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Returning Status from Dispatch Routines

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Note

For optimal reliability and performance, use file system minifilter drivers with Filter Manager support instead of legacy file system filter drivers. To port your legacy driver to a minifilter driver, see Guidelines for Porting Legacy Filter Drivers.

Except when completing an IRP, a dispatch routine that doesn't set a completion routine should always return the NTSTATUS value returned by IoCallDriver. Unless this value is STATUS_PENDING, it must match the value of Irp->IoStatus.Status set by the driver that completed the IRP.

A dispatch routine that sets a completion routine that might post the IRP to a work queue should do one of the following actions:

  • Return the NTSTATUS value that was returned by IoCallDriver.
  • Wait for the completion routine to signal an event and return the value of Irp->IoStatus.Status.
  • Mark the IRP pending, post it to a work queue, and return STATUS_PENDING.
  • If the completion routine might post the IRP to a work queue, the dispatch routine must mark the IRP pending and return STATUS_PENDING.

Which of these behaviors is correct or even possible depends on the specific operation. Some operations, such as directory change notifications, can't be made synchronous; and some operations, such as oplocks, can't be made asynchronous.

For more information about returning status from a dispatch routine, see Constraints on Dispatch Routines.