Once installed, a filter device driver can apply the following to the IORBs it is filtering:

• Generally, the filter device driver will retain the original IORB and create new IORBs to pass on to the downstream drivers.

• However, a filter device driver can modify an IORB it receives and pass on the same copy of the IORB data structure (as opposed to passing on a local copy of the IORB). If the adapter device driver does this, it must alter the notification address and restore any input fields it had modified prior to doing notification callouts back to the upstream driver.

The filter device driver must not assume that the contents of the pIORB->ADDWorkSpace field will be preserved by a downstream driver.