Handling Requests to Stop a Device
There are two circumstances in which, before asking a device's drivers to stop a device, the PnP manager asks the drivers if stopping the device is a good idea:
A user has plugged in a new device, and the PnP manager must redistribute the system's hardware resources to accommodate the new device.
A user has indicated that he or she would like to remove the device.
There are several ways in which a driver can handle these situations:
If your driver has called WdfDeviceSetSpecialFileSupport because a device is supporting a special file, and if a special file is open on the device, the framework will not allow the device to be stopped.
To temporarily prevent all stoppages for a relatively short period of time, the driver can call WdfDeviceSetStaticStopRemove.
If the device is not supporting special files, and if stopping or removing a device is never a problem for the driver or device, the driver doesn't provide EvtDeviceQueryStop and EvtDeviceQueryRemove callback functions and never calls WdfDeviceSetStaticStopRemove. In this case the PnP manager always stops the device without first checking to see if the driver allows it.
Sometimes the PnP manager must redistribute the system's hardware resources. Typically, this redistribution occurs because a bus driver has reported that a new device has been plugged in, and the new device requires already-assigned resources. Devices must be stopped before resources are reassigned.
If it is necessary for your driver to sometimes prevent the PnP manager from stopping a busy device, the driver can provide an EvtDeviceQueryStop callback function. If your driver's EvtDeviceQueryStop callback function returns an error status value, the PnP manager will not stop the device.
If the driver determines that it is safe to stop the device, the callback function returns STATUS_SUCCESS. If none of the device's other drivers prevent stoppage, the PnP manager temporarily stops the device.
For information about the order in which the framework calls a driver's event callback functions when the PnP manager stops a device to redistribute resources, see The PnP Manager Redistributes System Resources.
A user can remove or disable some devices. For example:
If your driver has set the Removable member (and not the SurpriseRemovalOK member) of the device's WDF_DEVICE_PNP_CAPABILITIES structure, the user can run the Unplug or Eject Hardware program and then unplug or eject the device.
If your driver has not set the NotDisableable member of the device's WDF_DEVICE_STATE structure, the user can use Device Manager to disable the device.
In such cases, the PnP manager attempts to stop the device before the user removes it.
If it is necessary for your driver to sometimes prevent removal of a busy device, the driver can provide an EvtDeviceQueryRemove callback function. If any driver's EvtDeviceQueryRemove callback function returns an error status value, the PnP manager will not stop the device.
If the driver determines that it is safe for the user to remove the device, the callback function returns STATUS_SUCCESS. If none of the device's other drivers prevent removal, the PnP manager stops the device.
For information about the order in which the framework calls a driver's event callback functions when stopping a device for removal, see A User Unplugs a Device.
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