Windows下USB驱动异步URB转IRP请求函数代码

URB有同步请求，也有异步请求。这里微软官方提供了一个异步请求URB的代码示例

// The SubmitUrbASync routine submits an URB asynchronously.
//
// Parameters:
//
// Parameters:
//      DeviceExtension: Pointer to the caller's device extension. The
//                       device extension must have a pointer to
//                       the next lower device object in the device stacks.  
//
//      Irp: Pointer to an IRP allocated by the caller.
//
//      Urb: Pointer to an URB that is allocated by  USBD_UrbAllocate,
//           USBD_IsochUrbAllocate, USBD_SelectConfigUrbAllocateAndBuild,
//           or USBD_SelectInterfaceUrbAllocateAndBuild.
//      CompletionRoutine: Completion routine.
//
//      CompletionContext: Context for the completion routine.
//
//
// Return Value:
//
//      NTSTATUS
NTSTATUS SubmitUrbASync ( PDEVICE_EXTENSION DeviceExtension,
                         PIRP Irp,
                         PURB Urb,  
                         PIO_COMPLETION_ROUTINE CompletionRoutine,  
                         PVOID CompletionContext)  
{
    // Completion routine is required if the URB is submitted asynchronously.
    // The caller's completion routine releases the IRP when it completes.
    NTSTATUS ntStatus = -1;  
    PIO_STACK_LOCATION nextStack = IoGetNextIrpStackLocation(Irp);  
    // Attach the URB to this IRP.
    nextStack->MajorFunction = IRP_MJ_INTERNAL_DEVICE_CONTROL;  
    // Attach the URB to this IRP.
    nextStack->Parameters.DeviceIoControl.IoControlCode = IOCTL_INTERNAL_USB_SUBMIT_URB;  
    // Attach the URB to this IRP.
    (void) USBD_AssignUrbToIoStackLocation (DeviceExtension->UsbdHandle, nextStack, Urb);  
    // Caller's completion routine will free the irp when it completes.
    ntStatus = IoSetCompletionRoutineEx ( DeviceExtension->NextDeviceObject,
        Irp,  
        CompletionRoutine,  
        CompletionContext,  
        TRUE,
        TRUE,
        TRUE);
    if (!NT_SUCCESS(ntStatus))
    {
        goto Exit;
    }
    (void) IoCallDriver(DeviceExtension->NextDeviceObject, Irp);
Exit:
    if (!NT_SUCCESS(ntStatus))
    {
        // We hit a failure condition,
        // We will free the IRP
        IoFreeIrp(Irp);
        Irp = NULL;
    }
    return ntStatus;
}

可以看到，这个代码和同步的方式类似，只是少了：

• 创建创建IRP完成时回调函数中需要激活的EVENT事件
• IoCallDriver后，不再要根据Pending状态等待事件。

当然，该IRP什么时候完成，这里就需要放在完成例程中实现了。而对于同步传输，后续的处理代码既可以放在完成例程中，也可以放在KeWaitForSingleObject之后，而对于异步传输，就只能放在完成例程中了。

注意：完成例程的中断请求级别比交高。