[pve-devel] [PATCH qemu-server 12/13] blockdev: add backing_chain 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 12/13] blockdev: add backing_chain support
Date: Tue,  3 Jun 2025 09:55:57 +0200
Message-ID: <20250603075558.627850-23-alexandre.derumier@groupe-cyllene.com>

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/Blockdev.pm                | 35 +++++++++++++++++++++++
 test/cfg2cmd/simple-backingchain.conf     | 21 ++++++++++++++
 test/cfg2cmd/simple-backingchain.conf.cmd | 30 +++++++++++++++++++
 test/run_config2command_tests.pl          | 26 +++++++++++++++++
 4 files changed, 112 insertions(+)
 create mode 100644 test/cfg2cmd/simple-backingchain.conf
 create mode 100644 test/cfg2cmd/simple-backingchain.conf.cmd

diff --git a/PVE/QemuServer/Blockdev.pm b/PVE/QemuServer/Blockdev.pm
index 60a996f3..692336c1 100644
--- a/PVE/QemuServer/Blockdev.pm
+++ b/PVE/QemuServer/Blockdev.pm
@@ -153,6 +153,7 @@ sub generate_file_blockdev {
     } elsif($storeid) {
 	my $blockdev_options = {};
 	$blockdev_options->{hints}->{'efi-disk'} = 1 if $drive_id =~ m/^efidisk(\d+)$/;
+	$blockdev_options->{'snapshot-name'} = $snap if $snap;
 	$blockdev = PVE::Storage::qemu_blockdev_options($storecfg, $volid, $blockdev_options);
 	$scfg = PVE::Storage::storage_config($storecfg, $storeid);
     } elsif (drive_is_cdrom($drive)) {
@@ -244,6 +245,34 @@ sub generate_format_blockdev {
     return $blockdev;
 }
 
+my sub generate_backing_blockdev;
+sub generate_backing_blockdev {
+    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 $snap_fmt_blockdev;
+}
+
+my sub generate_backing_chain_blockdev {
+    my ($storecfg, $deviceid, $drive) = @_;
+
+    my $volid = $drive->{file};
+
+    my $snapshots = PVE::Storage::volume_snapshot_info($storecfg, $volid);
+    my $parentid = $snapshots->{'current'}->{parent};
+    return undef if !$parentid;
+    return generate_backing_blockdev($storecfg, $snapshots, $deviceid, $drive, $parentid);
+}
+
 sub generate_drive_blockdev {
     my ($storecfg, $drive, $live_restore_name, $size) = @_;
 
@@ -262,6 +291,12 @@ sub generate_drive_blockdev {
     my $blockdev_file = generate_file_blockdev($storecfg, $drive);
     my $blockdev_format = generate_format_blockdev($storecfg, $drive, $blockdev_file, undef, $size);
 
+    my $support_qemu_snapshots = PVE::Storage::volume_support_qemu_snapshot($storecfg, $volid);
+    if ($support_qemu_snapshots && $support_qemu_snapshots eq 'external') {
+	my $backing_chain  = generate_backing_chain_blockdev($storecfg, "drive-$drive_id", $drive);
+	$blockdev_format->{backing} = $backing_chain if $backing_chain;
+    }
+
     my $blockdev_live_restore = undef;
     #pflash0 don't support throttle-filter
     return $blockdev_format if $drive_id eq 'pflash0';
diff --git a/test/cfg2cmd/simple-backingchain.conf b/test/cfg2cmd/simple-backingchain.conf
new file mode 100644
index 00000000..71664bd5
--- /dev/null
+++ b/test/cfg2cmd/simple-backingchain.conf
@@ -0,0 +1,21 @@
+# TEST: Simple test for external snapshot backing chain
+name: simple
+parent: snap3
+scsi0: localsnapext:8006/vm-8006-disk-0.qcow2,size=1G
+
+[snap1]
+name: simple
+scsi0: localsnapext:8006/vm-8006-disk-0.qcow2,size=1G
+snaptime: 1748933042
+
+[snap2]
+parent: snap1
+name: simple
+scsi0: localsnapext:8006/vm-8006-disk-0.qcow2,size=1G
+snaptime: 1748933043
+
+[snap3]
+parent: snap2
+name: simple
+scsi0: localsnapext:8006/vm-8006-disk-0.qcow2,size=1G
+snaptime: 1748933044
diff --git a/test/cfg2cmd/simple-backingchain.conf.cmd b/test/cfg2cmd/simple-backingchain.conf.cmd
new file mode 100644
index 00000000..739183ee
--- /dev/null
+++ b/test/cfg2cmd/simple-backingchain.conf.cmd
@@ -0,0 +1,30 @@
+/usr/bin/kvm \
+  -id 8006 \
+  -name 'simple,debug-threads=on' \
+  -no-shutdown \
+  -chardev 'socket,id=qmp,path=/var/run/qemu-server/8006.qmp,server=on,wait=off' \
+  -mon 'chardev=qmp,mode=control' \
+  -chardev 'socket,id=qmp-event,path=/var/run/qmeventd.sock,reconnect-ms=5000' \
+  -mon 'chardev=qmp-event,mode=control' \
+  -pidfile /var/run/qemu-server/8006.pid \
+  -daemonize \
+  -smp '1,sockets=1,cores=1,maxcpus=1' \
+  -nodefaults \
+  -boot 'menu=on,strict=on,reboot-timeout=1000,splash=/usr/share/qemu-server/bootsplash.jpg' \
+  -vnc 'unix:/var/run/qemu-server/8006.vnc,password=on' \
+  -cpu kvm64,enforce,+kvm_pv_eoi,+kvm_pv_unhalt,+lahf_lm,+sep \
+  -m 512 \
+  -global 'PIIX4_PM.disable_s3=1' \
+  -global 'PIIX4_PM.disable_s4=1' \
+  -device 'pci-bridge,id=pci.1,chassis_nr=1,bus=pci.0,addr=0x1e' \
+  -device 'pci-bridge,id=pci.2,chassis_nr=2,bus=pci.0,addr=0x1f' \
+  -device 'piix3-usb-uhci,id=uhci,bus=pci.0,addr=0x1.0x2' \
+  -device 'usb-tablet,id=tablet,bus=uhci.0,port=1' \
+  -device 'VGA,id=vga,bus=pci.0,addr=0x2' \
+  -device 'virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3,free-page-reporting=on' \
+  -iscsi 'initiator-name=iqn.1993-08.org.debian:01:aabbccddeeff' \
+  -device 'lsi,id=scsihw0,bus=pci.0,addr=0x5' \
+  -object '{"id":"throttle-drive-scsi0","limits":{},"qom-type":"throttle-group"}' \
+  -blockdev '{"driver":"throttle","file":{"backing":{"backing":{"cache":{"direct":true,"no-flush":false},"driver":"qcow2","file":{"aio":"io_uring","cache":{"direct":true,"no-flush":false},"detect-zeroes":"on","discard":"ignore","driver":"file","filename":"/var/lib/vz/images/8006/snap1-vm-8006-disk-0.qcow2","node-name":"e-aN9FfpTi1eqQ4kUSoMKsyEYSM6k"},"node-name":"f-aN9FfpTi1eqQ4kUSoMKsyEYSM6k","read-only":true},"cache":{"direct":true,"no-flush":false},"driver":"qcow2","file":{"aio":"io_uring","cache":{"direct":true,"no-flush":false},"detect-zeroes":"on","discard":"ignore","driver":"file","filename":"/var/lib/vz/images/8006/snap2-vm-8006-disk-0.qcow2","node-name":"e-Zu2dZCd1WKQe604KQ0Cy4AMmGww"},"node-name":"f-Zu2dZCd1WKQe604KQ0Cy4AMmGww","read-only":true},"cache":{"direct":true,"no-flush":false},"driver":"qcow2","file":{"aio":"io_uring","cache":{"direct":true,"no-flush":false},"detect-zeroes":"on","discard":"ignore","driver":"file","filename":"/var/lib/vz/images/8006/vm-8006-disk-0.qcow2","node-name":"e-8ps94lIsZyMk28qw4ggmas8MCki"},"node-name":"f-8ps94lIsZyMk28qw4ggmas8MCki","read-only":false},"node-name":"drive-scsi0","throttle-group":"throttle-drive-scsi0"}' \
+  -device 'scsi-hd,bus=scsihw0.0,scsi-id=0,drive=drive-scsi0,id=scsi0' \
+  -machine 'type=pc+pve0'
diff --git a/test/run_config2command_tests.pl b/test/run_config2command_tests.pl
index d689fc5b..83b513ec 100755
--- a/test/run_config2command_tests.pl
+++ b/test/run_config2command_tests.pl
@@ -33,6 +33,15 @@ my $base_env = {
 		type => 'dir',
 		shared => 0,
 	    },
+	    localsnapext => {
+		content => {
+		    images => 1,
+		},
+		path => '/var/lib/vz',
+		type => 'dir',
+		shared => 0,
+		snapext => 1,
+	    },
 	    noimages => {
 		content => {
 		    iso => 1,
@@ -492,6 +501,23 @@ my $storage_module = Test::MockModule->new("PVE::Storage");
 $storage_module->mock(
     activate_volumes => sub {
 	return;
+    },
+    volume_snapshot_info => sub {
+	my $snapshots = {
+	    current => {
+		file => '/var/lib/vz/images/8006/vm-8006-disk-0.qcow2',
+		parent => 'snap2'
+	    },
+	    snap2 => {
+		file => '/var/lib/vz/images/8006/snap2-vm-8006-disk-0.qcow2',
+		parent => 'snap1'
+	    },
+	    snap1 => {
+		file => '/var/lib/vz/images/8006/snap1-vm-8006-disk-0.qcow2',
+
+	    },
+	};
+	return $snapshots;
     }
 );
 
-- 
2.39.5



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