The hierarchy of the device tree reflects the structure in which the devices are attached in the machine. (A bus device is any device to which other physical, logical, or virtual devices can be attached.) You can see the hierarchy of devices in the device tree using Device Manager and choosing the view option that allows you to view devices by connection. The device tree is hierarchical, with devices on a bus represented as "children" of the bus adapter, controller or other bus device. For example, the Windows ACPI driver, Acpi.sys, looks in the ACPI namespace, the PCI driver queries PCI configuration space, and a USB hub driver follows the USB bus protocol. The bus driver determines its list of children according to its bus protocol. The PnP manager asks a bus driver for a list of its child devices using an IRP_MN_QUERY_DEVICE_RELATIONS request. Therefore, there is a devnode for each device stack. A devnode consists of the device objects for the device's drivers, plus internal information maintained by the system. The PnP manager builds this tree when the machine boots, using information from drivers and other components, and updates the tree as devices are added or removed.Įach node of the device tree is called a device node, or devnode. The device tree contains information about the devices present on the system. The following figure shows the device tree for a sample system configuration. The PnP manager maintains a device tree that keeps track of the devices in the system.
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