Re: [PATCH v4 14/16] qapi: deprecate "device" field of DEVICE_* events
Daniel P. Berrangé <berrange(a)redhat.com> 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.
I suggested to deprecate it in review of "[PATCH v3 14/15] qapi:
introduce DEVICE_ON event" (Message-ID: <873579x67l.fsf(a)pond.sub.org>).
Quote:
We commonly send both device ID and QOM path, mostly for historical
reasons: the former precede the latter.
There are exceptions, such as query-cpus-fast. Can't say offhand
whether CPUs can be created with IDs.
[...]
I'd be in favour of deprecating and deleting redundant device IDs in QMP
output.