[pve-devel] [PATCH v4 qemu-server 10/11] 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 v4 qemu-server 10/11] blockdev: add backing_chain support
Date: Tue, 11 Mar 2025 11:29:04 +0100
Message-ID: <20250311102905.2680524-17-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.pm       | 26 ++----------------
 PVE/QemuServer/Drive.pm | 60 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 62 insertions(+), 24 deletions(-)

diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
index d6aa5730..60481acc 100644
--- a/PVE/QemuServer.pm
+++ b/PVE/QemuServer.pm
@@ -54,7 +54,7 @@ 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);
-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);
+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 do_snapshots_with_qemu);
 use PVE::QemuServer::Machine;
 use PVE::QemuServer::Memory qw(get_current_memory);
 use PVE::QemuServer::MetaInfo;
@@ -3765,6 +3765,7 @@ sub config_to_command {
 	# extra protection for templates, but SATA and IDE don't support it..
 	$drive->{ro} = 1 if drive_is_read_only($conf, $drive);
 	my $blockdev = generate_drive_blockdev($storecfg, $vmid, $drive, $live_blockdev_name);
+	#FIXME: verify if external snapshot backing chain is matching config
 	push @$devices, '-blockdev', JSON->new->canonical->allow_nonref->encode($blockdev) if $blockdev;
 	push @$devices, '-device', print_drivedevice_full(
 	    $storecfg, $conf, $vmid, $drive, $bridges, $arch, $machine_type);
@@ -7559,29 +7560,6 @@ 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/;
-
-    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);
-
-    if ($qemu_snap_storage->{$scfg->{type}} && !$scfg->{krbd}){
-	return 1;
-    }
-
-    if ($volid =~ m/\.(qcow2|qed)$/){
-	return 1;
-    }
-
-    return;
-}
-
 sub qga_check_running {
     my ($vmid, $nowarn) = @_;
 
diff --git a/PVE/QemuServer/Drive.pm b/PVE/QemuServer/Drive.pm
index 5b281616..51513546 100644
--- a/PVE/QemuServer/Drive.pm
+++ b/PVE/QemuServer/Drive.pm
@@ -18,6 +18,7 @@ our @EXPORT_OK = qw(
 is_valid_drivename
 checked_parse_volname
 checked_volume_format
+do_snapshots_with_qemu
 drive_is_cloudinit
 drive_is_cdrom
 drive_is_read_only
@@ -1230,6 +1231,32 @@ sub generate_file_blockdev {
     return $blockdev;
 }
 
+my $qemu_snap_storage = {
+    rbd => 1,
+};
+
+sub do_snapshots_with_qemu {
+    my ($storecfg, $volid, $deviceid) = @_;
+
+    return if $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);
+
+    if ($qemu_snap_storage->{$scfg->{type}} && !$scfg->{krbd}){
+        return 1;
+    }
+
+    return 2 if $scfg->{snapext} || $scfg->{type} eq 'lvm' && $volid =~ m/\.(qcow2)/;
+
+    if ($volid =~ m/\.(qcow2|qed)$/){
+        return 1;
+    }
+
+    return;
+}
+
 sub generate_format_blockdev {
     my ($storecfg, $drive, $file, $snap, $nodename) = @_;
 
@@ -1272,6 +1299,37 @@ sub generate_format_blockdev {
     return $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 $snap_fmt_blockdev;
+}
+
+sub generate_backing_chain_blockdev {
+    my ($storecfg, $deviceid, $drive) = @_;
+
+    my $volid = $drive->{file};
+    my $do_snapshots_with_qemu = do_snapshots_with_qemu($storecfg, $volid, $deviceid);
+    return if !$do_snapshots_with_qemu || $do_snapshots_with_qemu != 2;
+
+    my $chain_blockdev = undef;
+    PVE::Storage::activate_volumes($storecfg, [$volid]);
+    my $snapshots = PVE::Storage::volume_snapshot_info($storecfg, $volid);
+    my $parentid = $snapshots->{'current'}->{parent};
+    $chain_blockdev = generate_backing_blockdev($storecfg, $snapshots, $deviceid, $drive, $parentid) if $parentid;
+    return $chain_blockdev;
+}
+
 sub generate_drive_blockdev {
     my ($storecfg, $vmid, $drive, $live_restore_name) = @_;
 
@@ -1293,6 +1351,8 @@ sub generate_drive_blockdev {
 
     my $blockdev_file = generate_file_blockdev($storecfg, $drive);
     my $blockdev_format = generate_format_blockdev($storecfg, $drive, $blockdev_file);
+    my $backing_chain  = generate_backing_chain_blockdev($storecfg, "drive-$drive_id", $drive);
+    $blockdev_format->{backing} = $backing_chain if $backing_chain;
 
     my $blockdev_live_restore = undef;
     if ($live_restore_name) {
-- 
2.39.5



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