Using IRP Completion 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.

File system filter drivers use completion routines that are similar to those used by device drivers. A completion routine performs completion processing on an IRP. Any driver routine that passes an IRP down to the next-lower-level driver can optionally register a completion routine for the IRP by calling IoSetCompletionRoutine before calling IoCallDriver.

Every IRP completion routine is defined as follows:

NTSTATUS
(*PIO_COMPLETION_ROUTINE) (
    IN PDEVICE_OBJECT DeviceObject,
    IN PIRP Irp,
    IN PVOID Context
    );

Completion routines are called at IRQL <= DISPATCH_LEVEL, in an arbitrary thread context.

Because they can be called at IRQL DISPATCH_LEVEL, completion routines cannot call kernel-mode routines that must be called at a lower IRQL, such as IoDeleteDevice. For the same reason, any data structures that are used in a completion routine must be allocated from nonpaged pool.

This section discusses the following topics:

How Completion Processing Is Performed

Checking the PendingReturned Flag

Returning Status from Completion Routines

Example: Simple Pass-Through Dispatch and Completion

Constraints on Completion Routines