[pve-devel] [PATCH qemu-server 07/11] cfg2cmd: allow PBS snapshots as backing files for drives

[Stefan Reiter <s.reiter@proxmox.com>]

Uses the custom 'alloc-track' filter node to redirect writes to the
original drives target, while unwritten blocks will be read from the
specified PBS snapshot.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
---
 PVE/QemuServer.pm | 42 +++++++++++++++++++++++++++++++++++++++---
 1 file changed, 39 insertions(+), 3 deletions(-)

diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
index d517dae..6de6ff6 100644
--- a/PVE/QemuServer.pm
+++ b/PVE/QemuServer.pm
@@ -3022,7 +3022,8 @@ sub query_understood_cpu_flags {
 }
 
 sub config_to_command {
-    my ($storecfg, $vmid, $conf, $defaults, $forcemachine, $forcecpu) = @_;
+    my ($storecfg, $vmid, $conf, $defaults, $forcemachine, $forcecpu,
+        $pbs_backing) = @_;
 
     my $cmd = [];
     my $globalFlags = [];
@@ -3521,6 +3522,32 @@ sub config_to_command {
 	my $drive_cmd = print_drive_commandline_full($storecfg, $vmid, $drive);
 	$drive_cmd .= ',readonly' if PVE::QemuConfig->is_template($conf);
 
+	if ($pbs_backing && defined($pbs_backing->{$ds})) {
+	    my $pbs_conf = $pbs_backing->{$ds};
+	    my $pbs_name = "drive-$ds-pbs";
+
+	    # add PBS block device to access snapshot from QEMU
+	    my $blockdev = "driver=pbs,node-name=$pbs_name,read-only=on";
+	    $blockdev .= ",repository=$pbs_conf->{repository}";
+	    $blockdev .= ",snapshot=$pbs_conf->{snapshot}";
+	    $blockdev .= ",archive=$pbs_conf->{archive}";
+	    $blockdev .= ",keyfile=$pbs_conf->{keyfile}" if $pbs_conf->{keyfile};
+	    push @$devices, '-blockdev', $blockdev;
+
+	    # modify drive command to put the desired target file behind an
+	    # 'alloc-track' node
+	    $drive_cmd =~ s/file=([^,]+)/file.file.filename=$1/;
+	    $drive_cmd =~ s/,format=([^,]+)/,file.driver=$1,format=alloc-track/;
+	    $drive_cmd .= ",backing=$pbs_name";
+	    $drive_cmd .= ",auto-remove=on";
+
+	    # note: 'cache' and 'aio' directly affect the 'drive' parameter, so
+	    # we don't need to change them to 'file.', but 'detect-zeroes' works
+	    # per blockdev and we want it to persist after the alloc-track is
+	    # removed, so put it on 'file' directly
+	    $drive_cmd =~ s/,detect-zeroes=([^,]+)/,file.detect-zeroes=$1/;
+	}
+
 	push @$devices, '-drive',$drive_cmd;
 	push @$devices, '-device', print_drivedevice_full(
 	    $storecfg, $conf, $vmid, $drive, $bridges, $arch, $machine_type);
@@ -4915,6 +4942,15 @@ sub vm_start {
 #   timeout => in seconds
 #   paused => start VM in paused state (backup)
 #   resume => resume from hibernation
+#   pbs-backing => {
+#      sata0 => {
+#         repository
+#         snapshot
+#         keyfile
+#         archive
+#      },
+#      virtio2 => ...
+#   }
 # migrate_opts:
 #   nbd => volumes for NBD exports (vm_migrate_alloc_nbd_disks)
 #   migratedfrom => source node
@@ -4961,8 +4997,8 @@ sub vm_start_nolock {
 	print "Resuming suspended VM\n";
     }
 
-    my ($cmd, $vollist, $spice_port) =
-	config_to_command($storecfg, $vmid, $conf, $defaults, $forcemachine, $forcecpu);
+    my ($cmd, $vollist, $spice_port) = config_to_command($storecfg, $vmid,
+	$conf, $defaults, $forcemachine, $forcecpu, $params->{'pbs-backing'});
 
     my $migration_ip;
     my $get_migration_ip = sub {
-- 
2.20.1