[PATCH 2/3] qemu: capabilities: Condemn the use of 'device.json' capability name

[Peter Krempa]

On Mon, Jan 03, 2022 at 16:56:32 +0100, Ján Tomko wrote:
> On a Monday in 2022, Peter Krempa wrote:
> > As a workaround for users using 'libvirt-7.9' and 'libvirt-7.10' with
> > 'qemu-6.2' who wish to use device hot-unplug we are going to be
> > suggesting to filter out the 'device.json' qemu capability via either
> > the global 'qemu.conf' config:
> > 
> >  capability_filters = [ "device.json" ]
> > 
> > or the per-VM XML capability override:
> > 
> > <domain type='kvm' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
> > 
> > [...]
> > 
> >  <qemu:capabilities>
> >    <qemu:del capability='device.json'/>
> >  </qemu:capabilities>
> > </domain>
> > 
> > Doing this poisons the capability name 'device.json' for any further
> > use, so to ensure that we can re-add JSON usage for -device also for
> > users which filtered it out originally once it's fixed in qemu we need
> > to condemn the old name and add a new one.
> > 
> > To achieve this the old capability is renamed to
> > 'X_QEMU_CAPS_DEVICE_JSON_BROKEN' and a new capability
> > 'QEMU_CAPS_DEVICE_JSON' is mapped to 'device.json-fixed'. For now we
> 
> I am not a fan of the new string but we can change it later once it's
> clear how to probe for this in QEMU.

In fact, I can leave this commit out for now, or replace it by just
noting in qemu_capabilities.h that the flag name was poisoned by
recomending users to filter it out and a new one must be picked when
re-instating this feature.