[libvirt] [PATCH 6/8] virQEMUCapsSetFromNodes: Skip setting deprecated flags

[Daniel P. Berrangé]

On Thu, Mar 07, 2019 at 12:52:46PM +0100, Erik Skultety wrote:
> > However, looking at the bigger picture is this a safe thing to do? I mean,
> > imagine the following scenario:
> >
> > 1) say there is capability X that affects certain part of cmd line. And
> > assume that those two possibilities are incompatible. If cmd line is
> > generated one way then migration to a qemu which has cmd line generated the
> > other way fails.
> >
> > 2) in release R we deprecate X and thus do not format it in <capabilities/>
> > in status XML.
> >
> > 3) user starts a domain D.
> >
> > 4) user saves D into a file
> >
> > 5) sysadmin downgrades libvirt to R-1
> 
> Do we even support downgrade this way? I know we migrate to older version but
> isn't that different?

Yeah, downgrades of libvirt are not something we claim is supported. If
will often work but we're not guaranteeing it & have broken it in the
past, especially for running guests.  You might be lucky if you have
upgraded & immedaitely downgrade, but if you've made changes to guests
while the new libvirt was running all bets are off.

Regards,
Daniel
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