Re: [PATCH v2 4/4] docs/firmware: add feature flag for qemu variable store

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Mar 19, 2025 at 02:03:09PM +0100, Gerd Hoffmann wrote:
>   Hi,
> 
> > > > > There is 'stateless' already for 'firmware image in r/o flash'.
> > > > 
> > > > What's the behaviour of UEFI if build with JSON vars support, but without
> > > > QEMU providing any JSON vars backend ?
> > > 
> > > It will panic.
> > 
> > In that case, we must not reuse 'stateless' with such builds, as that's
> > quite different semantics & incompatible with current usage.
> > 
> > We would need a new 'uefi-vars' mode, or just declare that we must
> > always use 'memory'  not 'flash' for such builds.
> 
> I don't see how 'flash.stateless' is any different than 'memory' (or
> 'kernel', or maybe 'igvm' some day).  If the 'host-uefi-vars' feature
> is present '-device uefi-vars-$kind' is required, no matter how you
> load the firmware.
> 
> What exactly will an old libvirt which does not know the
> 'host-uefi-vars' feature do in case it finds a firmware.json file with
> that feature?  Play safe and ignore the file?

No, unknown features are simply ignored. 

With regards,
Daniel
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