Re: [PATCH v3 03/12] vfio-user: define vfio-user-server object

[Peter Krempa]

On Fri, Nov 05, 2021 at 14:19:34 +0100, Kevin Wolf wrote:
> Am 05.11.2021 um 11:08 hat Markus Armbruster geschrieben:
> > Kevin Wolf <kwolf@redhat.com> writes:
> > 
> > > Am 04.11.2021 um 13:13 hat Markus Armbruster geschrieben:

[...]

> We can deprecate on two different levels. I think it's useful to do
> both:
> 
> 1. Broad deprecation: Stable non-JSON interfaces are degraded to
>    a HMP-like compatibility promise. Obviously, this can only be done
>    for options that support JSON. Peter Maydell also wants to do this
>    only after a big user (read: libvirt) has implemented and is
>    using JSON, basically as a proof that the alternative is working.
> 
>    So this can certainly be done for -object. I believe libvirt also
>    uses JSON for -device now, so this should be fine now, too. Possibly
>    -drive (in favour of -blockdev), though I'm not completely sure if we
>    have gotten rid of the final users of -drive. (CCing Peter Krempa for
>    details.)

Libvirt uses JSON exclusively with -object (starting from qemu-6.0) and
with -device (starting from qemu-6.2).

We could also easily do -netdev if JSON support will be added for the
option as internally we already create the JSON object (so that the code
is identical for QMP hotplug) and just convert it back to the
commandline syntax.

Libvirt also uses JSON with -blockdev since -blockdev support was
introduced (IIRC qemu-4.2 added all the necessary bits for us).
If -blockdev is used libvirt does not use -drive at all (except for SD
cards for ARM boards), but that is not tested very well.