[pve-devel] [PATCH qemu-server 14/14] 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 qemu-server 14/14] qcow2: add external snapshot support
Date: Tue, 22 Apr 2025 13:51:41 +0200
Message-ID: <20250422115141.808427-21-alexandre.derumier@groupe-cyllene.com>

Signed-off-by: Alexandre Derumier <alexandre.derumier@groupe-cyllene.com>
---
 PVE/QemuConfig.pm       |   4 +-
 PVE/QemuServer.pm       | 237 +++++++++++++++++++++++++++++++++++-----
 PVE/QemuServer/Drive.pm |  39 ++++---
 3 files changed, 239 insertions(+), 41 deletions(-)

diff --git a/PVE/QemuConfig.pm b/PVE/QemuConfig.pm
index 2609542c..785c84a2 100644
--- a/PVE/QemuConfig.pm
+++ b/PVE/QemuConfig.pm
@@ -378,7 +378,7 @@ sub __snapshot_create_vol_snapshot {
 
     print "snapshotting '$device' ($drive->{file})\n";
 
-    PVE::QemuServer::qemu_volume_snapshot($vmid, $device, $storecfg, $volid, $snapname);
+    PVE::QemuServer::qemu_volume_snapshot($vmid, $device, $storecfg, $drive, $snapname);
 }
 
 sub __snapshot_delete_remove_drive {
@@ -415,7 +415,7 @@ sub __snapshot_delete_vol_snapshot {
     my $storecfg = PVE::Storage::config();
     my $volid = $drive->{file};
 
-    PVE::QemuServer::qemu_volume_snapshot_delete($vmid, $storecfg, $volid, $snapname);
+    PVE::QemuServer::qemu_volume_snapshot_delete($vmid, $storecfg, $drive, $snapname);
 
     push @$unused, $volid;
 }
diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
index 5cce7094..aff430df 100644
--- a/PVE/QemuServer.pm
+++ b/PVE/QemuServer.pm
@@ -55,7 +55,7 @@ use PVE::QemuServer::Helpers qw(config_aware_timeout min_version kvm_user_versio
 use PVE::QemuServer::Cloudinit;
 use PVE::QemuServer::CGroup;
 use PVE::QemuServer::CPUConfig qw(print_cpu_device get_cpu_options get_cpu_bitness is_native_arch get_amd_sev_object get_amd_sev_type);
-use PVE::QemuServer::Drive qw(is_valid_drivename checked_volume_format drive_is_cloudinit drive_is_cdrom drive_is_read_only parse_drive print_drive print_drive_throttle_group generate_drive_blockdev generate_throttle_group);
+use PVE::QemuServer::Drive qw(is_valid_drivename checked_volume_format drive_is_cloudinit drive_is_cdrom drive_is_read_only parse_drive print_drive print_drive_throttle_group generate_drive_blockdev generate_throttle_group generate_blockdev_throttle generate_file_blockdev generate_format_blockdev);
 use PVE::QemuServer::Machine;
 use PVE::QemuServer::Memory qw(get_current_memory);
 use PVE::QemuServer::MetaInfo;
@@ -4518,20 +4518,193 @@ sub qemu_block_resize {
 }
 
 sub qemu_volume_snapshot {
-    my ($vmid, $deviceid, $storecfg, $volid, $snap) = @_;
+    my ($vmid, $deviceid, $storecfg, $drive, $snap) = @_;
 
+    my $volid = $drive->{file};
     my $running = check_running($vmid);
 
-    if ($running && do_snapshots_with_qemu($storecfg, $volid, $deviceid)) {
-	mon_cmd($vmid, 'blockdev-snapshot-internal-sync', device => $deviceid, name => $snap);
+    my $do_snapshots_with_qemu = do_snapshots_with_qemu($storecfg, $volid, $deviceid);
+
+    if ($running && $do_snapshots_with_qemu) {
+	if ($do_snapshots_with_qemu == 2) {
+	    print "internal qemu snapshot\n";
+	    mon_cmd($vmid, 'blockdev-snapshot-internal-sync', device => $deviceid, name => $snap);
+	} elsif ($do_snapshots_with_qemu == 3) {
+	    my $storeid = (PVE::Storage::parse_volume_id($volid))[0];
+	    my $scfg = PVE::Storage::storage_config($storecfg, $storeid);
+	    print "external qemu snapshot\n";
+	    my $snapshots = PVE::Storage::volume_snapshot_info($storecfg, $volid);
+	    my $parent_snap = $snapshots->{'current'}->{parent};
+	    blockdev_rename($storecfg, $vmid, $deviceid, $drive, 'current', $snap, $parent_snap);
+	    eval { blockdev_external_snapshot($storecfg, $vmid, $deviceid, $drive, $snap) };
+	    if ($@) {
+		print "error creating snapshot. Revert rename\n";
+		eval { blockdev_rename($storecfg, $vmid, $deviceid, $drive, $snap, 'current', $parent_snap) };
+	    }
+	}
     } else {
 	PVE::Storage::volume_snapshot($storecfg, $volid, $snap);
     }
 }
 
+sub blockdev_external_snapshot {
+    my ($storecfg, $vmid, $deviceid, $drive, $snap, $size) = @_;
+
+    my $volid = $drive->{file};
+
+    #preallocate add a new current file with reference to backing-file
+    PVE::Storage::volume_snapshot($storecfg, $volid, $snap, 1);
+
+    #be sure to add drive in write mode
+    delete($drive->{ro});
+
+    my $new_file_blockdev = generate_file_blockdev($storecfg, $drive);
+    my $new_fmt_blockdev = generate_format_blockdev($storecfg, $drive, $new_file_blockdev);
+
+    my $snap_file_blockdev = generate_file_blockdev($storecfg, $drive, $snap);
+    my $snap_fmt_blockdev = generate_format_blockdev($storecfg, $drive, $snap_file_blockdev, $snap);
+
+    #backing need to be forced to undef in blockdev, to avoid reopen of backing-file on blockdev-add
+    $new_fmt_blockdev->{backing} = undef;
+
+    PVE::QemuServer::Monitor::mon_cmd($vmid, 'blockdev-add', %$new_fmt_blockdev);
+
+    mon_cmd($vmid, 'blockdev-snapshot', node => $snap_fmt_blockdev->{'node-name'}, overlay => $new_fmt_blockdev->{'node-name'});
+}
+
+sub blockdev_delete {
+    my ($storecfg, $vmid, $drive, $file_blockdev, $fmt_blockdev, $snap) = @_;
+
+    #add eval as reopen is auto removing the old nodename automatically only if it was created at vm start in command line argument
+    eval { mon_cmd($vmid, 'blockdev-del', 'node-name' => $file_blockdev->{'node-name'}) };
+    eval { mon_cmd($vmid, 'blockdev-del', 'node-name' => $fmt_blockdev->{'node-name'}) };
+
+    #delete the file (don't use vdisk_free as we don't want to delete all snapshot chain)
+    print"delete old $file_blockdev->{filename}\n";
+
+    my $storage_name = PVE::Storage::parse_volume_id($drive->{file});
+
+    my $volid = $drive->{file};
+    PVE::Storage::volume_snapshot_delete($storecfg, $volid, $snap, 1);
+}
+
+sub blockdev_rename {
+    my ($storecfg, $vmid, $deviceid, $drive, $src_snap, $target_snap, $parent_snap) = @_;
+
+    print "rename $src_snap to $target_snap\n";
+
+    my $volid = $drive->{file};
+
+    my $src_file_blockdev = generate_file_blockdev($storecfg, $drive, $src_snap);
+    my $src_fmt_blockdev = generate_format_blockdev($storecfg, $drive, $src_file_blockdev, $src_snap);
+    my $target_file_blockdev = generate_file_blockdev($storecfg, $drive, $target_snap);
+    my $target_fmt_blockdev = generate_format_blockdev($storecfg, $drive, $target_file_blockdev, $target_snap);
+
+    #rename volume image
+    PVE::Storage::rename_volume($storecfg, $volid, $vmid, undef, $src_snap, $target_snap);
+
+    if($target_snap eq 'current' || $src_snap eq 'current') {
+	#rename from|to current
+
+	#add backing to target
+	if ($parent_snap) {
+	    my $parent_fmt_nodename = encode_nodename('fmt', $volid, $parent_snap);
+	    $target_fmt_blockdev->{backing} = $parent_fmt_nodename;
+	}
+	PVE::QemuServer::Monitor::mon_cmd($vmid, 'blockdev-add', %$target_fmt_blockdev);
+
+	#reopen the current throttlefilter nodename with the target fmt nodename
+	my $throttle_blockdev = generate_blockdev_throttle($drive, $target_fmt_blockdev->{'node-name'});
+	PVE::QemuServer::Monitor::mon_cmd($vmid, 'blockdev-reopen', options => [$throttle_blockdev]);
+    } else {
+        rename($src_file_blockdev->{filename}, $target_file_blockdev->{filename});
+
+	#intermediate snapshot
+	PVE::QemuServer::Monitor::mon_cmd($vmid, 'blockdev-add', %$target_fmt_blockdev);
+
+	#reopen the parent node with the new target fmt backing node
+	my $parent_file_blockdev = generate_file_blockdev($storecfg, $drive, $parent_snap);
+	my $parent_fmt_blockdev = generate_format_blockdev($storecfg, $drive, $parent_file_blockdev, $parent_snap);
+	$parent_fmt_blockdev->{backing} = $target_fmt_blockdev->{'node-name'};
+	PVE::QemuServer::Monitor::mon_cmd($vmid, 'blockdev-reopen', options => [$parent_fmt_blockdev]);
+
+	#change backing-file in qcow2 metadatas
+	PVE::QemuServer::Monitor::mon_cmd($vmid, 'change-backing-file', device => $deviceid, 'image-node-name' => $parent_fmt_blockdev->{'node-name'}, 'backing-file' => $target_file_blockdev->{filename});
+    }
+
+    # delete old file|fmt nodes
+    # add eval as reopen is auto removing the old nodename automatically only if it was created at vm start in command line argument
+    eval { PVE::QemuServer::Monitor::mon_cmd($vmid, 'blockdev-del', 'node-name' => $src_file_blockdev->{'node-name'})};
+    eval { PVE::QemuServer::Monitor::mon_cmd($vmid, 'blockdev-del', 'node-name' => $src_fmt_blockdev->{'node-name'})};
+}
+
+sub blockdev_commit {
+    my ($storecfg, $vmid, $deviceid, $drive, $src_snap, $target_snap) = @_;
+
+    my $volid = $drive->{file};
+
+    print "block-commit $src_snap to base:$target_snap\n";
+
+    my $target_file_blockdev = generate_file_blockdev($storecfg, $drive, $target_snap);
+    my $target_fmt_blockdev = generate_format_blockdev($storecfg, $drive, $target_file_blockdev, $target_snap);
+
+    my $src_file_blockdev = generate_file_blockdev($storecfg, $drive, $src_snap);
+    my $src_fmt_blockdev = generate_format_blockdev($storecfg, $drive, $src_file_blockdev, $src_snap);
+
+    my $job_id = "commit-$deviceid";
+    my $jobs = {};
+    my $opts = { 'job-id' => $job_id, device => $deviceid };
+
+    my $complete = undef;
+    if ($src_snap && $src_snap ne 'current') {
+	$complete = 'auto';
+	$opts->{'top-node'} = $src_fmt_blockdev->{'node-name'};
+	$opts->{'base-node'} = $target_fmt_blockdev->{'node-name'};
+    } else {
+	$complete = 'complete';
+	$opts->{'base-node'} = $target_fmt_blockdev->{'node-name'};
+	$opts->{replaces} = $src_fmt_blockdev->{'node-name'};
+    }
+
+    mon_cmd($vmid, "block-commit", %$opts);
+    $jobs->{$job_id} = {};
+    qemu_drive_mirror_monitor($vmid, undef, $jobs, $complete, 0, 'commit');
+
+    blockdev_delete($storecfg, $vmid, $drive, $src_file_blockdev, $src_fmt_blockdev, $src_snap);
+}
+
+sub blockdev_stream {
+    my ($storecfg, $vmid, $deviceid, $drive, $snap, $parent_snap, $target_snap) = @_;
+
+    my $volid = $drive->{file};
+    $target_snap = undef if $target_snap eq 'current';
+
+    my $parent_file_blockdev = generate_file_blockdev($storecfg, $drive, $parent_snap);
+    my $parent_fmt_blockdev = generate_format_blockdev($storecfg, $drive, $parent_file_blockdev, $parent_snap);
+
+    my $target_file_blockdev = generate_file_blockdev($storecfg, $drive, $target_snap);
+    my $target_fmt_blockdev = generate_format_blockdev($storecfg, $drive, $target_file_blockdev, $target_snap);
+
+    my $snap_file_blockdev = generate_file_blockdev($storecfg, $drive, $snap);
+    my $snap_fmt_blockdev = generate_format_blockdev($storecfg, $drive, $snap_file_blockdev, $snap);
+
+    my $job_id = "stream-$deviceid";
+    my $jobs = {};
+    my $options = { 'job-id' => $job_id, device => $target_fmt_blockdev->{'node-name'} };
+    $options->{'base-node'} = $parent_fmt_blockdev->{'node-name'};
+    $options->{'backing-file'} = $parent_file_blockdev->{filename};
+
+    mon_cmd($vmid, 'block-stream', %$options);
+    $jobs->{$job_id} = {};
+    qemu_drive_mirror_monitor($vmid, undef, $jobs, 'auto', 0, 'stream');
+
+    blockdev_delete($storecfg, $vmid, $drive, $snap_file_blockdev, $snap_fmt_blockdev, $snap);
+}
+
 sub qemu_volume_snapshot_delete {
-    my ($vmid, $storecfg, $volid, $snap) = @_;
+    my ($vmid, $storecfg, $drive, $snap) = @_;
 
+    my $volid = $drive->{file};
     my $running = check_running($vmid);
     my $attached_deviceid;
 
@@ -4543,13 +4716,36 @@ sub qemu_volume_snapshot_delete {
 	});
     }
 
+    my $do_snapshots_with_qemu = do_snapshots_with_qemu($storecfg, $volid, $attached_deviceid);
+
     if ($attached_deviceid && do_snapshots_with_qemu($storecfg, $volid, $attached_deviceid)) {
-	mon_cmd(
-	    $vmid,
-	    'blockdev-snapshot-delete-internal-sync',
-	    device => $attached_deviceid,
-	    name => $snap,
-	);
+	if ($do_snapshots_with_qemu == 2) {
+	    mon_cmd(
+		$vmid,
+		'blockdev-snapshot-delete-internal-sync',
+		device => $attached_deviceid,
+		name => $snap,
+	    );
+	} elsif ($do_snapshots_with_qemu == 3) {
+	    print "delete qemu external snapshot\n";
+
+	    my $path = PVE::Storage::path($storecfg, $volid);
+	    my $snapshots = PVE::Storage::volume_snapshot_info($storecfg, $volid);
+	    my $parentsnap = $snapshots->{$snap}->{parent};
+	    my $childsnap = $snapshots->{$snap}->{child};
+
+	    # if we delete the first snasphot, we commit because the first snapshot original base image, it should be big.
+	    # improve-me: if firstsnap > child : commit, if firstsnap < child do a stream.
+	    if(!$parentsnap) {
+		print"delete first snapshot $snap\n";
+		blockdev_commit($storecfg, $vmid, $attached_deviceid, $drive, $childsnap, $snap);
+		blockdev_rename($storecfg, $vmid, $attached_deviceid, $drive, $snap, $childsnap, $snapshots->{$childsnap}->{child});
+	    } else {
+		#intermediate snapshot, we always stream the snapshot to child snapshot
+		print"stream intermediate snapshot $snap to $childsnap\n";
+		blockdev_stream($storecfg, $vmid, $attached_deviceid, $drive, $snap, $parentsnap, $childsnap);
+	    }
+	}
     } else {
 	PVE::Storage::volume_snapshot_delete(
 	    $storecfg, $volid, $snap, $attached_deviceid ? 1 : undef);
@@ -7778,27 +7974,16 @@ sub foreach_storage_used_by_vm {
     }
 }
 
-my $qemu_snap_storage = {
-    rbd => 1,
-};
 sub do_snapshots_with_qemu {
     my ($storecfg, $volid, $deviceid) = @_;
 
-    return if $deviceid =~ m/tpmstate0/;
+    return if $deviceid && $deviceid =~ m/tpmstate0/;
 
-    my $storage_name = PVE::Storage::parse_volume_id($volid);
-    my $scfg = $storecfg->{ids}->{$storage_name};
-    die "could not find storage '$storage_name'\n" if !defined($scfg);
+    my $snapshot_type = PVE::Storage::volume_has_feature($storecfg, 'snapshot', $volid);
 
-    if ($qemu_snap_storage->{$scfg->{type}} && !$scfg->{krbd}){
-	return 1;
-    }
+    return $snapshot_type if $snapshot_type == 2 || $snapshot_type == 3;
 
-    if ($volid =~ m/\.(qcow2|qed)$/){
-	return 1;
-    }
-
-    return;
+    return undef;
 }
 
 sub qga_check_running {
diff --git a/PVE/QemuServer/Drive.pm b/PVE/QemuServer/Drive.pm
index 0737034d..93903a59 100644
--- a/PVE/QemuServer/Drive.pm
+++ b/PVE/QemuServer/Drive.pm
@@ -27,6 +27,9 @@ print_drive
 print_drive_throttle_group
 generate_drive_blockdev
 generate_throttle_group
+generate_blockdev_throttle
+generate_format_blockdev
+generate_file_blockdev
 );
 
 our $QEMU_FORMAT_RE = qr/raw|qcow|qcow2|qed|vmdk|cloop/;
@@ -1074,6 +1077,8 @@ sub print_drive_throttle_group {
 sub generate_file_blockdev {
     my ($storecfg, $drive, $snap, $nodename) = @_;
 
+    $snap = undef if $snap && $snap eq 'current';
+
     my $volid = $drive->{file};
     my $driveid = get_drive_id($drive);
 
@@ -1209,6 +1214,8 @@ sub generate_file_blockdev {
 sub generate_format_blockdev {
     my ($storecfg, $drive, $file, $snap, $nodename) = @_;
 
+    $snap = undef if $snap && $snap eq 'current';
+
     my $volid = $drive->{file};
     #nbd don't support format blockdev, return the fileblockdev
     return $file if $volid =~ /^nbd:/;
@@ -1280,6 +1287,15 @@ sub generate_backing_chain_blockdev {
     return $chain_blockdev;
 }
 
+sub generate_blockdev_throttle {
+    my ($drive, $blockdev_file) = @_;
+
+    my $drive_id = get_drive_id($drive);
+    #this is the topfilter entry point, use $drive-drive_id as nodename
+    my $blockdev_throttle = { driver => "throttle", 'node-name' => "drive-$drive_id", 'throttle-group' => "throttle-drive-$drive_id", 'file' => $blockdev_file };
+    return $blockdev_throttle;
+}
+
 sub generate_drive_blockdev {
     my ($storecfg, $drive, $live_restore_name) = @_;
 
@@ -1303,22 +1319,19 @@ sub generate_drive_blockdev {
     #pflash0 don't support throttle-filter
     return $blockdev_format if $drive_id eq 'pflash0';
 
-    my $blockdev_live_restore = undef;
-    if ($live_restore_name) {
-        die "$drive_id: Proxmox Backup Server backed drive cannot auto-detect the format\n"
-            if !$drive->{format};
+    return generate_blockdev_throttle($drive, $blockdev_format) if !$live_restore_name;
 
-        $blockdev_live_restore = { 'node-name' => "liverestore-drive-$drive_id",
-				    backing => $live_restore_name,
-				    'auto-remove' => 'on', format => "alloc-track",
-				    file => $blockdev_format };
-    }
+    die "$drive_id: Proxmox Backup Server backed drive cannot auto-detect the format\n"
+        if !$drive->{format};
 
-    #this is the topfilter entry point, use $drive-drive_id as nodename
-    my $blockdev_throttle = { driver => "throttle", 'node-name' => "drive-$drive_id", 'throttle-group' => "throttle-drive-$drive_id" };
     #put liverestore filter between throttle && format filter
-    $blockdev_throttle->{file} = $live_restore_name ? $blockdev_live_restore : $blockdev_format;
-    return $blockdev_throttle,
+    my $blockdev_live_restore = { 'node-name' => "liverestore-drive-$drive_id",
+                                  backing => $live_restore_name,
+                                  'auto-remove' => 'on', format => "alloc-track",
+                                  file => $blockdev_format };
+
+    return generate_blockdev_throttle($drive, $blockdev_live_restore);
+
 }
 
 sub encode_base62 {
-- 
2.39.5



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