SwCallbackInfoRec
Offset Size Contents
                                                                       
+0       4  pfrNext      address of next SwCallbackInfoRec in the
notification chain (or 0000:0000 if last entry)
+4       4  pfHandler    addr of notification-function handler
+8       4  res          (reserved)
+0c       4  pfarAPIs     address of list of SwApiInfoRec structures.
16               size of an SwCallbackInfoRec structure

pfrNext  this is the address of the next SwCallbackInfoRec in the
chain; it is stored by programs which intercept INT 2fH 4b01H
(build notification chain).

pfHandler  the FAR address of the code that will be called for various
notification functions.

pfarAPIs  the FAR address of the first of a series of SwApiInfoRec
structures that identify how much support this program
provides for various asynchronous request APIs.  The list ends
when the first field of that structure is 0000H.

This structure is used in SwSrvcFn 0004H (hook notification chain) and in
INT 2fH 4b01H (build notification chain).  It is part of the system that
allows programs to be notified when they are about to be switched out or
that they can resume operation, etc.

INT 2fH 4bxxH (switcher functions)
- -

SwCallbackInfoRec