Right now, you need to pair up object_new with object_delete. This is impractical when using reference counting because we would like to ensure that object_unref() also frees memory when needed.
The first few patches fix this problem by introducing a release callback so that objects that need special release behavior (i.e. g_free) can do that. Since link and child properties all hold references, in order to actually free an object, we need to break those links. User created devices end up as children of a container. But child properties cannot be removed which means there's no obvious way to remove the reference and ultimately free the object. We introduce the concept of "nullable child" properties to solve this. This is a child property that can be broken by writing NULL to the child link. Today we set all /peripheral* children to be nullable so that they can be deleted by management tools. In terms of modeling hotplug, we represent unplug by removing the object from the parent bus. We need to register a notifier for when this happens so that we can also remove the parent's child property to ultimately release the object. Putting it all together, we have: 1) qmp_device_del will issue a callback to a device. The default callback will do a forced eject (which means writing NULL to the parent_bus link). 2) PCI hotplug is a bit more sophisticated in that it waits for the guest to do the ejection. 3) qmp_device_del will register an eject notifier such that the device gets completely removed. There's a slightly change in behavior here. A device is not automatically destroyed based on a guest initiated eject. A management tool must explicitly break the parent's link to the child in order for the device to disappear completely. device_del behaves exactly as it does today though. This is an RFC. I've tested the series quite a lot (it was hard to get the reference counting right) but not enough to apply. I also don't think the series is quite split right and may not bisect cleanly. I also want to write up a document describing object life cycle since admittedly the above is probably not that easy to follow. I wanted to share this now though because it works and I think the concepts are right.
