On Thu, Jul 05, 2018 at 01:39:29PM +0100, Richard W.M. Jones wrote: > I was doing a bit of investigation around how different hypervisors > handle the VM Generation ID feature. QEMU's behaviour seems quite > strange, I wonder if this is a bug or expected? > > (1) I booted a Windows 2016 VM with: > > qemu-system-x86_64 -M pc,accel=kvm -m 2G -hda w2k16-mincore.img \ > -device vmgenid,guid=01020304-0506-0708-090a-0b0c0d0e0f00,id=vmgenid0 > > (2) Inside the guest I used the VMGENID.EXE program from: > > https://bugzilla.redhat.com/show_bug.cgi?id=1598350#c3 > > https://docs.microsoft.com/en-gb/windows/desktop/HyperV_v2/virtual-machine-generation-identifier > > Note this is self-compiled using mingw64-g++ (not using Visual Studio > which I don't have available), but I don't believe that could have > caused the problem. > > (3) The program prints: > > VmCounterValue: 708050601020304:f0e0d0c0b0a09 > > To make it easier to see, this is the same number but zero-extended: > > VmCounterValue: 07 08 05 06 01 02 03 04 : 00 0f 0e 0d 0c 0b 0a 09 > \________ LOW ________/ \_______ HIGH _______/ > WORD WORD > > As you can see it looks like there is no clear relationship between > the order of the bytes in the guid= parameter and the order that they > are seen by Windows.
OK after examining util/uuid.c and the qemu_uuid_bswap function, I sort of see what's going on here. FWIW other hypervisors seem to store these as two 64 bit integers. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW
