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Handling Enumeration Requests

Last Updated: 7/30/2016

The PnP manager can request a bus driver to enumerate its children at any time. (If you are familiar with WDM interfaces, enumeration requests are IRP_MN_QUERY_DEVICE_RELATIONS requests with a relation type of BusRelations.) Framework-based drivers do not see these requests. Instead, the framework handles the requests by using the information that is stored in a device's child list. The driver is responsible for keeping the child list up-to-date so that the framework can provide correct information when the PnP manager requests an enumeration.

Framework-based bus drivers that support dynamic enumeration can receive a request to reenumerate a particular child device. Such a request might be sent by the child device's function driver after the driver detects a device failure. (The framework supports this type of request by implementing the REENUMERATE_SELF_INTERFACE_STANDARD interface, which is a standard driver-defined interface that is defined in wdm.h.)

Framework-based bus drivers that support dynamic enumeration can provide an EvtChildListDeviceReenumerated callback function, which the framework calls when it receives a reenumeration request from a child device's driver. If this callback function returns TRUE or does not exist, the framework marks the child device as no longer being present and informs the PnP manager that the bus driver's child list has changed. As a result, the PnP manager requests a reenumeration and the framework calls the driver's EvtChildListCreateDevice callback function, which creates a new PDO for the child device.

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