Re: [PATCH v4 14/16] qapi: deprecate "device" field of DEVICE_* events

On 14/2/23 12:49, Markus Armbruster wrote: > Daniel P. Berrangé <berrange(a)redhat.com&gt; writes:

>> What's the documented way to construct a QOM path, given only an ID as >> input ? > > QOM paths a gap in our documentation, even though the composition tree > structure has been stable since day one, and is de facto ABI. > > Short answer: "/machine/peripheral/ID". > > Long answer follows. > > We have three "containers" under /machine that serve as parents for > devices: > > * /machine/peripheral/ > > Parent of user-created devices with ID. Children are named "ID". > > Put there by qdev_set_id(), called from qdev_device_add_from_qdict(). > > On "user-created": Nothing stops board code to abuse qdev_set_id() for > onboard devices, directly or indirectly, but it really, really > shouldn't. > > * /machine/peripheral-anon/ > > Parent of user-created devices without ID. Children are named > "device[N]", where N counts up from zero. > > Put there by qdev_set_id(), called from qdev_device_add_from_qdict(). > > Again, abuse by board code is possible, but would be wrong. > > Beware: a particular device's N changes when the set of devices > created before it grows or shrinks. Messing with the machine type can > change it (different onboard devices). > > * /machine/unattached/ > > Surrogate parent of onboard devices created without a parent. > > Put there by device_set_realized() (general case), > qdev_connect_gpio_out_named() (input pins) , memory_region_do_init() > (memory regions), qemu_create_machine() (the main sysbus). > > I believe this container was created as a convenience, so we don't > have to retrofit parents to existing code. Probably abused ever > since. Are you suggesting this is a stable interface and we can not move devices (like from /machine/unattached/ to /machine/peripheral/) without going thru the deprecation process?