Features/QDevCleanup

Summary

Cleanup qdev's object model and move it into a shared library.

Owner

• Name: Anthony Liguori
• Email: anthony@codemonkey.ws

Detailed Summary

From the ML discussion:

All devices should have a DeviceState associated with them.  Otherwise, there's really no point in having qdev at all.

We have lots of devices today that don't have DeviceState's associated with them because the have a separate qdev representation with a reference to the non-DeviceState object.

We have non-DeviceState objects because otherwise we end up with an inheritance diamond.  We have this problem because we want to have relationships like: DeviceState <- SystemDeviceState <- ISADevice <- ISASerialDevice.

But ISASerialDevice is not the only type of serial device.  You can also have a SystemSerialDevice that's directly attached to the System bus.  That means you'd have to have:

SerialDevice -> ISASerialDevice -> SystemDeviceState -> DeviceState
                     -> SystemSerialDevice -> SystemDeviceState -> DeviceState

Which is a classic MI diamond.  The only way to resolve this modelling problem is to split out the common code and rely on a has-a relationship instead of an is-a.  That gives you:

ISASerialDevice->SystemDeviceState->DeviceState
SystemSerialDevice->SystemDeviceState->DeviceState

ISASerialDevice has-a SerialDevice
SystemSerialDevice has-a SerialDevice

And since we want SerialDevice inherit from a DeviceState (recall, all devices should have DeviceStates):

SerialDevice->DeviceState

No more MI diamond and all devices have DeviceStates.  Coincidentally, it matches more closely how hardware works..

Generally speaking, any time we have one device that needs to sit on multiple busses, we're going to have to model it in this fashion. 

TODO

Item	Status
Refactor reset in qdev.c	Ready
Split monitor out of qdev.c	Ready
Split device_add out of qdev.c	Ready
Refactor hotplug in qdev	Ready
Get rid of no_user	Ready
Move sysbus out of qdev.c and use proper singleton	Ready
Make VMStateDescription have no code dependencies	Ready
Add FIDL based auto-serialization	Ready
Move vmstate_register out of qdev.c	In Progress
Add a required name parameter to qdev	In Progress
Build qdev.c in a library	In Progress
Unit tests for qdev
Refactor serial to use proper modeling	In Progress
Move serial (chip only) to libqdev
Unit tests for serial
Introduce hierarchical PIO/MMIO dispatch

Status

• http://repo.or.cz/w/qemu/aliguori.git features/qdev-cleanup