IoAttachDeviceToDeviceStackSafe routine

The IoAttachDeviceToDeviceStackSafe routine attaches the caller's device object to the topmost device object in a driver stack.


NTSTATUS IoAttachDeviceToDeviceStackSafe(
  _In_  PDEVICE_OBJECT SourceDevice,
  _In_  PDEVICE_OBJECT TargetDevice,
  _Out_ PDEVICE_OBJECT *AttachedToDeviceObject


SourceDevice [in]

Pointer to a caller-created device object.

TargetDevice [in]

Pointer to the device object in the stack to which the SourceDevice object is to be attached.

AttachedToDeviceObject [out]

On input, this parameter specifies the address of SourceDevice->DeviceExtension->AttachedToDeviceObject, which must contain a NULL pointer. On output, this parameter receives a pointer to the device object to which the SourceDevice was attached.

Return value

IoAttachDeviceToDeviceStackSafe returns STATUS_SUCCESS if SourceDevice is successfully attached above the TargetDevice; otherwise it returns STATUS_NO_SUCH_DEVICE.


Like IoAttachDeviceToDeviceStack, IoAttachDeviceToDeviceStackSafe establishes layering between drivers so that the same IRPs are sent to each driver in the stack. However, unlike IoAttachDeviceToDeviceStack, IoAttachDeviceToDeviceStackSafe has an additional parameter, AttachedToDeviceObject, which the filter driver uses to pass the address of the SourceDevice object's AttachedToDeviceObject field. IoAttachDeviceToDeviceStackSafe updates this field while holding the I/O system database lock. Because it holds this lock, IoAttachDeviceToDeviceStackSafe avoids a race condition that could otherwise occur if the SourceDevice object received an IRP before its AttachedToDeviceObject field was updated.

A file system filter driver calls IoAttachDeviceToDeviceStackSafe to attach its own filter device object (SourceDevice) above a device object (TargetDevice) belonging to a file system or another filter driver. Subsequent I/O requests sent to AttachedToDeviceObject are received first by the filter driver, which processes them and forwards them down to the next driver in the stack by calling IoCallDriver.

If the device object specified by TargetDevice is currently at the top of the driver stack, the SourceDevice is attached directly to the TargetDevice. In this case, TargetDevice and the returned AttachedToDeviceObject pointer are equal.

If one or more filter device objects are already attached above the TargetDevice in the driver stack, IoAttachDeviceToDeviceStackSafe attaches the SourceDevice to the topmost filter device object. A pointer to the latter is returned in AttachedToDeviceObject.

At the moment immediately after it is attached to the top of the stack, the SourceDevice occupies the top of the driver stack. Note, however, that this does not necessarily mean that the SourceDevice will remain at the top of the driver stack. Other filters can attach their own filter device objects above the SourceDevice in the stack.

IoAttachDeviceToDeviceStackSafe sets the AlignmentRequirement member of the device object pointed to by SourceDevice to the value of the corresponding in the next-lower device object and sets the StackSize in SourceDevice to the value in the next-lower-object plus one.


Target platform



This routine is available on Update Rollup for Windows 2000 Service Pack 4 (SP4) and on Windows XP and later.


Ntddk.h (include Ntddk.h)







See also




Send comments about this topic to Microsoft