On Fri, 24 Jan 2020 11:20:15 +0000 Salil Mehta <salil.me...@huawei.com> wrote:
> Hello, > I am working on vCPU Hotplug feature for ARM64 and I am in mid of > understanding some aspect of device_add/device_del interface of the QEMU. > > Observations: > 1. Any object initialised by qmp_device_add() gets into /machine/unattached > container. I traced the flow to code leg inside device_set_realized() > 2. I could see the reverse qmp_device_del() expects the device to be in > /machine/peripheral container. > 3. I could see any object initially added to unattached container did not had > their parents until object_add_property_child() was called further in the leg. > which effectively meant a new property was created and property table > populated and child was parented. > 4. Generally, container /machine/peripheral was being used wherever > DEVICE(dev)->id was present and non-null. > > Question: > 1. Wanted to confirm my understanding about the use of having separate > containers like unattached, peripheral and anonymous. > 2. At init time all the vcpus goes under *unattached* container. Now, > qmp_device_del() cannot be used to unplug them. I am wondering device is put into 'unattached' in case it wasn't assigned a parent. Usually it happens when board creates device directly. > if all the hotplug devices need to go under the *peripheral* container > while they are hotplugged and during object init time as well? theoretically device_del may use QOM path (the later users can get with query-hotpluggable-cpus), but I think it's mostly debugging feature. users are supposed to specify 'id' during -device/device_add if they are going to manage that device afterwards (like unplugging it). Then they could use that 'id' in other commands (including device_del) So 'id'-ed devices end up in 'peripheral' container > 3. I could not see any device being place under *anonymous* container during > init time. What is the use of this container? if I recall it right, devices created with help of device_add but without 'id' go to this container > > I would be thankful for your valuable insights and answers and help in > highlighting any gap in my understanding. > > Thanks in anticipation! > > Best Regards > Salil >
