{ The purpose of this procedure is to insure that a specified
{ portion of a segment exists in real memory.  When the request completes,
{ all pages totally or partially contained by the
{ range of addresses specified by <pva> to <pva>+<length> will be
{ in real memory.  The pages will be marked as recently used to reduce
{ the odds of having them removed from memory via aging. If the pages
{ already exist in real memory, no input request will be issued to
{ obtain them.  A call to this procedure cannot come from above ring 6.
{
{      MMP$READ (PVA, LENGTH, IOSTATUS_P, WAIT, STATUS)
{
{ PVA: (input) This parameter specifies the beginning address of data
{      the caller wants in real memory.
{
{ LENGTH: (input) This parameter specifies the number of bytes the caller
{      wants in real memory.  The maximum request length is 65536 bytes;
{      if the length is longer, the condition mme$request_length_too_long
{      will be returned in the status variable.  If the length is enough
{      to cause a request to span a segment boundary, then the condition
{      mme$invalid_pva_formed will be returned.
{
{ IOSTATUS_P: (input) This parameter specifies the address of
{      the IO status variable.  Possible values for the request_status field
{      are:
{        mmc$irs_active
{        mmc$irs_complete
{        mmc$irs_none
{      If iostatus_p^.request_status is set to mmc$irs_complete,
{      then possible values for the condition field are:
{        0--indicates i/o completed without error
{        ioc$unrecovered_disk_error
{        ioc$disk_media_error
{
{ WAIT: (input) This parameter specifies whether to wait for
{      completion of the request or to return to the user immediately
{      after initiating the required IO. If the user does not wait,
{      the user may later issue a MMP$CHECK_IO_STATUS request
{      to determine the status of the MMP$READ request.
{
{ STATUS: (output) This parameter specifies the request status.
{      Possible error codes are:
{        mme$request_length_too_long
{        mme$invalid_pva_formed
{        mme$invalid_pva
{        mme$read_beyond_eoi
{        mme$read_write_beyond_msl
{        mme$write_beyond_eoi_no_append
{        mme$ref_to_unrecovered_file
{        dfe$server_has_terminated
{     If status.normal is FALSE, then iostatus_p^.request_status is set to
{     mmc$irs_none.
{
