On Thu, Nov 28, 2019 at 04:00:06PM +0000, Peter Maydell wrote: > Hi; this is a question which came up in Damien's reset series > which I don't know the answer to: > > What is the interaction of the QOM device lifecycle (instance_init/realize/ > unrealize/instance_finalize) with hotplug and hot-unplug ? I couldn't > find any documentation of this but maybe I was looking in the wrong > place... > > Looking at device_set_realized() it seems like we treat "realize" > as meaning "and also do the hot-plug if this is a device we're > trying to hotplug". On the other hand hot-unplug is I think the > other way around: when we get a hot-unplug event we assume that > it should also imply an "unrealize" (but just unrealizing doesn't > auto-hot-unplug) ?
Your description seems accurate, and I agree it is confusing. It would be more consistent if realized=true didn't plug the device automatically, and qdev_device_add() asked the hotplug handler to plug the device instead. > > Once a device is hot-unplugged (and thus unrealized) is it valid > for it to be re-hot-plugged, or is the assumption that it's then > destroyed and a fresh device is created if the user wants to plug > something in again later ? Put another way, is it valid for a qdev > device to see state transitions realize -> unrealize -> realize ? My interpretation is that this is valid in theory, but likely to crash a large portion of our devices if we tried it. -- Eduardo
