Re: [PATCH 0/1] vmx: Fix <genid/> mapping

["Richard W.M. Jones" <rjones@redhat.com>]

On Thu, Sep 30, 2021 at 09:47:01AM +0100, Daniel P. Berrangé wrote:
> On Thu, Sep 30, 2021 at 08:33:48AM +0100, Richard W.M. Jones wrote:
> > I propose we deprecate the guid parameter in:
> > 
> >   -device vmgenid,guid=8987940a-0951-2cc5-e815-10634ff550b9,id=vmgenid0
> > 
> > Instead it will be replaced by bytes= which will simply write
> > the bytes, in the order they appear, into guest memory with no
> > attempt to interpret or byte-swap.  Something like:
> > 
> >   -device vmgenid,bytes=112233445566778899aabbccddeeff00,id=vmgenid0
> > 
> > (guid although deprecated will need to be kept around for a while,
> > along with its weird byte-swapping behaviour).
> > 
> > We will then have a plain and simple method to emulate the behaviour
> > of other hypervisors.  We will look at exactly what bytes they write
> > to guest memory and copy that behaviour when v2v converting from those
> > hypervisors.
> 
> From the libvirt POV, I'm not expecting anything in QEMU to change
> in this respect. If guid is replaced by a new attribute taking data
> in a different way, then libvirt will have to remap itself, so that
> existing usage in libvirt keeps working the same way as it did with
> guid.  Essentially from libvirt's POV, it is simply a documentation
> issue to specify how the libvirt XML representation translates to
> the guest visible representation, and ensure that all libvirt drivers
> implement it the same way. The QEMU genid support arrived first so
> that set the standard for how libvirt will represent it, that all
> further libvirt hypervisor drivers need to match.

I was going to suggest something like:

  <genid type="guid">aa-bb-cc..</genid>
or
  <genid type="binary">aabbcc..</genid>

with the type defaulting to guid for backwards compatibility.

Does libvirt XML have any other fields were you're passing
essentially small snippets of binary data?

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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