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

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

It turns out that changing the qemu implementation is painful,
particularly if we wish to maintain backwards compatibility of the
command line and live migration.

Instead I opted to document comprehensively what all the
different hypervisors do:

  https://github.com/libguestfs/virt-v2v/blob/master/docs/vm-generation-id-across-hypervisors.txt

On Thu, Sep 30, 2021 at 10:16:20AM +0100, Richard W.M. Jones wrote:
> I was going to suggest something like:
> 
>   <genid type="guid">aa-bb-cc..</genid>
> or
>   <genid type="binary">aabbcc..</genid>

After thinking about this some more, the real implementation on
Windows guest and host is two 64 bit little-endian integers[1].  How
about implementing this exactly the same way as Hyper-V (and VMware):

  <genid type="pair">
    <low>0x8877665544332211</low>
    <high>0x00ffeeddccbbaa99</high>
  </genid>

This would have to be mapped to the following qemu command line:

  qemu -device vmgenid,guid=44332211-6655-8877-99aa-bbccddeeff00

which would unmangle to the following in guest physical memory:

  11 22 33 44 55 66 77 88 99 aa bb cc dd ee ff 00

The equivalent back-compat option would be:

  <genid type="qemu">44332211-6655-8877-99aa-bbccddeeff00</genid>

Rich.

[1] No one has ever thought what to do about big-endian guests.

-- 
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