GetDVI, part 3

In this article, we look at the changes made in various places in conjunction with the GETDVI system call we've discussed in the previous two articles.

                         _Device : TUOS_Device ;

First, we add instance data to TResource. This is the device instance for the device associated with the resource.

        S := F.Name ;
        Dummy := pos( ':', S ) ;
        Device := Devices.TDevice( Get_Device( copy( S, 1, Dummy ) ) ) ;

In the TUOS_FiP.Create_File_Handle method, when a file is specified we pull the device name from the file name and assign the TResource's _Device instance data to that device.

        if( ( S <> '' ) and ( not Device.Mounted ) ) then
        begin
            Set_Last_Error( Create_Error( UOSErr_Device_Not_Mounted ) ) ;
            exit ;
        end else
        if( ( S = '' ) or ( Device.FS = nil ) ) then // No file structure on device or only device specified
        begin
            if( ( S <> '' ) and ( ( Flags and FO_Block_Mode ) = 0 ) ) then // Opening non-file-structured
            begin
                Set_Last_Error( Create_Error( UOSErr_Device_Not_File_Structured ) ) ;
                exit ;
            end ;

We altered the next part of the method slightyly. Whereas before we returned an error if the device is not mounted, now we only do this if a folder/file name was specified in addition to the device. This is to allow us to obtain a handle to an unmounted device. Generally we don't allow operations on unmounted devices, but there are a few exceptions. For now, we want to get information on the device. In the future, there are some cases where we will want to do other operations to unmounted devices. Additionally, we altered the code to allow a handle for a device if FO_Block_Mode is not specified if only the device was specified.

    Result._Device := Device ;

If a device is specified when a file handle is requested, we have to get the device instance to see if the file exists. So we assign that to _Device.

                       public // API...
                           function Buffer_Size : int64 ;
                           function Write_Locked : boolean ;
                           function Max_IO_Size : int64 ;
                           function Description : PChar ;
                           function Revision : PChar ;
                           function Operation_Count : int64 ;
                           function Queue_Length : int64 ;
                           function Serial_Number : PChar ;

We add several methods to the TDevice class.

function TDevice.Buffer_Size : int64 ;

begin
    Result := 0 ;
    if( FS <> nil ) then
    begin
        Result := FS.Store.Min_Storage ;
        exit ;
    end ;
    if( Terminal <> nil ) then
    begin
        Result := Terminal.Char_Columns ;
        exit ;
    end ;
    if( Stream <> nil ) then
    begin
        Result := Stream.Min_Record_Size ;
    end ;
end ;


function TDevice.Write_Locked : boolean ;

begin
    Result := False ;
    if( FS <> nil ) then
    begin
        Result := FS.Store.Read_Only ;
        exit ;
    end ;
    if( Stream <> nil ) then
    begin
        Result := Stream.Read_Only ;
        exit ;
    end ;
end ;


function TDevice.Max_IO_Size : int64 ;

begin
    Result := 1 ;
    if( FS <> nil ) then
    begin
        Result := FS.Store.Max_Storage ;
        exit ;
    end ;
    if( Terminal <> nil ) then
    begin
        Result := 255 ;
        exit ;
    end ;
    if( Stream <> nil ) then
    begin
        Result := Stream.Max_Record_Size ;
        exit ;
    end ;
end ;


function TDevice.Description : PChar ;

begin
    Result := nil ;
end ;


function TDevice.Revision : PChar ;

begin
    Result := nil ;
end ;


function TDevice.Operation_Count : int64 ;

begin
    Result := 0 ;
    if( Store <> nil ) then
    begin
        Result := Store.Reads + Store.Writes ;
    end else
    if( Terminal <> nil ) then
    begin
        Result := Terminal.Reads + Terminal.Writes ;
    end else
    if( Stream <> nil ) then
    begin
        Result := Stream.Reads + Stream.Writes ;
    end ;
end ;


function TDevice.Queue_Length : int64 ;

begin
    Result := 0 ;
end ;


function TDevice.Serial_Number : PChar ;

begin
    Result := nil ;
end ;

Some of these methods simply return 0/nil/null because we have yet to address the feature.
Buffer_Size is the device default buffer size, in bytes. For stores, this is the minimum allocation size. For terminals, the default buffer size is the number of character columns on the termianl, although this can be larger as needed. For all other streams, we return the minimum record size supported by that stream.
Max_IO_Size is the maximum amount of data, in bytes, that can be transferred to the device in a single operation. Other considerations may result in a difference from this theoretical value. As an example, there may not be enough memory to hold a buffer that would match the theoretical maximum I/O size. For stores, this is the entire size of the store. For terminals, it is the same as the default buffer size. For all other streams, we return the maximum record size.
Operation_Count returns the sum of the reads and writes for the appropriate device.
Write_Locked returns true if the device cannot be written to. This comes from the device and we simply pass the value on. The devices themselves expose this characteristic via their Read_Only methods.

      // Terminal flags...
const TT_M_SCOPE = 1 ; // Video (0 = hardcopy)
      TT_M_EIGHTBIT = 2 ; // Terminal uses the 8-bit ASCII character set otherwise use 7-bit ASCII code.
      TT_M_ESCAPE = 4 ; // Terminal generates escape sequences
      TT_M_HALFDUP = 8 ; // Terminal is in half-duplex mode
      TT_M_HOSTSYNC = 16 ; // Ctrl/Q and Ctrl/S are used to control data flow
      TT_M_LFFILL = 32 ; // Terminal requires fill after the line-feed character is processed.
      TT_M_UPPERCASE = 64 ; // Terminal doesn't have the lowercase character set.
      TT_M_MBXDSABL = 128 ; // Mailboxes associated with device not notified of unsolicited input or hangup
      TT_M_MECHFORM = 256 ; // Terminal has mechanical form feed.
      TT_M_MECHTAB = 512 ; // Terminal has mechanical tabs and is capable of tab expansion
      TT_M_MODEM = 1024 ; // Honor modem signals
      TT_M_NOBRDCST = 2048 ; // Terminal does not receive any broadcast messages.
      TT_M_NOECHO = 4096 ; // Input characters are not echoed on this terminal line
      TT_M_NOTYPEAHD = 8192 ; // Data must be solicited by a read operation.
      TT_M_READSYNC = 16384 ; // Host explicitly solicits all reads with Ctrl/Q and terminates with Ctrl/S.
      TT_M_REMOTE = 32768 ; // Dialup characteristic is enabled. Terminal returns to local mode on hangup
      TT_M_CRFILL = $10000 ; // Terminal requires fill after the Return key is pressed
      TT_M_TTSYNC = $20000 ; // Output to the terminal is controlled by terminal-generated Ctrl/Q or Ctrl/S.
      TT_M_WRAP = $40000 ; // A CRLF combination should be inserted if the cursor moves beyond right margin.

      TT2_M_ALTYPEAHD = $80000 ; // Alternate type-ahead buffer size is enabled
      TT2_M_ANSICRT = $100000 ; // ANSI CRT terminal is enabled.
      TT2_M_APP_KEYPAD = $200000 ; // Notifies applications of state to set the keypad to when exiting.
      TT2_M_AUTOBAUD = $400000 ; // Automatic baud rate detection is enabled.
      TT2_M_AVO = $800000 ; // Advanced video is enabled.
      TT2_M_BLOCK = $1000000 ; // Block mode is enabled.
      TT2_M_BRDCSTMBX = $2000000 ; // Broadcast messages are sent to an associated mailbox, if one exists.
      TT2_M_COMMSYNC = $4000000 ; // Enables devices such as printers to be connected to terminal ports.
      TT2_M_DECCRT = $8000000 ; // DIGITAL CRT terminal.
      TT2_M_DECCRT2 = $10000000 ; // DIGITAL CRT terminal.
      TT2_M_DECCRT3 = $20000000 ; // DIGITAL CRT terminal.
      TT2_M_DECCRT4 = $40000000 ; // DIGITAL CRT terminal.
      TT2_M_DIALUP = $80000000 ; // Terminal is a dialup line.
      TT2_M_DISCONNECT = $100000000 ; // Allows terminal disconnect when a hangup or disconnect occurs
      TT2_M_DMA = $200000000 ; // Direct memory access (DMA) mode.
      TT2_M_DRCS = $400000000 ; // Terminal supports loadable character fonts.
      TT2_M_EDIT = $800000000 ; // Terminal edit for those that support ANSI-defined advanced edit functions.
      TT2_M_EDITING = $1000000000 ; // Line editing is allowed.
      TT2_M_FALLBACK = $2000000000 ; // Transform output from 8-bit multinational characters to 7-bit ASCII
      TT2_M_NOHANGUP = $4000000000 ; // UOS will not force modem to hangup when user logs off.
      TT2_M_INSERT = $8000000000 ; // Sets default mode for insert or overstrike at the beginning of read.
      TT2_M_LOCALECHO = $10000000000 ; { Local echo. This characteristic is used with TT_M_NOECHO. If both
                          characteristics are set, only terminators and special control
                          characters are echoed. Use of this mode is restricted to command-line
                          read operations. Local echo is not compatible with line editing
                          (TT2_M_EDITING). }
      TT2_M_MODHANGUP = $20000000000 ; // Modify hangup.  Allow hangup with privileges.
      TT2_M_PASTHRU = $40000000000 ; // Terminal is in PASTHRU mode
      TT2_M_PRINTER = $80000000000 ; // Terminal with a local printer port.
      TT2_M_REGIS = $100000000000 ; // ReGIS graphics. The terminal supports ReGIS graphics instruction set.
      TT2_M_SIXEL = $200000000000 ; // SIXEL graphics. The terminal supports SIXEL graphics instruction set.
      TT2_M_SECURE = $400000000000 ; // Guarantees that no process is connected after BREAK is received.
      TT2_M_SETSPEED = $800000000000 ; // Set speed requries either LOG_IO or PHY_IO privilege.
      TT2_M_SYSPWD = $1000000000000 ; // The login procedure should require the system password
      TT2_M_XON = $2000000000000 ; // XON/XOFF control.
      TF_Query = $4000000000000 ; // Send query sequence to terminal
      TF_Graphics = $8000000000000 ; // Graphics device (0 = character)
      TF_Set_Host = $10000000000000 ; // Terminal is connected from remote node via set host
      // $20000000000000 - $4000000000000000 = reserved

Finally, we have the definitions of the VMS terminal flags. We've replaced some of the older TF_ constants with the appropriate VMS flags. But there are some flags that don't correspond to any VMS flags, these will remain prefixed with "TF_".

In the next article, we will look at the next lexical function.