{
{   The purpose  of  this  routine  is to open a volume set table whose device
{ file has already been attached.  The segment attributes are  established  so
{ that the file may be read or written from up to ring 3.  This verifies
{ that the stored version number is the same as the current version.
{
{       STP$OPEN_ATTACHED_VST (VOL, DATA_TO_BE_MODIFIED, SFID,
{         VST_SEGMENT_POINTER, STATUS)
{
{ VOL: (input)  This parameter specifies the volume whose device file is to be
{       opened.
{
{ DATA_TO_BE_MODIFIED: (input)  This parameter specifies whether the requestor
{       is going to modify the volume set table or merely read the volume
{       set table.
{
{ SFID: (input) This parameter specifies the system file  identifier  for  the
{       device file.
{
{ VST_SEGMENT_POINTER: (output) This parameter returns a pointer to the volume
{       set table.
{
{ STATUS: (output) This parameter returns the request status.
{
{       CONDITIONS: ste$open_error
{                   ste$vol_set_table_lost_data
{                   ste$incompatible_vst_version
{
{       IDENTIFIER: stc$set_management_id
{
