Browse Prior Art Database

Establishing Distributed File System Access to MVS Host Files

IP.com Disclosure Number: IPCOM000115230D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 88K

Publishing Venue

IBM

Related People

Berman, ES: AUTHOR [+2]

Abstract

Disclosed is a method for providing access to MVS host datasets through OSF's DCE/Distributed File System (DFS) with data integrity and consistency and without change to either MVS or to DCE applications. The method consists of two parts, one for accessing MVS datasets and one for releasing them.

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Establishing Distributed File System Access to MVS Host Files

      Disclosed is a method for providing access to MVS host datasets
through OSF's DCE/Distributed File System (DFS) with data integrity
and consistency and without change to either MVS or to DCE
applications.  The method consists of two parts, one for accessing
MVS datasets and one for releasing them.

      MVS applications share data through a process called dataset
allocation, whereby the application reserves the right to read or
read/write a dataset.  This is done prior to opening the dataset.
DCE applications accessing DFS files reserve those same rights
through the use of tokens.  The DCE host machine on which the
application resides requests the appropriate tokens, including an
open token, from DFS when the application opens the file.  If another
host requests the tokens for the same file, DFS manages conflicts by
revoking (requesting the return of) the token from the first host and
giving it to the second.  The first host must then reacquire the
token to proceed in its use of the file.

      In this disclosed method, the MVS Host File Access (HFA) is
registered as a DFS physical file system (PFS), thus mapping DFS
client calls to MVS data access services.  When a DCE application
requests tokens for a file that is actually an MVS dataset, HFA is
notified through a file lookup request.  This causes MVS dataset
allocation to reserve the dataset for DFS, allowing read/write access
by DFS, and specifying that no sharing be allowed with any other MVS
applications.  The native MVS dataset allocation facility will queue
subsequent requests until the dataset is deallocated.  DCE
applications
on multiple hosts may now share the dataset through normal DFS token
management.  DFS clients can also acquire file locks, and cache file
and
directory data, through standard DFS mechanisms.

      In order to optimize performance, when a DCE application closes
a file, the DFS client does not automatically return any of its
tokens associated with the file.  Instead, the tokens are returned
when either DFS revokes the tokens to give to another DFS client, or
the tokens expire (time out).

      HFA is, therefore, not notified when to deallocate the dataset
...