LOCK FILE PROTOCOL (LFP)


Status of this Memo

   This memo is a proposed specification for the Lock File Protocol (LPF).
   Distribution of this memo is currently limited.

   The following commands are currently in this edition of this specification.

      LOCK (lock a resource), UNLOCK (unlock a resource), QUIT (disconnect)


1.  INTRODUCTION

    The objectives of LPF are 1) to make administration of machines with a
    large number of users easier 2) to encourage a common mechanism for
    applications to share resources 3) to provide a platform neutral
    interface for applications.

    This specification tries to outline the minimal required features for
    a LPF.

2.  OVERVIEW

    Lock files can be located in as many as 10 different directories depending
    on the OS.  Writing applications that handle all of the lock directories
    is redundant and error prone.

    By enabling three commands much of the redundant work can be eliminated and
    a common locking scheme can be used.  The end result is a consistant easy
    to use interface.

2.1.  HISTORY

    Lock files have been used for a long time.  For more information on
    lock files see:

         The File System Hierarchy Standard
         http://www.pathname.com/fhs/
         UUCP Lock Files
         http://docs.freebsd.org/info/uucp/uucp.info.UUCP_Lock_Files.html
         FSSTND
         ftp://tsx-11.mit.edu/pub/linux/docs/linux-standards/fsstnd/
         Proposed Changes to the File System Hierarchy Standard
         ftp://scicom.alphacdc.com/pub/linux/devlock-0.X.tgz
         "UNIX Network Programming", W. Richard Stevens,
         Prentice-Hall, 1990, pages 96-101.

2.2  TERMINOLOGY

   lock file
   lock directory
   uucp lock
   fhs lock

2.3  THE LFP MODEL

	lock
        directory<----->Server<-----Client<---->User

3.  LOCKFILE FUNCTIONS
 
4.  LFP FUNCTIONS
4.1  LFP COMMANDS

   4.1.1   ACCEESS CONTROL COMMANDS

	QUIT  The session is ended.

   4.1.2   LOCK FILE CONTROL COMMANDS
	
	LOCK If the device that is trying to be locked and the pid of the
             requesting application are passed, an attempt will be made to
             lock the device.

	UNLOCK If the pid of the application requesting to unlock a device
             is passed an attempt will be made to unlock the device.

Lock File Protocol                                              January 2001

4.2  LFP REPLIES

	The following replies exist and try to follow the same format as FTP
        reply commands (rfc 959)

	200 Command okay.
	202 Command not implemented
        220 hostname Lock File Server (Version rxtx-1.5-9) ready
        221 Thank you for using the Lock File service on hostname
        450 : File busy
        500 'command': command not understood
        550 : Permission denied.

5.  DECLARATIVE SPECIFICATIONS
      5.1 Minimum IMPLEMENTATION

         The following commands must be in a minimum implementation
         QUIT, LOCK, UNLOCK.

      5.2  CONNECTIONS

          Currently on connections assisted by inetd are supported.
          Though not official, LFP currently listens on port 50001.
          Only connections from localhost should be allowed.

      5.3 COMMANDS

	  5.3.1  LFP COMMANDS

	     The following are the LFP COMMANDS

	     QUIT <CRLF>
             LOCK <SP> <device> <sp> <pid> <CRLF>
             UNLOCK <SP> <device> <sp> <pid> <CRLF>

          5.3.2  LFP COMMAND ARGUMENTS

	     <device> ::= <string>
	     <pid>    ::= any decimal integer

      5.4.  SEQUENCING OF COMMANDS AND REPLIES
		
		Connection Establisment
		LOCK
		UNLOCK
		QUIT

6.  STATE DIAGRAMS


   [ from rfc 959 ]

   Here we present state diagrams for a very simple minded LFP
   implementation.  Only the first digit of the reply codes is used.
   There is one state diagram for each group of LFP commands or command
   sequences.

   The command groupings were determined by constructing a model for
   each command then collecting together the commands with structurally
   identical models.

   For each command or command sequence there are three possible
   outcomes: success (S), failure (F), and error (E).  In the state
   diagrams below we use the symbol B for "begin", and the symbol W for
   "wait for reply".

Lock File Protocol                                              January 2001

   We present the diagram that represents the largest group of LFP
   commands:

                               1,3    +---+
                          ----------->| E |
                         |            +---+
                         |
      +---+    cmd    +---+    2      +---+
      | B |---------->| W |---------->| S |
      +---+           +---+           +---+
                         |
                         |     4,5    +---+
                          ----------->| F |
                                      +---+

      This diagram models the commands:
	
         QUIT, LOCK, UNLOCK.


7.  TYPICAL LFP SCENARIO

      $ telnet 127.0.0.1 50001
      Trying 127.0.0.1...
      Connected to 127.0.0.1.
      Escape character is '^]'.
      lock /dev/ttyS1 1234
      200 Command okay.
      unlock /dev/ttyS1 1234         
      200 Command okay.
      quit
      221 Thank you for using the Lock File Service on servertrent.korpivaara.org.
      Connection closed by foreign host.
      $