View source for Features/QDevCleanup

== Summary ==

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

== Owner ==

* '''Name:''' [[User:AnthonyLiguori|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 ==

{| class="wikitable" border="1"
|-
!  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

[[Category:Obsolete feature pages]]