On said example: Libvirt 2.5: Breakpoint 1, 0x00003fffb7c77ba8 in virDomainDiskDefForeachPath (disk=0x200ab490, ignoreOpenFailure=true, iter=0x20011dc0 <add_file_path>, opaque=0x3fffffffef70) at ../../../src/conf/domain_conf.c:24851 $1 = (virStorageSourcePtr) 0x200ab630 (gdb) p disk->src->path $2 = 0x200a9ff0 "/var/lib/uvtool/libvirt/images/kvmguest-artful-normal-a2.qcow" (gdb) p disk->src->backingStore $3 = (virStorageSourcePtr) 0x200ab720 (gdb) p disk->src->backingStore->path $4 = 0x200a9e30 "/var/lib/uvtool/libvirt/images/x-uvt-b64-Y29tLnVidW50dS5jbG91ZC5kYWlseTpzZXJ2ZXI6MTcuMTA6cHBjNjRlbCAyMDE3MDcxNg==" Libvirt 3.5: Breakpoint 1, 0x00003fffb7c6a3a8 in virDomainDiskDefForeachPath (disk=0x2008cb50, ignoreOpenFailure=true, iter=0x2000f5e0 <add_file_path>, opaque=0x3fffffffef70) at ../../../src/conf/domain_conf.c:25984 25984 ../../../src/conf/domain_conf.c: No such file or directory. (gdb) p disk->src->path $2 = 0x20085800 "/var/lib/uvtool/libvirt/images/kvmguest-artful-normal-a2.qcow" (gdb) p disk->src->backingStore $3 = (virStorageSourcePtr) 0x0 So it is the parsing of the XML into objects I have to track down. Maybe it is even some Ubuntu Delta that no more correctly matches. Will run on build from upstream master as well before next report.