{
{   The purpose of this request is to open a file for segment level access.
{
{       PFP$OPEN_FILE_SEGMENT (SYSTEM_FILE_ID, VALIDATION_RING,
{             SEGMENT_POINTER, STATUS);
{
{ SYSTEM_FILE_ID: (input) This parameter specifies the system_file_identifier
{       of file to be opened as a segment.
{
{ VALIDATION_RING: (input) This parameter specifies the ring of execution for
{       whom the segment is being opened.
{
{ SEGMENT_POINTER: (output) This parameter specifies a PVA to the beginning of
{       the segment.  The byte offset of the PVA is set to zero.
{
{ STATUS: (output) This parameter specifies the request status.
{
{       CONDITIONS:
{            dme$unable_to_get_fd_lock
{            dme$unable_to_locate_fde
{            mme$address_not_0_mod_16384
{            mme$asid_specified
{            mme$binding_attribute_invalid
{            mme$contig_mem_seg_violation
{            mme$execute_global_invalid
{            mme$invalid_asid_specified
{            mme$invalid_length_requested
{            mme$invalid_pva
{            mme$invalid_ring_brackets
{            mme$invalid_shadow_segment
{            mme$invalid_shared_taskid
{            mme$length_not_0_mod_16384
{            mme$pages_already_assigned
{            mme$ref_to_unrecovered_file
{            mme$ring_violation
{            mme$segment_number_is_in_use
{            mme$segment_number_not_in_use
{            mme$segment_number_too_big
{            mme$segment_origin_invalid
{            mme$segment_table_is_full
{            mme$software_attribute_invalid
{            mme$unable_to_assign_contig_mem
{            mme$unsupported_keyword
{            pfe$not_system_administrtor
{
