On Wed, Sep 29, 2021 at 11:10:35AM +0100, Daniel P. Berrangé wrote: > On Wed, Sep 29, 2021 at 10:57:19AM +0100, Richard W.M. Jones wrote: > > Looking at the qemu code the problem IMHO is: > > > > https://gitlab.com/qemu-project/qemu/-/blob/6b54a31bf7b403672a798b6443b1930ae6c74dea/docs/specs/vmgenid.txt#L189 > > https://gitlab.com/qemu-project/qemu/-/blob/6b54a31bf7b403672a798b6443b1930ae6c74dea/hw/acpi/vmgenid.c#L37 > > > > This byte swapping makes no sense to me. How do we know that the > > guest is little endian? What will this code do for BE guests? I > > think qemu would be better off treating the "GUID" as a list of bytes > > and writing that exactly into the guest memory. > > This is an artifact of the HyperV only caring about x86 and thus leaving > endianness unspecified in the spec for GenID. QEMU docs say > > > Endian-ness Considerations: > --------------------------- > > Although not specified in Microsoft's document, it is assumed that the > device is expected to use little-endian format. > > All GUID passed in via command line or monitor are treated as big-endian. > GUID values displayed via monitor are shown in big-endian format. > > > So by extension if libvirt is passing the value from its XML straight > to QEMU, then libvirt has effectively defined that the XML is storing > it big-endian too. > > This could be where the confusion with VMX config is coming into play, > though the byte re-ordering in v2v seems more complex than just an > endianess-fiddle ? qemu's qemu_uuid_bswap function only swaps some of the fields. I think even more that applying qemu_uuid_bswap to these (not really) "UUIDs" is a nonsense. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v
