On Thu, 17 Mar 2022 at 14:03, Daniel Henrique Barboza <danielhb...@gmail.com> wrote: > I've been looking into converting some vmstate_register() calls to use > dc->vmsd, > using as a base the docs in docs/devel/migration.rst. This doc mentions that > we > can either register the vmsd by using vmstate_register() or we can use > dc->vmsd > for qdev-based devices. > > When trying to convert this vmstate() call for the qdev alternative > (hw/ppc/spapr_drc.c, > drc_realize()) I found this: > > vmstate_register(VMSTATE_IF(drc), spapr_drc_index(drc), > &vmstate_spapr_drc, > drc); > > spapr_drc_index() is an unique identifier for these DRC devices and it's > being used > as instance_id. It is not clear to me how we can keep using this same > instance_id when > using the dc->vmsd alternative. By looking a bit into migration files I > understood > that if dc->vmsd is being used the instance_id is always autogenerated. Is > that correct?
Not entirely. It is the intended common setup, but because changing the ID value breaks migration compatibility there is a mechanism for saying "my device is special and needs to set the instance ID to something else" -- qdev_set_legacy_instance_id(). > Given that this is a 13 year old comment from Anthony Liguori I wanted to > confirm its > validity. Is there a long term goal of getting rid of instance_id? Can I > ignore its > role when converting these calls to dc->vmsd? Only if you're prepared to break migration compatibility, I think. -- PMM