,6 +83,7 @@ sub options {
 	is_mountpoint => { optional => 1 },
 	bwlimit => { optional => 1 },
 	preallocation => { optional => 1 },
+	snapext => { optional => 1 },
    };
 }
 
diff --git a/src/PVE/Storage/Plugin.pm b/src/PVE/Storage/Plugin.pm
index 85f761c..3f83fae 100644
--- a/src/PVE/Storage/Plugin.pm
+++ b/src/PVE/Storage/Plugin.pm
@@ -215,6 +215,11 @@ my $defaultData = {
 	    maximum => 65535,
 	    optional => 1,
 	},
+        'snapext' => {
+	    type => 'boolean',
+	    description => 'enable external snapshot.',
+	    optional => 1,
+        },
     },
 };
 
@@ -734,6 +739,8 @@ sub filesystem_path {
     my ($vtype, $name, $vmid, undef, undef, $isBase, $format) =
 	$class->parse_volname($volname);
 
+    $name = $class->get_snap_name($volname, $snapname) if $scfg->{snapext} && $snapname;
+
     # Note: qcow2/qed has internal snapshot, so path is always
     # the same (with or without snapshot => same file).
     die "can't snapshot this image format\n"
@@ -926,14 +933,8 @@ sub alloc_image {
 	umask $old_umask;
 	die $err if $err;
     } else {
-	my $cmd = ['/usr/bin/qemu-img', 'create'];
-
-	my $prealloc_opt = preallocation_cmd_option($scfg, $fmt);
-	push @$cmd, '-o', $prealloc_opt if defined($prealloc_opt);
 
-	push @$cmd, '-f', $fmt, $path, "${size}K";
-
-	eval { run_command($cmd, errmsg => "unable to create image"); };
+	eval { qemu_img_create($scfg, $fmt, $size, $path) };
 	if ($@) {
 	    unlink $path;
 	    rmdir $imagedir;
@@ -944,6 +945,19 @@ sub alloc_image {
     return "$vmid/$name";
 }
 
+sub alloc_snap_image {
+    my ($class, $storeid, $scfg, $volname, $backing_snap) = @_;
+
+    my $path = $class->path($scfg, $volname, $storeid);
+    my $backing_path = $class->path($scfg, $volname, $storeid, $backing_snap);
+
+    eval { qemu_img_create($scfg, 'qcow2', undef, $path, $backing_path) };
+    if ($@) {
+	unlink $path;
+	die "$@";
+    }
+}
+
 sub free_image {
     my ($class, $storeid, $scfg, $volname, $isBase, $format) = @_;
 
@@ -980,6 +994,51 @@ sub free_image {
 # TODO taken from PVE/QemuServer/Drive.pm, avoiding duplication would be nice
 my @checked_qemu_img_formats = qw(raw qcow qcow2 qed vmdk cloop);
 
+sub qemu_img_create {
+    my ($scfg, $fmt, $size, $path, $backing_path) = @_;
+
+    my $cmd = ['/usr/bin/qemu-img', 'create'];
+
+    my $options = [];
+
+    if($backing_path) {
+	push @$cmd, '-b', $backing_path, '-F', 'qcow2';
+	push @$options, 'extended_l2=on','cluster_size=128k';
+    };
+    push @$options, preallocation_cmd_option($scfg, $fmt);
+    push @$cmd, '-o', join(',', @$options) if @$options > 0;
+    push @$cmd, '-f', $fmt, $path;
+    push @$cmd, "${size}K" if !$backing_path;
+
+    run_command($cmd, errmsg => "unable to create image");
+}
+
+sub qemu_img_info {
+    my ($filename, $file_format, $timeout, $follow_backing_files) = @_;
+
+    my $cmd = ['/usr/bin/qemu-img', 'info', '--output=json', $filename];
+    push $cmd->@*, '-f', $file_format if $file_format;
+    push $cmd->@*, '--backing-chain' if $follow_backing_files;
+
+    my $json = '';
+    my $err_output = '';
+    eval {
+	run_command($cmd,
+	    timeout => $timeout,
+	    outfunc => sub { $json .= shift },
+	    errfunc => sub { $err_output .= shift . "\n"},
+	);
+    };
+    warn $@ if $@;
+    if ($err_output) {
+	# if qemu did not output anything to stdout we die with stderr as an error
+	die $err_output if !$json;
+	# otherwise we warn about it and try to parse the json
+	warn $err_output;
+    }
+    return $json;
+}
+
 # set $untrusted if the file in question might be malicious since it isn't
 # created by our stack
 # this makes certain checks fatal, and adds extra checks for known problems like
@@ -1043,25 +1102,9 @@ sub file_size_info {
 	warn "file_size_info: '$filename': falling back to 'raw' from unknown format '$file_format'\n";
 	$file_format = 'raw';
     }
-    my $cmd = ['/usr/bin/qemu-img', 'info', '--output=json', $filename];
-    push $cmd->@*, '-f', $file_format if $file_format;
 
-    my $json = '';
-    my $err_output = '';
-    eval {
-	run_command($cmd,
-	    timeout => $timeout,
-	    outfunc => sub { $json .= shift },
-	    errfunc => sub { $err_output .= shift . "\n"},
-	);
-    };
-    warn $@ if $@;
-    if ($err_output) {
-	# if qemu did not output anything to stdout we die with stderr as an error
-	die $err_output if !$json;
-	# otherwise we warn about it and try to parse the json
-	warn $err_output;
-    }
+    my $json = qemu_img_info($filename, $file_format, $timeout);
+
     if (!$json) {
 	die "failed to query file information with qemu-img\n" if $untrusted;
 	# skip decoding if there was no output, e.g. if there was a timeout.
@@ -1183,15 +1226,37 @@ sub volume_resize {
 }
 
 sub volume_snapshot {
-    my ($class, $scfg, $storeid, $volname, $snap) = @_;
+    my ($class, $scfg, $storeid, $volname, $snap, $running) = @_;
 
     die "can't snapshot this image format\n" if $volname !~ m/\.(qcow2|qed)$/;
 
-    my $path = $class->filesystem_path($scfg, $volname);
+    if($scfg->{snapext}) {
+
+	if ($running) {
+	    #rename with blockdev-reopen is done at qemu level when running
+	    $class->alloc_snap_image($storeid, $scfg, $volname, $snap);
+	    return;
+	}
 
-    my $cmd = ['/usr/bin/qemu-img', 'snapshot','-c', $snap, $path];
+	#rename current volume to snap volume
+	my $vmid = ($class->parse_volname($volname))[2];
+	$class->rename_volume($scfg, $storeid, $volname, $vmid, undef, 'current', $snap);
 
-    run_command($cmd);
+	$class->alloc_snap_image($storeid, $scfg, $volname, $snap);
+
+	if ($@) {
+	    eval { $class->free_image($storeid, $scfg, $volname, 0) };
+	    warn $@ if $@;
+	    eval { $class->rename_volume($scfg, $storeid, $volname, $vmid, undef, $snap, 'current') };
+	    warn $@ if $@;
+	}
+
+    } else {
+
+	my $path = $class->filesystem_path($scfg, $volname);
+	my $cmd = ['/usr/bin/qemu-img', 'snapshot','-c', $snap, $path];
+	run_command($cmd);
+    }
 
     return undef;
 }
@@ -1202,6 +1267,21 @@ sub volume_snapshot {
 sub volume_rollback_is_possible {
     my ($class, $scfg, $storeid, $volname, $snap, $blockers) = @_;
 
+    if ($scfg->{snapext}) {
+	#technically, we could manage multibranch, we it need lot more work for snapshot delete
+	#we need to implemente block-stream from deleted snapshot to all others child branchs
+	#when online, we need to do a transaction for multiple disk when delete the last snapshot
+	#and need to merge in current running file
+
+	my $snappath = $class->path($scfg, $volname, $storeid, $snap);
+	my $snapshots = $class->volume_snapshot_info($scfg, $storeid, $volname);
+	my $parentsnap = $snapshots->{current}->{parent};
+
+	return 1 if $parentsnap eq $snap;
+
+	die "can't rollback, '$snap' is not most recent snapshot on '$volname'\n";
+    }
+
     return 1;
 }
 
@@ -1212,9 +1292,21 @@ sub volume_snapshot_rollback {
 
     my $path = $class->filesystem_path($scfg, $volname);
 
-    my $cmd = ['/usr/bin/qemu-img', 'snapshot','-a', $snap, $path];
+    if ($scfg->{snapext}) {
+	#simply delete the current snapshot and recreate it
+	eval { $class->free_image($storeid, $scfg, $volname, 0) };
+	if ($@) {
+	    die "can't delete old volume $volname: $@\n";
+	}
 
-    run_command($cmd);
+	eval { $class->alloc_snap_image($storeid, $scfg, $volname, $snap) };
+	if ($@) {
+	    die "can't allocate new volume $volname: $@\n";
+	}
+    } else {
+	my $cmd = ['/usr/bin/qemu-img', 'snapshot','-a', $snap, $path];
+	run_command($cmd);
+    }
 
     return undef;
 }
@@ -1224,15 +1316,65 @@ sub volume_snapshot_delete {
 
     die "can't delete snapshot for this image format\n" if $volname !~ m/\.(qcow2|qed)$/;
 
-    return 1 if $running;
-
+    my $cmd = "";
     my $path = $class->filesystem_path($scfg, $volname);
 
-    $class->deactivate_volume($storeid, $scfg, $volname, $snap, {});
+    if ($scfg->{snapext}) {
+
+	if ($running) {
+	    my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) = $class->parse_volname($volname);
+	    $volname = $class->get_snap_volname($volname, $snap);
+	    $class->free_image($storeid, $scfg, $volname, $isBase, $format);
+	    return;
+	}
+
+	my $snapshots = $class->volume_snapshot_info($scfg, $storeid, $volname);
+	my $snappath = $snapshots->{$snap}->{file};
+	my $snap_volname = $snapshots->{$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};
+
+	#if first snapshot,as it should be bigger,  we merge child, and rename the snapshot to child
+	if(!$parentsnap) {
+	    print "commit: merge content of $childpath into $snappath\n";
+	    $cmd = ['/usr/bin/qemu-img', 'commit', $childpath];
+	    eval { run_command($cmd) };
+	    if ($@) {
+		die "error commiting $childpath to $snappath; $@\n";
+	    }
+	    print"rename $snappath to $childpath\n";
+	    eval { rename($snappath, $childpath) };
+            if ($@) {
+                die "error renaming snapshot: $@\n";
+            }
+	} else {
+	    #we rebase the child image on the parent as new backing image
+	    my $parentpath = $snapshots->{$parentsnap}->{file};
+	    print "rebase: merge diff content between $parentpath and $childpath into $childpath\n";
+	    $cmd = ['/usr/bin/qemu-img', 'rebase', '-b', $parentpath, '-F', 'qcow2', '-f', 'qcow2', $childpath];
+	    eval { run_command($cmd) };
+	    if ($@) {
+		die "error rebase $childpath from $parentpath; $@\n";
+	    }
+	    #delete the snapshot
+	    eval { $class->free_image($storeid, $scfg, $snap_volname, 0); };
+	    if ($@) {
+		die "error delete old snapshot volume $snap_volname: $@\n";
+	    }
+	}
+
+    } else {
 
-    my $cmd = ['/usr/bin/qemu-img', 'snapshot','-d', $snap, $path];
+	return 1 if $running;
 
-    run_command($cmd);
+	$class->deactivate_volume($storeid, $scfg, $volname, $snap, {});
+
+	$cmd = ['/usr/bin/qemu-img', 'snapshot','-d', $snap, $path];
+	run_command($cmd);
+    }
 
     return undef;
 }
@@ -1271,7 +1413,7 @@ sub volume_has_feature {
 	    current => { qcow2 => 1, raw => 1, vmdk => 1 },
 	},
 	rename => {
-	    current => {qcow2 => 1, raw => 1, vmdk => 1},
+	    current => { qcow2 => 1, raw => 1, vmdk => 1},
 	},
     };
 
@@ -1506,7 +1648,40 @@ sub status {
 sub volume_snapshot_info {
     my ($class, $scfg, $storeid, $volname) = @_;
 
-    die "volume_snapshot_info is not implemented for $class";
+    my $path = $class->filesystem_path($scfg, $volname);
+    my ($vtype, $name, $vmid, $basename, $basevmid, $isBase, $format) = $class->parse_volname($volname);
+
+    my $backing_chain = 1;
+    my $json = qemu_img_info($path, undef, 10, $backing_chain);
+    die "failed to query file information with qemu-img\n" if !$json;
+    my $snapshots = eval { decode_json($json) };
+    if ($@) {
+	die "Can't decode qemu snapshot list. Invalid JSON\n";
+    }
+    my $info = {};
+    my $order = 0;
+    for my $snap (@$snapshots) {
+
+	my $snapfile = $snap->{filename};
+	my $snapname = parse_snapname($snapfile);
+	$snapname = 'current' if !$snapname;
+	my $snapvolname = $class->get_snap_volname($volname, $snapname);
+
+	$info->{$snapname}->{order} = $order;
+	$info->{$snapname}->{file}= $snapfile;
+	$info->{$snapname}->{volname} = "$snapvolname";
+	$info->{$snapname}->{volid} = "$storeid:$snapvolname";
+	$info->{$snapname}->{ext} = 1;
+
+	my $parentfile = $snap->{'backing-filename'};
+	if ($parentfile) {
+	    my $parentname = parse_snapname($parentfile);
+	    $info->{$snapname}->{parent} = $parentname;
+	    $info->{$parentname}->{child} = $snapname;
+	}
+	$order++;
+    }
+    return $info;
 }
 
 sub activate_storage {
@@ -1907,4 +2082,30 @@ sub config_aware_base_mkdir {
     }
 }
 
+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) = @_;
+
+    my $vmid = ($class->parse_volname($volname))[2];
+    my $name = $class->get_snap_name($volname, $snapname);
+    return "$vmid/$name";
+}
+
+sub parse_snapname {
+    my ($name) = @_;
+
+    my $basename = basename($name);
+    if ($basename =~ m/^snap-(.*)-vm(.*)$/) {
+	return $1;
+    }
+    return undef;
+}
+
 1;
-- 
2.39.5



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