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Encoding/Decoding Scheme to Provide CD-ROM Filesystem Support to Distributed Computing Environment Distributed File Services

IP.com Disclosure Number: IPCOM000117714D
Original Publication Date: 1996-May-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 68K

Publishing Venue

IBM

Related People

Burnett, RC: AUTHOR [+2]

Abstract

Disclosed is a scheme for encoding and decoding additional information into a limited amount of data structure space when certain properties are known about the data. This technique is used to provide CD-ROM filesystem support to the Distributed Computing Environment's (DCE) Distributed File Services (DFS).

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Encoding/Decoding Scheme to Provide CD-ROM Filesystem Support to
Distributed Computing Environment Distributed File Services

      Disclosed is a scheme for encoding and decoding additional
information into a limited amount of data structure space when
certain properties are known about the data.  This technique is used
to provide CD-ROM filesystem support to the Distributed Computing
Environment's (DCE) Distributed File Services (DFS).

      DFS internally allows filesystem objects to be specified using
two 32-bit values known as a vnode and a uniquifier.  The AIX*
operating system maintains local CD-ROM filesystem information using
the vnode and uniquifier but in addition also uses a 16-bit value for
a hash value.  This encoding scheme allows for the additional CD-ROM
filesystem information to be stored in the space allowed by DFS.

This method works due to the following properties with regard to the
local CD-ROM filesystem:
  o  The smallest block offset is 512 bytes (which determines the
      uniquifier value)
  o  A directory is specified by an odd number in the uniquifier

      Given these assumptions, the spare bit fields in the uniquifier
may be used for encoding the hash value.  Otherwise, a separate
encoding in-memory table can be used to maintain encoding information
indirectly.  This table will maintain the CD-ROM file system triplet.
It should be noted that this scheme maintains the value of the vnode
throughout its implementation.

      The uniquifier and hash entities as shown with the following
representations.  Bits are displayed highest (31 or 15) to lowest (0)
in this representation.
         UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU
         HHHHHHHHHHHHHHHH

      The assumed state of the uniquifier is shown below.  Bits 1-7
are zero.
         UUUUUUUUUUUUUUU...