Description

The DpcForIsr routine finishes the servicing of an I/O operation, after an InterruptService routine returns.

Parameters

Dpc [in]

Caller-supplied pointer to a KDPC structure, which represents the DPC object that is associated with this DpcForIsr routine.

DeviceObject [in]

Caller-supplied pointer to a DEVICE_OBJECT structure. This is the device object for the target device, previously created by the driver's AddDevice routine.

Irp [in, out]

Caller-supplied pointer to an IRP structure that describes the I/O operation.

Context [in, optional]

Caller-supplied pointer to driver-defined context information, specified in a previous call to IoRequestDpc.

Remarks

To register a DpcForIsr routine for a specific device object, a driver must call IoInitializeDpcRequest, which causes the system to allocate and initialize one DPC object. (If you need multiple DPC routines, use CustomDpc routines.)

To queue a DpcForIsr routine for execution, a driver's InterruptService routine must call IoRequestDPC.

A DpcForIsr routine is typically responsible for at least the following tasks:

• Completing the I/O operation described by the received IRP.

• Dequeuing next IRP.

  If the driver uses the system-supplied IRP queue, the DpcForIsr routine should call IoStartNextPacket or IoStartNextPacketByKey, so the driver's StartIo routine will start processing the next I/O request.

  If the driver uses internal IRP queues, the DpcForIsr routine should dequeue the next IRP and begin processing for the next I/O request.

• Setting the I/O status block in the received IRP and calling IoCompleteRequest for the completed request.

A DpcForIsr routine might also retry a failed operation or set up the next transfer for a large I/O request that has been broken into smaller pieces.

For more information about DpcForIsr routines, see DPC Objects and DPCs.

Examples

To define a DpcForIsr callback routine, you must first provide a function declaration that identifies the type of callback routine you're defining. Windows provides a set of callback function types for drivers. Declaring a function using the callback function types helps Code Analysis for Drivers, Static Driver Verifier (SDV), and other verification tools find errors, and it's a requirement for writing drivers for the Windows operating system.

For example, to define a DpcForIsr callback routine that is named MyDpcForIsr, use the IO_DPC_ROUTINE type as shown in this code example:

IO_DPC_ROUTINE MyDpcForIsr;

Then, implement your callback routine as follows:

_Use_decl_annotations_
VOID
  MyDpcForIsr(
    PKDPC  Dpc,
    struct _DEVICE_OBJECT  *DeviceObject,
    struct _IRP  *Irp,
    PVOID  Context
    )
  {
      // Function body
  }

The IO_DPC_ROUTINE function type is defined in the Wdm.h header file. To more accurately identify errors when you run the code analysis tools, be sure to add the _Use_decl_annotations_ annotation to your function definition. The _Use_decl_annotations_ annotation ensures that the annotations that are applied to the IO_DPC_ROUTINE function type in the header file are used. For more information about the requirements for function declarations, see Declaring Functions by Using Function Role Types for WDM Drivers. For information about _Use_decl_annotations_, see Annotating Function Behavior.