{
{   The purpose  of this procedure is to attach the device file for the volume
{ set table.
{
{       STP$ATTACH_VST (VSN, SFID, STATUS)
{
{ VSN: (input) This parameter specifies the volume on  which  the  volume  set
{       table device file is to be attached.
{
{ SFID: (output)  This  parameter  returns  the  system file identifier of the
{       device file for the volume set table.
{
{ STATUS: (output) This parameter returns the request status.
{
{       CONDITIONS: ste$vol_not_in_set (no device file)
{                   ste$attach_df_error
{
{       IDENTIFIER: stc$set_management_id
{
