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| === Naming in QDev ===
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| QDev has three namespaces: the device namespace, the bus namespace, and property
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| namespaces.
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| The device namespace contains the names of qdev devices. qdev supports the
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| ability to have anonymous devices. Anonymous devices are usually created
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| through composition and are anonymous because the user controls the device
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| namespace and the user has no way of allocating names for devices created
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| through composition.
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|
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| The bus namespace is parallel to the device namespace. Unlike the device
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| namespace, busses cannot be anonymous. For busses that are created as a result
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| of composition, a name is derived either from the device name or via the type
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| name.
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|
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| In qdev, implicit bus names are not considered stable and may change across
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| invocations and/or versions of QEMU.
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|
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| Property namespaces are local to devices. The 'id' property is reserved to
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| refer to the name of the device. Property names do not reference child devices.
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|
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| Paths cannot be meaningfully constructed in QDev. Devices can only be addressed
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| directly by their name as there is no stable way to refer to busses under a
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| device, or children under a bus.
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|
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| === Naming in QOM ===
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| In QOM, there are only two namespaces, the device namespace and the property
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| namespace.
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| All devices have unique names. There are no exceptions. Devices created
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| through composition are given unique names by deriving the name based on the
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| parent device name and a special separator, "::", that cannot be used in user
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| supplied names.
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|
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| Since a bus is-a device in QOM, there is no notion of having multiple busses
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| under the same device. A device can implement multiple bus interfaces, but can
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| only be a single bus of any given bus interface.
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|
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| Device names are completely independent of pathnames. For devices that are no
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| user created, device names should be treated as opaque blobs with absolutely no
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| semantic meaning.
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|
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| All device relationships are identified as named properties. A QOM path name
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| consists of a named device, followed by a series of properties which may or may
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| not refer to other devices. For instance, all of the following are valid paths:
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| /i440fx/piix3/i8042/aux
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| /i440fx/slot[1.0]/i8042/aux
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| /i440fx/slot[1.0]/bus/piix3/i8042/aux
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|
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| All of these path names are interpreted as follows:
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|
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| def resolve_pathname(pathname):
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| root, props = pathname[1:].split('/')
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| dev = find_device(root)
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| for prop in props:
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| device_name = get_property(dev, prop)
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| dev = find_device(device_name)
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| return dev
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|
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| In this specific example, the i440fx object has two properties that both refer
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| to the PIIX3 device. The 'piix3' device is a property that reflects a device
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| composition relationship. The 'slot[1.0]' property represents a device backlink
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| relationship.
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|
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| The PIIX3 device has a 'i8042' property based on device composition of the PC
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| Keyboard Controller device. It also has a device backlink property, 'bus', that
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| points to the bus that it sits on (which is the 'i440fx' object).
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|
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| Finally, the PC Keyboard Controller device has an 'aux' property which is a
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| device backlink property that can point to a PS/2 Mouse device.
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|
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| The full set of devices names and properties used in this example are below:
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|
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| Type: I440FX
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| Is-a: Device
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| Implements: PciBus
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| Name: i440fx
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| Properties:
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| piix3: Composition<PIIX3>
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| slot[1.0]: Backlink<PciDevice>
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| Type: PIIX3
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| Isa-a: PciDevice
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| Implements: IsaBus
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| Name: i440fx::piix3
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| Properties:
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| i8042: Composition<I8042>
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| bus: Backlink<PciDevice> (inherited from PciDevice)
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|
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| Type: I8042
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| Isa-a: Device
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| Implements: Ps2Controller
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| Name: i440fx::piix3::i8042
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| Properties:
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| aux: Backlink<Ps2Mouse>
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|
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| == TODO ==
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|
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| 1. Eliminate anonymous devices. | | 1. Eliminate anonymous devices. |
| a. Will require touching any place in the tree that creates a qdev object and | | a. Will require touching any place in the tree that creates a qdev object and |
