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

Daniel P. Berrangé <berrange(a)redhat.com&gt; writes: > On Tue, Feb 14, 2023 at 09:54:22AM +0100, Markus Armbruster wrote: >> Daniel P. Berrangé <berrange(a)redhat.com&gt; writes: >> >>> On Mon, Feb 13, 2023 at 05:01:01PM +0300, Vladimir Sementsov-Ogievskiy wrote: >>>> The device field is redundant, because QOM path always include device >>>> ID when this ID exist. >>> >>> The flipside to that view is that applications configuring QEMU are >>> specifying the device ID for -device (CLI) / device_add (QMP) and >>> not the QOM path. IOW, the device ID is the more interesting field >>> than QOM path, so feels like the wrong one to be dropping. >> >> QOM path is a reliable way to identify a device. Device ID isn't: >> devices need not have one. Therefore, dropping the QOM path would be >> wrong. >> >>> Is there any real benefit to dropping this ? >> >> The device ID is a trap for the unwary: relying on it is fine until you >> run into a scenario where you have to deal with devices lacking IDs. > > When a mgmt app is configuring QEMU though, it does it exclusively > with device ID values. If I add a device "-device foo,id=dev0", > and then later hot-unplug it "device_del dev0", it is pretty > reasonable to then expect that the DEVICE_DELETED even will then > include the ID value the app has been using elsewhere. The management application would be well advised to use QOM paths with device_del, because only that works even for devices created by default (which have no ID), and devices the user created behind the management application's back. > If the mgmt app is using IDs everywhere when dealing with a device, > then trap effectively doesn't exist for their usage scenario.