Preventing an Imbalance of Create and Close Notifications to a Driver

Warning

UMDF 2 is the latest version of UMDF and supersedes UMDF 1. All new UMDF drivers should be written using UMDF 2. No new features are being added to UMDF 1 and there is limited support for UMDF 1 on newer versions of Windows 10. Universal Windows drivers must use UMDF 2.

For more info, see Getting Started with UMDF.

An upper UMDF driver can use the IWDFDeviceInitialize::AutoForwardCreateCleanupClose method to control when the framework automatically forwards create-file, cleanup-file, and close-file notifications to the next lower driver in the device stack. However, because the upper driver sets AutoForwardCreateCleanupClose to automatically forward only on a device level and not on a per-file level, forwarding must be the same for all files for a device. The framework ensures this forwarding behavior for cleanup-file and close-file notifications. If the upper driver implements the IQueueCallbackCreate::OnCreateFile callback function, it must ensure that its forwarding behavior is the same for all create-file requests and is consistent with the forwarding behavior for cleanup-file and close-file notifications. Failing to do so might cause lower drivers to receive an unequal amount of calls to their IQueueCallbackCreate::OnCreateFile method and IFileCallbackCleanup::OnCleanupFile and IFileCallbackClose::OnCloseFile methods.

To prevent lower drivers from receiving an unequal amount of create-file and close-file notifications, the upper driver must ensure, in its IQueueCallbackCreate::OnCreateFile callback function, that:

  • Its forwarding behavior is the same for all files for a device.

  • Its forwarding behavior is consistent with how it set the flag parameter of IWDFDeviceInitialize::AutoForwardCreateCleanupClose. That is:

    • If the driver set the flag to WdfTrue, the driver must forward all the create-file requests down the device stack.
    • If the driver set the flag to WdfFalse, the driver must not forward any of the create-file requests down the stack.
    • If the driver set the flag to WdfUseDefault and:
      • If the driver is a function driver, it must not forward any create-file requests down the stack.
      • If the driver is a filter driver, it must forward all create-file requests down the stack.

In situations where the driver cannot forward a create-file request, the driver can still generate a new create-file request for lower drivers by calling the IWDFDevice::CreateWdfFile method to create a new WDF file. The driver can then complete the original create-file request based on the results of the newly generated create-file request (that is, from the results of CreateWdfFile).